explanation      blue bibcodes open ADS page with paths to full text
Author name code: mathioudakis
ADS astronomy entries on 2022-09-14
author:"Mathioudakis, Mihalis" 

---------------------------------------------------------
Title: Radiative Hydrodynamic Modelling Of The Lyman Continuum During
    Solar Flares
Authors: Mclaughlin, Shaun; Simões, Paulo; Milligan, Ryan;
   Mathioudakis, Mihalis; Monson, Aaron; Kerr, Graham
2022cosp...44..845M    Altcode:
  Increases in solar irradiance associated with solar flares are known
  to drive dynamic and compositional changes in Earth's ionosphere,
  which can have adverse implications for modern technology on which
  society has become dependent. The EUV part of the solar spectrum can
  increase dramatically during the largest events. The 850-1027\AA\
  range, in particular, is absorbed at an altitude of around 105--120km
  in the ionosphere (E-layer), where it drives the partial dissociation
  of molecular oxygen. This part of the spectrum is dominated by the
  free-bound Lyman continuum of neutral hydrogen (<912\AA; LyC),
  along with higher-order Lyman emission lines. As LyC is formed
  in the solar chromosphere, it is highly sensitive to changes in
  the energy balance associated with solar flares. To understand the
  mechanism(s) responsible for driving the increases in LyC emission
  associated with solar flares, we generated synthetic LyC profiles
  using the 1D radiative hydrodynamic code, RADYN. The grid of RADYN
  models hosted at Queen's University Belfast simulates the response of
  the solar chromosphere to flare heating, assumed to be in the form
  of accelerated electrons. The specific intensity at the head of the
  continuum was found to be highly sensitive to the energy flux density of
  the nonthermal electrons, increasing by 3-4 orders of magnitude. This
  translates to a factor of five increase in irradiance during the
  largest events. The increase in LyC emission was found to be less
  sensitive to changes in the spectral index and low-energy cutoff of
  the nonthermal electron distribution. By fitting the LyC profile with
  a blackbody function, the plasma conditions at the formation height
  were determined. This revealed LyC to be optically thick, and formed
  at a deeper layer during flares compared to quiescent periods. Plots
  of the contribution function also suggest optically thin components
  of LyC emission formed higher in the solar atmosphere, deemed to be
  associated with chromospheric evaporation. These findings will help
  to diagnose the physical conditions in the flaring chromosphere that
  lead to increased geoeffective EUV emission under different heating
  regimes. They will also help guide the interpretation of spectral
  irradiance observations such as those provided by SDO/EVE and flare
  irradiance models such as FISM.

---------------------------------------------------------
Title: Photospheric Spectral Line Velocity Diagnostics in Solar and
    Stellar Flares.
Authors: Monson, Aaron; Milligan, Ryan; Kowalski, Adam; Mathioudakis,
   Mihalis
2022cosp...44.2449M    Altcode:
  We present radiative-hydrodynamic simulations of solar flares generated
  by the RADYN and RH codes to study the perturbations induced in
  photospheric Fe I lines by electron beam heating. We investigate the
  induced line-of-sight velocities by various electron beam parameter
  combinations, and the primary energy transport mechanisms responsible
  for heating the lower solar atmosphere. From these models, we synthesize
  several deep forming Fe I spectral lines and study the Doppler velocity
  information retrievable during the flare. It is shown that throughout
  the period of beam heating a significant proportion of the line
  intensity is contributed from the chromosphere, leading to erroneous
  Doppler shifts not reflective in the photospheric LOS velocities. The
  apparent m/s Doppler shifts can even indicate false downflows in the
  photosphere, making their study vital for correctly considering momentum
  transfer throughout the lower solar atmosphere. We have expanded our
  analysis to stellar flare scenarios, where the sensitivity of these deep
  forming spectral lines provides a powerful diagnostic tool for analysing
  extreme stellar flare effects and features in the chromosphere.

---------------------------------------------------------
Title: The many faces of small-scale solar magnetic features
Authors: Mathioudakis, Mihalis
2022cosp...44.2518M    Altcode:
  From impulsive events to quasi-stable structures, small-scale magnetic
  fields are ubiquitous in the quiet solar atmosphere and dominate its
  structure and dynamics. The processes and timescales that underpin
  their evolutionary characteristics depend on their size; the smaller
  the structures the faster they evolve. Their magnetic fields constitute
  the fundamental blocks of solar magnetism, provide a perpetual source of
  flux to the boundaries of the supergranular cells and play an important
  role to the energy budget of the outer solar atmosphere. Even areas
  which appear devoid of magnetic flux are likely to harbour weak magnetic
  fields that are below the detection limits of current instruments. We
  will review some of the latest results on this topic and highlight
  how our understanding of the physical parameters of small-scale solar
  structures can benefit other areas of astrophysics.

---------------------------------------------------------
Title: Exploring dynamic, small-scale quiet Sun magnetism at high
    S/N with the GREGOR/GRIS-IFU
Authors: Campbell, Ryan; Collados, Manuel; Quintero Noda, Carlos;
   Mathioudakis, Mihalis; Gafeira, Ricardo
2022cosp...44.2510C    Altcode:
  We have taken advantage of the improvements to GREGOR (Kleint et
  al. 2020, A&A, 641, A27), Europe's largest solar telescope,
  to reveal small-scale magnetism at the solar internetwork (IN) in
  unprecedented detail. The observations were carried out at solar disk
  centre with the highly magnetically sensitive Fe I line at 1565nm. Our
  observations suggest that GREGOR's overhaul has helped achieve a
  higher effective spatial resolution while our synthetic profiles
  produced from MHD simulations suggests this data have been obtained
  at the telescope diffraction limit in the near infrared. By observing
  with high signal-to-noise (S/N), and exceptional seeing conditions, we
  reveal that as much as 35% of the IN shows linear polarisation signal
  at the 5$\sigma$ level, the highest fraction of linear polarization
  ever recorded in the quiet Sun IN, while as much as 70% shows circular
  polarization. We use the Stokes inversion based on response functions
  (SIR) inversion code to retrieve the thermodynamic, kinematic and
  magnetic properties of the atmosphere. We statistically compare our
  results to previous GRIS-IFU observations (Campbell et al. 2021,
  647, A182) obtained in 2019, prior to GREGOR's overhaul, focusing on
  controversies surrounding the impact of noise on the retrieval of the
  magnetic inclination angle. We employ the new open-source SIR Explorer
  (SIRE) application to easily and efficiently study several dynamic,
  small-scale magnetic features. We see evidence for weak transverse
  and complex small-scale 'loop-like' structures, with transverse fields
  flanked between opposite polarity longitudinal fields. In the last part
  of the presentation, SIRE will be demonstrated live for the audience.

---------------------------------------------------------
Title: The Solar Activity Monitor Network - SAMNet
Authors: Erdélyi, Robertus; Korsós, Marianna B.; Huang, Xin; Yang,
   Yong; Pizzey, Danielle; Wrathmall, Steven A.; Hughes, Ifan G.;
   Dyer, Martin J.; Dhillon, Vikram S.; Belucz, Bernadett; Brajša,
   Roman; Chatterjee, Piyali; Cheng, Xuewu; Deng, Yuanyong; Domínguez,
   Santiago Vargas; Joya, Raúl; Gömöry, Peter; Gyenge, Norbert G.;
   Hanslmeier, Arnold; Kucera, Ales; Kuridze, David; Li, Faquan; Liu,
   Zhong; Xu, Long; Mathioudakis, Mihalis; Matthews, Sarah; McAteer,
   James R. T.; Pevtsov, Alexei A.; Pötzi, Werner; Romano, Paolo; Shen,
   Jinhua; Temesváry, János; Tlatov, Andrey G.; Triana, Charles; Utz,
   Dominik; Veronig, Astrid M.; Wang, Yuming; Yan, Yihua; Zaqarashvili,
   Teimuraz; Zuccarello, Francesca
2022JSWSC..12....2E    Altcode:
  The Solar Activity Magnetic Monitor (SAMM) Network (SAMNet) is a
  future UK-led international network of ground-based solar telescope
  stations. SAMNet, at its full capacity, will continuously monitor
  the Sun's intensity, magnetic, and Doppler velocity fields at
  multiple heights in the solar atmosphere (from photosphere to upper
  chromosphere). Each SAMM sentinel will be equipped with a cluster of
  identical telescopes each with a different magneto-optical filter (MOFs)
  to take observations in K I, Na D, and Ca I spectral bands. A subset
  of SAMM stations will have white-light coronagraphs and emission line
  coronal spectropolarimeters. The objectives of SAMNet are to provide
  observational data for space weather research and forecast. The goal
  is to achieve an operationally sufficient lead time of e.g., flare
  warning of 2-8 h and provide many sought-after continuous synoptic
  maps (e.g., LoS magnetic and velocity fields, intensity) of the lower
  solar atmosphere with a spatial resolution limited only by seeing or
  diffraction limit, and with a cadence of 10 min. The individual SAMM
  sentinels will be connected to their master HQ hub where data received
  from all the slave stations will be automatically processed and flare
  warning issued up to 26 h in advance.

---------------------------------------------------------
Title: HiRISE - High-Resolution Imaging and Spectroscopy Explorer
    - Ultrahigh resolution, interferometric and external occulting
    coronagraphic science
Authors: Erdélyi, Robertus; Damé, Luc; Fludra, Andrzej; Mathioudakis,
   Mihalis; Amari, T.; Belucz, B.; Berrilli, F.; Bogachev, S.; Bolsée,
   D.; Bothmer, V.; Brun, S.; Dewitte, S.; de Wit, T. Dudok; Faurobert,
   M.; Gizon, L.; Gyenge, N.; Korsós, M. B.; Labrosse, N.; Matthews,
   S.; Meftah, M.; Morgan, H.; Pallé, P.; Rochus, P.; Rozanov, E.;
   Schmieder, B.; Tsinganos, K.; Verwichte, E.; Zharkov, S.; Zuccarello,
   F.; Wimmer-Schweingruber, R.
2022ExA...tmp...21E    Altcode:
  Recent solar physics missions have shown the definite role of waves and
  magnetic fields deep in the inner corona, at the chromosphere-corona
  interface, where dramatic and physically dominant changes occur. HiRISE
  (High Resolution Imaging and Spectroscopy Explorer), the ambitious new
  generation ultra-high resolution, interferometric, and coronagraphic,
  solar physics mission, proposed in response to the ESA Voyage 2050
  Call, would address these issues and provide the best-ever and most
  complete solar observatory, capable of ultra-high spatial, spectral,
  and temporal resolution observations of the solar atmosphere, from the
  photosphere to the corona, and of new insights of the solar interior
  from the core to the photosphere. HiRISE, at the L1 Lagrangian
  point, would provide meter class FUV imaging and spectro-imaging,
  EUV and XUV imaging and spectroscopy, magnetic fields measurements,
  and ambitious and comprehensive coronagraphy by a remote external
  occulter (two satellites formation flying 375 m apart, with a
  coronagraph on a chaser satellite). This major and state-of-the-art
  payload would allow us to characterize temperatures, densities, and
  velocities in the solar upper chromosphere, transition zone, and inner
  corona with, in particular, 2D very high resolution multi-spectral
  imaging-spectroscopy, and, direct coronal magnetic field measurement,
  thus providing a unique set of tools to understand the structure and
  onset of coronal heating. HiRISE's objectives are natural complements
  to the Parker Solar Probe and Solar Orbiter-type missions. We present
  the science case for HiRISE which will address: i) the fine structure
  of the chromosphere-corona interface by 2D spectroscopy in FUV at
  very high resolution; ii) coronal heating roots in the inner corona by
  ambitious externally-occulted coronagraphy; iii) resolved and global
  helioseismology thanks to continuity and stability of observing at the
  L1 Lagrange point; and iv) solar variability and space climate with,
  in addition, a global comprehensive view of UV variability.

---------------------------------------------------------
Title: Implications of spicule activity on coronal loop heating and
    catastrophic cooling
Authors: Nived, V. N.; Scullion, E.; Doyle, J. G.; Susino, R.; Antolin,
   P.; Spadaro, D.; Sasso, C.; Sahin, S.; Mathioudakis, M.
2022MNRAS.509.5523N    Altcode: 2021arXiv211107967N; 2021MNRAS.tmp.3004N
  We report on the properties of coronal loop foot-point heating
  with observations at the highest resolution, from the CRisp Imaging
  Spectro-Polarimeter located at the Swedish 1-m Solar Telescope and
  co-aligned NASA Solar Dynamics Observatory observations, of Type II
  spicules in the chromosphere and their signatures in the extreme
  ultraviolet (EUV) corona. Here, we address one important issue,
  as to why there is not always a one-to-one correspondence, between
  Type II spicules and hot coronal plasma signatures, i.e. beyond
  TR temperatures. We do not detect any difference in their spectral
  properties in a quiet Sun region compared to a region dominated by
  coronal loops. On the other hand, the number density close to the
  foot-points in the active region is found to be an order of magnitude
  higher than in the quiet Sun case. A differential emission measure
  analysis reveals a peak at ~5 × 10<SUP>5</SUP> K of the order of
  10<SUP>22</SUP> cm<SUP>-5</SUP> K<SUP>-1</SUP>. Using this result as
  a constraint, we conduct numerical simulations and show that with an
  energy input of 1.25 × 10<SUP>24</SUP> erg (corresponding to ~10 RBEs
  contributing to the burst) we manage to reproduce the observation very
  closely. However, simulation runs with lower thermal energy input do not
  reproduce the synthetic AIA 171 Å signatures, indicating that there
  is a critical number of spicules required in order to account for the
  AIA 171 Å signatures in the simulation. Furthermore, the higher energy
  (1.25 × 10<SUP>24</SUP> erg) simulations reproduce catastrophic cooling
  with a cycle duration of ~5 h, matching a periodicity we observe in
  the EUV observations.

---------------------------------------------------------
Title: The high-energy Sun - probing the origins of particle
    acceleration on our nearest star
Authors: Matthews, S. A.; Reid, H. A. S.; Baker, D.; Bloomfield, D. S.;
   Browning, P. K.; Calcines, A.; Del Zanna, G.; Erdelyi, R.; Fletcher,
   L.; Hannah, I. G.; Jeffrey, N.; Klein, L.; Krucker, S.; Kontar, E.;
   Long, D. M.; MacKinnon, A.; Mann, G.; Mathioudakis, M.; Milligan,
   R.; Nakariakov, V. M.; Pesce-Rollins, M.; Shih, A. Y.; Smith, D.;
   Veronig, A.; Vilmer, N.
2021ExA...tmp..135M    Altcode:
  As a frequent and energetic particle accelerator, our Sun provides
  us with an excellent astrophysical laboratory for understanding
  the fundamental process of particle acceleration. The exploitation
  of radiative diagnostics from electrons has shown that acceleration
  operates on sub-second time scales in a complex magnetic environment,
  where direct electric fields, wave turbulence, and shock waves all
  must contribute, although precise details are severely lacking. Ions
  were assumed to be accelerated in a similar manner to electrons, but
  γ-ray imaging confirmed that emission sources are spatially separated
  from X-ray sources, suggesting distinctly different acceleration
  mechanisms. Current X-ray and γ-ray spectroscopy provides only a basic
  understanding of accelerated particle spectra and the total energy
  budgets are therefore poorly constrained. Additionally, the recent
  detection of relativistic ion signatures lasting many hours, without
  an electron counterpart, is an enigma. We propose a single platform
  to directly measure the physical conditions present in the energy
  release sites and the environment in which the particles propagate and
  deposit their energy. To address this fundamental issue, we set out
  a suite of dedicated instruments that will probe both electrons and
  ions simultaneously to observe; high (seconds) temporal resolution
  photon spectra (4 keV - 150 MeV) with simultaneous imaging (1 keV -
  30 MeV), polarization measurements (5-1000 keV) and high spatial and
  temporal resolution imaging spectroscopy in the UV/EUV/SXR (soft X-ray)
  regimes. These instruments will observe the broad range of radiative
  signatures produced in the solar atmosphere by accelerated particles.

---------------------------------------------------------
Title: Constraining the magnetic vector in the quiet solar photosphere
    and the impact of instrumental degradation
Authors: Campbell, R. J.; Shelyag, S.; Quintero Noda, C.; Mathioudakis,
   M.; Keys, P. H.; Reid, A.
2021A&A...654A..11C    Altcode: 2021arXiv210701519C
  Context. With the advent of next generation high resolution telescopes,
  our understanding of how the magnetic field is organized in the
  internetwork (IN) photosphere is likely to advance significantly. <BR />
  Aims: We aim to evaluate the extent to which we can retrieve accurate
  information about the magnetic vector in the IN photosphere using
  inversion techniques. <BR /> Methods: We use a snapshot produced from
  high resolution three-dimensional magnetohydrodynamic (MHD) simulations
  and employ the Stokes Inversions based on Response functions (SIR) code
  to produce synthetic observables in the same near infrared spectral
  window as observed by the GREGOR Infrared Spectrograph (GRIS), which
  contains the highly magnetically sensitive photospheric Fe I line pair
  at 15 648.52 Å and 15 652.87 Å. We then use a parallelized wrapper to
  SIR to perform nearly 14 million inversions of the synthetic spectra to
  test how well the `true' MHD atmospheric parameters can be constrained
  statistically. Finally, we degrade the synthetic Stokes vector
  spectrally and spatially to GREGOR resolutions and examine how this
  influences real observations, considering the impact of stray light,
  spatial resolution and signal-to-noise (S/N) in particular. <BR />
  Results: We find that the depth-averaged parameters can be recovered
  by the inversions of the undegraded profiles, and by adding simple
  gradients to magnetic field strength, inclination, and line of sight
  velocity we show that an improvement in the χ<SUP>2</SUP> value
  is achieved. We also evaluate the extent to which we can constrain
  these parameters at various optical depths, with the kinematic and
  thermodynamic parameters sensitive deeper in the atmosphere than
  the magnetic parameters. We find the S/N and spatial resolution both
  play a significant role in determining how the degraded atmosphere
  appears. At the same time, we find that the magnetic and kinematic
  parameters are invariant upon inclusion of an unpolarized stray
  light. We compare our results to recent IN observations obtained
  by GREGOR. We studied a linear polarization feature which resembles
  those recently observed by GRIS in terms of appearing as `loop-like'
  structures and exhibiting very similar magnetic flux density. Thus,
  we demonstrate that realistic MHD simulations are capable of showing
  close agreement with real observations, and the symbiosis between them
  and observations continues to prove essential. We finally discuss the
  considerations that must be made for DKIST-era observations.

---------------------------------------------------------
Title: Oscillations in the line-of-sight magnetic field strength in
    a pore observed by the GREGOR Infrared Spectrograph (GRIS)
Authors: Nelson, C. J.; Campbell, R. J.; Mathioudakis, M.
2021A&A...654A..50N    Altcode: 2021arXiv210710183N
  Context. Numerous magnetohydrodynamic oscillations have been reported
  within solar pores over the past few decades, including in line-of-sight
  (LOS) velocities, intensities, and magnetic field strengths. <BR />
  Aims: Our aim is to identify whether high-amplitude oscillations in the
  LOS magnetic field strength can be detected within a pore located in
  Active Region 12748 and to investigate which physical mechanisms could
  be responsible for them. <BR /> Methods: A solar pore was observed on
  1 September 2019 using the GREGOR Infrared Spectrograph instrument for
  around one hour. Full-Stokes vectors were sampled in a 37 Å window
  containing the Fe I 15 648.52 Å line (effective Landé g factor of
  3). The LOS magnetic field strength was inferred using the strong-field
  approximation. Additionally, the Stokes Inversion based on Response
  functions code was used to gain a more complete understanding of the
  physical properties of the solar atmosphere at the locations of these
  oscillations. <BR /> Results: Oscillations of more than 100 G are
  observed in the LOS magnetic field in the period window between 600
  and 1272 s at three localised (&gt; 1″<SUP>2</SUP>) regions. These
  oscillations have coherence across individual regions, indicating that
  jitter cannot account for their occurrence. Longer-period amplitude
  variations, amplitudes over 200 G, are also detected, but they
  have periods outside of the cone-of-influence. Numerical inversions
  confirm both oscillations in the LOS magnetic field strength at optical
  depths of around log τ<SUB>5000</SUB> = −0.5 (potentially caused by
  compression) and other effects (e.g. changes in the optical depth or the
  inclination of the magnetic field) may account for these changes. <BR />
  Conclusions: The oscillations in the separations of the Stokes-V lobes
  of the 15 648.52 Å line appear to be solar in nature. Future work will
  be required to understand whether these are truly oscillations in the
  magnetic field strength at a specific depth in the solar atmosphere
  or whether other effects are responsible for these signatures.

---------------------------------------------------------
Title: Flare-induced Sunquake Signatures in the Ultraviolet as
    Observed by the Atmospheric Imaging Assembly
Authors: Quinn, Sean; Mathioudakis, Mihalis; Nelson, Christopher J.;
   Milligan, Ryan O.; Reid, Aaron; Jess, David B.
2021ApJ...920...25Q    Altcode: 2021arXiv210505704Q
  Sunquakes (SQs) have been routinely observed in the solar photosphere,
  but it is only recently that signatures of these events have been
  detected in the chromosphere. We investigate whether signatures of
  SQs are common in ultraviolet (UV) continua that sample the solar
  plasma several hundred km above where SQs are typically detected. We
  analyze observations from the Solar Dynamics Observatory's Atmospheric
  Imaging Assembly (SDO/AIA) 1600 and 1700 Å passbands, for SQ signatures
  induced by the flares of Solar Cycle 24. We base our analysis on the
  62 SQs detected in the recent statistical study presented by Sharykin
  &amp; Kosovichev. We find that 9 out of 62 SQ candidates produced a
  response that is clearly detected in running-difference images from
  the AIA 1600 and 1700 Å channels. A binary frequency filter with a
  width of 2 mHz, centered on 6 mHz, was applied to the data. The first
  signature of each SQ was detected at distances between 5.2 and 25.7
  Mm from the associated flare ribbon. Time-distance and regression
  analysis allowed us to calculate the apparent transverse velocities
  of the SQs in the UV data sets and found maximum velocities as high
  as 41 km s<SUP>-1</SUP>, 87 Mm away from the SQ source. Our analysis
  shows that flare-induced SQ signatures can be detected in the SDO/AIA
  1600 and 1700 Å passbands, hinting at their presence in the lower
  chromosphere. There was no apparent correlation between GOES flare
  classification and the appearance of the SQ at these heights.

---------------------------------------------------------
Title: Temporal evolution of small-scale internetwork magnetic fields
    in the solar photosphere (Corrigendum)
Authors: Campbell, R. J.; Mathioudakis, M.; Collados, M.; Keys, P. H.;
   Asensio Ramos, A.; Nelson, C. J.; Kuridze, D.; Reid, A.
2021A&A...652C...2C    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Flare-induced Photospheric Velocity Diagnostics
Authors: Monson, Aaron J.; Mathioudakis, Mihalis; Reid, Aaron;
   Milligan, Ryan; Kuridze, David
2021ApJ...915...16M    Altcode: 2021arXiv210502199M
  We present radiative-hydrodynamic simulations of solar flares generated
  by the RADYN and RH codes to study the perturbations induced in
  photospheric Fe I lines by electron beam heating. We investigate how
  variations in the beam parameters result in discernible differences
  in the induced photospheric velocities. Line synthesis revealed a
  significant chromospheric contribution to the line profiles resulting
  in an apparent red asymmetry by as much as 40 m s<SUP>-1</SUP> close
  to the time of maximum beam heating, which was not reflective of the
  upflow velocities that arose from the radiative-hydrodynamic simulations
  at those times. The apparent redshift to the overall line profile was
  produced by significant chromospheric emission that was blueshifted
  by as much as 400 m s<SUP>-1</SUP> and fills in the blue side of
  the near-stationary photospheric absorption profile. The velocity
  information that can be retrieved from photospheric line profiles during
  flares must therefore be treated with care to mitigate the effects of
  higher parts of the atmosphere providing an erroneous velocity signal.

---------------------------------------------------------
Title: The National Science Foundation's Daniel K. Inouye Solar
    Telescope — Status Update
Authors: Rimmele, T.; Woeger, F.; Tritschler, A.; Casini, R.; de Wijn,
   A.; Fehlmann, A.; Harrington, D.; Jaeggli, S.; Anan, T.; Beck, C.;
   Cauzzi, G.; Schad, T.; Criscuoli, S.; Davey, A.; Lin, H.; Kuhn, J.;
   Rast, M.; Goode, P.; Knoelker, M.; Rosner, R.; von der Luehe, O.;
   Mathioudakis, M.; Dkist Team
2021AAS...23810601R    Altcode:
  The National Science Foundation's 4m Daniel K. Inouye Solar Telescope
  (DKIST) on Haleakala, Maui is now the largest solar telescope in the
  world. DKIST's superb resolution and polarimetric sensitivity will
  enable astronomers to unravel many of the mysteries the Sun presents,
  including the origin of solar magnetism, the mechanisms of coronal
  heating and drivers of flares and coronal mass ejections. Five
  instruments, four of which provide highly sensitive measurements
  of solar magnetic fields, including the illusive magnetic field of
  the faint solar corona. The DKIST instruments will produce large and
  complex data sets, which will be distributed through the NSO/DKIST Data
  Center. DKIST has achieved first engineering solar light in December
  of 2019. Due to COVID the start of the operations commissioning phase
  is delayed and is now expected for fall of 2021. We present a status
  update for the construction effort and progress with the operations
  commissioning phase.

---------------------------------------------------------
Title: Chromospheric Heating by Magnetohydrodynamic Waves and
    Instabilities
Authors: Srivastava, A. K.; Ballester, J. L.; Cally, P. S.; Carlsson,
   M.; Goossens, M.; Jess, D. B.; Khomenko, E.; Mathioudakis, M.;
   Murawski, K.; Zaqarashvili, T. V.
2021JGRA..12629097S    Altcode: 2021arXiv210402010S
  The importance of the chromosphere in the mass and energy transport
  within the solar atmosphere is now widely recognized. This review
  discusses the physics of magnetohydrodynamic waves and instabilities
  in large-scale chromospheric structures as well as in magnetic flux
  tubes. We highlight a number of key observational aspects that have
  helped our understanding of the role of the solar chromosphere
  in various dynamic processes and wave phenomena, and the heating
  scenario of the solar chromosphere is also discussed. The review
  focuses on the physics of waves and invokes the basics of plasma
  instabilities in the context of this important layer of the solar
  atmosphere. Potential implications, future trends and outstanding
  questions are also delineated.

---------------------------------------------------------
Title: Critical Science Plan for the Daniel K. Inouye Solar Telescope
    (DKIST)
Authors: Rast, Mark P.; Bello González, Nazaret; Bellot Rubio,
   Luis; Cao, Wenda; Cauzzi, Gianna; Deluca, Edward; de Pontieu, Bart;
   Fletcher, Lyndsay; Gibson, Sarah E.; Judge, Philip G.; Katsukawa,
   Yukio; Kazachenko, Maria D.; Khomenko, Elena; Landi, Enrico; Martínez
   Pillet, Valentín; Petrie, Gordon J. D.; Qiu, Jiong; Rachmeler,
   Laurel A.; Rempel, Matthias; Schmidt, Wolfgang; Scullion, Eamon; Sun,
   Xudong; Welsch, Brian T.; Andretta, Vincenzo; Antolin, Patrick; Ayres,
   Thomas R.; Balasubramaniam, K. S.; Ballai, Istvan; Berger, Thomas E.;
   Bradshaw, Stephen J.; Campbell, Ryan J.; Carlsson, Mats; Casini,
   Roberto; Centeno, Rebecca; Cranmer, Steven R.; Criscuoli, Serena;
   Deforest, Craig; Deng, Yuanyong; Erdélyi, Robertus; Fedun, Viktor;
   Fischer, Catherine E.; González Manrique, Sergio J.; Hahn, Michael;
   Harra, Louise; Henriques, Vasco M. J.; Hurlburt, Neal E.; Jaeggli,
   Sarah; Jafarzadeh, Shahin; Jain, Rekha; Jefferies, Stuart M.; Keys,
   Peter H.; Kowalski, Adam F.; Kuckein, Christoph; Kuhn, Jeffrey R.;
   Kuridze, David; Liu, Jiajia; Liu, Wei; Longcope, Dana; Mathioudakis,
   Mihalis; McAteer, R. T. James; McIntosh, Scott W.; McKenzie, David
   E.; Miralles, Mari Paz; Morton, Richard J.; Muglach, Karin; Nelson,
   Chris J.; Panesar, Navdeep K.; Parenti, Susanna; Parnell, Clare E.;
   Poduval, Bala; Reardon, Kevin P.; Reep, Jeffrey W.; Schad, Thomas A.;
   Schmit, Donald; Sharma, Rahul; Socas-Navarro, Hector; Srivastava,
   Abhishek K.; Sterling, Alphonse C.; Suematsu, Yoshinori; Tarr, Lucas
   A.; Tiwari, Sanjiv; Tritschler, Alexandra; Verth, Gary; Vourlidas,
   Angelos; Wang, Haimin; Wang, Yi-Ming; NSO and DKIST Project; DKIST
   Instrument Scientists; DKIST Science Working Group; DKIST Critical
   Science Plan Community
2021SoPh..296...70R    Altcode: 2020arXiv200808203R
  The National Science Foundation's Daniel K. Inouye Solar Telescope
  (DKIST) will revolutionize our ability to measure, understand,
  and model the basic physical processes that control the structure
  and dynamics of the Sun and its atmosphere. The first-light DKIST
  images, released publicly on 29 January 2020, only hint at the
  extraordinary capabilities that will accompany full commissioning of
  the five facility instruments. With this Critical Science Plan (CSP)
  we attempt to anticipate some of what those capabilities will enable,
  providing a snapshot of some of the scientific pursuits that the DKIST
  hopes to engage as start-of-operations nears. The work builds on the
  combined contributions of the DKIST Science Working Group (SWG) and
  CSP Community members, who generously shared their experiences, plans,
  knowledge, and dreams. Discussion is primarily focused on those issues
  to which DKIST will uniquely contribute.

---------------------------------------------------------
Title: Temporal evolution of small-scale internetwork magnetic fields
    in the solar photosphere
Authors: Campbell, R. J.; Mathioudakis, M.; Collados, M.; Keys, P. H.;
   Asensio Ramos, A.; Nelson, C. J.; Kuridze, D.; Reid, A.
2021A&A...647A.182C    Altcode: 2021arXiv210200942C
  Context. While the longitudinal field that dominates in photospheric
  network regions has been studied extensively, small-scale transverse
  fields have recently been found to be ubiquitous in the quiet
  internetwork photosphere and this merits further study. Furthermore,
  few observations have been able to capture how this field evolves. <BR
  /> Aims: We aim to statistically characterize the magnetic vector in
  a quiet Sun internetwork region and observe the temporal evolution of
  specific small-scale magnetic features. <BR /> Methods: We present
  two high spatio-temporal resolution observations that reveal the
  dynamics of two disk-centre internetwork regions taken by the new GREGOR
  Infrared Spectrograph Integral Field Unit with the highly magnetically
  sensitive photospheric Fe I line pair at 15648.52 Å and 15652.87
  Å. We record the full Stokes vector and apply inversions with the
  Stokes inversions based on response functions code to retrieve the
  parameters characterizing the atmosphere. We consider two inversion
  schemes: scheme 1 (S1), where a magnetic atmosphere is embedded in
  a field free medium, and scheme 2 (S2), with two magnetic models
  and a fixed 30% stray light component. <BR /> Results: The magnetic
  properties produced from S1 inversions returned a median magnetic
  field strength of 200 and 240 G for the two datasets, respectively. We
  consider the median transverse (horizontal) component, among pixels
  with Stokes Q or U, and the median unsigned longitudinal (vertical)
  component, among pixels with Stokes V, above a noise threshold. We
  determined the former to be 263 G and 267 G, and the latter to be 131
  G and 145 G, for the two datasets, respectively. Finally, we present
  three regions of interest, tracking the dynamics of small-scale magnetic
  features. We apply S1 and S2 inversions to specific profiles of interest
  and find that the latter produces better approximations when there is
  evidence of mixed polarities. We find patches of linear polarization
  with magnetic flux density of the order of 130−150 G and find that
  linear polarization appears preferentially at granule-intergranular
  lane boundaries. The weak magnetic field appears to be organized in
  terms of complex `loop-like' structures, with transverse fields often
  flanked by opposite polarity longitudinal fields.

---------------------------------------------------------
Title: Mapping the Magnetic Field of Flare Coronal Loops
Authors: Kuridze, David; Morgan, Huw; Oliver, Ramon; Mathioudakis,
   Mihalis; Koza, Julius
2021cosp...43E1791K    Altcode:
  The magnetic field is key to the dynamics, evolution, and heating
  of the solar atmosphere, yet direct measurements are rare and highly
  uncertain. We report on the unique observation of flaring coronal loops
  at the solar limb using high-resolution imaging spectropolarimetry from
  the Swedish 1-m Solar Telescope. The vantage position, orientation,
  and nature of the chromospheric material that filled the flare loops
  allowed us to determine their magnetic field with unprecedented accuracy
  using the weak-field approximation method. Our analysis reveals coronal
  magnetic field strengths as high as 350 G at heights up to 25 Mm above
  the solar limb. These measurements are substantially higher than a
  number of previous estimates and may have considerable implications
  for our current understanding of the extended solar atmosphere.

---------------------------------------------------------
Title: High-Cadence DST/ROSA Observations of the NUV/Blue Continuum
    Radiation in a Solar Flare
Authors: Kowalski, A. F.; Keys, P.; Mathioudakis, M.
2020AGUFMSH0500011K    Altcode:
  Radiative-hydrodynamic models of solar flares provide sophisticated
  predictions of the ultraviolet and optical continuum shape and
  strength on shorter than 1 s timescales covering a broad wavelength
  range. However, most optical observations of solar flares in the
  modern era are not obtained at fast cadence and are not optimized
  at blue continuum wavelengths, which provide a critical constraint
  on the heating properties at large column mass. To rectify this
  major gap in our knowledge of solar flare spectra, custom Balmer
  jump filters were designed for the ROSA instrument at the Dunn Solar
  Telescope. Unprecedented observations at 7.5 - 30 frames per second
  were obtained covering the C9.7 flare SOL20141025T15:52 in NOAA AR
  12192 during the NSO's Service Mode operations (and provided by the
  F-CHROMA solar flare database). We report on how the flare response in
  the 350 nm and 417 nm ROSA filters constrains several common assumptions
  employed in modern flare modeling, such as the duration of individual
  heating bursts. We also report on the Balmer jump properties in this
  flare and compare to several M dwarf flares, which have been observed
  in identical filters using the ULTRACAM and ARCTIC instruments on the
  4.2m WHT, the 3.6m NTT, and the 3.5m ARC telescope. We compare the
  light curves to radiative-hydrodynamic model predictions of the 350
  nm brightness evolution on short timescales.

---------------------------------------------------------
Title: An Introduction to Photospheric Flare Line Diagnostics
Authors: Monson, A.; Mathioudakis, M.; Milligan, R.; Reid, A.;
   Kuridze, D.
2020AGUFMSH057..04M    Altcode:
  In preparation for solar cycle 25, we present radiative hydrodynamic
  flare models from the F-CHROMA archive constructed using the RADYN and
  RH codes. We simulate potential observable perturbations seen in the
  line-of-sight velocity and heating induced in the photosphere during
  a flare. Many works have focused on the recreation of chromospheric
  spectral line profiles as the atmosphere rapidly heats and expands
  due to the injection of energy from magnetic reconnection. This
  extreme heating mechanism can permeate through the upper atmosphere
  and affect the lowest levels of the solar atmosphere. This results
  in an observable brightening and Doppler shifting of spectral lines
  formed in the deepest regions, though the extent of this photospheric
  reaction is still not fully characterised. We investigate how variations
  in the properties of a solar flare-accelerated electron beam result in
  discernible asymmetries in the flaring profiles of several deep forming
  Fe I spectral lines. Through analysis of the contribution functions
  and response functions of these lines during a flare, we have found
  an unprecedented level of high velocity chromospheric contribution
  which significantly alters the emergent profile of these lines. This
  comparatively weak, high velocity surplus contributing region of
  the chromosphere can result in false red shifts and/or significantly
  adds to the flaring Doppler shifted profile, resulting in a greater
  blue shift of the line core, which had previously been assumed as a
  purely photospheric velocity diagnostic. Based on this evidence, it
  is concluded that any future work using these photospheric lines to
  diagnose properties of the photosphere in a flaring atmosphere must
  be carefully analysed to mitigate effect of higher forming regions
  providing a surplus velocity signal.

---------------------------------------------------------
Title: The Daniel K. Inouye Solar Telescope - Observatory Overview
Authors: Rimmele, Thomas R.; Warner, Mark; Keil, Stephen L.; Goode,
   Philip R.; Knölker, Michael; Kuhn, Jeffrey R.; Rosner, Robert R.;
   McMullin, Joseph P.; Casini, Roberto; Lin, Haosheng; Wöger, Friedrich;
   von der Lühe, Oskar; Tritschler, Alexandra; Davey, Alisdair; de Wijn,
   Alfred; Elmore, David F.; Fehlmann, André; Harrington, David M.;
   Jaeggli, Sarah A.; Rast, Mark P.; Schad, Thomas A.; Schmidt, Wolfgang;
   Mathioudakis, Mihalis; Mickey, Donald L.; Anan, Tetsu; Beck, Christian;
   Marshall, Heather K.; Jeffers, Paul F.; Oschmann, Jacobus M.; Beard,
   Andrew; Berst, David C.; Cowan, Bruce A.; Craig, Simon C.; Cross,
   Eric; Cummings, Bryan K.; Donnelly, Colleen; de Vanssay, Jean-Benoit;
   Eigenbrot, Arthur D.; Ferayorni, Andrew; Foster, Christopher; Galapon,
   Chriselle Ann; Gedrites, Christopher; Gonzales, Kerry; Goodrich, Bret
   D.; Gregory, Brian S.; Guzman, Stephanie S.; Guzzo, Stephen; Hegwer,
   Steve; Hubbard, Robert P.; Hubbard, John R.; Johansson, Erik M.;
   Johnson, Luke C.; Liang, Chen; Liang, Mary; McQuillen, Isaac; Mayer,
   Christopher; Newman, Karl; Onodera, Brialyn; Phelps, LeEllen; Puentes,
   Myles M.; Richards, Christopher; Rimmele, Lukas M.; Sekulic, Predrag;
   Shimko, Stephan R.; Simison, Brett E.; Smith, Brett; Starman, Erik;
   Sueoka, Stacey R.; Summers, Richard T.; Szabo, Aimee; Szabo, Louis;
   Wampler, Stephen B.; Williams, Timothy R.; White, Charles
2020SoPh..295..172R    Altcode:
  We present an overview of the National Science Foundation's Daniel
  K. Inouye Solar Telescope (DKIST), its instruments, and support
  facilities. The 4 m aperture DKIST provides the highest-resolution
  observations of the Sun ever achieved. The large aperture of
  DKIST combined with state-of-the-art instrumentation provide the
  sensitivity to measure the vector magnetic field in the chromosphere
  and in the faint corona, i.e. for the first time with DKIST we will
  be able to measure and study the most important free-energy source
  in the outer solar atmosphere - the coronal magnetic field. Over its
  operational lifetime DKIST will advance our knowledge of fundamental
  astronomical processes, including highly dynamic solar eruptions
  that are at the source of space-weather events that impact our
  technological society. Design and construction of DKIST took over two
  decades. DKIST implements a fast (f/2), off-axis Gregorian optical
  design. The maximum available field-of-view is 5 arcmin. A complex
  thermal-control system was implemented in order to remove at prime
  focus the majority of the 13 kW collected by the primary mirror and
  to keep optical surfaces and structures at ambient temperature, thus
  avoiding self-induced local seeing. A high-order adaptive-optics
  system with 1600 actuators corrects atmospheric seeing enabling
  diffraction limited imaging and spectroscopy. Five instruments, four
  of which are polarimeters, provide powerful diagnostic capability
  over a broad wavelength range covering the visible, near-infrared,
  and mid-infrared spectrum. New polarization-calibration strategies
  were developed to achieve the stringent polarization accuracy
  requirement of 5×10<SUP>−4</SUP>. Instruments can be combined and
  operated simultaneously in order to obtain a maximum of observational
  information. Observing time on DKIST is allocated through an open,
  merit-based proposal process. DKIST will be operated primarily in
  "service mode" and is expected to on average produce 3 PB of raw
  data per year. A newly developed data center located at the NSO
  Headquarters in Boulder will initially serve fully calibrated data to
  the international users community. Higher-level data products, such as
  physical parameters obtained from inversions of spectro-polarimetric
  data will be added as resources allow.

---------------------------------------------------------
Title: Statistical Signatures of Nanoflare Activity. II. A Nanoflare
    Explanation for Periodic Brightenings in Flare Stars Observed by NGTS
Authors: Dillon, C. J.; Jess, D. B.; Mathioudakis, M.; Watson, C. A.;
   Jackman, J. A. G.; Wheatley, P. J.; Goad, M. R.; Casewell, S. L.;
   Anderson, D. R.; Burleigh, M. R.; Raynard, L.; West, R. G.
2020ApJ...904..109D    Altcode: 2020arXiv201004167D
  Several studies have documented periodic and quasi-periodic signals
  from the time series of dMe flare stars and other stellar sources. Such
  periodic signals, observed within quiescent phases (i.e., devoid of
  larger-scale microflare or flare activity), range in a period from
  1 to 1000 s and hence have been tentatively linked to ubiquitous
  p-mode oscillations generated in the convective layers of the star. As
  such, most interpretations for the observed periodicities have been
  framed in terms of magnetohydrodynamic wave behavior. However,
  we propose that a series of continuous nanoflares, based upon a
  power-law distribution, can provide a similar periodic signal in the
  associated time series. Adapting previous statistical analyses of
  solar nanoflare signals, we find the first statistical evidence for
  stellar nanoflare signals embedded within the noise envelope of M-type
  stellar lightcurves. Employing data collected by the Next Generation
  Transit Survey (NGTS), we find evidence for stellar nanoflare activity
  demonstrating a flaring power-law index of 3.25 ± 0.20, alongside
  a decay timescale of 200 ± 100 s. We also find that synthetic time
  series, consistent with the observations of dMe flare star lightcurves,
  are capable of producing quasi-periodic signals in the same frequency
  range as p-mode signals, despite being purely composed of impulsive
  signatures. Phenomena traditionally considered a consequence of wave
  behavior may be described by a number of high-frequency but discrete
  nanoflare energy events. This new physical interpretation presents a
  novel diagnostic capability, by linking observed periodic signals to
  given nanoflare model conditions.

---------------------------------------------------------
Title: Power-law energy distributions of small-scale impulsive events
on the active Sun: results from IRIS
Authors: Vilangot Nhalil, Nived; Nelson, Chris J.; Mathioudakis,
   Mihalis; Doyle, J. Gerry; Ramsay, Gavin
2020MNRAS.499.1385V    Altcode: 2020MNRAS.tmp.2719N; 2020arXiv200903123V
  Numerous studies have analysed inferred power-law distributions
  between frequency and energy of impulsive events in the outer solar
  atmosphere in an attempt to understand the predominant energy supply
  mechanism in the corona. Here, we apply a burst detection algorithm to
  high-resolution imaging data obtained by the Interface Region Imaging
  Spectrograph to further investigate the derived power-law index, γ,
  of bright impulsive events in the transition region. Applying the
  algorithm with a constant minimum event lifetime (of either 60 s or
  110 s) indicated that the target under investigation, such as Plage
  and Sunspot, has an influence on the observed power-law index. For
  regions dominated by sunspots, we always find γ &lt; 2; however,
  for data sets where the target is a plage region, we often find that
  γ &gt; 2 in the energy range (~10<SUP>23</SUP>, ~10<SUP>26</SUP>)
  erg. Applying the algorithm with a minimum event lifetime of three
  time-steps indicated that cadence was another important factor, with
  the highest cadence data sets returning γ &gt; 2 values. The estimated
  total radiative power obtained for the observed energy distributions
  is typically 10-25 per cent of what would be required to sustain the
  corona indicating that impulsive events in this energy range are not
  sufficient to solve coronal heating. If we were to extend the power-law
  distribution down to an energy of 10<SUP>21</SUP> erg, and assume parity
  between radiative energy release and the deposition of thermal energy,
  then such bursts could provide 25-50 per cent of the required energy
  to account for the coronal heating problem.

---------------------------------------------------------
Title: Umbral chromospheric fine structure and umbral flashes modelled
as one: The corrugated umbra
Authors: Henriques, Vasco M. J.; Nelson, Chris J.; Rouppe van der
   Voort, Luc H. M.; Mathioudakis, Mihalis
2020A&A...642A.215H    Altcode: 2020arXiv200805482H
  Context. The chromosphere of the umbra of sunspots features an
  assortment of dynamic fine structures that are poorly understood and
  often studied separately. Small-scale umbral brightenings (SSUBs),
  umbral microjets, spikes or short dynamic fibrils (SDFs), and umbral
  dark fibrils are found in any observation of the chromosphere with
  sufficient spatial resolution performed at the correct umbral flash
  stage and passband. Understanding these features means understanding
  the dynamics of the umbral chromosphere. <BR /> Aims: We aim to fully
  understand the dynamics of umbral chromosphere through analysis of the
  relationships between distinct observed fine features and to produce
  complete models that explain both spectral profiles and the temporal
  evolution of the features. We seek to relate such understanding to
  umbral flashes. <BR /> Methods: We studied the spatial and spectral
  co-evolution of SDFs, SSUBs, and umbral flashes in Ca II 8542 Å
  spectral profiles. We produced models that generate the spectral
  profiles for all classes of features using non-local thermodynamic
  equilibrium radiative transfer with a recent version of the NICOLE
  inversion code. <BR /> Results: We find that both bright SSUBs and dark
  SDF structures are described with a continuous feature in the parameter
  space that is distinct from the surroundings even in pixel-by-pixel
  inversions. We find a phase difference between such features and
  umbral flashes in both inverted line-of-sight velocities and timing
  of the brightenings. For umbral flashes themselves we resolve,
  for the first time in inversion-based semi-empirical modelling,
  the pre-flash downflows, post-flash upflows, and the counter-flows
  present during the umbral flash phase. We further present a simple
  time-dependent cartoon model that explains the dynamics and spectral
  profiles of both fine structure, dark and bright, and umbral flashes
  in umbral chromospheres. <BR /> Conclusions: The similarity of the
  profiles between the brightenings and umbral flashes, the pattern of
  velocities obtained from the inversions, and the phase relationships
  between the structures all lead us to put forward that all dynamic
  umbral chromospheric structures observed to this date are a locally
  delayed or locally early portion of the oscillatory flow pattern that
  generates flashes, secondary to the steepening large-scale acoustic
  waves at its source. Essentially, SSUBs are part of the same shock or
  merely compression front responsible for the spatially larger umbral
  flash phenomenon, but out of phase with the broader oscillation.

---------------------------------------------------------
Title: Evolution of downflows in the transition region above a
    sunspot over short time-scales
Authors: Nelson, C. J.; Krishna Prasad, S.; Mathioudakis, M.
2020A&A...640A.120N    Altcode: 2020arXiv200613617N
  Context. Downflows with potentially super-sonic velocities have been
  reported to occur in the transition region above many sunspots; however,
  how these signatures evolve over short time-scales in both spatial and
  spectral terms is still unknown and requires further research. <BR
  /> Aims: In this article, we investigate the evolution of downflows
  detected within spectral lines sampling the transition region on
  time-scales of the order of minutes and we search for clues as to
  the formation mechanisms of these features in co-temporal imaging
  data. <BR /> Methods: For the purposes of this article, we used
  high-resolution spectral and imaging data sampled by the Interface
  Region Imaging Spectrograph on the 20 and 21 May 2015 to identify and
  analyse downflows. Additionally, photospheric and coronal imaging data
  from the Hinode and Solar Dynamics Observatory satellites were studied
  to provide context about the wider solar atmosphere. <BR /> Results:
  Four downflows were identified and analysed through time. The potential
  super-sonic components of these downflows had widths of around 2″ and
  were observed to evolve over time-scales of the order of minutes. The
  measured apparent downflow velocities were structured both in time and
  space, with the highest apparent velocities occurring above a bright
  region detected in Si IV 1400 Å images. Downflows with apparent
  velocities below the super-sonic threshold that was assumed here
  were observed to extend a few arcseconds away from the foot-points,
  suggesting that the potential super-sonic components are linked to
  larger-scale flows. The electron density and mass flux for these events
  were found to be within the ranges of 10<SUP>9.6</SUP>-10<SUP>10.2</SUP>
  cm<SUP>-3</SUP> and 10<SUP>-6.81</SUP>-10<SUP>-7.48</SUP> g
  cm<SUP>-2</SUP> s<SUP>-1</SUP>, respectively. Finally, each downflow
  formed at the foot-point of thin "fingers", extending out around
  3-5″ in Si IV 1400 Å data with smaller widths (&lt; 1″) than
  the super-sonic downflow components. <BR /> Conclusions: Downflows
  can appear, disappear, and recur within time-scales of less than one
  hour in sunspots. As the potential super-sonic downflow signatures
  were detected at the foot-points of both extended fingers in Si IV
  1400 SJI data and sub-sonic downflows in Si IV 1394 Å spectra, it
  is likely that these events are linked to larger-scale flows within
  structures such as coronal loops.

---------------------------------------------------------
Title: Can active late-type stars contribute to the Galactic lithium
    abundance?
Authors: Kelly, Darnell E.; Christian, Damian J.; Mathioudakis,
   Mihalis; Jevremović, Darko
2020RAA....20..104K    Altcode:
  Lithium abundances in our Galaxy and especially <SUP>6</SUP>Li
  abundances provide important constraints on our understanding of
  Big Bang Nucleosynthesis (BBNS), stellar evolution and the creation
  of light elements by cosmic rays in the ISM. <SUP>6</SUP>Li has been
  detected in energetic solar events, one chromospherically active binary
  and several dwarf halo stars. Continuing our work on active late-type
  stars with high lithium abundances, we expand our study to consider
  if the flare origin of lithium created by spallation can contribute
  significantly to the Galactic abundance of lithium. We previously
  derived $\displaystyle \frac{{}^{6}{\rm{Li}}}{{}^{7}{\rm{Li}}}=0.030\pm
  0.010$?--&gt; for active K dwarf GJ 117 using VLT UVES observations. We
  find $\displaystyle \frac{{}^{6}{\rm{Li}}}{{}^{7}{\rm{Li}}}$?--&gt;
  ratios of 0.02 and 0.10 for two other stars in our sample, GJ 182
  and EUVE J1145-55.3A, respectively. Considering that these later
  type, active stars have significant flare rates and stellar winds,
  we have estimated the contribution of these stars to the Galactic
  lithium abundance. Given that K and M stars comprise over 84% of our
  Galaxy and that many of these can have significant stellar winds,
  we conclude that spallation in stellar flares can contribute 1% and
  up to 5% of the Galactic lithium abundance.

---------------------------------------------------------
Title: Spectral Characteristics and Formation Height of Off-limb
    Flare Ribbons
Authors: Kuridze, David; Mathioudakis, Mihalis; Heinzel, Petr; Koza,
   Július; Morgan, Huw; Oliver, Ramon; Kowalski, Adam F.; Allred, Joel C.
2020ApJ...896..120K    Altcode: 2020arXiv200510924K
  Flare ribbons are bright manifestations of flare energy dissipation
  in the lower solar atmosphere. For the first time, we report on
  high-resolution imaging spectroscopy observations of flare ribbons
  situated off limb in the Hβ and Ca II 8542 Å lines and make a detailed
  comparison with radiative hydrodynamic simulations. Observations of
  the X8.2 class solar flare SOL 2017-09-10T16:06 UT obtained with the
  Swedish Solar Telescope reveal bright horizontal emission layers
  in Hβ line-wing images located near the footpoints of the flare
  loops. The apparent separation between the ribbon observed in the Hβ
  wing and the nominal photospheric limb is about 300-500 km. The Ca II
  8542 Å line-wing images show much fainter ribbon emissions located
  right on the edge of the limb, without clear separation from the
  limb. RADYN models are used to investigate synthetic spectral line
  profiles for the flaring atmosphere, and good agreement is found
  with the observations. The simulations show that, toward the limb,
  where the line of sight is substantially oblique with respect to the
  vertical direction, the flaring atmosphere model reproduces the high
  contrast of the off-limb Hβ ribbons and their significant elevation
  above the photosphere. The ribbons in the Ca II 8542 Å line-wing
  images are located deeper in the lower solar atmosphere with a lower
  contrast. A comparison of the height deposition of electron beam energy
  and the intensity contribution function shows that the Hβ line-wing
  intensities can be a useful tracer of flare energy deposition in the
  lower solar atmosphere.

---------------------------------------------------------
Title: Chromospheric Bubbles in Solar Flares
Authors: Reid, A.; Zhigulin, B.; Carlsson, M.; Mathioudakis, M.
2020ApJ...894L..21R    Altcode: 2020arXiv200510586R
  We analyze a grid of radiative hydrodynamic simulations of solar flares
  to study the energy balance and response of the atmosphere to nonthermal
  electron beam heating. The appearance of chromospheric bubbles is one
  of the most notable features that we find in the simulations. These
  pockets of chromospheric plasma get trapped between the transition
  region and the lower atmosphere as it is superheated by the particle
  beam. The chromospheric bubbles are seen in the synthetic spectra,
  appearing as an additional component to Balmer line profiles with high
  Doppler velocities as high as 200 km s<SUP>-1</SUP>. Their signatures
  are also visible in the wings of Ca II 8542 Å line profiles. These
  bubbles of chromospheric plasma are driven upward by a wave front that
  is induced by the shock of energy deposition, and require a specific
  heating rate and atmospheric location to manifest.

---------------------------------------------------------
Title: Velocity Response of the Observed Explosive Events in the
    Lower Solar Atmosphere. I. Formation of the Flowing Cool-loop System
Authors: Srivastava, A. K.; Rao, Yamini K.; Konkol, P.; Murawski,
   K.; Mathioudakis, M.; Tiwari, Sanjiv K.; Scullion, E.; Doyle, J. G.;
   Dwivedi, B. N.
2020ApJ...894..155S    Altcode: 2020arXiv200402775S
  We observe plasma flows in cool loops using the Slit-Jaw Imager on board
  the Interface Region Imaging Spectrometer (IRIS). Huang et al. observed
  unusually broadened Si IV 1403 Šline profiles at the footpoints of
  such loops that were attributed to signatures of explosive events
  (EEs). We have chosen one such unidirectional flowing cool-loop
  system observed by IRIS where one of the footpoints is associated
  with significantly broadened Si IV line profiles. The line-profile
  broadening indirectly indicates the occurrence of numerous EEs below
  the transition region (TR), while it directly infers a large velocity
  enhancement/perturbation, further causing the plasma flows in the
  observed loop system. The observed features are implemented in a
  model atmosphere in which a low-lying bipolar magnetic field system
  is perturbed in the chromosphere by a velocity pulse with a maximum
  amplitude of 200 km s<SUP>-1</SUP>. The data-driven 2D numerical
  simulation shows that the plasma motions evolve in a similar manner
  as observed by IRIS in the form of flowing plasma filling the skeleton
  of a cool-loop system. We compare the spatio-temporal evolution of the
  cool-loop system in the framework of our model with the observations,
  and conclude that their formation is mostly associated with the velocity
  response of the transient energy release above their footpoints in
  the chromosphere/TR. Our observations and modeling results suggest
  that the velocity responses most likely associated to the EEs could
  be one of the main candidates for the dynamics and energetics of the
  flowing cool-loop systems in the lower solar atmosphere.

---------------------------------------------------------
Title: Evolution of supersonic downflows in a sunspot
Authors: Nelson, C. J.; Krishna Prasad, S.; Mathioudakis, M.
2020A&A...636A..35N    Altcode: 2020arXiv200302489N
  Context. Supersonic downflows have been observed in transition
  region spectra above numerous sunspots, however, little research
  has been conducted to date into how persistent these signatures
  are within sunspots on timescales longer than a few hours. <BR />
  Aims: We aim to analyse the lead sunspot of AR 12526 to infer the
  properties and evolution of supersonic downflows occurring within
  it using high-spatial and spectral resolution data. <BR /> Methods:
  We analysed 16 large, dense raster scans sampled by the Interface
  Region Imaging Spectrograph. These rasters tracked the lead sunspot
  of AR 12526 across the solar disc at discrete times between 27 March
  2016 and 2 April 2016, providing spectral profiles from the Si IV, O
  IV, Mg II, and C II lines. Additionally, we studied one sit-and-stare
  observation acquired on 1 April 2016 centred on the sunspot to analyse
  the evolution of supersonic downflows on shorter timescales. <BR />
  Results: Supersonic downflows are variable within this sunspot both
  in terms of spatial structuring and velocities. Thirteen of the 16
  raster scans display some evidence of supersonic downflows in the Si
  IV 1394 Å line co-spatial to a sustained bright structure detected
  in the 1400 Å slit-jaw imaging channel; a peak velocity of 112 km
  s<SUP>-1</SUP> is recorded on 29 March 2016. Evidence for supersonic
  downflows in the O IV 1401 Å line is found in 14 of these rasters; the
  spatial structuring in this line often differs from that inferred from
  the Si IV 1394 Å line. Only one example of a supersonic downflow is
  detected in the C II 1335 Å line and no downflows are found in the Mg
  II 2796 Å lines at these locations. In the sit-and-stare observations,
  no dual flow is initially detected, however, a supersonic downflow
  develops after approximately 60 min. This downflow accelerates from 73
  km s<SUP>-1</SUP> to close to 80 km s<SUP>-1</SUP> in both the Si IV
  1394 Å and O IV 1401 Å lines over the course of 20 min before the
  end of the observation. <BR /> Conclusions: Supersonic downflows are
  found in the Si IV 1394 Å line in 13 of the 16 rasters studied in this
  work. The morphology of these downflows evolved over the course of both
  hours and days and was often different in the Si IV 1394 Å and O IV
  1401 Å lines. These events were found co-spatial to a bright region
  in the core of the Si IV 1394 Å line, which appeared to form at the
  footpoints of coronal fan loops. Our results indicate that one raster
  is not enough to conclusively draw inferences about the properties of
  supersonic downflows within a sunspot during its lifetime.

---------------------------------------------------------
Title: Propagation of waves above a plage as observed by IRIS and SDO
Authors: Kayshap, P.; Srivastava, A. K.; Tiwari, S. K.; Jelínek,
   P.; Mathioudakis, M.
2020A&A...634A..63K    Altcode: 2019arXiv191011557K
  Context. Magnetohydrodynamic waves are proposed as the mechanism
  that transport sufficient energy from the photosphere to heat the
  transition region (TR) and corona. However, various aspects of these
  waves, such as their nature, propagation characteristics, and role
  in the atmospheric heating process, remain poorly understood and
  require further investigation. <BR /> Aims: We aim to investigate
  wave propagation within an active-region plage using IRIS and AIA
  observations. The main motivation is to understand the relationship
  between photospheric and TR oscillations. We identify the locations in
  the plage region where magnetic flux tubes are essentially vertical,
  and further we discuss the propagation and nature of these waves. <BR
  /> Methods: We used photospheric observations from AIA (i.e., AIA
  1700 Å) as well as TR imaging observations (IRIS SJI Si IV 1400.0
  Å). We investigated the propagation of the waves into the TR from the
  photosphere using wavelet analysis (e.g., cross power, coherence, and
  phase difference) with the inclusion of a customized noise model. <BR />
  Results: A fast Fourier transform algorithm shows the distribution of
  wave power at photospheric and TR heights. Waves with periods between
  2.0 and 9.0 min appear to be correlated between the photosphere and
  TR. We exploited a customized noise model to estimate the 95% confidence
  levels for the IRIS observations. On the basis of the sound speed in the
  TR and estimated propagation speed, these waves are best interpreted
  as slow magneto acoustic waves (SMAWs). It is found that almost all
  locations show correlation and propagation of waves over a broad range
  of periods from the photosphere to the TR. Our observations suggest
  that the SMAWs spatial occurrence frequency is stronly correlated
  between the photosphere and transition region within plage areas.

---------------------------------------------------------
Title: High-resolution spectropolarimetric observations of the
    temporal evolution of magnetic fields in photospheric bright points
Authors: Keys, P. H.; Reid, A.; Mathioudakis, M.; Shelyag, S.;
   Henriques, V. M. J.; Hewitt, R. L.; Del Moro, D.; Jafarzadeh, S.;
   Jess, D. B.; Stangalini, M.
2020A&A...633A..60K    Altcode: 2019arXiv191108436K
  Context. Magnetic bright points (MBPs) are dynamic, small-scale
  magnetic elements often found with field strengths of the order of a
  kilogauss within intergranular lanes in the photosphere. <BR /> Aims:
  Here we study the evolution of various physical properties inferred from
  inverting high-resolution full Stokes spectropolarimetry data obtained
  from ground-based observations of the quiet Sun at disc centre. <BR
  /> Methods: Using automated feature-tracking algorithms, we studied
  300 MBPs and analysed their temporal evolution as they evolved to
  kilogauss field strengths. These properties were inferred using
  both the NICOLE and SIR Stokes inversion codes. We employ similar
  techniques to study radiative magnetohydrodynamical simulations
  for comparison with our observations. <BR /> Results: Evidence was
  found for fast (∼30-100 s) amplification of magnetic field strength
  (by a factor of 2 on average) in MBPs during their evolution in our
  observations. Similar evidence for the amplification of fields is seen
  in our simulated data. <BR /> Conclusions: Several reasons for the
  amplifications were established, namely, strong downflows preceding
  the amplification (convective collapse), compression due to granular
  expansion and mergers with neighbouring MBPs. Similar amplification of
  the fields and interpretations were found in our simulations, as well
  as amplification due to vorticity. Such a fast amplification will have
  implications for a wide array of topics related to small-scale fields
  in the lower atmosphere, particularly with regard to propagating wave
  phenomena in MBPs.

---------------------------------------------------------
Title: Continuum Enhancements, Line Profiles, and Magnetic Field
    Evolution during Consecutive Flares
Authors: Zuccarello, Francesca; Guglielmino, Salvo L.; Capparelli,
   Vincenzo; Mathioudakis, Mihalis; Keys, Peter H.; Criscuoli, Serena;
   Falco, Mariachiara; Murabito, Mariarita
2020ApJ...889...65Z    Altcode: 2019arXiv191200859Z
  During solar flares, magnetic energy can be converted into
  electromagnetic radiation from radio waves to γ-rays. Enhancements in
  the continuum at visible wavelengths, as well as continuum enhancements
  in the FUV and NUV passbands, give rise to white-light flares. In
  addition, the strong energy release in these events can lead to
  the rearrangement of the magnetic field at the photospheric level,
  causing morphological changes in large and stable magnetic structures
  like sunspots. In this context, we describe observations acquired
  by satellite instruments (Interface Region Imaging Spectrograph
  (IRIS), Solar Dynamics Observatory/Helioseismic and Magnetic Imager,
  Hinode/Solar Optical Telescope) and ground-based telescopes (Rapid
  Oscillations in the Solar Atmosphere (ROSA)/Dunn Solar Telescope)
  during two consecutive C7.0 and X1.6 flares that occurred in active
  region NOAA 12205 on 2014 November 7. The flare was accompanied by an
  eruption. The results of the analysis show the presence of continuum
  enhancements during the evolution of the events, observed both in ROSA
  images and in IRIS spectra. In the latter, a prominent blueshifted
  component is observed at the onset of the eruption. We investigate
  the role played by the evolution of the δ sunspots of the active
  region in the flare triggering, and finally we discuss the changes in
  the penumbrae surrounding these sunspots as a further consequence of
  these flares.

---------------------------------------------------------
Title: Science Requirement Document (SRD) for the European Solar
    Telescope (EST) (2nd edition, December 2019)
Authors: Schlichenmaier, R.; Bellot Rubio, L. R.; Collados, M.;
   Erdelyi, R.; Feller, A.; Fletcher, L.; Jurcak, J.; Khomenko, E.;
   Leenaarts, J.; Matthews, S.; Belluzzi, L.; Carlsson, M.; Dalmasse,
   K.; Danilovic, S.; Gömöry, P.; Kuckein, C.; Manso Sainz, R.;
   Martinez Gonzalez, M.; Mathioudakis, M.; Ortiz, A.; Riethmüller,
   T. L.; Rouppe van der Voort, L.; Simoes, P. J. A.; Trujillo Bueno,
   J.; Utz, D.; Zuccarello, F.
2019arXiv191208650S    Altcode:
  The European Solar Telescope (EST) is a research infrastructure
  for solar physics. It is planned to be an on-axis solar telescope
  with an aperture of 4 m and equipped with an innovative suite of
  spectro-polarimetric and imaging post-focus instrumentation. The EST
  project was initiated and is driven by EAST, the European Association
  for Solar Telescopes. EAST was founded in 2006 as an association
  of 14 European countries. Today, as of December 2019, EAST consists
  of 26 European research institutes from 18 European countries. The
  Preliminary Design Phase of EST was accomplished between 2008 and
  2011. During this phase, in 2010, the first version of the EST Science
  Requirement Document (SRD) was published. After EST became a project
  on the ESFRI roadmap 2016, the preparatory phase started. The goal
  of the preparatory phase is to accomplish a final design for the
  telescope and the legal governance structure of EST. A major milestone
  on this path is to revisit and update the Science Requirement Document
  (SRD). The EST Science Advisory Group (SAG) has been constituted by
  EAST and the Board of the PRE-EST EU project in November 2017 and has
  been charged with the task of providing with a final statement on the
  science requirements for EST. Based on the conceptual design, the SRD
  update takes into account recent technical and scientific developments,
  to ensure that EST provides significant advancement beyond the current
  state-of-the-art. The present update of the EST SRD has been developed
  and discussed during a series of EST SAG meetings. The SRD develops
  the top-level science objectives of EST into individual science
  cases. Identifying critical science requirements is one of its main
  goals. Those requirements will define the capabilities of EST and the
  post-focus instrument suite. The technical requirements for the final
  design of EST will be derived from the SRD.

---------------------------------------------------------
Title: Spatially Resolved Signatures of Bidirectional Flows Observed
    in Inverted-Y Shaped Jets
Authors: Nelson, C. J.; Freij, N.; Bennett, S.; Erdélyi, R.;
   Mathioudakis, M.
2019ApJ...883..115N    Altcode: 2019arXiv190805132N
  Numerous apparent signatures of magnetic reconnection have been
  reported in the solar photosphere, including inverted-Y shaped jets. The
  reconnection at these sites is expected to cause localized bidirectional
  flows and extended shock waves; however, these signatures are rarely
  observed as extremely high spatial-resolution data are required. Here,
  we use Hα imaging data sampled by the Swedish Solar Telescope’s CRisp
  Imaging SpectroPolarimeter to investigate whether bidirectional flows
  can be detected within inverted-Y shaped jets near the solar limb. These
  jets are apparent in the Hα line wings, while no signature of either
  jet is observed in the Hα line core, implying reconnection took place
  below the chromospheric canopy. Asymmetries in the Hα line profiles
  along the legs of the jets indicate the presence of bidirectional flows,
  consistent with cartoon models of reconnection in chromospheric anemone
  jets. These asymmetries are present for over two minutes, longer than
  the lifetimes of Rapid Blue Excursions, and beyond ±1 Å into the wings
  of the line indicating that flows within the inverted-Y shaped jets
  are responsible for the imbalance in the profiles, rather than motions
  in the foreground. Additionally, surges form following the occurrence
  of the inverted-Y shaped jets. This surge formation is consistent with
  models, which suggests such events could be caused by the propagation
  of shock waves from reconnection sites in the photosphere to the
  upper atmosphere. Overall, our results provide evidence that magnetic
  reconnection in the photosphere can cause bidirectional flows within
  inverted-Y shaped jets and could be the driver of surges.

---------------------------------------------------------
Title: Hydrogen Emission in Type II White-light Solar Flares
Authors: Procházka, Ondřej; Reid, Aaron; Mathioudakis, Mihalis
2019ApJ...882...97P    Altcode: 2019arXiv190710888P
  Type II white-light flares (WLFs) have weak Balmer line emission
  and no Balmer jump. We carried out a set of radiative hydrodynamic
  simulations to understand how the hydrogen radiative losses vary with
  the electron-beam parameters and more specifically with the low-energy
  cutoff. Our results have revealed that for low-energy beams, the excess
  flare Lyman emission diminishes with increasing low-energy cutoff as
  the energy deposited into the top chromosphere is low compared to the
  energy deposited into the deeper layers. Some Balmer excess emission is
  always present and is driven primarily by direct heating from the beam
  with a minor contribution from Lyman continuum backwarming. The absence
  of Lyman excess emission in electron-beam driven models with high
  low-energy cutoff is a prominent spectral signature of type II WLFs.

---------------------------------------------------------
Title: The magnetic properties of photospheric magnetic bright points
    with high-resolution spectropolarimetry
Authors: Keys, Peter H.; Reid, Aaron; Mathioudakis, Mihalis; Shelyag,
   Sergiy; Henriques, Vasco M. J.; Hewitt, Rebecca L.; Del Moro, Dario;
   Jafarzadeh, Shahin; Jess, David B.; Stangalini, Marco
2019MNRAS.488L..53K    Altcode: 2019MNRAS.tmpL..98K; 2019MNRAS.tmpL..95K; 2019arXiv190607687K
  Magnetic bright points (MBPs) are small-scale magnetic elements
  ubiquitous across the solar disc, with the prevailing theory suggesting
  that they form due to the process of convective collapse. Employing a
  unique full Stokes spectropolarimetric data set of a quiet Sun region
  close to disc centre obtained with the Swedish Solar Telescope, we look
  at general trends in the properties of magnetic bright points. In total
  we track 300 MBPs in the data set and we employ NICOLE inversions to
  ascertain various parameters for the bright points such as line-of-sight
  magnetic field strength and line-of-sight velocity, for comparison. We
  observe a bimodal distribution in terms of maximum magnetic field
  strength in the bright points with peaks at ∼480 G and ∼1700 G,
  although we cannot attribute the kilogauss fields in this distribution
  solely to the process of convective collapse. Analysis of MURAM
  simulations does not return the same bimodal distribution. However,
  the simulations provide strong evidence that the emergence of new flux
  and diffusion of this new flux play a significant role in generating
  the weak bright point distribution seen in our observations.

---------------------------------------------------------
Title: The Chromospheric Response to the Sunquake Generated by the
    X9.3 Flare of NOAA 12673
Authors: Quinn, Sean; Reid, Aaron; Mathioudakis, Mihalis; Nelson,
   Christoper; Krishna Prasad, S.; Zharkov, Sergei
2019ApJ...881...82Q    Altcode: 2019arXiv190608545Q
  Active region NOAA 12673 was extremely volatile in 2017 September,
  producing many solar flares, including the largest of solar cycle 24,
  an X9.3 flare of 2017 September 06. It has been reported that this flare
  produced a number of sunquakes along the flare ribbon. We have used
  cotemporal and cospatial Helioseismic and Magnetic Imager (HMI) line of
  sight (LOS) and Swedish 1 m Solar Telescope (SST) observations to show
  evidence of the chromospheric response to these sunquakes. Analysis
  of the Ca II 8542 Å line profiles of the wavefronts revealed that
  the crests produced a strong blue asymmetry, whereas the troughs
  produced at most a very slight red asymmetry. We used the combined
  HMI, SST data sets to create time-distance diagrams and derive the
  apparent transverse velocity and acceleration of the response. These
  velocities ranged from 4.5 to 29.5 km s<SUP>-1</SUP> with a constant
  acceleration of 8.6 × 10<SUP>-3</SUP> km s<SUP>-2</SUP>. We employed
  NICOLE inversions, in addition to the center-of-gravity method to
  derive LOS velocities ranging from 2.4 km s<SUP>-1</SUP>-3.2 km
  s<SUP>-1</SUP>. Both techniques show that the crests are created by
  upflows. We believe that this is the first chromospheric signature of
  a flare induced sunquake.

---------------------------------------------------------
Title: Stellar Surface Magnetoconvection as a Source of Astrophysical
    Noise. III. Sun-as-a-Star Simulations and Optimal Noise Diagnostics
Authors: Cegla, H. M.; Watson, C. A.; Shelyag, S.; Mathioudakis, M.;
   Moutari, S.
2019ApJ...879...55C    Altcode: 2019arXiv190308446C
  Stellar surface magnetoconvection (granulation) creates asymmetries in
  the observed stellar absorption lines that can subsequently manifest
  themselves as spurious radial velocities (RVs) shifts. In turn, this
  can then mask the Doppler reflex motion induced by orbiting planets on
  their host stars and represents a particular challenge for determining
  the masses of low-mass, long-period planets. Herein, we study this
  impact by creating Sun-as-a-star observations that encapsulate
  the granulation variability expected from 3D magnetohydrodynamic
  simulations. These Sun-as-a-star model observations are in good
  agreement with empirical observations of the Sun but may underestimate
  the total variability relative to the quiet Sun due to the increased
  magnetic field strength in our models. We find numerous line profile
  characteristics that linearly correlate with the disk-integrated
  convection-induced velocities. Removing the various correlations
  with the line bisector, equivalent width, and the V <SUB>asy</SUB>
  indicator may reduce ∼50%-60% of the granulation noise in the measured
  velocities. We also find that simultaneous photometry may be a key
  diagnostic, as our proxy for photometric brightness also allowed us to
  remove ∼50% of the granulation-induced RV noise. These correlations
  and granulation-noise mitigations break down in the presence of low
  instrumental resolution and/or increased stellar rotation, as both
  act to smooth the observed line profile asymmetries.

---------------------------------------------------------
Title: Multi-wavelength observations of the 2014 June 11 M3.9 flare:
    temporal and spatial characteristics
Authors: Christian, Damian J.; Kuridze, David; Jess, David B.; Yousefi,
   Menoa; Mathioudakis, Mihalis
2019RAA....19..101C    Altcode: 2018arXiv181107077C
  We present multi-wavelength observations of an M-class flare (M3.9)
  that occurred on 2014 June 11. Our observations were conducted
  with the Dunn Solar Telescope (DST), employing adaptive optics,
  the multi-camera system Rapid Oscillations in Solar Atmosphere
  (ROSA), the new Hydrogen-Alpha Rapid Dynamics camera (HARDcam) in
  various wavelengths, such as Ca II K, Mg I b<SUB>2</SUB> (at 5172.7
  Å), and Hα narrow band and G-band continuum filters. Images were
  re-constructed using the Kiepenheuer-Institut Speckle Interferometry
  Package (KISIP) code, to improve our image resolution. We observed
  intensity increases of ≈120%-150% in the Mg, Ca K and Hα narrow band
  filters during the flare. Intensity increases for the flare observed
  in the SDO EUV channels were several times larger, and the X-rays,
  as recorded by GOES, increased over a factor of 30 for the harder
  band. Only a modest delay was found between the onset of flare ribbons
  of a nearby sympathetic flare and the main flare ribbons observed in
  these narrow band filters. The peak flare emission occurred within a
  few seconds for the Ca K, Mg and Hα bands. Time-distance techniques
  indicate propagation velocities of ≈60 km s<SUP>-1</SUP> for the
  main flare ribbon and as high as 300 km s<SUP>-1</SUP> for smaller
  regions, which we attribute to filament eruptions. This result and
  delays and velocities observed with SDO (≈100 km s<SUP>-1</SUP>)
  for different coronal heights agree well with the simple model of
  energy propagation versus height, although a more detailed model for
  the flaring solar atmosphere is needed. Finally, we detected marginal
  quasi-periodic pulsations (QPPs) in the 40-60 s range for the Ca K,
  Mg and Hα bands, and such measurements are important for disentangling
  the detailed flare-physics.

---------------------------------------------------------
Title: The Effect Of Cooling On Driven Kink Oscillations Of Coronal
    Loops
Authors: Nelson, Chris J.; Shukhobodskiy, Alexander A.; Erdélyi,
   Robertus; Mathioudakis, Mihalis
2019FrASS...6...45N    Altcode: 2019arXiv190513137N
  Ever since their detection two decades ago, standing kink oscillations
  in coronal loops have been extensively studied both observationally
  and theoretically. Almost all driven coronal loop oscillations
  (e.g., by flares) are observed to damp through time often with
  Gaussian or exponential profiles. Intriguingly, however, it has
  been shown theoretically that the amplitudes of some oscillations
  could be modified from Gaussian or exponential profiles if cooling
  is present in the coronal loop systems. Indeed, in some cases the
  oscillation amplitude can even increase through time. In this article,
  we analyse a flare-driven coronal loop oscillation observed by the
  Solar Dynamics Observatory's Atmospheric Imaging Assembly (SDO/AIA)
  in order to investigate whether models of cooling can explain the
  amplitude profile of the oscillation and whether hints of cooling can
  be found in the intensity evolution of several SDO/AIA filters. During
  the oscillation of this loop system, the kink mode amplitude appears to
  differ from a typical Gaussian or exponential profile with some hints
  being present that the amplitude increases. The application of cooling
  coronal loop modelling allowed us to estimate the density ratio between
  the loop and the background plasma, with a ratio of between 2.05-2.35
  being returned. Overall, our results indicate that consideration of
  the thermal evolution of coronal loop systems can allow us to better
  describe oscillations in these structures and return more accurate
  estimates of the physical properties of the loops (e.g., density,
  scale height, magnetic field strength).

---------------------------------------------------------
Title: Mapping the Magnetic Field of Flare Coronal Loops
Authors: Kuridze, D.; Mathioudakis, M.; Morgan, H.; Oliver, R.; Kleint,
   L.; Zaqarashvili, T. V.; Reid, A.; Koza, J.; Löfdahl, M. G.; Hillberg,
   T.; Kukhianidze, V.; Hanslmeier, A.
2019ApJ...874..126K    Altcode: 2019arXiv190207514K
  Here, we report on the unique observation of flaring coronal loops at
  the solar limb using high-resolution imaging spectropolarimetry from
  the Swedish 1 m Solar Telescope. The vantage position, orientation,
  and nature of the chromospheric material that filled the flare loops
  allowed us to determine their magnetic field with unprecedented accuracy
  using the weak-field approximation method. Our analysis reveals coronal
  magnetic field strengths as high as 350 G at heights up to 25 Mm above
  the solar limb. These measurements are substantially higher than a
  number of previous estimates and may have considerable implications
  for our current understanding of the extended solar atmosphere.

---------------------------------------------------------
Title: Statistical Signatures of Nanoflare Activity. I. Monte Carlo
    Simulations and Parameter-space Exploration
Authors: Jess, D. B.; Dillon, C. J.; Kirk, M. S.; Reale, F.;
   Mathioudakis, M.; Grant, S. D. T.; Christian, D. J.; Keys, P. H.;
   Krishna Prasad, S.; Houston, S. J.
2019ApJ...871..133J    Altcode: 2018arXiv181206978J
  Small-scale magnetic reconnection processes in the form of nanoflares
  have become increasingly hypothesized as important mechanisms for the
  heating of the solar atmosphere, driving propagating disturbances along
  magnetic field lines in the Sun’s corona, and instigating rapid
  jetlike bursts in the chromosphere. Unfortunately, the relatively
  weak signatures associated with nanoflares place them below the
  sensitivities of current observational instrumentation. Here we
  employ Monte Carlo techniques to synthesize realistic nanoflare
  intensity time series from a dense grid of power-law indices and
  decay timescales. Employing statistical techniques, which examine
  the modeled intensity fluctuations with more than 10<SUP>7</SUP>
  discrete measurements, we show how it is possible to extract and
  quantify nanoflare characteristics throughout the solar atmosphere,
  even in the presence of significant photon noise. A comparison
  between the statistical parameters (derived through examination of the
  associated intensity fluctuation histograms) extracted from the Monte
  Carlo simulations and Solar Dynamics Observatory (SDO)/Atmospheric
  Imaging Assembly (AIA) 171 and 94 Å observations of active region
  NOAA 11366 reveals evidence for a flaring power-law index within the
  range of 1.82 ≤ α ≤ 1.90, combined with e-folding timescales
  of 385 ± 26 and 262 ± 17 s for the SDO/AIA 171 and 94 Å channels,
  respectively. These results suggest that nanoflare activity is not the
  dominant heating source for the active region under investigation. This
  opens the door for future dedicated observational campaigns to not only
  unequivocally search for the presence of small-scale reconnection in
  solar and stellar environments but also quantify key characteristics
  related to such nanoflare activity.

---------------------------------------------------------
Title: Continuum emission enhancements and penumbral changes observed
    during flares by IRIS, ROSA, and Hinode
Authors: Zuccarello, F.; Guglielmino, S. L.; Capparelli, V.;
   Mathioudakis, M.; Keys, P.; Fletcher, L.; Criscuoli, S.; Falco, M.;
   Murabito, M.
2019NCimC..42...13Z    Altcode: 2019arXiv190101732Z
  In this paper we describe observations acquired by satellite instruments
  ( Hinode/SOT and IRIS) and ground-based telescopes (ROSA@DST) during
  two consecutive C7.0 and X1.6 flares occurred in active region NOAA
  12205 on 2014 November 7. The analysis of these data show the presence
  of continuum enhancements during the evolution of the events, observed
  both in ROSA images and in IRIS spectra. Moreover, we analyze the role
  played by the evolution of the δ sunspots of the active region in the
  flare triggering, indicating the disappearance of a large portion of
  penumbra around these sunspots.

---------------------------------------------------------
Title: Coronal and chromospheric observations of pre- and post-flare
    plasma evolution
Authors: Long, David; Reid, Aaron; Harra, Louise; Mathioudakis, Mihalis
2018csc..confE..16L    Altcode:
  Solar flares are among the most energetic and spectacular events
  occurring in our solar system, produced by the release of stored
  magnetic energy in the solar atmosphere through the reconnection
  of twisted magnetic fields. Although the magnetic field itself is
  difficult to observe in the solar atmosphere, we can gain vital
  insights into the reconnection process by studying the evolution
  of solar plasma prior to and following the flare. Here we present
  contemporaneous spectroscopic and imaging observations of an X9.3 solar
  flare from 2017-September-6. This was the largest flare of the current
  solar cycle to date, and was well observed in the corona by SDO/AIA
  and Hinode/EIS as well as in the chromosphere by instruments at the
  ground-based Swedish Solar Telescope. This combination of observations
  provides spectroscopic information throughout the solar atmosphere,
  giving a unique insight into the evolution of plasma in the lead-up
  to and following the flare.

---------------------------------------------------------
Title: Stellar Surface Magneto-convection as a Source of Astrophysical
    Noise. II. Center-to-limb Parameterization of Absorption Line Profiles
    and Comparison to Observations
Authors: Cegla, H. M.; Watson, C. A.; Shelyag, S.; Chaplin, W. J.;
   Davies, G. R.; Mathioudakis, M.; Palumbo, M. L., III; Saar, S. H.;
   Haywood, R. D.
2018ApJ...866...55C    Altcode: 2018arXiv180711423C
  Manifestations of stellar activity (such as star-spots, plage/faculae,
  and convective flows) are well-known to induce spectroscopic
  signals often referred to as astrophysical noise by exoplanet
  hunters. For example, setting an ultimate goal of detecting true
  Earth analogs demands reaching radial velocity (RV) precisions of
  ∼9 cm s<SUP>-1</SUP>. While this is becoming technically feasible
  with the latest generation of highly stabilized spectrographs, it
  is astrophysical noise that sets the true fundamental barrier on
  attainable RV precisions. In this paper, we parameterize the impact
  of solar surface magneto-convection on absorption line profiles, and
  extend the analysis from the solar disk center (Paper I) to the solar
  limb. Off disk-center, the plasma flows orthogonal to the granule tops
  begin to lie along the line of sight, and those parallel to the granule
  tops are no longer completely aligned with the observer. Moreover, the
  granulation is corrugated and the granules can block other granules, as
  well as the intergranular lane components. Overall, the visible plasma
  flows and geometry of the corrugated surface significantly impact the
  resultant line profiles and induce center-to-limb variations in shape
  and net position. We detail these herein, and compare to various solar
  observations. We find our granulation parameterization can recreate
  realistic line profiles and induced radial velocity shifts, across
  the stellar disk, indicative of both those found in computationally
  heavy radiative 3D magnetohydrodynamical simulations and empirical
  solar observations.

---------------------------------------------------------
Title: Construction update of the Daniel K. Inouye Solar Telescope
    project
Authors: Warner, Mark; Rimmele, Thomas R.; Martinez Pillet, Valentin;
   Casini, Roberto; Berukoff, Steve; Craig, Simon C.; Ferayorni, Andrew;
   Goodrich, Bret D.; Hubbard, Robert P.; Harrington, David; Jeffers,
   Paul; Johansson, Erik M.; Kneale, Ruth; Kuhn, Jeff; Liang, Chen; Lin,
   Haosheng; Marshall, Heather; Mathioudakis, Mihalis; McBride, William
   R.; McMullin, Joseph; McVeigh, William; Sekulic, Predrag; Schmidt,
   Wolfgang; Shimko, Steve; Sueoka, Stacey; Summers, Rich; Tritschler,
   Alexandra; Williams, Timothy R.; Wöger, Friedrich
2018SPIE10700E..0VW    Altcode:
  Construction of the Daniel K. Inouye Solar Telescope (DKIST) is
  well underway on the Haleakalā summit on the Hawaiian island of
  Maui. Featuring a 4-m aperture and an off-axis Gregorian configuration,
  the DKIST will be the world's largest solar telescope. It is designed
  to make high-precision measurements of fundamental astrophysical
  processes and produce large amounts of spectropolarimetric and
  imaging data. These data will support research on solar magnetism
  and its influence on solar wind, flares, coronal mass ejections,
  and solar irradiance variability. Because of its large aperture, the
  DKIST will be able to sense the corona's magnetic field—a goal that
  has previously eluded scientists—enabling observations that will
  provide answers about the heating of stellar coronae and the origins
  of space weather and exo-weather. The telescope will cover a broad
  wavelength range (0.35 to 28 microns) and operate as a coronagraph
  at infrared (IR) wavelengths. Achieving the diffraction limit of
  the 4-m aperture, even at visible wavelengths, is paramount to these
  science goals. The DKIST's state-of-the-art adaptive optics systems
  will provide diffraction-limited imaging, resolving features that are
  approximately 20 km in size on the Sun. At the start of operations,
  five instruments will be deployed: a visible broadband imager (VTF),
  a visible spectropolarimeter (ViSP), a visible tunable filter (VTF),
  a diffraction-limited near-IR spectropolarimeter (DLNIRSP), and a
  cryogenic near-IR spectropolarimeter (cryo-NIRSP). At the end of
  2017, the project finished its fifth year of construction and eighth
  year overall. Major milestones included delivery of the commissioning
  blank, the completed primary mirror (M1), and its cell. Commissioning
  and testing of the coudé rotator is complete and the installation
  of the coudé cleanroom is underway; likewise, commissioning of the
  telescope mount assembly (TMA) has also begun. Various other systems and
  equipment are also being installed and tested. Finally, the observatory
  integration, testing, and commissioning (IT&amp;C) activities have
  begun, including the first coating of the M1 commissioning blank and
  its integration within its cell assembly. Science mirror coating and
  initial on-sky activities are both anticipated in 2018.

---------------------------------------------------------
Title: Reproducing Type II White-light Solar Flare Observations with
    Electron and Proton Beam Simulations
Authors: Procházka, Ondřej; Reid, Aaron; Milligan, Ryan O.; Simões,
   Paulo J. A.; Allred, Joel C.; Mathioudakis, Mihalis
2018ApJ...862...76P    Altcode: 2018arXiv180600249P
  We investigate the cause of the suppressed Balmer series and the origin
  of the white-light continuum emission in the X1.0 class solar flare on
  2014 June 11. We use radiative hydrodynamic simulations to model the
  response of the flaring atmosphere to both electron and proton beams,
  which are energetically constrained using Ramaty High Energy Solar
  Spectroscopic Imager and Fermi observations. A comparison of synthetic
  spectra with the observations allows us to narrow the range of beam
  fluxes and low energy cutoff that may be applicable to this event. We
  conclude that the electron and proton beams that can reproduce the
  observed spectral features are those that have relatively low fluxes
  and high values for the low energy cutoff. While electron beams shift
  the upper chromosphere and transition region to greater geometrical
  heights, proton beams with a similar flux leave these areas of the
  atmosphere relatively undisturbed. It is easier for proton beams to
  penetrate to the deeper layers and not deposit their energy in the
  upper chromosphere where the Balmer lines are formed. The relatively
  weak particle beams that are applicable to this flare do not cause
  a significant shift of the τ = 1 surface and the observed excess WL
  emission is optically thin.

---------------------------------------------------------
Title: The Evolution of T = 10,000 K Blackbody-Like Continuum
    Radiation in the Impulsive Phase of dMe Flares
Authors: Kowalski, Adam F.; Mathioudakis, Mihalis; Hawley, Suzanne L.
2018csss.confE..42K    Altcode: 2018arXiv181007226K
  The near-ultraviolet and optical (white-light) continuum radiation
  in M dwarf flares exhibits a range of observed characteristics,
  suggesting that the amount of heating at large optical depth varies
  among impulsive-type and gradual-type flares. Specific flux ratios
  from high-time cadence spectra and narrowband continuum photometry
  have also shown that these characteristics vary from the peak to the
  gradual decay phases of flares. In these proceedings, we present the
  highest-time cadence ( 1 s), highest signal-to-noise ( 100) constraints
  on the optical color temperature evolution during the rise phase of a
  large, impulsive-type dMe flare event. The flare exhibits compelling
  evidence of a hot, color temperature (T 10,000 K), but the Balmer jump
  ratios show that the flare cannot be explained by isothermal slabs or
  blackbody surfaces at any time in the evolution. The new data analysis
  establish these properties as critical challenges for any flare model,
  and we discuss 1D radiative-hydrodynamic modeling that will be compared
  to the evolution of the flare colors in this intriguing event.

---------------------------------------------------------
Title: Status of the Daniel K. Inouye Solar Telescope: unraveling
    the mysteries the Sun.
Authors: Rimmele, Thomas R.; Martinez Pillet, Valentin; Goode, Philip
   R.; Knoelker, Michael; Kuhn, Jeffrey Richard; Rosner, Robert; Casini,
   Roberto; Lin, Haosheng; von der Luehe, Oskar; Woeger, Friedrich;
   Tritschler, Alexandra; Fehlmann, Andre; Jaeggli, Sarah A.; Schmidt,
   Wolfgang; De Wijn, Alfred; Rast, Mark; Harrington, David M.; Sueoka,
   Stacey R.; Beck, Christian; Schad, Thomas A.; Warner, Mark; McMullin,
   Joseph P.; Berukoff, Steven J.; Mathioudakis, Mihalis; DKIST Team
2018AAS...23231601R    Altcode:
  The 4m Daniel K. Inouye Solar Telescope (DKIST) currently under
  construction on Haleakala, Maui will be the world’s largest solar
  telescope. Designed to meet the needs of critical high resolution and
  high sensitivity spectral and polarimetric observations of the sun,
  this facility will perform key observations of our nearest star that
  matters most to humankind. DKIST’s superb resolution and sensitivity
  will enable astronomers to address many of the fundamental problems
  in solar and stellar astrophysics, including the origin of stellar
  magnetism, the mechanisms of coronal heating and drivers of the
  solar wind, flares, coronal mass ejections and variability in solar
  and stellar output. DKIST will also address basic research aspects of
  Space Weather and help improve predictive capabilities. In combination
  with synoptic observations and theoretical modeling DKIST will unravel
  the many remaining mysteries of the Sun.The construction of DKIST is
  progressing on schedule with 80% of the facility complete. Operations
  are scheduled to begin early 2020. DKIST will replace the NSO
  facilities on Kitt Peak and Sac Peak with a national facility with
  worldwide unique capabilities. The design allows DKIST to operate as
  a coronagraph. Taking advantage of its large aperture and infrared
  polarimeters DKIST will be capable to routinely measure the currently
  illusive coronal magnetic fields. The state-of-the-art adaptive optics
  system provides diffraction limited imaging and the ability to resolve
  features approximately 20 km on the Sun. Achieving this resolution
  is critical for the ability to observe magnetic structures at their
  intrinsic, fundamental scales. Five instruments will be available at
  the start of operations, four of which will provide highly sensitive
  measurements of solar magnetic fields throughout the solar atmosphere
  - from the photosphere to the corona. The data from these instruments
  will be distributed to the world wide community via the NSO/DKIST data
  center located in Boulder. We present examples of science objectives
  and provide an overview of the facility and project status, including
  the ongoing efforts of the community to develop the critical science
  plan for the first 2-3 years of operations.

---------------------------------------------------------
Title: Spectropolarimetric Inversions of the Ca II 8542 Å Line in
    an M-class Solar Flare
Authors: Kuridze, D.; Henriques, V. M. J.; Mathioudakis, M.; Rouppe
   van der Voort, L.; de la Cruz Rodríguez, J.; Carlsson, M.
2018ApJ...860...10K    Altcode: 2018arXiv180500487K
  We study the M1.9-class solar flare SOL2015-09-27T10:40 UT using
  high-resolution full Stokes imaging spectropolarimetry of the Ca II
  8542 Å line obtained with the CRISP imaging spectropolarimeter at the
  Swedish 1-m Solar Telescope. Spectropolarimetric inversions using the
  non-LTE code NICOLE are used to construct semiempirical models of the
  flaring atmosphere to investigate the structure and evolution of the
  flare temperature and magnetic field. A comparison of the temperature
  stratification in flaring and nonflaring areas reveals strong heating
  of the flare ribbon during the flare peak. The polarization signals
  of the ribbon in the chromosphere during the flare maximum become
  stronger when compared to its surroundings and to pre- and post-flare
  profiles. Furthermore, a comparison of the response functions to
  perturbations in the line-of-sight magnetic field and temperature in
  flaring and nonflaring atmospheres shows that during the flare, the
  Ca II 8542 Å line is more sensitive to the lower atmosphere where the
  magnetic field is expected to be stronger. The chromospheric magnetic
  field was also determined with the weak-field approximation, which
  led to results similar to those obtained with the NICOLE inversions.

---------------------------------------------------------
Title: First Evidence of the Frequency Filtering of Magnetoacoustic
    Waves in the Flaring Star EK Dra
Authors: Srivastava, A. K.; Pandey, J. C.; Karmakar, Subhajeet;
   Chowdhury, Partha; Moon, Y. -J.; Goossens, Marcel; Jelínek, P.;
   Mathioudakis, M.; Doyle, J. G.; Dwivedi, B. N.
2018arXiv180408858S    Altcode:
  Using the data obtained from XMM-Newton, we show the gradual evolution
  of two periodicities of ~4500 s and ~2200 s in the decay phase of the
  flare observed in a solar analog EK Dra. The longer period evolves
  firstly for first 14 ks, while the shorter period evolves for next
  10 ks in the decay phase. We find that these two periodicities are
  associated with the magnetoacoustic waves triggered in the flaring
  region. The flaring loop system shows cooling and thus it is subjected
  to the change in the scale height and the acoustic cut-off period. This
  serves to filter the longer period magnetoacoustic waves and enables
  the propagation of the shorter period waves in the later phase of
  the flare. We provide the first clues of the dynamic behaviour of
  EK Dra's corona which affects the propagation of waves and causes
  their filtering.

---------------------------------------------------------
Title: Stellar flare oscillations: evidence for oscillatory
    reconnection and evolution of MHD modes
Authors: Doyle, J. G.; Shetye, J.; Antonova, A. E.; Kolotkov, D. Y.;
   Srivastava, A. K.; Stangalini, M.; Gupta, G. R.; Avramova, A.;
   Mathioudakis, M.
2018MNRAS.475.2842D    Altcode: 2018MNRAS.tmp...77D
  Here, we report on the detection of a range of quasi-periodic
  pulsations (20-120 s; QPPs) observed during flaring activity of several
  magnetically active dMe stars, namely AF Psc, CR Dra, GJ 3685A,
  Gl 65, SDSS J084425.9+513830, and SDSS J144738.47+035312.1 in the
  GALEX NUV filter. Based on a solar analogy, this work suggests that
  many of these flares may be triggered by external drivers creating
  a periodic reconnection in the flare current sheet or an impulsive
  energy release giving rise to an avalanche of periodic bursts that
  occur at time intervals that correspond to the detected periods, thus
  generating QPPs in their rising and peak phases. Some of these flares
  also show fast QPPs in their decay phase, indicating the presence of
  fast sausage mode oscillations either driven externally by periodic
  reconnection or intrinsically in the post-flare loop system during
  the flare energy release.

---------------------------------------------------------
Title: Photospheric Observations of Surface and Body Modes in Solar
    Magnetic Pores
Authors: Keys, Peter H.; Morton, Richard J.; Jess, David B.; Verth,
   Gary; Grant, Samuel D. T.; Mathioudakis, Mihalis; Mackay, Duncan H.;
   Doyle, John G.; Christian, Damian J.; Keenan, Francis P.; Erdélyi,
   Robertus
2018ApJ...857...28K    Altcode: 2018arXiv180301859K
  Over the past number of years, great strides have been made in
  identifying the various low-order magnetohydrodynamic wave modes
  observable in a number of magnetic structures found within the solar
  atmosphere. However, one aspect of these modes that has remained
  elusive, until now, is their designation as either surface or body
  modes. This property has significant implications for how these modes
  transfer energy from the waveguide to the surrounding plasma. Here, for
  the first time to our knowledge, we present conclusive, direct evidence
  of these wave characteristics in numerous pores that were observed to
  support sausage modes. As well as outlining methods to detect these
  modes in observations, we make estimates of the energies associated
  with each mode. We find surface modes more frequently in the data,
  as well as that surface modes appear to carry more energy than those
  displaying signatures of body modes. We find frequencies in the range
  of ∼2-12 mHz, with body modes as high as 11 mHz, but we do not find
  surface modes above 10 mHz. It is expected that the techniques we have
  applied will help researchers search for surface and body signatures
  in other modes and in differing structures from those presented here.

---------------------------------------------------------
Title: X-ray line coincidence photopumping in a solar flare
Authors: Keenan, F. P.; Poppenhaeger, K.; Mathioudakis, M.; Rose,
   S. J.; Flowerdew, J.; Hynes, D.; Christian, D. J.; Nilsen, J.; Johnson,
   W. R.
2018MNRAS.474.3782K    Altcode: 2017arXiv171107761K
  Line coincidence photopumping is a process where the electrons of
  an atomic or molecular species are radiatively excited through the
  absorption of line emission from another species at a coincident
  wavelength. There are many instances of line coincidence photopumping
  in astrophysical sources at optical and ultraviolet wavelengths,
  with the most famous example being Bowen fluorescence (pumping of O
  III 303.80 Å by He II), but none to our knowledge in X-rays. However,
  here we report on a scheme where a He-like line of Ne IX at 11.000 Å
  is photopumped by He-like Na X at 11.003 Å, which predicts significant
  intensity enhancement in the Ne IX 82.76 Å transition under physical
  conditions found in solar flare plasmas. A comparison of our theoretical
  models with published X-ray observations of a solar flare obtained
  during a rocket flight provides evidence for line enhancement, with the
  measured degree of enhancement being consistent with that expected from
  theory, a truly surprising result. Observations of this enhancement
  during flares on stars other than the Sun would provide a powerful
  new diagnostic tool for determining the sizes of flare loops in these
  distant, spatially unresolved, astronomical sources.

---------------------------------------------------------
Title: Penumbral Waves Driving Solar Fan-shaped Chromospheric Jets
Authors: Reid, A.; Henriques, V. M. J.; Mathioudakis, M.; Samanta, T.
2018ApJ...855L..19R    Altcode:
  We use Hα imaging spectroscopy taken via the Swedish 1 m Solar
  Telescope to investigate the occurrence of fan-shaped jets at the solar
  limb. We show evidence for near-simultaneous photospheric reconnection
  at a sunspot edge leading to the jets appearance, with upward velocities
  of 30 km s<SUP>-1</SUP>, and extensions up to 8 Mm. The brightening at
  the base of the jets appears recurrent, with a periodicity matching that
  of the nearby sunspot penumbra, implying running penumbral waves could
  be the driver of the jets. The jets’ constant extension velocity
  implies that a driver counteracting solar gravity exists, possibly
  as a result of the recurrent reconnection erupting material into the
  chromosphere. These jets also show signatures in higher temperature
  lines captured from the Solar Dynamics Observatory, indicating a very
  hot jet front, leaving behind optically thick cool plasma in its wake.

---------------------------------------------------------
Title: Penumbral Waves driving Solar chromospheric fan-shaped jets
Authors: Reid, A.; Henriques, V. M. J.; Mathioudakis, M.; Samanta, T.
2018arXiv180207537R    Altcode:
  We use H$\alpha$ imaging spectroscopy taken via the Swedish 1-m Solar
  Telescope (SST) to investigate the occurrence of fan-shaped jets at
  the solar limb. We show evidence for near-simultaneous photospheric
  reconnection at a sunspot edge leading to the jets appearance, with
  upward velocities of 30\ks, and extensions up to 8~Mm. The brightening
  at the base of the jets appears recurrent, with a periodicity matching
  that of the nearby sunspot penumbra, implying running penumbral waves
  could be the driver of the jets. The jets' constant extension velocity
  implies that a driver counteracting solar gravity exists, possibly
  as a result of the recurrent reconnection erupting material into the
  chromosphere. These jets also show signatures in higher temperature
  lines captured from the Solar Dynamics Observatory (SDO), indicating
  a very hot jet front, leaving behind optically thick cool plasma in
  its wake.

---------------------------------------------------------
Title: Hα and Hβ emission in a C3.3 solar flare: comparison between
    observations and simulations
Authors: Zuccarello, F.; Simoes, P. J. D. A.; Capparelli, V.; Fletcher,
   L.; Romano, P.; Mathioudakis, M.; Cauzzi, G.; Carlsson, M.; Kuridze,
   D.; Keys, P.
2017AGUFMSH41A2742Z    Altcode:
  This work is based on the analysis of an extremely rare set of
  simultaneous observations of a C3.3 solar flare in the Hα and Hβ lines
  at high spatial and temporal resolution, which were acquired at the
  Dunn Solar Telescope. Images of the C3.3 flare (SOL2014-04-22T15:22)
  made at various wavelengths along the Hα line profile by the
  Interferometric Bidimensional Spectrometer (IBIS) and in the Hβ
  with the Rapid Oscillations in the Solar Atmosphere (ROSA) broadband
  imager are analyzed to obtain the intensity evolution. The analysis
  shows that Hα and Hβ intensity excesses in three identified flare
  footpoints are well correlated in time. In the stronger footpoints,
  the typical value of the the Hα/Hβ intensity ratio observed is ∼
  0.4 - 0.5, in broad agreement with values obtained from a RADYN non-LTE
  simulation driven by an electron beam with parameters constrained by
  observations. The weaker footpoint has a larger Hα/Hβ ratio, again
  consistent with a RADYN simulation but with a smaller energy flux.

---------------------------------------------------------
Title: Modelling of Electron and Proton Beams in a White-light
    Solar Flare
Authors: Procházka, O.; Reid, A.; Milligan, R. O.; Allred, J. C.;
   Mathioudakis, M.
2017AGUFMSH41A2756P    Altcode: 2017AGUFMSH41A2756M
  Observations of an X1 class WL solar flare on 2014 June 11 showed a
  surprisingly weak emission in both higher order Balmer and Lyman
  lines and continua. The flare was observed by RHESSI but low
  energy cut-off of non-thermal component was indeterminable due to
  the unusually hard electron spectrum (delta = 3). An estimate of
  power in non-thermal electron beams together with an area of WL
  emission observed by HMI yielded to an upper and lower estimate of
  flux 1E9 and 3E10 erg/cm2/s, respectively. We performed a grid of
  models using a radiative hydrodynamic code RADYN in order to compare
  synthetic spectra with observations. For low energy cut-off we chose
  a range from 20 to 120 keV with a step of 20 keV and delta parameter
  equal to 3. Electron beam-driven models show that higher low energy
  cut-off is more likely to produce an absorption Balmer line profile,
  if the total energy flux remains relatively low. On the other hand a
  detectable rise of HMI continuum (617 nm) lays a lower limit on the
  beam flux. Proton beam-driven models with equivalent fluxes indicate a
  greater penetration depth, while the Balmer lines reveal significantly
  weaker emission. Atmospheric temperature profiles show that for higher
  values of low energy cut-off the energy of the beam is deposited lower
  in chromosphere or even in temperature minimum region. This finding
  suggests, that suppressed hydrogen emission can indicate a formation
  of white-light continuum below chromosphere.

---------------------------------------------------------
Title: Non-thermal distributions and energy transport in the solar
    flares
Authors: Matthews, Sarah; del Zanna, Guilio; Calcines, Ariadna;
   Mason, Helen; Mathioudakis, Mihalis; Culhane, Len; Harra, Louise;
   van Driel-Gesztelyi, Lidia; Green, Lucie; Long, David; Baker, Deb;
   Valori, Gherardo
2017arXiv171200773M    Altcode:
  Determining the energy transport mechanisms in flares remains a central
  goal in solar flares physics that is still not adequately answered
  by the 'standard flare model'. In particular, the relative roles of
  particles and/or waves as transport mechanisms, the contributions of low
  energy protons and ions to the overall flare budget, and the limits of
  low energy non-thermal electron distribution are questions that still
  cannot be adequately reconciled with current instrumentation. In this
  'White Paper' submitted in response to the call for inputs to the Next
  Generation Solar Physics Mission review process initiated by JAXA,
  NASA and ESA in 2016, we outline the open questions in this area and
  possible instrumentation that could provide the required observations
  to help answer these and other flare-related questions.

---------------------------------------------------------
Title: Hα and Hβ Emission in a C3.3 Solar Flare: Comparison between
    Observations and Simulations
Authors: Capparelli, Vincenzo; Zuccarello, Francesca; Romano, Paolo;
   Simões, Paulo J. A.; Fletcher, Lyndsay; Kuridze, David; Mathioudakis,
   Mihalis; Keys, Peter H.; Cauzzi, Gianna; Carlsson, Mats
2017ApJ...850...36C    Altcode: 2017arXiv171004067C
  The hydrogen Balmer series is a basic radiative loss channel from
  the flaring solar chromosphere. We report here on the analysis of an
  extremely rare set of simultaneous observations of a solar flare in the
  {{H}}α and {{H}}β lines, at high spatial and temporal resolutions,
  that were acquired at the Dunn Solar Telescope. Images of the C3.3 flare
  (SOL2014-04-22T15:22) made at various wavelengths along the {{H}}α line
  profile by the Interferometric Bidimensional Spectrometer (IBIS) and in
  the {{H}}β with the Rapid Oscillations in the Solar Atmosphere (ROSA)
  broadband imager are analyzed to obtain the intensity evolution. The
  {{H}}α and {{H}}β intensity excesses in three identified flare
  footpoints are well-correlated in time. We examine the ratio of {{H}}α
  to {{H}}β flare excess, which was proposed by previous authors as
  a possible diagnostic of the level of electron-beam energy input. In
  the stronger footpoints, the typical value of the the {{H}}α /H β
  intensity ratio observed is ∼0.4-0.5, in broad agreement with values
  obtained from a RADYN non-LTE simulation driven by an electron beam
  with parameters constrained (as far as possible) by observation. The
  weaker footpoint has a larger {{H}}α /H β ratio, again consistent
  with a RADYN simulation, but with a smaller energy flux. The {{H}}α
  line profiles observed have a less prominent central reversal than is
  predicted by the RADYN results, but can be brought into agreement if
  the {{H}}α -emitting material has a filling factor of around 0.2-0.3.

---------------------------------------------------------
Title: The formation of small-scale umbral brightenings in sunspot
    atmospheres
Authors: Nelson, C. J.; Henriques, V. M. J.; Mathioudakis, M.; Keenan,
   F. P.
2017A&A...605A..14N    Altcode: 2017arXiv170505617N
  Context. Sunspot atmospheres have been shown to be highly inhomogeneous
  hosting both quasi-stable and transient features, such as small-scale
  umbral brightenings (previously named "umbral micro-jets") and dark
  fibril-like events. <BR /> Aims: We seek to understand the morphological
  properties and formation mechanisms of small-scale umbral brightenings
  (analogous to umbral micro-jets). In addition, we aim to understand
  whether links between these events and short dynamic fibrils,
  umbral flashes, and umbral dots can be established. <BR /> Methods:
  A Swedish 1 m Solar Telescope (SST) filtergram time-series sampling
  the Ca II H line and a CRisp Imaging Spectro-Polarimeter (SST/CRISP)
  full-Stokes 15-point Ca II 8542 Å line scan dataset were used. The
  spatial resolutions of these datasets are close to 0.1” and 0.18”
  with cadences of 1.4 s and 29 s, respectively. These data allowed
  us to construct light-curves, plot line profiles, and to perform
  a weak-field approximation in order to infer the magnetic field
  strength. <BR /> Results: The average lifetime and lengths of the 54
  small-scale brightenings identified in the sunspot umbra are found
  to be 44.2 s (σ = 20 s) and 0.56” (σ = 0.14”), respectively. The
  spatial positioning and morphological evolution of these events in
  Ca II H filtergrams was investigated finding no evidence of parabolic
  or ballistic profiles nor a preference for co-spatial formation with
  umbral flashes. Line scans in Ca II 8542 Å and the presence of Stokes
  V profile reversals provided evidence that these events could form in a
  similar manner to umbral flashes in the chromosphere (I.e. through the
  formation of shocks either due to the steepening of localised wavefronts
  or due to the impact of returning material from short dynamic fibrils,
  a scenario we find evidence for). The application of the weak-field
  approximation indicated that changes in the line-of-sight magnetic
  field were not responsible for the modifications to the line profile
  and suggested that thermodynamic effects are, in fact, the actual
  cause of the increased emission. Finally, a sub-set of small-scale
  brightenings were observed to form at the foot-points of short dynamic
  fibrils. <BR /> Conclusions: The small-scale umbral brightenings studied
  here do not appear to be jet-like in nature. Instead they appear to be
  evidence of shock formation in the lower solar atmosphere. We found
  no correlation between the spatial locations where these events were
  observed and the occurrence of umbral dots and umbral flashes. These
  events have lifetimes and spectral signatures comparable to umbral
  flashes and are located at the footpoints of short dynamic fibrils,
  during or at the end of the red-shifted stage. It is possible that
  these features form due to the shocking of fibrilar material in the
  lower atmosphere upon its return under gravity.

---------------------------------------------------------
Title: Spectroscopic Inversions of the Ca II 8542 Å Line in a
    C-class Solar Flare
Authors: Kuridze, D.; Henriques, V.; Mathioudakis, M.; Koza, J.;
   Zaqarashvili, T. V.; Rybák, J.; Hanslmeier, A.; Keenan, F. P.
2017ApJ...846....9K    Altcode: 2017arXiv170800472K
  We study the C8.4-class solar flare SOL2016-05-14T11:34 UT using
  high-resolution spectral imaging in the Ca II 8542 Å line obtained
  with the CRISP imaging spectropolarimeter on the Swedish 1 m Solar
  Telescope. Spectroscopic inversions of the Ca II 8542 Å line using
  the non-LTE code NICOLE are used to investigate the evolution of
  the temperature and velocity structure in the flaring chromosphere. A
  comparison of the temperature stratification in flaring and non-flaring
  areas reveals strong footpoint heating during the flare peak in the
  lower atmosphere. The temperature of the flaring footpoints between
  {log} {τ }<SUB>500</SUB> ≈ -2.5 {and} -3.5, where τ <SUB>500</SUB>
  is the continuum optical depth at 500 nm, is ∼ 5{--}6.5 {kK} close
  to the flare peak, reducing gradually to ∼ 5 {kK}. The temperature in
  the middle and upper chromosphere, between {log} {τ }<SUB>500</SUB>≈
  -3.5 and -5.5, is estimated to be ∼6.5-20 kK, decreasing to preflare
  temperatures, ∼5-10 kK, after approximately 15 minutes. However, the
  temperature stratification of the non-flaring areas is unchanged. The
  inverted velocity fields show that the flaring chromosphere is dominated
  by weak downflowing condensations at the formation height of Ca II
  8542 Å.

---------------------------------------------------------
Title: A Hot Downflowing Model Atmosphere for Umbral Flashes and
    the Physical Properties of Their Dark Fibrils
Authors: Henriques, V. M. J.; Mathioudakis, M.; Socas-Navarro, H.;
   de la Cruz Rodríguez, J.
2017ApJ...845..102H    Altcode: 2017arXiv170605311H
  We perform non-LTE inversions in a large set of umbral flashes,
  including the dark fibrils visible within them, and in the quiescent
  umbra by using the inversion code NICOLE on a set of full Stokes
  high-resolution Ca II λ8542 observations of a sunspot at disk
  center. We find that the dark structures have Stokes profiles that are
  distinct from those of the quiescent and flashed regions. They are
  best reproduced by atmospheres that are more similar to the flashed
  atmosphere in terms of velocities, even if with reduced amplitudes. We
  also find two sets of solutions that finely fit the flashed profiles:
  a set that is upflowing, featuring a transition region that is deeper
  than in the quiescent case and preceded by a slight dip in temperature,
  and a second solution with a hotter atmosphere in the chromosphere but
  featuring downflows close to the speed of sound at such heights. Such
  downflows may be related, or even dependent, on the presence of coronal
  loops, rooted in the umbra of sunspots, as is the case in the region
  analyzed. Similar loops have been recently observed to have supersonic
  downflows in the transition region and are consistent with the earlier
  “sunspot plumes,” which were invariably found to display strong
  downflows in sunspots. Finally, we find, on average, a magnetic field
  reduction in the flashed areas, suggesting that the shock pressure is
  moving field lines in the upper layers.

---------------------------------------------------------
Title: IRIS Burst Spectra Co-spatial to a Quiet-Sun Ellerman-like
    Brightening
Authors: Nelson, C. J.; Freij, N.; Reid, A.; Oliver, R.; Mathioudakis,
   M.; Erdélyi, R.
2017ApJ...845...16N    Altcode: 2017arXiv170705080N
  Ellerman bombs (EBs) have been widely studied over the past two
  decades; however, only recently have the counterparts of these events
  been observed in the quiet-Sun. The aim of this article is to further
  understand small-scale quiet-Sun Ellerman-like brightenings (QSEBs)
  through research into their spectral signatures, including investigating
  whether the hot signatures associated with some EBs are also visible
  co-spatial to any QSEBs. We combine Hα and Ca II 8542 Å line scans at
  the solar limb with spectral and imaging data sampled by the Interface
  Region Imaging Spectrograph (IRIS). Twenty-one QSEBs were identified
  with average lifetimes, lengths, and widths measured to be around 120 s,
  0.″63, and 0.″35, respectively. Three of these QSEBs displayed clear
  repetitive flaring through their lifetimes, comparable to the behavior
  of EBs in active regions. Two QSEBs in this sample occurred co-spatial
  to increased emission in SDO/AIA 1600 Å and IRIS slit-jaw imager 1400
  Å data; however, these intensity increases were smaller than those
  reported co-spatially with EBs. One QSEB was also sampled by the IRIS
  slit during its lifetime, displaying increases in intensity in the
  Si IV 1393 Å and Si IV 1403 Å cores, as well as the C II and Mg II
  line wings, analogous to IRIS bursts (IBs). Using RADYN simulations,
  we are unable to reproduce the observed QSEB Hα and Ca II 8542 Å
  line profiles, leaving the question of the temperature stratification
  of QSEBs open. Our results imply that some QSEBs could be heated to
  transition region temperatures, suggesting that IB profiles should be
  observed throughout the quiet-Sun.

---------------------------------------------------------
Title: Chromospheric Inversions of a Micro-flaring Region
Authors: Reid, A.; Henriques, V.; Mathioudakis, M.; Doyle, J. G.;
   Ray, T.
2017ApJ...845..100R    Altcode: 2017arXiv170700029R
  We use spectropolarimetric observations of the Ca II 8542 Å line, taken
  from the Swedish 1 m Solar Telescope, in an attempt to recover dynamic
  activity in a micro-flaring region near a sunspot via inversions. These
  inversions show localized mean temperature enhancements of ∼1000
  K in the chromosphere and upper photosphere, along with co-spatial
  bi-directional Doppler shifting of 5-10 km s<SUP>-1</SUP>. This heating
  also extends along a nearby chromospheric fibril, which is co-spatial
  to 10-15 km s<SUP>-1</SUP> downflows. Strong magnetic flux cancellation
  is also apparent in one of the footpoints, and is concentrated in the
  chromosphere. This event more closely resembles that of an Ellerman
  Bomb, though placed slightly higher in the atmosphere than what is
  typically observed.

---------------------------------------------------------
Title: An assessment of Fe xx-Fe xxii emission lines in SDO/EVE
    data as diagnostics for high-density solar flare plasmas using EUVE
    stellar observations
Authors: Keenan, F. P.; Milligan, R. O.; Mathioudakis, M.; Christian,
   D. J.
2017MNRAS.468.1117K    Altcode: 2017arXiv170208714K
  The Extreme Ultraviolet Variability Experiment (EVE) on the Solar
  Dynamics Observatory obtains extreme-ultraviolet (EUV) spectra of
  the full-disc Sun at a spectral resolution of ∼1 Å and cadence
  of 10 s. Such a spectral resolution would normally be considered
  to be too low for the reliable determination of electron density
  (N<SUB>e</SUB>) sensitive emission line intensity ratios, due
  to blending. However, previous work has shown that a limited
  number of Fe xxi features in the 90-160 Å wavelength region of
  EVE do provide useful N<SUB>e</SUB>-diagnostics at relatively low
  flare densities (N<SUB>e</SUB> ≃ 10<SUP>11</SUP>-10<SUP>12</SUP>
  cm<SUP>-3</SUP>). Here, we investigate if additional highly ionized
  Fe line ratios in the EVE 90-160 Å range may be reliably employed
  as N<SUB>e</SUB>-diagnostics. In particular, the potential for such
  diagnostics to provide density estimates for high N<SUB>e</SUB>
  (∼10<SUP>13</SUP> cm<SUP>-3</SUP>) flare plasmas is assessed. Our
  study employs EVE spectra for X-class flares, combined with
  observations of highly active late-type stars from the EUVE satellite
  plus experimental data for well-diagnosed tokamak plasmas, both of
  which are similar in wavelength coverage and spectral resolution
  to those from EVE. Several ratios are identified in EVE data,
  which yield consistent values of electron density, including Fe xx
  113.35/121.85 and Fe xxii 114.41/135.79, with confidence in their
  reliability as N<SUB>e</SUB>-diagnostics provided by the EUVE and
  tokamak results. These ratios also allow the determination of density in
  solar flare plasmas up to values of ∼10<SUP>13</SUP> cm<SUP>-3</SUP>.

---------------------------------------------------------
Title: Suppression of Hydrogen Emission in an X-class White-light
    Solar Flare
Authors: Procházka, Ondřej; Milligan, Ryan O.; Allred, Joel C.;
   Kowalski, Adam F.; Kotrč, Pavel; Mathioudakis, Mihalis
2017ApJ...837...46P    Altcode: 2017arXiv170200638P
  We present unique NUV observations of a well-observed X-class flare
  from NOAA 12087 obtained at the Ondřejov Observatory. The flare
  shows a strong white-light continuum but no detectable emission in
  the higher Balmer and Lyman lines. Reuven Ramaty High-Energy Solar
  Spectroscopic Imager and Fermi observations indicate an extremely
  hard X-ray spectrum and γ-ray emission. We use the RADYN radiative
  hydrodynamic code to perform two types of simulations: one where an
  energy of 3 × 10<SUP>11</SUP> erg cm<SUP>-2</SUP> s<SUP>-1</SUP>
  is deposited by an electron beam with a spectral index of ≈3, and a
  second where the same energy is applied directly to the photosphere. The
  combination of observations and simulations allows us to conclude
  that the white-light emission and the suppression or complete lack
  of hydrogen emission lines is best explained by a model where the
  dominant energy deposition layer is located in the lower layers of
  the solar atmosphere, rather than the chromosphere.

---------------------------------------------------------
Title: Solar Ellerman Bombs in 1D Radiative Hydrodynamics
Authors: Reid, A.; Mathioudakis, M.; Kowalski, A.; Doyle, J. G.;
   Allred, J. C.
2017ApJ...835L..37R    Altcode: 2017arXiv170104213R
  Recent observations from the Interface Region Imaging Spectrograph
  appear to show impulsive brightenings in high temperature lines,
  which when combined with simultaneous ground-based observations in
  Hα, appear co-spatial to Ellerman Bombs (EBs). We use the RADYN
  one-dimensional radiative transfer code in an attempt to try and
  reproduce the observed line profiles and simulate the atmospheric
  conditions of these events. Combined with the MULTI/RH line synthesis
  codes, we compute the Hα, Ca II 8542 Å, and Mg II h and k lines for
  these simulated events and compare them to previous observations. Our
  findings hint that the presence of superheated regions in the
  photosphere (&gt;10,000 K) is not a plausible explanation for the
  production of EB signatures. While we are able to recreate EB-like
  line profiles in Hα, Ca II 8542 Å, and Mg II h and k, we cannot
  achieve agreement with all of these simultaneously.

---------------------------------------------------------
Title: A Chromospheric Flare Model Consisting of Two Dynamical Layers:
    Critical Tests from IRIS Data of Solar Flares
Authors: Kowalski, Adam; Allred, Joel C.; Daw, Adrian N.; Cauzzi,
   Gianna; Carlsson, Mats; Inglis, Andrew; O'Neill, Aaron; Mathioudakis,
   Mihalis; Uitenbroek, Han
2017AAS...22933902K    Altcode:
  Recent 1D radiative-hydrodynamic simulations of flares have shown that
  a heated, chromospheric compression layer and a stationary layer, just
  below the compression, are produced in response to high flux electron
  beam heating. The hot blackbody-like continuum and redshifted intensity
  in singly ionized chromospheric lines in these model predictions are
  generally consistent with broad wavelength coverage spectra of M dwarf
  flares and with high spectral resolution observations of solar flares,
  respectively. We critically test this two-component chromospheric
  flare model against the Fe II profiles and NUV continuum brightness
  for several X-class solar flares observed with the Interface Region
  Imaging Spectrograph (IRIS). We present several new predictions for
  the Daniel K. Inoue Solar Telescope (DKIST).

---------------------------------------------------------
Title: Observations and Simulations of the Na I D<SUB>1</SUB> Line
    Profiles in an M-class Solar Flare
Authors: Kuridze, D.; Mathioudakis, M.; Christian, D. J.; Kowalski,
   A. F.; Jess, D. B.; Grant, S. D. T.; Kawate, T.; Simões, P. J. A.;
   Allred, J. C.; Keenan, F. P.
2016ApJ...832..147K    Altcode: 2016arXiv160908120K
  We study the temporal evolution of the Na I D<SUB>1</SUB> line profiles
  in the M3.9 flare SOL2014-06-11T21:03 UT, using observations at high
  spectral resolution obtained with the Interferometric Bidimensional
  Spectrometer instrument on the Dunn Solar Telescope combined with
  radiative hydrodynamic simulations. Our results show a significant
  increase in the intensities of the line core and wings during the
  flare. The analysis of the line profiles from the flare ribbons
  reveals that the Na I D<SUB>1</SUB> line has a central reversal
  with excess emission in the blue wing (blue asymmetry). We combine
  RADYN and RH simulations to synthesize Na I D<SUB>1</SUB> line
  profiles of the flaring atmosphere and find good agreement with
  the observations. Heating with a beam of electrons modifies the
  radiation field in the flaring atmosphere and excites electrons
  from the ground state 3s <SUP>2</SUP>S to the first excited state 3p
  <SUP>2</SUP>P, which in turn modifies the relative population of the
  two states. The change in temperature and the population density of
  the energy states make the sodium line profile revert from absorption
  into emission. Furthermore, the rapid changes in temperature break the
  pressure balance between the different layers of the lower atmosphere,
  generating upflow/downflow patterns. Analysis of the simulated spectra
  reveals that the asymmetries of the Na I D<SUB>1</SUB> flare profile
  are produced by the velocity gradients in the lower solar atmosphere.

---------------------------------------------------------
Title: Suppression of Hydrogen Emission in a White-light Solar Flare
Authors: Milligan, R. O.; Procházka, O.; Mathioudakis, M.; Allred,
   J. C.; Kowalski, A. F.
2016AGUFMSH31B2561P    Altcode: 2016AGUFMSH31B2561M
  We present an analysis of an X-class flare that occurred on 11
  June 2014 in active region NOAA 12087 using a newly developed high
  cadence Image Selector operated by Astronomical Institute in Ondrejov,
  Czech Republic. This instrument provides spectra in the 350-440 nm
  wavelength range, which covers the higher order Balmer lines as well
  as the Balmer jump at 364 nm. However, no detectable increase in these
  emissions were detected during the flare, and support observations from
  SDO/EVE MEGS-B also show that the Lyman line series and recombination
  continuum were also suppressed, particularly when compared to two
  other X-class flares on the preceding day. The X-class flare under
  investigation also showed strong white light emission in SDO/HMI
  data, as well as an extremely hard electron spectrum (delta 3.6),
  and gamma-ray emission, from RHESSI data. This unique combination
  of datasets was amended with radiative hydrodynamic model of direct
  minimum temperature region heating. The results allow us to conclude
  that the white light emission from this flare corresponds to a black
  body heated by high-energy electrons (and/or ions), as opposed to
  optical chromospheric emission from hydrogen.

---------------------------------------------------------
Title: Kelvin-Helmholtz Instability in Solar Chromospheric Jets:
    Theory and Observation
Authors: Kuridze, D.; Zaqarashvili, T. V.; Henriques, V.; Mathioudakis,
   M.; Keenan, F. P.; Hanslmeier, A.
2016ApJ...830..133K    Altcode: 2016arXiv160801497K
  Using data obtained by the high-resolution CRisp Imaging
  SpectroPolarimeter instrument on the Swedish 1 m Solar Telescope,
  we investigate the dynamics and stability of quiet-Sun chromospheric
  jets observed at the disk center. Small-scale features, such as rapid
  redshifted and blueshifted excursions, appearing as high-speed jets
  in the wings of the Hα line, are characterized by short lifetimes and
  rapid fading without any descending behavior. To study the theoretical
  aspects of their stability without considering their formation
  mechanism, we model chromospheric jets as twisted magnetic flux tubes
  moving along their axis, and use the ideal linear incompressible
  magnetohydrodynamic approximation to derive the governing dispersion
  equation. Analytical solutions of the dispersion equation indicate
  that this type of jet is unstable to Kelvin-Helmholtz instability
  (KHI), with a very short (few seconds) instability growth time at
  high upflow speeds. The generated vortices and unresolved turbulent
  flows associated with the KHI could be observed as a broadening of
  chromospheric spectral lines. Analysis of the Hα line profiles shows
  that the detected structures have enhanced line widths with respect to
  the background. We also investigate the stability of a larger-scale Hα
  jet that was ejected along the line of sight. Vortex-like features,
  rapidly developing around the jet’s boundary, are considered as
  evidence of the KHI. The analysis of the energy equation in the
  partially ionized plasma shows that ion-neutral collisions may lead
  to fast heating of the KH vortices over timescales comparable to the
  lifetime of chromospheric jets.

---------------------------------------------------------
Title: The Effects of Transients on Photospheric and Chromospheric
    Power Distributions
Authors: Samanta, T.; Henriques, V. M. J.; Banerjee, D.; Krishna
   Prasad, S.; Mathioudakis, M.; Jess, D.; Pant, V.
2016ApJ...828...23S    Altcode: 2016arXiv160406289S
  We have observed a quiet-Sun region with the Swedish 1 m Solar Telescope
  equipped with the CRISP Imaging SpectroPolarimeter. High-resolution,
  high-cadence, Hα line scanning images were taken to observe
  different layers of the solar atmosphere from the photosphere to upper
  chromosphere. We study the distribution of power in different period
  bands at different heights. Power maps of the upper photosphere
  and the lower chromosphere show suppressed power surrounding the
  magnetic-network elements, known as “magnetic shadows.” These also
  show enhanced power close to the photosphere, traditionally referred
  to as “power halos.” The interaction between acoustic waves and
  inclined magnetic fields is generally believed to be responsible
  for these two effects. In this study we explore whether small-scale
  transients can influence the distribution of power at different
  heights. We show that the presence of transients, like mottles, Rapid
  Blueshifted Excursions (RBEs), and Rapid Redshifted Excursions (RREs),
  can strongly influence the power maps. The short and finite lifetime of
  these events strongly affects all power maps, potentially influencing
  the observed power distribution. We show that Doppler-shifted transients
  like RBEs and RREs that occur ubiquitously can have a dominant effect
  on the formation of the power halos in the quiet Sun. For magnetic
  shadows, transients like mottles do not seem to have a significant
  effect on the power suppression around 3 minutes, and wave interaction
  may play a key role here. Our high-cadence observations reveal that
  flows, waves, and shocks manifest in the presence of magnetic fields
  to form a nonlinear magnetohydrodynamic system.

---------------------------------------------------------
Title: Construction status of the Daniel K. Inouye solar telescope
Authors: McMullin, Joseph P.; Rimmele, Thomas R.; Warner, Mark;
   Martinez Pillet, Valentin; Casini, Roberto; Berukoff, Steve; Craig,
   Simon C.; Elmore, David; Ferayorni, Andrew; Goodrich, Bret D.;
   Hubbard, Robert P.; Harrington, David; Hegwer, Steve; Jeffers, Paul;
   Johansson, Erik M.; Kuhn, Jeff; Lin, Haosheng; Marshall, Heather;
   Mathioudakis, Mihalis; McBride, William R.; McVeigh, William; Phelps,
   LeEllen; Schmidt, Wolfgang; Shimko, Steve; Sueoka, Stacey; Tritschler,
   Alexandra; Williams, Timothy R.; Wöger, Friedrich
2016SPIE.9906E..1BM    Altcode:
  We provide an update on the construction status of the Daniel
  K. Inouye Solar Telescope. This 4-m diameter facility is designed to
  enable detection and spatial/temporal resolution of the predicted,
  fundamental astrophysical processes driving solar magnetism at
  their intrinsic scales throughout the solar atmosphere. These data
  will drive key research on solar magnetism and its influence on
  solar winds, flares, coronal mass ejections and solar irradiance
  variability. The facility is developed to support a broad wavelength
  range (0.35 to 28 microns) and will employ state-of-the-art adaptive
  optics systems to provide diffraction limited imaging, resolving
  features approximately 20 km on the Sun. At the start of operations,
  there will be five instruments initially deployed: Visible Broadband
  Imager (VBI; National Solar Observatory), Visible SpectroPolarimeter
  (ViSP; NCAR High Altitude Observatory), Visible Tunable Filter (VTF
  (a Fabry-Perot tunable spectropolarimeter); Kiepenheuer Institute for
  Solarphysics), Diffraction Limited NIR Spectropolarimeter (DL-NIRSP;
  University of Hawaii, Institute for Astronomy) and the Cryogenic NIR
  Spectropolarimeter (Cryo-NIRSP; University of Hawaii, Institute for
  Astronomy). As of mid-2016, the project construction is in its 4th
  year of site construction and 7th year overall. Major milestones in
  the off-site development include the conclusion of the polishing of
  the M1 mirror by University of Arizona, College of Optical Sciences,
  the delivery of the Top End Optical Assembly (L3), the acceptance of
  the Deformable Mirror System (Xinetics); all optical systems have been
  contracted and are either accepted or in fabrication. The Enclosure
  and Telescope Mount Assembly passed through their factory acceptance
  in 2014 and 2015, respectively. The enclosure site construction
  is currently concluding while the Telescope Mount Assembly site
  erection is underway. The facility buildings (Utility and Support
  and Operations) have been completed with ongoing work on the thermal
  systems to support the challenging imaging requirements needed for the
  solar research. Finally, we present the construction phase performance
  (schedule, budget) with projections for the start of early operations.

---------------------------------------------------------
Title: The European Solar Telescope (EST)
Authors: Matthews, Sarah A.; Collados, Manuel; Mathioudakis, Mihalis;
   Erdelyi, Robertus
2016SPIE.9908E..09M    Altcode:
  The European Solar Telescope (EST) is being designed to optimize
  studies of the magnetic coupling between the lower layers of the solar
  atmosphere (the photosphere and chromosphere) in order to investigate
  the origins and evolution of the solar magnetic field and its role
  in driving solar activity. In order to achieve this, the thermal,
  dynamic and magnetic properties of the solar plasma must be probed
  over many scale heights and at intrinsic scales, requiring the use of
  multi wavelength spectroscopy and spectropolarimetry at high spatial,
  spectral and temporal resolution. In this paper we describe some of
  the over-arching science questions that EST will address and briefly
  outline the main features of the proposed telescope design and the
  associated instrumentation package.

---------------------------------------------------------
Title: Magnetic Flux Cancellation in Ellerman Bombs
Authors: Reid, A.; Mathioudakis, M.; Doyle, J. G.; Scullion, E.;
   Nelson, C. J.; Henriques, V.; Ray, T.
2016ApJ...823..110R    Altcode: 2016arXiv160307100R
  Ellerman Bombs (EBs) are often found to be co-spatial with bipolar
  photospheric magnetic fields. We use Hα imaging spectroscopy along with
  Fe I 6302.5 Å spectropolarimetry from the Swedish 1 m Solar Telescope
  (SST), combined with data from the Solar Dynamic Observatory, to study
  EBs and the evolution of the local magnetic fields at EB locations. EBs
  are found via an EB detection and tracking algorithm. Using NICOLE
  inversions of the spectropolarimetric data, we find that, on average,
  (3.43 ± 0.49) × 10<SUP>24</SUP> erg of stored magnetic energy
  disappears from the bipolar region during EB burning. The inversions
  also show flux cancellation rates of 10<SUP>14</SUP>-10<SUP>15</SUP>
  Mx s<SUP>-1</SUP> and temperature enhancements of 200 K at the detection
  footpoints. We investigate the near-simultaneous flaring of EBs due to
  co-temporal flux emergence from a sunspot, which shows a decrease in
  transverse velocity when interacting with an existing, stationary area
  of opposite polarity magnetic flux, resulting in the formation of the
  EBs. We also show that these EBs can be fueled further by additional,
  faster moving, negative magnetic flux regions.

---------------------------------------------------------
Title: Construction Status and Early Science with the Daniel K. Inouye
    Solar Telescope
Authors: McMullin, Joseph P.; Rimmele, Thomas R.; Warner, Mark;
   Martinez Pillet, Valentin; Craig, Simon; Woeger, Friedrich; Tritschler,
   Alexandra; Berukoff, Steven J.; Casini, Roberto; Goode, Philip R.;
   Knoelker, Michael; Kuhn, Jeffrey Richard; Lin, Haosheng; Mathioudakis,
   Mihalis; Reardon, Kevin P.; Rosner, Robert; Schmidt, Wolfgang
2016SPD....4720101M    Altcode:
  The 4-m Daniel K. Inouye Solar Telescope (DKIST) is in its seventh
  year of overall development and its fourth year of site construction
  on the summit of Haleakala, Maui. The Site Facilities (Utility
  Building and Support &amp; Operations Building) are in place with
  ongoing construction of the Telescope Mount Assembly within. Off-site
  the fabrication of the component systems is completing with early
  integration testing and verification starting.Once complete this
  facility will provide the highest sensitivity and resolution for study
  of solar magnetism and the drivers of key processes impacting Earth
  (solar wind, flares, coronal mass ejections, and variability in solar
  output). The DKIST will be equipped initially with a battery of first
  light instruments which cover a spectral range from the UV (380 nm)
  to the near IR (5000 nm), and capable of providing both imaging and
  spectro-polarimetric measurements throughout the solar atmosphere
  (photosphere, chromosphere, and corona); these instruments are being
  developed by the National Solar Observatory (Visible Broadband Imager),
  High Altitude Observatory (Visible Spectro-Polarimeter), Kiepenheuer
  Institute (Visible Tunable Filter) and the University of Hawaii
  (Cryogenic Near-Infrared Spectro-Polarimeter and the Diffraction-Limited
  Near-Infrared Spectro-Polarimeter). Further, a United Kingdom consortium
  led by Queen's University Belfast is driving the development of high
  speed cameras essential for capturing the highly dynamic processes
  measured by these instruments. Finally, a state-of-the-art adaptive
  optics system will support diffraction limited imaging capable of
  resolving features approximately 20 km in scale on the Sun.We present
  the overall status of the construction phase along with the current
  challenges as well as a review of the planned science testing and the
  transition into early science operations.

---------------------------------------------------------
Title: Quiet-Sun Hα Transients and Corresponding Small-scale
    Transition Region and Coronal Heating
Authors: Henriques, V. M. J.; Kuridze, D.; Mathioudakis, M.; Keenan,
   F. P.
2016ApJ...820..124H    Altcode: 2016arXiv160204820H
  Rapid blue- and redshifted excursions (RBEs and RREs) are likely to
  be the on-disk counterparts of Type II spicules. Recently, heating
  signatures from RBEs/RREs have been detected in IRIS slit-jaw
  images dominated by transition region (TR) lines around network
  patches. Additionally, signatures of Type II spicules have been observed
  in Atmospheric Imaging Assembly (AIA) diagnostics. The full-disk,
  ever-present nature of the AIA diagnostics should provide us with
  sufficient statistics to directly determine how important RBEs and RREs
  are to the heating of the TR and corona. We find, with high statistical
  significance, that at least 11% of the low coronal brightenings detected
  in a quiet-Sun region in He II 304 Å can be attributed to either RBEs
  or RREs as observed in Hα, and a 6% match of Fe IX 171 Å detected
  events to RBEs or RREs with very similar statistics for both types
  of Hα features. We took a statistical approach that allows for noisy
  detections in the coronal channels and provides us with a lower, but
  statistical significant, bound. Further, we consider matches based on
  overlapping features in both time and space, and find strong visual
  indications of further correspondence between coronal events and
  co-evolving but non-overlapping, RBEs and RREs.

---------------------------------------------------------
Title: M Dwarf Flare Continuum Variations on One-second Timescales:
    Calibrating and Modeling of ULTRACAM Flare Color Indices
Authors: Kowalski, Adam F.; Mathioudakis, Mihalis; Hawley, Suzanne L.;
   Wisniewski, John P.; Dhillon, Vik S.; Marsh, Tom R.; Hilton, Eric J.;
   Brown, Benjamin P.
2016ApJ...820...95K    Altcode: 2016arXiv160204879K
  We present a large data set of high-cadence dMe flare light curves
  obtained with custom continuum filters on the triple-beam, high-speed
  camera system ULTRACAM. The measurements provide constraints for models
  of the near-ultraviolet (NUV) and optical continuum spectral evolution
  on timescales of ≈1 s. We provide a robust interpretation of the
  flare emission in the ULTRACAM filters using simultaneously obtained
  low-resolution spectra during two moderate-sized flares in the dM4.5e
  star YZ CMi. By avoiding the spectral complexity within the broadband
  Johnson filters, the ULTRACAM filters are shown to characterize
  bona fide continuum emission in the NUV, blue, and red wavelength
  regimes. The NUV/blue flux ratio in flares is equivalent to a Balmer
  jump ratio, and the blue/red flux ratio provides an estimate for the
  color temperature of the optical continuum emission. We present a new
  “color-color” relationship for these continuum flux ratios at the
  peaks of the flares. Using the RADYN and RH codes, we interpret the
  ULTRACAM filter emission using the dominant emission processes from a
  radiative-hydrodynamic flare model with a high nonthermal electron beam
  flux, which explains a hot, T ≈ 10<SUP>4</SUP> K, color temperature
  at blue-to-red optical wavelengths and a small Balmer jump ratio as
  observed in moderate-sized and large flares alike. We also discuss the
  high time resolution, high signal-to-noise continuum color variations
  observed in YZ CMi during a giant flare, which increased the NUV flux
  from this star by over a factor of 100. <P />Based on observations
  obtained with the Apache Point Observatory 3.5 m telescope, which is
  owned and operated by the Astrophysical Research Consortium, based on
  observations made with the William Herschel Telescope operated on the
  island of La Palma by the Isaac Newton Group in the Spanish Observatorio
  del Roque de los Muchachos of the Instituto de Astrofsica de Canarias,
  and observations, and based on observations made with the ESO Telescopes
  at the La Silla Paranal Observatory under programme ID 085.D-0501(A).

---------------------------------------------------------
Title: Solar coronal magnetic fields derived using seismology
    techniques applied to omnipresent sunspot waves
Authors: Jess, David B.; Reznikova, Veronika E.; Ryans, Robert S. I.;
   Christian, Damian J.; Keys, Peter H.; Mathioudakis, Mihalis; Mackay,
   Duncan H.; Krishna Prasad, S.; Banerjee, Dipankar; Grant, Samuel D. T.;
   Yau, Sean; Diamond, Conor
2016NatPh..12..179J    Altcode: 2016arXiv160506112J
  Sunspots on the surface of the Sun are the observational signatures of
  intense manifestations of tightly packed magnetic field lines, with
  near-vertical field strengths exceeding 6,000 G in extreme cases. It
  is well accepted that both the plasma density and the magnitude of the
  magnetic field strength decrease rapidly away from the solar surface,
  making high-cadence coronal measurements through traditional Zeeman and
  Hanle effects difficult as the observational signatures are fraught
  with low-amplitude signals that can become swamped with instrumental
  noise. Magneto-hydrodynamic (MHD) techniques have previously been
  applied to coronal structures, with single and spatially isolated
  magnetic field strengths estimated as 9-55 G (refs ,,,). A drawback
  with previous MHD approaches is that they rely on particular wave modes
  alongside the detectability of harmonic overtones. Here we show, for
  the first time, how omnipresent magneto-acoustic waves, originating
  from within the underlying sunspot and propagating radially outwards,
  allow the spatial variation of the local coronal magnetic field to be
  mapped with high precision. We find coronal magnetic field strengths
  of 32 +/- 5 G above the sunspot, which decrease rapidly to values of
  approximately 1 G over a lateral distance of 7,000 km, consistent with
  previous isolated and unresolved estimations. Our results demonstrate
  a new, powerful technique that harnesses the omnipresent nature of
  sunspot oscillations to provide magnetic field mapping capabilities
  close to a magnetic source in the solar corona.

---------------------------------------------------------
Title: Hα Line Profile Asymmetries and the Chromospheric Flare
    Velocity Field
Authors: Kuridze, D.; Mathioudakis, M.; Simões, P. J. A.; Rouppe van
   der Voort, L.; Carlsson, M.; Jafarzadeh, S.; Allred, J. C.; Kowalski,
   A. F.; Kennedy, M.; Fletcher, L.; Graham, D.; Keenan, F. P.
2015ApJ...813..125K    Altcode: 2015arXiv151001877K
  The asymmetries observed in the line profiles of solar flares can
  provide important diagnostics of the properties and dynamics of the
  flaring atmosphere. In this paper the evolution of the Hα and Ca ii
  λ8542 lines are studied using high spatial, temporal, and spectral
  resolution ground-based observations of an M1.1 flare obtained with
  the Swedish 1 m Solar Telescope. The temporal evolution of the Hα
  line profiles from the flare kernel shows excess emission in the red
  wing (red asymmetry) before flare maximum and excess in the blue wing
  (blue asymmetry) after maximum. However, the Ca ii λ8542 line does
  not follow the same pattern, showing only a weak red asymmetry during
  the flare. RADYN simulations are used to synthesize spectral line
  profiles for the flaring atmosphere, and good agreement is found
  with the observations. We show that the red asymmetry observed in
  Hα is not necessarily associated with plasma downflows, and the blue
  asymmetry may not be related to plasma upflows. Indeed, we conclude
  that the steep velocity gradients in the flaring chromosphere modify
  the wavelength of the central reversal in the Hα line profile. The
  shift in the wavelength of maximum opacity to shorter and longer
  wavelengths generates the red and blue asymmetries, respectively.

---------------------------------------------------------
Title: Predicting and Disentangling Stellar Variability in Quiet
Stars: Implications for Low-mass Planet Confirmation
Authors: Cegla, Heather; Watson, Chris; Stassun, Keivan; Shelyag,
   Sergiy; Mathioudakis, Mihalis; Bastien, Fabienne; Pepper, Josh
2015IAUGA..2256546C    Altcode:
  Stellar variability is one of the main limiting factors in the detection
  and confirmation of low-mass planets. Even for magnetically quiet stars,
  astrophysical noise could be present at the 10m/s level. For these stars
  we demonstrate, using Kepler and GALEX data, that it may be possible to
  use photometric variability to predict the RV noise. Such a relationship
  creates a filtering mechanism to prioritize planetary candidates in
  transit surveys that are ideal for RV follow-up. Going beyond this, we
  use 3D magnetohydrodynamical (MHD) simulations to create Sun-as-a-star
  observations, focusing on stellar surface magneto-convection. Using
  these model observations we have identified correlations between the
  stellar line shape, brightness, and RV variability. We demonstrate
  that photometric observations may be key in disentangling stellar
  and planetary induced RV signals. Disentangling these signals allows
  us to reach the 10 cm/s noise level in our model star, indicating
  significant promise for the confirmation of low-mass planet candidates
  in the future.

---------------------------------------------------------
Title: Daniel K. Inouye Solar Telescope: Overview and Status
Authors: Rimmele, Thomas; McMullin, Joseph; Warner, Mark; Craig,
   Simon; Woeger, Friedrich; Tritschler, Alexandra; Cassini, Roberto;
   Kuhn, Jeff; Lin, Haosheng; Schmidt, Wolfgang; Berukoff, Steve; Reardon,
   Kevin; Goode, Phil; Knoelker, Michael; Rosner, Robert; Mathioudakis,
   Mihalis; DKIST TEAM
2015IAUGA..2255176R    Altcode:
  The 4m Daniel K. Inouye Solar Telescope (DKIST) currently under
  construction on Haleakala, Maui will be the world’s largest solar
  telescope. Designed to meet the needs of critical high resolution and
  high sensitivity spectral and polarimetric observations of the sun,
  this facility will perform key observations of our nearest star that
  matters most to humankind. DKIST’s superb resolution and sensitivity
  will enable astronomers to unravel many of the mysteries the Sun
  presents, including the origin of solar magnetism, the mechanisms of
  coronal heating and drivers of the solar wind, flares, coronal mass
  ejections and variability in solar output. The all-reflecting, off-axis
  design allows the facility to observe over a broad wavelength range and
  enables DKIST to operate as a coronagraph. In addition, the photon flux
  provided by its large aperture will be capable of routine and precise
  measurements of the currently elusive coronal magnetic fields. The
  state-of-the-art adaptive optics system provides diffraction limited
  imaging and the ability to resolve features approximately 20 km on
  the Sun. Five first light instruments, representing a broad community
  effort, will be available at the start of operations: Visible Broadband
  Imager (National Solar Observatory), Visible Spectro-Polarimeter (High
  Altitude Observatory), Visible Tunable Filter (Kiepenheuer Institute,
  Germany), Diffraction Limited NIR Spectro-Polarimeter (University
  of Hawaii) and the Cryogenic NIR Spectro-Polarimeter (University of
  Hawaii). High speed cameras for capturing highly dynamic processes
  in the solar atmosphere are being developed by a UK consortium. Site
  construction on Haleakala began in December 2012 and is progressing
  on schedule. Operations are scheduled to begin in 2019. We provide an
  overview of the facility, discuss the construction status, and present
  progress with DKIST operations planning.

---------------------------------------------------------
Title: Radiative hydrodynamic modelling and observations of the
    X-class solar flare on 2011 March 9
Authors: Kennedy, Michael B.; Milligan, Ryan O.; Allred, Joel C.;
   Mathioudakis, Mihalis; Keenan, Francis P.
2015A&A...578A..72K    Altcode: 2015arXiv150407541K
  <BR /> Aims: We investigated the response of the solar atmosphere to
  non-thermal electron beam heating using the radiative transfer and
  hydrodynamics modelling code RADYN. The temporal evolution of the
  parameters that describe the non-thermal electron energy distribution
  were derived from hard X-ray observations of a particular flare, and
  we compared the modelled and observed parameters. <BR /> Methods:
  The evolution of the non-thermal electron beam parameters during
  the X1.5 solar flare on 2011 March 9 were obtained from analysis of
  RHESSI X-ray spectra. The RADYN flare model was allowed to evolve for
  110 s, after which the electron beam heating was ended, and was then
  allowed to continue evolving for a further 300 s. The modelled flare
  parameters were compared to the observed parameters determined from
  extreme-ultraviolet spectroscopy. <BR /> Results: The model produced
  a hotter and denser flare loop than that observed and also cooled more
  rapidly, suggesting that additional energy input in the decay phase of
  the flare is required. In the explosive evaporation phase a region of
  high-density cool material propagated upward through the corona. This
  material underwent a rapid increase in temperature as it was unable to
  radiate away all of the energy deposited across it by the non-thermal
  electron beam and via thermal conduction. A narrow and high-density
  (n<SUB>e</SUB> ≤ 10<SUP>15</SUP> cm<SUP>-3</SUP>) region at the
  base of the flare transition region was the source of optical line
  emission in the model atmosphere. The collision-stopping depth of
  electrons was calculated throughout the evolution of the flare, and
  it was found that the compression of the lower atmosphere may permit
  electrons to penetrate farther into a flaring atmosphere compared to
  a quiet Sun atmosphere.

---------------------------------------------------------
Title: Ellerman Bombs with Jets: Cause and Effect
Authors: Reid, A.; Mathioudakis, M.; Scullion, E.; Doyle, J. G.;
   Shelyag, S.; Gallagher, P.
2015ApJ...805...64R    Altcode: 2015arXiv150305359R
  Ellerman Bombs (EBs) are thought to arise as a result of photospheric
  magnetic reconnection. We use data from the Swedish 1 m Solar
  Telescope to study EB events on the solar disk and at the limb. Both
  data sets show that EBs are connected to the foot points of forming
  chromospheric jets. The limb observations show that a bright structure
  in the Hα blue wing connects to the EB initially fueling it, leading
  to the ejection of material upwards. The material moves along a loop
  structure where a newly formed jet is subsequently observed in the
  red wing of Hα. In the disk data set, an EB initiates a jet which
  propagates away from the apparent reconnection site within the EB
  flame. The EB then splits into two, with associated brightenings in
  the inter-granular lanes. Micro-jets are then observed, extending
  to 500 km with a lifetime of a few minutes. Observed velocities of
  the micro-jets are approximately 5-10 km s<SUP>-1</SUP>, while their
  chromospheric counterparts range from 50 to 80 km s<SUP>-1</SUP>. MURaM
  simulations of quiet Sun reconnection show that micro-jets with
  properties similar to those of the observations follow the line of
  reconnection in the photosphere, with associated Hα brightening at
  the location of increased temperature.

---------------------------------------------------------
Title: Hα and EUV Observations of a Partial CME
Authors: Christian, Damian J.; Jess, David B.; Antolin, Patrick;
   Mathioudakis, Mihalis
2015ApJ...804..147C    Altcode: 2015arXiv150303982C
  We have obtained Hα high spatial and time resolution observations
  of the upper solar chromosphere and supplemented these with
  multi-wavelength observations from the Solar Dynamics Observatory
  (SDO) and the Hinode Extreme-ultraviolet Imaging Spectrometer. The Hα
  observations were conducted on 2012 February 11 with the Hydrogen-Alpha
  Rapid Dynamics Camera instrument at the National Solar Observatory’s
  Dunn Solar Telescope. Our Hα observations found large downflows
  of chromospheric material returning from coronal heights following a
  failed prominence eruption. We have detected several large condensations
  (“blobs”) returning to the solar surface at velocities of ≈200 km
  s<SUP>-1</SUP> in both Hα and several SDO Atmospheric Imaging Assembly
  band passes. The average derived size of these “blobs” in Hα is 500
  by 3000 km<SUP>2</SUP> in the directions perpendicular and parallel to
  the direction of travel, respectively. A comparison of our “blob”
  widths to those found from coronal rain, indicate that there are
  additional, smaller, unresolved “blobs” in agreement with previous
  studies and recent numerical simulations. Our observed velocities and
  decelerations of the “blobs” in both Hα and SDO bands are less
  than those expected for gravitational free-fall and imply additional
  magnetic or gas pressure impeding the flow. We derived a kinetic energy
  of ≈2 orders of magnitude lower for the main eruption than a typical
  coronal mass ejection, which may explain its partial nature.

---------------------------------------------------------
Title: The Radiated Energy Budget Of Chromospheric Plasma In A Major
    Solar Flare Deduced From Multi-Wavelength Observations
Authors: Milligan, Ryan; Kerr, Graham Stewart; Dennis, Brian; Hudson,
   Hugh; Fletcher, Lyndsay; Allred, Joel; Chamberlin, Phillip; Ireland,
   Jack; Mathioudakis, Mihalis; Keenan, Francis
2015TESS....130209M    Altcode:
  The response of the lower solar atmosphere is an important diagnostic
  tool for understanding energy transport during solar flares. The 15
  February 2011 X-class flare was fortuitously observed by a host of
  space-based instruments that sampled the chromospheric response over
  a range of lines and continua at &lt;20s cadence. These include the
  free-bound EUV continua of H I (Lyman), He I, and He II, plus the
  emission lines of He II at 304Å and H I (Lyα) at 1216Å by SDO/EVE,
  the UV continua at 1600Å and 1700Å by SDO/AIA, and the white light
  continuum at 4504Å, 5550Å, and 6684Å, along with the Ca II H line
  at 3968Å using Hinode/SOT. RHESSI also observed the entire event at
  energies up to ~100keV, making it possible to determine the properties
  of the nonthermal electrons deemed to be responsible for driving the
  enhanced chromospheric emission under the assumption of thick-target
  collisions. Integrating over the duration of the impulsive phase,
  the total energy contained in the nonthermal electrons was found to be
  &gt;2×10<SUP>31</SUP> erg. By comparison, the summed energy detected by
  instruments onboard SDO and Hinode amounted to ~3×10<SUP>30</SUP> erg;
  about 15% of the total nonthermal energy. The Lyα line was found to
  dominate the measured radiative losses in contrast to the predictions
  of numerical simulations. Parameters of both the driving electron
  distribution and the resulting chromospheric response are presented
  in detail to encourage the numerical modeling of flare heating for
  this event to determine the depth of the solar atmosphere at which
  these line and continuum processes originate, and the mechanism(s)
  responsible for their generation.

---------------------------------------------------------
Title: The Dynamics of Rapid Redshifted and Blueshifted Excursions
    in the Solar Hα Line
Authors: Kuridze, D.; Henriques, V.; Mathioudakis, M.; Erdélyi, R.;
   Zaqarashvili, T. V.; Shelyag, S.; Keys, P. H.; Keenan, F. P.
2015ApJ...802...26K    Altcode: 2015arXiv150106205K
  We analyze high temporal and spatial resolution time-series of spectral
  scans of the Hα line obtained with the CRisp Imaging SpectroPolarimeter
  instrument mounted on the Swedish Solar Telescope. The data reveal
  highly dynamic, dark, short-lived structures known as Rapid Redshifted
  and Blueshifted Excursions (RREs, RBEs) that are on-disk absorption
  features observed in the red and blue wings of spectral lines formed
  in the chromosphere. We study the dynamics of RREs and RBEs by tracking
  their evolution in space and time, measuring the speed of the apparent
  motion, line of sight (LOS) Doppler velocity, and transverse velocity
  of individual structures. A statistical study of their measured
  properties shows that RREs and RBEs have similar occurrence rates,
  lifetimes, lengths, and widths. They also display non-periodic,
  nonlinear transverse motions perpendicular to their axes at speeds of
  4-31 km s<SUP>-1</SUP>. Furthermore, both types of structures either
  appear as high speed jets and blobs that are directed outwardly from
  a magnetic bright point with speeds of 50-150 km s<SUP>-1</SUP>,
  or emerge within a few seconds. A study of the different velocity
  components suggests that the transverse motions along the LOS of
  the chromospheric flux tubes are responsible for the formation and
  appearance of these redshifted/blueshifted structures. The short
  lifetime and fast disappearance of the RREs/RBEs suggests that, similar
  to type II spicules, they are rapidly heated to transition region
  or even coronal temperatures. We speculate that the Kelvin-Helmholtz
  instability triggered by observed transverse motions of these structures
  may be a viable mechanism for their heating.

---------------------------------------------------------
Title: Stable umbral chromospheric structures
Authors: Henriques, V. M. J.; Scullion, E.; Mathioudakis, M.; Kiselman,
   D.; Gallagher, P. T.; Keenan, F. P.
2015A&A...574A.131H    Altcode: 2014arXiv1412.6100H
  <BR /> Aims: We seek to understand the morphology of the chromosphere in
  sunspot umbra. We investigate if the horizontal structures observed
  in the spectral core of the Ca II H line are ephemeral visuals
  caused by the shock dynamics of more stable structures, and examine
  their relationship with observables in the H-alpha line. <BR />
  Methods: Filtergrams in the core of the Ca II H and H-alpha lines
  as observed with the Swedish 1-m Solar Telescope are employed. We
  utilise a technique that creates composite images and tracks the
  flash propagation horizontally. <BR /> Results: We find 0.̋15 wide
  horizontal structures, in all of the three target sunspots, for every
  flash where the seeing is moderate to good. Discrete dark structures
  are identified that are stable for at least two umbral flashes, as well
  as systems of structures that live for up to 24 min. We find cases of
  extremely extended structures with similar stability, with one such
  structure showing an extent of 5”. Some of these structures have a
  correspondence in H-alpha, but we were unable to find a one-to-one
  correspondence for every occurrence. If the dark streaks are formed at
  the same heights as umbral flashes, there are systems of structures
  with strong departures from the vertical for all three analysed
  sunspots. <BR /> Conclusions: Long-lived Ca II H filamentary horizontal
  structures are a common and likely ever-present feature in the umbra
  of sunspots. If the magnetic field in the chromosphere of the umbra
  is indeed aligned with the structures, then the present theoretical
  understanding of the typical umbra needs to be revisited. <P />Movies
  associated to Figs. 3 and 4 are available in electronic form at <A
  href="http://www.aanda.org/10.1051/0004-6361/201424664/olm">http://www.aanda.org</A>

---------------------------------------------------------
Title: Time-Resolved Near-Ultraviolet Flare Spectra with the Hubble
    Space Telescope / Cosmic Origins Spectrograph
Authors: Kowalski, Adam F.; Hawley, Suzanne L.; Johns-Krull,
   Christopher M.; Schmidt, Sarah J.; Brown, Alexander; Wisniewski, John
   P.; Davenport, James R. A.; Farina, Cecilia; Pietro Gentile Fusillo,
   Nicola; Xilouris, Manolis; Mathioudakis, Mihalis; Osten, Rachel A.;
   Holtzman, Jon A.; Phan-Bao, Ngoc; Valenti, Jeff A.; Walkowicz, Lucianne
2015AAS...22544903K    Altcode:
  A large amount of the radiated energy during solar and stellar flares
  is emitted as white-light continuum emission, extending through the
  ultraviolet and optical wavelength regimes. Broadband photometry
  and optical spectral observations of M dwarf flares suggest that the
  white-light peak is located in the near-ultraviolet wavelength regime
  similar to a blackbody with T ~ 10,000 K, whereas radiative-hydrodynamic
  models using a solar-type flare heating mechanism (nonthermal electrons
  with a flux ~ 10<SUP>11</SUP> erg / s / cm<SUP>2</SUP> accelerated in
  the corona) predict that the peak lies at redder wavelengths at the
  head of the Balmer continuum. We have completed a successful flare
  monitoring campaign on the dM4e star GJ 1243, in order to constrain
  the time-evolution of the peak of the white-light continuum. The
  campaign took place over 12 hours on Aug 31/Sept 1, 2014, and included
  optical monitoring from nine ground-based telescopes as the Hubble
  Space Telescope recorded time-tagged spectra in the near-ultraviolet
  (2450-2840 Å) with the Cosmic Origins Spectrograph. Two flares occurred
  during the HST observations, and we show preliminary results relating
  the continuum and line (Fe II and Mg II) emission to the simultaneous
  ground-based optical spectra and photometry. This dataset provides new
  constraints for radiative-hydrodynamic modeling of the lower flaring
  atmosphere in addition to input for models of the effects of flares
  on biomarkers and habitability around M dwarfs.

---------------------------------------------------------
Title: Understanding Astrophysical Noise from Stellar Surface
    Magneto-Convection
Authors: Cegla, H. M.; Watson, C. A.; Shelyag, S.; Mathioudakis, M.
2015csss...18..567C    Altcode: 2014arXiv1408.2301C
  To obtain cm s^{-1} precision, stellar surface magneto-convection
  must be disentangled from observed radial velocities (RVs). In
  order to understand and remove the convective signature, we create
  Sun-as-a-star model observations based off a 3D magnetohydrodynamic
  solar simulation. From these Sun-as-a-star model observations, we
  find several line characteristics are correlated with the induced RV
  shifts. The aim of this campaign is to feed directly into future high
  precision RV studies, such as the search for habitable, rocky worlds,
  with forthcoming spectrographs such as ESPRESSO.

---------------------------------------------------------
Title: Nanoflare Activity in the Solar Chromosphere
Authors: Jess, D. B.; Mathioudakis, M.; Keys, P. H.
2014ApJ...795..172J    Altcode: 2014arXiv1409.6726J
  We use ground-based images of high spatial and temporal
  resolution to search for evidence of nanoflare activity in the solar
  chromosphere. Through close examination of more than 1 × 10<SUP>9</SUP>
  pixels in the immediate vicinity of an active region, we show that
  the distributions of observed intensity fluctuations have subtle
  asymmetries. A negative excess in the intensity fluctuations indicates
  that more pixels have fainter-than-average intensities compared with
  those that appear brighter than average. By employing Monte Carlo
  simulations, we reveal how the negative excess can be explained by a
  series of impulsive events, coupled with exponential decays, that are
  fractionally below the current resolving limits of low-noise equipment
  on high-resolution ground-based observatories. Importantly, our Monte
  Carlo simulations provide clear evidence that the intensity asymmetries
  cannot be explained by photon-counting statistics alone. A comparison
  to the coronal work of Terzo et al. suggests that nanoflare activity
  in the chromosphere is more readily occurring, with an impulsive
  event occurring every ~360 s in a 10,000 km<SUP>2</SUP> area of the
  chromosphere, some 50 times more events than a comparably sized region
  of the corona. As a result, nanoflare activity in the chromosphere
  is likely to play an important role in providing heat energy to this
  layer of the solar atmosphere.

---------------------------------------------------------
Title: The Radiated Energy Budget of Chromospheric Plasma in a Major
    Solar Flare Deduced from Multi-wavelength Observations
Authors: Milligan, Ryan O.; Kerr, Graham S.; Dennis, Brian R.; Hudson,
   Hugh S.; Fletcher, Lyndsay; Allred, Joel C.; Chamberlin, Phillip C.;
   Ireland, Jack; Mathioudakis, Mihalis; Keenan, Francis P.
2014ApJ...793...70M    Altcode: 2014arXiv1406.7657M
  This paper presents measurements of the energy radiated by the lower
  solar atmosphere, at optical, UV, and EUV wavelengths, during an
  X-class solar flare (SOL2011-02-15T01:56) in response to an injection
  of energy assumed to be in the form of nonthermal electrons. Hard
  X-ray observations from RHESSI were used to track the evolution of
  the parameters of the nonthermal electron distribution to reveal the
  total power contained in flare accelerated electrons. By integrating
  over the duration of the impulsive phase, the total energy contained
  in the nonthermal electrons was found to be &gt;2 × 10<SUP>31</SUP>
  erg. The response of the lower solar atmosphere was measured in
  the free-bound EUV continua of H I (Lyman), He I, and He II, plus
  the emission lines of He II at 304 Å and H I (Lyα) at 1216 Å by
  SDO/EVE, the UV continua at 1600 Å and 1700 Å by SDO/AIA, and the
  white light continuum at 4504 Å, 5550 Å, and 6684 Å, along with the
  Ca II H line at 3968 Å using Hinode/SOT. The summed energy detected
  by these instruments amounted to ~3 × 10<SUP>30</SUP> erg about 15%
  of the total nonthermal energy. The Lyα line was found to dominate
  the measured radiative losses. Parameters of both the driving electron
  distribution and the resulting chromospheric response are presented
  in detail to encourage the numerical modeling of flare heating for
  this event, to determine the depth of the solar atmosphere at which
  these line and continuum processes originate, and the mechanism(s)
  responsible for their generation.

---------------------------------------------------------
Title: F-CHROMA.Flare Chromospheres: Observations, Models and Archives
Authors: Cauzzi, Gianna; Fletcher, Lyndsay; Mathioudakis, Mihalis;
   Carlsson, Mats; Heinzel, Petr; Berlicki, Arek; Zuccarello, Francesca
2014AAS...22412339C    Altcode:
  F-CHROMA is a collaborative project newly funded under the EU-Framework
  Programme 7 "FP7-SPACE-2013-1", involving seven different European
  research Institutes and Universities. The goal of F-CHROMA is to
  substantially advance our understanding of the physics of energy
  dissipation and radiation in the flaring solar atmosphere, with a
  particular focus on the flares' chromosphere. A major outcome of the
  F-CHROMA project will be the creation of an archive of chromospheric
  flare observations and models to be made available to the community
  for further research.In this poster we describe the structure and
  milestones of the project, the different activities planned, as well
  as early results. Emphasis will be given to the dissemination efforts
  of the project to make results of these activities available to and
  usable by the community.

---------------------------------------------------------
Title: Dynamic properties of bright points in an active region
Authors: Keys, P. H.; Mathioudakis, M.; Jess, D. B.; Mackay, D. H.;
   Keenan, F. P.
2014A&A...566A..99K    Altcode: 2014arXiv1405.3923K
  Context. Bright points (BPs) are small-scale, magnetic features
  ubiquitous across the solar surface. Previously, we have observed and
  noted their properties for quiet Sun regions. Here, we determine the
  dynamic properties of BPs using simultaneous quiet Sun and active region
  data. <BR /> Aims: The aim of this paper is to compare the properties
  of BPs in both active and quiet Sun regions and to determine any
  difference in the dynamics and general properties of BPs as a result of
  the varying magnetic activity within these two regions. <BR /> Methods:
  High spatial and temporal resolution G-band observations of active
  region AR11372 were obtained with the Rapid Oscillations in the Solar
  Atmosphere instrument at the Dunn Solar Telescope. Three subfields of
  varying polarity and magnetic flux density were selected with the aid of
  magnetograms obtained from the Helioseismic and Magnetic Imager on board
  the Solar Dynamics Observatory. Bright points within these subfields
  were subsequently tracked and analysed. <BR /> Results: It is found that
  BPs within active regions display attenuated velocity distributions
  with an average horizontal velocity of ~0.6 km s<SUP>-1</SUP>,
  compared to the quiet region which had an average velocity of 0.9 km
  s<SUP>-1</SUP>. Active region BPs are also ~21% larger than quiet
  region BPs and have longer average lifetimes (~132 s) than their
  quiet region counterparts (88 s). No preferential flow directions are
  observed within the active region subfields. The diffusion index (γ) is
  estimated at ~1.2 for the three regions. <BR /> Conclusions: We confirm
  that the dynamic properties of BPs arise predominately from convective
  motions. The presence of stronger field strengths within active regions
  is the likely reason behind the varying properties observed. We believe
  that larger amounts of magnetic flux will attenuate BP velocities by a
  combination of restricting motion within the intergranular lanes and
  by increasing the number of stagnation points produced by inhibited
  convection. Larger BPs are found in regions of higher magnetic flux
  density and we believe that lifetimes increase in active regions as
  the magnetic flux stabilises the BPs.

---------------------------------------------------------
Title: Plasma properties and Stokes profiles during the lifetime of
    a photospheric magnetic bright point
Authors: Hewitt, R. L.; Shelyag, S.; Mathioudakis, M.; Keenan, F. P.
2014A&A...565A..84H    Altcode: 2014arXiv1404.0132H
  <BR /> Aims: In this paper we aim to investigate the evolution of plasma
  properties and Stokes parameters in photospheric magnetic bright points
  using 3D magneto-hydrodynamical simulations and radiative diagnostics of
  solar granulation. <BR /> Methods: Simulated time-dependent radiation
  parameters and plasma properties were investigated throughout the
  evolution of a bright point. Synthetic Stokes profiles for the FeI
  630.25 nm line were calculated, which also allowed the evolution of the
  Stokes-I line strength and Stokes-V area and amplitude asymmetries
  to be investigated. <BR /> Results: Our results are consistent
  with theoretical predictions and published observations describing
  convective collapse, and confirm this as the bright point formation
  process. Through degradation of the simulated data to match the spatial
  resolution of SOT, we show that high spatial resolution is crucial for
  the detection of changing spectro-polarimetric signatures throughout
  a magnetic bright point's lifetime. We also show that the signature
  downflow associated with the convective collapse process tends towards
  zero as the radiation intensity in the bright point peaks, because
  of the magnetic forces present restricting the flow of material in
  the flux tube. <P />Appendix A is available in electronic form at <A
  href="http://www.aanda.org/10.1051/0004-6361/201322882/olm">http://www.aanda.org</A>

---------------------------------------------------------
Title: Intensity Enhancement of O VI Ultraviolet Emission Lines in
    Solar Spectra due to Opacity
Authors: Keenan, F. P.; Doyle, J. G.; Madjarska, M. S.; Rose, S. J.;
   Bowler, L. A.; Britton, J.; McCrink, L.; Mathioudakis, M.
2014ApJ...784L..39K    Altcode: 2014arXiv1403.1470K
  Opacity is a property of many plasmas. It is normally expected that if
  an emission line in a plasma becomes optically thick, then its intensity
  ratio to that of another transition that remains optically thin
  should decrease. However, radiative transfer calculations undertaken
  both by ourselves and others predict that under certain conditions the
  intensity ratio of an optically thick to an optically thin line can show
  an increase over the optically thin value, indicating an enhancement
  in the former. These conditions include the geometry of the emitting
  plasma and its orientation to the observer. A similar effect can
  take place between lines of differing optical depths. While previous
  observational studies have focused on stellar point sources, here we
  investigate the spatially resolved solar atmosphere using measurements
  of the I(1032 Å)/I(1038 Å) intensity ratio of O VI in several regions
  obtained with the Solar Ultraviolet Measurements of Emitted Radiation
  instrument on board the Solar and Heliospheric Observatory satellite. We
  find several I(1032 Å)/I(1038 Å) ratios observed on the disk to be
  significantly larger than the optically thin value of 2.0, providing
  the first detection (to our knowledge) of intensity enhancement in
  the ratio arising from opacity effects in the solar atmosphere. The
  agreement between observation and theory is excellent and confirms
  that the O VI emission originates from a slab-like geometry in the
  solar atmosphere, rather than from cylindrical structures.

---------------------------------------------------------
Title: The Atmospheric Response to High Fluxes of Nonthermal Electrons
    during M Dwarf Flares
Authors: Kowalski, Adam; Allred, J. C.; Carlsson, M.; Hawley, S. L.;
   Holman, G. D.; Mathioudakis, M.; Osten, R. A.; Uitenbroek, H.
2014AAS...22315117K    Altcode:
  Flares are thought to be the result of magnetic fields in the stellar
  corona that undergo reconnection and accelerate charged particles
  into the lower atmosphere. Spectra of M dwarf flares in the optical
  and near-ultraviolet wavelength regimes can be used to constrain the
  heating mechanism of the lower stellar atmosphere. These observations
  show several ubiquitous properties of the continuum emission, which
  is not reproduced by models that use typical “solar-type” heating
  functions. We present results from a grid of new flare models using the
  RADYN code, which simultaneously calculates the radiative transfer and
  hydrodynamics on short timescales. We explore the atmospheric response
  to a short ~2 second burst of a very high heating rate from nonthermal
  electrons using a solar-type heating function, and we propose a new
  “M dwarf-type” heating variation that explains a range of observed
  spectral properties, such as ~10,000 K blackbody emission and a smooth
  continuum across the Balmer jump wavelength (3646A).

---------------------------------------------------------
Title: Comet C/2012 S1 (ISON): Observations of the Dust Grains from
    SOFIA and of the Atomic Gas from NSO Dunn and McMath-Pierce Solar
    Telescopes (Invited)
Authors: Wooden, D. H.; Woodward, C. E.; Harker, D. E.; Kelley, M. S.;
   Sitko, M.; Reach, W. T.; De Pater, I.; Gehrz, R. D.; Kolokolova,
   L.; Cochran, A. L.; McKay, A. J.; Reardon, K.; Cauzzi, G.; Tozzi,
   G.; Christian, D. J.; Jess, D. B.; Mathioudakis, M.; Lisse, C. M.;
   Morgenthaler, J. P.; Knight, M. M.
2013AGUFM.P24A..07W    Altcode:
  Comet C/2012 S1 (ISON) is unique in that it is a dynamically new comet
  derived from the Oort cloud reservoir of comets with a sun-grazing
  orbit. Infrared (IR) and visible wavelength observing campaigns were
  planned on NASA's Stratospheric Observatory For Infrared Astronomy
  (SOFIA) and on National Solar Observatory Dunn (DST) and McMath-Pierce
  Solar Telescopes, respectively. We highlight our early results. SOFIA
  (+FORCAST [1]) mid- to far-IR images and spectroscopy (~5-35 μm)
  of the dust in the coma of ISON are to be obtained by the ISON-SOFIA
  Team during a flight window 2013 Oct 21-23 UT (r_h≈1.18 AU). Dust
  characteristics, identified through the 10 μm silicate emission
  feature and its strength [2], as well as spectral features from
  cometary crystalline silicates (Forsterite) at 11.05-11.2 μm, and
  near 16, 19, 23.5, 27.5, and 33 μm are compared with other Oort cloud
  comets that span the range of small and/or highly porous grains (e.g.,
  C/1995 O1 (Hale-Bopp) [3,4,5] and C/2001 Q4 (NEAT) [6]) to large and/or
  compact grains (e.g., C/2007 N4 (Lulin) [7] and C/2006 P1 (McNaught)
  [8]). Measurement of the crystalline peaks in contrast to the broad
  10 and 20 μm amorphous silicate features yields the cometary silicate
  crystalline mass fraction [9], which is a benchmark for radial transport
  in our protoplanetary disk [10]. The central wavelength positions,
  relative intensities, and feature asymmetries for the crystalline
  peaks may constrain the shapes of the crystals [11]. Only SOFIA can
  look for cometary organics in the 5-8 μm region. Spatially resolved
  measurements of atoms and simple molecules from when comet ISON is
  near the Sun (r_h&lt; 0.4 AU, near Nov-20--Dec-03 UT) were proposed
  for by the ISON-DST Team. Comet ISON is the first comet since comet
  Ikeya-Seki (1965f) [12,13] suitable for studying the alkalai metals Na
  and K and the atoms specifically attributed to dust grains including
  Mg, Si, Fe, as well as Ca. DST's Horizontal Grating Spectrometer
  (HGS) measures 4 settings: Na I, K, C2 to sample cometary organics
  (along with Mg I), and [O I] as a proxy for activity from water [14]
  (along with Si I and Fe I). State-of-the-art instruments that will also
  be employed include IBIS [15], which is a Fabry-Perot spectral imaging
  system that concurrently measures lines of Na, K, Ca II, or Fe, and ROSA
  (CSUN/QUB) [16], which is a rapid imager that simultaneously monitors Ca
  II or CN. From McMath-Pierce, the Solar-Stellar Spectrograph also will
  target ISON (320-900 nm, R~21,000, r_h&lt;0.3 AU). Assuming survival,
  the intent is to target ISON over r_h&lt;0.4 AU, characteristic of
  prior Na detections [12,13,17,18,19]. References: [1] Adams, J.D., et
  al. 2012, SPIE, 8446, 16; [2] Kelley, M.S., Wooden, D.H. 2009, PSS, 57,
  1133; [3] Harker et al. 2002, ApJ, 580, 579; [4] Hayward et al. 2000,
  ApJ, 538, 428; [5] Hadamcik, E., Levasseur-Regourd, A.C. 2003, JQSRT,
  79-80, 661; [6] Wooden, D.H. 2004, ApJL, 612, L77; [7] Woodward et
  al. 2011, AJ, 141, 181; [8] Kelley et al. 2010, LPSC, 41, #2375;
  [9] Kelley, M.S. et al. 2011, AAS, 211, 560; [10] Wooden, D.H. 2008,
  SSRv, 138, 75; [11] Lindsay et al. 2013, ApJ, 766, 54; [12] Preston,
  G. W. 1967, ApJ, 147, 718; [13] Slaughter, C.D. 1969, AJ, 74, 929;
  [14] McKay et al. 2012, Icarus, 222, 684; [15] Cavallini, F., 2006,
  Solar Phys., 236, 415; [16] Jess et al., 2010, Solar Phys, 261, 363;
  [17] Watanabe, J-I. et al. 2003, ApJ, 585, L159; [18] Leblanc, F. et
  al. 2008, A&amp;A, 482, 293; [19] Fulle, M. et al. 2013, ApJL, 771, L21

---------------------------------------------------------
Title: Characteristics of Transverse Waves in Chromospheric Mottles
Authors: Kuridze, D.; Verth, G.; Mathioudakis, M.; Erdélyi, R.;
   Jess, D. B.; Morton, R. J.; Christian, D. J.; Keenan, F. P.
2013ApJ...779...82K    Altcode: 2013arXiv1310.3628K
  Using data obtained by the high temporal and spatial resolution
  Rapid Oscillations in the Solar Atmosphere instrument on the Dunn
  Solar Telescope, we investigate at an unprecedented level of detail
  transverse oscillations in chromospheric fine structures near the solar
  disk center. The oscillations are interpreted in terms of propagating
  and standing magnetohydrodynamic kink waves. Wave characteristics
  including the maximum transverse velocity amplitude and the phase
  speed are measured as a function of distance along the structure's
  length. Solar magnetoseismology is applied to these measured parameters
  to obtain diagnostic information on key plasma parameters (e.g.,
  magnetic field, density, temperature, flow speed) of these localized
  waveguides. The magnetic field strength of the mottle along the ~2 Mm
  length is found to decrease by a factor of 12, while the local plasma
  density scale height is ~280 ± 80 km.

---------------------------------------------------------
Title: Solar Flare Impulsive Phase Emission Observed with SDO/EVE
Authors: Kennedy, Michael B.; Milligan, Ryan O.; Mathioudakis, Mihalis;
   Keenan, Francis P.
2013ApJ...779...84K    Altcode: 2013arXiv1310.4649K
  Differential emission measures (DEMs) during the impulsive phase
  of solar flares were constructed using observations from the
  EUV Variability Experiment (EVE) and the Markov-Chain Monte Carlo
  method. Emission lines from ions formed over the temperature range log
  T<SUB>e</SUB> = 5.8-7.2 allow the evolution of the DEM to be studied
  over a wide temperature range at 10 s cadence. The technique was applied
  to several M- and X-class flares, where impulsive phase EUV emission
  is observable in the disk-integrated EVE spectra from emission lines
  formed up to 3-4 MK and we use spatially unresolved EVE observations
  to infer the thermal structure of the emitting region. For the nine
  events studied, the DEMs exhibited a two-component distribution during
  the impulsive phase, a low-temperature component with peak temperature
  of 1-2 MK, and a broad high-temperature component from 7 to 30 MK. A
  bimodal high-temperature component is also found for several events,
  with peaks at 8 and 25 MK during the impulsive phase. The origin of the
  emission was verified using Atmospheric Imaging Assembly images to be
  the flare ribbons and footpoints, indicating that the constructed DEMs
  represent the spatially average thermal structure of the chromospheric
  flare emission during the impulsive phase.

---------------------------------------------------------
Title: Ellerman Bombs—Evidence for Magnetic Reconnection in the
    Lower Solar Atmosphere
Authors: Nelson, C. J.; Shelyag, S.; Mathioudakis, M.; Doyle, J. G.;
   Madjarska, M. S.; Uitenbroek, H.; Erdélyi, R.
2013ApJ...779..125N    Altcode: 2013arXiv1310.7756N
  The presence of photospheric magnetic reconnection has long been thought
  to give rise to short and impulsive events, such as Ellerman bombs (EBs)
  and Type II spicules. In this article, we combine high-resolution,
  high-cadence observations from the Interferometric BIdimensional
  Spectrometer and Rapid Oscillations in the Solar Atmosphere instruments
  at the Dunn Solar Telescope, National Solar Observatory, New Mexico,
  with co-aligned Solar Dynamics Observatory Atmospheric Imaging Assembly
  and Hinode Solar Optical Telescope (SOT) data to observe small-scale
  events situated within an active region. These data are then compared
  with state-of-the-art numerical simulations of the lower atmosphere
  made using the MURaM code. It is found that brightenings, in both the
  observations and the simulations, of the wings of the Hα line profile,
  interpreted as EBs, are often spatially correlated with increases in
  the intensity of the Fe I λ6302.5 line core. Bipolar regions inferred
  from Hinode/SOT magnetic field data show evidence of flux cancellation
  associated, co-spatially, with these EBs, suggesting that magnetic
  reconnection could be a driver of these high-energy events. Through
  the analysis of similar events in the simulated lower atmosphere,
  we are able to infer that line profiles analogous to the observations
  occur co-spatially with regions of strong opposite-polarity magnetic
  flux. These observed events and their simulated counterparts are
  interpreted as evidence of photospheric magnetic reconnection at scales
  observable using current observational instrumentation.

---------------------------------------------------------
Title: Alfvén Waves in Simulations of Solar Photospheric Vortices
Authors: Shelyag, S.; Cally, P. S.; Reid, A.; Mathioudakis, M.
2013ApJ...776L...4S    Altcode: 2013arXiv1309.2019S
  Using advanced numerical magneto-hydrodynamic simulations of the
  magnetized solar photosphere, including non-gray radiative transport and
  a non-ideal equation of state, we analyze plasma motions in photospheric
  magnetic vortices. We demonstrate that apparent vortex-like motions in
  photospheric magnetic field concentrations do not exhibit "tornado"-like
  behavior or a "bath-tub" effect. While at each time instance the
  velocity field lines in the upper layers of the solar photosphere show
  swirls, the test particles moving with the time-dependent velocity
  field do not demonstrate such structures. Instead, they move in a
  wave-like fashion with rapidly changing and oscillating velocity field,
  determined mainly by magnetic tension in the magnetized intergranular
  downflows. Using time-distance diagrams, we identify horizontal
  motions in the magnetic flux tubes as torsional Alfvén perturbations
  propagating along the nearly vertical magnetic field lines with local
  Alfvén speed.

---------------------------------------------------------
Title: The Decaying Long-period Oscillation of a Stellar Megaflare
Authors: Anfinogentov, S.; Nakariakov, V. M.; Mathioudakis, M.;
   Van Doorsselaere, T.; Kowalski, A. F.
2013ApJ...773..156A    Altcode:
  We analyze and interpret the oscillatory signal in the decay phase of
  the U-band light curve of a stellar megaflare observed on 2009 January
  16 on the dM4.5e star YZ CMi. The oscillation is well approximated
  by an exponentially decaying harmonic function. The period of the
  oscillation is found to be 32 minutes, the decay time about 46 minutes,
  and the relative amplitude 15%. As this observational signature is
  typical of the longitudinal oscillations observed in solar flares at
  extreme ultraviolet and radio wavelengths, associated with standing
  slow magnetoacoustic waves, we suggest that this megaflare may be of a
  similar nature. In this scenario, macroscopic variations of the plasma
  parameters in the oscillations modulate the ejection of non-thermal
  electrons. The phase speed of the longitudinal (slow magnetoacoustic)
  waves in the flaring loop or arcade, the tube speed, of about 230
  km s<SUP>-1</SUP> would require a loop length of about 200 Mm. Other
  mechanisms, such as standing kink oscillations, are also considered.

---------------------------------------------------------
Title: Solar Flare Impulsive Phase Footpoint Emission Observed
    with SDO/EVE
Authors: Kennedy, Michael; Milligan, R. O.; Mathioudakis, M.
2013SPD....44...72K    Altcode:
  The differential emission measure of solar flare plasmas was constructed
  using observations from the EUV Variability Experiment (EVE) and the
  Markov-Chain Monte Carlo method. Emission lines from ions formed over
  the temperature range Log T = 5.8 - 7.4 allow for the evolution of the
  DEM to be studied over a wide temperature range at 10s cadence. The DEM
  construction technique is applied to several M and X-class flares where
  impulsive phase EUV emission is observable in the disk-integrated EVE
  spectra. The emission is verified using AIA images to be originating
  from the flare ribbons and footpoints and EVE observations are used to
  infer the thermal structure of the EUV emitting flare chromosphere. For
  the nine events studied the constructed differential emission measures
  have a two component distribution during the impulsive phase. The low
  temperature component has peak temperatures of 1 - 2 MK, and a high
  temperature component peaking at 10 MK.

---------------------------------------------------------
Title: A Pathway to Earth-like Worlds: Overcoming Astrophysical
    Noise due to Convection
Authors: Cegla, Heather M.; Watson, C.; Shelyag, S.; Mathioudakis, M.
2013AAS...22230402C    Altcode:
  One of the consequences of the plasma motions within the convective
  envelopes of low-mass stars (i.e. potential planet hosting stars)
  are the radial velocity (RV) shifts due to variable stellar
  line profile asymmetries, known as astrophysical noise (or
  stellar jitter). This can pose a major problem for planet hunters
  because RV follow-up is mandatory for most planet confirmation and
  characterization. Furthermore, as the net RV shifts produced from
  these photospheric convective motions are around the m/s level this is
  especially troublesome for confirmation of Earth-analogs that induce
  Doppler-wobbles on the cm/s level. The currently implemented noise
  removal technique for granulation rests on adapting observational
  strategies to average out such noise. However, this technique is
  extremely observationally intensive and does not provide information on
  the nature of jitter. We aim to go beyond these previous techniques
  by understanding the physical processes involved in granulation
  and removing the actual RV signature from granulation. We outline
  our techniques to characterize photospheric granulation as an
  astrophysical noise source. The backbone of this characterization is
  a state-of-the-art 3D magnetohydrodynamic solar simulation, coupled
  with detailed wavelength-dependent radiative transfer. Due to the
  time-intensive nature of these simulations, we use a short time-series
  to parameterize the granulation signal. This parameterization is then
  used to create full Sun-as-a-star observations from which we examine
  the convective noise. We present the results of this study, as well as
  the identification of variable gravitational redshift as a potential
  source of stellar jitter, both of which could impact the RV follow-up
  and confirmation of low-mass terrestrial planets and Earth-like worlds.

---------------------------------------------------------
Title: Alfvén Waves in the Solar Atmosphere. From Theory to
    Observations
Authors: Mathioudakis, M.; Jess, D. B.; Erdélyi, R.
2013SSRv..175....1M    Altcode: 2012SSRv..tmp...94M; 2012arXiv1210.3625M
  Alfvén waves are considered to be viable transporters of the
  non-thermal energy required to heat the Sun's quiescent atmosphere. An
  abundance of recent observations, from state-of-the-art facilities, have
  reported the existence of Alfvén waves in a range of chromospheric
  and coronal structures. Here, we review the progress made in
  disentangling the characteristics of transverse kink and torsional
  linear magnetohydrodynamic (MHD) waves. We outline the simple, yet
  powerful theory describing their basic properties in (non-)uniform
  magnetic structures, which closely resemble the building blocks of
  the real solar atmosphere.

---------------------------------------------------------
Title: Failed filament eruption inside a coronal mass ejection in
    active region 11121
Authors: Kuridze, D.; Mathioudakis, M.; Kowalski, A. F.; Keys, P. H.;
   Jess, D. B.; Balasubramaniam, K. S.; Keenan, F. P.
2013A&A...552A..55K    Altcode: 2013arXiv1302.5931K
  <BR /> Aims: We study the formation and evolution of a failed filament
  eruption observed in NOAA active region 11121 near the southeast limb on
  November 6, 2010. <BR /> Methods: We used a time series of SDO/AIA 304,
  171, 131, 193, 335, and 94 Å images, SDO/HMI magnetograms, as well as
  ROSA and ISOON Hα images to study the erupting active region. <BR />
  Results: We identify coronal loop arcades associated with a quadrupolar
  magnetic configuration, and show that the expansion and cancellation
  of the central loop arcade system over the filament is followed by
  the eruption of the filament. The erupting filament reveals a clear
  helical twist and develops the same sign of writhe in the form of
  inverse γ-shape. <BR /> Conclusions: The observations support the
  "magnetic breakout" process in which the eruption is triggered by
  quadrupolar reconnection in the corona. We propose that the formation
  mechanism of the inverse γ-shape flux rope is the magnetohydrodynamic
  helical kink instability. The eruption has failed because of the
  large-scale, closed, overlying magnetic loop arcade that encloses
  the active region. <P />Movies are available in electronic form at
  <A href="http://www.aanda.org">http://www.aanda.org</A>

---------------------------------------------------------
Title: Statistical Analysis of Small Ellerman Bomb Events
Authors: Nelson, C. J.; Doyle, J. G.; Erdélyi, R.; Huang, Z.;
   Madjarska, M. S.; Mathioudakis, M.; Mumford, S. J.; Reardon, K.
2013SoPh..283..307N    Altcode: 2013arXiv1301.1351N
  The properties of Ellerman bombs (EBs), small-scale brightenings in
  the Hα line wings, have proved difficult to establish because their
  size is close to the spatial resolution of even the most advanced
  telescopes. Here, we aim to infer the size and lifetime of EBs using
  high-resolution data of an emerging active region collected using
  the Interferometric BIdimensional Spectrometer (IBIS) and Rapid
  Oscillations of the Solar Atmosphere (ROSA) instruments as well as
  the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics
  Observatory (SDO). We develop an algorithm to track EBs through their
  evolution, finding that EBs can often be much smaller (around 0.3″)
  and shorter-lived (less than one minute) than previous estimates. A
  correlation between G-band magnetic bright points and EBs is also
  found. Combining SDO/HMI and G-band data gives a good proxy of the
  polarity for the vertical magnetic field. It is found that EBs often
  occur both over regions of opposite polarity flux and strong unipolar
  fields, possibly hinting at magnetic reconnection as a driver of these
  events.The energetics of EB events is found to follow a power-law
  distribution in the range of a nanoflare (10<SUP>22−25</SUP> ergs).

---------------------------------------------------------
Title: Tracking magnetic bright point motions through the solar
    atmosphere
Authors: Keys, P. H.; Mathioudakis, M.; Jess, D. B.; Shelyag, S.;
   Christian, D. J.; Keenan, F. P.
2013MNRAS.428.3220K    Altcode: 2012MNRAS.tmp..182K; 2012arXiv1210.5904K
  High-cadence, multiwavelength observations and simulations are
  employed for the analysis of solar photospheric magnetic bright
  points (MBPs) in the quiet Sun. The observations were obtained with
  the Rapid Oscillations in the Solar Atmosphere (ROSA) imager and
  the Interferometric Bidimensional Spectrometer at the Dunn Solar
  Telescope. Our analysis reveals that photospheric MBPs have an average
  transverse velocity of approximately 1 km s<SUP>-1</SUP>, whereas their
  chromospheric counterparts have a slightly higher average velocity of
  1.4 km s<SUP>-1</SUP>. Additionally, chromospheric MBPs were found to be
  around 63 per cent larger than the equivalent photospheric MBPs. These
  velocity values were compared with the output of numerical simulations
  generated using the muram code. The simulated results were similar,
  but slightly elevated, when compared to the observed data. An average
  velocity of 1.3 km s<SUP>-1</SUP> was found in the simulated G-band
  images and an average of 1.8 km s<SUP>-1</SUP> seen in the velocity
  domain at a height of 500 km above the continuum formation layer. Delays
  in the change of velocities were also analysed. Average delays of ∼4
  s between layers of the simulated data set were established and values
  of ∼29 s observed between G-band and Ca ii K ROSA observations. The
  delays in the simulations are likely to be the result of oblique
  granular shock waves, whereas those found in the observations are
  possibly the result of a semi-rigid flux tube.

---------------------------------------------------------
Title: Stellar Surface Magneto-convection as a Source of Astrophysical
    Noise. I. Multi-component Parameterization of Absorption Line Profiles
Authors: Cegla, H. M.; Shelyag, S.; Watson, C. A.; Mathioudakis, M.
2013ApJ...763...95C    Altcode: 2012arXiv1212.0236C
  We outline our techniques to characterize photospheric granulation
  as an astrophysical noise source. A four-component parameterization
  of granulation is developed that can be used to reconstruct stellar
  line asymmetries and radial velocity shifts due to photospheric
  convective motions. The four components are made up of absorption
  line profiles calculated for granules, magnetic intergranular lanes,
  non-magnetic intergranular lanes, and magnetic bright points at disk
  center. These components are constructed by averaging Fe I 6302 Å
  magnetically sensitive absorption line profiles output from detailed
  radiative transport calculations of the solar photosphere. Each
  of the four categories adopted is based on magnetic field and
  continuum intensity limits determined from examining three-dimensional
  magnetohydrodynamic simulations with an average magnetic flux of 200
  G. Using these four-component line profiles we accurately reconstruct
  granulation profiles, produced from modeling 12 × 12 Mm<SUP>2</SUP>
  areas on the solar surface, to within ~ ±20 cm s<SUP>-1</SUP> on a
  ~100 m s<SUP>-1</SUP> granulation signal. We have also successfully
  reconstructed granulation profiles from a 50 G simulation using the
  parameterized line profiles from the 200 G average magnetic field
  simulation. This test demonstrates applicability of the characterization
  to a range of magnetic stellar activity levels.

---------------------------------------------------------
Title: Observations of ubiquitous compressive waves in the Sun's
    chromosphere
Authors: Morton, Richard J.; Verth, Gary; Jess, David B.; Kuridze,
   David; Ruderman, Michael S.; Mathioudakis, Mihalis; Erdélyi, Robertus
2012NatCo...3.1315M    Altcode: 2012NatCo...3E1315M; 2013arXiv1306.4124M
  The details of the mechanism(s) responsible for the observed
  heating and dynamics of the solar atmosphere still remain a
  mystery. Magnetohydrodynamic waves are thought to have a vital role
  in this process. Although it has been shown that incompressible
  waves are ubiquitous in off-limb solar atmospheric observations,
  their energy cannot be readily dissipated. Here we provide, for the
  first time, on-disk observation and identification of concurrent
  magnetohydrodynamic wave modes, both compressible and incompressible,
  in the solar chromosphere. The observed ubiquity and estimated energy
  flux associated with the detected magnetohydrodynamic waves suggest
  the chromosphere is a vast reservoir of wave energy with the potential
  to meet chromospheric and coronal heating requirements. We are also
  able to propose an upper bound on the flux of the observed wave energy
  that is able to reach the corona based on observational constraints,
  which has important implications for the suggested mechanism(s) for
  quiescent coronal heating.

---------------------------------------------------------
Title: Coupled Effects of a Perturbation in a Complex Structure
    Observed with SDO/AIA, SDO/HMI and ROSA/HARDcam
Authors: Cadavid, A. C.; Lawrence, J. K.; Christian, D. J.; Jess,
   D. B.; Mathioudakis, M.
2012AGUFMSH51A2197C    Altcode:
  We study properties of intensity fluctuations in NOAA Active Region
  11250 observed on 13 July 2011 starting at UT 13:32. Included are
  data obtained in the EUV bands of the Atmospheric Imaging Assembly
  on board the Solar Dynamics Observatory (SDO/AIA) as well as nearly
  simultaneous observations of the chromosphere made, at much higher
  spatial and temporal resolution, with the Rapid Oscillations in the
  Solar Atmosphere (ROSA) and Hydrogen-Alpha Rapid Dynamics camera
  (HARDcam) systems at the Dunn Solar Telescope. A complex structure
  seen in both the ROSA/HARDcam and SDO data sets comprises a system of
  loops extending outward from near the boundary of the leading sunspot
  umbra. It is visible in the ROSA Ca II K and HARDcam Hα images, as
  well as the SDO 304 Å, 171 Å and 193 Å channels, and it thus couples
  the chromosphere, transition region and corona. In the ground-based
  images the loop structure is 4.1 Mm long. Some 17.5 Mm, can be traced
  in the SDO/AIA data. The chromospheric emissions observed by ROSA and
  HARDcam appear to occupy the inner, and apparently cooler and lower,
  quarter of the loop. We compare the intensity fluctuations of two points
  within the structure. From alignment with SDO/HMI images we identify a
  point "A" near the loop structure, which sits directly above a bipolar
  magnetic feature in the photosphere. Point "B" is characteristic of
  locations within the loops that are visible in both the ROSA/HARDcam
  and the SDO/AIA data. The intensity traces for point A are quiet
  during the first part of the data string. At time ~ 19 min they
  suddenly begin a series of impulsive brightenings. In the 171 Å and
  193 Å coronal lines the brightenings are localized impulses in time,
  but in the transition region line at 304 Å they are more extended
  in time. The intensity traces in the 304 Å line for point B shows
  a quasi-periodic signal that changes properties at about 19 min. The
  wavelet power spectra are characterized by two periodicities. A 6.7 min
  period extends from the beginning of the series until about 25 minutes,
  and another signal with period ~3 min starts at about 20 min. The 193
  Å power spectrum has a characteristic period of 5 min, before the
  20 min transition and a 2.5 min periodicity afterward. In the case of
  HARDcam Hα data a localized 4 min periodicity can be found until about
  7 min, followed by a quiet regime. After ~20 min a 2.3 min periodicity
  appears. Interestingly a coronal loop visible in the 94 Å line that
  is centrally located in the AR, running from the leading umbra to the
  following polarity, at about time 20 min undergoes a strong brightening
  beginning at the same moment all along 15 Mm of its length. The fact
  that these different signals all experience a clear-cut change at time
  about 20 min suggests an underlying organizing mechanism. Given that
  point A has a direct connection to the photospheric magnetic bipole,
  we conjecture that the whole extended structure is connected in a
  complex manner to the underlying magnetic field. The periodicities
  in these features may favor the wave nature rather than upflows and
  interpretations will be discussed.

---------------------------------------------------------
Title: Vortices in the Solar Photosphere
Authors: Shelyag, S.; Fedun, V.; Erdélyi, R.; Keenan, F. P.;
   Mathioudakis, M.
2012ASPC..463..107S    Altcode: 2012arXiv1202.1966S
  Using numerical simulations of the magnetized solar photosphere
  and radiative diagnostics of the simulated photospheric models,
  we further analyse the physical nature of magnetic photospheric
  intergranular vortices. We confirm the magnetic nature of the vortices
  and find that most MHD Umov-Poynting flux is produced by horizontal
  vortex motions in the magnetised intergranular lanes. In addition,
  we consider possible ways to directly observe photospheric magnetic
  vortices using spectropolarimetry. Although horizontal plasma motions
  cannot be detected in the spectropolarimetric observations of solar disk
  center, we find an observational signature of photospheric vortices in
  simulated observations of Stokes-V amplitude asymmetry close to the
  solar limb. Potential ways to find the vortices in the observations
  are discussed.

---------------------------------------------------------
Title: Turbulent Fluctuations in G-band and K-line Intensities
    Observed with the Rapid Oscillations in the Solar Atmosphere (ROSA)
    Instrument
Authors: Cadavid, A. C.; Lawrence, J. K.; Christian, D. J.; Jess,
   D. B.; Mathioudakis, M.
2012ASPC..463...75C    Altcode:
  Using the Rapid Oscillation in the Solar Atmosphere (ROSA) instrument at
  the Dunn Solar Telescope we have found that the spectra of fluctuations
  of the G-band (cadence 1.05 s) and Ca II K-line (cadence 4.2 s)
  intensities show correlated fluctuations above white noise out
  to frequencies beyond 300 mHz and up to 70 mHz, respectively. The
  noise-corrected G-band spectrum presents a scaling range (Ultra High
  Frequency “UHF”) for f = 25-100 mHz, with an exponent consistent
  with the presence of turbulent motions. The UHF power, is concentrated
  at the locations of magnetic bright points in the intergranular lanes,
  it is highly intermittent in time and characterized by a positive
  kurtosis κ. Combining values of G-band and K-line intensities, the UHF
  power, and κ, reveals two distinct “states” of the internetwork
  solar atmosphere. State 1, with κ ≍ 6, which includes almost all
  the data, is characterized by low intensities and low UHF power. State
  2, with κ ≍ 3, including a very small fraction of the data, is
  characterized by high intensities and high UHF power. Superposed epoch
  analysis shows that for State 1, the K-line intensity presents 3.5
  min chromospheric oscillations with maxima occurring 21 s after G-band
  intensity maxima implying a 150-210 km effective height difference. For
  State 2, the G-band and K-line intensity maxima are simultaneous,
  suggesting that in the highly magnetized environment sites of G-band
  and K-line emission may be spatially close together. Analysis of
  observations obtained with Hinode/SOT confirm a scaling range in the
  G-band spectrum up to 53 mHz also consistent with turbulent motions
  as well as the identification of two distinct states in terms of the
  H-line intensity and G-band power as functions of G-band intensity.

---------------------------------------------------------
Title: The Source of 3 Minute Magnetoacoustic Oscillations in
    Coronal Fans
Authors: Jess, D. B.; De Moortel, I.; Mathioudakis, M.; Christian,
   D. J.; Reardon, K. P.; Keys, P. H.; Keenan, F. P.
2012ApJ...757..160J    Altcode: 2012arXiv1208.3194J
  We use images of high spatial, spectral, and temporal resolution,
  obtained using both ground- and space-based instrumentation, to
  investigate the coupling between wave phenomena observed at numerous
  heights in the solar atmosphere. Analysis of 4170 Å continuum images
  reveals small-scale umbral intensity enhancements, with diameters
  ~0farcs6, lasting in excess of 30 minutes. Intensity oscillations
  of ≈3 minutes are observed to encompass these photospheric
  structures, with power at least three orders of magnitude higher
  than the surrounding umbra. Simultaneous chromospheric velocity and
  intensity time series reveal an 87° ± 8° out-of-phase behavior,
  implying the presence of standing modes created as a result of
  partial wave reflection at the transition region boundary. We find a
  maximum waveguide inclination angle of ≈40° between photospheric
  and chromospheric heights, combined with a radial expansion factor
  of &lt;76%. An average blueshifted Doppler velocity of ≈1.5 km
  s<SUP>-1</SUP>, in addition to a time lag between photospheric and
  chromospheric oscillatory phenomena, confirms the presence of upwardly
  propagating slow-mode waves in the lower solar atmosphere. Propagating
  oscillations in EUV intensity are detected in simultaneous coronal
  fan structures, with a periodicity of 172 ± 17 s and a propagation
  velocity of 45 ± 7 km s<SUP>-1</SUP>. Numerical simulations reveal that
  the damping of the magnetoacoustic wave trains is dominated by thermal
  conduction. The coronal fans are seen to anchor into the photosphere
  in locations where large-amplitude umbral dot (UD) oscillations
  manifest. Derived kinetic temperature and emission measure time series
  display prominent out-of-phase characteristics, and when combined with
  the previously established sub-sonic wave speeds, we conclude that
  the observed EUV waves are the coronal counterparts of the upwardly
  propagating magnetoacoustic slow modes detected in the lower solar
  atmosphere. Thus, for the first time, we reveal how the propagation
  of 3 minute magnetoacoustic waves in solar coronal structures is a
  direct result of amplitude enhancements occurring in photospheric UDs.

---------------------------------------------------------
Title: Time-dependent Density Diagnostics of Solar Flare Plasmas
    Using SDO/EVE
Authors: Milligan, Ryan O.; Kennedy, Michael B.; Mathioudakis, Mihalis;
   Keenan, Francis P.
2012ApJ...755L..16M    Altcode: 2012arXiv1207.1990M
  Temporally resolved electron density measurements of solar flare plasmas
  are presented using data from the EUV Variability Experiment (EVE) on
  board the Solar Dynamics Observatory. The EVE spectral range contains
  emission lines formed between 10<SUP>4</SUP> and 10<SUP>7</SUP> K,
  including transitions from highly ionized iron (gsim10 MK). Using
  three density-sensitive Fe XXI ratios, peak electron densities of
  10<SUP>11.2</SUP>-10<SUP>12.1</SUP> cm<SUP>-3</SUP> were found during
  four X-class flares. While previous measurements of densities at such
  high temperatures were made at only one point during a flaring event,
  EVE now allows the temporal evolution of these high-temperature
  densities to be determined at 10 s cadence. A comparison with GOES
  data revealed that the peak of the density time profiles for each line
  ratio correlated well with that of the emission measure time profile
  for each of the events studied.

---------------------------------------------------------
Title: Mechanisms for MHD Poynting Flux Generation in Simulations
    of Solar Photospheric Magnetoconvection
Authors: Shelyag, S.; Mathioudakis, M.; Keenan, F. P.
2012ApJ...753L..22S    Altcode: 2012arXiv1206.0030S
  We investigate the generation mechanisms of MHD Poynting flux in the
  magnetized solar photosphere. Using radiative MHD modeling of the
  solar photosphere with initial magnetic configurations that differ
  in their field strength and geometry, we show the presence of two
  different mechanisms for MHD Poynting flux generation in simulations
  of solar photospheric magnetoconvection. The weaker mechanism is
  connected to vertical transport of weak horizontal magnetic fields in
  the convectively stable layers of the upper photosphere, while the
  stronger is the production of Poynting flux in strongly magnetized
  intergranular lanes experiencing horizontal vortex motions. These
  mechanisms may be responsible for the energy transport from the solar
  convection zone to the higher layers of the solar atmosphere.

---------------------------------------------------------
Title: Solar Flare Observations of the EUV Continua
Authors: Milligan, Ryan O.; Chamberlin, P.; Hudson, H.; Woods, T.;
   Mathioudakis, M.; Fletcher, L.; Kowalski, A.; Keenan, F.
2012AAS...22052105M    Altcode:
  Recent solar flare simulations suggest that the energy deposited in the
  chromosphere by nonthermal electrons during a flare's impulsive phase
  is re-emitted in the form of recombination (free-bound) continua, in
  particular, the Lyman, Balmer, and Paschen continua of hydrogen, and
  the He I and He II continua (Allred et al. 2005). However, definitive
  observations of free-bound emission during solar flares have been scarce
  in recent years as many modern, space-based instruments do not have
  the required sensitivity, wavelength coverage, or duty cycle. With
  the launch of SDO, these observations are now routinely available
  thanks to the EUV Variability Experiment (EVE) instrument. Here we
  present unambiguous, spectrally and temporally resolved detections of
  enhanced free-free and free-bound continua during the first X-class
  solar flare of Solar Cycle 24. While we find that the flare energy
  in the EVE spectral range amounts to at most a few percent of the
  total flare energy, these findings highlight the capability of EVE
  in giving us the first comprehensive look at these diagnostically
  important continuum components.

---------------------------------------------------------
Title: Time-resolved NUV And Optical Spectra Of A Stellar Megaflare
    On YZ CMi With SALT/RSS
Authors: Brown, Benjamin; Kowalski, A. F.; Mathioudakis, M.; Hooper,
   E. J.; Hawley, S. L.; Osten, R. A.; Wisniewski, J. P.
2012AAS...22020452B    Altcode:
  The primary mode of radiative energy release in stellar flares is
  in the optical and near-ultraviolet (NUV) continuum. Active M-dwarf
  stares flare more frequently than the Sun, and their flares can be
  substantially more energetic. The dominant component in solar flare
  white light is thought to be Hydrogen recombination, whereas for stellar
  M dwarf flares, the dominant component is thought to be T 10,000 K
  blackbody emission. Recently we have obtained very high time-cadence
  spectral observations of the flaring M-dwarf YZ CMi (3200-6000A) using
  the Robert Stobie Spectrograph on the 11-meter South African Large
  Telescope (SALT/RSS), achieving 100x better temporal resolution than
  has previously been possible at the atmospheric limit. We observed
  a megaflare of over 100x flux enhancement in the NUV emission. Here
  we discuss the evolution of the stellar flare spectrum during the
  rapid impulsive phase of the flare and the implications for stellar
  flare models.

---------------------------------------------------------
Title: Transverse Oscillations in Chromospheric Mottles
Authors: Kuridze, D.; Morton, R. J.; Erdélyi, R.; Dorrian, G. D.;
   Mathioudakis, M.; Jess, D. B.; Keenan, F. P.
2012ApJ...750...51K    Altcode: 2012arXiv1202.5697K
  A number of recent investigations have revealed that transverse
  waves are ubiquitous in the solar chromosphere. The vast majority
  of these have been reported in limb spicules and active region
  fibrils. We investigate long-lived, quiet-Sun, on-disk features such as
  chromospheric mottles (jet-like features located at the boundaries of
  supergranular cells) and their transverse motions. The observations
  were obtained with the Rapid Oscillations in the Solar Atmosphere
  instrument at the Dunn Solar Telescope. The data set is comprised
  of simultaneous imaging in the Hα core, Ca II K, and G band of an
  on-disk quiet-Sun region. Time-distance techniques are used to study
  the characteristics of the transverse oscillations. We detect over
  40 transverse oscillations in both bright and dark mottles, with
  periods ranging from 70 to 280 s, with the most frequent occurrence
  at ~165 s. The velocity amplitudes and transverse displacements
  exhibit characteristics similar to limb spicules. Neighboring mottles
  oscillating in-phase are also observed. The transverse oscillations
  of individual mottles are interpreted in terms of magnetohydrodynamic
  kink waves. Their estimated periods and damping times are consistent
  with phase mixing and resonant mode conversion.

---------------------------------------------------------
Title: Solar Particle Acceleration Radiation and Kinetics (SPARK). A
    mission to understand the nature of particle acceleration
Authors: Matthews, Sarah A.; Williams, David R.; Klein, Karl-Ludwig;
   Kontar, Eduard P.; Smith, David M.; Lagg, Andreas; Krucker, Sam;
   Hurford, Gordon J.; Vilmer, Nicole; MacKinnon, Alexander L.; Zharkova,
   Valentina V.; Fletcher, Lyndsay; Hannah, Iain G.; Browning, Philippa
   K.; Innes, Davina E.; Trottet, Gerard; Foullon, Clare; Nakariakov,
   Valery M.; Green, Lucie M.; Lamoureux, Herve; Forsyth, Colin; Walton,
   David M.; Mathioudakis, Mihalis; Gandorfer, Achim; Martinez-Pillet,
   Valentin; Limousin, Olivier; Verwichte, Erwin; Dalla, Silvia; Mann,
   Gottfried; Aurass, Henri; Neukirch, Thomas
2012ExA....33..237M    Altcode: 2011ExA...tmp..124M
  Energetic particles are critical components of plasma populations
  found throughout the universe. In many cases particles are accelerated
  to relativistic energies and represent a substantial fraction of
  the total energy of the system, thus requiring extremely efficient
  acceleration processes. The production of accelerated particles
  also appears coupled to magnetic field evolution in astrophysical
  plasmas through the turbulent magnetic fields produced by diffusive
  shock acceleration. Particle acceleration is thus a key component
  in helping to understand the origin and evolution of magnetic
  structures in, e.g. galaxies. The proximity of the Sun and the range
  of high-resolution diagnostics available within the solar atmosphere
  offers unique opportunities to study the processes involved in particle
  acceleration through the use of a combination of remote sensing
  observations of the radiative signatures of accelerated particles, and
  of their plasma and magnetic environment. The SPARK concept targets the
  broad range of energy, spatial and temporal scales over which particle
  acceleration occurs in the solar atmosphere, in order to determine how
  and where energetic particles are accelerated. SPARK combines highly
  complementary imaging and spectroscopic observations of radiation from
  energetic electrons, protons and ions set in their plasma and magnetic
  context. The payload comprises focusing-optics X-ray imaging covering
  the range from 1 to 60 keV; indirect HXR imaging and spectroscopy
  from 5 to 200 keV, γ-ray spectroscopic imaging with high-resolution
  LaBr<SUB>3</SUB> scintillators, and photometry and source localisation
  at far-infrared wavelengths. The plasma environment of the regions
  of acceleration and interaction will be probed using soft X-ray
  imaging of the corona and vector magnetography of the photosphere
  and chromosphere. SPARK is designed for solar research. However,
  in addition it will be able to provide exciting new insights into the
  origin of particle acceleration in other regimes, including terrestrial
  gamma-ray flashes (TGF), the origin of γ-ray bursts, and the possible
  existence of axions.

---------------------------------------------------------
Title: Observations of Enhanced Extreme Ultraviolet Continua during
    an X-Class Solar Flare Using SDO/EVE
Authors: Milligan, Ryan O.; Chamberlin, Phillip C.; Hudson, Hugh S.;
   Woods, Thomas N.; Mathioudakis, Mihalis; Fletcher, Lyndsay; Kowalski,
   Adam F.; Keenan, Francis P.
2012ApJ...748L..14M    Altcode: 2012arXiv1202.1731M
  Observations of extreme ultraviolet (EUV) emission from an X-class solar
  flare that occurred on 2011 February 15 at 01:44 UT are presented,
  obtained using the EUV Variability Experiment (EVE) on board the
  Solar Dynamics Observatory. The complete EVE spectral range covers
  the free-bound continua of H I (Lyman continuum), He I, and He II,
  with recombination edges at 91.2, 50.4, and 22.8 nm, respectively. By
  fitting the wavelength ranges blueward of each recombination edge
  with an exponential function, light curves of each of the integrated
  continua were generated over the course of the flare, as was emission
  from the free-free continuum (6.5-37 nm). The He II 30.4 nm and Lyα
  121.6 nm lines, and soft X-ray (SXR; 0.1-0.8 nm) emission from GOES are
  also included for comparison. Each free-bound continuum was found to
  have a rapid rise phase at the flare onset similar to that seen in the
  25-50 keV light curves from RHESSI, suggesting that they were formed
  by recombination with free electrons in the chromosphere. However,
  the free-free emission exhibited a slower rise phase seen also in the
  SXR emission from GOES, implying a predominantly coronal origin. By
  integrating over the entire flare the total energy emitted via
  each process was determined. We find that the flare energy in the
  EVE spectral range amounts to at most a few percent of the total
  flare energy, but EVE gives us a first comprehensive look at these
  diagnostically important continuum components.

---------------------------------------------------------
Title: Stellar jitter from variable gravitational redshift:
    implications for radial velocity confirmation of habitable exoplanets
Authors: Cegla, H. M.; Watson, C. A.; Marsh, T. R.; Shelyag, S.;
   Moulds, V.; Littlefair, S.; Mathioudakis, M.; Pollacco, D.; Bonfils, X.
2012MNRAS.421L..54C    Altcode: 2011arXiv1112.1553C
  A variation of gravitational redshift, arising from stellar radius
  fluctuations, will introduce astrophysical noise into radial velocity
  measurements by shifting the centroid of the observed spectral
  lines. Shifting the centroid does not necessarily introduce line
  asymmetries. This is fundamentally different from other types
  of stellar jitter so far identified, which do result from line
  asymmetries. Furthermore, only a very small change in stellar radius,
  ∼0.01 per cent, is necessary to generate a gravitational redshift
  variation large enough to mask or mimic an Earth-twin. We explore
  possible mechanisms for stellar radius fluctuations in low-mass
  stars. Convective inhibition due to varying magnetic field strengths and
  the Wilson depression of starspots are both found to induce substantial
  gravitational redshift variations. Finally, we investigate a possible
  method for monitoring/correcting this newly identified potential source
  of jitter and comment on its impact for future exoplanet searches.

---------------------------------------------------------
Title: Propagating Wave Phenomena Detected in Observations and
    Simulations of the Lower Solar Atmosphere
Authors: Jess, D. B.; Shelyag, S.; Mathioudakis, M.; Keys, P. H.;
   Christian, D. J.; Keenan, F. P.
2012ApJ...746..183J    Altcode: 2012arXiv1201.1981J
  We present high-cadence observations and simulations of the solar
  photosphere, obtained using the Rapid Oscillations in the Solar
  Atmosphere imaging system and the MuRAM magnetohydrodynamic (MHD) code,
  respectively. Each data set demonstrates a wealth of magnetoacoustic
  oscillatory behavior, visible as periodic intensity fluctuations
  with periods in the range 110-600 s. Almost no propagating waves with
  periods less than 140 s and 110 s are detected in the observational
  and simulated data sets, respectively. High concentrations of power
  are found in highly magnetized regions, such as magnetic bright points
  and intergranular lanes. Radiative diagnostics of the photospheric
  simulations replicate our observational results, confirming that the
  current breed of MHD simulations are able to accurately represent the
  lower solar atmosphere. All observed oscillations are generated as
  a result of naturally occurring magnetoconvective processes, with no
  specific input driver present. Using contribution functions extracted
  from our numerical simulations, we estimate minimum G-band and 4170 Å
  continuum formation heights of 100 km and 25 km, respectively. Detected
  magnetoacoustic oscillations exhibit a dominant phase delay of -8°
  between the G-band and 4170 Å continuum observations, suggesting
  the presence of upwardly propagating waves. More than 73% of MBPs
  (73% from observations and 96% from simulations) display upwardly
  propagating wave phenomena, suggesting the abundant nature of
  oscillatory behavior detected higher in the solar atmosphere may be
  traced back to magnetoconvective processes occurring in the upper
  layers of the Sun's convection zone.

---------------------------------------------------------
Title: The Origin of Type I Spicule Oscillations
Authors: Jess, D. B.; Pascoe, D. J.; Christian, D. J.; Mathioudakis,
   M.; Keys, P. H.; Keenan, F. P.
2012ApJ...744L...5J    Altcode: 2011arXiv1111.5464J
  We use images of high spatial and temporal resolution, obtained with
  the Rapid Oscillations in the Solar Atmosphere instrument at the Dunn
  Solar Telescope, to reveal how the generation of transverse waves
  in Type I spicules is a direct result of longitudinal oscillations
  occurring in the photosphere. Here we show how pressure oscillations,
  with periodicities in the range of 130-440 s, manifest in small-scale
  photospheric magnetic bright points, and generate kink waves in
  the Sun's outer atmosphere with transverse velocities approaching
  the local sound speed. Through comparison of our observations with
  advanced two-dimensional magnetohydrodynamic simulations, we provide
  evidence for how magnetoacoustic oscillations, generated at the
  solar surface, funnel upward along Type I spicule structures, before
  undergoing longitudinal-to-transverse mode conversion into waves at
  twice the initial driving frequency. The resulting kink modes are
  visible in chromospheric plasma, with periodicities of 65-220 s, and
  amplitudes often exceeding 400 km. A sausage mode oscillation also
  arises as a consequence of the photospheric driver, which is visible
  in both simulated and observational time series. We conclude that the
  mode conversion and period modification is a direct consequence of
  the 90° phase shift encompassing opposite sides of the photospheric
  driver. The chromospheric energy flux of these waves are estimated to
  be ≈3 × 10<SUP>5</SUP> W m<SUP>-2</SUP>, which indicates that they
  are sufficiently energetic to accelerate the solar wind and heat the
  localized corona to its multi-million degree temperatures.

---------------------------------------------------------
Title: Towards Earth-like Worlds: Identifying and Removing Stellar
    Jitter
Authors: Cegla, Heather M.; Watson, C.; Marsh, T.; Shelyag, S.;
   Moulds, V.; Littlefair, S.; Mathioudakis, M.; Pollacco, D.; Bonfils, X.
2012AAS...21943203C    Altcode:
  Space-based, photometric surveys have moved us into a new era
  of exoplanet discovery. In order to confirm the masses and hence
  the planetary nature of exoplanet candidates from such surveys,
  radial velocity (RV) follow up is mandatory. To do this for low-mass
  planets typically requires cm/s RV precision. However, astrophysical
  noise sources (or stellar jitter) due to spots, plages, granulation
  and stellar oscillations, for example, become an issue at the m/s
  level. These phenomena alter the shape of the stellar absorption lines,
  injecting spurious or systematic RV signals that may mask or mimic
  planetary signals. As such, `quiet’ stars (those with little activity)
  are the most likely candidates for the detection of low-mass planets,
  but even these stars will still exhibit some stellar jitter. We present
  our techniques to explore the stellar jitter due to granulation through
  the use of sophisticated 3D magnetohydrodynamical simulations of the
  Sun. In addition, we also present the identification of an entirely new
  source of stellar jitter that has been hitherto unrecognized and that
  could impact the RV follow-up and confirmation of low-mass terrestrial
  planets and Earth-like worlds.

---------------------------------------------------------
Title: White Light Flare Continuum Observations with ULTRACAM
Authors: Kowalski, A. F.; Mathioudakis, M.; Hawley, S. L.; Hilton,
   E. J.; Dhillon, V. S.; Marsh, T. R.; Copperwheat, C. M.
2011ASPC..448.1157K    Altcode: 2011arXiv1103.0822K; 2011csss...16.1157K
  We present sub-second, continuous-coverage photometry of three flares
  on the dM3.5e star, EQ Peg A, using custom continuum filters with
  WHT/ULTRACAM. These data provide a new view of flare continuum emission,
  with each flare exhibiting a very distinct light curve morphology. The
  spectral shape of flare emission for the two large-amplitude flares
  is compared with synthetic ULTRACAM measurements taken from the
  spectra during the large 'megaflare' event on a similar type flare
  star. The white light shape during the impulsive phase of the EQ
  Peg flares is consistent with the range of colors derived from the
  megaflare continuum, which is known to contain a Hydrogen recombination
  component and compact, blackbody-like components. Tentative evidence
  in the ULTRACAM photometry is found for an anti-correlation between
  the emission of these components.

---------------------------------------------------------
Title: Rapid Fluctuations in the Lower Solar Atmosphere
Authors: Lawrence, J. K.; Cadavid, A. C.; Christian, D. J.; Jess,
   D. B.; Mathioudakis, M.
2011ApJ...743L..24L    Altcode: 2011arXiv1111.4253L
  The Rapid Oscillations in the Solar Atmosphere instrument reveals solar
  atmospheric fluctuations at high frequencies. Spectra of variations
  of the G-band intensity (I<SUB>G</SUB> ) and Ca II K-line intensity
  (I<SUB>K</SUB> ) show correlated fluctuations above white noise to
  frequencies beyond 300 mHz and 50 mHz, respectively. The noise-corrected
  G-band spectrum for f = 28-326 mHz shows a power law with exponent -1.21
  ± 0.02, consistent with the presence of turbulent motions. G-band
  spectral power in the 25-100 mHz ("UHF") range is concentrated at
  the locations of magnetic bright points in the intergranular lanes
  and is highly intermittent in time. The intermittence of the UHF
  G-band fluctuations, shown by a positive kurtosis κ, also suggests
  turbulence. Combining values of I<SUB>G</SUB> , I<SUB>K</SUB> , UHF
  power, and κ reveals two distinct states of the solar atmosphere. State
  1, including almost all the data, is characterized by low I<SUB>G</SUB>
  , I<SUB>K</SUB> , and UHF power and κ ≈ 6. State 2, including only a
  very small fraction of the data, is characterized by high I<SUB>G</SUB>
  , I<SUB>K</SUB> , and UHF power and κ ≈ 3. Superposed epoch analysis
  shows that the UHF power peaks simultaneously with spatio-temporal
  I<SUB>G</SUB> maxima in either state. For State 1, I<SUB>K</SUB>
  shows 3.5 minute chromospheric oscillations with maxima occurring 21
  s after I<SUB>G</SUB> maxima implying a 150-210 km effective height
  difference. However, for State 2 the I<SUB>K</SUB> and I<SUB>G</SUB>
  maxima are simultaneous; in this highly magnetized environment sites
  of G-band and K-line emission may be spatially close together.

---------------------------------------------------------
Title: The Velocity Distribution of Solar Photospheric Magnetic
    Bright Points
Authors: Keys, P. H.; Mathioudakis, M.; Jess, D. B.; Shelyag, S.;
   Crockett, P. J.; Christian, D. J.; Keenan, F. P.
2011ApJ...740L..40K    Altcode: 2011arXiv1109.3565K
  We use high spatial resolution observations and numerical simulations to
  study the velocity distribution of solar photospheric magnetic bright
  points. The observations were obtained with the Rapid Oscillations in
  the Solar Atmosphere instrument at the Dunn Solar Telescope, while the
  numerical simulations were undertaken with the MURaM code for average
  magnetic fields of 200 G and 400 G. We implemented an automated bright
  point detection and tracking algorithm on the data set and studied
  the subsequent velocity characteristics of over 6000 structures,
  finding an average velocity of approximately 1 km s<SUP>-1</SUP>, with
  maximum values of 7 km s<SUP>-1</SUP>. Furthermore, merging magnetic
  bright points were found to have considerably higher velocities,
  and significantly longer lifetimes, than isolated structures. By
  implementing a new and novel technique, we were able to estimate the
  background magnetic flux of our observational data, which is consistent
  with a field strength of 400 G.

---------------------------------------------------------
Title: A search for line intensity enhancements in the far-UV spectra
    of active late-type stars arising from opacity
Authors: Keenan, F. P.; Christian, D. J.; Rose, S. J.; Mathioudakis, M.
2011A&A...534A..71K    Altcode: 2011arXiv1109.0513K
  Context. Radiative transfer calculations have predicted intensity
  enhancements for optically thick emission lines, as opposed to the
  normal intensity reductions, for astrophysical plasmas under certain
  conditions. In particular, the results are predicted to be dependent
  both on the geometry of the emitting plasma and the orientation of the
  observer. Hence in principle the detection of intensity enhancement
  may provide a way of determining the geometry of an unresolved
  astronomical source. <BR /> Aims: To investigate such enhancements
  we have analysed a sample of active late-type stars observed in the
  far ultraviolet spectral region. <BR /> Methods: Emission lines of O
  vi in the FUSE satellite spectra of ɛ Eri, II Peg and Prox Cen were
  searched for intensity enhancements due to opacity. <BR /> Results:
  We have found strong evidence for line intensity enhancements due to
  opacity during active or flare-like activity for all three stars. The
  O vi 1032/1038 line intensity ratios, predicted to have a value of
  2.0 in the optically thin case, are found to be up to ~30% larger
  during several orbital phases. <BR /> Conclusions: Our measurements,
  combined with radiative transfer models, allow us to constrain both
  the geometry of the O vi emitting regions in our stellar sources and
  the orientation of the observer. A spherical emitting plasma can be
  ruled out, as this would lead to no intensity enhancement. In addition,
  the theory tells us that the line-of-sight to the plasma must be close
  to perpendicular to its surface, as observations at small angles to
  the surface lead to either no intensity enhancement or the usual line
  intensity decrease over the optically thin value. For the future, we
  outline a laboratory experiment, that could be undertaken with current
  facilities, which would provide an unequivocal test of predictions of
  line intensity enhancement due to opacity, in particular the dependence
  on plasma geometry.

---------------------------------------------------------
Title: The Search for Super-saturation in Chromospheric Emission
Authors: Christian, Damian J.; Mathioudakis, Mihalis; Arias, Tersi;
   Jardine, Moira; Jess, David B.
2011ApJ...738..164C    Altcode: 2011arXiv1107.1786C
  We investigate if the super-saturation phenomenon observed at X-ray
  wavelengths for the corona exists in the chromosphere for rapidly
  rotating late-type stars. Moderate resolution optical spectra
  of fast-rotating EUV- and X-ray-selected late-type stars were
  obtained. Stars in α Per were observed in the northern hemisphere
  with the Isaac Newton 2.5 m telescope and Intermediate Dispersion
  Spectrograph. Selected objects from IC 2391 and IC 2602 were observed
  in the southern hemisphere with the Blanco 4 m telescope and R-C
  spectrograph at CTIO. Ca II H and K fluxes were measured for all
  stars in our sample. We find the saturation level for Ca II K at log
  (L <SUB>CaK</SUB>/L <SUB>bol</SUB>) = -4.08. The Ca II K flux does
  not show a decrease as a function of increased rotational velocity
  or smaller Rossby number as observed in the X-ray. This lack of
  "super-saturation" supports the idea of coronal stripping as the cause
  of saturation and super-saturation in stellar chromospheres and coronae,
  but the detailed underlying mechanism is still under investigation.

---------------------------------------------------------
Title: Small-scale Hα jets in the solar chromosphere
Authors: Kuridze, D.; Mathioudakis, M.; Jess, D. B.; Shelyag, S.;
   Christian, D. J.; Keenan, F. P.; Balasubramaniam, K. S.
2011A&A...533A..76K    Altcode: 2011arXiv1108.1043K
  <BR /> Aims: High temporal and spatial resolution observations from
  the Rapid Oscillations in the Solar Atmosphere (ROSA) multiwavelength
  imager on the Dunn Solar Telescope are used to study the velocities
  of small-scale Hα jets in an emerging solar active region. <BR
  /> Methods: The dataset comprises simultaneous imaging in the Hα
  core, Ca ii K, and G band, together with photospheric line-of-sight
  magnetograms. Time-distance techniques are employed to determine
  projected plane-of-sky velocities. <BR /> Results: The Hα images
  are highly dynamic in nature, with estimated jet velocities as high
  as 45 km s<SUP>-1</SUP>. These jets are one-directional, with their
  origin seemingly linked to underlying Ca ii K brightenings and G-band
  magnetic bright points. <BR /> Conclusions: It is suggested that the
  siphon flow model of cool coronal loops is suitable for interpreting our
  observations. The jets are associated with small-scale explosive events,
  and may provide a mass outflow from the photosphere to the corona.

---------------------------------------------------------
Title: Rapid Oscillations in the Solar Atmosphere: Spectra and
    Physical Effects
Authors: Lawrence, John K.; Christian, D. J.; Cadavid, A. C.; Jess,
   D. B.; Mathioudakis, M.
2011SPD....42.1727L    Altcode: 2011BAAS..43S.1727L
  High-frequency fluctuations are observed with the Rapid Oscillations in
  the Solar Atmosphere (ROSA) instrument (Jess et al. 2010, Solar Phys,
  261, 363) at the Dunn Solar Telescope. This can produce simultaneous
  observations in up to six channels, at different heights in the
  photosphere and chromosphere, at an unprecedentedly high cadence of 0.5
  seconds, and at a spatial resolution of 100 km after photometrically
  correct speckle reconstruction. <P />Here we concentrate on observations
  at two levels. The first is in the G-band of the CH radical at 4305.5Å,
  bandpass 9.2Å, with height of formation z &lt; 250 km at a cadence
  of 0.525 sec corresponding to Nyquist frequency 950 mHz. The second
  is in the Ca II K-line core at 3933.7Å, bandpass 1.0Å, with height
  of formation z &lt; 1300 km, and cadence 4.2 sec giving Nyquist
  frequency 120 mHz. The data span 53 min, and the maximum field of
  view is 45 Mm. The data were taken on 28 May 2009 in internetwork
  and network near disk center. <P />Using both Fourier and Morlet
  wavelet methods we find evidence in the G-band spectra for intensity
  fluctuations above noise out to frequencies f &gt;&gt; 100 mHz. The
  K-line signal is noisier and is seen only for f &lt; 50 mHz. With
  wavelet techniques we find that G-band spectral power with 20 &lt;
  f &lt; 100 mHz is clearly concentrated in the intergranular lanes and
  especially at the locations of magnetic elements indicated by G-band
  bright points. This wavelet power is highly intermittent in time. By
  cross-correlating the data we find that pulses of high-frequency G-band
  power in the photosphere tend to be followed by increases in K-line
  emission in the chromosphere with a time lag of about 2 min.

---------------------------------------------------------
Title: Chromospheric velocities of a C-class flare
Authors: Keys, P. H.; Jess, D. B.; Mathioudakis, M.; Keenan, F. P.
2011A&A...529A.127K    Altcode: 2011arXiv1103.4252K
  <BR /> Aims: We use high spatial and temporal resolution observations
  from the Swedish Solar Telescope to study the chromospheric velocities
  of a C-class flare originating from active region NOAA 10969. <BR />
  Methods: A time-distance analysis is employed to estimate directional
  velocity components in Hα and Ca ii K image sequences. Also, imaging
  spectroscopy has allowed us to determine flare-induced line-of-sight
  velocities. A wavelet analysis is used to analyse the periodic nature
  of associated flare bursts. <BR /> Results: Time-distance analysis
  reveals velocities as high as 64 km s<SUP>-1</SUP> along the flare
  ribbon and 15 km s<SUP>-1</SUP> perpendicular to it. The velocities are
  very similar in both the Hα and Ca ii K time series. Line-of-sight Hα
  velocities are red-shifted with values up to 17 km s<SUP>-1</SUP>. The
  high spatial and temporal resolution of the observations have allowed
  us to detect velocities significantly higher than those found in
  earlier studies. Flare bursts with a periodicity of ≈60 s are also
  detected. These bursts are similar to the quasi-periodic oscillations
  observed at hard X-ray and radio wavelength data. <BR /> Conclusions:
  Some of the highest velocities detected in the solar atmosphere are
  presented. Line-of-sight velocity maps show considerable mixing of
  both the magnitude and direction of velocities along the flare path. A
  change in direction of the velocities at the flare kernel has also been
  detected which may be a signature of chromospheric evaporation. <P
  />Movies associated to Fig. 5 are only available in electronic form
  at <A href="http://www.aanda.org">http://www.aanda.org</A>

---------------------------------------------------------
Title: Observations of Sausage Modes in Magnetic Pores
Authors: Morton, R. J.; Erdélyi, R.; Jess, D. B.; Mathioudakis, M.
2011ApJ...729L..18M    Altcode: 2010arXiv1011.2375M
  We present here evidence for the observation of the magnetohydrodynamic
  (MHD) sausage modes in magnetic pores in the solar photosphere. Further
  evidence for the omnipresent nature of acoustic global modes is also
  found. The empirical decomposition method of wave analysis is used to
  identify the oscillations detected through a 4170 Å "blue continuum"
  filter observed with the Rapid Oscillations in the Solar Atmosphere
  (ROSA) instrument. Out of phase, periodic behavior in pore size and
  intensity is used as an indicator of the presence of magnetoacoustic
  sausage oscillations. Multiple signatures of the magnetoacoustic
  sausage mode are found in a number of pores. The periods range from
  as short as 30 s up to 450 s. A number of the magnetoacoustic sausage
  mode oscillations found have periods of 3 and 5 minutes, similar to
  the acoustic global modes of the solar interior. It is proposed that
  these global oscillations could be the driver of the sausage-type
  magnetoacoustic MHD wave modes in pores.

---------------------------------------------------------
Title: Vorticity in the solar photosphere
Authors: Shelyag, S.; Keys, P.; Mathioudakis, M.; Keenan, F. P.
2011A&A...526A...5S    Altcode: 2010arXiv1010.5604S
  <BR /> Aims: We use magnetic and non-magnetic 3D numerical simulations
  of solar granulation and G-band radiative diagnostics from the resulting
  models to analyse the generation of small-scale vortex motions in
  the solar photosphere. <BR /> Methods: Radiative MHD simulations of
  magnetoconvection are used to produce photospheric models. Our starting
  point is a non-magnetic model of solar convection, where we introduce
  a uniform magnetic field and follow the evolution of the field in the
  simulated photosphere. We find two different types of photospheric
  vortices, and provide a link between the vorticity generation and the
  presence of the intergranular magnetic field. A detailed analysis of
  the vorticity equation, combined with the G-band radiative diagnostics,
  allows us to identify the sources and observational signatures of
  photospheric vorticity in the simulated photosphere. <BR /> Results: Two
  different types of photospheric vorticity, magnetic and non-magnetic,
  are generated in the domain. Non-magnetic vortices are generated by the
  baroclinic motions of the plasma in the photosphere, while magnetic
  vortices are produced by the magnetic tension in the intergranular
  magnetic flux concentrations. The two types of vortices have different
  shapes. We find that the vorticity is generated more efficiently in
  the magnetised model. Simulated G-band images show a direct connection
  between magnetic vortices and rotary motions of photospheric bright
  points, and suggest that there may be a connection between the magnetic
  bright point rotation and small-scale swirl motions observed higher
  in the atmosphere.

---------------------------------------------------------
Title: The Area Distribution of Solar Magnetic Bright Points
Authors: Crockett, P. J.; Mathioudakis, M.; Jess, D. B.; Shelyag,
   S.; Keenan, F. P.; Christian, D. J.
2010ApJ...722L.188C    Altcode: 2010arXiv1009.2410C
  Magnetic bright points (MBPs) are among the smallest observable objects
  on the solar photosphere. A combination of G-band observations and
  numerical simulations is used to determine their area distribution. An
  automatic detection algorithm, employing one-dimensional intensity
  profiling, is utilized to identify these structures in the observed and
  simulated data sets. Both distributions peak at an area of ≈45,000
  km<SUP>2</SUP>, with a sharp decrease toward smaller areas. The
  distributions conform with log-normal statistics, which suggests
  that flux fragmentation dominates over flux convergence. Radiative
  magneto-convection simulations indicate an independence in the MBP
  area distribution for differing magnetic flux densities. The most
  commonly occurring bright point size corresponds to the typical width
  of inter-granular lanes.

---------------------------------------------------------
Title: A Study of Magnetic Bright Points in the Na I D<SUB>1</SUB>
    Line
Authors: Jess, D. B.; Mathioudakis, M.; Christian, D. J.; Crockett,
   P. J.; Keenan, F. P.
2010ApJ...719L.134J    Altcode: 2010arXiv1007.2515J
  High-cadence, multiwavelength, optical observations of solar magnetic
  bright points (MBPs), captured at the disk center using the ROSA and
  IBIS imaging systems on the Dunn Solar Telescope, are presented. MBPs
  manifesting in the Na I D<SUB>1</SUB> core are found to preferentially
  exist in regions containing strong downflows, in addition to cospatial
  underlying photospheric magnetic field concentrations. Downdrafts
  within Na I D<SUB>1</SUB> bright points exhibit speeds of up
  to 7 km s<SUP>-1</SUP>, with preferred structural symmetry in
  intensity, magnetic field, and velocity profiles about the bright
  point center. Excess intensities associated with G-band and Ca II K
  observations of MBPs reveal a power-law trend when plotted as a function
  of the magnetic flux density. However, Na I D<SUB>1</SUB> observations
  of the same magnetic features indicate an intensity plateau at weak
  magnetic field strengths below ≈150 G, suggesting the presence of a
  two-component heating process: one which is primarily acoustic and the
  other predominantly magnetic. We suggest that this finding is related to
  the physical expansion of magnetic flux tubes, with weak field strengths
  (≈50 G) expanding by ~76%, compared to a ~44% expansion when higher
  field strengths (≈150 G) are present. These observations provide the
  first experimental evidence of rapid downdrafts in Na I D<SUB>1</SUB>
  MBPs and reveal the nature of a previously unresolved intensity plateau
  associated with these structures.

---------------------------------------------------------
Title: A photospheric bright point model
Authors: Shelyag, S.; Mathioudakis, M.; Keenan, F. P.; Jess, D. B.
2010A&A...515A.107S    Altcode: 2010arXiv1003.1653S
  <BR /> Aims: A magneto-hydrostatic model is constructed with
  spectropolarimetric properties close to those of solar photospheric
  magnetic bright points. <BR /> Methods: Results of solar radiative
  magneto-convection simulations are used to produce the spatial
  structure of the vertical component of the magnetic field. The
  horizontal component of magnetic field is reconstructed using the
  self-similarity condition, while the magneto-hydrostatic equilibrium
  condition is applied to the standard photospheric model with the
  magnetic field embedded. Partial ionisation processes are found to be
  necessary for reconstructing the correct temperature structure of the
  model. <BR /> Results: The structures obtained are in good agreement
  with observational data. By combining the realistic structure of
  the magnetic field with the temperature structure of the quiet solar
  photosphere, the continuum formation level above the equipartition
  layer can be found. Preliminary results are shown of wave propagation
  through this magnetic structure. The observational consequences of the
  oscillations are examined in continuum intensity and in the Fe I 6302
  Å magnetically sensitive line.

---------------------------------------------------------
Title: Emission lines of FeXI in the 257-407Å wavelength region
    observed in solar spectra from EIS/Hinode and SERTS
Authors: Keenan, F. P.; Milligan, R. O.; Jess, D. B.; Aggarwal, K. M.;
   Mathioudakis, M.; Thomas, R. J.; Brosius, J. W.; Davila, J. M.
2010MNRAS.404.1617K    Altcode: 2010MNRAS.tmp..299K; 2010arXiv1001.3627K
  Theoretical emission-line ratios involving FeXI transitions in the
  257-407Å wavelength range are derived using fully relativistic
  calculations of radiative rates and electron impact excitation
  cross-sections. These are subsequently compared with both long
  wavelength channel Extreme-Ultraviolet Imaging Spectrometer (EIS)
  spectra from the Hinode satellite (covering 245-291Å) and first-order
  observations (~235-449Å) obtained by the Solar Extreme-ultraviolet
  Research Telescope and Spectrograph (SERTS). The 266.39, 266.60 and
  276.36Å lines of FeXI are detected in two EIS spectra, confirming
  earlier identifications of these features, and 276.36Å is found to
  provide an electron density (N<SUB>e</SUB>) diagnostic when ratioed
  against the 257.55Å transition. Agreement between theory and
  observation is found to be generally good for the SERTS data sets,
  with discrepancies normally being due to known line blends, while the
  257.55Å feature is detected for the first time in SERTS spectra. The
  most useful FeXI electron density diagnostic is found to be the
  308.54/352.67 intensity ratio, which varies by a factor of 8.4 between
  N<SUB>e</SUB> = 10<SUP>8</SUP> and 10<SUP>11</SUP>cm<SUP>-3</SUP>,
  while showing little temperature sensitivity. However, the
  349.04/352.67 ratio potentially provides a superior diagnostic,
  as it involves lines which are closer in wavelength, and varies
  by a factor of 14.7 between N<SUB>e</SUB> = 10<SUP>8</SUP> and
  10<SUP>11</SUP>cm<SUP>-3</SUP>. Unfortunately, the 349.04Å line is
  relatively weak, and also blended with the second-order FeX 174.52Å
  feature, unless the first-order instrument response is enhanced.

---------------------------------------------------------
Title: Microflare Activity Driven by Forced Magnetic Reconnection
Authors: Jess, D. B.; Mathioudakis, M.; Browning, P. K.; Crockett,
   P. J.; Keenan, F. P.
2010ApJ...712L.111J    Altcode: 2010arXiv1002.3792J
  High cadence, multiwavelength, optical observations of a solar active
  region, obtained with the Swedish Solar Telescope, are presented. Two
  magnetic bright points are seen to separate in opposite directions
  at a constant velocity of 2.8 km s<SUP>-1</SUP>. After a separation
  distance of ≈4400 km is reached, multiple Ellerman bombs are
  observed in both Hα and Ca-K images. As a result of the Ellerman
  bombs, periodic velocity perturbations in the vicinity of the magnetic
  neutral line, derived from simultaneous Michelson Doppler Imager data,
  are generated with amplitude ±6 km s<SUP>-1</SUP> and wavelength
  ≈1000 km. The velocity oscillations are followed by an impulsive
  brightening visible in Hα and Ca-K, with a peak intensity enhancement
  of 63%. We interpret these velocity perturbations as the magnetic field
  deformation necessary to trigger forced reconnection. A time delay of
  ≈3 minutes between the Hα-wing and Ca-K observations indicates that
  the observed magnetic reconnection occurs at a height of ~200 km above
  the solar surface. These observations are consistent with theoretical
  predictions and provide the first observational evidence of microflare
  activity driven by forced magnetic reconnection.

---------------------------------------------------------
Title: ROSA: A High-cadence, Synchronized Multi-camera Solar Imaging
    System
Authors: Jess, D. B.; Mathioudakis, M.; Christian, D. J.; Keenan,
   F. P.; Ryans, R. S. I.; Crockett, P. J.
2010SoPh..261..363J    Altcode: 2009arXiv0912.4118J; 2010SoPh..tmp...12J
  The Rapid Oscillations in the Solar Atmosphere (ROSA) instrument
  is a synchronized, six-camera high-cadence solar imaging instrument
  developed by Queen's University Belfast. The system is available on
  the Dunn Solar Telescope at the National Solar Observatory in Sunspot,
  New Mexico, USA, as a common-user instrument. Consisting of six 1k
  × 1k Peltier-cooled frame-transfer CCD cameras with very low noise
  (0.02 - 15 e s<SUP>−1</SUP> pixel<SUP>−1</SUP>), each ROSA camera
  is capable of full-chip readout speeds in excess of 30 Hz, or 200 Hz
  when the CCD is windowed. Combining multiple cameras and fast readout
  rates, ROSA will accumulate approximately 12 TB of data per 8 hours
  observing. Following successful commissioning during August 2008,
  ROSA will allow for multi-wavelength studies of the solar atmosphere
  at a high temporal resolution.

---------------------------------------------------------
Title: Automated detection and tracking of solar magnetic bright
    points
Authors: Crockett, P. J.; Jess, D. B.; Mathioudakis, M.; Keenan, F. P.
2009MNRAS.397.1852C    Altcode: 2009MNRAS.tmp..999C; 2009arXiv0905.3138C
  Magnetic bright points (MBPs) in the internetwork are among the
  smallest objects in the solar photosphere and appear bright against the
  ambient environment. An algorithm is presented that can be used for the
  automated detection of the MBPs in the spatial and temporal domains. The
  algorithm works by mapping the lanes through intensity thresholding. A
  compass search, combined with a study of the intensity gradient across
  the detected objects, allows the disentanglement of MBPs from bright
  pixels within the granules. Object growing is implemented to account
  for any pixels that might have been removed when mapping the lanes. The
  images are stabilized by locating long-lived objects that may have
  been missed due to variable light levels and seeing quality. Tests of
  the algorithm, employing data taken with the Swedish Solar Telescope,
  reveal that ~90 per cent of MBPs within a 75 × 75 arcsec<SUP>2</SUP>
  field of view are detected.

---------------------------------------------------------
Title: Possible Connection Between Umbral and Bright Point
    Oscillations
Authors: Andic, Aleksandra; Jess, D. B.; Mathioudakis, M.; Keenan,
   F. P.; Bloomfield, D. S.
2009SPD....40.0909A    Altcode:
  Active region NOAA 10794 was observed using the Rapid Dual Imager
  (RDI) instrument on the Dunn Solar Telescope at the National Solar
  Observatory, Sacramento Peak. G-band and H-alpha filters were employed
  for the observations, and the resulting data were subjected to both
  speckle reconstruction and wavelet analyses. <P />Intensity oscillations
  in the period range 8--584 s were detected. Those with frequencies
  near the Nyquist value of 125 mHz had a similar behavior to other
  oscillations detected in the period range of 8 - 60 s. <P />However,
  oscillations in the range around 180s observed above bright points
  show a temporal coincidence in the light curve shape and the number
  of the emitted frequencies in an umbral flash, indicating a possible
  connection.

---------------------------------------------------------
Title: Alfvén Waves in the Lower Solar Atmosphere
Authors: Jess, David B.; Mathioudakis, Mihalis; Erdélyi, Robert;
   Crockett, Philip J.; Keenan, Francis P.; Christian, Damian J.
2009Sci...323.1582J    Altcode: 2009arXiv0903.3546J
  The flow of energy through the solar atmosphere and the heating of the
  Sun’s outer regions are still not understood. Here, we report the
  detection of oscillatory phenomena associated with a large bright-point
  group that is 430,000 square kilometers in area and located near the
  solar disk center. Wavelet analysis reveals full-width half-maximum
  oscillations with periodicities ranging from 126 to 700 seconds
  originating above the bright point and significance levels exceeding
  99%. These oscillations, 2.6 kilometers per second in amplitude,
  are coupled with chromospheric line-of-sight Doppler velocities
  with an average blue shift of 23 kilometers per second. A lack of
  cospatial intensity oscillations and transversal displacements rules
  out the presence of magneto-acoustic wave modes. The oscillations
  are a signature of Alfvén waves produced by a torsional twist of
  ±22 degrees. A phase shift of 180 degrees across the diameter of the
  bright point suggests that these torsional Alfvén oscillations are
  induced globally throughout the entire brightening. The energy flux
  associated with this wave mode is sufficient to heat the solar corona.

---------------------------------------------------------
Title: Ultraviolet and extreme-ultraviolet line ratio diagnostics
    for O IV
Authors: Keenan, F. P.; Crockett, P. J.; Aggarwal, K. M.; Jess, D. B.;
   Mathioudakis, M.
2009A&A...495..359K    Altcode: 2009arXiv0901.2222K
  Aims: We generate theoretical ultraviolet and extreme-ultraviolet
  emission line ratios for O IV and show their strong versatility
  as electron temperature and density diagnostics for astrophysical
  plasmas. <BR />Methods: Recent fully relativistic calculations of
  radiative rates and electron impact excitation cross sections for O
  IV, supplemented with earlier data for A-values and proton excitation
  rates, are used to derive theoretical O IV line intensity ratios for
  a wide range of electron temperatures and densities. <BR />Results:
  Diagnostic line ratios involving ultraviolet or extreme-ultraviolet
  transitions in O IV are presented, that are applicable to a wide variety
  of astrophysical plasmas ranging from low density gaseous nebulae to the
  densest solar and stellar flares. Comparisons with observational data,
  where available, show good agreement between theory and experiment,
  providing support for the accuracy of the diagnostics. However,
  diagnostics are also presented involving lines that are blended in
  existing astronomical spectra, in the hope this might encourage further
  observational studies at higher spectral resolution.

---------------------------------------------------------
Title: Do All Flares Have White-Light Emission?
Authors: Jess, D. B.; Mathioudakis, M.; Crockett, P. J.; Keenan, F. P.
2008ApJ...688L.119J    Altcode: 2008arXiv0810.1443J
  High-cadence, multiwavelength optical observations of a solar active
  region (NOAA AR 10969), obtained with the Swedish Solar Telescope,
  are presented. Difference imaging of white light continuum data
  reveals a white-light brightening, 2 minutes in duration, linked to a
  cotemporal and cospatial C2.0 flare event. The flare kernel observed
  in the white-light images has a diameter of 300 km, thus rendering it
  below the resolution limit of most space-based telescopes. Continuum
  emission is present only during the impulsive stage of the flare,
  with the effects of chromospheric emission subsequently delayed
  by ≈2 minutes. The localized flare emission peaks at 300% above
  the quiescent flux. This large, yet tightly confined, increase in
  emission is only resolvable due to the high spatial resolution of
  the Swedish Solar Telescope. An investigation of the line-of-sight
  magnetic field derived from simultaneous MDI data shows that the
  continuum brightening is located very close to a magnetic polarity
  inversion line. In addition, an Hα flare ribbon is directed along
  a region of rapid magnetic energy change, with the footpoints of the
  ribbon remaining cospatial with the observed white-light brightening
  throughout the duration of the flare. The observed flare parameters
  are compared with current observations and theoretical models for M-
  and X-class events and we determine the observed white-light emission
  is caused by radiative back-warming. We suggest that the creation of
  white-light emission is a common feature of all solar flares.

---------------------------------------------------------
Title: <SUP>6</SUP>Li in the Atmosphere of GJ 117 Revisited
Authors: Christian, D. J.; Mathioudakis, M.; Jevremović, D.
2008ApJ...686..542C    Altcode: 2008arXiv0807.3693C
  Detection of <SUP>6</SUP>Li has been shown for energetic solar events,
  one chromospherically active binary, and several dwarf halo stars. We
  had previously found a <SUP>6</SUP>Li/<SUP>7</SUP>Li = 0.03 +/- 0.01
  for active K dwarf GJ 117 using VLT UVES observations. Here we present
  high signal-to-noise (&gt;1000) high spectral resolution observations
  taken with the McDonald Observatory's 2.7 m and echelle spectrometer
  of GJ 117. We have used the solar spectrum and template stars to
  eliminate possible blends, such as Ti I, in the <SUP>6</SUP>Li spectral
  region. Our new analysis, using an updated PHOENIX model atmosphere,
  finds <SUP>6</SUP>Li/<SUP>7</SUP>Li = 0.05 +/- 0.02. In addition,
  bisector analysis showed no significant red asymmetries that would
  affect the lithium line profile. No changes above the statistical
  uncertainties are found between the VLT and McDonald data. The amount
  of <SUP>6</SUP>Li derived for GJ 117 is consistent with creation
  in spallation reactions on the stellar surface, but we caution that
  uncertainties in the continuum level may cause additional uncertainty
  in the <SUP>6</SUP>Li fraction.

---------------------------------------------------------
Title: Transition Region Velocity Oscillations Observed by EUNIS-06
Authors: Jess, D. B.; Rabin, D. M.; Thomas, R. J.; Brosius, J. W.;
   Mathioudakis, M.; Keenan, F. P.
2008ApJ...682.1363J    Altcode: 2008arXiv0804.1629J
  Spectroscopic measurements of NOAA AR 10871, obtained with the Extreme
  Ultraviolet Normal Incidence Spectrograph (EUNIS) sounding rocket
  instrument on 2006 April 12, reveal velocity oscillations in the He
  II 303.8 Å emission line formed at T ≈ 5 × 10<SUP>4</SUP> K. The
  oscillations appear to arise in a bright active region loop arcade
  about 25<SUP>”</SUP> wide which crosses the EUNIS slit. The period
  of these transition region oscillations is 26 +/- 4 s, coupled with
  a velocity amplitude of ±10 km s<SUP>-1</SUP>, detected over four
  complete cycles. Similar oscillations are observed in lines formed at
  temperatures up to T ≈ 4 × 10<SUP>5</SUP> K, but we find no evidence
  for the coupling of these velocity oscillations with corresponding
  phenomena in the corona. We interpret the detected oscillations as
  originating from an almost purely adiabatic plasma, and infer that
  they are generated by the resonant transmission of MHD waves through
  the lower active region atmospheres. Through the use of seismological
  techniques, we establish that the observed velocity oscillations display
  wave properties most characteristic of fast body global sausage modes.

---------------------------------------------------------
Title: The 2008 RAS National Astronomy Meeting
Authors: Fitzsimmons, Alan; Mathioudakis, Mihalis
2008A&G....49c..11F    Altcode:
  This year's RAS National Astronomy Meeting was held at Queen's
  University Belfast from 31 March to 4 April. Also joining NAM 2008 were
  the meetings of the UK Solar Physics (UKSP) and the Magnetospheric,
  Ionospheric and Solar-Terrestrial (MIST) special interest groups. The
  event was organized by QUB scientists within the Astrophysics Research
  Centre and the Centre for Theoretical Atomic, Molecular and Optical
  Physics. Alan Fitzsimmons, Mihalis Mathioudakis and Andrew Kavanagh
  report.

---------------------------------------------------------
Title: Discovery of Spatial Periodicities in a Coronal Loop Using
    Automated Edge-Tracking Algorithms
Authors: Jess, D. B.; Mathioudakis, M.; Erdélyi, R.; Verth, G.;
   McAteer, R. T. J.; Keenan, F. P.
2008ApJ...680.1523J    Altcode: 2008arXiv0802.1971J
  A new method for automated coronal loop tracking, in both spatial
  and temporal domains, is presented. Applying this technique to TRACE
  data, obtained using the 171 Å filter on 1998 July 14, we detect a
  coronal loop undergoing a 270 s kink-mode oscillation, as previously
  found by Aschwanden et al. However, we also detect flare-induced,
  and previously unnoticed, spatial periodicities on a scale of 3500 km,
  which occur along the coronal loop edge. Furthermore, we establish a
  reduction in oscillatory power for these spatial periodicities of 45%
  over a 222 s interval. We relate the reduction in detected oscillatory
  power to the physical damping of these loop-top oscillations.

---------------------------------------------------------
Title: Line intensity enhancements in stellar coronal X-ray spectra
    due to opacity effects
Authors: Rose, S. J.; Matranga, M.; Mathioudakis, M.; Keenan, F. P.;
   Wark, J. S.
2008A&A...483..887R    Altcode: 2008arXiv0803.3184R
  Context: The I(15.01 Å)/I(16.78 Å) emission line intensity ratio
  in Fe xvii has been reported to deviate from its theoretical value
  in solar and stellar X-ray spectra. This is attributed to opacity in
  the 15.01 Å line, leading to a reduction in its intensity, and was
  interpreted in terms of a geometry in which the emitters and absorbers
  are spatially distinct. <BR />Aims: We study the I(15.01 Å)/I(16.78
  Å) intensity ratio for the active cool dwarf EV Lac, in both flare and
  quiescent spectra. <BR />Methods: The observations were obtained with
  the Reflection Grating Spectrometer on the XMM-Newton satellite. The
  emission measure distribution versus temperature reconstruction
  technique is used for our analysis. <BR />Results: We find that the
  15.01 Å line exhibits a significant enhancement in intensity over the
  optically thin value. To our knowledge, this is the first time that such
  an enhancement has been detected on such a sound statistical basis. We
  interpret this enhancement in terms of a geometry in which the emitters
  and absorbers are not spatially distinct, and where the geometry is such
  that resonant pumping of the upper level has a greater effect on the
  observed line intensity than resonant absorption in the line-of-sight.

---------------------------------------------------------
Title: High frequency oscillations in the solar chromosphere and
    their connection with heating
Authors: Andic, Aleksandra; Mathioudakis, M.; Keenan, F. P.; Jess,
   D. B.; Bloomfield, D. S.
2008IAUS..247..312A    Altcode: 2007IAUS..247..312A
  High frequency acoustic waves have been suggested as a source of
  mechanical heating in the quiet solar chromosphere. To investigate
  this, we have observed intensity oscillations of several lines in the
  frequency interval 1.64-70mHz using data from the VTT Tenerife and the
  Dunn Solar Telescope at the National Solar Observatory. Our analysis
  of Fe i 543.45 nm, Fe i 543.29 nm and the G-band, indicate that the
  majority of oscillations are connected with the magnetic fields and
  do not provide sufficient mechanical flux for the heating of the
  chromosphere. This correlation is also observed in quiet Sun areas.

---------------------------------------------------------
Title: Solar feature tracking in both spatial and temporal domains
Authors: Jess, D. B.; Mathioudakis, M.; Erdélyi, R.; Verth, G.;
   McAteer, R. T. J.; Keenan, F. P.
2008IAUS..247..288J    Altcode: 2007IAUS..247..288J
  A new method for automated coronal loop tracking, in both spatial and
  temporal domains, is presented. The reliability of this technique
  was tested with TRACE 171 Å observations. The application of this
  technique to a flare-induced kink-mode oscillation, revealed a 3500
  km spatial periodicity which occur along the loop edge. We establish
  a reduction in oscillatory power, for these spatial periodicities,
  of 45% over a 322 s interval. We relate the reduction in oscillatory
  power to the physical damping of these loop-top oscillations.

---------------------------------------------------------
Title: Twisting flux tubes as a cause of micro-flaring activity
Authors: Jess, D. B.; McAteer, R. T. J.; Mathioudakis, M.; Keenan,
   F. P.; Andic, A.; Bloomfield, D. S.
2008IAUS..247..360J    Altcode: 2007IAUS..247..360J
  High-cadence optical observations of an H-α blue-wing bright point
  near solar AR NOAA 10794 are presented. The data were obtained with the
  Dunn Solar Telescope at the National Solar Observatory/Sacramento Peak
  using a newly developed camera system, the rapid dual imager. Wavelet
  analysis is undertaken to search for intensity-related oscillatory
  signatures, and periodicities ranging from 15 to 370 s are found with
  significance levels exceeding 95%. During two separate microflaring
  events, oscillation sites surrounding the bright point are observed to
  twist. We relate the twisting of the oscillation sites to the twisting
  of physical flux tubes, thus giving rise to reconnection phenomena. We
  derive an average twist velocity of 8.1 km/s and detect a peak in the
  emitted flux between twist angles of 180° and 230°.

---------------------------------------------------------
Title: Twisting flux tubes as a cause of micro-flaring activity
Authors: Jess, D. B.; McAteer, R. T. J.; Mathioudakis, M.; Keenan,
   F. P.; Andic, A.; Bloomfield, D. S.
2007A&A...476..971J    Altcode: 2007arXiv0709.2268J
  High-cadence optical observations of an H-α blue-wing bright point
  near solar AR NOAA 10794 are presented. The data were obtained with the
  Dunn Solar Telescope at the National Solar Observatory/Sacramento Peak
  using a newly developed camera system, the rapid dual imager. Wavelet
  analysis is undertaken to search for intensity-related oscillatory
  signatures, and periodicities ranging from 15 to 370 s are found with
  significance levels exceeding 95%. During two separate microflaring
  events, oscillation sites surrounding the bright point are observed to
  twist. We relate the twisting of the oscillation sites to the twisting
  of physical flux tubes, thus giving rise to reconnection phenomena. We
  derive an average twist velocity of 8.1 km s<SUP>-1</SUP> and detect
  a peak in the emitted flux between twist angles of 180° and 230°. <P
  />Figure 4 is available as a movie at http://www.aanda.org

---------------------------------------------------------
Title: High-frequency oscillations in a solar active region observed
    with the RAPID DUAL IMAGER
Authors: Jess, D. B.; Andić, A.; Mathioudakis, M.; Bloomfield, D. S.;
   Keenan, F. P.
2007A&A...473..943J    Altcode: 2007arXiv0707.2716J
  High-cadence, synchronized, multiwavelength optical observations
  of a solar active region (NOAA 10794) are presented. The data
  were obtained with the Dunn Solar Telescope at the National Solar
  Observatory/Sacramento Peak using a newly developed camera system:
  the rapid dual imager. Wavelet analysis is undertaken to search
  for intensity related oscillatory signatures, and periodicities
  ranging from 20 to 370 s are found with significance levels exceeding
  95%. Observations in the H-α blue wing show more penumbral oscillatory
  phenomena when compared to simultaneous G-band observations. The H-α
  oscillations are interpreted as the signatures of plasma motions with
  a mean velocity of 20 km s<SUP>-1</SUP>. The strong oscillatory power
  over H-α blue-wing and G-band penumbral bright grains is an indication
  of the Evershed flow with frequencies higher than previously reported.

---------------------------------------------------------
Title: Detection of MHD waves in the solar chromosphere
Authors: Kontogiannis, Giannis; Bloomfield, D. Shaun; McAteer, James
   R. T.; Mathioudakis, Mihalis; Antonopoulou, E.
2007AIPC..895...80K    Altcode:
  One of the main features of the quiet solar chromosphere is the Network
  Bright Points (NBP), formed by emerging magnetic flux at the boundaries
  of supergranular cells. Using SSW IDL routines and wavelet analysis
  of series of images in four bandpasses (CaIIK3, Mgb1, Mgb2 and Hα
  core) we have detected MHD wave modes in the Network Bright Points
  of the solar chromosphere. The observations have been analyzed using
  cross-correlation techniques and we have drawn conclusions on wave
  propagation and mode-coupling.

---------------------------------------------------------
Title: The Influence of Magnetic Field on Oscillations in the Solar
    Chromosphere
Authors: Bloomfield, D. Shaun; McAteer, R. T. James; Mathioudakis,
   Mihalis; Keenan, Francis P.
2006ApJ...652..812B    Altcode: 2006astro.ph..8314B
  Two sequences of solar images obtained by the Transition Region and
  Coronal Explorer in three UV passbands are studied using wavelet
  and Fourier analysis and compared to the photospheric magnetic
  flux measured by the Michelson Doppler Interferometer on the Solar
  Heliospheric Observatory to study wave behavior in differing magnetic
  environments. Wavelet periods show deviations from the theoretical
  cutoff value and are interpreted in terms of inclined fields. The
  variation of wave speeds indicates that a transition from dominant
  fast-magnetoacoustic waves to slow modes is observed when moving from
  network into plages and umbrae. This implies preferential transmission
  of slow modes into the upper atmosphere, where they may lead to heating
  or be detected in coronal loops and plumes.

---------------------------------------------------------
Title: The periodic variations of a white-light flare observed
    with ULTRACAM
Authors: Mathioudakis, M.; Bloomfield, D. S.; Jess, D. B.; Dhillon,
   V. S.; Marsh, T. R.
2006A&A...456..323M    Altcode: 2006astro.ph..5196M
  High time resolution observations of a white-light flare on the active
  star EQ PegB show evidence of intensity variations with a period of
  ≈10 s. The period drifts to longer values during the decay phase of
  the flare. If the oscillation is interpreted as an impulsively-excited,
  standing-acoustic wave in a flare loop, the period implies a loop
  length of ≈3.4 Mm and ≈6.8 Mm for the case of the fundamental mode
  and the second harmonic, respectively. However, the small loop lengths
  imply a very high modulation depth making the acoustic interpretation
  unlikely. A more realistic interpretation may be that of a fast-MHD
  wave, with the modulation of the emission being due to the magnetic
  field. Alternatively, the variations could be due to a series of
  reconnection events. The periodic signature may then arise as a result
  of the lateral separation of individual flare loops or current sheets
  with oscillatory dynamics (i.e., periodic reconnection).

---------------------------------------------------------
Title: Opacity in the upper atmospheres of active stars. II. AD Leonis
Authors: Christian, D. J.; Mathioudakis, M.; Bloomfield, D. S.;
   Dupuis, J.; Keenan, F. P.; Pollacco, D. L.; Malina, R. F.
2006A&A...454..889C    Altcode: 2006astro.ph..2447C
  We present FUV and UV spectroscopic observations of AD Leonis, with
  the aim of investigating opacity effects in the transition regions
  of late-type stars. The C III lines in FUSE spectra show significant
  opacity during both the quiescent and flaring states of AD Leonis, with
  up to 30% of the expected flux being lost during the latter. Other FUSE
  emission lines tested for opacity include those of O VI, while C IV, Si
  IV and N V transitions observed with stis are also investigated. These
  lines only reveal modest amounts of opacity with losses during flaring
  of up to 20%. Optical depths have been calculated for homogeneous
  and inhomogeneous geometries, giving path lengths of ≈20-60 km and
  ≈10-30 km, respectively, under quiescent conditions. However path
  lengths derived during flaring are ≈2-3 times larger. These values
  are in excellent agreement with both estimates of the small-scale
  structure observed in the solar transition region, and path lengths
  derived previously for several other active late-type stars.

---------------------------------------------------------
Title: Traveling Waves In Network Bright Points
Authors: Kontogiannis, G.; Bloomfield, D. Shaun; McAteer, J. R. T.;
   Mathioudakis, M.; Antonopoulou, E.
2006AIPC..848..229K    Altcode:
  One of the main features of the quiet solar chromosphere is the
  Network Bright Points (NBP), formed by the emerging magnetic flux,
  at the boundaries of supergranular cells. Triggered by the motions
  of magnetic loop foot-points, at the top of the convection zone, MHD
  waves propagate inside the NBP's. Using SSW IDL routines and wavelet
  analysis of series of images in four bandpasses (CaII K3, Mgb1-0.4,
  Mgb2 and Ha core) we detected these MHD wave modes. The observations
  have been analyzed using cross-correlation techniques and we have
  drawn conclusions on wave propagation and mode coupling.

---------------------------------------------------------
Title: Observational Evidence of Gentle and Explosive Chromospheric
    Evaporation
Authors: Milligan, R. O.; Gallagher, P. T.; Mathioudakis, M.; Keenan,
   F. P.
2006ESASP.617E.138M    Altcode: 2006soho...17E.138M
  No abstract at ADS

---------------------------------------------------------
Title: Observational Evidence of Chromospheric Evaporation
Authors: Milligan, Ryan O.; Gallagher, P. T.; Mathioudakis, M.;
   Keenan, F. P.
2006SPD....37.0828M    Altcode: 2006BAAS...38R.662M
  Observational evidence for chromospheric evaporation during the
  impulsive phase of two solar flares is presented using data from the
  Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) and the
  Coronal Diagnostic Spectrometer (CDS) on board SOHO. For the first
  time, co-spatial imaging and spectroscopy have been used to observe
  both gentle and explosive evaporation processes within HXR emitting
  regions. For a GOES C9.1 flare, a low flux of non-thermal electrons
  was found to produce low-velocity upflows in the cool He I and O V
  emission lines and moderate upflows in the 8 MK Fe XIX line indicative
  of gentle evaporation. An M2.2 flare, on the other hand, showed
  low-velocity downflows in the He I and O V lines and high-velocity
  upflows in the Fe XIX line, for an electron flux value which was an
  order of magnitude higher, indicative of an explosive process. These
  findings confirm that the dynamic response of the solar atmosphere is
  sensitively dependent on the flux of incident electrons as predicted
  by current hydrodynamical simulations.

---------------------------------------------------------
Title: Opacity in the transition region of cool dwarfs: A powerful
    diagnostic
Authors: Mathioudakis, M.; Christian, D. J.; Bloomfield, D. S.;
   Keenan, F. P.; Linsky, J. L.; Dupuis, J.
2006ASPC..348..159M    Altcode:
  A detailed study of the C III 1176Å multiplet in active cool stars
  has shown significant deviations of the line flux from the optically
  thin approximation. These deviations become more pronounced during
  flares. Opacity can be used as a powerful diagnostic to estimate path
  lengths in the transition region. Our analysis reveals that stellar
  transition regions have very small spatial characteristics typically
  in the range of 10 - 100 km. These path lengths are in agreement with
  the small scale structure seen in the solar transition region.

---------------------------------------------------------
Title: A Comparative Study of Flaring Loops in Active Stars
Authors: Mullan, D. J.; Mathioudakis, M.; Bloomfield, D. S.; Christian,
   D. J.
2006ApJS..164..173M    Altcode:
  Dynamo activity in stars of different types is expected to generate
  magnetic fields with different characteristics. As a result, a
  differential study of the characteristics of magnetic loops in a broad
  sample of stars may yield information about dynamo systematics. In the
  absence of direct imaging, certain physical parameters of a stellar
  magnetic loop can be extracted if a flare occurs in that loop. In
  this paper we employ a simple nonhydrodynamic approach introduced by
  Haisch, to analyze a homogeneous sample of all of the flares we could
  identify in the EUVE DS database: a total of 134 flares that occurred
  on 44 stars ranging in spectral type from F to M and in luminosity
  class from V to III. All of the flare light curves that have been
  used in the present study were obtained by a single instrument (EUVE
  DS). For each flare, we have applied Haisch's simplified approach
  (HSA) in order to determine loop length, temperature, electron density,
  and magnetic field. For each of our target stars, a literature survey
  has been performed to determine quantitatively the extent to which our
  results are consistent with independent studies. The results obtained
  by HSA are found to be well supported by results obtained by other
  methods. Our survey suggests that, on the main sequence, short loops
  (with lengths &lt;=0.5R<SUB>*</SUB>) may be found in stars of all
  classes, while the largest loops (with lengths up to 2R<SUB>*</SUB>)
  appear to be confined to M dwarfs. Based on EUVE data, the transition
  from small to large loops on the main sequence appears to occur between
  spectral types K2 and M0. We discuss the implications of this result
  for dynamo theories.

---------------------------------------------------------
Title: Observational Evidence of Gentle Chromospheric Evaporation
    during the Impulsive Phase of a Solar Flare
Authors: Milligan, Ryan O.; Gallagher, Peter T.; Mathioudakis, Mihalis;
   Keenan, Francis P.
2006ApJ...642L.169M    Altcode: 2006astro.ph..3652M
  Observational evidence of gentle chromospheric evaporation during
  the impulsive phase of a C9.1 solar flare is presented using data
  from the Reuven Ramaty High-Energy Solar Spectroscopic Imager and the
  Coronal Diagnostic Spectrometer on board the Solar and Heliospheric
  Observatory. Until now, evidence of gentle evaporation has often
  been reported during the decay phase of solar flares, where thermal
  conduction is thought to be the driving mechanism. Here we show that
  the chromospheric response to a low flux of nonthermal electrons
  (&gt;=5×10<SUP>9</SUP> ergs cm<SUP>-2</SUP> s<SUP>-1</SUP>) results
  in plasma upflows of 13+/-16, 16+/-18, and 110+/-58 km s<SUP>-1</SUP>
  in the cool He I and O V emission lines and the 8 MK Fe XIX line,
  respectively. These findings, in conjunction with other recently
  reported work, now confirm that the dynamic response of the solar
  atmosphere is sensitively dependent on the flux of incident electrons.

---------------------------------------------------------
Title: RHESSI and SOHO CDS Observations of Explosive Chromospheric
    Evaporation
Authors: Milligan, Ryan O.; Gallagher, Peter T.; Mathioudakis, Mihalis;
   Bloomfield, D. Shaun; Keenan, Francis P.; Schwartz, Richard A.
2006ApJ...638L.117M    Altcode: 2005astro.ph..9664M
  Simultaneous observations of explosive chromospheric evaporation
  are presented using data from the Reuven Ramaty High-Energy Solar
  Spectroscopic Imager (RHESSI) and the Coronal Diagnostic Spectrometer
  (CDS) on board the Solar and Heliospheric Observatory. For the first
  time, cospatial imaging and spectroscopy have been used to observe
  explosive evaporation within a hard X-ray emitting region. RHESSI
  X-ray images and spectra were used to determine the flux of nonthermal
  electrons accelerated during the impulsive phase of an M2.2 flare. When
  we assumed a thick-target model, the injected electron spectrum was
  found to have a spectral index of ~7.3, a low-energy cutoff of ~20 keV,
  and a resulting flux of &gt;=4×10<SUP>10</SUP> ergs cm<SUP>-2</SUP>
  s<SUP>-1</SUP>. The dynamic response of the atmosphere was determined
  using CDS spectra; we found a mean upflow velocity of 230+/-38 km
  s<SUP>-1</SUP> in Fe XIX (592.23 Å) and associated downflows of
  36+/-16 and 43+/-22 km s<SUP>-1</SUP> at chromospheric and transition
  region temperatures, respectively, relative to an averaged quiet-Sun
  spectra. The errors represent a 1 σ dispersion. The properties of
  the accelerated electron spectrum and the corresponding evaporative
  velocities were found to be consistent with the predictions of theory.

---------------------------------------------------------
Title: Plasma diagnostics of active-region evolution and implications
    for coronal heating
Authors: Milligan, R. O.; Gallagher, P. T.; Mathioudakis, M.; Keenan,
   F. P.; Bloomfield, D. S.
2005MNRAS.363..259M    Altcode: 2005MNRAS.tmp..764M; 2005astro.ph..9219M
  A detailed study is presented of the decaying solar-active region NOAA
  10103 observed with the Coronal Diagnostic Spectrometer (CDS), the
  Michelson Doppler Imager (MDI) and the Extreme-ultraviolet Imaging
  Telescope (EIT) onboard the Solar and Heliospheric Observatory
  (SOHO). Electron-density maps formed using SiX (356.03 Å/347.41 Å)
  show that the density varies from ~10<SUP>10</SUP>cm<SUP>-3</SUP>
  in the active-region core to ~7 × 10<SUP>8</SUP>cm<SUP>-3</SUP>
  at the region boundaries. Over the 5d of observations, the average
  electron density fell by ~30 per cent. Temperature maps formed using
  FeXVI (335.41 Å)/FeXIV (334.18 Å) show electron temperatures of
  ~2.34 × 10<SUP>6</SUP> K in the active-region core and ~2.10 ×
  10<SUP>6</SUP> K at the region boundaries. Similarly to the electron
  density, there was a small decrease in the average electron temperature
  over the 5-d period. The radiative, conductive and mass-flow losses
  were calculated and used to determine the resultant heating rate
  (P<SUB>H</SUB>). Radiative losses were found to dominate the
  active-region cooling process. As the region decayed, the heating
  rate decreased by almost a factor of 5 between the first and last
  day of observations. The heating rate was then compared to the
  total unsigned magnetic flux , yielding a power law of the form
  P<SUB>H</SUB>~Φ<SUP>0.81+/-0.32</SUP><SUB>tot</SUB>. This result
  suggests that waves rather than nanoflares may be the dominant heating
  mechanism in this active region.

---------------------------------------------------------
Title: <SUP>6</SUP>Li in the Atmosphere of GJ 117
Authors: Christian, D. J.; Mathioudakis, M.; Jevremović, D.;
   Hauschildt, P. H.; Baron, E.
2005ApJ...632L.127C    Altcode: 2005astro.ph..9247C
  We present high-resolution VLT UVES observations of the active K dwarf
  GJ 117. <SUP>6</SUP>Li enhancement has been shown for energetic solar
  events, one chromospherically active binary, and several dwarf halo
  stars. Our analysis reveals the detection of <SUP>6</SUP>Li on this
  source with <SUP>6</SUP>Li/<SUP>7</SUP>Li = 0.030 +/- 0.010. We found
  no significant contribution from other lines, including Ti I, in the
  Li profile of GJ 117 and a template star of similar spectral type and
  metallicity. We discuss the possibility for <SUP>6</SUP>Li production
  by spallation and find it to be consistent with the activity levels
  of the object.

---------------------------------------------------------
Title: Chromospheric Response to Non-Thermal Electrons During Flares
    Using RHESSI and SOHO/CDS
Authors: Milligan, R. O.; Gallagher, P. T.; Mathioudakis, M.; Keenan,
   F. P.
2005AGUSMSP52A..04M    Altcode:
  Many current solar flare models predict a relationship between the
  amount of energy deposited in the chromospheric and transition region
  layers of the solar atmosphere by non-thermal electrons, and the
  velocity at which this superheated material rises. For the first time,
  we present findings from simultaneous observations of loop footpoints
  using RHESSI and SOHO/CDS. RHESSI HXR images and spectra are used to
  determine the flux of non-thermal electrons using the thick-target
  bremsstrahlung model, while upflow velocities in the Fe XIX emission
  line are observed using CDS.

---------------------------------------------------------
Title: AB Dor: Evidence for stellar coronal opacity in Fe XVII
Authors: Matranga, M.; Mathioudakis, M.; Kay, H. R. M.; Keenan, F. P.
2005ESASP.560..807M    Altcode: 2005csss...13..807M
  No abstract at ADS

---------------------------------------------------------
Title: Intensity oscillations during a flare on EQ Peg
Authors: Mathioudakis, M.; Bloomfield, D. S.; Dhillon, V. S.; Marsh,
   T. R.
2005ESASP.560..803M    Altcode: 2005csss...13..803M
  No abstract at ADS

---------------------------------------------------------
Title: Magnetohydrodynamic mode coupling in the quiet-Sun network
Authors: Bloomfield, D. S.; McAteer, R. T. J.; Mathioudakis, M.;
   Williams, D. R.; Keenan, F. P.
2005ESASP.560..449B    Altcode: 2005csss...13..449B
  No abstract at ADS

---------------------------------------------------------
Title: Flare X-Ray Observations of AB Doradus: Evidence of Stellar
    Coronal Opacity
Authors: Matranga, M.; Mathioudakis, M.; Kay, H. R. M.; Keenan, F. P.
2005ApJ...621L.125M    Altcode: 2005astro.ph..2063M
  X-ray spectra of the late-type star AB Dor obtained with the
  XMM-Newton satellite are analyzed. AB Dor was particularly active
  during the observations. An emission measure reconstruction technique
  is employed to analyze flare and quiescent spectra, with emphasis on
  the Fe XVII 15-17 Å wavelength region. The Fe XVII 16.78 Å/15.01 Å
  line ratio increases significantly in the hotter flare plasma. This
  change in the ratio is opposite to the theoretical predictions
  and is attributed to the scattering of 15.01 Å line photons from
  the line of sight. The escape probability technique indicates an
  optical depth of ~0.4 for the 15.01 Å line. During the flare, the
  electron density is 4.4<SUP>+2.7</SUP><SUB>-1.6</SUB>×10<SUP>10</SUP>
  cm<SUP>-3</SUP>, and the fractional Fe abundance is 0.5+/-0.1 of the
  solar photospheric value. Using these parameters, a path length of
  ~8000 km is derived. There is no evidence of opacity in the quiescent
  X-ray spectrum of the star.

---------------------------------------------------------
Title: Observations of Hα Intensity Oscillations in a Flare Ribbon
Authors: McAteer, R. T. James; Gallagher, Peter T.; Brown, Daniel S.;
   Bloomfield, D. Shaun; Moore, Ruth; Williams, David R.; Mathioudakis,
   Mihalis; Katsiyannis, A.; Keenan, Francis P.
2005ApJ...620.1101M    Altcode:
  High-cadence Hα blue wing observations of a C9.6 solar flare
  obtained at Big Bear Solar Observatory using the Rapid Dual Imager
  are presented. Wavelet and time-distance methods were used to study
  oscillatory power along the ribbon, finding periods of 40-80 s during
  the impulsive phase of the flare. A parametric study found statistically
  significant intensity oscillations with amplitudes of 3% of the peak
  flare amplitude, periods of 69 s (14.5 mHz) and oscillation decay times
  of 500 s. These measured properties are consistent with the existence
  of flare-induced acoustic waves within the overlying loops.

---------------------------------------------------------
Title: Wavelet Phase Coherence Analysis: Application to a Quiet-Sun
    Magnetic Element
Authors: Bloomfield, D. Shaun; McAteer, R. T. James; Lites, Bruce W.;
   Judge, Philip G.; Mathioudakis, Mihalis; Keenan, Francis P.
2004ApJ...617..623B    Altcode:
  A new application of wavelet analysis is presented that utilizes
  the inherent phase information residing within the complex Morlet
  transform. The technique is applied to a weak solar magnetic network
  region, and the temporal variation of phase difference between TRACE
  1700 Å and SOHO/SUMER C II 1037 Å intensities is shown. We present,
  for the first time in an astrophysical setting, the application of
  wavelet phase coherence, including a comparison between two methods
  of testing real wavelet phase coherence against that of noise. The
  example highlights the advantage of wavelet analysis over more
  classical techniques, such as Fourier analysis, and the effectiveness
  of the former to identify wave packets of similar frequencies but
  with differing phase relations is emphasized. Using cotemporal,
  ground-based Advanced Stokes Polarimeter measurements, changes in the
  observed phase differences are shown to result from alterations in
  the magnetic topology.

---------------------------------------------------------
Title: A Detailed Study of Opacity in the Upper Atmosphere of
    Proxima Centauri
Authors: Christian, D. J.; Mathioudakis, M.; Bloomfield, D. S.;
   Dupuis, J.; Keenan, F. P.
2004ApJ...612.1140C    Altcode:
  We present far-UV and UV spectroscopic observations of Proxima Centauri
  obtained as part of our continued investigation into the optically
  thin approximation assumed for the transition regions of late-type
  stars. Significant opacity is found in the C III lines during both
  the quiescent and flaring states of Proxima Cen, with up to 70% of the
  expected flux being lost in the latter. Our findings cast some doubt
  on the suitability of the C III λ977 line for estimating the electron
  density in stellar atmospheres. However, the opacity has no significant
  effect on the observed line widths. We calculate optical depths for
  homogeneous and inhomogeneous geometries and estimate an electron
  density of 6×10<SUP>10</SUP> cm<SUP>-3</SUP> for the transition region
  using the O IV line ratios at 1400 Å. The combination of electron
  density and optical depth indicates path lengths as low as ~10 km,
  which are in excellent agreement with estimates of the small-scale
  structure seen in the solar transition region.

---------------------------------------------------------
Title: Erratum: “Propagating Waves and Magnetohydrodynamic
    Mode Coupling in the Quiet-Sun Network” (<A
    href="/abs/2004ApJ...604..936B">ApJ, 604, 936 [2004]</A>)
Authors: Bloomfield, D. Shaun; McAteer, R. T. James; Mathioudakis,
   Mihalis; Williams, David R.; Keenan, Francis P.
2004ApJ...609..465B    Altcode:
  Proof corrections were not carried correctly to the
  final printed version of this paper, which resulted
  in an extra set of overbars appearing in both terms
  of the denominator of equation (3). The correct form of this equation
  is:C(Δt,ν)=(Σ[P<SUB>λ<SUB>1</SUB></SUB>(t,ν)-P<SUB>λ<SUB>1</SUB></SUB>(t,ν)][P<SUB>λ<SUB>2</SUB></SUB>(t+Δt,ν)-P<SUB>λ<SUB>2</SUB></SUB>(t+Δt,ν)])/(sqrt(Σ[P<SUB>λ<SUB>1</SUB></SUB>(t,ν)-P<SUB>λ<SUB>1</SUB></SUB>(t,ν)]<SUP>2</SUP>Σ[P<SUB>λ<SUB>2</SUB></SUB>(t,ν)-P<SUB>λ<SUB>2</SUB></SUB>(t,ν)]<SUP>2</SUP>)).
  (3)As noted in footnote 3, this correlation equation was stated
  incorrectly in our previous paper (eq. [4] in R. T. J. McAteer et al.,
  <A href="/abs/2004ApJ...604..936B">ApJ, 604, 936 [2004]</A>). However,
  the correct form of equation (3), now given here, was used for the
  analysis in both papers. <P />The press sincerely regrets this error.

---------------------------------------------------------
Title: Plasma Diagnostics of Active Region Evolution and Implications
    for Coronal Heating
Authors: Milligan, R. O.; Gallagher, P. T.; Mathioudakis, M.;
   Bloomfield, D. S.; Keenan, F. P.
2004AAS...204.9803M    Altcode: 2004BAAS...36..984M
  The decaying solar active region NOAA 10103 was observed during 2002
  September 10--14 using the Coronal Diagnostic Spectrometer (CDS) onboard
  the Solar and Heliospheric Observatory (SOHO). Electron density maps
  were created using the Si X (356Å/347Å) ratio, which show densities
  of ∼10<SUP>10</SUP>cm<SUP>-3</SUP> in the active region core, and
  ∼7x10<SUP>8</SUP>cm<SUP>-3</SUP> in the region boundaries. Over
  the five days of observations, the average electron density fell by
  approximately a factor of two. Temperature maps were created using
  the Fe XVI (335.4Å)/Fe XIV (334.2Å) ratio, which show electron
  temperatures of ∼2.2x10<SUP>6</SUP>K in the active region core,
  and ∼2.0x10<SUP>6</SUP>K in the region boundaries. Similarly to the
  electron density, the average electron temperature decreased over the
  five days, but by only ∼3%. The radiative and conductive losses, and
  resultant heating rate, were then calculated and compared to the total
  unsigned magnetic flux (Φ <SUB>tot</SUB> = ∫ dA |B<SUB>z|</SUB>)
  from Michelson Doppler Interferometer (MDI) magnetograms. Losses due to
  radiation were found to exceed conductive losses by a factor of ten. As
  the region decayed, the heating rate decreased by close to an order of
  magnitiude between the first and last day of observations. In line with
  several coronal heating theories, a power-law relationship of the form
  P<SUB>tot} ∼Φ <SUB>{tot</SUB><SUP>0.95±0.07</SUP></SUB> was found
  between the heating rate and the unsigned magnetic flux. This result
  provides further observational evidence for wave rather than nanoflare
  heating of solar active regions. <P />Ryan Milligan would like to
  thank the Solar Physics Division for being awarded an SPD Studentship.

---------------------------------------------------------
Title: Propagating Waves and Magnetohydrodynamic Mode Coupling in
    the Quiet-Sun Network
Authors: Bloomfield, D. Shaun; McAteer, R. T. James; Mathioudakis,
   Mihalis; Williams, David R.; Keenan, Francis P.
2004ApJ...604..936B    Altcode:
  High-cadence multiwavelength optical observations were taken with the
  Dunn Solar Telescope at the National Solar Observatory, Sacramento Peak,
  accompanied by Advanced Stokes Polarimeter vector magnetograms. A total
  of 11 network bright points (NBPs) have been studied at different
  atmospheric heights using images taken in wave bands centered on
  Mg I b<SUB>1</SUB> - 0.4 Å, Hα, and Ca II K<SUB>3</SUB>. Wavelet
  analysis was used to study wave packets and identify traveling
  magnetohydrodynamic waves. Wave speeds were estimated through the
  temporal cross-correlation of signals, in selected frequency bands
  of wavelet power, in each wavelength. Four mode-coupling cases were
  identified, one in each of four of the NBPs, and the variation of the
  associated Fourier power with height was studied. Three of the detected
  mode-coupling, transverse-mode frequencies were observed in the 1.2-1.6
  mHz range (mean NBP apparent flux density magnitudes over 99-111 Mx
  cm<SUP>-2</SUP>), with the final case showing 2.0-2.2 mHz (with 142 Mx
  cm<SUP>-2</SUP>). Following this, longitudinal-mode frequencies were
  detected in the range 2.6-3.2 mHz for three of our cases, with 3.9-4.1
  mHz for the remaining case. After mode coupling, two cases displayed a
  decrease in longitudinal-mode Fourier power in the higher chromosphere.

---------------------------------------------------------
Title: Ultraviolet Oscillations in the Chromosphere of the Quiet Sun
Authors: McAteer, R. T. James; Gallagher, Peter T.; Bloomfield,
   D. Shaun; Williams, David R.; Mathioudakis, Mihalis; Keenan, Francis P.
2004ApJ...602..436M    Altcode:
  Quiet-Sun oscillations in the four Transition Region and Coronal
  Explorer (TRACE) ultraviolet passbands centered on 1700, 1600,
  1216, and 1550 Å are studied using a wavelet-based technique. Both
  network and internetwork regions show oscillations with a variety of
  periods and lifetimes in all passbands. The most frequent network
  oscillation has a period of 283 s, with a lifetime of 2-3 cycles
  in all passbands. These oscillations are discussed in terms of
  upwardly propagating magnetohydrodynamic wave models. The most
  frequent internetwork oscillation has a period of 252 s, again with
  a lifetime of 2-3 cycles, in all passbands. The tendency for these
  oscillations to recur in the same position is discussed in terms of
  “persistent flashers.” The network contains greater oscillatory
  power than the internetwork at periods longer than 300 s in the
  low chromosphere. This value is shown to decrease to 250 s in the
  high chromosphere. The internetwork also displays a larger number of
  short-lifetime, long-period oscillations than the network, especially
  in the low chromosphere. Both network and internetwork regions contain
  a small number of nonrecurring long-lifetime oscillations.

---------------------------------------------------------
Title: Intensity Oscillations During a flare on II Peg
Authors: Avgoloupis, S.; Seiradakis, J. H.; Mathioudakis, M.;
   Bloomfield, D. Shaun; McAteer, J.
2004hell.conf..120A    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Oscillatory Signatures above Quiet Sun Magnetic Elements
Authors: Bloomfield, D. S.; McAteer, R. T. J.; Lites, B. W.; Judge,
   P. G.; Mathioudakis, M.; Keenan, F. P.
2004ESASP.547...51B    Altcode: 2004soho...13...51B
  A new application of wavelet analysis is presented. The data used are
  part of Joint Observing Proposal 72 between SoHO and TRACE, obtained on
  1998 May 16 with accompanying groundbased data taken with the Dunn Solar
  Telescope at Sacramento Peak, New Mexico. A weak magnetic network region
  is studied and the temporal variation of phase difference between TRACE
  1700 Å and SoHO/SUMER C II intensities is shown. The example clearly
  highlights the advantages of wavelet analysis over more classical
  techniques such as Fourier analysis, where the effectiveness of the
  technique to identify wavepackets with differing phase difference
  relations is emphasised.

---------------------------------------------------------
Title: An Automated Wavelet Analysis Approach to TRACE Quiet Sun
    Oscillations
Authors: McAteer, R. T. J.; Gallagher, P. T.; Williams, D. R. Williams
   D. R.; Bloomfield, D. S.; Mathioudakis, M.; Keenan, F. P.
2004ESASP.547..139M    Altcode: 2004soho...13..139M
  An automated wavelet analysis approach to TRACE UV quiet Sun datasets
  is discussed. Periodicity and lifetime of oscillations present in the
  network and internetwork are compared and contrasted. This provides
  a means of extending previous Fourier results into the time-localised
  domain. The longest lifetime oscillations occur around the acoustic band
  and the network tends to dominate over the internetwork at periods 4
  mins. However, it is shown that the internetwork can dominate over the
  network at long periods (7 - 20 mins), but only for short lifetimes
  ( 3 complete oscillations). These results are discussed in terms of
  chromospheric heating theories.

---------------------------------------------------------
Title: Coronal opacity variation during a flare on AB Doradus
Authors: Kay, H.; Mathioudakis, M.; Matranga, M.
2004cosp...35.1745K    Altcode: 2004cosp.meet.1745K
  One of the fundamental assumptions in the study of stellar transition
  regions and coronae is that the emission is optically thin. However,
  opacity effects have been seen in the solar corona for many years
  and there is evidence from FUSE observations of cool stars that they
  may also be important when considering stellar transition regions and
  coronae. The active star AB Doradus has been observed frequently by
  XMM-Newton as part of the instrument calibration programme. We present
  detailed analysis of the corona of AB Doradus and investigate possible
  changes in opacity, by means of the Fe XVII emission lines. The use
  of opacity as a diagnostic tool for constraining the scale-height and
  emitting volume are outlined

---------------------------------------------------------
Title: A New EUVE-detected Flare Star (EUVE J0613-23.9B)
Authors: Christian, D. J.; Mathioudakis, M.; Jevremovic, D.; Dupuis,
   J.; Vennes, S.; Kawka, A.
2003IBVS.5447....1C    Altcode:
  We present observations of a strong flare from EUVE J0613-23.9B,
  a source serendipitously detected with the EUVE Deep Survey Telescope
  2.5' south of HD 43162. Optical spectroscopy revealed EUVE J0613-23.9B
  to be an active dM3.5e star. A dM4e star was found 23” south of HD
  43162 that we associate with 1RXS J061345.1235205.

---------------------------------------------------------
Title: The Extreme-Ultraviolet Continuum of a Strong Stellar Flare
Authors: Christian, D. J.; Mathioudakis, M.; Jevremović, D.; Dupuis,
   J.; Vennes, S.; Kawka, A.
2003ApJ...593L.105C    Altcode:
  We present the serendipitous detection of an extreme-ultraviolet flare
  on EUVE J0613-23.9B. The flare showed over a 200-fold increase above the
  quiescent emission in the DS/Lexan 60-200 Å wavelength band. Optical
  spectroscopy revealed that the event was associated with an active
  dM3.5e star. The EUVE spectra are dominated by emission lines formed at
  temperatures in excess of 10<SUP>7</SUP> K. The observation is unique
  as we have detected, for the first time, a strong Lyman continuum in
  the EUVE long-wavelength range (320-650 Å). The flare in the continuum
  (T~20,000-30,000 K) was extremely short, lasting for less than 500 s,
  while in the DS (T~10<SUP>7</SUP> K) its duration was ~28 ks. The
  total energy of the flare in the DS is ~3×10<SUP>34</SUP> ergs. We
  have made a fit to the continuum using semiempirical model atmospheres
  and derived the time-averaged temperature and density structures.

---------------------------------------------------------
Title: White-light oscillations during a flare on II Peg.
Authors: Mathioudakis, M.; Seiradakis, J. H.; Williams, D. R.;
   Avgoloupis, S.; Bloomfield, D. S.; McAteer, R. T. J.
2003A&A...403.1101M    Altcode:
  We analyse the intensity oscillations observed in the gradual phase
  of a white-light flare on the RS CVn binary II Peg. Fast Fourier
  Transform power spectra and Wavelet analysis reveal a period of
  220 s. The reliability of the oscillation is tested using several
  criteria. Oscillating coronal loop models are used to derive physical
  parameters such as temperature, electron density and magnetic field
  strength associated with the coronal loop. The derived parameters
  are consistent with the near-simultaneous X-ray observations of the
  flare. There is no evidence for oscillations in the quiescent state
  of the binary.

---------------------------------------------------------
Title: Observational Evidence for Mode Coupling in the Chromospheric
    Network
Authors: McAteer, R. T. James; Gallagher, Peter T.; Williams, David R.;
   Mathioudakis, Mihalis; Bloomfield, D. Shaun; Phillips, Kenneth J. H.;
   Keenan, Francis P.
2003ApJ...587..806M    Altcode:
  Oscillations in network bright points (NBPs) are studied at a variety
  of chromospheric heights. In particular, the three-dimensional
  variation of NBP oscillations is studied using image segmentation
  and cross-correlation analysis between images taken in light of Ca II
  K<SUB>3</SUB>, Hα core, Mg I b<SUB>2</SUB>, and Mg I b<SUB>1</SUB>-0.4
  Å. Wavelet analysis is used to isolate wave packets in time and
  to search for height-dependent time delays that result from upward-
  or downward-directed traveling waves. In each NBP studied, we find
  evidence for kink-mode waves (1.3, 1.9 mHz), traveling up through the
  chromosphere and coupling with sausage-mode waves (2.6, 3.8 mHz). This
  provides a means for depositing energy in the upper chromosphere. We
  also find evidence for other upward- and downward-propagating waves in
  the 1.3-4.6 mHz range. Some oscillations do not correspond to traveling
  waves, and we attribute these to waves generated in neighboring regions.

---------------------------------------------------------
Title: Si IX Emission Lines in Spectra Obtained with the Solar euv
    Research Telescope and Spectrograph (Serts)
Authors: Keenan, F. P.; Katsiyannis, A. C.; Aggarwal, K. M.;
   Mathioudakis, M.; Brosius, J. W.; Davila, J. M.; Thomas, R. J.
2003SoPh..212...65K    Altcode:
  Theoretical electron-density-sensitive emission line ratios involving
  2s<SUP>2</SUP>2p<SUP>2</SUP>-2s2p<SUP>3</SUP> transitions in Si ix
  between 223 and 350 Å are presented. A comparison of these with
  an extensive dataset of solar-active-region, quiet-Sun, subflare
  and off-limb observations, obtained during rocket flights by the
  Solar EUV Research Telescope and Spectrograph (SERTS), reveals
  generally very good agreement between theory and experiment. This
  provides support for the accuracy of the line-ratio diagnostics,
  and hence the atomic data on which they are based. In particular,
  the density-sensitive intensity ratio I(258.10 Å)/I(349.87 Å)
  offers an especially promising diagnostic for studies of coronal
  plasmas, as it involves two reasonably strong emission lines and
  varies by more than an order of magnitude over the useful density
  range of 10<SUP>9</SUP>-10<SUP>11</SUP> cm<SUP>−3</SUP>. The
  2s<SUP>2</SUP>2p<SUP>2</SUP> <SUP>1</SUP>S<SUB>0</SUB>-2s2p<SUP>3</SUP>
  <SUP>1</SUP>P<SUB>1</SUB> transition at 259.77 Å is very marginally
  identified for the first time in the SERTS database, although it has
  previously been detected in solar flare observations.

---------------------------------------------------------
Title: Late-type Stars with Coronae but No Chromospheres?
Authors: Christian, D. J.; Mathioudakis, M.; Jevremovic, D.; Mullan,
   D. J.; Lehner, N.
2002AAS...201.1206C    Altcode: 2002BAAS...34.1113C
  We present high resolution optical observations of several late-type
  stars selected from ROSAT and EUVE surveys. These particular stars
  show no Balmer or Ca II emission typical of late-type stars with X-ray
  evidence for coronae. Since our sample shows no evidence for binarity
  in their optical spectra, these stars may have no chromospheres. We
  present preliminary results from simulated spectra using the MULTI
  code of Carlsson for solving multi-level non-LTE radiative transfer
  problems in plane parallel atmospheres. These simulations can reproduce
  the observed Ca II line profiles. Stars without chromospheres are
  expected to have high density coronae and transition regions, which
  we will investigate with future FUV and X-ray observations.

---------------------------------------------------------
Title: A Study Of Extreme Ultraviolet Flare Activity On Late-Type
    Stars
Authors: Bloomfield, D. S.; Mathioudakis, M.
2002ASPC..277..425B    Altcode: 2002sccx.conf..425B
  No abstract at ADS

---------------------------------------------------------
Title: The OIV and SIV intercombination lines in the ultraviolet
    spectra of astrophysical sources
Authors: Keenan, F. P.; Ahmed, S.; Brage, T.; Doyle, J. G.; Espey,
   B. R.; Exter, K. M.; Hibbert, A.; Keenan, M. T. C.; Madjarska, M. S.;
   Mathioudakis, M.; Pollacco, D. L.
2002MNRAS.337..901K    Altcode:
  New electron density diagnostic line ratios are presented for
  the OIV 2s<SUP>2</SUP>2p <SUP>2</SUP>P-2s2p<SUP>24</SUP>P and SIV
  3s<SUP>2</SUP>3p <SUP>2</SUP>P-3s3p<SUP>24</SUP>P intercombination
  lines around 1400Å. A comparison of these with observational data
  for the symbiotic star RR Telescopii (RR Tel), obtained with the
  Space Telescope Imaging Spectrograph (STIS), reveals generally
  very good agreement between theory and observation. However the
  SIV<SUP>2</SUP>P<SUB>3/2</SUB>-<SUP>4</SUP>P<SUB>1/2</SUB> transition
  at 1423.824Å is found to be blended with an unknown feature at
  1423.774Å. The linewidth for the latter indicates that the feature
  arises from a species with a large ionization potential. In addition,
  the SIV<SUP>2</SUP>P<SUB>1/2</SUB>-<SUP>4</SUP>P<SUB>3/2</SUB>
  transition at 1398.044Å is identified for the first time (to
  our knowledge) in an astrophysical source other than the Sun,
  and an improved wavelength of 1397.166 Å is measured for the
  OIV<SUP>2</SUP>P<SUB>1/2</SUB>-<SUP>4</SUP>P<SUB>3/2</SUB> line. The
  OIV and SIV line ratios in a sunspot plume spectrum, obtained with
  the Solar Ultraviolet Measurements of the Emitted Radiation (SUMER)
  instrument on the Solar and Heliospheric Observatory, are found to be
  consistent, and remove discrepancies noted in previous comparisons of
  these two ions.

---------------------------------------------------------
Title: An observational study of a magneto-acoustic wave in the
    solar corona
Authors: Williams, D. R.; Mathioudakis, M.; Gallagher, P. T.; Phillips,
   K. J. H.; McAteer, R. T. J.; Keenan, F. P.; Rudawy, P.; Katsiyannis,
   A. C.
2002MNRAS.336..747W    Altcode:
  The Solar Eclipse Corona Imaging System (SECIS) observed a strong 6-s
  oscillation in an active region coronal loop, during the 1999 August 11
  total solar eclipse. In the present paper we show that this oscillation
  is associated with a fast-mode magneto-acoustic wave that travels
  through the loop apex with a velocity of 2100 km s<SUP>-1</SUP>. We use
  near-simultaneous SOHO observations to calculate the parameters of the
  loop and its surroundings such as density, temperature and their spatial
  variation. We find that the temporal evolution of the intensity is in
  agreement with the model of an impulsively generated, fast-mode wave.

---------------------------------------------------------
Title: Detections of high-frequency oscillations in solar active
    region coronal loops
Authors: Katsiyannis, Athanassios C.; Williams, David R.; McAteer,
   R. T. James; Gallagher, Peter T.; Mathioudakis, Mihalis; Keenan,
   Francis P.
2002ESASP.505..441K    Altcode: 2002IAUCo.188..441K; 2002solm.conf..441K
  One of the mechanisms proposed as a possible solution to the
  Sun's coronal heating problem is the damping of energy carried by
  magnetohydrodynamic (MHD) waves that are expected to be present
  in active regions. Continuing previous work on total solar eclipse
  data, we provide further obervational evidence for the existence of
  high-frequency MHD waves in coronal loops. Wavelet analysis is used to
  identify 21 areas of 4×4 arcsec<SUP>2</SUP> with periodic intensity
  oscillations. The frequency range of these detections was 0.2-0.3 Hz
  and all last for at least 3 periods at a confidence level of more than
  99%. All of the above detections are made just outside known coronal
  loops, leading us to suggest a possible, unconventional mechanism.

---------------------------------------------------------
Title: Detection of propagating waves throughout the chromosphere
    in network bright points
Authors: McAteer, R. T. James; Gallagher, Peter T.; Williams, David
   R.; Mathioudakis, Mihalis; Phillips, Kenneth J. H.; Keenan, Francis P.
2002ESASP.505..305M    Altcode: 2002IAUCo.188..305M; 2002solm.conf..305M
  We analysed oscillations in individual Network Bright Points (NBPs)
  in Ca II K<SUB>3</SUB>, Hα core, Mg I b<SUB>2</SUB>, and Mg I
  b<SUB>1</SUB>-0.4 Å giving us a range of heights from the upper
  to the lower chromosphere. Lightcurves, and hence power spectra,
  were created by isolating distinct regions of the NBP via a simple
  intensity thresholding technique. Using this technique, it was
  possible to identify peaks in the power spectra with particular spatial
  positions within the NBPs. This was extended into the time domain by
  means of wavelet analysis. We track the temporal evolution of power
  in particular frequency bands by creating power curves. These are
  then cross-correlated across all observed wavelengths to search for
  propagating waves. In particular, long-period waves with periods of
  4-15 minutes (1-4 mHz) were found in the central portion of each NBP,
  indicating that these waves are certainly not acoustic, but possibly
  due to magneto-acoustic or magneto-gravity wave modes. We note the
  possible existence of fast-mode MHD waves in the lower chromosphere,
  coupling and transferring power top higher-frequency slow-mode MHD
  waves in the upper chromosphere.

---------------------------------------------------------
Title: Observations of a high-frequency, fast-mode wave in a
    coronal loop
Authors: Williams, David R.; Mathioudakis, Mihalis; Gallagher, Peter
   T.; Phillips, Kenneth J. H.; McAteer, R. T. James; Keenan, Francis P.;
   Katsiyannis, Athanassios C.
2002ESASP.505..615W    Altcode: 2002IAUCo.188..615W; 2002solm.conf..615W
  The high-cadence Solar Eclipse Corona Imaging System (SECIS) observed
  a strong 6-second oscillation in an active region coronal loop, during
  the 1999 August 11 total solar eclipse. In the present paper we show
  that this oscillation is associated with a fast-mode wave that travels
  through the loop apex with a velocity of ~2000 km s<SUP>-1</SUP>. We
  use near-simultaneous SoHO/CDS obervations to calculate the parameters
  of the loop and its surroundings such as density, temperature and their
  spatial variation. We also calculate radiative losses from the loop in
  the temperature range 10<SUP>5.8</SUP> - 10<SUP>6.4</SUP>K, and compare
  these losses with the wave energy density. Although the wave travels a
  distance greater than λ/4π and therefore meets a necessary criterion
  for slow dissipation, the dissipation length is well in excess of the
  loop length. The temporal evolution of the intensity is found to be
  in agreement with the model of an impulsively generated, fast-mode wave.

---------------------------------------------------------
Title: Opacity in the upper atmosphere of AU Mic
Authors: Bloomfield, D. S.; Mathioudakis, M.; Christian, D. J.;
   Keenan, F. P.; Linsky, J. L.
2002A&A...390..219B    Altcode:
  In this paper we investigate the validity of the optically thin
  assumption in the transition region of the late-type star AU Mic. We use
  Far-Ultraviolet Spectroscopic Explorer (FUSE) observations of the C Iii
  multiplet and O Vi resonance lines, hence yielding information at two
  different levels within the atmosphere. Significant deviations from the
  optically thin fluxes are found for C Iii in both quiescent and flare
  spectra, where only 60% of the flux is actually observed. This could
  explain the apparent deviation of C Iii observed in emission measure
  distributions. We utilize escape probabilities for both homogeneous and
  inhomogeneous geometries and calculate optical depths as high as 10 for
  the C Iii 1175.71 Åcomponent of the multiplet. Using a lower limit
  to the electron density (10<SUP>11</SUP> cm<SUP>-3</SUP>) we derive
  an effective thickness of &lt;100 km for the scattering layer. The
  emission originates from very small and compact regions, consistent
  with a filling factor of 10<SUP>-5</SUP> derived for the flare plasma.

---------------------------------------------------------
Title: EUVE J2244-15.9: A New Spectroscopic Binary
Authors: Christian, Damian J.; Mathioudakis, Mihalis; Vennes, Stephane
2002IBVS.5281....1C    Altcode:
  We report the detection of a new late-type spectroscopic binary, EUVE
  J224415.9 (HD 215341) using the 0.6 meter Coude auxiliary telescope
  and Hamilton echelle spectrograph at Lick observatory.

---------------------------------------------------------
Title: High-Resolution Optical Observations of
    Extreme-Ultraviolet-selected Active Late-type Stars
Authors: Christian, Damian J.; Mathioudakis, Mihalis
2002AJ....123.2796C    Altcode:
  We present high-resolution optical spectra of EUV-selected late-type
  stars. We have detected seven new spectroscopic binaries, including
  a pair of F stars and an RS Canum Venaticorum candidate. Many of the
  stars in our sample show remarkable Hα emission with equivalent widths
  up to 8 Å. Several sources show strong He I 5876 Å emission. We use
  cross-correlation techniques to estimate line-of-sight rotational
  velocities and find that they range from less than 5 to over 80 km
  s<SUP>-1</SUP>. Several of the stars show a strong Li 6707 Å line,
  which we use to determine their Li abundances. The EUV-to-bolometric
  luminosity, a measure of the coronal heating efficiency, is as high as
  10<SUP>-3</SUP>. The present sample extends the EUV-selected late-type
  stars to lower Rossby numbers and makes the coronal saturation boundary
  better pronounced. Our results indicate that there is a drop in the
  EUV emission from the corona in late M dwarfs possibly because of a
  change in the nature of the magnetic dynamo in fully convective stars.

---------------------------------------------------------
Title: Long-Period Chromospheric Oscillations in Network Bright Points
Authors: McAteer, R. T. James; Gallagher, Peter T.; Williams, David
   R.; Mathioudakis, Mihalis; Phillips, Kenneth J. H.; Keenan, Francis P.
2002ApJ...567L.165M    Altcode:
  The spatial variation of chromospheric oscillations in network bright
  points (NBPs) is studied using high-resolution observations in Ca II
  K3. Light curves and hence power spectra were created by isolating
  distinct regions of the NBP via a simple intensity thresholding
  technique. Using this technique, it was possible to identify peaks in
  the power spectra with particular spatial positions within the NBPs. In
  particular, long-period waves with periods of 4-15 minutes (1-4 mHz)
  were found in the central portions of each NBP, indicating that these
  waves are certainly not acoustic but possibly due to magnetoacoustic
  or magnetogravity wave modes. We also show that spatially averaged
  or low spatial resolution power spectra can lead to an inability to
  detect such long-period waves.

---------------------------------------------------------
Title: A Comparison of Theoretical mg vi Emission Line Strengths
    with Active-Region Observations From Serts
Authors: Keenan, F. P.; Mathioudakis, M.; Katsiyannis, A. C.;
   Ramsbottom, C. A.; Bell, K. L.; Thomas, R. J.; Brosius, J. W.
2002SoPh..205..265K    Altcode:
  R-matrix calculations of electron impact excitation
  rates in N-like Mg vi are used to derive theoretical
  electron-density-sensitive emission line ratios involving
  2s<SUP>2</SUP>2p<SUP>3</SUP>−2s2p<SUP>4</SUP>transitions in
  the 269-403 Å wavelength range. A comparison of these with
  observations of a solar active region, obtained during the
  1989 flight of the Solar EUV Rocket Telescope and Spectrograph
  (SERTS), reveals good agreement between theory and observation for the
  2s<SUP>2</SUP>2p<SUP>3</SUP><SUP>4</SUP>S−2s2p<SUP>4</SUP><SUP>4</SUP>Ptransitions
  at 399.28, 400.67, and 403.30 Å, and the
  2s<SUP>2</SUP>2p<SUP>3</SUP><SUP>2</SUP>P−2s2p<SUP>4</SUP><SUP>2</SUP>Dlines
  at 387.77 and 387.97 Å. However, intensities for the other lines
  attributed to Mg vi in this spectrum by various authors do not match the
  present theoretical predictions. We argue that these discrepancies are
  not due to errors in the adopted atomic data, as previously suggested,
  but rather to observational uncertainties or mis-identifications. Some
  of the features previously identified as Mg vi lines in the SERTS
  spectrum, such as 291.36 and 293.15 Å, are judged to be noise, while
  others (including 349.16 Å) appear to be blended.

---------------------------------------------------------
Title: A search for supersaturation in stellar chromospheres
Authors: Mathioudakis, Mihalis; Christian, Damian
2002noao.prop..225M    Altcode:
  The rotation-activity relations of late-type stars exhibit the effects
  of saturation in the chromospheric and coronal emission. Recent
  X-ray observations have shown that ultra fast rotators (vsini &gt;
  30 km sec^-1) show a decline in their coronal emission. This effect
  is called super-saturation. Theoretical models predict that as the
  increased rotational velocity decreases the apparent surface gravity,
  the hot coronal plasma becomes unstable and cools down to chromospheric
  temperatures. More cool loops emitting in chromospheric lines can exist
  but not in X-rays. We propose to observe the chromospheric lines of
  Ca II H&amp; K and hydrogen Balmer, in a group of EUV/X-ray selected
  active late-type stars. The rotational periods of these objects are
  in excess of 10 km s^-1. The requested observations will allow us to
  test the model predictions.

---------------------------------------------------------
Title: Solar coronal observations at high frequencies
Authors: Katsiyannis, A. C.; Mathioudakis, M.; Phillips, K. J. H.;
   Williams, D. R.; Keenan, F. P.
2001astro.ph.11447K    Altcode:
  The Solar Eclipse Coronal Imaging System (SECIS) is a simple and
  extremely fast, high-resolution imaging instrument designed for studies
  of the solar corona. Light from the corona (during, for example,
  a total solar eclipse) is reflected off a heliostat and passes via
  a Schmidt-Cassegrain telescope and beam splitter to two CCD cameras
  capable of imaging at 60 frames a second. The cameras are attached via
  SCSI connections to a purpose-built PC that acts as the data acquisition
  and storage system. Each optical channel has a different filter allowing
  observations of the same events in both white light and in the green
  line (Fe XIV at 5303 A). Wavelet analysis of the stabilized images
  has revealed high frequency oscillations which may make a significant
  contribution on the coronal heating process. In this presentation we
  give an outline of the instrument and its future development.

---------------------------------------------------------
Title: Electron Densities in the Coronae of the Sun and Procyon from
    Extreme-Ultraviolet Emission Line Ratios in Fe XI
Authors: Pinfield, D. J.; Keenan, F. P.; Mathioudakis, M.; Widing,
   K. G.; Gallagher, P. T.; Gupta, G. P.; Tayal, S. S.; Thomas, R. J.;
   Brosius, J. W.
2001ApJ...562..566P    Altcode:
  New R-matrix calculations of electron impact excitation rates for Fe
  XI are used to determine theoretical emission line ratios applicable
  to solar and stellar coronal observations. These are subsequently
  compared to solar spectra of the quiet Sun and an active region made
  by the Solar EUV Rocket Telescope and Spectrograph (SERTS-95), as well
  as Skylab observations of two flares. Line blending is identified,
  and electron densities of 10<SUP>9.3</SUP>, 10<SUP>9.7</SUP>,
  &gt;=10<SUP>10.8</SUP>, and &gt;=10<SUP>11.3</SUP> cm<SUP>-3</SUP>
  are found for the quiet Sun, active region, and the two flares,
  respectively. Observations of the F5 IV-V star Procyon, made with
  the Extreme Ultraviolet Explorer (EUVE) satellite, are compared and
  contrasted with the solar observations. It is confirmed that Procyon's
  average coronal conditions are very similar to those seen in the quiet
  Sun, with N<SUB>e</SUB>=10<SUP>9.4</SUP> cm<SUP>-3</SUP>. In addition,
  although the quiet Sun is the closest solar analog to Procyon, we
  conclude that Procyon's coronal temperatures are slightly hotter than
  solar. A filling factor of 25<SUP>+38</SUP><SUB>-12</SUB>% was derived
  for the corona of Procyon.

---------------------------------------------------------
Title: Extreme ultraviolet transitions of FeXXI in solar, stellar
    and laboratory spectra
Authors: Keenan, F. P.; Aggarwal, K. M.; Williams, D. R.; Mathioudakis,
   M.; Phillips, K. J. H.
2001MNRAS.326.1387K    Altcode:
  Recent &lt;b&gt;&lt;sansserif&gt;R&lt;/sansserif&gt;&lt;/b&gt;-matrix
  calculations of electron impact excitation rates for transitions
  among the 2s<SUP>2</SUP>2p<SUP>2</SUP>, 2s2p<SUP>3</SUP> and
  2p<SUP>4</SUP> levels of FeXXI are used to derive theoretical electron
  density (N<SUB>e</SUB>) sensitive emission-line ratios involving
  2s<SUP>2</SUP>2p<SUP>2</SUP>-2s2p<SUP>3</SUP> transitions in the
  ~98-146Å wavelength range. A comparison of these with observations
  from the PLT tokamak plasma, for which the electron density has been
  independently determined, reveals generally very good agreement between
  theory and experiment, and in some instances removes discrepancies
  found previously. The observed FeXXI ratios for a solar flare,
  obtained with the OSO-5 satellite, imply electron densities which are
  consistent, with discrepancies that do not exceed 0.2dex. In addition,
  the derived values of N<SUB>e</SUB> are similar to those estimated for
  the high-temperature regions of other solar flares. The good agreement
  between theory and observation, in particular for the tokamak spectra,
  provides experimental support for the accuracy of the present line-ratio
  calculations, and hence for the atomic data on which they are based.

---------------------------------------------------------
Title: High-frequency oscillations in a solar active region coronal
    loop
Authors: Williams, D. R.; Phillips, K. J. H.; Rudawy, P.; Mathioudakis,
   M.; Gallagher, P. T.; O'Shea, E.; Keenan, F. P.; Read, P.; Rompolt, B.
2001MNRAS.326..428W    Altcode:
  The Solar Eclipse Corona Imaging System (SECIS) was used to record
  high-cadence observations of the solar corona during the total solar
  eclipse of 1999 August 11. During the 2min 23.5s of totality, 6364
  images were recorded simultaneously in each of the two channels:
  a white light channel, and the Fexiv (5303Å) `green line' channel
  (T~2MK). Here we report initial results from the SECIS experiment,
  including the discovery of a 6-s intensity oscillation in an active
  region coronal loop.

---------------------------------------------------------
Title: The solar-stellar connection
Authors: Mathioudakis, M.
2001hell.confE..59M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Solar coronal observations in high frequencies
Authors: Katsiyannis, A. C.; Mathioudakis, M.; Phillips, K. J. H.;
   Williams, D. R.; Keenan, F. P.
2001hell.confE.174K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: X-ray and extreme-ultraviolet emission from the coronae
    of Capella
Authors: Phillips, K. J. H.; Mathioudakis, M.; Huenemoerder, D. P.;
   Williams, D. R.; Phillips, M. E.; Keenan, F. P.
2001MNRAS.325.1500P    Altcode:
  The primary objective of this work is the analysis and interpretation
  of coronal observations of Capella obtained in 1999 September
  with the High Energy Transmission Grating Spectrometer on the
  Chandra X-ray Observatory and the Extreme Ultraviolet Explorer
  (EUVE). He-like lines of O (Ovii) are used to derive a density of
  1.7×10<SUP>10</SUP>cm<SUP>-3</SUP> for the coronae of the binary,
  consistent with the upper limits derived from Fexxi, Neix and Mgxi
  line ratios. Previous estimates of the electron density based on Fexxi
  should be considered as upper limits. We construct emission measure
  distributions and compare the theoretical and observed spectra to
  conclude that the coronal material has a temperature distribution
  that peaks around 4-6MK, implying that the coronae of Capella were
  significantly cooler than in the previous years. In addition, we
  present an extended line list with over 100 features in the 5-24Å
  wavelength range, and find that the X-ray spectrum is very similar to
  that of a solar flare observed with SMM. The observed to theoretical
  Fexvii 15.012-Å line intensity reveals that opacity has no significant
  effect on the line flux. We derive an upper limit to the optical depth,
  which we combine with the electron density to derive an upper limit of
  3000km for the size of the Fexvii emitting region. In the same context,
  we use the Siiv transition region lines of Capella from HST/Goddard
  High-Resolution Spectrometer observations to show that opacity can be
  significant at T=10<SUP>5</SUP>K, and derive a path-length of ~75km
  for the transition region. Both the coronal and transition region
  observations are consistent with very small emitting regions, which
  could be explained by small loops over the stellar surfaces.

---------------------------------------------------------
Title: Opacity Effects in the Transition Region of Active Stars
(CD-ROM Directory: contribs/williams)
Authors: Williams, D. R.; Mathioudakis, M.; McKenny, J.; Keenan, F. P.
2001ASPC..223..889W    Altcode: 2001csss...11..889W
  No abstract at ADS

---------------------------------------------------------
Title: Coordinated Optical, Radio and EUV Observations of a Flare
on YZ CMi (CD-ROM Directory: contribs/robinson)
Authors: Robinson, R. D.; Airapetian, V.; Slee, O. B.; Mathioudakis,
   M.; Carpenter, K. G.
2001ASPC..223.1151R    Altcode: 2001csss...11.1151R
  No abstract at ADS

---------------------------------------------------------
Title: S xi Emission Lines in Active Region Spectra Obtained with
    the Solar euv Rocket Telescope and Spectrograph (Serts)
Authors: Keenan, F. P.; Pinfield, D. J.; Mathioudakis, M.; Aggarwal,
   K. M.; Thomas, R. J.; Brosius, J. W.
2000SoPh..197..253K    Altcode:
  Theoretical electron density sensitive emission line ratios involving
  a total of eleven 2s<SUP>2</SUP>2p<SUP>2</SUP>-2s2p<SUP>3</SUP>
  transitions in S xi between 187 and 292 Å are presented. A
  comparison of these with solar active region observations obtained
  during rocket flights by the Solar EUV Rocket Telescope and
  Spectrograph (SERTS) reveals generally good agreement between
  theory and experiment. However, the 186.87 Å line is masked by
  fairly strong Fe xii emission at the same wavelength, while 239.83
  Å is blended with an unknown feature, and 285.58 Å is blended with
  possibly N iv 285.56 Å. In addition, the 191.23 Å line appears to
  be more seriously blended with an Fe xiii feature than previously
  believed. The presence of several new S xi lines is confirmed in the
  SERTS spectra, at wavelengths of 188.66, 247.14 and 291.59 Å, in
  excellent agreement with laboratory measurements. In particular, the
  detection of the 2s<SUP>2</SUP>2p<SUP>2</SUP><SUP>3</SUP>P<SUB>1</SUB>
  -2s2p<SUP>3</SUP><SUP>3</SUP>P<SUB>0,1</SUB> transitions at 242.91
  Å is the first time (to our knowledge) that this feature has been
  identified in the solar spectrum. The potential usefulness of the S xi
  line ratios as electron density diagnostics for the solar transition
  region and corona is briefly discussed.

---------------------------------------------------------
Title: Extreme-Ultraviolet Flares in an F2 Star
Authors: Mullan, D. J.; Mathioudakis, M.
2000ApJ...544..475M    Altcode:
  We report on the coronal properties of two early F dwarfs. For
  both stars, spectroscopic data reveal a hot corona with material at
  temperatures as high as 10<SUP>7.1</SUP>-10<SUP>7.2</SUP> K. The EUV
  photometric observations of one of the stars (HR 120: F2) reveal two
  large flares with rapid decay times. The rapid decays are in striking
  contrast with previously published slowly decaying flares on a late
  type F star (HR 1817: F8/9). Analysis of decay times suggests that the
  loop sizes which flared in the F2 star are significantly shorter than
  those which flared in the F8/9 star. We discuss these results in the
  context of a proposal made by Giampapa &amp; Rosner.

---------------------------------------------------------
Title: The Radial and Angular Variation of Electron Density in the
    Solar Corona.
Authors: Gallagher, P. T.; Mathioudakis, M.; Phillips, K. J. H.;
   Tsinganos, K.; Keenan, F. P.
2000SPD....31.0234G    Altcode: 2000BAAS...32.1290G
  We derive, for the first time, electron densities as a function of
  both radius (R) and position angle (θ ) for the south-west quadrant of
  the off-limb corona, using the density-sensitive Si ix (349.9 Å/341.9
  Å) and Si x (356.0 Å/347.7 Å) extreme ultraviolet line ratios. The
  observations were made with the Coronal Diagnostic Spectrometer (cds)
  on board the Solar and Heliospheric Observatory (soho), over the range
  1.00R<SUB>⊙ </SUB> &lt; R &lt; 1.20R<SUB>⊙ </SUB> and 180° &lt;
  θ &lt; 270° . Within the south polar coronal hole, the density varies
  from 2.3 x 10<SUP>8</SUP> cm<SUP>-3</SUP> at 1.0R<SUB>⊙ </SUB> to 8.3x
  10<SUP>7</SUP> cm<SUP>-3</SUP> at 1.20R<SUB>⊙ </SUB>, while at the
  equator the density varies from 6.3 x 10<SUP>8</SUP> cm<SUP>-3</SUP>
  at 1.0R<SUB>⊙ </SUB> to 1.6x 10<SUP>8</SUP> cm<SUP>-3</SUP> at
  1.20R<SUB>⊙ </SUB>. The density falloff with height is therefore
  faster in the equatorial region. We also find that electron densities
  are, on average, a factor of 2.7 larger in the equatorial regions than
  in the polar coronal hole at a given radial distance. Finally, we find
  remarkable agreement between our measured densities as a function of
  radius and position angle and those predicted by a recent analytic
  MHD model of the solar wind, strongly supporting its basic premises.

---------------------------------------------------------
Title: Is Lithium produced in active stellar atmospheres?
Authors: Christian, Damian J.; Mathioudakis, Mihalis
2000noao.prop..165C    Altcode:
  Current mixing models predict that fast rotation leads to increased
  Li depletion in late-type stars. This is in sharp contrast with
  observations of stellar clusters where the largest Li abundances are
  found in the most active stars. One of the key assumptions in these
  models is that Li can not be produced on the stellar surface and its
  abundance will decrease as a function of time. The present proposal will
  investigate whether the unusually high Li abundance of very active flare
  stars, could be attributed to spallation reactions. Lithium production
  by particle induced spallation reactions will produce an isotope ratio
  of ^7Li/^6Li ~ 2. This isotope ratio will create a clear asymmetry in
  the red wing of the Li I 6707.8Aline profile. This asymmetry combined
  with any temporal variation of the Li equivalent width, will provide
  the observational signatures required to test the spallation theory.

---------------------------------------------------------
Title: Multi-wavelength observations of the 1998 September 27
    flare spray
Authors: Gallagher, Peter T.; Williams, David R.; Phillips, Kenneth
   J. H.; Mathioudakis, Mihalis; Smartt, Raymond N.; Keenan, Francis P.
2000SoPh..195..367G    Altcode:
  We report on observations of a large eruptive event associated with a
  flare that occurred on 27 September 1998 made with the Richard B. Dunn
  Solar Telescope at Sacramento Peak Observatory (several wave bands
  including off-line-center Hα), in soft and hard X-rays (GOES and
  BATSE), and in several TRACE wave bands (including Fe ix/x 171 Å,
  Fe xii 195 Å, and C iv 1550 Å). The flare initiation is signaled by
  two Hα foot-point brightenings which are closely followed by a hard
  X-ray burst and a subsequent gradual increase in other wavelengths. The
  flare light curves show a complicated, three-component structure which
  includes two minor maxima before the main GOES class C5.2 peak after
  which there is a characteristic exponential decline. During the initial
  stages, a large spray event is observed within seconds of the hard
  X-ray burst which can be directly associated with a two-ribbon flare
  in Hα. The emission returns to pre-flare levels after about 35 min,
  by which time a set of bright post-flare loops have begun to form at
  temperatures of about 1.0-1.5 MK. Part of the flare plasma also intrudes
  into the penumbra of a large sunspot, generally a characteristic of
  very powerful flares, but the flare importance in GOES soft X-rays is in
  fact relatively modest. Much of the energy appears to be in the form of
  a second ejection which is observed in optical and ultraviolet bands,
  traveling out via several magnetic flux tubes from the main flare site
  (about 60° from Sun center) to beyond the limb.

---------------------------------------------------------
Title: Rotational modulation and flares on RS CVn and BY Dra
    stars. XX. Photometry and spectroscopy of CC Eri in late 1989
Authors: Amado, P. J.; Doyle, J. G.; Byrne, P. B.; Cutispoto, G.;
   Kilkenny, D.; Mathioudakis, M.; Neff, J. E.
2000A&A...359..159A    Altcode:
  The active flaring binary CC Eri was studied via multi-wavelength
  observations involving multi-based photometry and ground- and
  space-based spectroscopy. Combining early spectroscopic data with
  the present implies an orbital period of P=1.5615 days. Furthermore,
  the spectroscopic data suggests spectral types of K7 and M3 for the
  system. The optical photometry indicated a small spot coverage in
  late 1989, consistent with data taken a year later which showed CC Eri
  entering its brightest-to-date phase. Two flares were detected in the
  ultraviolet spectral data. These flares radiated 2.7 10<SUP>31</SUP>
  erg and 1.6 10<SUP>31</SUP> erg in the C Iv line alone, each with a
  total estimated radiative energy budget of ~ 10<SUP>36</SUP> erg. For
  the higher-temperature lines, such as C Iv, there was no systematic
  variability with phase. The lower-temperature lines show a slight
  indication of rotational modulation. However, there is a much larger
  scatter in the individual measurements of the Mg Ii and C Iv fluxes
  than would be expected from measurement errors alone, consistent with
  an atmosphere showing continual small-scale activity.

---------------------------------------------------------
Title: Transition region and coronal structuring
Authors: O'Shea, E.; Gallagher, P. T.; Mathioudakis, M.; Phillips,
   K. J. H.; Keenan, F. P.; Katsiyannis, A. C.
2000A&A...358..741O    Altcode:
  In this paper we examine regions of internetwork, network and bright
  network emission, observed in the quiet Sun with the Coronal Diagnostic
  Spectrometer (cds) onboard SoHO. The slopes of the emission measure
  distributions, between 5.4 &lt;= log T<SUB>e</SUB> &lt;= 6.0, are
  found to differ in each region, suggesting the presence of different
  atmospheric structures. From an analysis of emission area the network
  is shown to have two populations of structures, a low transition region
  group and a coronal group. Using mdi magnetograms the bright network
  emission is shown to originate from regions of strong magnetic field
  composed of bipolar loops and unipolar funnels, that extend from the
  low transition region up to the corona. Up to 30% of all radiative
  losses between 5.7 &lt;= log T<SUB>e</SUB> &lt;= 6.3 are found to come
  from these continuous bright network structures. Cross-sectional areas
  calculated from redshift values suggest that the area expansion seen
  in the bright network emission is the result of flux tube expansion
  into the corona, accompanied by either a downflow or upflow of material.

---------------------------------------------------------
Title: Identification of the [Al II] Forbidden Line at 2661 Å in
    the Spectrum of RR Telescopii
Authors: Crawford, F. L.; Keenan, F. P.; Mathioudakis, M.; Aggarwal,
   K. M.; McKenna, F. C.; Feibelman, W. A.; Espey, B. R.
2000ASPC..204..387C    Altcode: 2000tiaf.conf..387C
  No abstract at ADS

---------------------------------------------------------
Title: Evidence for Non-Maxwellian Electron Energy Distributions in
the Solar Transition Region: Si III Line Ratios from SUMER
Authors: Pinfield, D. J.; Keenan, F. P.; Mathioudakis, M.; Phillips,
   K. J. H.; Curdt, W.; Wilhelm, K.
1999ApJ...527.1000P    Altcode:
  Recent calculations of Si III emission-line strengths are compared with
  SUMER observations from a quiet solar region, a coronal hole, and an
  active region. Diagnostic line ratios are used to derive T<SUB>e</SUB>
  and N<SUB>e</SUB> for the emitting plasma in each region, and good
  agreement between theory and observations is found. A major enhancement
  in the intensity of the 1313 Å emission line is observed, as well
  as some evidence of a small decrease in the temperature of maximum
  ionization fraction, as one moves from the coronal hole to the active
  region. Possible explanations for these effects are discussed, and
  it is concluded that they may be caused by the presence of nonthermal
  electrons in the transition region.

---------------------------------------------------------
Title: The effects of opacity in the transition region of YZ CMi
Authors: Mathioudakis, M.; McKenny, J.; Keenan, F. P.; Williams,
   D. R.; Phillips, K. J. H.
1999A&A...351L..23M    Altcode:
  It has generally been assumed that the emission from the upper
  atmosphere of late-type stars is optically thin. In the present paper we
  use the Si IV and C IV resonance lines to investigate this assumption
  for the active dMe star YZ CMi. The significant deviations of the line
  ratios from their optically thin values, demonstrate that opacity can
  be quite important particularly in the case of stellar flares. These
  deviations are combined with a method of escape probabilities to
  derive optical depths of approximately unity for the lines under
  consideration. We demonstrate that, if the electron density in the
  atmosphere is known, opacity can provide important information on the
  linear dimensions of the scattering layer. Using this technique, we
  have estimated path lengths of a few kilometers for one of the flares
  under consideration. Based on observations made with the NASA/ESA Hubble
  Space Telescope, obtained from the data archive at the Space Telescope
  Science Institute. STScI is operated by the Association of Universities
  for Research in Astronomy, Inc. under NASA contract NAS 5-26555.

---------------------------------------------------------
Title: A New Study of the Quiet Sun
Authors: O'Shea, E.; Gallagher, P. T.; Mathioudakis, M.; Phillips,
   K. J. H.; Keenan, F. P.
1999ESASP.446..519O    Altcode: 1999soho....8..519O
  In this paper we present results of an emission measure analysis
  performed on regions of cell, network and bright network emission
  which were observed in the quiet Sun at Sun centre with the Coronal
  Diagnostic Spectrometer (CDS) on board SOHO. Seperate emission from
  the three regions was obtained by a method of image segmentation
  using a histogram modification technique. From the averaged emission
  it was possible to produce emission measures over a broad temperature
  range. These emission measures were then used to produce estimates of
  radiative and conductive losses in the three regions considered. Using
  a magnetogram obtained from the MDI instrument on SOHO we show that
  the bright network emission originates from bipolar magnetic loops
  and from what appear to be monopole regions, which could be the
  remains of footpoints of larger loops. The bright network emission
  shows significantly higher mean magnetic field strength as well as
  significantly larger radiative energy losses than either of the other
  two regions. We find some evidence suggesting the presence of cool
  loops. The process of image segmentation also enabled us to obtain
  the relative areas of the cell, network and bright network emission
  as a function of temperature. We found that only the bright network
  emission showed an expansion in area with temperature and therefore
  height. Fitting this area curve with the functional form suggested
  by Rabin (1991),i.e A(T)/A(T<SUB>h</SUB>) = [1 + (Gamma<SUP>2</SUP>
  - 1)(T/T<SUB>h</SUB>)<SUP>nu</SUP>]<SUP>1/2</SUP>/Gamma , for the
  cross-sectional area of a flux tube, we obtain a value of Gamma=7.1
  and nu=2.5 for the constriction and shape factors respectively.

---------------------------------------------------------
Title: The Radial and Angular Variation of the Electron Density in
    the Solar Corona
Authors: Gallagher, P. T.; Mathioudakis, M.; Keenan, F. P.; Phillips,
   K. J. H.; Tsinganos, K.
1999ApJ...524L.133G    Altcode:
  We derive, for the first time, electron densities as a function
  of both radius (R) and position angle (θ) for the southwest
  quadrant of the off-limb corona, using the density-sensitive Si IX
  λ349.9/λ341.9 and Si X λ356.0/λ347.7 extreme-ultraviolet line
  ratios. The observations were made with the coronal diagnostic
  spectrometer on board the Solar and Heliospheric Observatory over
  the ranges of 1.00 R<SUB>solar</SUB>&lt;R&lt;1.20 R<SUB>solar</SUB>
  and 180<SUP>deg</SUP>&lt;θ&lt;270<SUP>deg</SUP>. Within the south
  polar coronal hole, the density varies from 2.3×10<SUP>8</SUP>
  cm<SUP>-3</SUP> at 1.0 R<SUB>solar</SUB> to 8.3×10<SUP>7</SUP>
  cm<SUP>-3</SUP> at 1.20 R<SUB>solar</SUB>, while at the equator,
  the density varies from 6.3×10<SUP>8</SUP> cm<SUP>-3</SUP> at 1.0
  R<SUB>solar</SUB> to 1.6×10<SUP>8</SUP> cm<SUP>-3</SUP> at 1.20
  R<SUB>solar</SUB>. The density falloff with height is therefore faster
  in the equatorial region. We also find that electron densities are,
  on average, a factor of 2.7 larger in the equatorial regions than in
  the polar coronal hole at a given radial distance. Finally, we find
  remarkable agreement between our measured densities as a function of
  radius and position angle and those predicted by a recent analytic
  MHD model of the solar wind, strongly supporting its basic premises.

---------------------------------------------------------
Title: [Alii] in the ultraviolet spectrum of the symbiotic star
    RR Telescopii
Authors: Keenan, F. P.; Espey, B. R.; Mathioudakis, M.; Aggarwal,
   K. M.; Crawford, F. L.; Feibelman, W. A.; McKenna, F. C.
1999MNRAS.309..195K    Altcode:
  An inspection of a GHRS/HST spectrum of the symbiotic star RR Telescopii
  reveals the presence of the [Alii] 3s^2 ^1S - 3s3p ^3P_2 line at a
  vacuum wavelength of 2661.06+/-0.08Å, 8.89+/-0.08Å away from the Alii]
  3s^2 ^1S - 3s3p ^3P_1 intercombination transition at 2669.95Å, in good
  agreement with the theoretical prediction of Δλ=8.80Å. We also find
  that the Alii] line profile is asymmetric, showing a strong low-density
  component with a weak high-density wing, redshifted by 30kms^-1, in
  agreement with the findings of Schild &amp; Schmid, which were based
  on optical observations. Our measurement of the emission-line ratio
  RI(2661.06Å)/I(2669.95Å)=0.027+/-0.003 implies logN_e=5.8+/-0.2,
  in good agreement with the densities found from other ions, such as
  Siiii. These results provide strong evidence that we have detected the
  [Alii] line, the first time (to our knowledge) that this feature has
  been reliably identified in an astrophysical or laboratory spectrum.

---------------------------------------------------------
Title: HR 1099 - A multi-wavelength study of a short period RS
    CVn binary
Authors: Mathioudakis, Mihalis; Christian, Damian; Keenan, Francis
1999noao.prop...50M    Altcode:
  The launch of AXAF in the summer of 1999 will open a new era in the
  study of stellar coronae. The active RS CVn binary HR 1099 is one of
  the AXAF primary calibration targets that will be observed in the
  first 3-4 months of the mission. We propose to carry out a ground
  based spectroscopic study of HR 1099. With the combination of optical
  and X- ray observations we will be able to : (i) Study the effects
  of rotational modulation in photospheric (TiO bands), chromospheric
  (H(alpha), Ca II H&amp; K) and coronal lines (e.g. Fe XVII) (ii)
  Carry out a near simultaneous estimate of photospheric and coronal
  abundances (iii) Investigate whether the absorption features that
  cross the H(alpha) profile are due to cool hydrogen prominences or mass
  transfer between the components of the binary. The requested observing
  time will allow us to cover ~ 3 rotational revolutions with an ~ 80%
  phase coverage.

---------------------------------------------------------
Title: Electron temperature diagnostics for the quiet Sun using SI
    BT IV lines
Authors: Ahmed, S.; Pinfield, D. J.; Mathioudakis, M.; Keenan, F. P.;
   Phillips, K. J. H.; Curdt, W.
1999A&A...346L..69A    Altcode:
  We compare SUMER observations of six Si riptsize IV emission lines
  detected at the quiet Sun disk centre with recent theoretical line ratio
  calculations. Good agreement is found between theory and observation
  for ratios involving the 1394, 1403 and 818 Ä line intensities. This
  agreement supports the theoretical prediction that the temperature
  where Si riptsize IV has its maximum ionisation fraction in ionisation
  equilibrium is T_max =~ 10(4.8) K, as well as showing that Lyman
  continuum absorption does not significantly effect line intensities
  for transitions with wavelengths below 912 Ä. We find that the 815,
  1122 and 1128 Ä lines are blended by approximately 30, 55 and 45%,
  respectively, in the SUMER transitions.

---------------------------------------------------------
Title: Soft X-ray emission lines of Ni XVIII in the solar spectrum
Authors: Keenan, F. P.; Mathioudakis, M.; Pinfield, D. J.; Brown,
   W. A.; Bruner, M. E.
1999SoPh..185..289K    Altcode:
  R-matrix calculations of electron impact excitation rates in Ni xviii
  are used to derive theoretical electron-temperature-sensitive emission
  line ratios involving 3s−4p,3p−4d,3p −4s, and 3d−4f transitions
  in the 41-53 Å wavelength range. A comparison of these with solar
  flare observations from a rocket-borne X-ray spectrograph (XSST) reveals
  generally excellent agreement between theory and experiment (within the
  experimental and theoretical uncertainties), which provides support
  for the atomic data adopted in the analysis. However the 3s 2S−4p
  2P1/2 line of Ni xviii at 41.22 Å appears to be blended with the Fe
  xix 13.74 Å feature observed by XSST in third order. In addition, the
  measured Ni xviii intensity ratio I(3p 2P3/2− 4s 2S)/I(3p 2P1/2−4s
  2S)=I(51.02 Å)/I(50.26 Å)=0.56, a factor of ∼3.8 smaller than the
  theoretical (temperature and density-insensitive) value of 2.1. The
  reason for this discrepancy is currently unexplained, but is unlikely
  to be due to blending of the 50.26 Å line, as the intensity of this
  feature is consistent with that expected from the other Ni xviii lines
  in the XSST spectrum. Future observations of the Ni xviii lines by
  the Advanced X-ray Astrophysics Facility (AXAF) should allow this
  problem to be resolved, and may also permit the use of the lines as
  electron-temperature diagnostics.

---------------------------------------------------------
Title: Magnetic activity in the extreme ultraviolet.
Authors: Mathioudakis, M.
1999TJPh...23..399M    Altcode:
  The wealth of astronomical observations obtained in the extreme
  ultraviolet in recent years, have allowed comprehensive studies of the
  stellar transition regions and coronae to be carried out. For the first
  time the author has been able to resolve individual coronal lines of
  various elements formed over a large temperature range (10<SUP>5</SUP> -
  10<SUP>7.2</SUP>K). The temperature, densities, abundances and magnetic
  field strengths of the stellar coronae can now be determined. The
  author reviews some of the observations in the field of cool stars
  and discusses the implications on atmospheric heating requirements.

---------------------------------------------------------
Title: HR 1817: the EUV properties of an active F dwarf
Authors: Mathioudakis, M.; Mullan, D. J.
1999A&A...342..524M    Altcode:
  We examine the coronal properties of the active F dwarf HR
  1817. Photometric observations with EUVE show that the source is
  in a near-continuous state of flare-like activity. Using IUE and
  EUVE spectroscopic observations we construct the emission measure
  distribution in the 10(4) -10(7.2) K temperature range. These
  observations reveal a hot corona and activity levels similar to those
  of RS CVn binaries. Based on Fe XXI line ratios we derive an upper
  limit of 10(11.7) cm(-3) for the coronal density of HR 1817 and a
  magnetic field strength of B&lt;= 160 Gauss. A comparison of the EUVE
  spectroscopic observations with synthetic spectra derived from ASCA
  and ROSAT fits, shows that optimal agreement is obtained for fits with
  sub-solar metal abundances. The reduced metal abundances increase the
  radiative losses significantly at temperatures above 10(6.5) K where
  Fe is no longer the dominant radiative cooling agent.

---------------------------------------------------------
Title: Magnetic Activity and Variability in Stellar Coronae (EUV)
Authors: Mathioudakis, M.
1999ASPC..158...38M    Altcode: 1999ssa..conf...38M
  No abstract at ADS

---------------------------------------------------------
Title: The O V 1213.9 Angstroms forbidden line in the quiet Sun
Authors: Pinfield, D. J.; Mathioudakis, M.; Keenan, F. P.; Phillips,
   K. J. H.; Curdt, W.
1998A&A...340L..15P    Altcode:
  We present the first unambiguous detection of the O v 1213.9 Angstrom
  (2s(2) (1) S_0 -&gt; 2s2p (3) P_2) forbidden line in the solar spectrum,
  using observations obtained with the SUMER instrument on board SOHO. The
  wavelength separation of the forbidden to the (2s(2) (1) S_0 -&gt;
  2s2p (3) P_1) intercombination line at 1218.35 Angstroms is 4.5+/-0.1
  Angstroms in excellent agreement with theoretical predictions. The
  observed line ratio, combined with the latest calculations, allows us
  to derive an electron density of log {N_e/cm(-3}) = 8.5 +/- 0.15 for
  the quiet Sun. However, the O v 1213.9 Angstroms line was not detected
  in the HST spectra of Procyon and we can only place a lower limit of
  log {N_e/cm(-3}) &gt;= 7.8 to the electron density in this object.

---------------------------------------------------------
Title: Extreme Ultraviolet Explorer Right Angle Program Observations
    of Cool Stars
Authors: Christian, D. J.; Drake, J. J.; Mathioudakis, M.
1998AJ....115..316C    Altcode:
  The Extreme Ultraviolet Explorer (EUVE) Right Angle Program (RAP)
  obtains photometric data in four bands centered at ~100 Å (Lexan/B),
  ~200 Å (Al/Ti/C), ~400 Å (Ti/Sb/Al), and ~550 Å (Sn/SiO) during
  pointed spectroscopic observations. RAP observations are up to 20 times
  more sensitive than those in the EUVE all-sky survey. We present RAP
  observations of two dozen late-type stars: BD +03 deg301, BD +05 deg300,
  HR 1262, BD +23 deg635, BD +22 deg669, Melotte 25 VA 334, Melotte 25
  1366, Melotte 25 59, Melotte 25 65, theta^1 Tau, V834 Tau, GJ 2037,
  BD -21 deg1074, GJ 205, RE J0532-030, GJ 9287A, HT Vir, BD +46 deg1944,
  Proxima Cen, alpha Cen A/B, HR 6094, HR 8883, CPD -48 deg10901, and HR
  8964. We derive surface fluxes from the Lexan/B and Al/Ti/C count rates
  and cataloged ROSAT Position Sensitive Proportional Counter (PSPC)
  data. The EUVE surface fluxes are reasonably correlated with surface
  fluxes calculated from PSPC measurements. The time variability of the
  sources has been examined. Most of the sources show no significant
  variability at the 99% confidence level. Flares were detected from the
  K7 V star Melotte 25 VA 334, the K3 V star V834 Tau (HD 29697), and the
  K3 + K8 Hyades binary BD +22 deg669. The BD +22 deg669 count rate at
  the peak of the flare is a factor of 6 higher than the quiescent count
  rate, with a peak Lexan/B luminosity of 7.9 x 10^29 ergs s^-1. The
  V834 Tau flare was detected in both Lexan/B and Al/Ti/C bands. The
  peak luminosity of the flare is 1.6 x 10^29 and 8 x 10^28 ergs s^-1
  for Lexan/B and Al/Ti/C, respectively.

---------------------------------------------------------
Title: The Extreme Ultraviolet Explorer Stellar Spectral Atlas
Authors: Craig, N.; Abbott, M.; Finley, D.; Jessop, H.; Howell, S. B.;
   Mathioudakis, M.; Sommers, J.; Vallerga, J. V.; Malina, R. F.
1997ApJS..113..131C    Altcode:
  We present an atlas of extreme ultraviolet (EUV) spectra of 95 bright
  stellar sources observed between 1992 July and 1996 June with the
  Extreme Ultraviolet Explorer (EUVE) spectrometers. These data are
  taken in the short- (SW; 70-190 Å), medium- (MW; 140-380 Å), and
  long-wavelength bandpasses (LW; 280-760 Å) at roughly 0.5, 1, and 2
  Å resolution, respectively. We describe the spectrometers and detail
  the procedure used to reduce the observational data to spectra. The
  atlas is grouped by the type of source: O-A stars, F-M stars, white
  dwarfs, and cataclysmic variables. We present a brief overview of
  the general nature and EUV spectral distribution of each group and
  present accompanying notes and individual spectra for each source. We
  show selected F-M sources in more detail with identifications of the
  brightest spectral lines illustrating the characteristics of the EUV
  spectra of stars of various temperatures. The current study is the
  most complete compilation to date of aggregate spectra of bright EUV
  stellar sources.

---------------------------------------------------------
Title: Faint Sources in the EUVE Survey: Identification of White
    Dwarfs, Active Late-Type Stars, and Galactic Nuclei
Authors: Polomski, Elisha; Vennes, Stéphane; Thorstensen, John R.;
   Mathioudakis, Mihalis; Falco, Emilio E.
1997ApJ...486..179P    Altcode:
  We report the classification of 21 new extreme-ultraviolet sources
  from the recent catalog of Lampton et al. The optical spectra presented
  identify the objects as 14 active late-type stars (including two double
  active stars and a possible T Tauri star), three white dwarfs, and
  six active galactic nuclei (a Seyfert galaxy, the BL Lac object 1ES
  1028+511 [=EUVE J1031+508], and four quasi-stellar objects). We have
  detected Ca II absorption lines in the BL Lac object and measured its
  redshift. Two of the white dwarfs are unusually massive (M &gt; 1.1
  M<SUB>⊙</SUB>). Our sample of late-type stars includes five previously
  known high proper motion objects (EUVE J1004+503, J2244-332A,B,
  J1802+642, and J1131-346), of which one is the well-known flare star
  TX PsA (EUVE J2244-332B). We report an unusually high level of activity
  for the primary component of the TX PsA system (EUVE J2244-332A), which
  may indicate flare activity. The group of late-type stars is on average
  almost 3 mag fainter (&lt;m&gt; ~ 13) than the typical member of the
  Extreme Ultraviolet Explorer (EUVE) all-sky survey catalog. All Galactic
  and extragalactic objects were also detected in the ROSAT Position
  Sensitive Proportional Counter survey, and most are at the faint limit
  of the EUVE detectors. These new identifications substantially increase
  the total number of EUV-selected extragalactic sources.

---------------------------------------------------------
Title: Radio and extreme-ultraviolet observations of CF Tucanae
Authors: Gunn, A. G.; Migenes, V.; Doyle, J. G.; Spencer, R. E.;
   Mathioudakis, M.
1997MNRAS.287..199G    Altcode:
  We present contemporaneous EUV and radio observations obtained for
  the totally eclipsing chromospherically active RS CVn-type binary CF
  Tucanae. Observations were made with the ATNF Compact Array at 6 and
  3.6cm over one complete orbital cycle of the system, and with the EUVE
  Deep Survey/Spectrometer telescope over five orbital cycles. We obtained
  a strong detection of the source (1.9mJy at 6cm and 1.1mJy at 3.6cm)
  in the radio. Both EUV and radio flux levels appear to show a clear
  modulation at the orbital period with a maximum at phase 0.5 which
  indicates the existence of an intra-binary region of activity. This
  has important consequences for the details of coronal formation and
  field interaction in active close binary stars. We interpret the EUV
  emission as an isotropically radiating thermal source; on the other
  hand, the radio emission shows evidence of intrinsic gyromagnetic
  directivity. We also demonstrate that contemporaneous EUV and radio
  observations are not sufficient to determine the characteristics of
  the gyro-emission electron population.

---------------------------------------------------------
Title: The intrinsic LY α to H α ratio in M dwarf stars.
Authors: Doyle, J. G.; Mathioudakis, M.; Andretta, V.; Short, C. I.;
   Jelinsky, P.
1997A&A...318..835D    Altcode:
  Using Ly α line profiles generated from a grid of M
  dwarf model atmospheres we calculate the attenuation factor
  [i.e. Lyα(obs)/Lyα(intrin)] due to the interstellar medium as
  a function of hydrogen column density. Then using selected model
  atmospheres, attenuation factors were calculated for those M dwarfs with
  available Ly α observations. The prime motivation in this work has been
  to look afresh at the intrinsic Ly α to H α flux ratio, an important
  constraint in the radiative transfer modelling of M dwarfs. For those
  active dMe stars where both lines were observed, the intrinsic ratio
  is ~3-5 (with ~50% variation). The major uncertainty in this work has
  been the interstellar hydrogen column density, emphasizing the need
  for further work in this area and in particular an accurate model of
  its variation in all directions.

---------------------------------------------------------
Title: An active K0 IV-V star and a hot white dwarf (EUVE J0702+129)
    in a wide binary.
Authors: Vennes, S.; Christian, D. J.; Mathioudakis, M.; Doyle, J. G.
1997A&A...318L...9V    Altcode:
  We present far ultraviolet and optical spectroscopy of the Extreme
  Ultraviolet Explorer (EUVE) survey source EUVE J0702+129 revealing
  a composite K0 star plus DA white dwarf spectrum. The International
  Ultraviolet Explorer spectra show continuum emission from a hot white
  dwarf (Teff=30-40,000K) and a rising contribution from the K0 star
  at λ&gt;2500Å. High resolution optical spectroscopy uncovers a high
  level of activity with strong Hα and Ca H&amp;K emission; application
  of the Wilson-Bappu relation indicates that the secondary star is
  slightly above the main sequence (K0 IV-V). Both objects are found at
  a distance of ~130pc and they likely constitute a physical pair. The
  EUV emission is dominated by the white dwarf, but the late-type star
  certainly contributes at higher energy. An interesting parallel is
  drawn with other DA+K0 pairs with moderately active secondaries such
  as HD 18131 and HR 1608. The present discovery as well as other recent
  ones demonstrate the existence of a large population of white dwarfs
  hidden by evolved companions (III-IV).

---------------------------------------------------------
Title: EUV Emission from RS Canum Venaticorum binaries.
Authors: Mitrou, C. K.; Mathioudakis, M.; Doyle, J. G.; Antonopoulou,
   E.
1997A&A...317..776M    Altcode:
  We performed a study of 104 RS CVn systems in the extreme ultraviolet
  (EUV) using the all-sky survey data obtained by the Extreme Ultraviolet
  Explorer (EUVE). The present sample includes several new RS CVn
  detections; 11 more than in the published EUVE catalogs, and 8 more
  than in the ROSAT Wide Field Camera catalog. The ratio of detections to
  non-detections remained constant throughout the sky, implying that our
  detections are not limited by the exposure time but are most likely
  limited by absorption from the interstellar medium. A general trend
  of increasing Lex/B (50-180Å) flux with decreasing rotational period
  is clear. The dwarf systems exhibit a leveling-off for the faster
  rotators. In contrast, the evolved systems exhibit no such effect. For
  the RS CVn systems the losses in the EUV represent a smaller fraction
  of the coronal radiative losses, as compared to active late-type dwarfs.

---------------------------------------------------------
Title: The Stellar Astrophysical Laboratory
Authors: Mathioudakis, M.
1997eaun.book..123M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: UV and EUV observations of the active binary UX Ari
Authors: Antonopoulou, E.; Mathioudakis, M.; Ferentinos, E.
1997jena.confE.104A    Altcode:
  We present a study in the UV and EUV region of the electromagnetic
  spectrum (60-3200AA), of UX Ari, an active RS CVn--type of binary
  system. Combining the UV and EUV observations we have been able to
  cover the atmosphere from the chromosphere all the way up into the lower
  corona, ie the temperature range between 10{^4} and 10^{7.2}K. The EUV
  spectra show several hot coronal lines of highly ionized Fe, formed at
  the higher end of this range. We construct the Emission Measure (EM)
  distribution, which is then used to generate synthetic spectra. A timing
  analysis of the EUV observations, shows the existence of a distinct
  "active phase" for this system. The spectrum of the active interval,
  contains the FeXXIV line which is formed by material at temperatures
  of logT = 7.2K. This line is not present in the quiescent spectrum. We
  have also found, in this system's active spectrum, a line at 114.39AA,
  which is not mentioned in the existing lists. This unidentified line
  was also present in the EUV spectrum of HR1099, a similarly active
  system. A discussion of the errors involved in obtaining the EM
  distribution and the synthetic spectra, is also given. The dominant
  error arises from the values of the atomic parameters.

---------------------------------------------------------
Title: Coronal variability of RS CVn binaries in the EUV
Authors: Antonopoulou, E.; Ferentinos, E.; Mathioudakis, M.; Mitrou,
   C. K.
1997jena.confE.221A    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Fe X Emission Lines in Solar and Stellar Spectra
Authors: Foster, V. J.; Mathioudakis, M.; Keenan, F. P.; Drake, J. J.;
   Widing, K. G.
1996ApJ...473..560F    Altcode:
  Theoretical electron density sensitive emission line ratios involving
  Fe X 3s<SUP>2</SUP>3p<SUP>5</SUP>-3s<SUP>2</SUP>3p<SUP>4</SUP>3d
  transitions in the 170-190 Å wavelength range are compared with
  observational data for a solar active region and flares, obtained
  during the Skylab mission, and Cen and Procyon observations from the
  Extreme Ultraviolet Explorer (EUVE) satellite. Electron densities
  derived from the majority of the ratios are consistent for the events
  but are in poor agreement with the values of N<SUB>e</SUB> estimated
  from diagnostic lines in other species observed in the spectra, casting
  doubt on the accuracy of the theoretical line ratio calculations and,
  hence, the atomic data of Mohan et al. used in their derivation. At
  low N<SUB>e</SUB>, the present ratios are significantly different
  from those of Young et al., while the latter imply densities that
  are in somewhat better agreement with densities derived from other
  diagnostics. This would appear to indicate that the electron impact
  excitation rates of Bhatia &amp; Doschek adopted by Young et al. are
  to be preferred over the Mohan et al. results.

---------------------------------------------------------
Title: A New K0 IV--V Plus White Dwarf Binary in The EUVE Survey
Authors: Christian, D. J.; Vennes, S.; Mathioudakis, M.
1996AAS...189.7902C    Altcode: 1996BAAS...28.1380C
  We present far ultraviolet and optical spectroscopy of the Extreme
  Ultraviolet Explorer (EUVE) survey source EUVE J0702+129 showing
  a composite K0 star plus DA white dwarf spectrum. International
  Ultraviolet Explorer spectra show continuum emission from a hot white
  dwarf (T_eff =30-40,000 K) and a rising contribution from the K0 star
  at lambda &gt;= 2500 Angstroms. High resolution optical spectroscopy
  reveals a moderate level of activity with Ca II H &amp; K emission;
  application of the Wilson-Bappu relation indicates that the secondary
  star is slightly above the main-sequence (K0 IV--V). Both objects are
  found at a distance of ~ 100 pc and probably constitute a physical
  pair. The EUV emission is probably dominated by the white dwarf, but
  the late-type star possibly contributes at higher energy. Interesting
  parallels are drawn with other DA+K0 pairs with moderately active
  secondaries such as HD 18131 and HR 1608. The present discovery as well
  as other recent ones demonstrate the existence of a large population
  of white dwarfs hidden by evolved companions (III--IV). This work is
  supported by NASA grant NAG-2405 and contract NAS5-29298.

---------------------------------------------------------
Title: Detection of Quiescent Extreme Ultraviolet Emission from
the Very Low Mass Dwarf van Biesbroeck 8: Evidence for a Turbulent
    Field Dynamo
Authors: Drake, Jeremy J.; Stern, Robert A.; Stringfellow, Guy;
   Mathioudakis, Mihalis; Laming, J. Martin; Lambert, David L.
1996ApJ...469..828D    Altcode:
  We report the detection of quiescent EUV emission from the very low
  mass dwarf VB 8 by the Extreme Ultraviolet Explorer (EUVE) in the
  Lexan/B band (65-190 Å). We interpret this emission in terms of a
  hot coronal plasma and combine this information with previous X-ray
  detections to estimate the quiescent plasma temperature and emission
  measure. The combined observations made by Einstein, ROSAT, and EUVE
  between 1979 and 1994 are consistent with a quiescent coronal plasma
  temperature of (2-6) x 10<SUP>6</SUP> degrees and indicate the same
  emission measure to within a factor of about 2. The nonflaring corona
  of VB 8 then appears relatively constant over timescales of more than
  10 yr. Our results are consistent with the picture of a turbulently
  driven or distributive dynamo for VB 8, rather than with a large-scale
  field dynamo which appears to dominate the solar corona. Evidence from
  X-ray and optical data concerning the long-term coronal variability of
  the more active stars of higher mass also points toward the idea that
  active late-type stars in general are dominated by a turbulent dynamo.

---------------------------------------------------------
Title: Discovery of a White Dwarf Companion (MS0354.6-3650 = EUVE
    J0356-366) to a G2V Star
Authors: Christian, Damian J.; Vennes, Stephane; Thorstensen, John R.;
   Mathioudakis, Mihalis
1996AJ....112..258C    Altcode:
  We present x-ray, ultraviolet, and optical observations
  of the mysterious EUV/soft x-ray source EUVE J0356-336 (=
  MS0354.6-3650). Initial Einstein observations identified this source
  with a cluster of galaxies, but the relatively high source count rate
  in the Extreme Ultraviolet Explorer (EUVE) 100 Å band and the lack
  of variability hinted that EUVE J0356-3650 might be a white dwarf;
  the UK Schmidt plate of the field surrounding this object found a 12.45
  magnitude G2V star that could hide a compact companion. This hypothesis
  was confirmed in an IUE ultraviolet spectrum that shows the definite
  signature of a hydrogen-rich white dwarf (DA). A model atmosphere
  analysis shows that the DA star is hot (T<SUB>eff</SUB>≥52,000 K)
  and may have a low abundance of heavy elements. We show that the G2V
  star and the DA star form a physical pair at a distance of 400 pc and
  therefore add to the list of white dwarf plus luminous main sequence
  star binaries discovered in EUV surveys.

---------------------------------------------------------
Title: Optical Identifications of Fainter Late-type Stars from EUVE
    and ROSAT Detections
Authors: Christian, D. J.; Craig, N.; Roberts, B.; Lampton, M. L.;
   Mathioudakis, M.; Drake, J. J.
1996AAS...188.7102C    Altcode: 1996BAAS...28..941C
  We present results of the continuing optical campaign to identify
  sources detected in the 100 Angstroms Extreme Ultraviolet Explorer
  (EUVE ) all-sky survey that are also detected in the ROSAT 0.25
  keV band. This paper concentrates on a dozen sources for which the
  optical counterparts are identified as Me stars. Data were obtained
  in 1995 December and 1996 February using the CTIO 1.5 m Cassegrain
  with resolution of 8 km s(-1) and covering a bandpass of 3500--6700
  Angstroms. All spectra show the Balmer series and Ca H &amp; K lines
  in emission. We present source identifications, spectral classes,
  distances, visual magnitudes, estimated hydrogen column densities,
  and the EUVE and ROSAT count rates. Implications for the fainter end
  of the EUV log N-log S distribution will be discussed. This work was
  supported by NASA contract NAS5-29298.

---------------------------------------------------------
Title: An EUVE Stellar Spectral Atlas
Authors: Abbott, M.; Craig, N.; Jessop, H.; Sommers, J.; Finley, D.;
   Vallerga, J. V.; Malina, R. F.; Howell, S. B.; Mathioudakis, M.
1996AAS...188.5509A    Altcode: 1996BAAS...28..909A
  We present an atlas of stellar Extreme Ultraviolet Explorer (EUVE )
  spectra. The spectra of approximately 80 stars acquired between 1992
  June and 1995 June have been uniformly processed from data in the EUVE
  public archive. Sources were chosen for inclusion in the atlas based
  on their brightness and the quality of their spectra. We have divided
  the atlas into four sections, representing classes of stellar sources
  seen by EUVE : early (O--F) stars, late (G--M) stars, white dwarfs,
  and cataclysmic variables. Other stellar and non-stellar classes will
  be presented in future atlases. For each section, we summarize the EUV
  spectral properties of the class and then show the spectra along with
  detailed comments on the individual sources. The spectra contained
  in the atlas will also be made available through the CEA WWW site at
  http://www.cea.berkeley.edu. This work was supported by NASA contract
  NAS5-29298 and NASA grant NAG5-2902.

---------------------------------------------------------
Title: The Secrets of EUVE J2056-17.1
Authors: Mathioudakis, M.; Drake, J. J.; Craig, N.; Kilkenny, D.;
   Doyle, J. C.; Sirk, M.; Dupuis, J.; Fruscione, A.; Christian, C. A.;
   Abbott, M. J.
1996aeu..conf..475M    Altcode: 1996IAUCo.152..475M
  No abstract at ADS

---------------------------------------------------------
Title: Observation and modelling of main sequence star
    chromospheres. V. Ultraviolet excess emission in active M dwarfs.
Authors: Houdebine, E. R.; Mathioudakis, M.; Doyle, J. G.; Foing, B. H.
1996A&A...305..209H    Altcode:
  The variation in the continuum intensity (50-5000nm) of late-type
  M dwarfs is investigated via two grids of model atmospheres with
  different temperature minima. It is shown that the (E)UV intensity
  is mostly dependent on the transition region pressure, although the
  temperature minimum also plays an important role. We also observe
  a significant frequency redistribution of the photospheric flux when
  changing the minimum temperature, and a black-body type of emission from
  the lower chromosphere. We examine the formation of the continuum and
  point out that, although some differences appear for very low or very
  high activity levels, in general the global picture is much alike the
  Sun. We show that the UV continua are very good diagnostics of cool
  dwarf atmospheres, from the temperature minimum to the transition
  region. Our calculations give a good overview of the domains where
  physical parameters and spectral signatures are most likely observed. We
  compute the UBV(RIJKL)_J_ broad band fluxes for our models and conclude
  that the chromospheric contribution should be detectable in the U
  band and possibly also in the B band. We compare our calculations to
  recent high resolution observations for selected stars in a narrow
  spectral range ((R-I)_K_=0.875+/-0.05); we show that Hα line profiles
  behave as expected, with a tight correlation between the line width
  and equivalent width. Hα emission line stars show an excess in U-B
  color but not in B-V. They are also more luminous than their less
  active absorption line counterparts, which indicates that active dwarfs
  have not yet reached the main sequence and are intermediate between T
  Tauri stars and main sequence stars. The anomalously large proportion
  of active stars towards late spectral types is attributed to the very
  slow contraction phase for low mass stars. We calculate the fluxes in
  the Extreme Ultraviolet Explorer Sn/SiO band (500-740A) and show that
  they are compatible with observed upper limits. We further compare
  our results for the upper activity range to pre-main sequence models
  and observations. They strongly support the case for a chromospheric
  contribution to Hα and the blue/UV excess for those objects (T
  Tauris, naked T Tauris, YSOs). An important conclusion is that at
  high pressures, corresponding to active dMe stellar atmospheres,
  the chromosphere becomes a very efficient radiator at continuum
  wavelengths. From log(M)~-5 (column mass), radiative losses in the
  continuum rise exponentially and faster than in Hydrogen spectral lines
  because of their larger optical depths. As a consequence, Hi spectral
  lines have a small or negligible contribution to the total Hi (lines and
  continua) and white light radiative budget. We show that the hydrogen
  series dominate the radiative cooling in spectral lines (from 40% to
  90%) for Hα emission line stars. The cooling in the (E)UV continuum
  overwhelms the total radiative budget and is much larger than that
  in outstanding chromospheric and transition region lines (e.g. CaII,
  MgII, HI Lyman and Balmer). We propose this as a possible contribution
  for the apparent saturation observed in some spectral lines, therefore
  questioning the suggestion of saturation in magnetic activity levels.

---------------------------------------------------------
Title: EUVE right angle program observations of cool stars
Authors: Christian, D. J.; Drake, J. J.; Mathioudakis, M.
1996ASPC..109..593C    Altcode: 1996csss....9..593C
  No abstract at ADS

---------------------------------------------------------
Title: The RS CVn binaries seen through the Eye of IRAS
Authors: Mitrou, C. K.; Doyle, J. G.; Mathioudakis, M.; Antonopoulou,
   E.
1996hell.conf..301M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: EM distribution and radiative losses of II Peg and lambda And
Authors: Mitrou, C. K.; Doyle, J. G.; Mathioudakis, M.; Antonopoulou,
   B.
1996ASPC..109..275M    Altcode: 1996csss....9..275M
  No abstract at ADS

---------------------------------------------------------
Title: Searching for a Fundamental Heating Mechanism in Low-activity
    Dwarfs
Authors: Mathioudakis, M.
1996ApL&C..34..187M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Searching EUVE Data for Transient/Flaring Extreme Ultraviolet
    Sources
Authors: Lewis, J.; Bowyer, S.; Lampton, M.; Wu, X.; Mathioudakis, M.
1996aeu..conf..481L    Altcode: 1996IAUCo.152..481L
  No abstract at ADS

---------------------------------------------------------
Title: The dependence of II Pegasi flare activity on the Phase of
    the short-term periodic light Variations
Authors: Mathioudakis, M.; Avgoloupis, S. I.; Mavridis, L. N.;
   Seiradakis, J. H.
1996hell.conf..234M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: The EUVE Optical Identification Campaign II: Late-Type and
    White Dwarf Stars
Authors: Craig, N.; Fruscione, A.; Dupuis, J.; Mathioudakis, M.; Drake,
   J. J.; Abbott, M.; Christian, C.; Green, R.; Boroson, T.; Howell, S. B.
1996aeu..conf..491C    Altcode: 1996IAUCo.152..491C
  No abstract at ADS

---------------------------------------------------------
Title: EUV Constraints on Models of Low Mass X-ray Binaries
Authors: Christian, D. J.; Edelstein, J. E.; Mathioudakis, M.;
   McDonald, K.; Sirk, M. M.
1996aeu..conf..425C    Altcode: 1996IAUCo.152..425C
  No abstract at ADS

---------------------------------------------------------
Title: The emission of the RS CVn binaries in the IRAS passbands.
Authors: Mitrou, C. K.; Doyle, J. G.; Mathioudakis, M.; Antonopoulou,
   E.
1996A&AS..115...61M    Altcode:
  In the literature, there is an ambiguity pertaining to the existence
  of a far-IR excess in RS CVn systems. In the current paper we undertook
  a study of the behaviour of 103 such systems in the IRAS passbands. We
  found 72 acceptable detections in the 12μm band, and 40 in the 25μm
  band (50% more than the IRAS Point Source Catalog). Although our
  findings may be interpreted as indicating towards the existence of an
  excess beyond 12μm for some systems, the evidence is not conclusive
  in all but two cases. These are systems GX Lib and HR 7428, with
  Capella being the only system where the IRAS fluxes in all four bands
  originate from the stellar photosphere. Given the accuracy of the data
  we did not find 12μm excess for any system. We argue that the IRAS
  data alone cannot settle the issue, as their uncertainty is, in many
  cases, higher than what the Signal-to-Noise ratio of each observation
  implies. Furthermore, at the higher wavelength bands the IRAS angular
  resolution drops from 0.5' at 12μm to 2' at 100μm and the background
  becomes very complex, so one cannot be certain about the origin of
  the observed flux. The existence of IR excess in the RS CVn stars is
  important as far as the evolutionary scenarios for these systems are
  concerned. Future missions such as the Infrared Space Observatory will
  return more sensitive and accurate measurements and the ambiguity can
  be removed. The fluxes we quote will be helpful when planning these
  future observations, as we provide more accurate photometry and for
  a larger selection of sources than the IRAS Point Source Catalog.

---------------------------------------------------------
Title: EUVE Right Angle Program Observations of Late-Type Stars
Authors: Christian, D. J.; Mathioudakis, M.; Drake, J. J.
1995AAS...18710320C    Altcode: 1995BAAS...27.1433C
  The EUVE Right Angle Program (RAP) obtains photometric data in four
  bands centered at ~ 100 Angstroms (Lexan/B), ~ 200 Angstroms (Al/Ti/C),
  ~ 400 Angstroms (Ti/Sb/Al), and ~ 550 Angstroms (Sn/SiO). RAP
  observations are up to 20 times more sensitive than the all-sky
  survey. We present RAP observations of the late-type stars: BD+03
  301, BD+05 300, HR 1262, BD+23 635, BD+22 669, Melotte 25 VA 334,
  Melotte 25 1366, Melotte 25 59, Melotte 25 65, theta (1) Tau, V834
  Tau, GJ 2037, BD-21 1074, GJ 205, RE J0532-030, GJ 9287A, HT Vir,
  BD+46 1944, Proxima Cen, alpha Cen A/B, HR 6094, CPD-48 10901, and
  HR 8883. We derive fluxes and emission measures from Lexan/B and
  Al/Ti/C count rates. The time variability of the sources has been
  examined. Most of the sources show no significant variability at the
  99% confidence level. Flares were detected from the K3V star V834 Tau
  (HD 29697) and the K0 star BD+22 669. The BD+22 669 count rate at the
  peak of the flare is a factor of 10 higher than the quiescent count
  rate with a peak Lexan/B luminosity of 7.9 x 10(29) erg s(-1) . The
  V834 Tau flare was detected in both Lexan/B and Al/Ti/C bands. The
  peak luminosity of the flare is 1.6 x 10(29) erg s(-1) and 8 x 10(28)
  ergs s(-1) for Lexan/B and Al/Ti/C, respectively. This is a factor of
  4.3 higher than the quiescent luminosity in Lexan/B, and a factor of
  4.6 in Al/Ti/C\@. This work is supported by NASA contract NAS5-29298.

---------------------------------------------------------
Title: Optical identification of EUV sources: the secrets of EUVE
    J2056-17.1.
Authors: Mathioudakis, M.; Drake, J. J.; Craig, N.; Kilkenny, D.;
   Doyle, J. G.; Sirk, M. M.; Dupuis, J.; Fruscione, A.; Christian,
   C. A.; Abbott, M. J.
1995A&A...302..422M    Altcode:
  We present optical, ultraviolet (UV), and extreme ultraviolet (EUV)
  results for a new active late-type dwarf star discovered by the Extreme
  Ultraviolet Explorer (EUVE). A large flare with an energy in excess of
  10^35^erg and duration of ~1.1 days was detected in the EUVE Lex/B band
  (60-200A). The energetics of the event indicate that radiative losses in
  the EUV are a significant contributor to the energy budget in stellar
  flares. The "quiescent" EUV emission of the source is similar to the
  most active flare stars with the "quiescent" optical spectrum showing
  strong Hα, Ca II H &amp; K, and Mg II h &amp; k emission. A strong
  Li I 6707.8A absorption line is also present in the spectrum. We have
  estimated a Li abundance of log N(Li)=2.5+/-0.4. Although the high
  Li abundance suggests that EUVE J2056-17.1 is a young object having
  recently arrived on the main sequence; the high flare activity favours
  an interpretation where the enhanced Li is sustained by spallation
  reactions.

---------------------------------------------------------
Title: The EUVE Optical Identification Campaign II: Late-Type and
    White Dwarf Stars
Authors: Craig, N.; Fruscione, A.; Dupuis, J.; Mathioudakis, M.; Drake,
   J. J.; Abbott, M.; Christian, C.; Green, R.; Boroson, T.; Howell, S. B.
1995AJ....110.1304C    Altcode:
  We present optical identifications of nine previously unidentified
  extreme ultraviolet (EUV) sources discovered during the Extreme
  Ultraviolet Explorer (EUVE) satellite surveys. The all-sky survey
  detected four of the sources and the more sensitive deep survey
  detected the other five sources. Three of the four all-sky survey
  sources, EUVE_J1918+599, EUVE_J2249+585, and EUVE_J2329+414, are
  listed in present catalogs as having possible associations with
  optical counterparts but without spectral class. The first two of these
  sources are hot DA white dwarfs showing an optical spectrum with broad
  Balmer lines. The source EUVE_J2329+414 is listed as having a possible
  association with an unclassified M star. We show that a pair of dMe
  stars are actually optical counterparts located within the error circle
  of the EUVE source position. The EUVE_J2114+503 remains unidentified
  even though all the possible candidates have been studied. Based on the
  count rates we predict a fainter white dwarf or a cataclysmic variable
  counterpart for this candidate. All five sources discovered with the
  EUVE deep survey, EUVE_J03 18+184, EUVE_J0419+217, EUVE_J2053-175,
  EUVE_J2056-171, and EUVE_J2233-096, have been identified as late-type
  stars. The spectral classes, distances, visual magnitudes, and estimated
  hydrogen column densities for these EUVE sources are presented.

---------------------------------------------------------
Title: Activity versus rotation in the extreme ultraviolet.
Authors: Mathioudakis, M.; Fruscione, A.; Drake, J. J.; McDonald,
   K.; Bowyer, S.; Malina, R. F.
1995A&A...300..775M    Altcode:
  This paper presents extreme ultraviolet (EUV) fluxes for 74
  main-sequence stars observed with the Extreme Ultraviolet Explorer
  (EUVE). The sample of stars was chosen on the basis of rotational
  period and includes 23 new EUV detections. These detections are in
  addition to the ROSAT WFC and EUVE catalogs and have increased the
  number of main-sequence stars detected in the extreme ultraviolet by
  ~12%. We present an activity-rotation relation in the EUV and show
  that in a sample of stars with different effective temperatures the
  Rossby number is a better parameter for describing the levels of EUV
  emission as compared to the rotational period. This is also known
  to be the case for the chromospheric emission. A comparison with the
  emission in the Mg II h and K lines shows that saturation in the EUV
  occurs in lower Rossby numbers than does chromospheric saturation,
  where saturation in X-rays occurs in the same Rossby numbers as in the
  EUV. The radiative losses in the EUV are comparable to the radiative
  losses in X-rays. The EUVE observations indicate that the low activity
  dM star Gl 685 has a cool corona with a characteristic temperature of
  &lt;2.5x10^6^K. A large amount of the coronal radiative losses in low
  activity dwarfs is expected to emerge in EUV wavelengths.

---------------------------------------------------------
Title: Discovery of a white dwarf companion (EUVE J0254-053) to the
    K0 IV star HD18131
Authors: Vennes, S.; Mathioudakis, M.; Doyle, J. G.; Thorstensen,
   J. R.; Byrne, P. B.
1995A&A...299L..29V    Altcode:
  New ultraviolet (UV) observations of late-type stars detected in
  the Extreme Ultraviolet Explorer (EUVE) all-sky survey revealed
  an unsuspected white dwarf companion to the K0 star HD18131. The
  International Ultraviolet Explorer (IUE) spectrum show a composite of a
  white dwarf and a late-type star. The white dwarf dominates the emission
  below 2000A while the K0 star prevails at longer wavelengths. A model
  atmosphere analysis of the new ultraviolet spectrophotometry and of
  the extreme ultraviolet (EUV) photometry reveals a hot, hydrogen-rich
  (DA) white dwarf (Teff~30000K) that is the most likely source of the
  EUV emission (EUVE J0254-053). We estimate a distance to the white
  dwarf of 70-90pc. The K0 star shows a modest level of chromospheric
  activity with the detection of Mg II h and k emission in the IUE
  spectrum. Optical spectroscopy revealed that the K0 star is a subgiant
  (K0 IV). The star is located at a distance of ~70pc, consistent with
  the estimated distance of the white dwarf. Therefore, it most likely
  constitutes a physical pair with the white dwarf. Until results of a
  radial velocity study are made available we cannot establish whether
  the pair is wide or close. In earlier works the strong EUV emission was
  attributed to the K0 star; however, our multiwavelength observations
  show the white dwarf as the most likely source. This discovery has
  important implications for the EUV white dwarf population survey and,
  in particular, for the binary frequency.

---------------------------------------------------------
Title: Erratum - a Preliminary Review of EUVE Science
Authors: Vennes, S.; Drake, J. J.; Mathioudakis, M.; Welsh, B.;
   Fruscione, A.; Hall, D. T.; Warren, J.; Howell, S. B.
1995IrAJ...22..228V    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Dissecting stellar coronae with EUVE.
Authors: Drake, J. J.; Mathioudakis, M.
1995IrAJ...22...10D    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: A Preliminary Review of EUVE Science
Authors: Vennes, S.; Drake, J. J.; Mathioudakis, M.; Welsh, B.;
   Fruscione, A.; Hall, D. T.; Warren, J.; Howell, S. B.
1995IrAJ...22....7V    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Optical Identification and Spectroscopy of EUV Sources
Authors: Craig, N.; Fruscione, A.; Abbott, M.; Christian, C. A.;
   Drake, J. J.; Dupuis, J.; Mathioudakis, M.; Green, R.; Boroson, T.
1994AAS...185.8014C    Altcode: 1994BAAS...26.1448C
  We present optical identification and analysis of previously
  unidentified extreme ultraviolet (EUV) sources (60--200 Angstroms)
  discovered with the Extreme Ultraviolet Explorer (EUVE) during the
  all-sky and deep surveys. Two EUVE deep survey sources, EUVE_J0318+184
  and EUVE_J2056-171, are identified as active, young, late-type
  stars. They display strong Hα , Ca ii H and K emission, and Li
  6707.8 Angstroms absorption suggesting spectral types of dM0e. A very
  strong flare with energy in excess of 10(35) erg was also observed
  on EUVE_J2056-171 (Mathioudakis et al. 1994, in prep.). We also
  identified four previously cataloged EUVE sources: EUVE_J1918+59.9,
  EUVE_J2249+58.5, EUVE_J0419+21.7, and EUVE_J2329+41.4. The first
  two sources are identified in both the ROSAT Wide Field Camera and
  the EUVE catalogs as unclassified “stars.” They are in fact hot
  DA white dwarfs showing a clean optical spectrum with broad Balmer
  lines. EUVE_J0419+21.7 was previously assigned a possible identification
  with 56 Tau, an A0sp star. Optical spectra of other candidates within
  the error circle, in addition to the bright A star, show three emission
  line dMe stars in the field. We attribute the EUV emission to one or
  more of this collection of dMe stars. The source EUVE_J2329+41.4 is
  currently identified as probably being G 190--28 with spectral type
  M. However we show that both G 190--28 and G 190--27 are dMe stars
  and are located within the error circle of the EUVE position of this
  source, and therefore both of these stars probably contribute to the
  EUV emission. This work has been supported by NASA contract NAS5-29298.

---------------------------------------------------------
Title: Detection of EUV emission from the low activity dwarf HD 4628:
    evidence for a cool corona.
Authors: Mathioudakis, M.; Drake, J. J.; Vedder, P. W.; Schmitt,
   J. H. M. M.; Bowyer, S.
1994A&A...291..517M    Altcode:
  We present observations of low activity late-type stars obtained with
  the Extreme Ultraviolet Explorer (EUVE). These stars are the slowest
  rotators, and acoustic heating may dominate their outer atmospheric
  heating process. We report detection of EUV emission from the low
  activity K dwarf HD 4628 during the EUVE Deep Survey in the Lexan/boran
  band. This detection, in conjunction with the non-detection of this
  object in the ROSAT PSPC all-sky survey, suggests the existence of a
  cool corona with a characteristic temperature of less than 10^6^K. The
  flux and spectral signature are consistent with current theories of
  acoustic heating.

---------------------------------------------------------
Title: Surface inhomogeneities on SZ Piscium.
Authors: Doyle, J. G.; Mitrou, C. K.; Mathioudakis, M.; Avgoloupis,
   S.; Mavridis, L. N.; Varvoglis, P. P.; Graos, F.; Antonopoulou, E.
1994A&A...291..135D    Altcode:
  Ultraviolet and optical data are used to look at surface inhomogeneities
  on the active close binary system SZ Piscium. Lower chromospheric
  emission lines such as Mg II h&amp;k, and to a lesser extend the
  upper chromospheric/lower transition region lines of O I 1305A and C
  II 1335A show a pronounced decrease when the F star is eclipsing the
  K sub-giant. However, higher temperature lines such as the resonance
  line of C IV 1550A do not show any change in flux. This suggests the
  presence of a plage with a high contrast at lower temperatures with
  a Mg II plage-to-K-star ratio of 5. Alternative explanations are
  explored. Monitoring of this system in the optical U-band and the
  ultraviolet lines such as C IV 1550A, indicates frequent high energy
  (10^35^-10^36^erg) flares.

---------------------------------------------------------
Title: Lower chromospheric activity in low activity M dwarfs
Authors: Doyle, J. G.; Houdebine, E. R.; Mathioudakis, M.; Panagi,
   P. M.
1994A&A...285..233D    Altcode:
  Four low activity dM(e) stars Gl 105B, Gl 643, Gl 813 and Gl 821
  were observed spectroscopically in the optical and ultraviolet
  regions. Despite relatively long integrations, only one of the four
  had detectable Ca II K&amp;H emission, Gl 821, which had an observed
  flux of 9 10^-15^ erg/cm2/s, giving a surface flux of only 0.8 10^4^
  erg/cm2/s. Similarly, the IUE observations implied very weak Mg II
  emission. In one of these stars, Gl 813, the Mg II h&amp;k surface
  flux was less than 0.4 10^4^ erg/cm2/s, which is a factor of two
  less than the previous known weakest dM(e) star, Gl 105B. Using
  radiative transfer techniques the Ca II H&amp;K fluxes have been
  derived for a range of model atmospheres. The zero Hα flux can be
  produced by a range of models, this line is therefore a rather poor
  constraint for the lower atmosphere. On the other hand, the Ca II K
  flux can be dramatically effected by simply varying the temperature
  minimum. Comparing our calculations to the observational data, we find
  that the Ca II H&amp;K surface fluxes cannot be reproduced with T_min_
  3000K. However, decreasing the temperature minimum by less than 400K
  produces Ca II H&amp;K fluxes of the order of 10^3^ erg/cm2/s, in very
  good agreement with the weakest dM(e) stars.

---------------------------------------------------------
Title: High-velocity evaporation during a flare on AT Microscopii
Authors: Gunn, A. G.; Doyle, J. G.; Mathioudakis, M.; Houdebine,
   E. R.; Avgoloupis, S.
1994A&A...285..489G    Altcode:
  We present and discuss observations of a flare event on the dM4.5e star
  AT Mic (Gl 799AB). These data show evidence of an energetic flare with
  a radiated energy of 3 10^31^erg in the range 3600-4200A. The Balmer
  emission lines display a prominent blue asymmetry which has been used
  to constrain the velocity of the associated bulk plasma motion. Simple
  models were applied to derive order of magnitude estimates for the mass
  and kinetic energy budget of the flare for assumed electron density,
  ionization fraction and temperature values. It is found that the
  kinetic energy of the flare plasma is two orders of magnitude less
  than the radiative energy release. The chromospheric Ca II H &amp;
  K lines are also observed to have a blue-shifted component which has
  not been observed prior to these results. We suggest that this is
  evidence of a very energetic particle beam penetrating to the cooler
  atmospheric layers where Ca II H &amp; K is formed.

---------------------------------------------------------
Title: The Extreme Ultraviolet (EUV) Rotation-activity Relation for
    Late-Type Stars
Authors: Mathioudakis, M.; Fruscione, A.; Drake, J. J.; McDonald,
   K.; Bowyer, S.; Malina, R. F.
1994AAS...184.0520M    Altcode: 1994BAAS...26Q.866M
  We present results on an optically selected sample of 44 main sequence
  stars, including 18 EUV sources not previously reported, detected
  with the Extreme Ultraviolet Explorer (EUVE) satellite. The sample
  covers a broad range of spectral types (early F to late M) with known
  rotation periods from 0.4 days to 50 days. A comparison of the EUV
  fluxes with activity related parameters shows that the dynamo related
  Rossby number is the best parameter for describing the levels of coronal
  activity. This is in agreement with the conclusion of Noyes et al. (ApJ,
  279,763) for the chromosphere. The saturated levels of coronal activity
  are discussed. This work has been supported by NASA contract NAS5-30180.

---------------------------------------------------------
Title: An optical flare on YZ Canis Minoris
Authors: Gunn, A. G.; Doyle, J. G.; Mathioudakis, M.; Avgoloupis, S.
1994A&A...285..157G    Altcode:
  We present and discuss observations of an energetic optical flare on
  the dM4.5e star YZ CMi (Gl 285). The flux-time variations and energy
  release of the flare are fully consistent with previous observations
  of this star. The observations have also revealed a symmetric excess
  emission in the bases of the chromospheric Balmer lines. If due to a
  bulk plasma motion event, the maximum extension in the Balmer wings
  represents a Doppler velocity of ~ 250 km/s.

---------------------------------------------------------
Title: Ultraviolet flare activity on the eclipsing binary SZ Piscium.
Authors: Doyle, J. G.; Mitrou, C. K.; Mathioudakis, M.; Antonopoulou,
   E.
1994A&A...283..522D    Altcode:
  The estimated total chromospheric, transition region and coronal
  losses for a flare observed on the eclipsing binary SZ Psc with the
  International Ultraviolet Explorer (IUE) satellite on 6 July 1990 is
  of the order of 4.5 10<SUP>36</SUP> ergs. This estimate is similar to
  that derived by Doyle et al. (1989) for an ultraviolet flare on another
  RS CVn star, II Peg, and is a substantial fraction of the total amount
  that is possible to store on these stars without having to evoke the
  presence of kiloGauss fields.

---------------------------------------------------------
Title: EUVE Observations of Late Type Stars with Minimum Levels
    of Activity
Authors: Mathioudakis, M.; Drake, J. J.; Vedder, P. W.; Patterer,
   R. J.; Bowyer, S.
1994ASPC...64...38M    Altcode: 1994csss....8...38M
  No abstract at ADS

---------------------------------------------------------
Title: H alpha Variability on HK Aqr: Coronal Condensations or Plages?
Authors: Byrne, P. B.; Mathioudakis, M.; Young, A.; Skumanich, A.
1994ASPC...64..375B    Altcode: 1994csss....8..375B
  No abstract at ADS

---------------------------------------------------------
Title: EUVE Photometry Observations of Cool Stars (Invited Review)
Authors: Vedder, P. W.; Brown, A.; Drake, J. J.; Patterer, R. J.;
   Mathioudakis, M.; Gully, S.; Pettersen, B. R.
1994ASPC...64...13V    Altcode: 1994csss....8...13V
  No abstract at ADS

---------------------------------------------------------
Title: The extreme ultraviolet (EUV) rotation-activity relation for
    late-type stars.
Authors: Mathioudakis, M.; Fruscione, A.; Drake, J. J.; McDonald,
   K.; Bowyer, S.; Malina, R. F.
1994BAAS...26R.866M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Low Activity M Dwarfs
Authors: Doyle, J. G.; Houdebine, E. R.; Mathioudakis, M.
1994ASPC...64..557D    Altcode: 1994csss....8..557D
  No abstract at ADS

---------------------------------------------------------
Title: Coronal Variability in the Extreme Ultraviolet
Authors: Drake, J. J.; Mathioudakis, M.; Pye, J. P.; Fruscione, A.;
   Bowyer, S.; Vedder, P. W.; Patterer, R. J.
1993AAS...183.1506D    Altcode: 1993BAAS...25.1314D
  Late-type stars are the most numerous among the many different
  categories of object detected in the first all-sky survey of the 60--760
  Angstroms region recently completed by the Extreme Ultraviolet Explorer
  satellite (EUVE). To date, this survey has yielded extreme ultraviolet
  (EUV) photometric data for nearly 200 late-type stars. Two years
  earlier, photometry was obtained by the ROSAT Wide Field Camera (WFC)
  in the 60--200 Angstroms band. Using both data sets, we have looked
  for changes over this two year period in the coronal emission from
  the late-type stars that have been detected by both EUVE and the ROSAT
  WFC. The results are discussed with reference to stellar activity cycles
  and flaring. This work has been supported by NASA contract NAS5--30180.

---------------------------------------------------------
Title: EUVE Observations of Planetary Nebulae
Authors: Fruscione, A.; Abbott, M.; Drake, J. J.; Dupuis, J.; Malina,
   R. F.; Mathioudakis, M.; McDonald, K.; Chu, K. C.
1993AAS...183.5112F    Altcode: 1993BAAS...25.1371F
  We present preliminary results of extreme ultraviolet observations
  (60--740 Angstroms) of a complete sample of planetary nebulae
  (PN) selected from the Strasbourg-ESO Catalog (Acker et al. 1992)
  and observed during the Extreme Ultraviolet Explorer (EUVE) all-sky
  survey. Our selection criteria are focused on minimizing the impact of
  the interstellar absorption on the extreme ultraviolet observations, and
  our sample includes the 26 closest PN (distances &lt;= 1 kpc) at high
  galactic latitude (|b|&gt;= 20deg ). During the EUVE all-sky survey at
  least five PN in our sample (NGC 246, NGC 1360, K1-16, Lo Tr5, NGC 4361)
  were detected in the shortest band (58--174 Angstroms). The extreme
  ultraviolet emission originates in the central star. Upper limits
  in the four EUVE bands (centered at ~ 100, 200, 400, 600 Angstroms)
  are given for all the sources. This work has been supported by NASA
  contract NAS5-30180.

---------------------------------------------------------
Title: Far infrared properties of late type dwarfs. Infrared fluxes
    of K and M dwarfs.
Authors: Mathioudakis, M.; Doyle, J. G.
1993A&A...280..181M    Altcode:
  IRAS fluxes/upper limits are presented for a large sample of K
  and M dwarfs. Good agreement is found between the 12 micrometer
  fluxes and those derived from the photospheric models of Mould
  (1976). Relationships between the optical and infrared colors are
  derived. The active dMe/dKe stars appear systematically brighter
  in the infrared compared with the less active dM/dK stars, which
  could be attributed to more efficient nonradiative heating in their
  atmosphere. Any systematic differences found in our results when
  compared with those obtained from previous studies are attributed to
  the different analysis packages used.

---------------------------------------------------------
Title: Rotational modulation and flares on the RS Canum Venaticorum
binary II Pagasi in July/September 1990 : spots and flares on II Peg.
Authors: Doyle, J. G.; Mathioudakis, M.; Murphy, H. M.; Avgoloupis,
   S.; Mavridis, L. N.; Seiradakis, J. H.
1993A&A...278..499D    Altcode:
  During ultraviolet spectroscopic observations of the RS CVn star II
  Peg in September 1990 a long duration (greater than or = 3 hrs.) flare
  was observed. During the early stage of the event, a feature at 1354
  A was present, however, within the spectral resolution of the data
  it is not possible to identify this line. A contribution from the
  hot coronal ion Fe XXI is suspected. From line diagnostic ratios, the
  electron pressure at flare peak was estimated to be 10<SUP>17</SUP>/cu
  cm K, decreasing to 10<SUP>16</SUP>/cu cm K towards the end of the
  flare. One other flare was observed with IUE, and three optical flares
  (unfortunately none of these were observed simultaneously). The
  chromospheric and transition region losses from the larger of
  the two IUE flares was approx. 3 x 10<SUP>31</SUP> erg/s at flare
  maximum, with total chromospheric/transition region radiative losses
  over the duration of the event being approx. 1.5 x 10<SUP>35</SUP>
  erg. Continuum radiative losses over the wavelength region 1150A to
  1950A were approximately 3% of the above figure. At flare maximum,
  the N V 1240 A line showed an enhancement factor of approx. 3 over the
  preflare value compared to 9 for the C IV 1550 A line. We interpret this
  difference as due to an underabundance of nitrogen during the flare,
  possibly related to photoionization of lower chromospheric material
  by soft X-ray photons sometime prior to the flare. No evidence of
  rotational modulation was present in any of the transition region lines,
  although the chromospheric lines did show a phase variation. However,
  these lines (H-alpha, Ca II K and Mg II h&amp;k) were not consistent
  with one another although it is clear that the H-alpha equivalent
  width showed variations faster than the star's rotation period, being
  perhaps related to the decay/activation of individual active regions.

---------------------------------------------------------
Title: Controversy on the Infrared Excess of GL:735
Authors: Mathioudakis, M.
1993IrAJ...21..152M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: The importance of surface inhomogeneities for K and M
    dwarfchromospheric fluxes.
Authors: Panagi, P. M.; Mathioudakis, M.
1993A&AS..100..343P    Altcode:
  We present published and archived spectroscopic and spectrophotometric
  data of H-alpha, Ca II, Mg II, and X-rays for a large sample of K
  and M dwarfs. The data set points to the importance that surface
  inhomogeneities have in the flux luminosity diagrams in these
  late-type dwarfs, irrespective of whether the Balmer lines are in
  emission or absorption. Although supporting the fact that cooler
  stars exhibit increasing levels of surface activity, evident through
  an increasing incidence of Balmer emission, surface inhomogeneities,
  or variations in the local temperature and density structure, at the
  chromospheric level, dominate the total Ca II and Mg II fluxes. We
  show that the flux-flux and luminosity-luminosity relations indicate
  differing extents of inhomogeneity from the chromosphere through to the
  corona. A good correlation between Ca II and Mg II fluxes indicates
  that they are formed in overlapping regions of the chromosphere,
  so that the contribution of surface inhomogeneities is not evident
  from this particular flux-flux diagram. In the region of the upper
  chromosphere through to the transition and corona, the correlation
  between Ly-alpha and X-ray fluxes indicates regions with similar levels
  of areal inhomogeneity. This appears to be uncorrelated with that at
  the chromospheric level.

---------------------------------------------------------
Title: Imaging the Photosphere &amp;Chromosphere of the Rapidly
    Rotating dMe Star, HK Aqr
Authors: Byrne, P. B.; Mathioudakis, M.
1993ASSL..183..435B    Altcode: 1993pssc.symp..435B
  No abstract at ADS

---------------------------------------------------------
Title: Chromospheric Heating in K &amp;M Dwarfs
Authors: Doyle, J. G.; Mathioudakis, M.
1993ASSL..183..471D    Altcode: 1993pssc.symp..471D
  No abstract at ADS

---------------------------------------------------------
Title: Dynamic phenomena on the RS Canum Venaticorum binary II Pegasi
    in August 1989. I. Observational data.
Authors: Doyle, J. G.; Kellett, B. J.; Butler, C. J.; Byrne, P. B.;
   Neff, J. E.; Brown, A.; Fox, D.; Linsky, J. L.; Bromage, G. E.;
   Avgoloupis, S.; Mavridis, L. N.; Seiradakis, J. H.; Mathioudakis,
   M.; Murphy, H. M.; Krzesinski, J.; Pajdosz, G.; Dadonas, V.;
   Sperauskas, J.; van Wyk, F.; Marang, F.; Olah, K.; Collier Cameron,
   A.; Antonomoulos, E.; Rovithis, P.; Rovithis-Livaniou, H.
1992A&AS...96..351D    Altcode:
  Observational results are given for two flares in Pi Pegasi that were
  detected by the GINGA and IUE satellites, as well as by ground-based
  Johnson U-band photometry and optical spectroscopy. The best-fitting
  results were obtained for a combination of a single-temperature
  plasma together with a power law; for a two-temperature model, the
  temperature of the second component was very high due to the tail in
  the photon distribution.

---------------------------------------------------------
Title: Limits on Detectability of Mass Loss from Cool Dwarfs
Authors: Mullan, D. J.; Doyle, J. G.; Redman, R. O.; Mathioudakis, M.
1992ApJ...397..225M    Altcode:
  Recent spectroscopic evidence supports the theoretical expectation
  that certain cool dwarfs may have stellar winds with M-dot values
  several orders of magnitude larger than the solar rate. For large
  enough values of M-dot, the emission from the wind is expected to have
  a spectrum which, at low enough frequencies, becomes a power law,
  S(v) about v exp alpha with alpha about 0.7. Data from IRAS and VLA
  suggest that such a spectrum may in fact occur in certain M dwarfs:
  a key test of the wind spectrum would be provided if the stars could
  be detected at lambda about 1 mm. We show that the M-dot required to
  ensure power-law emission is a few times 10 exp -10 solar mass/yr. With
  M-dot of this order, fluxes at lambda about 1 mm would be tens of
  mJy. Using the James Clerk Maxwell Telescope, we have tested this
  prediction on several stars: the data are suggestive but are near the
  limits of detection. Confirmation of our estimates will be important
  for evolution and for interstellar medium (ISM) physics: if even a
  few percent of all M dwarfs are losing mass at the above rates, the
  mass balance of the ISM will be dominated by M dwarfs.

---------------------------------------------------------
Title: Chromspheric diagnostics in M dwarfs
Authors: Mathioudakis, M.; Doyle, J. G.
1992IrAJ...20..272M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Chromospheric heating in late-type dwarfs : acoustic or
    magnetic ?
Authors: Mathioudakis, M.; Doyle, J. G.
1992A&A...262..523M    Altcode:
  Mg II h and k fluxes for 69 K and 88 M dwarfs have been analyzed. An
  empirical lower limit is found in the Mg II flux, extended down to
  the latest spectral types. Based on the data presented here it is the
  magnetic component that dominates the emission from the atmosphere of
  cool dwarfs, especially the M dwarfs. It, however, coexists with an
  acoustically heated component, which can only be identified in the
  stars with the lowest fluxes in the flux-color diagram, these stars
  possibly being the slowest rotators. Data for the dM(e) stars, i.e.,
  those stars with zero H-alpha, show that these are divided into two
  classes: (1) an inactive M dwarf star with very weak chromospheric
  heating, perhaps only by acoustic waves; and (2) an intermediate
  chromospheric activity star dominated by magnetic heating.

---------------------------------------------------------
Title: Limits on detectability of mass loss from cool dwarfs
Authors: Mullan, D. J.; Doyle, J. G.; Mathioudakis, M.; Redman, R. O.
1992AAS...180.6006M    Altcode: 1992BAAS...24..826M
  Recent spectroscopic evidence supports the theoretical expectation
  that certain cool dwarfs may have stellar winds with dot {M} values
  several orders of magnitude larger than the solar rate. For large
  enough values of dot {M}, the emission from the wind is expected to
  have a spectrum which, at low enough frequencies, becomes a power law,
  S_ν ~ nu (alpha ) with alpha ~ 0.7. Data from IRAS and VLA suggest
  that such a spectrum may in fact occur in certain M dwarfs: a key
  test of the wind spectrum would be provided if the stars could be
  detected at lambda ~ 1 mm. We show that the dot {M} required to ensure
  power law emission is a few times 10(-10) M<SUB>sun</SUB> \ yr(-1)
  . With dot {M} of this order, fluxes at lambda ~ 1 mm would be tens
  of mJy. Using the James Clerk Maxwell Telescope, we have tested this
  prediction on several stars: the data are suggestive but are near the
  limits of detection. Confirmation of our estimates will be important
  for studies of evolution of low mass stars and for interstellar medium
  (ISM) physics: if even a few percent of all M dwarfs are losing mass
  at the above rates, the mass balance of the ISM will be dominated by
  M dwarfs. Moreover, if flares on these stars are accompanied by mass
  ejecta, the ISM may become contaminated with deuterium produced in
  the surface layers of the star by energetic protons.

---------------------------------------------------------
Title: Optical flares on the RS CVn binary II Peg.
Authors: Mathioudakis, M.; Doyle, J. G.; Avgoloupis, V.; Mavridis,
   L. N.; Seiradakis, J. H.
1992MNRAS.255...48M    Altcode:
  During 57.4 hr of optical monitoring in the Johnson U- and B-bands of
  the RS CVn binary II Peg, 10 flares were detected. The absolute energies
  of these events are in the range 1-180 x 10 exp 33 erg. This implies
  a flare activity in the U-band of 0.17 flares per hour, compared with
  0.12 flares per hour from UV C IV data. A double power-law distribution
  is required to fit the cumulative flare-frequency distribution of the
  U-band flares.

---------------------------------------------------------
Title: Millimeter; Sub-Millimeter Emission from Flare Stars
Authors: Mullan, D. J.; Doyle, J. G.; Mathioudakis, M.; Redman, R. O.
1992ASPC...26..328M    Altcode: 1992csss....7..328M
  No abstract at ADS

---------------------------------------------------------
Title: GL 890 - The Magnetic Brake?
Authors: Byrne, P. B.; Doyle, J. G.; Mathioudakis, M.
1992ASPC...26..438B    Altcode: 1992csss....7..438B
  No abstract at ADS

---------------------------------------------------------
Title: The UV Spectrum of the RS CVn Binary SZ PSc
Authors: Danezis, E.; Antonopoulou, E.; Mathioudakis, M.; Theodossiou,
   E.
1992LNP...397..273D    Altcode: 1992sils.conf..273D
  No abstract at ADS

---------------------------------------------------------
Title: Magnetic activity phenomena in dwarf K and M stars
Authors: Mathioudakis, Mihalis
1992PhDT.......295M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Optical Flares on II Peg
Authors: Mathioudakis, M.; Doyle, J. G.; Avgoloupis, S.; Mavridis,
   L. N.; Seiradakis, J. H.
1992ASPC...26..303M    Altcode: 1992csss....7..303M
  No abstract at ADS

---------------------------------------------------------
Title: The Ultraviolet Spectrum of the Binary System Sz-Piscium
Authors: Danezis, E.; Antonopoulou, E.; Theodossiou, E.; Mathioudakis,
   M.
1992Ap&SS.187..307D    Altcode:
  In this paper we study the far-UV as well as the UV spectrum of the
  spectroscopic binary system SZ Psc in the wavelength ranges λλ1235
  1950 Å and λλ2710 3090 Å, respectively, from spectra obtained with
  the International Ultraviolet Explorer (IUE). The UV spectrum of SZ Psc
  is mainly an emission spectrum. The short wavelength region includes
  emission lines formed from the low chromosphere to the transition region
  (e.g., Si iv, Civ, and Nv) and also a deep and broad absorption line
  of Fe ii. The Mg ii[1] resonance doublet at about λ2800 Å presents
  a P Cygni profile and a multiple structure with two emission and two
  absorption satellite components. We also present the emission measure
  diagram in the temperature region 4.4&lt;logT <SUB> e </SUB>&lt;53.

---------------------------------------------------------
Title: The August 1989 Spot Lightcurve of II Peg and Related Flare
    Activity
Authors: Avgoloupis, S.; Doyle, J. G.; Mavridis, L. N.; Seiradakis,
   J. H.; Mathioudakis, M.
1992LNP...397..247A    Altcode: 1992sils.conf..247A
  No abstract at ADS

---------------------------------------------------------
Title: Rotationalmodulation and flares on RS Canum Venaticorum and BY
    Draconis stars. XVI. IUE spectroscopy and VLA observations of GL 182
    (=V 1005 Orionis) in October 1983.
Authors: Mathioudakis, M.; Doyle, J. G.; Rodono, M.; Gibson, D. M.;
   Byrne, P. B.; Avgoloupis, S.; Linsky, J. L.; Gary, D.; Mavridis,
   L. N.; Varvoglis, P.
1991A&A...244..155M    Altcode:
  A large flare was detected simultaneously with IUE and VLA on Gl 182 on
  October 5, 1983, this event showing the largest C IV flare enhancement
  yet observed by IUE. A smaller flare was also detected on October 4,
  although only with the IUE satellite. Line ratio and emission measure
  techniques are used to derive various physical parameters of the
  flares. The radiative losses in the temperature region log T(e) =
  4.3-5.4 in the two flares are 2.9 x 10 to the 33rd and 8.4 x 10 to
  the 32nd ergs, respectively. Total radiative losses over the whole
  temperature range log T(e) = 4.0-8.0 are estimated to be of the order
  of 6.4 x 10 to the 34th and 1.1 x 10 to the 34th ergs, respectively. In
  the October 5, flare, a very strong ultraviolet continuum is present
  with a total energy of 1.9 x 10 to the 33rd ergs over the wavelength
  range 1250-1950 A.

---------------------------------------------------------
Title: Active M-type stars from the ultraviolet to the infrared.
Authors: Mathioudakis, M.; Doyle, J. G.
1991A&A...244..433M    Altcode:
  Fluxes at 12 microns are presented for a group of seven active dMe
  stars. Five of these stars are considered as significant detections
  at 25 microns, while only two stars were detected at 60 microns and
  only one at 100 microns. Comparing with previous results it is found
  that the fluxes are systematically lower by 7-50 percent depending on
  the band. Above 60 microns there is a definite excess over a blackbody
  radiation curve.

---------------------------------------------------------
Title: Chromospheric diagnostics in late-type stars.
Authors: Mathioudakis, M.; Doyle, J. G.
1991A&A...244..409M    Altcode:
  Moderate and low resolution spectroscopic observations of late type
  dwarfs covering a broad range of activity are presented. The strength of
  the TiO band in 4762 A is used for spectral classification. Calibrated
  fluxes for the Balmer and the Ca II H and K lines are derived. H-alpha
  equivalent widths are given for those stars where the line is in
  absorption as well as those in emission. It is confirmed that stars
  with no detectable or very weak H-alpha do exist. It is also shown
  that stars with very weak or no detectable emission in Ca II H and K
  also exist, this occurring preferentially in late M dwarfs. Although
  this can be explained in terms of reduced nonradiative heating in
  the chromosphere, the results cannot be conclusive due to the limited
  resolution of the data.

---------------------------------------------------------
Title: Millimeter continuum emission from flare stars.
Authors: Doyle, J. G.; Mathioudakis, M.
1991A&A...241L..41D    Altcode:
  The first detection of continuum emission in the millimeter region
  for two dwarf M flare stars is reported. The observed flux at 1.1 and
  2 mm is weak, being just above background, but above that based on a
  black-body curve. This confirms the impression gained from infrared
  fluxes at 60 and 100 microns, which indicated excess emission at
  these wavelengths.

---------------------------------------------------------
Title: Circumstellar Material in the RS CVn System SZ Psc
Authors: Mathioudakis, M.
1991iue..prop.4081M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Chromospheric/Coronal Emission Correlations in 'Quiescent'
    and Eruptive Phenomena in M-Dwarf Stars (With 1 Figure)
Authors: Mathioudakis, M.; Doyle, J. G.
1991mcch.conf..279M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Discovery of flare activity on the dwarf M stars, GL 375 and
    GL 431.
Authors: Doyle, J. G.; Mathioudakis, M.; Panagi, P. M.; Butler, C. J.
1990A&AS...86..403D    Altcode:
  Optical and infrared photometry plus spectroscopic data is present
  for two new flare stars, Gl 375 and Gl 431. Both of these stars have
  the hydrogen Balmer lines strongly in emission. Several flares were
  detected on Gl 375 implying a high level of flare activity. The H-alpha
  surface flux of 1.0 x 10 to the 6th erg/sq cm per sec for both stars
  is similar to that of other active flare stars. Fluxes are given for
  several of the higher Balmer lines.

---------------------------------------------------------
Title: Chromospheric/coronal emission correlations in "quiscent"
    and eruptive phenomena in M-dwarf stars.
Authors: Mathioudakis, M.; Doyle, J. G.
1990A&A...240..357M    Altcode:
  A power correlation between 'quiescent' and flaring H-gamma and
  X-ray emission is presented for a group of active dwarf M stars. The
  relationship holds for both 'quiescent' and flaring conditions for
  several orders of magnitude change in energy. Explanations in terms
  of X-ray back-heating and microflaring are discussed.

---------------------------------------------------------
Title: IUE observations of GL 644 AB (=Wolf 630) in the wavelength
    region 1150-1950 A, in June 1981.
Authors: Mathioudakis, M.; Doyle, J. G.
1990A&A...232..114M    Altcode:
  IUE short wavelength observations of the flare star Gl 644, obtained
  in June 1981 are presented. A flare was detected in one of the spectra
  as a strong increase in C IV, He II, and continuum fluxes. The electron
  density of the flaring plasma, determined using line ratio techniques,
  is 4 x 10 to the 10th/cu cm, which is an increase by a factor of
  2.7 above the quiescent. The radiative losses of the flare are at
  least 1.3 x 10 to the 32nd erg and 4.0 x 10 to the 33rd erg over the
  temperature range log Te between 4.3 and 5.4 and log Te between 4.0
  and 8.0, respectively. This compares with continuum losses of 8.1 x
  10 to the 31st erg over the wavelength region 1250-1950 A.

---------------------------------------------------------
Title: Flare activity and orbital rotation of YY Geminorum.
Authors: Doyle, J. G.; Mathioudakis, M.
1990A&A...227..130D    Altcode:
  The observed flare activity on the eclipsing binary star YY Geminorum,
  as determined by the time-average flare energy, is more than as order
  of magnitude greater out-of-eclipse than that during eclipses. The
  out-of-eclipse value is however, heavily biased by four large
  flares. In the cumulative distribution diagram these larger flares
  have a substantially different statistical occurrence rate than the
  remainder of the flares. It is suggested that the small separation
  between the two stars leads to significantly enhanced magnetic field
  between the two components and thus to the occurrence of energetic
  flares, observable when the stars are out of eclipse.

---------------------------------------------------------
Title: Rotational Modulation of Plages on II Peg
Authors: Mathioudakis, M.
1990iue..prop.3874M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Flux-flux relation : MG II H and K versus X-rays in dwarf M
    and K stars.
Authors: Mathioudakis, M.; Doyle, J. G.
1989A&A...224..179M    Altcode:
  Surface X-ray and Mg II h and k fluxes are presented for a group of
  dMe, dKe, dM, and dK stars. No correlation is apparent between the
  fluxes for the group of stars as a whole, although a good correlation
  is present for a subgroup, i.e., the dMe/dKe's. The Mg II and X-ray
  luminosities for these active stars define an upper boundary, which
  is dependent upon the stellar radii. The Mg II luminosity from the
  less active dM/dK stars are also radii-dependent, but this is not the
  case for the X-ray luminosity. This may indicate a difference in the
  heating mechanisms for the chromosphere and corona, with acoustic wave
  heating being an important contributor in the chromosphere and/or a
  difference in the plage filling factors in the two regions.