Search

We present results of a high angular resolution survey of massive OB stars in the Cygnus OB2 association that we conducted with the NIRI camera and ALTAIR adaptive optics system of the Gemini North telescope. We observed 74 O- and early B-type stars in Cyg OB2 in the $JHK$ infrared bands in order to detect binary and multiple companions. The observations are sensitive to equal-brightness pairs at separations as small as 0.08 \arcsec, and progressively fainter companions are detectable out to $\Delta$ K = 9 mag at a separation of 2 arcsec. This faint contrast limit due to readnoise continues out to 10 arcsec near the edge of the detector. We assigned a simple probability of chance alignment to each companion based upon its separation and magnitude difference from the central target star and upon areal star counts for the general star field of Cyg OB2. Companion stars with a field membership probability of less than 1% are assumed to be physical companions. This assessment indicates that 47% of the targets have at least one resolved companion that is probably gravitationally bound. Including known spectroscopic binaries, our sample includes 27 binary, 12 triple, and 9 systems with four or more components. These results confirm studies of high mass stars in other environments that find that massive stars are born with a high multiplicity fraction. The results are important for the placement of the stars in the H-R diagram, the interpretation of their spectroscopic analyses, and for future mass determinations through measurement of orbital motion., Comment: 53 pages, 5 figures, Accepted to AJ

International audience; CHARA/SPICA (Stellar Parameters and Images with a Cophased Array) is currently being developed at Observatoire de la Cote d’Azur. It will be installed at the visible focus of the CHARA Array by the end of 2021. It has been designed to perform a large survey of fundamental stellar parameters with, in the possible cases, a detailed imaging of the surface or environment of stars. To reach the required precision and sensitivity, CHARA/SPICA combines a low spectral resolution mode R = 140 in the visible and single-mode fibers fed by the AO stages of CHARA. This setup generates additional needs before the interferometric combination: the compensation of atmospheric refraction and longitudinal dispersion, and the fringe stabilization. In this paper, we present the main features of the 6-telescopes fibered visible beam combiner (SPICA-VIS) together with the first laboratory and on-sky results of the fringe tracker (SPICA-FT). We describe also the new fringe-tracker simulator developed in parallel to SPICA-FT.

Rapid rotation is a fundamental characteristic of classical Be stars and a crucial property allowing for the formation of their circumstellar disks. Past evolution in a mass and angular momentum transferring binary system offers a plausible solution to how Be stars attained their fast rotation. Although the subdwarf remnants of mass donors in such systems should exist in abundance, only a few have been confirmed due to tight observational constraints. An indirect method of detecting otherwise hidden companions is offered by their effect on the outer parts of Be star disks, which are expected to be disrupted or truncated. In the context of the IR and radio continuum excess radiation originating in the disk, the disk truncation can be revealed by a turndown in the spectral energy distribution due to reduced radio flux levels. In this work we search for signs of spectral turndown in a sample of 57 classical Be stars with radio data, which include new data for 23 stars and the longest wavelength detections so far ($\lambda \approx$ 10\,cm) for 2 stars. We confidently detect the turndown for all 26 stars with sufficient data coverage (20 of which are not known to have close binary companions). For the remaining 31 stars, data are inconclusive as to whether the turndown is present or not. The analysis suggests that many if not all Be stars have close companions influencing their outer disks. If confirmed to be subdwarf companions, the mass transfer spin-up scenario might explain the existence of the vast majority of classical Be stars.

beta Lyr A is a complex binary system with an extensive observational dataset: light curves (from FUV to FIR), interferometric squared visibility, closure phase, triple product measurements, spectral-energy distribution (SED), high-resolution spectroscopy, differential visibility amplitude, and also differential phase. In particular, we use spectra from Ondrejov 2m telescope from 2013 to 2015, to measure the emission in Halpha, HeI, SiII, NeI, or CII lines, and differential interferometry by CHARA/VEGA from the 2013 campaign to measure wavelength-dependent sizes across Halpha and HeI 6678. This allows us to constrain not only optically thick objects (primary, secondary, accretion disk), but also optically thin objects (disk atmosphere, jets, shell). We extended our modelling tool Pyshellspec (based on Shellspec; a 1D LTE radiative transfer code) to include all new observables, to compute differential visibilities/phases, to perform a Doppler tomography, and to determine a joint chi^2 metric. After an optimisation of 38 free parameters, we derive a robust model of the beta Lyr A system. According to the model, the emission is formed in an extended atmosphere of the disk, two perpendicular jets expanding at ~700 km s^-1, and a symmetric shell with the radius ~70 R_S. The spectroscopy indicates a low abundance of carbon, 10^-2 of the solar value. We also quantify systematic differences between datasets and discuss alternative models, with higher resolution, additional asymmetries, or He-rich abundance., Comment: 19 pages, 31 figures

The most powerful tests of stellar models come from the brightest stars in the sky, for which complementary techniques, such as astrometry, asteroseismology, spectroscopy, and interferometry can be combined. The K2 Mission is providing a unique opportunity to obtain high-precision photometric time series for bright stars along the ecliptic. However, bright targets require a large number of pixels to capture the entirety of the stellar flux, and bandwidth restrictions limit the number and brightness of stars that can be observed. To overcome this, we have developed a new photometric technique, that we call halo photometry, to observe very bright stars using a limited number of pixels. Halo photometry is simple, fast and does not require extensive pixel allocation, and will allow us to use K2 and other photometric missions, such as TESS, to observe very bright stars for asteroseismology and to search for transiting exoplanets. We apply this method to the seven brightest stars in the Pleiades open cluster. Each star exhibits variability; six of the stars show what are most-likely slowly pulsating B-star (SPB) pulsations, with amplitudes ranging from 20 to 2000 ppm. For the star Maia, we demonstrate the utility of combining K2 photometry with spectroscopy and interferometry to show that it is not a 'Maia variable', and to establish that its variability is caused by rotational modulation of a large chemical spot on a 10 d time scale., Published in Monthly Notices of the Royal Astronomical Society. 20 pages, 10 figures and 10 tables

Stripped-envelope stars (SESs) form in binary systems after losing mass through Roche-lobe overflow. They bear astrophysical significance as sources of UV and ionizing radiation in older stellar populations and, if sufficiently massive, as stripped supernova progenitors. Binary evolutionary models predict them to be common, but only a handful of subdwarfs (i.e., SESs) with B-type companions are known. This could be the result of observational biases hindering detection, or an incorrect understanding of binary evolution. We reanalyze the well-studied post-interaction binary phi Persei. Recently, new data improved the orbital solution of the system, which contains a ~1.2 Msun SES and a rapidly rotating ~9.6 Msun Be star. We compare with an extensive grid of evolutionary models using a Bayesian approach and find initial masses of the progenitor of 7.2+/-0.4 Msun for the SES and 3.8+/-0.4 Msun for the Be star. The system must have evolved through near-conservative mass transfer. These findings are consistent with earlier studies. The age we obtain, 57+/-9 Myr, is in excellent agreement with the age of the alpha Persei cluster. We note that neither star was initially massive enough to produce a core-collapse supernova, but mass exchange pushed the Be star above the mass threshold. We find that the subdwarf is overluminous for its mass by almost an order of magnitude, compared to the expectations for a helium core burning star. We can only reconcile this if the subdwarf is in a late phase of helium shell burning, which lasts only 2-3% of the total lifetime as a subdwarf. This could imply that up to ~50 less evolved, dimmer subdwarfs exist for each system similar to phi Persei. Our findings can be interpreted as a strong indication that a substantial population of SESs indeed exists, but has so far evaded detection because of observational biases and lack of large-scale systematic searches., Comment: 11 pages, 5 figures, accepted for publication in A&A

This is an era of enormous opportunity in binary star research. The Leuven meeting provided an assessment of the broad scope of observational work, merits of the analysis methods, and connections with theory. Here I outline some of the issues related to spectroscopic, photometric, and high angular resolution observations of binary stars.

R144 is a WN6h star in the 30 Doradus region. It is suspected to be a binary because of its high luminosity and its strong X-ray flux, but no periodicity could be established so far. Here, we present new Xshooter multi-epoch spectroscopy of R144 obtained at the ESO Very Large Telescope (VLT). We detect variability in position and/or shape of all the spectral lines. We measure radial velocity variations with an amplitude larger than 250 km/s in NIV and NV lines. Furthermore, the NIII and NV line Doppler shifts are anti-correlated and the NIV lines show a double-peaked profile on six of our seven epochs. We thus conclude that R144 is a double-lined spectroscopic binary. Possible orbital periods range from 2 to 6 months, although a period up to one year is allowed if the orbit is highly eccentric. We estimate the spectral types of the components to be WN5-6h and WN6-7h, respectively. The high luminosity of the system (log Lbol/Lsun ~ 6.8) suggests a present-day total mass content in the range of about 200 to 300 Msun, depending on the evolutionary stage of the components. This makes R144 the most massive binary identified so far, with a total mass content at birth possibly as large as 400 Msun. We briefly discuss the presence of such a massive object 60 pc away from the R136 cluster core in the context of star formation and stellar dynamics., Comment: Accepted for publication in MNRAS Letters, 5 pages, 3 figures

We present interferometric observations of the Be star Zeta Tau obtained using the MIRC beam combiner at the CHARA Array. We resolved the disk during four epochs in 2007-2009. We fit the data with a geometric model to characterize the circumstellar disk as a skewed elliptical Gaussian and the central Be star as a uniform disk. The visibilities reveal a nearly edge-on disk with a FWHM major axis of ~ 1.8 mas in the H-band. The non-zero closure phases indicate an asymmetry within the disk. Interestingly, when combining our results with previously published interferometric observations of Zeta Tau, we find a correlation between the position angle of the disk and the spectroscopic V/R ratio, suggesting that the tilt of the disk is precessing. This work is part of a multi-year monitoring campaign to investigate the development and outward motion of asymmetric structures in the disks of Be stars., Comment: Accepted for publication in the Astronomical Journal. 27 pages, 7 Figures

Mass exchange and mass loss in close binaries can significantly affect their evolution, but a complete self-consistent theory of these processes is still to be developed. Processes such as radiative shielding due to a hot-spot region, or a hydrodynamical interaction of different parts of the gas stream have been studied previously. In order to test the respective predictions, it is necessary to carry out detailed observations of binaries undergoing the largescale mass exchange, especially for those that are in the rapid transfer phase.βLyr A is an archetype of such a system, having a long and rich observational history. Our goal for this first study is to quantitatively estimate the geometry and physical properties of the optically thick components, namely the Roche-lobe filling mass-losing star, and the accretion disk surrounding the mass-gaining star ofβLyr A. A series of continuum visible and NIR spectro-interferometric observations by the NPOI, CHARA/MIRC and VEGA instruments covering the whole orbit ofβLyr A acquired during a two-week campaign in 2013 were complemented withUBVRphotometric observations acquired during a three-year monitoring of the system. We included NUV and FUV observations from OAO A-2, IUE, and Voyager satellites. All these observations were compared to a complex model of the system. It is based on the simple LTE radiative transfer codeSHELLSPEC, which was substantially extended to compute all interferometric observables and to perform both global and local optimization of system parameters. Several shapes of the accretion disk were successfully tested – slab, wedge, and a disk with an exponential vertical profile – and the following properties were consistently found: the radius of the outer rim is 30.0±1.0R⊙, the semithickness of the disk 6.5±1.0R⊙, and the binary orbital inclinationi=93.5±1.0deg. The temperature profile is a power-law or a steady-disk in case of the wedge geometry. The properties of the accretion disk indicate that it cannot be in a vertical hydrostatic equilibrium, which is in accord with the ongoing mass transfer. The hot spot was also detected in the continuum but is interpreted as a hotter part of the accretion disk illuminated by the donor. As a by-product, accurate kinematic and radiative properties ofβLyr B were determined.

The emission-line Be star HD 215227 lies within the positional error circle of the newly identified gamma-ray source AGL J2241+4454. We present new blue spectra of the star, and we point out the morphological and variability similarities to other Be binaries. An analysis of the available optical photometry indicates a variation with a period of 60.37 +/- 0.04 d, which may correspond to an orbital modulation of the flux from the disk surrounding the Be star. The distance to the star of 2.6 kpc and its relatively large Galactic latitude suggest that the binary was ejected from the plane by a supernova explosion that created the neutron star or black hole companion. The binary and runaway properties of HD 215227 make it an attractive candidate as the optical counterpart of AGL J2241+4454 and as a new member of the small class of gamma-ray emitting binaries., Comment: 14 pages, 3 figures, 1 table. Accepted for publication in ApJ Letters on September 24, 2010

We present spectrophotometric data from 0.4 to 4.2 microns for bright, northern sky, Be stars and several other types of massive stars. Our goal is to use these data with ongoing, high angular resolution, interferometric observations to model the density structure and sky orientation of the gas surrounding these stars. We also present a montage of the H-alpha and near-infrared emission lines that form in Be star disks. We find that a simplified measurement of the IR excess flux appears to be correlated with the strength of emission lines from high level transitions of hydrogen. This suggests that the near-IR continuum and upper level line fluxes both form in the inner part of the disk, close to the star., 2010, PASP, 122, 379

We report on the discovery of a high velocity B star, HD 69686. We estimate its space velocity, distance, surface temperature, gravity, and age. With these data, we are able to reconstruct the trajectory of the star and to trace it back to its birthplace. We use evolutionary tracks for single stars to estimate that HD 69686 was born 73 Myr ago in the outer part of our Galaxy ($r \sim 12$ kpc) at a position well below the Galactic plane ($z \sim -1.8$ kpc), a very unusual birthplace for a B star. Along the star's projected path in the sky, we also find about 12 other stars having similar proper motions, and their photometry data suggest that they are located at the same distance as HD 69686 and probably have the same age. We speculate on the origin of this group by star formation in a high velocity cloud or as a Galactic merger fragment., Comment: 28 pages, 6 figures, accepted for publication in ApJ

We present a spectroscopic and photometric analysis of the remarkable massive binary system, BD +36 4063. We argue that the visible ON star is undergoing a rapid mass transfer episode that results in a thick and opaque disk that surrounds and renders invisible its massive companion. A comparison of the projected rotational velocity and the orbital semiamplitude of the visible star indicates a mass ratio near unity. Models for conservative mass transfer show that the equal mass state occurs at the point of minimum separation, and we argue that BD +36 4063 may represent the first system identified at this rapid and rare stage of massive binary evolution., 14 pages, 3 figures, accepted to ApJ Letters

High-resolution ultraviolet observations of Cygnus X-1 were obtained at two epochs roughly 1 year apart using the Space Telescope Imaging Spectrograph on the Hubble Space Telescope. Orbital phase ranges around orb = 0 and 0.5 were covered at each epoch, and the spectra show P Cygni line features from high (N V, C IV, Si IV) and absorption lines from low (Si II, C II) ionization state material. The high-ionization P Cygni profiles show a marked dependence on orbital phase; strong, broad absorption components when the X-ray source is behind the companion star and noticeably weaker absorption when the X-ray source is between us and the companion star. We fit the P Cygni profiles using the Sobolev with exact integration method applied to a spherically symmetric stellar wind subject to X-ray photoionization from the black hole. Of the wind-formed lines, the Si IV doublet provides the most reliable estimates of the parameters of the wind and X-ray illumination. The velocity v increases with radius r (normalized to the stellar radius) according to v = v∞(1 − r/r)β, with β ≈ 0.75 and v∞ ≈ 1420 km s−1. Our fit implies a ratio of X-ray luminosity (in units of 1038 erg s−1) to wind mass-loss rate (in units of 10−6 M☉ yr−1) of LX,38/−6 ≈ 0.033, measured at −6 = 4.8. Our models determine parameters that may be used to estimate the accretion rate onto the black hole and independently predict the X-ray luminosity. Our predicted LX matches that determined by contemporaneous RXTE ASM remarkably well, but is a factor of 3 lower than the rate according to Bondi-Hoyle-Littleton spherical wind accretion. We suggest that some of the energy of accretion may go into powering a jet.

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., 27 pages, 8 figures, Accepted for publication in ApJ

We present the results of an H-alpha monitoring campaign on the BeXRB and microquasar system LS I +61 303. We use radial velocity measurements of HeI lines in our spectra to re-evaluate the orbital elements and to better establish the time of periastron. We list equivalent widths and other parameters for the H-alpha 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 a day that probably resulted from exposure to a transient source of ionizing radiation. We argue that the increase in H-alpha 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-alpha 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., Comment: 18 pages including 7 figures and 2 tables, accepted to ApJ

The rapidly rotating Be star phi Persei was spun up by mass and angular momentum transfer from a now stripped-down, hot subdwarf companion. Here we present the first high angular resolution images of phi Persei made possible by new capabilities in longbaseline interferometry at near-IR and visible wavelengths. We observed phi Persei with the MIRC and VEGA instruments of the CHARA Array. Additional MIRC-only observations were performed to track the orbital motion of the companion, and these were fit together with new and existing radial velocity measurements of both stars to derive the complete orbital elements and distance. The hot subdwarf companion is clearly detected in the near-IR data at each epoch of observation with a flux contribution of 1.5% in the H band, and restricted fits indicate that its flux contribution rises to 3.3% in the visible. A new binary orbital solution is determined by combining the astrometric and radial velocity measurements. The derived stellar masses are 9.6+-0.3Msol and 1.2+-0.2Msol for the Be primary and subdwarf secondary, respectively. The inferred distance (186 +- 3 pc), kinematical properties, and evolutionary state are consistent with membership of phi Persei in the alpha Per cluster. From the cluster age we deduce significant constraints on the initial masses and evolutionary mass transfer processes that transformed the phi Persei binary system. The interferometric data place strong constraints on the Be disk elongation, orientation, and kinematics, and the disk angular momentum vector is coaligned with and has the same sense of rotation as the orbital angular momentum vector. The VEGA visible continuum data indicate an elongated shape for the Be star itself, due to the combined effects of rapid rotation, partial obscuration of the photosphere by the circumstellar disk, and flux from the bright inner disk., 16 pages, 6 figures, 1 Annex

υ Cyg is a Be star that shows variations at all timescales. We monitored its spectrum for several years from 1998 to 2004 and, in particular, during a spectroscopic multisite campaign in 2000. In this paper we present and analyse the data. We observed several outbursts including an intense one in 2000. Moreover, we found several periods of short-term variations, including two frequencies at 2.95 and 2.6 c d −1 , which are well reproduced by models of non radial pulsations with a retrograde mode with � = 3a ndm = 3 and a zonal mode with � = 3o r 4a ndm = 0, respectively. The stellar rotation is probably also identified at f ∼ 1. 5cd −1 , which is coherent with the rotation frequency deduced from our determination of stellar parameters. The peak-to-peak amplitude of variations also seems to vary in time, maybe due to a beating effect between close frequencies, but the resolution in time of our data does not allow us to separate such close frequencies. Finally, a longer timescale variation may be present, with a period around 11 years, which could be associated with a binary companion.

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., Comment: submitted to ApJL

We present results from new optical and UV spectroscopy of the unusual binary system SS 433, and we discuss the relationship of the particular spectral components we observe to the properties of the binary. (1) The continuum spectrum which we associate with flux from the super-Eddington accretion disk and the dense part of its wind. (2) H-alpha moving components which are formed far from the binary orbital plane in the relativistic jets. (3) H-alpha and He I "stationary" emission lines which we suggest are formed in the disk wind in a volume larger than the dimensions of the binary. (4) A weak "stationary" emission feature we identify as a C II 7231,7236 blend that attains maximum radial velocity at the orbital quadrature of disk recession. (5) Absorption and emission features from outflowing clumps in the disk wind (seen most clearly in an episode of blue-shifted Na I emission). (6) We found no clear evidence of the absorption line spectrum of the optical star, although we point out the presence of He I absorption features (blended with the stationary emission) with the expected radial velocity trend at the orbital and precessional phases when the star might best be seen. (7) A rich interstellar absorption spectrum of diffuse interstellar bands. The results suggest that the binary is embedded in an expanding thick disk (detected in recent radio observations) which is fed by the wind from the super-Eddington accretion disk.

We present the results of an all-sky survey made with the Fine Guidance Sensor on Hubble Space Telescope to search for angularly resolved binary systems among the massive stars. The sample of 224 stars is comprised mainly of Galactic O- and B-type stars and Luminous Blue Variables, plus a few luminous stars in the Large Magellanic Cloud. The FGS TRANS mode observations are sensitive to detection of companions with an angular separation between 0."01 and 1."0 and brighter than $\triangle m = 5$. The FGS observations resolved 52 binary and 6 triple star systems and detected partially resolved binaries in 7 additional targets (43 of these are new detections). These numbers yield a companion detection frequency of 29% for the FGS survey. We also gathered literature results on the numbers of close spectroscopic binaries and wider astrometric binaries among the sample, and we present estimates of the frequency of multiple systems and the companion frequency for subsets of stars residing in clusters and associations, field stars, and runaway stars. These results confirm the high multiplicity fraction, especially among massive stars in clusters and associations. We show that the period distribution is approximately flat in increments of log P. We identify a number of systems of potential interest for long term orbital determinations, and we note the importance of some of these companions for the interpretation of the radial velocities and light curves of close binaries that have third companions., 37 pages, 4 figures, 5 tables; AJ, in press; Full version with extended tables and large figure set can be found: http://www.astro.umontreal.ca/~emily/fgs.pdf

A classical nova occurs when material accreting onto the surface of a white dwarf in a close binary system ignites in a thermonuclear runaway. Complex structures observed in the ejecta at late stages could result from interactions with the companion during the common envelope phase. Alternatively, the explosion could be intrinsically bipolar, resulting from a localized ignition on the surface of the white dwarf or as a consequence of rotational distortion. Studying the structure of novae during the earliest phases is challenging because of the high spatial resolution needed to measure their small sizes. Here we report near-infrared interferometric measurements of the angular size of Nova Delphini 2013, starting from one day after the explosion and continuing with extensive time coverage during the first 43 days. Changes in the apparent expansion rate can be explained by an explosion model consisting of an optically thick core surrounded by a diffuse envelope. The optical depth of the ejected material changes as it expands. We detect an ellipticity in the light distribution, suggesting a prolate or bipolar structure that develops as early as the second day. Combining the angular expansion rate with radial velocity measurements, we derive a geometric distance to the nova of 4.54 +/- 0.59 kpc from the Sun., Comment: Published in Nature. 32 pages. Final version available at http://www.nature.com/nature/journal/v515/n7526/full/nature13834.html

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).

We present revised orbital elements for the massive interacting binary HD 163181, and we offer the first evidence of apsidal motion in the orbit (apsidal period U = 510±100 yr). We searched for but found no obvious evidence of the secondary's spectral lines in our optical spectra. We do observe, however, systematic profile variations with orbital phase that probably result from a gas stream from the Roche lobe-filling supergiant to the faint secondary. The relatively small projected rotational velocity of the primary (V sin i = 88±3 km s–1), the faintness of the secondary, the reported lack of orbital motion in the Hα emission, and the presence of an IR excess all suggest that the system is surrounded by an extensive circumbinary disk (as is found in a similar binary, RY Scuti).

We present an analysis of the kinematics of Be stars based upon Hipparcos proper motions and published radial velocities. We find approximately 23 of the 344 stars in our sample have peculiar space motions greater than 40 km s-1 and up to 102 km s-1. We argue that these high-velocity stars are the result of either a supernova that disrupted a binary or ejection by close encounters of binaries in young clusters. Be stars spun up by binary mass transfer will appear as high-velocity objects if there was significant mass loss during the supernova explosion of the initially more massive star, but the generally moderate peculiar velocities of Be X-ray binaries indicate that the progenitors lose most of their mass prior to the supernova (in accordance with model predictions). Binary formation models for Be stars predict that most systems bypass the supernova stage (and do not receive runaway velocities) to create ultimately Be + white dwarf binaries. The fraction of Be stars spun up by binary mass transfer remains unknown, since the post-mass transfer companions are difficult to detect.

The Be shell star EW Lac was observed in September 1993 during a multi-site campaign. Results from visual spectroscopy and polarimetry are summarized here. He I 6678 profiles have been compared to previous observations held in 1989 and show an additional complex and highly variable circumstellar component which can due to material expelled from the star just prior to these observations. Two groups of frequencies are found again in 1993 observations compared with 1989 ones. In the frame of nrp, they could be associated to low degree g-modes.

The rapid variable star, v Per (B0.5 IVIII), displays the largest amplitude pro—le —uctuations known among the growing number of massive, spectrum-variable stars. Here we present an analysis of a contin- uous 5 day run of IUE UV spectroscopy, and we show for the —rst time that the systematic, blue-to-red moving patterns observed in high-quality optical spectra are also present in the UV photospheric lines. We present cross-correlation functions of the individual spectra with that of a narrow-lined standard that produce a high signal-to-noise ratio representation of the blue-to-red moving bump patterns found in individual lines. We then use time series analysis methods to determine the periodic components of the pro—le variations (after reregistering the spectra to correct for binary motion). There are at least six periods present (ranging from 8.46 to 2.27 hr), and most of these signals are also found in optical line variations observed in 1986 (although the relative amplitudes have changed signi—cantly). Furthermore, analysis of a shorter time series of IUE spectra from 1984 shows that similar periods were present then. We also present Ha and He I j6678 pro—les obtained with the Georgia State University Multi-Telescope Telescope, which were made simultaneously with IUE, and we show that the pro—le variations are essen- tially identical in the UV and optical ranges. We rule out rotational modulation and circumstellar gas obscuration as possible causes, and we suggest instead that the variations are the result of photospheric nonradial pulsations of relatively low degree (l \ 3¨5). There were signi—cant changes (D10%) in the equivalent widths of the UV stellar wind lines during the IUE run, and we suggest that wind strength- ening events are related to episodes of large-amplitude, constructive interference between the NRP modes. Thus, intermode beating may play an important role in promoting wind loss from massive stars. Subject headings: binaries: spectroscopicstars: early-typestars: individual (v Persei) ¨ stars: oscillationsstars: winds, out—owsultraviolet: stars

We present new radial velocity measurements from IUE high-dispersion spectra of HDE 245770, the Be companion of the X-ray transient binary system, A0535+26. We formally derive the semiamplitude of the star's binary motion by fitting the UV and published radial velocity measurements with the other orbital parameters fixed according to the neutron star orbit from CGRO/BATSE results. The observational errors are still too large to claim detection of the Be star orbital motion, but we use limits on the semiamplitude (K1 < 10.6 km s–1), a classification based on UV criteria (O9.5 III-Ve), and the derived projected rotational velocity (V sin i = 250±15 km s–1) to reassess the system masses.

Cross-correlation provides an effective line-averaging function for spectra containing many line features, a result which can be exploited in order to perform time-series and spatial-domain analyses of absorption-line variability in data of (relatively) poor quality. We apply this method to high-resolution IUE spectra. For the known non-radial pulsator HD 93521 (09.5 V), time-series analysis of the cross-correlation function recovers two periods that are confirmed in independent optical data (P-1 = 1.77 h, P-2 = 2.90 h); there is no statistically significant excess power at these frequencies in lines formed in the stellar wind. By comparing phase information from the time-series analysis with results from pulsation models we estimate l=10+/-1 and 6+/-1 as the harmonic degrees for P-1 and P-2, respectively, with l+m less than or similar to 2 for each mode (where pn is the azimuthal order of the mode).We also present evidence for absorption-line variability in HD 64760 (HR 3090; B0.5 Ib), finding marginally significant signals with P-1 = 8.9 h (or, possibly, 14.2h) and P-2 = 29 h. The longer period is present, with a strong signal, in wind-formed lines. We consider possible circumstellar and (quasi-)photospheric origins for P-2, and conclude that this signal probably does not arise through rotational modulation (with the corollary that the stellar-wind signal also does not arise in corotating structures, contrary to previous suggestions). The phase behaviour of the signals is consistent with non-radial pulsation models characterized by l=5+/-1 (P-1) and 2+/-1 (P-2), with l+m less than or equal to 1, supporting a previous suggestion by Baade that both low- and higher-order modes are present; the wind modulation at P-2 may then result from leakage of pulsation energy into the supersonic outflow. The lack of significant photometric variability is a serious difficulty for this model (any sinusoidal photometric variability at P-2 has semiamplitude

We present the first high angular resolution observations in the nearinfrared H-band (1.6 microns) of the Luminous Blue Variable star P Cygni. We obtained six-telescope interferometric observations with the CHARA Array and the MIRC beam combiner. These show that the spatial flux distribution is larger than expected for the stellar photosphere. A two component model for the star (uniform disk) plus a halo (two-dimensional Gaussian) yields an excellent fit of the observations, and we suggest that the halo corresponds to flux emitted from the base of the stellar wind. This wind component contributes about 45% of the H-band flux and has an angular FWHM = 0.96 mas, compared to the predicted stellar diameter of 0.41 mas. We show several images reconstructed from the interferometric visibilities and closure phases, and they indicate a generally spherical geometry for the wind. We also obtained near-infrared spectrophotometry of P Cygni from which we derive the flux excess compared to a purely photospheric spectral energy distribution. The H-band flux excess matches that from the wind flux fraction derived from the two component fits to the interferometry. We find evidence of significant near-infrared flux variability over the period from 2006 to 2010 that appears similar to the variations in the H-alpha emission flux from the wind. Future interferometric observations may be capable of recording the spatial variations associated with temporal changes in the wind structure., 34 pages, 5 tables, 8 figures, accepted to ApJ

We report on a high angular resolution survey of circumstellar disks around 24 northern sky Be stars. The K-band continuum survey was made using the CHARA Array long baseline interferometer (baselines of 30 to 331 m). The interferometric visibilities were corrected for the flux contribution of stellar companions in those cases where the Be star is a member of a known binary or multiple system. For those targets with good uv coverage, we used a four parameter Gaussian elliptical disk model to fit the visibilities and to determine the axial ratio, position angle, K-band photospheric flux contribution, and angular diameter of the disk major axis. For the other targets with relatively limited uv coverage, we constrained the axial ratio, inclination angle, and or disk position angle where necessary in order to resolve the degeneracy between possible model solutions. We also made fits of the ultraviolet and infrared spectral energy distributions to estimate the stellar angular diameter and infrared flux excess of each target. The mean ratio of the disk diameter (measured in K-band emission) to stellar diameter (from SED modeling) is 4.4 among the 14 cases where we reliably resolved the disk emission, a value which is generally lower than the disk size ratio measured in the higher opacity Halpha emission line. We estimated the equatorial rotational velocity from the projected rotational velocity and disk inclination for 12 stars, and most of these stars rotate close to or at the critical rotational velocity.

The massive O and B-type stars will be among the first targets of the new generation of long baseline optical interferometers (such as the CHARA Array, a 400-m diameter distributed array of five 1-m telescopes). Many of these objects are binary stars for which joint astrometric and spectroscopic observations will provide masses and distances (e.g., 15 Mon; Gies et al. 1993), but there is also great interest in resolving disks of single stars. Early interferometric observations have already resolved the flattened circumstellar disks around some Be stars (Quirrenbach et al. 1994).

We report on new radial velocity measurements of massive stars that are either suspected binaries or lacking prior observations. This is part of a survey to identify and characterize spectroscopic binaries among O-type stars with the goal of comparing the binary fraction of field and runaway stars with those in clusters and associations. We present orbits for HDE 308813, HD 152147, HD 164536, BD-16 4826 and HDE 229232, Galactic O-type stars exhibiting single-lined spectroscopic variation. By fitting model spectra to our observed spectra we obtain estimates for effective temperature, surface gravity, and rotational velocity. We compute orbital periods and velocity semiamplitudes for each system and note the lack of photometric variation for any system. These binaries probably appear single-lined because the companions are faint and because their orbital Doppler shifts are small compared to the width of the rotationally broadened lines of the primary., 26 pages, 6 figures, accepted to AJ

International audience; Context.γ Cas is thought to be the prototype of classical Be stars and is the most studied object among this group. However, as for all Be stars, the origin and the physics of its circumstellar disk responsible for the observed near IR-excess, emission lines, and peculiar X-ray emission is still being debated. Aims: We constrain the geometry and kinematics of its circumstellar disk from the highest spatial resolution ever achieved on this star. This investigation is a part of a large multi-technique observing campaign to obtain the most complete picture of γ Cas which emphasizes the relation of the circumstellar environment to the star's X-ray flux. Methods: We present new observations in the near infrared (MIRC) and in the visible (VEGA) obtained with the CHARA interferometer. The VEGA instrument allows us to not only obtain a global disk geometry but also spectrally dispersed visibility modulus and phases within the Hα emission line, which enables us to study the kinematics within γ Cas's disk. Results: We obtain a disk extension in the nearby Hα continuum of 1.72 stellar diameter and 1.86 stellar diameter in the H band at 1.65 μm assuming a Gaussian disk model but also compatible with an elliptical ring model with a minor internal diameter of 1.38 stellar diameter in H. For the first time we demonstrate that the rotation mapped by the emission in the Hα line within the disk of γ Cas and up to 10 R⋆ is Keplerian. Conclusions: These observations have pushed the size of the disk to greater proportions. γ Cas was also confirmed to be a nearly critical rotator. The disk imaging gives neither indication of a 1-arm spiral feature nor evidence of a secondary star reinforcing the interpretation that the secondary is certainly a low-mass and low-luminosity star or a degenerate companion.

We present a catalog of 56 candidate intermediate mass eclipsing binary systems extracted from the 3rd data release of the All Sky Automated Survey. We gather pertinent observational data and derive orbital properties, including ephemerides, for these systems as a prelude to anticipated spectroscopic observations. We find that 37 of the 56, or ~66% of the systems are not identified in the Simbad Astronomical Database as known binaries. As a specific example, we show spectroscopic data obtained for the system HI Mon (B0 V + B0.5 V) observed at key orbital phases based on the computed ephemeris, and we present a combined spectroscopic and photometric solution for the system and give stellar parameters for each component., 83 pages, 63 figures

We report on Hα spectroscopy of the 2009.0 spectroscopic event of η Carinae collected via SMARTS observations using the Cerro Tololo Interamerican Observatory 1.5 m telescope and echelle spectrograph. Our observations were made almost every night over a two-month interval around the predicted minimum of η Car. We observed a significant fading of the line emission that reached a minimum 7 days after the X-ray minimum. About 17 days prior to the Hα flux minimum, the Hα profile exhibited the emergence of a broad, P Cygni type, absorption component (near a Doppler shift of -500 km s-1) and a narrow absorption component (near -144 km s-1 and probably associated with intervening gas from the Little Homunculus Nebula). All these features were observed during the last event in 2003.5 and are probably related to the close periastron passage of the companion. We argue that these variations are consistent with qualitative expectations about changes in the primary star's stellar wind that result from the wind-wind collision with a massive binary companion and from atmospheric eclipses of the companion., Facultad de Ciencias Astronómicas y Geofísicas

Context. One way to understand the still mysterious Be phenomenon is to study the time variations of particular Be stars with a long observational history. ζ Tau is one obvious candidate. Aims. Using our rich series of spectral and photometric observations and a critical compilation of available radial velocities, spectrophotometry of H α , and $U\!B{}V$ photometry, we characterize the pattern of time variations of ζ Tau over about a century. Our goal is to find the true timescales of its variability and confront them with the existing models related to various aspects of the Be phenomenon. Methods. Spectral reductions were carried out using the IRAF and SPEFO programs. The HEC22 program was used for both photometric reductions and transformations to $U\!B{}V$. Orbital solutions were derived with the latest publicly available version of the program FOTEL, period analyses employed both the PDM and Fourier techniques – programs HEC27 and PERIOD04. Results. We derived a new orbital ephemeris $T_{\rm RV max.}=$ HJD (2447025.6 ± 1.8) + (132$^{\rm d}\!\!.$987 ± 0$^{\rm d}\!\!.$050) $\times E$. The analysis of long-term spectral and light variations shows a clear correlation between the RV and $V/R$ changes, and a very complex behaviour of the light changes. The character of the orbital light and $V/R$ changes varies from season to season.

We present the first resolved images of the eclipsing binary Beta Lyrae, obtained with the CHARA Array interferometer and the MIRC combiner in the H band. The images clearly show the mass donor and the thick disk surrounding the mass gainer at all six epochs of observation. The donor is brighter and generally appears elongated in the images, the first direct detection of photospheric tidal distortion due to Roche-lobe filling. We also confirm expectations that the disk component is more elongated than the donor and is relatively fainter at this wavelength. Image analysis and model fitting for each epoch were used for calculating the first astrometric orbital solution for Beta Lyrae, yielding precise values for the orbital inclination and position angle. The derived semi-ma jor axis also allows us to estimate the distance of Beta Lyrae; however, systematic differences between the models and the images limit the accuracy of our distance estimate to about 15%. To address these issues, we will need a more physical, self-consistent model to account for all epochs as well as the multi-wavelength information from the eclipsing light curves., 13 Pages, 3 Figures; Accepted by ApJL

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 2.247409 +/- 0.000010 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 degrees for the configuration of the secondary star being more tidally distorted and i = 55 degrees 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 M_1 = 47 +/- 2 M_Sun and R_1 = 11.4 +/- 0.1 R_Sun for the primary, and M_2 = 28 +/- 1 M_Sun and R_2 = 8.1 +/- 0.1 R_Sun for the secondary. Our analysis places LH 54-425 amongst 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 about 1.5 Myr., Comment: 21 pages, 6 figures. Accepted in ApJ. To appear vol. 683, Aug. 10th

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 d) 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 (M_2 > 0.30 M_sun), 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., 18 pages, 2 figures, ApJL in press

We present new results from a radial velocity study of six bright OB stars with little or no prior measurements. One of these, HD 45314, may be a long-period binary, but the velocity variations of this Be star may be related to changes in its circumstellar disk. Significant velocity variations were also found for HD 60848 (possibly related to nonradial pulsations) and HD 61827 (related to wind variations). The other three targets, HD 46150, HD 54879, and HD 206183, are constant velocity objects, but we note that HD 54879 has H$\alpha$ emission that may originate from a binary companion. We illustrate the average red spectrum of each target., Comment: Accepted for publication in PASP July 2007 issue

We present results from an H-alpha monitoring campaign of the Be X-ray binary systems HDE 245770 = A 0535+26 and X Per. We use the H-alpha 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 H-alpha half-maximum emission radius of the disk surrounding X Per reached a size about six 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., accepted to ApJ, 24 pages including 3 tables & 10 figures

Many short-period binary stars have distant orbiting companions that have played a role in driving the binary components into close separation. Indirect detection of a tertiary star is possible by measuring apparent changes in eclipse times of eclipsing binaries as the binary orbits the common center of mass. Here we present an analysis of the eclipse timings of 41 eclipsing binaries observed throughout the NASA Kepler mission of long duration and precise photometry. This subset of binaries is characterized by relatively deep and frequent eclipses of both stellar components. We present preliminary orbital elements for seven probable triple stars among this sample, and we discuss apparent period changes in seven additional eclipsing binaries that may be related to motion about a tertiary in a long period orbit. The results will be used in ongoing investigations of the spectra and light curves of these binaries for further evidence of the presence of third stars.

In 2005 we obtained very precise interferometric measurements of the pole-on rapid rotator Vega (A0 V) with the longest baselines of the Center for High Angular Angular Resolution (CHARA) Array and the Fiber Linked Unit for Optical Recombination (FLUOR). For the analysis of these data, we developed a code for mapping sophisticated PHOENIX model atmospheres on to the surface of rotationally distorted stars described by a Roche-von Zeipel formalism. Given a set of input parameters for a star or binary pair, this code predicts the interferometric visibility, spectral energy distribution and high-resolution line spectrum expected for the system. For the gravity-darkened Vega, our model provides a very good match to the K-band interferometric data, a good match to the spectral energy distribution – except below 160 nm – and a rather poor match to weak lines in the high dispersion spectrum where the model appears overly gravity darkened. In 2006, we used the CHARA Array and FLUOR to obtain high precision measurements of the massive, non-eclipsing, double-line spectroscopic binary Spica, a 4-day period system where both components are gravity darkened rapid rotators. These data supplement recent data obtained with the Sydney University Stellar Interferometer (SUSI). Our study follows the classic 1971 study by Herbison-Evans et al. who resolved Spica as a binary with the Narrabri Stellar Intensity Interferometer (NSII). We will report on our progress modeling the new interferometric and archival spectroscopic data, with the goal towards better constraining the apsidal constant.

We present new results from a study of high quality, red spectra of the massive binary star system HD 1383 (B0.5 Ib + B0.5 Ib). We determined radial velocities and revised orbital elements (P = 20.28184 +/- 0.0002 d) and made Doppler tomographic reconstructions of the component spectra. A comparison of these with model spectra from non-LTE, line blanketed atmospheres indicates that both stars have almost identical masses (M_2/M_1 = 1.020 +/- 0.014), temperatures (T_eff = 28000 +/- 1000 K), gravities (log g = 3.25 +/- 0.25), and projected rotational velocities (V sin i < 30 km/s). We investigate a number of constraints on the radii and masses of the stars based upon the absence of eclipses, surface gravity, stellar wind terminal velocity, and probable location in the Perseus spiral arm of the Galaxy, and these indicate a range in probable radius and mass of R/R_sun = 14 - 20 and M/M_sun = 16 - 35, respectively. These values are consistent with model evolutionary masses for single stars of this temperature and gravity. Both stars are much smaller than their respective Roche radii, so the system is probably in a pre-contact stage of evolution. A fit of the system's spectral energy distribution yields a reddening of E(B-V)=0.55 +/- 0.05 and a ratio of total-to-selective extinction of R=2.97 +/- 0.15. We find no evidence of H-alpha emission from colliding stellar winds, which is probably the consequence of the low gas densities in the colliding winds zone., Accepted for publication in ApJ: 20 pages, 5 figures

We have measured the angular diameters of six M dwarfs with the CHARA Array, a long-baseline optical interferometer located at Mount Wilson Observatory. Spectral types range from M1.0 V to M3.0 V and linear radii from 0.38 to 0.69 Rsun. These results are consistent with the seven other M-dwarf radii measurements from optical interferometry and with those for sixteen stars in eclipsing binary systems. We compare all directly measured M dwarf radii to model predictions and find that current models underestimate the true stellar radii by up to 15-20%. The differences are small among the metal-poor stars but become significantly larger with increasing metallicity. This suggests that theoretical models for low mass stars may be missing some opacity source that alters the computed stellar radii., 24 pages, 5 figures, accepted for publication in the ApJ

We derive the effective temperatures and gravities of 461 OB stars in 19 young clusters by fitting the H-gamma profile in their spectra. We use synthetic model profiles for rotating stars to develop a method to estimate the polar gravity for these stars, which we argue is a useful indicator of their evolutionary status. We combine these results with projected rotational velocity measurements obtained in a previous paper on these same open clusters. We find that the more massive B-stars experience a spin down as predicted by the theories for the evolution of rotating stars. Furthermore, we find that the members of binary stars also experience a marked spin down with advanced evolutionary state due to tidal interactions. We also derive non-LTE-corrected helium abundances for most of the sample by fitting the He I 4026, 4387, 4471 lines. A large number of helium peculiar stars are found among cooler stars with Teff < 23000 K. The analysis of the high mass stars (8.5 solar masses < M < 16 solar masses) shows that the helium enrichment process progresses through the main sequence (MS) phase and is greater among the faster rotators. This discovery supports the theoretical claim that rotationally induced internal mixing is the main cause of surface chemical anomalies that appear during the MS phase. The lower mass stars appear to have slower rotation rates among the low gravity objects, and they have a large proportion of helium peculiar stars. We suggest that both properties are due to their youth. The low gravity stars are probably pre-main sequence objects that will spin up as they contract. These young objects very likely host a remnant magnetic field from their natal cloud, and these strong fields sculpt out surface regions with unusual chemical abundances., 50 pages 18 figures, accepted by ApJ

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., Comment: Accepted for publication in The Astrophysical Journal, 44 pages w/ 14 figures