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Flare Stars in the Solar Vicinity: a Search for Young Stars

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Flare Stars in the Solar Vicinity: a Search for Young Stars Flare Stars In The Solar Vicinity A Search For Young Stars Dissertation der Fakultat¨ fur¨ Physik der Ludwig-Maximilians-Universitat¨ Munchen¨ vorgelegt am 08.09.2003 von Brigitte Konig¨ aus Starnberg Erstgutachter: Prof. Dr. Dr. h.c Gregor Morfill Zweitgutachter: Prof. Dr. Ralph Neuh¨auser Tag der m¨undlichen Pr¨ufung:22.12.2003 Contents Contents iii List of Figures vii Kurzzusammenfassung 1 Abstract 3 1 Introduction 5 1.1 The model developed in the 1960’s . 5 1.1.1 From a gas and dust cloud to a protostar . 5 1.1.2 What can we observe at this phase? . 6 1.1.3 The phase of slow contraction . 6 1.1.4 Collapse under selfgravitation . 7 1.2 Improved models . 7 1.2.1 Centrally concentrated clouds . 7 1.2.2 Inhomogeneous gas clouds . 7 1.2.3 Rotation of the cloud . 8 1.2.4 Magnetic field in protostars and young stars . 9 1.3 Observed evolution stages . 9 1.4 Stars on the main sequence . 11 1.5 Post-main sequence stars . 12 1.6 What do we know about local young stars . 12 1.7 Details of flare stars . 14 1.7.1 Definition of flare stars . 15 1.7.2 The nature of other types of flare stars . 17 2 The sample 21 2.1 Revising the catalogs . 21 2.2 The flare stars in the H-R diagram . 22 2.3 Space velocity of the sample stars . 23 2.4 Observation and Data Reduction . 24 2.4.1 Low resolution spectroscopy . 25 2.4.2 High resolution spectroscopy . 26 3 Stellar atmospheres models 29 3.1 Assumptions . 29 3.2 Energy transport . 31 3.2.1 Radiative energy transport . 31 3.2.2 Convective energy transport . 31 iv CONTENTS 3.2.3 Heat transport . 33 3.3 Interaction between radiation and material . 33 3.3.1 Atomic excitation and ionisation in TE . 33 3.3.2 Radiative interaction . 34 3.4 Hydrostatic equilibrium . 35 3.5 Sources of opacities . 35 3.5.1 Continuous opacity sources . 35 3.5.2 Line opacities . 36 3.6 Computed spectral lines . 37 3.6.1 Dependence on the element abundance . 37 3.6.2 Dependency on other stellar parameters . 37 3.7 How to derive abundances . 40 4 Flare stars in stellar associations 41 4.1 The Ursa Major association . 41 4.1.1 χ1 Orionis B . 42 4.1.2 [GKL 99] 104, HIP 18512 A, HD 24916 A . 54 4.1.3 [GKL 99] 109, HIP 19855, HD 26913 . 54 4.1.4 [GKL 99] 231, HIP 53985 . 55 4.1.5 [GKL 99] 239 and [GKL 99] 240, or HIP 55454 A & B . 55 4.2 Local association . 55 4.3 The region of TW Hydrae Association . 55 4.3.1 The sample in TWA . 57 4.3.2 Kinematics and multiplicity . 59 4.3.3 Hertzsprung-Russell diagram . 60 4.3.4 X-ray emission . 61 4.3.5 Near-infrared imaging of HIP 57269 . 61 4.3.6 Spectroscopic follow up of companion candidates . 62 4.3.7 Summary and Discussion . 65 4.4 The flare stars in the region of Tuc and HorA . 66 4.5 The Tucana Association . 66 4.6 The Horologium Association . 68 4.6.1 The Tucana - Horologium association . 69 4.6.2 [GKL 99] 428, HIP 111766 . 69 4.6.3 [GKL 99] 414, HIP 108405 . 70 4.6.4 [GKL 99] 72 . 71 4.7 Stars with space motion consistent with AnA . 71 4.7.1 [GKL 99] 423, HIP 110526 . 71 4.8 Stars in the Pleiades . 71 4.8.1 [GKL 99] 74, HIP 12351 . 72 4.8.2 [GKL 99] 312, HIP 73555 . 73 4.8.3 [GKL 99] 306, EK Dra, HIP 71631, HD 129333 . 75 4.8.4 [GKL 99] 210, GJ 3562 . 77 4.8.5 Summary . 77 4.9 Hercules-Lyra association . 77 4.9.1 [GKL 99] 410, HN Peg, HIP 107350, HD 206860 . 78 4.9.2 HIP 114385, and [GKL 99] 440, HIP 114379 . 80 4.10 β Pictoris moving group . 81 4.10.1 [GKL 99] 82, HIP 13402, HD 17925 . 82 4.10.2 [GKL 99] 145, HIP 26779 . 82 CONTENTS v 4.10.3 [GKL 99] 132, HIP 23200 . 82 4.10.4 [GKL 99] 137 and [GKL 99] 136, or GJ 3331 A & B . 82 4.10.5 [GKL 99] 146, GJ 1083 A & B . 83 4.10.6 [GKL 99] 387 and [GKL 99] 388, or HIP 102141 A & B . 83 4.10.7 [GKL 99] 394, HIP 102409 . 83 4.11 The translucent cloud MBM 12 . 83 4.12 Stars belonging to the Hyades Cluster . 83 4.12.1 [GKL 99] 15, HIP 1803, HD 1835, HR 88 . 84 4.13 Summary . 84 4.14 Discussion - Why not use Photometry? . 86 4.14.1 The colors of a star . 87 4.14.2 Narrow band photometry . 87 4.14.3 Low resolution spectroscopy . 90 5 Radial velocity monitoring 91 5.1 Observations . 92 5.2 Data analysis . 93 5.3 Error sources . 94 5.3.1 Stellar spots . 94 5.3.2 Plage regions . 95 5.3.3 Solution . 97 5.4 Results . 98 6 R´esum´e 105 6.1 The Sample . 105 6.2 Evaluation of the sample . 106 6.3 Results . 107 Bibliography 111 Revised data of the input catalog 123 Space velocity of the flare stars 129 Observation logfile 135 Danksagung 139 Lebenslauf 141 List of Figures 1.1 Classification scheme of young stellar objects according to their infrared emis- sion. Taken from Feigelson & Montmerle (1999). 10 2.1 D’Antona & Mazzitelli (1994) tracks and isochrones underlaying the sample stars. The sample stars are plotted using the revised input data and the spectral type with temperature conversion taken from Kenyon & Hartmann (1995) and Luhman (1999). The corrections for binary stars and the distance show that the stars are quite homogeneously spread on the lower part of the main sequence. Only the stars with an available distance are shown with a distance from 2.5 pc to 100 pc. Masses are in units of a solar mass and ages are given as log t/yr. 23 2.2 Space velocities in the UV-plane of the sample stars compared to the mean space velocity of known local young associations of stars. The flare stars of the Gershberg sample are marked with gray dots and the big black crosses mark the mean space velocity of the young associations. 24 3.1 A schematic view of the different layer in the sun. For the modeling of the star only the atmosphere is important. The atmosphere includes the photosphere and the chromosphere. ..
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