- ID:
- ivo://CDS.VizieR/J/AJ/154/224
- Title:
- Transiting planets in young clusters from K2
- Short Name:
- J/AJ/154/224
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Detection of transiting exoplanets around young stars is more difficult than for older systems owing to increased stellar variability. Nine young open cluster planets have been found in the K2 data, but no single analysis pipeline identified all planets. We have developed a transit search pipeline for young stars that uses a transit-shaped notch and quadratic continuum in a 12 or 24 hr window to fit both the stellar variability and the presence of a transit. In addition, for the most rapid rotators (P_rot_<2 days) we model the variability using a linear combination of observed rotations of each star. To maximally exploit our new pipeline, we update the membership for four stellar populations observed by K2 (Upper Scorpius, Pleiades, Hyades, Praesepe) and conduct a uniform search of the members. We identify all known transiting exoplanets in the clusters, 17 eclipsing binaries, one transiting planet candidate orbiting a potential Pleiades member, and three orbiting unlikely members of the young clusters. Limited injection recovery testing on the known planet hosts indicates that for the older Praesepe systems we are sensitive to additional exoplanets as small as 1-2 R_{Earth}_, and for the larger Upper Scorpius planet host (K2-33) our pipeline is sensitive to ~4 R_{Earth}_ transiting planets. The lack of detected multiple systems in the young clusters is consistent with the expected frequency from the original Kepler sample, within our detection limits. With a robust pipeline that detects all known planets in the young clusters, occurrence rate testing at young ages is now possible.
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Search Results
- ID:
- ivo://CDS.VizieR/J/AJ/152/24
- Title:
- Trigonometric parallaxes of 134 low-mass stars
- Short Name:
- J/AJ/152/24
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report trigonometric parallaxes for 134 low-mass stars and brown dwarfs, of which 38 have no previously published measurement and 79 more have improved uncertainties. Our survey focused on nearby targets, so 119 are closer than 30pc. Of the 38 stars with new parallaxes, 14 are within 20pc and seven are likely brown dwarfs (spectral types later than L0). These parallaxes are useful for studies of kinematics, multiplicity, and spectrophotometric calibration. Two objects with new parallaxes are confirmed as young stars with membership in nearby young moving groups: LP 870-65 in AB Doradus and G161-71 in Argus. We also report the first parallax for the planet-hosting star GJ3470; this allows us to refine the density of its Neptune-mass planet. T-dwarf 2MASSJ12590470-4336243, previously thought to lie within 4pc, is found to be at 7.8pc, and the M-type star 2MASSJ01392170-3936088 joins the ranks of nearby stars as it is found to be within 10pc. Five stars that are overluminous and/or too red for their spectral types are identified and deserve further study as possible young stars.
- ID:
- ivo://CDS.VizieR/J/AJ/127/2915
- Title:
- Triple systems (cool primary + hot binary)
- Short Name:
- J/AJ/127/2915
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In the course of comparing parameters of evolved cool star plus hot main-sequence star binaries with theoretical isochrones, some discrepancies are found between implied stellar masses and the spectroscopic binary mass function or the measured angular separation. These are naturally explained if there is a third star in the system. Multiplicity is also required to explain some comparisons of "cool plus hot binary" IUE and optical spectral energy distribution analysis with measured flux ratios, especially Tycho's two-color photometry of separate components. Out of a sample of 136 cool-plus-hot binary star systems under study, measurements are now indicating several systems considered double (HD 5373, 23089, 26673, 29094, 49126, 71129, 149379, 179002, 187299), and probably a few others (including HD 136415), to have at least three stellar components. Several other cases of suspected triple systems are confirmed. For comparison, there are eight known triples included in the project. In all, about 25% of the systems contain three or more components within a few arcseconds. Estimated separations are provided, which may be of use when not known from interferometry. In general, the triple systems have one post-main-sequence component and two upper main-sequence components, usually revolving around each other. One new triple system, HD 149379, has as its middle component an F giant in the brief first crossing of the Hertzsprung gap.
- ID:
- ivo://CDS.VizieR/J/ApJ/753/156
- Title:
- T/Y brown dwarfs with WISE photometry
- Short Name:
- J/ApJ/753/156
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the discovery of another seven Y dwarfs from the Wide-field Infrared Survey Explorer (WISE). Using these objects, as well as the first six WISE Y dwarf discoveries from Cushing et al. (2011ApJ...743...50C), we further explore the transition between spectral types T and Y. We find that the T/Y boundary roughly coincides with the spot where the J-H colors of brown dwarfs, as predicted by models, turn back to the red. Moreover, we use preliminary trigonometric parallax measurements to show that the T/Y boundary may also correspond to the point at which the absolute H (1.6{mu}m) and W2 (4.6{mu}m) magnitudes plummet. We use these discoveries and their preliminary distances to place them in the larger context of the solar neighborhood. We present a table that updates the entire stellar and substellar constituency within 8pc of the Sun, and we show that the current census has hydrogen-burning stars outnumbering brown dwarfs by roughly a factor of six. This factor will decrease with time as more brown dwarfs are identified within this volume, but unless there is a vast reservoir of cold brown dwarfs invisible to WISE, the final space density of brown dwarfs is still expected to fall well below that of stars. We also use these new Y dwarf discoveries, along with newly discovered T dwarfs from WISE, to investigate the field substellar mass function. We find that the overall space density of late-T and early-Y dwarfs matches that from simulations describing the mass function as a power law with slope -0.5<{alpha}<0.0; however, a power law may provide a poor fit to the observed object counts as a function of spectral type because there are tantalizing hints that the number of brown dwarfs continues to rise from late-T to early-Y. More detailed monitoring and characterization of these Y dwarfs, along with dedicated searches aimed at identifying more examples, are certainly required.
- ID:
- ivo://CDS.VizieR/J/A+A/619/L8
- Title:
- Ultra-cool dwarfs candidates in Gaia DR2
- Short Name:
- J/A+A/619/L8
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The second Gaia data release (Gaia DR2) contains high-precision positions, parallaxes, and proper motions for 1.3 billion sources. The resulting Hertzsprung-Russel diagram reveals fine structures throughout the mass range. This paper aims to investigate the content of Gaia DR2 at the low-mass end and to characterize ultra-cool and brown dwarfs. We first retrieved the sample of spectroscopically confirmed ultra-cool and brown dwarfs in Gaia DR2.We used their locus in the precise Hertzsprung-Russel diagram to select new candidates and to investigate their properties. The number of spectroscopically confirmed objects recovered in Gaia DR2 corresponds to 61% and 74% of the expected number of objects with an estimated Gaia magnitude G_est_<=21.5 and 20.3, respectively. This fills much of the gap to Gaia DR1. Furthermore, Gaia DR2 contains ~13000>=M7 and 631 new L candidates. A tentative classification suggests that a few hundred of them are young or subdwarf candidates. Their distance distribution shows that the solar neighborhood census is still incomplete. Conclusions. Gaia DR2 offers a great wealth of information on low-mass objects. It provides a homogeneous and precise catalog of candidates that is worthwhile to be further characterized with spectroscopic observations.
- ID:
- ivo://CDS.VizieR/J/MNRAS/449/3966
- Title:
- Ultracool white dwarfs
- Short Name:
- J/MNRAS/449/3966
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present parallax observations and a detailed model atmosphere analysis of 54 cool and ultracool (Teff<4000K) white dwarfs (WDs) in the solar neighbourhood. For the first time, a large number of cool and ultracool WDs have distance and tangential velocities measurements available. Our targets have distances ranging from 21pc to >100pc, and include five stars within 30pc. Contrary to expectations, all but two of them have tangential velocities smaller than 150km/s thus suggesting Galactic disc membership. The oldest WDs in this sample have WD cooling ages of 10Gyr, providing a firm lower limit to the age of the thick disc population. Many of our targets have uncharacteristically large radii, indicating that they are low-mass WDs. It appears that we have detected the brighter population of cool and ultracool WDs near the Sun. The fainter population of ultracool CO-core WDs remain to be discovered in large numbers. The Large Synoptic Survey Telescope should find these elusive, more massive ultracool WDs in the solar neighbourhood.
- ID:
- ivo://CDS.VizieR/J/ApJS/235/6
- Title:
- Updated Multiple Star Catalog (MSC): Sept 2021
- Short Name:
- J/ApJS/235/6
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The catalog of hierarchical stellar systems with three or more components is an update of the original 1997 version (Tokovinin, 1997-1999, J/A+AS/124/75). For 2000 hierarchies, the new Multiple Star Catalog (MSC) provides distances, component masses and periods, and supplementary information (astrometry, photometry, identifiers, orbits, notes). The MSC content and format are explained, and its incompleteness and strong observational selection are stressed. Nevertheless, the MSC can be used for statistical studies and is a valuable source for planning observations of multiple stars. Rare classes of stellar hierarchies found in the MSC (with six or seven components, extremely eccentric orbits, planar and possibly resonant orbits, hosting planets) are briefly presented. High-order hierarchies have smaller velocity dispersion compared to triples and are often associated with moving groups. The paper concludes with an analysis of the ratio of periods and separations between inner and outer subsystems. In wide hierarchies, the ratio of semimajor axes, estimated statistically, is distributed between 3 and 300, with no evidence of dynamically unstable systems.
- ID:
- ivo://CDS.VizieR/J/MNRAS/504/356
- Title:
- Updated parameters of 1743 open clusters
- Short Name:
- J/MNRAS/504/356
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this study, we follow up our recent paper (Monteiro et al., )2020MNRAS.499.1874M and present a homogeneous sample of fundamental parameters of open clusters in our Galaxy, entirely based on Gaia DR2 data. We used published membership probability of the stars derived from Gaia DR2 data and applied our isochrone fitting code, updated as in Monteiro et al. (2020MNRAS.499.1874M), to G_BP_ and G_RP_Gaia DR2 data for member stars. In doing this, we take into account the nominal errors in the data and derive distance, age, and extinction of each cluster. This work therefore provides parameters for 1743 open clusters and, as a by-product, a list of likely not physical or dubious open clusters is provided as well for future investigations. Furthermore, it was possible to estimate the mean radial velocity of 831 clusters (198 of which are new and unpublished so far), using stellar radial velocities from Gaia DR2 catalogue. By comparing the open cluster distances obtained from isochrone fitting with those obtained from a maximum likelihood estimate of individual member parallaxes, we found a systematic offset of (-0.05 {\pm} 0.04) mas.
- ID:
- ivo://CDS.VizieR/J/other/NatAs/6.89
- Title:
- Upper Scorpius members
- Short Name:
- J/other/NatAs/6.
- Date:
- 03 Mar 2022 16:55:14
- Publisher:
- CDS
- Description:
- The nature and origin of free-floating planets (FFPs) are still largely unconstrained because of a lack of large homogeneous samples to enable a statistical analysis of their properties. So far, most FFPs have been discovered using indirect methods; microlensing surveys have proved particularly successful to detect these objects down to a few Earth masses. However, the ephemeral nature of microlensing events prevents any follow-up observations and individual characterization. Several studies have identified FFPs in young stellar clusters and the Galactic field but their samples are small or heterogeneous in age and origin. Here we report the discovery of between 70 and 170 FFPs (depending on the assumed age) in the region encompassing Upper Scorpius and Ophiuchus, the closest young OB association to the Sun. We found an excess of FFPs by a factor of up to seven compared with core-collapse model predictions, demonstrating that other formation mechanisms may be at work. We estimate that ejection from planetary systems might have a contribution comparable to that of core collapse in the formation of FFPs. Therefore, ejections due to dynamical instabilities in giant exoplanet systems must be frequent within the first 10Myr of a system's life.
- ID:
- ivo://CDS.VizieR/J/AJ/160/44
- Title:
- Upper Scorpius spectroscopy and photometry
- Short Name:
- J/AJ/160/44
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have refined the census of stars and brown dwarfs in the Upper Sco association (~10Myr, ~145pc) by (1) updating the selection of candidate members from our previous survey to include the high-precision astrometry from the second data release of Gaia, (2) obtaining spectra of a few hundred candidate members to measure their spectral types and verify their youth, and (3) assessing the membership (largely with Gaia astrometry) of 2020 stars toward Upper Sco that show evidence of youth in this work and previous studies. We arrive at a catalog of 1761 objects that are adopted as members of Upper Sco. The distribution of spectral types among the adopted members is similar to those in other nearby star-forming regions, indicating a similar initial mass function. In previous studies, we have compiled mid-infrared photometry from the Wide-field Infrared Survey Explorer and the Spitzer Space Telescope for members of Upper Sco and used those data to identify the stars that show evidence of circumstellar disks; we present the same analysis for our new catalog of members. As in earlier work, we find that the fraction of members with disks increases with lower stellar masses, ranging from <~10% for >1M{sun} to ~22% for 0.01-0.3M{sun}. Finally, we have estimated the relative ages of Upper Sco and other young associations using their sequences of low-mass stars in M_G_RP__ versus G_BP_-G_RP_. This comparison indicates that Upper Sco is a factor of two younger than the {beta}Pic association (21-24Myr) according to both nonmagnetic and magnetic evolutionary models.
