- ID:
- ivo://CDS.VizieR/J/A+A/585/A141
- Title:
- Galactic center early-type stars catalog
- Short Name:
- J/A+A/585/A141
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- It is still unclear whether the Sagittarius spiral arm is a major spiral arm in the Galaxy or whether it just outlines a region of enhanced star formation because of the local compression of gas. The best way to separate these scenarios out is to study the kinematics across the arm to determine the velocity perturbation it induces. A survey of early-type stars in the direction of the Galactic center is performed covering an area of 100 sq. deg with the aim of identifying candidates for a radial velocity study. Objective prism plates were obtained with the 4{deg} prism on the ESO Schmidt telescope using IIaO, 4415, and IIIaJ emulsions. The plates were digitized and more than 100k spectra were extracted down to a limiting magnitude of B=15m. The spectra were cross-correlated with a template with Balmer lines, which yielded a candidate list of 12675 early-type stars. Magnitudes and equivalent widths of strong lines were calculated from the spectra, which allowed us to estimate the individual extinctions and distances for 11075 stars.
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- ID:
- ivo://CDS.VizieR/J/ApJS/181/110
- Title:
- Galactic center X-ray sources
- Short Name:
- J/ApJS/181/110
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalog of 9017 X-ray sources identified in Chandra observations of a 2{deg}x0.8{deg} field around the Galactic center. This enlarges the number of known X-ray sources in the region by a factor of 2.5. The catalog incorporates all of the ACIS-I observations as of 2007 August, which total 2.25Ms of exposure. At the distance to the Galactic center (8kpc), we are sensitive to sources with luminosities of 4x10^32^erg/s (0.5-8.0keV; 90% confidence) over an area of 1deg^2^, and up to an order of magnitude more sensitive in the deepest exposure (1.0Ms) around Sgr A*. The positions of 60% of our sources are accurate to <1" (95% confidence), and 20% have positions accurate to <0.5". We search for variable sources, and find that 3% exhibit flux variations within an observation, and 10% exhibit variations from observation-to-observation. We also find one source, CXOUGC J174622.7-285218, with a periodic 1745s signal (1.4% chance probability), which is probably a magnetically accreting cataclysmic variable. We compare the spatial distribution of X-ray sources to a model for the stellar distribution, and find 2.8{sigma} evidence for excesses in the numbers of X-ray sources in the region of recent star formation encompassed by the Arches, Quintuplet, and Galactic center star clusters. These excess sources are also seen in the luminosity distribution of the X-ray sources, which is flatter near the Arches and Quintuplet than elsewhere in the field. These excess point sources, along with a similar longitudinal asymmetry in the distribution of diffuse iron emission that has been reported by other authors, probably have their origin in the young stars that are prominent at l~0.1{deg}.
- ID:
- ivo://CDS.VizieR/J/A+A/623/A116
- Title:
- Galactic Cepheids and RR Lyrae multiplicity. I.
- Short Name:
- J/A+A/623/A116
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Classical Cepheids (CCs) and RR Lyrae stars (RRLs) are important classes of variable stars used as standard candles to estimate galactic and extragalactic distances. Their multiplicity is imperfectly known, particularly for RRLs. Astoundingly, only one RRL is convincingly demonstrated to be a binary as of today, TU UMa, out of tens of thousands of known RRLs. We aim at detecting the binary and multiple stars present in a sample of Milky Way CCs and RRLs. In the present article, we combine the Hipparcos and Gaia DR2 positions to determine the mean proper motion of the targets, and we search for proper motion anomalies (PMa) caused by close-in orbiting companions. We identify 57 CC binaries from PMa out of 254 tested stars, and 75 additional candidates, confirming the high binary fraction of these massive stars. For 28 binary CCs, we determine the companion mass by combining their spectroscopic orbital parameters and astrometric PMa. We detect 13 RRLs showing a significant PMa out of 198 tested stars, and 61 additional candidates. We determine that the binarity fraction of CCs is likely above 80%, while that of RRLs is at least 7%. The newly detected systems will be useful to improve our understanding of their evolutionary states. The discovery of a significant number of RRLs in binary systems also resolves the long-standing mystery of their extremely low apparent binarity fraction.
- ID:
- ivo://CDS.VizieR/J/A+A/584/A93
- Title:
- Galactic cold cores. V. Dust opacity
- Short Name:
- J/A+A/584/A93
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The project Galactic Cold Cores has carried out Herschel photometric observations of interstellar clouds where Planck satellite survey has located cold and compact clumps. The sources represent different stages of cloud evolution from starless clumps to protostellar cores and are located in different Galactic environments. We examine this sample of 116 Herschel fields to estimate the submillimetre dust opacity and to look for variations that could be attributed to the evolutionary stage of the sources or to environmental factors, including the location within the Galaxy. The submillimetre dust opacity is derived from Herschel data and near-infrared observations of the reddening of background stars are converted to near-infrared optical depth. We investigate the systematic errors affecting these parameters and use modelling to make corrections for the expected biases. The ratio of 250{mu}m and J band opacities is correlated with the Galactic location and the star formation activity. Local variations in the ratio {tau}(250{mu}m)/{tau}(J) are searched using the correlation plots and maps of the opacity ratio. We find a median ratio of {tau}(250{mu}m)/{mu}(J)=(1.6+/-0.2)*10^-3^, which is more than three times the mean value reported for the diffuse medium. Assuming an opacity spectral index {beta}=1.8 instead of {beta}=2.0, the value would be smaller by ~30%. No significant systematic variation is detected with Galactocentric distance or with Galactic height. Examination of the {tau}(250{mu}m)/{tau}(J) maps reveals half a dozen fields with clear indications of local increase of submillimetre opacity, up to {tau}(250{mu}m)/{tau}(J)~4*10^-3^, towards the densest clumps. These are all nearby fields with spatially resolved clumps of high column density. We interpret the increase in the far-infrared opacity as a sign of grain growth in the densest and coldest regions of interstellar clouds.
- ID:
- ivo://CDS.VizieR/J/MNRAS/492/3408
- Title:
- Galactic disc RR Lyrae stars
- Short Name:
- J/MNRAS/492/3408
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a kinematical study of 314 RR Lyrae stars in the solar neighbourhood using the publicly available photometric, spectroscopic, and Gaia DR2 astrometric data to explore their distribution in the Milky Way. We report an overdensity of 22 RR Lyrae stars in the solar neighbourhood at a pericentre distance of between 5 and 9kpc from the Galactic Centre. Their orbital parameters and their chemistry indicate that these 22 variables share the kinematics and the [Fe/H] values of the Galactic disc, with an average metallicity and tangential velocity of [Fe/H]=-0.60dex and v_theta_=241km/s, respectively. From the distribution of the Galactocentric spherical velocity components, we find that these 22 disc-like RR Lyrae variables are not consistent with the Gaia Sausage (Gaia-Enceladus), unlike almost half of the local RR Lyrae stars. Chemical information from the literature shows that the majority of the selected pericentre-peak RR Lyrae variables are alpha-poor, a property shared by typically much younger stars in the thin disc. Using the available photometry, we rule out a possible misclassification with the known classical and anomalous Cepheids. The similar kinematic, chemical, and pulsation properties of these disc RR Lyrae stars suggest they share a common origin. In contrast, we find that the RR Lyrae stars associated with the Gaia- Enceladus based on their kinematics and chemical composition show a considerable metallicity spread in the old population (approximately 1dex).
- ID:
- ivo://CDS.VizieR/J/AZh/95/54
- Title:
- Galactic-field RR Lyrae abundances and kinematics
- Short Name:
- J/AZh/95/54
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Data of our compiled catalog containing the positions, velocities, and metallicities of 415 RR Lyrae variable stars and the relative abundances [el/Fe] of 12 elements for 101 RR Lyrae stars, including four {alpha} elements (Mg, Ca, Si, and Ti), are used to study the relationships between the chemical and spatial-kinematic properties of these stars. In general, the dependences of the relative abundances of {alpha} elements on metallicity and velocity for the RR Lyrae stars are approximately the same as those for field dwarfs. Despite the usual claim that these stars are old, among them are representatives of the thin disk, which is the youngest subsystem of the Galaxy. Attention is called to the problem of low metallicity RR Lyrae stars. Most RR Lyrae stars that have the kinematic properties of thick disk stars have metallicities [Fe/H]<-1.0 and high ratios [{alpha}/Fe]~=0.4, whereas only about 10% of field dwarfs belonging to the so-called "low-metallicity tail" have this chemical composition. At the same time, there is a sharp change in [{alpha}/Fe] in RR Lyrae stars belonging just to the thick disk, providing evidence for a long period of formation of this subsystem. The chemical compositions of SDSS J1707+58, V455 Oph, MACHO176.18833.411, V456 Ser, and BPS CS 30339-046 do not correspond to their kinematics. While the first three of these stars belong to the halo, according to their kinematics, the last two belong to the thick disk. It is proposed that they are all most likely extragalactic, but the possible appearance of some of them in the solar neighborhood as a result of the gravitational action of the bar on field stars cannot be ruled out.
- ID:
- ivo://CDS.VizieR/J/MNRAS/482/5138
- Title:
- Galactic GC mean proper motions & velocities
- Short Name:
- J/MNRAS/482/5138
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have derived the mean proper motions and space velocities of 154 Galactic globular clusters and the velocity dispersion profiles of 141 globular clusters based on a combination of Gaia DR2 proper motions with ground-based line-of-sight velocities. Combining the velocity dispersion profiles derived here with new measurements of the internal mass functions allows us to model the internal kinematics of 144 clusters, more than 90 per cent of the currently known Galactic globular cluster population. We also derive the initial cluster masses by calculating the cluster orbits backwards in time applying suitable recipes to account for mass-loss and dynamical friction. We find a correlation between the stellar mass function of a globular cluster and the amount of mass lost from the cluster, pointing to dynamical evolution as one of the mechanisms shaping the mass function of stars in clusters. The mass functions also show strong evidence that globular clusters started with a bottom-light initial mass function. Our simulations show that the currently surviving globular cluster population has lost about 80 per cent of its mass since the time of formation. If globular clusters started from a lognormal mass function, we estimate that the Milky Way contained about 500 globular clusters initially, with a combined mass of about 2.5x10^8^M_{sun}_. For a power-law initial mass function, the initial mass in globular clusters could have been a factor of three higher.
- ID:
- ivo://CDS.VizieR/J/A+A/623/A128
- Title:
- Galactic halo CEMP stars abundances & kinematics
- Short Name:
- J/A+A/623/A128
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Carbon-enhanced metal-poor (CEMP) stars span a wide range of stellar populations, from bona fide second-generation stars to later-forming stars that provide excellent probes of binary mass transfer and stellar evolution. Here we analyse 11 metal-poor stars (8 of which are new to the literature), and demonstrate that 10 are CEMP stars. Based on high signal-to-noise ratio (S/N) X-Shooter spectra, we derive abundances of 20 elements (C, N, O, Na, Mg, Ca, Sc, Ti, Cr, Mn, Fe, Ni, Sr, Y, Ba, La, Ce, Pr, Nd, and Eu). From the high-S/N spectra, we were able to trace the chemical contribution of the rare earth elements (REE) from various possible production sites, finding a preference for metal-poor low-mass asymptotic giant branch (AGB) stars of 1.5M_{sun}_ in CEMP-s stars, while CEMP-r/s stars may indicate a more massive AGB contribution (2-5M_{sun}_). A contribution from the r-process -- possibly from neutron star--neutron star mergers (NSM) -- is also detectable in the REE stellar abundances, especially in the CEMP-r/s sub-group rich in both slow(s)\ and rapid(r) neutron-capture elements. Combining spectroscopic data with Gaia DR2 astrometric data provides a powerful chemodynamical tool for placing CEMP stars in the various Galactic components, and classifying CEMP stars into the four major elemental-abundance sub-groups, which are dictated by their neutron-capture element content. The derived orbital parameters indicate that all but one star in our sample (and the majority of the selected literature stars) belong to the Galactic halo. These stars exhibit a median orbital eccentricity of 0.7, and are found on both prograde and retrograde orbits. We find that the orbital parameters of CEMP-no and CEMP-s stars are remarkably similar in the 98 stars we study. A special case is the CEMP-no star HE 0020-1741, with very low Sr and Ba content, which possesses the most eccentric orbit among the stars in our sample, passing close to the Galactic centre. Finally, we propose an improved scheme to sub-classify the CEMP stars, making use of the Sr/Ba ratio, which can also be used to separate very metal-poor stars from CEMP stars. We explore the use of [Sr/Ba] versus [Ba/Fe] in 93 stars in the metallicity range -4.2<~[Fe/H]<-2. We show that the Sr/Ba ratio can also be successfully used for distinguishing CEMP-s, CEMP-r/s, and CEMP-no stars. Additionally, the Sr/Ba ratio is found to be a powerful astro-nuclear indicator, since the metal-poor AGB stars exhibit very different Sr/Ba ratios compared to fast-rotating massive stars and NSM, and is also reasonably unbiased by NLTE and 3D corrections.
- ID:
- ivo://CDS.VizieR/J/AJ/150/147
- Title:
- Galactic HII regions. I. Stellar distances
- Short Name:
- J/AJ/150/147
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new catalog of spectrophotometric distances and line of sight systemic velocities to 103 HII regions between 90{deg}{<=}l<=195{deg} (longitude quadrants II and part of III). Two new velocities for each region are independently measured using 1 arcmin resolution 21cm HI and 2.6mm^12^CO line maps (from the Canadian Galactic Plane Survey and Five College Radio Astronomy Observatory Outer Galaxy Surveys) that show where gaseous shells are observed around the periphery of the ionized gas. Known and neighboring O- and B-type stars with published UBV photometry and MK classifications are overlaid onto 21cm continuum maps, and those stars observed within the boundary of the HII emission (and whose distance is not more than three times the standard deviation of the others) are used to calculate new mean stellar distances to each of the 103 nebulae. Using this approach of excluding distance outliers from the mean distance to a group of many stars in each HII region lessens the impact of anomalous reddening for certain individuals. The standard deviation of individual stellar distances in a cluster is typically 20% per stellar distance, and the error in the mean distance to the cluster is typically +/-10%. Final mean distances of nine common objects with very long baseline interferometry parallax distances show a 1:1 correspondence. Further, comparison with previous catalogs of HII regions in these quadrants shows a 50% reduction in scatter for the distance to Perseus spiral arm objects in the same region, and a reduction by ~1/2^0.5^ in scatter around a common angular velocity relative to the Sun {Omega}-{Omega}_0_(km/s/kpc). The purpose of the catalog is to provide a foundation for more detailed large-scale Galactic spiral structure and dynamics (rotation curve, density wave streaming) studies in the 2nd and 3rd quadrants, which from the Sun's location is the most favorably viewed section of the Galaxy.
- ID:
- ivo://CDS.VizieR/J/ApJ/738/27
- Title:
- Galactic HII regions RRL and continuum data
- Short Name:
- J/ApJ/738/27
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The distribution of metals in the Galaxy provides important information about galaxy formation and evolution. HII regions are the most luminous objects in the Milky Way at mid-infrared to radio wavelengths and can be seen across the entire Galactic disk. We used the National Radio Astronomy Observatory (NRAO) Green Bank Telescope to measure radio recombination line (RRL) and continuum emission in 81 Galactic HII regions. We calculated LTE electron temperatures using these data. In thermal equilibrium metal abundances are expected to set the nebular electron temperature with high abundances producing low temperatures. Our HII region distribution covers a large range of Galactocentric radius (5-22kpc) and samples the Galactic azimuth range 330-60{deg}. Using our highest quality data (72 objects) we derived an O/H Galactocentric radial gradient of -0.0383+/-0.0074dex/kpc. Combining these data with a similar survey made with the NRAO 140 Foot telescope we get a radial gradient of -0.0446+/-0.0049dex/kpc for this larger sample of 133 nebulae.
