William G. Bagnuolo

ICCD Speckle Observations of Binary Stars. XIX. An Astrometric/Spectroscopic Survey of O Stars

We present the results of a speckle interferometric survey made with the CHARA speckle camera and 4 m–class telescopes of Galactic O-type stars with V 59% have a visual or spectroscopic companion) but less so among field and especially runaway stars. There are many triple systems among the speckle binaries, and we discuss their possible role in the ejection of stars from clusters. The period distribution of the binaries is bimodal in log P, but we suggest that binaries with periods of years and decades may eventually be found to fill the gap. The mass ratio distribution of the visual binaries increases toward lower mass ratios, but low mass ratio companions are rare among close, spectroscopic binaries (probably because of the difficulty of spectroscopic detection rather than a real deficit). We present distributions of the eccentricity and longitude of periastron for spectroscopic binaries with elliptical orbits, and we find strong evidence of a bias in the longitude of periastron distribution (the Barr effect), which is probably caused by line distortions introduced by circumstellar gas.

First results from the chara array. II. A description of the instrument

The CHARA Array is a six 1 m telescope optical/IR interferometric array located on Mount Wilson, California, designed and built by the Center for High Angular Resolution Astronomy of Georgia State University. In this paper we describe the main elements of the Array hardware and software control systems, as well as the data reduction methods currently being used. Our plans for upgrades in the near future are also described.

First results from the chara array. I. An interferometric and spectroscopic study of the fast rotator α leonis (Regulus)

We report on K-band interferometric observations of the bright, rapidly rotating star Regulus (type B7 V) made with the CHARA Array on Mount Wilson, California. Through a combination of interferometric and spectroscopic measurements, we have determined for Regulus the equatorial and polar diameters and temperatures, the rotational velocity and period, the inclination and position angle of the spin axis, and the gravity darkening coefficient. These first results from the CHARA Array provide the first interferometric measurement of gravity darkening in a rapidly rotating star and represent the first detection of gravity darkening in a star that is not a member of an eclipsing binary system.

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

CHARA Array K'-Band Measurements of the Angular Dimensions of Be Star Disks

We present the firstK 0 -band,long-baseline interferometric observations of the northern Be starsCas,� Per,� Tau, andDra. The measurements were made with multiple telescope pairs of the CHARA Array interferometer and in every case the observations indicate that the circumstellar disks of the targets are resolved. We fit the interferometric visibilities with predictions from a simple disk model that assumes an isothermal gas in Keplerian rotation. We derive fitsof thefourmodelparameters(diskbasedensity,radialdensityexponent,disknormalinclination,andpositionangle) for each of the targets. The resulting densities are in broad agreement with prior studies of the IR excess flux, and the resultingorientationsgenerallyagreewiththosefrominterferometricHandcontinuumpolarimetricobservations.We find that the angular size of the K 0 diskemissionis smaller thanthatdeterminedfor the Hemission, and weargue that thedifferenceisthe resultof a larger Hopacityandtherelativelylarger neutral hydrogenfractionwithincreasingdisk radius. All the targets are known binaries with faint companions, and we find that companions appear to influence the interferometric visibilities in the cases ofPer andDra. We also present contemporaneous observations of the H� , H� ,andBremissionlines.Syntheticmodelprofilesoftheselinesthatarebasedonthesamediskinclinationandradial densityexponentasderivedfromtheCHARA Arrayobservationsmatchtheobservedemissionlinestrengthif thedisk base density is reduced by � 1.7 dex.

Tomographic separation of composite spectra - The components of the O-star spectroscopic binary AO Cassiopeiae

The UV photospheric lines of the short-period, double-lined O-star spectroscopic binary AO Cas are analyzed. Archival data from IUE (16 spectra uniformly distributed in orbital phase) were analyzed with a tomography algorithm to produce the separate spectra of the two stars in six spectral regions. The spectral classifications of the primary and secondary, O9.5 III and O8 V, respectively, were estimated through a comparison of UV line ratios with those in spectral standard stars. An intensity ratio of 0.5-0.7 (primary brighter) at 1600 A is compatible with the data. 22 refs.

Tomographic separation of composite spectra. 2: The components of 29 UW Canis Majoris

We have analyzed the UV photospheric lines of 29 CMa, a 4.39 day period, double-lined O-type spectroscopic binary. Archival data from International Ultraviolet Explorer (IUE)(28 spectra well distributed in oribital phase) were analyzed with several techniques. We find that the mass ratio is q = 1.20 +/- 0.16 (secondary more massive) based on three independent arguments. A tomography algorithm was used to produce the separate spectra of the two stars in six UV spectral regions. The MK spectral classifications of the primary and secondary, O7.5-8 Iab and O9.7 Ib, respectively, were estimated through a comparison of UV line ratios with those in spectral standard stars. The flux ratio of the stars in the UV is 0.36 +/- 0.07 (primary brighter). The primary has a strong P Cygni NIV wavelength 1718 feature, indicating a strong stellar wind. We also present tomographic reconstructions of visual spectral data in the range 4300-4950 A, based on seven observations of differing orbital phases, which confirm the UV classifications, and show that the primary is an Of star. From the spectral classifications, we estimate the temperatures of the stars to be 33,750 K and 29,000 K for primary and secondary, respectively. We then fit visual and UV light curves and show that reasonably good fits can be obtained with these temperatures, a semicontact configuration, an inclination of 74 deg. +/- 2 deg., and an intensity ratio r is less than 0.5.

Binary Star Differential Photometry Using the Adaptive Optics System at Mount Wilson Observatory

We present photometric and astrometric results for 36 binary systems observed with the natural guide star adaptive optics system of the Mount Wilson Institute on the 100 inch (2.5 m) Hooker Telescope. The measurements consist of differential photometry in U, B, V, R, and I filters along with astrometry of the relative positions of system components. Magnitude differences were combined with absolute photometry found in the literature of the combined light for systems to obtain apparent magnitudes for the individual components at standard bandpasses, which in turn led to color determinations and spectral types. The combination of these results with Hipparcos parallax measurements yielded absolute magnitudes and allowed us to plot the components on an H-R diagram. To further examine the reliability and self-consistency of these data, we also estimated system masses from the spectral types.

BINARY AND MULTIPLE O-TYPE STARS IN THE CASSIOPEIA OB6 ASSOCIATION

We present the results of time-resolved spectroscopy of 13 O-type stars in the Cas OB6 stellar association. We conducted a survey for radial velocity variability in search of binary systems, which are expected to be plentiful in young OB associations. Here we report the discovery of two new single-lined binaries, and we present new orbital elements for three double-lined binaries (including one in the multiple-star system HD 17505). One of the doublelined systems is the eclipsing binarysystem DN Cas, and we present a preliminary light-curve analysis that yields the system inclination,masses, and radii. Wecompare thespectraof thesinglestarsand theindividual components ofthe binary stars with model synthetic spectra to estimate the stellar effective temperatures, gravities, and projected

A Spectroscopic Orbit for Regulus

We present a radial velocity study of the rapidly rotating B star Regulus that indicates the star is a single-lined spectroscopic binary. The orbital period (40.11 days) and probable semimajor axis (0.35 AU) are large enough that the system is not interacting at present. However, the mass function suggests that the secondary has a low mass (M2 > 0.30 M☉), and we argue that the companion may be a white dwarf. Such a star would be the remnant of a former mass donor that was the source of the large spin angular momentum of Regulus itself.