M. V. McSwain

The N Enrichment and Supernova Ejection of the Runaway Microquasar LS 5039

We present an investigation of new optical and ultraviolet spectra of the mass donor star in the massive X-ray binary LS 5039. The optical band spectral line strengths indicate that the atmosphere is N-rich and C-poor, and we classify the stellar spectrum as type ON6.5 V((f)). The N-strong and C-weak pattern is also found in the stellar wind P Cygni lines of N V lambda1240 and C IV lambda1550 (narrow absorption components in the former indicate that the wind terminal velocity is V∞=2440+/-190 km s-1). We suggest that the N enrichment may result from internal mixing if the O star was born as a rapid rotator or the O star may have accreted N-rich gas prior to a common envelope interaction with the progenitor of the supernova. We reevaluated the orbital elements to find an orbital period of P=4.4267+/-0.0005 days. We compared the spectral line profiles with new non-LTE line-blanketed model spectra from Lanz and Hubeny, from which we derive an effective temperature Teff=37.5+/-1.7 kK, gravity logg=4.0+/-0.1, and projected rotational velocity Vsini=140+/-8 km s-1. We fitted the UV, optical, and IR flux distribution by using a model spectrum and extinction law with parameters E(B-V)=1.28+/-0.02 and R=3.18+/-0.07. We confirm the covariability of the observed X-ray flux and stellar wind mass-loss rate derived from the Halpha profile, which supports the wind accretion scenario for the X-ray production in LS 5039. Wind accretion models indicate that the compact companion has mass MX/Msolar=1.4+/-0.4, consistent with its identification as a neutron star. We argue that the O star has mass in the range 20-35 Msolar (based on a lower limit for the distance and the lack of eclipses). The observed eccentricity and runaway velocity of the binary can be reconciled only if the neutron star received a modest kick velocity due to a slight asymmetry in the supernova explosion (during which more than 5 Msolar was ejected).

Joint Hα and X-Ray Observations of Massive X-Ray Binaries. II. The Be X-Ray Binary and Microquasar LS I +61 303

We present the results of an H? monitoring campaign on the BeXRB and microquasar system LS I +61 303. We use radial velocity measurements of He I lines in our spectra to reevaluate the orbital elements and to better establish the time of periastron. We list equivalent widths and other parameters for the H? emission line and discuss the orbital phase related variations observed. We call attention to a dramatic episode of emission weakening that occurred in less than 1 day that probably resulted from exposure to a transient source of ionizing radiation. We argue that the increase in H? and X-ray emission following periastron probably results from the creation of an extended density wave in the disk created by tidal forces. We also discuss estimates of the size of the disk from the H? equivalent width measurements, and we suggest that the disk radius from the average equivalent width corresponds to a resonant truncation radius of the disk while the maximum equivalent width corresponds to a radius limited by the separation of the stars at periastron. We note that a nearby faint companion is probably an unrelated foreground object.

The Spectrum of the Mass Donor Star in SS 433

We present results from a short series of blue, moderate-resolution spectra of the microquasar binary SS 433. The observations were made at a time optimized to find the spectrum of the donor star, i.e., when the donor was in the foreground and well above the plane of the obscuring disk. In addition to the well-known stationary and jet emission lines, we find evidence of a weak absorption spectrum that resembles that of an A-type evolved star. These lines display radial velocity shifts opposite to those associated with the disk surrounding the compact star, and they appear strongest when the disk is maximally eclipsed. All these properties suggest that these absorption lines form in the atmosphere of the hitherto unseen mass donor star in SS 433. The radial velocity shifts observed are consistent with a mass ratio MX/MO = 0.57 ± 0.11 and masses of MO = 19 ± 7 M☉ and MX = 11 ± 5 M☉. These results indicate that the system consists of an evolved, massive donor and a black hole mass gainer.

Joint Hα and X-Ray Observations of Massive X-Ray Binaries. III. The Be X-Ray Binaries HDE 245770 = A0535+26 and X Persei

We present results from an Hα monitoring campaign of the Be X-ray binary systems HDE 245770 = A0535+26 and X Per. We use the Hα equivalent widths together with adopted values of the Be star effective temperature, disk inclination, and disk outer boundary to determine the half-maximum emission radius of the disk as a function of time. The observations of HDE 245770 document the rapid spectral variability that apparently accompanied the regeneration of a new circumstellar disk. This disk grew rapidly during the years 1998-2000, but then slowed in growth in subsequent years. The outer disk radius is probably truncated by resonances between the disk gas and neutron star orbital periods. Two recent X-ray outbursts appear to coincide with the largest disk half-maximum emission radius attained over the last decade. Our observations of X Per indicate that its circumstellar disk has recently grown to near-record proportions, and concurrently the system has dramatically increased in X-ray flux, presumably the result of enhanced mass accretion from the disk. We find that the Hα half-maximum emission radius of the disk surrounding X Per reached a size about 6 times larger than the stellar radius, a value, however, that is well below the minimum separation between the Be star and neutron star. We suggest that spiral arms excited by tidal interaction at periastron may help lift disk gas out to radii where accretion by the neutron star companion becomes more effective.

The Orbit of the Massive X-Ray Binary LS 5039

We present the first spectroscopic orbit for the massive X-ray binary LS 5039, which we find to be a short-period (P = 4.117 ± 0.011 days) and highly eccentric (e = 0.41 ± 0.05) system. The low-mass function for the orbit appears to be most consistent with a neutron star companion, although a black hole remains a possibility if the system has a low inclination. The spectrum of the O7 V optical star appears to be normal for its type (suggesting that there is little flux in the red from an accretion disk) except that the C IV λλ5801, 5812 lines are very weak, perhaps indicating the presence of CNO-processed gas in the O star. There is no evidence of Hα emission, so the system is probably not currently undergoing Roche lobe overflow. The projected rotational velocity, V sin i = 131 ± 6 km s-1, suggests that the optical star is rotating faster than synchronously with the orbit. The peculiar component of the systemic radial velocity is -17 ± 3 km s-1, so the system is not a runaway star (at least not in this dimension).

Joint Hα and X-Ray Observations of Massive X-Ray Binaries. I. The B Supergiant System LS I +65 010 = 2S 0114+650

We report on a 3 yr spectroscopic monitoring program of the Hα emission in the massive X-ray binary LS I +65 010 = 2S 0114+650, which consists of a B supergiant and a slowly rotating X-ray pulsar. We present revised orbital elements that yield a period of P = 11.5983 ± 0.0006 days and confirm that the orbit has a nonzero eccentricity e = 0.18 ± 0.05. The Hα emission profile is formed in the base of the wind of the B supergiant primary, and we show how this spectral feature varies on timescales that are probably related to the rotational period of the B supergiant. We also examine the X-ray fluxes from the Rossi X-ray Timing Explorer All-Sky Monitor instrument, and we show that the X-ray orbital light curve has a maximum at periastron and a minimum at the inferior conjunction of the B supergiant. We also show that the wind emission strength and the high-energy X-ray flux appear to vary in tandem on timescales of approximately 1 yr.

Wind Accretion and Binary Evolution of the Microquasar LS 5039

There is much evidence to suggest that stellar wind capture, rather than Roche lobe overflow, serves as the accretion mechanism onto the compact secondary object in the massive X-ray binary LS 5039. The lack of significant emission combined with only a modest X-ray flux provide observational evidence that no large-scale mass transfer is occurring (consistent with our estimate of the radius of the O6.5 V((f)) optical star that is smaller than its critical Roche radius). Here we determine the mass loss rate of the optical star from the broad, residual emission in the H-alpha profile. Using a stellar wind accretion model for a range in assumed primary mass, we compute the predicted X-ray luminosity for the system. We compare our results to the observed X-ray luminosity to determine the mass of the compact object for each case. The companion appears to be a neutron star with a mass between 1 and 3 solar masses. With our new constraints on the masses of both components, we discuss their implications on the evolution of the system before and after the supernova event that created the compact companion. The binary experienced significant mass loss during the supernova, and we find that the predictions for the resulting runaway velocity agree well with the observed peculiar space velocity. LS 5039 may be the fastest runaway object among known massive X-ray binaries.

The Long-Period, Massive Binaries HD 37366 and HD 54662: Potential Targets for Long-Baseline Optical Interferometry*

We present the results from an optical spectroscopic analysis of the massive stars HD 37366 and HD 54662. We find that HD 37366 is a double-lined spectroscopic binary with a period of 31.8187 ± 0.0004 days, and HD 54662 is also a double-lined binary with a much longer period of 557.8 ± 0.3 days. The primary of HD 37366 is classified as O9.5 V, and it contributes approximately two-thirds of the optical flux. The less luminous secondary is a broad-lined, early B-type main-sequence star. Tomographic reconstruction of the individual spectra of HD 37366 reveals absorption lines present in each component, enabling us to constrain the nature of the secondary and physical characteristics of both stars. Tomographic reconstruction was not possible for HD 54662; however, we do present mean spectra from our observations that show that the secondary component is approximately half as bright as the primary. The observed spectral energy distributions (SEDs) were fit with model SEDs and galactic reddening curves to determine the angular sizes of the stars. By assuming radii appropriate for their classifications, we determine distance ranges of 1.4-1.9 and 1.2-1.5 kpc for HD 37366 and HD 54662, respectively.

Mass and Angular Momentum Transfer in the Massive Algol Binary RY Persei

We present an investigation of the Hα emission-line variations observed in the massive Algol binary RY Per. We give new radial velocity data for the secondary based on our optical spectra and for the primary based on high-dispersion UV spectra. We present revised orbital elements and an estimate of the primarys projected rotational velocity (which indicates that the primary is rotating 7 times faster than the synchronous rate). We use a Doppler tomography algorithm to reconstruct the individual primary and secondary spectra in the region of Hα, and we subtract the latter from each of our observations to obtain profiles of the primary and its disk alone. Our Hα observations of RY Per show that the mass-gaining primary is surrounded by a persistent but time-variable accretion disk. The profile that is observed outside eclipse has weak double-peaked emission flanking a deep central absorption, and we find that these properties can be reproduced by a disk model that includes the absorption of photospheric light by the band of the disk seen in projection against the face of the star. We developed a new method to reconstruct the disk surface density distribution from the ensemble of Hα profiles observed around the orbit, and this method accounts for the effects of disk occultation by the stellar components, the obscuration of the primary by the disk, and flux contributions from optically thick disk elements. The resulting surface density distribution is elongated along the axis joining the stars in the same way as seen in hydrodynamical simulations of gas flows that strike the mass gainer near the trailing edge of the star. This type of gas stream configuration is optimal for the transfer of angular momentum, and we show that rapid rotation is found in other Algol systems that have passed through a similar stage.

The Massive Triple Star System HD 16429 A

HD 16429 A is a triple star system consisting of a single-lined spectroscopic binary and a widely separated third component, previously identified via speckle interferometry. Here I present the first orbital elements for the unblended spectroscopic binary as well as estimates of the spectral types and relative flux contributions for each visible component based on a Doppler tomographic reconstruction of their spectra. There are several stars around HD 16429 A, including the nearby Be X-ray binary and microquasar LS I +61°303, which all probably belong to a subcluster within the Cas OB6 association.