ASTRONOMY & ASTROPHYSICS OCTOBER II 1996, PAGE 211 SUPPLEMENT SERIES Astron. Astrophys. Suppl. Ser. 119, 211-219 (1996) A library of IUE white dwarf spectra for stellar population analyses? E. Bica, C. Bonatto and O. Giovannini Universidade Federal do Rio Grande do Sul, IF, CP 15051, Porto Alegre 91501–970, RS, Brazil Received October 30, 1995; accepted February 27, 1996 Abstract. — We present high Signal to Noise ratio IUE spectra of different classes of white dwarfs, to be used as templates for stellar population analyses in the ultraviolet region. We present average stellar parameters associated to each group. The library contains 6 groups for DA’s, 2 for DO’s and 5 for DB’s. We also present equivalent widths of spectral features, and continuum measurements. We call attention to the spectral characteristics which are promising indicators of the presence of white dwarfs in the spectra of composite stellar populations. Key words: (stars): white dwarfs — ultraviolet: stars 1. Introduction spectra of much higher signal to noise ratio (S/N)than those of individual stars. This paper is structured as fol- White dwarfs are not luminous objects, but they are lows: in Sect. 2 we present the IUE white dwarf sample, very common: there are 1279 cataloged white dwarfs in gather information on individual stars from the literature, McCook & Sion (1987, hereafter MS87). Many of them and measure fluxes in the present data; in Sect. 3 we build have trigonometric parallaxes indicating distances below the groups and present the average parameters associated 100 pc from the Sun. Since hot white dwarfs emit most of to them; in Sect. 4 we measure equivalent widths, contin- their light in the ultraviolet, it is in this spectral region uum slopes and discuss the results; in Sect. 5 we present where they can most probably be detected in spectra of the concluding remarks of this work. composite stellar populations. In a recent paper, evidence was found of the presence of white dwarfs of type DA 5 in the spectra of early-type galaxies and globular clusters 2. The white dwarf sample (Bica et al. 1996). We gathered the IUE spectra for the present sam- The International Ultraviolet Explorer (IUE) has been ple from the IUE Uniform Low Dispersion Archive collecting spectra of white dwarfs for the last 17 years, and (ULDA Version 4.0) database as stored at the Instituto several of them already have a relatively large number of Astronˆomico e Geof´ısico of the Universidade de S˜ao Paulo individual spectra stored in the IUE database. (IAG–USP). Details on the ULDA calibration processes Much information on stellar parameters have been de- and access can be found in Courvoisier & Paltani (1992, rived from the IUE spectra of individual white dwarfs, just and references therein). Some obvious r´eseau marks and to mention a few: Wesemael et al. (1985) for DO’s, Liebert bad pixels have been corrected by a linear interpolation. et al. (1986) and Wegner & Nelan (1987) for DB’s, and The population synthesis of composite spectra such as Kepler & Nelan (1993) and Bergeron et al. (1995) for those of galaxies and/or star clusters, requires the knowl- DA’s. A spectrophotometric atlas of individual white edge of the observational and theoretical parameters asso- dwarfs was compiled from IUE archives by Wegner & ciated to the different stellar types. With this in mind, we Swanson (1991). searched for white dwarfs which had information on spec- In order to further explore this database, in the present tral classification and/or atmospheric parameters from the paper we group stars of similar spectral characteristics literature. The sample contains 86 white dwarfs, and is into distinct white dwarf classes, which can be very useful not intended to be complete in any sense: we gathered for, e.g., stellar population analyses. We obtain template enough spectra in order to achieve a good (S/N)foreach Send offprint requests to:E.Bica group. We show the results for the individual early-type ?Based upon data collected with the International Ultraviolet DA stars in Table1 and for late-type DA’s in Table2, for Explorer (IUE) Satellite, supported by NASA, SERC and ESA DO’s in Table 3 and DB’s in Table4. By Cols. (1) and (2) 212 E. Bica et al.: A library of IUE white dwarf spectra for stellar population analyses Table 1. Data on individual early-type DA stars 14 WD# Other Spectral Teff(K) Teff(K) log gMV 10 fλ (2646) d × 2 1 1 Names Type (Optical) (UV) ( erg cm− s− A˚− )(pc) WD A1 0136+251 PG 0136+251 DA 1 34 980 9.7 1.68 0346 011 GD 50 DA 2 43 102 9.09 11.4 12.10 29.9† − GR 228 40 540 11.8 0548+000 GD 257 DA 1 9.0 3.67 162.9 GR 289 0549+158 GD 71 DA 1 33 753 32 800 7.76 9.3 21.90 56.5 LTT 11733 EG 210 L1241-036 0612+177 G104-27 DA 2 25 938 7.97 10.3 42.6 EG 46 24 660 10.4 ‡ LTT 11818 L1244-026 1254+223 EG 187 DA 1 40 432 41 200 7.85 10.1 18.50 46.1 PG 1254+223 1314+293 HZ 43A DA 1 38 200 50 000 7.90 8.7 31.70 65.2 PG 1314 EG 98 1615 154 G153-41 DA 2 29 833 8.08 10.2 16.60 44.0 − LTT 6497 29 730 EG 118 1620 391 GR 274 DA 2 24 406 24 800 8.10 10.6 116.0 12.0 − CD-38 10980 2014 575 L210-114 DA 28 373 7.88 10.0 11.60 40.2 2111+498− GD 394 DA 2 39 450 37 000 9.3 26.40 55.0 EG 244 DA 1.5 2309+105 GD 246 DA 1 57 990 54 000 7.91 11.1 28.20 25.1 EG 233 BPM 97895 WD A2 0047 524 BPM 16274 DA 2 18 745 18 015 7.83 10.7 4.50 50.1 − L219-48 0109 264 GD 691 DA 1 18.80 − PHL1003 † 0134+833 GD 419 DA 2 18 730 8.07 11.1 12.80 24.9 GR 308 LP2-534 0214+568 EG 17 DA 2 21 180 7.83 10.5 43.2 H PER1166 ‡ 0227+050 FEIGE 22 DA 3 19 070 7.66 10.6 17.00 27.9 EG 19 0410+117 HZ 2 DA 3 20 790 19 575 7.81 10.7 6.57 42.8 EG 31 1042 690 BPM 6502 DA 3 21 380 7.86 10.5 17.80 32.5 − L101-80 1337+705 G238-44 DA 2.5 20 230 8.05 10.7 15.60 26.2 EG 102 LTT 18341 2136+828 EG 147 DA 3 16 940 17 016 7.60 10.4 12.10 33.4 G261-45 10.9 2149+021 EG 150 DA 3 20 547 7.99 10.7 14.80 25.5 G93-48 18 250 11.0 17 653 WD A3 0232+525 GR 314 DA 3 17 050 8.13 11.5 28.2 G174-5 ‡ 0310 688 EG 21 DA 3 16 181 15 546 8.06 11.3 41.90 10.5 − LB3303 CPD-69 177 1105 048 EG 76 DA 3 15 576 16 720 7.80 11.0 9.33 24.2 − G163-50 15 300 LTT 4099 15 540 15 870 Table Notes. ( ) - no LWP/R spectrum available; ( ) - distance not available. ‡ † E. Bica et al.: A library of IUE white dwarf spectra for stellar population analyses 213 Table 2. Data on individual late-type DA stars 14 WD# Other Spectral Teff(K) Teff(K) log gMV 10 fλ (2646) d × 2 1 1 Names Type (Optical) (UV) ( erg cm− s− A˚− )(pc) WD A4 0352+096 EG 26 DA 4 14 420 15 000 8.10 11.5 2.32 40.2 HZ 4 15 100 13 824 0406+169 EG 29 DA 4 15 300 16 100 8.50 11.2 1.19 67.6 LP414-101 15 740 15 077 0954 710 BPM 6082 DA 4 13 915 13 876 7.72 11.1 5.48 29.9 − L64-27 1327 083 G14-58 DA 4.5 14 350 15 520 7.82 11.3 16.60 13.8 − WOLF485A 12 800 11.9 EG 99 BD-07 3632A 14 670 1919+145 GD 219 DA 4 15 080 15 700 8.08 11.5 9.37 19.7 EG 201 14 632 2047+372 EG 261 DA 4 14 660 15 100 8.16 11.6 9.33 20.2 G210-36 14 001 WD A4.5 0133 116 ROSS 548 DA 4 11 830 12 400 7.97 11.6 32.5 − EG 10 11 990 12 130 ‡ G271-106 10 000 ZZ Cet 0231 054 GD 31 DA 4 12 840 12 910 11.9 29.5 − EG 207 ‡ 0401+250 G8-8 DA 4 12 120 12 227 8.20 11.9 3.34 24.0 EG 28 13 248 13 500 0713+584 GD 294 DA 3.4 13 400 4.94 0858+363 GD 99 DA 4 11 100 12 000 8.08 11.8 1.24 35.5† EG 219 0921+354 EG 65 DA 4 11 620 13 150 7.97 11.7 57.5 G117-B15A 12 500 11 890 11.6 ‡ 11 840 1425 811 L19-2 DA 4 12 100 12 310 8.21 11.9 4.32 23.4 − EG 110 12 230 12 640 MY Aps 1647+591 G226-29 DA 4 12 120 12 270 8.29 11.6 13.20 13.4 GR 368 12 460 12 280 DN Dra 1855+338 EG 127 DA 4.5 10 500 12 060 12.1 1.74 31.5 G207-9 12 040 1935+276 G185-32 DA 4 12 130 11 930 8.05 11.7 6.58 17.9 GR 277 11 970 12 370 PY Vul WD A5 1236 495 BPM 37093 DA 4.5 12 100 11 530 8.81 11.9 3.35 21.5 − LTT 4816 11 200 11 560 12.7 12 899 1559+369 ROSS 808 DA 4.5 11 160 11 180 8.04 11.9 1.58 31.0 G180-23 10 880 11 560 EG 115 11 200 TY CrB 2326+049 G29-38 DA 4 11 820 11 650 8.14 11.9 5.93 16.8 EG 159 11 900 ZZ Psc Table Notes.