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Chemically Peculiar Stars

Chemically Peculiar Stars. Dennis Lamenti A540, Prof. Pilachowski Spring 2007. Outline. History Identifying CP Stars Classification Description of types Overall Properties Explanation of Peculiar Abundances Evolution of CP Stars. History. 1897 Antonia Maury

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Chemically Peculiar Stars

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  1. Chemically Peculiar Stars Dennis Lamenti A540, Prof. Pilachowski Spring 2007

  2. 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

  4. 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

  5. Teff < 7000K homogenous 7000 < Teff < 30,000K

  6. CP Classification Smith, K.C., 1996

  7.  Boo • First spectrum 1943 MK&K • 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 CI

  8. 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

  9. 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)

  11. 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)

  12. 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)

  13. Location on HR diagram Open cluster data (North, 1993)

  14. Frequency of CP Frequency by spectral type from BSC Smith, K.C., 1996

  15. Rotational Velocity Smith, K.C., 1996

  16. Frequency in Binary Systems Smith, K.C., 1996

  17. Element Abundances Smith, K.C., 1996

  18. Dipolar B Field Kochukhov et al. 2004

  19. Explanation of Peculiar Abundances? • Radiation Diffusion • Michaud 1970 • Selective Accretion • Havnes, Conti 1971

  20. Radiative Diffusion Theory Michaud, 1986

  21. Selective Accretion Havnes, Conti 1971

  22. Evolution of CP Stars Gomez, 1998

  23. Evolution of CP Stars Hubrig, 2000 Hubrig, 2000

  24. Evolution of CP Stars Pöhnl, et.al., 2003

  25. 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

  26. References Babcock, H 1947 PASP…59…260b Gomez, et.al. 1998 A&A 336:953-959 Hubrig, et. al. 2000 Ap.J. 539:352 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 A&A 424:935 Pöhnl, et.al. 2003 A&A 402:247-252 Preston, George 1974 Annu. Rev. Astro. Astrophys. 12:257-277 Shorlin, et.al. 2002 A&A 392:637-652 Smith,K.C. 1996 Ap&SS 237:77-105 Image Credit M3, N.A.Sharp, Vanessa Harvey/REU program/NOAO/AURA/NSF

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