Michelle L. Thaller

Hubble Space Telescope Goddard High Resolution Spectrograph Observations of the Be + sdO Binary ϕ Persei*

Mass transfer during the evolution of intermediate-mass stars in a close binary system can result in a rejuvenated and spun-up secondary star (which may appear as a rapidly rotating Be star) orbiting an unseen, stripped-down, remnant companion. One of the best candidates for such a system is the long- period (127 days) binary / Per. Here we present new Hubble Space Telescope Goddard High Resolution Spectrograph spectra of / Per in several UV regions that show clearly for the -rst time the spectral signature of the faint remnant companion. We derive a double-lined solution for the radial velocity curve that yields masses of 9.3 ^ 0.3 and 1.14 ^ 0.04 for the Be star and companion, respectively. A M _ M _ Doppler tomographic reconstruction of the secondary spectrum shows a rich spectrum dominated by sharp Fe IV and Fe V lines, similar to those observed in hot sdO stars. Non-LTE spectrum synthesis indicates that the subdwarf has temperature kK and gravity log g \ 4.2 ^ 0.1 and that the T eff \ 53 ^ 3 subdwarfEtoEBe star Nux ratio is 0.165 ^ 0.006 and 0.154 ^ 0.009 for the 1374 and 1647 regions, Ae respectively. The spectrum of the Be primary appears normal for a very rapidly rotating early B-type star, but we argue that the star is overluminous for its mass (perhaps owing to accretion-induced mixing). Additional sharp lines of Fe IV appear when the companion is in the foreground, and we show that these form in a heated region of the Be starIs disk that faces the hot subdwarf. Subject headings: stars: binaries: spectroscopic E stars: emission-line, Be E stars: evolution E stars: individual (/ Persei, HD 10516) E stars: subdwarfs

Binary star orbits from speckle interferometry. 5: A combined speckle/spectroscopic study of the O star binary 15 Monocerotis

We report on the discovery of a speckle binary companion to the O7 V (f) star 15 Monocerotis. A study of published radial velocities in conjunction with new measurements from Kitt Peak National Observatory (KPNO) and IUE suggests that the star is also a spectroscopic binary with a period of 25 years and a large eccentricity. Thus, 15 Mon is the first O star to bridge the gap between the spectroscopic and visual separation regimes. We have used the stars membership in the cluster NGC 2264 together with the cluster distance to derive masses of 34 and 19 solar mass for the primary and secondary, respectively. Several of the He I line profiles display a broad shallow component which we associate with the secondary, and we estimate the secondarys classification to be O9.5 Vn. The new orbit leads to several important predictions that can be tested over the next few years.

A Survey for Hα Emission in Massive Binaries: The Search for Colliding Wind Candidates

I report the results of the first all-sky survey of Hα emission in the spectra of O-type binaries. The survey includes 26 systems, of which 10 have emission that extends clearly above the continuum. This is the first report of emission for four of these. An additional three systems show small distortions in the Hα profile that may result from weak emission. I compare the distribution of emission systems in H-R diagrams for both binary and single stars, using a survey of single O-type stars done by Conti (1974). Emission in main-sequence systems is extremely rare and is completely absent in my sample of binary stars. Among binary stars, 78% of the systems containing giants show some emission, while no single giants in Contis sample do. In the case of supergiants, 78% of single stars show emission, while all supergiant binaries show strong emission. Hα emission may come from a variety sources, but the fact that binaries have a higher incidence and strength of emission in post-main-sequence stages may indicate that wind interactions are a common source of emission in massive binaries. To ascertain whether or not colliding winds have been observed, it will be necessary to study the Hα line profile throughout several orbits of each candidate colliding wind system and look for recurring orbital-phase-related variations. Such a study is underway.

THE O-TYPE BINARY 15 MONOCEROTIS NEARS PERIASTRON

We present new radial velocity measurements for the massive binary 15 Monocerotis which indicate that the system is now very close to periastron (1996.9) in its 24 yr orbit. The velocity separation in the coming year may be large enough to permit an accurate estimate of mass ratio. We also present our first astrometric measurement of 15 Mon made with the Hubble Space Telescope Fine Guidance Sensors (FGS). The FGS transfer functions are consistent with an advanced orbital position close to periastron, and we present preliminary orbital elements for the combined spectroscopic and astrometric orbit.

Colliding Winds in Massive Binary Systems

Stellar winds are a well-observed phenomenon, and in massive stars this process may result in significant mass loss from the system with dramatic evolutionary ramifications. In close binary systems of massive stars, the individual stellar winds will collide and form a shock front between the stars. The existence of this shock can be established through orbital phase–related variations in UV wind features and optical emission lines. High-density regions in the wind (near the photospheres and the shock region) will produce Ha and He i emission which can be used to map out the mass-flow structure of the system. The existence of a shock front between the stars may influence the balance of mass loss versus mass transfer in massive binary evolution since matter lost to one star as a result of Roche lobe overflow may hit the shock and be deflected before it can accrete onto the other star. I report here the results of an all-sky, high-resolution spectroscopic survey of massive binaries and identify those systems which show evidence of excess emission. Data were obtained in both the southern and northern hemispheres, and spectra from two other groups of observers, Gies and Kaper and their collaborators, were also included. The results are compared with two independent surveys of massive stars and show that binaries have a higher incidence and intensity of emission when compared to single stars of similar spectral type. Seven systems in my survey (plus four identified by earlier surveys) show significant phase-related variations in emission. I identify these as likely colliding-wind candidates. For three systems, HD 149404, HD 152248, and HD 163181, I present a simple model of the mass distribution and flow based on Ha, He i l6678, and in some cases, the UV resonance lines. Figure 1 shows, as an example, Ha profiles of the O8.5 I 1 O6.5 III binary HD 149404 plotted against heliocentric radial velocity. The profiles are arranged in order of orbital phase. Each spectrum is placed so that the continuum equals the phase of observation. The lower frame shows a gray-scale representation of the profile variations. Ha is composed of two broad emission components which appear to show clear orbital motion, as indicated by the opposite patterns in the gray-scale S diagram. However, the patterns are not those expected from the orbital motion of the stars. Analysis of the radial velocity curves suggests that these features arise in the gas flows or focused winds from the stars interacting with a shock region.