Author name code: unruh ADS astronomy entries on 2022-09-14 author:"Unruh, Yvonne" ------------------------------------------------------------------------ Title: Making the Most of Transmission Spectra in Light of Stellar Activity: Needs Identified by ExoPAG's Study Analysis Group 21 Authors: Rackham, Benjamin V.; Espinoza, Néstor; Berdyugina, Svetlana V.; Korhonen, Heidi; MacDonald, Ryan J.; Montet, Benjamin T.; Morris, Brett M.; Oshagh, Mahmoudreza; Shapiro, Alexander I.; Unruh, Yvonne C.; Quintana, Elisa V.; Zellem, Robert T.; SAG 21 Committee Bibcode: 2022BAAS...54e4404R Altcode: Transmission spectroscopy, a method for studying exoplanetary atmospheres by measuring the wavelength-dependent radius of a planet as it transits its star, relies on a precise understanding of the spectrum of the star being occulted. However, stars are not homogeneous, constant light sources but have temporally evolving photospheres and chromospheres with inhomogeneities like spots, faculae, and plages. Study Analysis Group 21 (SAG21) of NASA's Exoplanet Exploration Program Analysis Group (ExoPAG) was organized to study the effect of stellar photospheric heterogeneity on space-based transmission spectroscopy. This SAG brought together an interdisciplinary team of more than 100 scientists, with observers and theorists from the heliophysics, stellar astrophysics, planetary science, and exoplanetary atmosphere research communities, to study the current needs that can be addressed in this context to make the most of transit studies from NASA facilities like HST and JWST. Here we report on the main conclusions of this analysis, highlighting needs to be addressed and mitigation efforts underway. The analysis produced 14 findings, which fall into three Science Themes that encompass (1) how the Sun is used as our best laboratory to calibrate our understanding of stellar heterogeneities ("The Sun as the Stellar Benchmark"), (2) how stars other than the Sun extend our knowledge of heterogeneities ("Surface Heterogeneities of Other Stars"), and (3) how to incorporate information gathered for the Sun and other stars into transit studies ("Mapping Stellar Knowledge to Transit Studies"). Addressing the needs identified through this large community effort will ensure that we can optimally leverage space-based transmission spectra in light of stellar activity. Title: Energy deposition in Saturn's equatorial upper atmosphere Authors: Chadney, J. M.; Koskinen, T. T.; Hu, X.; Galand, M.; Lavvas, P.; Unruh, Y. C.; Serigano, J.; Hörst, S. M.; Yelle, R. V. Bibcode: 2022Icar..37214724C Altcode: 2021arXiv211008014C We construct Saturn equatorial neutral temperature and density profiles of H, H2, He, and CH4, between 10-12 and 1 bar using measurements from Cassini's Ion Neutral Mass Spectrometer (INMS) taken during the spacecraft's final plunge into Saturn's atmosphere on 15 September 2017, combined with previous deeper atmospheric measurements from the Cassini Composite InfraRed Spectrometer (CIRS) and from the UltraViolet Imaging Spectrograph (UVIS). These neutral profiles are fed into an energy deposition model employing soft X-ray and Extreme UltraViolet (EUV) solar fluxes at a range of spectral resolutions (Δλ = 4 × 10-3 nm to 1 nm) assembled from TIMED/SEE, from SOHO/SUMER, and from the Whole Heliosphere Interval (WHI) quiet Sun campaign. Our energy deposition model calculates ion production rate profiles through photo-ionisation and electron-impact ionisation processes, as well as rates of photo-dissociation of CH4. The ion reaction rate profiles we determine are important to obtain accurate ion density profiles, meanwhile methane photo-dissociation is key to initiate complex organic chemical processes. We assess the importance of spectral resolution in the energy deposition model by using a high-resolution H2 photo-absorption cross section, which has the effect of producing additional ionisation peaks near 800 km altitude. We find that these peaks are still formed when using low-resolution (Δλ = 1 nm) or mid-resolution (Δλ = 0 . 1 nm) solar spectra, as long as high-resolution cross sections are included in the model. Title: Final Report for SAG 21: The Effect of Stellar Contamination on Space-based Transmission Spectroscopy Authors: Rackham, Benjamin V.; Espinoza, Néstor; Berdyugina, Svetlana V.; Korhonen, Heidi; MacDonald, Ryan J.; Montet, Benjamin T.; Morris, Brett M.; Oshagh, Mahmoudreza; Shapiro, Alexander I.; Unruh, Yvonne C.; Quintana, Elisa V.; Zellem, Robert T.; Apai, Dániel; Barclay, Thomas; Barstow, Joanna K.; Bruno, Giovanni; Carone, Ludmila; Casewell, Sarah L.; Cegla, Heather M.; Criscuoli, Serena; Fischer, Catherine; Fournier, Damien; Giampapa, Mark S.; Giles, Helen; Iyer, Aishwarya; Kopp, Greg; Kostogryz, Nadiia M.; Krivova, Natalie; Mallonn, Matthias; McGruder, Chima; Molaverdikhani, Karan; Newton, Elisabeth R.; Panja, Mayukh; Peacock, Sarah; Reardon, Kevin; Roettenbacher, Rachael M.; Scandariato, Gaetano; Solanki, Sami; Stassun, Keivan G.; Steiner, Oskar; Stevenson, Kevin B.; Tregloan-Reed, Jeremy; Valio, Adriana; Wedemeyer, Sven; Welbanks, Luis; Yu, Jie; Alam, Munazza K.; Davenport, James R. A.; Deming, Drake; Dong, Chuanfei; Ducrot, Elsa; Fisher, Chloe; Gilbert, Emily; Kostov, Veselin; López-Morales, Mercedes; Line, Mike; Močnik, Teo; Mullally, Susan; Paudel, Rishi R.; Ribas, Ignasi; Valenti, Jeff A. Bibcode: 2022arXiv220109905R Altcode: Study Analysis Group 21 (SAG21) of the Exoplanet Exploration Program Analysis Group (ExoPAG) was organized to study the effect of stellar contamination on space-based transmission spectroscopy, a method for studying exoplanetary atmospheres by measuring the wavelength-dependent radius of a planet as it transits its star. Transmission spectroscopy relies on a precise understanding of the spectrum of the star being occulted. However, stars are not homogeneous, constant light sources but have temporally evolving photospheres and chromospheres with inhomogeneities like spots, faculae, and plages. This SAG has brought together an interdisciplinary team of more than 100 scientists, with observers and theorists from the heliophysics, stellar astrophysics, planetary science, and exoplanetary atmosphere research communities, to study the current needs that can be addressed in this context to make the most of transit studies from current NASA facilities like HST and JWST. The analysis produced 14 findings, which fall into three Science Themes encompassing (1) how the Sun is used as our best laboratory to calibrate our understanding of stellar heterogeneities ("The Sun as the Stellar Benchmark"), (2) how stars other than the Sun extend our knowledge of heterogeneities ("Surface Heterogeneities of Other Stars") and (3) how to incorporate information gathered for the Sun and other stars into transit studies ("Mapping Stellar Knowledge to Transit Studies"). Title: MPS-ATLAS: A fast all-in-one code for synthesising stellar spectra Authors: Witzke, V.; Shapiro, A. I.; Cernetic, M.; Tagirov, R. V.; Kostogryz, N. M.; Anusha, L. S.; Unruh, Y. C.; Solanki, S. K.; Kurucz, R. L. Bibcode: 2021A&A...653A..65W Altcode: 2021arXiv210513611W Context. Stellar spectral synthesis is essential for various applications, ranging from determining stellar parameters to comprehensive stellar variability calculations. New observational resources as well as advanced stellar atmosphere modelling, taking three dimensional effects from radiative magnetohydrodynamics calculations into account, require a more efficient radiative transfer.
Aims: For accurate, fast and flexible calculations of opacity distribution functions (ODFs), stellar atmospheres, and stellar spectra, we developed an efficient code building on the well-established ATLAS9 code. The new code also paves the way for easy and fast access to different elemental compositions in stellar calculations.
Methods: For the generation of ODF tables, we further developed the well-established DFSYNTHE code by implementing additional functionality and a speed-up by employing a parallel computation scheme. In addition, the line lists used can be changed from Kurucz's recent lists. In particular, we implemented the VALD3 line list.
Results: A new code, the Merged Parallelised Simplified ATLAS, is presented. It combines the efficient generation of ODF, atmosphere modelling, and spectral synthesis in local thermodynamic equilibrium, therefore being an all-in-one code. This all-in-one code provides more numerical functionality and is substantially faster compared to other available codes. The fully portable MPS-ATLAS code is validated against previous ATLAS9 calculations, the PHOENIX code calculations, and high-quality observations. Title: Forward modelling of Kepler-band variability due to faculae and spots Authors: Johnson, Luke J.; Norris, Charlotte M.; Unruh, Yvonne C.; Solanki, Sami K.; Krivova, Natalie; Witzke, Veronika; Shapiro, Alexander I. Bibcode: 2021MNRAS.504.4751J Altcode: 2021arXiv210411544J; 2021MNRAS.tmp.1190J Variability observed in photometric light curves of late-type stars (on time-scales longer than a day) is a dominant noise source in exoplanet surveys and results predominantly from surface manifestations of stellar magnetic activity, namely faculae and spots. The implementation of faculae in light-curve models is an open problem, with scaling typically based on spectra equivalent to hot stellar atmospheres or assuming a solar-derived facular contrast. We modelled rotational (single period) light curves of active G2, K0, M0, and M2 stars, with Sun-like surface distributions and realistic limb-dependent contrasts for faculae and spots. The sensitivity of light-curve variability to changes in model parameters such as stellar inclination, feature area coverage, spot temperature, facular region magnetic flux density, and active band latitudes is explored. For our light-curve modelling approach we used ACTRESS, a geometrically accurate model for stellar variability. ACTRESS generates two-sphere maps representing stellar surfaces and populates them with user-prescribed spot and facular region distributions. From this, light curves can be calculated at any inclination. Quiet star limb darkening and limb-dependent facular contrasts were derived from MURaM 3D magnetoconvection simulations using ATLAS9. 1D stellar atmosphere models were used for the spot contrasts. We applied ACTRESS in Monte Carlo simulations, calculating light-curve variability amplitudes in the Kepler band. We found that, for a given spectral type and stellar inclination, spot temperature and spot area coverage have the largest effect on variability of all simulation parameters. For a spot coverage of $1{{\ \rm per\ cent}}$, the typical variability of a solar-type star is around 2 parts per thousand. The presence of faculae clearly affects the mean brightness and light-curve shape, but has relatively little influence on the variability. Title: Simulating Variability due to Faculae and Spots on GKM Stars Authors: Johnson, Luke; Unruh, Yvonne; Norris, Charlotte; Solanki, Sami; Krivova, Natalie; Witzke, Veronika; Shapiro, Alexander Bibcode: 2020EPSC...14..844J Altcode: Stellar variability is a dominant noise source in exoplanet surveys and results largely from the presence of photospheric faculae and spots. The implementation of faculae in lightcurve models is an open problem, with scaling based on spectra equivalent to hot stellar atmospheres or assuming a solar-derived facular contrast. We model the lightcurves of active late-type stars as they rotate, using emergent intensity spectra calculated from 3D magnetoconvection simulations of G, K and M-type stellar atmosphere regions at different viewing angles to reproduce centre-to-limb brightness variations. We present mean expected variability levels for several cases and compare with solar and stellar observations. We also investigate the wavelength dependence of variability. Fig. 1: Example of our geometrically accurate lightcurve modelling approach. Top: normalised intensity maps of a limb darkened, solar-type star viewed in the \textit{Kepler} band at rotational phase 0.5 with stellar inclinations 90 deg (left) and 30 deg (right). At 90 deg, the star is viewed equator-on. Middle: Corresponding lightcurves calculated at inclinations 90 deg (black line) and 30 deg (red line). Bottom: HealPix map representing the active stellar surface, cosine-scaled in latitude and flattened in longitude to resemble a solar synoptic map. The quiet photosphere is displayed in orange, facular regions are bright yellow and spot regions are dark blue. The crosses represent the centres of the stellar discs in the top panel. Fig. 2: Example showing simulated lightcurves calculated at different wavelengths. Rotational lightcurves are on the left, transit lightcurves on the right. In the centre, one hemisphere of the simulated stellar surface is shown, with a quarter of the disc shown in each wavelength band. 'Giant' spots and facular regions are used in this example. The transit path is highlighted in grey. Title: Connecting measurements of solar and stellar brightness variations Authors: Nèmec, N. -E.; Işık, E.; Shapiro, A. I.; Solanki, S. K.; Krivova, N. A.; Unruh, Y. Bibcode: 2020A&A...638A..56N Altcode: 2020arXiv200406974N Context. A comparison of solar and stellar brightness variations is hampered by the difference in spectral passbands that are used in observations, and also by the possible difference in the inclination of the solar and stellar rotation axes from the line of sight.
Aims: We calculate the rotational variability of the Sun as it would be measured in passbands used for stellar observations. In particular, we consider the filter systems used by the CoRoT, Kepler, TESS, and Gaia space missions. We also quantify the effect of the inclination of the rotation axis on the solar rotational variability.
Methods: We employed the spectral and total irradiance reconstruction (SATIRE) model to calculate solar brightness variations in different filter systems as observed from the ecliptic plane. We then combined the simulations of the surface distribution of the magnetic features at different inclinations using a surface flux transport model with the SATIRE calculations to compute the dependence of the variability on the inclination.
Results: For an ecliptic-bound observer, the amplitude of the solar rotational variability, as observed in the total solar irradiance (TSI), is 0.68 mmag (averaged over solar cycles 21-24). We obtained corresponding amplitudes in the Kepler (0.74 mmag), CoRoT (0.73 mmag), TESS (0.62 mmag), Gaia G (0.74 mmag), Gaia GRP (0.62 mmag), and Gaia GBP (0.86 mmag) passbands. Decreasing the inclination of the rotation axis decreases the rotational variability. For a sample of randomly inclined stars, the variability is on average 15% lower in all filter systems we considered. This almost compensates for the difference in amplitudes of the variability in TSI and Kepler passbands, making the amplitudes derived from the TSI records an ideal representation of the solar rotational variability for comparison to Kepler stars with unknown inclinations.
Conclusions: The TSI appears to be a relatively good measure of solar variability for comparisons with stellar measurements in the CoRoT, Kepler, TESS Gaia G, and Gaia GRP filters. Whereas the correction factors can be used to convert the variability amplitude from solar measurements into the values expected for stellar missions, the inclination affects the shapes of the light curves so that a much more sophisticated correction than simple scaling is needed to obtain light curves out of the ecliptic for the Sun. Title: IGAPS: the merged IPHAS and UVEX optical surveys of the northern Galactic plane Authors: Monguió, M.; Greimel, R.; Drew, J. E.; Barentsen, G.; Groot, P. J.; Irwin, M. J.; Casares, J.; Gänsicke, B. T.; Carter, P. J.; Corral-Santana, J. M.; Gentile-Fusillo, N. P.; Greiss, S.; van Haaften, L. M.; Hollands, M.; Jones, D.; Kupfer, T.; Manser, C. J.; Murphy, D. N. A.; McLeod, A. F.; Oosting, T.; Parker, Q. A.; Pyrzas, S.; Rodríguez-Gil, P.; van Roestel, J.; Scaringi, S.; Schellart, P.; Toloza, O.; Vaduvescu, O.; van Spaandonk, L.; Verbeek, K.; Wright, N. J.; Eislöffel, J.; Fabregat, J.; Harris, A.; Morris, R. A. H.; Phillipps, S.; Raddi, R.; Sabin, L.; Unruh, Y.; Vink, J. S.; Wesson, R.; Cardwell, A.; de Burgos, A.; Cochrane, R. K.; Doostmohammadi, S.; Mocnik, T.; Stoev, H.; Suárez-Andrés, L.; Tudor, V.; Wilson, T. G.; Zegmott, T. J. Bibcode: 2020A&A...638A..18M Altcode: 2020arXiv200205157M The INT Galactic Plane Survey (IGAPS) is the merger of the optical photometric surveys, IPHAS and UVEX, based on data from the Isaac Newton Telescope (INT) obtained between 2003 and 2018. Here, we present the IGAPS point source catalogue. It contains 295.4 million rows providing photometry in the filters, i, r, narrow-band Hα, g, and URGO. The IGAPS footprint fills the Galactic coordinate range, |b| < 5° and 30° < ℓ < 215°. A uniform calibration, referred to as the Pan-STARRS system, is applied to g, r, and i, while the Hα calibration is linked to r and then is reconciled via field overlaps. The astrometry in all five bands has been recalculated in the reference frame of Gaia Data Release 2. Down to i ∼ 20 mag (Vega system), most stars are also detected in g, r, and Hα. As exposures in the r band were obtained in both the IPHAS and UVEX surveys, typically a few years apart, the catalogue includes two distinct r measures, rI and rU. The r 10σ limiting magnitude is approximately 21, with median seeing of 1.1 arcsec. Between approximately 13th and 19th mag in all bands, the photometry is internally reproducible to within 0.02 mag. Stars brighter than r = 19.5 mag are tested for narrow-band Hα excess signalling line emission, and for variation exceeding |rI - rU| = 0.2 mag. We find and flag 8292 candidate emission line stars and over 53 000 variables (both at > 5σ confidence).

The catalogue of 174 columns in total and full Tables D.1-D.4 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.frftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/638/A18 Title: VizieR Online Data Catalog: IGAPS. merged IPHAS and UVEX of northern Galactic plane (Monguio+, 2020) Authors: Monguio, M.; Greimel, R.; Drew, J. E.; Barentsen, G.; Groot, P. J.; Irwin, M. J.; Casares, J.; Gaensicke, B. T.; Carter, P. J.; Corral-Santana, J. M.; Gentile-Fusillo, N. P.; Greiss, S.; van Haaften, L. M.; Hollands, M.; Jones, D.; Kupfer, T.; Manser, C. J.; Murphy, D. N. A.; McLeod, A. F.; Oosting, T.; Parker, Q. A.; Pyrzas, S.; Rodriguez-Gil, P.; van Roestel, J.; Scaringi, S.; Schellart, P.; Toloza, O.; Vaduvescu, O.; van Spaandonk, L.; Verbeek, K.; Wright, N. J.; Eisloeel, J.; Fabregat, J.; Harris, A.; Morris, R. A. H.; Phillipps, S.; Raddi, R.; Sabin, L.; Unruh, Y.; S Vink, J.; Wesson, R.; Cardwell, A.; de Burgos, A.; Cochrane, R. K.; Doostmohammadi, S.; Mocnik, T.; Stoev, H.; Suarez-Andres, L.; Tudor, V.; Wilson, T. G.; Zegmott, T. J. Bibcode: 2020yCat.5165....0M Altcode: The INT Galactic Plane Survey (IGAPS) was formed from merging the IPHAS (Drew et al., 2005MNRAS.362..753D) and UVEX (Groot et al., 2009MNRAS.399..323G, Cat. J/MNRAS/399/323) surveys of the northern Galactic plane, based on data from the Isaac Newton Telescope (INT) obtained between 2003 and 2018. It is a catalogue of 174 columns and almost 300 million rows, spanning the r magnitude range from 12-13th mag down to 21st mag (10σ). The astrometry in all five photometric bands has been placed in the Gaia DR2 reference frame. Broadband g, r, and i have been uniformly calibrated using PanSTARRS data resting on that project's 'Ubercal' (Magnier et al. 2013ApJS..205...20M). We estimate the reproducibility of the photometry in these bands (and in Hα) to be in the region of 0.02mag at magnitudes brighter than 19th mag.

(1 data file). Title: Readdressing the UV solar variability with SATIRE-S: non-LTE effects Authors: Tagirov, R. V.; Shapiro, A. I.; Krivova, N. A.; Unruh, Y. C.; Yeo, K. L.; Solanki, S. K. Bibcode: 2019A&A...631A.178T Altcode: 2019arXiv190911736T Context. Solar spectral irradiance (SSI) variability is one of the key inputs to models of the Earth's climate. Understanding solar irradiance fluctuations also helps to place the Sun among other stars in terms of their brightness variability patterns and to set detectability limits for terrestrial exoplanets.
Aims: One of the most successful and widely used models of solar irradiance variability is Spectral And Total Irradiance REconstruction model (SATIRE-S). It uses spectra of the magnetic features and surrounding quiet Sun that are computed with the ATLAS9 spectral synthesis code under the assumption of local thermodynamic equilibrium (LTE). SATIRE-S has been at the forefront of solar variability modelling, but due to the limitations of the LTE approximation its output SSI has to be empirically corrected below 300 nm, which reduces the physical consistency of its results. This shortcoming is addressed in the present paper.
Methods: We replaced the ATLAS9 spectra of all atmospheric components in SATIRE-S with spectra that were calculated using the Non-LTE Spectral SYnthesis (NESSY) code. To compute the spectrum of the quiet Sun and faculae, we used the temperature and density stratification models of the FAL set.
Results: We computed non-LTE contrasts of spots and faculae and combined them with the corresponding fractional disc coverages, or filling factors, to calculate the total and spectral irradiance variability during solar cycle 24. The filling factors have been derived from solar full-disc magnetograms and continuum images recorded by the Helioseismic and Magnetic Imager on Solar Dynamics Observatory (SDO/HMI).
Conclusions: The non-LTE contrasts yield total and spectral solar irradiance variations that are in good agreement with empirically corrected LTE irradiance calculations. This shows that the empirical correction applied to the SATIRE-S total and spectral solar irradiance is consistent with results from non-LTE computations. Title: What do astronomers want from the STFC? Authors: Serjeant, Stephen; Bolton, James; Gandhi, Poshak; Helling, Christiane; Mazzali, Paolo; Stappers, Ben; Unruh, Yvonne; Verma, Aprajita Bibcode: 2019A&G....60b2.13S Altcode: Stephen Serjeant and the STFC's Astronomy Advisory Panel summarize community responses to its consultation on research priorities, undertaken in November 2018. Title: ACTReSS: ACTive Rotating Star Simulator Authors: Johnson, Luke Jonathan; Norris, Charlotte; Unruh, Yvonne; Solanki, Sami; Krivova, Natalie Bibcode: 2018csss.confE..58J Altcode: Variability of late-type stars on timescales of days or longer is largely due to magnetic surface features (starspots and faculae). We present ACTReSS, a software tool to calculate rotational lightcurves of stars. The model uses limb-dependent intensities derived from MURaM 3-D magneto-convection simulations (Beeck et al. 2014) for quiet stellar photospheres and bright active regions. This allows us to investigate the dependence of the flux variation on spectral type, inclination and wavelength. Title: Reconstructing Total Solar Irradiance with the help of MHD simulations Authors: Leng Yeo, Kok; Solanki, Sami; Noris, Charlotte; Unruh, Yvonne; Krivova, Natalie; Beeck, Benjamin Bibcode: 2018EGUGA..20.8166L Altcode: The variation in the solar irradiance is an important input into the climate system. Whereas it is commonly thought that solar irradiance variability is driven by the evolving surface magnetism, verifying this assumption has been more difficult. Making use of 3D MHD simulations of the solar atmosphere layers and state-of-the-art solar magnetograms from the Solar Dynamics Observatory, we present a model of total solar irradiance (TSI) that does not require any calibration of the modeled TSI by the measured TSI. I.e., the modeled irradiance variability is entirely independent of the observational record, except for the absolute level. The model replicates 95% of the observed variability between April 2010 and July 2016, leaving little scope for alternative drivers of solar irradiance variability, at least over the time scales examined (days to years). Title: Effect of stellar flares on the upper atmospheres of HD 189733b and HD 209458b Authors: Chadney, J. M.; Koskinen, T. T.; Galand, M.; Unruh, Y. C.; Sanz-Forcada, J. Bibcode: 2017A&A...608A..75C Altcode: 2017arXiv171008365C Stellar flares are a frequent occurrence on young low-mass stars around which many detected exoplanets orbit. Flares are energetic, impulsive events, and their impact on exoplanetary atmospheres needs to be taken into account when interpreting transit observations. We have developed a model to describe the upper atmosphere of extrasolar giant planets (EGPs) orbiting flaring stars. The model simulates thermal escape from the upper atmospheres of close-in EGPs. Ionisation by solar radiation and electron impact is included and photo-chemical and diffusive transport processes are simulated. This model is used to study the effect of stellar flares from the solar-like G star HD 209458 and the young K star HD 189733 on their respective planets, HD 209458b and HD 189733b. The Sun is used as a proxy for HD 209458, and ɛ Eridani, as a proxy for HD 189733. A hypothetical HD 209458b-like planet orbiting the very active M star AU Microscopii is also simulated. We find that the neutral upper atmosphere of EGPs is not significantly affected by typical flares on HD 209458 and HD 189733. Therefore, stellar flares alone would not cause large enough changes in planetary mass loss to explain the variations in HD 189733b transit depth seen in previous studies, although we show that it may be possible that an extreme stellar proton event could result in the required mass loss. Our simulations do however reveal an enhancement in electron number density in the ionosphere of these planets, the peak of which is located in the layer where stellar X-rays are absorbed. Electron densities are found to reach 2.2 to 3.5 times pre-flare levels and enhanced electron densities last from about 3 to 10 h after the onset of the flare, depending on the composition of the ionospheric layer. The strength of the flare and the width of its spectral energy distribution affect the range of altitudes in the ionosphere that see enhancements in ionisation. A large broadband continuum component in the XUV portion of the flaring spectrum in very young flare stars, such as AU Mic, results in a broad range of altitudes affected in planets orbiting this star. Indeed, as well as the X-ray absorption layer, the layer in which EUV photons are absorbed is also strongly enhanced. Title: Spectral variability of photospheric radiation due to faculae. I. The Sun and Sun-like stars Authors: Norris, Charlotte M.; Beeck, Benjamin; Unruh, Yvonne C.; Solanki, Sami K.; Krivova, Natalie A.; Yeo, Kok Leng Bibcode: 2017A&A...605A..45N Altcode: 2017arXiv170504455N Context. Stellar spectral variability on timescales of a day and longer, arising from magnetic surface features such as dark spots and bright faculae, is an important noise source when characterising extra-solar planets. Current 1D models of faculae do not capture the geometric properties and fail to reproduce observed solar facular contrasts. Magnetoconvection simulations provide facular contrasts accounting for geometry.
Aims: We calculate facular contrast spectra from magnetoconvection models of the solar photosphere with a view to improve (a) future parameter determinations for planets with early G type host stars and (b) reconstructions of solar spectral variability.
Methods: Regions of a solar twin (G2, log g = 4.44) atmosphere with a range of initial average vertical magnetic fields (100 to 500 G) were simulated using a 3D radiation-magnetohydrodynamics code, MURaM, and synthetic intensity spectra were calculated from the ultraviolet (149.5 nm) to the far infrared (160 000 nm) with the ATLAS9 radiative transfer code. Nine viewing angles were investigated to account for facular positions across most of the stellar disc.
Results: Contrasts of the radiation from simulation boxes with different levels of magnetic flux relative to an atmosphere with no magnetic field are a complicated function of position, wavelength and magnetic field strength that is not reproduced by 1D facular models. Generally, contrasts increase towards the limb, but at UV wavelengths a saturation and decrease are observed close to the limb. Contrasts also increase strongly from the visible to the UV; there is a rich spectral dependence, with marked peaks in molecular bands and strong spectral lines. At disc centre, a complex relationship with magnetic field was found and areas of strong magnetic field can appear either dark or bright, depending on wavelength. Spectra calculated for a wide variety of magnetic fluxes will also serve to improve total and spectral solar irradiance reconstructions. Title: Solar Irradiance Variability is Caused by the Magnetic Activity on the Solar Surface Authors: Yeo, K. L.; Solanki, S. K.; Norris, C. M.; Beeck, B.; Unruh, Y. C.; Krivova, N. A. Bibcode: 2017PhRvL.119i1102Y Altcode: 2017arXiv170900920Y The variation in the radiative output of the Sun, described in terms of solar irradiance, is important to climatology. A common assumption is that solar irradiance variability is driven by its surface magnetism. Verifying this assumption has, however, been hampered by the fact that models of solar irradiance variability based on solar surface magnetism have to be calibrated to observed variability. Making use of realistic three-dimensional magnetohydrodynamic simulations of the solar atmosphere and state-of-the-art solar magnetograms from the Solar Dynamics Observatory, we present a model of total solar irradiance (TSI) that does not require any such calibration. In doing so, the modeled irradiance variability is entirely independent of the observational record. (The absolute level is calibrated to the TSI record from the Total Irradiance Monitor.) The model replicates 95% of the observed variability between April 2010 and July 2016, leaving little scope for alternative drivers of solar irradiance variability at least over the time scales examined (days to years). Title: VizieR Online Data Catalog: New OB star candidates in Carina Arm (Mohr-Smith+, 2015) Authors: Mohr-Smith, M.; Drew, J. E.; Barentsen, G.; Wright, N. J.; Napiwotzki, R.; Corradi, R. L. M.; Eisloffel, J.; Groot, P.; Kalari, V.; Parker, Q. A.; Raddi, R.; Sale, S. E.; Unruh, Y. C.; Vink, J. S.; Wesson, R. Bibcode: 2017yCat..74503855M Altcode: We make use of the photometry from two VPHAS+ fields, numbered 1678 and 1679, that are, respectively, centred on RA=10:18:10.91, DE=-58:03:52.3 (J2000) and on RA=10:25:27.27, DE=-58:03:52.3 (J2000). These were observed in succession in the u, g and r filters on the night of 2012 January 22. The red filter data in Hα, r and i were obtained on 2012 April 29.

(2 data files). Title: The VST Photometric Halpha Survey of the Southern Galactic Plane and Bulge (VPHAS+). Second VPHAS data release (DR2). Authors: Drew, J. E.; Gonzales-Solares, E.; Greimel, R.; Irwin, M. J.; Kupcu Yoldas, A.; Lewis, J.; Barentsen, G.; Eisloffel, J.; Farnhill, H. J.; Martin, W. E.; Walsh, J. R.; Walton, N. A.; Mohr-Smith, M.; Raddi, R.; Sale, S. E.; Wright, N. J.; Groot, P.; Barlow, M. J.; Corradi, R. L. M.; Drake, J. J.; Fabregat, J.; Frew, D. J.; Gansicke, B. T.; Knigge, C.; Mampaso, A.; Morris, R. A. H.; Naylor, T.; Parker, Q. A.; Phillipps, S.; Ruhland, C.; Steeghs, D.; Unruh, Y. C.; Vink, J. S.; Wesson, R.; Zijlstra, A. A. Bibcode: 2016yCat.2341....0D Altcode: No abstract at ADS Title: Modelling the Spectral Contrasts of Stellar Faculae. Authors: Norris, Charlotte M.; Beeck, Benjamin; Unruh, Yvonne; Solanki, Sami; Yeo, Kok Leng; Krivova, Natalie Bibcode: 2016csss.confE..63N Altcode: Facular contrasts are an important parameter in modelling stellar variability and exoplanet transits. The ultimate goal of this work will be to model the contrasts of faculae for different spectral types and thus improve the modelling of solar and stellar photospheric variability. This is done by using a radiative transfer algorithm (ATLAS9) on magneto-convection simulations. Starting with solar twins, we derive facular contrasts as a function of limb angle and discuss their wavelength dependence. Title: Reconstruction of spectral solar irradiance since 1700 from simulated magnetograms Authors: Dasi-Espuig, M.; Jiang, J.; Krivova, N. A.; Solanki, S. K.; Unruh, Y. C.; Yeo, K. L. Bibcode: 2016A&A...590A..63D Altcode: 2016arXiv160502039D
Aims: We present a reconstruction of the spectral solar irradiance since 1700 using the SATIRE-T2 (Spectral And Total Irradiance REconstructions for the Telescope era version 2) model. This model uses as input magnetograms simulated with a surface flux transport model fed with semi-synthetic records of emerging sunspot groups.
Methods: The record of sunspot group areas and positions from the Royal Greenwich Observatory (RGO) is only available since 1874. We used statistical relationships between the properties of sunspot group emergence, such as the latitude, area, and tilt angle, and the sunspot cycle strength and phase to produce semi-synthetic sunspot group records starting in the year 1700. The semi-synthetic records are fed into a surface flux transport model to obtain daily simulated magnetograms that map the distribution of the magnetic flux in active regions (sunspots and faculae) and their decay products on the solar surface. The magnetic flux emerging in ephemeral regions is accounted for separately based on the concept of extended cycles whose length and amplitude are linked to those of the sunspot cycles through the sunspot number. The magnetic flux in each surface component (sunspots, faculae and network, and ephemeral regions) was used to compute the spectral and total solar irradiance (TSI) between the years 1700 and 2009. This reconstruction is aimed at timescales of months or longer although the model returns daily values.
Results: We found that SATIRE-T2, besides reproducing other relevant observations such as the total magnetic flux, reconstructs the TSI on timescales of months or longer in good agreement with the PMOD composite of observations, as well as with the reconstruction starting in 1878 based on the RGO-SOON data. The model predicts an increase in the TSI of 1.2+0.2-0.3 Wm-2 between 1700 and the present. The spectral irradiance reconstruction is in good agreement with the UARS/SUSIM measurements as well as the Lyman-α composite.

The complete total and spectral (115 nm-160 μm) irradiance reconstructions since 1700 will be available from http://www2.mps.mpg.de/projects/sun-climate/data.html Title: The Sun as a planet-host star: proxies from SDO images for HARPS radial-velocity variations Authors: Haywood, R. D.; Collier Cameron, A.; Unruh, Y. C.; Lovis, C.; Lanza, A. F.; Llama, J.; Deleuil, M.; Fares, R.; Gillon, M.; Moutou, C.; Pepe, F.; Pollacco, D.; Queloz, D.; Ségransan, D. Bibcode: 2016MNRAS.457.3637H Altcode: 2016arXiv160105651H The Sun is the only star whose surface can be directly resolved at high resolution, and therefore constitutes an excellent test case to explore the physical origin of stellar radial-velocity (RV) variability. We present HARPS observations of sunlight scattered off the bright asteroid 4/Vesta, from which we deduced the Sun's activity-driven RV variations. In parallel, the Helioseismic and Magnetic Imager instrument on board the Solar Dynamics Observatory provided us with simultaneous high spatial resolution magnetograms, Dopplergrams and continuum images of the Sun in the Fe I 6173 Å line. We determine the RV modulation arising from the suppression of granular blueshift in magnetized regions and the flux imbalance induced by dark spots and bright faculae. The rms velocity amplitudes of these contributions are 2.40 and 0.41 m s-1, respectively, which confirms that the inhibition of convection is the dominant source of activity-induced RV variations at play, in accordance with previous studies. We find the Doppler imbalances of spot and plage regions to be only weakly anticorrelated. Light curves can thus only give incomplete predictions of convective blueshift suppression. We must instead seek proxies that track the plage coverage on the visible stellar hemisphere directly. The chromospheric flux index R^' }_{HK} derived from the HARPS spectra performs poorly in this respect, possibly because of the differences in limb brightening/darkening in the chromosphere and photosphere. We also find that the activity-driven RV variations of the Sun are strongly correlated with its full-disc magnetic flux density, which may become a useful proxy for activity-related RV noise. Title: VizieR Online Data Catalog: Lagoon Nebula M8 T tauri accretion rates (Kalari+, 2015) Authors: Kalari, V. M.; Vink, J. S.; Drew, J. E.; Barentsen, G.; Drake, J. J.; Eisloffel, J.; Martin, E. L.; Parker, Q. A.; Unruh, Y. C.; Walton, N. A.; Wright, N. J. Bibcode: 2016yCat..74531026K Altcode: VPHAS+ imaging is obtained by the OmegaCAM CCD imager mounted on the 2.6m VLT Survey Telescope (VST) on Cerro Paranal, Chile. The imager captures a 1° square field of view at a resolution of 0.21arcsec/pix. Each pointing is supplemented by at least one offset exposure to minimize CCD gaps. Imaging is carried out through broad-band ugri filters and a purpose-built Hα filter. The central wavelength and bandpass of the Hα filter are 6588 and 107Å, respectively. Exposure times are 150, 30, 25, 25, and 120s, respectively. VPHAS+ reaches a 5σ depth at Hα=20.5-21.0mag and g=22.2-22.7mag. Practical constraints have meant that the blue (ug) and red (riHα) observations are carried out separately. An additional r observation is carried out with every blue observation to serve as a linking reference.

(2 data files). Title: EUV-driven ionospheres and electron transport on extrasolar giant planets orbiting active stars Authors: Chadney, J. M.; Galand, M.; Koskinen, T. T.; Miller, S.; Sanz-Forcada, J.; Unruh, Y. C.; Yelle, R. V. Bibcode: 2016A&A...587A..87C Altcode: 2016arXiv160103216C The composition and structure of the upper atmospheres of extrasolar giant planets (EGPs) are affected by the high-energy spectrum of their host stars from soft X-rays to the extreme ultraviolet (EUV). This emission depends on the activity level of the star, which is primarily determined by its age. In this study, we focus upon EGPs orbiting K- and M-dwarf stars of different ages - ɛ Eridani, AD Leonis, AU Microscopii - and the Sun. X-ray and EUV (XUV) spectra for these stars are constructed using a coronal model. These spectra are used to drive both a thermospheric model and an ionospheric model, providing densities of neutral and ion species. Ionisation - as a result of stellar radiation deposition - is included through photo-ionisation and electron-impact processes. The former is calculated by solving the Lambert-Beer law, while the latter is calculated from a supra-thermal electron transport model. We find that EGP ionospheres at all orbital distances considered (0.1-1 AU) and around all stars selected are dominated by the long-lived H+ ion. In addition, planets with upper atmospheres where H2 is not substantially dissociated (at large orbital distances) have a layer in which H3+ is the major ion at the base of the ionosphere. For fast-rotating planets, densities of short-lived H3+ undergo significant diurnal variations, with the maximum value being driven by the stellar X-ray flux. In contrast, densities of longer-lived H+ show very little day/night variability and the magnitude is driven by the level of stellar EUV flux. The H3+ peak in EGPs with upper atmospheres where H2 is dissociated (orbiting close to their star) under strong stellar illumination is pushed to altitudes below the homopause, where this ion is likely to be destroyed through reactions with heavy species (e.g. hydrocarbons, water). The inclusion of secondary ionisation processes produces significantly enhanced ion and electron densities at altitudes below the main EUV ionisation peak, as compared to models that do not include electron-impact ionisation. We estimate infrared emissions from H3+, and while, in an H/H2/He atmosphere, these are larger from planets orbiting close to more active stars, they still appear too low to be detected with current observatories. Title: Classical T Tauri stars with VPHAS+ - I. H α and u-band accretion rates in the Lagoon Nebula M8 Authors: Kalari, V. M.; Vink, J. S.; Drew, J. E.; Barentsen, G.; Drake, J. J.; Eislöffel, J.; Martín, E. L.; Parker, Q. A.; Unruh, Y. C.; Walton, N. A.; Wright, N. J. Bibcode: 2015MNRAS.453.1026K Altcode: 2015arXiv150706786K We estimate the accretion rates of 235 Classical T Tauri star (CTTS) candidates in the Lagoon Nebula using ugri H α photometry from the VST Photometric H α survey+. Our sample consists of stars displaying H α excess, the intensity of which is used to derive accretion rates. For a subset of 87 stars, the intensity of the u-band excess is also used to estimate accretion rates. We find the mean variation in accretion rates measured using H α and u-band intensities to be ∼0.17 dex, agreeing with previous estimates (0.04-0.4 dex) but for a much larger sample. The spatial distribution of CTTS align with the location of protostars and molecular gas suggesting that they retain an imprint of the natal gas fragmentation process. Strong accretors are concentrated spatially, while weak accretors are more distributed. Our results do not support the sequential star-forming processes suggested in the literature. Title: Modelling the ionosphere of gas-giant exoplanets irradiated by low-mass stars Authors: Chadney, J.; Galand, M.; Unruh, Y.; Koskinen, T.; Sanz-Forcada, J. Bibcode: 2015EPSC...10..307C Altcode: The composition and structure of the upper atmosphere of Extrasolar Giant Planets (EGPs) are affected by the high-energy spectrum of the host star from soft X-rays to Extreme UltraViolet (EUV) (0.1-10 nm). This emission depends on the activity level of the star, which is primarily determined by its age [1]. In this study, we focus upon EGPs orbiting K- and M-dwarf stars of different ages. XUV spectra for these stars are constructed using a coronal model [2]. These spectra are used to drive both a thermospheric [3] and an ionospheric model, providing densities of neutral and ion species. Ionisation is included through photo-ionisation and electronimpact processes. The former is calculated by solving the Lambert-Beer law, while the latter is calculated from a supra-thermal electron transport model [4]. Planets orbiting far from the star are found to undergo Jeans escape, whereas close-orbiting planets undergo hydrodynamic escape. The critical orbital distance of transition between the two regimes is dependent on the level of stellar activity. We also find that EGP ionospheres at all orbital distances considered (0.1-1 AU) and around all stars selected (eps Eri, AD Leo, AU Mic) are dominated by the long-lived H+ ion. In addition, planets in the Jeans escape regime also have a layer in which H3 + is the major ion at the base of the ionosphere. For fast-rotating planets, densities of short-lived H3 + undergo significant diurnal variations, their peak value being determined by the stellar X-ray flux. In contrast, densities of longer-lived H+ show very little day/night variability and their value is determined by the level of stellar EUV flux. The H3 + peak in EGPs in the hydrodynamic escape regime under strong stellar illumination is pushed to altitudes below the homopause, where this ion is likely to be destroyed through reactions with heavy species (e.g., hydrocarbons, water). Infrared emissions from H3 + shall also be discussed, as well as the impact of stellar variability. Title: UV solar irradiance in observations and the NRLSSI and SATIRE-S models Authors: Yeo, K. L.; Ball, W. T.; Krivova, N. A.; Solanki, S. K.; Unruh, Y. C.; Morrill, J. Bibcode: 2015JGRA..120.6055Y Altcode: 2015arXiv150701224Y Total solar irradiance and UV spectral solar irradiance has been monitored since 1978 through a succession of space missions. This is accompanied by the development of models aimed at replicating solar irradiance by relating the variability to solar magnetic activity. The Naval Research Laboratory Solar Spectral Irradiance (NRLSSI) and Spectral And Total Irradiance REconstruction for the Satellite era (SATIRE-S) models provide the most comprehensive reconstructions of total and spectral solar irradiance over the period of satellite observation currently available. There is persistent controversy between the various measurements and models in terms of the wavelength dependence of the variation over the solar cycle, with repercussions on our understanding of the influence of UV solar irradiance variability on the stratosphere. We review the measurement and modeling of UV solar irradiance variability over the period of satellite observation. The SATIRE-S reconstruction is consistent with spectral solar irradiance observations where they are reliable. It is also supported by an independent, empirical reconstruction of UV spectral solar irradiance based on Upper Atmosphere Research Satellite/Solar Ultraviolet Spectral Irradiance Monitor measurements from an earlier study. The weaker solar cycle variability produced by NRLSSI between 300 and 400 nm is not evident in any available record. We show that although the method employed to construct NRLSSI is principally sound, reconstructed solar cycle variability is detrimentally affected by the uncertainty in the SSI observations it draws upon in the derivation. Based on our findings, we recommend, when choosing between the two models, the use of SATIRE-S for climate studies. Title: New OB star candidates in the Carina Arm around Westerlund 2 from VPHAS+ Authors: Mohr-Smith, M.; Drew, J. E.; Barentsen, G.; Wright, N. J.; Napiwotzki, R.; Corradi, R. L. M.; Eislöffel, J.; Groot, P.; Kalari, V.; Parker, Q. A.; Raddi, R.; Sale, S. E.; Unruh, Y. C.; Vink, J. S.; Wesson, R. Bibcode: 2015MNRAS.450.3855M Altcode: 2015arXiv150404342M O and early B stars are at the apex of galactic ecology, but in the Milky Way, only a minority of them may yet have been identified. We present the results of a pilot study to select and parametrize OB star candidates in the Southern Galactic plane, down to a limiting magnitude of g = 20. A 2 deg2 field capturing the Carina Arm around the young massive star cluster, Westerlund 2, is examined. The confirmed OB stars in this cluster are used to validate our identification method, based on selection from the (u - g, g - r) diagram for the region. Our Markov Chain Monte Carlo fitting method combines VPHAS+ u, g, r, i with published J, H, K photometry in order to derive posterior probability distributions of the stellar parameters log (Teff) and distance modulus, together with the reddening parameters A0 and RV. The stellar parameters are sufficient to confirm OB status while the reddening parameters are determined to a precision of σ(A0) ∼ 0.09 and σ(RV) ∼ 0.08. There are 489 objects that fit well as new OB candidates, earlier than ∼B2. This total includes 74 probable massive O stars, 5 likely blue supergiants and 32 reddened subdwarfs. This increases the number of previously known and candidate OB stars in the region by nearly a factor of 10. Most of the new objects are likely to be at distances between 3 and 6 kpc. We have confirmed the results of previous studies that, at these longer distances, these sight lines require non-standard reddening laws with 3.5 < RV < 4. Title: VizieR Online Data Catalog: VPHAS+ survey synthetic colours (Drew+, 2014) Authors: Drew, J. E.; Gonzalez-Solares, E.; Greimel, R.; Irwin, M. J.; Kupcu Yoldas, A.; Lewis, J.; Barentsen, G.; Eisloffel, J.; Farnhill, H. J.; Martin, W. E.; Walsh, J. R.; Walton, N. A.; Mohr-Smith, M.; Raddi, R.; Sale, S. E.; Wright, N. J.; Groot, P.; Barlow, M. J.; Corradi, R. L. M.; Drake, J. J.; Fabregat, J.; Frew, D. J.; Gansicke, B. T.; Knigge, C.; Mampaso, A.; Morris, R. A. H.; Naylor, T.; Parker, Q. A.; Phillipps, S.; Ruhland, C.; Steeghs, D.; Unruh, Y. C.; Vink, J. S.; Wesson, R.; Zijlstra, A. A. Bibcode: 2015yCat..74402036D Altcode: Synthetic colours for main sequence stars, computed as described in Section 4 from model atmospheres, are here tabulated in full for three representative reddening laws (RV = 2.5, 3.1 and 3.8) and a range of reddenings (A0 = 0, 2, 4, 6, 8, 10). The form of the reddening laws used is due to Fitzpatrick & Massa (2007ApJ...663..320F, Cat. J/ApJ/663/320). When using the blue-filter tables, it should be borne in mind that beyond g-r~3, the red leak in the u filter signif- icantly alters u-g. In this domain we expect the synthetic colours to progressively become less reliable as they increas- ingly depend on hard-to-measure very low levels of red trans- mission. Objects that appear to have these extreme, peculiar colours are likely to be reddened red giants or supergiants, since reddened K-M main sequence stars are too faint to be detected in VPHAS+ exposures. Beyond g-r~3.5 these table entries are italicised. Two further tables of synthetic colours are included for K-M giants that have been computed using P98 library spectra. Data are provided for the RV=3.1 mean Galactic law only, for the limited purposes of (a) giving an impres- sion of how these luminous red objects may contaminate (u-g, g-r) diagrams at redder (g-r) through u red leak (b) enabling comparisons with the M-giant spur commonly seen in (r-Hα, r-i) colour-colour diagrams.

(8 data files). Title: XUV-driven mass loss from extrasolar giant planets orbiting active stars Authors: Chadney, J. M.; Galand, M.; Unruh, Y. C.; Koskinen, T. T.; Sanz-Forcada, J. Bibcode: 2015Icar..250..357C Altcode: 2014arXiv1412.3380C Upper atmospheres of Hot Jupiters are subject to extreme radiation conditions that can result in rapid atmospheric escape. The composition and structure of the upper atmospheres of these planets are affected by the high-energy spectrum of the host star. This emission depends on stellar type and age, which are thus important factors in understanding the behaviour of exoplanetary atmospheres. In this study, we focus on Extrasolar Giant Planets (EPGs) orbiting K and M dwarf stars. XUV spectra for three different stars - ɛ Eridani, AD Leonis and AU Microscopii - are constructed using a coronal model. Neutral density and temperature profiles in the upper atmosphere of hypothetical EGPs orbiting these stars are then obtained from a fluid model, incorporating atmospheric chemistry and taking atmospheric escape into account. We find that a simple scaling based solely on the host star's X-ray emission gives large errors in mass loss rates from planetary atmospheres and so we have derived a new method to scale the EUV regions of the solar spectrum based upon stellar X-ray emission. This new method produces an outcome in terms of the planet's neutral upper atmosphere very similar to that obtained using a detailed coronal model of the host star. Our results indicate that in planets subjected to radiation from active stars, the transition from Jeans escape to a regime of hydrodynamic escape at the top of the atmosphere occurs at larger orbital distances than for planets around low activity stars (such as the Sun). Title: The second data release of the INT Photometric Hα Survey of the Northern Galactic Plane (IPHAS DR2) Authors: Barentsen, Geert; Farnhill, H. J.; Drew, J. E.; González-Solares, E. A.; Greimel, R.; Irwin, M. J.; Miszalski, B.; Ruhland, C.; Groot, P.; Mampaso, A.; Sale, S. E.; Henden, A. A.; Aungwerojwit, A.; Barlow, M. J.; Carter, P. J.; Corradi, R. L. M.; Drake, J. J.; Eislöffel, J.; Fabregat, J.; Gänsicke, B. T.; Gentile Fusillo, N. P.; Greiss, S.; Hales, A. S.; Hodgkin, S.; Huckvale, L.; Irwin, J.; King, R.; Knigge, C.; Kupfer, T.; Lagadec, E.; Lennon, D. J.; Lewis, J. R.; Mohr-Smith, M.; Morris, R. A. H.; Naylor, T.; Parker, Q. A.; Phillipps, S.; Pyrzas, S.; Raddi, R.; Roelofs, G. H. A.; Rodríguez-Gil, P.; Sabin, L.; Scaringi, S.; Steeghs, D.; Suso, J.; Tata, R.; Unruh, Y. C.; van Roestel, J.; Viironen, K.; Vink, J. S.; Walton, N. A.; Wright, N. J.; Zijlstra, A. A. Bibcode: 2014MNRAS.444.3230B Altcode: 2014arXiv1406.4862B The INT/WFC Photometric Hα Survey of the Northern Galactic Plane (IPHAS) is a 1800 deg2 imaging survey covering Galactic latitudes |b| < 5° and longitudes ℓ = 30°-215° in the r, i, and Hα filters using the Wide Field Camera (WFC) on the 2.5-m Isaac Newton Telescope (INT) in La Palma. We present the first quality-controlled and globally calibrated source catalogue derived from the survey, providing single-epoch photometry for 219 million unique sources across 92 per cent of the footprint. The observations were carried out between 2003 and 2012 at a median seeing of 1.1 arcsec (sampled at 0.33 arcsec pixel-1) and to a mean 5σ depth of 21.2 (r), 20.0 (i), and 20.3 (Hα) in the Vega magnitude system. We explain the data reduction and quality control procedures, describe and test the global re-calibration, and detail the construction of the new catalogue. We show that the new calibration is accurate to 0.03 mag (root mean square) and recommend a series of quality criteria to select accurate data from the catalogue. Finally, we demonstrate the ability of the catalogue's unique (r - Hα, r - i) diagram to (i) characterize stellar populations and extinction regimes towards different Galactic sightlines and (ii) select and quantify Hα emission-line objects. IPHAS is the first survey to offer comprehensive CCD photometry of point sources across the Galactic plane at visible wavelengths, providing the much-needed counterpart to recent infrared surveys. Title: A New SATIRE-S Spectral Solar Irradiance Reconstruction for Solar Cycles 21-23 and Its Implications for Stratospheric Ozone* Authors: Ball, William T.; Krivova, Natalie A.; Unruh, Yvonne C.; Haigh, Joanna D.; Solanki, Sami K. Bibcode: 2014JAtS...71.4086B Altcode: 2014arXiv1408.0365B We present a revised and extended total and spectral solar irradiance (SSI) reconstruction, which includes a wavelength-dependent uncertainty estimate, spanning the last three solar cycles using the SATIRE-S model. The SSI reconstruction covers wavelengths between 115 and 160,000 nm and all dates between August 1974 and October 2009. This represents the first full-wavelength SATIRE-S reconstruction to cover the last three solar cycles without data gaps and with an uncertainty estimate. SATIRE-S is compared with the NRLSSI model and SORCE/SOLSTICE ultraviolet (UV) observations. SATIRE-S displays similar cycle behaviour to NRLSSI for wavelengths below 242 nm and almost twice the variability between 242 and 310 nm. During the decline of last solar cycle, between 2003 and 2008, SSI from SORCE/SOLSTICE version 12 and 10 typically displays more than three times the variability of SATIRE-S between 200 and 300 nm. All three datasets are used to model changes in stratospheric ozone within a 2D atmospheric model for a decline from high solar activity to solar minimum. The different flux changes result in different modelled ozone trends. Using NRLSSI leads to a decline in mesospheric ozone, while SATIRE-S and SORCE/SOLSTICE result in an increase. Recent publications have highlighted increases in mesospheric ozone when considering version 10 SORCE/SOLSTICE irradiances. The recalibrated SORCE/SOLSTICE version 12 irradiances result in a much smaller mesospheric ozone response than when using version 10 and now similar in magnitude to SATIRE-S. This shows that current knowledge of variations in spectral irradiance is not sufficient to warrant robust conclusions concerning the impact of solar variability on the atmosphere and climate. Title: Variability of Sun-like stars: reproducing observed photometric trends Authors: Shapiro, A. I.; Solanki, S. K.; Krivova, N. A.; Schmutz, W. K.; Ball, W. T.; Knaack, R.; Rozanov, E. V.; Unruh, Y. C. Bibcode: 2014A&A...569A..38S Altcode: 2014arXiv1406.2383S Context. The Sun and stars with low magnetic activity levels become photometrically brighter when their activity increases. Magnetically more active stars display the opposite behavior and become fainter when their activity increases.
Aims: We reproduce the observed photometric trends in stellar variations with a model thattreats stars as hypothetical suns with coverage by magnetic features different from that of the Sun.
Methods: The model attributes the variability of stellar spectra to the imbalance between the contributions from different components of the solar atmosphere, such as dark starspots and bright faculae. A stellar spectrum is calculated from spectra of the individual components by weighting them with corresponding disk-area coverages. The latter are obtained by extrapolating the solar dependences of spot and facular disk-area coverages on chromospheric activity to stars with different levels of mean chromospheric activity.
Results: We find that the contribution by starspots to the variability increases faster with chromospheric activity than the facular contribution. This causes the transition from faculae-dominated variability and direct activity-brightness correlation to spot-dominated variability and inverse activity-brightness correlation with increasing chromospheric activity level. We show that the regime of the variability also depends on the angle between the stellar rotation axis and the line-of-sight and on the latitudinal distribution of active regions on the stellar surface. Our model can be used as a tool for extrapolating the observed photometric variability of the Sun to Sun-like stars at different activity levels, which makes a direct comparison between solar and stellar irradiance data possible.

Appendices are available in electronic form at http://www.aanda.org Title: VizieR Online Data Catalog: IPHAS DR2 Source Catalogue (Barentsen+, 2014) Authors: Barentsen, G.; Farnhill, H. J.; Drew, J. E.; Gonzalez-Solares, E. A.; Greimel, R.; Irwin, M. J.; Miszalski, B.; Ruhland, C.; Groot, P.; Mampaso, A.; Sale, S. E.; Henden, A. A.; Aungwerojwit, A.; Barlow, M. J.; Carter, P. J.; Corradi, R. L. M.; Drake, J. J.; Eisloffel, J.; Fabregat, J.; Gansicke, B. T.; Gentile Fusillo, N. P.; Greiss, S.; Hales, A. S.; Hodgkin, S.; Huckvale, L.; Irwin, J.; King, R.; Knigge, C.; Kupfer, T.; Lagadec, E.; Lennon, D. J.; Lewis, J. R.; Mohr-Smith, M.; Morris, R. A. H.; Naylor, T.; Parker, Q. A.; Phillipps, S.; Pyrzas, S.; Raddi, R.; Roelofs, G. H. A.; Rodriguez-Gil, P.; Sabin, L.; Scaringi, S.; Steeghs, D.; Suso, J.; Tata, R.; Unruh, Y. C.; van Roestel, J.; Viironen, K.; Vink, J. S.; Walton, N. A.; Wright, N. J.; Zijlstra, A. A. Bibcode: 2014yCat.2321....0B Altcode: The INT/WFC Photometric H-Alpha Survey of the Northern Galactic Plane (IPHAS) is a 1860 deg2 imaging survey of the Northern Milky Way at red visible wavelengths. It covers Galactic latitudes |b|<5° and longitudes l=30 to 215° in the broad-band r, i and narrow-band H-alpha filters using the Wide Field Camera (WFC) on the 2.5-m Isaac Newton Telescope (INT) in La Palma.

IPHAS Data Release 2 (DR2) is the first quality-controlled and globally calibrated source catalogue derived from the survey, providing single-epoch photometry for 219 million unique sources across 92% of the footprint. The observations were carried out between 2003 and 2012 at a median seeing of 1.1 arcsec (sampled at 0.33 arcsec/pixel) and to a mean 5-sigma depth of 21.2 (r), 20.0 (i) and 20.3 (H-alpha). The photometric calibration is in the Vega magnitude system and carries an external precision of 0.03mag (root-mean-square error).

The catalogue includes all the sources which have been detected at a signal-to-noise ratio of 5 or better in at least one band. Many applications will require a combination of quality criteria to be applied to avoid faint stars or confused sources. The choice of quality criteria tensions completeness against reliability, and hence depends on the requirements of a project. To aid users, the data release paper (arXiv:1406.4862) recommends two sets of quality criteria, named "a10" and "a10point", which should satisfy most projects. As a minimum, the "a10" criteria select objects which have been detected at the minimum level of 10-sigma in all bands, without being saturated. Additional constraints are provided by the "a10point" criteria, which require objects to be point sources free of blending, unaffected by nearby bright stars, as well as being unsaturated >10-sigma detections in all bands. Sources in both categories are flagged in the catalogue using the boolean columns a10 and a10point.

Imaging and auxiliary data are available from the project website (www.iphas.org).

(1 data file). Title: Planets and stellar activity: hide and seek in the CoRoT-7 system Authors: Haywood, R. D.; Collier Cameron, A.; Queloz, D.; Barros, S. C. C.; Deleuil, M.; Fares, R.; Gillon, M.; Lanza, A. F.; Lovis, C.; Moutou, C.; Pepe, F.; Pollacco, D.; Santerne, A.; Ségransan, D.; Unruh, Y. C. Bibcode: 2014MNRAS.443.2517H Altcode: 2014arXiv1407.1044H Since the discovery of the transiting super-Earth CoRoT-7b, several investigations have yielded different results for the number and masses of planets present in the system, mainly owing to the star's high level of activity. We re-observed CoRoT-7 in 2012 January with both HARPS and CoRoT, so that we now have the benefit of simultaneous radial-velocity and photometric data. This allows us to use the off-transit variations in the star's light curve to estimate the radial-velocity variations induced by the suppression of convective blueshift and the flux blocked by starspots. To account for activity-related effects in the radial velocities which do not have a photometric signature, we also include an additional activity term in the radial-velocity model, which we treat as a Gaussian process with the same covariance properties (and hence the same frequency structure) as the light curve. Our model was incorporated into a Monte Carlo Markov Chain in order to make a precise determination of the orbits of CoRoT-7b and CoRoT-7c. We measure the masses of planets b and c to be 4.73 ± 0.95 and 13.56 ± 1.08 M⊕, respectively. The density of CoRoT-7b is (6.61 ± 1.72)(Rp/1.58 R⊕)-3 g cm-3, which is compatible with a rocky composition. We search for evidence of an additional planet d, identified by previous authors with a period close to 9 d. We are not able to confirm the existence of a planet with this orbital period, which is close to the second harmonic of the stellar rotation at ∼7.9 d. Using Bayesian model selection, we find that a model with two planets plus activity-induced variations is most favoured. Title: The VST Photometric Hα Survey of the Southern Galactic Plane and Bulge (VPHAS+) Authors: Drew, J. E.; Gonzalez-Solares, E.; Greimel, R.; Irwin, M. J.; Küpcü Yoldas, A.; Lewis, J.; Barentsen, G.; Eislöffel, J.; Farnhill, H. J.; Martin, W. E.; Walsh, J. R.; Walton, N. A.; Mohr-Smith, M.; Raddi, R.; Sale, S. E.; Wright, N. J.; Groot, P.; Barlow, M. J.; Corradi, R. L. M.; Drake, J. J.; Fabregat, J.; Frew, D. J.; Gänsicke, B. T.; Knigge, C.; Mampaso, A.; Morris, R. A. H.; Naylor, T.; Parker, Q. A.; Phillipps, S.; Ruhland, C.; Steeghs, D.; Unruh, Y. C.; Vink, J. S.; Wesson, R.; Zijlstra, A. A. Bibcode: 2014MNRAS.440.2036D Altcode: 2014arXiv1402.7024D; 2014MNRAS.tmp..599D; 2014MNRAS.tmp..608D The VST Photometric Hα Survey of the Southern Galactic Plane and Bulge (VPHAS+) is surveying the southern Milky Way in u, g, r, i and Hα at ∼1 arcsec angular resolution. Its footprint spans the Galactic latitude range -5o < b < +5° at all longitudes south of the celestial equator. Extensions around the Galactic Centre to Galactic latitudes ±10° bring in much of the Galactic bulge. This European Southern Observatory public survey, begun on 2011 December 28, reaches down to ∼20th magnitude (10σ) and will provide single-epoch digital optical photometry for ∼300 million stars. The observing strategy and data pipelining are described, and an appraisal of the segmented narrow-band Hα filter in use is presented. Using model atmospheres and library spectra, we compute main-sequence (u - g), (g - r), (r - i) and (r - Hα) stellar colours in the Vega system. We report on a preliminary validation of the photometry using test data obtained from two pointings overlapping the Sloan Digital Sky Survey. An example of the (u - g, g - r) and (r - Hα, r - i) diagrams for a full VPHAS+ survey field is given. Attention is drawn to the opportunities for studies of compact nebulae and nebular morphologies that arise from the image quality being achieved. The value of the u band as the means to identify planetary-nebula central stars is demonstrated by the discovery of the central star of NGC 2899 in survey data. Thanks to its excellent imaging performance, the VLT Survey Telescope (VST)/OmegaCam combination used by this survey is a perfect vehicle for automated searches for reddened early-type stars, and will allow the discovery and analysis of compact binaries, white dwarfs and transient sources. Title: Disentangling planetary orbits from stellar activity in radial-velocity surveys Authors: Haywood, R. D.; Collier Cameron, A.; Queloz, D.; Barros, S. C. C.; Deleuil, M.; Fares, R.; Gillon, M.; Hatzes, A.; Lanza, A. F.; Lovis, C.; Moutou, C.; Pepe, F.; Pollacco, D.; Santerne, A.; Ségransan, D.; Unruh, Y. Bibcode: 2014IJAsB..13..155H Altcode: The majority of extra-solar planets have been discovered (or confirmed after follow-up) through radial-velocity (RV) surveys. Using ground-based spectrographs such as High Accuracy Radial Velocity Planetary Search (HARPS) and HARPS-North, it is now possible to detect planets that are only a few times the mass of the Earth. However, the presence of dark spots on the stellar surface produces RV signals that are very similar in amplitude to those caused by orbiting low-mass planets. Disentangling these signals has thus become the biggest challenge in the detection of Earth-mass planets using RV surveys. To do so, we use the star's lightcurve to model the RV variations produced by spots. Here we present this method and show the results of its application to CoRoT-7. Title: Modelling of Hot Jupiter thermospheres and ionospheres under irradiation from active stars Authors: Chadney, J.; Galand, M.; Unruh, Y.; Koskinen, T.; Sanz-Forcada, J. Bibcode: 2014EPSC....9..579C Altcode: Upper atmospheres of Hot Jupiters are subject to extreme radiation conditions that can result in atmospheric escape. The composition and structure of the thermosphere and ionosphere of these planets are affected by the high-energy spectrum of the host star. This emission depends on stellar type and age, which are thus important factors in understanding the behaviour of exoplanetary atmospheres. In this study, we focus on Hot Jupiter planets orbiting K and M dwarf stars. As an example, XUV spectra for three different stars - ɛ Eridani, AD Leonis and AU Microscopii - are constructed using a coronal model. Neutral density and temperature profiles in the thermosphere of hypothetical, Hot Jupiters orbiting these stars are then obtained from a fluid model of the upper atmosphere, incorporating atmospheric chemistry and taking atmospheric escape into account. Using these models of both the host star and the planetary atmosphere, we have derived a method to scale the X-ray and EUV regions of the solar spectrum to produce a very similar outcome in terms of the planet's neutral thermosphere as using a detailed coronal model of the host star. We also calculate ion production rates and densities in the ionospheres of such planets, considering ionisation through both photo-ionisation and electronimpact processes. We find that in planets subjected to radiation from more active stars, the transition to a regime of hydrodynamic escape from the top of the atmosphere occurs at larger orbital distances. A greater X-ray to EUV flux ratio in these stars compared with the solar case also produces ionospheres that extend to lower altitudes and are significantly more pronounced. Title: Planets and Stellar Activity: Hide and Seek in the CoRoT-7 system Authors: Haywood, R. D.; Cameron, A. C.; Queloz, D.; Barros, S. C. C.; Deleuil, M.; Fares, R.; Gillon, M.; Hatzes, A.; Lanza, A. F.; Lovis, C.; Moutou, C.; Pepe, F.; Pollacco, D.; Santerne, A.; Ségransan, D.; Unruh, Y. Bibcode: 2014IAUS..299..237H Altcode: Since the discovery of the transiting Super-Earth CoRoT-7b, several investigations have been made of the number and precise masses of planets present in the system, but they all yield different results, owing to the star's high level of activity. Radial velocity (RV) variations induced by stellar activity therefore need to be modelled and removed to allow a reliable detection of all planets in the system. We re-observed CoRoT-7 in January 2012 with both HARPS and the CoRoT satellite, so that we now have the benefit of simultaneous RV and photometric data. We fitted the off-transit variations in the CoRoT lightcurve using a harmonic decomposition similar to that implemented in Queloz et al. (2009). This fit was then used to model the stellar RV contribution, according to the methods described by Aigrain et al. (2011). This model was incorporated into a Monte Carlo Markov Chain in order to make a precise determination of the orbits of CoRoT-7b and CoRoT-7c. We also assess the evidence for the presence of one or two additional planetary companions. Title: VST Photometric H-alpha Survey of the Southern Galactic Plane and Bulge (VPHAS+) Authors: Drew, J. E.; Barentsen, G.; Fabregat, J.; Farnhill, H.; Mohr-Smith, M.; Wright, N. J.; Gonzalez-Solares, E.; Irwin, M. J.; Lewis, J.; Yoldas, A. K.; Greimel, R.; Eislöffel, J.; Groot, P.; Barlow, M. J.; Corradi, R.; Gänsicke, B. T.; Knigge, C.; Mampaso, A.; Morris, R.; Naylor, T.; Parker, Q. A.; Raddi, R.; Sale, S. E.; Steeghs, D.; Unruh, Y. C.; Vink, J. S.; Walsh, J. R.; Walton, N. A.; Wesson, R.; Zijlstra, A. Bibcode: 2013Msngr.154...41D Altcode: The VST Photometric H-alpha survey of the Southern Galactic Plane and Bulge (VPHAS+) is collecting single-epoch Sloan u, g, r, i and H-alpha narrowband photometry, at arcsecond resolution, down to point-source (Vega) magnitudes of ~ 21. The survey footprint encloses the entire southern Galactic Plane within the Galactic latitude range -5° < b < +5°, expanding to b = ±10° in the Galactic Bulge. This brief description of VPHAS+ includes sample data and examples of early science validation. Title: Hot-Jupiter ionospheres irradiated by low-mass stars Authors: Chadney, J.; Galand, M.; Unruh, Y.; Koskinen, T.; Sanz-Forcada, J. Bibcode: 2013EPSC....8..800C Altcode: We present a modelling study of the upper atmospheres of extra-solar planets, focussing on the influence of different stellar radiation spectra on the composition and structure of the ionosphere around a gas-giant planet. In particular, we concentrate on hot-Jupiter planets orbiting low mass stars, of K and M type. Compared to a solar type star, the XUV radiation of these stars is extremely variable and they have a much higher XUV-to-bolometric-flux ratio than similarly aged solar type stars - greatly affecting the planetary ionospheres they irradiate. In this work, XUV spectra for the different stars selected are constructed using a combination of spectral data from various space telescopes, as well as coronal models of the stars. Ion production rates and densities are then calculated for a given H2/H/He background atmosphere, taking into account ionisation through both primary and secondary processes. Additionally, the effect of orbital separation on ionospheric composition is examined. Results show that in atmospheres subjected to radiation from active M-dwarf stars, ion production is boosted in the lower ionosphere, which is also the region most affected by secondary ionisation processes. Title: Studying the Sun's radial velocity jitter to improve low-mass exoplanet detections Authors: Haywood, R. D.; Cameron, A. C.; Queloz, D.; Fares, R.; Llama, J.; Deleuil, M.; Gillon, M.; Hatzes, A.; Lanza, A. F.; Lovis, C.; Moutou, C.; Pepe, F.; Pollaco, D.; Ségransan, D.; Unruh, Y. Bibcode: 2013EPSC....8..215H Altcode: One of the most common methods used to discover extra-solar planets is to monitor a star's radial velocity (RV) in order to detect the reflex orbital motion caused by one or more planets orbiting the star. When looking for "small" planets (Neptune or Earth mass), the RV signals induced by these planets are entangled with the jitter arising from the star's magnetic activity. The Sun's activity is well known and it is possible to remove all RV components induced by all other bodies of the solar system. We have obtained its activity-driven RV variations over two solar rotations using HARPS by observing sunlight reflected off the bright asteroid Vesta. We aim to model the solar RV jitter in terms of the continuum lightcurve, the chromospheric Ca II H&K emission, and the line-profile distortions produced by spots drifting across the face of the Sun. By using the "ground truth" of solar observations in this way, we will identify photometric and spectroscopic proxies that will make it possible to model and remove the stellar activity RV contribution from exoplanet RV curves. Title: A Collaborative FP7 Effort towards the First European Comprehensive SOLar Irradiance Data Exploitation (SOLID) Authors: Haberreiter, Margit; Dasi, Maria; Delouille, Veronique; Del Zanna, Giulio; Dudok de Wit, Thierry; Ermolli, Ilaria; Kretzschmar, Matthieu; Krivova, Natalie; Mason, Helen; Qahwaji, Rami; Schmutz, Werner; Solanki, Sami; Thuillier, Gerard; Tourpali, Kleareti; Unruh, Yvonne; Verbeeck, Cis; Weber, Mark; Woods, Tom Bibcode: 2013EGUGA..1513079H Altcode: Variations of solar irradiance are the most important natural factor in the terrestrial climate and as such, the time dependent spectral solar irradiance is a crucial input to any climate modelling. There have been previous efforts to compile solar irradiance but it is still uncertain by how much the spectral and total solar irradiance changed on yearly, decadal and longer time scales. Observations of irradiance data exist in numerous disperse data sets. Therefore, it is important to bring together the European expertise in the field to analyse and merge the complete set of European irradiance data, complemented by archive data that include data from non-European missions. We report on the initiation of a collaborative effort to unify representatives from all European solar space experiments and European teams specialized in multi-wavelength solar image processing. It is intended to include the European groups involved in irradiance modelling and reconstruction. They will work with two different state of the art approaches to produce reconstructed spectral and total solar irradiance data as a function of time. These results will be used to bridge gaps in time and wavelength coverage of the observational data. This will allow the proposing SOLID team to reduce the uncertainties in the irradiance time series - an important requirement by the climate community - and to provide uniform data sets of modelled and observed solar irradiance data from the beginning of the space era to the present including proper error and uncertainty estimates. Climate research needs these data sets and therefore, the primary benefit is for the climate community, but the stellar community, planetary, lunar, and ionospheric researchers are also interested in having at their disposition incident radiation of the Sun. The proposing team plans to realize a wide international synergy in solar physics from 7 European countries, and collaborators from the US, complemented by representatives from the climate community, who will accompany their research work with wide dissemination activities. Title: Modeling the variability of Sun-like stars Authors: Shapiro, Alexander; Knaack, Reto; Krivova, Natalie; Schmutz, Werner; Solanki, Sami; Unruh, Yvonne Bibcode: 2013EGUGA..15.9981S Altcode: We present a model which attributes the variability of the stellar radiative energy flux to the imbalance between the contributions from dark starspots and bright faculae. The stellar radiative energy flux variations are modeled from the individual component's spectra, by weighting them with corresponding filling factors. The filling factors are deduced by extrapolating the sunspot and facular filling factors dependencies on solar CaII S-index to stars with different levels of the chromospheric activity. Our approach allows us to model the stellar photometric variability vs. activity dependency and reproduce the transition from spot-dominated to facula-dominated regimes of variability. We show how the effect of inclination (arising due to the random position of the Earth-bound observer relative to the directions of stellar rotational axis) can affect these dependencies and present the modeling of the individual stellar photometric light curves. Title: Recent variability of the solar spectral irradiance and its impact on climate modelling Authors: Ermolli, I.; Matthes, K.; Dudok de Wit, T.; Krivova, N. A.; Tourpali, K.; Weber, M.; Unruh, Y. C.; Gray, L.; Langematz, U.; Pilewskie, P.; Rozanov, E.; Schmutz, W.; Shapiro, A.; Solanki, S. K.; Woods, T. N. Bibcode: 2013ACP....13.3945E Altcode: 2012ACPD...1224557E; 2013arXiv1303.5577E The lack of long and reliable time series of solar spectral irradiance (SSI) measurements makes an accurate quantification of solar contributions to recent climate change difficult. Whereas earlier SSI observations and models provided a qualitatively consistent picture of the SSI variability, recent measurements by the SORCE (SOlar Radiation and Climate Experiment) satellite suggest a significantly stronger variability in the ultraviolet (UV) spectral range and changes in the visible and near-infrared (NIR) bands in anti-phase with the solar cycle. A number of recent chemistry-climate model (CCM) simulations have shown that this might have significant implications on the Earth's atmosphere. Motivated by these results, we summarize here our current knowledge of SSI variability and its impact on Earth's climate.

We present a detailed overview of existing SSI measurements and provide thorough comparison of models available to date. SSI changes influence the Earth's atmosphere, both directly, through changes in shortwave (SW) heating and therefore, temperature and ozone distributions in the stratosphere, and indirectly, through dynamical feedbacks. We investigate these direct and indirect effects using several state-of-the art CCM simulations forced with measured and modelled SSI changes. A unique asset of this study is the use of a common comprehensive approach for an issue that is usually addressed separately by different communities.

We show that the SORCE measurements are difficult to reconcile with earlier observations and with SSI models. Of the five SSI models discussed here, specifically NRLSSI (Naval Research Laboratory Solar Spectral Irradiance), SATIRE-S (Spectral And Total Irradiance REconstructions for the Satellite era), COSI (COde for Solar Irradiance), SRPM (Solar Radiation Physical Modelling), and OAR (Osservatorio Astronomico di Roma), only one shows a behaviour of the UV and visible irradiance qualitatively resembling that of the recent SORCE measurements. However, the integral of the SSI computed with this model over the entire spectral range does not reproduce the measured cyclical changes of the total solar irradiance, which is an essential requisite for realistic evaluations of solar effects on the Earth's climate in CCMs.

We show that within the range provided by the recent SSI observations and semi-empirical models discussed here, the NRLSSI model and SORCE observations represent the lower and upper limits in the magnitude of the SSI solar cycle variation.

The results of the CCM simulations, forced with the SSI solar cycle variations estimated from the NRLSSI model and from SORCE measurements, show that the direct solar response in the stratosphere is larger for the SORCE than for the NRLSSI data. Correspondingly, larger UV forcing also leads to a larger surface response.

Finally, we discuss the reliability of the available data and we propose additional coordinated work, first to build composite SSI data sets out of scattered observations and to refine current SSI models, and second, to run coordinated CCM experiments. Title: Solar and stellar spectral variability Authors: Unruh, Yvonne; Ball, William Bibcode: 2013EGUGA..15.8414U Altcode: Measurements of the changes in the solar spectral irradiance are available for three solar cycles and there is a good understanding of the irradiance changes on time scales ranging from a day to a few years. Observing longer-term changes (tens of years and longer) is more difficult, and there is much uncertainty regarding the Sun's long-term behaviour. Stellar comparisons are often used to explore a wider range of activity regimes and to estimate past and future solar variability levels. At the same time, we want to find out how different the solar example is and whether we can use it as a paradigm when finding and characterising exoplanets around cool stars. We will discuss some of the challenges that we encounter when comparing solar and stellar variability, such as, e.g., the spread of stellar inclinations and effective temperatures, and uncertainties in the relative area coverages and contrasts of dark and bright features. Considering different levels of spot and facular coverage for a range of effective temperatures, we investigate the expected spectral variability and compare it to observed solar and stellar variability. Title: Solar irradiance variability Authors: Solanki, S. K.; Unruh, Y. C. Bibcode: 2013AN....334..145S Altcode: 2013csss...17..145S; 2012arXiv1210.5911S The Sun has long been considered a constant star, to the extent that its total irradiance was termed the solar constant. It required radiometers in space to detect the small variations in solar irradiance on timescales of the solar rotation and the solar cycle. A part of the difficulty is that there are no other constant natural daytime sources to which the Sun's brightness can be compared. The discovery of solar irradiance variability rekindled a long-running discussion on how strongly the Sun affects our climate. A non-negligible influence is suggested by correlation studies between solar variability and climate indicators. The mechanism for solar irradiance variations that fits the observations best is that magnetic features at the solar surface, i.e. sunspots, faculae and the magnetic network, are responsible for almost all variations (although on short timescales convection and p-mode oscillations also contribute). In spite of significant progress important questions are still open. Thus there is a debate on how strongly irradiance varies on timescales of centuries (i.e. how much darker the Sun was during the Maunder minimum than it is today). It is also not clear how the solar spectrum changes over the solar cycle. Both these questions are of fundamental importance for working out just how strongly the Sun influences our climate. Another interesting question is how solar irradiance variability compares with that of other cool dwarfs, particularly now that observations from space are available also for stars. Title: Ionisation of gas-giant type exoplanetary atmospheres under stellar radiation Authors: Chadney, J.; Galand, M.; Unruh, Y.; Koskinen, T. Bibcode: 2012epsc.conf..474C Altcode: 2012espc.conf..474C Characterising extra-solar planetary atmospheres is the new frontier in exoplanetary research. Future space-based missions will provide consistent and stable measurements of star systems with known transiting exoplanets. These missions, that are currently at selection stage, are ESA's Exoplanet Characterisation Observatory (EChO) and NASA's Fast INfrared Exoplanet Spectroscopy Survey Explorer (FINESSE). Once up and running, they will deliver high stability, long duration observations in the visible to midinfrared. In the meantime, modelling studies of the atmospheres of extra-solar planets, such as the one undertaken in this work, will be useful to help plan the observational process and provide insight into the data analysis and interpretation, after the missions are launched. The purpose of this work is to study the influence of differing stellar radiation profiles on the composition and structure of an ionosphere around a typical gas-giant planet. Particular interest is focused upon M and K-type dwarf stars. Typical XUV spectra for the different star types are constructed by combining data from various satellites. Unobserved parts of the spectrum are filled using a combination of extrapolation and results from a correlation study of the solar spectrum. The constructed spectra are then used to calculate ion densities, produced through photo-ionisation, in a H2/H/He atmosphere, considering the neutral atmosphere as a constant background. Preliminary results show that in planets irradiated by K-type stars, photo-ionisation production rates are remarkably similar to those in planets orbiting Sun-like stars. The case of atmospheres subjected to radiation from flaring Mstars is altogether more interesting: an extension of the production rate peak towards lower altitudes is predicted. Title: Solar Irradiance Models and Measurements: A Comparison in the 220-240 nm wavelength band Authors: Unruh, Yvonne C.; Ball, Will T.; Krivova, Natalie A. Bibcode: 2012SGeo...33..475U Altcode: 2011arXiv1111.2068U; 2011SGeo..tmp..121U Solar irradiance models that assume solar irradiance variations to be due to changes in the solar surface magnetic flux have been successfully used to reconstruct total solar irradiance on rotational as well as cyclical and secular time scales. Modelling spectral solar irradiance is not yet as advanced, and also suffers from a lack of comparison data, in particular on solar cycle time scales. Here, we compare solar irradiance in the 220-240 nm band as modelled with SATIRE-S and measured by different instruments on the UARS and SORCE satellites. We find good agreement between the model and measurements on rotational time scales. The long-term trends, however, show significant differences. Both SORCE instruments, in particular, show a much steeper gradient over the decaying part of cycle 23 than the modelled irradiance or that measured by UARS/SUSIM. Title: Reconstruction of total solar irradiance 1974-2009 Authors: Ball, W. T.; Unruh, Y. C.; Krivova, N. A.; Solanki, S.; Wenzler, T.; Mortlock, D. J.; Jaffe, A. H. Bibcode: 2012A&A...541A..27B Altcode: 2012arXiv1202.3554B Context. The study of variations in total solar irradiance (TSI) is important for understanding how the Sun affects the Earth's climate.
Aims: Full-disk continuum images and magnetograms are now available for three full solar cycles. We investigate how modelled TSI compares with direct observations by building a consistent modelled TSI dataset. The model, based only on changes in the photospheric magnetic flux can then be tested on rotational, cyclical and secular timescales.
Methods: We use Kitt Peak and SoHO/MDI continuum images and magnetograms in the SATIRE-S model to reconstruct TSI over cycles 21-23. To maximise independence from TSI composites, SORCE/TIM TSI data are used to fix the one free parameter of the model. We compare and combine the separate data sources for the model to estimate an uncertainty on the reconstruction and prevent any additional free parameters entering the model.
Results: The reconstruction supports the PMOD composite as being the best historical record of TSI observations, although on timescales of the solar rotation the IRMB composite provides somewhat better agreement. Further to this, the model is able to account for 92% of TSI variations from 1978 to 2009 in the PMOD composite and over 96% during cycle 23. The reconstruction also displays an inter-cycle, secular decline of 0.20+0.12-0.09 W m-2 between cycle 23 minima, in agreement with the PMOD composite.
Conclusions: SATIRE-S is able to recreate TSI observations on all timescales of a day and longer over 31 years from 1978. This is strong evidence that changes in photospheric magnetic flux alone are responsible for almost all solar irradiance variations over the last three solar cycles. Title: Solar Irradiance Models and Measurements: A Comparison in the 220–240 nm wavelength band Authors: Unruh, Yvonne C.; Ball, Will T.; Krivova, Natalie A. Bibcode: 2012omee.book..143U Altcode: No abstract at ADS Title: The large-scale magnetic field and poleward mass accretion of the classical T Tauri star TW Hya Authors: Donati, J. -F.; Gregory, S. G.; Alencar, S. H. P.; Bouvier, J.; Hussain, G.; Skelly, M.; Dougados, C.; Jardine, M. M.; Ménard, F.; Romanova, M. M.; Unruh, Y. C. Bibcode: 2011MNRAS.417..472D Altcode: 2011arXiv1106.4162D; 2011MNRAS.tmp.1284D We report here results of spectropolarimetric observations of the ≃8 Myr classical T Tauri star (cTTS) TW Hya carried out with ESPaDOnS at the Canada-France-Hawaii Telescope in the framework of the 'Magnetic Protostars and Planets' programme, and obtained at two different epochs (2008 March and 2010 March). Obvious Zeeman signatures are detected at all times, both in photospheric lines and in accretion-powered emission lines. Significant intrinsic variability and moderate rotational modulation are observed in both photospheric and accretion proxies.

Using tomographic imaging, we reconstruct maps of the large-scale field of the photospheric brightness and the accretion-powered emission at the surface of TW Hya at both epochs. We find that the magnetic topology is mostly poloidal and axisymmetric with respect to the rotation axis of the star and that the octupolar component of the large-scale field (2.5-2.8 kG at the pole) largely dominates the dipolar component. This large-scale field topology is characteristic of partly convective stars, supporting the conclusion (from evolutionary models) that TW Hya already hosts a radiative core. We also show that TW Hya features a high-latitude photospheric cool spot overlapping with the main magnetic pole (and producing the observed radial velocity fluctuations); this is also where accretion concentrates most of the time, although accretion at lower latitudes is found to occur episodically.

We propose that the relatively rapid rotation of TW Hya (with respect to AA Tau-like cTTSs) directly reflects the weakness of the large-scale dipole, no longer capable of magnetically disrupting the accretion disc up to the corotation radius (at which the Keplerian period equals the stellar rotation period). We therefore conclude that TW Hya is in a phase of rapid spin-up as its large-scale dipole field progressively vanishes. Title: Solar irradiance variability: a six-year comparison between SORCE observations and the SATIRE model Authors: Ball, W. T.; Unruh, Y. C.; Krivova, N. A.; Solanki, S.; Harder, J. W. Bibcode: 2011A&A...530A..71B Altcode: 2011arXiv1104.0885B
Aims: We investigate how well modeled solar irradiances agree with measurements from the SORCE satellite, both for total solar irradiance and broken down into spectral regions on timescales of several years.
Methods: We use the SATIRE model and compare modeled total solar irradiance (TSI) with TSI measurements over the period 25 February 2003 to 1 November 2009. Spectral solar irradiance over 200-1630 nm is compared with the SIM instrument on SORCE over the period 21 April 2004 to 1 November 2009. We discuss the overall change in flux and the rotational and long-term trends during this period of decline from moderate activity to the recent solar minimum in ~10 nm bands and for three spectral regions of significant interest: the UV integrated over 200-300 nm, the visible over 400-691 nm and the IR between 972-1630 nm.
Results: The model captures 97% of the observed TSI variation. This is on the order at which TSI detectors agree with each other during the period considered. In the spectral comparison, rotational variability is well reproduced, especially between 400 and 1200 nm. The magnitude of change in the long-term trends is many times larger in SIM at almost all wavelengths while trends in SIM oppose SATIRE in the visible between 500 and 700 nm and again between 1000 and 1200 nm. We discuss the remaining issues with both SIM data and the identified limits of the model, particularly with the way facular contributions are dealt with, the limit of flux identification in MDI magnetograms during solar minimum and the model atmospheres in the IR employed by SATIRE. However, it is unlikely that improvements in these areas will significantly enhance the agreement in the long-term trends. This disagreement implies that some mechanism other than surface magnetism is causing SSI variations, in particular between 2004 and 2006, if the SIM data are correct. Since SATIRE was able to reproduce UV irradiance between 1991 and 2002 from UARS, either the solar mechanism for SSI variation fundamentally changed around the peak of cycle 23, or there is an inconsistency between UARS and SORCE UV measurements. We favour the second explanation. Title: Intensity contrast from MHD simulations and HINODE observations Authors: Afram, N.; Unruh, Y. C.; Solanki, S. K.; Schüssler, M.; Lagg, A.; Vögler, A. Bibcode: 2011A&A...526A.120A Altcode: 2010arXiv1011.6102A Context. Changes in the solar surface area, which is covered by small-scale magnetic elements, are thought to cause long-term changes in the solar spectral irradiance, which are important for determining the impact on Earth's climate.
Aims: To study the effect of small-scale magnetic elements on the total and spectral irradiance, we derive their contrasts from 3-D MHD simulations of the solar atmosphere. These calculations are necessary because measurements of small-scale flux tube contrasts are confined to a few wavelengths and affected by scattered light and instrument defocus, even for space observations.
Methods: To test the contrast calculations, we compare rms contrasts from simulations with those obtained with the broad-band filter imager mounted on the Solar Optical Telescope (SOT) onboard the Hinode satellite and also analyse centre-to-limb variations (CLV). The 3-D MHD simulations include the interaction between convection and magnetic flux tubes. They are performed by assuming non-grey radiative transfer and using the MURaM code. The simulations have an average vertical magnetic field of 0 G, 50 G, and 200 G. Emergent intensities are calculated with the spectral synthesis code ATLAS9 and are convolved with a theoretical point-spread function to account for the properties of the observations' optical system.
Results: We find reasonable agreement between simulated and observed intensity distributions in the visible continuum bands. Agreement is poorer for the CN and G-bands. The analysis of the simulations uncovers a potentially more realistic centre-to-limb behaviour than calculations based on 1-D model atmospheres.
Conclusions: We conclude that starting from 3-D MHD simulations represents a powerful approach to obtaining intensity contrasts for a wide wavelength coverage and different positions across on the solar disk. This also paves the way for future calculations of facular and network contrast as a function of magnetic fluxes. Title: Towards a long-term record of solar total and spectral irradiance Authors: Krivova, N. A.; Solanki, S. K.; Unruh, Y. C. Bibcode: 2011JASTP..73..223K Altcode: 2009arXiv0911.4002K The variation of total solar irradiance (TSI) has been measured since 1978 and that of the spectral irradiance for an even shorter amount of time. Semi-empirical models are now available that reproduce over 80% of the measured irradiance variations. An extension of these models into the more distant past is needed in order to serve as input to climate simulations. Here we review our most recent efforts to model solar total and spectral irradiance on time scales from days to centuries and even longer. Solar spectral irradiance has been reconstructed since 1947. Reconstruction of solar total irradiance goes back to 1610 and suggests a value of about 1-1.5W/m2 for the increase in the cycle-averaged TSI since the end of the Maunder minimum, which is significantly lower than previously assumed but agrees with other modern models. First steps have also been made towards reconstructions of solar total and spectral irradiance on time scales of millennia. Title: Magnetospheric accretion and spin-down of the prototypical classical T Tauri star AA Tau Authors: Donati, J. -F.; Skelly, M. B.; Bouvier, J.; Gregory, S. G.; Grankin, K. N.; Jardine, M. M.; Hussain, G. A. J.; Ménard, F.; Dougados, C.; Unruh, Y.; Mohanty, S.; Aurière, M.; Morin, J.; Farès, R.; MAPP Collaboration Bibcode: 2010MNRAS.409.1347D Altcode: 2010arXiv1007.4407D; 2010MNRAS.tmp.1622D From observations collected with the ESPaDOnS spectropolarimeter at the Canada-France-Hawaii Telescope (CFHT) and with the NARVAL spectropolarimeter at the Télescope Bernard Lyot (TBL), we report the detection of Zeeman signatures on the prototypical classical T Tauri star AA Tau, both in photospheric lines and accretion-powered emission lines. Using time series of unpolarized and circularly polarized spectra, we reconstruct at two epochs maps of the magnetic field, surface brightness and accretion-powered emission of AA Tau. We find that AA Tau hosts a 2-3 kG magnetic dipole tilted at ≃20° to the rotation axis, and of presumably dynamo origin. We also show that the magnetic poles of AA Tau host large cool spots at photospheric level and accretion regions at chromospheric level.

The accretion rate at the surface of AA Tau at the time of our observations (estimated from the emission in the He I D3 line mainly) is strongly variable, ranging from -9.6 to -8.5 and equal to -9.2 in average (in logarithmic scale and in M⊙ yr-1); this is an order of magnitude smaller than the disc accretion rate at which the magnetic truncation radius (below which the disc is disrupted by the stellar magnetic field) matches the corotation radius (where the Keplerian period equals the stellar rotation period) - a necessary condition for accretion to occur. It suggests that AA Tau is largely in the propeller regime, with most of the accreting material in the inner disc regions being expelled outwards and only a small fraction accreted towards the surface of the star. The strong variability in the observed surface mass accretion rate and the systematic time-lag of optical occultations (by the warped accretion disc) with respect to magnetic and accretion-powered emission maxima also support this conclusion.

Our results imply that AA Tau is being actively spun-down by the star/disc magnetic coupling and appears as an ideal laboratory for studying angular momentum losses of forming suns in the propeller regime. Title: IPHAS A-type Stars with Mid-IR Excesses in Spitzer Surveys Authors: Hales, Antonio S.; Barlow, Michael J.; Drew, Janet E.; Unruh, Yvonne C.; Greimel, Robert; Irwin, Michael J.; González-Solares, Eduardo Bibcode: 2010HiA....15..815H Altcode: The Isaac Newton Photometric H-Alpha Survey (IPHAS) provides (r‧-Hα)-(r‧-i‧) colors, which can be used to select AV0-5 Main Sequence star candidates (age~20-200 Myr). By combining a sample of 23050 IPHAS-selected A-type stars with 2MASS, GLIMPSE and MIPSGAL photometry we searched for mid-infrared excesses attributable to dusty circumstellar disks. Positional cross-correlation yielded a sample of 2692 A-type stars, of which 0.6% were found to have 8-μm excesses above the expected photospheric values. The low fraction of main sequence stars with mid-IR excesses found in this work indicates that dust disks in the terrestrial planet zone of Main Sequence intermediate mass stars are rare. Dissipation mechanisms such as photo-evaporation, grain growth, collisional grinding or planet formation could possibly explain the depletion of dust detected in the inner regions of these disks. Title: Quiet-sun Intensity Contrasts in the Near-ultraviolet as Measured from SUNRISE Authors: Hirzberger, J.; Feller, A.; Riethmüller, T. L.; Schüssler, M.; Borrero, J. M.; Afram, N.; Unruh, Y. C.; Berdyugina, S. V.; Gandorfer, A.; Solanki, S. K.; Barthol, P.; Bonet, J. A.; Martínez Pillet, V.; Berkefeld, T.; Knölker, M.; Schmidt, W.; Title, A. M. Bibcode: 2010ApJ...723L.154H Altcode: We present high-resolution images of the Sun in the near-ultraviolet spectral range between 214 nm and 397 nm as obtained from the first science flight of the 1 m SUNRISE balloon-borne solar telescope. The quiet-Sun rms intensity contrasts found in this wavelength range are among the highest values ever obtained for quiet-Sun solar surface structures—up to 32.8% at a wavelength of 214 nm. We compare the rms contrasts obtained from the observational data with theoretical intensity contrasts obtained from numerical magnetohydrodynamic simulations. For 388 nm and 312 nm the observations agree well with the numerical simulations whereas at shorter wavelengths discrepancies between observed and simulated contrasts remain. Title: Quiet-Sun intensity contrasts in the near ultraviolet Authors: Hirzberger, Johann; Feller, Alex; Riethmüller, Tino L.; Schüssler, Manfred; Borrero, Juan M.; Afram, Nadine; Unruh, Yvonne C.; Berdyugina, Svetlana V.; Gandorfer, Achim; Solanki, Sami K.; Barthol, Peter; Bonet, Jose A.; Martínez Pillet, Valentin; Berkefeld, Thomas; Knölker, Michael; Schmidt, Wolfgang; Title, Alan M. Bibcode: 2010arXiv1009.1050H Altcode: We present high-resolution images of the Sun in the near ultraviolet spectral range between 214 nm and 397 nm as obtained from the first science flight of the 1-m Sunrise balloon-borne solar telescope. The quiet-Sun rms intensity contrasts found in this wavelength range are among the highest values ever obtained for quiet-Sun solar surface structures - up to 32.8% at a wavelength of 214 nm. We compare with theoretical intensity contrasts obtained from numerical magneto-hydrodynamic simulations. For 388 nm and 312 nm the observations agree well with the numerical simulations whereas at shorter wavelengths discrepancies between observed and simulated contrasts remain. Title: Dynamo processes in the T Tauri star V410 Tau Authors: Skelly, M. B.; Donati, J. -F.; Bouvier, J.; Grankin, K. N.; Unruh, Y. C.; Artemenko, S. A.; Petrov, P. Bibcode: 2010MNRAS.403..159S Altcode: 2009arXiv0911.5476S; 2010MNRAS.tmp..187S We present new brightness and magnetic images of the weak-line T Tauri star V410 Tau, made by using data from the Narval spectropolarimeter at Télescope Bernard Lyot (TBL). The brightness image shows a large polar spot and significant spot coverage at lower latitudes. The magnetic maps show a field that is predominantly dipolar and non-axisymmetric with a strong azimuthal component. The field is 50 per cent poloidal and 50 per cent toroidal, and very little differential rotation is apparent from the magnetic images.

A photometric monitoring campaign on this star has previously revealed V-band variability of up to 0.6 mag, but in 2009 the light curve is much flatter. The Doppler image presented here is consistent with this low variability. Calculating the flux predicted by the mapped spot distribution gives a peak-to-peak variability of 0.04 mag. The reduction in the amplitude of the light curve, compared with previous observations, appears to be related to a change in the distribution of the spots rather than the number or area.

This paper is the first from a Zeeman-Doppler imaging campaign being carried out on V410 Tau between 2009 and 2012 at the TBL. During this time, it is expected that the light curve will return to a high-amplitude state, allowing us to ascertain whether the photometric changes are accompanied by a change in the magnetic field topology.

Based on observations obtained at the Télescope Bernard Lyot (TBL), operated by Centre national de la recherche scientifique/Institut national des sciences de l'Univers (CNRS/INSU)

E-mail: mskelly@ast.obs-mip.fr Title: Complex magnetic topology and strong differential rotation on the low-mass T Tauri star V2247 Oph Authors: Donati, J. -F.; Skelly, M. B.; Bouvier, J.; Jardine, M. M.; Gregory, S. G.; Morin, J.; Hussain, G. A. J.; Dougados, C.; Ménard, F.; Unruh, Y. Bibcode: 2010MNRAS.402.1426D Altcode: 2009arXiv0911.1080D; 2009MNRAS.tmp.1895D From observations collected with the ESPaDOnS spectropolarimeter at the Canada-France-Hawaii Telescope, we report the detection of Zeeman signatures on the low-mass classical T Tauri star (cTTS) V2247 Oph. Profile distortions and circular polarization signatures detected in photospheric lines can be interpreted as caused by cool spots and magnetic regions at the surface of the star. The large-scale field is of moderate strength and highly complex; moreover, both the spot distribution and the magnetic field show significant variability on a time-scale of only 1 week, as a likely result of strong differential rotation. Both properties make V2247 Oph very different from the (more massive) prototypical cTTS BP Tau; we speculate that this difference reflects the lower mass of V2247 Oph.

During our observations, V2247 Oph was in a low-accretion state, with emission lines showing only weak levels of circular polarization; we nevertheless find that excess emission apparently concentrates in a mid-latitude region of a strong radial field, suggesting that it is the footpoint of an accretion funnel.

The weaker and more complex field that we report on V2247 Oph may share similarities with those of very-low-mass late-M dwarfs and potentially explain why low-mass cTTSs rotate on average faster than intermediate-mass ones. These surprising results need confirmation from new independent data sets on V2247 Oph and other similar low-mass cTTSs.

Based on observations obtained at the Canada-France-Hawaii Telescope, operated by the National Research Council of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France and the University of Hawaii.

E-mail: donati@ast.obs-mip.fr (J-FD); mskelly@ast.obs-mip.fr (MBS); jerome.bouvier@obs.ujf-grenoble.fr (JB); mmj@st-andrews.ac.uk (MMJ); sg64@st-andrews.ac.uk (SGG); jmorin@ast.obs-mip.fr (JM); ghussain@eso.org (GAJH); catherine.dougados@obs.ujf-grenoble.fr (CD); francois.menard@obs.ujf-grenoble.fr (FM); y.unruh@imperial.ac.uk (YU) Title: VizieR Online Data Catalog: Simulated UVEX colors with reddening (Groot+, 2009) Authors: Groot, P. J.; Verbeek, K.; Greimel, R.; Irwin, M.; Gonzalez-Solares, E.; Gansicke, B. T.; de Groot, E.; Drew, J.; Augusteijn, T.; Aungwerojwit, A.; Barlow, M.; Barros, S.; van den Besselaar, E. J. M.; Casares, J.; Corradi, R.; Corral-Santana, J. M.; Deacon, N.; van Ham, W.; Hu, H.; Heber, U.; Jonker, P. G.; King, R.; Knigge, C.; Mampaso, A.; Marsh, T. R.; Morales-Rueda, L.; Napiwotzki, R.; Naylor, T.; Nelemans, G.; Oosting, T.; Pyrzas, S.; Pretorius, M.; Rodriguez-Gil, P.; Roelofs, G. H. A.; Sale, S.; Schellart, P.; Steeghs, D.; Szyszka, C.; Unruh, Y.; Walton, N. A.; Weston, S.; Witham, A.; Woudt, P.; Zijlstra, A. Bibcode: 2010yCat..73990323G Altcode: To interpret the UVEX observations, simulations of the colours of stars and the effect of reddening are a very powerful and important tool. In obtaining the simulated colours, we follow the procedure as outlined in Drew et al. (2005MNRAS.362..753D) for the IPHAS.

(6 data files). Title: A comparison of measured and simulated solar network contrast Authors: Afram, N.; Unruh, Y. C.; Solanki, S. K.; Schüssler, M.; Mathew, S. K. Bibcode: 2010IAUS..264...63A Altcode: 2009arXiv0910.0976A Long-term trends in the solar spectral irradiance are important to determine the impact on Earth's climate. These long-term changes are thought to be caused mainly by changes in the surface area covered by small-scale magnetic elements. The direct measurement of the contrast to determine the impact of these small-scale magnetic elements is, however, limited to a few wavelengths, and is, even for space instruments, affected by scattered light and instrument defocus. In this work we calculate emergent intensities from 3-D simulations of solar magneto-convection and validate the outcome by comparing with observations from Hinode/SOT. In this manner we aim to construct the contrast at wavelengths ranging from the NUV to the FIR. Title: The structure of the outer Galactic disc as revealed by IPHAS early A stars Authors: Sale, S. E.; Drew, J. E.; Knigge, C.; Zijlstra, A. A.; Irwin, M. J.; Morris, R. A. H.; Phillipps, S.; Drake, J. J.; Greimel, R.; Unruh, Y. C.; Groot, P. J.; Mampaso, A.; Walton, N. A. Bibcode: 2010MNRAS.402..713S Altcode: 2009arXiv0909.3857S; 2009MNRAS.tmp.1816S This study is an investigation of the stellar density profile of the Galactic disc in the anticentre direction. We select over 40000 early A stars from INT/WFC Photometric Hα Survey of the Northern Galactic Plane (IPHAS) photometry in the Galactic longitude range 160° < l < 200° close to the equatorial plane (-1° < b < +1°). We then compare their observed reddening-corrected apparent magnitude distribution with simulated photometry obtained from parametrized models in order to set constraints on the anticentre stellar density profile. By selecting A stars, we are appraising the properties of a population only ~100 Myr old. We find that the stellar density profile of young stars is well fit to an exponential with length-scale of (3020 +/- 120statistical +/- 180systematic) pc, which is comparable to that obtained in earlier studies, out to a Galactocentric radius of RT = (13.0 +/- 0.5statistical +/- 0.6systematic) kpc. At larger radii, the rate of decline appears to increase with the scalelength dropping to (1200 +/- 300statistical +/- 70systematic) pc. This result amounts to a refinement of the conclusions reached in previous studies that the stellar density profile is abruptly truncated. The IPHAS A star data are not compatible with models that propose a sudden change in metallicity at RG = 10 kpc. Title: IPHAS and the symbiotic stars . II. New discoveries and a sample of the most common mimics Authors: Corradi, R. L. M.; Valentini, M.; Munari, U.; Drew, J. E.; Rodríguez-Flores, E. R.; Viironen, K.; Greimel, R.; Santander-García, M.; Sabin, L.; Mampaso, A.; Parker, Q.; DePew, K.; Sale, S. E.; Unruh, Y. C.; Vink, J. S.; Rodríguez-Gil, P.; Barlow, M. J.; Lennon, D. J.; Groot, P. J.; Giammanco, C.; Zijlstra, A. A.; Walton, N. A. Bibcode: 2010A&A...509A..41C Altcode: 2009arXiv0910.5930C Context. Knowledge of the total population of symbiotic stars in the Galaxy is important for understanding basic aspects of stellar evolution in interacting binaries and the relevance of this class of objects in the formation of supernovae of type Ia.
Aims: In a previous paper, we presented the selection criteria needed to search for symbiotic stars in IPHAS, the INT Hα survey of the Northern Galactic plane. IPHAS gives us the opportunity to make a systematic, complete search for symbiotic stars in a magnitude-limited volume.
Methods: Follow-up spectroscopy at different telescopes worldwide of a sample of sixty two symbiotic star candidates is presented.
Results: Seven out of nineteen S-type candidates observed spectroscopically are confirmed to be genuine symbiotic stars. The spectral type of their red giant components, as well as reddening and distance, were computed by modelling the spectra. Only one new D-type symbiotic system, out of forty-three candidates observed, was found. This was as expected (see discussion in our paper on the selection criteria). The object shows evidence for a high density outflow expanding at a speed ≥65 km s-1. Most of the other candidates are lightly reddened classical T Tauri stars and more highly reddened young stellar objects that may be either more massive young stars of HAeBe type or classical Be stars. In addition, a few notable objects have been found, such as three new Wolf-Rayet stars and two relatively high-luminosity evolved massive stars. We also found a helium-rich source, possibly a dense ejecta hiding a WR star, which is surrounded by a large ionized nebula.
Conclusions: These spectroscopic data allow us to refine the selection criteria for symbiotic stars in the IPHAS survey and, more generally, to better understand the behaviour of different Hα emitters in the IPHAS and 2MASS colour-colour diagrams.

Based on observations obtained at; the 2.6 m Nordic Optical Telescope operated by NOTSA; the 2.5 m INT and 4.2 m WHT telescopes of the Isaac Newton Group of Telescopes in the Spanish Observatorio del Roque de Los Muchachos of the Instituto de Astrofísica de Canarias; the 2.3 m ANU telescope at Siding Spring Observatory, Australia; the Asiago 1.82 m telescope of the INAF Astronomical Observatory of Padova, Italy; and the 2.1 m telescope at San Pedro Martir, Mexico. Some of the INT spectra incorporated into this paper were obtained as part of a CCI International Time Programme awarded to the IPHAS collaboration. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. This research has also made use of the SIMBAD database, operated at CDS, Strasbourg, France. Title: Modelling rotational and cyclical spectral solar irradiance variations Authors: Unruh, Yvonne Bibcode: 2010cosp...38...18U Altcode: 2010cosp.meet...18U Solar irradiance changes are highly wavelength dependent: solar-cycle variations in the UV can be on the order of tens of percent, while changes in the visible are typically only of the order of one or two permille. With the launch of a number of instruments to measure spectral solar irradiance, we are now for a first time in a good position to explore the changing solar irradiance over a large range of wavelengths and to test our irradiance models as well as some of their underlying assumptions. I will introduce some of the current modelling approaches and present model-data comparisons, using the SATIRE irradiance model and SORCE/SIM measurements as an example. I will conclude by highlighting a number of outstanding questions regarding the modelling of spectral irradiance and current approaches to address these. Title: Total and spectral irradiance comparisons between SIM and the SATIRE model in the declining phase of cycle 23 Authors: Ball, Will; Unruh, Yvonne; Krivova, Natalie; Solanki, Sami K.; Harder, Jerald Bibcode: 2010cosp...38..136B Altcode: 2010cosp.meet..136B Climate models rely on accurate total and spectral solar irradiance inputs, but until 2003 con-tinuous spectral irradiance information across a large portion of the solar spectrum was lacking. Since the launch of the Solar Radiation and Climate Experiment (SORCE), with the Spectral Irradiance Monitor (SIM) observing the UV, visible and IR, data have been accumulating and now cover a significant portion of a cycle. For the first time this allows spectral models to be tested over periods greater than a solar rotation. We present six years of total and spectral irradiance reconstructions using the SATIRE model that incorporates SOHO/MDI continuum and magnetogram images for the period April 2004 to November 2009 in the declining phase of cycle 23 and through the recent unusual minimum. We compare these results with the SIM instrument and so cover the spectral region 200 -1600 nm. While detrended, short-term, variation is recreated well by the model, there are discrepancies in longer-term trends between observations and the model. This may become important when considering the radiative forcing from the Sun used in climate research and so understanding why there is such a significant disagreement is an important area of investigation. Title: Near-IR spectra of IPHAS extremely red Galactic AGB stars Authors: Wright, N. J.; Barlow, M. J.; Greimel, R.; Drew, J. E.; Matsuura, M.; Unruh, Y. C.; Zijlstra, A. A. Bibcode: 2009MNRAS.400.1413W Altcode: 2009arXiv0909.2642W; 2009MNRAS.tmp.1324W We present a library of 139 near-IR spectra of cool asymptotic giant branch stars that will be useful for comparison with theoretical model atmosphere calculations and for modelling the integrated emission from intermediate-age stellar populations. The source list was selected from the `extremely red' region of the Isaac Newton Telescope (INT) Photometric Hα Survey (IPHAS) colour-colour plane that is overwhelmingly dominated by very late-type stars. The spectral library also includes a large fraction of S-type and carbon stars. We present a number of spectral classification sequences highlighting the various molecular features identified and discuss a number of rare features with uncertain identifications in the literature. With its focus on particularly cool photospheres, this catalogue serves as a companion to recent spectroscopic atlases of MK standards in the near-IR. Finally, the relationship between IPHAS (r' - i') and (r' - Hα) colours and spectroscopically determined properties is discussed and a strong correlation between the (r' - Hα) colour and the C/O abundance index for S-type and carbon stars is noted. This relation has the potential to separate O-rich, S-type and carbon stars in the Galaxy based on their photometry alone. Title: Doppler images and chromospheric variability of TWA 17 Authors: Skelly, M. B.; Unruh, Y. C.; Barnes, J. R.; Lawson, W. A.; Donati, J. -F.; Collier Cameron, A. Bibcode: 2009MNRAS.399.1829S Altcode: 2009arXiv0907.2777S We present Doppler imaging and a Balmer line analysis of the weak-line T Tauri star TWA 17. Spectra were taken in 2006 with the University College London Echelle Spectrograph on the Anglo-Australian Telescope. Using least-squares deconvolution to improve the effective signal-to-noise ratio, we produced a Doppler map of the surface spot distribution. This shows similar features to maps of other rapidly rotating T Tauri stars, i.e. a polar spot with more spots extending out of it down to the equator.

In addition to the photospheric variability, the chromospheric variability was studied using the Balmer emission. The mean Hα profile has a narrow component consistent with rotational broadening and a broad component extending out to 220 km s-1. The variability in Hα suggests that the chromosphere has at least one slingshot prominence 3R* above the surface. Title: VizieR Online Data Catalog: Near-IR spectra of extremely red AGB stars (Wright+, 2009) Authors: Wright, N. J.; Barlow, M. J.; Greimel, R.; Drew, J. E.; Matsuura, M.; Unruh, Y. C.; Zijlstra, A. A. Bibcode: 2009yCat..74001413W Altcode: No abstract at ADS Title: The UV-Excess survey of the northern Galactic plane Authors: Groot, Paul J.; Verbeek, Kars; Greimel, Robert; Irwin, Mike; González-Solares, Eduardo; Gänsicke, Boris T.; de Groot, Eelco; Drew, Janet; Augusteijn, Thomas; Aungwerojwit, Amornrat; Barlow, Mike; Barros, Susana; van den Besselaar, Else J. M.; Casares, Jorge; Corradi, Romano; Corral-Santana, Jesús M.; Deacon, Niall; van Ham, Wilbert; Hu, Haili; Heber, Uli; Jonker, Peter G.; King, Rob; Knigge, Christian; Mampaso, Antonio; Marsh, Tom R.; Morales-Rueda, Luisa; Napiwotzki, Ralf; Naylor, Tim; Nelemans, Gijs; Oosting, Tim; Pyrzas, Stylianos; Pretorius, Magaretha; Rodríguez-Gil, Pablo; Roelofs, Gijs H. A.; Sale, Stuart; Schellart, Pim; Steeghs, Danny; Szyszka, Cezary; Unruh, Yvonne; Walton, Nicholas A.; Weston, Simon; Witham, Andrew; Woudt, Patrick; Zijlstra, Albert Bibcode: 2009MNRAS.399..323G Altcode: 2009arXiv0906.3498G; 2009MNRAS.tmp.1184G The UV-Excess survey of the northern Galactic plane images a 10° × 185° wide band, centred on the Galactic equator using the 2.5-m Isaac Newton Telescope in four bands (I5875) down to ~21-22 mag ( in I5875). The setup and data reduction procedures are described. Simulations of the colours of main-sequence stars, giant, supergiants, DA and DB white dwarfs and AM Canum Venaticorum stars are made, including the effects of reddening. A first look at the data of the survey (currently 30 per cent complete) is given. Title: Solar Surface Magnetism and Irradiance on Time Scales from Days to the 11-Year Cycle Authors: Domingo, V.; Ermolli, I.; Fox, P.; Fröhlich, C.; Haberreiter, M.; Krivova, N.; Kopp, G.; Schmutz, W.; Solanki, S. K.; Spruit, H. C.; Unruh, Y.; Vögler, A. Bibcode: 2009SSRv..145..337D Altcode: The uninterrupted measurement of the total solar irradiance during the last three solar cycles and an increasing amount of solar spectral irradiance measurements as well as solar imaging observations (magnetograms and photometric data) have stimulated the development of models attributing irradiance variations to solar surface magnetism. Here we review the current status of solar irradiance measurements and modelling efforts based on solar photospheric magnetic fields. Thereby we restrict ourselves to the study of solar variations from days to the solar cycle. Phenomenological models of the solar atmosphere in combination with imaging observations of solar electromagnetic radiation and measurements of the photospheric magnetic field have reached high enough quality to show that a large fraction (at least, about 80%) of the solar irradiance variability can be explained by the radiative effects of the magnetic activity present in the photosphere. Also, significant progress has been made with magnetohydrodynamic simulations of convection that allow us to relate the radiance of the photospheric magnetic structures to the observations. Title: An IPHAS-based search for accreting very low-mass objects using VO tools Authors: Valdivielso, L.; Martín, E. L.; Bouy, H.; Solano, E.; Drew, J. E.; Greimel, R.; Gutiérrez, R.; Unruh, Y. C.; Vink, J. S. Bibcode: 2009mavo.proc..175V Altcode: We prove that accreting very low-mass (VLM) stars and brown dwarfs (BDs) can be identified in IPHAS, an Hα emission survey of the northern Milky Way. Full exploitation of the IPHAS database and a future extension of it in the southern hemisphere will be useful in identifying VLM accreting objects near to and far from well-known star-forming regions. We have used Virtual Observatory (VO) tools to cross-match the IPHAS catalogue with the 2MASS catalogue. We defined photometric criteria to identify Hα emission sources with near-infrared colours similar to those of known young VLM stars and BDs. 4000 candidates were identified that met our criteria over an area of 1600 square degrees. Title: New young planetary nebulae in IPHAS Authors: Viironen, K.; Mampaso, A.; Corradi, R. L. M.; Rodríguez, M.; Greimel, R.; Sabin, L.; Sale, S. E.; Unruh, Y.; Delgado-Inglada, G.; Drew, J. E.; Giammanco, C.; Groot, P.; Parker, Q. A.; Sokoloski, J.; Zijlstra, A. Bibcode: 2009A&A...502..113V Altcode: 2009arXiv0904.1937V Aims: We search for very small-diameter galactic planetary nebulae (PNe) representing the earliest phases of PN evolution. The IPHAS catalogue of Hα-emitting stars provides a useful basis for this study since all sources present in this catalogue must be of small angular diameter.
Methods: The PN candidates are selected based on their location in two colour-colour diagrams: IPHAS (r' - Hα) vs. (r' - i'), and 2MASS (J - H) vs. (H - K_s). Spectroscopic follow-up was carried out on a sample of candidates to confirm their nature.
Results: We present a total of 83 PN candidates. We were able to obtain spectra or find the classification from the literature for 35 candidates. Five of these objects are likely to be new PNe, including one large bipolar PN discovered serendipitously close to an emission-line star. PN distances deduced from extinction-distance relations based on IPHAS field-star photometry are presented for the first time. These yield distance estimates for our objects in the range 2 kpc and 6 kpc. From the data in hand, we conclude that four of the discovered objects are probably young PNe. Title: An IPHAS-based search for accreting very low-mass objects using VO tools Authors: Valdivielso, L.; Martín, E. L.; Bouy, H.; Solano, E.; Drew, J. E.; Greimel, R.; Gutiérrez, R.; Unruh, Y. C.; Vink, J. S. Bibcode: 2009A&A...497..973V Altcode: 2008arXiv0810.4042V Context: The main goal of this paper is to prove that accreting very low-mass stars and brown dwarfs can be identified in IPHAS, an Hα emission survey of the northern Milky Way. Full exploitation of the IPHAS database and a future extension of it in the southern hemisphere will be useful in identifying very low-mass accreting objects near to and far from well-known star-forming regions.
Aims: We have used Virtual Observatory tools to cross-match the IPHAS catalogue with the 2MASS catalogue. We defined photometric criteria to identify Hα emission sources with near-infrared colours similar to those of known young very low-mass stars and brown dwarfs. 4000 candidates were identified that met our criteria over an area of 1600 square degrees. We present low-resolution optical spectra of 113 candidates. Spectral types have been derived for the 33 candidates that have spectroscopically confirmed Hα emission, negligible reddening and spectral class M. We have also measured Hα emission and investigated the NaI doublet (818.3 nm, 819.5 nm) in these 33 objects.
Methods: We confirm that 33 IPHAS candidates have strong Hα emission indicative of disc accretion for their spectral type. Twenty-three of them have spectral class M4 or later, of which ten have classes in the range M5.5-M7.0 and could thus be very young brown dwarfs. Many objects also have a weak NaI doublet, an indication of low surface gravity.
Results: IPHAS provides a very valuable database for identifying accreting very low-mass stars and brown dwarfs. Virtual Observatory tools provide an efficient method for identifying these objects over large areas of the sky. Based on our success rate of 23 Hα emission objects with spectral type in the range M4-M7 out of 113 candidates with spectroscopic follow-up, we estimate that there could be hundreds of such objects in the full IPHAS survey. Title: Iphas A-Type Stars with Mid-Infrared Excesses in Spitzer Surveys Authors: Hales, Antonio S.; Barlow, Michael J.; Drew, Janet E.; Unruh, Yvonne C.; Greimel, Robert; Irwin, Michael J.; González-Solares, Eduardo Bibcode: 2009ApJ...695...75H Altcode: 2009arXiv0901.0909H We have identified 17 A-type stars in the Galactic Plane that have mid-infrared (mid-IR) excesses at 8 μm. From observed colors in the (r' - Hα) - (r' - i') plane, we first identified 23,050 early A-type main-sequence (MS) star candidates in the Isaac Newton Photometric H-Alpha Survey (IPHAS) point source database that are located in Spitzer Galactic Legacy Mid-Plane Survey Extraordinaire Galactic plane fields. Imposing the requirement that they be detected in all seven Two Micron All Sky Survey and Infrared Astronomical Satellite bands led to a sample of 2692 candidate A-type stars with fully sampled 0.6 to 8 μm spectral energy distributions (SEDs). Optical classification spectra of 18 of the IPHAS candidate A-type MS stars showed that all but one could be well fitted using MS A-type templates, with the other being an A-type supergiant. Out of the 2692 A-type candidates 17 (0.6%) were found to have 8 μm excesses above the expected photospheric values. Taking into account non-A-Type contamination estimates, the 8 μm excess fraction is adjusted to ~0.7%. The distances to these sources range from 0.7 to 2.5 kpc. Only 10 out of the 17 excess stars had been covered by Spitzer MIPSGAL survey fields, of which five had detectable excesses at 24 μm. For sources with excesses detected in at least two mid-IR wavelength bands, blackbody fits to the excess SEDs yielded temperatures ranging from 270 to 650 K, and bolometric luminosity ratios L IR/L sstarf from 2.2 × 10-3 - 1.9 × 10-2, with a mean value of 7.9 × 10-3 (these bolometric luminosities are lower limits as cold dust is not detectable by this survey). Both the presence of mid-IR excesses and the derived bolometric luminosity ratios are consistent with many of these systems being in the planet-building transition phase between the early protoplanetary disk phase and the later debris disk phase. Title: High spatial resolution empirical 3D extinction mapping with IPHAS Authors: Sale, S. E.; Drew, J. E.; Greimel, R.; Unruh, Y. C.; IPHAS Consortium Bibcode: 2009IAUS..254P..67S Altcode: No abstract at ADS Title: Towards Long-Term Solar Irradiance Modelling: Network Contrasts from Magneto-Convection Simulations Authors: Unruh, Y. C.; Solanki, S. K.; Schüssler, M.; Vögler, A.; Garcia-Alvarez, D. Bibcode: 2009AIPC.1094..768U Altcode: 2009csss...15..768U Solar irradiance changes on a wide range of time scales and is a key driver of the Earth's climate where secular variability in particular is relevant. This is, however, not well understood and our knowledge relies on reconstructions based on sunspot numbers and similar proxies.

The prime candidate to produce secular variability is a change in the surface coverage of small-scale magnetic elements. Direct observational determination of the flux emitted by these magnetic elements is difficult, especially as information covering a large spectral range is needed. Here we present a theoretical approach to this problem using intensity calculations from 3-D simulations of solar magneto-convection and compare these with the intensity calculations used in the successful semi-empirical S ATIRE models at disk centre. Eventually, such a comparison should lead to the removal of the last free parameter from S ATIRE-based irradiance reconstruction. Title: High spatial resolution Galactic 3D extinction mapping with IPHAS Authors: Sale, Stuart E.; Drew, J. E.; Unruh, Y. C.; Irwin, M. J.; Knigge, C.; Phillipps, S.; Zijlstra, A. A.; Gänsicke, B. T.; Greimel, R.; Groot, P. J.; Mampaso, A.; Morris, R. A. H.; Napiwotzki, R.; Steeghs, D.; Walton, N. A. Bibcode: 2009MNRAS.392..497S Altcode: 2008arXiv0810.2547S We present an algorithm (MEAD, for `Mapping Extinction Against Distance') which will determine intrinsic (r' - i') colour, extinction, and distance for early-A to K4 stars extracted from the IPHAS r'/i'/Hα photometric data base. These data can be binned up to map extinction in three dimensions across the northern Galactic plane. The large size of the IPHAS data base (~200 million unique objects), the accuracy of the digital photometry it contains and its faint limiting magnitude (r' ~ 20) allow extinction to be mapped with fine angular (~10 arcmin) and distance (~ 0.1 kpc) resolution to distances of up to 10 kpc, outside the solar circle. High reddening within the solar circle on occasion brings this range down to ~2 kpc. The resolution achieved, both in angle and depth, greatly exceeds that of previous empirical 3D extinction maps, enabling the structure of the Galactic Plane to be studied in increased detail. MEAD accounts for the effect of the survey magnitude limits, photometric errors, unresolved interstellar medium (ISM) substructure and binarity. The impact of metallicity variations, within the range typical of the Galactic disc is small. The accuracy and reliability of MEAD are tested through the use of simulated photometry created with Monte Carlo sampling techniques. The success of this algorithm is demonstrated on a selection of fields and the results are compared to the literature. Title: Extremely red stellar objects revealed by IPHAS Authors: Wright, N. J.; Greimel, R.; Barlow, M. J.; Drew, J. E.; Cioni, M. -R. L.; Zijlstra, A. A.; Corradi, R. L. M.; González-Solares, E. A.; Groot, P.; Irwin, J.; Irwin, M. J.; Mampaso, A.; Morris, R. A. H.; Steeghs, D.; Unruh, Y. C.; Walton, N. Bibcode: 2008MNRAS.390..929W Altcode: 2008MNRAS.tmp.1113W; 2008arXiv0808.2441W We present photometric analysis and follow-up spectroscopy for a population of extremely red stellar objects extracted from the point-source catalogue of the Isaac Newton Telescope (INT) Photometric Hα Survey (IPHAS) of the northern Galactic plane. The vast majority of these objects have no previous identification. Analysis of optical, near- and mid-infrared photometry reveals that they are mostly highly reddened asymptotic giant branch stars, with significant levels of circumstellar material. We show that the distribution of these objects traces galactic extinction, their highly reddened colours being a product of both interstellar and circumstellar reddening. This is the first time that such a large sample of evolved low-mass stars has been detected in the visual and allows optical counterparts to be associated with sources from recent infrared surveys.

Follow-up spectroscopy on some of the most interesting objects in the sample has found significant numbers of S-type stars which can be clearly separated from oxygen-rich objects in the IPHAS colour-colour diagram. We show that this is due to the positions of different molecular bands relative to the narrow-band Hα filter used for IPHAS observations. The IPHAS (r' - Hα) colour offers a valuable diagnostic for identifying S-type stars. A selection method for identifying S-type stars in the Galactic plane is briefly discussed and we estimate that over a thousand new objects of this type may be discovered, potentially doubling the number of known objects in this short but important evolutionary phase. Title: IPHAS identification of IGR J19267+1325 as a Cataclysmic Variable Authors: Steeghs, D.; Knigge, C.; Drew, J.; Unruh, Y.; Greimel, R. Bibcode: 2008ATel.1653....1S Altcode: We report on optical observations of the galactic plane containing the X-ray source IGR J19267+1325=1RXS J192626.8+132153 (ATEL #1649,#1323) using data from the INT Photometric H-Alpha Survey (IPHAS; http://www.iphas.org ). The field containing the X-ray source was observed in good observing conditions on August 22 2004 using the Isaac Newton Telescope at La Palma Observatory and its Wide Field Camera. Title: Initial data release from the INT Photometric Hα Survey of the Northern Galactic Plane (IPHAS) Authors: González-Solares, E. A.; Walton, N. A.; Greimel, R.; Drew, J. E.; Irwin, M. J.; Sale, S. E.; Andrews, K.; Aungwerojwit, A.; Barlow, M. J.; van den Besselaar, E.; Corradi, R. L. M.; Gänsicke, B. T.; Groot, P. J.; Hales, A. S.; Hopewell, E. C.; Hu, Haili; Irwin, J.; Knigge, C.; Lagadec, E.; Leisy, P.; Lewis, J. R.; Mampaso, A.; Matsuura, M.; Moont, B.; Morales-Rueda, L.; Morris, R. A. H.; Naylor, T.; Parker, Q. A.; Prema, P.; Pyrzas, S.; Rixon, G. T.; Rodríguez-Gil, P.; Roelofs, G.; Sabin, L.; Skillen, I.; Suso, J.; Tata, R.; Viironen, K.; Vink, J. S.; Witham, A.; Wright, N. J.; Zijlstra, A. A.; Zurita, A.; Drake, J.; Fabregat, J.; Lennon, D. J.; Lucas, P. W.; Martín, E. L.; Phillipps, S.; Steeghs, D.; Unruh, Y. C. Bibcode: 2008MNRAS.388...89G Altcode: 2008MNRAS.tmp..707G; 2007arXiv0712.0384G The INT/WFC Photometric Hα Survey of the Northern Galactic Plane (IPHAS) is an imaging survey being carried out in Hα, r' and i' filters, with the Wide Field Camera (WFC) on the 2.5-m Isaac Newton Telescope (INT) to a depth of r' = 20 (10σ). The survey is aimed at revealing the large scale organization of the Milky Way and can be applied to identifying a range of stellar populations within it. Mapping emission line objects enables a particular focus on objects in the young and old stages of stellar evolution ranging from early T-Tauri stars to late planetary nebulae. In this paper we present the IPHAS Initial Data Release, primarily a photometric catalogue of about 200 million unique objects, coupled with associated image data covering about 1600 deg2 in three passbands. We note how access to the primary data products has been implemented through use of standard virtual observatory publishing interfaces. Simple traditional web access is provided to the main IPHAS photometric catalogue, in addition to a number of common catalogues (such as 2MASS) which are of immediate relevance. Access through the AstroGrid VO Desktop opens up the full range of analysis options, and allows full integration with the wider range of data and services available through the Virtual Observatory. The IDR represents the largest data set published primarily through VO interfaces to date, and so stands as an exemplar of the future of survey data mining. Examples of data access are given, including a cross-matching of IPHAS photometry with sources in the UKIDSS Galactic Plane Survey that validates the existing calibration of the best data. Title: Spectral irradiance variations: comparison between observations and the SATIRE model on solar rotation time scales Authors: Unruh, Y. C.; Krivova, N. A.; Solanki, S. K.; Harder, J. W.; Kopp, G. Bibcode: 2008A&A...486..311U Altcode: 2008arXiv0802.4178U Aims: We test the reliability of the observed and calculated spectral irradiance variations between 200 and 1600 nm over a time span of three solar rotations in 2004.
Methods: We compare our model calculations to spectral irradiance observations taken with SORCE/SIM, SoHO/VIRGO, and UARS/SUSIM. The calculations assume LTE and are based on the SATIRE (Spectral And Total Irradiance REconstruction) model. We analyse the variability as a function of wavelength and present time series in a number of selected wavelength regions covering the UV to the NIR. We also show the facular and spot contributions to the total calculated variability.
Results: In most wavelength regions, the variability agrees well between all sets of observations and the model calculations. The model does particularly well between 400 and 1300 nm, but fails below 220 nm, as well as for some of the strong NUV lines. Our calculations clearly show the shift from faculae-dominated variability in the NUV to spot-dominated variability above approximately 400 nm. We also discuss some of the remaining problems, such as the low sensitivity of SUSIM and SORCE for wavelengths between approximately 310 and 350 nm, where currently the model calculations still provide the best estimates of solar variability. Title: Magnetospheric accretion on the T Tauri star BP Tauri Authors: Donati, J. -F.; Jardine, M. M.; Gregory, S. G.; Petit, P.; Paletou, F.; Bouvier, J.; Dougados, C.; Ménard, F.; Collier Cameron, A.; Harries, T. J.; Hussain, G. A. J.; Unruh, Y.; Morin, J.; Marsden, S. C.; Manset, N.; Aurière, M.; Catala, C.; Alecian, E. Bibcode: 2008MNRAS.386.1234D Altcode: 2008MNRAS.tmp..461D; 2008arXiv0802.2052D From observations collected with the ESPaDOnS and NARVAL spectropolarimeters, we report the detection of Zeeman signatures on the classical T Tauri star (cTTS) BP Tau. Circular polarization signatures in photospheric lines and in narrow emission lines tracing magnetospheric accretion are monitored throughout most of the rotation cycle of BP Tau at two different epochs in 2006. We observe that rotational modulation dominates the temporal variations of both unpolarized and circularly polarized spectral proxies tracing the photosphere and the footpoints of accretion funnels.

From the complete data sets at each epoch, we reconstruct the large-scale magnetic topology and the location of accretion spots at the surface of BP Tau using tomographic imaging. We find that the field of BP Tau involves a 1.2 kG dipole and 1.6 kG octupole, both slightly tilted with respect to the rotation axis. Accretion spots coincide with the two main magnetic poles at high latitudes and overlap with dark photospheric spots; they cover about 2 per cent of the stellar surface. The strong mainly axisymmetric poloidal field of BP Tau is very reminiscent of magnetic topologies of fully convective dwarfs. It suggests that magnetic fields of fully convective cTTSs such as BP Tau are likely not fossil remants, but rather result from vigorous dynamo action operating within the bulk of their convective zones.

Preliminary modelling suggests that the magnetosphere of BP Tau extends to distances of at least 4R* to ensure that accretion spots are located at high latitudes, and is not blown open close to the surface by a putative stellar wind. It apparently succeeds in coupling to the accretion disc as far out as the corotation radius, and could possibly explain the slow rotation of BP Tau.

Based on observations obtained at the Canada-France-Hawaii Telescope (CFHT) and at the Télescope Bernard Lyot (TBL). CFHT is operated by the National Research Council of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France (INSU/CNRS) and the University of Hawaii, while TBL is operated by CNRS/INSU.

E-mail: donati@ast.obs-mip.fr (J-FD); mmj@st-andrews.ac.uk (MMJ); sg64@st-andrews.ac.uk (SGG); petit@ast.obs-mip.fr (PP); fpaletou@ast.obs-mip.fr (FP); jerome.bouvier@obs.ujf-grenoble.fr (JB); catherine.dougados@obs.ujf-grenoble.fr (CD); francois.menard@obs.ujf-grenoble.fr (FM); acc4@st-andrews.ac.uk (ACC); th@astro.ex.ac.uk (TJH); ghussain@eso.org (GAJH); y.unruh@imperial.ac.uk (YU); jmorin@ast.obs-mip.fr (JM); scm@aao.gov.au (SCM); manset@cfht.hawaii.edu (NM); auriere@ast.obs-mip.fr (MA); claude.catala@obspm.fr (CC); evelyne.alecian@obspm.fr (EA) Title: Doppler images and chromospheric variability of TWA 6 Authors: Skelly, M. B.; Unruh, Y. C.; Collier Cameron, A.; Barnes, J. R.; Donati, J. -F.; Lawson, W. A.; Carter, B. D. Bibcode: 2008MNRAS.385..708S Altcode: 2008MNRAS.tmp..221S; 2008arXiv0801.0541S We present Doppler imaging and Balmer line analysis of the weak-line T Tauri star TWA 6. Using these data we have made one of the first attempts to measure differential rotation in a T Tauri star, and the first detection of a slingshot prominence in such a star. We also show the most direct evidence to date of the existence of solar-type plages in a star other than the Sun.

Observations were made over six nights: 2006 February 11-13 and 2006 February 18-20, when spectra were taken with the UCL Echelle Spectrograph on the 3.9-m Anglo-Australian Telescope. Using least-squares deconvolution to improve the effective signal-to-noise ratio we produced two Doppler maps. These show similar features to maps of other rapidly rotating T Tauri stars, i.e. a polar spot with more spots extending out of it down to equator. Comparison of the two maps was carried out to measure the differential rotation. Cross-correlation and parameter fitting indicates that TWA 6 does not have detectable differential rotation.

The Balmer emission of the star was studied. The mean Hα profile has a narrow component consistent with rotational broadening and a broad component extending out to +/-250kms-1. The variability in Hα suggests that the chromosphere has active regions that are cospatial with the spots in the photosphere, similar to the `plages' observed on the Sun. In addition the star has at least one slingshot prominence 3R* above the surface - the first such detection in a T Tauri star. Title: Five WC9 stars discovered in the AAO/UKST Hα survey Authors: Hopewell, E. C.; Barlow, M. J.; Drew, J. E.; Unruh, Y. C.; Parker, Q. A.; Pierce, M. J.; Crowther, P. A.; Knigge, C.; Phillipps, S.; Zijlstra, A. A. Bibcode: 2005MNRAS.363..857H Altcode: 2005MNRAS.tmp..842H; 2005astro.ph..8187H We report the discovery of five massive Wolf-Rayet (WR) stars resulting from a programme of follow-up spectroscopy of candidate emission-line stars in the Anglo-Australian Observatory United Kingdom Schmidt Telescope (AAO/UKST) Southern Galactic Plane Hα survey. The 6195-6775 Åspectra of the stars are presented and discussed. A WC9 class is assigned to all five stars through comparison of their spectra with those of known late-type WC stars, bringing the known total number of Galactic WC9 stars to 44. Whilst three of the five WC9 stars exhibit near-infrared (NIR) excesses characteristic of hot dust emission (as seen in the great majority of known WC9 stars), we find that two of the stars show no discernible evidence of such excesses. This increases the number of known WC9 stars without NIR excesses to seven. Reddenings and distances for all five stars are estimated. Title: The INT Photometric Hα Survey of the Northern Galactic Plane (IPHAS) Authors: Drew, Janet E.; Greimel, R.; Irwin, M. J.; Aungwerojwit, A.; Barlow, M. J.; Corradi, R. L. M.; Drake, J. J.; Gänsicke, B. T.; Groot, P.; Hales, A.; Hopewell, E. C.; Irwin, J.; Knigge, C.; Leisy, P.; Lennon, D. J.; Mampaso, A.; Masheder, M. R. W.; Matsuura, M.; Morales-Rueda, L.; Morris, R. A. H.; Parker, Q. A.; Phillipps, S.; Rodriguez-Gil, P.; Roelofs, G.; Skillen, I.; Sokoloski, J. L.; Steeghs, D.; Unruh, Y. C.; Viironen, K.; Vink, J. S.; Walton, N. A.; Witham, A.; Wright, N.; Zijlstra, A. A.; Zurita, A. Bibcode: 2005MNRAS.362..753D Altcode: 2005MNRAS.tmp..738D; 2005astro.ph..6726D The Isaac Newton Telescope (INT) Photometric Hα Survey of the Northern Galactic Plane (IPHAS) is a 1800-deg2 CCD survey of the northern Milky Way spanning the latitude range -5° < b < + 5° and reaching down to r'~= 20 (10σ). Representative observations and an assessment of point-source data from IPHAS, now underway, are presented. The data obtained are Wide Field Camera images in the Hα narrow-band, and Sloan r' and i' broad-band filters. We simulate IPHAS (r'-Hα,r'-i') point-source colours using a spectrophotometric library of stellar spectra and available filter transmission profiles: this defines the expected colour properties of (i) solar metallicity stars, without Hα emission, and (ii) emission-line stars. Comparisons with observations of fields in Aquila show that the simulations of normal star colours reproduce the observations well for all spectral types earlier than M. A further comparison between colours synthesized from long-slit flux-calibrated spectra and IPHAS photometry for six objects in a Taurus field confirms the reliability of the pipeline calibration. Spectroscopic follow-up of a field in Cepheus shows that sources lying above the main stellar locus in the (r'- Hα,r'-i') plane are confirmed to be emission-line objects with very few failures. In this same field, examples of Hα deficit objects (a white dwarf and a carbon star) are shown to be readily distinguished by their IPHAS colours. The role IPHAS can play in studies of spatially resolved northern Galactic nebulae is discussed briefly and illustrated by a continuum-subtracted mosaic image of Shajn 147 (a supernova remnant, 3° in diameter). The final catalogue of IPHAS point sources will contain photometry on about 80 million objects. Used on its own, or in combination with near-infrared photometric catalogues, IPHAS is a major resource for the study of stellar populations making up the disc of the Milky Way. The eventual yield of new northern emission-line objects from IPHAS is likely to be an order of magnitude increase on the number already known. Title: Probing the circumstellar structures of T Tauri stars and their relationship to those of Herbig stars Authors: Vink, Jorick S.; Drew, Janet E.; Harries, Tim J.; Oudmaijer, René D.; Unruh, Yvonne Bibcode: 2005MNRAS.359.1049V Altcode: 2005MNRAS.tmp..371V; 2005astro.ph..2535V We present Hα spectropolarimetry observations of a sample of 10 bright T Tauri stars, supplemented with new Herbig Ae/Be star data. A change in the linear polarization across Hα is detected in most of the T Tauri (9/10) and Herbig Ae (9/11) objects, which we interpret in terms of a compact source of line photons that is scattered off a rotating accretion disc. We find consistency between the position angle (PA) of the polarization and those of imaged disc PAs from infrared and millimetre imaging and interferometry studies, probing much larger scales. For the Herbig Ae stars AB Aur, MWC 480 and CQ Tau, we find the polarization PA to be perpendicular to the imaged disc, which is expected for single scattering. On the other hand, the polarization PA aligns with the outer disc PA for the T Tauri stars DR Tau and SU Aur and FU Ori, conforming to the case of multiple scattering. This difference can be explained if the inner discs of Herbig Ae stars are optically thin, whilst those around our T Tauri stars and FU Ori are optically thick. Furthermore, we develop a novel technique that combines known inclination angles and our recent Monte Carlo models to constrain the inner rim sizes of SU Aur, GW Ori, AB Aur and CQ Tau. Finally, we consider the connection of the inner disc structure with the orientation of the magnetic field in the foreground interstellar medium: for FU Ori and DR Tau, we infer an alignment of the stellar axis and the larger magnetic field direction. Title: IPHAS: Surveying the North Galactic Plane in Hα Authors: Drew, J. E.; Lennon, D. J., Greimel, R.; Zijlstra, A.; Irwin, J.; Aungwerowijt, A.; Barlow, M. J.; Corradi, R.; Evans, C. J.; Gaensicke, B.; Groot, P.; Hales, A.; Hopewell, E.; Irwin, M. J.; Jaigirdar, M.; Knigge, C.; Leisy, P.; Mampaso, A.; Matsuura, M.; Morales Rueda, L.; Morris, R.; Parker, Q. A.; Phillipps, S.; Rodríguez Gil, P.; Roelofs, G.; Skillen, I.; Steeghs, D.; Unruh, Y. C.; Viironen, K.; Vink, J.; Walton, N. A.; Witham, A.; Wright, N.; Zurita, A. Bibcode: 2005INGN....9....3D Altcode: H-alpha emission is ubiquitous in our Galaxy. It traces ionised gas of assorted nebulae such as HII regions, planetary nebulae, Wolf-Rayet nebulae, and supernova remnants. It is a strong signature of active stars, interacting binaries, very massive stars (especially supergiants, Luminous Blue Variables and Wolf-Rayet stars), Be stars, post-AGB stars, pre-main-sequence stars and so on. These objects represent important evolutionary phases which are generally short lived, and are hence few in number and difficult to find. Their discovery is therefore well worth the effort of a concerted programme and in August 2003 a major new survey project was started using the Wide Field Camera (WFC) on the Isaac Newton Telescope (INT) to do just that. It is called the INT Photometric H-alpha Survey of the Northern Galactic Plane, or IPHAS for short. Title: IPHAS: The INT/WFC Photometric H-alpha Survey of the Northern Galactic Plane Authors: Walton, N. A.; Drew, J.; Barlow, M. J.; Corradi, R.; Drake, J.; Gaensicke, B.; Greimel, R.; Groot, P.; Irwin, M. J.; Knigge, C.; Leisy, P.; Lennon, D. J.; Mampaso, A.; Masheder, M.; Morris, R.; Parker, Q. A.; Phillipps, S.; Pretorius, M.; Rodriguez-Gil, P.; Skillen, I.; Sokoloski, J.; Steegs, D.; Unruh, Y.; Witham, A.; Zijlstra, A.; Zurita, A.; IPHAS Collaboration Bibcode: 2004AAS...20511303W Altcode: 2004BAAS...36.1541W H-alpha emission both traces diffuse ionised nebulae and is commonly prominent in the spectra of pre- and post-main-sequence stars and interacting binaries. Since these are mostly relatively short-lived phases of evolution, they represent a minority of objects in a mature galaxy like our own at any one time. In the case of interacting binaries, they are simply hard to find. This scarcity, in turn, has acted as a brake on our understanding of these crucial evolutionary stages that, in youth, help shape the growth of planetary systems, and in old age, determine stellar end states along with the recycling of energy and chemically enriched matter back into the galactic environment.

IPHAS is our H-alpha survey of the Northern Galactic Plane being carried out with the 2.5-m Isaac Newton telescope's Wide Field Camera. Some ∼1800 deg2 of the northern Galactic plane, over latitudes 5 < b < 5, is being imaged in H-alpha, r', i' to a depth of r' ∼20 mag.

Here we report on the first 120 nights of observations. We comment on the advanced reduction pipeline employed to generate object catalogues. Early results are noted, including the discovery of a number of new, hitherto rare, quadropolar planetary nebulae. The IPHAS objects have been mined to select candidate samples for followup spectroscopic studies. Extreme emission line objects are selected from the (r' - H-alpha) v (r' - i') colour-colour plot. First detections of low mass young stars in the massive OB association Cyg OB2 are presented.

We note how this data set will be a valuable resource for the emerging Virtual Observatory, and will be especially powerful when compared with matching multi-colour IR and optical surveys (e.g. 2MASS and SDSS). Title: Discovery of a WO star in the Scutum-Crux arm of the inner Galaxy Authors: Drew, Janet E.; Barlow, M. J.; Unruh, Y. C.; Parker, Q. A.; Wesson, R.; Pierce, M. J.; Masheder, M. R. W.; Phillipps, S. Bibcode: 2004MNRAS.351..206D Altcode: 2004astro.ph..3482D We report the discovery of only the fourth massive WO star to be found in the Milky Way, and only the seventh identified within the Local Group. This has resulted from the first observations made in a programme of follow-up spectroscopy of candidate emission-line stars from the AAO/UKST Southern Galactic Plane Hα Survey. The optical spectrum of this star, to become WR 93b in the Catalogue of Galactic Wolf-Rayet stars, is presented and described. WR 93b is classified as WO3 and is shown to be highly reddened [E(B-V) = 2.1 +/- 0.1]. A recombination-line analysis of the emission lines yields the abundance ratios C/He = 0.95 and O/He = 0.13 (by number). Comparisons at near-infrared wavelengths of reddening-corrected photometry between WR 93b and both of Sand 2 (WO3, D= 49 kpc) and Sand 5 (WO2, D= 1.75 kpc) yield a consistent distance to WR 93b of 3.4 kpc. Positioned at Galactic coordinates , the star is most likely located in the Scutum-Crux arm of the inner Milky Way. We note that none of the four Galactic WO stars lies significantly beyond the solar circle (with two well inside).

Estimation of the wind terminal velocity in WR 93b at 5750 km s-1 makes this star the current wind-speed record holder among all non-degenerate stars. Title: Multisite observations of SU Aurigae Authors: Unruh, Y. C.; Donati, J. -F.; Oliveira, J. M.; Collier Cameron, A.; Catala, C.; Henrichs, H. F.; Johns-Krull, C. M.; Foing, B.; Hao, J.; Cao, H.; Landstreet, J. D.; Stempels, H. C.; de Jong, J. A.; Telting, J.; Walton, N.; Ehrenfreund, P.; Hatzes, A. P.; Neff, J. E.; Böhm, T.; Simon, T.; Kaper, L.; Strassmeier, K. G.; Granzer, Th. Bibcode: 2004MNRAS.348.1301U Altcode: 2004astro.ph..1081U We present results from the 1996 Multi-Site Continuous Spectroscopy (MUSICOS) campaign on the T Tauri star SU Aurigae. We find a 2.7-d periodicity in the HeI (587.6 nm) line, and somewhat longer, less well-pronounced periodicities in the Balmer lines and in Na D. Our observations support the suggestion that the wind and infall signatures are out of phase on SU Aur. We present Doppler images of SU Aur that have been obtained from least-squares deconvolved profiles. Images taken about one rotation apart show only limited overlap, in particular at low latitudes. This is due in part to limitations in signal-to-noise ratio, and in part to line-profile deformations that arise from short-lived and/or non-surface features. The agreement at high latitudes is better and suggests that at least some longer-lived features are present. The analysis of Stokes V profiles yields a marginal magnetic field detection during one of the phases. Title: Spot sizes on Sun-like stars Authors: Solanki, S. K.; Unruh, Y. C. Bibcode: 2004MNRAS.348..307S Altcode: 2003astro.ph.11310S The total area coverage by starspots is of interest for a variety of reasons, but direct techniques only provide estimates of this important quantity. Sunspot areas exhibit a lognormal size distribution irrespective of the phase of the activity cycle, implying that most sunspots are small. Here we explore the consequences if starspot areas were similarly distributed. The solar data allow for an increase in the fraction of larger sunspots with increasing activity. Taking this difference between the size distribution at sunspot maximum and minimum, we extrapolate to higher activity levels, assuming different dependences of the parameters of the lognormal distribution on total spot coverage. We find that, even for very heavily spotted (hypothetical) stars, a large fraction of the spots are smaller than the current resolution limit of Doppler images and hence might be missed on traditional Doppler maps. Title: Specific Causes of Solar Cycle Irradiance Variability Authors: Unruh, Y. C. Bibcode: 2004cosp...35.4362U Altcode: 2004cosp.meet.4362U The total solar irradiance has varied by about 0.1% between solar cycle minimum and maximum during the last couple of cycles. These variations are highly wavelength dependent with changes of an order of magnitude larger in the UV than in the visible. I discuss some of the proposed causes of total and spectral solar irradiance variability, and in particular the contribution of magnetic surface features. Title: Resolved polarization changes across Hα in the classical T Tauri star RY Tauri Authors: Vink, Jorick S.; Drew, J. E.; Harries, T. J.; Oudmaijer, R. D.; Unruh, Y. C. Bibcode: 2003A&A...406..703V Altcode: 2003astro.ph..6095V We present linear Hα spectropolarimetry of the classical T Tauri star RY Tau. A change in the polarization percentage and position angle across Hα is detected, which suggests that line photons are scattered in a rotating disc. We derive the position angle from the slope of the loop in the (Q,U) diagram and find it to be 146 +/- 3 degree. This is perpendicular to the position angle of the disc of 48 +/- 5 degree as deduced from millimeter imaging by Koerner & Sargent (\cite{Koerner1995}). This finding is consistent, as scattering off the imaged millimeter disc is expected to yield a polarization signature in a direction that is rotated by 90 degree from this disc. The observed spectropolarimetric behaviour of RY Tau is reminiscent of that seen in a large group of Herbig Ae stars, suggesting a common circumstellar origin of the polarized photons. Title: Reconstruction of solar irradiance variations in cycle 23: Is solar surface magnetism the cause? Authors: Krivova, N. A.; Solanki, S. K.; Fligge, M.; Unruh, Y. C. Bibcode: 2003A&A...399L...1K Altcode: A model of solar irradiance variations is presented which is based on the assumption that solar surface magnetism is responsible for all total irradiance changes on time scales of days to years. A time series of daily magnetograms and empirical models of the thermal structure of magnetic features (sunspots, faculae) are combined to reconstruct total (and spectral) irradiance from 1996 to 2002. Comparisons with observational data reveal an excellent correspondence, although the model only contains a single free parameter. This provides strong support for the hypothesis that solar irradiance variations are caused by changes in the amount and distribution of magnetic flux at the solar surface. Title: Solar Variability and Climate Change; Poster Summary Authors: Unruh, Y. Bibcode: 2002EGSGA..27.6708U Altcode: I will give a brief overview of the posters presented in session ST20 and link them into the context of the talks presented. This will be complemented by my necessarily incomplete and personal selection of some poster highlights. Title: Irradiance Medels based on Magnetic Activity Authors: Solanki, S.; Krivova, N.; Unruh, Y. Bibcode: 2002cosp...34E1357S Altcode: 2002cosp.meetE1357S An introduction is given to the modelling of irradiance variations based on solar surface magnetism. We describe how a time series of daily magnetograms and empirical models of the thermal structure of magnetic features (sunspots, magnetic elements) are combined to reconstruct total and spectral irradiance on a time scale of weeks to years. Comparisons with observational data reveal an excellent correspondence. On a longer time scale of decades to centuries we first need to know how the Sun's magnetic field evolved. Hence reconstructions of the Sun's total magnetic flux are briefly introduced, before we present longer term reconstructions of the total and spectral irradiance since the Maunder minimum. Title: The influence of an inclined rotation axis on solar irradiance variations Authors: Knaack, R.; Fligge, M.; Solanki, S. K.; Unruh, Y. C. Bibcode: 2001A&A...376.1080K Altcode: Compared with Sun-like stars, the irradiance variations of the Sun over the solar cycle appear to be relatively small for its average activity level (Lockwood et al. \cite{Lockwood:etal:1992}; Radick et al. \cite{Radick:etal:1998}). It has been proposed that the special position of Earth-based observers in the ecliptic plane may give the impression of a subdued solar photometric variability (Schatten \cite{Schatten:1993}). The aim of the present paper is to examine the influence on irradiance variations of a solar rotation axis inclined towards the observer. A three-component model is used to calculate relative flux variations of a given active-region distribution on the surface of the Sun as a function of inclination and wavelength. Wavelength-dependent intensity spectra are used to describe the contributions of the undisturbed photosphere, sunspots and faculae. The spectra result from models that have successfully been used to reproduce a host of solar data and thus represent realistic estimates of the radiative output from these solar features. We find that an inclined rotation axis increases the total solar irradiance variations maximally by 40%. The most probable value is approximately 6%. This is much less than that suggested by former studies, which were based on simple contrast functions. In the averaged Strömgren filters we estimate a most probable increase of the solar variability of 30%. In addition, we estimate the dependence of the flux in the chromospheric Ca II H&K lines on inclination. We find that the average chromospheric activity level depends only slightly on the inclination angle. The chromospheric variability of Sun-like stars, however, is significantly affected. Nonetheless, our results indicate that a different average inclination of stellar rotation axes relative to the observer cannot explain the discrepancy between the brightness variations of the Sun and Sun-like stars. Title: Diagnostics from Spectral Irradiance Measurements Authors: Unruh, Y. C.; Solanki, S. K. Bibcode: 2001AGUSM..SP32B01U Altcode: Solar irradiance varies in tune with solar activity. The irradiance changes show a strong wavelength dependence, being an order of magnitude larger in the UV than in the visible. The spectral dependence of the irradiance variations can be used to differentiate between mechanisms that may be responsible for the irradiance changes. I review some of the mechanisms that have been invoked in the past to explain the solar irradiance variations and compare their predicted spectral irradiance changes with solar irradiance measurements. The comparisons imply that surface magnetic features alone are sufficient to explain solar irradiance data. Title: Stellar Irradiance Variations Caused by Magnetic Activity: The Influence of an Inclined Rotation Axis Authors: Knaack, R.; Fligge, M.; Solanki, S. K.; Unruh, Y. C. Bibcode: 2001ASPC..248..227K Altcode: 2001mfah.conf..227K No abstract at ADS Title: Are the Sun's Brightness Variations Really Tamer than Those of Other Comparable Solar-type Stars? (CD-ROM Directory: contribs/unruh1) Authors: Unruh, Y. C.; Knaack, R.; Fligge, M.; Solanki, S. K. Bibcode: 2001ASPC..223..748U Altcode: 2001csss...11..748U No abstract at ADS Title: Doppler Images of LW Hydrae (CD-ROM Directory: contribs/unruh2) Authors: Unruh, Y. C.; Gatti, A. A.; Drew, J. E.; Roberts, G.; van Wyk, F.; Marang, F.; Kilkenny, D. Bibcode: 2001ASPC..223.1320U Altcode: 2001csss...11.1320U No abstract at ADS Title: Variations of the Solar Spectral Irradiance Authors: Solanki, S. K.; Fligge, M.; Unruh, Y. C. Bibcode: 2001IAUS..203...66S Altcode: Not just the total solar irradiance is known to vary, but also the solar spectrum. Observations and models of solar spectral irradiance variations are presented. Title: Preliminary MUSICOS 96 results on Balmer line variability on the T Tauri star SU aurigae Authors: Oliveira, J. M.; Unruh, Y. C.; Foing, B. H.; MUSICOS 1996 Collaboration Bibcode: 2001AdSpR..26.1747O Altcode: The study of young stellar objects is essential for the further understanding of the early evolutionary stages of the Sun and similar low-mass stars. In this context, T Tauri stars supply valuable information on their pre-main sequence evolution. SU Aur is a classical T Tauri star that shows little veiling and few emission lines. The Balmer line profiles are extremely variable, even on short time scales. We present results from the analysis of the variability of these spectral lines, based on a data set obtained during the world-wide multi-site spectroscopic MUSICOS 1996 campaign. We attempt to describe the interaction of the stellar magnetosphere and the accretion disk, and search for the signatures of mass inflow and ejection. Title: Spectral Line Variability in the Circumstellar Environment of the Classical T Tauri Star SU Aurigae (CD-ROM Directory: contribs/oliveira) Authors: Oliveira, J. M.; Foing, B. H.; Unruh, Y. C. Bibcode: 2001ASPC..223..539O Altcode: 2001csss...11..539O No abstract at ADS Title: Modelling solar irradiance variations: Comparison with observations, including line-ratio variations Authors: Unruh, Y. C.; Solanki, S. K.; Fligge, M. Bibcode: 2000SSRv...94..145U Altcode: Solar irradiance variations show a strong temporal and spectral dependence. The progression of the Sun through its activity cycle as well as solar rotation are mirrored in the irradiance variations. The spectral dependence is such that the variations are several magnitudes larger in the EUV than in the visible or infrared. We present a simple 3-component model that is based on the assumption that changes in the solar flux are exclusively due to changes in spot and facular coverage. We compare our model to observations of the spectral solar irradiance variations. Despite its simplicity, we find that the agreement between our model and the observations is surprisingly good. We also explore the reliability and the limitations of our approach by comparing observations of the solar facular contrast and of the changes in spectral line depths with our calculations. Title: Modelling Short-Term Spectral Irradiance Variations Authors: Fligge, M.; Solanki, S. K.; Unruh, Y. C. Bibcode: 2000SSRv...94..139F Altcode: On time-scales of the solar rotation most of the solar irradiance variations are caused by the changing distribution of solar surface magnetic features. We model these short-term irradiance variations using calculations of sunspot and facular contrasts as a function of wavelength and limb angle on the Sun. The position of active regions on the solar disc is derived from the MDI magnetograms. The reconstructed irradiance variations are compared with total and spectral irradiance measurements obtained by the VIRGO experiment on SOHO. Title: Magnetospheric accretion and winds on the T Tauri star SU Aurigae. Multi-spectral line variability and cross-correlation analysis Authors: Oliveira, J. M.; Foing, B. H.; van Loon, J. Th.; Unruh, Y. C. Bibcode: 2000A&A...362..615O Altcode: 2000astro.ph..9087O SU Aurigae is a T Tauri star that was well monitored during the MUSICOS 96 multi-site campaign. We present the results of the spectroscopic analysis of the circumstellar environment of this star, particularly of the Hα , Hβ , Na I D and He I D3 line profiles. The signatures of modulated outflows and mass accretion events are analysed, as well as transient spectral features. We compute the cross-correlation function (CCF) of several pairs of (velocity bins in) spectral lines to better investigate the profiles' temporal variability. We found increasing time lags between the variability of He I D3, Na I D and Hβ . We propose this may be understood in terms of azimuthal distortion of the magnetic field lines due to the different rotation rates of the star and the disk. We find the slightly blueshifted absorption features in Hα , Hβ \ and Na I D to be anti-correlated with the accretion flow signatures. We propose that the transient absorption features in the blue wings of Hα , Hβ \ and Na I D (signatures of mass outflows), and flare brightenings are related to the disruption of distorted magnetospheric field lines. Based on observations obtained during the MUSICOS~96 campaign in which were involved: Isaac Newton Telescope (INT, La Palma), Observatoire de Haute Provence (OHP, France), McDonald Observatory (MDO, USA), Beijing Astronomical Observatory (BAO, Xinglong, China) and Canada-France-Hawaii Telescope (CFHT, Hawaii). Title: Modelling irradiance variations from the surface distribution of the solar magnetic field Authors: Fligge, M.; Solanki, S. K.; Unruh, Y. C. Bibcode: 2000A&A...353..380F Altcode: An important question in solar physics is to what extent solar surface magnetism affects the solar irradiance. Previous attempts to answer this question have employed proxies of the magnetic field to reconstruct the irradiance and compare it with observations. Here we present the first model calculations of solar irradiance variations based on variations of the surface distribution of the solar magnetic field. The irradiance reconstruction makes use of sunspot and facular contrasts calculated as a function of wavelength and limb angle on the Sun. The position and size of magnetic features on the solar disk are extracted from full-disk magnetograms obtained by the Michelson Doppler Interferometer (MDI) onboard the SOHO spacecraft. The reconstructed spectral irradiance variations are compared with total and spectral contrast measurements obtained by the VIRGO instrument onboard SOHO. Our reconstructions are able to reproduce variations on the time-scale of the solar rotation with much greater accuracy than previous models based on disk-integrated magnetic proxies. Title: The influence of an inclined rotation axis on solar irradiance variations Authors: Knaack, R.; Fligge, M.; Solanki, S. K.; Unruh, Y. C. Bibcode: 2000ssls.work...45K Altcode: The irradiance variations of the Sun over the solar cycle are relatively small compared with sun-like stars (Radick et al., 1998). It has been proposed that a random distribution of stellar rotation axes relative to the ecliptic plane could explain their larger variability (Schatten, 1993). We examine the influence on total irradiance variations of the inclination of the solar rotation axis relative to an observer. A three-component model is used to calculate the relative flux variations of a given distribution of active regions on the surface of the Sun as a function of the inclination. One component is the quiet Sun, another is a sunspot component and the third describes the faculae. We find that the inclination effect increases the total irradiance variations of the Sun maximally by 40%. The most probable value is approximately 5%. This is much less than former studies (Schatten, 1993, Radick et al., 1998) suggested. Title: Solar Surface Magnetism and the Increase of Solar Irradiance between Activity Minimum and Maximum Authors: Fligge, M.; Solanki, Sami K.; Meunier, Nadege; Unruh, Yvonne C. Bibcode: 2000ESASP.463..117F Altcode: 2000sctc.proc..117F No abstract at ADS Title: Modelling Solar Irradiance Variations: Comparison with Observations, Including Line-Ratio Variations Authors: Unruh, Y. C.; Solanki, S. K.; Fligge, M. Bibcode: 2000svc..book..145U Altcode: No abstract at ADS Title: Modelling Short-Term Spectral Irradiance Variations Authors: Fligge, M.; Solanki, S. K.; Unruh, Y. C. Bibcode: 2000svc..book..139F Altcode: No abstract at ADS Title: Spectral Line Variability in the Circumstellar Environment of the Classic al T Tauri Star SU Aurigae Authors: Oliveira, J. M.; Foing, B. H.; Unruh, Y. C. Bibcode: 1999astro.ph.12199O Altcode: SU Aurigae is a classical T Tauri star of spectral type G2. This star was one of the scientific targets of the MUSICOS 96 multi-site campaign that provided a wealth of high resolution cross-dispersed spectral data with a good continuous time coverage. We present the results of the analysis of the complex circumstellar environment of this star, with particular regard to magnetospheric models, in which the accretion from the disk is channelled onto the star along magnetic field lines. The signatures of modulated outflows and mass accretion events are present in the spectra, as well as transient spectral features. We computed auto-correlation and cross-correlation functions to better investigate the source of the profiles' variability. The comparison of the profiles of different spectral lines allows us to study the footprints of events effectively observed at different distances from the stellar surface. Title: Coronal emission and dynamo saturation Authors: Jardine, M.; Unruh, Y. C. Bibcode: 1999A&A...346..883J Altcode: We show that the observed saturation of X-ray emission with increasing rotation rate in solar-type stars does not necessarily imply saturation of the underlying dynamo. This effect can be caused by the centrifugal stripping of the corona. As the stellar rotation rate is increased, centrifugal forces cause a rise in the pressure and density in the outer parts of the largest magnetic loops. This may explain the observed formation of large prominences close to the co-rotation radius where centrifugal forces begin to dominate over gravity. In order for these massive prominences to be contained against centrifugal ejection, the coronal magnetic field must be highly stressed and must be evolving on a timescale of a few days as determined by the observed prominence lifetime. We postulate that the co-rotation radius marks the position at which the corona becomes distorted by centrifugal forces. As the stellar rotation rate is increased, the co-rotation radius moves closer to the surface, reducing the extent of the ``undisturbed'' corona. We take as illustrative examples two simple field topologies and show that if the X-ray emission comes only from this undisturbed volume, then a saturation of the X-ray emission with increasing rotation rate occurs naturally. This effect may mimic true dynamo saturation or disguise its onset. Title: Short-term spectroscopic variability in the pre-main sequence Herbig AE star AB Aurigae during the MUSICOS 96 campaign Authors: Catala, C.; Donati, J. F.; Böhm, T.; Landstreet, J.; Henrichs, H. F.; Unruh, Y.; Hao, J.; Collier Cameron, A.; Johns-Krull, C. M.; Kaper, L.; Simon, T.; Foing, B. H.; Cao, H.; Ehrenfreund, P.; Hatzes, A. P.; Huang, L.; de Jong, J. A.; Kennelly, E. J.; ten Kulve, E.; Mulliss, C. L.; Neff, J. E.; Oliveira, J. M.; Schrijvers, C.; Stempels, H. C.; Telting, J. H.; Walton, N.; Yang, D. Bibcode: 1999A&A...345..884C Altcode: We present results of the spectroscopic monitoring of AB Aur obtained during the MUSICOS 96 campaign. The analysis is mainly focussed on the He I D3 line, on the Hα line, and on a set of photospheric lines. The star was monitored irregularly for more than 200 hours. We confirm the high level of variability of spectral lines in AB Aur. We find that the photospheric lines have a profile differing significantly from a classical rotational profile. The dominant features of this abnormal photospheric profile are a blue component, in absorption, whose velocity is modulated with a 34hr period, and a red component, stable in velocity but of variable intensity, with a possible periodicity near 43 hrs. The He I D3 line exhibits two well-defined components: a blue component, always in emission with a velocity modulated with a 45hr period, and a red component of variable intensity, alternatively in emission and in absorption, occurring at a fixed velocity, with a variable intensity possibly modulated with a 45 hr period. The Hα line, showing a P Cygni profile, also exhibits pseudo-periodic variations of its blue absorption component, but its variability appears more complicated than that of the other lines studied here. We suggest that the blue component of the photospheric lines is modulated by the star's rotation, with a period of 34 hrs, due to a highly inhomogeneous photosphere, involving significant radial flows. Our model also involves downflows onto the stellar pole to account for the red components of the photospheric lines and of the He I D3 line. We propose two different interpretations of the behavior of the blue component of the He I D3 line. In the first one, this component is formed in a wind originating from the star's equatorial regions. In this interpretation, the rotation period of the equatorial regions of the star is 45 hrs, implying a 25% surface differential rotation, with the pole rotating faster than the equator. The second interpretation involves a wind originating from a region of a circumstellar disk, at a distance of 1.6 stellar radii from the star's center, with a rotation period of 45 hrs. We are not able to decide which one of these two interpretations is more likely, on the basis of the data presented here. Based on observations obtained during the MUSICOS 96 MUlti-SIte COntinuous Spectroscopic campaign, collected at the Canada-France Hawaii, the McDonald 2.1m, the La Palma 2.5m Isaak Newton, the Observatoire de Haute-Provence 1.93m, the Xinglong 2.16m, and the Ritter Observatory 1m telescopes Title: Optical and ultraviolet observations of a strong flare in the young, single K2 dwarf LQ Hya Authors: Montes, D.; Saar, S. H.; Collier Cameron, A.; Unruh, Y. C. Bibcode: 1999MNRAS.305...45M Altcode: 1998astro.ph.11452M We present high-resolution optical echelle spectra and IUE observations during a strong flare on 1993 December 22 in the very active, young, rapidly rotating, single K2 dwarf LQ Hya. The initial impulsive phase of the flare, which started sometime between 2:42 ut and 4:07 ut, was characterized by strong optical continuum enhancement and blueshifted emission lines with broad wings. The optical chromospheric lines reached their maximum intensity at ~ 5:31 ut, by which time the blueshift vanished and the optical continuum enhancement had sharply decreased. Thereafter, the line emission slowly decreased and the lines redshift in a gradual phase that lasted at least two more hours. The Mg II lines behaved similarly. Quiescent C IV flux levels were not recovered until 21 h later, though a data gap and a possible second flare make the interpretation uncertain. In addition to the typically flare-enhanced emission lines (e.g., H alpha and H beta), we observe He I D_3 going into emission, plus excess emission (after subtraction of the quiescent spectrum) in other He I and several strong neutral metal lines (e.g., Mg I b). Flare enhancement of the far-ultraviolet continuum generally agrees with an Si I recombination model. We estimate the total flare energy, and discuss the broad components, asymmetries and Doppler shifts seen in some of the emission lines. Title: The spectral dependence of facular contrast and solar irradiance variations Authors: Unruh, Y. C.; Solanki, S. K.; Fligge, M. Bibcode: 1999A&A...345..635U Altcode: We present model calculations of facular and sunspot contrasts as a function of wavelength and limb angle on the Sun. These are the first such calculations; they assume LTE and are based on opacity distribution functions (ODFs). The calculated facular contrasts as a function of limb angle fit into the general picture of contrast measurements, and the behaviour of the contrast with wavelength at a given limb angle is in excellent agreement with the measurements. The calculated intensity spectra are used to construct the solar flux spectrum for different levels of solar activity. It is assumed that the irradiance or flux variations are due to changes in the sunspot and facular filling factors. The model atmosphere used to calculate the facular intensities has been tuned so that the calculated irradiance variations match the observed total and spectral irradiance variations during the last solar cycles. The model calculations have also been used to estimate the relative importance of continuum and spectral-line variations in producing irradiance variations. The results suggest that the continuum variations only contribute negligibly to the total irradiance variations on solar-cycle time scales. Title: Latitude distributions and lifetimes of star-spots on G dwarfs in the alpha Persei cluster Authors: Barnes, J. R.; Collier Cameron, A.; Unruh, Y. C.; Donati, J. F.; Hussain, G. A. J. Bibcode: 1998MNRAS.299..904B Altcode: We present a set of maximum-entropy reconstructions of the star-spot distributions on two rapidly rotating G dwarfs in the alpha Persei cluster, from spectra taken at the William Herschel Telescope on three nights in 1996 October and November. Since these stars are too faint for conventional Doppler imaging, which makes use of only one or a few lines, we take the large number of photospheric metal lines available in an echelle spectrum, and deconvolve them into a single, high signal-to-noise ratio profile. We show that this technique results in a typical multiplex gain of 22.5 in signal-to-noise ratio for a given spectrum, the equivalent of using a single line obtained on a 63-m telescope. The image reconstructions demonstrate that both these stars have cool high-latitude regions or polar crowns, and low-latitude features, in contradiction to the suggestion that only high-latitude spots should be present. Cross-correlation between image reconstructions of He 699, 31 days apart, reveals a lack of correlation between detailed small-scale structures. This places an upper limit for the lifetime of the observed features at less than one month. The Hα profiles are also found to exhibit absorption features indicating the presence of prominence clouds, at or below the corotation radius. Title: A model of solar total and spectral irradiance variations Authors: Fligge, M.; Solanki, S. K.; Unruh, Y. C.; Froehlich, C.; Wehrli, Ch. Bibcode: 1998A&A...335..709F Altcode: We model solar spectral irradiance variations under the assumption that they are produced by sunspots and faculae alone. The model is based on three components, i.e. quiet Sun, assumed to be temporally invariant, sunspots and faculae whose temporal variations are mimicked using time series of sunspot areas and Mg II core-to-wing ratios. The detailed flux spectrum for each component is employed. The results are compared to spectral irradiance measurements at 402 nm, 500 nm and 862 nm obtained between February 22 and December 31, 1996 by the three-channel sunphotometers (SPM) which are part of the VIRGO package onboard SOHO. Our model shows a good correlation with the measured variations of the three colour channels and of the total irradiance. Since it also successfully reproduces changes in the UV spectral irradiance, irradiance variations and observed variations of the faculae-to-spots filling factor ratio since 1978, our model supports earlier suggestions that a large part of the solar irradiance variations is caused by magnetic fields at the solar surface. Finally, we use the model to test whether the difference between the magnitude of solar and stellar brightness variations reported by Lockwood et al. (1992) is due to the particular filters they use for their stellar observations. Our results suggest that this effect can explain only a small part of the discrepancy. Title: Surface inhomogeneities and line variability on DF Tau Authors: Unruh, Y. C.; Collier Cameron, A.; Guenther, E. Bibcode: 1998MNRAS.295..781U Altcode: We have mapped surface inhomogeneities on the classical T Tauri star DF Tau, using the Lii doublet at 670.8 nm, the Cai lines at 612.2 nm and 643.9 nm and a calcium and iron blend at 646.3 nm. We find compelling evidence that there are hotspots with temperatures of more than 5000 K. Two of the hotspots produce line-profile deformations that can be traced as they move through the cross-correlated profiles. When one of the hotspots crosses the stellar disc, redshifted absorption components appear in the Na D lines. As these redshifted absorption features are usually tracers for mass-infall we interpret this hotspot as an accretion shock close to the stellar surface. Parts of the surface of DF Tau are covered with a hot chromosphere that is visible in the Caii infrared triplet lines and the narrow component of Hei. We find no correlation between the veiling and the lines that originate from the hot chromosphere, suggesting that the veiling and the chromospheric emission are produced in physically distinct regions. Title: Prominences on Rapidly-Rotating Solar-Type Stars Authors: Jardine, M.; Barnes, J.; Unruh, Y.; Collier Cameron, A. Bibcode: 1998ASPC..150..235J Altcode: 1998npsp.conf..235J; 1998IAUCo.167..235J No abstract at ADS Title: MUSICOS Observations of SU AUR Authors: Unruh, Yvonne C.; Donati, J. -F.; Balona, L.; Bohm, T.; Cao, H.; Catala, C.; Collier Cameron, A.; Ehrenfreund, P.; Foing, B.; Granzer, T.; Hao, J.; Hatzes, A.; Henrichs, H.; Johns-Krull, C.; de Jong, J.; Kennelly, T.; Landstreet, J.; Morrison, N.; Mullis, C.; Neff, J.; Oliveira, J.; Schrijvers, C.; Simon, T.; Stempels, E.; Strassmeier, K. G.; Telting, J.; Walton, N. Bibcode: 1998ASPC..154.2064U Altcode: 1998csss...10.2064U We present first results of the high-resolution observations of SU Aur obtained through the MUSICOS network in 1996 Nov. The data set is unique in that it gives us complete phase coverage for almost two rotation periods of SU Aur. This is particularly valuable for T Tauri stars as they can vary dramatically on the time scale of one rotation period. Title: A model of the wavelength dependence of solar irradiance variations Authors: Solanki, S. K.; Unruh, Y. C. Bibcode: 1998A&A...329..747S Altcode: The variation of the solar irradiance over the solar cycle has a strong wavelength dependence, being larger at shorter wavelengths. Here we present simple models of the spectral dependence of irradiance variations between solar activity maximum and minimum. We find that the observations (which concentrate on the UV) cannot be reproduced by a change in effective temperature of the Sun (or of parts of its surface) alone. We can, however, reproduce the data with either a 2-component or a 3-component model, of which one component is the quiet Sun, another is a facular component, and the third (in the case of the 3-component model) represents the temperature stratification of sunspots. The facular component is found to be very close to the facular models F or P of Fontenla et al. (1993). The success of these models supports the assumption underlying many studies of total solar irradiance variations that these are caused mainly by magnetic fields at the solar surface. Our investigation also allows an improved estimate of the relative contribution of the various layers in the solar photosphere and of the different wavelength regions to the total irradiance variations. Title: The Wavelength Dependence of Solar Irradiance Variations Authors: Unruh, Yvonne C.; Solanki, Sami K. Bibcode: 1998ASPC..154..700U Altcode: 1998csss...10..700U The observed irradiance variations over a solar cycle show a strong wavelength dependence; the variations are strongest in the UV and very weak in the visible. Here we present a simple model of the spectral dependence of the solar irradiance. We can exclude models that postulate a change in the effective temperature of the Sun or of parts of the Sun. However, we find that the observed irradiance variations can be matched with a model that includes the different temperature stratification of the quiet photosphere, the faculae and the sunspots. Title: MUSICOS Observations of SU Aurigae Authors: Unruh, Y. C.; Donati, J. -F.; et al. Bibcode: 1998cvsw.conf..355U Altcode: No abstract at ADS Title: A Strong Flare on the K Dwarf LQ Hya Authors: Montes, D.; Saar, S. H.; Collier Cameron, A.; Unruh, Y. C. Bibcode: 1998ASPC..154.1508M Altcode: 1998csss...10.1508M We present high resolution optical echelle spectra and IUE SWP observations during a strong flare on 1993 December 22 in the very active, young, rapidly rotating, single K2 dwarf LQ Hya. The temporal evolution of the flare consists of an initial impulsive phase, characterized by strong continuum enhancement, which started between 02:42 UT (quiescent spectrum) and 04:36 UT (first spectrum with a strong increase in the chromospheric lines). The chromospheric lines reached their maximum intensity ~55 min later, by which time the continuum enhancement had sharply decreased. Thereafter, the line emission slowly decreased in a gradual phase that lasted at least until the end of the observation (07:29 UT). IUE data indicate that quiescent C iv flux levels were not recovered after ~4 UT on the following day. We describe the variation of the continuum enhancement, the optical and the UV lines during the flare. In addition to the emission lines that show strong flare enhancement (e.g., Hα and Hβ), we observe He i D3 going into emission. After subtraction of the quiescent spectrum, we also observe excess emission in He i lines at 4921.9, 5015.7, and 6678.1AA, and in other metal lines such as the Na i D1 and D2, the Mg i b triplet and several Fe i and Fe ii lines. We estimate the energy release during the flare, and analyze the broad components and asymmetries seen in some of the emission lines. Title: Balmer Line Profiles Variations in SU Aurigae from the MUSICOS 96 Multi-site Campaign Authors: Oliveira, J. M.; Unruh, Y. C.; Foing, B. H.; MUSICOS 96 Collaboration Bibcode: 1998Ap&SS.261..143O Altcode: 1999Ap&SS.261..143O No abstract at ADS Title: Modelling Spectral Irradiance Variations obtained by VIRGO Authors: Fligge, M.; Solanki, S. K.; Unruh, Y.; Frohlich, C.; Wehrli, Ch. Bibcode: 1998ASPC..140..311F Altcode: 1998ssp..conf..311F No abstract at ADS Title: Wavelength Dependence of Solar Irradiance Variability from VIRGO Onboard SOHO Authors: Wehrli, C.; Fröhlich, C.; Anklin, M.; Fligge, M.; SOlanki, S. K.; Unruh, Y. Bibcode: 1997ESASP.415..497W Altcode: 1997cpsh.conf..497W No abstract at ADS Title: Does chromospheric emission mimic polar starspots in Doppler images? Authors: Unruh, Y. C.; Collier Cameron, A. Bibcode: 1997MNRAS.290L..37U Altcode: We have used time-series spectra of the sodium doublet at 589.0 and 589.6nm in AB Doradus to investigate the effects of a chromospheric temperature rise on Doppler images derived from strong lines whose cores are formed in the upper photosphere and lower chromosphere. On solar-type stars, the NaD lines probe a range of heights and tend to be much more sensitive to the chromospheric temperature structure than the weaker photospheric lines that are commonly used for Doppler imaging. Contrary to suggestions that polar spots may be an artefact arising from chromospheric emission reversals, we find that the images obtained from the NaD lines show less high-latitude structure, and give more reliable light-curve predictions, than images derived previously from fits to several weaker photospheric lines. Title: Doppler imaging of AB Doradus using the Lii 6708 line Authors: Hussain, G. A. J.; Unruh, Y. C.; Collier Cameron, A. Bibcode: 1997MNRAS.288..343H Altcode: We present maximum entropy reconstructions of the stellar surface of the K0 dwarf AB Doradus using observations obtained in 1993 November. Doppler images are produced using the Lii 6708-Angstroms line and compared to images produced using Cai and Fei lines. An Li abundance of log N(Li) = 2.9 +/- 0.3 is measured using local thermodynamic equilibrium (LTE) profile synthesis. By assessing how enhanced spot Li abundances affect fits between synthetic reconstructions and the observed data, we conclude that the presence of starspots is unlikely to lead to an overestimation of the photospheric Li abundance. Moreover, Li abundances in starspots do not appear to be enhanced with respect to the photospheric level. The equivalent width measurements for the Lii 6708-Angstroms line are strengthened by the presence of starspots. This effect is probably due to their lower effective temperatures. Because the spots were widely distributed in longitude at the time of observation, the extent to which the Lii line equivalent width is modulated as the star rotates is diluted. Title: Magnetic loops on rapidly rotating stars. Authors: Unruh, Y. C.; Jardine, M. Bibcode: 1997A&A...321..177U Altcode: We present models for the thermal and mechanical equilibria of slender magnetic loops on rapidly-rotating stars. These loops are embedded within an arcade located on the stellar equator. The loop properties are governed principally by the specified base pressure and conductive flux. While rapid rotation is important in determining the pressure structure within the loop, its main effect on the loop shape is through its influence on the base values of magnetic field strength, pressure, and conductive flux. We have compared our models with observations of the temperatures and X-ray fluxes of stars with a range of rotation rates. By using the observed variation of the differential emission measure with rotation rate {OMEGA} and allowing the base magnetic field strength to scale as B {prop.to}{OMEGA}^q^ (q=0.5,0.75,1.0) we can explain the variation of the temperature and X-ray flux of the slower rotators. For the most rapid rotators, however (approximately {OMEGA}/{OMEGA}sun_>10) it appears that a single value of q for all rotation rates cannot explain the observations and some other mechanism is needed to explain the saturation in the X-ray flux. We have also investigated the effect of using a heating function that is proportional to the density and one that falls off exponentially with height. With the parameters that we can calculate from these models it is not possible to discriminate between these two types of heating. Title: Reliability tests for Doppler imaging Authors: Unruh, Y. C. Bibcode: 1996IAUS..176...35U Altcode: No abstract at ADS Title: The Evolution of Surface Structures on Ab-Doradus Authors: Unruh, Y. C.; Collier Cameron, A.; Cutispoto, G. Bibcode: 1995MNRAS.277.1145U Altcode: We present the third set of a long-term series of Doppler images of the starspot distribution on AB Doradus, a rapidly rotating active K0 dwarf. The images were obtained from simultaneous spectroscopic and photometric observations taken on the Anglo-Australian Telescope and the European Southern Observatory in 1993 November. Our images show two active latitudes, a low-latitude band producing most of the photometric modulation, and a high-latitude band centred at 60°. The spot distribution at low latitudes is very stable and persists over 5 stellar rotations. It is also remarkably similar to the distribution found in 1992 December. The high-latitude structure is more variable and seems to change on the order of a few rotation periods. In agreement with measurements from 1992 January, we find no indication for differential rotation on AB Doradus. Title: The sensitivity of Doppler imaging to line profile models Authors: Unruh, Y. C.; Collier Cameron, A. Bibcode: 1995MNRAS.273....1U Altcode: In recent years there have been a number of successful reconstructions of the surfaces of fast rotating stars using Doppler imaging. As a large proportion of the imaged stars show large high-latitude spots, some doubt remains as to whether these high-latitude spots might be artefacts. In this paper we investigate how sensitive Doppler imaging is to the exact shape of the mapping line profile and its variation as a function of limb angle. We find that Doppler imaging is surprisingly robust against errors in the limb dependence of the profile, but that errors in the shape of the profile, and in particular the neglect of blends at considerable distances from the mapping line, will lead to spurious banding in the reconstructed images. Title: Surface structures on young solar-type stars. Authors: Collier Cameron, A.; Unruh, Y. C. Bibcode: 1995mscs.conf..201C Altcode: No abstract at ADS Title: Surface structure on DF Tau Authors: Unruh, Y. C.; Collier-Cameron, A.; Guenther, E. Bibcode: 1995IAUS..176P..93U Altcode: No abstract at ADS Title: Doppler images of AB Doradus in 1992 January. Authors: Collier Cameron, A.; Unruh, Y. C. Bibcode: 1994MNRAS.269..814C Altcode: We present a set of maximum entropy reconstructions of the starspot distribution on the surface of the rapidly rotating KO dwarf AB Doradus. The images were obtained from three independent data sets secured on three consecutive nights of observation at the Anglo-Australian Telescope in 1992 January. We discuss the effects of several potential types of systematic error in Doppler imaging, and methods of eliminating them. Independent reconstructions are presented in the three photo spheric lines: Ca I 643.9 nm, Fe I 666.3 nm and Ca I 671.8 nm. All the images indicate a bimodal latitude distribution of spot area coverage, with a broad low-latitude band and a circumpolar `crown'. The gross azimuthal structures in the polar crown and the low-latitude band show no evidence of longitude shifts over the duration of the observing run. On the time-scale of a single stellar rotation the star's surface layers thus appear to be in a state of nearly solid-body rotation. Key words: techniques: image processing - stars: activity - stars: atmospheres - stars: individual: AB Dor - stars: magnetic fields - stars: rotation. Title: Doppler imaging of late-type stars Authors: Unruh, Y. C. Bibcode: 1994PhDT........12U Altcode: No abstract at ADS Title: The Sensitivity of Doppler Imaging to Errors in the Line Profile Shape Authors: Unruh, Yvonne C.; Collier Cameron, Andrew Bibcode: 1994ASPC...64..667U Altcode: 1994csss....8..667U No abstract at ADS Title: Doppler imaging of late-type stars Authors: Unruh, Yvonne Christine Bibcode: 1994PhDT........15U Altcode: No abstract at ADS Title: Photospheric inhomogeneities on cool stars Authors: Collier Cameron, A.; Jeffery, C. S.; Unruh, Y. C. Bibcode: 1992sccw.conf...81C Altcode: No abstract at ADS