- ID:
- ivo://CDS.VizieR/J/ApJ/847/142
- Title:
- Ultra-metal-poor stars LTE and NLTE abundances
- Short Name:
- J/ApJ/847/142
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new ultra-metal-poor stars parameters with [Fe/H] < -4.0 based on line-by-line non-local thermodynamic equilibrium (NLTE) abundances using an up-to-date iron model atom with a new recipe for non-elastic hydrogen collision rates. We study the departures from LTE in their atmospheric parameters and show that they can grow up to ~1.00dex in [Fe/H], ~150K in Teff and ~0.5dex in logg toward the lowest metallicities. Accurate NLTE atmospheric stellar parameters, in particular [Fe/H] being significantly higher, are the first step to eventually providing full NLTE abundance patterns that can be compared with Population III supernova nucleosynthesis yields to derive properties of the first stars. Overall, this maximizes the potential of these likely second-generation stars to investigate the early universe and how the chemical elements were formed.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+AS/108/79
- Title:
- Ultra-steep spectrum radiosources
- Short Name:
- J/A+AS/108/79
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Radio sources with ultra-steep spectra (USS; spectral index <~ -1.0) have been found to be excellent tracers of galaxies at redshifts z>~2. The samples are selected from the set of catalogues referenced below, in a range of frequencies from 38 to 408MHz; they are are fainter by a factor of three than the previously well-studied samples of USS sources from 4C. Snapshot observations of sources from these samples have been made with the VLA at 1.5arcsec resolution and are presented in the printed paper. The list of the sources (Appendix A of the paper) includes positions, flux densities and radio structures for a total number of 605 sources derived from these observations.
- ID:
- ivo://CDS.VizieR/J/AJ/123/637
- Title:
- Ultra-steep-spectrum radio sources
- Short Name:
- J/AJ/123/637
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present optical and/or near-IR images of 128 ultra-steep-spectrum radio sources. Roughly half of the objects are identified in the optical images (R<~24), while in the near-IR images, more than 94% are detected at K<~22. The mean K magnitude is 19.26 within a 2" diameter aperture. The distribution of R-K colors indicates that at least one-third of the objects observed have very red colors (R-K>5). The major axes of the identifications in the K band are preferentially oriented along the radio axes, with half of them having compact morphologies. The 22 sources with spectroscopic redshifts and K-band magnitudes follow the K-z relation found from previous radio samples, but with a larger scatter.
- ID:
- ivo://CDS.VizieR/J/A+A/436/457
- Title:
- Ultra-steep spectrum radio sources
- Short Name:
- J/A+A/436/457
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of radio (VLA) and optical (ESO/La Silla) imaging of a sample of 52 radio sources having an ultra-steep radio spectrum with {alpha} mostly steeper than -1.1 at decimetre wavelengths (median {alpha}=-1.22). Radio-optical overlays are presented to an astrometric accuracy of ~1". For 41 of the sources, radio spectral indices are newly determined using unpublished observations made with the 100-m Effelsberg radio telescope. For 14 of the sources identified with relatively brighter optical counterparts, spectroscopic observations were also carried out at La Silla and their redshifts are found to lie in the range 0.4 to 2.6.
- ID:
- ivo://CDS.VizieR/J/A+A/569/A52
- Title:
- Ultra steep spectrum radio sources
- Short Name:
- J/A+A/569/A52
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Ultra steep spectrum (USS) radio sources are one of the efficient tracers of powerful high-z radio galaxies (HzRGs). In contrast to searches for powerful HzRGs from radio surveys of moderate depths, fainter USS samples derived from deeper radio surveys can be useful in finding HzRGs at even higher redshifts and in unveiling a population of obscured weaker radio-loud AGN at moderate redshifts. Using our 325MHz GMRT observations (5{sigma}~800{mu}Jy) and 1.4GHz VLA observations (5{sigma}~80-100{mu}Jy) available in two subfields (VLA-VIMOS VLT Deep Survey (VLA-VVDS) and Subaru X-ray Deep Field (SXDF)) of the XMM-LSS field, we derive a large sample of 160 faint USS radio sources and characterize their nature. The optical and IR counterparts of our USS sample sources are searched using existing deep surveys, at respective wavelengths. We attempt to unveil the nature of our faint USS sources using diagnostic techniques based on mid-IR colors, flux ratios of radio to mid-IR, and radio luminosities. Redshift estimates are available for 86/116 (~74%) USS sources in the VLA-VVDS field and for 39/44 (~87%) USS sources in the SXDF fields with median values (z_median_)~1.18 and ~1.57, respectively, which are higher than estimates for non-USS radio sources (z_median non-USS_ ~0.99 and ~0.96), in the two subfields. The MIR color-color diagnostic and radio luminosities are consistent with most of our USS sample sources at higher redshifts (z>0.5) being AGN. The flux ratio of radio to mid-IR (S_1.4GHz_/S_3.6{mu}m_) versus redshift diagnostic plot suggests that more than half of our USS sample sources distributed over z~0.5 to 3.8 are likely to be hosted in obscured environments. A significant fraction (~26% in the VLA-VVDS and ~13% in the SXDF) of our USS sources without redshift estimates mostly remain unidentified in the existing optical, IR surveys, and exhibit high radio to mid-IR flux ratio limits similar to HzRGs, and so, can be considered as potential HzRG candidates. Our study shows that the criterion of ultra steep spectral index remains a reasonably efficient method to select high-z sources even at sub-mJy flux densities. In addition to powerful HzRG candidates, our faint USS sample also contains populations of weaker radio-loud AGNs potentially hosted in obscured environments.
- ID:
- ivo://CDS.VizieR/J/A+AS/143/303
- Title:
- Ultra steep spectrum radio sources catalog
- Short Name:
- J/A+AS/143/303
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The three tables contain the 669 Ultra Steep Spectrum sources from the 3 samples WN (WENSS-NVSS), TN (TEXAS-NVSS) and MP (MRC-PMN) (tables A.1, A.2 and A.3). For each source, the radio fluxes from the surveys and from VLA or ATCA observations are given, as well as coordinates, radio structure, angular size and position angle determined from the radio map indicated in the last column.
- ID:
- ivo://CDS.VizieR/J/MNRAS/406/197
- Title:
- Ultra-steep spectrum radio sources in SDSS
- Short Name:
- J/MNRAS/406/197
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyse optical and radio properties of radio galaxies detected in the Sloan Digital Sky Survey. The sample of radio sources is selected from the catalogue of Kimball & Ivezic (2008AJ....136..684K) with flux densities at 325, 1400 and 4850MHz, using Westerbork Northern Sky Survey, NRAO VLA Sky Survey and Green Bank 6cm radio surveys and from flux measurements at 74MHz taken from Very Large Array Low-Frequency Sky Survey (Cohen et al. 2006, Cat. VIII/79). We study radio galaxy spectral properties using radio colour-colour diagrams and find that our sample follows a single power law from 74 to 4850MHz.
21958. Ultraviolet Excess Galaxies
- ID:
- ivo://CDS.VizieR/VII/63
- Title:
- Ultraviolet Excess Galaxies
- Short Name:
- VII/63
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The catalog contains a list of 412 faint galaxies selected for their apparent ultraviolet excess. The galaxies were selected from a 3-color (UBV) plate taken with the Palomar 48-inch Schmidt telescope. The 14-inch-square plates cover an area of 30 square degrees centered on Kapteyn Selected Area 28. The catalog includes running numbers, coordinates, color codes, magnitude codes, morphologies, diameters, and notes. The catalogued galaxies were selected by eye from the Palomar Schmidt 3-color (UBV) plate PS24771, centered on Kapteyn Selexted Area 28 and taken by Usher under conditions of good seeing and transparency.
- ID:
- ivo://CDS.VizieR/J/ApJ/861/153
- Title:
- Ultraviolet Extinction in the GALEX Bands. UVEXT
- Short Name:
- J/ApJ/861/153
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Interstellar extinction in ultraviolet is the most severe in comparison with optical and infrared wavebands and a precise determination plays an important role in correctly recovering the ultraviolet brightness and colors of objects. By finding the observed bluest colors at the given effective temperature and metallicity range of dwarf stars, stellar intrinsic colors, C_B,V_^0^, C_NUV,B_^0^, C_FUV,B_^0^, and C_FUV,NUV_^0^, are derived according to the stellar parameters from the LAMOST spectroscopic survey and photometric results from the GALEX and APASS surveys. With the derived intrinsic colors, the ultraviolet color excesses are calculated for about 25,000 A- and F-type dwarf stars. Analysis of the color excess ratios yields the extinction law related to the GALEX UV bands: E_NUV,B_/E_B,V_=3.77, E_FUV,B_/E_B,V_=3.39, and E_FUV,NUV_/E_B,V_=-0.38. The results agree very well with previous works in the NUV band and in general with the extinction curve derived by Fitzpatrick (1999PASP..111...63F) for R_V_=3.35.
- ID:
- ivo://nasa.heasarc/uitmaster
- Title:
- Ultraviolet Imaging Telescope Master Catalog
- Short Name:
- UITMASTER
- Date:
- 21 Feb 2025
- Publisher:
- NASA/GSFC HEASARC
- Description:
- The Ultraviolet Imaging Telescope (UIT) was one of three ultraviolet telescopes on the ASTRO-1 mission flown on the Space Shuttle Columbia during the period of 2 - 10 December 1990. The same three instruments were later flown on the Space Shuttle Endeavour during 3 - 17 March 1995, as part of the ASTRO-2 mission. Exposures were obtained on 70-mm photographic film in the 1200-3300 Angstrom range using broadband filters and later digitized using a Perkin-Elmer microdensitometer. The image resolution was 3 arcseconds over a 40 arcminute field of view and images of targets as faint as 21st (ultraviolet) magnitude were recorded. Overall, the UIT-1 mission obtained 821 exposures of 66 targets (361 near-UV and 460 far-UV), and UIT-2 obtained 758 images of 193 targets (all far-UV), for a total of 1579 exposures. This table contains only 1481 rows, 777 UIT-1 exposures (347 near-UV and 430 far-UV) and 704 UIT-2 exposures (all far-UV), implying that 98 exposures are 'missing' from this table. This table was created by the HEASARC in April 2012 based on <a href="https://cdsarc.cds.unistra.fr/ftp/cats/VI/104">CDS Catalog VI/104</a> file uitlist.dat. This is a service provided by NASA HEASARC .
