- ID:
- ivo://CDS.VizieR/J/other/RMxAA/56.139
- Title:
- On the evolution of angular momentum
- Short Name:
- J/other/RMxAA/56
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Selecting the best quality data, I find that nearly all 0.5 to 1.2M_{sun}_ main sequence stars converge to a single rotational mass dependent sequence after 750Myr; when the mass is larger than 0.8M_{sun}_, most of them converge in ~120Myr. If stars rotate as rigid bodies, the angular momentum of the vast majority is within clearly outlined bounds. The lower boundary defines a terminal main sequence rotational isochrone, the upper one coincides with slow rotators from the Pleiades and stars from Praesepe delineate a third one. Mass dependent exponential relationships between angular momentum and age are determined from these isochrones. Age estimates based on the angular momentum, are acceptable in middle aged stars older than 750Myr and more massive than 0.6-0.7M_{sun}_. The evolution of the Rossby number indicates that the Parker dynamo may cease early on in stars where M/M_{sun}_>=1.1. An empirical formula for the torque, an idealized model for it and a relation between rotational period and magnetic field, lead to a formula for the evolution of the mass loss rate, predicting that the present solar rate is close to a minimum and that it was around five times more vigorous when life on Earth started.
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- ID:
- ivo://CDS.VizieR/J/MNRAS/481/2458
- Title:
- On the nature of small galaxy systems
- Short Name:
- J/MNRAS/481/2458
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We aim at defining homogeneous selection criteria of small galaxy systems in order to build catalogues suitable to compare main properties of pairs, triplets, and groups with four or more members. To this end we use spectroscopic and photometric Sloan Digital Sky Survey (SDSS) data to identify systems with a low number of members. We study global properties of these systems and the properties of their member galaxies finding that galaxies in groups are systematically redder and with lower star formation activity indicators than galaxies in pairs which have a higher fraction of star-forming galaxies. Triplet galaxies present intermediate trends between pairs and groups. We also find an enhancement of star formation activity for galaxies in small systems with companions closer than 100kpc, irrespective of the number of members. We have tested these analyses on SDSS mock catalogues derived from the Millennium simulation, finding as conservative thresholds 76 per cent completeness and a contamination of 23 per cent in small galaxy systems, when considering an extreme case of incompleteness due to fiber collisions. Nevertheless, we also found that the results obtained are not likely affected by projection effects. Our studies suggest that an extra galaxy in a system modify the properties of the member galaxies. In pairs, galaxy-galaxy interactions increase gas density and trigger starbursts. However, repeated interactions in triplets and groups can generate gas stripping, turbulence, and shocks quenching the star formation in these systems.
- ID:
- ivo://CDS.VizieR/J/MNRAS/484/4833
- Title:
- Oosterhoff dichotomy in Galactic bulge
- Short Name:
- J/MNRAS/484/4833
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a study of the Oosterhoff (Oo) dichotomy in the Galactic bulge using 8141 fundamental-mode RR Lyrae stars. We used public photometric data from the Optical Gravitational Lensing Experiment and the Vista Variables in the Via Lactea survey. We carefully selected fundamental-mode stars without modulation and without association with any globular cluster located towards the Galactic bulge. Subsequently, we identified and separated the Oosterhoff groups I and II on the basis of their period-amplitude distribution and using a relation fitted to the Oosterhoff I locus. Both Oosterhoff groups were then compared to observations of two bulge globular clusters and with models of stellar pulsation and evolution. We found that some of the variables classified as Oo II belong to a third Oo group. The Oosterhoff II variables are more metal-poor on average, more massive, and cooler than their Oosterhoff I counterparts. The analysis of their spatial distribution shows a systematic difference between foreground, central, and background regions in the occurrence of the Oosterhoff II group. The difference between the Oo I and II groups is also seen in their distance distributions with respect to the Galactic bar, but neither group is associated with the bar.
- ID:
- ivo://CDS.VizieR/J/MNRAS/470/4285
- Title:
- Open cluster King 1 photometry
- Short Name:
- J/MNRAS/470/4285
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyse the poorly studied open cluster King 1 in the second Galactic quadrant. From wide-field photometry, we have studied the spatial distribution of this cluster. We determined that the centre of King 1 is located at {alpha}_2000_=00:22 and {delta}_2000_=+64:23. By parameterizing the stellar density with a King profile, we have obtained a central density of {rho}_0_= 6.5+/-0.2star/arcmin^2^ and a core radius of r_core_=1.9+/-0.2arcmin. By comparing the observed colour-magnitude diagram of King 1 with those of similar open clusters and with different sets of isochrones, we have estimated an age of 2.8+/-0.3Gyr, a distance modulus of (m-M)_o_=10.6+/-0.1mag and a reddening of E(B-V)=0.80+/-0.05mag. To complete our analysis, we acquired medium resolution spectra for 189 stars in the area of King 1. From their derived radial velocities, we determined an average velocity <V_r_>=-53.1+/-3.1km/s. From the strength of the infrared CaII lines in red giants we have determined an average metallicity of <[M/H]>=+0.07+/-0.08dex. From spectral synthesis, we have also estimated an {alpha}-elements abundance of <[{alpha}/M]>=-0.10+/-0.08dex.
4675. Open cluster Pis 20
- ID:
- ivo://CDS.VizieR/J/A+AS/111/85
- Title:
- Open cluster Pis 20
- Short Name:
- J/A+AS/111/85
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The very young open cluster Pis 20 has been investigated using CCD UBVR photometry. New blue faint members were found down to V=19mag. With them we obtain a better definition of the lower cluster main sequence. Using the fitting method, we derive a cluster distance of d=3600pc (V_0_-M_V_=12.80). The mean color excess is <E_B-V_>=1.24mag.
- ID:
- ivo://CDS.VizieR/J/AJ/136/118
- Title:
- Open clusters as galactic disk tracers. I.
- Short Name:
- J/AJ/136/118
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have begun a survey of the chemical and dynamical properties of the Milky Way disk as traced by open star clusters. In this first contribution, the general goals of our survey are outlined and the strengths and limitations of using star clusters as a Galactic disk tracer sample are discussed. We also present medium-resolution (R~150000) spectroscopy of open cluster stars obtained with the Hydra multi-object spectrographs on the Cerro Tololo Inter-American Observatory 4m and WIYN 3.5m telescopes. Here we use these data to determine the radial velocities of 3436 stars in the fields of open clusters within about 3kpc, with specific attention to stars having proper motions in the Tycho-2 catalog. Additional radial velocity members (without Tycho-2 proper motions) that can be used for future studies of these clusters were also identified.
- ID:
- ivo://CDS.VizieR/J/A+AS/108/151
- Title:
- Open clusters CCD photometry. I.
- Short Name:
- J/A+AS/108/151
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- (no description available)
- ID:
- ivo://CDS.VizieR/J/MNRAS/459/880
- Title:
- Open clusters in Auriga OB2
- Short Name:
- J/MNRAS/459/880
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the area around the HII region Sh 2-234, including the young open cluster Stock 8, to investigate the extent and definition of the association Aur OB2 and the possible role of triggering in massive cluster formation. We obtained Stromgren and J, H, Ks photometry for Stock 8 and Stromgren photometry for two other cluster candidates in the area, which we confirm as young open clusters and name Alicante 11 and Alicante 12. We took spectroscopy of ~33 early-type stars in the area, including the brightest cluster members. We calculate a common distance of 2.80+0.27-0.24kpc for the three open clusters and surrounding association. We derive an age 4-6Ma for Stock 8, and do not find a significantly different age for the other clusters or the association. The star LS V +34 23, with spectral type O8 II(f), is likely the main source of ionization of Sh 2-234. We observe an important population of pre-main-sequence stars, some of them with discs, associated with the B-type members lying on the main sequence. We interpret the region as an area of recent star formation with some residual and very localized ongoing star formation. We do not find evidence for sequential star formation on a large scale. The classical definition of Aur OB2 has to be reconsidered, because its two main open clusters, Stock 8 and NGC 1893, are not at the same distance. Stock 8 is probably located in the Perseus arm, but other nearby HII regions whose distances also place them in this arm show quite different distances and radial velocities and, therefore, are not connected.
- ID:
- ivo://CDS.VizieR/J/A+A/511/A38
- Title:
- Open clusters in third galactic quadrant
- Short Name:
- J/A+A/511/A38
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We aim to determine accurate distances and ages of eight open clusters in order to: (1) assess their possible binarity (2) provide probes to trace the structure of the Third Galactic Quadrant. Cluster reddenings, distances, ages and metallicities are derived from ZAMS and isochrone fits in UBVRI photometric diagrams. Field contamination is reduced by restricting analysis to stars within the cluster limits derived from star counts. Further membership control is done by requiring that stars have consistent positions in several diagrams and by using published spectral types.
- ID:
- ivo://CDS.VizieR/J/MNRAS/470/3937
- Title:
- 1876 open clusters multimembership catalog
- Short Name:
- J/MNRAS/470/3937
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The main objective of this work is to determine the cluster members of 1876 open clusters, using positions and proper motions of the astrometric fourth United States Naval Observatory (USNO) CCD Astrograph Catalog (UCAC4). For this purpose, we apply three different methods, all based on a Bayesian approach, but with different formulations: a purely parametric method, another completely non-parametric algorithm and a third, recently developed by Sampedro & Alfaro (2016MNRAS.457.3949S), using both formulations at different steps of the whole process. The first and second statistical moments of the members' phase-space subspace, obtained after applying the three methods, are compared for every cluster. Although, on average, the three methods yield similar results, there are also specific differences between them, as well as for some particular clusters. The comparison with other published catalogues shows good agreement. We have also estimated, for the first time, the mean proper motion for a sample of 18 clusters. The results are organized in a single catalogue formed by two main files, one with the most relevant information for each cluster, partially including that in UCAC4, and the other showing the individual membership probabilities for each star in the cluster area. The final catalogue, with an interface design that enables an easy interaction with the user, is available in electronic format at the Stellar Systems Group (SSG-IAA) web site (http://ssg.iaa.es/en/content/sampedro-cluster-catalog).
