Juan Fabregat

The VST Photometric Hα Survey of the Southern Galactic Plane and Bulge (VPHAS

The VST Photometric HSurvey of the Southern Galactic Plane and Bulge (VPHAS+) is surveying the southern Milky Way in u,g,r,i and Hat �1 arcsec angular resolution. Its footprint spans the Galactic latitude range 5 o < b < +5 o at all longitudes south of the celestial equator. Extensions around the Galactic Centre to Galactic latitudes ±10 ◦ bring in much of the Galactic Bulge. This ESO public sur- vey, begun on 28th December 2011, reaches down to �20th magnitude (10�) and will provide single-epoch digital optical photometry for �300 million stars. The observing strategy and data pipelining is described, and an appraisal of the segmented narrow- band Hfilter in use is presented. Using model atmospheres and library spectra, we compute main-sequence (u g), (g r), (r i) and (r H�) stellar colours in the Vega system. We report on a preliminary validation of the photometry using test data obtained from two pointings overlapping the Sloan Digital Sky Survey. An example of the (u g,g r) and (r H�,r i) diagrams for a full VPHAS+ survey field is given. Attention is drawn to the opportunities for studies of compact nebulae and nebular morphologies that arise from the image quality being achieved. The value of the u band as the means to identify planetary-nebula central stars is demonstrated by the discovery of the central star of NGC 2899 in survey data. Thanks to its excellent imaging performance, the VST/OmegaCam combination used by this survey is a per- fect vehicle for automated searches for reddened early-type stars, and will allow the discovery and analysis of compact binaries, white dwarfs and transient sources.

A slitless spectroscopic survey for Hα emission-line objects in SMC clusters

Context. A fair fraction of all single early-type stars display emission lines well before their supergiant phase. Very rapid rotation is necessary for these stars to form rotationally supported decretion disks. However, it is unknown whether and which other parameters may be important. Aims. We assess the roles of metallicity and evolutionary age in the appearance of the so-called Be phenomenon. Methods. Slitless CCD spectra were obtained covering the bulk (about 3 square degrees) of the Small Magellanic Cloud. For Hα line-emission twice as strong as the ambient continuum, the survey is complete to spectral type B2/B3 on the main sequence. About 8120 spectra of 4437 stars were searched for emission lines in 84 open clusters, and 370 emission-line stars were found, among them at least 231 close to the main sequence. For 176 of them, photometry is available from the OGLE database. For comparison with a higher-metallicity environment, the Galactic sample of the photometric Hα survey by McSwain & Gies (2005, ApJS, 161, 118) was used. Results. Among early spectral sub-types, Be stars are more frequent by a factor ∼3–5 in the SMC than in the Galaxy. The distribution with spectral type is similar in both galaxies, i.e., not strongly dependent on metallicity. The fraction of Be stars does not seem to vary with local star density. The Be phenomenon mainly sets in towards the end of the main-sequence evolution (this trend may be more pronounced in the SMC); but some Be stars already form with Be-star characteristics. In small subsamples (such as single clusters), even if they appear identical, the fraction of emission-line stars can deviate drastically from the mean. Conclusions. In all probability, the fractional critical angular rotation rate, Ω/Ωc, is one of the main parameters governing the occurrence of the Be phenomenon. If the Be character is only acquired during the course of evolution, the key circumstance is the evolution of Ω/Ωc, which is not only dependent on metallicity but differently so for different mass ranges. As a result, even if the Be phenomenon is driven basically by a single parameter (namely Ω/Ωc), it can assume a complex multi-parametric appearance. The large cluster-to-cluster differences, which seem stronger than all other variations, serve as a caveat that this big picture may undergo significant second-order modulations (e.g., pulsations, initial angular momentum, etc.).

Be stars and binaries in the field of the SMC open cluster NGC 330 with VLT-FLAMES

Aims. Observations of hot stars belonging to the young cluster SMC-NGCxa0330 and its surrounding region were obtained with the VLT-GIRAFFE facilities in MEDUSA mode. We investigated the B and Bexa0star properties and proportions in this environment of low metallicity. We also searched for rapid variability in Bexa0stars using photometric databases. Methods. Using spectroscopic measurements, we characterized the emission and properties of Bexa0stars. 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 Bexa0stars. Results. We report on the global characteristics of the Bexa0star sample (131 objects). We find that the proportion of early Bexa0stars with a large equivalent width of the H α emission line is higher in the SMC than in the LMC and MW. We find a slight increase in the proportion of Bexa0stars 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 Bexa0stars with short-term variability. We determine their period(s) and find that 9 Bexa0stars are multiperiodic.

A study of the B and Be star population in the field of the LMC open cluster NGC 2004 with VLT-FLAMES

Observations of hot stars belonging to the young cluster LMC-NGC 2004 and its surrounding region have been obtained with the VLT-GIRAFFE facilities in MEDUSA mode. 25 Be stars were discovered; the proportion of Be stars compared to B-type stars is found to be of the same order in the LMC and in the Galaxy fields. 23 hot stars were discovered as spectroscopic binaries (SB1 and SB2), 5 of these are found to be eclipsing systems from the MACHO database, with periods of a few days. About 75% of the spectra in our sample are polluted by hydrogen (H

Discovery of a Transition to Global Spin-Up in EXO 2030+375

alpha

The Absolute Flux Calibration of the UVBY Photometric System

and H

Short-term variations in Be stars observed by the CoRoT and K epler space missions

gamma

Multiwaveband study of a major X‐ray outburst from the Be/X‐ray transient system A1118–616

), [S II] and [N II] nebular lines. These lines are typical of H II regions. They could be associated with patchy nebulosities with a bi-modal distribution in radial velocity, with higher values (+335 km s-1) preferentially seen inside the southern part of the known bubble LMC4 observed in H I at 21 cm.

Non-radial pulsations in the Be/X binaries 4U 0115+63 and SAX J2103.5+4545

EXO 2030+375, a 42 s transient X-ray pulsar with a Be star companion, has been observed to undergo an outburst at nearly every periastron passage for the last 13.5 years. From 1994 through 2002, the global trend in the pulsar spin frequency was spin-down. Using Rossi X-Ray Timing Explorer (RXTE) data from 2003 September, we have observed a transition to global spin-up in EXO 2030+375. Although the spin-frequency observations are sparse, the relative spin-up between 2002 June and 2003 September observations, along with an overall brightening of the outbursts since mid-2002 observed with the RXTE All-Sky Monitor, accompanied by an increase in density of the Be disk, indicated by infrared magnitudes, suggest that the pattern observed with BATSE of a roughly constant spin frequency, followed by spin-up, followed by spin-down is repeating. If so, this pattern has approximately an 11 yr period, similar to the 15 ± 3 yr period derived by Wilson et al. for the precession period of a one-armed oscillation in the Be disk. If this pattern is indeed repeating, we predict a transition from spin-up to spin-down in 2005.

The Be/X-ray transient 4U 0115+63/V635 Cassiopeiae - II. Outburst mechanisms

We present the absolute flux calibration for the uvby photometric system passbands, derived from homogeneous spectroscopic and photometric standard star lists, and referred to the Vega absolute flux calibration of Hayes (1985).