Hunting down the Hunting down the subdwarf subdwarf

populationspopulations

Peter NemethPeter NemethRoy Østensen and Joris VosRoy Østensen and Joris Vos

KU Leuven, Belgium;KU Leuven, Belgium;

In collaboration with In collaboration with

Stephane Vennes and Adela KawkaStephane Vennes and Adela Kawka

Astronomical Institute of the Czech RepublicAstronomical Institute of the Czech Republic

SDOB6; Tucson AZ, USA; May 20, 2013

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A A GALEXGALEX sample sample

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How it got startedHow it got started

Classical nova X-ray spectra New model atoms from Topbase and NIST Chi-by-eye fitting

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The sampleThe sample

~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

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The fitting methodThe 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 methodThe 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 spectraComposite spectraMust be addressed, ~20 % of the sample shows a significant IR excess.

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Composite spectraComposite spectraMust be addressed, ~20 % of the sample shows a significant IR excess.

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Temperature – gravityTemperature – gravity

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Temperature – gravityTemperature – gravity

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He abundanceHe abundance

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

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AbundancesAbundances

• 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?

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AbundancesAbundances

• 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

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AbundancesAbundances

• 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?

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Luminosity distributionLuminosity distribution**

* before GAIA

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

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Abundance evolution? Abundance evolution? Speculations...Speculations...

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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Abundance evolution? Abundance evolution? Complicated...Complicated...

UV flux induces convection, turbulence, mixing, wind ... lots of complications.

eg.: Unglaub, 2008

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Puzzling questionsPuzzling 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?

These questions remain and need more attention.

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The SD1000 CollaborationThe 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 needed...

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New improvements in New improvements in XTGRIDXTGRID

Rotational broadening; first application for CD 3011223: v sin(i) ~170 km/sVennes 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 “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

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Highlight from Paper III: GALEX Highlight from Paper III: GALEX J2349+3844 is a short-period J2349+3844 is a short-period

eccentric binaryeccentric binary

Kawka et al.; in prep.