Hunting down the subdwarf populations Peter Nemeth KU Leuven, Belgium Bamberg, Germany; Sep 13,...

Hunting down the Hunting down the subdwarf subdwarf

populationspopulations

Peter NemethPeter NemethKU Leuven, BelgiumKU Leuven, Belgium

Bamberg, Germany; Sep 13, 2013

Bamberg - September 13, 2013 3

How it got startedHow it got started

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


A Galex sample (Vennes et A Galex sample (Vennes et al. 2011)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 The fitting method (XT(XTGRIDGRID) )

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.


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)


Puzzling questionsPuzzling 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 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 can join at: http://stelweb.asu.cas.cz/~nemeth/work/sd1000/


Improvements in XTImprovements in XTGRIDGRID

Rotational broadening; first application for CD-30 11223: 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. 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 SpectraMMT Spectra

Data for 8 BHB stars were provided by Betsy Green after the sdOB6 conference

MMT Blue Channel Spectrograph

R = 4500 SNR ~ 200


Tlusty ModelsTlusty Models


Two conclusionsTwo conclusions Spectral fitting with 30 elements is not a dream job The effects of metal abundances and not just their presence are important:

Tlusty NLTE, H/He Tlusty NLTE, 30 elements

Name Teff log g log nHe/nH Teff log g log nHe/nH

PG 1553+273 24600

±590

4.83

±0.07

-2.98

±0.2

20150 4.61 -3.33

BD+48 2721 22580

±340

4.90

±0.04

-1.99

±0.05

20790 4.93 -2.12

Feige 86 19990

±320

4.66

±0.05

-2.26

±0.08

16100 4.33 -2.07

PG 1451+492 22470

±400

4.81

±0.05

-2.07

±0.06

19510 4.78 -1.98

PG 0848+186 20320

±400

4.58

±0.07

-0.78

±0.05

18500 4.58 -0.76

Balloon 82000001 21830

±500

4.76

±0.08

-0.94

±0.05

19170 4.71 -0.69

PG 1400+389 20670

±390

4.73

±0.07

-0.69

±0.05

18770 4.76 -0.64

KIC1718290 22210

±420

4.82

±0.06

-0.41

±0.03

21400 4.77 -0.49


Comparison with M22Comparison with M22


Abundance patternsAbundance patterns

Grevesse & Sauval (1998)

Solar abundances in Tlusty


Balloon 82000001 (HIP Balloon 82000001 (HIP 65388)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.


The optical dataThe optical data


A small part of the FUSE A small part of the FUSE spectrumspectrum


Final remarksFinal 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.

Hunting down the subdwarf populations Peter Nemeth KU Leuven, Belgium Bamberg, Germany; Sep 13,...

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