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Hunting down the subdwarf populations. Peter Nemeth KU Leuven, Belgium. Bamberg, Germany; Sep 13, 2013. How it got started. Classical nova X-ray spectra New model atoms from Topbase and NIST Chi-by-eye fitting. A Galex sample (Vennes et al. 2011). ~700 UV-excess objects,

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hunting down the subdwarf populations

Hunting down the subdwarf populations

Peter Nemeth

KU Leuven, Belgium

Bamberg, Germany; Sep 13, 2013

how it got started
How it got started
  • Classical nova X-ray spectra
  • New model atoms from Topbase and NIST
  • Chi-by-eye fitting
a galex sample vennes et al 2011
A Galex sample (Vennes et al. 2011)
  • ~700 UV-excess objects,

NUV-V < 0.5

  • 7 observing runs at KPNO and ESO, 2007-2011
  • Low-resolution, optical spectroscopy
  • ~200 targets, 6 new WDs
  • 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
the fitting method xt grid
The fitting method (XTGRID)

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

the fitting method xt grid1
The fitting method (XTGRID)

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

composite spectra
Composite spectra

Must be addressed, ~20 % of the sample shows a significant IR excess.

composite spectra1
Composite spectra

Must be addressed, ~20 % of the sample shows a significant IR excess.

he abundance
He abundance

H. Edelmann, U. Heber, H.-J. Hagen et al.; 2003, A&A, 400, 939

abundances
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
  • Are C&N class sdB and He-sdO stars related?
abundances1
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
  • Are C&N class sdB and He-sdO stars related?

C. Binary: 4%

Nitrogen: 70%

C. Binary: 30%

Nitrogen: 22%

S. Charpinet, E. M. Green, A. Baglin et al.; 2010; A&A 516 L6

abundances2
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
  • Are C&N class sdB and He-sdO stars related?
luminosity distribution
Luminosity distribution*

* before GAIA

Correlates with observed mass distribution, eg. SPY (Lisker et al. 2005)

puzzling questions
Puzzling questions
  • How 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?
  • These questions remain and need more attention.
the sd1000 collaboration
The SD1000 Collaboration
  • Spectroscopy for the largest possible sample for a better statistics and distribution.
  • Homogeneous analysis to find subtle trends and correlations among surface parameters.
    • ERC: From inhomogeneous data?
  • Find connections to RGs and WDs
  • Provide a statistically significant sample for GAIA and derive absolute luminosities and masses.
  • Find binary fractions and correlations between surface and binary parameters.
  • Collaborators can join at: http://stelweb.asu.cas.cz/~nemeth/work/sd1000/
improvements in xt grid
Improvements in XTGRID
  • Rotational broadening; first application for CD-30 11223: v sin(i) ~170 km/s

Vennes et al. (2012); Geier et al. (2013)

  • Simultaneous fit and radial velocity correction for multiple datasets
  • Efforts to speed-up model calulations with Iron-peak elements by adjusting opacity sampling parameters. However, it is still demanding...
  • “ICHANG”; examine the ionization balance
  • ... and numerous bug fixes

New directions:

  • Abundance stratification
  • Resolve lower mass MS companions in the IR
  • Radial velocities from composite spectra
mmt spectra
MMT Spectra
  • Data for 8 BHB stars were provided by Betsy Green after the sdOB6 conference
  • MMT Blue Channel Spectrograph
  • R = 4500
  • SNR ~ 200
two conclusions
Two conclusions
  • Spectral fitting with 30 elements is not a dream job
  • The effects of metal abundances and not just their presence are important:
abundance patterns
Abundance patterns

Grevesse & Sauval (1998)

Solar abundances in Tlusty

balloon 82000001 hip 65388
Balloon 82000001 (HIP 65388)
  • HIP 65388 is the only star in Betsy’s sample that has FUSE observations.
  • Not much recent work is available on the star.
    • Tobin, W. 1986, A&A, 155, 326
    • de Boer, K.S., Richtler, T., Heber, U. 1988, A&A, 202, 113
    • Conlon, E.S., Brown, P.J.F., Dufton, P.L., Keenan, F.P. 1989, A&A, 224, 65
  • Dissertation: Martin, J.C. 2006, AJ, 131, 3047
  • Simbad: also PB 166
    • Galactic coordinates: 109.3 +66.9
    • Spectral type: sdB – B2
    • V = 12.48 mag
    • vrad = -30 – -43 km/s
    • π = 6.45 mas (155 pc) ?
  • The star was observed by FUSE for 9890 sec in 2002 (PI Edward Fitzpatrick, Data ID: C1180701). According to the proposal the original intent was to carry out a complex abundance analysis in serach for the origins of halo subdwarfs.
  • Only one reference in MAST to the FUSE observation:
    • Gianninas, A., Bergeron, P., Dupuis, J., and Ruiz, M.T., 2010, ApJ, 720, 581
  • Using the results from the optical spectrum, I fit the optical and UV data simultaneously. Still, for 2 months.
final remarks
Final remarks
  • Field BHB stars show a similar dichotomy like sdB stars.
  • BHB stars are interesting and might help us understand the formation of sdB stars. They are challenging and not well analised objects.
  • H/He fits are a quick way to derive atmospheric parameters, however if one is interested in metal abundances and precision spectroscopy, CNO and Fe must not be avoided in the structure calculations.
  • Element stratification might be responsible for some of the observed line profile inconsistencies and must be investigated.
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