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Author name code: mullan
ADS astronomy entries on 2022-09-14
author:"Mullan, Dermott J."

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Title: Magnetic Fields in Low-mass Stars Increase Photometric Masses,
    Thereby Reducing Inferred Radius Inflation
Authors: MacDonald, J.; Mullan, D. J.
2022RNAAS...6..146M    Altcode:
  Standard evolution models of a given age provide a relationship between
  stellar mass and T <SUB>eff</SUB>. Based on this, Cruz et al. have
  derived stellar masses and radii for a sample of Kepler stars using
  photometry alone: their radii are found to be inflated by up to 100%
  relative to standard models. However, magnetic fields distort the M-T
  <SUB>eff</SUB> relationship in a systematic way: here, we quantify this
  distortion, and show that radius inflations in the Cruz et al. stars
  are likely to be significantly smaller than 100%.

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Title: Rotationally Constrained Convection in the Sun: Applicable
    to Planetary Atmospheres?
Authors: Mullan, D. J.
2022RNAAS...6...83M    Altcode:
  Rotational suppression of convection can occur on length scales which
  are larger than a critical length. Featherstone &amp; Hindman suggest
  that this can account for a second preferred length-scale in solar
  convection on supergranule scales. Here, I explore if rotational
  suppression of convection also occurs in the atmospheres of Earth
  and Venus.

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Title: Mechanical Energy Deposition in Cool Star Atmospheres:
    Resonant Coupling to Coronal Loops in M Dwarfs
Authors: Mullan, D. J.
2021ApJ...922..164M    Altcode:
  The efficiency of coronal heating ɛ(cor) in a star can be quantified by
  L <SUB>X</SUB>/L <SUB>bol</SUB>, i.e., the ratio of X-ray luminosity to
  bolometric luminosity. The efficiency of chromospheric heating in the
  same star ɛ(chr) is typically assumed to be proportional to L(H α)/L
  <SUB>bol</SUB> or L(Ca K)/L <SUB>bol</SUB> where the lines H α and Ca
  K are often the two strongest emission lines in the visible spectrum:
  the constant of proportionality (η = ɛ(chr)/[L(Hα)/L <SUB>bol</SUB>]
  &gt; 1) includes contributions from many other lines emitted by the
  chromosphere. In the case of the quiet Sun, it has been known for
  decades that, in the Sun, the efficiency of chromospheric heating is
  larger by a factor of ɛ(chr)/ɛ(cor) &gt; 10 than the efficiency of
  coronal heating. Over the intervening years, data pertaining to ɛ(cor)
  and ɛ(chr) have been estimated for an increasingly large sample of
  main-sequence stars with spectral types later than the Sun. These data
  suggest that among M dwarfs, the efficiency ratio ɛ(chr)/ɛ(cor) may
  in some stars become smaller than in the solar case. The effect of
  this is such that the value of ɛ(cor) may become comparable to the
  value of ɛ(chr). Here, we seek to understand why coronal heating may
  be &gt;10 times more efficient (relative to chromospheric heating) in
  certain M dwarfs than in the Sun. Using data on coronal loop properties
  in flaring stars, we examine the hypothesis that in M dwarfs, the
  enhanced efficiency of coronal heating may be related to resonant
  coupling between coronal loops and the source of mechanical energy in
  the convection zone.

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Title: Simultaneous Multiwavelength Flare Observations of EV Lacertae
Authors: Paudel, Rishi R.; Barclay, Thomas; Schlieder, Joshua E.;
   Quintana, Elisa V.; Gilbert, Emily A.; Vega, Laura D.; Youngblood,
   Allison; Silverstein, Michele; Osten, Rachel A.; Tucker, Michael A.;
   Huber, Daniel; Do, Aaron; Hamaguchi, Kenji; Mullan, D. J.; Gizis,
   John E.; Monsue, Teresa A.; Colón, Knicole D.; Boyd, Patricia T.;
   Davenport, James R. A.; Walkowicz, Lucianne
2021ApJ...922...31P    Altcode: 2021arXiv210804753P
  We present the first results of our ongoing project conducting
  simultaneous multiwavelength observations of flares on nearby active
  M dwarfs. We acquired data of the nearby dM3.5e star EV Lac using five
  different observatories: NASA's Transiting Exoplanet Survey Satellite
  (TESS), NASA's Neil Gehrels Swift Observatory (Swift), NASA's Neutron
  Interior Composition Explorer (NICER), the University of Hawaii
  2.2-meter telescope (UH88), and the Las Cumbres Observatory Global
  Telescope (LCOGT) Network. During the ~25 days of TESS observations,
  we acquired three simultaneous UV/X-ray observations using Swift that
  total ~18 ks, 21 simultaneous epochs totaling ~98 ks of X-ray data
  using NICER, one observation (~3 hr) with UH88, and one observation
  (~3 hr) with LCOGT. We identified 56 flares in the TESS light curve with
  estimated energies in the range log E<SUB>T</SUB> (erg) = (30.5-33.2),
  nine flares in the Swift UVM2 light curve with estimated energies in
  the range log E<SUB>UV</SUB> (erg) = (29.3-31.1), 14 flares in the
  NICER light curve with estimated minimum energies in the range log
  E<SUB>N</SUB> (erg) = (30.5-32.3), and 1 flare in the LCOGT light curve
  with log E<SUB>L</SUB> (erg) = 31.6. We find that the flare frequency
  distributions (FFDs) of TESS and NICER flares have comparable slopes,
  β<SUB>T</SUB> = -0.67 ± 0.09 and β<SUB>N</SUB> = - 0.65 ± 0.19,
  and the FFD of UVOT flares has a shallower slope (β<SUB>U</SUB> =
  -0.38 ± 0.13). Furthermore, we do not find conclusive evidence for
  either the first ionization potential (FIP) or the inverse FIP effect
  during coronal flares on EV Lac.

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Title: THOR 42: A Test of Magnetic Models for Pre-main-sequence Stars
Authors: MacDonald, J.; Mullan, D. J.
2021ApJ...907...27M    Altcode:
  Precise masses and radii have been reported by Murphy et al. for the
  components of the THOR 42 binary. Murphy et al. provide evidence that,
  in their opinion, supports an earlier suggestion by Bell et al. that
  THOR 42 is a member of the 32 Ori moving group, which, according to
  Bell et al., has an age of about 24 Myr. From the positions of the THOR
  2 components in the mass-radius diagram (MRD), Murphy et al. derive
  ages of 22-26 Myr using standard (nonmagnetic) models. However,
  they also find that these models cannot simultaneously reproduce
  the observed masses, radii, effective temperatures, and luminosities
  of the assumed coeval components. Their Hertzsprung-Russell diagram
  (HRD) ages are found to be 2-4 times younger than the MRD ages, and
  the masses determined from the HRD are found to be ∼50% smaller than
  the dynamical masses. Here, we attempt to replicate the precise global
  properties of THOR 24 by applying a model of magnetoconvection. We find
  that MRD isochrones and HRD isochrones lead to consistent ages provided
  that the surface magnetic fields have strengths of 300-400 G. However,
  the ages that our models yield for THOR 24 are in the vicinity of 40
  Myr. If this age estimate is correct, it could call into question the
  membership of THOR 42 in the 32 Ori moving group.

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Title: Pre-main-sequence Stars in Taurus: Comparison of Magnetic
    and Nonmagnetic Model Fits to the Low-mass Stars
Authors: Mullan, D. J.; MacDonald, J.
2020ApJ...904..108M    Altcode:
  Stellar associations should be co-eval, but some associations exhibit
  apparently discrepant ages: M stars appear younger than FG stars. Among
  M stars in the Upper Sco association (age ≍ 11 Myr), magnetic effects
  have been shown to slow down evolution of the lowest mass stars, thereby
  alleviating the age discrepancy. A recent study of pre-main-sequence
  (PMS) stars in the much younger Taurus star-forming region (SFR) suggest
  that an age discrepancy may also exist there. Our goal is to compare
  two approaches to magnetic/nonmagnetic modeling of the Taurus stars. In
  one approach, Simon et al. concluded that an age discrepancy exists, but
  it can be resolved by magnetic models if one imposes an "equipartition
  condition" on the photospheric field of each star. In this paper, we
  examine an independent sample of seven Taurus PMS stars reported by
  Rizzuto et al. Our approach to modeling magneto-convection imposes no
  condition on the photospheric field strength. We find that nonmagnetic
  isochrones can successfully fit the stars in the Rizzuto et al. sample
  with ages 1.6-2.4 Myr, without the need to invoke magnetic effects. An
  upper limit on the vertical field strength on the surfaces of the
  Rizzuto stars is found to be ∼300 G for the low-mass secondaries of FF
  Tau and HP Tau/G2 and ∼100 G for the other, more massive stars. The
  Taurus SFR is so large (extending over many square degrees in the sky)
  that magnetic conditions may plausibly differ from star to star.

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Title: K2 Ultracool Dwarfs Survey - VI. White light superflares
    observed on an L5 dwarf and flare rates of L dwarfs
Authors: Paudel, R. R.; Gizis, J. E.; Mullan, D. J.; Schmidt, S. J.;
   Burgasser, A. J.; Williams, P. K. G.
2020MNRAS.494.5751P    Altcode: 2020MNRAS.tmp.1373P; 2020arXiv200410579P
  Kepler K2 long cadence data are used to study white light flares
  in a sample of 45 L dwarfs. We identified 11 flares on 9 L dwarfs
  with equivalent durations of (1.3-198) h and total (UV/optical/IR)
  energies of ≥0.9 × 10<SUP>32</SUP> erg. Two superflares with
  energies of &gt;10<SUP>33</SUP> erg were detected on an L5 dwarf
  (VVV BD001): this is the coolest object so far on which flares have
  been identified. The larger superflare on this L5 dwarf has an energy
  of 4.6 × 10<SUP>34</SUP> erg and an amplitude of &gt;300 times the
  photospheric level: so far, this is the largest amplitude flare detected
  by the Kepler/K2 mission. The next coolest star on which we identified
  a flare was an L2 dwarf: 2MASS J08585891+1804463. Combining the energies
  of all the flares which we have identified on 9 L dwarfs with the total
  observation time which was dedicated by Kepler to all 45 L dwarfs,
  we construct a composite flare frequency distribution (FFD). The FFD
  slope is quite shallow (-0.51 ± 0.17), consistent with earlier results
  reported by Paudel et al. for one particular L0 dwarf, for which the FFD
  slope was found to be -0.34. Using the composite FFD, we predict that,
  in early- and mid-L dwarfs, a superflare of energy 10<SUP>33</SUP>
  erg occurs every 2.4 yr and a superflare of energy 10<SUP>34</SUP>
  erg occurs every 7.9 yr. Analysis of our L dwarf flares suggests that
  magnetic fields of ≥0.13-1.3 kG are present on the stellar surface:
  such fields could suppress Type II radio bursts.

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Title: A Transition of Dynamo Modes in M Dwarfs: Narrowing Down the
    Spectral Range Where the Transition Occurs
Authors: Mullan, D. J.; Houdebine, E. R.
2020ApJ...891..128M    Altcode: 2020arXiv200108721M
  Houdebine et al. combined Ca II data with projected rotational
  velocities (V sin I) to construct rotation-activity correlations (RAC)
  in K-M dwarfs. The RAC slopes were used to argue that a transition
  between dynamo modes occurs at a spectral type between M2 and M3. H17
  suggested that the dynamo transition corresponds to a transition to
  complete convection (TTCC). An independent study of GAIA data led Jao
  et al. to suggest that the TTCC sets in "near M3.0V," close to the H17
  result. However, the changes in a star that cause TTCC signatures in
  GAIA data might not lead to changes in Ca II emission at an identical
  spectral type: the latter are also affected by magnetic effects, which
  depend on certain properties of convection in the core. Here, we use
  Ca II emission fluxes in a sample of ∼600 M dwarfs, and attempt to
  narrow down the transition from one dynamo mode to another: rather
  than relying on RAC slopes, we quantify how the Ca II emission flux
  varies with spectral type to identify "steps" where the flux decreases
  significantly across a narrow range of spectral types. We suggest that
  the dynamo mode transition may be narrowed down to between M2.1 and
  M2.3. This is close to, but earlier than, the TTCC location identified
  by Jao et al. We suggest that the transition in dynamo mode may be
  related to the existence of a small convective core, which occurs for
  a finite time interval in certain low-mass stars.

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Title: Mass Loss on the Red Giant Branch: Plasmoid-driven Winds
    above the RGB Bump
Authors: Mullan, D. J.; MacDonald, J.
2019ApJ...885..113M    Altcode: 2019arXiv190909204M
  The onset of cool massive winds in evolved giants is correlated
  with an evolutionary feature on the red giant branch (RGB) known
  as the “bump.” Also at the bump, shear instability in the
  star leads to magnetic fields that occur preferentially on small
  length-scales. Pneuman has suggested that the emergence of small-scale
  flux tubes in the Sun can give rise to enhanced acceleration of
  the solar wind as a result of plasmoid acceleration (the so-called
  “melon-seed mechanism”). In this paper, we examine Pneuman’s
  formalism to determine if it may shed some light on the process
  that drives mass loss in stars above the RGB bump. Because we do not
  currently have detailed information for some of the relevant physical
  parameters, we are not yet able to derive a detailed model: instead,
  our goal in this paper is to explore a “proof of concept.” Using
  parameters that are known to be plausible in cool giants, we find that
  the total mass-loss rate from such stars can be replicated. Moreover,
  we find that the radial profile of the wind speed in such stars can be
  steep or shallow depending on the fraction of the mass-loss rate that
  is contained in the plasmoids: this is consistent with empirical data
  that indicate that the velocity profiles of winds from cool giants
  span a range of steepnesses.

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Title: VizieR Online Data Catalog: Stellar parameters of M and K
    dwarfs (Houdebine+, 2019)
Authors: Houdebine, E. R.; Mullan, D. J.; Doyle, J. G.; de La
   Vieuville, G.; Butler, C. J.; Paletou, F.
2019yCat..51580056H    Altcode:
  Observations of (R-I)<SUB>C</SUB> (Cousin's photometric system) or
  (R-I)&lt;SU photometric system) for our samples of K and M dwarfs
  were taken from several papers. We selected eight samples of K and M
  dwarfs according to their (R-I)<SUB>C</SUB> colors. This represents
  a total sample of 2765 K and M dwarfs. Most stars in this sample
  are nearby or large proper motion stars. We also completed these
  samples of stars with a ninth sample of stars: the M0-M1 sample,
  which includes some stars from the samples of stars from B12 and M15
  (see Table 1), as well as several stars initially from the M2 sample,
  which were found to have higher temperatures (we included in the M0-M1
  sample stars down to the spectral type dM1.5). <P />(3 data files).

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Title: The Mass-Activity Relationships in M and K Dwarfs. I. Stellar
    Parameters of Our Sample of M and K Dwarfs
Authors: Houdebine, Éric R.; Mullan, D. J.; Doyle, J. G.; de La
   Vieuville, Geoffroy; Butler, C. J.; Paletou, F.
2019AJ....158...56H    Altcode: 2019arXiv190507921H
  Empirical correlations between stellar parameters such as rotation
  or radius and magnetic activity diagnostics require estimates
  of the effective temperatures and the stellar radii. The aim of
  this study is to propose simple methods that can be applied to
  large samples of stars in order to derive estimates of the stellar
  parameters. Good empirical correlations between red/infrared colors
  (e.g., (R - I)<SUB> C </SUB>) and effective temperatures have been
  well established for a long time. The more recent (R - I)<SUB> C
  </SUB> color-T <SUB>eff</SUB> correlation using the data of Mann et
  al. (hereafter M15) and Boyajian et al. (hereafter B12) shows that
  this color can be applied as a temperature estimate for large samples
  of stars. We find that the mean scatter in T <SUB>eff</SUB> relative
  to the (R - I)<SUB> C </SUB>-T <SUB>eff</SUB> relationship of B12 and
  M15 data is only ±3σ = 44.6 K for K dwarfs and ±3σ = 39.4 K for M
  dwarfs. These figures are small and show that the (R - I)<SUB> C </SUB>
  color can be used as a first-guess effective temperature estimator
  for K and M dwarfs. We derive effective temperatures for about 1910
  K and M dwarfs using the calibration of (R - I)<SUB> C </SUB> color-T
  <SUB>eff</SUB> from B12 and M15 data. We also compiled T <SUB>eff</SUB>
  and metallicity measurements available in the literature using the
  VizieR database. We determine T <SUB>eff</SUB> for 441 stars with
  previously unknown effective temperatures. We also identified 21 new
  spectroscopic binaries and one triple system from our high-resolution
  spectra. <P />Based on Gaia DR2 and Hipparcos parallax measurements.

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Title: K2 Ultracool Dwarfs Survey - V. High superflare rates on
    rapidly rotating late-M dwarfs
Authors: Paudel, R. R.; Gizis, J. E.; Mullan, D. J.; Schmidt, S. J.;
   Burgasser, A. J.; Williams, P. K. G.; Youngblood, A.; Stassun, K. G.
2019MNRAS.486.1438P    Altcode: 2019MNRAS.tmp..860P; 2018arXiv181207631P
  We observed strong superflares (defined as flares with energy in excess
  of 10<SUP>33</SUP> erg) on three late-M dwarfs: 2MASS J08315742+2042213
  (hereafter 2M0831+2042; M7 V), 2MASS J08371832+2050349 (hereafter
  2M0837+2050; M8 V), and 2MASS J08312608+2244586 (hereafter 2M0831+2244;
  M9 V). 2M0831+2042 and 2M0837+2050 are members of the young (∼700
  Myr) open cluster Praesepe. The strong superflare on 2M0831+2042 has
  an equivalent duration (ED) of 13.7 h and an estimated energy of 1.3
  × 10<SUP>35</SUP> erg. We observed five superflares on 2M0837+2050,
  on which the strongest superflare has an ED of 46.4 h and an estimated
  energy of 3.5 × 10<SUP>35</SUP> erg. This energy is larger by 2.7
  orders of magnitude than the largest flare observed on the older (7.6
  Gyr) planet-hosting M8 dwarf TRAPPIST-1. Furthermore, we also observed
  five superflares on 2M0831+2244 which is probably a field star. The
  estimated energy of the strongest superflare on 2M0831+2244 is 6.1 ×
  10<SUP>34</SUP> erg. 2M0831+2042, 2M0837+2050, and 2M0831+2244 have
  rotation periods of 0.556 ± 0.002, 0.193 ± 0.000, and 0.292 ± 0.001
  d, respectively, which we measured by using K2 light curves. We compare
  the flares of younger targets with those of TRAPPIST-1 and discuss
  the possible impacts of such flares on planets in the habitable zone
  of late-M dwarfs.

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Title: Pathways for Ecological Change in Canadian High Arctic Wetlands
    Under Rapid Twentieth Century Warming
Authors: Sim, T. G.; Swindles, G. T.; Morris, P. J.; Gałka, M.;
   Mullan, D.; Galloway, J. M.
2019GeoRL..46.4726S    Altcode:
  We use paleoecological techniques to investigate how Canadian High
  Arctic wetlands responded to a mid-twentieth century increase in growing
  degree days. We observe an increase in wetness, moss diversity, and
  carbon accumulation in a polygon mire trough, likely related to ice
  wedge thaw. Contrastingly, the raised center of the polygon mire showed
  no clear response. Wet and dry indicator testate amoebae increased
  concomitantly in a valley fen, possibly relating to greater inundation
  from snowmelt followed by increasing evapotranspiration. This occurred
  alongside the appearance of generalist hummock mosses. A coastal
  fen underwent a shift from sedge to shrub dominance. The valley and
  coastal fens transitioned from minerogenic to organic-rich wetlands
  prior to the growing degree days increase. A subsequent shift to moss
  dominance in the coastal fen may relate to intensive grazing from
  Arctic geese. Our findings highlight the complex response of Arctic
  wetlands to warming and have implications for understanding their
  future carbon sink potential.

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Title: Origin of Radio-quiet Coronal Mass Ejections in Flare Stars
Authors: Mullan, D. J.; Paudel, R. R.
2019ApJ...873....1M    Altcode: 2019arXiv190200810M
  Type II radio bursts are observed in the Sun in association with
  many coronal mass ejections (CMEs). In view of this association,
  there has been an expectation that, by scaling from solar flares to
  the flares that are observed on M dwarfs, radio emission analogous to
  solar type II bursts should be detectable in association with M dwarf
  flares. However, several surveys have revealed that this expectation
  does not seem to be fulfilled. Here we hypothesize that the presence
  of larger global field strengths in low-mass stars, suggested by recent
  magnetoconvective modeling, gives rise to such large Alfvén speeds in
  the corona that it becomes difficult to satisfy the conditions for the
  generation of type II radio bursts. As a result, CMEs propagating in
  the corona/wind of flare stars are expected to be “radio-quiet”
  as regards type II bursts. In view of this, we suggest that, in the
  context of type II bursts, scaling from solar to stellar flares is of
  limited effectiveness.

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Title: The Umbral-penumbral Boundary in Sunspots in the Context
    of Magnetoconvection
Authors: Mullan, D. J.; MacDonald, J.
2019ApJ...873L..10M    Altcode: 2019arXiv190209431M
  Jurcak et al. have reported that, in a sample of more than 100 umbral
  cores in sunspots, the umbral-penumbral boundary (UPB) is characterized
  by a remarkably narrowly defined numerical value (1867 G) of the
  vertical component of the magnetic field. Gough &amp; Tayler, in
  their study of magnetoconvection, showed that the onset of convection
  in the presence of a magnetic field is controlled by a parameter δ,
  which also depends on the vertical component of the field. Combining
  the Jurcak et al. result with various empirical models of sunspots
  leads us to propose the following hypothesis: the UPB occurs where the
  vertical field is strong enough to increase the effective adiabatic
  temperature gradient by ≥100% over its non-magnetic value.

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Title: VizieR Online Data Catalog: K2 ultracool dwarfs
    survey. III. M6-L0 flares (Paudel+, 2018)
Authors: Paudel, R. R.; Gizis, J. E.; Mullan, D. J.; Schmidt, S. J.;
   Burgasser, A. J.; Williams, P. K. G.; Berger, E.
2019yCat..18580055P    Altcode:
  All the 10 targets listed in Table 1 were observed by Kepler K2
  in various campaigns (see the campaign number in Table 1) in both
  long-cadence mode (~30 min) and short-cadence mode (~1 min). We used
  short-cadence data to study white light flares (WLFs) on all of our
  targets. <P />(3 data files).

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Title: Magnetic Fields on the Flare Star Trappist-1: Consequences
    for Radius Inflation and Planetary Habitability
Authors: Mullan, D. J.; MacDonald, J.; Dieterich, S.; Fausey, H.
2018ApJ...869..149M    Altcode: 2018arXiv181104149M
  We construct evolutionary models of Trappist-1 in which magnetic
  fields impede the onset of convection according to a physics-based
  criterion. In the models that best fit all observational constraints,
  the photospheric fields in Tr-1 are found to be in the range 1450-1700
  G. These are weaker by a factor of about 2 than the fields we obtained
  in previous magnetic models of two other cool dwarfs (GJ 65A/B). Our
  results suggest that Tr-1 possesses a global poloidal field that is
  ∼100 times stronger than the Sun's global field. In the context of
  exoplanets in orbit around Tr-1, the strong poloidal fields on the star
  may help to protect the planets from the potentially destructive effects
  of coronal mass ejections. This, in combination with previous arguments
  about the beneficial effects of flare photons in the ultraviolet and
  visible portions of the spectrum, suggests that conditions on Tr-1
  are not necessarily harmful to life on a planet in the habitable zone
  of Tr-1.

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Title: Photosynthesis on a Planet Orbiting an M Dwarf: Enhanced
    Effectiveness during Flares
Authors: Mullan, D. J.; Bais, H. P.
2018ApJ...865..101M    Altcode: 2018arXiv180705267M
  On planets near M dwarfs, oxygenic photosynthesis (PS) will occur
  with an effectiveness that depends on the supply of visible photons
  with wavelengths between 400 and 700 nm. In this paper, we quantify
  the effectiveness of PS in two contexts that are relevant for
  M dwarfs. First, using photons from an M dwarf in its quiescent
  (nonflaring) state, we find that PS on an M dwarf planet in the
  habitable zone (HZ) of its parent star is less effective than on Earth
  by a factor of 10 for a flare star with mid-M spectral type. For a flare
  star with late-M spectral type, PS effectiveness (PSE) is smaller than
  on Earth by a factor of 100 or more. Second, using photons that are
  incident on the HZ planet during flares, we find that PSE can increase
  by factors of 5-20 above the quiescent values. In the case of a flare
  star with mid-M spectral type, we find that the PSE during a flare can
  increase up to as much as 50%-60% of the values on Earth. However,
  for a late-M flare star, even during flares, the PSE remains almost
  one order of magnitude smaller than on Earth. We suggest that for
  biological processes on M dwarf planets, the stellar activity cycle
  may replace the orbital period as the “year.”

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Title: K 2 Ultracool Dwarfs Survey. IV. Monster Flares Observed on
    the Young Brown Dwarf CFHT-BD-Tau 4
Authors: Paudel, Rishi R.; Gizis, John E.; Mullan, D. J.; Schmidt,
   Sarah J.; Burgasser, Adam J.; Williams, Peter K. G.; Berger, Edo
2018ApJ...861...76P    Altcode: 2018arXiv180511185P
  We present photometric measurements of two superflares observed on a
  very young brown dwarf, CFHT-BD-Tau 4, observed during Campaign 13 of
  the Kepler K 2 mission. The stronger of the two superflares brightened
  by a factor of ∼48 relative to the quiescent photospheric level, with
  an increase in Kepler magnitude {{Δ }}\tilde{{K}<SUB>p</SUB>}=-4.20. It
  has an equivalent duration of ∼107 hr, a flare duration of 1.7 days,
  and an estimated total bolometric (ultraviolet/optical/infrared) energy
  up to 2.1 × 10<SUP>38</SUP> erg. The weaker of the two superflares
  is a complex (multipeaked) flare with an estimated total bolometric
  (UV/optical/IR) energy up to 4.7 × 10<SUP>36</SUP> erg. They are the
  strongest flares observed on any brown dwarf so far. The flare energies
  are strongly dependent on the value of the visual extinction parameter A
  <SUB> V </SUB> used for extinction correction. If we apply a solar flare
  model to interpret the two superflares, we find that the magnetic fields
  are required to be stronger by as much as an order of magnitude than
  previous reports of field measurements in CFHT-BD-Tau 4 by Reiners et
  al. On the other hand, if we interpret our data in terms of accretion,
  we find that the requisite rate of accretion for the stronger superflare
  exceeds the rates that have been reported for other young brown dwarfs.

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Title: White Light Flare Rates of M5-L5 dwarfs using K2 data
Authors: Paudel, Rishi R.; Gizis, John E.; Mullan, D. J.; Schmidt,
   Sarah J.; Burgasser, Adam J.; Williams, Peter K. G.
2018csss.confE..78P    Altcode:
  The K2 mission's unique combination of wide area coverage and
  continuous time coverage over months has enabled us to study white
  light flare rates of cool stars of various spectral types. We have
  shown that the white light flares are ubiquitous in some late-M and
  early L dwarfs. Some early L dwarfs are even capable of producing
  superflares with bolometric flare energies greater than 10<SUP>33</SUP>
  erg despite having lower effective temperatures. We update our results
  on the white light flare rates of very-low-mass stars with a wide
  range of spectral types: M5-L5, obtained by using both short cadence
  ( 1 min) and long cadence ( 30 min) K2 data. We analyze the possible
  relation between flare rates of very-low-mass stars in our sample and
  different properties like spectral type, age, etc. Strong magnetic
  fields of order of 5-10 kilogauss are required to explain the most
  energetic flares. Using constraints on magnetic fields from the biggest
  flares, we discuss the nature and evolution of the magnetic dynamo
  on very-low-mass stars. Our results will be helpful in predicting the
  number of flares on the low-mass cool stars which will be observed by
  future photometric surveys like TESS.

---------------------------------------------------------
Title: The Magnetic Binary GJ 65: A Test of Magnetic Diffusivity
    Effects
Authors: MacDonald, James; Mullan, D. J.; Dieterich, Sergio
2018ApJ...860...15M    Altcode: 2017arXiv171109434M
  GJ 65 is an M dwarf binary system consisting of the two flare stars
  BL Cet (GJ 65A) and UV Cet (GJ 65B). Two teams of investigators have
  recently reported total magnetic fluxes corresponding to fields of 4.5
  and 5.2 kG for GJ 65A and 5.8 and 6.7 kG for GJ 65B: for each component,
  the magnetic results obtained by the two teams agree with each other to
  within 1σ. For the first time, we can directly compare the predictions
  of our magneto-convective models, based on fitting observed stellar
  parameters, with measured field strengths. We find that our models
  agree with the observed field strengths, provided the effects of
  finite conductivity are accounted for. Thus, GJ 65 provides us with
  an opportunity to use observations of field strengths to distinguish
  between the predictions of our models that assume perfect electrical
  conductivity and those that allow for finite conductivity.

---------------------------------------------------------
Title: K2 Ultracool Dwarfs Survey. III. White Light Flares Are
    Ubiquitous in M6-L0 Dwarfs
Authors: Paudel, Rishi R.; Gizis, John E.; Mullan, D. J.; Schmidt,
   Sarah J.; Burgasser, Adam J.; Williams, Peter K. G.; Berger, Edo
2018ApJ...858...55P    Altcode: 2018arXiv180307708P
  We report the white light flare rates for 10 ultracool dwarfs using
  Kepler K2 short-cadence data. Among our sample stars, two have spectral
  type M6, three are M7, three are M8, and two are L0. Most of our
  targets are old low-mass stars. We identify a total of 283 flares in
  all of the stars in our sample, with Kepler energies in the range log
  E <SUB>Kp</SUB> ∼ (29-33.5) erg. Using the maximum-likelihood method
  of line fitting, we find that the flare frequency distribution (FFD)
  for each star in our sample follows a power law with slope -α in the
  range -(1.3-2.0). We find that cooler objects tend to have shallower
  slopes. For some of our targets, the FFD follows either a broken power
  law, or a power law with an exponential cutoff. For the L0 dwarf 2MASS
  J12321827-0951502, we find a very shallow slope (-α = -1.3) in the
  Kepler energy range (0.82-130) × 10<SUP>30</SUP> erg: this L0 dwarf
  has flare rates which are comparable to those of high-energy flares in
  stars of earlier spectral types. In addition, we report photometry
  of two superflares: one on the L0 dwarf 2MASS J12321827-0951502
  and another on the M7 dwarf 2MASS J08352366+1029318. In the case of
  2MASS J12321827-0951502, we report a flare brightening by a factor of
  ∼144 relative to the quiescent photospheric level. Likewise, for
  2MASS J08352366+1029318, we report a flare brightening by a factor
  of ∼60 relative to the quiescent photospheric level. These two
  superflares have bolometric (ultraviolet/optical/infrared) energies 3.6
  × 10<SUP>33</SUP> erg and 8.9 × 10<SUP>33</SUP> erg respectively,
  while the full width half maximum timescales are very short, ∼2
  min. We find that the M8 star TRAPPIST-1 is more active than the
  M8.5 dwarf 2M03264453+1919309, but less active than another M8 dwarf
  (2M12215066-0843197).

---------------------------------------------------------
Title: Frequencies of Flare Occurrence: Interaction between Convection
    and Coronal Loops
Authors: Mullan, D. J.; Paudel, R. R.
2018ApJ...854...14M    Altcode: 2018arXiv180107708M
  Observations of solar and stellar flares have revealed the presence of
  power-law dependences between the flare energy and the time interval
  between flares. Various models have been proposed to explain these
  dependences and the numerical value of the power-law indices. Here,
  we propose a model in which convective flows in granules force
  the footpoints of coronal magnetic loops, which are frozen-in to
  photospheric gas, to undergo a random walk. In certain conditions,
  this can lead to a twist in the loop, which drives the loop unstable
  if the twist exceeds a critical value. The possibility that a solar
  flare is caused by such a twist-induced instability in a loop has been
  in the literature for decades. Here, we quantify the process in an
  approximate way with a view to replicating the power-law index. We find
  that, for relatively small flares, the random walk twisting model leads
  to a rather steep power-law slope that agrees very well with the index
  derived from a sample of 56,000+ solar X-ray flares reported by the GOES
  satellites. For relatively large flares, we find that the slope of the
  power law is shallower. The empirical power-law slopes reported for
  flare stars also have a range that overlaps with the slopes obtained
  here. We suggest that in the coolest stars, a significant change in
  slope should occur when the frozen-flux assumption breaks down due to
  low electrical conductivity.

---------------------------------------------------------
Title: The most powerful white light flare observed on a young
    brown dwarf.
Authors: Paudel, Rishi R.; Gizis, John E.; Mullan, Dermott; Schmidt,
   Sarah J.; Burgasser, Adam J.; Williams, Peter Kelsey George; Berger,
   Edo
2018AAS...23134910P    Altcode:
  We have been using NASA's Kepler K2 mission short cadence (∼1 minute)
  and long cadence (∼30 minutes) data to estimate the flare rates of
  ultracool dwarfs of various spectral types and ages. These flare rates
  will be helpful to understand the nature and evolution of magnetic
  dynamo operating in cool objects. We report the detection of the most
  powerful white light superflare on a very young brown dwarf. This
  superflare has total bolometric energy &gt;10<SUP>36 </SUP>erg
  with an equivalent duration of ∼110 hours and flare duration of
  ∼1.84 days. This is the biggest superflare observed on any brown
  dwarf. In addition to it, we also observed another superflare on same
  target, which is complex (multipeaked) with total bolometric energy
  &gt;10<SUP>34</SUP> erg. The occurence of two superflares in a single
  K2 campaign implies a higer flare rate of this young dwarf. We compare
  its flare rate with other UCDs we have been studying.

---------------------------------------------------------
Title: Magnetic Modeling of Inflated Low-mass Stars Using Interior
    Fields No Larger than ∼10 kG
Authors: MacDonald, James; Mullan, D. J.
2017ApJ...850...58M    Altcode: 2017arXiv170806994M
  We have previously reported on models of low-mass stars in which the
  presence of inflated radii is ascribed to magnetic fields that impede
  the onset of convection. Some of our magneto-convection models have
  been criticized because, when they were first reported by Mullan &amp;
  MacDonald, the deep interior fields were found to be very large (50-100
  MG). Such large fields are now known to be untenable. For example,
  Browning et al. used stability arguments to suggest that interior fields
  in low-mass stars cannot be larger than ∼1 MG. Moreover, 3D models
  of turbulent stellar dynamos suggest that fields generated in low-mass
  interiors may be not much stronger than 10-20 kG. In the present paper,
  we present magneto-convective models of inflated low-mass stars in
  which the interior fields are not permitted to be stronger than 10
  kG. These models are used to fit empirical data for 15 low-mass stars
  for which precise masses and radii have been measured. We show that
  our 10 kG magneto-convective models can replicate the empirical radii
  and effective temperatures for 14 of the stars. In the case of the
  remaining star (in the Praesepe cluster), two different solutions have
  been reported in the literature. We find that one of these solutions
  can be fitted well with our model using the nominal age of Praesepe
  (800 Myr). However, the second solution cannot be fitted unless the
  star’s age is assumed to be much younger (∼150 Myr).

---------------------------------------------------------
Title: VizieR Online Data Catalog: Rotation-Activity Correlations
    in K-M dwarfs. I. (Houdebine+, 2016)
Authors: Houdebine, E. R.; Mullan, D. J.; Paletou, F.; Gebran, M.
2017yCat..18220097H    Altcode:
  We selected a sample of 419 late-K dwarfs on the basis of (R-I)
  measurements available in the literature. Searching through databases
  at the European Southern Observatory (ESO) and Observatoire de Haute
  Provence (OHP), we identified spectra of 112 different stars that
  are suitable for our purposes. The spectra that we use to determine
  vsini came from two different echelle spectrographs: HARPS (High
  Accuracy Radial velocity Planet Search, ESO; R=115000) and SOPHIE
  (OHP; R=75000). <P />(6 data files).

---------------------------------------------------------
Title: VizieR Online Data Catalog: Rotation-Activity Correlations
    in K-M dwarfs II. (Houdebine+, 2017)
Authors: Houdebine, E. R.; Mullan, D. J.; Bercu, B.; Paletou, F.;
   Gebran, M.
2017yCat..18370096H    Altcode:
  The spectra that we use for determining the CaII and Hα equivalent
  widths in the present study of dK4-dM4 stars came from three different
  echelle spectrographs; HARPS (High Accuracy Radial velocity Planet
  Search, ESO), SOPHIE (OHP), and FEROS (The Fiber-fed Extended Range
  Optical Spectrograph). <P />The stars in our samples include all stars
  from all observing programs that have been carried out with HARPS
  and SOPHIE for stars belonging to the following spectral sub-types:
  dK4, dK6, dM2, and dM3. For dM4 stars, we compiled all measurements
  of vsini available in the literature (see Paper I; Houdebine+ 2016,
  J/ApJ/822/97). For the dK6 and dM3 samples, we also supplemented
  our own measurements with measurements available in the literature,
  notably for active stars (see Paper I). <P />(7 data files).

---------------------------------------------------------
Title: K2 Ultracool Dwarfs Survey. II. The White Light Flare Rate
    of Young Brown Dwarfs
Authors: Gizis, John E.; Paudel, Rishi R.; Mullan, Dermott; Schmidt,
   Sarah J.; Burgasser, Adam J.; Williams, Peter K. G.
2017ApJ...845...33G    Altcode: 2017arXiv170308745G
  We use Kepler K2 Campaign 4 short-cadence (one-minute) photometry to
  measure white light flares in the young, moving group brown dwarfs 2MASS
  J03350208+2342356 (2M0335+23) and 2MASS J03552337+1133437 (2M0355+11),
  and report on long-cadence (thirty-minute) photometry of a superflare
  in the Pleiades M8 brown dwarf CFHT-PL-17. The rotation period (5.24
  hr) and projected rotational velocity (45 km s<SUP>-1</SUP>) confirm
  2M0335+23 is inflated (R≥slant 0.20 {R}<SUB>⊙ </SUB>) as predicted
  for a 0.06 {M}<SUB>⊙ </SUB>, 24 Myr old brown dwarf βPic moving
  group member. We detect 22 white light flares on 2M0335+23. The flare
  frequency distribution follows a power-law distribution with slope
  -α =-1.8+/- 0.2 over the range 10<SUP>31</SUP> to 10<SUP>33</SUP>
  erg. This slope is similar to that observed in the Sun and warmer
  flare stars, and is consistent with lower-energy flares in previous
  work on M6-M8 very-low-mass stars; taking the two data sets together,
  the flare frequency distribution for ultracool dwarfs is a power law
  over 4.3 orders of magnitude. The superflare (2.6× {10}<SUP>34</SUP>
  erg) on CFHT-PL-17 shows higher-energy flares are possible. We detect no
  flares down to a limit of 2× {10}<SUP>30</SUP> erg in the nearby L5γ
  AB Dor moving group brown dwarf 2M0355+11, consistent with the view
  that fast magnetic reconnection is suppressed in cool atmospheres. We
  discuss two multi-peaked flares observed in 2M0335+23, and argue that
  these complex flares can be understood as sympathetic flares, in which
  fast-mode magnetohydrodynamic waves similar to extreme-ultraviolet waves
  in the Sun trigger magnetic reconnection in different active regions.

---------------------------------------------------------
Title: LSPM J1314+1320: An Oversized Magnetic Star with Constraints
    on the Radio Emission Mechanism
Authors: MacDonald, James; Mullan, D. J.
2017ApJ...843..142M    Altcode: 2017arXiv170304488M
  LSPM J1314+1320 (=NLTT 33370) is a binary star system consisting of
  two nearly identical pre-main-sequence stars of spectral type M7. The
  system is remarkable among ultracool dwarfs for being the most luminous
  radio emitter over the widest frequency range. Masses and luminosities
  are at first sight consistent with the system being coeval at age ∼80
  Myr according to standard (nonmagnetic) evolutionary models. However,
  these models predict an average effective temperature of ∼2950 K,
  which is 180 K hotter than the empirical value. Thus, the empirical
  radii are oversized relative to the standard models by ≈13%. We
  demonstrate that magnetic stellar models can quantitatively account
  for the oversizing. As a check on our models, we note that the radio
  emission limits the surface magnetic field strengths: the limits
  depend on identifying the radio emission mechanism. We find that the
  field strengths required by our magnetic models are too strong to
  be consistent with gyrosynchrotron emission but are consistent with
  electron cyclotron maser emission.

---------------------------------------------------------
Title: The Rotation-Activity Correlations in K and M Dwarfs. II. New
    Constraints on the Dynamo Mechanisms in Late-K and M Dwarfs Before
    and At the Transition to Complete Convection
Authors: Houdebine, E. R.; Mullan, D. J.; Bercu, B.; Paletou, F.;
   Gebran, M.
2017ApJ...837...96H    Altcode: 2017arXiv170107608H
  We study the rotation-activity correlations (RACs) in a sample of
  stars from spectral type dK4 to dM4. We study RACs using chromospheric
  data and coronal data. We study the Ca II line surface fluxes-P/\sin
  I RACs. We fit the RACs with linear homoscedastic and heteroscedastic
  regression models. We find that these RACs differ substantially from
  one spectral sub-type to another. For dM3 and dM4 stars, we find
  that the RACs cannot be described by a simple model, but instead
  that there may exist two distinct RAC behaviors for the low-activity
  and the high-activity stellar sub-samples, respectively. Although
  these results are preliminary and will need confirmation, the data
  suggest that these distinct RACs may be associated with different
  dynamo regimes. We also study {R}<SUB>{HK</SUB>}<SUP>\prime </SUP>
  as a function of the Rossby number R <SUB>0</SUB>. We find (I) for
  dK4 stars, {R}<SUB>{HK</SUB>}<SUP>\prime </SUP> as a function of R
  <SUB>0</SUB> agrees well with previous results for F-G-K stars and
  (II) in dK6, dM2, dM3, and dM4 stars, at a given R <SUB>0</SUB>, the
  values of {R}<SUB>{HK</SUB>}<SUP>\prime </SUP> lie at a factor of 3,
  10, 20, and 90, respectively, below the F-G-K RAC. Our results suggest
  a significant decrease in the efficiency of the dynamo mechanism(s)
  as regards chromospheric heating before and at dM3, I.e., before and at
  the transition to complete convection. We also show that the ratio of
  coronal heating to chromospheric heating L <SUB>X</SUB>/L <SUB>HK</SUB>
  increases by a factor of 100 between dK4 and dM4 stars. <P />Based
  on observations available at Observatoire de Haute Provence and the
  European Southern Observatory databases and on Hipparcos parallax
  measurements.

---------------------------------------------------------
Title: The Age of the KIC 7177553 System
Authors: MacDonald, James; Mullan, D. J.
2017ApJ...834...99M    Altcode: 2016arXiv160900942M
  KIC 7177553 is a quadruple system containing two binaries of orbital
  periods 16.5 and 18 days. All components have comparable masses and
  are slowly rotating with spectral types of ∼G2V. The longer period
  binary is eclipsing with component masses and radii M<SUB>1</SUB>
  = 1.043 ± 0.014 M<SUB>⊙</SUB>, R<SUB>1</SUB> = 0.940 ± 0.005
  R<SUB>⊙</SUB> and M<SUB>2</SUB> = 0.986 ± 0.015 M<SUB>⊙</SUB>,
  R<SUB>2</SUB> = 0.941 ± 0.005 R<SUB>⊙</SUB>. The essentially equal
  radii measurements are inconsistent with the two stars being on the man
  sequence at the same age using standard nonmagnetic stellar evolution
  models. Instead a consistent scenario is found if the stars are in
  their pre-main-sequence phase of evolution and have an age of 32-36
  Myr. We have also computed evolutionary models of magnetic stars,
  but we find that our nonmagnetic models fit the empirical radii and
  effective temperatures better than the magnetic models.

---------------------------------------------------------
Title: Apparent Non-coevality among the Stars in Upper Scorpio:
    Resolving the Problem Using a Model of Magnetic Inhibition of
    Convection
Authors: MacDonald, James; Mullan, D. J.
2017ApJ...834...67M    Altcode: 2016arXiv160802136M
  Two eclipsing binaries in the USco association have recently yielded
  precise values of masses and radii for four low-mass members of the
  association. Standard evolution models would require these dM4.5-dM5
  stars to have ages which are younger than those of more massive
  stars in the association by factors which appear (in extreme cases)
  to be as large as ∼3. Are the stars in the association therefore
  non-coeval? We suggest that the answer is no: by incorporating the
  effects of magnetic inhibition of convective onset, we show that the
  stars in USco can be restored to coevality provided the four low-mass
  member stars have vertical surface fields in the range 200-700 G. Fields
  of such magnitude have already been measured on the surface of certain
  solar-type stars in other young clusters.

---------------------------------------------------------
Title: Rotation-Activity Correlations in K and M Dwarfs. I. Stellar
    Parameters and Compilations of v sin I and P/sin I for a Large Sample
    of Late-K and M Dwarfs
Authors: Houdebine, E. R.; Mullan, D. J.; Paletou, F.; Gebran, M.
2016ApJ...822...97H    Altcode: 2016arXiv160407920H
  The reliable determination of rotation-activity correlations (RACs)
  depends on precise measurements of the following stellar parameters:
  T <SUB>eff</SUB>, parallax, radius, metallicity, and rotational speed
  v sin I. In this paper, our goal is to focus on the determination of
  these parameters for a sample of K and M dwarfs. In a future paper
  (Paper II), we will combine our rotational data with activity data
  in order to construct RACs. Here, we report on a determination of
  effective temperatures based on the (R-I)<SUB> C </SUB> color from
  the calibrations of Mann et al. and Kenyon &amp; Hartmann for four
  samples of late-K, dM2, dM3, and dM4 stars. We also determine stellar
  parameters (T <SUB>eff</SUB>, log(g), and [M/H]) using the principal
  component analysis-based inversion technique for a sample of 105 late-K
  dwarfs. We compile all effective temperatures from the literature for
  this sample. We determine empirical radius-[M/H] correlations in our
  stellar samples. This allows us to propose new effective temperatures,
  stellar radii, and metallicities for a large sample of 612 late-K and
  M dwarfs. Our mean radii agree well with those of Boyajian et al. We
  analyze HARPS and SOPHIE spectra of 105 late-K dwarfs, and we have
  detected v sin I in 92 stars. In combination with our previous v sin
  I measurements in M and K dwarfs, we now derive P/sin I measures for
  a sample of 418 K and M dwarfs. We investigate the distributions of
  P/sin I, and we show that they are different from one spectral subtype
  to another at a 99.9% confidence level. <P />Based on observations
  available at Observatoire de Haute Provence and the European Southern
  Observatory databases and on Hipparcos parallax measurements.

---------------------------------------------------------
Title: Mechanical Energy Fluxes Associated with Saturated Coronal
Heating in M Dwarfs: Comparison with Predictions of a Turbulent Dynamo
Authors: Mullan, D. J.; MacDonald, J.
2016ApJ...818..154M    Altcode: 2016arXiv160203079M
  Empirically, the X-ray luminosity L<SUB>X</SUB> from M dwarfs has been
  found to have an upper limit of about 0.2% of the bolometric flux
  L<SUB>bol</SUB>. In the limit where magnetic fields in M dwarfs are
  generated in equipartition with convective motions, we use stellar
  models to calculate the energy flux of Alfvén waves F<SUB>A</SUB>
  as a function of depth in the sub-surface convection zone. Since
  Alfvén waves have the optimal opportunity for wave modes to reach
  the corona, we suggest that F<SUB>A</SUB> sets an upper limit on the
  mechanical flux F<SUB>mech</SUB> which causes coronal heating. This
  suggestion accounts quantitatively for the “saturated” values of
  L<SUB>X</SUB>/L<SUB>bol</SUB> which have been reported empirically
  for M dwarfs.

---------------------------------------------------------
Title: A Model for Interface Dynamos in Late K and Early M Dwarfs
Authors: Mullan, D. J.; Houdebine, E. R.; MacDonald, J.
2015ApJ...810L..18M    Altcode:
  Measurements of the equivalent width EW(CaK) of emission in the Ca ii
  K line have been obtained by Houdebine et al. for stars with spectral
  types from dK5 to dM4. In order to explain the observed variations
  of EW(CaK) with spectral sub-type, we propose a quantitative model of
  interface dynamos in low-mass stars. Our model leads to surface field
  strengths B<SUB>s</SUB> which turn out to be essentially linearly
  proportional to EW(CaK). This result is reminiscent of the Sun, where
  Skumanich et al. found that the intensity of CaK emission in solar
  active regions is linearly proportional to the local field strength.

---------------------------------------------------------
Title: Magnetoconvective models of red dwarfs: constraints imposed
    by the lithium abundance
Authors: MacDonald, J.; Mullan, D. J.
2015MNRAS.448.2019M    Altcode: 2015arXiv150104550M
  Magnetic fields impede the onset of convection, thereby altering the
  thermal structure of a convective envelope in a low-mass star: this has
  an effect on the amount of lithium depletion in a magnetized star. In
  order to quantify this effect, we have applied a magnetoconvective
  model to two low-mass stars for which lithium abundances and precise
  structural parameters are known: YY Gem and CU Cnc. For both stars,
  we have obtained models which satisfy empirical constraints on the
  following parameters: R, L, surface magnetic field strength, and
  Li abundance. In the case of YY Gem, we have obtained a model which
  satisfies the empirical constraints with an internal magnetic field
  of several megagauss: such a field strength is within the range of
  a dynamo where the field energy is in equipartition with rotational
  energy deep inside the convection zone. However, in the case of CU
  Cnc, the Li requires an internal magnetic field which is probably too
  strong for a dynamo origin: we suggest possible alternatives which
  might account for the reported Li abundance in CU Cnc.

---------------------------------------------------------
Title: Dynamics of Rotation in M Dwarfs: Indications for a Change
    in the Dynamo Regime in Stars at the Onset of Complete Convection
Authors: Houdebine, E. R.; Mullan, D. J.
2015ApJ...801..106H    Altcode: 2015arXiv150201266H
  We have measured vsin i with high precision for a sample of dM3 stars
  (86 targets). We detected rotation in 82 stars (73 dM3 stars and
  nine dM3e stars). We compare our measurements of vsin i for all of
  the stars in our dM0, dM2, dM3, and dM4 samples to those from other
  authors. We find a good agreement down to vsin i values of less than
  1 km s<SUP>-1</SUP>. The mean of the differences between measurements
  is only 0.42 km s<SUP>-1</SUP>. We find that the distribution of P/sini
  for our dM3 stars is different from the distribution of P/sini among our
  samples of dM2 and dM4 stars. The mean rotation rate for the dM3 stars
  (excluding dM3e and sdM3 stars) is significantly slower (25.8 days) than
  for dM2 (14.4 days) and dM4 stars (11.4 days). Analogous behavior also
  emerges among the faster rotators (dMe stars): we find that a longer
  rotation period also occurs at spectral subtype dM3e. Our data suggest
  that, as regards the rotational properties of lower main-sequence stars,
  spectral subtype dM3 stands out as exhibiting unusually slow rotation
  compared to that of adjoining subtypes. Our data lead us to suggest that
  the unusual rotational properties of M3 dwarfs may represent a signature
  of the transition to complete convection. <P />Based on observations
  available at Observatoire de Haute Provence and the European Southern
  Observatory databases and on Hipparcos parallax measurements.

---------------------------------------------------------
Title: Surface Magnetic Field Strengths: New Tests of
    Magnetoconvective Models of M Dwarfs
Authors: MacDonald, James; Mullan, D. J.
2014ApJ...787...70M    Altcode:
  Precision modeling of M dwarfs has become worthwhile in recent years
  due to the increasingly precise values of masses and radii which
  can be obtained from eclipsing binary studies. In a recent paper,
  Torres has identified four prime M dwarf pairs with the most precise
  empirical determinations of masses and radii. The measured radii are
  consistently larger than standard stellar models predict by several
  percent. These four systems potentially provide the most challenging
  tests of precision evolutionary models of cool dwarfs at the present
  time. We have previously modeled M dwarfs in the context of a criterion
  due to Gough &amp; Tayler in which magnetic fields inhibit the onset
  of convection according to a physics-based prescription. In the
  present paper, we apply our magnetoconvective approach to the four
  prime systems in the Torres list. Going a step beyond what we have
  already modeled in CM Dra (one of the four Torres systems), we note
  that new constraints on magnetoconvective models of M dwarfs are now
  available from empirical estimates of magnetic field strengths on the
  surfaces of these stars. In the present paper, we consider how well our
  magnetoconvective models succeed when confronted with this new test of
  surface magnetic field strengths. Among the systems listed by Torres,
  we find that plausible magnetic models work well for CM Dra, YY Gem,
  and CU Cnc. (The fourth system in Torres's list does not yet have
  enough information to warrant magnetic modeling.) Our magnetoconvection
  models of CM Dra, YY Gem, and CU Cnc yield predictions of the magnetic
  fluxes on the stellar surface which are consistent with the observed
  correlation between magnetic flux and X-ray luminosity.

---------------------------------------------------------
Title: The theoretical instability strip of M dwarf stars
Authors: Rodríguez-López, C.; MacDonald, J.; Amado, P. J.; Moya,
   A.; Mullan, D.
2014MNRAS.438.2371R    Altcode: 2013arXiv1312.2743R; 2013MNRAS.tmp.2985R
  The overstability of the fundamental radial mode in M dwarf models
  was theoretically predicted recently by Rodríguez-López et al. The
  periods were found to be in the ranges ∼25-40 min and ∼4-8 h,
  depending on stellar age and excitation mechanism. We have extended
  our initial M dwarf model grid in mass, metallicity and mixing length
  parameter. We have also considered models with boundary conditions from
  PHOENIX NEXTGEN atmospheres to test their influence on the pulsation
  spectra. We find instability of non-radial modes with radial orders up
  to k = 3, degree ℓ = 0-3, including p- and g-modes, with the period
  range extending from 20 min up to 11 h. Furthermore, we find theoretical
  evidence of the potential of M dwarfs as solar-like oscillators.

---------------------------------------------------------
Title: Lithium abundance and surface magnetic fields: new constraints
    in magnetic models of M dwarfs
Authors: MacDonald, James; Mullan, Dermott
2013arXiv1311.3246M    Altcode:
  Precision modeling of M dwarfs has become worthwhile in recent years
  due to the increasingly precise values of masses and radii which can be
  obtained from eclipsing binary studies. Torres (2013) has identified
  4 prime M dwarf pairs with the most precise empirical determinations
  of masses and radii. The measured radii are consistently larger than
  standard stellar models predict. We have previously modeled M dwarfs in
  the context of a criterion due to Gough &amp; Tayler in which magnetic
  fields inhibit the onset of convection according to a physics-based
  prescription. New constraints on the models of M dwarfs are now provided
  by measurements of lithium abundances. The key aspect of Li in terms of
  setting constraints on magnetic modeling is that Li burning starts at T
  = 2.5 MK, and temperatures of just such magnitude are associated with
  the base of the convection zone: magnetic inhibition of convective
  onset can shift this base slightly closer to the surface, i.e. to
  slightly lower temperatures, thereby reducing the amount of Li depletion
  compared to a non-magnetic model. In the present paper, we consider how
  our magneto-convection models handle the new test of stellar structure
  provided by Li measurements. Among the prime systems listed by Torres,
  we find that plausible magnetic models work well for CM Dra and YY Gem
  but not for CU Cnc. (The fourth system in Torres's list does not yet
  have enough information to warrant magnetic modeling.) For CU Cnc,
  we suggest that the observed lithium may have been accreted from a
  circumstellar disk. We find that our magneto-convection models of CM
  Dra, YY Gem and CU Cnc yield results which are consistent with the
  observed correlation between magnetic flux and X-ray luminosity.

---------------------------------------------------------
Title: Magnetic Effects and Oversized M Dwarfs in the Young Open
    Cluster NGC 2516
Authors: MacDonald, James; Mullan, Dermott J.
2013ApJ...765..126M    Altcode: 2013arXiv1302.2941M
  By combining rotation periods with spectroscopic determinations of
  projected rotation velocity, Jackson et al. have found that the mean
  radii for low-mass M-dwarfs in the young, open cluster NGC 2516 are
  larger than model predictions at a given absolute I magnitude or I -
  K color and also larger than measured radii of magnetically inactive
  M-dwarfs. The relative radius difference is correlated with magnitude,
  increasing from a few percent at M<SUB>I</SUB> = 7 to greater than 50%
  for the lowest luminosity stars in their sample at M<SUB>I</SUB> ~
  9.5. Jackson et al. have suggested that a two-temperature star spot
  model is capable of explaining the observations, but their model
  requires spot coverage fractions of at least 50% in rapidly rotating
  M-dwarfs. Here we examine these results in terms of stellar models that
  include the inhibiting effects of magnetic fields on convective energy
  transport, with and without the effects of star spots. We find that a
  pure spot model is inconsistent with the color-magnitude diagram. The
  observations of radii versus color and radii versus absolute magnitude
  in NGC 2516 are consistent with models which include only magnetic
  inhibition or a combination of magnetic inhibition and spots. At a
  given mass we find a large dispersion in the strength of the vertical
  component of the magnetic field in the stellar photosphere but the
  general trend is that the vertical field increases with decreasing
  mass from a few hundred Gauss at 0.65 M <SUB>⊙</SUB> to 600-900 G,
  depending on spot coverage, in the lowest mass stars in the sample at
  0.25 M <SUB>⊙</SUB>.

---------------------------------------------------------
Title: Solar Cycle Variation of Sound Speed inside the Sun
Authors: Mullan, D. J.; MacDonald, J.; Rabello-Soares, M. C.
2012ApJ...755...79M    Altcode:
  Empirical radial profiles of the changes in sound speed inside the
  Sun between solar minimum and solar maximum have been extracted
  from Michelson Doppler Imager data by Baldner &amp; Basu and
  Rabello-Soares. Here, we compare these results with the theoretical
  radial profiles predicted by a model of magnetic inhibition of
  convective onset: In the model, the degree of magnetic inhibition
  is characterized by a parameter δ, which is essentially the ratio of
  magnetic pressure to gas pressure. We find that the theoretical profiles
  overlap significantly with the empirical results in the outer half of
  the convection zone. But differences in the deeper layers indicate that
  the model needs to be modified there. The main result that emerges in
  the present comparison is that the value of δ must be larger near the
  surface than at great depth. A secondary result is that, in the course
  of the solar cycle, the magnetic field magnitude at the base of the
  convection zone may be out of phase with the field near the surface.

---------------------------------------------------------
Title: Precision modelling of M dwarf stars: the magnetic components
    of CM Draconis
Authors: MacDonald, J.; Mullan, D. J.
2012MNRAS.421.3084M    Altcode: 2011arXiv1106.1452M; 2012MNRAS.tmp.2466M
  The eclipsing binary CM Draconis (CM Dra) contains two nearly identical
  red dwarfs of spectral class dM4.5. The masses and radii of the two
  components have been reported with unprecedentedly small statistical
  errors: for M, these errors are 1 part in 260, while for R, the errors
  reported by Morales et al. are 1 part in 130. When compared with
  standard stellar models with appropriate mass and age (≈4 Gyr),
  the empirical results indicate that both components are discrepant
  from the models in the following sense: the observed stars are larger
  in R ('bloated'), by several standard deviations, than the models
  predict. The observed luminosities are also lower than the models
  predict. Here, we attempt at first to model the two components of CM
  Dra in the context of standard (non-magnetic) stellar models using a
  systematic array of different assumptions about helium abundances (Y),
  heavy element abundances (Z), opacities and mixing length parameter
  (α). We find no 4-Gyr-old models with plausible values of these four
  parameters that fit the observed L and R within the reported statistical
  error bars. <P />However, CM Dra is known to contain magnetic fields,
  as evidenced by the occurrence of star-spots and flares. Here we ask:
  can inclusion of magnetic effects into stellar evolution models lead to
  fits of L and R within the error bars? Morales et al. have reported that
  the presence of polar spots results in a systematic overestimate of R by
  a few per cent when eclipses are interpreted with a standard code. In a
  star where spots cover a fraction f of the surface area, we find that
  the revised R and L for CM Dra A can be fitted within the error bars
  by varying the parameter α. The latter is often assumed to be reduced
  by the presence of magnetic fields, although the reduction in α as a
  function of B is difficult to quantify. An alternative magnetic effect,
  namely inhibition of the onset of convection, can be readily quantified
  in terms of a magnetic parameter δ≈B<SUP>2</SUP>/4πγp<SUB>gas</SUB>
  (where B is the strength of the local vertical magnetic field). In the
  context of δ models in which B is not allowed to exceed a 'ceiling'
  of 10<SUP>6</SUP> G, we find that the revised R and L can also be
  fitted, within the error bars, in a finite region of the f-δ plane. The
  permitted values of δ near the surface leads us to estimate that the
  vertical field strength on the surface of CM Dra A is about 500 G,
  in good agreement with independent observational evidence for similar
  low-mass stars. Recent results for another binary with parameters close
  to those of CM Dra suggest that metallicity differences cannot be the
  dominant explanation for the bloating of the two components of CM Dra.

---------------------------------------------------------
Title: Modeling Low-mass Stars in the Presence of Magnetic Fields
Authors: Mullan, D. J.; MacDonald, J.
2011ASPC..448.1209M    Altcode: 2011csss...16.1209M
  In the presence of a vertical magnetic field, the onset of convection
  in a star is inhibited relative to its onset in a non-magnetic
  star. Following early work of Gough and Tayler for a perfectly
  conducting medium, and including subsequent modifications due to finite
  magnetic resistivity, we have computed models of low-mass stars using a
  magnetically-altered criterion for the onset of convection. Our models
  have larger radii and cooler effective temperatures than non-magnetic
  models with the same mass and age. Our magnetic models provide a
  unified framework for interpreting a range of observational data,
  including radii which are observed to be "bloated" by as much as 10%
  relative to standard models, and reduced effective temperatures,
  for stars ranging in spectral types from solar to brown dwarfs.

---------------------------------------------------------
Title: The M4 Transition: Toward a Comprehensive Understanding of
    the Transition into the Fully Convective Regime
Authors: Stassun, K. G.; Hebb, L.; Covey, K.; West, A. A.; Irwin,
   J.; Jackson, R.; Jardine, M.; Morin, J.; Mullan, D.; Reid, I. N.
2011ASPC..448..505S    Altcode: 2010arXiv1012.2580S; 2011csss...16..505S
  The difference in stellar structure above and below spectral type
  ∼M4 is expected to be a very important one, connected directly or
  indirectly to a variety of observational phenomena in cool stars --
  such as rotation, activity, magnetic field generation and topology,
  timescales for evolution of these, and even the basic mass-radius
  relationship. In this Cool Stars XVI Splinter Session, we aimed to
  use the M4 transition as an opportunity for discussion about the
  interiors of low-mass stars and the mechanisms which determine their
  fundamental properties. By the conclusion of the session, several key
  points were elucidated. Although M dwarfs exhibit significant changes
  across the fully convective boundary, this "M4 transition" is not
  observationally sharp or discrete. Instead, the properties of M dwarfs
  (radius, effective temperature, rotation, activity lifetime, magnetic
  field strength and topology) show smooth changes across M3-M6 spectral
  types. In addition, a wide range of stellar masses share similar
  spectral types around the fully convective transition. There appears to
  be a second transition at M6-M8 spectral types, below which there exists
  a clear dichotomy of magnetic field topologies. Finally, we used the
  information and ideas presented in the session to construct a framework
  for how the structure of an M dwarf star, born with specific mass and
  chemical composition, responds to the presence of its magnetic field,
  itself driven by a feedback process that links the star's rotation,
  interior structure, and field topology.

---------------------------------------------------------
Title: Threshold effects in assembling a cell on a young planet
Authors: Mullan, D. J.
2011SPIE.8152E..14M    Altcode: 2011SPIE.8152E..29M
  Molecules in the young Earth's oceans underwent a finite number C
  of collisions during the time interval which elapsed between Earth's
  formation and the emergence of life. The finiteness of C sets an upper
  limit G on the number of constituent molecules which could have been
  randomly assembled into a genetic molecule from a reservoir of the
  relevant constituent molecules for use in the first cell. A viable cell
  requires a certain minimum number of genes in order to be functional:
  this means that the genetic material must include a minimum number M of
  the constituent molecules which encode for information. The question
  we address here is: is it mathematically possible for G to take on
  values which are at least as large as M? The answer is Yes, provided
  that we allow for the fact that there is a large amount of flexibility
  ("non-specificity") in the operation of biological molecules. When
  this flexibility is allowed for, we find that G can be comparable to M
  provided that the mass of constituent molecules which were available
  in the pre-biotic Earth exceeded a certain threshold. Our estimates
  indicate that a mass on the order of a few tons would satisfy the
  threshold.

---------------------------------------------------------
Title: Estimates of Densities and Filling Factors from a Cooling
    Time Analysis of Solar Microflares Observed with RHESSI
Authors: Baylor, R. N.; Cassak, P. A.; Christe, S.; Hannah, I. G.;
   Krucker, Säm; Mullan, D. J.; Shay, M. A.; Hudson, H. S.; Lin, R. P.
2011ApJ...736...75B    Altcode: 2011arXiv1107.3997B
  We use more than 4500 microflares from the RHESSI microflare data set to
  estimate electron densities and volumetric filling factors of microflare
  loops using a cooling time analysis. We show that if the filling factor
  is assumed to be unity, the calculated conductive cooling times are
  much shorter than the observed flare decay times, which in turn are
  much shorter than the calculated radiative cooling times. This is likely
  unphysical, but the contradiction can be resolved by assuming that the
  radiative and conductive cooling times are comparable, which is valid
  when the flare loop temperature is a maximum and when external heating
  can be ignored. We find that resultant radiative and conductive cooling
  times are comparable to observed decay times, which has been used as an
  assumption in some previous studies. The inferred electron densities
  have a mean value of 10<SUP>11.6</SUP> cm<SUP>-3</SUP> and filling
  factors have a mean of 10<SUP>-3.7</SUP>. The filling factors are lower
  and densities are higher than previous estimates for large flares,
  but are similar to those found for two microflares by Moore et al.

---------------------------------------------------------
Title: Magneto-convection and Lithium Age Estimates of the β Pictoris
    Moving Group
Authors: Macdonald, J.; Mullan, D. J.
2010ApJ...723.1599M    Altcode: 2010arXiv1006.1308M
  Although the means of the ages of stars in young groups determined
  from Li depletion often agree with mean ages determined from
  Hertzsprung-Russell (H-R) diagram isochrones, there are often
  statistically significant differences in the ages of individual stars
  determined by the two methods. We find that inclusion of the effects of
  inhibition of convection due to the presence of magnetic fields leads
  to consistent ages for the individual stars. We illustrate how age
  consistency arises by applying our results to the β Pictoris moving
  group (BPMG). We find that, although magnetic inhibition of convection
  leads to increased ages from the H-R diagram isochrones for all stars,
  Li ages are decreased for fully convective M stars and increased for
  stars with radiative cores. Our consistent age determination for BPMG
  of 40 Myr is larger than previous determinations by a factor of about
  two. We have also considered models in which the mixing length ratio is
  adjusted to give consistent ages. We find that our magneto-convection
  models, which give quantitative estimates of magnetic field strength,
  provide a viable alternative to models in which the effects of magnetic
  fields (and other processes) are accounted for by reducing the mixing
  length ratio.

---------------------------------------------------------
Title: Patterns of X-ray, Chromospheric, and Radio Emission in
Low-mass Stars: Fast and Slow Magnetic Reconnection
Authors: Mullan, D. J.
2010ApJ...721.1034M    Altcode:
  Magnetic reconnection events in the atmospheres of low-mass dwarf stars
  can be classified as either slow or fast, depending on whether ohmic
  diffusion or Hall currents dominate in the reconnection process. We
  suggest that the separation of reconnection into slow and fast
  categories can help to explain some systematics of low-mass dwarfs as
  regards their emissions in X-rays, Hα, and radio. On the one hand, in
  the warmer dwarfs (&lt;M7), where electrical resistivities are small,
  fast reconnection is permitted, and this can explain the occurrence of
  flares and "quiescent" coronal heating. On the other hand, the fact
  that the coolest dwarfs (&gt;M7) are inefficient emitters in Hα and
  X-rays but strong emitters in radio, may be understood in the context
  that only slow reconnection is permitted to occur in those stars,
  as a result of high electrical resistivity. However, even though only
  slow reconnection is permitted in the latter stars, the speed of the
  outflow jets from reconnection sites can serve as efficient sources of
  radio emission as a result of the electron cyclotron maser instability.

---------------------------------------------------------
Title: Magnetic Models of the Brown Dwarfs HD 130948b and HD 130948c
Authors: Mullan, D. J.; MacDonald, J.
2010ApJ...713.1249M    Altcode:
  Dynamical masses have been obtained by Dupuy et al. for the brown
  dwarf binary HD 130948BC. The components have luminosities log (L/L
  <SUB>sun</SUB>) of -3.82 and -3.90, and masses of 0.0555 and 0.0530
  M <SUB>sun</SUB>. In a luminosity-age diagram, Dupuy et al. found
  that L <SUB>bol</SUB> for both B and C are brighter than theoretical
  tracks by factors of 2-3, if the age of the system is as old as their
  estimate of 0.79 Gyr (based on gyrochronology). Here, we apply our
  model of magnetic convection, in which the onset of convection is
  impeded in the presence of a vertical magnetic field: our goal is
  to replicate the observed properties not only in the luminosity-age
  diagram, but simultaneously in the T <SUB>eff</SUB> -age diagram and
  in the H-R diagram. Expressing the internal magnetic pressure as a
  fraction δ of the gas pressure, we obtain evolutionary tracks which
  fit both stars in an H-R diagram provided that δ lies in the range
  0.007-0.038. With such values of δ, our models replicate the observed
  luminosities of both B and C, provided that the age is no larger than
  ~0.39 Gyr. This is significantly younger than the mean age estimated by
  Dupuy et al. for the primary star in the system, HD 130948A. However,
  there is sufficient uncertainty in the empirical parameters that an
  age as young as the one suggested by our magnetic models (~0.39 Gyr)
  is marginally within the permitted range.

---------------------------------------------------------
Title: Non-sparse Sampling of the Genomic Phase-Space of a Proto-cell
    in the Young Earth
Authors: Mullan, D. J.
2009ASPC..420..287M    Altcode:
  We estimate the numbers of reactions which occurred between certain
  molecules in liquid water during an interval of 200 My on the young
  Earth. We compare this with the size of genomic phase-space for a
  primitive cell whose genetic material consists of single-strand RNA. We
  find that the reactions which occurred in 200 My are sufficiently
  numerous to allow non-sparse sampling of a genome containing p ≍
  15 genes, provided the genetic code used doublet codons. We argue on
  general grounds that p ≥ 10 could give rise to a viable cell.

---------------------------------------------------------
Title: Flares on a Bp Star
Authors: Mullan, D. J.
2009ApJ...702..759M    Altcode:
  Two large X-ray flares have been reported from the direction of a
  magnetic B2p star (σ Ori E). Sanz-Forcada et al. have suggested that
  the flares did not occur on the B2p star but on a companion of late
  spectral type. A star which is a candidate for a late-type flare star
  near σ Ori E has recently been identified by Bouy et al. However,
  based on the properties of the flares, and based on a recent model of
  rotating magnetospheres, we argue that, rather than attributing the two
  flares to a late-type dwarf, it is a viable hypothesis that the flares
  were magnetic phenomena associated with the rotating magnetosphere of
  the B2p star itself.

---------------------------------------------------------
Title: Big bang nucleosynthesis: The strong nuclear force meets the
    weak anthropic principle
Authors: MacDonald, J.; Mullan, D. J.
2009PhRvD..80d3507M    Altcode: 2009arXiv0904.1807M
  Contrary to a common argument that a small increase in the strength
  of the strong force would lead to destruction of all hydrogen in
  the big bang due to binding of the diproton and the dineutron with
  a catastrophic impact on life as we know it, we show that provided
  the increase in strong force coupling constant is less than about 50%
  substantial amounts of hydrogen remain. The reason is that an increase
  in strong force strength leads to tighter binding of the deuteron,
  permitting nucleosynthesis to occur earlier in the big bang at higher
  temperature than in the standard big bang. Photodestruction of the less
  tightly bound diproton and dineutron delays their production to after
  the bulk of nucleosynthesis is complete. The decay of the diproton can,
  however, lead to relatively large abundances of deuterium.

---------------------------------------------------------
Title: Structural Effects of Magnetic Fields in Brown Dwarfs
Authors: MacDonald, J.; Mullan, D. J.
2009ApJ...700..387M    Altcode:
  In the brown dwarf (BD) binary 2M0535 - 05, Stassun et al. have reported
  that the more massive primary has a lower T <SUB>eff</SUB> than the less
  massive secondary. Here, we report results obtained by an evolutionary
  code in which the criterion for the onset of convection in the primary
  is modified in the presence of a magnetic field. Structural alterations
  to the primary lead to a lower T <SUB>eff</SUB> and a larger radius
  than would occur in a non-magnetic BD of the same age mass and age. The
  observed value of T <SUB>eff</SUB> can be explained if the field in
  the primary increases in strength from 120-320 G at the surface to
  5-13 MG at the center. With zero field in the secondary, our models
  indicate that both components can be co-eval with an age of 1.0-1.3
  Myr. Because the binary is so young, the components have not yet had
  time to synchronize their rotations: differences in angular velocity may
  explain why one component has developed a field while the other has not.

---------------------------------------------------------
Title: The Nonlinear Dynamics of Magnetic Reconnection and
    Applications to Solar Eruptions
Authors: Cassak, P. A.; Shay, M. A.; Drake, J. F.; Eckhardt, B.;
   Mullan, D. J.
2008AGUFMSM23C..01C    Altcode:
  It is widely accepted that magnetic reconnection plays a fundamental
  role in releasing magnetic energy in solar eruptions, but what
  initiates an eruption remains an unresolved problem. We present
  a model for the catastrophic onset of fast magnetic reconnection
  in weakly collisional plasmas, which potentially explains why
  the energy release begins abruptly. In particular, we show that
  magnetic reconnection is bistable: both the slow (Sweet-Parker)
  and fast (Hall) modes of reconnection independently exist for a wide
  range of parameters. However, the Sweet-Parker solution disappears
  catastrophically at a critical condition, leading to the onset of
  Hall reconnection and the accompanying increase in the rate of
  magnetic energy release by many orders of magnitude. We present
  theory and simulations confirming the model. We propose that the
  disappearance of reconnection solutions is caused by saddle-node
  bifurcations controlling the nonlinear dynamics of reconnection, and
  derive a simple nonlinear model that displays this dynamical behavior
  [1]. The model predicts the existence of an unstable reconnection
  solution, which we demonstrate numerically. The unstable solution
  reveals that the physics controlling the onset of Hall reconnection
  occurs locally near the X-line as opposed to remotely at the boundaries
  [2]. We discuss potential mechanisms for onset and show that the model
  is consistent with results from laboratory experiments and solar and
  stellar flare observations. [1] P. A. Cassak, Doctoral Thesis, 2006;
  [2] P. A. Cassak et al., Phys. Rev. Lett., 98, 215001, 2007.

---------------------------------------------------------
Title: The Role of Magnetic Reconnection in Self-Organization of
the Corona: Theory and Observations
Authors: Cassak, P. A.; Mullan, D. J.; Shay, M. A.
2008AGUFMNG41A..03C    Altcode:
  Based on observations that solar flares obey power law statistics, it
  was suggested that the solar corona is in a state of self-organized
  criticality [1]. However, the physical mechanism underlying the
  dynamics is not well understood. A recent model [2] describing the
  catastrophic onset of fast (Hall) magnetic reconnection in weakly
  collisional plasmas may potentially contribute to this discussion. We
  suggest that the condition at which the catastrophic onset of
  reconnection occurs sets the critical state of the corona and the
  physics of reconnection organizes the corona into this critical state
  [3]. (See also [4].) The model makes a quantitative prediction for the
  conditions of the corona at the onset of eruptions, which is known
  to be consistent with observations of the solar corona. We present
  new observational evidence from stellar flares (107 events in 37
  sun-like stars) that stellar coronae are near the same critical state
  at flare onset. This provides observational evidence in support of the
  model and suggests that magnetic reconnection plays an active role in
  constraining the conditions in solar and stellar coronae. Implications
  for self-organization in coronal heating and solar eruptions will
  be discussed. [1] E. T. Lu and R. J. Hamilton, Ap. J., 380, L89,
  1991; [2] P. A. Cassak et al., Phys. Rev. Lett., 95, 235002, 2005;
  P. A. Cassak et al., Ap. J. Lett., 644, L145, 2006; [3] P. A. Cassak
  et al., Ap. J. Lett., 676, L69, 2008; [4] D. A. Uzdensky, Ap. J., 671,
  2139, 2007.

---------------------------------------------------------
Title: From Solar and Stellar Flares to Coronal Heating: Theory and
    Observations of How Magnetic Reconnection Regulates Coronal Conditions
Authors: Cassak, P. A.; Mullan, D. J.; Shay, M. A.
2008ApJ...676L..69C    Altcode: 2007arXiv0710.3399C
  There is currently no explanation of why the corona has the temperature
  and density it has. We present a model that explains how the dynamics
  of magnetic reconnection regulates the conditions in the corona. A
  bifurcation in magnetic reconnection at a critical state enforces
  an upper bound on the coronal temperature for a given density. We
  present observational evidence from 107 flares in 37 Sun-like stars
  that stellar coronae are near this critical state. The model may be
  important to self-organized criticality models of the solar corona.

---------------------------------------------------------
Title: Observational Evidence of the Role of Collisionless Magnetic
    Reconnection in Self- Organization of Solar and Stellar Coronae
Authors: Mullan, D.; Cassak, P. A.; Shay, M. A.
2007AGUFMSH41C..03M    Altcode:
  Magnetic reconnection is widely accepted to be the driver of eruptive
  activity in the solar corona. However, questions about how a large
  amount of magnetic energy can accumulate before an eruption without
  triggering fast reconnection, why fast magnetic reconnection begins
  abruptly, and under what coronal conditions an eruption occurs
  remain unanswered. Observations of solar and stellar flares have
  revealed similar phenomenologies and power law statistics, suggesting
  that eruptions in solar and stellar coronae are driven by the same
  physical process. The existence of power law statistics has prompted
  the suggestion that solar and stellar coronae are self-organized, but
  the physical foundation of this theory has been lacking. We present
  observational evidence from 107 flare events in 37 sun-like stars
  that solar and stellar coronae self-organize into a state in which the
  coronal plasma is marginally collisional. This corroborates a recent
  model in which coronal eruptions are initiated by a catastrophic
  onset of collisionless magnetic reconnection [1]. These results
  demonstrate that the dynamics of magnetic reconnection play an active
  role in constraining the conditions of solar and stellar coronae. [1]
  P. A. Cassak, M. A. Shay, and J. F. Drake, Phys. Rev. Lett., 95, 235002
  (2005).

---------------------------------------------------------
Title: Magnetic Cycles in the Sun: Modeling the Changes in Radius,
    Luminosity, and p-Mode Frequencies
Authors: Mullan, D. J.; MacDonald, J.; Townsend, R. H. D.
2007ApJ...670.1420M    Altcode:
  We report on the results obtained with a stellar evolution code in
  which cyclic magnetic fields are imposed in the convection zone of a 1.0
  M<SUB>solar</SUB> star. Magnetic effects are incorporated in two ways:
  (1) the field pressure and energy density are included in the equations
  of hydrostatic equilibrium and conservation of energy; and (2) the field
  inhibits the onset of convection according to a prescription derived by
  Gough &amp; Tayler (1966). Inserting magnetic fields into the convection
  zone with strengths comparable to the observed global fields in the
  Sun, and assuming a simple depth dependence for the field strength,
  we find differences in luminosity and radius between nonmagnetic and
  magnetic models that are consistent in amplitude with the observed
  activity-related changes in the Sun. Using the same magnetic fields,
  and computing p-mode frequencies for nonmagnetic and magnetic models, we
  find that the frequencies in a magnetic model are larger than those for
  a nonmagnetic model. The frequency differences between nonmagnetic and
  magnetic models agree in sign, and overlap in magnitude and frequency
  dependence, with the shifts in frequency which have been observed
  in the Sun between solar minimum and solar maximum. We find that the
  luminosity variations are out of phase with the magnetic variations:
  in order to help reconcile this result with empirical solar data,
  we note that the global (poloidal) fields in the Sun are observed
  to pass through minimum values at times that correspond roughly with
  times of maximum toroidal fields.

---------------------------------------------------------
Title: Spitzer Observations of Nearby M Dwarfs
Authors: Riaz, Basmah; Mullan, D. J.; Gizis, John E.
2006ApJ...650.1133R    Altcode: 2006astro.ph..7405R
  We present Spitzer IRAC and MIPS observations for a sample of eight
  M dwarfs: six dMe, one dM, and one sdMe star. All of our targets
  are found to have SEDs that are fitted within the error bars by a
  purely photospheric spectrum out to 24 μm. We find no evidence for
  IR excess. None of our targets are detected in the MIPS 70 and 160
  μm bands. The estimated ages for all are &gt;10 Myr, suggesting
  that enough disk dissipation has occurred within the inner several
  AU of the star. For four of these, Mullan et al. had reported IRAS
  detections at 12 μm, although the reported fluxes were below the
  5 σ IRAS detection limit (~0.2 Jy). Mullan et al. also pointed
  out that V-K colors in dMe stars are larger than those in dM stars,
  possibly because of the presence of a chromosphere. Here we suggest
  that metallicity effects provide a better explanation of the V-K
  data. For reasons of observational selection, our targets are not
  the most active flare stars known, but being dMe stars indicates
  the presence of a chromosphere. Scaling from Houdebine's model of
  the AU Mic chromosphere, we have computed the free-free IR excesses
  for a range of densities. Our Spitzer 24 μm data show that the
  chromospheres in two of our targets are less dense than in AU Mic
  by a factor of 10 or more. This is consistent with the fact that our
  sample includes the less active flare stars. Our models also indicate
  that the chromospheric contribution to the observed AU Mic emission
  at submillimeter wavelengths is only about 2%.

---------------------------------------------------------
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: Solar Wind Statistics at 1 AU: Alfven Speed and Plasma Beta
Authors: Mullan, D. J.; Smith, C. W.
2006SoPh..234..325M    Altcode:
  The phenomenon of MHD wave refraction is useful in interpreting
  the properties of the magnetic fluctuations in certain parcels of
  solar wind. In the physics of MHD wave refraction, variations in the
  Alfvén speed V<SUB>Alf</SUB> play a dominant role. Here, we compile
  statistics of the 1-min averages of V<SUB>Alf</SUB> at the location
  of the ACE spacecraft during its first 5 years of operation. We
  find that monthly distributions of V<SUB>Alf</SUB> are close to
  log-normal, with standard deviations σ<SUB>V</SUB> as small as 0.11
  in the logarithm. Variations in the monthly mean V<SUB>Alf</SUB> are
  correlated significantly with sunspot number. We also compile monthly
  distributions of the plasma β parameter. The distributions of both
  V<SUB>Alf</SUB> and β are significantly narrower than they would be if
  the various solar wind parameters were statistically independent. In
  the T<SUB>p</SUB>-V<SUB>Alf</SUB> plane, we find a zone of avoidance
  at low V<SUB>Alf</SUB>: for V<SUB>Alf</SUB> ≤10 - 15 km/s, there
  are no samples in the 1-min data that are cooler than T<SUB>p</SUB>
  = 10 000 - 15 000 K. This feature can be understood in the context of
  MHD wave refraction, although other explanations are also possible.

---------------------------------------------------------
Title: Winds from OB Stars: A Two-Component Scenario?
Authors: Mullan, D. J.; Waldron, W. L.
2006ApJ...637..506M    Altcode:
  X-ray spectroscopy of several OB stars with massive winds has revealed
  that many X-ray line profiles exhibit unexpectedly small blueshifts
  and are almost symmetric. Moreover, the hottest X-ray lines appear
  to originate closest to the star. These properties appear to be
  inconsistent with the standard model of X-rays originating in shocked
  material in line-driven spherically symmetric winds. Here we raise
  the question, can the X-ray line data be understood in terms of a
  two-component wind? We consider a scenario in which one component of
  the wind is a standard line-driven wind that emerges from a broad range
  of latitudes centered on the equator. The second component of the wind
  emerges from magnetically active regions in extensive polar caps. The
  existence of such polar caps is suggested by a recent model of dynamo
  action in massive stars. We describe how the two-component model is
  consistent with a variety of observational properties of OB star winds.

---------------------------------------------------------
Title: Spitzer observations of active M dwarfs
Authors: Mullan, D. J.; Riaz, B.; Gizis, J. E.
2005AAS...20718201M    Altcode: 2005BAAS...37.1463M
  We present Spitzer Space Telescope observations of eight active M
  dwarfs in the IRAC and MIPS bands. Based on their IRAC colors, we have
  classified these M dwarfs as Weak T Tauri Stars (WTTS). Four of our
  targets display small excesses at 160 μm. Over the wavelength range
  from a few microns to tens of μm the flux densities can be fitted
  well with a Rayleigh-Jeans curve. We do not detect evidence for the
  presence of any appreciable dust in our target stars. We argue that any
  small excess that we see may be due to a chromosphere/corona. Assuming
  that the opacity is dominated by free-free processes, we interpret our
  observations over the Spitzer wavelength range in terms of the rise in
  temperature from the photosphere into the chromosphere/corona. In order
  to model the free-free absorption as a function of height, we start
  with a model chromosphere which was derived by E. R. Houdebine (1990,
  Ph.D. dissertation) for the active M dwarf AU Mic. Houdebine derived a
  semi-empirical model based on fitting the emission line profiles of Hα
  and Hβ. In the model, the temperature is assumed to rise linearly with
  log m (where m is mass loading) from a temperature minimum of 3255 K
  up to T = 8000 K at log m (g cm<SUP>-2</SUP>) = -2.9. Above T = 8000 K,
  the temperature rises abruptly to T = 3 x 10<SUP>5</SUP> K. We consider
  a range of models in which the electron densities are allowed to be
  uniformly larger or smaller than in the Houdebine model, by factors
  of 0.1-100. Using these, we have obtained good fits to our Spitzer
  observations, suggesting that the IR excesses in our target M dwarfs are
  consistent with the existence of a moderately dense chromosphere/corona.

---------------------------------------------------------
Title: Dynamo-generated magnetic fields at the surface of a massive
    star
Authors: Mullan, D. J.; MacDonald, James
2005MNRAS.356.1139M    Altcode:
  Spruit has shown that an astrophysical dynamo can operate in the
  non-convective material of a differentially rotating star as a
  result of a particular instability in the magnetic field (the Tayler
  instability). By assuming that the dynamo operates in a state of
  marginal instability, Spruit has obtained formulae which predict
  the equilibrium strengths of azimuthal and radial field components in
  terms of local physical quantities. Here, we apply Spruit's formulae to
  our previously published models of rotating massive stars in order to
  estimate Tayler dynamo field strengths. There are no free parameters
  in Spruit's formulae. In our models of 10- and 50-M<SUB>solar</SUB>
  stars on the zero-age main sequence, we find internal azimuthal fields
  of up to 1 MG, and internal radial components of a few kG. Evolved
  models contain weaker fields. In order to obtain estimates of the field
  strength at the stellar surface, we examine the conditions under which
  the Tayler dynamo fields are subject to magnetic buoyancy. We find
  that conditions for Tayler instability overlap with those for buoyancy
  at intermediate to high magnetic latitudes. This suggests that fields
  emerge at the surface of a massive star between magnetic latitudes of
  about 45° and the poles. We attempt to estimate the strength of the
  field which emerges at the surface of a massive star. Although these
  estimates are very rough, we find that the surface field strengths
  overlap with values which have been reported recently for line-of-sight
  fields in several O and B stars.

---------------------------------------------------------
Title: Coronal and Chromospheric Heating in Active Dwarf Stars
Authors: Gizis, John; Mullan, Dermott
2004sptz.prop.3562G    Altcode:
  We propose to observe a sample of highly active M dwarfs with IRAC and
  MIPS. Such active dwarfs are known to have large infrared excesses. We
  argue that the excesses are likely to result from the hot chromospheres
  and coronae above the photosphere. In this context, our proposed
  measurements of the (excess) infrared spectral energy distribution
  will allow us to reliably map the temperature rise in the chromosphere.

---------------------------------------------------------
Title: Magnetic fields in massive stars: dynamics and origin
Authors: MacDonald, James; Mullan, D. J.
2004MNRAS.348..702M    Altcode:
  Evidence continues to accumulate in favour of the presence of magnetic
  fields on the surfaces of massive stars. Some authors hypothesize that
  such fields originate in a dynamo in the convective core, with buoyancy
  bringing flux tubes to the surface. Here we show that, when realistic
  stellar models are used, this `core dynamo hypothesis' encounters a
  serious difficulty: in order for surface fields to originate in a core
  dynamo, the core must create magnetic fields that are much stronger than
  equipartition values. <P />As an alternative hypothesis for the origin
  of magnetic fields in OB stars, we suggest that a dynamo is operating in
  shear-unstable gas in the radiative stellar envelope. Using a recently
  developed code for the evolution of rotating stars, we find that in a
  10-M<SUB>solar</SUB> zero-age main sequence (ZAMS) star with a typical
  rotation period, more than 90 per cent of the volume of the star is
  subject to shear instability. We have recently proposed that dynamo
  operation in shear-unstable gas helps to explain certain properties
  of mass loss in cool giants. Here, in the context of hot stars, we
  show that fields which originate in the shear-unstable regions of the
  envelope can reach the surface without violating the constraints of
  equipartition. Such fields rise to the surface on time-scales which
  are short compared to main-sequence lifetimes.

---------------------------------------------------------
Title: Further evidence of wave refraction associated with extended
    rarefaction events in the solar wind
Authors: Smith, Charles W.; Mullan, Dermott J.; Ness, Norman F.
2004JGRA..109.1111S    Altcode:
  We examine the turbulence and low-frequency wave properties of
  three extended rarefaction intervals observed by the Advanced
  Composition Explorer (ACE) spacecraft in 1999 and 2002 while in orbit
  at L<SUB>1</SUB>. The proton densities drop to values lower than 1
  cm<SUP>-3</SUP> and in one case reach 0.1 cm<SUP>-3</SUP>. During each
  interval, the amplitudes of magnetic fluctuations fall to unusually low
  levels. Moreover, the fluctuations that are present are more Alfvénic
  in nature than in the typical low-latitude wind. The constant and near
  average interplanetary magnetic field during these times results in
  elevated Alfvén speeds. We suggest that the relative isolation of the
  rarefaction intervals from sources of turbulence-generating transients
  allows wave refraction to become a significant dynamic controlling the
  evolution of the magnetized plasma. We present analyses of the intervals
  that support the hypothesis that wave refraction explains the reduced
  fluctuation levels and enhanced Alfvénicity during these times.

---------------------------------------------------------
Title: Onset of Shear Instability in Rotating Red Giants
Authors: MacDonald, J.; Mullan, D. J.
2003ApJ...598..560M    Altcode:
  We incorporate into an evolutionary code a unified treatment of
  turbulent transport due to convective and shear instabilities in a
  rotating star. The effects of composition gradients are included in a
  consistent way. We use the code to follow the evolution of rotating
  stars from the pre-main sequence to near the tip of the red giant
  branch. We find that at a certain stage in the red giant evolution
  of a 1 M<SUB>solar</SUB> star, when the convectively unstable region
  occupies an extensive outer envelope, shear instability sets in in
  a zone just below the H-burning shell. However, at a later time,
  shear instability also develops in a second (outer) region that lies
  between the H-burning shell and the convective envelope. The onset
  of the outer region of shear instability coincides closely in time
  with a well-defined feature of red giant evolution: the “bump”
  (so-called because of its effect on the luminosity function of
  clusters). This evolutionary bump has recently been identified as a
  significant empirical marker among red giants: cool massive winds
  have been found to set in abruptly after the star evolves through
  the bump. The results we report in the present paper suggest that the
  onset of mass loss in red giants may be correlated with the onset of
  an outer region of shear instability inside the star. We offer some
  speculations concerning the possible physics of such a correlation.

---------------------------------------------------------
Title: Structure and Evolution of Low-mass Stars: Where Do Magnetic
    stars Become Completely Convective?
Authors: Mullan, D. J.; MacDonald, J.
2003csss...12..893M    Altcode:
  Stars on the main sequence are expected to be completely convective
  if their mass lies below a certain value, M<SUB>cc</SUB>. Standard
  stellar structure codes suggest that M<SUB>cc</SUB> is in the range
  (0.3-0.4)M<SUB>⊙</SUB>. However, certain physical effects that are not
  incorporated in standard models may alter the value of M<SUB>cc</SUB>
  significantly. Here we quantify the alterations that are brought
  about in M<SUB>cc</SUB> when we include magnetic field effects. In
  particular, we modify the criterion for convective stability in the
  manner prescribed by Gough and Tayler (1966). We find that magnetic
  M dwarfs tend to have radii that are larger than expected for their
  T<SUB>eff</SUB> values, or T<SUB>eff</SUB> values that are too low
  for their radii. Available observational data provide quantitative
  support for these structural findings. Moreover, we find that,
  given the magnetic fields which are allowed to exist stably in
  low-mass stars, M<SUB>cc</SUB> may fall to values that are as small
  as 0.1M<SUB>⊙</SUB>. We suggest that this result is pertinent to
  understanding why coronae and chromospheres in active M dwarfs fail
  to exhibit detectable alterations at spectral class M3-M4.

---------------------------------------------------------
Title: Day the Solar Wind Almost Disappeared: Magnetic Field
    Fluctuations and Wave Refraction
Authors: Smith, Charles W.; Mullan, Dermott J.; Ness, Norman F.;
   Skoug, Ruth M.; Steinberg, John
2003AIPC..679..509S    Altcode:
  On May 11, 1999 the Advanced Composition Explorer (ACE) spacecraft
  observed a rarefied parcel of solar wind that has come to be known as
  “The Day the Solar Wind Disappeared.” Little if any change is seen
  in the large-scale interplanetary magnetic field during this time,
  but the magnetic field fluctuations are depressed and significantly
  more transverse to the mean field. The high Alfvén speed resulting
  from the constant field intensity and low ion density enhances wave
  refraction, and we examine this as a possible explanation for the
  fluctuation properties.

---------------------------------------------------------
Title: Turbulent dissipation in the solar wind and corona
Authors: Matthaeus, W. H.; Dmitruk, P.; Oughton, S.; Mullan, D.
2003AIPC..679..427M    Altcode:
  Models based upon anisotropic magnetohydrodynamic (MHD) cascade offer
  promising explanations for observations of both interplanetary and
  coronal turbulence and heating, which are reviewed here. In the standard
  picture the cascade proceeds by driving at the energy-containing scales,
  transfers through the inertial range, and into small scales where it
  drives small-scale random turbulent reconnection events. In order to
  understand more fully the heating and dissipation processes, one also
  needs to understand how small-scale MHD-driven reconnection - involving
  current sheets and filaments - induces kinetic plasma processes that
  thermalize the fluid energy. Here we suggest that in these reconnection
  sites MHD electric fields drive ion beam instabilities and nonlinear
  electron dynamics involving electron solitary wave structures, in
  analogy with the kinetic physics observed near parallel electric field
  auroral regions by the FAST spacecraft.

---------------------------------------------------------
Title: Onset of Mass Loss in Red Giants: Association with an
    Evolutionary Event
Authors: Mullan, D. J.; MacDonald, J.
2003ApJ...591.1203M    Altcode:
  Stencel &amp; Mullan used asymmetries in the Mg II k emission line
  profile to determine the location of a “velocity dividing line”
  (VDL) in the H-R diagram. Stars to the right of (and above) the
  VDL were observed to have asymmetries that are consistent with the
  presence of cool massive winds. Stars to the left of (and below) the
  VDL showed no evidence for winds. We show that the VDL lies close to a
  certain event of stellar evolution on the red giant branch (RGB). The
  event occurs when the hydrogen-burning shell evolves outward through
  a discontinuity in molecular weight. In some low-mass stars, this
  event causes a kink in the evolutionary track of an individual low-mass
  star. In a cluster, the combined effects of such kinks create a “bump”
  in the luminosity function. Our result suggests that evolution through
  the kink (or bump) on the RGB is associated with the onset of a cool
  massive wind. Theoretical possibilities to explain this association
  will be explored in a subsequent paper.

---------------------------------------------------------
Title: Onset of mass loss in red giants: association with an
    evolutionary event
Authors: Mullan, D. J.; MacDonald, J.
2003AAS...202.5504M    Altcode: 2003BAAS...35R.774M
  Stencel and Mullan (1980) used asymmetries in the MgII k emission
  line profile to determine the location of a “velocity dividing line"
  (VDL) in the H-R diagram. Stars to the right of (and above) the VDL were
  observed to have asymmetries which are consistent with the presence of
  cool massive winds. Stars to the left of (and below) the VDL showed no
  evidence for winds. We show that the VDL lies close to a certain event
  of stellar evolution on the red giant branch (RGB). The event occurs
  when the hydrogen-burning shell evolves outward through a discontinuity
  in molecular weight. In some low-mass stars, this event causes a kink
  in the evolutionary track of an individual low mass star. In a cluster,
  the combined effects of such kinks create a “bump" in the luminosity
  function. We conclude that evolution through the kink (or bump) on the
  RGB is associated with the onset of a cool massive wind. We speculate
  that this evolutionary event is associated with a change in dynamo
  mode. <P />Work supported by NASA DE Space Grant.

---------------------------------------------------------
Title: Short-Period Magnetic Fluctuations in Advanced Composition
Explorer Solar Wind Data: Evidence for Anticorrelation with Alfvén
    Speed
Authors: Mullan, D. J.; Smith, C. W.; Ness, N. F.; Skoug, R. M.
2003ApJ...583..496M    Altcode:
  Short-period rms fluctuations δB<SUB>rms</SUB> in the interplanetary
  magnetic field have been derived from Advanced Composition Explorer/MAG
  data for 50 solar rotations between 1998 and 2001. We find that in
  many cases, individual maxima in δB<SUB>rms</SUB> are associated
  with local minima in the Alfvén speed V<SUB>Alf</SUB>. To determine
  whether this anticorrelation persists in large data sets, we compute
  the correlation coefficient between the temporal gradients (in the
  spacecraft frame) δB<SUB>rms</SUB> and V<SUB>Alf</SUB> for each of
  the 50 solar rotations in the data set. We find that, in 48 of the 50
  rotations, δB<SUB>rms</SUB> is anticorrelated with V<SUB>Alf</SUB>. The
  confidence level of the anticorrelation is greater than 90% in 35
  rotations and is greater than 99.95% in 14 rotations. We find that in
  some low-V<SUB>Alf</SUB> regions of solar wind, there is a pronounced
  enhancement of non-Alfvénic (compressive) fluctuations. We suggest
  that refraction effects operating on MHD waves contribute to these
  aspects of the magnetic field fluctuation properties of the solar wind.

---------------------------------------------------------
Title: Wave Refraction During the May 2002 Rarefaction Event
Authors: Smith, C. W.; Mullan, D. J.; Ness, N. F.; Skoug, R. M.
2002AGUFMSH72C..08S    Altcode:
  In previous work [Smith et al., 2001] we examined IMF wave refraction
  during the May 1999 rarefaction interval known as “The Day The Solar
  Wind Disappeared.” On that day, Alfvén speeds remained elevated over
  an extended region. Analysis of the recorded ACE fields and plasma data
  revealed depressed magnetic fluctuation levels, reduced compression in
  the fluctuations, and a reduced wave-like component within the region
  of elevated Alfvén speed, all consistent with wave refraction. The
  May 2002 event provides a third such period (the second identified
  event occured 2 weeks prior to the May 1999 period) and it again
  demonstrates properties which are consistent with refraction. Smith,
  C.~W., D.~J. Mullan, N.~F. Ness, R.~M. Skoug, and J.~Steinberg, Day
  the solar wind almost disappeared: Magnetic field fluctuations, wave
  refraction and dissipation, J. Geophys. Res., A106, 18,625--18,634,
  2001. Efforts at the Bartol Research Institute were supported by CIT
  subcontract PC251439 under NASA grant NAG5-6912 for support of the
  ACE magnetic field experiment and by the NASA Delaware Space College
  Grant. Work at Los Alamos was performed under the auspices of the
  U.S. Department of Energy with financial support from the NASA ACE
  program.

---------------------------------------------------------
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: The origin of the FIP effect in solar and stellar atmospheres
Authors: Mullan, D. J.
2002APS..DPPQM2001M    Altcode:
  When elemental abundances are normalized to their values in the solar
  photosphere, it is found that elements with low values of the First
  Ionization Potential (FIP) are enhanced in abundance in the solar
  corona relative to elements with high values of the FIP. In order to
  account for this so-called "FIP effect", we suggest that the corona
  is supplied with material from localized sites where magnetic flux
  tubes of opposite polarity come into contact. When this process of
  opposite-flux-tube-interaction (OFTI) occurs in a partially ionized
  medium, it provides a natural method for enhancing low-FIP elements
  in the corona. Numerical modelling of OFTI using a two-fluid code has
  been reported by Arge and Mullan (1998): the enhancement of low-FIP
  elements depends on the ratio of two time-scales, one for ions the
  other for atoms. The model contains the important feature that,
  because of a particular feature of the chromosphere in solar-like
  stars, there is a built-in regulatory mechanism of the enhancement of
  the low-FIP elements. This is especially important in the context of
  recent discoveries of FIP bias in stars other than the Sun.

---------------------------------------------------------
Title: Coronal Heating Distribution Due to Low-Frequency, Wave-driven
    Turbulence
Authors: Dmitruk, P.; Matthaeus, W. H.; Milano, L. J.; Oughton, S.;
   Zank, G. P.; Mullan, D. J.
2002ApJ...575..571D    Altcode: 2002astro.ph..4347D
  The heating of the lower solar corona is examined using numerical
  simulations and theoretical models of magnetohydrodynamic turbulence
  in open magnetic regions. A turbulent energy cascade to small length
  scales perpendicular to the mean magnetic field can be sustained by
  driving with low-frequency Alfvén waves reflected from mean density and
  magnetic field gradients. This mechanism deposits energy efficiently
  in the lower corona, and we show that the spatial distribution of the
  heating is determined by the mean density through the Alfvén speed
  profile. This provides a robust heating mechanism which can explain
  observed high coronal temperatures and accounts for the significant
  heating (per unit volume) distribution below 2 solar radii needed
  in models of the origin of the solar wind. The obtained heating per
  unit mass, on the other hand, is much more extended, indicating that
  the heating on a per-particle basis persists throughout all the lower
  coronal region considered here.

---------------------------------------------------------
Title: V471 Tauri and SuWt 2: The Exotic Descendants of Triple
    Systems?
Authors: Bond, Howard E.; O'Brien, M. Sean; Sion, Edward M.; Mullan,
   Dermott J.; Exter, Katrina; Pollacco, Don L.; Webbink, Ronald F.
2002ASPC..279..239B    Altcode: 2002esce.conf..239B; 2002IAUCo.187..239B
  No abstract at ADS

---------------------------------------------------------
Title: Detection of Coronal Mass Ejections in V471 Tauri with the
    Hubble Space Telescope
Authors: Bond, Howard E.; Mullan, D. J.; O'Brien, M. Sean; Sion,
   Edward M.
2001ApJ...560..919B    Altcode: 2001astro.ph..6400B
  V471 Tauri, an eclipsing system consisting of a hot DA white dwarf
  (WD) and a dK2 companion in a 12.5 hr orbit, is the prototype of
  the precataclysmic binaries. The late-type component is magnetically
  active, due to its being constrained to rotate synchronously with the
  short orbital period. During a program of ultraviolet spectroscopy of
  V471 Tau, carried out with the Goddard High Resolution Spectrograph
  (GHRS) on board the Hubble Space Telescope, we serendipitously
  detected two episodes in which transient absorptions in the Si III
  1206 Å resonance line appeared suddenly, on a timescale of &lt;~2
  minutes. The observations were taken in a narrow spectral region around
  Lyα and were all obtained near the two quadratures of the binary
  orbit, i.e., at maximum projected separation (~3.3 R<SUB>solar</SUB>)
  of the WD and K star. We suggest that these transient features arise
  when coronal mass ejections (CMEs) from the K2 dwarf pass across
  the line of sight to the WD. Estimates of the velocities, densities,
  and masses of the events in V471 Tau are generally consistent with
  the properties of solar CMEs. Given our detection of two events
  during 6.8 hr of GHRS observing, along with a consideration of the
  restricted range of latitudes and longitudes on the K star's surface
  that can give rise to trajectories passing in front of the WD as seen
  from Earth, we estimate that the active V471 Tau dK star emits some
  100-500 CMEs day<SUP>-1</SUP>, as compared to ~1-3 day<SUP>-1</SUP>
  for the Sun. The K dwarf's mass-loss rate associated with CMEs is
  at least (5-25)×10<SUP>-14</SUP> M<SUB>solar</SUB> yr<SUP>-1</SUP>,
  but it may well be orders of magnitude higher if most of the silicon
  is in ionization states other than Si III. Based on observations with
  the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope
  Science Institute, which is operated by AURA, Inc., under NASA contract
  NAS 5-26555.

---------------------------------------------------------
Title: Day the solar wind almost disappeared: Magnetic field
    fluctuations, wave refraction and dissipation
Authors: Smith, Charles W.; Mullan, Dermott J.; Ness, Norman F.;
   Skoug, Ruth M.; Steinberg, John
2001JGR...10618625S    Altcode:
  On May 11, 1999, the Advanced Composition Explorer (ACE) spacecraft
  observed a rarefied parcel of solar wind. This has come to be known as
  “The Day the Solar Wind Disappeared.” Little if any change is seen
  in the large-scale interplanetary magnetic field during this time,
  but the magnetic field fluctuations are depressed and significantly
  more transverse to the mean field. The high Alfvén speed resulting
  from the constant field intensity and low ion density enhances wave
  refraction, and we examine this as a possible explanation for the
  fluctuation properties. The solar wind possesses a very low proton β,
  thereby separating the cyclotron and ion inertial length scales and
  permitting a test of possible dissipation dynamics. We find that the
  test favors the ion inertial scale theories.

---------------------------------------------------------
Title: Are Magnetically Active Low-Mass M Dwarfs Completely
    Convective?
Authors: Mullan, D. J.; MacDonald, J.
2001ApJ...559..353M    Altcode:
  Stars on the main sequence are expected to be completely convective
  if their mass lies below a certain value, M<SUB>cc</SUB>. Standard
  stellar structure codes suggest that M<SUB>cc</SUB> is in the range
  0.3-0.4 M<SUB>solar</SUB>. In the present paper we examine several
  nonstandard additions to stellar structure in order to quantify their
  effects on the value of M<SUB>cc</SUB>. We find that by including
  magnetic field effects, M<SUB>cc</SUB> may fall to values that are
  significantly smaller than the standard range. This result is of
  interest in understanding why coronae and chromospheres in active
  M dwarfs fail to exhibit detectable alterations at spectral class
  M3-M4. The structural properties of our magnetic models also explain
  why active M dwarfs tend to have radii that are larger than expected
  for their T<SUB>eff</SUB> values or T<SUB>eff</SUB> values that are
  too low for their radii. Our results lead us to predict that certain
  stars that are classified as late L or T stars may actually have masses
  of 0.1-0.15 M<SUB>solar</SUB>.

---------------------------------------------------------
Title: Particle channels in the solar wind: Magnetic Field
    Fluctuations, Wave Refraction and Dissipation
Authors: Mullan, D. J.; Ness, C. W.; Smith, N. F.; Skoug, J.;
   Steinberg, R.
2001ICRC....8.3349M    Altcode: 2001ICRC...27.3349M
  Buttighofer has reported the existence of "channels" in the solar
  wind through which solar energetic particles can propagate almost
  scatter-free. We draw attention to an event observed by the ACE
  spacecraft on May 11 1999 that has many of the characteristics of
  Buttighofer's channels. The ACE event is known as `The Day the Solar
  Wind (Almost) Disappeared'. During this unusual rarefaction event, the
  solar wind density dropped by almost 2 orders of magnitude relative to
  the value that is typically seen at ACE. However, the magnetic field
  remained almost constant during the rarefaction. The most striking
  feature of the magnetic field as measured by ACE was the fact that the
  r.m.s. (root mean square) field fluctuations dropped to unusually low
  values (about 0.1 nT). These low r.m.s. values are reminiscent of the
  behavior reported by Buttighofer in the particle channels. Moreover,
  the fluctuations that remained in the ACE rarefaction region were found
  to be significantly more transverse to the mean field than usual, again
  analogous to a feature reported by Buttighofer in the channels. We
  suggest that the phenomenon of refraction allows us to understand the
  properties of the magnetic fluctuations inside the ACE rarefaction
  region, and by extension, in the Buttighofer particle channels as well.

---------------------------------------------------------
Title: The Day the Solar Wind (Almost) Disappeared: Refraction
    and Dissipation
Authors: Mullan, D. J.; Smith, C. W.; Ness, N. F.; Skoug, R. M.;
   Steinberg, J.
2001AGUSM..SP61A01M    Altcode:
  On May 11, 1999 the ACE spacecraft spent several hours in an unusually
  rarefied parcel of solar wind. During this rarefaction interval,
  the Alfven speed was exceptionally high while the ion temperature
  was low. These properties provide a rare opportunity to examine two
  distinct physical processes that operate in the solar wind. First,
  refraction of MHD waves: fast-mode waves are excluded from the rarefied
  parcel, but Alfven waves are not affected. Second, dissipation of
  magnetic fluctuations: when ACE is in the rarefaction interval,
  the location of dissipation onset in the magnetic power spectrum
  shifts towards a distinctly lower frequency. The direction of this
  shift is consistent with dissipation processes that operate at the
  ion inertial length-scale. But the observed shift in dissipation
  frequency is not compatible with the widely discussed mechanism of
  ion cyclotron resonance.

---------------------------------------------------------
Title: Coronal Heating Distribution due to Alfvenic Driven
    Magnetohydrodynamic Turbulence
Authors: Dmitruk, P.; Matthaeus, W. H.; Milano, L. J.; Oughton, S.;
   Mullan, D. J.; Zank, G. P.
2001AGUSM..SH22E02D    Altcode:
  We establish a direct connection between the heating rate function
  in the lower open corona and the background radial plasma density and
  magnetic field profiles in that region. The confinement of the heating
  between 1-2 solar radius is achieved through Alfven waves injected
  from the base and reflected due to inhomogeneities of the medium,
  which provide the necessary counter-propagating fluctuations to sustain
  quasi-2D MHD turbulence. A phenomenological description is considered
  as well as direct numerical simulations of the reduced MHD equations. A
  simple approximation is applied to obtain an explicit relation between
  the heating rate function q and the Alfven velocity profile. Some
  example profiles are presented, which show a radial exponentially
  decaying behavior for the heating, with a dissipation length of the
  order of the medium inhomogeneity length. Other quantities, such as
  cross helicity and fluctuations intensity are also analyzed.

---------------------------------------------------------
Title: A Reduced Magnetohydrodynamic Model of Coronal Heating in
    Open Magnetic Regions Driven by Reflected Low-Frequency Alfvén Waves
Authors: Oughton, S.; Matthaeus, W. H.; Dmitruk, P.; Milano, L. J.;
   Zank, G. P.; Mullan, D. J.
2001ApJ...551..565O    Altcode:
  A reduced magnetohydrodynamic (RMHD) description is employed to
  examine a suggestion made by W. H. Matthaeus and colleagues in 1999
  that coronal heating might be sustained by a cascade of low-frequency
  MHD turbulence. Here RMHD simulations show that the low-frequency
  cascade to high transverse wavenumbers can be driven by an externally
  maintained flux of low-frequency propagating Alfvén waves, in
  combination with reflection caused by an inhomogeneous background
  medium. The simulations show that the suggestions made previously on
  the basis of a phenomenology are indeed realizable. In addition, the
  effect is seen to sensitively depend on the presence of reflection,
  as the background turbulence level needed to maintain the cascade
  can be sustained only when reflection is imposed. The steady level
  of turbulence is insensitive to the initial seed turbulence level
  (provided it is nonzero). Consequences of this model for realistic
  models of coronal heating in open field-line regions are discussed.

---------------------------------------------------------
Title: The Oversized Magnetically Active dK Component of V471 Tauri
Authors: Bond, H. E.; O'Brien, M. S.; Mullan, D. J.; Sion, E. M.
2001AGM....18S0709B    Altcode: 2001AGAb...18R..79B
  V471 Tauri is an eclipsing binary in the Hyades cluster containing a
  hot white dwarf (WD) and a dK2 companion. The K2 star is extremely
  active, due to its synchronous rotation with the 12.5-hour orbital
  period. During UV spectroscopy of V471 Tau, obtained with the GHRS on
  the Hubble Space Telescope, we serendipitously detected two episodes
  in which the Si III 1206 Å absorption line appeared suddenly in
  the WD spectrum, on a timescale of &lt;2 min. The spectra were taken
  near maximum projected separation (~3.3 R<SUB>solar</SUB>) of the WD
  and K star. looseness=-1 The Si III transients appear to arise when
  coronal mass ejections (CME's) from the K2 star pass in front of the
  WDνll. The velocities, densities, and masses of the features in V471
  Tau are similar to those of solar CME's. Given our detection of 2 events
  during 6.8 hr of GHRS observing, along with a consideration of the
  restricted range of latitudes and longitudes on the K star's surface
  that can give rise to trajectories passing in front of the WD as seen
  from Earth, we estimate that the dK star emits some 100-500 CME's per
  day, compared to ~1-3 per day for the Sun. The K dwarf's mass-loss
  rate associated with CME's is at least (5-25)×10<SUP>-14</SUP>
  M<SUB>solar</SUB> yr<SUP>-1</SUP>, but could be orders of magnitude
  higher. Measurements of the eclipse duration show that the radius of
  the dK star is ~18% larger than that of a Hyades dwarf of the same mass
  (0.93 M<SUB>solar</SUB>)νll. We attribute the large radius to the dK
  star's surface activity: because about 25% of the star's surface is
  covered with starspots, the star must expand so that it can continue
  to radiate the luminosity produced in its core.

---------------------------------------------------------
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: Extended Atmospheres
Authors: Mullan, D.
2000eaa..bookE1846M    Altcode:
  During a total ECLIPSE of the Sun, when the Moon blocks out the
  intensely bright disk of the Sun, a faint white `halo' can be seen
  surrounding the Sun (see figure 1). This halo, officially called
  the Sun's `CORONA' (i.e. `crown'), exists mainly because there are
  electrons in the outer solar atmosphere: even though the disk of the
  Sun is hidden from direct view, the electrons scatter a fraction o...

---------------------------------------------------------
Title: MHD-driven Kinetic Dissipation in the Solar Wind and Corona
Authors: Leamon, R. J.; Matthaeus, W. H.; Smith, C. W.; Zank, G. P.;
   Mullan, D. J.; Oughton, S.
2000ApJ...537.1054L    Altcode:
  Mechanisms for the deposition of heat in the lower coronal plasma
  are discussed, emphasizing recent attempts to reconcile the fluid and
  kinetic perspectives. Structures at magnetohydrodynamic (MHD) scales may
  drive a nonlinear cascade, preferentially exciting high perpendicular
  wavenumber fluctuations. Relevant dissipative kinetic processes must be
  identified that can absorb the associated energy flux. The relationship
  between the MHD cascade and direct cyclotron absorption, including
  cyclotron sweep, is discussed. We conclude that for coronal and solar
  wind parameters the perpendicular cascade cannot be neglected and may
  be more rapid than cyclotron sweep. Solar wind observational evidence
  suggests the relevance of the ion inertial scale, which is associated
  with current sheet thickness during reconnection. We conclude that a
  significant fraction of dissipation in the corona and solar wind likely
  proceeds through a perpendicular cascade and small-scale reconnection,
  coupled to kinetic processes that act at oblique wavevectors.

---------------------------------------------------------
Title: The Origin of the FIP Effect in the Solar Atmosphere
Authors: Mullan, D. J.; Arge, C. N.
2000ASPC..206...71M    Altcode: 2000hesp.conf...71M
  No abstract at ADS

---------------------------------------------------------
Title: Solar Physics: From the Deep Interior to the Hot Corona
Authors: Mullan, Dermott J.
2000LNP...556....1M    Altcode: 2000stga.conf....1M; 2000fsga.conf....1M
  We present an overview of the thermal properties of the Sun from the
  hot interior to the hot corona. For pedagogical reasons, we confine
  the discussion to certain relevant solutions of the energy conservation
  equation. In the interior, quantitative information can be obtained by
  using a polytropic equation of state: internal temperatures obtained
  in this way are found to be reliable to about 10%, and we can obtain a
  good estimate of the depth of the convection zone. In the chromosphere,
  acoustic waves originating in the convection zone do work on the gas: as
  the gas heats up, the atomic energy levels of many elements (especially
  hydrogen) exert a strong thermostatic control so that the temperature
  is confined to a steady value in the range 5000-10<SUP>4</SUP> K. In
  long-lived coronal loops, a steady state balance between thermal
  conduction and radiative losses causes the temperature of the electrons
  to lie in the range (1-2) million K. Coronal ions are heated to greater
  temperatures than electrons. In flares, processes of heating and cooling
  are explicitly non-steady, and short-lived excursions to temperatures
  as high as 25 million K (or more) are observed in the largest flares.

---------------------------------------------------------
Title: Plasma Flows In Coronal Hole Regions
Authors: Landi, E.; Mullan, D.; Poletto, G.; Wilhelm, K.
1999ESASP.446..417L    Altcode: 1999soho....8..417L
  More than two decades after coronal holes (CH) had been recognized
  to be the source regions of solar wind, we still do not know which
  structures, within CH, most contribute to the solar wind mass flux. In
  a recent work, Hassler et al. (1999) obtained velocity maps of a
  coronal hole region, in the Ne VIII 770 Angstrom line, which suggest
  that localized areas within the network might be sources of the solar
  wind. On the opposite, an earlier work of Dupree et al. (1996), from
  an analysis of the He I 10830 Angstrom line, suggested cell regions
  as sources of the solar wind. In the present work, we reinvestigate
  this issue analysing SUMER data taken in an equatorial and in a polar
  coronal hole, observed respectively on 29 August 1996 and 21 September
  1996. We study the behavior of Si II, C IV, O V, N V, Ne VIII, Mg X and
  Fe XII ions, whose temperatures of formation range from chromospheric
  (around 2x10<SUP>4</SUP> K) to coronal values (around 1.5x10<SUP>5</SUP>
  K). In particular, we analysed intensity and velocity distributions
  of these lines, and illustrate changes in the plasma velocity pattern
  as a function of the temperature regime where lines form.

---------------------------------------------------------
Title: Gravity damping of Alfvén waves: numerical modelling
Authors: Mullan, D. J.; Khabibrakhmanov, I. K.
1999ESASP.446..503M    Altcode: 1999soho....8..503M
  Estimates of Alfven wave dissipation in the fluid approximation have
  been in the literature for years. Here we report on a numerical study
  of Alfven wave dissipation in a non-fluid context. We consider a nearly
  collisionless magnetized plasma. A test particle moves in this medium
  in the presence of an Alfven wave propagating along a vertical field
  line in the presence of gravity. The model includes the randomizing
  effects of collisions which occur infrequently enough that the particle
  undergoes many gyrations between successive collisions. Our results
  indicate that the test particle gains energy from the wave at a rate
  which is larger than the linear predictions of Khabibrakhmanov and
  Mullan (1994).

---------------------------------------------------------
Title: Coronal Heating by Magnetohydrodynamic Turbulence Driven by
    Reflected Low-Frequency Waves
Authors: Matthaeus, W. H.; Zank, G. P.; Oughton, S.; Mullan, D. J.;
   Dmitruk, P.
1999ApJ...523L..93M    Altcode:
  A candidate mechanism for the heating of the solar corona in open
  field line regions is described. The interaction of Alfvén waves,
  generated in the photosphere or chromosphere, with their reflections
  and the subsequent driving of quasi-two-dimensional MHD turbulence
  is considered. A nonlinear cascade drives fluctuations toward short
  wavelengths which are transverse to the mean field, thereby heating at
  rates insensitive to restrictive Alfvén timescales. A phenomenology
  is presented, providing estimates of achievable heating efficiency
  that are most favorable.

---------------------------------------------------------
Title: GHRS Observations of Cool, Low-Gravity Stars. V. The Outer
    Atmosphere and Wind of the Nearby K Supergiant λ Velorum
Authors: Carpenter, Kenneth G.; Robinson, Richard D.; Harper, Graham
   M.; Bennett, Philip D.; Brown, Alexander; Mullan, Dermott J.
1999ApJ...521..382C    Altcode:
  UV spectra of λ Velorum taken with the Goddard High Resolution
  Spectrograph (GHRS) on the Hubble Space Telescope are used to probe the
  structure of the outer atmospheric layers and wind and to estimate the
  mass-loss rate from this K5 Ib-II supergiant. VLA radio observations at
  λ=3.6 cm are used to obtain an independent check on the wind velocity
  and mass-loss rate inferred from the UV observations. Parameters
  of the chromospheric structure are estimated from measurements of
  UV line widths, positions, and fluxes and from the UV continuum flux
  distribution. The ratios of optically thin C II] emission lines indicate
  a mean chromospheric electron density of logN<SUB>e</SUB>~8.9+/-0.2
  cm<SUP>-3</SUP>. The profiles of these lines indicate a chromospheric
  turbulence (v<SUB>0</SUB>~25-36 km s<SUP>-1</SUP>), which greatly
  exceeds that seen in either the photosphere or wind. The centroids
  of optically thin emission lines of Fe II and of the emission
  wings of self-reversed Fe II lines indicate that they are formed in
  plasma approximately at rest with respect to the photosphere of the
  star. This suggests that the acceleration of the wind occurs above
  the chromospheric regions in which these emission line photons are
  created. The UV continuum detected by the GHRS clearly traces the
  mean flux-formation temperature as it increases with height in the
  chromosphere from a well-defined temperature minimum of 3200 K up to
  about 4600 K. Emission seen in lines of C III] and Si III] provides
  evidence of material at higher than chromospheric temperatures in the
  outer atmosphere of this noncoronal star. The photon-scattering wind
  produces self-reversals in the strong chromospheric emission lines,
  which allow us to probe the velocity field of the wind. The velocities
  to which these self-absorptions extend increase with intrinsic line
  strength, and thus height in the wind, and therefore directly map
  the wind acceleration. The width and shape of these self-absorptions
  reflect a wind turbulence of ~9-21 km s<SUP>-1</SUP>. We further
  characterize the wind by comparing the observations with synthetic
  profiles generated with the Lamers et al. Sobolev with Exact Integration
  (SEI) radiative transfer code, assuming simple models of the outer
  atmospheric structure. These comparisons indicate that the wind in
  1994 can be described by a model with a wind acceleration parameter
  β~0.9, a terminal velocity of 29-33 km s<SUP>-1</SUP>, and a mass-loss
  rate~3×10<SUP>-9</SUP> M<SUB>solar</SUB> yr<SUP>-1</SUP>. Modeling
  of the 3.6 cm radio flux observed in 1997 suggests a more slowly
  accelerating wind (higher β) and/or a higher mass-loss rate than
  inferred from the UV line profiles. These differences may be due to
  temporal variations in the wind or from limitations in one or both
  of the models. The discrepancy is currently under investigation. <P
  />Based on observations with the NASA/ESA Hubble Space Telescope,
  which is operated by the Association of Universities for Research in
  Astronomy, Inc., under NASA contract NAS 5-26555.

---------------------------------------------------------
Title: Gravity damping of Alfvén waves: Theory and numerical modeling
Authors: Khabibrakhmanov, I. K.; Mullan, D. J.
1999AIPC..471..349K    Altcode: 1999sowi.conf..349K
  In a collisionless medium where gravity and magnetic field are parallel,
  a charged particle and an electromagnetic wave can exchange energy
  and momentum at a rate which is proportional to the gravitational
  acceleration. As a result, plasma energization can occur. A test
  particle approach to the problem has demonstrated that the total energy
  of the particle increases at the rate predicted by the gravity damping
  mechanism. Moreover, the test particle undergoes significant upward
  motion in an exponential atmosphere. This indicates that gravity
  damping can contribute to the solar wind formation in two distinct
  ways. First, implicitly, through plasma heating: the pressure gradient
  created in this way is the main driving force of the solar wind in
  a fluid model. Second, the particle experiences direct lift due to
  energy exchange with the wave and the up-down asymmetry of collision
  rates in a stratified atmosphere.

---------------------------------------------------------
Title: Heating and Acceleration of the Solar Wind via Gravity Damping
    of Alfvén Waves
Authors: Cuseri, Iolanda; Mullan, Dermott; Noci, Giancarlo; Poletto,
   Giannina
1999ApJ...514..989C    Altcode:
  In this paper we present a two-fluid model for the heating of the solar
  corona and acceleration of the solar wind, based on the dissipation
  of Alfvén waves by gravity damping. This mechanism was proposed by
  Khabibrakhmanov &amp; Mullan but has not previously been applied in
  modeling efforts. After extending the Khabibrakhmanov &amp; Mullan
  theory to give an expression for the evolution of the Alfvén wave
  amplitude as a function of the local parameters of the atmosphere,
  we show how gravity damping compares with other mechanisms that have
  been proposed for the dissipation of Alfvén waves. Then we introduce
  the system of equations that we use for the wind model: this includes,
  in the energy equation, a gravity dissipation term and, in the momentum
  equation, a different wave acceleration term from that which is usually
  adopted. Initial conditions for the integration of the equations
  are compatible with recent Ulysses measurements, and the integration
  proceeds from 1 AU toward the base of the solar corona and into the
  transition region [where T=(1-2)×10<SUP>5</SUP> K]. Our results show
  that the gravity damping of Alfvén waves heats protons in the solar
  plasma to several million degrees and accelerates the solar wind
  to 600-700 km s<SUP>-1</SUP>. Model predictions at low heliocentric
  distances compare favorably with recently acquired data. One prediction
  of our model is that the damping process is most effective in regions
  where the Alfvén speed is low. Another prediction is that although
  the energy is deposited mainly into protons, the deposition occurs
  close enough to the Sun that collisional coupling also leads to
  effective heating of the electrons (to T<SUB>e</SUB>~10<SUP>6</SUP>
  K). We compare and contrast the present model with models based on
  ion-cyclotron resonant processes.

---------------------------------------------------------
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: Fluctuations, Dissipation and Heating in the Corona
Authors: Matthaeus, W. H.; Zank, G. P.; Leamon, R. J.; Smith, C. W.;
   Mullan, D. J.; Oughton, S.
1999SSRv...87..269M    Altcode:
  Mechanisms for the deposition of heat in the lower coronal plasma
  are discussed, emphasizing recent attempts to reconcile the fluid
  and kinetic perspectives. Structures at the MHD scales are believed
  to act as reservoirs for fluctuation energy, which in turn drive a
  nonlinear cascade process. Kinetic processes act at smaller spatial
  scales and more rapid time scales. Cascade-driven processes are
  contrasted with direct cyclotron absorption, and this distinction is
  echoed in the contrast between frequency and wavenumber spectra of the
  fluctuations. Observational constraints are also discussed, along with
  estimates of the relative efficiency of cascade and cyclotron processes.

---------------------------------------------------------
Title: Nonprimordial Deuterium in the Interstellar Medium
Authors: Mullan, D. J.; Linsky, J. L.
1999ApJ...511..502M    Altcode:
  Contrary to a widespread assumption, deuterium is not simply destroyed
  in stars: deuterium is also synthesized in the atmospheres of active
  stars. This nonprimordial synthesis of D arises when protons accelerated
  in flares interact with the atmosphere, create a flux of free neutrons,
  and these neutrons then undergo radiative capture on atmospheric
  protons. Radiative capture does not result in excess production of
  Li, Be, or B. Ejection of flare-processed material contaminates the
  interstellar medium (ISM), as was originally suggested by Coleman
  &amp; Worden. Estimates of the amount of flare-created D are subject
  to considerable uncertainties, but we find, using stellar parameters
  within permitted ranges, that flares may contribute significantly to
  the current ISM D content. Observational data indicate that different
  clouds of gas in the ISM exhibit variations in the value of D/H. We
  suggest that contamination of the ISM by D-enriched material ejected
  from stellar flares contributes to the observed D/H inhomogeneity. More
  precise estimates of the efficiency of D ejection from flares into
  the solar wind are required to evaluate this suggestion.

---------------------------------------------------------
Title: Coronal Heating: a Comparison of Ion-cyclotron and Gravity
    Damping Models
Authors: Cuseri, I.; Mullan, D.; Poletto, G.
1999SSRv...87..153C    Altcode:
  SOHO/UVCS data indicate that minor ions in the corona are heated more
  than hydrogen, and that coronal heating results in T<SUB>⊥</SUB>
  larger than T<SUB>‖</SUB>. Analogous behavior has been known from
  in situ measurements in solar wind for many years. Here we compare
  and contrast two mechanisms which have been proposed to account for
  the above behavior: ion-cyclotron resonance and gravity damping.

---------------------------------------------------------
Title: The Chromosphere, Wind, and Mass-Loss Rate of lambda Velorum
    (K5 Ib) as Revealed by UV Emission Line Profiles
Authors: Carpenter, K. G.; Robinson, R. D.; Harper, G. M.; Bennett,
   P. D.; Brown, A.; Mullan, D. J.
1998AAS...193.4502C    Altcode: 1998BAAS...30Q1317C
  The Goddard High Resolution Spectrograph (GHRS) on the HST has been
  used to acquire high-quality UV spectra of the nearby K-supergiant
  lambda Velorum. These spectra contain a wide variety of chromospheric
  emission lines, many of which are self-reversed by wind absorption,
  and thus allow us to probe the structure of both the chromosphere
  and wind. The observed line widths, positions, and fluxes indicate a
  chromosphere with a mean log n_e ~ 8.9 +/- -0.2 cm(-3) , a turbulence
  (indicated by line cores with ~ 25 km s(-1) Doppler widths) greatly
  in excess of the photospheric value, and no general systematic flows
  (i.e. the wind acceleration appears to occur above the region of
  photon creation). We compare synthetic Fe II line profiles from the
  approximate Lamers et al. (1987) Sobelev with Exact Integration (SEI)
  method, and from an exact comoving frame CRD calculation, with the
  observations. The width and shape of the wind self-absorptions implies
  a terminal velocity of 29--33 km s(-1) , and a wind turbulence of ~
  9-21 km s(-1) . We find that the wind in the 1994 GHRS observations
  can be described by a model with an acceleration parameter beta ~ 0.9
  and a mass-loss rate of ~ 3 x 10(-9) M<SUB>sun</SUB> yr(-1) . However,
  this model is not consistent with the VLA 3.6 cm radio continuum flux
  observed in 1997.

---------------------------------------------------------
Title: Modelling of magnetic interactions in partially-ionized gas:
    application to the FIP effect
Authors: Arge, C. N.; Mullan, D. J.
1998SoPh..182..293A    Altcode:
  We have adapted the ZEUS code to model magnetic interactions in
  partially ionized gas. When two regions of opposite polarity come into
  contact with each other, ions drifting in response to the Lorentz force
  fall into the minimum of the magnetic field, and then the drifting
  ions force the neutrals to take part in the flow. Because of the finite
  time required for ion-atom collisions to occur, the gas which emerges
  from the interaction site has an ion/atom ratio which may be altered
  relative to that in the ambient medium. In order to model this effect,
  we adapt the Zeus code to a two-step iterative process involving
  a cycle between the hydrodynamic (HD) and the magnetohydrodynamic
  (MHD) versions of the code. The ion and atom fluids are coupled by
  collisions. Our simulations show that in chromospheric conditions,
  outflowing gas exhibits enhancements in ion/atom ratios which may be
  as large as a factor of 10 or more. The magnitude of the enhancements
  is determined by two key ratios which enter into the problem: the
  degree of ionization (ni/na), and the plasma β parameter. We show
  that, in the context of the mechanism we propose here, the amplitude
  of the ion/atom enhancements in the solar chromosphere is subject to
  a remarkable self-regulation because the ion density ni is almost
  invariant over the height range of interest to us. Our results are
  relevant in the context of the Sun, where the coronal abundances of
  elements with low first ionization potential (FIP) are systematically
  enhanced in certain magnetic structures. Although data for stars other
  than the Sun are sparse, we point out that our results are also useful
  for interpreting the available stellar data.

---------------------------------------------------------
Title: Large Variations in the Winds of Single Cool Giants: λ
    Velorum and γ Crucis
Authors: Mullan, D. J.; Carpenter, K. G.; Robinson, R. D.
1998ApJ...495..927M    Altcode:
  UV spectra of the “noncoronal” single K supergiant λ Vel and of
  the single M giant γ Cru obtained with IUE and the Hubble Space
  Telescope at various epochs indicate that the profiles of many lines
  formed in the wind exhibit striking alterations in shape with time. We
  parameterize the wind profiles in terms of an empirical optical depth
  τ<SUB>emp</SUB> by reflecting the red wing about line center and
  comparing the reflected intensity with that of the blue wing. In the λ
  Vel wind the terminal velocity v<SUB>∞</SUB> was found to be close
  to 40 km s<SUP>-1</SUP> in 1978, 1982, and 1994, but was at least 20
  km s<SUP>-1</SUP> greater in 1990. The faster wind in 1990 also had
  a total optical depth that was a factor of 2-6 times greater than at
  the other epochs. <P />Based on observations with the NASA/ESA Hubble
  Space Telescope, which is operated by the Association of Universities
  for Research in Astronomy, Inc., under NASA contract NAS 5-26555,
  and on observations with the International Ultraviolet Explorer.

---------------------------------------------------------
Title: Large-eddy simulation of astrophysical convection and acoustic
    emission
Authors: Mullan, D. J.
1998ASPC..138..253M    Altcode: 1998stas.conf..253M
  No abstract at ADS

---------------------------------------------------------
Title: Comparing Observations of Cyclical Variability in - and
    Cool-Star Winds
Authors: Mullan, D. J.
1998cvsw.conf..173M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: A new heating and acceleration mechanism for the fast
    solar wind
Authors: Cuseri, I.; Mullan, D. J.; Noci, G.; Poletto, G.
1998MmSAI..69..745C    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Periodic Modulation of X-Ray Intensity from Coronal Loops -
    Heating by Resonant Absorption?
Authors: McKenzie, D. E.; Mullan, D. J.
1997SoPh..176..127M    Altcode:
  We have applied time-series analysis to sequences of coronal loop images
  obtained with the Yohkoh soft X-ray telescope (SXT). Using images
  obtained in fast-cadence mode (δ t = 4 s), we have generated X-ray
  light curves and power spectra for multiple subregions of a number
  of coronal loops. Our analysis indicates that out of 544 spectra
  of loops which range in length L from 40 Mm to 150 Mm, there are
  16 cases where the X-ray brightness is modulated periodically with
  ≥99.5% confidence. The periods τ range from 9.6 s to 61.6 s, and
  the amplitudes range from 0.4% to 1.8%. Our result is statistically
  significant at the 8σ level.

---------------------------------------------------------
Title: Response to Comment by J. V. Hollweg
Authors: Khabibrakhmanov, I. K.; Mullan, D. J.
1997ApJ...488..898K    Altcode:
  The preceding comment by J. V. Hollweg presents criticisms of a paper
  that had reported estimates of the damping rates of Alfvén waves in
  the presence of gravitational acceleration. Here we point out that
  there is actually significant overlap between the conclusions of the
  former and the latter. We agree with a new point raised by the comment
  concerning up/down asymmetry of gravity damping.

---------------------------------------------------------
Title: Cyclic convection in a zone bounded by stable layers
Authors: Hossain, Murshed; Mullan, D. J.
1997PhRvE..55.2769H    Altcode:
  We have simulated compressible convection in two distinct but related
  cases: (i) a single layer of unstable material is in contact with
  impenetrable boundaries and (ii) a layer of unstable material that is
  identical to that of case (i) except that it is now 'sandwiched' between
  two thick stable layers. The convection is driven equally strongly in
  both cases. We find that convection in the single layer is steady,
  whereas in the 'sandwich' case, the convection exhibits nonsteady
  behavior of a particular kind: the convection is cyclic. During one
  part of the cycle, the convective flux F<SUB>C</SUB> falls to levels
  that are too small for energy balance. During the second part of the
  cycle, conduction increases in an attempt to restore energy, but this
  eventually drives the fluid back to convective instability, with a
  subsequent increase in F<SUB>C</SUB> . In the course of the cycle,
  the fluctuations in F<SUB>C</SUB> are large (factors of 2-3). We
  comment on the applicability of our results to convection in the sun.

---------------------------------------------------------
Title: Radiative Transfer Effects on the Stability of Sound Waves
    in a Polytropic Atmosphere
Authors: MacDonald, James; Mullan, Dermott
1997ApJ...481..963M    Altcode:
  From a perturbation analysis of the boundary value problem that
  describes the behavior of optically thin disturbances to a polytropic
  atmosphere initially in hydrostatic and radiative equilibrium, we derive
  criteria for the overstability of acoustic modes. Our criteria are more
  general than those found by Spiegel, which are strictly valid only if
  the radiative cooling time is uniform over the atmosphere, i.e., if
  the polytropic index m = 6. Our criteria for overstability are valid
  for any value of m. Applying our results to the Sun and giant stars,
  we find that sound waves in the envelope of the Sun do not appear to
  be unstable but that instability may occur in the envelopes of red
  giants. We note that, if acoustic waves become overstable as a star
  evolves into a giant, then the acoustic power in the envelopes of cool
  giants will be greater than one would have expected on the basis of the
  predictions of Lighthill theory. We propose that chromospheric heating
  in nonmagnetic stars (such as old giants in globular clusters) contains
  a significant component that arises from acoustic overstability.

---------------------------------------------------------
Title: Two-Dimensional Time-Dependent MHD in Partially Ionized Gas:
    Application to the FIP problem.
Authors: Arge, Charles N.; Mullan, Dermott J.
1997SPD....28.0240A    Altcode: 1997BAAS...29..900A
  We study the two-dimensional behavior of partially ionized gas in
  magnetized regions of the solar atmosphere. The highly time-dependent
  nature of solar magnetic fields frequently produce interacting
  oppositely directed magnetic fields. Since in partially ionized gases
  the ions "feel" the field more than the neutral atoms, the gas which
  emerges from such interacting fields may have a different ion/atom ratio
  than the ambient medium. By extending the ZEUS-3D code to apply to a
  partially ionized gas, we have quantified this effect. Our simulations
  show that enhancements in ion/atom ratios may be as large as a factor of
  almost 12. These results may be relevant to understanding EUV data from
  SKYLAB which suggest that the abundance of elements with low FIP in the
  solar corona are systematically enhanced in certain magnetic structures.

---------------------------------------------------------
Title: Wind Properties of Evolved Stars: Effects on Particle
    Acceleration
Authors: Mullan, D. J.
1997cwh..conf..197M    Altcode: 2006mslp.conf..197M
  No abstract at ADS

---------------------------------------------------------
Title: Acceleration of the solar wind: effects of plasmoids
Authors: Mullan, D. J.
1997AIPC..385..205M    Altcode: 1997recs.conf..205M
  Magnetic plasmoids in the solar corona and wind are subject to outward
  Lorentz forces in regions where the ambient magnetic field is decreasing
  outwards. We compute velocity profiles V(r) for a spherically symmetric
  solar wind containing plasmoids. In regions where the plasmoids occupy
  a progressively larger fraction of the solar wind, the wind accelerates
  rapidly, with radial gradients as much as 4-5 times steeper than the
  maximum gradient in an isothermal wind. Reconnection causes plasmoids
  eventually to lose their identity, and when the plasmoid fraction
  becomes small, the velocity profile becomes almost flat, with radial
  gradients shallower than in the isothermal wind by factors of about 2.

---------------------------------------------------------
Title: Discrete sources of the solar wind: observability with
    Solar Probe
Authors: Mullan, D. J.
1997AIPC..385..235M    Altcode: 1997recs.conf..235M
  There is observational evidence that X-ray bright points act as
  discrete sources of solar wind: theoretical ideas suggest that the
  discrete sources are in the form of magnetic plasmoids with dimensions
  of order 10 Mm. If the corona is heated by nanoflare events, the
  magnetic reconnection process which is at the heart of a nanoflare
  may also create magnetic plasmoids which supply mass to the solar
  wind in discrete events: plasmoids from nanoflares are expected to
  have dimensions of a few hundred km. Estimates of the properties of
  the plasmoids suggest that they will preserve their identity long
  enough to be detectable by plasma instruments on board a Solar Probe
  which penetrates in to 4R<SUB>solar</SUB>. Photons from individual
  nanoflares should also be identifiable at closest approach.

---------------------------------------------------------
Title: Coronal Heating in dMe and dM Stars: Clues from the X-Ray
    Surface Fluxes
Authors: Mullan, D. J.; Fleming, T. A.
1996ApJ...464..890M    Altcode:
  The mean X-ray surface fluxes F<SUB>x</SUB> from a nearly
  complete sample of M dwarfs within 6-7 pc of the Sun fall into two
  groups: most dMe stars have F<SUB>x</SUB> above a critical value
  F<SUB>c</SUB>, while most dM stars have F<SUB>x</SUB> below the
  same F<SUB>c</SUB>. The formal value of F<SUB>c</SUB>, where the
  distribution functions of dMe and dM stars are maximally different,
  is ≍ 10<SUP>5.3</SUP>-10<SUP>5.4</SUP> ergs cm<SUP>-2</SUP>
  s<SUP>-1</SUP>. The value of F<SUB>c</SUB> is close to an upper limit
  computed by Mullan &amp; Cheng for a model of acoustically heated
  coronae in an M dwarf (F<SUB>ac</SUB> ≍ 10<SUP>5.1</SUP> cgs). These
  results provide quantitative support for the hypothesis that the
  coronal heating process in dMe stars cannot be predominantly acoustic in
  nature. <P />A Monte Carlo analysis of the X-ray data suggests that X-
  active regions on dMe stars occupy at least 45%-50% of the surface,
  while, on dM stars the X- active regions occupy no more than 10% of
  the surface. This analysis leads to the conclusion that quiet coronal
  regions in both dM and dMe stars may be heated acoustically.

---------------------------------------------------------
Title: Structure of the heliospheric MHD bow shock: Effects of
    ion-atom drifts
Authors: Mullan, D. J.; Arge, C. N.
1996JGR...101.2535M    Altcode:
  We report on the structure of a perpendicular MHD shock in the
  partially ionized gas of the local interstellar medium (LISM). In
  situations where the flow speed is sub-Alfvenic in the ion gas and
  supersonic in the atom gas, the ions and atoms behave differently
  in the shock. Ion-atom drifts provide a dissipation mechanism which
  permits computation of the steady state structure of the transition
  between upstream and downstream conditions. Using parameter ranges
  which are appropriate for the LISM, we find that the heliospheric bow
  shock may be many hundreds of AU thick.

---------------------------------------------------------
Title: Correlating Coronal Temperature and Gravitational Potential:
    A Test of the Nonthermal Boundary Hypothesis
Authors: Williams, L. L.; Mullan, D. J.
1996ApJ...457L..95W    Altcode:
  It has been suggested that a nonthermal boundary condition can
  account for the existence of a coronal temperature inversion in
  stars. The nonthermal hypothesis makes falsifiable predictions of
  the maximum coronal temperature obtainable. This maximum temperature
  corresponds to the depth of the potential well at the boundary,
  which is effectively R*, and so varies as M*/R*. Here, we compare
  this prediction with one-temperature fits to single stars in Einstein
  data. We find that the coronal temperatures in dwarfs are consistent
  with a nonthermal boundary condition, but the nonthermal hypothesis
  cannot readily account for the coronal temperatures of class III
  giants. However, interpreting the emission from the non-compliant
  giants in alternate terms suggests that a dwarf companion may be
  the source of the X-rays. More generally, gravitational potential is
  found to be a useful quantity to ordering coronal observations: (1)
  the "dividing line" near K4, beyond which giant star coronae are not
  observed, corresponds to a rather precipitous factor of 10 drop in the
  strength of the stellar gravitational potential; and (2) M dwarfs and
  A stars of class III--V, whose coronae have been somewhat of a puzzle,
  all have relatively deep gravitational potentials.

---------------------------------------------------------
Title: Remote Sensing of the Solar Wind Using Radio Waves: Part 2
Authors: Yakovlev, O. I.; Mullan, D. J.
1996IrAJ...23....7Y    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Test of an Acoustic Mechanism for Atmospheric Heating in
    Dynamo-Deficient F Stars
Authors: Mullan, D. J.
1996nasa.reptU....M    Altcode:
  In a qualitative sense, the heating of chromospheres and coronae has
  long been ascribed to either acoustic or magnetic heating. However,
  quantitative discussions of the energy balance with detailed comparison
  to the fluxes of chromospheric emission lines have begun to appear only
  recently. The aim of this work is to observe F stars where magnetic
  effects might be expected to be rather small, thereby allowing us
  hopefully to access acoustically heated atmospheres.

---------------------------------------------------------
Title: Acoustic and Magnetic Heating of Chromospheres/Coronae:
    Are There Distinct Signatures?
Authors: Mullan, D. J.
1996nasa.reptT....M    Altcode:
  In a qualitative sense, the heating of chromospheres and coronae has
  long been ascribed to either acoustic or magnetic heating. However,
  quantitative discussions of the energy balance with detailed comparison
  to the fluxes of chromospheric emission lines have begun to appear
  only recently. The aim of this work is to obtain more quantitative
  information on the acoustic/magnetic mechanisms by comparing data
  with models of acoustically heated atmospheres. Mechanical energy
  in acoustic form is inevitably present in all stars with convective
  envelopes. Once the acoustic waves are generated, their propagation
  and dissipation in the chromosphere and corona can be computed by ab
  initio models, again using the well defined equations of compressible
  hydrodynamics (e.g. Mullan and Cheng: Papers I-III). In contrast to the
  ubiquitous acoustic modes, magnetic modes need not be present. And even
  in stars where magnetic heating is at work, the atmospheric heating
  always includes an acoustic component as well. In order to evaluate
  the magnetic contribution in such stars, we need to separate out the
  acoustic contribution. To address the "acoustic-magnetic" mixture, and
  separate the components, our strategy in this work has been to select
  stars in those parts of the HR diagram where the magnetic contribution
  is "turning on". By studying such stars, we hope to quantify the
  acoustic component which pervades the atmospheres of all cool stars,
  and characterize how the magnetic components alter the emission measure
  distribution in the atmosphere. Two groups of stars are suitable for
  our purposes: they are the groups which have recently been the subject
  of detailed quantitative modelling as regards acoustic propagation,
  i.e. the coolest dwarfs and the warm stars.

---------------------------------------------------------
Title: Mass loss from active dwarf stars
Authors: Mullan, D. J.
1996ASPC..109..461M    Altcode: 1996csss....9..461M
  No abstract at ADS

---------------------------------------------------------
Title: Remote Sensing of the Solar Wind Using Radio Waves: Part 1
Authors: Mullan, D. J.; Yakovlev, O. I.
1995IrAJ...22..119M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Destabilization of Compressible Convection by Radiation:
    Quantitative Evaluation
Authors: Cheng, Q. Q.; Hossain, Murshed; Mullan, D. J.
1995ApJ...447..789C    Altcode:
  We simulate time-dependent compressible hydrodynamic convection
  including the effects of radiative transfer (RT). The gray RT
  equation is solved along bundles of parallel rays using an integral
  method. Applying a perturbation to an initial polytrope, we follow the
  flows for many sound-crossing times. In the linear regime, we report
  on a case where, in the presence of radiation, the critical Rayleigh
  number Ra<SUB>c</SUB>(rad) for onset of convection is at least 20%-30%
  smaller than the value of Ra<SUB>c</SUB> in the absence of radiation. In
  the nonlinear regime, we report on another case where the entropy
  gradients and maximum flow speeds in the presence of radiation are
  larger by factors of at least 40%-60% than the corresponding quantities
  in the nonradiative case.

---------------------------------------------------------
Title: Coronal Heating in Flare Stars: Resonant MHD Absorption?
Authors: Mullan, D. J.; Johnson, M.
1995ApJ...444..350M    Altcode:
  We report on the occurrence of periodicity in X-rays from certain
  flare stars. Statistically significant periods in the range 70-200
  s are present in Einstein data for EQ Vir, Proxima Cen, and AD
  Leo. Periodicities are also present (although with lower statistical
  significance) in ROSAT data for AD Leo, and in EXOSAT data for EQ Vir
  and AD Leo. In UV Cet, we also find periodicity in Einstein data, but
  with lower statistical significance than for the above three stars:
  however, the UV Cet X-ray period is close to a period discovered by
  Gary et al. (1982) in microwaves in the close companion L726-8A. We
  argue that the properties of magnetic loops in flare stars are such
  that the variations in a single magnetic loop may be detectable in
  integrated flux. The period which we find in the X-ray flux from
  Proxima Cen is consistent with a global Alfven wave resonance in a
  large loop whose properties were derived some years ago by Haisch
  (1983) using an entirely different line of reasoning from what we use
  here. The periods, amplitudes, and durations of the variations which
  we have found in X-ray emission are consistent with the hypothesis
  that resonant absorption of MHD waves is occurring at certain times
  in coronal loops in the above four stars.

---------------------------------------------------------
Title: Magnetic Moments and Angular Momenta of Stars and Planets
Authors: Arge, C. N.; Mullan, D. J.; Dolginov, A. Z.
1995ApJ...443..795A    Altcode:
  Using published data on magnetic fields, radii, masses, and rotation,
  we have compiled a data set of magnetic moments mu and angular momenta
  L for stars and planets. In our subsample of hotter stars (classes A,
  B, and O), there are 171 objects. In the subsample of cooler stars
  (classes F, G, K, and M), there are 54 objects. We include 33 white
  dwarfs, of which 19 are in cataclysmic variables. The pulsar subsample
  contains 32 pulsars in binaries and 429 isolated pulsars. Som subsamples
  exhibit significant empirical correlations between log mu and log
  L. For the hot and cool stars, the correlations are positive. However,
  the hot-star correlation is significantly shallower than for the cool
  stars. In the solar system subsample, the correlation has essentially
  the same slope as for the cool stars, although the magnetic moments are
  two to three orders of magnitude smaller for the solar system objects
  at a given L value. For isolated white dwarfs, the correlations are
  weak or absent. Pulsars and white dwarfs in close binaries show strong
  negative correlations: the results are quantitatively consistent with
  magnetically enforced synchronism with the orbital period. When we
  consider the centers of gravity of the different subsamples of objects,
  a significant positive correlation appears between log mu and log L.

---------------------------------------------------------
Title: Intrinsic Time-dependence in Astrophysical Convection
Authors: Hossain, M.; Mullan, D. J.
1995SPD....26..104H    Altcode: 1995BAAS...27..950H
  No abstract at ADS

---------------------------------------------------------
Title: Acoustic heating in Procyon: comparison of theory with
    EUVE data
Authors: Mullan, D. J.; Cheng, Q. Q.
1995IAUS..176P.208M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: A dividing line between dM and dMe stars: X-ray surface fluxes
Authors: Mullan, D. J.; Fleming, T. A.; Schmitt, J. H. M. M.
1995IAUS..176P.210M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Coronal loops in flare stars: heating by resonant MHD
    absorption
Authors: Mullan, D. J.; Johnson, M.
1995IAUS..176P.206M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Acoustic Heating of the Chromosphere and Cool Corona in the
    F Star alpha Canis Minoris (Procyon)
Authors: Mullan, D. J.; Cheng, Q. Q.
1994ApJ...435..435M    Altcode:
  We report on a hydrodynamical model of acoustic wave energy deposition
  in the atmosphere of the F star Procyon. The model treats radiative
  losses in the photosphere by solving the continuum radiative transfer
  (RT) problem; it treats radiative losses in the chromosphere by solving
  the RT equation in two representative strong lines (Mg II k and Lyman
  alpha); and it includes optically thin emission from the corona. We
  find a temperature minimum of 4440 K and a transition region at a
  height of 3500-4000 km above the photosphere. Our acoustic model
  accounts for the reported fluxes of Mg II and Lyman alpha emission
  lines, as well as for the X-ray flux from the cool (T less than 1 MK)
  coronal component reported by Lemen et al. (1989). The differential
  emission measure distribution in our model agrees quite well with
  empirical results of Jordan et al. (1986).

---------------------------------------------------------
Title: Accurate Frequencies of Polytropic Models
Authors: Christensen-Dalsgaard, J.; Mullan, D. J.
1994MNRAS.270..921C    Altcode:
  Observations of solar oscillations are already yielding frequencies
  with a relative accuracy exceeding 10 new experiments will increase
  this accuracy by about an order of magnitude during the coming
  decade. Full utilization of such data requires comparable accuracy in
  the computation of frequencies of stellar models. A very convenient
  test of the calculation of adiabatic oscillation frequencies is
  provided by the polytropic models: the models are completely well
  defined and can easily be computed with the required precision;
  hence their frequencies can serve as references against which to
  test oscillation codes before these are applied to more realistic
  models. Here we analyse the computation of such frequencies. Their
  accuracy is tested in different ways, including the comparison of two
  independently derived sets of results, and tables of frequencies are
  given. More extensive sets of frequencies can be obtained directly
  from the authors, in computer-readable form. The analysis of the
  polytropic models provides interesting illustrations of a problem
  in the labelling of dipolar modes, as well as of the effects on the
  frequencies of the perturbation in the gravitational potential. Key
  words: Sun: oscillations - stars: interiors - stars: oscillations.

---------------------------------------------------------
Title: Gravitational Damping of Alfven Waves in Stellar Atmospheres
    and Winds
Authors: Khabibrakhmanov, I. K.; Mullan, D. J.
1994ApJ...430..814K    Altcode:
  We consider how gravity affects the propagation of Alfven waves in a
  stellar atmosphere. We show that when the ion gyrofrequency exceeds
  the collision rate, the waves are absorbed at a rate proportional to
  the gravitational acceleration g. Estimates show that this mechanism
  can readily account for the observed energy losses in the solar
  chromosphere. The mechanism predicts that the pressure at the top of
  the chromosphere P<SUB>Tc</SUB> should scale with g as P<SUB>Tc</SUB>
  proportional to g<SUP>delta</SUP>, where delta approximately equals 2/3;
  this is close to empirical results which suggest delta approximately
  equals 0.6. Gravitational damping leads to deposition of energy at a
  rate proportional to the mass of the particles. Hence, heavier ion
  are heated more effectively than protons. This is consistent with
  the observed proportionality between ion temperature and mass in the
  solar wind. Gravitational damping causes the local g to be effectively
  decreased by an amount proportional to the wave energy. This feature
  affects the acceleration of the solar wind. Gravitational damping
  may also lead to self-regulation of the damping of Alfven waves in
  stellar winds: this is relevant in the context of slow massive winds
  in cool giants.

---------------------------------------------------------
Title: Acoustically Heated Chromospheres in M Dwarfs
Authors: Mullan, D. J.; Cheng, Q. Q.
1994ASSL..187..587M    Altcode: 1994fsgb.book..587M
  No abstract at ADS

---------------------------------------------------------
Title: Test of an Acoustic Mechanism for Atmospheric Heating in
    Dynamo-deficient F Stars
Authors: Mullan, Dermott
1994euve.prop...29M    Altcode:
  Stars in the spectral range from late A to mid F have convection zones
  which are thought to be too shallow to allow for efficient dynamo
  operation. As a result, such stars almost certainly do not rely
  on magnetic processes to heat their chromospheres and coronae. And
  yet there is evidence that chromospheres and coronae are present in
  these stars. This suggests the presence of non-magnetic mechanical
  heating. The nature of this heating is not yet known. Recent work
  on an acoustic mechanism has led to the prediction that if acoustic
  heating is at work, the differential emission measure (DEM) should have
  a certain shape, with a well defined minimum at temperatures between
  10^5 and 10^6 K, and steep slopes on both sides of the minimum. The
  EUVE spectrometer is ideally suited to observe lines formed in the
  temperature range 10^{5-6} K. We propose an observing program to
  determine the DEM in 6 F stars. Comparisons with acoustic predictions
  will enable us to assess critically and quantitatively how viable the
  acoustic mechanism is in these stars.

---------------------------------------------------------
Title: Acoustic Waves in M Dwarfs: Maintaining a Corona
Authors: Mullan, D. J.; Cheng, Q. Q.
1994ApJ...420..392M    Altcode:
  We use a time-dependent hydrodynamics code to follow the propagation
  of acoustic waves into the corona of an M dwarf star. An important
  qualitative difference between M dwarfs and stars such as the Sun is
  that the acoustic spectrum in M dwarfs is expected to peak at periods
  close to the acoustic cutoff P<SUB>A</SUB>: this allows more effective
  penetration of waves into the corona. In our code, radiative losses in
  the photosphere, chromosphere, and corona are computed using Rosseland
  mean opacities, Mg II kappa and Ly alpha emission, and optically
  thin emissivities respectively. We find that acoustic heating can
  maintain a corona with a temperature of order 0.7-1 x 10<SUP>6</SUP>
  K and a surface X-ray flux as large as 10<SUP>5</SUP>ergs/sq cm/s. In
  a recent survey of X-rays from M dwarfs, some (20%-30%) of the stars
  lie at or below this limiting X-ray flux: we suggest that such stars
  may be candidates for acoustically maintained coronae.

---------------------------------------------------------
Title: Acoustic Heating of Coronae in Inactive M Dwarfs
Authors: Cheng, Q. Q.; Mullan, D. J.
1993AAS...183.1508C    Altcode: 1993BAAS...25.1314C
  We have used a time-dependent hydrodynamics code to follow the
  propagation of acoustic waves from the photosphere of an M dwarf star
  upwards into the chromosphere and corona. An important qualitative
  difference between M dwarfs and stars such as the Sun is that the
  acoustic spectrum in M dwarfs is believed to peak at periods close
  to the acoustic cut-off P_A: as a result of this, the waves can more
  effectively penetrate into the corona, rather than being essentially
  entirely dissipated in the chromosphere. In our code, radiative
  losses in the photosphere, chromosphere, and corona are computed using
  Rosseland mean opacities, MgII k and Ly-alpha emission, and optically
  thin emissivities respectively. Our results indicate that acoustic
  heating can maintain a corona in an M dwarf with a temperature of order
  0.7-1 million K and a surface X-ray flux F_X up to (1-1.5) times 10(5)
  ergs cm(-2) sec(-1) . We find that it is not possible for acoustic
  waves to generate larger F_X values: when we attempt to raise the F_X
  values by supplying more input flux at the photosphere, the effect is
  to push the transition region to greater heights, thereby reducing the
  emission measure of the X-ray plasma. Preliminary results from a ROSAT
  study of a nearly complete sample of dK/dM stars out to several parsecs
  (J. Schmitt and T. Fleming, 1993, priv. comm.) indicate that most
  inactive dwarfs have log F_X no larger than 5.1-5.2, and temperature
  no hotter than about 1 million K. In view of the good correspondence
  between our calculations and these data, we suggest that such inactive
  stars may be candidates for acoustically maintained coronae. This work
  has been supported by NASA Grant NAGW-2456.

---------------------------------------------------------
Title: Penetrative Stellar Convection
Authors: Hossain, M.; Mullan, D. J.
1993AAS...18311103H    Altcode: 1993BAAS...25Q1457H
  We have reported recently on a comparative study of boundary conditions
  in simulations of compressible convection, and how these determine
  certain aspects of the solutions (M. Hossain and D. J. Mullan, ApJ
  416, 733 [1993]). In that work, the simulations were confined to a
  layer which was convectively unstable throughout its extent. Since
  the medium is compressible, the solutions contain not only convective
  modes but also acoustic components. The results indicated that the
  relative contribution of the acoustic components to the overall flows
  can vary significantly depending on which boundary conditions are
  applied. We are now extending the work to investigate how the addition
  of convectively stable layers below and/or above the unstable layer will
  affect the solutions. As far as the convective modes are concerned,
  it is already known that the presence of an overlying stable layer
  may increase or decrease the critical Rayleigh number depending on
  the degree of stability (V. Savolainen et al. Phys. Fluids A4, 626
  [1992]). Here, we use simulations to investigate how the acoustic
  components are affected. To avoid numerical difficulties, both the
  initial states and the transport coefficients are taken as analytic
  functions of depth. Preliminary results from such attempts will be
  reported. This work has been supported by NASA grant NAGW-2456.

---------------------------------------------------------
Title: Magnetic Moments and Angular Momenta in Stars and Planets
Authors: Arge, N.; Mullan, D. J.; Dolginov, A.
1993AAS...18311101A    Altcode: 1993BAAS...25.1456A
  Using published data on magnetic fields, radii, masses, and rotation,
  we have compiled a dataset of magnetic moment M and angular momentum
  J for stars and planets. The stellar sub-sample extends from spectral
  class O to class M, with members of all classes represented. Among the
  hotter stars (classes A, B, and O), the sample includes 134 objects. For
  the cooler stars (classes F, G, K, and M), there are 33 objects. Our
  sub-sample of white dwarfs includes 33 objects, some in cataclysmic
  variables. The neutron star sub-sample contains 17 pulsars in binaries
  and 86 isolated pulsars. The solar system sub-sample contains seven
  planets plus the Sun. We find statistically significant positive
  correlations between log M and log J in the hot sub-sample and in the
  cool sub-sample: however, the slopes of the correlations are quite
  different for hot and cool stars. In the solar system sub-sample,
  the correlation has essentially the same slope as for the cool stars,
  although the intercept is almost two orders of magnitude smaller
  for the solar-system objects. For the isolated pulsars, we find no
  statistically significant correlation, while pulsars in binaries show
  a significant anti-correlation. Anti-correlation also appears in the
  white dwarf sub-sample, but this result relies heavily on five systems
  where rotational information is ambiguous. This work has been supported
  by NASA Grant NAGW-2456.

---------------------------------------------------------
Title: Periodic X-ray Emission in Flare Stars: Resonant MHD
    Absorption?
Authors: Mullan, D. J.; Johnson, M.
1993AAS...183.1503M    Altcode: 1993BAAS...25.1313M
  Magnetic fields play a role in the heating of coronae in the Sun
  and cool dwarfs, but the physical processes at work are not yet
  clear. Several magnetic models have been proposed for coronal
  heating. In one class of models, resonant absorption of MHD waves
  in closed loops is believed to be at work. In a very general sense,
  resonance implies the existence of a preferred frequency. Thus,
  resonant absorption models would be subject to a decisive test if
  periodicities could be identified in the coronal emission. We have
  searched for periodicities in the EINSTEIN X-ray fluxes of 15 cool
  dwarfs. Statistically significant periodicities have been detected
  in several stars, including EQ Vir, AD Leo, and Prox Cen. The period
  detected in Prox Cen is consistent with MHD resonance in the loop
  for which parameters were derived by Haisch in his study of X-ray
  light curves in Einstein data. For AD Leo, ROSAT/HRI and EXOSAT data
  also suggest the presence of periodicity at the same period as in the
  EINSTEIN data. For EQ Vir, EXOSAT data suggest the presence of the same
  period as in the EINSTEIN data. However, the statistical significance of
  the ROSAT and EXOSAT periods is not as good as those for EINSTEIN. This
  work has been supported by NASA Grant NAGW-2456, by the NASA Space
  Grant College program, and by the NASA Astrophysical Data Program.

---------------------------------------------------------
Title: Simulation of Compressible Convection: A Comparative Study
    of Boundary Conditions
Authors: Hossain, Murshed; Mullan, D. J.
1993ApJ...416..733H    Altcode:
  Numerical simulation of compressible hydrodynamics in the context
  of astrophysical convection is necessarily restricted to a limited
  volume of an entire star: however, the physical parameters inside
  that volume are determined by what goes on throughout the star as a
  whole. The aim of boundary conditions (BCs) is to model the contact
  (both mechanical and thermal) between the computational domain and the
  rest of the star. Different investigators have used various combinations
  of BCs. Here we explore how the choice of BC affects certain aspects
  of the solutions of three-dimensional compressible convection. As
  regards mechanical BCs, we examine both closed and open domains. In
  the case of open domains, some of the BC sets we examine are based
  on recent suggestions by Poinsot &amp; Lele for applying the method
  of characteristics to dissipative flows. Our results indicate that
  the hydrodynamic solutions can be qualitatively different depending
  on the choice of BC. <P />As a specific example of the differences,
  we examine how the BCs affect the relative contributions of acoustic
  and incompressible components to the overall flow. In recently
  reported simulations of homogeneous decaying turbulence, Ghosh &amp;
  Mattheaus have found that the relative contribution of acoustic
  components depends sensitively on the choice of conditions in the
  initial state. Analogously, the ratio R<SUB>ai</SUB> of acoustic to
  incompressible power in convective simulations in statistically steady
  state might be expected to depend on the choice of certain conditions
  also: in convection, the controlling factors would be expected to
  be the boundary conditions. To investigate that possibility, it is
  necessary to treat the two modes of a stratified compressible medium
  (the gravity-driven and acoustic modes) on an equal footing: both
  modes are subject to instability (if radiative effects are at work)
  although the criteria for onset of instability are different for the two
  modes. (In the surface layers of the Sun, convective and acoustic modes
  seem to have comparable amplitudes, as if both modes may be experiencing
  instability.) We report results of an exploration of a small subset
  of BCs which indicate that the value of R<SUB>ai</SUB> does exhibit
  significant variation depending on BCs. In the astrophysical context,
  this conclusion has implications for the modeling of chromospheres in
  cool stars.

---------------------------------------------------------
Title: MG II and LY alpha Fluxes in M Dwarfs: Evaluation of an
    Acoustic Model
Authors: Mullan, D. J.; Cheng, Q. Q.
1993ApJ...412..312M    Altcode:
  Surface fluxes of Mg II and Ly-alpha from a sample of M dwarfs have been
  reported by Panagi and Mathioudakis (PM, 1992). In order to determine if
  acoustic effects can reproduce the fluxes in the least active ('basal')
  stars in the PM sample, we have constructed steady state models of
  plane-parallel atmospheres with T(eff) = 3000 and 4000 K including
  heating by shock dissipation. The models incorporate radiative losses in
  the chromosphere by solving the transfer equation for two strong lines
  (Mg II k and Ly-alpha). Predictions of standard weak shock theory
  are expected to overestimate the rate of energy deposition in the
  chromospheres of M dwarfs compared to the rate of deposition in F,
  G, or K dwarfs. In order to incorporate this effect in M dwarfs, we
  compute a series of atmospheric models in which, for a given T(eff),
  the standard weak shock dissipation rate is reduced by a series of
  factors F(r). Although the input acoustic flux F(mech) may in principle
  be determined uniquely by T(eff) and log g, the correct value to use
  in any particular case is not well known. We therefore use F(mech) and
  F(r) as parameters to construct a family of M dwarf models at various
  T(eff) and g. Comparing with the observed fluxes in the least active M
  dwarfs of the PM sample, we find that our models reproduce the observed
  fluxes of both Mg II and Ly-alpha best if F(mech) is close to the value
  predicted by Bohn (1984) and if F(r) is approximately equal to 10-20.

---------------------------------------------------------
Title: Simulation of Compressible Convection: A Comparative Study
    of Boundary Conditions
Authors: Hossain, M.; Mullan, D. J.
1993BAAS...25.1194H    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Mass Loss from Cool Dwarfs: Limits on Detectability
Authors: Doyle, J. G.; Mullan, D. J.
1993ASSL..183..401D    Altcode: 1993pssc.symp..401D
  No abstract at ADS

---------------------------------------------------------
Title: Shock heating in inactive M dwarf atmospheres
Authors: Mullan, D. J.; Cheng, Q. Q.
1992AAS...181.5105M    Altcode: 1992BAAS...24.1206M
  Surface fluxes of MgII and Ly-alpha have recently been reported for
  a sample of M dwarfs. We have developed a model to determine if the
  minimum (basal) fluxes in stars with effective temperatures 3000-4000
  K can be understood in terms of shock dissipation. Using a prescribed
  input of mechanical energy at the lower boundary, the hydrodynamic
  equations, including radiative and conductive losses, are evolved
  to a (nearly) stationary state. Radiative losses and/or gains in the
  photosphere are handled using opacities tabulated by Kurucz. In the
  chromosphere, radiative losses are treated by solving the transfer
  equation for the two strongest lines emitted by the chromosphere: MgII
  and Ly-alpha . We find that the models are successful in reproducing the
  lower envelope of the observed Ly-alpha versus MgII fluxes. In M dwarfs,
  the transmission of acoustic power upwards into the corona is expected
  to be more efficient than in the Sun: using plausible choices for the
  coronal transmission parameters, we have explored the possibility that
  the X-ray fluxes observed in the least active M dwarfs might also be
  due largely to acoustic heating.

---------------------------------------------------------
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: Three-dimensional Compressible Hydrodynamic Convection in
the Sun and Stars: Erratum
Authors: Hossain, Murshed; Mullan, D. J.
1992ApJ...397..353H    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Book Review: Mechanisms of chromospheric and coronal heating /
    Springer, 1991
Authors: Fontenla, J. M.; Mullan, D. J.; Fontenla, J. M.
1992SoPh..139..409F    Altcode: 1992SoPh..139..409U
  No abstract at ADS

---------------------------------------------------------
Title: Book Review: The sun and cool stars: activity, magnetism,
    dynamos / Springer-Verlag, 1991
Authors: Mullan, D. J.
1992SoPh..139..409M    Altcode: 1992SoPh..139..409T
  No abstract at ADS

---------------------------------------------------------
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: Transient Periodicities in X-Ray--active Red Dwarfs: First
    Results from Mount Cuba and Interpretation with an Oscillating
    Loop Model
Authors: Mullan, D. J.; Herr, R. B.; Bhattacharyya, S.
1992ApJ...391..265M    Altcode:
  Results from a program at the Mount Cuba Astronomical Observatory
  to optically monitor transient periodicities in flare stars are
  reported. The data are analyzed for periodicities by means of a modified
  autocorrelation approach. A randomization technique is used to assess
  the statistical significance of periods. In AD Leonis, variability
  with amplitude 0.4 percent and a period of 4.1 min was detected during
  one run on March 6, 1991: the probability that this periodicity is
  due to chance is 10 exp -5. Further observations obtained on AD Leo
  within 1-2 hr on the same night showed no significant variability
  (0.01). It is shown that optical periodicities of the sort detected
  may be interpreted as arising from oscillations in coronal loops.

---------------------------------------------------------
Title: Transient Optical Periodicities in Red Dwarfs: Loop
    Oscillations in the Corona
Authors: Mullan, D. J.; Herr, R. B.; Bhattacharyya, S.
1992ASPC...26..306M    Altcode: 1992csss....7..306M
  No abstract at ADS

---------------------------------------------------------
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: Transient optical periodicities in coronal red dwarfs.
Authors: Herr, Richard B.; Mullan, Dermott J.
1992MmSAI..63..747H    Altcode:
  Evidence is presented for the existence of transient low-amplitude
  (several tenths of a percent of total visible light) periods in the
  range of several minutes, in the optical monitoring of dwarf M stars
  with high X-ray luminosities using the 61-cm Cassegrain at Mt. Cuba
  Observatory in Delaware (USA). The stars observed include AD Leo,
  Gliese 549, and DT Vir.

---------------------------------------------------------
Title: Surface Inhomogeneities on Late-Type Stars
Authors: Byrne, Patrick B.; Mullan, Dermott J.
1992LNP...397.....B    Altcode: 1992QB843.C6S87....; 1992sils.conf.....B
  No abstract at ADS

---------------------------------------------------------
Title: Summary and Conclusions (Invited)
Authors: Mullan, D. J.
1992LNP...397..233M    Altcode: 1992sils.conf..233M
  No abstract at ADS

---------------------------------------------------------
Title: Three-dimensional Compressible Hydrodynamic Convection in
    the Sun and Stars
Authors: Hossain, Murshed; Mullan, D. J.
1991ApJ...380..631H    Altcode:
  A pseudospectral code is used to obtain numerical solutions of 3D
  compressible hydrodynamic convection in a stratified medium where
  the boundaries are open and where radiative losses are strongest
  at the top. Results are presented for a series of three simulations
  in progressively deeper boxes. The code does not make the anelastic
  approximation, but follows sound waves explicitly. Spatial organization
  is found in the form of vertical 'stacking' of smaller structures
  on top of larger ones, with each structure being roughly Hp to a
  vertical extent. Compressibility effects are apparent in the density:
  the snapshots indicate that, on a horizontal plane, the density at
  certain points may be of an order of 10 percent larger or smaller than
  elsewhere on that plane.

---------------------------------------------------------
Title: Transient Optical Periodicities of Red Dwarfs with High
    X-Ray Luminosities
Authors: Herr, R. B.; Mullan, D. J.
1991BAAS...23.1383H    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Survival of discrete structures in the solar wind
Authors: Mullan, D. J.
1991A&A...248..256M    Altcode:
  Survival time scales are estimated for structures ejected from the
  sun into the solar wind, which are subject to decay processes during
  their transit from the sun to the earth. With the assumption that
  the structures are magnetic, MHD estimates are made to determine the
  time scales for reconnection into the ambient magnetic field. It is
  found that for structures smaller than a few tens of Mm at the sun, the
  probability of surviving the transit to the earth is low. The transition
  in size between structures that survive the sun-earth transit and
  those that do not (20-30 Mm at the sun) corresponds to scales of (4-6)
  x 10 to the 11th cm at the earth orbit (assuming radial expansion).

---------------------------------------------------------
Title: Corona: Coordinated research on non-thermal processes in
    astrophysics
Authors: Mullan, Dermott J.
1991udnw.rept.....M    Altcode:
  Several problems in astrophysics are examined where departures from
  purely thermal behavior are expected to produce effects which are
  detectable by a variety of NASA satellites. The problems identified
  as worthy of study include coronal heating in stars, deposition
  of non-thermal particle energy in stars from external sources, and
  turbulence in atmospheres and winds of stars. The progress in solving
  these problems is summarized.

---------------------------------------------------------
Title: Inefficient Accretion by the DA2 White Dwarf in V471 Tauri
Authors: Mullan, D. J.; Shipman, H. L.; Sion, E. M.; MacDonald, J.
1991ApJ...374..707M    Altcode:
  The results are reported of an analysis of eight-high-resolution
  International Ultraviolet Explorer (IUE) short-wavelength primary
  spectra of V471 Tauri, an eclipsing-spectroscopic, precataclysmic
  binary in the Hyades. The coaddition in velocity space of regions
  surrounding principle high- and low-excitation ion species on a common
  velocity scale was used. Identifiable lines were found to fall into
  three categories: interstellar absorption in the line of sight to the
  Hyades cluster; broad features due to absorption by the stellar wind
  from the K2 dwarf; and narrow high-velocity circumbinary absorption
  independent of orbital phase. The white dwarf in V471 Tauri is estimated
  to have accreted some 40,000 times more material than the determined
  upper limits. It is proposed that the barrier presented by the white
  drawf's rotating magnetosphere reduces accretion from the K2V stellar
  wind to levels which are undetectable with the IUE satellite.

---------------------------------------------------------
Title: Three-Dimensional Hydrodynamic Stellar Convection
Authors: Hossain, M.; Mullan, D. J.
1991BAAS...23.1047H    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Convection in Stars and Heating of Coronae
Authors: Mullan, D. J.
1991IrAJ...20....1M    Altcode:
  The properties of convection in the sun and other cool stars are
  summarized. Recent studies of convection which have involved the use of
  supercomputers to model the flow of compressible gas in three dimensions
  are discussed. It is shown how the results of these computations may
  eventualy provide an understanding of how nonthermal processes heat
  coronal gas to temperatures of millions of degrees.

---------------------------------------------------------
Title: Coronal Heating by Nanoflares: Possible Evidence of Plasmoids
    in Radio Occultation Data
Authors: Mullan, D. J.
1991mcch.conf..637M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Inefficient Accretion by the DA2 White Dwarf in V471 Tauri
Authors: Mullan, D. J.; Shipman, H. L.; Sion, E. M.; MacDonald, J.
1991BAAS...23..828M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Globular Clusters - where have all the Light Stars Gone
Authors: Mullan, D. J.
1990IrAJ...19..177M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: On the “Fast Electron Hypothesis” for Stellar Flares
Authors: Mullan, D. J.
1990ApJ...361..215M    Altcode:
  It is pointed out that Gurzadyan's (1988) fast-electron hypothesis for
  stellar flares encounters certain difficulties. The origin of the fast
  electrons is obscure. Negative flares and predicted ratios of X-ray
  to optical fluxes are not necessarily a proof of the fast-electron
  hypothesis. When the electrons thermalize, they will yield X-ray
  fluxes which are orders of magnitude too large to be consistent with
  observations.

---------------------------------------------------------
Title: Sources of the solar wind - What are the smallest-scale
    structures?
Authors: Mullan, D. J.
1990A&A...232..520M    Altcode:
  Data obtained by a variety of observing techniques are summarized to
  show that the solar wind is structured over a wide range of scale sizes
  (from one to one millionth solar radius). The possible contribution
  of reconnection sites as sources of momentum for the solar wind
  is examined. It is pointed out that, as plasmoids ejected from the
  reconnection sites traverse the stratified corona, they may expand
  sufficiently to occupy all of the available volume. It is suggested
  that the solar wind, at its origin, is composed essentially of these
  plasmoids.

---------------------------------------------------------
Title: New Numerical Solutions of Three-dimensional Compressible
    Hydrodynamic Convection
Authors: Hossain, Murshed; Mullan, D. J.
1990ApJ...354L..33H    Altcode:
  Numerical solutions of three-dimensional compressible hydrodynamics
  (including sound waves) in a stratified medium with open boundaries
  are presented. Convergent/divergent points play a controlling role in
  the flows, which are dominated by a single frequency related to the
  mean sound crossing time. Superposed on these rapid compressive flows,
  slower eddy-like flows eventually create convective transport. The
  solutions contain small structures stacked on top of larger ones,
  with vertical scales equal to the local pressure scale heights,
  H<SUB>p.</SUB> Although convective transport starts later in the
  evolution, vertical scales of H<SUB>p</SUB> are apparently selected
  at much earlier times by nonlinear compressive effects.

---------------------------------------------------------
Title: A Model of 3-Dimensional Compressible Convection
Authors: Hossain, M.; Mullan, D. J.
1990BAAS...22..897H    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Astrophysics in Antarctica : Newark, Delaware, 1989
Authors: Mullan, Dermott J.; Pomerantz, Martin A.; Stanev, Todor
1990AIPC..198.....M    Altcode: 1989AIPC..198.....M; 1990asan.conf.....M
  The present conference discusses the use of Antarctic bases for
  very high energy gamma-ray astronomy and neutrino astronomy, design
  considerations for a TeV telescope at the South Pole, the microwave
  detection of ultrahigh-energy neutrinos in ice, cosmic background
  radiation anisotropy and Galactic emission observations from Antarctica,
  IR astronomy in Antarctica, and the atmospheric transparency over
  Antarctica of the spectrum from mid-IR to cm wavelengths. Also
  discussed are Antarctic detection of LF and MF high latitude terrestrial
  emissions, zero-pressure balloon behavior in Antarctica, long-duration
  ballooning at midlatitudes and Antarctica, solar and stellar
  observations at the South Pole, South Pole photometry of selected
  variable stars, and astrophysical experimentation in Antarctica.

---------------------------------------------------------
Title: A search for evidence of wind accreation by the DA2 white
    dwarf in V471 Tauri.
Authors: Sion, E. M.; Mullan, D. J.; Shipman, H. L.
1990apcb.conf..155S    Altcode: 1990cvlm.proc..155S
  The authors report the results of an analysis of eight high-resolution
  International Ultraviolet Explorer SWP (1200 Å - 2000 Å) spectra
  of the Hyades eclipsing-spectroscopic pre-cataclysmic binary V471
  Tauri. The technique utilized was the coaddition in velocity space of
  regions surrounding principal high-excitation and low-excitation ion
  species on a common velocity scale. Certain images were compensated
  for the orbital motion of the white dwarf during the exposure. The
  authors' line detections fell into three categories: (1) interstellar
  absorption in the line of sight to the Hyades cluster; (2) broad stellar
  wind features; and (3) narrow, high-velocity circumbinary absorption
  independent of orbital phase. In the absence of strong evidence for
  accreted photospheric metals and/or helium at the Einstein-redshifted
  velocity of the white dwarf surface layers, the authors favor, as a
  possible explanation, that the white dwarf does not accrete from the
  K2V stellar wind in detectable amounts due to the barrier presented
  by its rotating magnetosphere.

---------------------------------------------------------
Title: Discrete Sources of Solar Wind: What are the Smallest
    Structures?
Authors: Mullan, D. J.
1989BAAS...21.1187M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Far-Infrared Properties of Flare Stars and dM Stars
Authors: Mullan, D. J.; Stencel, R. E.; Backman, D. E.
1989ApJ...343..400M    Altcode:
  Results are reported from a search of the IRAS data base for flare
  stars and for a control sample of dM stars. At 12 microns, 70-80
  percent of both samples have been detected. The K-12 colors of flare
  stars are significantly different from those of dM stars: for a given
  K magnitude, a flare star is about 70 percent brighter at 12 microns
  than a dM star. At 100 microns, 27 percent of the flare stars which are
  sources at 12 microns have been detected, while none of the comparable
  dM stars has been detected. Implications for microflaring are discussed.

---------------------------------------------------------
Title: Discovery of a Cool Expanding Shell at -1200 Kilometers per
    Second around V471 Tauri
Authors: Sion, Edward M.; Bruhweiler, Fred C.; Mullan, Dermott;
   Carpenter, Ken
1989ApJ...341L..17S    Altcode:
  High-resolution IUE spectra of V471 Tauri reveal the presence of a
  very-high-velocity cool expanding gas in the line of sight to the
  binary system with an expansion velocity of -1200 km/s. The summed
  strength of the coadded absorption is 125 mA + or - 25 mA, with FWHM =
  30 km/s. It is suggested that the observed absorption may be related to
  the narrow coadded absorption at -590 km/s noted by Bruhweiler and Sion
  (1966). The large expansion velocity suggests a possible association
  with an ancient nova outburst.

---------------------------------------------------------
Title: Evidence for a Cool Wind from the K2 Dwarf in the Detached
    Binary V471 Tauri
Authors: Mullan, D. J.; Sion, E. M.; Bruhweiler, F. C.; Carpenter,
   K. G.
1989ApJ...339L..33M    Altcode:
  Evidence for mass loss from the K2 dwarf in V471 Tauri is found in the
  form of discrete absorption features in lines of various elements (Mg,
  Fe, Cr, Mn) and ionization stages (Mg I, Mg II, Fe I, Fe II). Resonant
  Mg II absorption indicates a mass loss rate of at least 10 to the
  -11th solar masses per year. The wind appears to be cool (no more than
  a few times 10,000 K).

---------------------------------------------------------
Title: Solar and Stellar Flares - Questions and Problems
Authors: Mullan, D. J.
1989SoPh..121..239M    Altcode: 1989IAUCo.104..239M
  Although progress has been made in understanding certain aspects of
  the physics of solar and stellar flares, there are a number of topics
  which, in the author's opinion, still pose a problem. We summarize
  these topics here.

---------------------------------------------------------
Title: Far-Infrared Properties of Flare Stars and dM Stars
Authors: Mullan, D. J.; Stencel, R. E.; Backman, D. E.
1989BAAS...21..795M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: G-Mode Pulsations in Polytropes: High-Precision Eigenvalues
    and the Approach to Asymptotic Behavior
Authors: Mullan, D. J.
1989ApJ...337.1017M    Altcode:
  In an extension of previous work on oscillations of polytropes, high
  precision eigenfrequencies for the g-modes are obtained. The range of
  periods covered here extends from a fraction of 1 hr to 100,000 s for
  a polytrope with solar mass and radius. The results are presented in
  a format which indicates quantitatively how the period separations
  between adjacent modes approaches the asymptotic behavior predicted
  by Tassoul (1980). As before, the oscillation code is based on the
  Cowling approximation (as assumed by Tassoul).

---------------------------------------------------------
Title: V471 Tauri
Authors: Sion, E. M.; Bruhweiler, F. C.; Carpenter, K.; Mullan, D. J.
1988IAUC.4667....2S    Altcode: 1988IAUC.4667....0S
  E. M. Sion, Villanova University; F. C. Bruhweiler, Catholic
  University of America; K. Carpenter, Goddard Space Flight Center,
  NASA; and D. J. Mullan, Bartol Research Institute, report: "IUE
  High-Resolution SWP and LWP spectra of the Hyades member V471 Tau
  (an eclipsing-spectroscopic, pre-cataclysmic, close binary having
  spectral types K2 V + DA2) reveal very-high-velocity, cool, expanding
  gas (Fe II, Si II, C II, Mg II, O I), along the line-of-sight to the
  binary system, with an expansion velocity of -1200 km/s. There is no
  variation of the co-added absorption feature with orbital phase and
  its equivalent width is 0.035 nm, with FWHM = 30 km/s. The absorption
  appears in seven lines of the Fe II uv1 multiplet (258.5-261.7 nm),
  co-added in velocity space for each of the 11 LWP images around the
  orbit, in co-added LWP velocity plots of Mg II, Mn II, and Cr II,
  as well as in SWP plots of C II (133.5 nm), Si II (126.0 nm), and O I
  (130.2 nm), co-added in velocity space. This feature very likely has an
  origin distinct from the persistent lower velocity (-500, -260 km/s)
  absorption components of the K2 V stellar wind discovered by Mullan
  et al. (1988, ESA SP-281, p. 378; Ap.J. Letters, submitted) and from
  the narrow co-added feature of C II, Si II, and O I, at -590 km/s
  discovered by Bruhweiler and Sion (1986, Ap.J. 202, L45). The large
  expansion velocity suggests the possibility of its association with an
  ancient nova outburst. Further observations in other wavelength regions,
  including deep CCD imaging and direct photography, are strongly urged."

---------------------------------------------------------
Title: Detection of a Cool Wind From the K Dwarf in V471 Tauri
Authors: Mullan, D. J.; Sion, E. M.; Bruhweiler, F.; Carpenter, K.
1988BAAS...20..997M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: V471 Tauri: The Oldest and Nearest Old Nova?
Authors: Sion, E. M.; Bruhweiler, F. C.; Carpenter, K.; Mullan, D. J.
1988BAAS...20S1021S    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Radial and Nonradial Pulsations of Polytropes: High-Precision
    Eigenvalues and the Approach of p-Modes to Asymptotic Behavior
Authors: Mullan, D. J.; Ulrich, R. K.
1988ApJ...331.1013M    Altcode:
  In order to extract eigenfrequencies of high-order p-modes with
  precisions of one part in 500,000, a careful numerical treatment
  is necessary for both the input stellar model and the oscillation
  code. Here, polytropes are used to avoid uncertainties associated
  with the input model. Eigenfrequencies were obtained in a number of
  polytropes for l-values of 0-3 and radial orders up to about 40. It
  was that, in order to have the frequencies converge with the necessary
  precision, the input model must contain several thousand shells,
  and the oscillation code must contain at least several dozen grid
  points in each loop of the eigenfunction. The outermost loop requires
  many more points: the converged models contain several hundred grid
  points between the last node and the surface. An important check on
  the results is provided by a comparison of the asymptotic behavior
  of adjacent mode separations with the limiting behavior predicted by
  Tassoul (1980). The present oscillation code is based on the Cowling
  (1941) approximation (as assumed by Tassoul).

---------------------------------------------------------
Title: Mass loss from the K dwarf in V471 Tauri
Authors: Mullan, D. J.; Bruhweiler, F.; Sion, E. M.
1988ESASP.281a.423M    Altcode: 1988uvai....1..423M; 1988IUE88...1..423M
  Spectra of Mg II h and k were obtained for V471 Tau at phases zero (K
  dwarf in front) and 0.5 (white dwarf in front). At phase zero, strong
  blueshifted absorption is present, suggestive of a wind from the K dwarf
  with terminal velocity 600 to 400 km/sec and mass loss rate at least 3
  orders of magnitude greater than solar. Discrete blue-shifted absorption
  features occur at velocities of 200 and 500 km/sec. At phase 0.5,
  the blueshifted absorption is much weaker, although still detectable.

---------------------------------------------------------
Title: Discovery of a Stellar Wind in V471 Tauri: Accretion, Magnetic
    Braking and Pre-CV Evolution
Authors: Sion, E. M.; Mullan, D. J.; Bruhweiler, F. C.
1988BAAS...20..706S    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Chromospheric velocities at the location of helium 10830 Å
    dark points.
Authors: Holt, Rush D.; Mullan, Dermott J.
1988sscd.conf...80H    Altcode:
  The authors has observed apparent outflows of several km/sec from
  the solar chromosphere at the location of He dark points in coronal
  holes. The flows do not appear at dark points outside coronal holes. In
  addition to a summary of results from the observing program over several
  years, the authors report here on observations from an individual day.

---------------------------------------------------------
Title: Magnetohydrodynamic Modeling of Coronal Bright Points
Authors: Waldron, W. L.; Mullan, D. J.
1987ApJ...319..971W    Altcode:
  Coronal bright points are known to be magnetic in nature. The authors
  have developed a two-dimensional MHD code to investigate the response
  of a stratified atmosphere to a localized magnetic structure. If a
  bright point occurs at a region where flux tubes of opposite polarity
  have encountered by chance, in the presence of stratification, a net
  upward mass flux results. Upflow velocities of up to one half of the
  Alfvén speed are produced. The implications of these results for mass
  outflows from bright points in coronal holes are discussed.

---------------------------------------------------------
Title: Velocity Fields in a Low-Latitude Coronal Hole: Results from
    the Solar Maximum Mission
Authors: Mullan, D. J.; Waldron, W. L.
1987ApJ...317..487M    Altcode:
  The Solar Maximum Mission (SMM) satellite has been used to observe
  Doppler signatures in C IV in a low-latitude coronal hole as it
  crossed the central meridian (1985 February 2-8). Scatter plots of
  C IV emission intensity versus velocity do not show the pronounced
  positive correlation which has been reported in other regions on the
  sun. These data suggest that the coronal hole may control the gross
  velocity field in the solar atmosphere at the level where C IV is
  formed. Some localized regions of upflow coincide with EUV bright
  points in the coronal hole.

---------------------------------------------------------
Title: X-Rays from Globular Clusters
Authors: Mullan, D. J.
1987IrAJ...18...54M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: How to Recognize a Black-Hole
Authors: Mullan, D. J.
1987IrAJ...18...52M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Different Types of Solar Flares
Authors: Mullan, D. J.
1987IrAJ...18....1M    Altcode:
  The characteristics of three forms of energy that emerge in solar
  flares, hot plasma, fast particles, and bulk motion of the surrounding
  gas, are described. Consideration is given to thermal X-rays from
  flares, temperature variations during a flare, the origin of hard X-rays
  from flares, and gamma rays from flares. The magnetic constraints and
  turbulence related to bulk motion in flares are examined. Flares with
  energetic ions in space and flares rich in He-3 are analyzed. The
  distinction between fast electrons created by a flare at the flare
  site and in interplanetary space is investigated. Electron rich flares,
  solar cosmic rays, and the positive charge on solar cosmic ray ions are
  studied. The relation between ion cyclotron waves and the acceleration
  of certain particles and the release of magnetic energy in the sun
  are discussed.

---------------------------------------------------------
Title: Coronal Bright Points: Ca II K Line Shifts and MHD Modelling
Authors: Mullan, D. J.; Holt, R. D.; Waldron, W. L.
1986BAAS...18R1042M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Ernst Julius Öpik, 23 October 1893 - 10 September 1985.
Authors: Wayman, P. A.; Mullan, D. J.
1986QJRAS..27..508W    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Ionic Charge States of Solar Energetic Particles: Effects of
    Flare X-Rays
Authors: Mullan, D. J.; Waldron, W. L.
1986ApJ...308L..21M    Altcode:
  Ionic charge states of solar energetic particles (SEP) from three
  flares have been reported by Luhn et al. (1984). Interpretations of the
  mean charges in terms of a source temperature Ts (assuming collisional
  ionization equilibrium) yield inconsistent results. For Mg, the required
  Ts (up to 8 x 10 to the 6th K) are larger than for N and Si by factors
  of up to 5. Here it is pointed out that flare X-rays photoionize the
  ambient corona, causing apparent ionization temperatures there to exceed
  the local electron temperature, Te. Using realistic flare X-ray fluxes,
  it is shown that the charge data for six elements (C, N, Ne, Mg, Si,
  and S) can be fitted if the source is at coronal temperatures (Te =
  1-2 x 10 to the 6th K), but the ionization equilibrium is radiation
  dominated. For oxygen, a slight inconsistency persists in the three
  flares.

---------------------------------------------------------
Title: Displaced narrow absorption components in the spectra of
mass-losing OB stars : indications of corotating interaction regions ?
Authors: Mullan, D. J.
1986A&A...165..157M    Altcode:
  The discovery of displaced narrow components (DNCs) in an increasingly
  large number of stars of various spectral types suggests that
  an explanation of these features may contribute significantly to
  understanding of winds from stars of all types. The reported properties
  of DNCs are summarized here with a view to evaluating one particular
  scenario for DNC formation which involves corotating interaction regions
  (CIRs) in the stellar wind. The relevant features of the CIR scenario
  are summarized, and the extent to which DNC properties support the
  CIR scenario is discussed.

---------------------------------------------------------
Title: Is There a Difference Between Coronal Heating and Flaring in
    the Sun
Authors: Mullan, D. J.
1986IrAJ...17..518M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Ultraviolet observations of astronomical phenomena
Authors: Mullan, D. J.
1986udnw.reptS....M    Altcode:
  The purpose was to study various aspects of mass loss in stars of
  different types. The observational part of the research was directed at
  three Cepheid variables; the archival part of the research was directed
  at hot stars (for information on corotating interaction regions) and
  at cool giants (for study of variability in the mass losing part of
  the atmosphere).

---------------------------------------------------------
Title: E.J. Opik - an Astronomer's Astronomer
Authors: Mullan, D. J.
1986IrAJ...17..425M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Winds in Hot Stars - X-Ray Driven Flip-Flops
Authors: Mullan, D. J.
1986IrAJ...17..521M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: A search for outflows from X-ray bright points in coronal holes
Authors: Mullan, D. J.; Waldron, W. L.
1986udnw.reptR....M    Altcode:
  Properties of X-ray bright points using two of the instruments on Solar
  Maximum Mission were investigated. The mass outflows from magnetic
  regions were modeled using a two dimensional MHD code. It was concluded
  that mass can be detected from X-ray bright points provided that the
  magnetic topology is favorable.

---------------------------------------------------------
Title: Shifts of the Ca II K line in He I 10830 dark points.
Authors: Holt, Rush D.; Mullan, D. J.
1986SoPh..107...63H    Altcode: 1987SoPh..107...63H
  We investigate the velocity field of the solar chromosphere at the
  location of 65 He I 10830 dark points (DP's). We have obtained spectra
  of such points in the vicinity of the Ca II K line. As a measure of
  differential chromospheric velocity, we use the shift of the K line
  center relative to a nearby photospheric Fe I line. We find that in
  He I DP's, the distribution of K line shifts is skewed towards the
  blue: the blueward skewing is more pronounced in He I DP's located
  in coronal holes. To the extent that He I DP's are proxies of coronal
  bright points, our study is relevant to previous reports of outflows
  from such bright points.

---------------------------------------------------------
Title: Ionic charge distributions of energetic particles from
    solar flares
Authors: Mullan, D. J.; Waldron, W. L.
1986udnw.reptQ....M    Altcode:
  The effects which solar flare X-rays have on the charge states of solar
  cosmic rays is determined quantitatively. Rather than to characterize
  the charge distribution by temperature alone, it is proposed that the
  X-ray flux at the acceleration site also is used. The effects of flare
  X-rays are modeled mathematically.

---------------------------------------------------------
Title: Circumstellar Matter around Cool Stars
Authors: Mullan, D. J.
1986IrAJ...17..364M    Altcode:
  The circumstellar environment encompasses gas and dust, and in
  addition magnetic fields that are difficult to adduce observational
  evidence for. The existence of velocity fields is closely related
  to the phenomenon of mass loss, which is perhaps the most important
  data to be obtained from an evolutionary standpoint in the course of
  circumstellar environment studies. Magnetic fields, however, remain
  the circumstellar component about which least is known. Attention is
  presently given to the location of circumstellar matter, the reason for
  that position, and the mechanism of such matter's generation by a star.

---------------------------------------------------------
Title: Models of Transition Regions in Hybrid Stars
Authors: Brosius, J. W.; Mullan, D. J.
1986ApJ...301..650B    Altcode:
  Models for the transition regions of six hybrid stars, four bright
  giants and two supergiants, are calculated. The models include mass
  loss and prescribe Alfven waves as the source of mechanical energy. The
  momentum and energy deposition rates required at each level of the
  atmosphere are evaluated. The final models for all six stars have
  mass loss rates lying below the current VLA upper limits by factors
  of two to ten, and have densities which agree with those derived by
  density-sensitive line ratios. The density vs. temperature structure in
  Alpha TrA agree well with that derived by Hartmann et al. (1985). Wave
  amplitudes and magnetic field strengths are derived as functions of
  height, and the amplitudes are found to agree well with the observed
  line widths in Alpha TrA.

---------------------------------------------------------
Title: M dwarfs: Theoretical work
Authors: Mullan, Dermott J.
1986NASSP.492..455M    Altcode: 1986mts..book..455M
  Theoretical work on the atmospheres of M dwarfs has progressed along
  lines parallel to those followed in the study of other classes
  of stars. Such models have become increasingly sophisticated as
  improvements in opacities, in the equation of state, and in the
  treatment of convection were incorporated during the last 15 to 20
  years. As a result, spectrophotometric data on M dwarfs can now be
  fitted rather well by current models. The various attempts at modeling
  M dwarf photospheres in purely thermal terms are summarized. Some
  extensions of these models to include the effects of microturbulence
  and magnetic inhomogeneities are presented.

---------------------------------------------------------
Title: X-Ray Stars in Our Galaxy - Further Notes from the Einstein
    Satellite
Authors: Mullan, D. J.
1985IrAJ...17..153M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Radio outbursts in RS Canum Venaticorum stars : Coronal
    heating and electron runaway.
Authors: Mullan, D. J.
1985ApJ...295..628M    Altcode:
  Radio outbursts of RS CVn stars are sometimes thought of as analogs
  of flares in red dwarf stars. The author examines the possibility that
  the outbursts are not due to flares, but rather to a highly efficient
  case of coronal heating: mechanical energy reaching the corona from
  the convection zone of an RS CVn star gives rise to induced electric
  fields which may be so large that electron runaway becomes possible. It
  is proposed that gyrosynchrotron emission from fast electrons which
  are produced by the process are the source of radio outbursts from RS
  CVn stars.

---------------------------------------------------------
Title: Anomalous Abundances of Solar Energetic Particles and Coronal
Gas: Coulomb Effects and First Ionization Potential (fip) Ordering
Authors: Mullan, D. J.
1985ICRC....4..237M    Altcode: 1985ICRC...19d.237M
  The first ionization potential (FIP) ordering of elemental abundances in
  solar energetic particles and in the corona which can both be explained
  Coulomb effects is discussed. Solar energetic particles (SEP) and
  coronal gas have anomalous abundances relative to the photosphere. The
  anomalies are similar in both cases: which led to the conclusion that
  SEP acceleration is not selective, but merely preserves the source
  abundances. It is argued that SEP acceleration can be selective, because
  identical selectivity operates to determine the coronal abundances. The
  abundance anomalies are ordered by first ionization potential (FIP).

---------------------------------------------------------
Title: Formation of the H-alpha absorption line in the chromospheres
    of cool stars
Authors: Cram, L. E.; Mullan, D. J.
1985ApJ...294..626C    Altcode:
  The authors discuss the theory of the formation of the Hα absorption
  line in the chromospheres of cool stars and present a number of results
  which demonstrate that observations of this line can provide valuable
  information on certain properties of stellar chromospheres. It is
  shown that the widespread existence of strong Hα absorption in
  cool stars indicates the equally widespread existence of stellar
  chromospheres. The calculations also reinforce the idea that the great
  widths of Hα absorption lines in late-type giant stars are due to
  nonthermal chromospheric velocity fields.

---------------------------------------------------------
Title: Co-rotating Interaction Regions In Stellar Winds: Particle
    Acceleration and Non-Thermal Radio Emission in Hot Stars
Authors: Mullan, D. J.
1985ASSL..116...39M    Altcode: 1985rst..conf...39M
  A co-rotating interaction region (CIR) forms in a stellar wind when a
  fast stream from a rotating star overtakes a slow stream. CIR's have
  been studied in detail in the solar wind over the past decade primarily
  because they are efficient sources of particle acceleration. Here,
  the author points out the usefulness of CIR's in OB star winds to
  explain two properties of such winds: deposition of non-radiative
  energy in the wind far from the stellar surfaces and acceleration of
  non-thermal particles.

---------------------------------------------------------
Title: Non-Thermal Radio Emission from Flare Stars and RS CVn Systems
    (Invited Paper)
Authors: Mullan, D. J.
1985ASSL..116..173M    Altcode: 1985rst..conf..173M
  The observations of continuum radio emission from flares on red dwarf
  stars and from outbursts on RS CVn Systems are reviewed. In the RS
  CVn systems, the emission appears to be mainly incoherent, whereas
  in the flare stars, particularly at the lower frequencies, a coherent
  mechanism must be at work. In the RS CVn systems, it appears that during
  a radio outburst, a large fraction of the coronal electrons become
  highly energetic. This is interpreted in the context of deposition
  of mechanical energy in the corona, followed by a turbulent cascade,
  and it is found that the electric fields induced in the corona of an
  RS CVn star may be large enough to give rise to electron runaway in
  certain large magnetic loops.

---------------------------------------------------------
Title: Observations of the Ca II K spectral line in He 10830 Å
    dark points.
Authors: Holt, R.; Fortune, N.; Braun, D.; Mullan, D.
1985BAAS...17..760H    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Search for Chromospheric Velocity Signatures of HeI 10830Å
    Dark Points
Authors: Holt, R.; Park, A.; Archibald, J.; Mullan, D.
1985BAAS...17Q.593H    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Search for chromospheric velocity signatures of He I 10830
    Å darkpoints.
Authors: Holt, R.; Park, A.; Archibald, J.; Mullan, D.
1985BAAS...17..593H    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Observations of the Ca II K spectral line in He 10830 Å
    dark points.
Authors: Holt, R.; Fortune, N.; Braun, D.; Mullan, D.
1985BAAS...17..933H    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Rotational modulation of chromospheric emission in cool giants
    and "hybrid" stars.
Authors: Brosius, J. W.; Mullan, D. J.; Stencel, R. E.
1985ApJ...288..310B    Altcode:
  Archival data from the International Ultraviolet Explorer have been
  used to study temporal variations of the Mg II h and k emission lines
  in eight late-type giants. Evidence is presented that the variations
  are periodic in nature. It is argued that the periodicities can be
  interpreted in terms of rotation. It is found that the four fastest
  rotators in the sample are 'hybrid' stars.

---------------------------------------------------------
Title: Energy dissipation mechanisms in flare stars
Authors: Mullan, D. J.
1985IAUS..107..245M    Altcode:
  The author summarizes the relevant physical conditions in the atmosphere
  of a flare star. He finds that even outside flares, the dissipation
  of mechanical energy in the atmospheres of flare stars is in a certain
  sense qualitatively different from what is observed in the sun. Further,
  he discusses energy dissipation in flares and finds that, at least in
  the very coolest flare stars, the distinction between the flaring and
  the non-flaring states of the star becomes difficult to define.

---------------------------------------------------------
Title: Co-rotating interaction regions in stellar winds: particle
    acceleration and non-thermal radio emission in hot stars.
Authors: Mullan, D. J.
1985NASCP2358..130M    Altcode: 1985onhm.rept..130M
  A co-rotating interaction region (CIR) forms in a stellar wind when a
  fast stream from a rotating star overtakes a slow stream. The author
  points out the usefulness of CIR's in OB star winds to explain two
  properties of such winds: deposition of non-radiative energy in the wind
  far from the stellar surfaces and acceleration of non-thermal particles.

---------------------------------------------------------
Title: Radio Flare Stars under a "Microscope"
Authors: Mullan, D. J.
1985IrAJ...17...67M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: A Study of Mass Loss in a Long-Period Cepheid Variable
Authors: Mullan, Dermott J.
1985iue..prop.2183M    Altcode:
  We propose to study mass loss in a Cepheid. The target star is unique
  among Cepheids in that it lies at the center of 4-5 concentric rings
  of dust. The ring structure suggests that the Cepheid (RS Puppis) has
  experienced several mass loss events or shock ejection events in the
  recent past. The mechanism by which Cepheids lose mass is currently
  unknown, but since RS Pup shows signs of having experienced mass loss
  in the past, it is a prime candidate for searching for mass loss at the
  present time. With this in mind, we propose to obtain high resolution
  magnesium line profiles to search for circumstellar absorption at or
  beyond the escape speed. Although there is as yet no proof that it is
  the stellar pulsation which provides the mechanical energy to power mass
  loss (if any) from a Cepheid, it is natural to inquire if the mass loss
  varies during the pulsation cycle. Therefore, we propose to obtain MgII
  line profiles at specially chosen phases in the cycle (e.g. at maximum
  acceleration and deceleration, and at the "bump" on the light curve)
  as well as at light maximum. Because of the long exposures necessary,
  this is a collaborative effort with European proposers.

---------------------------------------------------------
Title: Co-rotating interaction regions in stellar winds.
Authors: Mullan, D. J.
1984NASCP2349..458M    Altcode: 1984fiue.rept..458M
  A co-rotating interaction region (CIR) forms in a stellar wind when a
  fast stream from a rotating star overtakes a slow stream. CIR's have
  been studied in detail in the solar wind over the past decade. Here, the
  author points out their usefulness in interpreting several spectroscopic
  features in stars of various types, including "hybrid" stars, OB stars,
  and cool supergiants.

---------------------------------------------------------
Title: Rotational modulation of chromospheric emission in cool giants
    and "hybrid" stars.
Authors: Brosius, J. W.; Mullan, D. J.; Stencel, R. E.
1984NASCP2349..476B    Altcode: 1984fiue.rept..476B; 1984IUE84......476B
  The authors have used IUE archival data to study temporal variations of
  the Mg II h and k emission lines in 8 late-type giants. They present
  evidence that the variations are periodic in nature. They argue that
  the periodicities can be interpreted in terms of rotation and find
  that the four fastest rotators in their sample are "hybrid" stars.

---------------------------------------------------------
Title: Asymmetries in stellar MG II H and K and CA II H and K line
    profiles - Discrepancies between MG and CA asymmetries
Authors: Mullan, D. J.
1984ApJ...284..769M    Altcode:
  "Discrepant asymmetry" stars are cool giants which show the opposite
  sense of asymmetry in the emission cores of Ca and Mg (i.e., red
  peak dominant in Mg, blue peak dominant in Ca). The author suggests
  that these discrepancies can be understood in terms of corotating
  interaction regions in the winds.

---------------------------------------------------------
Title: Corotating interaction regions in stellar winds
Authors: Mullan, D. J.
1984ApJ...283..303M    Altcode:
  In a stellar wind, a corotating interaction region (CIR) is formed when
  a rotating star emits wind in a non-spherically symmetric manner. CIRs
  have been studied in detail in the solar wind: here, their role in
  stellar winds is considered. The radial distance at which CIRs form
  (in terms of the stellar radius) is proportional to the ratio of wind
  speed to the rotational speed at the stellar surface: in the sun, this
  ratio is approximately 200, but it may be much smaller than that in
  other stars. The properties of CIRs appear to be able to account for
  certain features of 'hybrid stars' (i.e., cool giants with cool winds
  plus 'warm' lines in their UV spectra), for X-ray emitting structures
  in hot star winds, and for the appearance of extended chromospheres
  in cool supergiants.

---------------------------------------------------------
Title: On the possibility of resonant electrodynamic coupling in
    the coronaeof red dwarfs.
Authors: Mullan, D. J.
1984ApJ...282..603M    Altcode:
  The authors suggest that, in the context of Ionson's electrodynamic
  coupling theory of coronal heating, the coupling efficiency may pass
  through a resonance in lower main-sequence stars. It is proposed that
  this resonance contributes to the strong observed X-ray emission in
  early-M dwarfs. In the coolest M dwarfs, the efficiency is expected
  to decrease rapidly as conditions move away from resonance.

---------------------------------------------------------
Title: Alfven waves in the solar wind in association with solar
    energetic particles - Sunspot umbral origin?
Authors: Mullan, D. J.; Owens, A. J.
1984ApJ...280..346M    Altcode:
  The paper reports on a search for Alfven waves in the solar wind during
  solar particle events using ISEE 3 data. During the period June 6-8,
  1979, signatures of outgoing Alfven waves are found which could have
  been released from the sun simultaneously with the initial release
  of energetic particles. The waves have durations of 200-900 s. An
  isolated Alfven wave is also seen when the first particles (with E
  greater than or approximately equal to 57 MeV) are detected by ISEE 3;
  the width of this wave is about 950 s. A series of five small-amplitude
  'spikes' in the magnetic field are also seen, preceding the arrival
  of the first particles by a few hours. The spikes are separated by
  intervals of 854 + or - 20 s. It is suggested that these periodicities
  may be determined by the propagation characteristics of Alfven waves
  in the solar atmosphere. The features which have been detected appear
  to be consistent with Alfven waves released from the umbra of a sunspot
  during a flare.

---------------------------------------------------------
Title: A note on the magnetic field strengths on the surfaces of
    cool dwarfs
Authors: Mullan, D. J.
1984ApJ...279..746M    Altcode:
  Various techniques have been used to detect and measure magnetic fields
  in cool dwarf stars. In the case of one of the stars discussed by Linsky
  and Gary (1983), it is shown that if the emission is optically thick
  gyrosynchrotron, then the fields at the surface of the star are in the
  range from 10 to 20 kilogauss. These field strengths have been labeled
  'unrealistic' by Linsky and Gary. In the present investigation, it is
  shown that currently available observational data do not exclude the
  possibility that fields with field strengths in the range from 10 to 20
  kilogauss exist in dark spots on the surfaces of cool dwarf stars. Thus,
  contrary to the statement of Linsky and Gary, photospheric fields in
  the 10-20 kilogauss range need not be 'unrealistic'.

---------------------------------------------------------
Title: Co-rotating Interaction Regions in Stellar Winds
Authors: Mullan, D. J.
1984BAAS...16Q.522M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Rotational Modulation of Chromospheric Emission in Cool Giants
    and `Hybrid' Stars
Authors: Brosius, J. W.; Mullan, D. J.; Stencel, R. E.
1984BAAS...16..491B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Acceleration of particles in shocked magnetic neutral sheets
Authors: Mullan, D. J.; Perez-Peraza, J.; Galvez, M.; Alvarez, M.
1984AdSpR...4b.157M    Altcode: 1984AdSpR...4..157M
  We report on a study of particle acceleration in a magnetic neutral
  sheet which has been struck by a passing MHD shock, such as occurs in
  the sun when a flare occurs near a helmet streamer. Using trajectory
  calculations, we derive energy spectra. We propose that long-lived
  particle events with energies up to 10-100 MeV following solar flares
  may be explained by the mechanism described here.

---------------------------------------------------------
Title: Do Magnetic Fields Drive Mass Loss in Hot and Cool Stars?
Authors: Mullan, D. J.
1983IrAJ...16..107M    Altcode:
  It is pointed out that since the original discoveries of 'quiescent'
  mass loss in cool stars and in hot stars, the study of mechanisms
  for driving such mass loss has tended along different directions
  for hot and cool stars. The present investigation is concerned with
  a possible common feature in the winds of hot and cool stars, taking
  into account magnetic field effects. Difficulties with current models
  of mass loss are examined, giving attention to the sun, cool giants,
  and hot stars. The role of magnetic fields is studied, and it is shown
  that certain aspects of magnetic fields in the atmospheres of both
  hot and cool stars might aid the mass loss process. Unstable magnetic
  loops are considered along with the motion of plasmoid in ambient
  field, interactions between fast and slow streams in stellar winds,
  X-ray photon driven winds, and origins of magnetic loops in hot stars.

---------------------------------------------------------
Title: Momentum flux invariance in the solar wind
Authors: Mullan, D. J.
1983ApJ...272..325M    Altcode:
  On the basis of data from the ISEE C satellite, the results of Steinitz
  and Eyni (1980), Eyni and Steinitz (1981), and Steinitz (1981) are
  corroborated. In addition, the scope is extended to another phase of
  the solar cycle when solar wind conditions are quite different. The
  temperature of the wind is seen to be related to the velocity in a
  way that alters with time. This indicates that the rate of energy
  deposition, or its distribution between thermal and kinetic forms,
  fluctuates during the solar cycle. On the other hand, the coefficients
  in the density-velocity relation have apparently remained unchanged
  between solar minimum and solar maximum conditions, thereby keeping the
  momentum flux remarkably constant. Barring the possibility of chance
  coincidence, the momentum flux in the solar wind may be even more
  invariant than Steinitz and Eyni suspected. This strengthens their
  conclusion that the momentum-flux invariance derives from initial
  constraints determining the evolution of the solar wind.

---------------------------------------------------------
Title: Solar particle corotating events from shocked neutral sheets.
Authors: Mullan, D. J.; Perez-Peraza, J.; Galvez, M.; Alvarez, M.
1983ICRC...10..307M    Altcode: 1983ICRC...18j.307M
  The authors study the effect of a travelling shock wave on a magnetic
  neutral sheet. Specifically, they consider the interaction between a
  flare shock and a large coronal neutral sheet, such as that which is
  associated with a helmet-streamer.

---------------------------------------------------------
Title: Solar Particle Corrotating Events from Shocked Neutral Sheets
Authors: Mullan, D. J.; Perez-Peraza, J.; Galvez, M.; Alvarez-Madrigal,
   M.
1983ICRC....4...25M    Altcode: 1983ICRC...18d..25M
  No abstract at ADS

---------------------------------------------------------
Title: Release of solar cosmic rays from the corona - Rayleigh-Taylor
    instability and reconnection
Authors: Mullan, D. J.
1983ApJ...269..765M    Altcode:
  An analytical model for coronal propagation and the release of solar
  cosmic rays (SCR) is formulated and compared with data correlating type
  II bursts with SCR enhancements in interplanetary space. Consideration
  is given to the various time scales of acceleration of the particles
  and electrons at flare sites. The bottle model is discussed, which
  regards the SCR and flare ejecta as being formed on initially closed
  magnetic field lines. The possibilities that either the onset of a
  Rayleigh-Taylor instability (RT) or reconnection of open and closed
  magnetic field lines open the bottle are examined. It is found that
  solar P events involve flare conditions which can feature an RT that
  has sufficient stability for opening to occur. Energetic electrons
  may be emitted by the same process that opens the bottle.

---------------------------------------------------------
Title: Isotopic anomalies among solar energetic particles Contribution
    of preacceleration in collapsing magnetic neutral sheets
Authors: Mullan, D. J.
1983ApJ...268..385M    Altcode:
  Anomalous abundances of elements among solar flare particles
  have previously been interpreted in terms of a contribution from
  pre-acceleration in collapsing magnetic neutral sheets. Here, we examine
  the isotopic anomalies which are predicted by this pre-acceleration
  mechanism. We find enhancements of neutron-rich isotopes, but the
  enhancements are not a monotonic function of the mass ratio. Thus,
  enhancement of <SUP>22</SUP>Ne/<SUP>20</SUP>Ne need not be accompanied
  by any significant enhancements in, say, <SUP>18</SUP>O/<SUP>16</SUP>O
  or <SUP>26</SUP>Mg/<SUP>24</SUP>Mg. High temperatures (such as those
  in flares) favor enhancement of <SUP>22</SUP>Ne/<SUP>20</SUP>Ne as the
  dominant isotopic anomaly. These results may help to account for some
  of the observed isotopic anomalies among solar energetic particles.

---------------------------------------------------------
Title: Closed and open magnetic fields in stellar winds
Authors: Mullan, D. J.; Steinolfson, R. S.
1983ApJ...266..823M    Altcode:
  A numerical study of the interaction between a thermal wind and a
  global dipole field in the sun and in a giant star is reported. In
  order for closed field lines to persist near the equator (where a
  helmet-streamer-like configuration appears), the coronal temperature
  must be less than a critical value Tc, which scales as M/R. This
  condition is found to be equivalent to the following: for a static
  helmet streamer to persist, the sonic point above the helmet must not
  approach closer to the star than 2.2-2.6 stellar radii. Implications
  for rapid mass loss and X-ray emission from cool giants are pointed
  out. The results strengthen the case for identifying empirical dividing
  lines in the H-R diagram with a magnetic topology transition locus
  (MTTL). Support for the MTTL concept is also provided by considerations
  of the breakdown of magnetostatic equilibrium.

---------------------------------------------------------
Title: Alfven waves in the solar wind in association with solar
energetic particles: Sunspot umbral origin
Authors: Mullan, D. J.; Owens, A. J.
1983udnw.rept.....M    Altcode:
  We report on a search for Alfven waves in the solar wind during
  solar particle events. During the period June 6-8, 1979, we find
  clear signatures of outgoing Alfven waves which could have been
  released from the sun simultaneously with the initial release of
  energetic particles. The waves are soliton-like, with durations of
  200-900 seconds. An isolated square Alfven solution is also seen when
  the first particles (with E approximately 57 MeV) are detected: the
  width of this solution is approximately 950 seconds. A series of five
  small amplitude spikes in the magnetic field are also seen, preceding
  the arrival of the first particles by a few hours. The spikes are
  separated by intervals of 854 + or - 20 seconds. We suggest that these
  periodicities are determined by conditions at the sun. The features
  which we have detected are consistent with Alfven waves released from
  the umbra of a sunspot during a flare.

---------------------------------------------------------
Title: Closed and open magnetic fields in stellar atmospheres Effects
    on mass loss from cool giant stars
Authors: Mullan, D. J.
1983IAUS..102..487M    Altcode:
  The author proposes that the onset of rapid mass loss among cool giants,
  and the absence of hot coronal material from their atmospheres, is
  associated with a transition in the large-scale magnetic topology
  of the atmosphere from closed to open. According to this view, field
  loops in the atmospheres of giants of spectral class K and later cannot
  find equilibrium, but are in a state of dynamical evolution throughout
  their lifetime in the atmosphere.

---------------------------------------------------------
Title: Models of spots and flares
Authors: Mullan, D. J.
1983ASSL..102..527M    Altcode: 1983IAUCo..71..527M; 1983ards.proc..527M
  Reference is made to laboratory experiments carried out in recent
  years showing that there are many more ways to drive a plasma out of
  equilibrium than to preserve equilibrium. With this in mind, it may be
  easier to understand why flares should occur in a stellar atmosphere
  (where convective jostling of field lines creates potential for driving
  a large number of instabilities) than why a long-lived feature such as a
  dark spot should persist. Work done on the equilibrium structure of cool
  spots in the sun and stars is summarized. Since spots involve complex
  interaction between convective flows and magnetic fields, observations
  are used as an aid in identifying the dominant processes that should
  enter into the modeling. The summary begins with a discussion of certain
  relevant properties of spots in the solar atmosphere. Attention is
  then given to the concentration of magnetic fields, the stability of
  spots, spot cooling and missing flux, and the relationship between
  spots and flares.

---------------------------------------------------------
Title: Activity in Red Dwarf Stars
Authors: Mullan, D. J.
1982IrAJ...15..288M    Altcode:
  Recent observational and theoretical investigations of activity in red
  dwarfs are reviewed in a summary of papers given at the IAU Colloquium
  in Catania, Sicily, in August, 1982. Consideration is given to the
  physical properties of active dwarfs, such as effective temperature,
  opacity, stellar structure, convection and chromospheric heating,
  coronal heating, rotation, starspots, and magnetic fields. Observations
  discussed include optical, UV, and X-ray data on flares (F), spots,
  and precursors; activity cycles in stars; activity on stars other
  than red dwarfs; and applicable (mainly VLA) observations of the
  sun. Theoretical studies of such problems as the high-temperature
  extension of the 'nebular' model, coronal heating versus F, energy
  release and dissipation in F, electrodynamic coupling between
  photosphere and corona, the role of the photosphere in F, the
  fast-electron hypothesis of F light, the gas dynamics of a stellar
  atmosphere during F and starspots are summarized.

---------------------------------------------------------
Title: 'Hybrid' Stars and the Onset of Magnetically Driven Winds in
    Cool Giants
Authors: Mullan, D. J.
1982BAAS...14..894M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Onset of rapid mass loss in cool giant stars - Magnetic
    field effects
Authors: Mullan, D. J.
1982A&A...108..279M    Altcode:
  The possibility that closed magnetic field loops exist in steady state
  in stellar atmospheres in the HR diagram is examined. A model derived by
  Pneuman (1968) for helmet streamers in the solar corona is applied using
  a semi-empirical technique, to find that long-lived closed loops exist
  only below a certain boundary in the HR diagram. The region below this
  boundary is occupied by stars which are known to have hot coronae and
  slow mass loss. It is suggested that rapid mass loss sets in when closed
  field loops can no longer exist in steady state in the atmosphere.

---------------------------------------------------------
Title: Model chromospheres of RS CVn stars : Balmer line profiles
    in lam And.
Authors: Mullan, D. J.; Cram, L. E.
1982A&A...108..251M    Altcode:
  Two models have been constructed for the chromosphere of the RS CVn
  star Gamma And, one with a low-pressure transition zone, and one with
  a high pressure transition zone. The high pressure model predicts an
  H alpha line profile which agrees fairly well with high resolution
  observations of Gamma And, without the need to include nonthermal
  line broadening. The low pressure model predicts an H alpha profile
  which agrees very well with the observations, after application of
  macroturbulent broadening with a gaussian velocity parameter of about 30
  km/sec. Methods which could distinguish between the two alternatives
  are discussed, and it is suggested that if the low-pressure model
  is valid, the large macroturbulence may be associated with unstable
  magnetic flux loops in the atmosphere.

---------------------------------------------------------
Title: Magnesium emission variability among late-type giant stars.
Authors: Mullan, D. J.; Stencel, R. E.
1982ApJ...253..716M    Altcode:
  Profiles of the Mg II h and k emission features in the spectra of 21
  late-type giant stars were obtained. Emission strengths were separately
  measured in the shortward (S) and longward (L) components. Variations
  in total emission intensity (S + L) can be interpreted as evidence
  for variations in the rate of mechanical energy deposition in the
  chromosphere. Mass loss processes in the corona/outer atmosphere may
  be strong enough to affect the ratio of S/L: thus, rapid mass loss
  causes S/L to be less than unity. Rapid mass loss is likely caused by
  deposition of mechanical energy by stellar wind. Variations in S/L are
  a measure of variations in the rate of mechanical energy deposition
  in the corona/outer atmosphere. The stellar sample variations were
  divided into four classes: (1) variations in S/L; (2) variations in the
  circumstellar absorption components; (3) variations in the total flux;
  and (4) no evidence for variations found on the time scales used.

---------------------------------------------------------
Title: Theoretical studies of the RS Canum Venaticorum stars
Authors: Mullan, D. J.
1982udnw.rept.....M    Altcode:
  The activity in RS Canum Venaticorum (CVn) is investigated. Models
  for chromospheric structure are developed and the role of magnetic
  fields both in the photosphere as well as in the chromosphere and
  upper atmosphere are examined. T Tau stars are also studied from the
  same points of view. The properties of magnetic field loops are used
  to help understand the atmospheric structure in RS CVn stars. The
  concepts developed in the case of these stars appear to be applicable
  over a much broader region of the HR diagram. The absence of stable
  magnetic loops in the atmospheres of late type giant stars suggests
  that the atmospheres of RS CVn active components are qualitatively
  distinct from the solar atmosphere.

---------------------------------------------------------
Title: Isotopic anomalies in cosmic rays: effects of pre-acceleration
    in collapsing magnetic neutral sheets.
Authors: Mullan, D. J.
1982BAAS...14..577M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Coronal Holes - Mass Loss Driven by Magnetic Reconnection
Authors: Mullan, D. J.; Ahmad, I. A.
1982SoPh...75..347M    Altcode:
  We propose that bubbles of matter ejected from magnetic reconnection
  sites in polar plumes drive the solar wind in coronal holes.

---------------------------------------------------------
Title: Caution! High winds beyond this point.
Authors: Mullan, D. J.
1982Ast....10a..74M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: "Discrepant asymmetry" stars: the role of unsteady magnetic
    flux loops in the atmospheres of late-type giant stars.
Authors: Mullan, D. J.; Stencel, R. E.
1982NASCP2238..235M    Altcode: 1982auva.nasa..235M; 1982IUE82......235M; 1982NASCP2338..235M
  A number of spectroscopic peculiarities of K giants and other
  stars which lie in a wedge in the HR diagram are discussed. These
  peculiarities can be understood in terms of unsteady magnetic flux
  loops emerging into the stellar atmosphere from beneath the surface.

---------------------------------------------------------
Title: Preacceleration in collapsing magnetic neutral sheets and
    anomalous abundances of solar flare particles
Authors: Mullan, D. J.; Levine, R. H.
1981ApJS...47...87M    Altcode:
  Levine's (1974) concept of a collapsing magnetic neutral sheet
  which can accelerate ambient protons to several times the mean
  thermal speed, provided that the collapse time scale is shorter
  than the proton Coulomb loss time, is applied to heavier elements
  in an investigation of the composition of the particles which can
  be accelerated by such a sheet. Tables of ionization equilibrium are
  combined with the thermal structure of a constant pressure loop in order
  to calculate phi<SUB>x</SUB> (the fraction of an element x which is
  accelerated) of 18 heavy elements, from carbon to nickel which satisfy
  a maximum-ionization criterion. Normalizing phi<SUB>x</SUB> to oxygen,
  it is found that relative to the composition of the ambient materials,
  C and N can be depleted by factors of up to 2-10, while other heavy
  elements, along with hydrogen, are enhanced. The numerical results
  obtained are qualitatively similar to anomalous abundances reported
  among solar flare particles.

---------------------------------------------------------
Title: X-Rays from Stars
Authors: Mullan, D. J.
1981IrAJ...15..147M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: The solar "constant".
Authors: Mullan, D. J.
1981IrAJ...15..143M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Enhanced emission of Alfvén waves from sunspots during
    proton flares
Authors: Mullan, D. J.
1981SoPh...70..381M    Altcode:
  Thomas (1978) has shown that, if Alfvén waves exist in a sunspot umbra,
  they are normally reflected so strongly by the temperature minimum as
  to be essentially undetectable in the upper solar atmosphere. However,
  it is known that in many proton flares, chromospheric emission overlies
  the umbra of a sunspot, indicating that the transition region (TR)
  between chromosphere and corona in the umbral flux tube has moved
  down to lower altitudes. As a result of this lowering, umbral Alfvén
  waves have readier access to the corona: the coronal leakage depends
  exponentially on the altitude of the TR. We find that the Alfvén
  wave flux which leaks out of the umbra into the corona can exceed
  10<SUP>7</SUP> ergs cm<SUP>-2</SUP> s<SUP>-1</SUP>. A flux of this
  magnitude is expected to dissipate rapidly in the corona, thereby
  contributing to a positive feedback loop which ensures prolonged (∼1
  hr) leakage of the umbral Alfvén waves into the corona. We propose
  that these Alfvén waves may contribute significantly to prolonged
  energization of proton flares in which umbral coverage occurs.

---------------------------------------------------------
Title: Are Discrepant Asymmetry Red Giants Necessarily Hybrid Stars?
Authors: Mullan, D. J.; Stencel, R. E.
1981BAAS...13..886M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Large Macroturbulence in the Chromosphere of an RS CVn Star
Authors: Cram, L. E.; Mullan, D. J.
1981BAAS...13..514C    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Variable mass loss and magnetic topology in cool giant stars.
Authors: Mullan, D. J.; Stencel, R. E.
1981BAAS...13..547M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Theoretical studies of the RS cannum venaticorum stars
Authors: Mullan, D. J.
1981udnw.rept.....M    Altcode:
  Four areas of research were investigated: chromospheric modelling;
  starspot modelling; supersonic transition locus (STL) crossing; and
  STL crossing and T Tauri phenomena. Relationships among these areas
  of research are presented. Stellar structure and mass ejection for
  these stars were examined along with chromospheric analysis.

---------------------------------------------------------
Title: The Origin of Cosmic Rays
Authors: Mullan, D. J.
1981IrAJ...15....9M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Mass loss from warm giants - Magnetic effects
Authors: Mullan, D. J.
1981ASSL...88..355M    Altcode: 1981pprg.work..355M
  (Previously announced in STAR as N80-34332)

---------------------------------------------------------
Title: Obs. of Discr Chromo Em Line Prof Asymm &amp; Var Asymm in
    UV Spectra of Late-Type Stars
Authors: Mullan, Dermott J.
1981iue..prop..795M    Altcode:
  Based on our observing programs dealing with the Mg II chromospheric
  emission features among cool post-main-sequence stars, we are in a
  position to continue the search for asymmetry and profile variations
  among the three kinds of asymmetry variables identified to date: (i)
  the radical asymmetry variables which exhibit discrepant asymmetries
  in Mg II K (V/R &lt; 1) relative to Ca II K (V/R &gt; 1); (11) the
  circumstellar variables which exhibit changes in their circumstellar
  thickness and velocities along the line of sight; and (iii) the
  "non-variables" which may in fact be variables over time scales greater
  than the one year so far spent in any such investigation. Stars in group
  (i) also show discrepant Wilson-Bappu line-widths. The radical asymmetry
  variables occur among objects slightly cooler and more luminous than
  a Magnetic Topology Transition Locus (M.T.T.L.) lying close to, but
  distinct from, a previously defined transition locus (formerly known
  as the Supersonic Transition Locus). The MTTL separates solar-type
  objects which possess static high temperature coronal material and
  circulation-type asymmetries, from the non-solartype objects which
  possess lower temperature outer atmospheres, substantial mass loss,
  and outflow asymmetries. The MTTL segregates stars according to whether
  the magnetic field topology dominating their outer atmospheres is open
  or closed. The radical asymmetry variables, lying close to the MTTL,
  afford our best opportunity to see the interplay between the archetypal
  magnetic configurations and to understand the physics involved.

---------------------------------------------------------
Title: Pre-Acceleration in Collapsing Magnetic Neutral Sheets and
    Composition Anomalies among Solar Flare Particles
Authors: Mullan, D. J.; Levine, R. H.
1981ICRC....3..410M    Altcode: 1981ICRC...17c.410M
  In flares occurring in magnetic neutral sheets, the collapsing of the
  magnetic fields toward the neutral sheet results in their acting as
  mirrors in a first-order Fermi acceleration process and constitutes
  an intrinsic source of particle pre-acceleration. Although modest, the
  acceleration injects particles into the main flare acceleration with a
  composition which is different from that of the ambient corona. Upon
  calculating the fractions of 18 elements which are accelerated in
  the collapsing mirrors, covering the series from C to N, and then
  normalizing to O, peak abundances are found at Si and Fe, with local
  minima at N and in the S-Ca region. There is a qualitative similarity
  between these relative abundances and the relative enhancement factors
  of the elements among solar flare particles.

---------------------------------------------------------
Title: High resolution flux profiles of the Mg II h &amp; k lines
    in evolved F8 to M5 stars.
Authors: Stencel, R. E.; Mullan, D. J.; Basri, G. S.; Linsky, J. L.
1981NASCP2171..317S    Altcode: 1980IUE80......317S; 1981uviu.nasa..317S; 1981NASCP3171..317S
  The central results of a survey of the Mg II resonance line
  emission in a sample of over 50 evolved late type stars, including
  spectral-luminosity type F8 to M5 and La to IV are presented. Observed
  and surface fluxes are derived and correlations noted. The major
  findings include: (1) Mg II k emission core asymmetry transition near
  K1 III, analogous to that known for Ca II K; (2) a small gravity and
  temperature dependence of the Mg II chromospheric radiative loss rate.

---------------------------------------------------------
Title: Possible Evidence for Attenuation of AN MHD Shock by a Magnetic
    Neutral Sheet in the Solar Corona
Authors: Mullan, D. J.
1981ICRC....3...51M    Altcode: 1981ICRC...17c..51M
  The possibility that H-alpha filaments in the solar chromosphere
  are markers beneath regions where coronal shocks experience severe
  attenuation, and are thus the areas where particles can be ejected
  from the corona, is examined from data from flares of Aug. 4, 1972 and
  Nov. 9, 1979. Both flares produced gamma rays with 2.2 MeV energy, and
  data exists for the energetic protons received at earth stations. The
  efficiency of transport was high for the August event and two magnitudes
  lower for the November event. H-alpha filtergrams of the two flares show
  that in the second flare the shock propagation crossed two or three
  filaments lying in its path. The low efficiency of particle transport
  is taken to indicate a degraded shock in the region above the filaments,
  indicating that the particles needed a different route to escape.

---------------------------------------------------------
Title: The outher atmospheres of cool stars. VII. High resolution,
    absolute flux profiles of the MG II H and K lines in stars of spectral
    types F8 to M5.
Authors: Stencel, R. E.; Mullan, D. J.; Linsky, J. L.; Basri, G. S.;
   Worden, S. P.
1980ApJS...44..383S    Altcode:
  We present high-resolution lUE spectra of the emission cores of the
  Mg II resonance doublet at 280 nm in a selection of 54 stars covering
  a range of spectral type from F8 to MS and of luminosity class from
  supergiant (Ia) to subgiant (IV). These spectra were obtained with the
  LWR echelle system onboard the IUE satellite, and have been calibrated
  in absolute flux units using OAO 2 photometry of Eta UMa as a standard,
  plus the Barnes and Evans relations for stellar angular diameters. The
  uncertainty in flux is probably of order 20%. We discuss the qualitative
  line profile groupings, as determined by Basri and Linsky, and derive
  chromospheric radiative losses in the h and k lines; we discuss
  these loss rates as functions of effective temperature and luminosity
  class. We make further comparisons of these rates with rates derived
  for the Ca II H and K lines by Linsky and his colleagues. Chromospheric
  velocity fields and indicators of circumstellar envelopes are discussed
  in terms of profile asymmetries and other diagnostics. Line width
  measures and velocity shifts of the central reversals are tabulated,
  among other quantities, and several correlations noted. Finally, we
  discuss the relation of the Wilson K index and stellar coronae to Mg
  II emission, and note the occurrence of Fe II emission lines in the
  middle range of the UV of late-type stars.

---------------------------------------------------------
Title: Magnetohydrodynamic shock propagation in the vicinity of a
    magnetic neutral sheet
Authors: Steinolfson, R. S.; Mullan, D. J.
1980ApJ...241.1186S    Altcode:
  This paper reports a numerical investigation of the propagation of
  magnetohydrodynamic (MHD) shocks in the vicinity of magnetic neutral
  sheets. The attenuation of a shock after passing through a neutral sheet
  has been evaluated (assuming infinite electrical conductivity). In a
  parameter study, values of shock speed, polytropic index, plasma beta,
  and neutral-sheet thickness which are representative of solar coronal
  conditions have been examined. If solar cosmic rays are accelerated
  in association with a flare-induced shock (as seems most likely),
  then our results suggest that the spatial structure of solar particle
  sources will be influenced by helmet streamers. Such streamers are most
  readily detectable by H alpha filaments in the underlying chromosphere.

---------------------------------------------------------
Title: Addendum - Detection of Mass Loss in Stellar Chromospheres
Authors: Stencel, R. E.; Mullan, D. J.
1980ApJ...240..718S    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Mass Loss from Coronal Holes Driven by Magnetic Reconnection
Authors: Ahmad, I. A.; Mullan, D. J.
1980BAAS...12..918A    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: A Search for Mg II Asymmetry Variations Among Cool Evolved
    Stars
Authors: Mullan, D.; Stencel, R.
1980BAAS...12..801M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Detection of mass loss in stellar chromospheres.
Authors: Stencel, R. E.; Mullan, D. J.
1980ApJ...238..221S    Altcode:
  IUE observations of 47 cool giants have been made in a search for
  the onset of expansion in the Mg II h and k emission cores. It
  is found that, in a statistical sense, the longward emission peak
  becomes dominant above a velocity dividing line in the H-R diagram,
  which lies close to a temperature dividing line reported by Linsky
  and Haisch (1979). Also discussed are asymmetries in emission cores,
  collected asymmetry data including the evaluation of absolute visual
  magnitude by MK classification, Ca K emission width, and Mg k emission
  width, and evolutionary implications for the hypothesized supersonic
  transition locus (Mullan, 1978).

---------------------------------------------------------
Title: Stochastic acceleration of solar cosmic rays in an expanding
    coronal magnetic bottle
Authors: Mullan, D. J.
1980ApJ...237..244M    Altcode:
  It is noted that the major apparent difficulty with the 'magnetic
  bottle' proposed by Schatten and Mullan is that expansion of the
  closed model might have a severe cooling effect on the cosmic rays
  trapped inside. The present paper examines this difficulty by applying
  the equation for stochastic acceleration to an expanding bottle. The
  scattering centers are taken to be small-scale magnetic inhomogeneities
  which are present in the corona prior to the flare, and which are
  set into turbulent motion when a flare induced shock passes by. It
  is found that acceleration efficiencies can be high enough to offset
  expansive cooling. It is concluded that the results indicate that the
  flux of particles which are accelerated to 100 MeV is very sensitive
  to shock speed if this speed is less than about 1000 km per s.

---------------------------------------------------------
Title: Coronal Propagation of a Magnetohydrodyamic Shock in the
    Vicinity of a Magnetic Neutral Sheet
Authors: Mullan, D. J.; Steinolfson, R. S.
1980IAUS...91..323M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Non-Thermal Stellar Winds in Cool Stars
Authors: Mullan, D. J.
1980SAOSR.389..189M    Altcode: 1980csss....1..189M
  No abstract at ADS

---------------------------------------------------------
Title: Variable Mass Loss Among Stars at or Near the Supersonic
    Transition Locus
Authors: Mullan, Dermott J.
1980iue..prop..483M    Altcode:
  We propose to utilize the IUE to continue LWR observations of G, K and
  M stars as was done during our proposal during the second year of IUE
  operation. The Mg II emission cores were observed in a sample of 47 cool
  giants, and we found that in a statistical sense, the longward emission
  peak becomes dominant above a certain locus in the HR diagram. This
  locus lies close to a "temperature dividing line" reported by Linsky
  and Haisch. Combining the Mg results with earlier Ca II K data and with
  circumstellar shell data, a fundamental change in the structure of the
  upper atmosphere of cool giants, consistent with the predictions of
  a supersonic transition locus-hypothesis advanced by Mullan, has been
  determined. Two major questions remain which can only be answered by
  further IUE observations: (1) how sharp is this STL division in the
  HR diagram?; and (2) do the stars nearest the STL exhibit variable
  asymmetry due to instabilities in their upper atmospheres which alter
  the coupling between corona and chromosphere? The first of these
  questions can be addressed with observations of new target stars
  which will Improve the statistics. The second can be addressed with
  repeat observations of selected objects close to the STL to search
  for variations on a 1 year timescale.

---------------------------------------------------------
Title: Mass loss from warm giants: Magnetic effects
Authors: Mullan, D. J.
1980STIN...8034322M    Altcode:
  Among warm giant stars, rapid mass loss sets in along a well defined
  velocity dividing line (VDL). Hot corona also disappear close to the
  VDL and thermal pressure cannot drive the observed rapid mass loss in
  these stars. The VDL may be associated with magnetic fields changing
  from closed to open. Such a change is consistent with the lack of
  X-rays from late-type giants. A magnetic transition locus based on
  Pneuman's work on helmet streamer stability agrees well with the
  empirical VDL. The change from closed to open fields not only makes
  rapid mass loss possible, but also contributes to energizing the mass
  loss in the form of discrete bubbles.

---------------------------------------------------------
Title: Model chromospheres of flare stars.I. Balmer-line profiles.
Authors: Cram, L. E.; Mullan, D. J.
1979ApJ...234..579C    Altcode:
  In preparation for using the Balmer lines in flare stars as
  chromospheric diagnostics, we have computed a grid of model
  chromospheres by superposing prescribed temperature rises on published
  models for M dwarf photospheres. The chromospheric equation of state
  is dominated by the non-LTE ionization of hydrogen, which is treated
  by using a model hydrogen atom with five bound levels. The radiative
  transfer equation is solved explicitly for the Lyman continuum and
  the Balmer lines Ha, Hfl, and H)'. In the absence of a chromosphere,
  Ha, Hfl, and H)' appear as weak absorption lines. As the amount of
  chromospheric material (between temperatures Te = 5500 K and 50,000 K)
  increases, these absorption lines first become deeper, then develop
  emission peaks on the outer edges of their wings, and finally, when the
  chromosphere is sufficiently massive, the Balmer lines become strong
  emission lines. The results obtained here will be used to interpret
  the profiles and decrements of the Balmer lines in flare stars, in both
  quiescent and flaring states. Subject headings: line profiles - stars:
  atmospheres - stars: chromospheres - stars: flare - stars: late-type

---------------------------------------------------------
Title: Can flare stars be the source of galactic cosmic rays?
Authors: Mullan, D. J.
1979ApJ...234..588M    Altcode:
  Lovell has proposed that flare stars may provide a substantial
  contribution to the energy in galactic cosmic rays (GCR). Here his
  arguments are reexamined, taking into account recent improvements
  in stellar statistical data and in our understanding of the processes
  involved in acceleration of protons in association with solar flares. It
  is found that flare stars contribute no more than 0.0002 of the GCR
  energy. A result of this order had previously been derived by Edwards
  and McQueen on the basis of scaling X-ray fluxes and energetic particle
  fluxes in solar flares; however, the present work is not subject to
  the uncertainties associated with X-ray and particle flux scaling.

---------------------------------------------------------
Title: Long-lived sources of solar cosmic rays
Authors: Mullan, D. J.
1979AIPC...56..163M    Altcode: 1979pama.work..163M
  The high correlation between prompt solar cosmic rays and
  a flare-induced MHD shock is well known. We point out that the
  propagation properties of such a shock cause shock heating of the solar
  atmosphere to be confined to a unipolar magnetic region. As a result,
  if particles can be accelerated within the shock-processed part of
  the corona, the fluxes of suc particles will exhibit sharp spatial
  gradients near quiescent filaments. The passage of an MHD shock leads
  to the rapid collapse of magnetic neutral regions which prior to shock
  passage were collapsing too slowly to accelerate particles. We suggest
  that these newly triggered magnetic acceleration regions provide a
  third phase of solar flare acceleration regions provide a third phase
  of solar flare acceleration which may persist for many days after a
  flare. Collapsing magnetic regions with lengths scales of order 100
  km can explain a variety of coronal phenomena.

---------------------------------------------------------
Title: Heating of Chromospheres and Coronae in Cool Stars
Authors: Mullan, D. J.
1979IrAJ...14...73M    Altcode:
  Recent evidence is summarized that suggests that neither of two
  traditional views of chromospheric heating (that the flux of energy
  required to heat the solar chromosphere) is only a small fraction of
  the total radiative energy emerging from the solar interior and that
  chromospheres are heated by acoustic waves generated in the convection
  zone (which lies close to the surface of the star) is valid. Particular
  attention is given to cool stars, both dwarfs and giants. The directions
  in which research is currently heading in attempting to understand
  heating of chromospheres and coronae in these stars are indicated. Hot
  stars are excluded from consideration because radiation pressure plays
  an important role in their atmospheric heating. It is concluded that the
  role of magnetic fields in giants is different from the role in dwarfs.

---------------------------------------------------------
Title: On the detectability of starspot magnetic fields.
Authors: Mullan, D. J.
1979ApJ...231..152M    Altcode:
  A starspot is considered as the surface manifestation of a submerged
  magnetic dipole. It seems likely that in red dwarfs the dipole is
  generated by dynamo action within the outer convection zone. As
  a result, a starspot-associated dipole is highly decentered. By
  integrating the field of a decentered dipole over the disk of a spotted
  star, the effective longitudinal field, the effective transverse
  field, and the mean surface field are derived. If the axial field in
  a starspot is 10 kilogauss, it is found that in most favorable cases,
  the effective longitudinal field is about 150 gauss, the effective
  transverse field is approximately 1.1 kilogauss, and the mean surface
  field is roughly 1.3 kilogauss.

---------------------------------------------------------
Title: Motion of solar cosmic rays in the coronal magnetic field.
Authors: Mullan, D. J.; Schatten, K. H.
1979SoPh...62..153M    Altcode:
  Trajectories of solar cosmic rays have been calculated in a static
  ninth-order coronal magnetic field. It is found that as a result of
  field curvature and gradients, protons drift across the field lines at
  a rate of up to 200 γβ<SUP>2</SUP> deg hr<SUP>−1</SUP>. These drift
  rates are of the same order as, but somewhat smaller than, empirically
  derived rates. Localized enhancements of magnetic field have been
  inserted into the ninth-order field in order to model (in a highly
  idealized manner) the effects of the small-scale magnetic features
  which give rise to X-ray bright points. The motions of the particles
  in the presence of these scattering centers can be parameterized
  approximately by a cross-field diffusion coefficient. Our estimates
  of this coefficient, although crude, overlap with empirical values
  which have been deduced over a wide range of energies.

---------------------------------------------------------
Title: Coronal Propagation of AN MHD Shock in the Vicinity of a
    Magnetic Neutral Sheet
Authors: Steinolfson, R. S.; Mullan, D. J.
1979ICRC....5...15S    Altcode: 1979ICRC...16e..15S
  No abstract at ADS

---------------------------------------------------------
Title: Proton Flares and the Missing Energy in Sunspots
Authors: Mullan, D. J.
1979ICRC....5...22M    Altcode: 1979ICRC...16e..22M
  No abstract at ADS

---------------------------------------------------------
Title: Pre-Main Sequence Stars and Galactic Cosmic Rays
Authors: Mullan, D. J.; Owens, A. J.
1979ICRC....2...98M    Altcode: 1979ICRC...16b..98M
  No abstract at ADS

---------------------------------------------------------
Title: Can Solar Flares BE the Cause of Ancient Catastrophes?
Authors: Mullan, D. J.; Kent, D. W.
1979ICRC....5..323M    Altcode: 1979ICRC...16e.323M
  No abstract at ADS

---------------------------------------------------------
Title: Observable Influence of Stellar Winds on Late-Type
    Chromospheres
Authors: Mullan, Dermott J.
1979iue..prop..224M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Can Flare Stars BE the Source of Galactic Cosmic Rays?
Authors: Mullan, D. J.
1979ICRC....2...92M    Altcode: 1979ICRC...16b..92M
  No abstract at ADS

---------------------------------------------------------
Title: Supersonic stellar winds and rapid mass loss in cool stars.
Authors: Mullan, D. J.
1978ApJ...226..151M    Altcode:
  Rapid mass loss from cool giants and supergiants via supersonic stellar
  winds is considered. It is proposed that when a star evolves to a
  state in which its wind, driven by hydrodynamic expansion, becomes
  supersonic at the base of the corona, the rate of mass loss from the
  star should increase essentially discontinuously by an amount equal
  to the ratio of gas densities at the top of the chromosphere and the
  base of the corona. Empirically determined chromospheric gas pressures
  are combined with the minimum-flux coronal model of Hearn (1975) in
  order to derive the locus in the H-R diagram along which stellar winds
  undergo a transition from transonic (fed by purely coronal material) to
  supersonic (fed by chromospheric material). This locus is found to agree
  well with the boundary of the domain occupied by circumstellar-shell
  stars (in which rapid mass loss is known to occur). An estimate of
  the mass-loss rate under supersonic conditions is made and shown to
  be consistent with observed rates.

---------------------------------------------------------
Title: Fast azimuthal transport of solar cosmic rays via a coronal
    magnetic bottle
Authors: Schatten, K. H.; Mullan, D. J.
1977JGR....82.5609S    Altcode:
  Key observations pertaining to the fast azimuthal propagation of solar
  cosmic ray particles are reviewed. Briefly, protons and electrons with
  a wide range of energies from 40° to 60° heliolongitude on either
  side of a flare site have access to the earth-sun interplanetary
  field line within an hour of flare onset. We propose that coronal
  magnetic bottles, produced by flares, serve as temporary traps for
  solar cosmic rays in some instances. It is the expansion of these
  bottles at velocities of 300-500 km/s which allows fast azimuthal
  propagation of solar cosmic rays independent of energy. As a result
  of the Rayleigh-Taylor instability, cosmic rays originally trapped
  inside the bottle are released into interplanetary space at a time of
  the order of 0.5-1 hour after the flare.

---------------------------------------------------------
Title: Dust from the sun?
Authors: Mullan, D. J.
1977A&A....61..369M    Altcode:
  It was previously proposed that the sun might be the source of
  rare-earth-rich submicron particles detected in rocket flights from
  Kiruna, Sweden, but not in flights originating from sites at lower
  latitudes. The problem of sputtering in the solar atmosphere is
  examined and found to be serious enough that a nonsolar origin must
  be considered for the particles. The motion of grains in a variety of
  solar model atmospheres is calculated, and it is shown that sputtering
  rates in active regions are probably so large that submicron grains
  of rare-earth-rich material are reduced to such small sizes that they
  cannot be repelled from the sun by radiation pressure. It is suggested
  that the rare-earth-rich submicron particles detected at Kiruna but
  nowhere else are the product of local mining of rare-earth-rich ores
  in the vicinity of Kiruna.

---------------------------------------------------------
Title: Rapid Mass Loss and Supersonic Stellar Winds.
Authors: Mullan, D. J.
1977BAAS....9..649M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Solar and stellar flares.
Authors: Mullan, D. J.
1977SoPh...54..183M    Altcode:
  Short-lived increases in the brightness of many red dwarfs have been
  observed for the last 30 yr, and a variety of more or less exotic
  models have been proposed to account for such flares. Information about
  flares in the Sun has progressed greatly in recent years as a result
  of spacecraft experiments, and properties of coronal flare plasma
  are becoming increasingly better known. In this paper, after briefly
  reviewing optical, radio and X-ray observations of stellar flares, we
  show how a simplified model which describes conductive plus radiative
  cooling of the coronal flare plasma in solar flares has been modified
  to apply to optical and X-ray stellar flare phenomena. This model
  reproduces many characteristic features of stellar flares, including
  the mean UBV colors of flare light, the direction of flare decay in
  the two-color diagram, precursors, Stillstands, secondary maxima, lack
  of sensitivity of flare color to flare amplitude, low flux of flare
  X-rays, distinction between so-called spike flares and slow flares,
  Balmer jumps of as much as 6-8, and emission line redshifts up to 3000
  km s<SUP>−1</SUP>. In all probability, therefore, stellar flares
  involve physical processes which are no more exotic (and no less!) than
  those in solar flares. Advantages of observing stellar flares include
  the possibilities of (i) applying optical diagnostics to coronal flare
  plasma, whereas this is almost impossible in the Sun, and (ii) testing
  solar flare models in environments which are not generally accessible
  in the solar atmosphere.

---------------------------------------------------------
Title: A model for nonmonotonic optical light curves of stellar
    flares.
Authors: Mullan, D. J.
1977ApJ...212..171M    Altcode:
  An idealized model of flare decay is considered, including both
  radiative and conductive cooling of the hot expanding plasma. The
  optical light curve has contributions from both conductive power and
  X-ray heating. In contrast to the monotonic decay predicted when only
  radiative cooling is included, the present results include features
  which may be analogous to observed stillstands and secondary maxima and
  to a certain class of precursor events. Stillstands, secondary maxima,
  and precursors are here considered to be different manifestations of
  the same physical phenomenon.

---------------------------------------------------------
Title: Influence of stellar flare X-rays on the optical light curve.
Authors: Mullan, D. J.; Tarter, C. B.
1977ApJ...212..179M    Altcode:
  The steady-state interaction of an incident flux of bremsstrahlung
  X-rays with the optically thick atmosphere of a flare star is
  computed. A significant fraction of the incident flux is converted
  into nonionizing photons. The emerging optical radiation has colors
  which, when combined with previously estimated colors of radiation
  emitted directly by the flare region, are in the correct sense to
  account for the evolution of decaying flare light in the two-color
  diagram. Emission lines contribute up to 10% of the intensity in the
  B filter. Red asymmetries of the emission lines may be associated with
  radiation pressure.

---------------------------------------------------------
Title: Heterogeneity of the solar atmosphere.
Authors: Mullan, D. J.
1977oehs.conf..377M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Mean colors of stellar flare continuum.
Authors: Mullan, D. J.
1976ApJ...210..702M    Altcode:
  Shmeleva and Syrovatskii have shown that under certain circumstances
  the temperature structure in the hotter regions (T&gt; 2 x l0 K)
  of a solar flare is characterized by two universal functions: one
  for constant density conditions, the second for constant pressure
  conditions. Here we show that the U - B, B - V colors of optically
  thin thermal bremsstrahlung emitted by both of these temperature
  structures are consistent with the mean colors of stellar flares near
  maximum light and also with the observed evolution of flare light
  in the two-color diagram during flare cooling. We suggest that the
  transition which occurs in the character of stellar flare light from
  mostly continuum emission near flare maximum to mostly line emission
  later in the flare is related to the transition which must occur from
  the constant density regime to the constant pressure regime on a time
  scale of order 1-2 minutes. The two types of flares (spike flares and
  slow flares) identified by Moffett are ascribed to these two different
  regimes. The flare light-curve model described here resembles in
  some respects a model previously proposed by Andrews, but there are
  differences in detail. Subject headings: stars: flare - Sun: flares

---------------------------------------------------------
Title: Second-stage acceleration in solar flares.
Authors: Mullan, D. J.
1976A&A....52..305M    Altcode:
  A model proposed by Chevalier and Scott (1975) to account for cosmic-ray
  acceleration in an expanding supernova remnant is applied to the case
  of a shock wave injected into the solar corona by a flare. Certain
  features of solar cosmic rays can be explained by this model

---------------------------------------------------------
Title: Properties of minimum-flux coronae in dwarfs and giants.
Authors: Mullan, D. J.
1976ApJ...209..171M    Altcode:
  Hearn's (1975) minimum-flux corona model is applied to main-sequence and
  giant stars. In this model, the corona is assumed to have a strictly
  radial magnetic field and to adjust itself in such a way that for
  a given pressure at its base, the sum of radiative, conductive, and
  stellar-wind energy fluxes from it is a minimum. Numerical results for
  main-sequence stars of spectral type M6 V through O5 V are presented
  in terms of coronal temperatures and efficiency factors for converting
  thermal energy to mechanical energy. Similar results are given for
  the giant stars Alpha Aur, Beta Gem, Alpha Boo, and Alpha Tau. It is
  shown that: (1) coronae of red dwarfs must be up to three times cooler
  than the solar corona unless the efficiency of conversion increases
  by many orders of magnitude in later spectral types relative to the
  efficiency of the sun; (2) coronae of upper-main-sequence stars may
  be twice as hot as the solar corona; (3) the coronae of Beta Gem and
  Alpha Aur are hot enough to explain the presence of O V, O VI, Si III,
  and N V lines; (4) the coronae of Alpha Boo and Alpha Tau are so cool
  that insignificant O V emission is expected; and (5) line asymmetries
  due to stellar winds are most easily detectable in Alpha Boo and Alpha
  Aur because of the larger mass-loss rates per unit area in these stars.

---------------------------------------------------------
Title: Flare Stars: II. Physical Characteristics of the Flares
Authors: Mullan, D. J.
1976IrAJ...12..277M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Flares on white dwarfs and gamma-ray bursts.
Authors: Mullan, D. J.
1976ApJ...208..199M    Altcode:
  Using the known properties of stellar flares on red dwarfs, the
  characteristics of flares on magnetic white dwarfs are predicted. On
  the basis of these predictions, the hypothesis that gamma-ray bursts
  are thermal radiation from a high-temperature analog of normal stellar
  flares occurring on magnetic white dwarfs, with surface fields of 10
  to the 7th to 10 to the 8th gauss is examined. It appears unlikely
  that main-sequence stars are the sites of the bursts. Various observed
  properties of the gamma-ray bursts are shown to be analogous to known
  properties of normal stellar flares. In Particular, multiple peaks
  within a burst are ascribed to sympathetic flares. Independent arguments
  suggest that the gamma-ray bursts occur on white dwarfs at distances
  of order 100-300 pc. It is proposed that fluctuations in the luminosity
  of certain white dwarfs may be related to starspots and flare activity.

---------------------------------------------------------
Title: Thermal X-rays from stellar flares: reevaluation of scaling
    from solar flares.
Authors: Mullan, D. J.
1976ApJ...207..289M    Altcode:
  A simple method of estimating the ratio of thermal X-ray luminosity
  to optical luminosity in stellar flares is presented which is valid at
  times close to and following peak flare luminosity. It is proposed that
  at such times, the X-ray and optical luminosities are, respectively,
  the energy radiated by the plasma and the energy conducted out of
  the plasma. If the conductive energy directed downward toward the
  photosphere and lower chromosphere is regarded as the energy source
  for optical flares, then the luminosity ratio is equal to the ratio
  of conductive to radiative cooling times in the hot flare plasma. A
  self-consistent model for red-dwarf flares is discussed in which the
  decay time of the optical light curve is controlled by the time scale
  for thermal conduction from the hot flare plasma. The condition that the
  two times must be approximately equal leads to estimates of electron
  densities in flares, provided the flare temperatures are known; it is
  argued that stellar flare temperatures are 1 to 4 times higher than
  the mean temperature of solar flares. Numerical results are given for
  the luminosity ratio in flares of seven UV Ceti stars. It is concluded
  that if the solar luminosity ratio is used in attempting to predict
  thermal X-ray fluxes from stellar flares, the predicted X-ray flux
  accompanying an optical flare of given amplitude will provide only an
  upper limit on the actual thermal X-ray flux.

---------------------------------------------------------
Title: Erratum: Sympathetic Stellar Flares and Electron Precipitation
    as Probes of Coronal Structure in Flare Stars
Authors: Mullan, D. J.
1976ApJ...206..672M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Flare Stars: Note added in Proof
Authors: Mullan, D. J.
1976IrAJ...12..231M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Flare Stars: I. Physical Characteristics
Authors: Mullan, D. J.
1976IrAJ...12..161M    Altcode:
  The properties of flare stars - a group of dwarf stars of late spectral
  type characterized by intermittent short-lived increases in brightness -
  are examined. Particular attention is given to properties which pertain
  to the generation of strong magnetic fields, since hypotheses according
  to which stellar flares derive their energy ultimately from magnetic
  field energy appear to be the most attractive.

---------------------------------------------------------
Title: Sympathetic stellar flares and electron precipitation as
    probes of coronal structure in flare stars.
Authors: Mullan, D. J.
1976ApJ...204..530M    Altcode:
  We have previously suggested that sympathetic stellar flares might
  be triggered by a hydromagnetic (Moreton) wave propagating from one
  starspot to another. Electron cyclotron waves (whistlers) are expected
  to propagate with speeds exceeding Moreton wave speeds by factors of
  up to 30. We suggest that short-period (13 s) oscillations observed
  by Rodono during a large flare in the Hyades flare star H II 2411 are
  the whistler analog of sympathetic flares, and are due to electron
  precipitation triggered by whistlers propagating between starspots
  at opposite rotation poles of the star. According to this model,
  if starspot fields are as strong ( 10 gauss) as a recent starspot
  model suggests, then the coronal density at about 7-8 stellar radii
  in H II 2411 is in the range (0.5-10) x 106 . These densities are
  larger by factors of than the densities in the solar corona at 7-8
  solar radii. Adopting ne = 2 x 106 at 7.5 stellar radii in the corona
  of a flare star thought to be very similar to H II 2411 (YZ CMi), we
  find that the coronal temperature in the flare star is lower than in
  the solar corona by a factor of 3-10. Using the Kennel-Petschek model
  originally developed for precipitation of electrons from the terrestrial
  radiation belts, we interpret Rodono's flare observations to mean that
  spectral indices of the differential energy spectrum of electrons in
  three flares on H II 2411 lie in the range 2.5 .0. Subject headings:
  stars: coronae - stars: flare

---------------------------------------------------------
Title: Possible evidence for the occurrence of magnetic fields of
    order 10 kilogauss in the red dwarf star BY Draconis.
Authors: Mullan, D. J.; Bell, R. A.
1976ApJ...204..818M    Altcode:
  Koch and Pfeiffer have reported the presence of linear polarization in
  broad-band observations of the light from the spotted dwarf BY Dra. Here
  we examine the hypothesis that the polarization is produced by the
  cumulative effects of the Zeeman patterns of individual absorption
  lines within the bandpass. We compute the polarization expected in a
  cool (0e = 1.5) dwarf observed in UBVR filters. Comparing our results
  with observations of BY Dra, we find that the surface field strength on
  this star is at times of order 10 kilogauss. Peak linear polarization
  is observed to occur when the site previously occupied by a large
  starspot is optimally visible. We suggest that the presence of fields
  of order 10 kilogauss in an old bipolar region is consistent with a
  recent model of starspots on a cool dwarf. Subject headings: stars:
  late-type - stars: magnetic

---------------------------------------------------------
Title: Properties of Minimum Flux Coronae in Dwarfs and Giants
Authors: Mullan, D. J.
1976BAAS....8..307M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: A Comment on 'A Comment on the Damping of Magnetohydrodynamic
    Waves' by Bibhas R. De
Authors: Mullan, D. J.
1976Ap&SS..44L...9M    Altcode:
  We point out that in the case of sunspots, when Coulomb collisions
  are included, the reduction in Lundqvist number due to anisotropic
  conductivity is several orders of magnitude less than the reduction
  estimated by Dc. This result suggests that, contrary to De's conclusion,
  sunspot conditions do permit efficient MHD wave propagation

---------------------------------------------------------
Title: Polarized light from lower main-sequence stars: is it due to
    synchrotron emission?
Authors: Mullan, D. J.
1975ApJ...201..630M    Altcode:
  Broadband plane polarization (0.1-10%) has been observed in the
  light emitted by flare stars outside flares. The possibility that the
  polarization might be due to synchrotron radiation is examined. On
  the basis of the electron energy spectrum which would be required,
  it is suggested that synchrotron radiation is probably not responsible
  for the observed polarization.

---------------------------------------------------------
Title: E. M. Lindsay, An All-Ireland Astronomer
Authors: Mullan, D. J.
1975IrAJ...12..110M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Are stellar flares energized by the missing energy in
    starspots?
Authors: Mullan, D. J.
1975ApJ...200..641M    Altcode:
  It is suggested that the energy released in stellar flares is provided
  by a steady accumulation of a fraction of the missing energy in
  starspots. The analysis is based on the assumption that starspots are
  necessary for flare activity since they are highly efficient generators
  of nonthermal energy. The rate of occurrence of flares of given absolute
  magnitude on a star of given absolute visual magnitude is determined,
  and an expression is obtained for the dependence of the cooling time
  of optically thick flare plasma on the absolute magnitude and gravity
  of a star. The results are found to be in excellent agreement with
  the observed statistical properties of stellar flares over a range of
  almost 10 magnitudes in intrinsic visual luminosity. It is noted that
  the formulas can be applied in an approximate way to solar flares and
  sunspots, and that the lack of flare stars in spectral types earlier
  than KO may mean that starspots become very small in late G-type stars.

---------------------------------------------------------
Title: Magnetic fields in dMe stars: how effective is the battery
    mechanism?
Authors: Mullan, D. J.
1975PASP...87..455M    Altcode:
  Although we agree with Worden (1974) that the surfaces of dMe stars
  may be the sites of magnetic fields as large as 1-100 kilogauss,
  we disagree with his conclusion that Biermann's battery mechanism is
  responsible for generating such large fields. We believe that it is
  more probable that field generation occurs in convective conditions,
  where the battery cannot operate efficiently. We also disagree with
  the argument used by Worden to relate magnetic energies with observed
  properties of flare stars. Key words: dMe stars - magnetic fields -
  flare stars

---------------------------------------------------------
Title: On the possibility of magnetic starspots on the primary
    components of W Ursae Majoris type binaries.
Authors: Mullan, D. J.
1975ApJ...198..563M    Altcode:
  We examine the hypothesis that magnetic starspots occur in W
  UMa stars. Crude estimates of toroidal field strength in these
  rapidly-rotating stars suggest that the fields may be large enough
  (2-10 kilogauss) to permit spots to form. The probability of spot
  formation is larger on the primary component than on the secondary,
  especially in Rucinski's W type systems. It is shown that the existence
  of starspots on the primary component in W UMa systems can account
  for the apparent temperature excess of the secondary relative to the
  primary in W type systems, and for the much smaller variations in the
  light curve exhibited by Rucinski's A type systems. We predict upper
  limits on the amplitude of the distortions which can occur in the
  light curve of these systems due to starspot activity. The presence
  of starspots leads to flare activity, but flares with amplitudes as
  large as Amv = 1 mag are expected to occur very rarely, only once every
  few years in W UMa. Flares of amplitude 0.01 mag, may, however, occur
  sufficiently frequently to explain short-term deviations from mean
  light curves occurring within a single night's observations. Cycles
  of starspot activity appear to have periods of 5-10 years in two of
  these systems. Tidal effects may be important in determining preferred
  starspot longitudes. Subject heading: W Ursae Majoris stars

---------------------------------------------------------
Title: Magnetic fields and dense chromospheres in dMe stars.
Authors: Mullan, D. J.
1975A&A....40...41M    Altcode:
  The hypothesis is investigated that dense chromospheres of dMe stars are
  heated by dissipation of hydromagnetic waves which may be generated in
  active regions where the nonspot magnetic field strength can be as large
  as 5 to 10 kG. It is proposed that dMe stars are a set of magnetic stars
  on the lower main sequence which have strong fields generated by dynamo
  action in deep convective envelopes, while dM stars are nonmagnetic
  or weakly magnetic stars having no starspots on their surfaces. The
  combination of magnetic fields and dense chromospheres in dMe stars is
  shown to provide consistent evidence for several conclusions, including:
  (1) the dMe stars which are most likely to be flare stars are those
  with hydrogen emission lines and (2) propagation of flare-initiated
  coronal waves can trigger sympathetic stellar flares. It is suggested
  that grain formation occurs in starspots of dMe stars and that such
  grains in a circumstellar shell are responsible for the systematic IR
  excesses of dMe stars relative to dM stars.

---------------------------------------------------------
Title: The Relation Between Flares and the Missing Energy in Spots
Authors: Mullan, D. J.
1975BAAS....7S.362M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Broad-band Polarization Expected in Magnetic M Dwarfs.
Authors: Mullan, D. J.; Bell, R. A.
1975BAAS....7..271M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Magnetic fields in the sun.
Authors: Mullan, D. J.
1974FrInJ.298..341M    Altcode:
  The observed properties of solar magnetic fields are reviewed, with
  particular reference to the complexities imposed on the field by
  motions of the highly conducting gas. Turbulent interactions between
  gas and field lead to heating or cooling of the gas according as
  the field energy density is less or greater than the maximum kinetic
  energy density in the convection zone. The field strength above which
  cooling sets in is 700 G. A weak solar dipole field may be primeval,
  but dynamo action is also important in generating new flux. The dynamo
  is probably not confined to the convection zone, but extends throughout
  most of the volume of the sun. Planetary tides appear to play a role
  in driving the dynamo.

---------------------------------------------------------
Title: Is Magnetic Convection Important in the Sun?
Authors: Mullan, D. J.
1974SoPh...38....9M    Altcode:
  Although magnetic convection in all probability does operate inside the
  Sun, the energy flux which it can carry is 5-6 orders of magnitude
  smaller than the total solar flux. Thus the effects of magnetic
  convection on the internal temperature structure of the Sun are
  probably small.

---------------------------------------------------------
Title: Starspots on flare stars.
Authors: Mullan, D. J.
1974ApJ...192..149M    Altcode:
  Sizes of starspots on flare stars can be derived from the author's
  convection-cell hypothesis. The sizes are in fair agreement with
  those observed on YY Gem, CC Eri, and BY Dra by Bopp and Evans. The
  hypothesis predicts that periodic brightness variations due to
  starspots are restricted to stars brighter than a critical absolute
  visual magnitude. A convective model of a starspot on YY Gem has been
  computed, assuming that the missing flux is in the form of Alfve'n
  waves. It is found that the surface field must exceed 10 gauss, and is
  probably less than about 3 x 10 gauss. With a surface field of 2 x 10
  gauss, the effective temperature of the spot is in the range Te = K,
  depending on the field gradient. These figures are to be compared with
  Te = 2000 K estimated from observations by Bopp and Evans. Efficient
  dynamo action is shown to be a possible mechanism for generating
  such large surface fields. There is a possibility that tidal effects
  may influence starspot formation. Subject headings: flare stars -
  hydromagnetics - late-type stars - magnetic stars

---------------------------------------------------------
Title: Magnetic Fields on Spotted Red Dwarfs.
Authors: Mullan, D. J.
1974BAAS....6..333M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Sunspot Models with Alfvin Wave Emission
Authors: Mullan, D. J.
1974ApJ...187..621M    Altcode:
  Sunspot models have been computed on the assumption that the missing
  flux is transported by undissipated Alfve'n waves. In order to
  estimate the flux of these waves, we propose an extension of C)pik's
  cellular model of convection to include the effects of a vertical
  magnetic field on horizontal gas flow. Horizontal motions, not vertical
  motions, are impeded more or less severely depending on the electrical
  conductivity, and this reduces the convective flux. These motions,
  however, shake the field lines; and this is assumed to be a source
  of Alfve'n waves, compensating for the reduction in the convective
  flux. The free parameter D/H (ratio of cell diameter to cell depth) is
  adjusted such that the total sum of radiative, convective, and Alfve'n
  wave fluxes remains constant at all depths and equals the undisturbed
  solar flux entering the spot from below. Our treatment is speculative
  to some extent, but it leads to a unique spot model for a given field
  strength. We derive the depth-dependence of the effective temperature T,
  in a spot, and find that it increases nonmonotonically from a low value
  at the surface (2750 K in a spot with magnetic field B = 3000 gauss) to
  the solar value (5780 K) at depth z. The latter turns out to lie within
  1 percent of the depth of the solar convection zone in all cases of
  interest. Convection cells in sunspots are found to be narrow cylinders
  (DIH &lt; 0.2 and decreasing, the stronger the field) aligned along
  the field lines. The diameter of a cell at the top of a spot with B =
  3000 gauss is about 80 km. The depth ZA where the Alfve'n wave flux
  has a maximum is found to be 841 km in a spot with B = 3000 gauss, and
  ZA decreases with decreasing B. The values of ZA seem to correspond
  with the "Wilson depression. Radiative influx of heat from the walls
  of a spot is found to be minimal for B = gauss, and increases rapidly
  outside this range. Thus spots with B in this range are expected to live
  longest, and the most common observed field strengths are expected to
  lie in this range. If radiative heating is responsible for the lower
  limit on the permissible field strength in spots (1200 gauss), then
  there should also be an upper limit on spot field strength at 5300
  gauss. Subject headings: hydromagnetics - sunspots

---------------------------------------------------------
Title: Sunspots, Supergranules, and the Depth of the Solar Convection
    Zone
Authors: Mullan, D. J.
1973ApJ...186.1059M    Altcode:
  It is suggested that a large sunspot or a sunspot group can be regarded
  as a special kind of convection cell penetrating the entire depth of
  the solar convection zone (analogous to a supergranule, according to
  the author's model). Theoretical results of Vickers are used to show
  that the diameters of supergranules and large sunspots should lie in the
  range 18,000-65,000 km. This agrees well with results of Bumba et al.,
  who found preferred spot sizes in large groups ranging from 18,000
  to 54,000 km. Spots with diameters less than 18,000 km are probably
  shallower than the convection zone, i.e., they have depths less than
  10,000 km. Implications for flare stars are noted. Subject headings:
  convection - granules, solar - sunspots

---------------------------------------------------------
Title: Comments on Papers by P. R. Wilson Concerning Sunspots
Authors: Mullan, D. J.
1973SoPh...32..441M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Flare Triggering by Coherent Oscillations
Authors: Mullan, D. J.
1973ApJ...185..353M    Altcode:
  Energy fluxes in coherent oscillations observed by Tanaka in Ha plages
  are estimated to be very large, (0.954.50) x 1010 ergs cm-2 5 1 During
  their lifetime ( 10 s) these oscillations transmit up to 1 0 ergs to
  the chromosphere, sufficient to provide for a large flare even if the
  efficiency of conversion into electromagnetic and corpuscular energies
  is only 1 percent. If these oscillations do not in fact provide the
  energy released in a flare, they are expected to be at least important
  in triggering a flare, as Tanaka has observed. The coherent oscillations
  are thought to be free modes of the Sun (as described by C. L. Wolff),
  preferentially excited in plages near sunspots where subphotospheric
  magnetic fields modify the structure of the convection zone. Subject
  headings: flares, solar - plages, solar - solar atmospheric motions

---------------------------------------------------------
Title: Fast Rotation of Metal-poor Stars
Authors: Mullan, D. J.
1973A&A....27..379M    Altcode:
  Summary. Mass loss in stellar winds is expected to be a sensitive
  function of maximum convective velocity in the outer convection zone of
  stars. Metal-poor stars are expected to have low mass loss rates, and
  therefore their rotational velocities are not braked as efficiently
  as are those of metal-rich stars. This explains an observational
  correlation described by Danziger and Faber (1972). Key words: stellar
  rotation - metal abundance

---------------------------------------------------------
Title: Correction of Sunspot Intensities for Scattering Light
Authors: Mullan, D. J.
1973SoPh...32...65M    Altcode:
  Correction of sunspot intensities for scattered light usually
  involves fitting theoretical curves to observed aureoles (Zwaan, 1965;
  Staveland, 1970, 1972). In this paper we examine the inaccuracies in the
  determination of scattered light by this method. Earlier analyses are
  extended to examine uncertainties due to the choice of the expression
  for limb darkening, including terms up to sin<SUP>12</SUP>θ. For the
  spread function we consider Lorentzians and Gaussians for which analytic
  expressions for the aureole can be written down. Lorentzians lead to
  divergence and normalization difficulties, and should not be used in
  scattered light determinations. Gaussian functions are more suitable.

---------------------------------------------------------
Title: Earthquake Waves and the Geomagnetic Dynamo
Authors: Mullan, Dermott J.
1973Sci...181..553M    Altcode:
  It is proposed that earthquake waves energize the geomagnetic
  dynamo. Fluid motions generated by earthquakes may have enough energy
  to be in equipartition with fields as large as 100 gauss. Seismic waves
  from meteoritic impacts with energies sufficient to reverse the field
  occur every 170,000 years.

---------------------------------------------------------
Title: On the Possibility of Constructing a Radiative Sunspot Model
    in Magnetohydrostatic Equilibrium
Authors: Mullan, D. J.
1973SoPh...30...75M    Altcode:
  It is currently believed that it is impossible to construct a
  radiative sunspot model in magnetohydrostatic equilibrium unless
  magnetic fields below the surface are excessively large (&gt; 100
  kG). This belief is based on results obtained using the mixing length
  theory of convection. We wish to point out that by using a different
  theory of convection, due to Öpik (1950), it is possible to compute
  a radiative sunspot model in which the field becomes no greater than
  9000 G. By applying two boundary conditions, (i) depth of spot equals
  depth of convection zone, (ii) magnetic field has zero gradient at
  the base of the spot, we show that a radiative spot has a unique
  effective temperature for a given Wilson depression, Δ. For Δ = 650
  km, we find T<SUB>e</SUB> = 3800K ; for Δ = 150 km, T<SUB>e</SUB> =
  3950K. According to our model, spots having T<SUB>e</SUB> cooler than
  these values should not exist.

---------------------------------------------------------
Title: Can Oscillations Grow in a Sunspot Umbra?
Authors: Mullan, D. J.; Yun, H. S.
1973SoPh...30...83M    Altcode:
  Umbral flashes and running penumbral waves have been attributed by
  Moore (1972) to overstable oscillations in the umbra. His numerical
  results were derived by inserting physical conditions at two particular
  depths beneath the umbral surface. Seven variables must be specified
  at each point. We have extended Moore's analysis to examine the
  depth-dependence of overstable oscillations in a recently computed
  umbral model. Electrical conductivity is evaluated taking full account
  of partial ionization and magnetic fields. In the surface layers,
  within 250 km of the top of the umbral convection zone, the conductivity
  is so low that Joule dissipation is more rapid than the growth rate
  of oscillations. In these layers, Moore's results are therefore not
  applicable. At greater depths, oscillations can grow and we agree
  with Moore that both umbral flashes and penumbral waves may be due
  to overstable oscillations. However, we suggest that both phenomena
  can arise at the same depth in the spot, and not in two layers, as
  Moore suggests.

---------------------------------------------------------
Title: Are Penumbral Filaments Convection Rolls?
Authors: Mullan, D. J.
1973A&A....24..103M    Altcode:
  Summary. The occurrence of strong magnetic fields in dark filaments
  in sunspot penumbrae is shown to be only marginally consistent with
  the hypothesis of penumbral convection rolls. Convection rolls are
  not permitted if the field in dark filaments exceeds that in bright
  filaments by more than 2 %. The upper limit to this excess may be as
  small as 0.8 %, if not in fact negative. Key words: sunspot penumbra -
  magnetic fields in filaments - convection rolls

---------------------------------------------------------
Title: Convection in A Stars: Suppressed in Magnetic Stars?
Authors: Mullan, D. J.
1973IrAJ...11...32M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Seven Color Photometry of Umbral Cores with the Bartol Coudé
    Telescope.
Authors: Mullan, D. J.; Wyller, A. A.
1973BAAS....5...20M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Transition from Shallow to Deep Convection Zones in Stars
Authors: Mullan, D. J.
1972ApL....12...13M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Thin Solar Convection Zone and Sunspots
Authors: Mullan, D. J.
1972NPhS..235...58M    Altcode: 1972Natur.235...58M
  THERE is a remarkable coincidence between the depth of a sunspot
  (1.05 × 10<SUP>4</SUP> km according to Hong Sik Yun<SUP>1</SUP>)
  and my recent determination<SUP>2</SUP> of the depth of the solar
  convection zone, namely 1.04 × 10<SUP>4</SUP> km.

---------------------------------------------------------
Title: New Variable Stars in the Large Magellanic Clouds
Authors: Andrews, A. D.; Mullan, D. J.
1971IrAJ...10..149A    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Sequences for Binocular Variables
Authors: Mullan, D. J.
1971JBAA...81..454M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Books Reviewed or Received: "Cosmic Gamma Rays" by
    F. W. Stecker
Authors: Mullan, D. J.
1971IrAJ...10..113M    Altcode: 1971IrAJ...1O..113M
  No abstract at ADS

---------------------------------------------------------
Title: Books Reviewed or Received: "Radio Astronomy and the Galactic
    System", edited by H. van Woerden
Authors: Mullan, D. J.
1971IrAJ...10..114M    Altcode: 1971IrAJ...1O..114M
  No abstract at ADS

---------------------------------------------------------
Title: The Space Between the Stars
Authors: Mullan, D. J.
1971IrAJ...10....1M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: News and Comments: Possible Identifications of Molecular
    Helium in White Dwarfs
Authors: Mullan, D. J.
1971IrAJ...10...25M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Effects of Rotation on Solar Convection: Cyclones in the
    Solar Atmosphere
Authors: Mullan, D. J.
1971IrAJ...10...12M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Book Review: "Stellar Physics" by Hong-Yee Chiu
Authors: Mullan, D. J.
1971IrAJ...10..151M    Altcode: 1971IrAJ...1O..151M
  No abstract at ADS

---------------------------------------------------------
Title: Cellular convection in model stellar envelopes
Authors: Mullan, D. J.
1971MNRAS.154..467M    Altcode:
  Model envelopes have been constructed using a theory of cellular
  convection due to Opik, in which turbulent heat exchange between
  rising and falling gas is allowed for by introducing an experimentally
  determined coefficient. Radiative heat losses are also included. A model
  of the solar convection zone is found to be only x io km deep, with a
  bottom temperature of x , and a gas pressure log Pg = . Supergranules
  are considered to be convection cells penetrating the entire convection
  zone. Temperature inhomogeneities in the upper convection zone exhibit
  a plateau in the region 0.5&lt;7 &lt; I 3. In models of main sequence
  stars, the maximum convective velocity is found to have a peak value
  ( km s-') at spectral type A6, with a rapid drop at earlier spectral
  types. Supergranule cells increase in size abruptly by a factor of
  almost a between spectral types Go and Ga. Metal-poor stars have lower
  convective velocities than metalrich stars in the deeper layers.

---------------------------------------------------------
Title: The structure of transverse hydromagnetic shocks in regions
    oflow ionization
Authors: Mullan, D. J.
1971MNRAS.153..145M    Altcode:
  The compression of a magnetic field by a shock in a predominantly
  neutral gas is discussed. By solving the fluid equations, a steady-state
  structure is determined for a one-dimensional shock front propagating
  through a partially ionized gas in a direction perpendicular to
  the field lines. Temperatures and velocities of ions, electrons,
  and atoms are calculated as a function of the spatial coordinate
  moving with the shock frame. When the degree of ionization is small,
  field compression occurs at the expense of the momentum carried by
  the neutral atoms. The neutral momentum is transferred indirectly to
  the field by way of the ions. To effect the transfer, many ion-atom
  collisions are required. Shock widths from several hundred to several
  times I0 ion- atom mean free paths are required. Within the broad
  profile, a narrow atom shock is imbedded near the hot end if the
  shock speed exceeds a critical value. Within the broad region of
  changing field, the transient momentum in the ions causes them to drift
  relative to the atoms, and to become hotter than the atoms. Shocks in
  interstellar clouds of predominantly neutral hydrogen are discussed
  in detail. Within such shocks, the ion temperature rises to several
  hundred degrees hotter than the atom temperature, and ions drift
  relative to atoms with speeds of the order of a few kilometres per
  second. Detection of these ion-atom differences may be possible in
  the case of weak shocks, for it is only in weak, broad shocks that
  radiation carries a significant fraction of the energy flux. In the
  weakest shock for which numerical results are available, the radiative
  flux amounts to about ao per cent of the convected flux. Suggested
  lines for observation of ion-atom differences are the ionized carbon
  line at I 6 microns and the neutral oxygen line at 147 microns. It
  is suggested that ion-atom velocity differences within shocks lead to
  efficient removal of the magnetic field from a contracting protostar,
  thereby permitting fragmentation into masses as small as one solar
  mass. Application of the results to a model which has been proposed
  for solar flares, and to conditions in laboratory experiments are noted.

---------------------------------------------------------
Title: Cellular convection in stellar envelopes.
Authors: Mullan, D. J.
1971IrAJ....9..310M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Cellular Convection in Stellar Envelopes
Authors: Mullan, D. J.
1970IrAJ....9..310M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Identification of Parkes Radio Sources on ADH plates
Authors: Mullan, D. J.
1970IrAJ....9..246M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: The Interstellar Medium as a Detector of Cosmic Rays
Authors: Mullan, D. J.
1970IrAJ....9..250M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Flares of red dwarf stars.
Authors: Gershberg, R. E.; Mullan, D. J.
1970frds.book.....G    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: The structure of hydromagnetic shocks in regions of very
    low ionization.
Authors: Mullan, D. J.
1969PhDT.......156M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: The Structure of Hydromagnetic Shocks in Regions of Very
    Low Ionization.
Authors: Mullan, Dermott Joseph
1969PhDT........10M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: First List of Emission Objects in the LMC
Authors: Lindsay, E. M.; Mullan, D. J.
1963IrAJ....6...51L    Altcode:
  No abstract at ADS