- ID:
- ivo://CDS.VizieR/J/PAZh/34/868
- Title:
- Red giant clump in the Tycho-2 catalog
- Short Name:
- J/PAZh/34/868
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Tycho-2 proper motions and Tycho-2 and 2MASS photometry are used to select 97348 red giant clump (RGC) stars. The interstellar extinction and photometric distance are calculated for each of the stars. The selected stars are shown to form a selection-unbiased sample of RGC stars within about 350 pc of the Sun with the addition of more distant stars. The distribution of the selected stars in space and their motion are consistent with the assumption that the RGC contains Galactic disk stars with various ages and metallicities, including a significant fraction of stars younger than 1Gyr with masses of more than 2 solar masses. These young stars show differences of their statistical characteristics from those of older RGC stars, including differences in the variations of their distribution density with distance from the Galactic plane and in the dispersion of their velocities found using radial velocities and proper motions. The Sun has been found to rise above the Galactic plane by 13+/-1pc. The distribution density of the stars under consideration in space is probably determined by the Local Spiral Arm and the distribution of absorbing matter in the plane of the Gould Belt. Data are also available at: http://www.geocities.com/orionspiral/
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/795/52
- Title:
- Red giant star sample from SDSS
- Short Name:
- J/ApJ/795/52
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have obtained a sample of ~22000 red giant branch (RGB) stars based on stellar parameters, provided by the ninth data release of the Sloan Digital Sky Survey (Cat. V/139), and the CH(G)/MgH indices, measured from the included spectra. The Galactic rest-frame velocity of V_gsr_ versus longitude for the sample shows the existence of several groups of stars from globular clusters and known streams. Excluding these substructures, a sample of ~16000 RGB stars from the general field is used to investigate the properties of the thick disk, the inner halo, and the outer halo of our Galaxy. The metallicity and rotational velocity distributions are investigated for stars at 0 kpc<|Z|<10 kpc. It is found that the canonical thick disk dominates at 0 kpc<|Z|<2 kpc and its contribution becomes negligible at |Z|>3 kpc. The MWTD is present and overlaps with the inner halo at 1 kpc<|Z|<3 kpc. The inner halo starts at 2 kpc<|Z|<3 kpc and becomes the dominated population for 4 kpc<|Z|<10 kpc. For halo stars with |Z|>5 kpc, bimodal metallicity distributions are found for 20 kpc<|Z|<25 kpc and 35 kpc<RR<45 kpc, which suggests a dual halo, the inner and the outer halo, as reported in Carollo et al. (2007Natur.450.1020C) at low|Z| values. The peak of metallicity for the inner halo is at [Fe/H]~-1.6 and appears to be at [Fe/H]~-2.3 for the outer halo. The transition point from the inner to the outer halo is located at|Z|~20 kpc and RR~35 kpc.
- ID:
- ivo://CDS.VizieR/J/ApJ/866/99
- Title:
- Revised radii of KIC stars & planets using Gaia DR2
- Short Name:
- J/ApJ/866/99
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- One bottleneck for the exploitation of data from the Kepler mission for stellar astrophysics and exoplanet research has been the lack of precise radii and evolutionary states for most of the observed stars. We report revised radii of 177911 Kepler stars derived by combining parallaxes from the Gaia Data Release 2 with the DR25 Kepler Stellar Properties Catalog. The median radius precision is ~8%, a typical improvement by a factor of 4-5 over previous estimates for typical Kepler stars. We find that ~67% (~120000) of all Kepler targets are main-sequence stars, ~21% (~37000) are subgiants, and ~12% (~21000) are red giants, demonstrating that subgiant contamination is less severe than some previous estimates and that Kepler targets are mostly main-sequence stars. Using the revised stellar radii, we recalculate the radii for 2123 confirmed and 1922 candidate exoplanets. We confirm the presence of a gap in the radius distribution of small, close-in planets, but find that the gap is mostly limited to incident fluxes >200F_{Earth}_, and its location may be at a slightly larger radius (closer to ~2R_{Earth}_) when compared to previous results. Furthermore, we find several confirmed exoplanets occupying a previously described "hot super-Earth desert" at high irradiance, show the relation between a gas-giant planet's radius and its incident flux, and establish a bona fide sample of eight confirmed planets and 30 planet candidates with Rp<2R_{Earth}_ in circumstellar "habitable zones" (incident fluxes between 0.25 and 1.50F_{Earth}_). The results presented here demonstrate the potential for transformative characterization of stellar and exoplanet populations using Gaia data.
- ID:
- ivo://CDS.VizieR/J/ApJS/229/30
- Title:
- Revised stellar properties of Q1-17 Kepler targets
- Short Name:
- J/ApJS/229/30
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The determination of exoplanet properties and occurrence rates using Kepler data critically depends on our knowledge of the fundamental properties (such as temperature, radius, and mass) of the observed stars. We present revised stellar properties for 197096 Kepler targets observed between Quarters 1-17 (Q1-17), which were used for the final transiting planet search run by the Kepler Mission (Data Release 25, DR25). Similar to the Q1-16 catalog by Huber+ (2014, J/ApJS/211/2), the classifications are based on conditioning published atmospheric parameters on a grid of Dartmouth isochrones, with significant improvements in the adopted method and over 29000 new sources for temperatures, surface gravities, or metallicities. In addition to fundamental stellar properties, the new catalog also includes distances and extinctions, and we provide posterior samples for each stellar parameter of each star. Typical uncertainties are ~27% in radius, ~17% in mass, and ~51% in density, which is somewhat smaller than previous catalogs because of the larger number of improved logg constraints and the inclusion of isochrone weighting when deriving stellar posterior distributions. On average, the catalog includes a significantly larger number of evolved solar-type stars, with an increase of 43.5% in the number of subgiants. We discuss the overall changes of radii and masses of Kepler targets as a function of spectral type, with a particular focus on exoplanet host stars.
- ID:
- ivo://CDS.VizieR/J/MNRAS/508/2370
- Title:
- Revisiting the Cygnus OB associations
- Short Name:
- J/MNRAS/508/2370
- Date:
- 24 Jan 2022 09:16:32
- Publisher:
- CDS
- Description:
- OB associations play an important role in Galactic evolution, though their origins and dynamics remain poorly studied, with only a small number of systems analysed in detail. In this paper we revisit the existence and membership of the Cygnus OB associations. We find that of the historical OB associations only Cyg OB2 and OB3 stand out as real groups. We search for new OB stars using a combination of photometry, astrometry, evolutionary models and an SED fitting process, identifying 4680 probable OB stars with a reliability of >90%. From this sample we search for OB associations using a new and flexible clustering technique, identifying 6 new OB associations. Two of these are similar to the associations Cyg OB2 and OB3, though the others bear no relationship to any existing systems. We characterize the properties of the new associations, including their velocity dispersions and total stellar masses, all of which are consistent with typical values for OB associations. We search for evidence of expansion and find that all are expanding, albeit anistropically, with stronger and more significant expansion in the direction of Galactic longitude. We also identify two large-scale (160pc and 25km/s) kinematic expansion patterns across the Cygnus region, each including three of our new associations, and attribute this to the effects of feedback from a previous generation of stars. This work highlights the need to revisit the existence and membership of the historical OB associations, if they are to be used to study their properties and dynamics.
- ID:
- ivo://CDS.VizieR/J/ApJ/776/26
- Title:
- RRab stars in the Orphan stream distances
- Short Name:
- J/ApJ/776/26
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report positions, velocities, and metallicities of 50 ab-type RR Lyrae (RRab) stars observed in the vicinity of the Orphan stellar stream. Using about 30 RRab stars classified as being likely members of the Orphan stream, we study the metallicity and the spatial extent of the stream. We find that RRab stars in the Orphan stream have a wide range of metallicities, from -1.5dex to -2.7dex. The average metallicity of the stream is -2.1dex, identical to the value obtained by Newberg et al. (2010ApJ...711...32N) using blue horizontal branch stars. We find that the most distant parts of the stream (40-50kpc from the Sun) are about 0.3dex more metal-poor than the closer parts (within ~30kpc), suggesting a possible metallicity gradient along the stream's length. We have extended the previous studies and have mapped the stream up to 55kpc from the Sun. Even after a careful search, we did not identify any more distant RRab stars that could plausibly be members of the Orphan stream. If confirmed with other tracers, this result would indicate a detection of the end of the leading arm of the stream. We have compared the distances of Orphan stream RRab stars with the best-fit orbits obtained by Newberg et al. We find that model 6 of Newberg et al. cannot explain the distances of the most remote Orphan stream RRab stars, and conclude that the best fit to distances of Orphan stream RRab stars and to the local circular velocity is provided by potentials where the total mass of the Galaxy within 60kpc is M_60_~2.7x10^11^M_{sun}_, or about 60% of the mass found by previous studies. More extensive modeling that would consider non-spherical potentials and the possibility of misalignment between the stream and the orbit is highly encouraged.
- ID:
- ivo://CDS.VizieR/J/ApJ/854/47
- Title:
- RRab stars of Monoceros Ring & A13 overdensities
- Short Name:
- J/ApJ/854/47
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Monoceros Ring (also known as the Galactic Anticenter Stellar Structure) and A13 are stellar overdensities at estimated heliocentric distances of d~11kpc and 15kpc observed at low Galactic latitudes toward the anticenter of our Galaxy. While these overdensities were initially thought to be remnants of a tidally disrupted satellite galaxy, an alternate scenario is that they are composed of stars from the Milky Way (MW) disk kicked out to their current location due to interactions between a satellite galaxy and the disk. To test this scenario, we study the stellar populations of the Monoceros Ring and A13 by measuring the number of RR Lyrae and M giant stars associated with these overdensities. We obtain low-resolution spectroscopy for RR Lyrae stars in the two structures and measure radial velocities to compare with previously measured velocities for M giant stars in the regions of the Monoceros Ring and A13, to assess the fraction of RR Lyrae to M giant stars (f_RR:MG_) in A13 and Mon/GASS. We perform velocity modeling on 153 RR Lyrae stars (116 in the Monoceros Ring and 37 in A13) and find that both structures have very low f_RR:MG_. The results support a scenario in which stars in A13 and Mon/GASS formed in the MW disk. We discuss a possible association between Mon/GASS, A13, and the Triangulum-Andromeda overdensity based on their similar velocity distributions and f_RR:MG_.
- ID:
- ivo://CDS.VizieR/J/ApJ/831/165
- Title:
- RR Lyrae as tracers in the Virgo overdensity region
- Short Name:
- J/ApJ/831/165
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use a combination of spatial distribution and radial velocity to search for halo substructures in a sample of 412 RR Lyrae stars (RRLSs) that covers a region of ~525 square degrees of the Virgo overdensity (VOD) and spans distances from the Sun from 4 to 75kpc. With a friends-of-friends algorithm we identified six high-significance groups of RRLSs in phase space, which we associate mainly with the VOD and with the Sagittarius stream. Four other groups were also flagged as less significant overdensities. Three high-significance and three lower-significance groups have distances between ~10 and 20kpc, which places them in the distance range attributed by others to the VOD. The largest of these is the Virgo stellar stream at 19kpc, which has 18 RRLSs, a factor of two increase over the number known previously. While these VOD groups are distinct according to our selection criteria, their overlap in position and distance and, in a few cases, similarity in radial velocity are suggestive that they may not all stem from separate accretion events. Even so, the VOD appears to be caused by more than one overdensity. The Sagittarius (Sgr) stream is a very obvious feature in the background of the VOD at a mean distance of 44kpc. Two additional high-significance groups were detected at distances >40kpc. Their radial velocities and locations differ from the expected path of the Sgr debris in this part of the sky, and they are likely to be remnants of other accretion events.
- ID:
- ivo://CDS.VizieR/J/ApJ/849/150
- Title:
- RR Lyrae candidates in the MW outer halo
- Short Name:
- J/ApJ/849/150
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- RR Lyrae stars are ideal massless tracers that can be used to study the total mass and dark matter content of the outer halo of the Milky Way (MW). This is because they are easy to find in the light-curve databases of large stellar surveys and their distances can be determined with only knowledge of the light curve. We present here a sample of 112 RR Lyr stars beyond 50kpc in the outer halo of the MW, excluding the Sgr streams, for which we have obtained moderate-resolution spectra with Deimos on the Keck II Telescope. Four of these have distances exceeding 100kpc. These were selected from a much larger set of 447 candidate RR Lyr stars that were data-mined using machine-learning techniques applied to the light curves of variable stars in the Palomar Transient Facility database. The observed radial velocities taken at the phase of the variable corresponding to the time of observation were converted to systemic radial velocities in the Galactic standard of rest. From our sample of 112 RR Lyr stars we determine the radial velocity dispersion in the outer halo of the MW to be ~90km/s at 50kpc, falling to about 65km/s near 100 kpc once a small number of major outliers are removed. With reasonable estimates of the completeness of our sample of 447 candidates and assuming a spherical halo, we find that the stellar density in the outer halo declines as r^-4^.
- ID:
- ivo://CDS.VizieR/J/ApJ/863/79
- Title:
- RR Lyrae cand. in the Galactic Center
- Short Name:
- J/ApJ/863/79
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Deep near-IR images from the VISTA Variables in the Via Lactea (VVV) Survey were used to search for RR Lyrae stars within 100 arcmin from the Galactic Center. A large sample of 960 RR Lyrae of type ab (RRab) stars were discovered. A catalog is presented featuring the positions, magnitudes, colors, periods, and amplitudes for the sample, in addition to estimated reddenings, distances, and metallicities, and measured individual relative proper motions. We use the reddening-corrected Wesenheit magnitudes, defined as W_Ks_=Ks-0.428x(J-Ks), in order to isolate bona fide RRL belonging to the Galaxy Center, finding that 30 RRab are foreground/background objects. We measure a range of extinctions from A_Ks_=0.19 to 1.75mag for the RRab in this region, finding that large extinction is the main cause of the sample incompleteness. The mean period is P=0.5446+/-0.0025d, yielding a mean metallicity of [Fe/H]=-1.30+/-0.01 ({sigma}=0.33)dex for the RRab sample in the Galactic Center region. The median distance for the sample is D=8.05+/-0.02kpc. We measure the RRab surface density using the less reddened region sampled here, finding a density of 1000 RRab/sq deg at a projected Galactocentric distance R_G_=1.6deg. Under simple assumptions, this implies a large total mass (M>10^9^M_{sun}_) for the old and metal-poor population contained inside RG. We also measure accurate relative proper motions, from which we derive tangential velocity dispersions of {sigma}V_l_=125.0 and {sigma}V_b_=124.1km/s along the Galactic longitude and latitude coordinates, respectively. The fact that these quantities are similar indicate that the bulk rotation of the RRab population is negligible, and implies that this population is supported by velocity dispersion. In summary, there are two main conclusions of this study. First, the population as a whole is no different from the outer bulge RRab, predominantly a metal-poor component that is shifted with respect to the Oosterhoff type I population defined by the globular clusters in the halo. Second, the RRab sample, as representative of the old and metal-poor stellar population in the region, has high velocity dispersions and zero rotation, suggesting a formation via dissipational collapse.
