- ID:
- ivo://CDS.VizieR/J/A+A/616/A114
- Title:
- CIV BAL disappearance in SDSS QSOs
- Short Name:
- J/A+A/616/A114
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Broad absorption lines (BALs) in the spectra of quasi-stellar objects (QSOs) originate from outflowing winds along our line of sight; winds are thought to originate from the inner regions of the QSO accretion disk, close to the central supermassive black hole (SMBH). These winds likely play a role in galaxy evolution and are responsible for aiding the accretion mechanism onto the SMBH. Several works have shown that BAL equivalent widths can change on typical timescales from months to years; such variability is generally attributed to changes in the covering factor (due to rotation and/or changes in the wind structure) and/or in the ionization level of the gas. We investigate BAL variability, focusing on BAL disappearance. We analyze multi-epoch spectra of more than 1500 QSOs - the largest sample ever used for such a study - observed by different programs from the Sloan Digital Sky Survey-I/II/III (SDSS-I/II/III), and search for disappearing CIV BALs. The spectra cover a rest-frame time baseline ranging from 0.28 to 4.9yr; the source redshifts range from 1.68 to 4.27. We detect 73 disappearing BALs in the spectra of 67 unique sources. This corresponds to 3.9% of BALs disappearing within 4.9yr (rest frame), and 5.1% of our BAL QSOs exhibit at least one disappearing BAL within 4.9yr (rest frame). We estimate the average lifetime of a BAL along our line of sight (~=80-100yr), which appears consistent with the accretion disk orbital time at distances where winds are thought to originate. We inspect various properties of the disappearing BAL sample and compare them to the corresponding properties of our main sample. We also investigate the existence of a correlation in the variability of multiple troughs in the same spectrum, and find it persistent at large velocity offsets between BAL pairs, suggesting that a mechanism extending on a global scale is necessary to explain the phenomenon. We select a more reliable sample of disappearing BALs on the basis of some criteria adopted in a previous publication, where a subset of our current sample was analyzed, and compare the findings from the two works, obtaining generally consistent results.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/454/3962
- Title:
- 188 CIV BAL QSOs from SDSS DR7
- Short Name:
- J/MNRAS/454/3962
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The variability of broad absorption lines (BALs) is investigated for a sample of 188 BAL quasars (QSOs) (z>1.7) with at least two epoch observations from the Sloan Digital Sky Survey Data Release 7, covering a time-scale of about 0.001-3yr in the rest frame. Considering only the longest time-scale between epochs for each QSO, 73 variable regions in the CIV BAL troughs are detected for 43 BAL QSOs. The proportion of BAL QSOs showing variable regions increases with longer time-interval than about 1 yr in the rest frame. The velocity width of variable regions is narrow compared to the BAL-trough outflow velocity. For 43 BAL QSOs with variable regions, it is found that there is a medium strong correlation between the variation of the continuum luminosity at 1500{AA} and the variation of the spectral index. With respect to the total 188 QSOs, a larger proportion of BAL QSOs with variable regions appears bluer during their brighter phases, which implies that the origin of BAL variable regions is related to the central accretion process. For 43 BAL QSOs with variable regions, it is possible that there is a negative medium strong correlation between the absolute variation of the equivalent width and the Mgii-based black hole mass, and a medium strong correlation between the maximum outflow velocity of variable regions and the Eddington ratio. These results imply a connection between the BAL-trough variation and the central accretion process.
- ID:
- ivo://CDS.VizieR/J/ApJ/791/88
- Title:
- C IV BAL troughs properties in quasars
- Short Name:
- J/ApJ/791/88
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We consider how the profile and multi-year variability properties of a large sample of C IV Broad Absorption Line (BAL) troughs change when BALs from Si IV and/or Al III are present at corresponding velocities, indicating that the line of sight intercepts at least some lower ionization gas. We derive a number of observational results for C IV BALs separated according to the presence or absence of accompanying lower ionization transitions, including measurements of composite profile shapes, equivalent width (EW), characteristic velocities, composite variation profiles, and EW variability. We also measure the correlations between EW and fractional-EW variability for C IV, Si IV, and Al III. Our measurements reveal the basic correlated changes between ionization level, kinematics, and column density expected in accretion-disk wind models; e.g., lines of sight including lower ionization material generally show deeper and broader C IV troughs that have smaller minimum velocities and that are less variable. Many C IV BALs with no accompanying Si IV or Al III BALs may have only mild or no saturation.
224. CIV candidates
- ID:
- ivo://CDS.VizieR/J/ApJ/708/868
- Title:
- CIV candidates
- Short Name:
- J/ApJ/708/868
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We surveyed the Hubble Space Telescope UV spectra of 49 low-redshift quasars for z<1 CIV candidates, relying solely on the characteristic wavelength separation of the doublet. After consideration of the defining traits of CIV doublets (e.g., consistent line profiles, other associated transitions, etc.), we defined a sample of 38 definite (group G=1) and five likely (G=2) doublets with rest equivalent widths W_r_ for both lines detected at >=3{sigma}_W_r__. We conducted Monte Carlo completeness tests to measure the unblocked redshift ({Delta}z) and co-moving path length ({Delta}X) over which we were sensitive to CIV doublets of a range of equivalent widths and column densities. Using the power-law model of f(N(C^+3^)), we measured the C^+3^ mass density relative to the critical density: {Omega}_C^+3^_=(6.20^+1.82^_-1.52_)x10^-8^ for 13<=logN(C^+3^)<=15.
- ID:
- ivo://CDS.VizieR/J/ApJS/239/23
- Title:
- CIV NAL systems from SDSS-DR14 quasar spectra
- Short Name:
- J/ApJS/239/23
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using the quasar spectra from the Sloan Digital Sky Survey, all with two-epoch to six-epoch observations, we search for CIV{lambda}{lambda}1548,1551 narrow absorption doublets in spectral data from the blue wing {upsilon}r=30000km/s until the red wing of CIV{lambda}1549 emission lines. We have obtained 21239 CIV narrow absorption line (NAL) systems, of which 647 systems were significantly changed on timescales from {Delta}MJD=0.24 to 1842.38 days at rest-frame. Both samples of the C IV NAL systems with multi-epoch observations and the variable C IV NAL systems are the largest ones to date. The offset velocity distribution of the variable C IV NALs from quasars has a peak at {upsilon}r~2000km/s and gently extends to a larger offset velocity. There are 110 variable C IV NALs with {upsilon}r>12000km/s. In addition, about 10% intrinsic C IV NALs show time variability on a timescale of <2000 days. We find that the variations of C IV NALs are positively or negatively correlated with the alternations of quasar continua. The two kinds of correlations suggest that the variable C IV NALs included in our absorber catalog can be classified into at least two populations: (1) highly ionized systems that are dominated by highly ionized absorbing gas and negatively respond to the fluctuations of quasar emissions; and (2) lowly ionized systems that are dominated by lowly ionized absorbing gas and positively respond to fluctuations of quasar emissions. We also find that the absolute fractional changes in the absorption strengths of C IV NALs are inversely correlated with absorption strengths.
- ID:
- ivo://CDS.VizieR/J/ApJS/236/39
- Title:
- CIV narrow absorption line systems in SDSS-DR14
- Short Name:
- J/ApJS/236/39
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We assemble 207 variable quasars from the Sloan Digital Sky Survey, all with at least 3 observations, to analyze CIV narrow absorption doublets, and obtain 328 CIV narrow absorption line systems. We find that 19 out of 328 CIV narrow absorption line systems were changed by |{Delta}W_r_^{lambda}1548^|>=3{sigma}_{Delta}Wr_^{lambda}1548^ on timescales from 15.9 to 1477 days at rest-frame. Among the 19 obviously variable CIV systems, we find that (1) 14 systems have relative velocities {upsilon}_r_>0.01c and 4 systems have {upsilon}_r_>0.1c, where c is the speed of light; (2) 13 systems are accompanied by other variable CIV systems; (3) 9 systems were changed continuously during multiple observations; and (4) 1 system with {upsilon}_r_=16862km/s was enhanced by {Delta}W_r_^{lambda}1548^=2.7{sigma}_{Delta}Wr_^{lambda}1548^ in 0.67 day at rest-frame. The variations of absorption lines are inversely correlated with the changes in the ionizing continuum. We also find that large variations of CIV narrow absorption lines are form differently over a short timescale.
227. Clusters in GEHRs
- ID:
- ivo://CDS.VizieR/J/AJ/108/1276
- Title:
- Clusters in GEHRs
- Short Name:
- J/AJ/108/1276
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Photometry in BVR continuum bands and in the emission line of Halpha+ [N II] are presented for a sample of H II complexes in disk, spiral arm and nuclear regions of galaxies NGC 1365, 1566, 2366, 2903, 2997, 3351, 4303, 4449, and 5253. Main sources of errors on H II region photometry are discussed. Errors due to background subtraction are parametrized in terms of background nonuniformity and fractional background contribution and are described separately in the Appendix. Our photometric data are compared with the existing data in the literature. Photometric properties of the sample regions are analyzed statistically and its implications on star formation are briefly discussed. Colors and Halpha+[N II] equivalent widths of nuclear H II regions are found to be distinctly different from disk H II regions, suggesting different star formation histories. We have identified a few high Halpha+[N II] equivalent width regions, which are fainter than average in both emission line and continuum fluxes, thus accounting for the low frequency of occurence of such regions in flux limited samples.
- ID:
- ivo://CDS.VizieR/J/MNRAS/390/1733
- Title:
- CN column densities and excitation temperatures
- Short Name:
- J/MNRAS/390/1733
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyse abundances and rotational temperatures of the interstellar CN molecule. We have calculated the column densities and excitation temperatures of the molecule along 73 lines of sight basing on our original measurements of the B^2^{SIGMA}^+^-X^2^{SIGMA}^+^(0,0) vibrational band recorded in high signal-to-noise ratio spectra and also for 88 directions based on measurements already available in literature. We compare the column densities obtained from different bands of CN molecule available to ground-based instruments. The obtained excitation temperatures in the analysed directions show always an excess over the cosmic microwave background radiation (CMBR) temperature.
- ID:
- ivo://CDS.VizieR/J/A+A/353/528
- Title:
- CNO abundances in carbon stars
- Short Name:
- J/A+A/353/528
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The lines of ^12^CO, ^12^C^12^C, and ^12^CN used in the analysis are listed in the table. The stars analyzed here are TX Psc, V Aql, and BL Ori, and the lines selected for the analysis are listed for each star. The data given in the table are the wavenumber, gf-value, and the lower excitation potential of each selected line, together with the observed equivalent width.
- ID:
- ivo://CDS.VizieR/J/PASJ/57/65
- Title:
- CNO abundances of solar-type stars
- Short Name:
- J/PASJ/57/65
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We determined the C, N, and O abundances of 160 nearby F, G, and K dwarfs and subgiants by using spectra obtained with the HIDES spectrograph at Okayama Astrophysical Observatory, with the purposes of (1) establishing the runs of [C/Fe], [N/Fe], and [O/Fe] for these galactic disk stars in the metallicity range of -1<~[Fe/H]~<+0.4, (2) searching for any difference in the CNO abundances of planet-host stars as compared to non-planet-host stars, and (3) examining the consistency of the abundances derived from different lines to check the validity of the analysis. The non-LTE effect on the abundance determination was taken into consideration based on our extensive statistical-equilibrium calculations.
