- ID:
- ivo://CDS.VizieR/J/MNRAS/489/3093
- Title:
- Gaia DR2 parallax of globular clusters
- Short Name:
- J/MNRAS/489/3093
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have established a mixture model approach to derive the parallax of the MilkyWay globular clusters. It avoids the problem of cluster membership determination and provides a completely independent astrometrical solution by purely using the parallax data. This method is validated with simulated clusters of Pancino et al.. We have resolved 120 real globular clusters by the mixture model using parallaxes of the second data release of Gaia. They construct the largest direct parallax sample up to now. In comparison with other direct parallax results based on cluster members, including 75 clusters of Gaia Collaboration, our method presents its accuracy, especially for some particular clusters. A systematic offset of -27.6+/-1.7 uas, together with a scatter of 22.8+/-1.3 uas is found in comparison with other indirect parallax measurements. They are consistent with the global value and the variation of the zero-point of current Gaia parallaxes. Distances of several specific nearby globular clusters are discussed while the closest ones can reach high precisions, even taking the systematic error into account.
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- ID:
- ivo://CDS.VizieR/J/ApJ/863/89
- Title:
- Gaia DR2 PMs of stars in ultra-faint MW satellites
- Short Name:
- J/ApJ/863/89
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The second data release from the Gaia mission (DR2) provides a comprehensive and unprecedented picture of the motions of astronomical sources in the plane of the sky, extending from the solar neighborhood to the outer reaches of the Milky Way. I present proper-motion measurements based on Gaia DR2 for 17 ultra-faint dwarf galaxies within 100kpc of the Milky Way. I compile the spectroscopically confirmed member stars in each dwarf bright enough for Gaia astrometry from the literature, producing member samples ranging from two stars in Triangulum II to 68 stars in Bootes I. From the spectroscopic member catalogs, I estimate the proper motion of each system. I find good agreement with the proper motions derived by the Gaia collaboration for Bootes I and Leo I. The tangential velocities for 14 of the 17 dwarfs are determined to better than 50km/s, more than doubling the sample of such measurements for Milky Way satellite galaxies. The orbital pericenters are well constrained, with a mean value of 38kpc. Only one satellite, Tucana III, is on an orbit passing within 15kpc of the Galactic center, suggesting that the remaining ultra-faint dwarfs are unlikely to have experienced severe tidal stripping. As a group, the ultra-faint dwarfs are on high-velocity, eccentric, retrograde trajectories, with nearly all of them having space motions exceeding 370km/s. A large majority of the objects are currently close to the pericenters of their orbits. In a low-mass (M_vir_=0.9x10^12^M_{sun}_) Milky Way potential, eight out of the 17 galaxies lack well-defined apocenters and appear likely to be on their first infall, indicating that the Milky Way mass may be larger than previously estimated or that many of the ultra-faint dwarfs are associated with the Magellanic Clouds. The median eccentricity of the ultra-faint dwarf orbits is 0.79, similar to the values seen in numerical simulations but distinct from the rounder orbits of the more luminous dwarf spheroidals.
4933. Gaia DR1 QSO magnitude
- ID:
- ivo://CDS.VizieR/J/A+A/611/A52
- Title:
- Gaia DR1 QSO magnitude
- Short Name:
- J/A+A/611/A52
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The first release of the Gaia catalog is available since 14 September 2016. It is a first step in the realization of the future Gaia reference frame. This reference frame will be materialized by the optical positions of the sources and will be compared with and linked to the International Celestial Reference Frame, materialized by the radio position of extragalactic sources. As in the radio domain, it can be reasonably postulated that quasar optical flux variations can alert us to potential changes in the source structure. These changes could have important implications for the position of the target photocenters (together with the evolution in time of these centers) and in parallel have consequences for the link of the reference systems. A set of nine optical telescopes was used to monitor the magnitude variations, often at the same time as Gaia, thanks to the Gaia Observation Forecast Tool. The Allan variances, which are statistical tools widely used in the atomic time and frequency community, are introduced.
- ID:
- ivo://CDS.VizieR/VII/285
- Title:
- Gaia DR2 quasar and galaxy classification
- Short Name:
- VII/285
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We provide probabilistic quasar and galaxy classifications for 2.7 million sources in Gaia Data Release 2. This has been achieved using a supervised classification method (Gaussian Mixture Models) based only on photometric and astrometric data (8 features) in Gaia-DR2. The model is trained empirically to classify objects into three classes - star, quasar, galaxy - for all objects with G>=14.5mag down to the Gaia magnitude limit of G=21.0mag. We provide the probabilities for being a quasar (pqso) and a galaxy (pgal); the probability of being a star is pstar = 1-(pqso+pgal), and all other Gaia data can be obtained by cross-matching Gaia-DR2 using the source identifier. As our main goal is to identify extragalactic objects, we only report objects with pqso+pgal>0.5. These probabilities incorporate a sensible class prior, namely that quasars are 500 times rarer than stars, and that galaxies 7500 times rarer than stars. See the paper for details of the purity and completeness of samples drawn from this catalogue, and for more details of its construction, contents, and validation.
- ID:
- ivo://CDS.VizieR/J/A+A/616/A7
- Title:
- Gaia DR2 radial velocity standard stars catalog
- Short Name:
- J/A+A/616/A7
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Radial Velocity Spectrometer (RVS) on board the ESA satellite mission Gaia has no calibration device. Therefore, the radial velocity zero point needs to be calibrated with stars that are proved to be stable at a level of 300m/s during the Gaia observations. We compiled a dataset of ~71000 radial velocity measurements from five high-resolution spectrographs. A catalogue of 4813 stars was built by combining these individual measurements. The zero point was established using asteroids. The resulting catalogue has seven observations per star on average on a typical time baseline of 6yr, with a median standard deviation of 15m/s. A subset of the most stable stars fulfilling the RVS requirements was used to establish the radial velocity zero point provided in Gaia Data Release 2. The stars that were not used for calibration are used to validate the RVS data.
- ID:
- ivo://CDS.VizieR/J/A+A/616/A12
- Title:
- Gaia DR2 sources in GC and dSph
- Short Name:
- J/A+A/616/A12
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The goal of this paper is to demonstrate the outstanding quality of the second data release of the Gaia mission and its power for constraining many different aspects of the dynamics of the satellites of the Milky Way. We focus here on determining the proper motions of 75 Galactic globular clusters, nine dwarf spheroidal galaxies, one ultra-faint system, and the Large and Small Magellanic Clouds. Using data extracted from the Gaia archive, we derived the proper motions and parallaxes for these systems, as well as their uncertainties. We demonstrate that the errors, statistical and systematic, are relatively well understood. We integrated the orbits of these objects in three different Galactic potentials, and characterised their properties. We present the derived proper motions, space velocities, and characteristic orbital parameters in various tables to facilitate their use by the astronomical community. Our limited and straightforward analyses have allowed us for example to (i) determine absolute and very precise proper motions for globular clusters; (ii) detect clear rotation signatures in the proper motions of at least five globular clusters; (iii) show that the satellites of the Milky Way are all on high-inclination orbits, but that they do not share a single plane of motion; (iv) derive a lower limit for the mass of the Milky Way of 9.8^+6.7^_-2.7_x10^11^M_{sun}_ based on the assumption that the Leo~I dwarf spheroidal is bound; (v) derive a rotation curve for the Large Magellanic Cloud based solely on proper motions that is competitive with line-of-sight velocity curves, now using many orders of magnitude more sources; and (vi) unveil the dynamical effect of the bar on the motions of stars in the Large Magellanic Cloud. All these results highlight the incredible power of the Gaia astrometric mission, and in particular of its second data release.
- ID:
- ivo://CDS.VizieR/J/A+A/620/A128
- Title:
- Gaia DR2 study of Herbig Ae/Be stars
- Short Name:
- J/A+A/620/A128
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use Gaia Data Release 2 (DR2, Cat. I/345) to place 252 Herbig Ae/Be stars in the HR diagram and investigate their characteristics and properties. For all known Herbig Ae/Be stars with parallaxes in Gaia DR2, we collected their atmospheric parameters and photometric and extinction values from the literature. To these data we added near- and mid-infrared photometry, collected Halpha emission line properties such as equivalent widths and line profiles, and their binarity status. In addition, we developed a photometric variability indicator from Gaia's DR2 information. We provide masses, ages, luminosities, distances, photometric variabilities and infrared excesses homogeneously derived for the most complete sample of Herbig Ae/Be stars to date. We find that high mass stars have a much smaller infrared excess and have much lower optical variabilities compared to lower mass stars, with the break at around 7M_{sun}_. Halpha emission is generally correlated with infrared excess, with the correlation being stronger for infrared emission at wavelengths tracing the hot dust closest to the star. The variability indicator as developed by us shows that approximately 25% of all Herbig Ae/Be stars are strongly variable. We observe that the strongly variable objects display doubly peaked Halpha line profiles, indicating an edge-on disk. The fraction of strongly variable Herbig Ae stars is close to that found for A-type UX Ori stars. It had been suggested that this variability is in most cases due to asymmetric dusty disk structures seen edge-on. The observation here is in strong support of this hypothesis. Finally, the difference in dust properties occurs at 7M_{sun}_, while various properties traced at UV/optical wavelengths differ at a lower mass, 3M_{sun}_. The latter has been linked to different accretion mechanisms at work whereas the differing infrared properties and photometric variabilities are related to different or differently acting (dust-)disk dispersal mechanisms.
4938. Gaia DR1 TGAS at ESA
- ID:
- ivo://esavo/gaia/csdr1/tgas
- Title:
- Gaia DR1 TGAS at ESA
- Short Name:
- GAIA DR1 TGAS
- Date:
- 07 Feb 2024 10:15:55
- Publisher:
- European Space Agency
- Description:
- This table is a subset of DR1 GaiaSource comprising those stars in the Hipparcos and Tycho-2 Catalogues for which a full 5-parameter astrometric solution has been possible in Gaia Data Release 1. This is possible because the early Hipparcos epoch positions break some degeneracies due to the limited Gaia time coverage. This table contains a substantial fraction of the around 2.5 million stars in the Hipparcos and Tycho-2 catalogue. Many stars have been excluded due to several reasons, such as saturation, cross-match errors or bad astrometric solution.
- ID:
- ivo://CDS.VizieR/J/AJ/160/138
- Title:
- 68 Gaia DR2 ultra-short-period planet host stars
- Short Name:
- J/AJ/160/138
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- It has been unambiguously shown both in individual systems and at the population level that hot Jupiters experience tidal inspiral before the end of their host stars main-sequence lifetimes. Ultra-short-period (USP) planets have orbital periods P<1 day, rocky compositions, and are expected to experience tidal decay on similar timescales to hot Jupiters if the efficiency of tidal dissipation inside their host stars parameterized as Q_*_' is independent of P and/or secondary mass M_p_. Any difference between the two classes of systems would reveal that a model with constant Q_*_' is insufficient. If USP planets experience tidal inspiral, then USP planet systems will be relatively young compared to similar stars without USP planets. Because it is a proxy for relative age, we calculate the Galactic velocity dispersions of USP planet candidate host and non-host stars using data from Gaia Data Release 2 supplemented with ground-based radial velocities. We find that main-sequence USP planet candidate host stars have kinematics consistent with similar stars in the Kepler field without observed USP planets. This indicates that USP planet hosts have similar ages to field stars and that USP planets do not experience tidal inspiral during the main-sequence lifetimes of their host stars. The survival of USP planets requires that Q_*_'>~10^7^ at P~0.7day and M_p_~2.6M{Earth}. This result demands that Q_*_' depend on the orbital period and/or mass of the secondary in the range 0.5day<~P<~5days and 1M{Earth}<~M_p_<~1000M{sun}.
- ID:
- ivo://CDS.VizieR/J/A+A/618/A12
- Title:
- Gaia DR1 Upper Scorpius new member candidates
- Short Name:
- J/A+A/618/A12
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Selecting a cluster in proper motion space is an established method for identifying members of a star forming region. The first data release from Gaia (DR1) provides an extremely large and precise stellar catalogue, which when combined with the Tycho-2 catalogue gives the 2.5 million parallaxes and proper motions contained within the Tycho-Gaia Astrometric Solution (TGAS). We aim to identify new member candidates of the nearby Upper Scorpius subgroup of the Scorpius-Centaurus Complex within the TGAS catalogue. In doing so, we also aim to validate the use of the DBSCAN clustering algorithm on spatial and kinematic data as a robust member selection method. We constructed a method for member selection using a density-based clustering algorithm (DBSCAN) applied over proper motion and distance. We then applied this method to Upper Scorpius, and evaluated the results and performance of the method. We identified 167 member candidates of Upper Scorpius, of which 78 are new, distributed within a 10{deg} radius from its core. These member candidates have a mean distance of 145.6+/-7.5pc, and a mean proper motion of (-11.4, -23.5)+/-(0.7, 0.4)mas/yr. These values are consistent with measured distances and proper motions of previously identified bona-fide members of the Upper Scorpius association.