The Group ofThe Group of BootisBootis StarsStars

Dr. Ernst PaunzenDr. Ernst PaunzenInstitute for Astronomy Institute for Astronomy University of ViennaUniversity of Vienna

Abundance PatternAbundance Pattern

C, N, O und S solar abundantC, N, O und S solar abundant Heavier elements underabundant, (Na)Heavier elements underabundant, (Na) Large ScatterLarge Scatter

Paunzen et al. (1999)Paunzen et al. (2002a)

Heiter (2002)

Evolutionary StatusEvolutionary Status

Paunzen et al. (2002b)

Group propertiesGroup properties

About 50 membersAbout 50 membersTypical abundance patternTypical abundance patternTemperature range: 11000 to 6500KTemperature range: 11000 to 6500KFrom ZAMS to TAMSFrom ZAMS to TAMSNo magnetic fields detectedNo magnetic fields detectedNot found in open clustersNot found in open clustersOnly spectroscopic binaries of the type Only spectroscopic binaries of the type

„„Bootis“Bootis“

Diffusion/Mass-lossDiffusion/Mass-loss

Mass-loss „conserves“ He convection zoneMass-loss „conserves“ He convection zone BUT: Rotation induces mixingBUT: Rotation induces mixing Time scale: ca. 1 GyrTime scale: ca. 1 Gyr

Charbonneau (1993)

Diffusion/AccretionDiffusion/Accretion

Star accretes gas component of the Star accretes gas component of the interstellar environmentinterstellar environment

Diffusion mixes atmosphereDiffusion mixes atmosphereNumber of measurements Heiter et al. (2002)

Turcotte & Charbonneau (1993)

Diffusion/AccretionDiffusion/Accretion

Source of material only from star Source of material only from star formationformation

Time scale: max. 100 MyrTime scale: max. 100 Myr

Diffusion/AccretionDiffusion/Accretion

Disk visible in IRDisk visible in IR Measurements for 26 Measurements for 26 Bootis StarsBootis Stars Six with IR Excess, upper limits otherwiseSix with IR Excess, upper limits otherwise

Paunzen et al. (2003)

Theories versus Theories versus ObservationsObservations

A New Accretion ModelA New Accretion Model

What happens if a star crosses denser What happens if a star crosses denser ISM?ISM?

Questions:

•Time scale

•Needed densities of ISM

•Relative velocity range

•Accretion of gas realistic

•Range of spectral types

•Statistical frequency

A New Accretion ModelA New Accretion Model

ISM model: „standard“ abundances, density ISM model: „standard“ abundances, density about 10 about 10 cm-3

Velocity range: 10 to 20 kms-1

Time Scale: 1 pc, Time Scale: 1 pc, 17 kms-1, ca. 60000 yr

Hot end: Stellar Winds, 12000KHot end: Stellar Winds, 12000K Cool end: Convection, 6500KCool end: Convection, 6500K Dust is blown away Open Clusters: no gas to accrete Statistics: about 15 objects predicted within

60 pc, 9 knownKamp & Paunzen (2002)

Theories versus Theories versus ObservationsObservations

Pulsating Pulsating Bootis StarsBootis Stars

Koen et al. (2003)Paunzen et al. (2002b)

Bootis versus Bootis versus Scuti Scuti

Instability strip shifted Pulsational constants smaller, Overtones excited

Paunzen et al. (2002b)

Which Mechanism can be Which Mechanism can be studied?studied?

DiffusionDiffusionAccretionAccretionRotationRotationPulsationPulsation

depending on:

•Metallicity

•Age

•Stellar Environment

ReferencesReferences

Charbonneau, 1993, ApJ, 405, 720Charbonneau, 1993, ApJ, 405, 720 Heiter, 2002, A&A, 381, 959Heiter, 2002, A&A, 381, 959 Heiter, Weiss, Paunzen, 2002, A&A, 381, 971Heiter, Weiss, Paunzen, 2002, A&A, 381, 971 Kamp, Paunzen, 2002, MNRAS, 335, L45Kamp, Paunzen, 2002, MNRAS, 335, L45 Koen, Paunzen, van Wyk, et al., 2003, MNRAS, 338, 931Koen, Paunzen, van Wyk, et al., 2003, MNRAS, 338, 931 Paunzen, Kamp, Iliev, et al., 1999, A&A, 345, 597Paunzen, Kamp, Iliev, et al., 1999, A&A, 345, 597 Paunzen, Iliev, Kamp, Barzova, 2002a, MNRAS, 336, 1030Paunzen, Iliev, Kamp, Barzova, 2002a, MNRAS, 336, 1030 Paunzen, Handler, Weiss, et al., 2002b, A&A, 392, 515Paunzen, Handler, Weiss, et al., 2002b, A&A, 392, 515 Paunzen, Kamp, Weiss, Wiesemeyer, 2003, A&A, 404, 579Paunzen, Kamp, Weiss, Wiesemeyer, 2003, A&A, 404, 579 Turcotte, Charbonneau, 1993, ApJ, 413, 376Turcotte, Charbonneau, 1993, ApJ, 413, 376