In this paper, we examine the nearest 100 pc entries in Data Release 2 of Gaia to identify previously unrecognized candidate members in young associations. We analyze 695 952 stars with the BANYAN ...Bayesian classification software and discover 898 new high-likelihood candidate members that span a wide range of properties, from spectral types B9 to L2, including 104 comoving systems, 111 brown dwarfs, and 31 new bona fide members. Our sample is mostly composed of highly active M dwarfs and will be crucial in examining the low-mass end of the initial mass function of young associations. Our sample includes new candidate members near the Galactic plane where previous surveys suffered from a high rate of contamination. This paper represents the first step toward a full reassessment of young associations in the solar neighborhood with the second data release of the Gaia mission.
Abstract
BANYAN Σ is a new Bayesian algorithm to identify members of young stellar associations within 150 pc of the Sun. It includes 27 young associations with ages in the range ∼1–800 Myr, modeled ...with multivariate Gaussians in six-dimensional (6D)
XYZUVW
space. It is the first such multi-association classification tool to include the nearest sub-groups of the Sco-Cen OB star-forming region, the IC 2602, IC 2391, Pleiades and Platais 8 clusters, and the
ρ
Ophiuchi, Corona Australis, and Taurus star formation regions. A model of field stars is built from a mixture of multivariate Gaussians based on the Besançon Galactic model. The algorithm can derive membership probabilities for objects with only sky coordinates and proper motion, but can also include parallax and radial velocity measurements, as well as spectrophotometric distance constraints from sequences in color–magnitude or spectral type–magnitude diagrams. BANYAN Σ benefits from an analytical solution to the Bayesian marginalization integrals over unknown radial velocities and distances that makes it more accurate and significantly faster than its predecessor BANYAN II. A contamination versus hit rate analysis is presented and demonstrates that BANYAN Σ achieves a better classification performance than other moving group tools available in the literature, especially in terms of cross-contamination between young associations. An updated list of bona fide members in the 27 young associations, augmented by the Gaia-DR1 release, as well as all parameters for the 6D multivariate Gaussian models for each association and the Galactic field neighborhood within 300 pc are presented. This new tool will make it possible to analyze large data sets such as the upcoming Gaia-DR2 to identify new young stars. IDL and Python versions of BANYAN Σ are made available with this publication, and a more limited online web tool is available at
http://www.exoplanetes.umontreal.ca/banyan/banyansigma.php
.
We present a sample of 74,216 M and L dwarfs constructed from two existing catalogs of cool dwarfs spectroscopically identified in the Sloan Digital Sky Survey (SDSS). We cross-matched the SDSS ...catalog with Gaia DR2 to obtain parallaxes and proper motions and modified the quality cuts suggested by the Gaia Collaboration to make them suitable for late-M and L dwarfs. We also provide relations between Gaia colors and absolute magnitudes with spectral type and conclude that (G − ) has the tightest relation to spectral type for M and L dwarfs. In addition, we study magnetic activity as a function of position on the color-magnitude diagram, finding that H magnetically active stars have, on average, redder colors and/or brighter magnitudes than inactive stars. This effect cannot be explained by youth alone and might indicate that active stars are magnetically inflated, binaries, and/or high metallicity. Moreover, we find that vertical velocity and vertical action dispersion are correlated with H emission, confirming that these two parameters are age indicators. We also find that stars below the main sequence have high tangential velocity, which is consistent with a low metallicity and old population of stars that belong to the halo or thick disk.
Abstract
We propose that 14 co-moving groups of stars uncovered by Kounkel & Covey may be related to known nearby moving groups and bridge those and nearby open clusters with similar ages and space ...velocities. This indicates that known nearby moving groups may be spatially much more extended than previously thought, and some of them might be parts of tidal tails around the cores of known open clusters, reminiscent of those recently found around the Hyades and a handful of other nearby clusters. For example, we find that both the nearby Carina and Columba associations may be linked to Theia 208 from Kounkel & Covey and together form parts of a large tidal tail around the Platais 8 open cluster. The AB Doradus moving group and Theia 301 may form a trailing tidal tail behind the Pleiades open cluster, with hints of a possible leading tidal tail in Theia 369. Similarly, we find that IC 2391 and its tidal tails identified by Meingast et al. may be extended by the nearby Argus association and are possibly further extended by Theia 115. The nearby Octans and Octans-Near associations, as well as Theia 94 and 95, may form a large tidal tail leading the poorly studied Platais 5 open cluster candidate. While a preliminary analysis of Gaia color–magnitude sequences hint that these structures are plausibly related, more observational evidence is still required to corroborate their consistent ages and space velocities. These observations may change our current understanding of nearby moving groups and the different pathways through which they can form. While some moving groups may have formed loosely in extended star formation events with rich spatial structure, others may in fact correspond to the tidal tails of nearby open clusters.
We present a search for stellar members of young associations within 150 pc of the Sun, based on TGAS and an updated version of the BANYAN software to determine Bayesian membership probabilities that ...includes Gaia-2MASS color-magnitude diagrams. We identify 32 new F0-M3-type bona fide members of the 10-200 Myr old Sco-Cen, Carina, Tucana-Horologium, Columba, and Octans associations and the AB Doradus, β Pictoris, and Carina-Near moving groups. These new bona fide members have measurements of their full kinematics and literature data consistent with a young age. We also confirm the membership of 66 previously known candidate members using their Gaia-Tycho trigonometric distances or new literature radial velocities, and identify 219 additional new candidate members, most of which do not yet have a radial velocity measurement. This work is the first step toward a completeness-corrected survey of young association members based on Gaia DR2 in the near future.
We present a characterization of the new Volans-Carina Association (VCA) of stars near the Galactic plane (b −10°) at a distance of 75-100 pc, previously identified as group 30 by Oh et al. We ...compile a list of 19 likely members from Gaia DR2 with spectral types B8-M2, and 46 additional candidate members from Gaia DR2, 2MASS, and AllWISE with spectral types A0-M9 that require further follow-up for confirmation. We find an isochronal age of Myr based on MIST isochrones calibrated with Pleiades members. This new association of stars is slightly younger than the Pleiades, with less members but located at a closer distance, making its members 3 times as bright as those of the Pleiades on average. It is located further than members of the AB Doradus moving group, which have a similar age, but it is more compact on the sky, which makes it less prone to contamination from random field interlopers. Its members will be useful benchmarks to understand the fundamental properties of stars, brown dwarfs, and exoplanets at 90 Myr. We also provide an updated version of the BANYAN Bayesian classification tool that includes the VCA.
We present thermal phase curve measurements for the hot Jupiter WASP-103b observed with Hubble/WFC3 and Spitzer/IRAC. The phase curves have large amplitudes and negligible hotspot offsets, indicative ...of poor heat redistribution to the nightside. We fit the phase variation with a range of climate maps and find that a spherical harmonics model generally provides the best fit. The phase-resolved spectra are consistent with blackbodies in the WFC3 bandpass, with brightness temperatures ranging from 1880 40 K on the nightside to 2930 40 K on the dayside. The dayside spectrum has a significantly higher brightness temperature in the Spitzer bands, likely due to CO emission and a thermal inversion. The inversion is not present on the nightside. We retrieved the atmospheric composition and found that it is moderately metal-enriched ( ) and the carbon-to-oxygen ratio is below 0.9 at 3 confidence. In contrast to cooler hot Jupiters, we do not detect spectral features from water, which we attribute to partial H2O dissociation. We compare the phase curves to 3D general circulation models and find that magnetic drag effects are needed to match the data. We also compare the WASP-103b spectra to brown dwarfs and young, directly imaged companions. We find that these objects have significantly larger water features, indicating that surface gravity and irradiation environment play an important role in shaping the spectra of hot Jupiters. These results highlight the 3D structure of exoplanet atmospheres and illustrate the importance of phase curve observations for understanding their complex chemistry and physics.
The CatWISE2020 Catalog Marocco, Federico; Eisenhardt, Peter R. M.; Fowler, John W. ...
The Astrophysical journal. Supplement series,
03/2021, Letnik:
253, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Abstract
The CatWISE2020 Catalog consists of 1,890,715,640 sources over the entire sky selected from Wide-field Infrared Survey Explorer (WISE) and NEOWISE survey data at 3.4 and 4.6
μ
m (W1 and W2) ...collected from 2010 January 7 to 2018 December 13. This data set adds two years to that used for the CatWISE Preliminary Catalog, bringing the total to six times as many exposures spanning over 16 times as large a time baseline as the AllWISE catalog. The other major change from the CatWISE Preliminary Catalog is that the detection list for the CatWISE2020 Catalog was generated using
crowdsource
from Schlafly et al., while the CatWISE Preliminary Catalog used the detection software used for AllWISE. These two factors result in roughly twice as many sources in the CatWISE2020 Catalog. The scatter with respect to Spitzer photometry at faint magnitudes in the COSMOS field, which is out of the Galactic Plane and at low ecliptic latitude (corresponding to lower WISE coverage depth) is similar to that for the CatWISE Preliminary Catalog. The 90% completeness depth for the CatWISE2020 Catalog is at W1 = 17.7 mag and W2 = 17.5 mag, 1.7 mag deeper than in the CatWISE Preliminary Catalog. In comparison to Gaia, CatWISE2020 motions are accurate at the 20 mas yr
−1
level for W1∼15 mag sources and at the ∼100 mas yr
−1
level for W1∼17 mag sources. This level of accuracy represents a 12× improvement over AllWISE. The CatWISE catalogs are available in the WISE/NEOWISE Enhanced and Contributed Products area of the NASA/IPAC Infrared Science Archive.
Abstract
We present the results of a density-based clustering analysis of the 6D
XYZ
Galactic positions and
UVW
-space velocities of nearby (≤200 pc) Gaia Early Data Release 3 stars with radial ...velocities using HDBSCAN, in opposition to previous studies (Kounkel & Covey 2019; Meingast et al. 2021) that only included positions and tangential velocities. Among the 241 recovered clusters, we identify more than 50 known associations, 32 new candidate stellar streams aged 100 Myr to 3 Gyr, nine extensions of known Theia groups uncovered by Kounkel & Covey, and eight newly recognized coronae around nearby open clusters. Three confirmed exoplanet-hosting stars and three more TESS transiting exoplanet candidates are part of the new groups discovered here, including TOI–1807 and TOI–2076 from Hedges et al. (2021) that were suspected to belong to a yet unidentified moving group. The new groups presented here were not previously recognized because of their older ages, low spatial density, and projection effects that spread out the tangential velocities of their nearby comoving members. Several newly identified structures reach distances within 60 pc of the Sun, providing new grounds for the identification of isolated planetary-mass objects. The nearest member of the newly recognized corona of Volans–Carina is V419 Hya, a known young debris disk star at a distance of 22 pc. This study outlines the importance of further characterization of young associations in the immediate solar neighborhood, which will provide new laboratories for the precise age calibration of nearby stars, exoplanets, and substellar objects.
LACEwING: A New Moving Group Analysis Code Riedel, Adric R.; Blunt, Sarah C.; Lambrides, Erini L. ...
The Astronomical journal,
03/2017, Letnik:
153, Številka:
3
Journal Article
Recenzirano
We present a new nearby young moving group (NYMG) kinematic membership analysis code, LocAting Constituent mEmbers In Nearby Groups (LACEwING), a new Catalog of Suspected Nearby Young Stars, a new ...list of bona fide members of moving groups, and a kinematic traceback code. LACEwING is a convergence-style algorithm with carefully vetted membership statistics based on a large numerical simulation of the Solar Neighborhood. Given spatial and kinematic information on stars, LACEwING calculates membership probabilities in 13 NYMGs and three open clusters within 100 pc. In addition to describing the inputs, methods, and products of the code, we provide comparisons of LACEwING to other popular kinematic moving group membership identification codes. As a proof of concept, we use LACEwING to reconsider the membership of 930 stellar systems in the Solar Neighborhood (within 100 pc) that have reported measurable lithium equivalent widths. We quantify the evidence in support of a population of young stars not attached to any NYMGs, which is a possible sign of new as-yet-undiscovered groups or of a field population of young stars.
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