J/MNRAS/465/1807    Deep OB star population in Carina        (Mohr-Smith+, 2017)
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Beginning of ReadMe : J/MNRAS/465/1807 Deep OB star population in Carina (Mohr-Smith+, 2017) ================================================================================ The deep OB star population in Carina from the VST Photometric H-alpha Survey (VPHAS+). Mohr-Smith M., Drew J.E., Napiwotzki R., Simon-Diaz S., Wright N.J., Barentsen G., Eisloeffel J., Farnhill H. J., Greimel R., Monguio M., Kalari V., Parker Q.A., Vink J.S. <Mon. Not. R. Astron. Soc. 465, 1807 (2017)> =2017MNRAS.465.1807M (SIMBAD/NED BibCode) ================================================================================ ADC_Keywords: Galactic plane ; Stars, early-type ; Photometry, SDSS ; Photometry, H-alpha ; Reddening Keywords: surveys - stars: early-type - dust, extinction - Galaxy: disc - open clusters and associations: general Abstract: Massive OB stars are critical to the ecology of galaxies, and yet our knowledge of OB stars in the Milky Way, fainter than V 12, remains patchy. Data from the VST Photometric H-alpha Survey (VPHAS+) permit the construction of the first deep catalogues of blue excess-selected OB stars, without neglecting the stellar field. A total of 14900 candidates with 2MASS cross-matches are blue-selected from a 42 square-degree region in the Galactic longitude range 282deg<l<293deg Spectral energy distribution fitting is performed on these candidates' combined VPHAS+ u/g/r/i and 2MASS J/H/K magnitudes. This delivers: effective temperature constraints, statistically separating O from early-B stars; high-quality extinction parameters, A_0_ and R_V_ (random errors typically <0.1). The high confidence O-B2 candidates number 5915 and a further 5170 fit to later B spectral type. Spectroscopy of 276 of the former confirms 97% of them. The fraction of emission line stars among all candidate B stars is 7-8%. Greyer (R_V_>3.5) extinction laws are ubiquitous in the region, over the distance range 2.5-3kpc to  10kpc. Near prominent massive clusters, R_V_ tends to rise, with particularly large and chaotic excursions to R_V_ 5 seen in the Carina Nebula. The data reveal a hitherto unnoticed association of 108 O-B2 stars around the O5If+ star LSS 2063 (l=289.77deg, b=-1.22deg). Treating the OB star scale-height as a constant within the thin disk, we find an orderly mean relation between extinction (A_0_) and distance in the Galactic longitude range, 287.6deg<l< 293.5deg, and infer the subtle onset of thin-disk warping. A halo around NGC 3603, roughly a degree in diameter, of  500 O-B2 stars with 4<A_0_(mag)<7 is noted. Description: The sky positions and photometric measurements from VPHAS+ (and 2MASS) for 14900 candidate OB stars blue-selected from the Carina region of the Galactic plane are set out in the first 24 columns. The optical magnitudes are expressed in the Vega system. These are followed by the parameters and their error estimates obtained from main-sequence fits to the optical/NIR magnitudes, along with the chi-squared measure of goodness of fit (columns 25 to 33). For the 3 degrees of freedom involved, chi-squared values up to 7.82 may be regarded as 'good fits': 5915 objects are good fits in this sense and have estimated effective temperatures high enough to place them into the O-B2 range. The fitting process delivers effective temperatures, (highly uncertain) distance moduli, and the extinction parameters, A_0_ and R_V_. Subsequent columns (34 to 37) identify which candidates are: good O-B2 fits; likely to be emission line stars (based on r-Halpha excess); candidate sub-luminous stars; candidate higher-luminosity evolved objects. The 'Notes' in column 38 provide information on cross-identifications to known objects, where these exist. Columns 39 to 49 present spectroscopically-derived parameters and associated errors for the subset of 276 stars with spectra.