- 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.
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Search Results
- 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/150/33
- Title:
- Photometry and spectroscopy of HATS-9 and HATS-10
- Short Name:
- J/AJ/150/33
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the discovery of two transiting extrasolar planets by the HATSouth survey. HATS-9b orbits an old (10.8+/-1.5Gyr) V=13.3 G dwarf star with a period p~~1.9153days. The host star has a mass of 1.03M_{sun}_, radius of 1.503R_{sun}_, and effective temperature 5366+/-70K. The planetary companion has a mass of 0.837M_J_ and radius of 1.065R_J_, yielding a mean density of 0.85g/cm^-3^. HATS-10b orbits a V=13.1 G dwarf star with a period p~~3.3128days. The host star has a mass of 1.1M_{sun}_, radius of 1.11R_{sun}_, and effective temperature 5880+/-120K. The planetary companion has a mass of 0.53M_J_ and radius of 0.97R_J_, yielding a mean density of 0.7g/cm3. Both planets are compact in comparison with planets receiving similar irradiation from their host stars and lie in the nominal coordinates of Field 7 of K2, but only HATS-9b falls on working silicon. Future characterization of HATS-9b with the exquisite photometric precision of the Kepler telescope may provide measurements of its reflected light signature.
- ID:
- ivo://CDS.VizieR/J/AJ/156/37
- Title:
- Photometry & Li abund. of cool dwarfs in M35
- Short Name:
- J/AJ/156/37
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Hydra spectra of 85 G-K dwarfs in the young cluster M35 near the Li 6708 {AA} line region are analyzed. From velocities and Gaia astrometry, 78 are likely single-star members that, combined with previous work, produce 108 members with T_eff_ ranging from 6150 to 4000 K as defined by multicolor, broadband photometry, E(B-V)=0.20, and [Fe/H]=-0.15, though there are indications the metallicity may be closer to solar. The Lithium abundance A(Li) follows a well-delineated decline from 3.15 for the hottest stars to upper limits =<1.0 among the coolest dwarfs. Contrary to earlier work, M35 includes single stars at systematically higher A(Li) than the mean cluster relation. This subset exhibits higher V_ROT_ than the more Li-depleted sample and, from photometric rotation periods, is dominated by stars classed as convective (C); all others are interface (I) stars. The cool, high-Li rapid rotators (RRs) are consistent with models that simultaneously consider rapid rotation and radius inflation; RRs hotter than the Sun exhibit excess Li depletion, as predicted by the models. The A(Li) distribution with color and rotation period, when compared to the Hyades/Praesepe and the Pleiades, is consistent with gyrochronological analysis placing M35's age between the older M34 and younger Pleiades. However, the Pleiades display a more excessive range in A(Li) and rotation period than M35 on the low-Li, slow-rotation side of the distribution, with supposedly younger stars at a given T_eff_ in the Pleiades spinning slower, with A(Li) reduced by more than a factor of four compared to M35.
- ID:
- ivo://CDS.VizieR/J/A+A/497/497
- Title:
- Physical parameters from JHK flux
- Short Name:
- J/A+A/497/497
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The effective temperature scale of FGK stars, especially at the lowest metallicities remains a major problem in the chemical abundance analysis of metal-poor stars. We present a new implementation of the infrared flux method (IRFM) using the 2MASS catalogue.
- ID:
- ivo://CDS.VizieR/J/A+A/531/A141
- Title:
- Physical parameters of PMS in open clusters
- Short Name:
- J/A+A/531/A141
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Our aims are twofold: To determine the physical parameters of PMS members in young open clusters (YOCs), and to check and compare the performances of different model isochrones. We compare UBVRI photometric observations of eleven YOCs to theoretical isochrones in the photometric diagrams. The comparison simultaneously provides membership assignments for MS and PMS stars and estimates for the masses, ages, and spatial distribution of the candidate members. The relations found between the different cluster parameters show that the procedure applied to assign cluster membership, and to measure physical parameters for the selected members, is well founded.
- ID:
- ivo://CDS.VizieR/J/MNRAS/407/2269
- Title:
- Polarisation of a sample of late M dwarfs
- Short Name:
- J/MNRAS/407/2269
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present here the final results of the first spectropolarimetric survey of a small sample of active M dwarfs, aimed at providing observational constraints on dynamo action on both sides of the full-convection threshold (spectral type M4). Our two previous studies (Donati et al. 2008. Cat. J/MNRAS/390/545; Morin et al., 2008, Cat. J/MNRAS/384/77) were focused on early and mid M dwarfs. The present paper examines 11 fully convective late M dwarfs (spectral types M5-M8). Tomographic imaging techniques were applied to time-series of circularly polarised profiles of 6 stars, in order to infer their large-scale magnetic topologies. For 3 other stars we could not produce such magnetic maps, because of low variability of the Stokes V signatures, but were able to derive some properties of the magnetic fields. We find 2 distinct categories of magnetic topologies: on the one hand strong axisymmetric dipolar fields (similar to mid M dwarfs), and on the other hand weak fields generally featuring a significant non-axisymmetric component, and sometimes a significant toroidal one. Comparison with unsigned magnetic fluxes demonstrates that the second category of magnetic fields shows less organization (less energy in the large scales), similarly to partly convective early M dwarfs. Stars in both categories have similar stellar parameters, our data do not evidence a separation between these 2 categories in the mass-rotation plane. We also report marginal detection of a large-scale magnetic field on the M8 star VB 10 featuring a significant toroidal axisymmetric component, whereas no field is detectable on VB 8 (M7).
- ID:
- ivo://CDS.VizieR/J/ApJ/775/84
- Title:
- Polarization from stars behind IC63 nebula
- Short Name:
- J/ApJ/775/84
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In the interstellar medium (ISM), molecular hydrogen is expected to form almost exclusively on the surfaces of dust grains. Due to that molecule's large formation energy (-4.5eV), several dynamical effects are likely associated with the process, including the alignment of asymmetric dust grains with the ambient magnetic field. Such aligned dust grains are, in turn, believed to cause the broadband optical/infrared polarization observed in the ISM. Here, we present the first observational evidence for grain alignment driven by H_2_ formation, by showing that the polarization of the light from stars behind the reflection nebula IC 63 appears to correlate with the intensity of H_2_ fluorescence. While our results strongly suggest a role for "Purcell rockets" in grain alignment, additional observations are needed to conclusively confirm their role. By showing a direct connection between H_2_ formation and a probe of the dust characteristics, these results also provide one of the first direct confirmations of the grain-surface formation of H_2_. We compare our observations to ab initio modeling based on Radiative Torque Alignment (RAT) theory.
- ID:
- ivo://CDS.VizieR/J/A+A/513/L7
- Title:
- Post common envelope binaries from SDSS. VIII
- Short Name:
- J/A+A/513/L7
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a large survey of post common envelope binaries (PCEBs) among white dwarf/main sequence (WDMS) binaries from the SDSS that allows to determine the fraction of PCEBs as a function of secondary star mass and therewith to ultimately test the disrupted magnetic braking hypothesis. We obtained multiple spectroscopic observations spread over at least two nights of 589 WDMS binaries. Using mostly the NaI 8183.27,8194.81 absorption doublet we determined the corresponding radial velocities.
