- ID:
- ivo://CDS.VizieR/J/ApJ/793/135
- Title:
- Positions and distances of RR Lyrae stars
- Short Name:
- J/ApJ/793/135
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Almost every known low-luminosity Milky Way dwarf spheroidal (dSph) satellite galaxy contains at least one RR Lyrae star. Assuming that a fraction of distant (60<d_helio_<100 kpc) Galactic halo RR Lyrae stars are members of yet to be discovered low-luminosity dSph galaxies, we perform a guided search for these low-luminosity dSph galaxies. In order to detect the presence of dSph galaxies, we combine stars selected from more than 123 sightlines centered on RR Lyrae stars identified by the Palomar Transient Factory. We find that this method is sensitive enough to detect the presence of Segue 1-like galaxies (M_V_=-1.5_-0.8_^+0.6^, r_h_=30 pc) even if only ~20 sightlines were occupied by such dSph galaxies. Yet, when our method is applied to the Sloan Digital Sky Survey Data Release 10 imaging catalog, no signal is detected. An application of our method to sightlines occupied by pairs of close (<200 pc) horizontal branch stars, also did not yield a detection. Thus, we place upper limits on the number of low-luminosity dSph galaxies with half-light radii from 30 pc to 120 pc, and in the probed volume of the halo. Stronger constraints on the luminosity function may be obtained by applying our method to sightlines centered on RR Lyrae stars selected from the Pan-STARRS1 survey, and eventually, from the Large Synoptic Survey Telescope. In Appendix A, we present spectroscopic observations of an RRab star in the Bootes 3 dSph and a light curve of an RRab star near the Bootes 2 dSph.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/643/A138
- Title:
- Possible runaway stars list
- Short Name:
- J/A+A/643/A138
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The spectral classifications of the Galactic O-Star Spectroscopic Survey (GOSSS) and the astrometric and photometric data from Gaia have significantly improved our ability to measure distances and determine memberships of stellar groups (clusters, associations, or parts thereof) with OB stars. In the near future, the situation will be further improved thanks to subsequent Gaia data releases and new photometric and spectroscopic surveys. We initiated a program to identify and determine the membership of Galactic stellar groups with OB stars and measure distances to them. Given the data currently available, we started with the identification and distance determinations of groups with O stars. In this paper, we concentrate on groups that contain stars with the earliest spectral subtypes. We used GOSSS to select Galactic stellar groups with O2-O3.5 stars and the method described in paper 0 of this series, which combines Gaia DR2 G + G_BP_ + G_RP_ photometry, positions, proper motions, and parallaxes to assign robust memberships and measure distances. We also included Collinder 419 and NGC 2264, the clusters cited in that paper, to generate our first list of 16 O-type Galactic stellar groups. We derived distances, determined the membership, and analyzed the structure of sixteen Galactic stellar groups with O stars, Villafranca O-001 to Villafranca O-016, including the fourteen groups with the earliest-O-type optically accessible stars known in the Milky Way. We compared our distance with previous results from the literature and establish that the best consistency is with (the small number of) VLBI parallaxes and the worst is with kinematic distances. Our results indicate that very massive stars can form in relatively low-mass clusters or even in near-isolation, as is the case for the Bajamar star in the North America nebula. This lends support to the hierarchical scenario of star formation, where some stars are born in well-defined bound clusters but others are born in associations that are unbound from the beginning: groups of newborn stars come in many shapes and sizes. We propose that HD 64568 and HD 64315 AB could have been ejected simultaneously from Haffner 18 (Villafranca O-012 S). Our results are consistent with a difference of =~20{mu}as in the Gaia DR2 parallax zero point between bright and faint stars.
- ID:
- ivo://CDS.VizieR/J/AJ/156/142
- Title:
- Precision cluster abund. for APOGEE using SDSS DR14
- Short Name:
- J/AJ/156/142
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Open Cluster Chemical Abundances and Mapping (OCCAM) survey aims to produce a comprehensive, uniform, infrared-based spectroscopic data set for hundreds of open clusters, and to constrain key Galactic dynamical and chemical parameters from this sample. This second contribution from the OCCAM survey presents analysis of 259 member stars with [Fe/H] determinations in 19 open clusters, using Sloan Digital Sky Survey Data Release 14 (SDSS/DR14) data from the Apache Point Observatory Galactic Evolution Experiment and ESA Gaia. This analysis, which includes clusters with R_GC_ ranging from 7 to 13 kpc, measures an [Fe/H] gradient of -0.061+/-0.004 dex/kpc. We also confirm evidence of a significant positive gradient in the {alpha}-elements ([O/Fe], [Mg/Fe], and [Si/Fe]) and present evidence for a significant negative gradient in iron-peak elements ([Mn/Fe] and [Ni/Fe]).
- ID:
- ivo://CDS.VizieR/J/A+A/645/A69
- Title:
- PRM catalogue of halo MS stars
- Short Name:
- J/A+A/645/A69
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Gaia mission has provided the largest ever astrometric chart of the Milky Way. Using it to map the Galactic halo is helpful for disentangling its merger history. The identification of halo stars in Gaia DR2 with reliable distance estimates requires special methods because such stars are typically farther away and scarce. We applied the reduced proper motion (RPM) method to identify halo main sequence stars on the basis of Gaia photometry and proper motions. Using the colour-absolute-magnitude relation for this type of star, we calculated photometric distances. Our selection results in a set of 10^7^ tentative main sequence halo stars with typical distance uncertainties of 7% and with median velocity errors of 20km/s. The median distance of our sample is ~4.4kpc, with the faintest stars located at ~16kpc. The spatial distribution of the stars in our sample is centrally concentrated. A visual inspection of the mean velocities of stars on the sky reveals large-scale patterns as well as clear imprints of the GD-1 stream and tentative hints of the Jhelum and Leiptr streams. Incompleteness and selection effects limit our ability to interpret the patterns reliably as well as to identify new substructures. We define a pseudo-velocity space by setting the line-of-sight velocities of our sample stars to zero. In this space, we recover several known structures such as the footprint of Gaia-Enceladus (i.e. the Gaia-Sausage) as well as the Helmi Streams and some other retrograde substructures (Sequoia, Thamnos). We show that the two-point velocity correlation function reveals significant clustering on scales smaller than 100km/s of a similar amplitude as found for the 6D Gaia halo sample. This clumping of stars in velocity space might hint at the presence of nearby streams that are predominantly phase-mixed. A spectroscopic follow-up of our halo main sequence sample is bound to yield unprecedented views of Galactic history and dynamics. In future Gaia data releases, the level of systematics will be reduced and the astrometry will be more precise, which will allow for the identification of more substructures at larger distances.
- ID:
- ivo://CDS.VizieR/J/A+A/632/A116
- Title:
- Proper motion catalogue of Galactic Centre
- Short Name:
- J/A+A/632/A116
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Proper motion studies of stars in the centre of the Milky Way have typically been limited to the Arches and Quintuplet clusters, and to the central parsec. Here we present the first results of a large-scale proper motion study of stars within several tens of parsecs of Sagittarius A* based on our 0.2" angular resolution GALACTICNUCLEUS survey (epoch 2015) combined with NICMOS/HST data from the Paschen-alpha survey (epoch 2008). This comprises the first extensive proper motion study of the central ~36'x16' of the Galaxy, which is not covered adequately by any of the existing astronomical surveys, such as Gaia, because of the extreme interstellar extinction(AV>~30mag). Proper motions can help us to disentangle the different stellar populations along the line-of-sight and interpret their properties in combination with multi-wavelength photometry from GALACTICNUCLEUS and other sources. It also allows us to infer the dynamics and interrelationships between different stellar components (Galactic bulge, nuclear stellar disk, nuclear stellar cluster) of the Galactic centre (GC). In particular, we use proper motions to detect co-moving groups of stars which are able to trace low-mass or partially-dissolved young clusters in the GC that can hardly be discovered by any other means. Our pilot study for this work is based on a field in the nuclear bulge associated with Hii regions that show the presence of young stars. We have detected the first group of co-moving stars coincident with an HII region. Using colour-magnitude diagrams, we have inferred that the co-moving stars are consistent with the post-main sequence stars with ages of few Myr. Simulations show that this group of stars is a real group that can indicate the existence of a dissolving or low-to-intermediate-mass young cluster. A census of these undiscovered clusters will ultimately help us to constrain star formation at the GC in the past few ten Myr.
- ID:
- ivo://CDS.VizieR/J/PASP/118/1639
- Title:
- Proper motions of faint UV-bright sources
- Short Name:
- J/PASP/118/1639
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Proper motions with values >=10 or <=10mas/yr have been extracted from the USNOB1.0 and Tycho2 catalogs for all Lanning UV-bright sources identified in the Sandage Two-Color Survey of the Galactic Plane and presented in Papers I-VI (Cat. <II/257>. Of the 572 sources examined, we find at least 213 that exhibit a significantly large proper motion. Based on the location of the sources in a reduced proper motion diagram, we demonstrate that about two-thirds of the high proper motion sources are likely or very likely to be heretofore unidentified white dwarfs.
- ID:
- ivo://CDS.VizieR/J/MNRAS/484/2832
- Title:
- Proper motions of Milky Way globular clusters
- Short Name:
- J/MNRAS/484/2832
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use Gaia Data Release 2 to determine the mean proper motions for 150 Milky Way globular clusters (almost the entire known population), with a typical uncertainty of 0.05mas/yr limited mainly by systematic errors. Combining them with distance and line-of-sight velocity measurements from the literature, we analyse the distribution of globular clusters in the 6D phase space, using both position/velocity and action/angle coordinates. The population of clusters in the central 10kpc has a mean rotational velocity reaching 50-80km/s, and a nearly isotropic velocity dispersion 100-120km/s, while in the outer galaxy, the cluster orbits are strongly radially anisotropic. We confirm a concentration of clusters at high radial action in the outer region of the Galaxy. Finally, we explore a range of equilibrium distribution function-based models for the entire globular cluster system, and the information they provide about the potential of the Milky Way. The dynamics of clusters is best described by models with the circular velocity between 10 and 50kpc staying in the range 210-240km/s.
- ID:
- ivo://CDS.VizieR/J/MNRAS/435/3206
- Title:
- Properties of field RR Lyrae variables
- Short Name:
- J/MNRAS/435/3206
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use accurate absolute UCAC4 proper motions, V-band photoelectric and CCD photometry including our own and compiled data, WISE W1-band mid-IR photometry, as well as extensive compiled radial-velocity and [Fe/H] data for 403 Galactic field RR Lyrae type variables to determine the kinematical parameters of the Galactic RR Lyrae population and constrain the zero-points of the V-, W1-, and Ks-band period-metallicity-luminosity relations for RR Lyraes via statistical parallax.
- ID:
- ivo://CDS.VizieR/J/ApJ/859/L8
- Title:
- Properties of TriAnd stars
- Short Name:
- J/ApJ/859/L8
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The nature of the Triangulum-Andromeda (TriAnd) system has been debated since the discovery of this distant, low-latitude Milky Way (MW) overdensity more than a decade ago. Explanations for its origin are either as a halo substructure from the disruption of a dwarf galaxy, or a distant extension of the Galactic disk. We test these hypotheses using the chemical abundances of a dozen TriAnd members from the Sloan Digital Sky Survey-IV's (SDSS-IV's) 14th Data Release (DR14) of Apache Point Observatory Galactic Evolution Experiment (APOGEE) data to compare to APOGEE abundances of stars with similar metallicity from both the Sagittarius (Sgr) dSph and the outer MW disk. We find that TriAnd stars are chemically distinct from Sgr across a variety of elements, (C+N), Mg, K, Ca, Mn, and Ni, with a separation in [X/Fe] of about 0.1 to 0.4dex depending on the element. Instead, the TriAnd stars, with a median metallicity of about -0.8, exhibit chemical abundance ratios similar to those of the lowest metallicity ([Fe/H]~-0.7) stars in the outer Galactic disk, and are consistent with expectations of extrapolated chemical gradients in the outer disk of the MW. These results suggest that TriAnd is associated with the MW disk, and, therefore, that the disk extends to this overdensity-i.e., past a Galactocentric radius of 24kpc-albeit vertically perturbed about 7kpc below the nominal disk midplane in this region of the Galaxy.
- ID:
- ivo://CDS.VizieR/J/A+A/619/A132
- Title:
- Pseudo-photometric distances of 30 open clusters
- Short Name:
- J/A+A/619/A132
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We demonstrate that reliable photometric distances of stellar clusters, and more generally of stars, can be obtained using pseudomagnitudes and rough spectral type without having to correct for visual absorption. We determine the mean absolute pseudomagnitude of all spectral (sub)types between B and K. Distances are computed from the difference between the star's observed pseudomagnitude and its spectral type's absolute pseudomagnitude. We compare the distances of 30 open clusters thus derived against the distances derived from TGAS parallaxes. Our computed distances, up to distance modulus 12, agree within 0.1mag rms with those obtained from TGAS parallaxes, proving excellent distance estimates. We show additionally that there are actually two markedly different distances in the cluster NGC 2264. We suggest that the pseudomagnitude distance estimation method, which is easy to perform, can be routinely used in all large-scale surveys where statistical distances on a set of stars, such as an open cluster, are required.
