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331. MEGA-H proper motion catalog
ID:
ivo://CDS.VizieR/V/126
Title:
MEGA-H proper motion catalog
Short Name:
V/126
Date:
21 Oct 2021
Publisher:
CDS
Description:
The catalogue MEGA-H is a result of a merging of star lists from the catalogue of stellar proper motions with respect to galaxies in 47 selected areas near the Main Meridional Section of the Galaxy (MEGA-G) (Kharchenko 1987) and from All-sky Compiled Catalogue of 2.5 Million Stars (ASCC-2.5) (Cat. <I/280>). Proper motions from the catalogue MEGA-G were reduced to the Hipparcos system by means of common with the ASCC-2.5 stars. The compiled proper motions in the Hipparcos system and their standard errors were computed as the weighted means. Equatorial coordinates are reduced to the equinox J2000 and epoch 1991.25. The catalogue MEGA-H contains 18169 stars. Stars are sorted in right ascension J2000 order.
332. Membership and lithium of young clusters
ID:
ivo://CDS.VizieR/J/A+A/659/A85
Title:
Membership and lithium of young clusters
Short Name:
J/A+A/659/A85
Date:
10 Mar 2022 07:23:16
Publisher:
CDS
Description:
It is now well known that pre-main sequence models with inflated radii should be taken into account to simultaneously reproduce the colour-magnitude diagram and the lithium depletion pattern observed in young open star clusters. We test a new set of pre-main sequence models including radius inflation due to the presence of starspots or to magnetic inhibition of convection, using five clusters observed by the Gaia-ESO Survey, spanning the age range ~10-100Myr where such effects could be important. The Gaia-ESO Survey radial velocities are combined with astrometry from Gaia EDR3 to obtain clean lists of high-probability members for the five clusters. A Bayesian maximum likelihood method is adopted to fit the observed cluster sequences to theoretical predictions to derive the best model parameters and the cluster reddening and age. Models are calculated with different values of the mixing length parameter ({alpha}_ML_=2.0, 1.5 and 1.0), for the cases with no spots or with effective spot coverage {beta}_spot_=0.2 and 0.4. The models are also compared with the observed lithium depletion patterns. To reproduce the colour-magnitude diagram and the observed lithium depletion pattern in Gamma Vel A and B and in 25 Ori one needs to assume both a reduced convection efficiency, with {alpha}_ML_=1.0, and an effective surface spot coverage of about 20%. We obtained ages of 18^+1.5^_-4.0_ Myr and 21^+3.5^_-3.0_ Myr for Gamma Vel A and B, respectively, and 19^+1.5^_-7.0_ Myr for 25 Ori. However, a single isochrone is not sufficient to account for the lithium dispersion, and an increasing level of spot coverage as mass decreases seems to be required. On the other hand, the older clusters (NGC 2451B at 30^+3.0^_-5.0_Myr, NGC 2547 at 35^+4.0^_-4.0_Myr, and NGC 2516 at 138^+48^_-42_Myr) are consistent with standard models, with {alpha}_ML_=2.0 and no spots, except at low masses: a 20% spot coverage appears to better reproduce the sequence of M-type stars and might explain the observed spread in lithium abundances. The quality of Gaia-ESO data combined with Gaia allows us to gain important insights on pre-main sequence evolution. Models including starspots can provide a consistent explanation of the cluster sequences and lithium abundances observed in young clusters, although a range of starspot coverage is required to fully reproduce the data.
333. Membership and spectroscopy of IC 2391
ID:
ivo://CDS.VizieR/J/A+A/461/509
Title:
Membership and spectroscopy of IC 2391
Short Name:
J/A+A/461/509
Date:
21 Oct 2021
Publisher:
CDS
Description:
Young open clusters provide important clues to the interface between the main sequence and pre-main-sequence phases of stellar evolution. The young and nearby open cluster IC 2391 is well-suited to studies of these two evolutionary phases. We establish a bona fide set of cluster members and then analyze this set in terms of binary frequency, projected rotational velocities, [Fe/H], and lithium abundance. In the wake of the Hipparcos distance controversy for the Pleiades, we compare the main-sequence fitting distance modulus to the Hipparcos mean parallax for IC 2391.
334. Membership catalog for M12 (NGC6218) stars
ID:
ivo://CDS.VizieR/J/other/RAA/18.126
Title:
Membership catalog for M12 (NGC6218) stars
Short Name:
J/other/RAA/18.1
Date:
21 Oct 2021
Publisher:
CDS
Description:
Using astrometric techniques developed by Anderson et al., we determine proper motions (PMs) in the ~14.60x16.53arcmin^2^ area of the kinematically "thick-disk" globular cluster M12. The cluster's proximity and sparse nature makes it a suitable target for ground-based telescopes. Archive images with time gap of ~11.1-years were observed with the wide-field imager (WFI) mosaic camera mounted on the ESO 2.2m telescope. The median value of PM error in both components is ~0.7mas/yr for the stars having V<=20mag. PMs are used to determine membership probabilities and to separate field stars from the cluster sample. In electronic form, a membership catalog of 3725 stars with precise coordinates, PMs and BV RI photometry is being provided. One of the possible applications of the catalog is demonstrated by gathering the membership information of the variable stars, blue stragglers and X-ray sources reported earlier in the cluster's region.
335. Membership of Praesepe and Coma Berenices clusters
ID:
ivo://CDS.VizieR/J/AJ/134/2340
Title:
Membership of Praesepe and Coma Berenices clusters
Short Name:
J/AJ/134/2340
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results of a stellar membership survey of the nearby open clusters Praesepe and Coma Berenices. We have combined archival survey data from the SDSS, 2MASS, USNOB1.0, and UCAC-2.0 surveys to compile proper motions and photometry for ~5 million sources over 300{deg}^2^. Of these sources, 1010 stars in Praesepe and 98 stars in Coma Ber are identified as candidate members with probability >80%; 442 and 61 are identified as high-probability candidates for the first time. We estimate that this survey is >90% complete across a wide range of spectral types (F0-M5 in Praesepe, F5-M6 in Coma Ber). We have also investigated the stellar mass dependence of each cluster's mass and radius in order to quantify the role of mass segregation and tidal stripping in shaping the present-day mass function and spatial distribution of stars.
336. Members in Serpens Molecular Cloud with Gaia DR2
ID:
ivo://CDS.VizieR/J/ApJ/878/111
Title:
Members in Serpens Molecular Cloud with Gaia DR2
Short Name:
J/ApJ/878/111
Date:
18 Jan 2022 15:09:42
Publisher:
CDS
Description:
The dense clusters within the Serpens Molecular Cloud are among the most active regions of nearby star formation. In this paper, we use Gaia DR2 parallaxes and proper motions to statistically measure ~1167 kinematic members of Serpens, few of which have been previously identified, to evaluate the star formation history of the complex. The optical members of Serpens are concentrated in three distinct groups located at 380-480pc; the densest clusters are still highly obscured by optically thick dust and have few optical members. The total population of young stars and protostars in Serpens is at least 2000 stars, including past surveys that were most sensitive to protostars and disks, and may be much higher. Distances to dark clouds measured from deficits in star counts are consistent with the distances to the optical star clusters. The Serpens Molecular Cloud is seen in the foreground of the Aquila Rift, dark clouds located at 600-700pc, and behind patchy extinction, here called the Serpens Cirrus, located at ~250pc. Based on the lack of a distributed population of older stars, the star formation rate throughout the Serpens Molecular Cloud increased by at least a factor of 20 within the past ~5Myr. The optically bright stars in Serpens Northeast are visible because their natal molecular cloud has been eroded, not because they were flung outwards from a central factory of star formation. The separation between subclusters of 20-100pc and the absence of an older population together lead to speculation that an external forcing was needed to trigger the active star formation.
337. Members of 5 cluster in Ori OB1a association
ID:
ivo://CDS.VizieR/J/A+A/631/A166
Title:
Members of 5 cluster in Ori OB1a association
Short Name:
J/A+A/631/A166
Date:
21 Oct 2021
Publisher:
CDS
Description:
The Orion complex is arguably the most studied star-forming region in the Galaxy. While stars are still being born in the Orion nebula, the oldest part was believed to be no more than 13Myr old. In order to study the full hierarchy of star formation across the Orion complex, we perform a clustering analysis of the Ori OB1a region using new stellar surveys and derive robust ages for each identified stellar aggregate. We use Gaia DR2 parameters supplemented with radial velocities from the GALAH and APOGEE surveys to perform clustering of the Ori OB1a association. Five overdensities are resolved in a six-dimensional parameter space (positions, distance, proper motions, and radial velocity). Most correspond to previously known structures (ASCC 16, 25 Orionis, ASCC 20, ASCC 21). We use Gaia DR2, Pan-STARRS1 and 2MASS photometry to fit isochrones to the colour-magnitude diagrams of the identified clusters. The ages of the clusters can thus be measured with 10% precision. While four of the clusters have ages between 11 and 13Myr, the ASCC 20 cluster stands out at an age of 21+/-3Myr. This is significantly greater than the age of any previously known component of the Orion complex. To some degree, all clusters overlap in at least one of the six phase-space dimensions. We argue that the formation history of the Orion complex, and its relation to the Gould belt, must be reconsidered. A significant challenge in reconstructing the history of the Ori OB1a association is to understand the impact of the newly discovered 21Myr old population on the younger parts of the complex, including their formation.
338. Member stars of the GD-1 tidal stream
ID:
ivo://CDS.VizieR/J/ApJ/877/13
Title:
Member stars of the GD-1 tidal stream
Short Name:
J/ApJ/877/13
Date:
21 Oct 2021
Publisher:
CDS
Description:
With the photometric data from the SDSS survey, the spectroscopic data from the SDSS/SEGUE and the LAMOST surveys, and the astrometric data from the Gaia DR2, we have identified 67 highly probable member stars of the GD-1 cold stellar stream spread along almost its entire length (i.e., from 126{deg} to 203{deg} in R.A.). With the accurate spectroscopic (i.e., metallicity and line-of-sight velocity) and astrometric (i.e., proper motions) information, the position-velocity diagrams, i.e., {phi}_1_-{mu}_{alpha}_, {phi}_1_-{mu}_{delta}_, and {phi}_1_-v_gsr_, of the GD-1 stream are well mapped. The stream has an average metallicity [Fe/H]=-1.96. The rich information of member stars of the stream now available allow one not only to model its origin, but also to place strong constraints on the mass distribution and the gravitational potential of the Milky Way.
339. Metal-poor stars in the thick disk of the Galaxy
ID:
ivo://CDS.VizieR/J/ApJ/794/58
Title:
Metal-poor stars in the thick disk of the Galaxy
Short Name:
J/ApJ/794/58
Date:
21 Oct 2021
Publisher:
CDS
Description:
A new set of very high signal-to-noise (S/N>100/1), medium-resolution (R~3000) optical spectra have been obtained for 302 of the candidate "weak-metal" stars selected by Bidelman & MacConnell (1973AJ.....78..687B, Cat. III/46). We use these data to calibrate the recently developed generalization of the Sloan Extension for Galactic Exploration and Understanding and Exploration (SEGUE) Stellar Parameter Pipeline, and obtain estimates of the atmospheric parameters (T_eff_, log g, and [Fe/H]) for these non-Sloan Digital Sky Survey/SEGUE data; we also obtain estimates of [C/Fe]. The new abundance measurements are shown to be consistent with available high-resolution spectroscopic determinations, and represent a substantial improvement over the accuracies obtained from the previous photometric estimates reported in Paper I of this series (Norris et al. 1985ApJS...58..463N). The apparent offset in the photometric abundances of the giants in this sample noted by several authors is confirmed by our new spectroscopy; no such effect is found for the dwarfs. The presence of a metal-weak thick-disk (MWTD) population is clearly supported by these new abundance data. Some 25% of the stars with metallicities -1.8<[Fe/H]<=-0.8 exhibit orbital eccentricities e<0.4, yet are clearly separated from members of the inner-halo population with similar metallicities by their location in a Lindblad energy versus angular momentum diagram. A comparison is made with recent results for a similar-size sample of Radial Velocity Experiment stars from Ruchti et al. (2010ApJ...721L..92R ; 2011ApJ...737....9R). We conclude, based on both of these samples, that the MWTD is real, and must be accounted for in discussions of the formation and evolution of the disk system of the Milky Way.
340. Milky Way Age-Metallicity-orbital energy relation
ID:
ivo://CDS.VizieR/J/AJ/162/42
Title:
Milky Way Age-Metallicity-orbital energy relation
Short Name:
J/AJ/162/42
Date:
21 Mar 2022 00:01:52
Publisher:
CDS
Description:
Globular clusters can form inside their host galaxies at high redshift when gas densities are higher and gas-rich mergers are common. They can also form inside lower-mass galaxies that have since been accreted and tidally disrupted, leaving their globular cluster complement bound to higher-mass halos. We argue that the age-metallicity-specific orbital energy relation in a galaxy's globular cluster system can be used to identify its origin. Gas-rich mergers should produce tightly bound systems in which metal-rich clusters are younger than metal-poor clusters. Globular clusters formed in massive disks and then scattered into a halo should have no relationship between age and specific orbital energy. Accreted globular clusters should produce weakly bound systems in which age and metallicity are correlated with eachother but inversely correlated with specific orbital energy. We use precise relative ages, self-consistent metallicities, and space-based proper motion-informed orbits to show that the Milky Way's metal-poor globular cluster system lies in a plane in age-metallicity-specific orbital energy space. We find that relatively young or metal-poor globular clusters are weakly bound to the Milky Way, while relatively old or metal-rich globular clusters are tightly bound to the Galaxy. While metal-rich globular clusters may be formed either in situ or ex situ, our results suggest that metal-poor clusters are formed outside of the Milky Way in now-disrupted dwarf galaxies. We predict that this relationship between age, metallicity, and specific orbital energy in a L* galaxy's globular cluster system is a natural outcome of galaxy formation in a {Lambda}CDM universe.