Investigations of HeII Ly{alpha} (304{AA} rest-frame) absorption toward a half-dozen quasars at z~3-4 have demonstrated the great potential of helium studies of the intergalactic medium, but the current critically small sample size of clean sightlines for the HeII Gunn-Peterson test limits confidence in cosmological inferences, and a larger sample is required. Although the unobscured quasar sightlines to high redshift are extremely rare, the Sloan Digital Sky Survey (SDSS) DR6 provides thousands of z>2.8 quasars. We have cross-correlated these SDSS quasars with the Galaxy Evolution Explorer (GALEX) GR2/GR3 to establish a catalog of 200 higher-confidence (~70% secure) cases of quasars at z=2.8-5.1 potentially having surviving far-UV (rest-frame) flux. We also catalog another 112 likely far-UV-bright quasars from GALEX cross-correlation with other (non-SDSS) quasar compilations. Reconnaissance UV prism observations with the Hubble Space Telescope (HST) of 24 of our SDSS/GALEX candidates confirm 12 as detected in the far-UV, with at least nine having flux extending to very near the HeII break; with refinements our success rate is even higher. Our SDSS/GALEX selection approach is thereby confirmed to be an order of magnitude more efficient than previous HeII quasar searches, more than doubles the number of spectroscopically confirmed clean sightlines to high redshift, and provides a resource list of hundreds of high-confidence sightlines for upcoming HeII and other far-UV studies from the HST. Our reconnaissance HST prism spectra suggest some far-UV diversity, confirming the need to obtain a large sample of independent quasar sightlines across a broad redshift range to assess such issues as the epoch(s) of helium reionization, while averaging over individual-object pathology and/or cosmic variance.
Absorption along quasar sightlines remains among the most sensitive direct measures of HeII reionization in much of the intergalactic medium (IGM). Until recently, fewer than a half-dozen unobscured quasar sightlines suitable for the HeII Gunn-Peterson test were known; although these handful demonstrated great promise, the small sample size limited confidence in cosmological inferences. We have recently added nine more such clean HeII quasars, exploiting Sloan Digital Sky Survey (SDSS) quasar samples, broadband ultraviolet (UV) imaging from Galaxy Evolution Explorer (GALEX), and high-yield UV spectroscopic confirmations from Hubble Space Telescope (HST). Here we markedly expand this approach by cross-correlating SDSS DR7 and GALEX GR4+5 to catalog 428 SDSS and 165 other quasars with z>2.78 having likely (~70%) GALEX detections, suggesting they are bright into the far-UV. Reconnaissance HST Cycle 16 Supplemental prism data for 29 of these new quasar-GALEX matches spectroscopically confirm 17 as indeed far-UV bright. At least 10 of these confirmations have clean sightlines all the way down to HeII Ly{alpha}, substantially expanding the number of known clean HeII quasars, and reaffirming the order of magnitude enhanced efficiency of our selection technique. Combined confirmations from this and our past programs yield more than 20 HeII quasars, quintupling the sample. These provide substantial progress toward a sample of HeII quasar sightlines large enough, and spanning a sufficient redshift range, to enable statistical IGM studies that may avoid individual object peculiarity and sightline variance. Our expanded catalog of hundreds of high-likelihood far-UV-bright QSOs additionally will be useful for understanding the extreme-UV properties of the quasars themselves.
This table contains data from the first data release (DR1) from the UV-bright Quasar Survey (UVQS) for new z ~ 1 active galactic nuclei (AGN) across the sky. Using simple GALEX UV and WISE near-IR color selection criteria, the authors generated a list of 1,450 primary candidates with FUV < 18.5 mag, that is contained in the HEASARC table (entries with source_sample = 'P'). They obtained discovery spectra, primarily on 3m-class telescopes, for 1,040 of these candidates and confirmed 86% as AGN, with redshifts generally at z > 0.5. Including a small set of observed secondary candidates, the authors report the discovery of 217 AGN with GALEX FUV magnitudes < 18 mag that previously had no reported spectroscopic redshifts. These are excellent potential targets for UV spectroscopy before the end of the Hubble Space Telescope mission. The main data products of UVQS are publicly available through the Mikulski Archive for Space Telescopes (MAST). The authors have performed an all-sky survey for z ~ 1, FUV-bright quasars selected from GALEX and WISE photometry. In several of the observing runs, conditions were unexpectedly favorable and we exhausted the primary candidates at certain right ascension ranges. To fill the remaining observing time, they generated a secondary candidate list. This secondary set of 2,010 candidates is also contained in this HEASARC table (entries with source_sample = 'S'). The authors proceeded to obtain discovery-quality long-slit spectra (i.e., low-dispersion, large-wavelength coverage, modest signal-to-noise ratio (S/N) of their UV-bright Quasar Survey (UVQS) candidates in one calendar year. The principal facilities were: (i) the dual Kast spectrometer on the 3m Shane telescope at the Lick Observatory; (ii) the Boller & Chivens (BCS) spectrometer on the Irenee du Pont 100-inch telescope at the Las Campanas Observatory; and (iii) the Calar Alto Faint Object Spectrograph on the CAHA 2.2-meter telescope at the Calar Alto Observatory (CAHA). They acquired an additional ~20 spectra on larger aperture telescopes (Keck/ESI, MMT/MBC, Magellan/MagE) during twilight or under poor observing conditions. Typical exposure times were limited to < ~200s, with adjustments for fainter sources or sub-optimal observing conditions. Table 3 in the reference paper provides a list of the details of the observations of these candidates. From the total candidates list of 3,460 objects, the authors measured high-quality redshifts (redshift quality flag values of 3 or greater) for 1,121 sources. They assumed that every source with a recessional velocity v<sub>r</sub> = z * c < 500 km s<sup>-1</sup> was "Galactic", which they associate with the Galaxy and members of the Local Group. This included sources where the eigenspectra fits were poor yet a low v<sub>r</sub> was indisputable (e.g., stars). Many of these were assigned z = 0 exactly. The remainder of the UVQS sources were assumed to be extragalactic AGN, and the derived redshift information for these sources (which was given in Table 4 of the reference paper) has been incorporated into this HEASARC representation of UVQS. Finally, there were 93 sources with good-quality spectra for which we cannot the authors could not recover a secure redshift. The majority of these have been previously cataloged as blazars (or BL Lac objects). Table 6 in the reference paper lists the sample of these unknown or insecure redshift objects. This table was created by the HEASARC in April 2017 based upon the <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/AJ/152/25">CDS Catalog J/AJ/152/25</a> files table1.dat, table2.dat, and table4.dat. This is a service provided by NASA HEASARC .
We have performed a wide-area ultraviolet (UV) imaging survey using the GALaxy Evolution eXplorer to search for bright, point-like UV sources behind M31's extended halo. Our survey consisted of 46 pointings covering an effective area of ~50deg^2^, in both the far-UV and near-UV channels. We combined these data with optical R-band observations acquired with the WIYN Mosaic-1 imager on the Kitt Peak National Observatory 0.9-m WIYN telescope. An analysis of the brightness and colours of sources matched between our photometric catalogues yielded ~100 UV-bright quasar candidates. We have obtained discovery spectra for 76 of these targets with the Kast spectrometer on the Lick 3-m telescope and confirmed 30 active galactic nuclei and quasars, 29 galaxies at z>0.02 including several early-type systems, 16 Galactic stars (hot main-sequence stars) and one featureless source previously identified as a BL Lac object. Future UV spectroscopy of the brightest targets with the Cosmic Origins Spectrograph on the Hubble Space Telescope will enable a systematic search for diffuse gas in the extended halo of M31.
This catalogue contains observations carried out by the S2/68 Ultraviolet Sky Survey Telescope (UVSST) aboard the ESRO Satellite TD-1, which measured the absolute ultraviolet flux distribution between 2740A (274nm) and 1350A (135nm). The data presented in this catalogue were obtained during the first observation period, which lasted from 19 March 1972 to 31 October 1972, and contains the brightest objects, for which the signal is good enough to give valuable spectrophotometric information. The Faint Star Catalogue, which contains the photometric data of the stars up to the limit of detectability of the instrument, is known as the "Catalogue of Ultraviolet Fluxes", by Thompson et al. (catalog <II/59>) The S2/68 experiment has been described by Boksenberg et al. (=1973MNRAS.163..291B) and the absolute calibration by Humphries et al. (=1976A&A....49..389H).
This catalogue is a supplement of the Ultraviolet Bright Star Spectrophotometric Catalogue (=III/39A). It contains observations carried out by the S2/68 Ultraviolet Sky Survey Telescope (UVSST) aboard the ESRO satellite TD-1. The data presented in this supplement were obtained during the second and third observation periods, which lasted from 19 February 1973 to 30 September 1973 and from 16 February to 6 May 1974. The S2/68 experiment has been described by Boksenberg et al. (=1973MNRAS.163..291B) Owing to the optical scanning mode, most of the stars observed during the first observational period, the spectra of which are included in the "Ultraviolet Bright-Star Spectrophotometric Catalogue", were seen again by the telescope. This supplement, however, has been limited to the spectra of stars that were not observed during the first period. The data reduction and selection criteria are identical to those underlying the main Catalogue and hence the data presented in the Supplement are directly comparable with those in the main Catalogue. The Supplement contains data for 435 stars. For a statistical summary of the observed stars, see the tables I and II in the published version of the Supplement. The spectrum scanning itself was achieved by the movement of a star image across the wide entrance slot of the spectrophotometer, which caused the corresponding spectrum image to pass over the three exit slits in the direction of dispersion. The motion of the primary image during each detector integration interval (0.148 s) was equivalent to 19.4 A, depending on the channel. The wavelength range covered was 1350 - 2550 A. The passband of the photometer channel, defined by a glass transmission filter and the photocathode tube response, was centered at 2740 A and had a full width at half height of 310 A.
Photometric UBVri observations of the symbiotic star AG Dra in Piwnice Observatory, Torun, Poland, are presented in tables 2 and 3. The 60cm telescope and a single-channel photoelectric photometer have been used. Table 2 lists observations with the EMI9558B photomultiplier tube from March 1996 to September 1999. Table 3 lists observations with the cooled C31034 photomultiplier tube from October 2001 to May 2003. Table 4 lists equivalent widths (EW) of the four emission lines in the spectrum of AG Dra: The Raman scattered line at 6825{AA}, H{alpha}, H{beta} and He II 4686{AA}. The spectroscopic observations have been performed in Tartu Observatory, Estonia, using the 1.5m telescope and a Cassegrain spectrograph. The time interval extends from September 1997 to March 2003.
This catalogue is an updated version of the one published in 1990 (Hauck and Mermilliod, 1990) and contains data for more than 63,300 stars in the Galaxy and Magellanic Clouds. In a first table, we present the catalogue itself, giving for each star identifications, coordinates (B1950), visual magnitude, and the mean value of the photoelectric data concerning the star and the data sources. In the second table, we give for each star, the individual measurements. These measurements from which these values were computed were collected from observations published until the middle of 1996. The catalogue includes 533 references.
Accurate standard uvby indices are presented for 73 southern B, A, F and G stars in the V magnitude range 8.2 to 10.9. They cover all three transformation regions of the uvby system (Olsen 1983A&AS...54...55O) well. Standard {beta} indices are included for the 55 B, A, and F stars in the sample. Our results provide a useful set of secondary standards for uvby {beta} CCD photometry with southern hemisphere 1-2m class telescopes. A critical comparison with published photometry, in general based on fewer observations, is given.
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