- 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.
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Search Results
- 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.
- ID:
- ivo://CDS.VizieR/J/AJ/159/18
- Title:
- Jovian-type planets around M dwarfs with MIRI/JWST
- Short Name:
- J/AJ/159/18
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The upcoming launch of the James Webb Space Telescope (JWST) will dramatically increase our understanding of exoplanets, particularly through direct imaging. Microlensing and radial velocity surveys indicate that some M dwarfs host long-period giant planets. Some of these planets will likely be just a few parsecs away and a few astronomical units from their host stars, a parameter space that cannot be probed by existing high-contrast imagers. We studied whether the coronagraphs on the Mid-infrared Instrument on JWST can detect Jovian-type planets around nearby M dwarfs. For a sample of 27 very nearby M dwarfs, we simulated a sample of Saturn-Jupiter-mass planets with three atmospheric configurations and three orbital separations, observed in three different filters. We found that the f1550c 15.5 {mu}m filter is best suited for detecting Jupiter-like planets. Jupiter-like planets with patchy cloud cover, 2 au from their star, are detectable at 15.5 {mu}m around 14 stars in our sample, while Jupiters with clearer atmospheres are detectable around all stars in the sample. Saturns were most detectable at 10.65 and 11.4 {mu}m (f1065c and f1140c filters), but only with cloud-free atmospheres and within 3 pc (six stars). Surveying all 27 stars would take <170 hr of JWST integration time, or just a few hours for a shorter survey of the most favorable targets. There is one potentially detectable known planet in our sample: GJ 832 b. Observations aimed at detecting this planet should occur in 2024-2026, when the planet is maximally separated from the star.
- ID:
- ivo://CDS.VizieR/J/A+A/597/A52
- Title:
- K and G dwarfs stellar granulation variability
- Short Name:
- J/A+A/597/A52
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In solar-type stars, the attenuation of convective blueshift by stellar magnetic activity dominates the RV (radial velocity) variations over the low amplitude signal induced by low mass planets. Models of stars that differ from the Sun will require a good knowledge of the attenuation of the convective blueshift to estimate its impact on the variations. It is therefore crucial to precisely determine not only the amplitude of the convective blueshift for different types of stars, but also the dependence of this convective blueshift on magnetic activity, as these are key factors in our model producing the RV. We studied a sample of main sequence stars with spectral types from G0 to K2 and focused on their temporally averaged properties: the activity level and a criterion allowing to characterise the amplitude of the convective blueshift. This criterion is derived from the dependence of the convective blueshift with the intensity at the bottom of a large set of selected spectral lines.
