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

Be stars and binaries in the field of the SMC open cluster NGC330 with VLT-FLAMES

Observations of hot stars belonging to the young cluster SMC-NGC330 and its surrounding region were obtained with the VLT-GIRAFFE facilities in MEDUSA mode. We investigated the B and Be star properties and proportions in this environment of low metallicity. We also searched for rapid variability in Be stars using photometric databases. With spectroscopic measurements we characterized the emission and properties of Be stars. By cross-correlation with photometric databases such as MACHO and OGLE, we searched for binaries in our sample of hot stars, as well as for short-term variability in Be stars. We report on the global characteristics of the Be star sample (131 objects). We find that the proportion of early Be stars with a large equivalent width of the Halpha emission line is higher in the SMC than in the LMC and MW. We find a slight increase in the proportion of Be stars compared to B-type stars with decreasing metallicity. We also discovered spectroscopic and photometric binaries, and for the latter we give their orbital period. We identify 13 Be stars with short-term variability. We determine their period(s) and find that 9 Be stars are multiperiodic.Comment: english not yet corrected, 23 pages, 4th article about the study in the LMC NGC2004 and SMC NGC33

Analysis of the circumstellar environment of the B[e] star HD 45677 (FS CMa)

We studied the circumstellar environment of the B[e] star HD 45677 through the analysis of the emission lines from ionized metals. We used the statistical approach of the self absorption curve method (SAC) to derive physical parameters of the line emitting region. The Fe II and Cr II double-peaked emission line structure is explained by the presence of a thin absorption component red shifted by ~3 km/s. This absorption component can be interpreted geometricaly as being due to infalling material perpendicularly to the disk seen nearly pole-on, as indicated by the emission line structure. The Cr II and Fe II emission lines have a complex structure with two (narrow and broad) components, of 45 and 180 km/s FWHM for the permitted lines and 25 and 100 km/s FWHM for the forbidden ones, respectively. We argue that the narrow components are principaly emitted by an optically thin disk seen nearly pole-on, in a region whose minimum radius is estimated to be 4 10^12 cm, while the broad ones are formed in a disk-linked wind.Comment: 14 pages, submitted to Astronomy and Astrophysic

A GLIMPSE into the Nature of Galactic Mid-IR Excesses

We investigate the nature of the mid-IR excess for 31 intermediate-mass stars that exhibit an 8 micron excess in either the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire or the Mid-Course Space Experiment using high resolution optical spectra to identify stars surrounded by warm circumstellar dust. From these data we determine projected stellar rotational velocities and estimate stellar effective temperatures for the sample. We estimate stellar ages from these temperatures, parallactic distances, and evolutionary models. Using MIPS [24] measurements and stellar parameters we determine the nature of the infrared excess for 19 GLIMPSE stars. We find that 15 stars exhibit Halpha emission and four exhibit Halpha absorption. Assuming that the mid-IR excesses arise in circumstellar disks, we use the Halpha fluxes to model and estimate the relative contributions of dust and free-free emission. Six stars exhibit Halpha fluxes that imply free-free emission can plausibly explain the infrared excess at [24]. These stars are candidate classical Be stars. Nine stars exhibit Halpha emission, but their Halpha fluxes are insufficient to explain the infrared excesses at [24], suggesting the presence of a circumstellar dust component. After the removal of the free-free component in these sources, we determine probable disk dust temperatures of Tdisk~300-800 K and fractional infrared luminosities of L(IR)/L(*)~10^-3. These nine stars may be pre-main-sequence stars with transitional disks undergoing disk clearing. Three of the four sources showing Halpha absorption exhibit circumstellar disk temperatures ~300-400 K, L(IR)/L(*)~10^-3, IR colors K-[24]< 3.3, and are warm debris disk candidates. One of the four Halpha absorption sources has K-[24]> 3.3 implying an optically thick outer disk and is a transition disk candidate.Comment: 17 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 local stellar population of nova regions in the Large Magellanic Cloud

This study aims at identifying and understanding the parent population of novae in the Large Magellanic Cloud (LMC) by studying the local, projected, stellar population. The star formation history of the local environment around novae is studied based on photometric data of stars and star clusters in the nova neighbourhood, available in the OGLE II survey and star cluster catalogues. The ages of stellar population within a few arcmin around novae regions are estimated using isochrone fits to the V vs (V-I) colour-magnitude diagrams. The fraction of stars in various evolutionary states are compared using luminosity functions of the main-sequence stars and the red giant stars. The age, density and luminosity function of the stellar population are estimated around 15 novae. The upper limit of the age of the intermediate stellar population is found to be 4 Gyr in all the regions, excepting the region around the slow nova LMC 1948. Star formation in these regions is found to have started between 4 - 2.0 Gyr, with a majority of the regions starting the star formation at 3.2 Gyr. This star formation event lasted until 1.6 - 0.8 Gyr The star formation history of the underlying population of both the fast and moderately fast novae indicate their parent population to be similar and likely to be in the age range 3.2 - 1.0 Gyr. This is in good agreement with the theoretical age estimates for Galactic cataclysmic variables. The region around the slow nova shows a stellar population in the age range 1 - 10 Gyr, with a good fraction belonging to an older population, consistent with the idea that the progenitors of slow novae belong to older population.Comment: to appear in A&A (final version - error analysis included, typos corrected, figures 17 and 18 changed

Photometric Observations of Three High Mass X-Ray Binaries and a Search for Variations Induced by Orbital Motion

We searched for long period variation in V-band, Ic-band and RXTE X-ray light curves of the High Mass X-ray Binaries (HMXBs) LS 1698 / RX J1037.5-5647, HD 110432 / 1H 1249-637 and HD 161103 / RX J1744.7-2713 in an attempt to discover orbitally induced variation. Data were obtained primarily from the ASAS database and were supplemented by shorter term observations made with the 24- and 40-inch ANU telescopes and one of the robotic PROMPT telescopes. Fourier periodograms suggested the existence of long period variation in the V-band light curves of all three HMXBs, however folding the data at those periods did not reveal convincing periodic variation. At this point we cannot rule out the existence of long term V-band variation for these three sources and hints of longer term variation may be seen in the higher precision PROMPT data. Long term V-band observations, on the order of several years, taken at a frequency of at least once per week and with a precision of 0.01 mag, therefore still have a chance of revealing long term variation in these three HMXBs.Comment: Accepted, RAA, May, 201

VdBH 222: a starburst cluster in the inner Milky Way

Context. It has been suggested that the compact open cluster VdBH 222 is a young massive distant object.Aims. We set out to characterise VdBH 222 using a comprehensive set of multi-wavelength observations.Methods.We obtained multi-band optical (UBVR) and near-infrared (JHKS) photometry of the cluster field, as well as multi-object and long-slit optical spectroscopy for a large sample of stars in the field. We applied classical photometric analysis, as well as more sophisticated methods using the CHORIZOS code, to determine the reddening to the cluster. We then plotted dereddened HR diagrams and determined cluster parameters via isochrone fitting.Results. We have identified a large population of luminous supergiants confirmed as cluster members via radial velocity measurements. We find nine red supergiants (plus one other candidate) and two yellow supergiants. We also identify a large population of OB stars. Ten of them are bright enough to be blue supergiants. The cluster lies behind ≈7.5 mag of extinction for the preferred value of RV = 2.9. Isochrone fitting allows for a narrow range of ages between 12 and 16 Ma. The cluster radial velocity is compatible with distances of ~6 and ~10 kpc. The shorter distance is inconsistent with the age range and Galactic structure. The longer distance implies an age ≈ 12 Ma and a location not far from the position where some Galactic models place the far end of the Galactic bar.Conclusions. VdBH 222 is a young massive cluster with a likely mass >20 000 M⊙. Its population of massive evolved stars is comparable to that of large associations, such as Per OB1. Its location in the inner Galaxy, presumably close to the end of the Galactic bar, adds to the increasing evidence for vigorous star formation in the inner regions of the Milky Way

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