- 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.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJS/220/18
- Title:
- BDKP IV. RVs of late-M and L dwarfs with MagE
- Short Name:
- J/ApJS/220/18
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Radial velocity measurements are presented for 85 late M- and L-type very low-mass stars and brown dwarfs obtained with the Magellan Echellette spectrograph. Targets primarily have distances within 20pc of the Sun, with more distant sources selected for their unusual spectral energy distributions. We achieved precisions of 2-3km/s, and combined these with astrometric and spectrophotometric data to calculate UVW velocities. Most are members of the thin disk of the Galaxy, and velocity dispersions indicate a mean age of 5.2+/-0.2Gyr for sources within 20pc. We find significantly different kinematic ages between late-M dwarfs (4.0+/-0.2Gyr) and L dwarfs (6.5+/-0.4Gyr) in our sample that are contrary to predictions from prior simulations. This difference appears to be driven by a dispersed population of unusually blue L dwarfs which may be more prevalent in our local volume-limited sample than in deeper magnitude-limited surveys. The L dwarfs exhibit an asymmetric U velocity distribution with a net inward flow, similar to gradients recently detected in local stellar samples. Simulations incorporating brown dwarf evolution and Galactic orbital dynamics are unable to reproduce the velocity asymmetry, suggesting non-axisymmetric perturbations or two distinct L dwarf populations. We also find the L dwarfs to have a kinematic age-activity correlation similar to more massive stars. We identify several sources with low surface gravities, and two new substellar candidate members of nearby young moving groups: the astrometric binary DENIS J08230313-4912012AB, a low-probability member of the {beta} Pictoris Moving Group; and 2MASS J15104786-2818174, a moderate-probability member of the 30-50Myr Argus Association.
- ID:
- ivo://CDS.VizieR/J/AJ/160/32
- Title:
- beta Cephei light curves from KELT project
- Short Name:
- J/AJ/160/32
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a search for Galactic {beta} Cephei stars, which are massive pulsating stars with both pressure modes and mixed modes. Thus, these stars can serve as benchmarks for seismological studies of the interiors of massive stars. We conducted the search by performing a frequency analysis on the optical light curves of known O- and B-type stars with data from the Kilodegree Extremely Little Telescope exoplanet survey. We identify 113 {beta} Cephei stars, of which 86 are new discoveries, which altogether represent a 70% increase in the number currently known. An additional 97 candidates are identified. Among our targets, we find five new eclipsing binaries and 22 stars with equal frequency spacings suggestive of rotational splitting of nonradial pulsation modes. Candidates for runaway stars among our targets and a number of interesting individual objects are discussed. Most of the known and newly discovered {beta} Cephei stars will be observed by the Transiting Exoplanet Survey Satellite mission, providing by far the most comprehensive observational data set of massive main-sequence pulsating stars of sufficient quality for detailed asteroseismic studies. Future analysis of these light curves has the potential to dramatically increase our understanding of the structure of stellar interiors and the physical processes taking place therein.
- ID:
- ivo://CDS.VizieR/VI/32
- Title:
- Bidelman-Parsons Spectroscopic/Bibliographic Cat
- Short Name:
- VI/32
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Bidelman-Parsons Spectroscopic and Bibliographical Catalog (BPSB; Parsons, Buta, and Bidelman 1980a, b) contains data compiled from the astronomical literature by W. P. Bidelman. These data include diverse catalogs and lists, especially from pre-1950 journals (minor as well as major), and from pre-1962 observatory publications. From more recent years, the data on any object frequently are limited to one item with a reference; for example, a spectral type. No data published after 1973 are included. Over 200 publications are represented. The BPSB has information on 40,312 objects. The catalog contains most of the same information on MK spectral types as the Catalogue of Stellar Spectra Classified in the Morgan-Keenan System (Jaschek, Conde, and de Sierra 1964) and its updates, but it also includes such items as spectral types without a luminosity class (certainly better than nothing); spectroscopic absolute magnitudes; notes on multiplicity; notes on high proper motion or radial velocity (with the values, if probably variable, or if greater than 60 km/s); unpublished remarks and spectral types from several sources, including Bidelman and Henize; and Bidelman's preliminary identifications of many sources in the Two-Micron Sky Survey (Neugebauer and Leighton 1969). Some of the longer lists included in the catalog are those of OB stars from the Tonantzintla-Tacubaya and Heidelberg-Koenigstuhl surveys (Iriarte and Chavira 1957; Chavira 1958; Klare and Szeidl 1966); that of OB stars with emission from the Case-Hamburg surveys (Hardorp et al. 1959; Stock, Nassau, and Stephenson 1960; Hardorp, Theile, and Voigt 1964; Nassau and Stephenson 1963; Hardorp, Theile, and Voigt 1965; Nassau, Stephenson, and MacConnell 1965; Stephenson and Sanduleak 1971); and stars from the General Catalogue of Variable Stars (Kukarkin et al. 1969); and the Catalogue of Suspected Variable Stars (Kukarkin et al. 1951, 1965). Although the catalog is mainly of stellar data, it includes many galactic nebulae of various kinds.
- ID:
- ivo://CDS.VizieR/J/AJ/152/16
- Title:
- Bolometric flux estimation for cool evolved stars
- Short Name:
- J/AJ/152/16
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Estimation of bolometric fluxes (F_BOL_) is an essential component of stellar effective temperature determination with optical and near-infrared interferometry. Reliable estimation of F_BOL_ simply from broadband K-band photometry data is a useful tool in those cases were contemporaneous and/or wide-range photometry is unavailable for a detailed spectral energy distribution (SED) fit, as was demonstrated in Dyck et al. Recalibrating the intrinsic F_BOL_ versus observed F_2.2{mu}m_ relationship of that study with modern SED fitting routines, which incorporate the significantly non-blackbody, empirical spectral templates of the INGS spectral library (an update of the library in Pickles) and estimation of reddening, serves to greatly improve the accuracy and observational utility of this relationship. We find that F_BOL_ values predicted are roughly 11% less than the corresponding values predicted in Dyck et al., indicating the effects of SED absorption features across bolometric flux curves.
- ID:
- ivo://CDS.VizieR/J/ApJ/838/73
- Title:
- Brown dwarf surface gravities with Keck/NIRSPEC
- Short Name:
- J/ApJ/838/73
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We combine 131 new medium-resolution (R~2000) J-band spectra of M, L, and T dwarfs from the Keck NIRSPEC Brown Dwarf Spectroscopic Survey (BDSS) with 97 previously published BDSS spectra to study surface-gravity-sensitive indices for 228 low-mass stars and brown dwarfs spanning spectral types M5-T9. Specifically, we use an established set of spectral indices to determine surface gravity classifications for all of the M6-L7 objects in our sample by measuring the equivalent widths (EW) of the K I lines at 1.1692, 1.1778, and 1.2529{mu}m, and the 1.2{mu}m FeH_J_ absorption index. Our results are consistent with previous surface gravity measurements, showing a distinct double peak-at ~L5 and T5-in K I EW as a function of spectral type. We analyze the K I EWs of 73 objects of known ages and find a linear trend between log(Age) and EW. From this relationship, we assign age ranges to the very low gravity, intermediate gravity, and field gravity designations for spectral types M6-L0. Interestingly, the ages probed by these designations remain broad, change with spectral type, and depend on the gravity-sensitive index used. Gravity designations are useful indicators of the possibility of youth, but current data sets cannot be used to provide a precise age estimate.
- ID:
- ivo://CDS.VizieR/J/ApJ/842/118
- Title:
- Brown dwarfs with spectral type later than T6
- Short Name:
- J/ApJ/842/118
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The survey of the mid-infrared sky by the Wide-field Infrared Survey Explorer (WISE) led to the discovery of extremely cold, low-mass brown dwarfs, classified as Y dwarfs, which extend the T class to lower temperatures. Twenty-four Y dwarfs are known at the time of writing. Here we present improved parallaxes for four of these, determined using Spitzer images. We give new photometry for four late-type T and three Y dwarfs and new spectra of three Y dwarfs, obtained at Gemini Observatory. We also present previously unpublished photometry taken from HST, ESO, Spitzer, and WISE archives of 11 late-type T and 9 Y dwarfs. The near-infrared data are put onto the same photometric system, forming a homogeneous data set for the coolest brown dwarfs. We compare recent models to our photometric and spectroscopic data set. We confirm that nonequilibrium atmospheric chemistry is important for these objects. Nonequilibrium cloud-free models reproduce well the near-infrared spectra and mid-infrared photometry for the warmer Y dwarfs with 425<=T_eff_(K)<=450. A small amount of cloud cover may improve the model fits in the near-infrared for the Y dwarfs with 325<=T_eff_(K)<=375. Neither cloudy nor cloud-free models reproduce the near-infrared photometry for the T_eff_=250K Y dwarf WISEJ085510.83-071442.5 (W0855). We use the mid-infrared region, where most of the flux originates, to constrain our models of W0855. We find that W0855 likely has a mass of 1.5-8 Jupiter masses and an age of 0.3-6Gyr. The Y dwarfs with measured parallaxes are within 20pc of the Sun and have tangential velocities typical of the thin disk. The metallicities and ages we derive for the sample are generally solar-like. We estimate that the known Y dwarfs are 3 to 20 Jupiter-mass objects with ages of 0.6-8.5Gyr.
- ID:
- ivo://CDS.VizieR/J/ApJ/764/114
- Title:
- BVRI photometry of stars in Orion A
- Short Name:
- J/ApJ/764/114
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We extend our previous study of the stellar population of L1641, the lower-density star-forming region of the Orion A cloud south of the dense Orion Nebula Cluster (ONC), with the goal of testing whether there is a statistically significant deficiency of high-mass stars in low-density regions. Previously, we compared the observed ratio of low-mass stars to high-mass stars with theoretical models of the stellar initial mass function (IMF) to infer a deficiency of the highest-mass stars in L1641. We expand our population study to identify the intermediate-mass (late B to G) L1641 members in an attempt to make a more direct comparison with the mass function of the nearby ONC. The spectral-type distribution and the K-band luminosity function of L1641 are similar to those of the ONC, but problems of incompleteness and contamination prevent us from making a detailed test for differences. We limit our analysis to statistical tests of the ratio of high-mass to low-mass stars, which indicate a probability of only 3% that the ONC and the southern region of L1641 were drawn from the same population, supporting the hypothesis that the upper-mass end of the IMF is dependent on environmental density.
- ID:
- ivo://CDS.VizieR/J/ApJ/877/75
- Title:
- BVRI photom. of DV Psc and known short-period EBs
- Short Name:
- J/ApJ/877/75
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using 27 sets of new multiband photometry light curves acquired from our long-term photometric campaign carried out in the last 5yr and high-resolution spectroscopic data from seven nights, we analyzed the physical mechanisms of period variation, starspot cycle, optical flares, and chromospheric activities of the eclipsing binary DV Psc. Our updated O-C diagram covering a period of approximately 20yr shows an oscillation in its orbital period. This variations might be caused by a third body with an orbital period of 14.58+/-0.28yr. There are two active regions of starspots at longitude belts of about 90{deg} and 270{deg}. We obtained its starspot cycles with periods of 3.60+/-0.03yr and 3.42+/-0.02yr at about 90{deg} and 270{deg}, respectively. Moreover, the magnitude difference of Max.I-Max.II shows cyclic oscillation of 5.15+/-0.01yr. During our decade long photometric campaign, we observed DV Psc a total of 326.4hr, detected 18 outbursts (12 of them have never been reported) with flare energies in the range of (6.62-1106.85)x10^24^J. The slope of the relationship between the phase of the max flare and spots is 0.842 +/-0.083, implying a correlation between spots and flares. We discovered evidence for a correlation between the rotation period and the activity cycle for the short-period eclipsing binaries. Our high-resolution spectroscopic observations of DV Psc show obvious emissions above continuum in the H{alpha} line and small self-reversal emissions of the CaII IRT lines.
- ID:
- ivo://CDS.VizieR/J/AJ/149/78
- Title:
- Candidate IR variables from SAGE-SMC survey
- Short Name:
- J/AJ/149/78
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present our study on the infrared variability of point sources in the Small Magellanic Cloud (SMC). We use the data from the Spitzer Space Telescope Legacy Program "Surveying the Agents of Galaxy Evolution in the Tidally Stripped, Low Metallicity Small Magellanic Cloud" (SAGE-SMC) and the "Spitzer Survey of the Small Magellanic Cloud" (S^3^MC) survey, over three different epochs, separated by several months to 3 years. Variability in the thermal infrared is identified using a combination of Spitzer's InfraRed Array Camera 3.6, 4.5, 5.8, and 8.0{mu}m bands, and the Multiband Imaging Photometer for Spitzer 24{mu}m band. An error-weighted flux difference between each pair of three epochs ("variability index") is used to assess the variability of each source. A visual source inspection is used to validate the photometry and image quality. Out of ~2 million sources in the SAGE-SMC catalog, 814 meet our variability criteria. We matched the list of variable star candidates to the catalogs of SMC sources classified with other methods, available in the literature. Carbon-rich Asymptotic Giant Branch (AGB) stars make up the majority (61%) of our variable sources, with about a third of all of our sources being classified as extreme AGB stars. We find a small, but significant population of oxygen-rich (O-rich) AGB (8.6%), Red Supergiant (2.8%), and Red Giant Branch (<1%) stars. Other matches to the literature include Cepheid variable stars (8.6%), early type stars (2.8%), Young-stellar objects (5.8%), and background galaxies (1.2%). We found a candidate OH maser star, SSTISAGE1C J005212.88-730852.8, which is a variable O-rich AGB star, and would be the first OH/IR star in the SMC, if confirmed. We measured the infrared variability of a rare RV Tau variable (a post-AGB star) that has recently left the AGB phase. 59 variable stars from our list remain unclassified.
