Chemically Peculiar Stars

1
Chemically Peculiar Stars

• Dennis Lamenti
• A540, Prof. Pilachowski
• Spring 2007

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Outline

• History
• Identifying CP Stars
• Classification
• Description of types
• Overall Properties
• Explanation of Peculiar Abundances
• Evolution of CP Stars

3
History

• 1897 Antonia Maury
• 1931 W.W. Morgan Eu II, Cr II varied in HD 125248
• 1947 Horace Babcock, dipolar B field 78 Virginis
• 1958 Babcock, Catalogue of similar dipolar stars
• 1974 Preston classification

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How are CP stars identified?

• Peculiar and/or variable line strengths
• Quadrature of line variability with radial
  velocity changes
• Photometric variability with same periodicity
• Slow rotation inferred by sharp spectral lines
• Some with rapid oscillations
• Variable strength of magnetic fields

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Teff lt 7000K homogenous 7000 lt Teff lt 30,000K
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CP Classification
Smith, K.C., 1996
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? Boo

• First spectrum 1943 MKK
• Characteristics in visual (Gray 1988,1991)
• Weak Mg II ?4481
• Ca II K-line type of A0
• Hydrogen-line type btwn A0-F0
• Weak metallic-line spectrum
• 50 ? Boö stars known (Gray Corbally 2002)
• No detectable magnetic field (Shorlin, et.al
  2002)
• IUE noted strong C I

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Am-Fm

• Metallic lines classified by Titus
• Morgan (1940)
• MK classification Roman, Morgan Eggen
• (1948)
• Characteristics in visual
• Weak Ca II K-line
• Strong metallic lines
• Slow rotation
• High Binary frequency
• No magnetic field detected (Shorlin, et.al 2002)
• Best known Am star is Sirius

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Bp-Ap

• Several spectroscopic types (Jaschek Jaschek
  1958)
• SiCrEu, SrCrEu, Si, Sr
• Strong Magnetic Field (Shorlin, et.al 2002)
• Slow rotation
• Subset roAp (rapidly oscillating)
• Few mins period
• Small amplititude (mmag) oscillation

10
HgMn

• 1906 Lockyer Baxendall unable to id lines at
• 3944, 3984,4137,4206 4282 Å
• 1931 Morgan id 13 stars with spectra similar to
  prototype ? And, thus put these into a
  classification
• 1914 Baxendall all but 3984 were Mn lines
• 1961 Bidelman showed 3984 Å as Hg II
• Slow rotation
• No detecable magnetic fields (Shorlin, et.al
  2002)

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He-weak

• 1960 Bidelman spectrum of 3 Cen A
• B5 star with weak He I
• Sharp lines P II, Ga II and noble gas elements
• 1961 Jugaku Sargent ? Scl
• B4 star weak He I
• Cr II, Ti II and Sr II
• Subclasses
• P-Ga (Phosphorus stars) 3 Cen A
• Sr-Ti ? Scl stars
• Si (blue helium-weak stars, Jaschek Jaschek,
  1974)
• Slow rotation
• Magnetic Field (Shorlin, et.al 2002)

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He-rich

• Consider only intermediate helium stars
• 1958 ? Ori E (Greenstein Wallerstein)
• Classified from other He rich stars by normal H
  lines and Population I space velocities
• Magnetic fields (Shorlin, et.al 2002)

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Location on HR diagram

• Open cluster data (North, 1993)

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Frequency of CP
Smith, K.C., 1996

• Frequency by spectral type from BSC

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Rotational Velocity
Smith, K.C., 1996
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Frequency in Binary Systems
Smith, K.C., 1996
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Element Abundances
Smith, K.C., 1996
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Dipolar B Field
Kochukhov et al. 2004
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Explanation of Peculiar Abundances?

• Radiation Diffusion
• Michaud 1970
• Selective Accretion
• Havnes, Conti 1971

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Radiative Diffusion Theory
Michaud, 1986
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Selective Accretion
Havnes, Conti 1971
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Evolution of CP Stars
Gomez, 1998
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Evolution of CP Stars
Hubrig, 2000
Hubrig, 2000
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Evolution of CP Stars
Pöhnl, et.al., 2003
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Current Work

• Origin of Magnetic Fields
• Fossil or dynamo
• Evolution of CP2
• Peculiar at ZAMS
• Peculiar after 30 of MS lifetime
• Parallel evolution of spectroscopic and magnetic
  peculiarities
• Diffusion model does not work for some element
  abundances
• Atmospheric modeling to include magnetic fields
• Non-LTE models

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References

• Babcock, H 1947 PASP59260b
• Gomez, et.al. 1998 AA 336953-959
• Hubrig, et. al. 2000 Ap.J. 539352
• Institute for Astronomy, University of Vienna,
  The Delta a and Stellar Aggregates Research
  Group,http//www.univie.ac.at/dasa/, 12/03/07
• Kochukhov, et.al. 2004 AA 424935
• Pöhnl, et.al. 2003 AA 402247-252
• Preston, George 1974 Annu. Rev. Astro. Astrophys.
  12257-277
• Shorlin, et.al. 2002 AA 392637-652
• Smith,K.C. 1996 ApSS 23777-105
• Image Credit
• M3, N.A.Sharp, Vanessa Harvey/REU
  program/NOAO/AURA/NSF