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1982Apj. . .255. . .70H the Astrophysical Journal .70H . .255. The Astrophysical Journal, 255:70-78, 1982 April 1 . © 1982. The American Astronomical Society. All rights reserved. Printed in U.S.A. 1982ApJ. INTERNATIONAL ULTRAVIOLET EXPLORER SPECTROSCOPY OF HOT STARS IN THE EMC AND SMC: THE SMC EXTINCTION LAW, STELLAR FLUX DISTRIBUTIONS, AND DETAILS OF THE STELLAR WINDS J. B. Hutchings Dominion Astrophysical Observatory; Herzberg Institute of Astrophysics Victoria, British Columbia Received 1981 May 5 ; accepted 1981 October 12 ABSTRACT Data are presented from high-dispersion observations of 7 stars in each of the Magellanic Clouds, and from low-dispersion observations of 14 more in each cloud. The SMC ultraviolet extinction curve is found to be much steeper than in the Galaxy or the LMC. Stellar effective temperatures and luminosities are derived for all stars and found to be similar to those in the Galaxy. Stellar wind phenomena are not always present and are generally weak when present in the SMC, and stronger in the LMC though still weak compared with galactic star phenomena. The implied consequences of these findings are discussed briefly. Subject headings: galaxies: Magellanic Clouds — interstellar: matter — stars: early-type — stars: winds — ultraviolet: spectra I. INTRODUCTION longer than originally anticipated because of the high UV Initial investigations of hot stars in the Magellanic interstellar extinction. Low-dispersion data were ob- Clouds for stellar parameters and stellar winds (Hut- tained of stars chosen to give as good a sample as possible chings 1980a, Paper I; Prévôt et al. 1980) indicated that of spectral types, luminosity, and reddening. These were the resonance lines of N v, Si iv, and C iv are weak generally obtained in both long-wavelength and short- compared with galactic stars. Since these are considered wavelength regions to enable continuum and extinction to be one of the drivers of stellar mass-loss, by radiation studies. A few stars were observed at both dispersions, to pressure, a more detailed and extensive investigation was provide empirical calibration of the continuum fitting called for. Other questions needing investigation con- and line strength measures. cerned the temperature scale for Magellanic Cloud stars Table 1 summarizes the data which, in addition to the and the UV extinction in the SMC. The LMC extinction new spectra, include copies that were obtained of IUE was already known to differ considerably from the spectra of Magellanic Cloud stars previously observed by Galaxy (Nandy et al 1980; Koornneef 1980). others, and the data from Paper I. While the latter two Examination of the former point calls for high- data sets were not obtained specifically for the purposes dispersion data, in order to derive line profiles and of this paper, they contribute a valuable addition to the intensities, to resolve interstellar from stellar features, and data base. to measure radial velocities. Investigation of the latter The principal line features were measured for wave- points requires low-dispersion observations of a sample length and intensity on all spectra, with particular atten- which both overlaps the high-dispersion sample tion to the stellar wind resonance lines of C iv, Si iv, and and extends to larger reddening and to lower luminosity. N v. The overlap between high and low dispersion gives a Few cloud stars are bright enough in the UV for measure of the accuracy of the low-dispersion data, and of International Ultraviolet Explorer (IUE) observation at the amount of interstellar absorption which is blended high dispersion, and those which are tend to be extraor- with stellar at low resolution. In general, stellar, local dinary objects. Obviously peculiar stars were not ob- interstellar, and the cloud interstellar features were distin- served, although some were included in the data set if they guishable in high-dispersion spectra. had already been observed. The data analyzed thus suffer The continuum intensity distribution was derived by from several undesirable selection effects. Nevertheless, inspection of all spectra (see Paper I). The principal the results appear to have some general relevance and do line-blending regions in the low-dispersion data are well at least address the points of interest in this paper in much known and were, in any case, verified by inspection of the more detail than before. high-dispersion data. The continuum intensity distribu- tions were derived for all spectra observed, including the II. OBSERVATIONS AND MEASUREMENTS high-dispersion data using a high-dispersion calibration. The primary data in the program were high-dispersion This calibration was collated principally by Dr. T. Ake of short-wavelength spectra of bright stars in both clouds. the IUE staff and agreed well with one derived from Only a few of these were obtained, since radiation levels galactic star data in my possession. The high-dispersion during the observing shifts were unusually high, attenuat- and low-dispersion intensity distributions agree quite ing exposure times. Also, SMC exposure times were satisfactorily (<20% mean difference per star). 70 © American Astronomical Society • Provided by the NASA Astrophysics Data System .70H . .255. TABLE 1 . International Ultraviolet Explorer Spectra 3 Exposure (min)b Star Dispersion Spectrum" mv B-V* 1982ApJ. SMC HD 4862 260 HS, 6 LL B3-B5 la 11.0 -0.04 HD 5045 270 HS, 5 LL B0-B3 la 11.0 -0.03 HD 7099 260 HS, 7 LS, 5 LL B3 la 11.0 -0.05 SK 13.... (63 LS, 29 LL) B1I 12.5 0.04 18.... (16 LS, 10 LL) O7-B0I 12.5 -0.19 45.. 20 LS, 15 LL .B5-AO la . 11.5 0.06 65.. 40 LS, 25 LL .B0-B5 I . 13.2 -0.01 80.. (300 HS) .07-9 If . 12.4 -0.20 82.... (14, 16 LS, 8, 8 LL) BO-1 I 12.2 -0.18 85.. (17 LS, 8 LL) .BO.5-1.5 I . 12.1 -0.12 94.. (25 LS*) .BO I . 12.4 -0.15 101 .. 30 LL 09 1 12.9 0.0 108 .. (300 HS) 15, 15 LS, 10 LL O6.5-B0 + WN3 12.3 -0.26 Ill .. 34 LS, 20 LL BO-B8I 13.1 -0.09 124 .. (14 LS, 6 LL) Bl.5-2 I 11.5 -0.02 157 .. (13 LS, 6 LL) 09.5 III 12.2 -0.21 159 .. (452 HS, 10 LS, 6 LL) OB 11.8 160 .. (440 HS) BO la 13.2 -0.16 164 .. 45 LS, 20 LL B2-B6 I 13.3 -0.13 188 .. 10 LL OB + W 12.7 LMC HD 32228 .... 150 HS, 4 LL 08-9 + WC5 10.8 -0.15 HD 36402 .... (300 HS) O + WC5 11.2 -0.17 HD 38268 .... 180 HS 0 + WN5 9.4 0.14 HDE 269006 . 260 HS B2.5I 9.8 -0.02 269546 . 130 HS, 8 LS*, 3 LL* B5 I + W 9.9 -0.02 269698 . (240 HS) 04-6f 12.2 -0.20 269700 . 240 HS, 5 LL Bl la 10.5 -0.02 R51 30 LS* B1.5 la 11.3 -0.08 67 20 LS, 15 LL B0 + M 11.6 0.30 84 10 LS, 8 LL B0 + M 11.7 0.20 93 15 LS, 15 LL B0-0.5 12.6 -0.16 99 7, 20 LS, 15 LL 07 P 11.5 0.27 108 20 LL Bl + M 12.8 1.3 112 12 LS* B1.5 la 11.2 -0.01 113.. 7 LS .06 e ....... 11.5 -0.11 122.. 12, 12 LS, 8 LL 06-7 12.3 -0.20 129 15 LS, 10 LL 091 11.3 0.0 148 35 LS, 25 LL B5I 12.0 0.24 Slll-68 ...... 15 LS, 10 LL Bl 12.0 -0.08 Dl-9 25 LS, 25 LL BO 13.6 -0.22 BI 150 35 LS Bl 14.4 -0.24 Note.—All observations with large aperture unless specified with an asterisk. Exposures in parentheses from other observations. 3 SK, from Sanduleak 1968, 1969; R, from Feast, Thackery, and Wesselink 1960; D, BI, from Rousseau et al. 1978. b HS, high-dispersion, short-wavelength; LL, low-dispersion, long-wavelength; LS, low-dispersion, short-wavelength. Values in parentheses are previously observed data, from National Space Science Data Center. c From Buscombe 1982. © American Astronomical Society Provided by the NASA Astrophysics Data System 72 HUTCHINGS Vol. 255 The observed spectra were progressively dereddened extinction was assumed to match both the galactic and and fitted to model atmosphere distributions in order to LMC curves at 22500. define a locus of (EB-V, Te{{ ) values and to choose the best The curve derived suffers from the fact that none of the set of these values. The purpose was to arrive at values SMC stars are very reddened. However, with one or two determined independently from the spectral type and pathological exceptions, the UBV color and derived UV color information from ground-based spectra and to look extinction yield EB„V values which agree well in the for consistency. The UV and ground-based data also give mean. At the lowest values, the UBV extinction tends to independent estimates of Mbol for each star. be higher. However, there is a small constant foreground These procedures were performed for Paper I. The reddening, presumably with the galactic extinction newer data are better because of improvements in the curve, which applies to all stars and is most significant in background smoothing and subtraction routines and the “ unreddened ” objects. A mean foreground extinction the corrected intensity transfer function, all of which have of Eb_v = 0.02 accounts well for the effect and is there- been introduced within the past year or so. The IUE fore built into all the numbers that were derived.
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