Warm Gas in the Inner Disks around Young Intermediate Mass Stars

The characterization of gas in the inner disks around young stars is of particular interest because of its connection to planet formation. In order to study the gas in inner disks, we have obtained high-resolution K-band and M-band spectroscopy of 14 intermediate mass young stars. In sources that have optically thick inner disks, i.e. E(K-L)>1, our detection rate of the ro-vibrational CO transitions is 100% and the gas is thermally excited. Of the five sources that do not have optically thick inner disks, we only detect the ro-vibrational CO transitions from HD 141569. In this case, we show that the gas is excited by UV fluorescence and that the inner disk is devoid of gas and dust. We discuss the plausibility of the various scenarios for forming this inner hole. Our modeling of the UV fluoresced gas suggests an additional method by which to search for and/or place stringent limits on gas in dust depleted regions in disks around Herbig Ae/Be stars

Multiwavelength study of the transient X-ray binary IGR J01583+6713

We have investigated multiband optical photometric variability and stability of the H$\alpha$ line profile of the transient X-ray binary IGR J01583+6713. We set an upper limit of 0.05 mag on photometric variations in the {\it V} band over a time scale of 3 months. The H$\alpha$ line is found to consist of non-Gaussian profile and quite stable for a duration of 2 months. We have identified the spectral type of the companion star to be B2 IVe while distance to the source is estimated to be $\sim$ 4.0 kpc. Along with the optical observations, we have also carried out analysis of X-ray data from three short observations of the source, two with the {\it Swift}--XRT and one with the {\it RXTE}--PCA. We have detected a variation in the absorption column density, from a value of 22.0 $\times$ 10$^{22}$ cm$^{-2}$ immediately after the outburst down to 2.6 $\times$ 10$^{22}$ cm$^{-2}$ four months afterwards. In the quiescent state, the X-ray absorption is consistent with the optical reddening measurement of E(B - V) = 1.46 mag. From one of the {\it Swift} observations, during which the X-ray intensity was higher, we have a possible pulse detection with a period of 469.2 s. For a Be X-ray binary, this indicates an orbital period in the range of 216--561 days for this binary system.Comment: 22 pages, 8 figures, accepted for publication in MNRA

Optical Continuum and Emission-Line Variability of Seyfert 1 Galaxies

We present the light curves obtained during an eight-year program of optical spectroscopic monitoring of nine Seyfert 1 galaxies: 3C 120, Akn 120, Mrk 79, Mrk 110, Mrk 335, Mrk 509, Mrk 590, Mrk 704, and Mrk 817. All objects show significant variability in both the continuum and emission-line fluxes. We use cross-correlation analysis to derive the sizes of the broad Hbeta-emitting regions based on emission-line time delays, or lags. We successfully measure time delays for eight of the nine sources, and find values ranging from about two weeks to a little over two months. Combining the measured lags and widths of the variable parts of the emission lines allows us to make virial mass estimates for the active nucleus in each galaxy. The virial masses are in the range 10^{7-8} solar masses.Comment: 24 pages, 16 figures. Accepted for publication in Ap

Properties of the H-alpha-emitting Circumstellar Regions of Be Stars

Long-baseline interferometric observations obtained with the Navy Prototype Optical Interferometer of the H-alpha-emitting envelopes of the Be stars eta Tauri and beta Canis Minoris are presented. For compatibility with the previously published interferometric results in the literature of other Be stars, circularly symmetric and elliptical Gaussian models were fitted to the calibrated H-alpha observations. The models are sufficient in characterizing the angular distribution of the H-alpha-emitting circumstellar material associated with these Be stars. To study the correlations between the various model parameters and the stellar properties, the model parameters for eta Tau and beta CMi were combined with data for other Be stars from the literature. After accounting for the different distances to the sources and stellar continuum flux levels, it was possible to study the relationship between the net H-alpha emission and the physical extent of the H-alpha-emitting circumstellar region. A clear dependence of the net H-alpha emission on the linear size of the emitting region is demonstrated and these results are consistent with an optically thick line emission that is directly proportional to the effective area of the emitting disk. Within the small sample of stars considered in this analysis, no clear dependence on the spectral type or stellar rotation is found, although the results do suggest that hotter stars might have more extended H-alpha-emitting regions.Comment: 24 pages, 16 figures, accepted for publication in Ap

The central binary and surrounding nebula of the symbiotic star V1016 Cygni

We present HST/WFPC2 images of the symbiotic star V1016 Cyg which, for the first time, directly explore the inner regions of the nebula to AU scales at optical wavelengths. They also suggest that the [OIII] 4959,5007 emission takes place in a bipolar outflow. We use these images to determine the position of the two stars and hence a projected binary separation of 84 AU (assuming a distance of 2 kpc) and a position angle of 143.5 degrees. Furthermore, we combine our images with VLA radio imaging which enables diagnostic tests to be applied and properties of the circumstellar nebula to be determined. Finally we have obtained archive HST/STIS spectra of V1016 Cyg with which we were able to spatially resolve the source at various positions in the nebula. This enabled discovery of the ultraviolet counterpart to the ~25 arcsec extended emission found by Bang et al. (1992).Comment: Accepted for publication in Ap

Evidence for Companion-Induced Secular Changes in the Turbulent Disk of a Be Star in the LMC MACHO Database

The light curve of a blue variable in the MACHO LMC database (FTS ID 78.5979.72) appeared nearly unvarying for ~4 years (quasi-flat segment) but then rapidly changed to become periodic with noisy minima for the remaining 4 years (periodic segment); there are no antecedent indications of a gradual approach to this change. Lomb Periodogram analyses indicate the presence of two distinct periods of ~61 days and 8 days in both the quasi-flat and the periodic segments. Minima of the periodic segment cover at least 50% of the orbital period and contain spikes of light with the 8-day period; maxima do not show this short period. The system typically shows maxima to be redder than minima. The most recent OGLE-III light curve shows only a 30-day periodicity. The variable's V and R magnitudes and color are those of a Be star, and recent sets of near infrared spectra four days apart, secured during the time of the OGLE-III data, show H-alpha emission near and at a maximum, confirming its Be star characteristics. The model that best fits the photometric behavior consists of a thin ring-like circumstellar disk of low mass with four obscuring sectors orbiting the central B star in unison at the 61-day period. The central star peers through the three equi- spaced separations between the four sectors producing the 8-day period. The remainder of the disk contains hydrogen in emission making maxima appear redder. A companion star of lower mass in an inclined and highly eccentric orbit produces an impulsive perturbation near its periastron to change the disk's orientation, changing eclipses from partial to complete within ~ 10 days.Comment: 42 pages, 14 figures, and 2 tables Submitted to AJ v3: Title changed, figures added, model modifie

Investigating ChaMPlane X-ray sources in the Galactic Bulge with Magellan LDSS2 spectra

We have carried out optical and X-ray spectral analyses on a sample of 136 candidate optical counterparts of X-ray sources found in five Galactic-bulge fields included in our Chandra Multi-wavelength Plane Survey. We use a combination of optical spectral fitting and quantile X-ray analysis to obtain the hydrogen column density towards each object, and a three-dimensional dust model of the Galaxy to estimate the most probable distance in each case. We present the discovery of a population of stellar coronal emission sources, likely consisting of pre-main sequence, young main sequence and main sequence stars, as well as a component of active binaries of RS CVn or BY Dra type. We identify one candidate quiescent low-mass X-ray binary with a sub-giant companion; we note that this object may also be an RS CVn system. We report the discovery of three new X-ray detected cataclysmic variables (CVs) in the direction of the Galactic Center (at distances ~2kpc). This number is in excess of predictions made with a simple CV model based on a local CV space density of <~ 10^-5 pc^-3, and a scale height ~200pc. We discuss several possible reasons for this observed excess.Comment: 41 pages, 11 figures. Accepted for publication in Astrophysical Journal, September 10 editio

Bispectrum speckle interferometry of the B[e] star MWC 349A

We present the results of bispectrum speckle interferometry of the B[e] star MWC 349A obtained with the SAO 6m telescope. Our diffraction-limited J-, H-, and K-band images (resolutions 43--74 mas) suggest the star is surrounded by a circumstellar disk seen almost edge-on. The observed visibility shape is consistent with a two-component elliptical disk model, probably corresponding to the gaseous and dusty components of the disk. We show that the classification of the object as a pre-main-sequence star or a young planetary nebula is problematic. An analysis of the uncertainties in the basic parameter determination lead us to the conclusion that MWC 349A is probably either a B[e] supergiant or a binary system, in which the B[e]-companion dominates the observed properties.Comment: 8 pages, 16 figures, accepted for publication in A&

What is the real nature of HD 108 ?

Since the beginning of the past century, the nature of HD 108 has been a subject of intense debate. One after another, astronomers explored its variability and attributed it either to binarity, or to changes in the stellar wind of a single star. In this article, we analyse a 30 years long campaign of spectroscopic observations of this star with special emphasis on the last 15 years during which photographic plates have been replaced by CCD detectors. Our investigation of the radial velocities of HD 108 yields no significant short- or long-term period and does not confirm the published periodicities either. Though the radial velocity of HD 108 appears clearly variable, the variations cannot be explained by the orbital motion in a spectroscopic binary. However, our data reveal spectacular changes in the H I Balmer lines and some He I profiles over the years. These lines continuously evolved from P Cygni profiles to `pure' absorption lines. A similar behaviour was already observed in the past, suggesting that these changes are recurrent. HD 108 seems to share several characteristics of Oe stars and we discuss different hypotheses for the origin of the observed long-term variations. As we are now in a transition period, a continuous monitoring of HD 108 should be considered for the next few years.Comment: 13 pages with 9 figures, published in A&A. The paper is also available at http://vela.astro.ulg.ac.be/Preprints/P65/index.htm

Optical spectroscopy of Be/gamma-ray binaries

© ESO, 2016.We report optical spectroscopic observations of the Be/γ-ray binaries LSI+61303, MWC 148 and MWC 656. The peak separation and equivalent widths of prominent emission lines (Hα, Hβ, Hγ, HeI, and FeII) are measured. We estimated the circumstellar disc size, compared it with separation between the components, and discussed the disc truncation. We find that in LSI+61°303 the compact object comes into contact with the outer parts of the circumstellar disc at periastron, in MWC 148 the compact object goes deeply into the disc during the periastron passage, and in MWC 656 the black hole is accreting from the outer parts of the circumstellar disc along the entire orbit. The interstellar extinction was estimated using interstellar lines. The rotation of the mass donors appears to be similar to the rotation of the mass donors in Be/X-ray binaries. We suggest that X-ray/optical periodicity ~1 day deserves to be searched for