- ID:
- ivo://CDS.VizieR/J/A+A/638/A104
- Title:
- Gaia DR2 candidate RR Lyrae of Sgr stream & dwarf
- Short Name:
- J/A+A/638/A104
- Date:
- 14 Jan 2022 08:12:04
- Publisher:
- CDS
- Description:
- The Sagittarius (Sgr) stream is one of the best tools that we currently have to estimate the mass and shape of our Galaxy. However, assigning membership and obtaining the phase-space distribution of the stars that form the tails is quite challenging. Our goal is to produce a catalogue of RR Lyrae stars of Sgr and obtain an empiric measurement of the trends along the stream in sky position, distance and tangential velocities. We generate two initial samples from the Gaia DR2 RR Lyrae catalogue: one, selecting only the stars within +/-20{deg} of the orbital plane of Sagittarius (Strip) and the other, the result of applying the Pole Count Map (nGC3) algorithm. We then use the model-independent, deterministic method developed in this work to remove most of the contamination by detecting and isolating the stream in distance and proper motions. The output is two empiric catalogues: the Strip sample (higher-completeness, lower-purity) which contains 11677 stars, and the nGC3 sample (higher-purity, lower-completeness) with 6608 stars. We characterise the changes along the stream in all the available dimensions, the 5 astrometric ones plus the metallicity, covering more than 2{pi}rad in the sky and obtain new estimates for the apocentres and the mean [Fe/H] of the RR Lyrae population. Also, we show the first map of the two components of the tangential velocity, thanks to the combination of distances and proper motions. Finally, we detect the bifurcation in the leading arm and report no significant difference between the two branches, either in metallicity, kinematics or distance. We provide the largest sample of RR Lyrae candidates of Sgr, which can be used as an input for a spectroscopic follow-up or as a reference for the new generation of models of the stream through the interpolators in distance and velocity that we have constructed.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/618/A59
- Title:
- Gaia DR2 confirmed new nearby open clusters
- Short Name:
- J/A+A/618/A59
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The publication of the Gaia Data Release 2 (Gaia DR2) opens a new era in astronomy. It includes precise astrometric data (positions, proper motions, and parallaxes) for more than 1.3 billion sources, mostly stars. To analyse such a vast amount of new data, the use of data-mining techniques and machine-learning algorithms is mandatory. A great example of the application of such techniques and algorithms is the search for open clusters (OCs), groups of stars that were born and move together, located in the disc. Our aim is to develop a method to automatically explore the data space, requiring minimal manual intervention. We explore the performance of a density-based clustering algorithm, DBSCAN, to find clusters in the data together with a supervised learning method such as an artificial neural network (ANN) to automatically distinguish between real OCs and statistical clusters. The development and implementation of this method in a five-dimensional space (l, b, p, {mu}_{alpha}_^*^, {mu}_{delta}_) with the Tycho-Gaia Astrometric Solution (TGAS) data, and a posterior validation using Gaia DR2 data, lead to the proposal of a set of new nearby OCs. We have developed a method to find OCs in astrometric data, designed to be applied to the full Gaia DR2 archive.
- ID:
- ivo://CDS.VizieR/J/MNRAS/502/L90
- Title:
- Gaia DR2 Galactic bulge new star clusters
- Short Name:
- J/MNRAS/502/L90
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the discovery of 34 new open clusters and candidates as a result of a systematic search carried out in 200 adjacent fields of 1x1 square degrees area projected towards the Galactic bulge, using Gaia DR2 data. The objects were identified and characterized by a joint analysis of their photometric, kinematic and spatial distribution, which has been consistently used and proved to be effective in our previous works. The discoveries were validated by cross-referencing the objects position and astrometric parameters with the available literature. Besides their coordinates and astrometric parameters, we also provide sizes, ages, distances and reddening for the discovered objects. In particular, 32 clusters are closer than 2kpc from the Sun, which represents an increment of nearly 39% of objects with astrophysical parameters determined in the nearby inner disk. Although these objects fill an important gap in the open clusters distribution along the Sagittarius arm, this arm, traced by known clusters, appears to be interrupted, which may be an artifact due to the incompleteness of the cluster census.
- ID:
- ivo://CDS.VizieR/J/A+A/646/A99
- Title:
- Gaia DR2 Monoceros and ACS candidates
- Short Name:
- J/A+A/646/A99
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Gaia astrometric sample allows us to study the outermost Galactic disc, the halo, and their interface. It is precisely at the very edge of the disc where the effects of external perturbations are expected to be the most noticeable. Our goal is to detect the kinematic substructure present in the halo and at the edge of the Milky Way (MW) disc and provide observational constraints on their phase-space distribution. We download, one HP at a time, the proper motion histogram of distant stars, to which we apply a wavelet transformation to reveal the significant overdensities. We then analyse the large coherent structures that appear in the sky. We reveal a sharp yet complex anticentre dominated by Monoceros (MNC) and the Anticentre Stream (ACS) in the north - which we find have intensities comparable to the Magellanic Clouds and the Sagittarius stream - and by MNC South and TriAnd at negative latitudes. Our method allows us to perform a morpho-logical analysis of MNC and the ACS, both of which span more than 100{deg} in longitude, and to provide a high purity sample of giants with which we track MNC down to latitudes as low as ~5{deg}. Their colour-magnitude diagram is consistent with extended structures at a distance of ~10-11kpc that originated in the disc, with a very low ratio of RR-Lyrae over M giants, and with kinematics compatible with the rotation curve at those distances or slightly slower. We present a precise characterisation of MNC and the ACS, two previously known structures that our method reveals naturally, allowing us to detect them without limiting ourselves to a particular stellar type and, for the first time, using only kinematics. Our results will allow future studies to model their chemo-dynamics and evolution, thus constraining some of the most influential processes that shaped the MW.
- ID:
- ivo://CDS.VizieR/J/A+A/633/A99
- Title:
- Gaia DR2 open clusters in the Milky Way. II
- Short Name:
- J/A+A/633/A99
- Date:
- 02 Mar 2022 11:45:02
- Publisher:
- CDS
- Description:
- Many of the open clusters listed in modern catalogues were first reported by visual astronomers as apparent over-densities of bright stars. As observational techniques and analysis methods improved, some of them have been shown to be chance alignments of stars and are not true clusters. Recent publications making use of Gaia DR2 data provided membership list for over a thousand clusters, but many nearby objects listed in the literature have so far evaded detection. We update the Gaia DR2 cluster census by performing membership determinations for known clusters that had been missed by previous studies, and for recently discovered clusters. We investigate a subset of non-detected clusters that according to their literature parameters should be easily visible in the Gaia . Confirming or disproving the existence of old, inner-disc, high-altitude clusters is especially important as their survival or disruption is linked to the dynamical processes that drive the evolution of the Milky Way. We employ the Gaia DR2 catalogue and a membership assignment procedure, as well as visual inspection of spatial, proper motion, and parallax distributions. We use membership lists provided by other authors when they are available. We derive membership lists for 150 objects, including 10 that were known prior to Gaia . We compile a final list of members for 1481 clusters. Among the objects that we are still unable to identify with Gaia data, we argue that many (mostly putative old, relatively nearby, high-altitude objects) are not true clusters. At present, the only confirmed cluster located further than 500pc away from the Galactic plane within the Solar circle is NGC 6791. It is likely that the objects discussed in this study only represent a fraction of the non-physical groupings erroneously listed in the catalogues as genuine open clusters, and that those lists need further cleaning.
- ID:
- ivo://CDS.VizieR/IV/35
- Title:
- Gaia DR2-WISE Galactic Plane Matches
- Short Name:
- IV/35
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Faint, hidden contaminants in the point-spread functions (PSFs) of stars cause shifts to their measured positions. Wilson & Naylor (2017MNRAS.468.2517W) showed failing to account for these shifts can lead to a drastic decrease in the number of returned catalogue matches in crowded fields. Here we highlight the effect these perturbations have on cross-matching, for matches between Gaia DR2 and WISE stars in a crowded Galactic plane region. Applying the uncertainties as quoted to Gaussian-based astrometric uncertainty functions (AUFs) can lead, in dense Galactic fields, to only matching 55% of the counterparts. We describe the construction of empirical descriptions for AUFs, building on the cross-matching method of Wilson & Naylor (2018MNRAS.473.5570W), utilising the magnitudes of both catalogues to discriminate between true and false counterparts. We apply the improved cross-matching method to the Galactic plane |b|<10. We provide the most likely counterpart matches and their respective probabilities. We also analyse several cases to verify the robustness of the results, highlighting some important caveats and considerations. Finally, we discuss the effect PSF resolution has by comparing the intra- catalogue nearest neighbour separation distributions of a sample of likely contaminated WISE objects and their corresponding Spitzer counterpart. We show that some WISE contaminants are resolved in Spitzer, with smaller intra-catalogue separations. We have highlighted the effect contaminant stars have on WISE, but it is important for all photometric catalogues, playing an important role in the next generation of surveys, such as LSST.
- ID:
- ivo://CDS.VizieR/J/A+A/594/A120
- Title:
- Gaia-ESO Survey: Hydrogen lines in red giants
- Short Name:
- J/A+A/594/A120
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Red giant stars are perhaps the most important type of stars for Galactic and extra-galactic archaeology: they are luminous, occur in all stellar populations, and their surface temperatures allow precise abundance determinations for many different chemical elements. Yet, the full star formation and enrichment history of a galaxy can be traced directly only if two key observables can be determined for large stellar samples: age and chemical composition. While spectroscopy is a powerful method to analyse the detailed abundances of stars, stellar ages are the missing link in the chain, since they are not a direct observable. However, spectroscopy should be able to estimate stellar masses, which for red giants directly infer ages provided their chemical composition is known. Here we establish a new empirical relation between the shape of the hydrogen line in the observed spectra of red giants and stellar mass determined from asteroseismology. The relation allows determining stellar masses and ages with an accuracy of 10-15%. The method can be used with confidence for stars in the following range of stellar parameters: 4000<T_eff_<5000K, 0.5<logg<3.5, -2.0<[Fe/H]<0.3, and luminosities logL/L_{sun}_<2.5. Our analysis provides observational evidence that the H_{alpha}_ spectral characteristics of red giant stars are tightly correlated with their mass and therefore their age. We also show that the method samples well all stellar populations with ages above 1Gyr. Targeting bright giants, the method allows obtaining simultaneous age and chemical abundance information far deeper than would be possible with asteroseismology, extending the possible survey volume to remote regions of the Milky Way and even to neighbouring galaxies such as Andromeda or the Magellanic Clouds even with current instrumentation, such as the VLT and Keck facilities.
- ID:
- ivo://CDS.VizieR/J/A+A/591/A37
- Title:
- Gaia-ESO Survey. Parameters for cluster members
- Short Name:
- J/A+A/591/A37
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The nature of the metallicity gradient inside the solar circle (R_GC_<8kpc) is poorly understood, but studies of Cepheids and a small sample of open clusters suggest that it steepens in the inner disk. We investigate the metallicity gradient of the inner disk using a sample of inner disk open clusters that is three times larger than has previously been studied in the literature to better characterize the gradient in this part of the disk. We used the Gaia-ESO Survey (GES) [Fe/H] values and stellar parameters for stars in 12 open clusters in the inner disk from GES-UVES data. Cluster mean [Fe/H] values were determined based on a membership analysis for each cluster. Where necessary, distances and ages to clusters were determined via comparison to theoretical isochrones. The GES open clusters exhibit a radial metallicity gradient of -0.10+/-0.02dex/kpc, consistent with the gradient measured by other literature studies of field red giant stars and open clusters in the range R_GC_~6-12kpc. We also measure a trend of increasing [Fe/H] with increasing cluster age, as has also been found in the literature. We find no evidence for a steepening of the inner disk metallicity gradient inside the solar circle as earlier studies indicated. The age-metallicity relation shown by the clusters is consistent with that predicted by chemical evolution models that include the effects of radial migration, but a more detailed comparison between cluster observations and models would be premature.
- ID:
- ivo://CDS.VizieR/J/MNRAS/505/1135
- Title:
- Gaia/IPHAS catalogue of Ha-excess sources
- Short Name:
- J/MNRAS/505/1135
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- We present a catalogue of point-like H{alpha}-excess sources in the Northern Galactic Plane. Our catalogue is created using a new technique that leverages astrometric and photometric information from Gaia to select H{alpha}-bright outliers in the INT Photometric H{alpha} Survey of the Northern Galactic Plane (IPHAS), across the colour-absolute magnitude diagram. To mitigate the selection biases due to stellar population mixing and to extinction, the investigated objects are first partitioned with respect to their positions in the Gaia colour-absolute magnitude space, and in the Galactic coordinates space, respectively. The selection is then performed on both partition types independently. Two significance parameters are assigned to each target, one for each partition type. These represent a quantitative degree of confidence that the given source is a reliable H{alpha}-excess candidate, with reference to the other objects in the corresponding partition. Our catalogue provides two flags for each source, both indicating the significance level of the H{alpha}-excess. By analysing their intensity in the H{alpha} narrow band, 28496 objects out of 7474835 are identified as H{alpha}-excess candidates with a significance higher than 3. The completeness fraction of the H{alpha} outliers selection is between 3% and 5%. The suggested 5sigma conservative cut yields a purity fraction of 81.9%.
- ID:
- ivo://CDS.VizieR/IV/36
- Title:
- Gaia-IPHAS/KIS Value-Added Catalogues
- Short Name:
- IV/36
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a sub-arcsecond cross-match of Gaia DR2 (Cat. I/345) against the INT Photometric H-alpha Survey of the Northern Galactic Plane Data Release 2 (IPHAS DR2, Cat. II/321) and the Kepler-INT Survey (KIS, Cat. J/AJ/144/24). The resulting value-added catalogues (VACs) provide additional precise photometry to the Gaia photometry (r, i and H-alpha for IPHAS, with additional U and g for KIS). In building the catalogue, proper motions given in Gaia DR2 are wound back to match the epochs of IPHAS DR2, thus ensuring high proper motion objects are appropriately cross-matched. The catalogues contain 7927224 and 791071 sources for IPHAS and KIS, respectively. The requirement of >5 sigma parallax detection for every included source means that distances out to 1-1.5kpc are well covered. We define two additional parameters for each catalogued object: (i) fc, a magnitude-dependent tracer of the quality of the Gaia astrometric fit; (ii) fFP, the false-positive rate for parallax measurements determined from astrometric fits of a given quality at a given magnitude. Selection cuts based on these parameters can be used to clean colour-magnitude and colour-colour diagrams in a controlled and justified manner. We provide both full and light versions of the VAC, with VAC-light containing only objects that represent our recommended trade-off between purity and completeness. Uses of the catalogues include the identification of new variable stars in the matched data sets, and more complete identification of H-alpha-excess emission objects thanks to separation of high-luminosity stars from the main sequence.
