- ID:
- ivo://CDS.VizieR/J/A+AS/114/109
- Title:
- Cha X-ray sources & optical identifications
- Short Name:
- J/A+AS/114/109
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the observations of the ROSAT all-sky survey (RASS) in the direction of the Chamaeleon cloud complex, as well as the spectroscopic identifications of the detected X-ray sources. The main purpose of this identification program was the search for low mass pre-main sequence stars. Sixteen previously known PMS stars were detected with high confidence by ROSAT. Eight are classical T Tauri stars and eight are weak-line T Tauri stars. Seventy-seven new weak-line T Tauri stars were identified on the basis of the presence of strong Li {lambda}6707 absorption, spectral type later than F0 and chromospheric emission. We give coordinates and count rates of the X-ray sources, and present optical spectra and finding charts for the sources identified optically as new pre-main sequence stars. Optical UBV(RI)c and near-infrared JHKLM photometry for this sample of stars is also provided. In addition, 6 new dKe-dMe candidates are found among the RASS sources.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/576/A122
- Title:
- 3C 273 high energy spectrum
- Short Name:
- J/A+A/576/A122
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The high energy spectrum of 3C 273 is usually understood in terms of inverse-Compton emission in a relativistic leptonic jet. This model predicts variability patterns and delays that could be tested with simultaneous observations from the radio to the GeV range. The instruments IBIS, SPI, JEM-X on board INTEGRAL, PCA on board RXTE, and LAT on board Fermi have enough sensitivity to follow the spectral variability of 3C 273 from the keV to the GeV. We looked for correlations between the different energy bands, including radio data at 37GHz collected at the Metsahovi Radio Observatory and built quasi-simultaneous multiwavelength spectra in the high energy domain when the source is flaring either in the X-rays or in the {gamma} rays.
- ID:
- ivo://CDS.VizieR/J/AJ/131/1262
- Title:
- Circular polarization images at 15GHz of AGN jets
- Short Name:
- J/AJ/131/1262
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report first-epoch circular polarization results for 133 active galactic nuclei in the MOJAVE (Monitoring of Jets in Active Galactic Nuclei with VLBA Experiments) program to monitor the structure and polarization of a flux-limited sample of extragalactic radio jets with the VLBA at 15GHz. We found strong circular polarization (0.3%) in approximately 15% of our sample. The circular polarization was usually associated with jet cores; however, we did find a few strong jet components to be circularly polarized.
- ID:
- ivo://CDS.VizieR/J/ApJ/796/140
- Title:
- Circumgalactic medium surrounding z~2 quasars
- Short Name:
- J/ApJ/796/140
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We survey the incidence and absorption strength of the metal-line transitions C II 1334 and C IV 1548 from the circumgalactic medium (CGM) surrounding z~2 quasars, which act as signposts for massive dark matter halos M_halo_~10^12.5^ M_{sun}_. On scales of the virial radius (r_vir_~160 kpc), we measure a high covering fraction f_C_=0.73+/-0.10 to strong C II 1334 absorption (rest equivalent width W_1334_>=0.2 {AA}), implying a massive reservoir of cool (T~10^4^ K) metal enriched gas. We conservatively estimate a metal mass exceeding 10^8^ M_{sun}_. We propose that these metals trace enrichment of the incipient intragroup/intracluster medium that these halos eventually inhabit. This cool CGM around quasars is the pinnacle among galaxies observed at all epochs, as regards covering the fraction and average equivalent width of H I Ly{alpha} and low-ion metal absorption. We argue that the properties of this cool CGM primarily reflect the halo mass, and that other factors such as feedback, star-formation rate, and accretion from the intergalactic medium are secondary. We further estimate that the CGM of massive, z~2 galaxies accounts for the majority of strong Mg II absorption along random quasar sightlines. Last, we detect an excess of strong C IV 1548 absorption (W_1548_>=0.3 {AA}) over random incidence to the 1 Mpc physical impact parameter and measure the quasar-C IV cross-correlation function: {zeta}_CIV_-Q(r)=(r/r_0_)^-{gamma}^ with r_0_=7.5_-1.4_^+2.8^ h^-1^ Mpc and {gamma}=1.7_-0.2_^+0.1^. Consistent with previous work on larger scales, we infer that this highly ionized C IV gas traces massive (10^12^ M_{sun}_) halos.
- ID:
- ivo://CDS.VizieR/J/ApJ/666/757
- Title:
- CIV 1549{AA} emission line in AGNs
- Short Name:
- J/ApJ/666/757
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We are exploring a spectroscopic unification for all types of broad-line emitting AGNs. The four-dimensional Eigenvector 1 (4DE1) parameter space organizes quasar diversity in a sequence primarily governed by Eddington ratio. This paper considers the role of CIV {lambda}1549 measures as 4DE1 diagnostics. We use HST archival spectra for 130 sources with S/N high enough to permit reliable CIV {lambda}1549 broad-component measures.
- ID:
- ivo://CDS.VizieR/J/MNRAS/449/1593
- Title:
- CIV absorption in BAL QSOs
- Short Name:
- J/MNRAS/449/1593
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- There is a large diversity in the CIV broad absorption line (BAL) profile among BAL quasars (BALQs). We quantify this diversity by exploring the distribution of the CIV BAL properties, full width at half-maximum (FWHM), maximum depth of absorption and its velocity shift (v_md_), using the Sloan Digital Sky Survey DR7 quasar catalogue. We find the following: (i) Although the median CIV BAL profile in the quasar rest-frame becomes broader and shallower as the UV continuum slope ({alpha}UV at 1700-3000{AA}) gets bluer, the median individual profile in the absorber rest-frame remains identical, and is narrow (FWHM=3500km/s) and deep. Only 4 percent of BALs have FWHM>10000km/s. (ii) As the HeII emission equivalent width (EW) decreases, the distributions of FWHM and v_md_ extend to larger values, and the median maximum depth increases. These trends are consistent with theoretical models in which softer ionizing continua reduce overionization, and allow radiative acceleration of faster BAL outflows. (iii) As {alpha}_UV_ becomes bluer, the distribution of v_md_ extends to larger values. This trend may imply faster outflows at higher latitudes above the accretion disc plane. (iv) For non-BALQs, the CIV emission line decreases with decreasing HeII EW, and becomes more asymmetric and blueshifted. This suggests an increasing relative contribution of emission from the BAL outflow to the Civ emission line as the ionizing spectral energy distribution (SED) gets softer, which is consistent with the increasing fraction of BALQs as the ionizing SED gets softer.
- ID:
- ivo://CDS.VizieR/J/A+A/473/791
- Title:
- CIV absorption in DLAs and sub-DLAs systems
- Short Name:
- J/A+A/473/791
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a study of CIV absorption in a sample of 63 damped Lyman-{alpha} (DLA) systems and 11 sub-DLAs in the redshift range 1.75<z_abs_<3.61, using a dataset of high-resolution (6.6km/s FWHM), high signal-to-noise VLT/UVES spectra. The complex absorption line profiles show both narrow and broad CIV components, indicating the presence of both warm, photoionized and hot, collisionally ionized gas. We report new correlations between the metallicity (measured in the neutral-phase) and each of the CIV column density, the CIV total line width, and the maximum CIV velocity.
- ID:
- ivo://CDS.VizieR/J/ApJ/702/767
- Title:
- CIV and FeK{alpha} Baldwin effects in AGNs
- Short Name:
- J/ApJ/702/767
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use UV/optical and X-ray observations of 272 radio-quiet Type 1 active galactic nuclei and quasars to investigate the CIV Baldwin Effect (BEff). The UV/optical spectra are drawn from the Hubble Space Telescope, International Ultraviolet Explorer and Sloan Digital Sky Survey archives. The X-ray spectra are from the Chandra and XMM-Newton archives. We apply correlation and partial-correlation analyses to the equivalent widths (EWs), continuum monochromatic luminosities, and {alpha}_ox_, which characterizes the relative X-ray to UV brightness. The EW of the CIV{lambda}1549 emission line is correlated with both {alpha}_ox_ and luminosity. In our sample, narrow Fe K{alpha} 6.4keV emission lines are detected in 50 objects.
- ID:
- ivo://CDS.VizieR/J/ApJ/777/168
- Title:
- CIV and SiIV broad absorption line troughs in SDSS
- Short Name:
- J/ApJ/777/168
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a detailed investigation of the variability of 428 CIV and 235 SiIV broad absorption line (BAL) troughs identified in multi-epoch observations of 291 quasars by the Sloan Digital Sky Survey-I/II/III. These observations primarily sample rest-frame timescales of 1-3.7yr over which significant rearrangement of the BAL wind is expected. We derive a number of observational results on, e.g., the frequency of BAL variability, the velocity range over which BAL variability occurs, the primary observed form of BAL-trough variability, the dependence of BAL variability upon timescale, the frequency of BAL strengthening versus weakening, correlations between BAL variability and BAL-trough profiles, relations between CIV and SiIV BAL variability, coordinated multi-trough variability, and BAL variations as a function of quasar properties. We assess implications of these observational results for quasar winds. Our results support models where most BAL absorption is formed within an order-of-magnitude of the wind-launching radius, although a significant minority of BAL troughs may arise on larger scales. We estimate an average lifetime for a BAL trough along our line-of-sight of a few thousand years. BAL disappearance and emergence events appear to be extremes of general BAL variability, rather than being qualitatively distinct phenomena. We derive the parameters of a random-walk model for BAL EW variability, finding that this model can acceptably describe some key aspects of EW variability. The coordinated trough variability of BAL quasars with multiple troughs suggests that changes in "shielding gas" may play a significant role in driving general BAL variability.
- 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.
