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The Group of l Bootis Stars

The Group of l Bootis Stars. Dr. Ernst Paunzen Institute for Astronomy University of Vienna. Abundance Pattern. C, N, O und S solar abundant Heavier elements underabundant, (Na) Large Scatter. Heiter (2002). Paunzen et al. (1999) Paunzen et al. (2002a). Evolutionary Status.

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The Group of l Bootis Stars

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  1. The Group oflBootisStars Dr. Ernst PaunzenInstitute for Astronomy University of Vienna

  2. Abundance Pattern • C, N, O und S solar abundant • Heavier elements underabundant, (Na) • Large Scatter Heiter (2002) Paunzen et al. (1999) Paunzen et al. (2002a)

  3. Evolutionary Status Paunzen et al. (2002b)

  4. Group properties • About 50 members • Typical abundance pattern • Temperature range: 11000 to 6500K • From ZAMS to TAMS • No magnetic fields detected • Not found in open clusters • Only spectroscopic binaries of the type „l Bootis“

  5. Diffusion/Mass-loss • Mass-loss „conserves“ He convection zone • BUT: Rotation induces mixing • Time scale: ca. 1 Gyr Charbonneau (1993)

  6. Diffusion/Accretion • Star accretes gas component of the interstellar environment • Diffusion mixes atmosphere Turcotte & Charbonneau (1993) Number of measurements Heiter et al. (2002)

  7. Diffusion/Accretion • Source of material only from star formation • Time scale: max. 100 Myr

  8. Diffusion/Accretion • Disk visible in IR • Measurements for 26 l Bootis Stars • Six with IR Excess, upper limits otherwise Paunzen et al. (2003)

  9. Theories versus Observations

  10. A New Accretion Model • What happens if a star crosses denser ISM? • Questions: • Time scale • Needed densities of ISM • Relative velocity range • Accretion of gas realistic • Range of spectral types • Statistical frequency

  11. A New Accretion Model • ISM model: „standard“ abundances, density about 10 cm-3 • Velocity range: 10 to 20 kms-1 • Time Scale: 1 pc, 17 kms-1, ca. 60000 yr • Hot end: Stellar Winds, 12000K • Cool end: Convection, 6500K • Dust is blown away • Open Clusters: no gas to accrete • Statistics: about 15 objects predicted within 60 pc, 9 known Kamp & Paunzen (2002)

  12. Theories versus Observations

  13. Pulsating l Bootis Stars Paunzen et al. (2002b) Koen et al. (2003)

  14. l Bootis versus d Scuti Paunzen et al. (2002b) Pulsational constants smaller, Overtones excited Instability strip shifted

  15. Which Mechanism can be studied? • Diffusion • Accretion • Rotation • Pulsation • depending on: • Metallicity • Age • Stellar Environment

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

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