PoS(NIC-IX)101 , http://pos.sissa.it/ 3 ce. high fraction of massive compact panions to derive their masses and ave very massive companions like y evolution. to constrain inclination angle and rs and black holes are fundamental ave masses that are compatible with ocity of the stars with high accuracy. pectral analysis. With high resolution e results of an analysis of subluminous from time resolved spectroscopy. The n the Cosmos — IX hire and R. Napiwotzki , 1 rn@star.herts.ac.uk , [email protected] , , U. Heber 2 ive Commons Attribution-NonCommercial-ShareAlike Licen , H. Edelmann 1 , C. Karl 1 ∗ [email protected] white dwarfs or late type mainheavy sequence white stars. dwarfs, But neutron four stars sdBs h or even black holes. Such a to astrophysics, but very difficult to measure.B We present (sdB) th stars in close binary systems with unseen compact com spectra we were able to measure the projected rotational vel companion mass of the binaries. Five invisible companions h companions can not be explained with current models of binar The masses of compact objects like white dwarfs, neutron sta clarify their nature. Radial velocityatmospheric curves parameters were were obtained determined in a quantitative s The assumption of orbital synchronization made it possible Speaker. ∗ Copyright owned by the author(s) under the terms of the Creat c International Symposium on Nuclear Astrophysics —June Nuclei 25-30 i 2006 CERN, Geneva, Switzerland [email protected] [email protected]

Dr.Remeis-Sternwarte Sternwartstraße 7, 96049 Bamberg, Germany McDonald Observatory, University of Texas at1 Austin University Station, C1402, Austin, TXCentre 78712-0259, for USA Astrophysics Research, University of Hertfords College Lane, Hatfield AL10 9AB, UK E-mail: S. Geier Spectroscopic Analysis of subluminous B StarsBinaries in 1 2 3 PoS(NIC-IX)101 , sdB (1.1) (1.2) M S. Geier s (Han et al. 2002, r, a direct measurement is for sdBs in binaries, which ite dwarfs or late type main ⊙ ese systems common envelope t formation channels have been es the red giant branch, another stribution shows a sharp peak at d, which contains a helium core s (sdBs), show the same spectral ry with a white dwarf companion . ion mass can be derived. With the r to the companion is dynamically o stellar cores loose orbital energy, tions can be calculated. 3 ssoul 1992 [16]), which means that G rogen envelopes and masses around s are very rare, only few sdB+NS or are members of short period binaries 0.48 M stem. The heavier one will first reach 002, 2003 [6,7]). In this scenario two e of the binary period. Eventually the π d therefore their orbital motion cannot ut are much less luminous. They are overcome. ay evolve into a neutron star (NS) or a ellar evolution. In binaries such faint, PK 2 systems are first choice. White dwarfs, − are determined by the RV curve, al velocities are considered to be tidally d of the companions. If the companions y reveal no information about the orbital = P . can be calculated. 2 ) rot = 0.30 sdB i v 3 P R sdB π sdB M 2 2 sin M + = 3 comp rot comp M v and the period M ( K = m f is given by the mass radius relation. R remain free parameters. Binary population synthesis model i . ⊙ M 46 . and sin . The formation of these objects is still puzzling. Differen ⊙ Although the RV semi-amplitude The stellar radius The mass of a star is it’s most fundamental parameter. Howeve M comp 5 . locked to their orbital motions (Zahn 1977 [17], Tassoul & Ta For close binary systems, the components’ stellar rotation the orbital period of the systemare equals synchronized the in rotational this way perio the rotational velocity underwent the common envelope ejectionabout channel. 0 The mass di 2003 [6,7]) indicate a possible mass range of M motion of the sdBs’ companions, and thus only their mass func discussed. As it turned out,(Maxted a et. large fraction al of theejection 2001 is sdB [10], the stars most Napiwotzki probable et formationmain al. channel sequence (Han stars et of 2004 al. different [14]). masses 2 the evolve in red For a giant binary th phase sy andunstable, fill a its common Roche envelope is lobe. formed.which is If Due deposited the to within friction mass the the transfe envelopecommon tw and leads envelope to is a ejected shortag andburning a sdB close and binary a system maincommon is envelope sequence forme phase companion. is possible If andand this can an lead star sdB. to reach All a knownsequence close companions stars. bina of If massive sdBs stars in areblack such involved, hole the (BH) systems primary rather are m than wh asdB+BH white systems dwarf. are expected Since to massive be star Since found. the spectra of the program stars are single-lined, the possible in some binary stars only.neutron Eclipsing, stars double and lined stellar blackcompact holes objects are are outshined the by aftermath their brightbe of companions measured. st an As a consequence onlyanalysis lower method limits shown to here, the these compan limitationsSubluminous can B partly be stars, which arecharacteristics also as known main as sequence hot starsconsidered sudwarf to of star be spectral helium type core B,0 burning b stars with very thin hyd Spectroscopic Analysis of sdB Binaries 1. Introduction PoS(NIC-IX)101 and (1.4) (1.3) g S. Geier 1 a lower , log ≤ P i , K trum for the visible therefore allows to constrain ne curve. Lower left i y to measure at La Palma (Napiwotzki et al. on spectrograph UVES at the uipped with EMMI), the Calar ann et al. 2005 [5]). The data was sin 4503) based on 47 UVES ived. Because of sin − rot v rmined by calculating the shifts of the ped for every instrument. g 2 G P G 2 g π sdB 4 2 rotsini M 3 v s ≥ as free parameter the mass function can be solved and = sdB R 136, TONS 183) were observed with the high resolution sdB M − M 4503 system (left panel). Upper left panel: Measured − . With i Sample model fit for an sdB star (HE 0532 spectra (right panel). Sample best fitsdB RV curve star and in power spec the HE 0532 panel: Power spectrum. radial velocities as a function of orbital phase and fitted si Figure 1. with high accuracy. i To constrain the system parameters in this way it is necessar Ten stars were observed at least twice with the high resoluti The measurement of the projected rotational velocities sin rot the inclination angle as well as the companion mass can be der limit for the sdB mass is given by the systems’ inclination angles v 2. Observations and Radial Velocity Curves ESO VLT. Additional observations were madeAlto at Observatory the 3.5 ESO m NTT telescope (eq (TWIN) and2003 the [11]). 4 m Two WHT of (ISIS) the stars (PG 1232 reduced with different software packages speciallyRadial develo velocities of the individual observations were dete FEROS instrument at the 2.2 m ESO telescope at La Silla (Edelm Spectroscopic Analysis of sdB Binaries PoS(NIC-IX)101 lines, I S. Geier ution for ) and the P e core. We 5 and , ) as a function of 2 or the sam- χ tal periods ( ed line marks the e the overall spectral trend, ue is plotted as black adenings of 0 profile we used an additional α 4503. The orbital parameters of , Fig. 1 (left panel) displays the ngth of the Lorentzian was fixed ed residuals ( eriod, the ephemeris, the system’s ch was carried out by means of a ki et al. 2001 [12]). The difference − thod. For a large range of periods the ns to the observed line profiles using 136 (right panel). The filled 9]). heoretical RV curve for each phase set pectrum which allows to determine the − We focussed on all available He 4 ) are given in Tab. 1. K 4503 (left panel) and PG 1232 − 136 were taken from Edelmann et al. (2005) [5]. An orbital sol line profile because of its sharp and well-defined non-LTE lin − α Projected rotational velocity as a function of wavelength f 1 − 0436 was published by Napiwotzki et al. (2001) [12]. The orbi − Figure 2. ple stars HE 0532 squares are measurements of single metal lines.horizontal The line. mean val The small boxesbest show solution a and sample the fit, narrow where black the lines r fixed rotational bro 10kms period. This method finally results inmost the probable data-set’s period power of s variability (seeFrom Lorenz the et best al. fit 1998 RV [ curvevelocity corresponding to and the the most probable semi-amplitude p resulting were power derived. spectrum and As best-fit an sine example curve for HE 0532 TONS 183 and PG 1232 HE 1047 radial velocity semi-amplitudes ( performed a simultaneous fit of athe set ESO of mathematical MIDAS functio package.and a A Gaussian linear for function the was innermost used line core. to reproduc In order to fit the H Lorentzian to model theto broad that line of wings. theperiodogram The Gaussian based central on for the wavele physical ’Singular Value Decomposition’ reasons. me best fitting The sine-shaped RV period curve sear wasbetween computed the (see observed Napiwotz radial velocitieswas and evaluated the in best terms fitting of t the logarithm of the sum of the squar Spectroscopic Analysis of sdB Binaries measured wavelengths relative to their laboratory values. and on the observed H PoS(NIC-IX)101 ) g ned, S. Geier 0342 is a white dwarf. − ), surface gravities (log eff T ard deviation were calculated 136 have even higher compan- But taking into account, that the adopted the mass range for sdBs D 0107 it. There are only two kinds of patible with either white dwarfs l broadening than Balmer or he- − s - neutron stars (NS) and stellar asses can be seen in Tab. 2. Four rrected for the measured RV and t panel). se cause an extra broadening of the ere carried out to identify potential LTE model spectra. The procedure e stellar parameters given in Tab. 1 . nd Lisker et al. (2005) [8]. Because atures ( , which makes this the most probable f companions visible. Main sequence neous fit of elemental abundance and ⊙ method. As the lower limit we derived ed, which is consistent with the analysis r every identified line using the FITSB2 M o be negligible compared to the statistical esults and will be discussed in detail later. 46 . 5 4503 and PG 1232 − line was excluded from this analysis. The atmospheric α 136 were taken from Edelmann et al. (2005) [5]. Results − could therefore be excluded because of their high luminosi- ) were determined by fitting simultaneously each observed ] ⊙ 0424 and TONS 183 have a wide companion mass range. For H n M − / 45 , we compared the observed spectra with rotationally broade . He i n [ sin rot v . 1 − 5kms > i To constrain the companion masses and inclination angles we Since sharp metal lines are much more sensitive to rotationa In order to derive Prior to quantitative spectral analysis the spectra were co sin rot sdB mass, the companionobjects masses known exceed with the such Chandrasekhar highblack lim masses holes (BH). and The such two low systems luminositie HE 0532 ion masses, which exceed the Chandrasekhar limit in any case The very similar binaries HE 0929 ties in comparison to theof sdB the stars. analysed The systems possible have(WD) companion companion or masses, m late main which sequence are stars com (late MS). The companion of W very low mass sdBs the companiontheoretical could sdB be a mass heavy distribution white has dwarf. a sharp peak at 0 hydrogen and helium line withused a is grid described of in metal-line detail blanketed of in its Napiwotzki sensitivity to et non-LTE al. effects, the (1999) H [13] a 5. Nature of the unseen Companions variations. No significant microturbulence could be measur of Edelmann (2003) [4]. Unconsideredlines. effects would This in fact is any important ca for the interpretation of the r from Han et al. (2002) [6].stars There with are masses no higher spectral than signatures 0 o All other possible sources of systematic errors turned out t synthetic line profiles. Theusing latter the LINFOR ones program. were computed for th lium lines, all visible metalprojected lines rotational were velocity was included. performedroutine A separately simulta fo (Napiwotzki et al.from all measurements 2004b (see Fig. [15]).sources 2). of errors, Numerical Mean the simulations value sensitivity w v limit and and stand accuracy of the parameters of TONS 183 and PG 1232 and helium abundances (log 4. Projected Rotational Velocity are displayed in Tab. 1, and a sample fit is shown in Fig. 1 (righ Spectroscopic Analysis of sdB Binaries 3. Quantitative Spectral Analysis coadded in order to increase the S/N ratio. Effective temper PoS(NIC-IX)101 S. Geier ries nnel (Han et al. yr (Fig. 4 right panel). The lines mark the the- 8 and were not consistent with mary mass in case of 202 could not be solved with 10 ⊙ − 6], but unfortunately they are not ≈ M ved consistently. These three bi- o far (Podsiadlowski priv. comm.). 3 . This fraction of 8 % is much too . ttled, all timescales have to be taken object class. From about 50 analysed Zahn (1977) [17] and Tassoul & Tas- on. The question, which mechanism its were observed to be synchronized EHB gain. t ective cores were used to compare them n times near or above the EHB lifetime. al structure of sdBs into account, are not retical timescales for synchronization are 136 (right panel). The red horizontal − 6 0238 and WD 0048 − 0510, HE 2150 − Companion mass as a function of primary (sdB) mass of the bina 4503 (left panel) and PG 1232 − HE 0532 line marks the Chandrasekhar limit.oretical sdB The mass red range dotted2002 for vertical [6]). the The dotted common blue envelope linepost-RGB ejection in evolution the cha (Driebe left et panel al. marks the 1998 pri [3]). Figure 3. available and urgently needed. red diamonds denote the threenaries have systems, the which longest could orbital not periodsBut and be as synchronizatio long sol as thewith question caution. of Detailed tidal calculations, synchronization which is take not the se intern the theoretical mass range. Binaries hosting a neutron star orsdB a binaries black hole in are our a samples, veryhigh rare we to found be compatible four with candidate anyFor systems binary this evolution reason model known the s results themselvesOur have method to be rests discussed on a theis assumption most of responsible for orbital this synchronizati effect,given is by not Zahn yet (e.g. settled. Theo 1977)consistent [17] in and any Tassoul & case. Tassoul (1992) Many(e.g. [1 eclipsing Claret binaries et al. in 1996, closeThe 1997 orb approximation [1,2]). formulas for the synchronizationsoul time (1992) of [16] for stars with radiativewith envelopes the and lifetime conv on the Extreme Horizontal Branch (EHB) the described method. The minimum sdB masses exceeded 1 The three binaries HE 1448 Spectroscopic Analysis of sdB Binaries PoS(NIC-IX)101 S. Geier binaries. very sensible to this . d al currents in ra- 3 . the lifetime on the enotes the limiting nes synchronization easonably. The projected ro- nalysis. h radiative envelope and measured broadening is then due d projected rotational velocities as in. Only the high precision of the . But the unexpectedly high masses i sured rotational broadening is higher ted systematic effects would therefore ssumption of tidally locked rotation is limit. As described above we tried to c effects (e.g. short period pulsations), horter than 1 sin sults were very consistent. Only slight rot v 7 Synchronization time over orbital period of the 12 analysed would lead to inconsistent solutions, because the method is i sin rot v The filled diamonds mark synchronizationdiative envelopes caused (Tassoul % by Tassoul meridion 1992)through [16], tidal the friction blank of o the equilibrium tide for stars wit Extreme Horizontal Branch (EHB). Theorbital dotted period vertical for line tidal synchronization d derived from our a convective core (Zahn 1977) [17]. The horizontal line marks Figure 4. measurements made it possible to constrain the parameters r i sin rot of the companions are caused bycan the be seen unexpectedly from low the measure equations inlead the to introduction. even Unaccoun higher companion masses. parameter. But even if there would bethey unaccounted systemati would always cause anto extra rotation broadening and of the unaccounted the effects, lines.than which the means The the real mea one. All systematic effects lead to lower tational velocities were low andquantify very all close to possible the systematic detection effectschanges in and the overall re Finally the reliability ofv our method has to be discussed aga From these considerations we draw thereasonable conclusion, that in the case a of close sdB binaries for orbital period s Spectroscopic Analysis of sdB Binaries PoS(NIC-IX)101 S. Geier ] i 1 0.9 0.7 0.6 0.7 0.8 0.5 1.1 0.6 1.3 2.5 1.3 1.0 − sin ± ± ± ± ± ± ± ± ± ± ± ± rot ] [kms 1.0 20.4 1.4 7.1 0.2 11.1 1 ses and possible 1.0 6.7 0.04 6.2 1.5 12.7 0.62.0 6.9 3.0 6.7 1.4 6.2 1.1 8.3 0.4 6.7 7.2 NS/BH NS/BH ities, orbital peri- − ± ± ± Companion ± ± ± ± ± ± ± ± ± WD/NS/BH WD/NS/BH are 500 K and 0.05 dex g onal velocities of the vis- ] 2.40 3.60 7.00 0.952.40 0.35 WD WD/late MS 0.45 WD/late MS 0.30 WD/late MS 0.60 WD/late MS ⊙ − − − − − − − − − comp M M and log eff 0.00020 84.8 0.00030 129.6 0.00050 135.0 0.00020 114.3 0.00050 64.1 0.000300.00100 90.5 0.00001 55.5 0.00500 94.0 0.01300 96.3 0.01500 53.7 47.9 0.00010 101.5 T ] [ 1 ± ± ± ± ± ± ± ± ± ± ± ± − rot 8 29 18 0.60 1719 4722 2529 1.40 3350 2.00 18 0.45 2190 0.60 90 0.18 890 8 0.35 7 0.15 0.35 g P Kv i v –– – – – – not solved not solved – – – not solved − − − − − − − − − [deg] [kms log 22 13 14 17 23 38 66 56 62 eff T [K] [d] [kms 342† 202 26100 5.20 0.82770 27500 5.6224300 0.36300 5.3229470 0.38000 5.7131100 0.44000 5.60 0.44300 30000 5.8429570 0.92400 5.5530242 1.18800 5.6630200 1.21325 5.8334690 1.32090 5.5929960 7.15880 5.50 7.44360 25390 5.32 0.26560 1206 0436 0238 4503 4323 3749 0510 0424 136 − − − − − − − − − − − 342† 202 Inclination angles, rotational velocities, companion mas Stellar parameters: Effective temperatures, surface grav 3749 4503 1206 0436 0238 0510 4323 0424 136 − − − − − − − − − − − System HE 1421 HE 1047 HE 2150 HE 0532 HE 0230 HE 2135 PG 1232 WD 0107 HE 1448 WD 0048 HE 0929 TONS 183 respectively. † Orbital parameters of this system are still preliminary ible components. Typical error margins for ods, radial velocity semi-amplitudes and projected rotati nature of the unseen companions. † Derived parameters of this system are still preliminary Table 2. Table 1. HE 2135 HE 0532 System WD 0107 HE 1421 HE 1047 HE 2150 HE 1448 WD 0048 HE 0230 HE 0929 TONS 183 PG 1232 Spectroscopic Analysis of sdB Binaries PoS(NIC-IX)101 dina ]. S. Geier MNRAS , ]. 724. ence of detached Hot subdwarfs 299 A&A nal constraints for the , mpatible with white dwarfs astro-ph/9809079 ]. The Origin of Subdwarf B Star (I): 123 [ ron stars or black holes. This high hat of heavy compact objects like astro-ph/0507024 amples opens several questions. Is , University of Erlangen-Nuremberg parameters and cool companions of to find more of these exotic objects? 339 spectrographs are needed to enhance 187. reement with binary evolution simula- sible through strong X-ray emission? es, which leads to the conclusion, that ism of Tassoul vanova, hesis) , D. Homeier, D. Reimers, 1023 [ culation. More observations of close sdB 318 High resolution spectroscopy of bright A&A , The Origin of Subdwarf B Star (II) 442 A&A The binary fraction of extreme horizontal branch The evolution of helium white dwarfs: I. The , ]. ]. SPY - The ESO Supernovae type Ia Progenitor 9 A&A , astro-ph/0206130 Circularization and synchronization times in the main 449 [ SZ Camelopardalis - an early-type eclipsing binary embedde 336 ]. 909. astro-ph/0409136 astro-ph/0103342 Circularization and synchronization times in the main sequ MNRAS 25. , 332 223 [ 112 1391 [ A&A 430 , 326 Spectroscopic analyses of subluminous B stars: Observatio A&A astro-ph/0301380 , ESO Msngr , MNRAS , 669 [ stars survey multiple system 341 from the ESO Supernova Ia ProgenitorsdB Survey. I. stars Atmospheric the Formation Channels subdwarf B stars - I. Radial velocity variables 2003. companion of the millisecond pulsar PSR J1012+5307 sequence of detached eclipsing binaries I. Using the formal theory of stellar evolution, pulsation and diffusion (PhD t eclipsing binaries II. Using the formalism of Zahn Out of 12 analysed sdB binaries, five have companion masses co [9] R. Lorenz, P. Mayer, H. Drechsel, [8] T. Lisker, U. Heber, R. Napiwotzki, N. Christlieb, Z. Han [7] Z. Han, P. Podsiadlowski, P.F.L. Maxted, T.R. Marsh, [6] Z. Han, P. Podsiadlowski, P.F.L. Maxted, T.R. Marsh, N. I [5] H. Edelmann, U. Heber, M. Altmann, C. Karl, T. Lisker, [4] H. Edelmann, [3] T. Driebe, D. Schönberner, T. Blöcker, F. Herwig, [1] A. Claret, A. Gimenéz, N.C.S. Cunha, [2] A. Claret, N.C.S. Cunha, [10] P.F.L. Maxted, U. Heber, T.R. Marsh, R.C. North, [11] R. Napiwotzki, N. Christlieb, H. Drechsel, et al., or late type main sequence stars.tions. These systems Four are binaries in have full surprisingly ag highthe companions companion have mass to be veryfraction heavy cannot white be dwarfs explained or with even current neut evolutionary cal the size of our samples. The presence of such athe high formation fraction of and heavy evolution binaries ofneutron in stars sdB our or stars s black somewhat holes? linked CanIs to sdB there stars a t be hidden used population as of tracers these objects, which is not vi References Spectroscopic Analysis of sdB Binaries 6. Conclusion binaries and candidate systems with high and low resolution PoS(NIC-IX)101 L17 S. Geier 378 Binaries A&A , n in close , ASP Conference ]. ]. of the Close Binary Stars, hite dwarf system vnik, Croatia el, E.-M. Pauli, N. Christlieb, 383. eb, D. Reimers, G. Nelemans, D. 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