- ID:
- ivo://CDS.VizieR/J/A+A/623/L12
- Title:
- sdOB star Feige 46 spectrum
- Short Name:
- J/A+A/623/L12
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the discovery of long-period, low-amplitude, g-mode pulsations in the intermediate He-rich hot subdwarf (sdOB) star Feige 46. So far, only one other He-enriched sdOB star (LS IV -14116) was known to exhibit such pulsations. From our ground-based light curves of Feige 46, we extracted five independent periodicities ranging from 2294s to 3400s. We fit our optical spectrum of the star with our grid of non-local thermodynamic equilibrium (NLTE) model atmospheres and derived the following atmospheric parameters: Teff=36120+/-230K, logg=5.93+/-0.04, and log N(He)/N(H)=-0.32+/-0.03 (formal fitting errors only). These parameters are very similar to those of LS IV -14116 and place Feige 46 well outside of the instability strip where the hydrogen-rich g-mode sdB pulsators are found. We used the Gaia parallax and proper motion of Feige 46 to perform a kinematic analysis of this star and found that it likely belongs to the Galactic halo population. This is most certainly an intriguing and interesting result given that LS IV -14116 is also a halo object.The mechanism responsible for the pulsations in these two peculiar objects remains unclear, but a possible scenario involves the epsilon-mechanism. Although they are the only two members in their class of variable stars, these pulsators appear to have more in common than just their pulsation properties.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/732/110
- Title:
- SDSS 2175{AA} extinction bump candidates
- Short Name:
- J/ApJ/732/110
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report detections of 39 2175{AA} dust extinction bump candidates associated with strong MgII absorption lines at z~1-1.8 on quasar spectra in Sloan Digital Sky Survey (SDSS) DR3. These strong MgII absorption line systems are detected among 2951 strong MgII absorbers with a rest equivalent width W_r_{lambda}2796>1.0{AA} at 1.0<z<1.86, which is part of a full sample of 7421 strong MgII absorbers compiled by Prochter et al. (2006, Cat. J/ApJ/639/766). The redshift range of the absorbers is chosen to allow the 2175{AA} extinction features to be completely covered within the SDSS spectrograph operation wavelength range. An upper limit of the background quasar emission redshift at z=2.1 is set to prevent the Ly{alpha} forest lines from contaminating the sensitive spectral region for the 2175{AA} bump measurements. A total of 12 absorbers are detected with 2175{AA} bumps at a 5{sigma} level of statistical significance, 10 are detected at a 4{sigma} level, and 17 are detected at a 3{sigma} level. Most of the candidate bumps in this work are similar to the relatively weak 2175{AA} bumps observed in the Large Magellanic Cloud LMC2 supershell rather than the strong ones observed in the Milky Way.
- ID:
- ivo://CDS.VizieR/J/ApJ/854/160
- Title:
- SDSS and DES long-term extreme variability QSOs
- Short Name:
- J/ApJ/854/160
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We perform a systematic search for long-term extreme variability quasars (EVQs) in the overlapping Sloan Digital Sky Survey and 3 Year Dark Energy Survey imaging, which provide light curves spanning more than 15 years. We identified ~1000 EVQs with a maximum change in g-band magnitude of more than 1 mag over this period, about 10% of all quasars searched. The EVQs have L_bol_~10^45^-10^47^erg/s and L/L_Edd_~0.01-1. Accounting for selection effects, we estimate an intrinsic EVQ fraction of ~30%-50% among all g<~22 quasars over a baseline of ~15yr. We performed detailed multi-wavelength, spectral, and variability analyses for the EVQs and compared them to their parent quasar sample. We found that EVQs are distinct from a control sample of quasars matched in redshift and optical luminosity: (1) their UV broad emission lines have larger equivalent widths; (2) their Eddington ratios are systematically lower; and (3) they are more variable on all timescales. The intrinsic difference in quasar properties for EVQs suggests that internal processes associated with accretion are the main driver for the observed extreme long-term variability. However, despite their different properties, EVQs seem to be in the tail of a continuous distribution of quasar properties, rather than standing out as a distinct population. We speculate that EVQs are normal quasars accreting at relatively low rates, where the accretion flow is more likely to experience instabilities that drive the changes in flux by a factor of a few on multi-year timescales.
- ID:
- ivo://CDS.VizieR/J/A+A/525/A157
- Title:
- SDSS automated morphology classification
- Short Name:
- J/A+A/525/A157
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an automated morphological classification in 4 types (E, S0, Sab, Scd) of ~700 000 galaxies from the SDSS DR7 spectroscopic sample based on support vector machines. The main new property of the classification is that we associate a probability to each galaxy of being in the four morphological classes instead of assigning a single class. The classification is therefore better adapted to nature where we expect a continuous transition between different morphological types. The algorithm is trained with a visual classification and then compared to several independent visual classifications including the Galaxy Zoo first-release catalog. We find a very good correlation between the automated classification and classical visual ones.
- ID:
- ivo://CDS.VizieR/J/ApJ/719/1672
- Title:
- SDSS binary quasars at high redshift. I.
- Short Name:
- J/ApJ/719/1672
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The clustering of quasars on small scales yields fundamental constraints on models of quasar evolution and the buildup of supermassive black holes. This paper describes the first systematic survey to discover high-redshift binary quasars. Using color-selection and photometric redshift techniques, we searched 8142deg^2^ of Sloan Digital Sky Survey imaging data for binary quasar candidates, and confirmed them with follow-up spectroscopy. Our sample of 27 high-redshift binaries (24 of them new discoveries) at redshifts 2.9<z<4.3 with proper transverse separations 10kpc<R_T_<650kpc increases the number of such objects known by an order of magnitude. Eight members of this sample are very close pairs with R_T_<100kpc, and of these close systems four are at z>3.5. The completeness and efficiency of our well-defined selection algorithm are quantified using simulated photometry and we find that our sample is ~50% complete.
- ID:
- ivo://CDS.VizieR/J/AJ/126/2125
- Title:
- SDSS candidate type II quasars
- Short Name:
- J/AJ/126/2125
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Type II quasars are the long-sought luminous analogs of type 2 (narrow emission line) Seyfert galaxies, suggested by unification models of active galactic nuclei (AGNs) and postulated to account for an appreciable fraction of the cosmic hard X-ray background. We present a sample of 291 type II AGNs at redshifts 0.3<z<0.83 from the spectroscopic data of the Sloan Digital Sky Survey. These objects have narrow (FWHM<2000km/s), high equivalent width emission lines with high-ionization line ratios. We describe the selection procedure and discuss the optical properties of the sample. About 50% of the objects have [O III] {lambda}5008 line luminosities in the range 3x10^8^-10^10^L_{sun}_, comparable to those of luminous (-27<M_B_<-23) quasars; this, along with other evidence, suggests that the objects in the luminous subsample are type II quasars.
- ID:
- ivo://CDS.VizieR/J/ApJ/869/122
- Title:
- SDSS-DR14 and LAMOST DR6 spectra in GD-1 stream
- Short Name:
- J/ApJ/869/122
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Combining data from Gaia DR2, SDSS DR14, and LAMOST DR6, we update the fit to model of the properties of the stellar stream GD-1 and find that it has an age of ~13Gyr, [Fe/H] of -2.2+/-0.12, and a distance from the Sun of ~8kpc. We tabulate six-dimensional (6D) phase-space fiducial points along the GD-1 stream orbit over a 90{deg} arc. The fitted orbit shows that the stream has an eccentricity e~0.3, perigalacticon of 14.2kpc, apogalacticon of 27.0kpc, and inclination i~40{deg}. There is evidence along the arc for four candidate stellar overdensities, one candidate gap, two candidate stellar underdensities, and that the stream is cut off at {phi}_1_~2{deg} (in the stream-aligned ({phi}_1_, {phi}_2_) coordinate system of Koposov+ 2010ApJ...712..260K). The spur originating at {phi}_1_~-40{deg} implies stars were pulled away from the stream trace by an encounter (potentially a dark matter subhalo). The narrowest place (FWHM~44.6pc) of the GD-1 trace is at ({phi}_1_, {phi}2^c^)~(-14{deg}, 0.15{deg}), which is ~(178.18{deg}, 52.19{deg}) in (RA, DE), where the progenitor is possibly located. We also find six blue horizontal branch and 10 blue stragglers spectroscopic stars in the GD-1 stream.
2218. SDSS DR2 BAL QSOs
- ID:
- ivo://CDS.VizieR/J/ApJ/665/990
- Title:
- SDSS DR2 BAL QSOs
- Short Name:
- J/ApJ/665/990
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have investigated a sample of 5088 quasars from the SDSS DR2 in order to determine how the frequency and properties of BALs depend on black hole mass, bolometric luminosity, Eddington fraction (L/L_Edd_), and spectral slope. We focus only on high-ionization BALs and find a number of significant results. While quasars accreting near the Eddington limit are more likely to show BALs than lower L/LEdd systems, BALs are present in quasars accreting at only a few percent Eddington. We find a stronger effect with bolometric luminosity, such that the most luminous quasars are more likely to show BALs. There is an additional effect, previously known, that BAL quasars are redder on average than unabsorbed quasars. The strongest effects involving the quasar physical properties and BAL properties are related to terminal outflow velocity. Maximum observed outflow velocities increase with both the bolometric luminosity and the blueness of the spectral slope, suggesting that the ultraviolet luminosity to a great extent determines the acceleration. These results support the idea of outflow acceleration via ultraviolet line scattering.
- ID:
- ivo://CDS.VizieR/J/MNRAS/397/1713
- Title:
- SDSS DR3 flat-spectrum radio quasars
- Short Name:
- J/MNRAS/397/1713
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We constructed a sample of 185 flat-spectrum radio quasars (FSRQs) by cross-correlating Shen et al.'s (2006MNRAS.369.1639S) Sloan Digital Sky Survey Data Release 3 (SDSS DR3) X-ray quasar sample with the Faint Images of the Radio Sky at Twenty Centimeters (FIRST) and Green Bank 6-cm survey (GB6) radio catalogues. From the spectral energy distribution (SED) constructed using multi-band (radio, UV, optical, infrared and X-ray) data, we derived the synchrotron peak frequency and peak luminosity. The black hole mass MBH and the broad-line region (BLR) luminosity (then the bolometric luminosity Lbol) were obtained by measuring the linewidth and strength of broad emission lines from SDSS spectra. We define a subsample of 118 FSRQs for which non-thermal jet emission is thought to dominate over thermal emission from the accretion disc and host galaxy.
- ID:
- ivo://CDS.VizieR/J/AJ/142/122
- Title:
- SDSS DR7 galaxy/QSOs pairs
- Short Name:
- J/AJ/142/122
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The aim of this project is to identify low-redshift host galaxies of quasar absorption-line systems by selecting galaxies that are seen in projection onto quasar sightlines. To this end, we use the Seventh Data Release of the Sloan Digital Sky Survey to construct a parent sample of 97489 galaxy/quasar projections at impact parameters of up to 100 kpc to the foreground galaxy. We then search the quasar spectra for absorption-line systems of CaII and NaI within +/-500km/s1 of the galaxy's velocity. This yields 92 CaII and 16 NaI absorption systems.
