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Characterisation of Young Nearby Stars – the Ursa Major Group

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Characterisation of Young Nearby Stars – the Ursa Major Group FRIEDRICH-SCHILLER-UNIVERSITAT¨ JENA Physikalisch-Astronomische Fakult¨at Characterisation of young nearby stars – The Ursa Major group Dissertation zur Erlangung des akademischen Grades doctor rerum naturalium (Dr. rer. nat.) vorgelegt dem Rat der Physikalischen-Astronomischen Fakult¨at der Friedrich-Schiller-Universit¨at Jena von Dipl.-Phys. Matthias Ammler geboren am 10.01.1977 in Neuburg a. d. Donau Gutachter 1. Prof. Dr. Ralph Neuh¨auser 2. Dr. habil. Matthias H¨unsch 3. Prof. Dr. Artie P. Hatzes Tag der letzten Rigorosumspr¨ufung: 26. Juni 2006 Tag der ¨offentlichen Verteidigung: 11. Juli 2006 Meinen Eltern Contents List of Figures vii List of Tables ix Abstract xi Zusammenfassung xiii Remarks and Acknowledgements xv 1 Introduction 1 1.1 WhatistheUrsaMajorgroup? . 1 1.1.1 Co-movingstarsin the BigDipper constellation . .... 1 1.1.2 Stellarmotionandmovinggroups . 1 1.1.3 Formation and evolution of open clusters and associations ... 6 1.1.4 The nature of the UMa group – cluster or association, or some- thingelse? ............................ 8 1.2 WhyistheUMagroupinteresting?. 8 1.2.1 Asnapshotinstellarevolution . 8 1.2.2 Alaboratoryinfrontofthedoor . 9 1.2.3 Thecensusofthesolarneighbourhood . 10 1.3 ConstrainingtheUMagroup–previousapproaches . ..... 11 1.3.1 Spatialclustering . 11 1.3.2 Kinematic criteria – derived from a “canonical” memberlist . 12 1.3.3 Kinematic parameters – derived from kinematic clustering ... 15 1.3.4 Stellarparametersandabundances . 17 1.3.5 TheageoftheUMagroup–photometriccriteria . 19 1.3.6 Spectroscopicindicatorsforageandactivity . .... 19 1.3.7 Combining kinematic, spectroscopic, and photometric criteria . 21 1.4 Anewhomogeneousspectroscopicstudy . 21 1.4.1 Definingthesample ....................... 22 1.4.2 Howtoobtainprecisestellarparameters? . .. 23 2 Observations,reductionandcalibration 25 2.1 Requireddata ............................... 25 2.2 Instruments ................................ 26 2.3 Observations ............................... 26 iii Contents 2.4 Reductionandcalibrations . 34 3 Derivingthestellarparameters–Methods 39 3.1 Differentialanalysis............................ 39 3.2 Modelatmospheresandsyntheticlineformation . ...... 40 3.2.1 Radiativetransfer. 40 3.2.2 Radiative transfer in solar-like stars – defining the geometry . 41 3.2.3 Thermodynamicequilibrium . 42 3.2.4 Localthermodynamicequilibrium(LTE) . 43 3.2.5 Contributionstoabsorptionandemission . .. 43 3.2.6 Lineprofiles ........................... 45 3.2.7 Hydrostaticequilibrium . 50 3.2.8 Convection ............................ 50 3.2.9 Three-dimensional hydrodynamics versus one-dimensional hy- drostatics ............................. 52 3.3 Thestellarparameters........................... 52 3.3.1 Effectivetemperature. 52 3.3.2 Surfacegravity .......................... 53 3.3.3 Abundancesandmicroturbulence . 60 3.3.4 Instrumental profile, rotation, and macroturbulence ....... 61 3.3.5 Estimatingthestellarmass . 61 4 ResultsandimplicationsfortheUMagroup 63 4.1 How accurate are the resulting stellar parameters? . ........ 63 4.1.1 TheMoonspectraandthesolarparameters . 65 4.1.2 ConsistencywithFuhrmann(2004) . 65 4.1.3 Comparison of spectroscopic distance with Hipparcos distance. 66 4.1.4 Notesonindividualstars . 69 4.1.5 Comparison of single star parameters with previous determinations 70 4.2 ThepropertiesoftheUMagroup. 76 4.2.1 Kieldiagram ........................... 76 4.2.2 Abundancesofironandmagnesium . 76 4.2.3 Rotation.............................. 79 4.2.4 Equivalent width of the LiI λ6707.8Åabsorptionline . 80 4.2.5 Filling-inof the Hα linecore................... 83 4.3 Conclusionsontheage .......................... 85 4.4 Concludingremarksonmembershipcriteria . .... 85 5 Summary and outlook 87 Bibliography 91 iv Contents A ThekinematicmembershipcriteriaofEggen(1958,1995) i A.1 Preliminaries ............................... i A.2 Movingclustermethod .......................... i A.3 Peculiarvelocitycriterion. .. ii A.4 Radialvelocitycriterion . ii A.5 AdaptionbyMontesetal.(2001a) . ii B Details on the used spectra v C Line data vii D Solution of the model atmosphere problem with MAFAGS xi D.1 Fluxconservation............................. xi D.2 Solutionofthemodelatmosphere . xi E Individual spectra near Hα andLiI6707.8Å xiii F Residuals of LTE fits to the observed Hα profile. xxi Index xxiii Personliche¨ Danksagung xxvii Ehrenwortliche¨ Erklarung¨ xxix Lebenslauf xxxi v Contents vi List of Figures 1.1 TheBigDipperintheconstellationUrsaMajor . .... 2 1.2 TheUMagroup.............................. 3 1.3 AphotographoftheBigDipper . 3 1.4 Comovingstars .............................. 5 1.5 Clustersequences............................. 7 1.6 DistributionofdistancesofUMagroupmembers . .... 9 1.7 Distribution of total proper motions of UMa group members ...... 10 1.8 Spacevelocitiesofthekinematicsample . .... 16 2.1 Spectral layout of frames of FOCES and of the Tautenburg Coud´espec- trograph.................................. 27 2.2 Types of flat-fields taken with FOCES .................. 31 2.3 Typesofflat-fieldstakeninTautenburg. ... 32 2.4 Normalisation of an order with a clearly perceivable relativecontinuum 35 2.5 Mergingof two Echelleorders´ ...................... 35 2.6 Rectification splines of Tautenburg and FOCES Echelleorders´ . 37 2.7 Normalisation of an order with a masked relative continuum ...... 38 3.1 Depthsoflineformation . .. .. .. .. .. .. .. 44 3.2 Fitting the Balmer lines of a moon spectrum in order to derive the effec- tivetemperature.............................. 54 3.3 The solar surface gravity derived from the iron ionisationequilibrium . 56 3.4 ThesolarMgIbtriplet .......................... 59 3.5 Estimation of mass in the Hertzsprung-Russell diagram . ........ 62 4.1 Comparison of spectroscopic distances with Hipparcos distances . 67 4.2 Comparison with effective temperatures from previous analyses . 71 4.3 Comparison with the surface gravities from other work . ....... 72 4.4 Comparisonwiththeiron abundances from other work . ..... 72 4.5 Temperature residuals vs. iron abundance residuals of this work with respecttoKing&Schuler(2005). 74 4.6 Comparison of the microturbulence parameter ξt withFuhrmann(2004) 75 4.7 KieldiagramoftheUMagroup. 77 4.8 Magnesiumvs.ironabundance. 78 4.9 Projected rotational velocityof UMa group members . ...... 78 4.10 Effectivetemperaturevs. lithiumequivalentwidth . ... 82 4.11 Effective temperature vs. Hα coreintensity . .. .. .. .. 84 vii List of Figures E.1 The LiI resonance doublet at 6707.8Å of UMa group candidates. .. xiv E.2 TheHα lineofUMagroupcandidates . xv E.3 TheHα lineofUMagroupcandidates . xvi E.4 TheHα lineofUMagroupcandidates . xvii E.5 TheHβ lineofUMagroupcandidates . xviii E.6 TheHβ lineofUMagroupcandidates . xix E.7 TheHβ lineofUMagroupcandidates . xx F.1 LTEHα residualfluxes .......................... xxii viii List of Tables 1.1 The UMa group kinematic parameters compiled frome some recent studies 11 1.2 The kinematic sample – space velocities and membership . ....... 13 1.3 Theliteraturedata–Example:HD39587 . 18 1.4 Thekinematicsample–stellarnamesandpositions . ...... 22 2.1 Properties and configuration of telescopes and instruments ....... 27 2.2 Overview over the observing runs in chronological order ........ 28 2.3 Completeness of the observations – kinematic members . ....... 29 2.4 The layout of the observations with typical exposure times ....... 33 3.1 Theadoptedsolarelementalabundancepattern . ..... 51 4.1 Thesetofhomogeneousstellarparameters. .... 64 4.2 ParametersoftheSun........................... 65 4.3 The stellar parameters of the probable UMa group member HD 217813 comparedtotheresultsofFuhrmann(2004).. 66 4.4 Properties determined from the derived parameters . ....... 68 4.5 Lithium equivalent widths, lithium abundances, and filling-in of the Hα line .................................... 81 B.1 Listofthespectrawhichwereincludedinthiswork . ...... vi C.1 Linedata ................................. vii ix List of Tables x Abstract This work presents a homogeneous set of stellar parameters for a larger sample of kine- matic Ursa Major (UMa) group members with spectral types late-F to early-K. The UMa group is comprised of the stars in the UMa cluster in the Big Dipper constel- lation and of many co-moving stars spread over the whole sky. The definition of kine- matic membership criteria has ever been difficult so that spectroscopic criteria should be added. Previous work indicated that the UMa group members are young with an age of roughly 300 Myrs. The youth leaves traces in the stellar spectrum, i.e. the LiI λ6707.8Å absorption line, and activity features, e.g. partial filling-in of the core of the Hα line due to chromospheric emission. Furthermore rotational line broadening is stronger than that of older stars. Additional to the youth indicators, iron abundance is an appropriate mem- bership criterion in case it is different from that of other groups of stars. Spectroscopic properties of the UMa group already have been specified but resulting membership cri- teria are rather inconclusive. For this thesis, a sample of kinematic members was drawn from Montes et al. (2001a) and King et al. (2003) in order to derivethe spectroscopic properties of mid- and late-type λ UMa group members homogeneously. Spectra with high resolving power ( ∆λ 60000) and signal-to-noise ratio (& 200) were obtained for twenty stars with spectral types≈ late-F to M. Based on the quantitative spectral analysis of Fuhrmann (2004), the stellar parameters such as effective temperatures, surface
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