- ID:
- ivo://CDS.VizieR/J/A+A/501/519
- Title:
- Extremely metal-poor turnoff stars abundances
- Short Name:
- J/A+A/501/519
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The detailed chemical abundances of extremely metal-poor (EMP) stars are key guides to understanding the early chemical evolution of the Galaxy. Most existing data, however, treat giant stars that may have experienced internal mixing later. We aim to compare the results for giants with new, accurate abundances for all observable elements in 18 EMP turnoff stars. VLT/UVES spectra at ~45000 and S/N ~130 per pixel (330-1000nm) are analysed with OSMARCS model atmospheres and the TURBOSPECTRUM code to derive abundances for C, Mg, Si, Ca, Sc, Ti, Cr, Mn, Co, Ni, Zn, Sr, and Ba. For Ca, Ni, Sr, and Ba, we find excellent consistency with our earlier sample of EMP giants, at all metallicities. However, our abundances of C, Sc, Ti, Cr, Mn and Co are ~0.2dex larger than in giants of similar metallicity. Mg and Si abundances are ~0.2dex lower (the giant [Mg/Fe] values are slightly revised), while Zn is again ~0.4dex higher than in giants of similar [Fe/H] (6 stars only). For C, the dwarf/giant discrepancy could possibly have an astrophysical cause, but for the other elements it must arise from shortcomings in the analysis. Approximate computations of granulation (3D) effects yield smaller corrections for giants than for dwarfs, but suggest that this is an unlikely explanation, except perhaps for C, Cr, and Mn. NLTE computations for Na and Al provide consistent abundances between dwarfs and giants, unlike the LTE results, and would be highly desirable for the other discrepant elements as well. Meanwhile, we recommend using the giant abundances as reference data for Galactic chemical evolution models.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/743/77
- Title:
- Extremely metal-poor (XMP) galaxies in SDSS
- Short Name:
- J/ApJ/743/77
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We carry out a systematic search for extremely metal-poor (XMP) galaxies in the spectroscopic sample of Sloan Digital Sky Survey (SDSS) data release 7 (DR7). The XMP candidates are found by classifying all the galaxies according to the form of their spectra in a region 80{AA} wide around H{alpha}. Due to the data size, the method requires an automatic classification algorithm. We use k-means. Our systematic search renders 32 galaxies having negligible [NII] lines, as expected in XMP galaxy spectra. Twenty-one of them have been previously identified as XMP galaxies in the literature - the remaining 11 are new. This was established after a thorough bibliographic search that yielded only some 130 galaxies known to have an oxygen metallicity 10 times smaller than the Sun (explicitly, with 12+log(O/H)<=7.65). XMP galaxies are rare; they represent 0.01% of the galaxies with emission lines in SDSS/DR7. Although the final metallicity estimate of all candidates remains pending, strong-line empirical calibrations indicate a metallicity about one-tenth solar, with the oxygen metallicity of the 21 known targets being 12+log(O/H)~7.61+/-0.19. Since the SDSS catalog is limited in apparent magnitude, we have been able to estimate the volume number density of XMP galaxies in the local universe, which turns out to be (1.32+/-0.23)x10^-4^Mpc^-3^. The XMP galaxies constitute 0.1% of the galaxies in the local volume, or ~0.2% considering only emission-line galaxies. All but four of our candidates are blue compact dwarf galaxies, and 24 of them have either cometary shape or are formed by chained knots.
- ID:
- ivo://CDS.VizieR/J/A+A/432/69
- Title:
- Extremely Red Objects XMM-Newton observations
- Short Name:
- J/A+A/432/69
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a deep (about 80ks) XMM-Newton survey of the largest sample of near-infrared selected Extremely Red Objects (R-K>5) available to date to Ks<~19.2.
- ID:
- ivo://nasa.heasarc/erosxmm
- Title:
- Extremely Red Objects XMM-Newton Survey Catalog
- Short Name:
- EROSXMM
- Date:
- 27 Sep 2024
- Publisher:
- NASA/GSFC HEASARC
- Description:
- This table contains the results of a deep (about 80 ks) XMM-Newton survey of the largest sample of near-infrared-selected Extremely Red Objects (R-K > 5) available to date to K<sub>s</sub> < ~19.2. At the relatively bright X-ray fluxes ((F(2-10 keV) >~ 4 x 10<sup>-15</sup> erg cm<sup>-2</sup> s<sup>-1</sup>) and near-infrared magnitude probed by the present observations, the fraction of AGN (i.e. X-ray detected) among the ERO population is small (~3.5%); conversely, the fraction of EROs among hard X-ray selected sources is much higher (~20%). The X-ray properties of the 9 EROs detected in this XMM-Newton observation indicate absorption in excess of 10<sup>22</sup> cm<sup>-2</sup> in a large fraction of them. The X-ray, optical and near-infrared properties of those X-ray selected EROs with a spectroscopic or photometric redshift nicely match those expected for type 2 quasars, the high-luminosity, high-redshift obscured AGNs predicted in baseline XRB synthesis models. A close correlation is detected between X-ray and K-band fluxes. This table contains the X-ray and optical information for the sources detected in the sum of 3 separate XMM-Newton observations of a field centered on 14 49 25, +09 00 13 (J2000.0 RA and Dec) known as the "Daddi" field (Daddi et al. 2000, A&A, 361, 535) in which 257 EROs are known to be present. The data from all 3 EPIC instruments (PN, MOS1 and MOS2) obtained in the 3 observations was combined, yielding a total exposure time for the PN of ~82 ks, and for the MOS instruments of ~78 ks. The X-ray hardness ratio (HR) and the optical to near-infrared color (R and K magnitudes) are reported for all the detected X-ray sources and their counterparts, along with the reliability of the X-ray to optical or near-infrared associations as measured by the likelihood ratios, LR(R) and LR(K). This table lists data for the 111 proposed optical/infrared counterparts for the 97 detected X-ray sources, i.e., X-ray sources with more than one possible optical/IR counterpart will have multiple entries in this table, one for each counterpart, as follows: 73 X-ray sources have secure optical/near-IR counterparts (counterpart_status=1), 7 X-ray sources have 2 possible 'likely' counterparts, and 1 X-ray source has 3 such counterparts (counterpart_status=2), 6 X-ray sources have only low-likelihood counterparts all of which lie outside the 3" matching radii (counterpart_status=3), and the remaining 9 X-ray sources lack optical and infrared photometry (counterpart_status=4). This table was created by the HEASARC in February 2007 based on the <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/A+A/432/69">CDS Catalog J/A+A/432/69</a> files table1.dat and table2.dat. This is a service provided by NASA HEASARC .
- ID:
- ivo://CDS.VizieR/J/A+A/566/A24
- Title:
- Extremely strong damped Lyman-{alpha} systems
- Short Name:
- J/A+A/566/A24
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a study of ~100 high redshift (z ~2-4) extremely strong damped Lyman-{alpha} systems (ESDLA, with N(HI)>=0.5x10^22^cm^-2^) detected in quasar spectra from the Baryon Oscillation Spectroscopic Survey (BOSS) of the Sloan Digital Sky Survey (SDSS-III) Data Release 11. We study the neutral hydrogen, metal, and dust content of this elusive population of absorbers and confirm our previous finding that the high column density end of the N(HI) frequency distribution has a relatively shallow slope with power-law index -3.6, similar to what is seen from 21-cm maps in nearby galaxies. The stacked absorption spectrum indicates a typical metallicity ~1/20th solar, similar to the mean metallicity of the overall DLA population. The relatively small velocity extent of the low-ionisation lines suggests that ESDLAs do not arise from large-scale flows of neutral gas. The high column densities involved are in turn more similar to what is seen in DLAs associated with gamma-ray burst afterglows (GRB-DLAs), which are known to occur close to star-forming regions. This indicates that ESDLAs arise from a line of sight passing at very small impact parameters from the host galaxy, as observed in nearby galaxies. This is also supported by simple theoretical considerations and recent high-z hydrodynamical simulations. We strongly substantiate this picture by the first statistical detection of Ly{alpha} emission with <L_ESDLA_(Ly{alpha})>=~(0.6+/-0.2)x10^42^erg/s in the core of ESDLAs (corresponding to about 0.1L^*^ at z~2-3), obtained through stacking the fibre spectra (of radius 1" corresponding to ~8kpc at z~2.5). Statistical errors on the Ly{alpha} luminosity are of the order of 0.1x10^42^erg/s but we caution that the measured Ly{alpha} luminosity may be overestimated by ~35% due to sky light residuals and/or FUV emission from the quasar host and that we have neglected flux-calibration uncertainties. We estimate a more conservative uncertainty of 0.2x10^42^erg/s. The properties of the Ly{alpha} line (luminosity distribution, velocity width and velocity offset compared to systemic redshift) are very similar to that of the population of Lyman-{alpha} emitting galaxies (LAEs) with L_LAE_(Ly{alpha})>=10^41^erg/s detected in long-slit spectroscopy or narrow-band imaging surveys. By matching the incidence of ESDLAs with that of the LAEs population, we estimate the high column density gas radius to be about r_gas_=2.5kpc, i.e., significantly smaller than the radius corresponding to the BOSS fibre aperture, making fibre losses likely negligible. Finally, the average measured Ly{alpha} luminosity indicates a star-formation rate consistent with the Schmidt-Kennicutt law, SFR (M_{sun}_/yr)=~0.6/f_esc_, where f_esc_<1 is the Ly{alpha} escape fraction. Assuming the typical escape fraction of LAEs, f_esc_~0.3, the Schmidt-Kennicutt law implies a galaxy radius of about r_gal_=~2.5kpc. Finally, we note that possible overestimation of the Ly{alpha} emission would result in both smaller r_gas_ and r_gal_. Our results support a close association between LAEs and strong DLA host galaxies.
- ID:
- ivo://CDS.VizieR/J/ApJ/860/83
- Title:
- 22 extreme [OIII] emitters at z~0.5 from SDSS-DR14
- Short Name:
- J/ApJ/860/83
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have found a sample of extreme emission-line galaxies (EELGs) with strong [OIII]{lambda}5007 emission at z~0.5. Using broadband photometric selection and requiring small uncertainties in photometry, we searched the 14th Data Release of the Sloan Digital Sky Survey (SDSS) and found 2658 candidates with strong i-band excess (i-z<=r-i-0.7). We further obtained 649 SDSS spectra of these objects, and visually identified 22 [OIII] emitters lying at 0.40<z<0.63. Having constructed their ultraviolet-infrared spectral energy distributions, we found that they have fairly blue r-W2 and red W1-W4 colors, indicative of strong, warm dust emission. Their rest-frame [OIII]{lambda}5007 equivalent widths are mostly 200-600{AA}, and their high [OIII]{lambda}5007/H{beta} ratios put them at the boundary of star-forming galaxies and active galactic nuclei on line ratio classification diagrams. The typical E(B-V) and electron temperature of [OIII] emitters are ~0.1-0.3mag and ~104K, respectively. The lowest metallicity of our [OIII] emitters with S/N[OIII]{lambda}4363>3 is 12+log(O/H)=7.98_-0.02_^+0.12^, with a median value of 8.24_-0.04_^+0.05^. Our [OIII] emitters exhibit remarkably high line luminosity-18/22 have L[OIII]{lambda}5007>5x10^42^erg/s and 5/22 have L[OIII]{lambda}5007>10^43^erg/s. Their estimated volume number density at z~0.5 is ~2x10^-8^Mpc^-3^, with L[OIII]{lambda}5007 down to ~3x10^42^erg/s. The cumulative number distribution of EELGs across different redshifts is indicative of a strong redshift evolution at the bright end of the [OIII] luminosity function.
- ID:
- ivo://CDS.VizieR/J/MNRAS/498/4033
- Title:
- Extreme quasar X-ray variability
- Short Name:
- J/MNRAS/498/4033
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze 1598 serendipitous Chandra X-ray observations of 462 radio-quiet quasars to constrain the frequency of extreme amplitude X-ray variability that is intrinsic to the quasar corona and innermost accretion flow. The quasars in this investigation are all spectroscopically confirmed, optically bright (m_i_<=20.2), and contain no identifiable broad absorption lines in their optical/ultraviolet spectra. This sample includes quasars spanning z~0.1-4 and probes X-ray variability on timescales of up to ~12 rest-frame years. Variability amplitudes are computed between every epoch of observation for each quasar and are analyzed as a function of timescale and luminosity. The tail-heavy distributions of variability amplitudes at all timescales indicate that extreme X-ray variations are driven by an additional physical mechanism and not just typical random fluctuations of the coronal emission. Similarly, extreme X-ray variations of low-luminosity quasars seem to be driven by an additional physical mechanism, whereas high-luminosity quasars seem more consistent with random fluctuations. The amplitude at which an X-ray variability event can be considered extreme is quantified for different timescales and luminosities. Extreme X-ray variations occur more frequently at long timescales ({DELTA}t>=300-days) than at shorter timescales, and in low-luminosity quasars compared to high-luminosity quasars over a similar timescale. A binomial analysis indicates that extreme intrinsic X-ray variations are rare, with a maximum occurrence rate of <2.4% of observations. Finally, we present X-ray variability and basic optical emission-line properties of three archival quasars that have been newly discovered to exhibit extreme X-ray variability.
- ID:
- ivo://archive.stsci.edu/euve
- Title:
- Extreme Ultraviolet Explorer
- Short Name:
- EUVE
- Date:
- 22 Jul 2020 21:28:51
- Publisher:
- Space Telescope Science Institute Archive
- Description:
- Launched in June, 1992, The Extreme Ultraviolet Explorer (EUVE) conducted the first extreme ultraviolet (70-760 Angstroms) survey of the sky and subsequently began a Guest Observer Program of pointed
- ID:
- ivo://CDS.VizieR/J/AJ/113/1026
- Title:
- Fabry-Perot Observations of M15
- Short Name:
- J/AJ/113/1026
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have used an Imaging Fabry-Perot Spectrophotometer with the Sub-arcsecond Imaging Spectrograph on the Canada-France-Hawaii Telescope to measure velocities for 1534 stars in the globular cluster M15 (NGC 7078) with uncertainties between 0.5 and 10km/s. Combined with previous velocity samples, the total number of stars with measured velocities in M15 is 1597. An average seeing of 0.8" allowed us to obtain velocities for 144 stars within 10" of the center of M15, including 12 stars within 2". The velocity dispersion profile for M15 remains flat at a value of 11km/s from a radius of 0.4 into our innermost reliable point at 0.02 (0.06pc). Assuming an isotropic velocity dispersion tensor, this profile and the previously-published surface brightness profile can be equally well represented either by a stellar population whose M/L varies with radius from 1.7 in solar units at large radii to 3 in the central region, or by a population with a constant M/L of 1.7 and a central black hole of 1000M_{sun}_. A non-parametric mass model that assumes no black hole, no rotation, and isotropy constrains the mass density of M15 to better than 30% at a radius of 0.07 parsecs. The mass-density profile of this model is well represented by a power law with an exponent of -2.2, the value predicted by models of cluster core-collapse. Using the assumption of local thermodynamic equilibrium, we estimate the present-day mass function and infer a significant number of 0.6-0.7 M_{sun}_ objects in the central few parsecs, 85% of which may be in the form of stellar remnants. Not only do we detect rotation; we find that the position angle of the projected rotation axis in the central 10" is 100deg different from that of the whole sample. We also detect an increase in the amplitude of the rotation at small radii. Although this increase needs to be confirmed with better-seeing data, it may be the result of a central mass concentration. (Copyright) 1997 American Astronomical Society.
- ID:
- ivo://CDS.VizieR/J/A+AS/106/451
- Title:
- Face-on disk galaxies photometry. I.
- Short Name:
- J/A+AS/106/451
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- (no description available)