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- ID:
- ivo://CDS.VizieR/J/AJ/127/2771
- Title:
- HST proper-motions of M4 main-sequence stars
- Short Name:
- J/AJ/127/2771
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new results from a photometric study of the main-sequence stars in M4 (NGC 6121=C1620-264), the closest globular cluster to the Sun. Multifield, multiepoch observations at approximately 1, 2, and 6 core radii were obtained with WFPC2 on the Hubble Space Telescope through either the F606W filter or the F555W (V) and F814W (I) filters. The multi-epoch observations allowed us to clean the data on the basis of proper motion and thus separate cluster from field stars or extragalactic objects.
- ID:
- ivo://CDS.VizieR/J/AJ/160/253
- Title:
- Infrared photometry of late-type dwarfs in Kepler Field
- Short Name:
- J/AJ/160/253
- Date:
- 08 Dec 2021
- Publisher:
- CDS
- Description:
- While it is well-established that giant-planet occurrence rises rapidly with host star metallicity, it is not yet clear if small-planet occurrence around late-type dwarf stars depends on host star metallicity. Using the Kepler Data Release 25 planet candidate list and its completeness data products, we explore planet occurrence as a function of metallicity in the Kepler field's late-type dwarf stellar population. We find that planet occurrence increases with metallicity for all planet radii Rp down to at least Rp~2R{Earth}, and that in the range 2R{Earth}<~Rp<~5R{Earth}, planet occurrence scales linearly with metallicity Z. Extrapolating our results, we predict that short-period planets with Rp<~2R{Earth} should be rare around early-M dwarf stars with [M/H]<~-0.5 or late-M dwarf stars with [M/H]<~+0.0. This dependence of planet occurrence on metallicity observed in the Kepler field emphasizes the need to control for metallicity in estimates of planet occurrence for late-type dwarf stars like those targeted by Kepler's K2 extension and the Transiting Exoplanet Survey Satellite. We confirm the theoretical expectation that the small-planet occurrence-host star metallicity relation is stronger for low-mass stars than for solar-type stars. We establish that the expected solid mass in planets around late-type dwarfs in the Kepler field is comparable to the total amount of planet-making solids in their protoplanetary disks. We argue that this high efficiency of planet formation favors planetesimal accretion over pebble accretion as the origin of the small planets observed by Kepler around late-type dwarf stars.
- ID:
- ivo://CDS.VizieR/J/A+A/501/1059
- Title:
- Infrared spectra of 9 T dwarfs
- Short Name:
- J/A+A/501/1059
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Aims: We determine the effective temperature, surface gravity and projected rotational velocity of nine T dwarfs from the comparison of high-resolution near-infrared spectra and synthetic models, and estimate the mass and age of the objects from state-of-the-art models. Methods: We use the AMES-COND cloudless solar metallicity models provided by the PHOENIX code to match the spectra of nine T-type field dwarfs observed with the near-infrared high-resolution spectrograph NIRSPEC using ten echelle orders to cover part of the J band from 1.147 to 1.347{mu}m with a resolving power R~20000. The projected rotational velocity, effective temperature and surface gravity of the objects are determined based on the minimum root mean square of the differences between the modelled and observed relative fluxes. Estimates of the mass and age of the objects are obtained from effective temperature-surface gravity diagrams, where our results are compared with existing solar metallicity models. Results: The modelled spectra reproduce quite well the observed features for most of the T dwarfs, with effective temperatures in the range of 922-1009K, and surface gravities between 10^4.1^ and 10^4.9^cm/s^2^. Our results support the assumption of a dust free atmosphere for T dwarfs later than T5, where dust grains form and then gravitationally sediment into the low atmosphere. The modelled spectra do not accurately mimic some individual very strong lines like the KI doublet at 1.2436 and 1.2525{mu}m. Our modelled spectra does not match well the observed spectra of the two T dwarfs with earlier spectral types, namely SDSSp J125453.90-012247.4 (T2) and 2MASS J05591914-1404488 (T4.5), which is likely due to the presence of condensate clouds that are not incorporated in the models used here. By comparing our results and their uncertainties to evolutionary models, we estimate masses in the interval ~5-75M_J_ for T dwarfs later than T5, which are in good agreement with those found in the literature. We found apparent young ages that are typically between 0.1 and a few Gyr for the same T dwarfs, which is consistent with recent kinematical studies.
- ID:
- ivo://CDS.VizieR/J/MNRAS/437/391
- Title:
- IR excess in Sun-like stars observed by WISE
- Short Name:
- J/MNRAS/437/391
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a search for infrared-excess (IR-excess) candidates in a comprehensive (29000 stars) magnitude-limited sample of dwarf stars, spanning the spectral range F2-K0, and brighter than V=15mag. We searched the sample within the WISE all sky survey data base for objects within 1 arcsec of the coordinates provided by the SIMBAD data base, and found over 9000 sources detected in all WISE bands. The sample excludes objects that are flagged as extended sources and those images that are affected by various optical artefacts. For each detected object, we compared the observed W4/W2 (22{mu}m/4.6{mu}m) flux ratio with the expected photospheric value and identified 197 excess candidates at 3{sigma}. For the vast majority of candidates, the results of this analysis represent the first reported evidence of an IR excess. Through the comparison with a simple blackbody emission model, we derive estimates of the dust temperature, as well as of the dust fractional luminosities. For more than 80 percent of the sample, this temperature is higher than 120K, suggesting the presence of warm circumstellar dust. Complementary observations at longer wavelengths (far-IR and submillimetre) are required for better characterizing and explaining the origin of this emission.
- ID:
- ivo://CDS.VizieR/J/ApJ/686/1195
- Title:
- IR photometry in the {gamma} Vel cluster
- Short Name:
- J/ApJ/686/1195
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new Spitzer Space Telescope observations of stars in the young (~5Myr) {gamma} Velorum stellar cluster. Combining optical and 2MASS photometry, we have selected 579 stars as candidate members of the cluster. With the addition of the Spitzer mid-infrared data, we have identified five debris disks around A-type stars and five to six debris disks around solar-type stars, indicating that the strong radiation field in the cluster does not completely suppress the production of planetesimals in the disks of cluster members. However, we find some evidence that the frequency of circumstellar primordial disks is lower, and the infrared flux excesses are smaller than for disks around stellar populations with similar ages.
- ID:
- ivo://CDS.VizieR/J/A+A/522/A112
- Title:
- i'z' photometry of L5 and later dwarf candidates
- Short Name:
- J/A+A/522/A112
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Thanks to recent and ongoing large scale surveys, hundreds of brown dwarfs have been discovered in the last decade. The Canada-France Brown Dwarf Survey is a wide-field survey for cool brown dwarfs conducted with the MegaCam camera on the Canada-France-Hawaii Telescope. Our objectives are to find ultracool brown dwarfs and to constrain the field brown-dwarf luminosity function and the mass function from a large and homogeneous sample of L and T dwarfs. We identify candidates in CFHT/MegaCam i' and z' images and follow them up with pointed near infrared (NIR) imaging on several telescopes. Halfway through our survey we found ~50 T dwarfs and ~170 L or ultra cool M dwarfs drawn from a larger sample of 1400 candidates with typical ultracool dwarfs i'-z' colours, found in 780 square degrees.
- ID:
- ivo://CDS.VizieR/J/A+A/400/891
- Title:
- IZ photometry of Pleiades brown dwarfs
- Short Name:
- J/A+A/400/891
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a 6.4 square degrees imaging survey of the Pleiades cluster in the I and Z-bands. The survey extends up to 3{deg} from the cluster center and is 90% complete down to I~=22. It covers a mass range from 0.03M_{sun}_ to 0.48M_{sun}_ and yields 40 brown dwarf candidates (BDCs) of which 29 are new. The spatial distribution of BDCs is fitted by a King profile in order to estimate the cluster substellar core radius. The Pleiades mass function is then derived across the stellar-substellar boundary and we find that, between 0.03M_{sun}_ and 0.48M_{sun}_, it is well represented by a single power-law, dN/dM{prop.to}M^-{alpha}^, with an index alpha=0.60+/-0.11. Over a larger mass domain, however, from 0.03M_{sun}_ to 10M_{sun}_, the mass function is better fitted by a log-normal function. We estimate that brown dwarfs represent about 25% of the cluster population which nevertheless makes up less than 1.5% of the cluster mass. The early dynamical evolution of the cluster appears to have had little effect on its present mass distribution at an age of 120Myr. Comparison between the Pleiades mass function and the Galactic field mass function suggests that apparent differences may be mostly due to unresolved binary systems.
- ID:
- ivo://CDS.VizieR/J/AJ/127/3553
- Title:
- JHK photometry and spectroscopy for L and T dwarfs
- Short Name:
- J/AJ/127/3553
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new JHK photometry on the MKO-NIR (Mauna Kea Observatories Near-Infrared) system and JHK spectroscopy for a large sample of L and T dwarfs. Photometry has been obtained for 71 dwarfs, and spectroscopy for 56. The sample comprises newly identified very red objects from the Sloan Digital Sky Survey (SDSS, http://www.sdss.org/) and known dwarfs from the SDSS and the Two Micron All Sky Survey (2MASS, Cat. <II/246>). Spectral classification has been carried out using four previously defined indices from Geballe et al. (2002ApJ...564..466G) that measure the strengths of the near infrared water and methane bands.
- ID:
- ivo://CDS.VizieR/J/MNRAS/361/211
- Title:
- JHK photometry of brown dwarfs in Orion
- Short Name:
- J/MNRAS/361/211
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the results of a deep near-infrared (JHK) survey of the outer parts of the Trapezium Cluster with Gemini South/Flamingos. 396 sources were detected in a 26-arcmin^2^ area, including 138 brown dwarf candidates, defined as M<0.075M_{sun}_ for an assumed age of 1Myr. Only 33 of the brown dwarf candidates are planetary mass candidates with estimated masses in the range 0.003<M<0.012M_{sun}_. In an extinction-limited sample (AV<5) complete to approximately 0.005M_{sun}_ (5M_Jup_) the mass function appears to drop by a factor of 2 at the deuterium burning threshold, i.e. at planetary masses. After allowing for background contamination it is likely that planetary mass objects at 3-13M_Jup_ number <10% of the cluster population, with an upper limit of 13%. Analysis of the spatial distribution of stars and brown dwarf candidates suggests that brown dwarfs and very low-mass stars (M<0.1M_{sun}_) are less likely than more massive stars to have wide (>150AU) binary companions.
