- ID:
- ivo://CDS.VizieR/J/ApJ/757/164
- Title:
- Oxygen abundances of dwarf stars
- Short Name:
- J/ApJ/757/164
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Oxygen abundances of 67 dwarf stars in the metallicity range -1.6<[Fe/H]<-0.4 are derived from a non-LTE analysis of the 777nm OI triplet lines. These stars have precise atmospheric parameters measured by Nissen and Schuster (Cat. J/A+A/511/L10), who find that they separate into three groups based on their kinematics and {alpha}-element (Mg, Si, Ca, Ti) abundances: thick disk, high-{alpha} halo, and low-{alpha} halo. We find the oxygen abundance trends of thick-disk and high-{alpha} halo stars very similar. The low-{alpha} stars show a larger star-to-star scatter in [O/Fe] at a given [Fe/H] and have systematically lower oxygen abundances compared to the other two groups. Thus, we find the behavior of oxygen abundances in these groups of stars similar to that of the {alpha} elements. We use previously published oxygen abundance data of disk and very metal-poor halo stars to present an overall view (-2.3<[Fe/H]<+0.3) of oxygen abundance trends of stars in the solar neighborhood. Two field halo dwarf stars stand out in their O and Na abundances. Both G53-41 and G150-40 have very low oxygen and very high sodium abundances, which are key signatures of the abundance anomalies observed in globular cluster (GC) stars. Therefore, they are likely field halo stars born in GCs. If true, we estimate that at least 3%+/-2% of the local field metal-poor star population was born in GCs.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/784/156
- Title:
- Parallaxes for 1507 nearby mid-to-late M dwarfs
- Short Name:
- J/ApJ/784/156
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The MEarth survey is a search for small rocky planets around the smallest, nearest stars to the Sun as identified by high proper motion with red colors. We augmented our planetary search time series with lower cadence astrometric imaging and obtained two million images of approximately 1800 stars suspected to be mid-to-late M dwarfs. We fit an astrometric model to MEarth's images for 1507 stars and obtained trigonometric distance measurements to each star with an average precision of 5mas. Our measurements, combined with the Two Micron All Sky Survey photometry, allowed us to obtain an absolute K_s_ magnitude for each star. In turn, this allows us to better estimate the stellar parameters than those obtained with photometric estimates alone and to better prioritize the targets chosen to monitor at high cadence for planetary transits. The MEarth sample is mostly complete out to a distance of 25pc for stars of type M5.5V and earlier, and mostly complete for later type stars out to 20pc. We find eight stars that are within 10pc of the Sun for which there did not exist a published trigonometric parallax distance estimate. We release with this work a catalog of the trigonometric parallax measurements for 1507 mid-to-late M dwarfs, as well as new estimates of their masses and radii.
- ID:
- ivo://CDS.VizieR/J/AJ/159/174
- Title:
- Parameters & abundances for Hyades/Field G-K dwarfs
- Short Name:
- J/AJ/159/174
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- It has been suggested that Fe abundances of K dwarfs derived from FeI and FeII lines show considerable discrepancies, and oxygen abundances determined from high-excitation OI-7771-5 triplet lines are appreciably overestimated (the problem becoming more serious toward lower Teff), which, however, has not yet been widely confirmed. With the aim of clarifying this issue, we spectroscopically determined the atmospheric parameters of 148 G-K dwarfs (Hyades cluster stars and field stars) by assuming the classical FeI/FeII ionization equilibrium as usual, and determined their oxygen abundances by applying the non-local thermal equilibrium spectrum fitting analysis to OI-7771-5 lines. It turned out that the resulting parameters did not show any significant inconsistency with those determined by other methods (for example, the mean differences in Teff and logg from the well-determined solutions of Hyades dwarfs are mostly <~100K and <~0.1dex). Likewise, the oxygen abundances of Hyades stars are around [O/H]~+0.2dex (consistent with the metallicity of this cluster) without exhibiting any systematic Teff-dependence. Accordingly, we conclude that parameters can be spectroscopically evaluated to a sufficient precision in the conventional manner (based on the Saha-Boltzmann equation for FeI/FeII) and oxygen abundances can be reliably determined from the OI-7771-5 triplet for K dwarfs as far as stars of Teff>~4500K are concerned. We suspect that previously reported strongly Teff-dependent discrepancies may have stemmed mainly from overestimation of weak-line strengths and/or improper Teff scale.
- ID:
- ivo://CDS.VizieR/J/A+A/589/A49
- Title:
- Photometric brown-dwarf classification
- Short Name:
- J/A+A/589/A49
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a homogeneous sample of 1361 L and T dwarfs brighter than J=17.5 (of which 998 are new), from an effective area of 3070deg^2^, classified by the photo-type method to an accuracy of one spectral sub-type using izY JHKW1W2 photometry from SDSS+UKIDSS+WISE. Other than a small bias in the early L types, the sample is shown to be effectively complete to the magnitude limit, for all spectral types L0 to T8. The nature of the bias is an incompleteness estimated at 3% because peculiar blue L dwarfs of type L4 and earlier are classified late M. There is a corresponding overcompleteness because peculiar red (likely young) late M dwarfs are classified early L. Contamination of the sample is confirmed to be small: so far spectroscopy has been obtained for 19 sources in the catalogue and all are confirmed to be ultracool dwarfs. We provide coordinates and izY JHKW1W2 photometry of all sources. We identify an apparent discontinuity, {Delta}m~0.4mag., in the Y-K colour between spectral types L7 and L8. We present near-infrared spectra of nine sources identified by photo-type as peculiar, including a new low-gravity source ULAS J005505.68+013436.0, with spectroscopic classification L2{gamma}. We provide revised izYJHKW1W2 template colours for late M dwarfs, types M7 to M9.
- ID:
- ivo://CDS.VizieR/J/AJ/154/226
- Title:
- Photometry and radial velocities of K2-131
- Short Name:
- J/AJ/154/226
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the discovery of a new ultra-short-period planet and summarize the properties of all such planets for which the mass and radius have been measured. The new planet, K2-131b, was discovered in K2 Campaign 10. It has a radius of 1.81_-0.12_^+0.16^ R_{Earth}_ and orbits a G dwarf with a period of 8.9 hr. Radial velocities obtained with Magellan/PFS and TNG/HARPS-N show evidence for stellar activity along with orbital motion. We determined the planetary mass using two different methods: (1) the "floating chunk offset" method, based only on changes in velocity observed on the same night; and (2) a Gaussian process regression based on both the radial velocity and photometric time series. The results are consistent and lead to a mass measurement of 6.5+/-1.6 M_{Earth}_ and a mean density of 6.0_-2.7_^+3.0^ g/cm^3^.
- ID:
- ivo://CDS.VizieR/J/AJ/160/192
- Title:
- Photometry and RVs of K2-25b with HPF
- Short Name:
- J/AJ/160/192
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using radial velocity data from the Habitable Zone Planet Finder, we have measured the mass of the Neptune-sized planet K2-25b, as well as the obliquity of its M4.5 dwarf host star in the 600-800Myr Hyades cluster. This is one of the youngest planetary systems for which both of these quantities have been measured and one of the very few M dwarfs with a measured obliquity. Based on a joint analysis of the radial velocity data, time-series photometry from the K2 mission, and new transit light curves obtained with diffuser-assisted photometry, the planet's radius and mass are 3.44{+/-}0.12R_{Earth}_ and 24.5_-5.2_^+5.7^M_{Earth}_. These properties are compatible with a rocky core enshrouded by a thin hydrogen-helium atmosphere (5% by mass). We measure an orbital eccentricity of e=0.43{+/-}0.05. The sky-projected stellar obliquity is {lambda}=3{deg}{+/-}16{deg}, compatible with spin- orbit alignment, in contrast to other "hot Neptunes" that have been studied around older stars.
- ID:
- ivo://CDS.VizieR/J/AJ/153/15
- Title:
- Photometry and spectroscopy of EPIC 201702477
- Short Name:
- J/AJ/153/15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the discovery of EPIC 201702477b, a transiting brown dwarf in a long period (40.73691+/-0.00037day) and eccentric (e=0.2281+/-0.0026) orbit. This system was initially reported as a planetary candidate based on two transit events seen in K2 Campaign 1 photometry and later validated as an exoplanet candidate. We confirm the transit and refine the ephemeris with two subsequent ground-based detections of the transit using the Las Cumbres Observatory Global Telescope 1m telescope network. We rule out any transit timing variations above the level of ~30s. Using high precision radial velocity measurements from HARPS and SOPHIE we identify the transiting companion as a brown dwarf with a mass, radius, and bulk density of 66.9+/-1.7M_J_, 0.757+/-0.065R_J_, and 191+/-51g/cm^3^ respectively. EPIC 201702477b is the smallest radius brown dwarf yet discovered, with a mass just below the H-burning limit. It has the highest density of any planet, substellar mass object, or main-sequence star discovered so far. We find evidence in the set of known transiting brown dwarfs for two populations of objects-high mass brown dwarfs and low mass brown dwarfs. The higher-mass population have radii in very close agreement to theoretical models, and show a lower-mass limit around 60M_J_. This may be the signature of mass-dependent ejection of systems during the formation process.
- ID:
- ivo://CDS.VizieR/J/AJ/150/85
- Title:
- Photometry and spectroscopy of HAT-P-56
- Short Name:
- J/AJ/150/85
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the discovery of HAT-P-56b by the HATNet survey, an inflated hot Jupiter transiting a bright F-type star in Field 0 of NASA's K2 mission. We combine ground-based discovery and follow-up light curves with high precision photometry from K2, as well as ground-based radial velocities from the Tillinghast Reflector Echelle Spectrograph on the Fred Lawrence Whipple Observatory 1.5m telescope to determine the physical properties of this system. HAT-P-56b has a mass of 2.18M_J_, radius of 1.47R_J_, and transits its host star on a near-grazing orbit with a period of 2.7908day. The radius of HAT-P-56b is among the largest known for a planet with M_P_>2M_J_. The host star has a V-band magnitude of 10.9, mass of 1.30M_{sun}_, and radius of 1.43R_{sun}_. The periodogram of the K2 light curve suggests that the star is a {gamma} Dor variable. HAT-P-56b is an example of a ground-based discovery of a transiting planet, where space-based observations greatly improve the confidence in the confirmation of its planetary nature, and also improve the accuracy of the planetary parameters.
- ID:
- ivo://CDS.VizieR/J/AJ/150/49
- Title:
- Photometry and spectroscopy of HATS-8
- Short Name:
- J/AJ/150/49
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- HATS-8b is a low density transiting super-Neptune discovered as part of the HATSouth project. The planet orbits its solar-like G-dwarf host (V=14.03+/-0.10, T_eff_=50K) with a period of 3.5839days. HATS-8b is the third lowest-mass transiting exoplanet to be discovered from a wide-field ground-based search, and with a mass of 0.138+/0.019M_J_ it is approximately halfway between the masses of Neptune and Saturn. However, HATS-8b has a radius of 0.873^+0.123^_-0.075_, resulting in a bulk density of just 0.259+/-0.091g/cm3. The metallicity of the host star is super-solar ([Fe/H]=0.210+/-0.080), providing evidence against the idea that low-density exoplanets form from metal-poor environments. The low density and large radius of HATS-8b results in an atmospheric scale height of almost 1000km, and in addition to this there is an excellent reference star of nearly equal magnitude at just 19'' separation in the sky. These factors make HATS-8b an exciting target for future atmospheric characterization studies, particularly for long-slit transmission spectroscopy.
- ID:
- ivo://CDS.VizieR/J/AJ/149/166
- Title:
- Photometry and spectroscopy of HATS-6
- Short Name:
- J/AJ/149/166
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the discovery by the HATSouth survey of HATS-6b, an extrasolar planet transiting a V=15.2mag, i=13.7mag M1V star with a mass of 0.57M_{Sun}_ and a radius of 0.57R_{sun}_ . HATS-6b has a period of P=3.3253d, mass of M_p_=0.32M_J_, radius of R_p_=1.00R_J_, and zero-albedo equilibrium temperature of T_eq_=712.8+/-5.1K. HATS-6 is one of the lowest mass stars known to host a close-in gas giant planet, and its transits are among the deepest of any known transiting planet system. We discuss the follow-up opportunities afforded by this system, noting that despite the faintness of the host star, it is expected to have the highest K-band S/N transmission spectrum among known gas giant planets with T_eq_<750K. In order to characterize the star we present a new set of empirical relations between the density, radius, mass, bolometric magnitude, and V-, J-, H- and K-band bolometric corrections for main sequence stars with M<0.80M_{Sun}_, or spectral types later than K5. These relations are calibrated using eclipsing binary components as well as members of resolved binary systems. We account for intrinsic scatter in the relations in a self-consistent manner. We show that from the transit-based stellar density alone it is possible to measure the mass and radius of a ~0.6M_{Sun}_ star to ~7 and ~2% precision, respectively. Incorporating additional information, such as the V-K color, or an absolute magnitude, allows the precision to be improved by up to a factor of two.
