Cr> Γ- ΟΟ [ Publications of the Astronomical Society of the Pacific

cr> - ΟΟΓ [ Publications of the Astronomical Society of the Pacific cs] 102:379-411, April 1990 \—I0 ωCu 1 PUBLICATIONS OF THE 2 ASTRONOMICAL SOCIETY OF THE PACIFIC

Vol. 102 April 1990 No. 650

CONTEMPORARY OPTICAL SPECTRAL CLASSIFICATION OF THE OB STARS: A DIGITAL ATLAS*

NOLAN R. WALBORNt Space Telescope Science Institute, φ 3700 San Martin Drive, Baltimore, Maryland 21218 AND EDWARD L. FITZPATRICKf Princeton University Observatory, Peyton Hall, Princeton, New Jersey 08544 Received 1990

ABSTRACT Some recent developments in the optical classification of OB spectra are reviewed in terms of a comprehensive atlas of new blue-violet digital data from the CTIO 1-meter photon-counting system. These developments include the OS spectral type; luminosity criteria for the O stars; OBN/OBC anomalies; and refined, interpolated late-O/early-B types. Examples of these phenomena are included among extensive spectral- and luminosity-class sequences, comprising 75 standard objects arranged into 27 montages and covering the wavelength range 3950 Â-4750 A for types OS-BS (-B8 at Iö). It is intended that this atlas serve a reference function analogous to that of the printed MK atlases, for morphological investigations of OB spectra based on digital data, which will supersede photographic techniques in most future applications. Key words: spectral atlas-OB stars

1. Introduction and Background The Μ Κ classification was based on blue-violet The system of spectral classification provided one (3900 Â-4900 A) photographic spectrograms of disper- Μ Κ -1 of the foundations of stellar astrophysics. Far from being sion ~ 100 A mm (resolution ~ 2 A) and widening at rendered obsolete by the development of the latter, how- least 0.5 mm. This wavelength range represented a happy ever, morphological techniques maintain a vital system- correspondence between the sensitivity maximum of atic role as modern astronomical spectroscopy expands photographic emulsions and the highest density of optical wavelength, information content, and apparent-magni- absorption lines offered by stellar spectra. The widening tude limits, revealing ever more of the phenomenological permitted reliable results at a relatively low formal S/N by intricacies inherent in stellar spectra. The difficult task of providing a third dimension which allowed ready discrim- extracting the physical information contained in these ination between weak lines and noise of comparable am- phenomena is usually facilitated by prior morphological plitude. One of the precepts of Μ Κ classification was that analysis. the defining standard objects be obtained with the same instrumental characteristics as the unknowns, the latter *One in a series of invited review papers currently appearing in these then being described differentially relative to the stan- Publications. tVisiting Astronomer, Cerro Tololo Inter-American Observatory, dards, which provided an approximate photographic as National Optical Astronomy Observatories, operated by the Association well as empirical line-ratio calibration. Nevertheless, the of Universities for Research in Astronomy, Inc., under contract with the practical application of the system benefited greatly from National Science Foundation. extensive printed atlases, which both guided the selec- ^Operated by the Association of Universities for Research in Astron- omy, Inc., under contract with the National Aeronautics and Space tion of standards and criteria, and supported interpola- Administration. tions among them when the complete grid could not be

379 © Astronomical Society of the Pacific · Provided by the NASA Astrophysics Data System 380 WALBORN AND FITZPATRICK observed (Morgan, Keenan, and Kellman 1943; Abt et al. telescopes do not permit the acquisition of extensive 1968; Yamashita, Nariai, and Norimoto 1977; Morgan, standard sets, the more so if the detector has a count-rate Abt, andTapscott 1978). limit. The availability of very similar detector systems at The OB blue-violet domain was reexamined with a the CTIO 1-meter and 4-meter telescopes has encour- greater resolution (60 A mm-1, 1.2 A) and widening (1.2 aged us to address this problem for the OB stars. Indeed, mm) by Walborn (1970, 1971a,fc,c). The increased infor- the high quality of initial results from the 1-meter for a mation content of these spectrograms allowed the detec- systematic program on LMC B-supergiants (Fitzpatrick tion and description of several new phenomena: O stars in 1988a; Walborn et al. 1989; Fitzpatrick 1990) directly the Carina nebula with spectral types earlier than the inspired the present project. The objects observed here earliest previous MK standard, for which the extrapolated were either standards or otherwise well observed in the type 03 was introduced (see also Walborn 1982); luminos- previous photographic work; most of them are morpho- ity classification criteria for the early O stars, which did logically normal, although a substantial sample of ON/OC not exist in the Μ Κ system earlier than 09 (Walborn spectra is also included. Hence, this paper transfers the 1973); CNO absorption-line anomalies in OB spectra, previous photographic systematics to the digital data, leading to the OBN and OBC categories (Walborn 1976); providing a comprehensive reference atlas for future and additional interpolated spectral types in the complex, work. Users should still obtain as many key overlap line-rich 09.5-B1 range (09.7, B0.2, and B0.7), which standards as is feasible with their own instrumental sys- sharpened the discrimination between the two funda- tems, but the Atlas should reduce the number required mental (temperature-luminosity) classification dimen- for reliable results. Related atlases for the Ofpe/WN9 sions there. Correlative atlases including illustrations of class in the LMC have been presented by Bohannan these phenomena were presented for the yellow-red and Walborn (1989), for a new Β Ν supergiant with appro- (5400 Â-6600 A) wavelength range by Walborn (1980) priate comparison objects by Walborn, Fitzpatrick, and and for the space UV (1200 Â-1900 A) by Walborn, Nichols-Bohlin (1990), and will be presented for several Nichols-Bohlin, and Panek (1985) and by Walborn and categories of peculiar emission-line OB and WN spectra Nichols-Bohlin (1987). Independently and simulta- by Walborn and Fitzpatrick (1990). An additional cur- neously with this work, P. S. Conti and collaborators rent digital investigation of O-type spectra which, al- developed a quantitative classification for O-type spectra though based on a relatively restricted wavelength range based on equivalent-width measurements in high-resolu- (4300 A-4800 A), should be mentioned because of its ex- tion spectrograms (Conti and Alschuler 1971; Conti tent and quality, is that by Mathys (1988, 1989) who has 1973a,fo, 1974; Conti and Leep 1974; Conti and Frost already discovered several new ON objects. 1977). While operationally distinct from the Μ Κ methodology, this work shows good systematic agreement with 2. Observations and Reductions the morphological results and provides a vital point of The new digital data were obtained with the Shectman/ contact with the model atmospheres. Heathcote two-dimensional, photon-counting detector Currently, digital detector systems are supplanting on the Cassegrain spectrograph at the CTIO 1-meter photography for most astronomical spectroscopy; indeed, telescope during October 1988 and March 1989. The many of the instruments used in the earlier work are no 3-pixel resolution is 1.5 A, and the full wavelength cover- longer available. Fortunately, several of the new systems age is 3800 A-5000 A. Four observations at different loca- now provide the combination of wavelength coverage and tions along the slit are added to reduce fixed-pattern resolution, S/N, and definition of weak absorption lines in noise. All stars except for a few in the Magellanic Clouds faint objects required for spectral classification work, were neutral-density filtered as closely as possible to the which until recently could be achieved only photographi- bright limit of ß ~ 11 for this system, which required a cally. A higher formal S/N is required in the digital data total exposure time of 40 minutes. The typical maximum for comparable results, in lieu of the third dimension. S/N is about 80 per resolution element, being somewhat With the added advantages of speed, sky subtraction, degraded as is the resolution itself at the extremes of the linear response, and multiple-object capabilities, these wavelength range. systems offer high promise for future morphological stud- The data were extracted and rectified (not flux cali- ies, including faint extragalactic objects. However, the brated) with IRAF1 software at CTIO and subsequently methodological considerations which led to the success of 3-pixel smoothed and plotted with the DISSPLA graphics the photographic work apply fully to the digital data and package at the Joint Institute for Laboratory Astrophysics have not yet been extensively addressed. In particular, a of the University of Colorado. Considerable care was well-defined reference frame of standard objects, relative to which unknowns are described differentially with simi- ^RAF is distributed by National Optical Astronomy Observatories, lar observational parameters, remains essential for sys- which is operated by the Association of Universities for Research in tematically reliable results. Of course, short runs on large Astronomy, Inc., under contract to the National Science Foundation.

© Astronomical Society of the Pacific · Provided by the NASA Astrophysics Data System OB SPECTRAL ATLAS 381 taken in the spline-based rectification process in order to 08.5 V is more clear. Type 07 is defined by He II X4541 preserve broad, low-intensity emission features found to = He I X4471. Also by definition, the O-type luminosity underlie the Of lines in some objects (see also Underbill, class V spectra all have strong He π λ.4686 absorption; Gilroy, and Hill 1989). A high-order spline fit, required to the notation ((f)) signifies that in addition weak Ν III rectify the spectrograms completely, would tend to dis- λλ4634-4640-4642 emission is present. Among the spec- tort or eliminate such features. After some experimenta- tra so classified photographically, the latter feature would tion the procedure adopted was to divide all of the spec- be clearly detected without prior knowledge only in trograms by a uniform template derived from several HD 46223 and perhaps in HD 101190 and 15 Monocero- program objects with simple continua, and then remove tis in the digital data, indicating that a higher S/N will be any mild residual curvature with a low-order (typically 3 required to attain the same systematic sensitivity to this to 5) spline fit, which does not affect any spectral features subtle feature digitally. The moderate nitrogen enhance- of interest. ment of HD 48279 (Walborn 1976) is well shown by the digital data. 3. The Atlas Figures 4 and 5 show 03-08f supergiant spectra. The Atlas is organized into 27 montages containing (Some representatives of the intermediate O luminosity three or four spectrograms each, of which the initial 13 classes are included in the luminosity sequences dis- deal with the O stars and the final 14 with the Β stars. cussed below. ) The notation f* signifies Ν IV X4058 emis- Within each of the two major types there is first a series of sion stronger than Ν πι X4640, which is a characteristic of illustrations of spectral-class sequences at fixed luminos- 03 spectra, while f+ denotes Si iv λλ.4089,4116 in emis- ity class, in order of increasing luminosity, followed by a sion as well as the Of features. HDE 269698 is in the series of luminosity-class sequences at fixed spectral class, LMC and Sanduleak 80 in the SMC; the weakness of the in order of advancing spectral class from one montage to Si iv X4089 absorption in the latter is probably due to the the next. The wavelength range shown throughout is systemic metal deficiency. Zeta Puppis is a rapid rotator; 3950 A-4750 A, and numerous spectral features are iden- see Walborn (1971c) for the definition of the extended η tified in the figures and captions. The salient spectral parameter. Note the low-intensity broad emission under- characteristics and classification criteria will be discussed lying the Of lines in HD 93129A, HD 163758, and within each of these groupings. HD 151804; this feature has recently been well shown and discussed by Underbill et al. (1989). The spectra in 3.1 The O Stars Figure 5 also show the unidentified emission lines at 3.1.1 O-Type Spectral-Class Sequences λλ4485,4503. Figures 1-3 display the O3-B0 main sequence. The Figures 6 and 7 show 09-09.7 supergiant spectra, principal horizontal (i.e., spectral-class or temperature) including several of types ON and OC. The CNO anoma- classification criteria in this range are He π X4541/He I lies are very well-defined in the digital data, particularly λ4471 and He π X4200/He 1(+11) λ4026; at the later types by Ν πι λ4097 and the ratio Ν m X4640/C πι λ4650. He π X4541/He ι λ4387 and He π X4200/He I X4144 are HDE 269896 is in the LMC; its unusual He π λ4686 useful checks, since the former ratios become very small, emission feature is presumed due to superluminosity, but with care since the latter ratios are also sensitive to representing an extrapolation of the diagonal boundary luminosity. Throughout the Atlas the previous photo- in the H-R diagram for the Of effect (Walborn 1971c, graphic spectral types are given, but they will be dis- 1977). A similar feature in the spectrum of Sanduleak cussed critically in terms of the appearance of the criteria —660169, also in the LMC but with normal CNO spectra, in the quite different digital data. The tradeoff between has recently been discovered by Fitzpatrick (1988fc). widening and S/N does not always produce the same HD 152249 and HD 152424 are in Scorpius OBI (Wal- effect, and the eye is probably more sensitive to the born 1976). The primary defining criterion for the new equivalent widths of the absorption lines in the photo- interpolated type 09.7 is He π λ4541 ~ Si m λ4552 (Wal- graphic spectrograms but to the central depths in the born 1971c). On this count the digital spectrogram of digital data, so that some systematic or individual differ- HD 123008 would certainly be classified as 09.5; further ences may result. The definition of type 03 in the 60 A -1 observations are required to determine whether this dis- mm photographic classification was that He I is not crepancy is due to higher quality of the digital spectro- seen, but X4471 appears to have been detected in the gram or to spectral variability. Several of these spectra present observation of HDE 303308, so that the distinc- also show the λλ4485,4503 unidentified emission lines, tion between the 03 V and 04 V spectra is not clear in which clearly do not correlate with the CNO anomalies. these digital data. Similarly, the 06 V and 06.5 V spectra are not strongly differentiated here—the weak features 3.1.2 O-Type Luminosity Sequences which appear near Ηδ in the latter are rather close to the Figure 8 shows a luminosity sequence at spectral class noise level—whereas the distinction between OS V and 03. HD 93129A, located in the Carina nebula, is the

© Astronomical Society of the Pacific · Provided by the NASA Astrophysics Data System 382 WALBORN AND FITZPATRICK prototype OS supergiant (Walborn 1971&); the strong, 3.2 The Β Stars narrow Ν IV λ4058 emission feature and Ν ν λλ4604,4620 3.2.1 B-Type Spectral-Class Sequences absorption lines are the outstanding spectral character- Figures 14 and 15 display the B0.2-B3 main sequence istics of the type. These features are of intermediate (the B0 V standard can be found in Figs. 3 and 23). In the strength in the class III spectrum of HDE 269810, which early B-type spectra, the principal horizontal classifica- is located in the LMC; as discussed by Walborn (1982) the tion criterion shifts from the helium ionization ratio to distinction between giant and supergiant spectra at class those of silicon, first Si in X4552/Si IV λ4089 and then Si π XX4128-4130/Si m λ4552. The new interpolated types OS may not correspond to a significant physical luminos- -1 ity difference. There are close relationships between B0.2 and B0.7 were introduced in the 60 A mm photographic classification by Walborn (1971c), in order to 03 If* and WN-A spectra (Walborn 1974; Walborn and sharpen the discrimination of the two classification di- Fitzpatrick 1990) which are perhaps enhanced by the mensions in the line-rich B0-B1 range; they do not rep- weak, broad He π λ4686 emission component, not clearly resent classification to a hundredth of a spectral class. Tau detected in the previous photographic spectrograms. Scorpii was classified B0 V in the Μ Κ system, but the Figures 9-11 display rather similar luminosity se- weaker He π along with stronger Si m and O Ii relative to quences at spectral classes 06-06.5, 07, and 08, re- υ Orionis (also of Μ Κ type B0 V, Figs. 3 and 23) motivated spectively, which illustrate well the O-type luminosity its adoption as the primary standard for the new spectral criteria. On the main sequence one finds strong He π type B0.2 V. The alternative hypothesis that the weaker λ4686 absorption often accompanied by weak Ν m He π λ4686 in τ Seo could be due to a higher luminosity λλ4634-4640-4642 emission, a combination denoted than that of ν Ori is flatly contradicted by the smaller ((f)); in the intermediate luminosity classes the λ4686 Si iv/He l ratios in τ Seo, whereas a slightly later type for τ absorption weakens and may become neutralized while Seo satisfies all of the criteria; the derived absolute magni- the Ν πι emission strength increases—the (f) category; tudes confirm this solution (Walborn 1972). On the main and finally, the Of supergiants have both of these selec- sequence Si ill and Ο π have their maximum strengths at tive He π and Ν πι features strongly in emission. In these type B0.5, where Si m X4552 — Si iv X4089. He π X4686 high-quality data one can also see a correlative increase is last seen at types B0.5-B0.7V with this resolution. with luminosity in the strengths of the Si IV absorption Due to the weakness of all the silicon features, the declin- lines flanking Ηδ, except as already noted in Sanduleak 80 ing strengths of the C in + Ο π blends at λλ4070 and 4650 due to the SMC metal deficiency, and in HD 93130 since are used as supporting criteria in the B1-B2 V range. Type B2, of course, represents the He I maximum. Later it is of earlier type than the other spectra in Figure 9; the than that type, Si π λλ4128-4130 and Mg π X4481 in- Si IV absorption strength is a primary luminosity criterion crease in prominence. Eta Hydrae is the only object in at types O9-B0, as will be seen below. Note also the the Atlas whose prior photographic spectral type is not of luminosity effect in the ratio He X4541/He 4387, π ι λ high weight; in fact, it was classified B4 V by Lesh (1968), particularly in the 08 spectra. Photographic spectro- and the Si π appears weaker than might be expected at grams of these same or similar stars are reproduced by type B3, although the C π and M g π appear reasonable. Walborn (1971c, 1973). As also noted above, HD 48279 is Eta Ursae Majoris and η Aurigae are preferable primary moderately nitrogen enhanced. standards at type B3 V, unfortunately not accessible from Finally, Figures 12 and 13 illustrate luminosity se- CTIO. quences at spectral classes 08.5-09 and 09.5-09.7, Figures 16-19 show spectral-class sequences at the respectively; for the most luminous supergiants of the intermediate B-type luminosity classes: B0.2-B0.7 IV, latter types one must refer back to Figures 6 and 7. In this B0-B2 III, B1-B2 II, and B0-B3Ifc, respectively. The spectral-type range the luminosity criteria are the classi- first two illustrate well the significance of the new inter- cal Μ Κ positive effect in the Si IV λλ4089,4116 absorption polated spectral types (a luminosity sequence B0.2 V-III lines and negative effect in the He π X4686 absorption. is discussed in Fig. 24 below). Photographic spectrograms The luminosity classification for the earlier O types was of the same or similar B0-B1 III objects are reproduced originally based on the hypothesis that this latter effect is and discussed in detail by Walborn (1971c); the reasoning due to emission filling by the Of mechanism (Walborn behind the criteria for the interpolated types given there 1970, 1971c), although λ4686 was not known to appear in is analogous to that in the τ Seo vs. ν Ori comparison above emission above the continuum at such late O types with and need not be repeated here. One should note par- this resolution until the superluminous HDE 269896 was ticularly the smooth progressions in the fundamental found (Fig. 7 above; Walborn 1977). Delta and ζ Orionis Si m/Si iv ratio and the disappearance of He π λ4686, as (Orion Belt) are moderately nitrogen deficient (Walborn well as the correlative behavior of the CNO features, 1976); the contrast in the Ν m features between the latter which are normal in all of the spectra in Figures 16-18, and the morphologically normal spectrum of HD 47432 is with the possible exception of Ν π λ3995 in HD 48434. striking. The lb spectra in Figure 19 require further comment.

however. The relative strength of Si πι λ4552 with re- the incipient Ο π features. The ratio Si ill X4552/He I spect to Si IV λ4089 in the supergiants is < at BO, ^ at λ4387 becomes useful as an additional luminosity crite- BO. 5, at BO. 7, and > at B1 (type BO. 2 has not been used rion at type B0.2. for the supergiants). This progression is well shown in Figures 25 and 26 together provide an extended Figure 19, but the Ν π spectrum of HD 109867, although luminosity sequence at type B1 from class V through not described as such by Walborn (1976), is clearly mod- la +. The primary luminosity criterion at this type is Si ill erately enhanced relative to that of HD 86606, since the X4552/He ι λ4387, which shows a smooth progression normal Ν II maximum occurs at type B2 Ια (see Fitz- along the sequence. The correlated rise of the rich O II patrick and Walborn 1990). No extreme BN/BC spectra spectrum to its normal maximum at class la/la + is spec- are included in the Atlas, but similar montages contain- tacular. Rho Leonis breaks the CNO sequence somewhat ing Massas star, HD 93840, BN1IZ?, and HD 96248, since it is moderately nitrogen enhanced (Walborn 1976; BC1.5Ia¿, are presented and discussed by Walborn Walborn et al. 1990). et al. (1990). The principal virtue of including the spec- Finally, Figure 27 presents a B2 V-II luminosity se- trum of ι Canis Majoris in Figure 19 may be to disabuse quence. The B2 la standard is shown in Figure 21. Si m any notion that the distinction between B1 and B3 super- X4552/He I \4387 remains the principal luminosity crite- giant spectra might be a subtle one! rion, while other metallic lines show correlated positive Figures 20-22 display the spectacular B0-B8 la se- luminosity effects. A very large He I λλ4144/4121 ratio is quence, including two superluminous Ia+ objects. The a characteristic of the B2 main-sequence spectra. principal horizontal classification criteria have all been 4. Conclusion discussed in the preceding paragraphs and need not be repeated; the spectral features are more dramatic in these The discussion of the Atlas demonstrates that the phe- -1 objects because of the positive luminosity effect in the nomena and criteria of the 60 A mm photographic clas- metallic lines, as demonstrated in the next section. Ep- sification have been reproduced in substantial detail by silon Orionis (Orion Belt) is moderately nitrogen deficient the digital data. Hence, the productive Μ Κ methodology (Walborn 1976); compare Ν πι λ4097 in the blue wing of can be applied to optical digital investigations of OB Ηδ (not marked) with HD 122879. The CNO spectra in spectra with comparable systematic accuracy, and the the remainder of this sequence are morphologically nor- present Atlas will provide a useful guide for that purpose. mal. The rich Ο π spectrum has a sharp normal maximum Of course, it is highly desirable that analogous digital at type B1 Ia(+) and the comparably prolific Ν π likewise atlases be constructed for other specialized regions of the at B2 la. Si π λλ4128-4130 rivals Si m λ4552 at B3 la and H-R diagram. exceeds it at B5 la, although the Si π strength relative to REFERENCES those of the adjacent He I λλ4121,4144 lines provides a Abt, Η. Α., Meinel, A. B., Morgan, W. W., and Tapscott, J. W. 1968, more convenient, sensitive criterion. Mg π X4481/He I An Atlas of Low-Dispersion Grating Stellar Spectra λ4471 is also very useful at mid- to late-B types, although Bohannan, B., and Walborn, N. R. 1989, Pub. A.S.P., 101, 520. it is sensitive to both classification dimensions. The Conti, P. S. 1973a, Ap.J., 179, 161. stronger Fe II lines make their appearance at type B8 la. 1973k, Ap./., 179, 181. The far-UV spectra in nearly the same sequence have 1974, Ap./., 187, 539. been presented by Walborn and Nichols-Bohlin (1987). Conti, P. S., and Alschuler, W. R. 1971, Ap.]., 170, 325. Conti, P. S., and Frost, S. A. 1977, Ap./., 212, 728. 3.2.2 B-Type Luminosity Sequences Conti, P. S., and Leep, Ε. M. 1974, Ap./., 193, 113. Fitzpatrick, E. L. 1988a, in 1AU Symposium 132, The Impact of Very Figures 23 and 24 show B0 Y-lab and B0.2 V-III lumi- High S/N Spectroscopy on Stellar Physics, ed. G. Cayrel de Strobel nosity sequences, respectively. The principal luminosity and M. Spite (Dordrecht: Kluwer), p. 559. criteria here are the ratios of Si IV λ4089 to the nearby 1988fr, Αρ. /., 335, 703. He I lines λλ4026,4121, and/or 4144 as well as the ratio of 1990, in preparation. the closely spaced pair Si iv X4116/He ι λ4121; and the Fitzpatrick, E. L., and Walborn, N. R. 1990, A./., 99, in press. negative luminosity effect in the He π λ4686 absorption Lesh, J. R. 1968, Ap. /. Suppl., 17, 371. Mathys, G. 1988, Astr. Ap. Suppl., 76, 427. line, e.g., relative to He ι λ4713, which remains useful 1989, Astr. Ap. Suppl., 81, 237. although not as sensitive as in the late-O types. The He π Morgan, W. W., Abt, Η. Α., and Tapscott, J. W. 1978, Revised MK λ4686 remains in absorption even at type B0 la (Fig. 20). Spectral Atlas for Stars Earlier Than the Sun A comparison between Figures 23 and 24 shows clearly Morgan, W. W., Keenan, P. C., and Kellman, E. 1943, An Atlas of that a monotonie variation of these luminosity criteria Stellar Spectra (Chicago: University of Chicago Press). would be impossible if all of these spectra were to be Underbill, A. B., Gilroy, Κ. K., and Hill, G. M. 1989, A./., 98, 1063. Walborn, N. R. 1970, Ap./. (Letters), 161, L149. classified as B0, whereas the interpolated B0.2 type 1971a, Ap.J. (Letters), 164, L67. (again, based primarily on the Si m/Si iv ratios) allows all 1971h, Ap. J. (Letters), 167, L31. of them to be described in a consistent manner, as well as 1971c, Ap.J. Suppl, 23, 257.

1972, AJ., 77, 312. Walborn, N. R., Fitzpatrick, E. L., and Nichols-Bohlin, J. 1990, Pub. 1973, AJ., 78, 1067. A.S.P., 102, forthcoming. 1974, Ap.J., 189, 269. Walborn, N. R., Nichols-Bohlin, J., and Panek, R. J. 1985, Interna- 1976, Ap./., 205, 419. tional Ultraviolet Explorer Atlas of O-Type Spectra from 1200 to 1977, Ap./., 215, 53. 1900 λ (NASA RP-1155). 1980, Ap. /. SuppL, 44, 535. Walborn, N. R., Prévôt, M. L., Prévôt, L., Wamsteker, W., González, 1982, Ap.J. (Letters), 254, L15. R., Gilmozzi, R., and Fitzpatrick, E. L. 1989, Asir. Αρ., 219, 229. Walborn, N. R., and Fitzpatrick, E. L. 1990, in preparation. Yamashita, Y., Nariai, K., and Norimoto, Y. 1977, An Atlas of Represen- Walborn, N. R., and Nichols-Bohlin, J. 1987, Pub. A.S.P., 99, 40. tative Stellar Spectra (Tokyo; University of Tokyo Press).

Κ to f-H»-H σΓ I

O TS ΦG o 3 o S θ" ï>O o o CD

!> 5 n¿ o ^00 8c o co c3 iO i: S ^ g r-í W rH^ ¿32 ^ "S C\J ^ 2" *¿£ o ^ 2 o - ^ oC ffi I Ρ S 2^ ^o O o Q Β CO X ^

<ü T3 S S S 3 T2 2 o S o S ^ C\2 S tí 'S ι

O O s (ü 05 cü 1>oq <3υ oo g^Q O o o 00 o CD jA o í§ cq § O. ^c\| fe

s -¾ i S w α s; χ c

O O

o o CO

O o ITD

O O

o o CO "φ

o o C\2

O o

o o o

η g O ^ J. o fe fe c/5

<ΰ 0c TJ§ V3 '3g oqII 5Λ O1 ^rt O T| o

Is B-q x o i Ώ § o I QO CO

§ Q tu ^í -Sc ^ o Sil o íD 10 fÇû

o 2^ ^ rS y<*< bC ' > O ' ^ S o I^ TSδ ^χ 1 rú (ü V3 S fi α ·Β i i" o ^o ®V3 o g-S CO ffi I ρ s LO .2 o o C\2 κ- -σ g Tí b « ^> (J SC^l O <ü o Β ^ ^3 τ—ι ! I 1i ooo ' ^ Λ .52

O O

o o CO I W i I ; υ

o o LO cô a

ír >- o o o > be

·££ *o O Β § o o CO fi n

o o ι Φ CV2

o O■ Λ Η "O ^ ^

~~O O O~~

~~© Astronomical Society of the Pacific · Provided by the NASA Astrophysics Data System OB SPECTRAL ATLAS~~

~~<Λ d)~~

~~O o~~

~~n ν s o •5 o % CO~~

~~O iD O .bb 00~~

~~-Ö ^5/3 o §C g o O)-< -=3-5 Ζ fi á.-2 C .525Λ s rt o o o il CO~~

~~o o w~~

~~ça .g <üfi ιfi <ü o α3 o .y Ii j ® O íS s o ¿ ω o § £ <ü — α3 oc l> <35 u ζ o t>ι ü « b X~~

© Astronomical Society of the Pacific · Provided by the NASA Astrophysics Data System © Astronomical Society of the Pacific · Provided by the NASA Astrophysics Data System OB SPECTRAL ATLAS ^ cu 0C rzr¡

~~«S (α oqυ tυ A § ^ O 1 ü S fi O ^ bo2 O a ν Ζ s~~

Q .5 O .2 ^ O CO 3 (-! ςθ "fi ^ P (1^ε ^s Tf O o 2 c « Μ^ -fi -fiυ o o S -£ ΙΩ ^ 53fi S = §.2 g j 'S ^O -fi^ Vm<ü ^ 0 O > .¾ O Κ i i 1 « ^r._5 D oq boG o ¿3 § Ρ θo·> -S^ ^Ü &o ofi >>£'·£ •sΟ -s εO - Ig Tf Λ 5 Φ Jι a CO ^ a 3 a i S fe Η ¿Λ

~~© Astronomical Society of the Pacific · Provided by the NASA Astrophysics Data System © Astronomical Society of the Pacific · Provided by the NASA Astrophysics Data System OB SPECTRAL ATLAS~~

~~Κ o~~

~~05 ^2~~

~~O O~~

~~O o CO~~

~~o o LO~~

~~o o~~

~~o o CO~~

~~o o C\2~~

~~o o τ—Η~~

~~o o o~~

~~^ s I I "t, <Ü - 8 ffi Ü. ^cq fe á~~

~~© Astronomical Society of the Pacific · Provided by the NASA Astrophysics Data System 396 WALBORN AND FITZPATRICK~~

~~^-H 00to~~

~~^i* cu~~

~~CD Ö ΙΛ —<-g~~

o Û υ o ffi á s ^(ü -¾0) ^πΰ ~ C O . ^ o CO fe ^ Η û ^ Ε ^ o G ς!ZΛ o « -α LO "¡—Γ Λ . ^ fe cq^ f-Gi "-t^ ^CN sfrr o ^ § û 3 o κ á C ffi ΛΪΛ ÍT05 u ® « 3 00oq ->1 o o ^ o 05 52 CO Q I

~~<υ ¢+1 Λ ■■ö ^ O o (X2~~

~~O -ι- o <υ τ—ι S~~

~~ó ^*< O ce H o £ O o o _-. "Ñh ) Ïfi~~

~~Oö -H bC "5 H2~~~

~~© Astronomical Society of the Pacific · Provided by the NASA Astrophysics Data System OB SPECTRAL ATLAS~~

*1 ^ 0) ^ 'S Og -oΒ 3 > <υ o <υ o c G ^ a ^o .¾s STf s cT ^ fe ^ ^o «^υ o ^ TSo o a S CD ^ CD co 'u ^Tf OW» 1> Λfl O ^ S O 00 5 lO 5 Û "-iC\¡ bq .Sf

~~O o 6 Λ o 'C^ ^s< .¾O ffi .-s O O >Λ CO Λ S c Λ~~

~~O <üc ^c O ^ 3 C\2 5Λ O Β ^ 1 i-H X O ζΛ l> o ^ I τ—I Ρ s ^ai =a O Ζ Ά s φ ^ O cö Û o ^ Κ o Ο - ?> § Ä~~

~~ü. cq^ 1 fe ί~~

~~© Astronomical Society of the Pacific · Provided by the NASA Astrophysics Data System 398 WALBORN AND FITZPATRICK~~

~~O ^ ^ .S ^ G 1 'S 8 'C 5/5α ^ <ü oα fS ^ O CO O "Ö -Η § I j-H Ν ^ 'C g .& O o CO ^ í4 cqrH~~

~~OTt< icc~~

~~-φ «3 -« 4)c a "Ο <=~~

~~Ο Ο CO~~

~~ο ο C\2~~

~~o o τ—Η~~

~~Ο ο ο~~

~~© Astronomical Society of the Pacific · Provided by the NASA Astrophysics Data System OB SPECTRALATLAS 399~~

~~O 00 O s< W) S Ί3~~

~~oqςο O o CO oco 00I pHCM~~

~~o o LO~~

~~O o~~

~~.bp ê- o α> o 05 CO CO Q ffi~~

~~o o c\2 F G πΰ «<ü O O 0) τ—I ^(ϋ <ίϋ* Χ -Β ν ο ί Ί O O 8 I g bß- o CPρ 1 ν % * I § S c? ^ « ^ «^ -gfi . >. ϋ ffi fe Ρ~~

~~© Astronomical Society of the Pacific · Provided by the NASA Astrophysics Data System 400 WALBORN AND FITZPATRICK OB SPECTRAL ATLAS~~

~~O O~~

~~o o co~~

~~o o LO~~

~~o o~~

~~1 Η ^ ! υ 'S o o CO~~

~~o o Cv2~~

~~O o τ—ι "sf4~~

~~o o o~~

~~» 10~~

~~fe o~~

~~© Astronomical Society of the Pacific · Provided by the NASA Astrophysics Data System 402 WALBORN AND FITZPATRICK a o O Ζ (M *< o~~

G <ü 3 <ü O 0 O !> ör* ^ "6 í I ^ δ + ^ a i o ¿í J o i> 3 co 3l> sς£> >>00 κs ^ + O pH Η o !rO iO i-H<Μ α; ζβ 0OQ ^C σ> ^ 1 ^ o a o s0 35 s O ^ςθ ^> m .'Zí <35CO _C o xí Λ o _a G< CO Ζ üυ α) cû. λ c 00 Μ 1—1S "SC Ή 3 o Û o o HM!Τ! ζ^Ο Cv2 n3 a ça-¾ o νc +a 1 2 O l· ^ o 3 Τ g ë lü-* Ι3"§

~~á --î o H ^ Ε- o I ! o Ιbß ^ ^ a 2 ^ ^ Iα M § § pHι Tf «I tiι .s ?0 ι. ό. <üIm~~

~~© Astronomical Society of the Pacific · Provided by the NASA Astrophysics Data System OB SPECTRAL ATLAS 403~~

~~© Astronomical Society of the Pacific · Provided by the NASA Astrophysics Data System 404 WALBORN AND FITZPATRICK~~

~~O O~~

~~o o CÔ CD :-o-~~

~~o o LO £¡ β ro "±3~~

~~O o~~

~~o o C\2~~

~~O O τ—H I £«3~~

~~o o o~~

~~O 05 ioι~~

~~O O~~

~~o o CO~~

~~o o LO~~

~~o o~~

~~o o CO~~

~~o o Cv2~~

~~o o T-H~~

~~o o o~~

~~I s~~

~~oo rt (ü ^ α a ^ bC rrs O ^ ς) O CD ^ - ^ ¿31 rt 00CO i« COτ G o § .i o 3 s ^ .22 CO a ■■d fe<ϋ Oα CO¿Γ Λo 00I SV3 C~~

~~Tf Π3 ^ I . ^ 5Λ O oob- -ao o S-I TPrf ^ν SI W) c\|co "0fi o O^ HHrt o 8 κ CO "a ^<ü rj Χ Η o IU §Tf O o o CQ. C\2 .fi ' '"O cö<υ G TS~~

~~o ¿I O S O •g)|U C0 la J Ζ S i á| á ·£o O 'c? fe S~~

~~O O~~

~~o o CO~~

~~o o LO~~

~~o o~~

~~o o CO~~

~~o o C\2~~

~~o o~~

~~> CO~~

~~o o o~~

~~1s £'^ s Î~~

~~g3 Ix« co~~

~~© Astronomical Society of the Pacific · Provided by the NASA Astrophysics Data System © Astronomical Society of the Pacific · Provided by the NASA Astrophysics Data System OB SPECTRAL ATLAS~~

~~51 4- ^ ^ αΙΛ c a 3 ^ ΙcTΟ :5Jâ O O t^T 0) Ι"TΟ ^3'C Ttl £:g ^^ § 8 ^ «υ o í ·£ o 5J CO !— t> ^Γ 00CO~~

~~00 ffi o - iooq o Tf^3 Î5τρ LO (Ν C^l ^ >Λ <Ό ^ § ϊ σ^ JS o 8 o <υ ffi ο ^ 1 Ο οοςθ >. eqI~~

~~bCG~~

~~® 9COo ^ ñ I i 16- '0 jT Ό~~

~~O o~~

~~o o CO~~

~~o o IT) -φ~~

~~o o ■φ •φ~~

~~o o CO ■"φ~~

~~o o 02~~

~~o o~~

~~o o o~~

~~I—I -H .£D £)G . bCs o ^ S ê fe β ^ 'S~~

~~O O~~

~~o o CO~~

~~o o LO~~

~~o o -41~~

~~o o CO~~

~~o o C\2~~

~~5/5 •52 ^r-s o o τ—I~~

~~o o o~~

Cr&gt; Γ- ΟΟ [ Publications of the Astronomical Society of the Pacific

Cr> Γ- ΟΟ [ Publications of the Astronomical Society of the Pacific