- ID:
- ivo://CDS.VizieR/J/MNRAS/448/2717
- Title:
- Bayesian analysis of resolved stellar spectra
- Short Name:
- J/MNRAS/448/2717
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We introduce a Bayesian method for fitting faint, resolved stellar spectra in order to obtain simultaneous estimates of redshift and stellar-atmospheric parameters. We apply the method to thousands of spectra - covering 5160-5280{AA} at resolution R~20000 - that we have acquired with the MMT/Hectochelle fibre spectrograph for red giant and horizontal branch candidates along the line of sight to the Milky Way's dwarf spheroidal satellite in Draco. The observed stars subtend an area of ~4deg^2^, extending ~3 times beyond Draco's nominal 'tidal' radius. For each spectrum, we tabulate the first four moments - central value, variance, skewness and kurtosis - of posterior probability distribution functions representing estimates of the following physical parameters: line-of-sight velocity (v_los_), effective temperature (T_eff_), surface gravity (logg) and metallicity ([Fe/H]). After rejecting low-quality measurements, we retain a new sample consisting of 2813 independent observations of 1565 unique stars, including 1879 observations for 631 stars with (as many as 13) repeat observations. Parameter estimates have median random errors of v_los_=0.88km/s, T_eff_=162K, {sigma}logg=0.37dex and {sigma}[Fe/H]=0.20dex. Our estimates of physical parameters distinguish ~470 likely Draco members from interlopers in the Galactic foreground.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/752/56
- Title:
- BDKP. III. Parallaxes for 70 ultracool dwarfs
- Short Name:
- J/ApJ/752/56
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report parallax measurements for 70 ultracool dwarfs (UCDs) including 11 late-M, 32 L, and 27 T dwarfs. In this sample, 14 M and L dwarfs exhibit low surface gravity features, 6 are close binary systems, and 2 are metal-poor subdwarfs. We combined our new measurements with 114 previously published UCD parallaxes and optical-mid-IR photometry to examine trends in spectral-type/absolute magnitude, and color-color diagrams. We report new polynomial relations between spectral type and M_JHK_. Including resolved L/T transition binaries in the relations, we find no reason to differentiate between a "bright" (unresolved binary) and a "faint" (single source) sample across the L/T boundary. Isolating early T dwarfs, we find that the brightening of T0-T4 sources is prominent in M_J_ where there is a [1.2-1.4] mag difference. A similar yet dampened brightening of [0.3-0.5] mag happens at M_H_ and a plateau or dimming of [-0.2 to -0.3] mag is seen in M_K_. Comparison with evolutionary models that vary gravity, metallicity, and cloud thickness verifies that for L into T dwarfs, decreasing cloud thickness reproduces brown dwarf near-IR color-magnitude diagrams. However we find that a near constant temperature of 1200 +/-100 K along a narrow spectral subtype of T0-T4 is required to account for the brightening and color-magnitude diagram of the L-dwarf/T-dwarf transition. There is a significant population of both L and T dwarfs which are red or potentially "ultra-cloudy" compared to the models, many of which are known to be young indicating a correlation between enhanced photospheric dust and youth. For the low surface gravity or young companion L dwarfs we find that 8 out of 10 are at least [0.2-1.0] mag underluminous in M_JH_and/or M_K_compared to equivalent spectral type objects. We speculate that this is a consequence of increased dust opacity and conclude that low surface gravity L dwarfs require a completely new spectral-type/absolute magnitude polynomial for analysis.
- ID:
- ivo://CDS.VizieR/J/ApJ/731/119
- Title:
- BHB candidates in Sagittarius stream
- Short Name:
- J/ApJ/731/119
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use a sample of blue horizontal branch (BHB) stars from the Sloan Digital Sky Survey Data Release 7 (Cat. II/294) to explore the structure of the tidal tails from the Sagittarius Dwarf Galaxy. We use a method yielding BHB star candidates with up to ~70% purity from photometry alone. The resulting sample has a distance precision of roughly 5% and can probe distances in excess of 100kpc. Using this sample, we identify a possible extension to the trailing arm at distances of 60-80kpc from the Sun with an estimated significance of at least 3.8{sigma}. Current models predict that a distant "returning" segment of the debris stream should exist, but place it substantially closer to the Sun where no debris is observed in our data. Exploiting the distance precision of our tracers, we estimate the mean line-of-sight thickness of the leading arm to be ~3kpc, and show that the two "bifurcated" branches of the debris stream differ by only 1-2kpc in distance. With a spectroscopic very pure BHB star subsample, we estimate the velocity dispersion in the leading arm, 37km/s, which is in reasonable agreement with models of Sgr disruption. We finally present a sample of high-probability Sgr BHB stars in the leading arm of Sgr, selected to have distances and velocities consistent with Sgr membership, to allow further study.
- ID:
- ivo://CDS.VizieR/J/AJ/130/1097
- Title:
- BHB stars in Century Survey Galactic Halo Project
- Short Name:
- J/AJ/130/1097
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We discuss a 175{deg}2 spectroscopic survey for blue horizontal branch (BHB) stars in the Galactic halo. We use the Two Micron All Sky Survey (2MASS, <II/246>) and the Sloan Digital Sky Survey (SDSS) to select BHB candidates, and we find that the 2MASS and SDSS color selection is 38% and 50% efficient, respectively, for BHB stars. Our samples include one likely runaway B7 star 6kpc below the Galactic plane.
- ID:
- ivo://CDS.VizieR/J/ApJ/799/72
- Title:
- Binary AGNs from the VLA Stripe 82 survey
- Short Name:
- J/ApJ/799/72
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Galaxy mergers play an important role in the growth of galaxies and their supermassive black holes. Simulations suggest that tidal interactions could enhance black hole accretion, which can be tested by the fraction of binary active galactic nuclei (AGNs) among galaxy mergers. However, determining the fraction requires a statistical sample of binaries. We have identified kiloparsec-scale binary AGNs directly from high-resolution radio imaging. Inside the 92deg^2^ covered by the high-resolution Very Large Array survey of the Sloan Digital Sky Survey (SDSS) Stripe 82 field, we identified 22 grade A and 30 grade B candidates of binary radio AGNs with angular separations less than 5" (10kpc at z=0.1). Eight of the candidates have optical spectra for both components from the SDSS spectroscopic surveys and our Keck program. Two grade B candidates are projected pairs, but the remaining six candidates are all compelling cases of binary AGNs based on either emission line ratios or the excess in radio power compared to the H{alpha}-traced star formation rate. Only two of the six binaries were previously discovered by an optical spectroscopic search. Based on these results, we estimate that ~60% of our binary candidates would be confirmed once we obtain complete spectroscopic information. We conclude that wide-area high-resolution radio surveys offer an efficient method to identify large samples of binary AGNs. These radio-selected binary AGNs complement binaries identified at other wavelengths and are useful for understanding the triggering mechanisms of black hole accretion.
- ID:
- ivo://CDS.VizieR/J/AJ/131/1
- Title:
- Binary quasars in the SDSS
- Short Name:
- J/AJ/131/1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a sample of 221 new quasar pairs with proper transverse separations R_prop_<1h^1^Mpc over the redshift range 0.5<z<3.0, discovered from an extensive follow-up campaign to find companions around the Sloan Digital Sky Survey (Cat. <VII/243>) and 2dF QSO Redshift Survey (Cat. <VII/241>) quasars. This sample includes 26 new binary quasars with separations R_prop_<50h^-1^kpc ({thetas}<10"), more than doubling the number of such systems known. We define a statistical sample of binaries selected with homogeneous criteria and compute its selection function, taking into account sources of incompleteness. The first measurement of the quasar correlation function on scales 10h^-1^kpc<R_prop_<400h^-1^kpc is presented.
- ID:
- ivo://CDS.VizieR/J/ApJ/794/35
- Title:
- Binary white dwarfs atmospheric parameters
- Short Name:
- J/ApJ/794/35
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a detailed spectroscopic analysis of 61 low-mass white dwarfs and provide precise atmospheric parameters, masses, and updated binary system parameters based on our new model atmosphere grids and the most recent evolutionary model calculations. For the first time, we measure systematic abundances of He, Ca, and Mg for metal-rich, extremely low mass white dwarfs and examine the distribution of these abundances as a function of effective temperature and mass. Based on our preliminary results, we discuss the possibility that shell flashes may be responsible for the presence of the observed He and metals. We compare stellar radii derived from our spectroscopic analysis to model-independent measurements and find good agreement except for white dwarfs with T_eff_<~10000 K. We also calculate the expected gravitational wave strain for each system and discuss their significance to the eLISA space-borne gravitational wave observatory. Finally, we provide an update on the instability strip of extremely low mass white dwarf pulsators.
38. BL Lac from SDSS
- ID:
- ivo://CDS.VizieR/J/AJ/129/2542
- Title:
- BL Lac from SDSS
- Short Name:
- J/AJ/129/2542
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a sample of 386 BL Lacertae candidates identified from 2860deg^2^ of the Sloan Digital Sky Survey (SDSS) spectroscopic database. The candidates are primarily selected to have quasi-featureless optical spectra and low proper motions as measured from SDSS and USNO-B positions; however, our ability to separate Galactic from extragalactic quasi-featureless objects (QFOs) on the basis of proper motion alone is limited by the lack of reliable proper motion measurements for faint objects. Based largely on this remarkably clean color separation, we subdivide the sample into 240 probable candidates and 146 additional less probable (likely stellar) candidates.
- ID:
- ivo://CDS.VizieR/J/A+A/538/A26
- Title:
- BL Lac objects beyond z=1.3
- Short Name:
- J/A+A/538/A26
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Observations of the {gamma}-ray sky with Fermi led to significant advances towards understanding blazars, the most extreme class of active galactic nuclei. A large fraction of the population detected by Fermi is formed by BL Lacertae (BL Lac) objects, whose sample has always suffered from a severe redshift incompleteness due to the quasi-featureless optical spectra. Our goal is to provide a significant increase of the number of confirmed high-redshift BL Lac objects contained in the 2 LAC Fermi/LAT catalog.
- ID:
- ivo://CDS.VizieR/J/MNRAS/438/557
- Title:
- BLR-less AGNs in Stripe82
- Short Name:
- J/MNRAS/438/557
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This is the first paper in a dedicated series to study the properties of the optically-selected broad-line-region-less (BLR-less) active galactic nuclei (AGNs; with no-hidden central broad emission line regions). We carried out a systematic search for the BLR-less AGNs through the Sloan Digital Sky Survey Legacy Survey (SDSS Stripe82 Database). Based on the spectral decomposition results for all the 136 676 spectroscopic objects (galaxies and quasars) with redshift less than 0.35 covered by the SDSS Stripe82 region, our spectroscopic sample for the BLR-less AGNs includes 22 693 pure narrow line objects without broad emission lines but with apparent AGN continuum emission R_AGN_>0.3 and apparent stellar lights R_ssp_>0.3. Then, using the properties of the photometry magnitude RMS (RMS) and Pearson's coefficients (R_1,2_) between two different SDSS band light curves: RMS_k_>3xRMS_Mk_ and R_1,2_>~0.8, the final 281 pure narrow line objects with true photometry variabilities are our selected reliable candidates for the BLR-less AGNs. The selected candidates with higher confidence levels not only have the expected spectral features of the BLR-less AGNs, but also show significant true photometry variabilities. The reported sample enlarges at least four times the current sample of the BLR-less AGNs, and will provide more reliable information to explain the lack of the BLRs of AGNs in our following studies.
