OpenNGC is a database containing positions and main data of NGC (New
General Catalogue) and IC (Index Catalogue) objects. It has been built
by merging data from NED, HyperLEDA, SIMBAD, and several databases
available at HEASARC.
In this VO publication, we have changed most of the column names,
mostly to make them work as ADQL column names without resorting to
delimited identifiers. The mapping should be obvious.
The results are reported of an objective-prism survey of stars, mostly earlier than spectral type F5, for two fields at (l;b) = (90 deg and 270 deg; -45 deg). The fields, each of approximately 70 square degrees, are examined on plates taken with the Schmidt Telescope of the Anglo-Australian Observatory. The brightness range of the stars classified is 10 < V < 15. The prism combination used provides a dispersion of 600 A/mm at Hgamma. The spectral classification presented is defined by the equality of equivalent widths of Ca II K and Hdelta at type "F0" and the absence of Ca II K in stars with significant Balmer lines at type "A0". Positions listed in the catalog were measured on the Stromlo PDS microdensitometer. Most stars were subsequently identified with objects in the ST ScI-NASA-ESO Hubble Space Telescope Guide Star Catalog in which positions have an accuracy of near +/- 1.0 arcsec.
We have carefully selected a sample of 60 galaxies that reside in the deepest underdensities of geometrically identified voids within the Sloan Digital Sky Survey. HI imaging of 55 galaxies with the Westerbork Synthesis Radio Telescope reveals morphological and kinematic signatures of ongoing interactions and gas accretion. We probe a total volume of 485Mpc^3^ within the voids, with an angular resolution of 8kpc at an average distance of 85Mpc. We reach column density sensitivities of 5x10^19^/cm^-2^, corresponding to an HI mass limit of 3x10^8^M_{sun}_. We detect HI in 41 galaxies, with total masses ranging from 1.7x10^8^ to 5.5x10^9^M_{sun}_. The upper limits on the 14 non-detections are not inconsistent with their luminosities, given their expected HI mass-to-light ratios. We find that the void galaxies are generally gas-rich, low-luminosity, blue disk galaxies, with optical and HI properties that are not unusual for their luminosity and morphology. The sample spans a range of absolute magnitudes (-16.1>M_r_>-20.4) and colors (0.06<g-r<0.87), and includes disk and irregular galaxies. We also identify three as early-type galaxies, all of which are not detected in HI. All galaxies have stellar masses less than 3x10^10^M_{sun}_, and many have kinematic and morphological signs of ongoing gas accretion, suggesting that the void galaxy population is still in the process of assembling. The small-scale clustering in the void, within 600kpc and 200km/s, is similar to that in higher density regions, and we identify 18 HI-rich neighboring galaxies in the voids. Most are within 100kpc and 100km/s of the targeted galaxy, and we find no significant population of HI-rich low-luminosity galaxies filling the voids, contrary to what is predicted by simulations.
We present the source catalog and the properties of the B-, R-, and I-band images obtained to support the AKARI North Ecliptic Pole Wide (NEP-Wide) survey. The NEP-Wide is an AKARI infrared imaging survey of the north ecliptic pole covering a 5.8deg^2^ area over 2.5-6um wavelengths. The optical imaging data were obtained at the Maidanak Observatory in Uzbekistan using the Seoul National University 4kx4k Camera on the 1.5m telescope. These images cover 4.9deg^2^ where no deep optical imaging data are available. Our B-, R-, and I-band data reach the depths of ~23.4, ~23.1, and ~22.3mag(AB) at 5{sigma}, respectively. The source catalog contains 96460 objects in the R band, and the astrometric accuracy is about 0.15" at 1{sigma} in each RA and DEC direction. These photometric data will be useful for many studies including identification of optical counterparts of the infrared sources detected by AKARI, analysis of their spectral energy distributions from optical through infrared, and the selection of interesting objects to understand the obscured galaxy evolution.
We present optical light curves of variable stars consistent with the positions of X-ray sources identified with the Chandra X-ray Observatory for the Chandra Galactic Bulge Survey (GBS). Using data from the Mosaic-II instrument on the Blanco 4m Telescope at CTIO, we gathered time-resolved photometric data on timescales from ~2hr to 8 days over the 3/4 of the X-ray survey containing sources from the initial GBS catalog. Among the light curve morphologies we identify are flickering in interacting binaries, eclipsing sources, dwarf nova outbursts, ellipsoidal variations, long period variables, spotted stars, and flare stars. Eighty-seven percent of X-ray sources have at least one potential optical counterpart. Twenty-seven percent of these candidate counterparts are detectably variable; a much greater fraction than expected for randomly selected field stars, which suggests that most of these variables are real counterparts. We discuss individual sources of interest, provide variability information on candidate counterparts, and discuss the characteristics of the variable population.
We present optical spectroscopic identifications of X-ray sources in ~3deg^2^ of the XMM-Large Scale Structure survey (XMM-LSS), also covered by the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS), obtained with the AAOmega instrument at the Anglo-Australian Telescope. In a flux-limited sample of 829 point-like sources in the optical band with g'<=22mag and the 0.5-2keV flux (f_0.5-2keV_)>10^-15^erg/cm^2^/s, we observed 693 objects and obtained reliable spectroscopic identification for 487 sources, approximately 59 per cent of the overall sample.
We present optical candidates for 75 X-ray sources in a 1deg^2^ overlapping region with the 1997 medium-deep ROSAT survey by Molthagen et al. (1996, Cat. <J/A+AS/126/509>). These candidates are selected using the multicolor CCD imaging observations made for the T329 field of the Beijing-Arizona-Taiwan-Connecticut (BATC) Sky Survey, which uses the NAOC 0.6/0.9m Schmidt telescope with 15 intermediate-band filters covering the wavelength range 3360-9745{AA}. These X-ray sources are relatively faint (CR<<0.2ct/s) and thus are mostly not included in the ROSAT Bright Source Catalogue; they also remain as X-ray sources without optical candidates in a previous identification program carried out by the Hamburg Quasar Survey (1998, <J/A+AS/128/507> and 1999, <J/A+AS/134/483>).
The Spitzer Survey for Stellar Structure in Galaxies (S4G) and its more recently approved extension will lead to a set of 3.6 and 4.5um images for 2829 galaxies, which can be used to study many different aspects of the structure and evolution of local galaxies. We have collected and re-reduced optical images of 1768 of the survey galaxies, aiming to make these available to the community as ready-to-use FITS files to be used in conjunction with the mid-IR images. Our sky-subtraction and mosaicking procedures were optimised for imaging large galaxies. We also produce false-colour images of some of these galaxies to be used for illustrative and public outreach purposes. We collected and re-processed images in five bands from the Sloan Digital Sky Survey for 1657 galaxies.
Future space-borne astrometry missions, such as Gaia, will be able to determine the optical positions of hundreds of quasars with submilliarcsecond accuracies comparable to those achieved in radio by very long baseline interferometry (VLBI). Comparisons of coordinate systems from space-borne missions and VLBI will be very important, first for investigations of possible systematic errors and second for investigations of possible shifts between centroids of radio and optical emissions in active galactic nuclei. In order to make such a comparison more robust, a program for densification of the grid of radio sources detectable with both VLBI and Gaia was launched in 2006. Program sources are 398 quasars with declinations >-10{deg} that are brighter than 18mag at the V band. The first two observing campaigns were run in 2007-2008. In the third campaign, a set of 291 objects from that list was observed with the VLBA+EVN in 2010-2011 with the primary goal of producing their images with milliarcsecond resolution. In this paper, following the method of absolute astrometry, coordinates of observed sources have been derived with milliarcsecond accuracies from analysis of these observations. The catalog of positions of 295 target sources, estimates of their correlated flux densities at 2.2 and 8.4GHz, and their images are presented. The accuracies of source coordinates are in a range of 2-200mas, with a median of 3.2mas.
This catalog presents a sample of 229236 optically variable quasar candidates identified in the AllWISE and Pan-STARRS1 data releases at 2-sigma and 3-sigma variability levels. Mid-IR bands (3.4, 4.6, 12 and 22um) are selected from the AllWISE data release, and 5 optical bands (grizy) are from Pan-STARRS1. 127350 quasars are found to be variable at the 3-sigma level.
