We present the second public data release of the VISTA EXtension to Auxiliary Surveys (VEXAS DR2), where we classify objects into stars, galaxies and quasars based on an ensemble of machine learning algorithms. The aim of VEXAS is to build the widest multi-wavelength catalogue, providing reference magnitudes, colours and morphological information for a large number of scientific uses. We apply an ensemble of thirty-two different machine learning models, based on three different algorithms and on different magnitude sets, training samples and classification problems (two or three classes) on the three VEXAS Data Release 1 (DR1) optical+infrared (IR) tables. The tables were created in DR1 cross-matching VISTA near-infrared data with Wide-field Infrared Survey Explorer far-infrared data and with optical magnitudes from the Dark Energy Survey (VEXAS-DESW), the Sky Mapper Survey (VEXAS-SMW), and the Panoramic Survey Telescope and Rapid Response System Survey (VEXAS-PSW). We assemble a large table of spectroscopically confirmed objects (VEXAS-SPEC-GOOD, 415 628 unique objects), based on the combination of six different spectroscopic surveys that we use for training. We develop feature imputation to classify also objects for which magnitudes in one or more bands are missing. We classify in total 90106 objects in the Southern Hemisphere. Among these, ~62.9x10^6^ (~52.6x10^6^) are classified as 'high confidence' ('secure') stars, ~920000 (~750000) as 'high confidence' ('secure') quasars and ~34.8 (~34.1) millions as 'high confidence' ('secure') galaxies, with pclass>=0.7 (pclass>=0.9). The DR2 tables update the DR1 with the addition of imputed magnitudes and membership probabilities to each of the three classes. The density of high-confidence extragalactic objects varies strongly with the survey depth: at pclass>0.7; there are 111/deg^2^ quasars in the VEXAS-DESW footprint and 103/deg^2^ in the VEXAS-PSW footprint, while only 10.7/deg^2^ in the VEXASSM footprint. Improved depth in the midIR and coverage in the optical and nearIR are needed for the SM footprint that is not already covered by DESW and PSW.
We present spectral classifications for 438 B-type stars observed as part of the VLT-FLAMES Tarantula Survey (VFTS) in the 30 Doradus region of the Large Magellanic Cloud. Radial velocities are provided for 307 apparently single stars, and for 99 targets with radial-velocity variations which are consistent with them being spectroscopic binaries. We investigate the spatial distribution of the radial velocities across the 30 Dor region, and use the results to identify candidate runaway stars. Excluding potential runaways and members of two older clusters in the survey region (SL639 and Hodge301), we determine a systemic velocity for 30 Dor of 271.6+/-12.2km/s from 273 presumed single stars. Employing a 3{sigma} criterion we identify nine candidate runaway stars (2.9% of the single stars with radial-velocity estimates). The projected rotational velocities of the candidate runaways appear to be significantly different to those of the full B-type sample, with a strong preference for either large (>=345km/s) or small (<=65km/s) rotational velocities. Of the candidate runaways, VFTS358 (classified B0.5: V) has the largest differential radial velocity (-106.9+/-16.2km/s), and a preliminary atmospheric analysis finds a significantly enriched nitrogen abundance of 12+log(N/H)> 8.5. Combined with a large rotational velocity (v_e_sini=345+/-22km/s), this is suggestive of past binary interaction for this star.
Detailed spectral classifications are presented for 352 O-B0 stars in the VLT-FLAMES Tarantula Survey ESO Large Programme, of which 213 O-type are judged of sufficiently high quality for further morphological analysis. Among them, six subcategories of special interest are distinguished. (1) Several new examples of the earliest spectral types O2-O3 have been found, while a previously known example has been determined to belong to the nitrogen-rich ON2 class. (2) A group of extremely rapidly rotating main-sequence objects has been isolated, including the largest vsini values known, the spatial and radial-velocity distributions of which suggest ejection from the two principal ionizing clusters NGC 2070 and NGC 2060. (3) Several new examples of the evolved, rapidly rotating Onfp class show similar evidence, although at least some of them are spectroscopic binaries. (4) No fewer than 48 members of the Vz category, hypothesized to be on or near the zero-age main sequence, are found in this sample; in contrast to the rapid rotators, they are strongly concentrated to the ionizing clusters and a newly recognized region of current and recent star formation to the north, supporting their interpretation as very young objects, as do their relatively faint absolute magnitudes. (5) A surprisingly large fraction of the main-sequence spectra belong to the recently recognized V((fc)) class, with CIII emission lines of similar strength to the usual NIII in V((f)) spectra, although a comparable number of the latter are also present, as well as six objects with very high-quality data but no trace of either emission feature, presenting new challenges to physical interpretations. (6) Two mid-O Vz and three late-O giant/supergiant spectra with morphologically enhanced nitrogen lines have been detected. Absolute visual magnitudes have been derived for each star with individual extinction laws, and composite Hertzsprung-Russell diagrams provide evidence of the multiple generations present in this field. Spectroscopic binaries, resolved visual multiples, and possible associations with X-ray sources are noted. Astrophysical and dynamical analyses of this unique dataset underway will provide new insights into the evolution of massive stars and starburst clusters.
OVz stars, a subclass of O-type dwarfs characterized by having HeII{lambda}4686 stronger in absorption than any other helium line in their blue-violet spectra, have been suggested to be on or near the zero-age main sequence (ZAMS). If their youth were confirmed, they would be key objects with which to advance our knowledge of the physical properties of massive stars in the early stages of their lives. We test the hypothesis of OVz stars being at a different (younger) evolutionary stage than are normal O-type dwarfs. We have performed the first comprehensive quantitative spectroscopic analysis of a statistically meaningful sample of OVz and OV stars in the same star-forming region, exploiting the large number of OVz stars identified by the VLT-FLAMES Tarantula Survey in the 30 Doradus region of the Large Magellanic Cloud (LMC). We obtained the stellar and wind parameters of 38 OVz stars (and a control sample of 46 OV stars) using the FASTWIND stellar atmosphere code and the IACOB-GBAT, a grid-based tool developed for automated quantitative analysis of optical spectra of O stars. In the framework of a differential study, we compared the physical and evolutionary properties of both samples, locating the stars in the logg vs. logT_eff_, logQ vs. logT_eff_, and logL/L_{sun}_ vs. logT_eff_ diagrams. We also investigated the predictions of the FASTWIND code regarding the OVz phenomenon.
We present a catalog of the 48 Voronoi Galaxy Cluster Finder (VGCF) cluster detections. We provide a cluster ID, signal to noise ratios (SNR) in the B, V, R and I bands, positions, angular radius of the cluster, photometric redshift estimates (derived from color-magnitude diagrams (CMD)) and PDCS redshift estimate (Postman et al., 1996AJ....111..615P), if available. Table 5 contains cluster detections in F0028+0515, F0027+0555, F0228+0115 and F0226+0026 fields and other two regions that overlap PDCS 0h and 2h fields.
V-band CCD observations of the cataclysmic variable V795 Her obtained between 2008 and 2010. The observing run on a given night consisted of a dense series of V-band images (exposure time of 20 seconds). Heliocentric Julian Date of each CCD image is given for the center of the exposure. A typical standard deviation of a single measurement of the magnitude of V795 Her on a given CCD frame was about 0.01 mag. GSC 02595-00575 (GSC2.3 N3JJ000148) was used as the comparison star (abbreviated as C) while GSC 02595-00718 served as the check star (abbreviated as C1).
The results of a study of the integrated brightness of the SU UMa eclipsing binary V1239 Her are presented. The system was monitored on nine nights in 2013-2014 when the binary was in quiescence. The orbital period is refined (P_orb_=0.100082222(2)d) and the system's light curves obtained. These curves provide evidence for active processes in the system between outbursts: the depths of both minima and the amplitude of the pre-eclipse hump vary, and one of the light curves exhibits no hump at all. The parameters of the accretion disk, hot spot, and gas stream in V1239 Her for several epochs are determined in a "combined" model taking into account the contributions to the total radiation flux from the opaque part of the gas stream and the hot spot on the lateral surface of the disk.
V446 Her is the best example of an old nova which has developed dwarf nova (DN) eruptions in the post-nova state. We report on observed properties of the long-term light curve of V446 Her, using photometry over 19 years.
We present new CCD photometric observations of V1044 Her obtained on May 22, 23 and 24, 2015. From our data, we derived five new light curve minimum times. Combining our new results with previously available CCD light minimum times, we derived an updated ephemeris and discovered that the period of this binary system exhibits an oscillation. The cyclic variation may be caused by the light-time effect via the presence of a third body or magnetic activity cycle. We calculated the corresponding period of the third body to be 14.1+/-1.4 years or magnetic cycle to be 12.2+/-0.7 years. We analyzed our new asymmetric light curves to obtain photometric solutions and starspot parameters using the Wilson and Devinney program. The final results show that V1044 Her is a contact binary system with a degree of contact factor f=3.220(+/-0.002)%.
Charge-coupled device (CCD) photometry in the Johnson V, Kron-Cousins I and Washington CMT1 systems is presented in the field of the poorly known open cluster NGC 2627.
