We have studied white dwarfs in common proper motion pairs (CPMPs) to improve
the semi-empirical initial–final mass relationship of white dwarfs. In this contribution, we re-
port new results obtained from spectroscopic observations of both members of several CPMPs
composed of a F, G or K type star and a DA white dwarf.Peer Reviewe

Allende Prieto, C.

Catalán, S.

García-Berro Montilla, Enrique

Isern Vilaboy, Jordi

Ribas Vila, Immaculada

English

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Proceedings Title IAU SymposiumProceedings IAU Symposium No. 240, 2006A.C. Editor, B.D. Editor & C.E. Editor, eds.c© 2006 International Astronomical UnionDOI: 00.0000/X000000000000000XThe initial–final mass relationship of whitedwarfs in common proper motion pairs andopen clustersS. Catala´n1,2, I. Ribas1,2, J. Isern1,2,E. Garc´ıa–Berro1,3 and C. Allende Prieto41Institut d’Estudis Espacials de Catalunya, c/ Gran Capita` 2–4, 08034 Barcelona, Spainemail: catalan@ieec.uab.es2Institut de Cie`ncies de l’Espai, CSIC, Facultat de Cie`ncies, UAB, 08193 Bellaterra, Spain3Departament de F´ısica Aplicada, Escola Polite`cnica Superior de Castelldefels, UniversitatPolite`cnica de Catalunya, Avda. del Canal Ol´ımpic s/n, 08860 Castelldefels, Spain4McDonald Observatory and Dep. of Astronomy, University of Texas, Austin, TX 78712, USAAbstract. We have studied white dwarfs in common proper motion pairs (CPMPs) to improvethe semi-empirical initial–final mass relationship of white dwarfs. In this contribution, we re-port new results obtained from spectroscopic observations of both members of several CPMPscomposed of a F, G or K type star and a DA white dwarf.Keywords. stars: white dwarfs, stars: abundances, stars: evolution, binaries: visual1. Introduction and observationsThe initial–final mass relationship connects the properties of a white dwarf with thoseof its main-sequence progenitor. This function is important for determining the ages ofglobular clusters and their distances, for studying the chemical evolution of galaxies,and also for understanding the properties of the galactic population of white dwarfs.Despite its relevance, this relationship is still poorly constrained. A promising approachto decrease the uncertainties is to study white dwarfs for which external constraints areavailable. This is the case of white dwarfs in common proper motion pairs (CPMPs). Im-portant information of the white dwarf can be inferred from the study of the companion,since they were born at the same time and with the same initial chemical composition.The list of CPMPs under study was selected from the available literature (Wegner &Reid 1991, Silvestri et al. 2001). Each CPMP (11 in total) is composed of a white dwarfclassified as DA and a F, G or K type star. The observations were carried out using a suiteof telescope/instrument configurations. The white dwarf members were observed with theLCS spectrograph of the HJS (2.7 m) telescope at McDonald Observatory (Texas, USA)and with the TWIN spectrograph of the 3.5 m telescope at Calar Alto Observatory(CAHA, Almer´ıa, Spain), obtaining a FWHM resolving power of ∼ 4 − 5 A˚. The FGKcompanions were observed with the FOCES echelle spectrograph of the 2.2 m telescopeat CAHA and with the SARG echelle spectrograph at the TNG telescope in la Palma(Canary Islands, Spain) with resolutions of R ∼ 47000 and R ∼ 57000, respectively.These spectroscopic observations have revealed that only 5 of the 11 white dwarfs werein fact of the DA type, whereas the rest were misclassified.119120 S. Catala´n et al.Table 1. Stellar parameters derived for the observed FGK stars.Name Teff (K) Z log(L/L⊙) Age (Gyr)G158-771 4387± 27 − − −BD+441847 5627± 49 0.011± 0.003 −0.188± 0.059 −2BD+2325391 5666± 48 − − −BD+342473 6268± 68 0.030± 0.008 0.369± 0.109 2.1± 1.5BD-085980 5669± 52 0.012± 0.004 −0.151± 0.040 −21Not analyzed because of low S/N . More observations are underway.2The ages obtained from isochrone fits are not reliable (see text).Table 2. Stellar parameters derived for the observed white dwarfs.Name Teff (K) log g Mf (M⊙) tcool (Gyr) tms (Gyr) Mi (M⊙)WD0023+109 10377± 230 7.92± 0.08 0.56± 0.03 0.49± 0.08 − −WD0913+442 8918± 111 8.29± 0.02 0.78± 0.01 1.72± 0.06 − −WD1304+227 10798± 120 8.21± 0.05 0.73± 0.13 0.73± 0.06 − −WD1354+340 13650± 437 7.80± 0.15 0.49± 0.10 0.14± 0.02 2.03± 1.57 1.62+1.00−0.30WD2253-081 7200± 170 8.40± 0.08 0.87± 0.03 3.75± 0.19 − −2. Analysis and resultsTo determine the total age of each system, we analyzed the spectra of the FGK starsfollowing this procedure: first, we derived the effective temperatures, Teff , using the avail-able V JHK photometry and following the method of Masana et al. (2006). Then, wefitted the observed spectra using the SYNSPEC program and synthetic spectra basedon Kurucz atmospheres to derive their metallicities, Z, focusing on spectral windowswhere unblended lines of FeI, FeII and NiI are present. If the distance and the apparentmagnitude are known the calculation of the luminosity, L, is straightforward. Finally, weinterpolated the stellar models of Schaller et al. 1992 using Teff , Z and L to obtain theages of these stars, and, consequently, the total ages of the CPMPs — see Table 1. Wehave found that some of the observed stars are fairly unevolved and so, isochrone fitsdo not provide reliable ages. Other age indicators such as the chromospheric activity orX-ray luminosity are currently being considered.The atmospheric parameters of each white dwarf, Teff and log g, were derived from thefitting of the theoretical models of D. Koester to the observed Balmer lines using thepackage SPECFIT of IRAF following the procedure described in Bergeron et al. (1992)— see Table 2. Then, we derived its mass, Mf , and cooling time, tcool, using the coolingsequences of Salaris et al. (2000). Since we know the total age of the white dwarf (from thecompanion), we obtain the main sequence lifetime of the progenitor, tms, by subtractingits cooling time to the age of the system. Finally, using the stellar models of Domı´nguezet al. (1999) we compute the mass of the progenitor in the main sequence, Mi.In Fig. 1 we show the final mass versus the initial mass of the white dwarf in a CPMPfor which the analysis has been completed. Also plotted are the results for the whitedwarfs in the open clusters M 35 (Williams et al. 2004) and M 37 (Kalirai et al. 2005).We used the Teff and log g reported by these authors and then, for internal consistency,we followed the same procedure as for the white dwarfs in our list. By comparing theobservational data it can be noted that the error obtained for the Mi in the case of thewhite dwarf in a CPMP is higher than those obtained for white dwarfs in open clusters.In fact, the uncertainty in the determination of the ages is the main drawback of usingCPMPs, but it can be minimized by selecting the pairs with evolved companions.The IFMR of white dwarfs in common proper motion pairs 121Figure 1. Final masses versus the initial masses obtained for one of the CPMPs in our sample(circle) and for white dwarfs in the open clusters M 35 (squares) and M 37 (triangles).However, the fact that these systems are potentially more abundant and closer tous makes this a promising approach to improve the semi–empirical initial–final massrelation, since a better spectroscopic study of both members of the pairs can be done.White dwarfs in CPMPs also provide a wider age coverage of this relation, in contrastwith open clusters, which are younger and do not contribute to its low–mass range.A thorough comparison of the semi–empirical data with different theoretical relation-ships is currently underway and reveals a large scatter in the distribution (Fig. 1). Thiscould be due to the fact that maybe the initial–final mass relationship is not a single–valued function. More observational data and improved theoretical stellar models (mainlyin the AGB phase) will help to better establish this function. In this sense, to furtherextend the sample, a cross–correlation of the SIMBAD database and the Villanova WhiteDwarf Catalog has provided us with more pairs, which we expect to study shortly.AcknowledgementsThis research was partially supported by the MCYT grant AYA05–08013–C03–01 and02, by the European Union FEDER funds and by the AGAUR.ReferencesBergeron, P., Wesemael, F. & Fontaine, G. 1992, ApJ, 387, 288Domı´nguez, I., Chieffi, A., Limongi, M., & Straniero, O. 1999, ApJ, 524, 226Kalirai, J.S., Richer, H.B., Reitzel, D., Hansen, B.M.S., Rich, R.M., Fahlman, G.G., Gibson,B.K. & von Hippel, T. 2005, ApJ, 618, L123Masana, E., Jordi, C. & Ribas, I. 2006, A&A, 450, 735Salaris, M., Garc´ıa–Berro, E., Hernanz, M., Isern, J. & Saumon, D. 2000, ApJ, 544, 1036Schaller, G., Schaerer, D., Meynet, G. & Maeder, A. 1992, A&AS, 96, 269Silvestri, N.M., Oswalt, T.D., Wood, M.A., Smith, J.A., Reid, I.N. & Sion, E.M. 2001, AJ, 121,503Wegner, G. & Reid, I.N. 1991, ApJ, 375, 674Williams, K.A., Bolte, M. & Koester, D. 2004, ApJ, 615, L49

The initial–final mass relationship of white dwarfs in common proper motion pairs and open clusters

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The initial–final mass relationship of white dwarfs in common proper motion pairs and open clusters

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