Laura R. Penny

Orbits of four very massive binaries in the r136 cluster

We present radial velocity and photometry for four early-type, massive, double-lined spectroscopic binaries in the R136 cluster. Three of these systems are eclipsing, allowing orbital inclinations to be determined. One of these systems, R136-38 (O3 V + O6 V), has one of the highest masses ever measured for the primary, 57 M☉. Comparison of our masses with those derived from standard evolutionary tracks shows excellent agreement. We also identify five other light variables in the R136 cluster that are worthy of follow-up study.

A FUSE SURVEY OF THE ROTATION RATES OF VERY MASSIVE STARS IN THE SMALL AND LARGE MAGELLANIC CLOUDS

We present projected rotational velocity values for 97 Galactic, 55 SMC, and 106 LMC O-B type stars from archival FUSE observations. The evolved and unevolved samples from each environment are compared through the Kolmogorov-Smirnov test to determine if the distribution of equatorial rotational velocities is metallicity dependent for these massive objects. Stellar interior models predict that massive stars with SMC metallicity will have significantly reduced angular momentum loss on the main sequence compared to their Galactic counterparts. Our results find some support for this prediction but also show that even at Galactic metallicity, evolved and unevolved massive stars have fairly similar fractions of stars with large Vsin i values. Macroturbulent broadening that is present in the spectral features of Galactic evolved massive stars is lower in the LMC and SMC samples. This suggests the processes that lead to macroturbulence are dependent upon metallicity.

Tomographic Separation of Composite Spectra. VIII. The Physical Properties of the Massive Compact Binary in the Triple Star System HD 36486 (δ Orionis A)

We present the first double-lined spectroscopic orbital elements for the central binary in the massive triple δ Orionis A. The solutions are based on fits of cross-correlation functions of IUE high-dispersion UV spectra and He I λ6678 profiles. The orbital elements for the primary agree well with previous results, and in particular, we confirm the apsidal advance with a period of 224.5 ± 4.5 yr. We also present tomographic reconstructions of the primary and secondary stars spectra that confirm the O9.5 II classification of the primary and indicate a B0.5 III type for the secondary. The relative line strengths between the reconstructed spectra suggest magnitude differences of Δm = -2.5 log(Fs/Fp) = 2.6 ± 0.2 in the UV and Δm = 2.5 ± 0.3 at 6678 A. The widths of the UV cross-correlation functions are used to estimate the projected rotational velocities, V sin i = 157 ± 6 and 138 ± 16 km s-1 for the primary and secondary, respectively (which implies that both the primary and the secondary rotate faster than the orbital motion). We used the spectroscopic results to make a constrained fit of the Hipparcos light curve of this eclipsing binary, and the model fits limit the inclination to the range i = 67°-77°. The lower limit corresponds to a near Roche-filling configuration that has an absolute magnitude that is consistent with the photometrically determined distance to Ori OB1b, the Orion Belt cluster in which δ Ori resides. The i = 67° solution results in masses of Mp = 11.2 and Ms = 5.6 M☉, both of which are substantially below the expected masses for stars of their luminosity. The binary may have experienced a mass ratio reversal caused by case A Roche lobe overflow or the system may have suffered extensive mass loss through a binary interaction (perhaps during a common envelope phase) in which most of the primarys mass was lost from the system rather than transferred to the secondary. We also made three-component reconstructions to search for the presumed stationary spectrum of the close visual companion δ Ori Ab (Hei 42 Ab). There is no indication of the spectral lines of this tertiary in the UV spectrum, but a broad and shallow feature is apparent in the reconstruction of He I λ6678 indicative of an early B-type star. The tertiary may be a rapid rotator (V sin i ≈ 300 km s-1) or a spectroscopic binary.

PHOTOMETRIC AND SPECTROSCOPIC STUDIES OF MASSIVE BINARIES IN THE LARGE MAGELLANIC CLOUD. I. INTRODUCTION AND ORBITS FOR TWO DETACHED SYSTEMS: EVIDENCE FOR A MASS DISCREPANCY?*

The stellar mass-luminosity relation is poorly constrained by observations for high-mass stars. We describe our program to find eclipsing massive binaries in the Magellanic Clouds using photometry of regions rich in massive stars, and our spectroscopic follow-up to obtain radial velocities and orbits. Our photometric campaign identified 48 early-type periodic variables, of which only 15 (31%) were found as part of the microlensing surveys. Spectroscopy is now complete for 17 of these systems, and in this paper we present analysis of the first two, LMC 172231 and ST2-28, simple detached systems of late-type O dwarfs of relatively modest masses. Our orbit analysis yields very precise masses (~2%), and we use tomography to separate the components and determine effective temperatures by model fitting, necessary for determining accurate (0.05-0.07 dex) bolometric luminosities in combination with the light-curve analysis. Our approach allows more precise comparisons with evolutionary theory than previously possible. To our considerable surprise, we find a small, but significant, systematic discrepancy: all of the stars are slightly undermassive, by typically 11% (or overluminous by 0.2 dex) compared with that predicted by the evolutionary models. We examine our approach for systematic problems, but find no satisfactory explanation. The discrepancy is in the same sense as the long-discussed and elusive discrepancy between the masses measured from stellar atmosphere analysis with the stellar evolutionary models, and might suggest that either increased rotation or convective overshooting is needed in the models. Additional systems will be discussed in future papers of this series, and will hopefully confirm or refute this trend.

Tomographic Separation of Composite Spectra. VI. The Physical Properties of the Massive Close Binary HD 152248

We present the results of a Doppler tomographic reconstruction of the UV spectra of the double-lined O binary HD 152248 based on observations made with IUE. We used cross-correlation methods to obtain radial velocities, confirm the orbital elements, estimate the UV flux ratio, and determine projected rotational velocities. The individual component spectra are classified as O7 I + O7 I using UV criteria defined by Penny, Gies, & Bagnuolo. We present a model fit of the eclipsing light curve from which we derive an orbital inclination, i=72? ? 3?. This analysis indicates that neither star is currently experiencing Roche lobe overflow. We place the individual components in the theoretical H-R diagram and show that the individual masses (Mp/M?=24.2 ? 2.0; Ms/M?=25.8 ? 2.0) derived from the combined spectroscopic and photometric analysis are significantly lower than those computed from evolutionary tracks for single stars.

Effects of Metallicity on the Rotational Velocities of Massive Stars

Recent theoretical predictions for low-metallicity massive stars predict that these stars should have drastically reduced equatorial winds (mass loss) while on the main sequence, and so should retain most of their angular momentum. Observations of both the Be/(B + Be) ratio and the blue-to-red supergiant ratio appear to have a metallicity dependence that may be caused by high rotational velocities. We have analyzed 39 archival Hubble Space Telescope Imaging Spectrograph (STIS), high-resolution, ultraviolet spectra of O-type stars in the Magellanic Clouds to determine their projected rotational velocities V sin i. Our methodology is based on a previous study of the projected rotational velocities of Galactic O-type stars using International Ultraviolet Explorer (IUE) short-wavelength prime (SWP) camera high-dispersion spectra, which resulted in a catalog of V sin i values for 177 O-type stars. Here we present complementary V sin i values for 21 Large Magellanic Cloud and 22 Small Magellanic Cloud O-type stars based on STIS and IUE UV spectroscopy. The distribution of V sin i values for O-type stars in the Magellanic Clouds is compared to that of Galactic O-type stars. Despite the theoretical predictions and indirect observational evidence for high rotation, the O-type stars in the Magellanic Clouds do not appear to rotate faster than their Galactic counterparts.

Tomographic separation of composite spectra. x. the massive close binary hd 101131

We present the first orbital elements for the massive close binary HD 101131, one of the brightest objects in the young open cluster IC 2944. This system is a double-lined spectroscopic binary in an elliptical orbit with a period of 9.64659 ± 0.00012 days. It is a young system of unevolved stars (approximately 2 million yr old) that are well within their critical Roche surfaces. We use a Doppler tomography algorithm to reconstruct the individual component optical spectra, and we apply well-known criteria to arrive at classifications of O6.5 V((f)) and O8.5 V for the primary and secondary, respectively. We compare the reconstructed spectra of the components to single-star spectrum standards to determine a flux ratio of f2/f1 = 0.55 ± 0.08 in the V band. Both components are rotating faster than synchronously. We estimate the temperatures and luminosities of the components from the observed spectral classifications, composite V magnitude, and cluster distance modulus. The lower limits on the masses derived from the orbital elements and the lack of eclipses are 25 and 14 M☉ for the primary and secondary, respectively. These limits are consistent with the somewhat larger masses estimated from the positions of the stars in the Hertzsprung-Russell diagram and evolutionary tracks for single stars.

Tomographic Separation of Composite Spectra. VII. The Physical Properties of the Massive Triple System HD 135240 (δ Circini)

We present the results of a radial velocity study of the massive, double-lined, O binary HD 135240 based primarily on UV spectroscopy from the International Ultraviolet Explorer. Cross-correlation methods indicate the presence of a third stationary spectral line component which indicates that the system is a triple consisting of a central 3.9 day close binary with a distant companion. We measured radial velocities from the cross-correlation functions after removal of the third component, and we combined these with velocities obtained from Ha spectroscopy to reassess the orbital elements. We applied a Doppler tomography algorithm to reconstruct the individual UV spectra of all three stars, and we deter)

The Struve-Sahade Effect: A Tale of Three Stars

The Struve-Sahade effect (S-S effect) is the apparent weakness of lines of the secondary in massive binaries when the secondary is receding. This effect poses problems for the accurate reconstruction of the separated primary and secondary spectra. We have reexamined IUE spectra of three classical, hot binaries studied by D. Stickland in 1997. From various cross-correlation and tomographic techniques we find different results for each of the three systems. For HD 1337 (AO Cas), we find a slight S-S effect which can be explained by a mechanism of localized heating by the colliding stellar winds, as proposed by Gies, Bagnuolo, & Penny in 1997. For HD 47129 (Plasketts star), no consistent S-S effect was found, and none is expected based on the wind heating model because the secondary has a slightly stronger wind. Finally, for HD 57060 (29 UW CMa), a strong S-S effect was found during the receding phases (0.13-0.63). In addition, we find a strong feature near phase 0.2, similar to the secondary in spectral type but shifted by ≈-400 km s-1. We explain this by absorption and reemission by strong winds wrapping around the secondary. Thus, in general, we find that the S-S effect may arise from several distinct mechanisms.

Dynamical Masses for the Large Magellanic Cloud Massive Binary System [L72] LH 54-425

We present results from an optical spectroscopic investigation of the massive binary system [L72] LH 54-425 in the LH 54 OB association in the Large Magellanic Cloud. We revise the ephemeris of [L72] LH 54-425 and find an orbital period of 2.24741 ± 0.00004 days. We find spectral types of O3 V for the primary and O5 V for the secondary. We made a combined solution of the radial velocities and previously published V-band photometry to determine the inclination for two system configurations, i = 52+ 2−3 degrees for the configuration of the secondary star being more tidally distorted and i = 55°± 1° for the primary as the more tidally distorted star. We argue that the latter case is more probable, and this solution yields masses and radii of M1 = 47 ± 2 M☉ and R1 = 11.4 ± 0.1 R☉ for the primary, and M2 = 28 ± 1 M☉ and R2 = 8.1 ± 0.1 R☉ for the secondary. Our analysis places LH 54-425 among the most massive stars known. Based on the position of the two stars plotted on a theoretical HR diagram, we find the age of the system to be ~1.5 Myr.