- ID:
- ivo://CDS.VizieR/J/MNRAS/435/3306
- Title:
- Candidate type II QSOs in SDSS III
- Short Name:
- J/MNRAS/435/3306
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- At low redshifts, dust-obscured quasars often have strong yet narrow permitted lines in the rest-frame optical and ultraviolet, excited by the central active nucleus, earning the designation type II quasars. We present a sample of 145 candidate type II quasars at redshifts between 2 and 4.3, encompassing the epoch at which quasar activity peaked in the universe. These objects, selected from the quasar sample of the Baryon Oscillation Spectroscopic Survey of the Sloan Digital Sky Survey III, are characterized by weak continuum in the rest-frame ultraviolet (typical continuum magnitude of i~22) and strong lines of CIV and Ly{alpha}, with full width at half-maximum less than 2000km/s. The continuum magnitudes correspond to an absolute magnitude of -23 or brighter at redshift 3, too bright to be due exclusively to the host galaxies of these objects. Roughly one third of the objects are detected in the shorter wavelength bands of the Wide-Field Infrared Survey Explorer survey; the spectral energy distributions of these objects appear to be intermediate between classic type I and type II quasars seen at lower redshift. Five objects are detected at rest frame 6{mu}m by Spitzer, implying bolometric luminosities of several times 10^46^erg/s. We have obtained polarization measurements for two objects; they are roughly 3 percent polarized. We suggest that these objects are luminous quasars, with modest dust extinction (A_V_~0.5mag), whose ultraviolet continuum also includes a substantial scattering contribution. Alternatively, the line of sight to the central engines of these objects may be obscured by optically thick material whose covering fraction is less than unity.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/ApJS/194/6
- Title:
- Candidate X-ray emitting OB stars in Carina
- Short Name:
- J/ApJS/194/6
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the results of a new survey of massive, OB stars throughout the Carina Nebula using the X-ray point source catalog provided by the Chandra Carina Complex Project (CCCP) in conjunction with infrared (IR) photometry from the Two Micron All-Sky Survey and the Spitzer Space Telescope Vela-Carina survey. Mid-IR photometry is relatively unaffected by extinction, hence it provides strong constraints on the luminosities of OB stars, assuming that their association with the Carina Nebula, and hence their distance, is confirmed. We fit model stellar atmospheres to the optical (UBV) and IR spectral energy distributions (SEDs) of 182 OB stars with known spectral types and measure the bolometric luminosity and extinction for each star. Using X-ray emission as a strong indicator of association with Carina, we identify 94 candidate OB stars with L_bol_>~10^4^L_{sun}_ by fitting their IR SEDs. If the candidate OB stars are eventually confirmed by follow-up spectroscopic observations, the number of cataloged OB stars in the Carina Nebula will increase by ~50%.
- ID:
- ivo://CDS.VizieR/J/ApJ/838/61
- Title:
- Candidate X-ray OB stars in MYStIX regions
- Short Name:
- J/ApJ/838/61
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Massive O-type and early B-type (OB) stars in the nearby Galaxy remain incompletely cataloged due to high extinction, bright visible and infrared nebular emission in H II regions, and high field star contamination. These difficulties are alleviated by restricting the search to stars with X-ray emission. Using the X-ray point sources from the Massive Young Star-forming Complex Study in Infrared and X-Rays (MYStIX) survey of OB-dominated regions, we identify 98 MYStIX candidate OB (MOBc) stars by fitting their 1-8{mu}m spectral energy distributions (SEDs) with reddened stellar atmosphere models. We identify 27 additional MOBc stars based on JHK_S_ photometry of X-ray stars lacking SED fitting. These candidate OB stars indicate that the current census of stars earlier than B1, taken across the 18 MYStIX regions studied, is less than 50% complete. We also fit the SEDs of 239 previously published OB stars to measure interstellar extinction and bolometric luminosities, revealing six candidate massive binary systems and five candidate O-type (super)giants. As expected, candidate OB stars have systematically higher extinction than previously published OB stars. Notable results for individual regions include identification of the OB population of a recently discovered massive cluster in NGC 6357, an older OB association in the M17 complex, and new massive luminous O stars near the Trifid Nebula. In several relatively poorly studied regions (RCW 38, NGC 6334, NGC 6357, Trifid, and NGC 3576), the OB populations may increase by factors of 2.
- ID:
- ivo://CDS.VizieR/J/AJ/158/235
- Title:
- Candidate X-ray sources in IRAS 09002-4732 region
- Short Name:
- J/AJ/158/235
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- IRAS 09002-4732 is a poorly studied embedded cluster of stars in the Vela Molecular Ridge at a distance of 1.7 kpc. Deep observations with the Chandra X-ray Observatory, combined with existing optical and infrared surveys, produce a catalog of 441 probable pre-main-sequence members of the region. The stellar spatial distribution has two components: most stars reside in a rich, compact, elliptical cluster, but a minority reside within a molecular filament several parsecs long that straddles the cluster. The filament has active distributed star formation with dozens of unclustered protostars. The cluster pre-main-sequence population is =<0.8 Myr old and deeply embedded; its most massive member is extremely young, producing an ultracompact H II region. The cluster total population deduced from the X-ray luminosity function is surprisingly rich, twice that of the Orion Nebula Cluster. The cluster core is remarkably dense where strong N-body interactions should be occurring; its initial mass function may be deficient in massive stars. We infer that IRAS 09002-4732 is a rare case where a rich cluster is forming today in a molecular filament, consistent with astrophysical models of cluster formation in clouds that involve the hierarchical formation and merging of groups in molecular filaments.
- ID:
- ivo://CDS.VizieR/J/ApJ/822/49
- Title:
- Candidate YSOs in AFGL 333 with NEWFIRM & Spitzer
- Short Name:
- J/ApJ/822/49
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- One of the key questions in the field of star formation is the role of stellar feedback on the subsequent star formation process. The W3 giant molecular cloud complex at the western border of the W4 super bubble is thought to be influenced by the massive stars in W4. This paper presents a study of the star formation activity within AFGL 333, a ~10^4^M_{sun}_ cloud within W3, using deep JHKs photometry obtained from the NOAO Extremely Wide Field Infrared Imager combined with Spitzer IRAC and MIPS photometry. Based on the infrared excess, we identify 812 candidate young stellar objects (YSOs) in the complex, of which 99 are Class I and 713 are Class II sources. The stellar density analysis of YSOs reveals three major stellar aggregates within AFGL333, namely AFGL 333 Main, AFGL 333 NW1 and AFGL 333 NW2. The disk fraction within AFGL 333 is estimated to be ~50%-60%. We use the extinction map made from the H-K_s_ colors of the background stars and CO data to understand the cloud structure and to estimate the cloud mass. From the stellar and cloud mass associated with AFGL 333, we infer that the region is currently forming stars with an efficiency of ~4.5% and at a rate of ~2-3M_{sun}_/Myr/pc^2^. In general, the star formation activity within AFGL 333 is comparable to that of nearby low mass star-forming regions. We do not find any strong evidence to suggest that the stellar feedback from the massive stars of nearby W4 super bubble has affected the global star formation properties of the AFGL 333 region.
- ID:
- ivo://CDS.VizieR/J/AJ/130/1177
- Title:
- C and N abundances for M15 stars
- Short Name:
- J/AJ/130/1177
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an analysis of a large sample of moderate-resolution Keck Low Resolution Imaging Spectrometer spectra of subgiants and stars at the base of the red giant branch (RGB) in the Galactic globular cluster (GC) M15 (NGC 7078), most within the range 16.5<V<19.5 (1.2<M_V_<4.2), with the goal of deriving C abundances (from the G band of CH) and N abundances (from the NH band at 3360{AA}).
- ID:
- ivo://CDS.VizieR/J/A+A/506/711
- Title:
- Canis Major R1 X-ray sources
- Short Name:
- J/A+A/506/711
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The CMa R1 star-forming region contains several compact clusters as well as many young early-B stars. It is associated with a well-known bright rimmed nebula, the nature of which is unclear (fossil HII region or supernova remnant). To help elucidate the nature of the nebula, our goal was to reconstruct the star-formation history of the CMa R1 region, including the previously unknown older, fainter low-mass stellar population, using X-rays. We analyzed images obtained with the ROSAT satellite, covering ~5deg^2^. Complementary VRI photometry was performed with the Gemini South telescope. Colour-magnitude and colour-colour diagrams were used in conjunction with pre-main sequence evolutionary tracks to derive the masses and ages of the X-ray sources.
- ID:
- ivo://CDS.VizieR/J/MNRAS/376/313
- Title:
- Carbon star in Magellanic Cloud
- Short Name:
- J/MNRAS/376/313
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Dust radiative transfer models are presented for 60 carbon stars in the Magellanic Clouds (MCs) for which 535m Spitzer infrared spectrograph (IRS) spectra and quasi-simultaneous ground-based JHKL photometry are available. From the modelling, the luminosity and mass-loss rate are derived (under the assumption of a fixed expansion velocity and dust-to-gas ratio), and the ratio of silicon carbide (SiC) to amorphous carbon (AMC) dust is also derived. This ratio is smaller than observed in Galactic carbon stars, as has been noted before. Light curves for 36 objects can be retrieved from the massive compact halo object (MACHO) and optical gravitational lensing experiment (OGLE) data bases, and periods can be derived for all but two of these. Including data from the literature, periods are available for 53 stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/765/12
- Title:
- Carbon stars and DQ white dwarfs from SDSS-DR7+DR8
- Short Name:
- J/ApJ/765/12
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Among stars showing carbon molecular bands (C stars), the main-sequence dwarfs, likely in post-mass transfer binaries, are numerically dominant in the Galaxy. Via spectroscopic selection from the Sloan Digital Sky Survey, we retrieve 1220 high galactic latitude C stars, ~5 times more than previously known, including a wider variety than past techniques such as color or grism selection have netted, and additionally yielding 167 DQ white dwarfs. Of the C stars with proper motion measurements, we identify 69% clearly as dwarfs (dCs), while ~7% are giants. The dCs likely span absolute magnitudes M_i_ from ~6.5 to 10.5. "G-type" dC stars with weak CN and relatively blue colors are probably the most massive dCs still cool enough to show C_2_bands. We report Balmer emission in 22 dCs, none of which are G-types. We find 8 new DA/dC stars in composite spectrum binaries, quadrupling the total sample of these "smoking guns" for AGB binary mass transfer. Eleven very red C stars with strong red CN bands appear to be "N"-type AGB stars at large Galactocentric distances, one likely a new discovery in the dIrr galaxy Leo A. Two such stars within 30' of each other may trace a previously unidentified dwarf galaxy or tidal stream at ~40 kpc. We explore the multiwavelength properties of the sample and report the first X-ray detection of a dC star, which shows strong Balmer emission. Our own spectroscopic survey additionally provides the dC surface density from a complete sample of dwarfs limited by magnitude, color, and proper motion.
- ID:
- ivo://CDS.VizieR/J/ApJS/226/1
- Title:
- Carbon stars from LAMOST DR2 data
- Short Name:
- J/ApJS/226/1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this work, we present the new catalog of carbon stars from the LAMOST DR2 catalog. In total, 894 carbon stars are identified from multiple line indices measured from the stellar spectra. We are able to identify the carbon stars by combining the CN bands in the red end with C_2_ and other lines. Moreover, we also classify the carbon stars into spectral sub-types of C-H, C-R, and C-N. These sub-types show distinct features in the multi-dimensional line indices, implying that in the future they can be used to identify carbon stars from larger spectroscopic data sets. While the C-N stars are clearly separated from the others in the line index space, we find no clear separation between the C-R and C-H sub-types. The C-R and C-H stars seem to smoothly transition from one to another. This may hint that the C-R and C-H stars may not be different in their origins, instead their spectra look different because of different metallicities. Due to the relatively low spectral resolution and lower signal-to-noise ratio, the ratio of ^12^C/^13^C is not measured and thus the C-J stars are not identified.
