- ID:
- ivo://CDS.VizieR/J/AJ/142/140
- Title:
- Optical spectroscopy of {rho} Oph stars. II.
- Short Name:
- J/AJ/142/140
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have completed an optical spectroscopic survey of an unbiased, extinction-limited sample of candidate young stars covering 1.3deg^2^ of the {rho} Ophiuchi star-forming region. While infrared, X-ray, and optical surveys of the cloud have identified many young stellar objects (YSOs), these surveys are biased toward particular stages of stellar evolution and are not optimal for studies of the disk frequency and initial mass function. We have obtained over 300 optical spectra to help identify 135 association members based on the presence of H{alpha} in emission, lithium absorption, X-ray emission, a mid-infrared excess, a common proper motion, reflection nebulosity, and/or extinction considerations.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/860/49
- Title:
- Optical spectroscopy of young {alpha}-rich stars
- Short Name:
- J/ApJ/860/49
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report chemical abundances of 14 young {alpha}-rich stars including neutron-capture elements based on high-quality optical spectra from HIRES/Keck I and differential line-by-line analysis. From a comparison of the abundance patterns of young {alpha}-rich stars to those of nearby bright red giants with a similar metallicity range (-0.7<[Fe/H]{<}-0.2), we confirm their high {alpha}-element abundances reported by previous studies based on near-infrared spectroscopy. We reveal for the first time low abundances of s-process elements and high abundances of r-process elements. All the abundances are consistent with those seen in the typical {alpha}-rich population of the Galactic disk, and no abundance anomalies are found except for Li-enhancement in one object previously reported and mild enhancement of Na in two stars. In particular, the lack of s-process enhancement excludes the hypothesis that mass transfer from asymptotic giant branch stars plays an important role in the formation of young {alpha}-rich stars. The high frequency of radial velocity variation (more than 50%) is also confirmed. We argue that mass transfer from low-mass red giants is the likely dominant formation mechanism for young {alpha}-rich stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/844/138
- Title:
- Optical spectroscopy toward Orion B fields
- Short Name:
- J/ApJ/844/138
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from high-resolution optical spectra toward 66 young stars in the Orion B molecular cloud to study their kinematics and other properties. Observations of the H{alpha} and Li I 6707{AA} lines are used to check membership and accretion properties. While the stellar radial velocities of NGC 2068 and L1622 are in good agreement with that of the molecular gas, many of the stars in NGC 2024 show a considerable offset. This could be a signature of either the expansion of the cluster, the high degree of the ejection of the stars from the cluster through dynamical interaction, or the acceleration of the gas due to stellar feedback.
- ID:
- ivo://CDS.VizieR/J/ApJ/784/19
- Title:
- Orphan stream high-resolution spectroscopic study
- Short Name:
- J/ApJ/784/19
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first high-resolution spectroscopic study on the Orphan stream for five stream candidates, observed with the Magellan Inamori Kyocera Echelle spectrograph on the Magellan Clay telescope. The targets were selected from the low-resolution catalog of Casey et al. (2013ApJ...764...39C): three high-probability members, one medium, and one low-probability stream candidate were observed. Our analysis indicates that the low- and medium-probability targets are metal-rich field stars. The remaining three high-probability targets range over ~1 dex in metallicity, and are chemically distinct compared to the other two targets and all standard stars: low [{alpha}/Fe] abundance ratios are observed, and lower limits are ascertained for [Ba/Y], which sit well above the Milky Way trend. These chemical signatures demonstrate that the undiscovered parent system is unequivocally a dwarf spheroidal galaxy, consistent with dynamical constraints inferred from the stream width and arc. As such, we firmly exclude the proposed association between NGC 2419 and the Orphan stream. A wide range in metallicities adds to the similarities between the Orphan stream and Segue 1, although the low [{alpha}/Fe] abundance ratios in the Orphan stream are in tension with the high [{alpha}/Fe] values observed in Segue 1. Open questions remain before Segue 1 could possibly be claimed as the "parent" of the Orphan stream. The parent system could well remain undiscovered in the southern sky.
- ID:
- ivo://CDS.VizieR/J/ApJ/764/78
- Title:
- Oxygen abundances in nearby FGK stars
- Short Name:
- J/ApJ/764/78
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Atmospheric parameters and oxygen abundances of 825 nearby FGK stars are derived using high-quality spectra and a non-local thermodynamic equilibrium analysis of the 777nm OI triplet lines. We assign a kinematic probability for the stars to be thin-disk (P_1_), thick-disk (P_2_), and halo (P_3_) members. We confirm previous findings of enhanced [O/Fe] in thick-disk (P_2_>0.5) relative to thin-disk (P_1_>0.5) stars with [Fe/H]<~-0.2, as well as a "knee" that connects the mean [O/Fe]-[Fe/H] trend of thick-disk stars with that of thin-disk members at [Fe/H]>~-0.2. Nevertheless, we find that the kinematic membership criterion fails at separating perfectly the stars in the [O/Fe]-[Fe/H] plane, even when a very restrictive kinematic separation is employed. Stars with "intermediate" kinematics (P_1_<0.7, P_2_<0.7) do not all populate the region of the [O/Fe]-[Fe/H] plane intermediate between the mean thin-disk and thick-disk trends, but their distribution is not necessarily bimodal. Halo stars (P_3_>0.5) show a large star-to-star scatter in [O/Fe]-[Fe/H], but most of it is due to stars with Galactocentric rotational velocity V<-200km/s; halo stars with V>-200km/s follow an [O/Fe]-[Fe/H] relation with almost no star-to-star scatter. Early mergers with satellite galaxies explain most of our observations, but the significant fraction of disk stars with "ambiguous" kinematics and abundances suggests that scattering by molecular clouds and radial migration have both played an important role in determining the kinematic and chemical properties of solar neighborhood stars.
- ID:
- ivo://CDS.VizieR/J/A+A/415/155
- Title:
- Oxygen abundances in the Galactic disk
- Short Name:
- J/A+A/415/155
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Oxygen abundances for the 72 program stars. Column one gives the Hipparcos number, columns 2-6 the derived oxygen abundances for the different indicators relative to the photospheric oxygen abundance {epsilon}(O)_{sun}_=8.83). Columns 7-11 give the abundances relative to our solar abundances, i.e. [O/H]_{sun}_=0 for all indicators. Columns 12-14 give the abundances for the triplet that have been corrected for NLTE effects according the the prescription in Gratton et al. (1999, Cat. <J/A+A/350/955>), and normalized to the new NLTE corrected abundance for the Sun. Column 15 gives the NLTE correction terms from Gratton et al. (1999, Cat. <J/A+A/350/955>) (GCEG) that were applied to the abundances in columns 12-14. Column 15 gives the empirical NLTE correction we determined (Eq. 1 in article}. Columns 16-19 give the measured equivalent widths for the forbidden [OI] line at 636.3nm and the permitted oxygen triplet lines at 777nm.
- ID:
- ivo://CDS.VizieR/J/ApJ/617/240
- Title:
- Oxygen abundances in the GOODS-North field
- Short Name:
- J/ApJ/617/240
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We measure nebular oxygen abundances for 204 emission-line galaxies with redshifts 0.3<z<1.0 in the Great Observatories Origins Deep Survey-North (GOODS-N) field using spectra from the Team Keck Redshift Survey, Cat. <J/AJ/127/3121>. We also provide an updated analytic prescription for estimating oxygen abundances using the traditional strong emission line ratio, R_23_, based on the photoionization models of Kewley & Dopita (2002ApJS..142...35K). We include an analytic formula for very crude metallicity estimates using the [NII]_{lambda}6584_/H{alpha} ratio.
- ID:
- ivo://CDS.VizieR/J/ApJ/817/1
- Title:
- Palomar/MSU and SDSS-DR7 M dwarfs with GALEX obs.
- Short Name:
- J/ApJ/817/1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalog of Galaxy Evolution Explorer Near-UV (NUV) and Far-UV (FUV) photometry for the Palomar/MSU and SDSS DR7 spectroscopic M dwarf catalogs. The catalog contains NUV measurements matched to 577 spectroscopically confirmed M dwarfs and FUV measurements matched to 150 spectroscopically confirmed M dwarfs. Using these data, we find that NUV and FUV luminosities strongly correlate with H{alpha} emission, a typical indicator of magnetic activity in M dwarfs. We also examine the fraction of M dwarfs with varying degrees of strong line emission at NUV wavelengths. Our results indicate that the frequency of M dwarf NUV emission peaks at intermediate spectral types, with at least ~30% of young M4-M5 dwarfs having some level of activity. For mid-type M dwarfs, we show that NUV emission decreases with distance from the Galactic plane, a proxy for stellar age. Our complete matched source catalog is available online.
- ID:
- ivo://CDS.VizieR/J/MNRAS/463/296
- Title:
- PanSTARRS-1 slow-blue nuclear hypervariables
- Short Name:
- J/MNRAS/463/296
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We discuss 76 large amplitude transients ({Delta}m>1.5) occurring in the nuclei of galaxies, nearly all with no previously known active galactic nucleus (AGN). They have been discovered as part of the Pan-STARRS1 (PS1) 3{pi} survey, by comparison with Sloan Digital Sky Survey (SDSS) photometry a decade earlier, and then monitored with the Liverpool Telescope, and studied spectroscopically with the William Herschel Telescope (WHT). Based on colours, light-curve shape, and spectra, these transients fall into four groups. A few are misclassified stars or objects of unknown type. Some are red/fast transients and are known or likely nuclear supernovae. A few are either radio sources or erratic variables and so likely blazars. However the majority (~66 per cent) are blue and evolve slowly, on a time-scale of years. Spectroscopy shows them to be AGN at z ~0.3-1.4, which must have brightened since the SDSS photometry by around an order of magnitude. It is likely that these objects were in fact AGN a decade ago, but too weak to be recognized by SDSS; they could then be classed as 'hypervariable' AGN. By searching the SDSS Stripe 82 quasar database, we find 15 similar objects. We discuss several possible explanations for these slow-blue hypervariables - (i) unusually luminous tidal disruption events; (ii) extinction events; (iii) changes in accretion state; and (iv) large amplitude microlensing by stars in foreground galaxies. A mixture of explanations (iii) and (iv) seems most likely. Both hold promise of considerable new insight into the AGN phenomenon.
- ID:
- ivo://CDS.VizieR/J/A+A/439/1137
- Title:
- PHOENIX model chromospheres of M dwarfs
- Short Name:
- J/A+A/439/1137
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an extensive identification catalog of chromospheric emission lines in the optical range. The data were obtained with ESO's Kueyen telescope equipped with the UVES spectrograph from March, 13th to 16th in 2002. The instrument was operated in dichroic mode (spectral coverage from 3030 to 3880 and from 4580 to 6680{AA}). The data for the stars Prox Cen, UV Ceti and LHS 292 were obtained with the same instrument in winter 2000/2001 with a monochroic setup providing only the blue part of the spectrum. We tabulated measured wavelength, equivalent width (EW) and FWHM for every line and star and also provide the rest wavelength from the Moore catalog which was used for identification (Moore 1972). Few lines were identified with the NIST database. The spectra were all corrected for radial velocity besides Kelu-1, DENIS-P J1058.7-1548 and 2MASSI J1315309-264951. DENIS-P J1058.7-1548 has no detected lines, and therefore no data in the table.
