The Group of l Bootis Stars

1
The Group of l Bootis Stars

• Dr. Ernst PaunzenInstitute for Astronomy
  University of Vienna

2
Abundance Pattern
Heiter (2002)

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

Paunzen et al. (1999) Paunzen et al. (2002a)
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Evolutionary Status
Paunzen et al. (2002b)
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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

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Diffusion/Mass-loss
Charbonneau (1993)

• Mass-loss conserves He convection zone
• BUT Rotation induces mixing
• Time scale ca. 1 Gyr

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Diffusion/Accretion
Turcotte Charbonneau (1993)

• Star accretes gas component of the interstellar
  environment
• Diffusion mixes atmosphere

Number of measurements
Heiter et al. (2002)
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Diffusion/Accretion

• Source of material only from star formation
• Time scale max. 100 Myr

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Diffusion/Accretion

• Disk visible in IR
• Measurements for 26 l Bootis Stars
• Six with IR Excess, upper limits otherwise

Paunzen et al. (2003)
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Theories versus Observations
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A New Accretion Model

• Questions
• Time scale
• Needed densities of ISM
• Relative velocity range
• Accretion of gas realistic
• Range of spectral types
• Statistical frequency

• What happens if a star crosses denser ISM?

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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)
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Theories versus Observations
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Pulsating l Bootis Stars
Paunzen et al. (2002b)
Koen et al. (2003)
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l Bootis versus d Scuti
Paunzen et al. (2002b)
Pulsational constants smaller, Overtones excited
Instability strip shifted
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Which Mechanism can be studied?

• Diffusion
• Accretion
• Rotation
• Pulsation

• depending on
• Metallicity
• Age
• Stellar Environment

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References

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