Hunting down the subdwarf populations

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

SDOB6 - Tucson - May 20, 2013 2

A A GALEXGALEX sample sample


How it got startedHow it got started

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


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


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


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


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


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


Temperature – gravityTemperature – gravity


Temperature – gravityTemperature – gravity


He abundanceHe abundance

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


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?




• Can abundance patterns indicate the evolution or other properties, like pulsations, of these stars?




C. Binary: 4%

Nitrogen: 70%

C. Binary: 30%

Nitrogen: 22%

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




• Can abundance patterns indicate the evolution or other properties, like pulsations of these stars?





Luminosity distributionLuminosity distribution**

* before GAIA

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


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


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

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

eg.: Unglaub, 2008


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.


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...


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


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.

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Hunting down the subdwarf populations