spectroscopy and the evolution of hot subdwarf stars
DESCRIPTION
Spectroscopy and the evolution of hot subdwarf stars. Peter Nemeth Astronomical Institute of the Czech Republic. Pannon Observatory and Visitor Center Bakonyb él. Subdwarf stars?. The Hertzsprung-Russell diagram Red Giants, White dwarfs. Stellar evolution Stellar populations - PowerPoint PPT PresentationTRANSCRIPT
Spectroscopy and the evolution of hot subdwarf stars
Peter NemethAstronomical Institute of the Czech Republic
K. U. Leuven - Nov. 9., 2012.
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Pannon Observatory and Visitor CenterBakonybél
K. U. Leuven - Nov. 9., 2012.
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Subdwarf stars?
• The Hertzsprung-Russell diagram
• Red Giants, White dwarfs.
• Stellar evolution
• Stellar populations
• Cool/hot subdwarfs
• Globular cluster CMD
• EHB stars.
• Heavy traffic of evolved stars around the EHB
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Globular cluster CMD
Heber, U., 2009, ARA&A, 47, 211
Yi, S.K., 2008, ASPC, 392, 3NGC 2880
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What we know
Progenitor MS mass between 1 and ~5 Mʘ
Evolved, core helium burning stars Thin hydrogen layer Many in binaries with MS or WD companions Direct evolution towards white dwarfs
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Structure of subdwarfs
sdB sdO
From Wikipedia
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Spectral classification sdO – dominant H and He II absorption lines
sdB – dominant H lines, weak He I absorption lines
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A GALEX sample
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The sample 694 UV-excess objects, NUV-
V < 0.5 7 observing runs, 2007-2011 ~200 targets Low-resolution, optical
spectroscopy Modeling with TLUSTY-
SYNSPEC Paper I: 52 stars,
interpolation in 3 grids, H, He
Paper II: 180 stars, steepest-descent with a constant level structure, H, He, CNO
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The fitting method
Green: Model, T = 40 000 K, log g = 5.6, log He = -1, log CNO = -2
Red: J2059+4232, T = 20 700 K, log g = 4.5, log He = -0.4
log C = -2.8, log N = -2.9, log O < -2.6
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The fitting method
Green: Model, T = 40 000 K, log g = 5.6, log He = -1, log CNO = -2
Red: J2059+4232, T = 20 700 K, log g = 4.5, log He = -0.4
log C = -2.8, log N = -2.9, log O < -2.6
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Composite spectra
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Temperature – gravity
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Abundances
• Multiple dichotomies
• Can abundance patterns indicate the evolution or other properties, like pulsations, of these stars?
• HST STIS shows high abundances of iron-peak elements, but not much Fe. (O’Toole & Heber, 2006)
• Slow, rapid and hybrid pulsators are well separated, but not preictable
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Luminosity distribution
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Spectral evolution?
Canonical Hot-flasher
e.g.: Miller Bertolami M. M. et al., 2008, A&A, 491, 253e.g.: Zhang X., Jeffery S. C., 2012, MNRAS, 419, 452
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Spectral evolution? Complicated.
UV flux induces convection, turbulence, mixing, wind ... lots of complications.
(Unglaub, 2008)
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Formation channels
Canonical Common Envelope Roche Lobe Overflow WD Mergers
Hot-flasher Deep mixing Shallow mixing No mixing
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Puzzling questions
How do subdwarfs form? Which formation scenarios are viable and what are their contributions to the observed SD distribution?
What drives the mass-loss on the RGB? He-sdO ? sdB How clean is the observed population from
ELM WD, post-AGB, CSPN stars?
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The SD1000 Collaboration
We need spectroscopy for a large sample Repeat (and later extend) the analysis in a
homogeneous way Derive homogeneous parameters Collaborations are important because
subdwarfs link RGs to WDs GAIA will provide distances and masses Find binaries
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References
Østensen, R.H.; Comm. in Asteroseismology, 2008, 159, 75 Heber, U.; ARA&A, 2009, 47, 211 sdB sdO page on Wikipedia Zhang, X., Jeffery, S. C.; 2012, MNRAS, 419, 452 Miller Bertolami, M. M. et al.; 2008, A&A, 491, 253 Yi, S.K.; 2008, ASPC, 392, 3 O’Toole, S.J; Heber, U.; 2006, A&A, 452, 579 Unglaub, K.; 2008, A&A, 486, 923