Hunting down the subdwarf populations Peter Nemeth KU Leuven, Belgium Bamberg, Germany; Sep 13, 2013

Bamberg - September 13, A GALEX sample

Bamberg - September 13, How it got started Classical nova X-ray spectra New model atoms from Topbase and NIST Chi-by-eye fitting

Bamberg - September 13, A Galex sample (Vennes et al. 2011) ~700 UV-excess objects, N UV -V < observing runs at KPNO and ESO, 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

Bamberg - September 13, The fitting method (XT GRID ) Green: Model, T = K, log g = 5.6, log He = -1, log CNO = -2 Red: J , T = K, log g = 4.5, log He = -0.4 log C = -2.8, log N = -2.9, log O < -2.6

Bamberg - September 13, The fitting method (XT GRID ) Green: Model, T = K, log g = 5.6, log He = -1, log CNO = -2 Red: J , T = K, log g = 4.5, log He = -0.4 log C = -2.8, log N = -2.9, log O < -2.6

Bamberg - September 13, Composite spectra Must be addressed, ~20 % of the sample shows a significant IR excess.

Bamberg - September 13, Composite spectra Must be addressed, ~20 % of the sample shows a significant IR excess.

Bamberg - September 13, Temperature – gravity

Bamberg - September 13, Temperature – gravity

Bamberg - September 13, He abundance H. Edelmann, U. Heber, H.-J. Hagen et al.; 2003, A&A, 400, 939

Bamberg - September 13, 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?

Bamberg - September 13, 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? C. Binary: 4% Nitrogen: 70% C. Binary: 30% Nitrogen: 22% S. Charpinet, E. M. Green, A. Baglin et al.; 2010; A&A 516 L6

Bamberg - September 13, 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?

Bamberg - September 13, Luminosity distribution * * before GAIA Correlates with observed mass distribution, eg. SPY (Lisker et al. 2005)

Bamberg - September 13, Abundance evolution? Speculations... CanonicalHot-flasher e.g.: Miller Bertolami M. M. et al., 2008, A&A, 491, 253e.g.: Zhang X., Jeffery S. C., 2012, MNRAS, 419, 452

Bamberg - September 13, Abundance evolution? Complicated... UV flux induces convection, turbulence, mixing, wind... lots of complications. eg.: Unglaub, 2008

Bamberg - September 13, 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.

Bamberg - September 13, 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:

Bamberg - September 13, Improvements in XT GRID Rotational broadening; first application for CD : 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

Bamberg - September 13, MMT Spectra Data for 8 BHB stars were provided by Betsy Green after the sdOB6 conference MMT Blue Channel Spectrograph R = 4500 SNR ~ 200

Bamberg - September 13, Tlusty Models

Bamberg - September 13, Two 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/HeTlusty NLTE, 30 elements NameT eff log glog nHe/nHT eff log glog nHe/nH PG ± ± ± BD ± ± ± Feige ± ± ± PG ± ± ± PG ± ± ± Balloon ± ± ± PG ± ± ± KIC ± ± ±

Bamberg - September 13, Comparison with M22

Bamberg - September 13, Comparison with M22

Bamberg - September 13, Abundance patterns Grevesse & Sauval (1998) Solar abundances in Tlusty

Bamberg - September 13, Balloon (HIP 65388) HIP 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: Spectral type: sdB – B2 V = mag v rad = -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: C ). 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.

Bamberg - September 13, The optical data

Bamberg - September 13, A small part of the FUSE spectrum

Bamberg - September 13, 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.