R. Lamontagne

Spectroscopic evidence for rapid blob ejection in Wolf-Rayet stars

The five bright Cygnus WN stars in the unblended He II 5411A emission line has been monitored at high spectral resolution and high S/N during four or five nights. Typical data are presented here for the two single WN6 stars HD 191765 and HD 192163. The spectra reveal narrow emission bumps superposed on a broad smooth background wind profile with FWHM of about 2-10 A and height 10 percent or less in continuum units for HD 191765. The bumps always appear to accelerate outward along with the general wind, on a time scale of hours. 20 references.

The Luminous Eclipsing SMC OB + WN Binary HD 5980 before and during the Recent LBV-like Outburst: An Extreme Case of Colliding Winds

The 1994 LBV-(luminous blue variable)like outburst of one of the luminous, hot components of the binary HD 5980 made it the brightest star in the Small Magellanic Cloud for an interval of 5 months. The most intriguing question to arise from this event is the following: Why did the HD 5980 spectrum change from an H-poor WN3 with veiled OB absorption lines about 20 yr ago to an H-rich WN11 without central absorption lines during the outburst? In an attempt to answer this apparent enigma, we present and analyze new phase-dependent spectroscopic, polarimetric, and light-curve observations. Together with other published data, these new observations allow us to improve the orbital parameters considerably, except for the radial velocity amplitudes and hence the masses, which are only roughly constrained. Especially important in HD 5980 is the strong collision of the two nearly equal pre-outburst winds. The emission-line spectrum generated by the collision tends to mask the underlying line spectra of both components when the system is relatively quiescent. We argue that the pre-erupting system consists of a very luminous but moderately massive H-rich O type supergiant, possibly with emission lines, and a low-mass, H-poor, relatively faint WN companion, whose lines are mostly drowned out by wind collision emission, the spectrum of which largely imitates that of a WNE star. It was the O supergiant that erupted in a normal way as an H-rich, visually bright WN11 star. In this way, the need for peculiar evolutionary scenarios (e.g., rapid evolution from a faint, low-mass, H-poor WNE star to a luminous, H-rich WNL star) is avoided.

Studies of hot B subdwarfs. VIII : Strömgren photometry of hot, hydrogen-rich subdwarf candidates in the Palomar-Green and Kitt Peak-Downes surveys

We present the results of an extensive program of photoelectric observations on the Stromgren system of 310 hot, hydrogen-rich (B and OB) subdwarf candidates in the Palomar-Green and Kitt Peak-Downes colorimetric surveys

A Deep Survey for Galactic Wolf-Rayet Stars. II. Implications for Galactic Structure and Massive Star Formation*

We have completed a direct narrowband-broadband Schmidt plate survey of large areas of the southern Milky Way for new Wolf-Rayet (W-R) stars as faint as 19th b magnitude. The 31 newly detected stars in the completed survey are among the reddest and/or most distant known in the Galaxy. We have obtained spectra of all candidate W-R stars in the 22 fields stretching from l = 282° to l = 341° in longitude and Δb = 35 in latitude, covering about 180 square degrees. We also observed two isolated Milky Way fields centered at l = 0° and l = 8°. Eighteen new W-R stars are reported here for the first time. Combined with the 13 new W-R stars we have already reported in Carina, our list of 31 new Galactic W-R stars reaches 3–4 mag fainter than previous surveys. Thirteen of our 18 new W-R stars reported here are of subtype WN, while five are of subtype WC. We present and describe their spectra and subtypes, derive their distances, and discuss the significance of their locations along with all other W-R stars in the Galaxy. Our new W-R stars clearly demonstrate an increasing number ratio of WN to WC stars with increasing Galactocentric distance. We conclude with predictions of the total number of Galactic W-R stars that should be discovered in future IR surveys.

Photometry, polarimetry, spectroscopy, and spectropolarimetry of the enigmatic Wolf-Rayet star EZ Canis Majoris

New observations of the peculiar Wolf-Rayet star EZ Canis Majoris collected since 1987 are presented, and photometric, polarimetric, spectroscopic, and spectropolarimetric data are discussed. Linear polarization data are well fitted with an eccentric binary model where an additional free parameter is included to allow for epoch-dependent changes of the geometrical electron distribution in the W-R envelope. This yields a set of basic parameters, including an eccentricity e = 0.39 +/- 0.02 and an orbital inclination i = 114 deg +/- 3 deg. The spectroscopic data show global profile variations for all three observed strong emission lines He II 5412 A, C IV 5807 A, and He I 5876 A. Radial velocities of the lines vary with the 3.766-day period. Radially expanding inhomogeneities are superposed on the line profiles and variable polarization in the lines is observed.

Light Curve Solution of HD 93205 (O3 V + O8 V) Containing the Earliest Known Star in a Well-studied Binary

We present the results of an extensive photometric study of the O3 V + O8 V binary HD 93205 (P 608, e = 0.46). The primary O3 V star has by far the earliest known spectral type of a normal star in a cataloged close binary. Some 186 individual differential observations, each of precision ~0.003 mag, were obtained over a contiguous interval of ~3 months in a narrow, visual-continuum bandpass. The amplitude of photometric variability is very low, about 0.02 mag, with most of the light changes occurring near periastron passage. Analysis of the light variations with a state-of-the-art binary model in an eccentric orbit leads to the conclusion that the system does not exhibit eclipses. Rather, the light variations are due mainly to orbital revolution of tidally distorted stars. However, there is an additional very small, but real, systematic decreasing trend in the light curve of the system approximately centered on the apastron passage, i.e., between orbital phases 0.35 and 1.0, which cannot be accounted for with present models. A nonuniform brightness distribution on the surface of the star(s), whose origin remains a mystery, may be responsible for this effect. Another plausible explanation of the trend may be related to turbulent viscosity, causing tidal lag. Despite this problem, one can estimate the range of possible values for the orbital inclination angle, e.g., at the 5% significance level, 75° ≥ i ≥ 35°, which leads to the masses MO3 32-154 M☉ and MO8 14-68 M☉. The best-fit value, i = 60°, yields MO3 = 45 M☉ and MO8 = 20 M☉. The latter value is compatible with the reliable masses of the two O8 V stars (22 M☉) in the detached eclipsing binary system EM Car. This would imply that at least one of the earliest known main-sequence O3 stars has relatively modest mass, compared to evolutionary masses of the most massive stars, which are claimed elsewhere in the literature to reach up to at least 100 M☉.

The Montreal-Cambridge-Tololo Survey of Southern Subluminous Blue Stars: The South Galactic Cap

Results for the south Galactic cap region of the Montreal-Cambridge-Tololo survey of blue subluminous stars are presented. This region overlaps the 840 deg2 region studied almost three decades ago by Slettebak & Brundage. We present a list of equatorial coordinates, photographic photometry, and spectroscopic identifications, as well as finding charts, for 188 blue objects [(U-B)pg ≤ -0.6] brighter than Bpg = 16.5 in this area. Completeness of the survey and comparisons with other similar efforts are discussed.

Studies of hot B subdwarfs. V - Continuing investigation of the C, N, and SI abundance patterns in the atmospheres of sdB stars

Observations UV a haute dispersion de deux sous naines chaudes, riches en hydrogene, obtenues par le satellite IUE

High-speed photometric observations of the pulsating DA white dwarf GD 165

New high-speed photometric observations of the pulsating DA white dwarf GD 165 are presented. The Fourier spectrum of the light curve of GD 165 exhibits two main regions of power at 120 and 193 s. The presence of a high-amplitude long period mode near ∼1800 s reported by Bergeron and McGraw is not confirmed by these new observations. Light curves obtained with the Canada-France-Hawaii Telescope reveal previously undetected low-amplitude harmonic oscillations. Observations with the Whole Earth Telescope are used to resolve the two principal regions of power. The 120 and 193 s peaks are shown to be multiplets composed of at least three, and possibly five frequency components. The most likely explanation is that these two peaks correspond to nonradial gravity modes with different values of the radial order k and with l=1 or 2 split into 2l+1 components by slow rotation

Studies of hot B subdwarfs. III - Carbon, nitrogen, and silicon abundances in three sdB stars

Optical and high-dispersion IUE observations of three hot B subdwarfs (UV 1758 + 36, Ton S-227, and Feige 65) are presented. These data are analyzed with model atmosphere techniques, and element abundances for C, N, and Si are derived. The abundances are either near (N) or below (C, Si) the solar value; large variations (1) in the extent of underabundances of carbon and silicon among the objects, as well as (2) in the abundances (with respect to the solar values) characterizing each star are observed. A preliminary interpretation of the observed variations in these and other hot subdwarfs in terms of radiative forces disrupting the downward diffusion of heavy elements is presented.