- ID:
- ivo://CDS.VizieR/J/A+A/464/573
- Title:
- VI photometry of 5 open clusters
- Short Name:
- J/A+A/464/573
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The stellar populations in the outer Galactic disk are a subject of wide interest nowadays. To contribute to a better picture of this part of the Galaxy, we have studied the nature of five marginally investigated star clusters (Collinder 74, Berkeley 27, Haffner 8, NGC 2509, and VdB-Hagen4) by means of accurate CCD photometry in the V and I passbands. These clusters are in fact located in the third Galactic quadrant. We aim to obtain the basic parameters of these objects, which in some cases are still disputed in the literature. In the case of VdB-Hagen 4 we provide the first estimate of its fundamental parameters, while for Haffner 8 we present the first CCD photometry. The analysis is based on the comparison between field star decontaminated color-magnitude diagrams and stellar models. Particular care is devoted to the the assessment of the data quality and the statistical field star decontamination. The Padova library of stellar isochrones is adopted in this study. The analysis we carried out allowed us to solve a few inconsistencies in the literature regarding Haffner 8 and NGC 2509. Collinder 74 is found to be significantly older than reported before. VdB-Hagen 4 is a young open cluster located more than 20kpc from the Galactic center. Such an extreme distance is compatible with the cluster belonging to the Norma-Cygnus arm.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+AS/127/423
- Title:
- VI photometry of Westerlund 1 and 2
- Short Name:
- J/A+AS/127/423
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have carried out CCD observations of stars in the region of the open cluster Westerlund 1 through the V and I passbands. The direct images were obtained with the 24-inch telescope of the University of Toronto Southern Observatory situated at Las Campanas Observatory, Chile. After cross-correlating all independent V, (V-I) tables we have obtained a improved set of colour and magnitude values as compared to those based on a single measure.
- ID:
- ivo://CDS.VizieR/J/ApJ/754/30
- Title:
- VISTA IR photometry of {sigma} Ori cluster
- Short Name:
- J/ApJ/754/30
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on our analysis of the VISTA Orion ZY JHK_s_ photometric data (completeness magnitudes of Z=22.6 and J=21.0 mag) focusing on a circular area of 2798.4arcmin^2^ around the young {sigma} Orionis star cluster (~3Myr, ~352pc, and solar metallicity). The combination of the VISTA photometry with optical, WISE and Spitzer data allows us to identify a total of 210 {sigma} Orionis member candidates with masses in the interval 0.25-0.004M_{sun}_, 23 of which are new planetary-mass object findings. These discoveries double the number of cluster planetary-mass candidates known so far. One object has colors compatible with a T spectral type. The {sigma} Orionis cluster harbors about as many brown dwarfs (69, 0.072-0.012M_{sun}_) and planetary-mass objects (37, 0.012-0.004M_{sun}_) as very low mass stars (104, 0.25-0.072M_{sun}_). Based on Spitzer data, we derive a disk frequency of ~40% for very low mass stars, brown dwarfs, and planetary-mass objects in {sigma} Orionis. The radial density distributions of these three mass intervals are alike: all are spatially concentrated within an effective radius of 12' (1.2pc) around the multiple star {sigma} Ori, and no obvious segregation between disk-bearing and diskless objects is observed.
- ID:
- ivo://CDS.VizieR/J/AJ/134/2272
- Title:
- Visual binaries in the Orion Nebula Cluster
- Short Name:
- J/AJ/134/2272
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have carried out a major survey for visual binaries toward the Orion Nebula Cluster, using images obtained with the Advanced Camera for Surveys on the Hubble Space Telescope through an Halpha filter. From 1051 stars more than 60" from theta^1^ Ori C, we have selected 781 that fulfill the criteria for membership in the Orion Nebula Cluster. Among these, we find 78 multiple systems (75 binaries and 3 triples), of which 55 are new discoveries, in the range from 0.1" to 1.5". We perform a statistical study of the 72 binaries and 3 triples that have separations in the limited range 0.15" to 1.5", within which we need no incompleteness correction.
- ID:
- ivo://CDS.VizieR/J/AJ/147/42
- Title:
- V light curves of EP Cep, ES Cep, and V369 Cep
- Short Name:
- J/AJ/147/42
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- NGC 188 is a good laboratory for studying the formation and evolution of W UMa type contact binaries due to its rich populations of them. We present a detailed photometric study of three short-period close binaries, EP Cep, ES Cep, and V369 Cep, in the old open cluster NGC 188 based on our two-set photometric observations. We discovered that both EP Cep and ES Cep are shallow-contact binaries with continuously decreasing periods. The difference is in their mass ratios. EP Cep has an extremely low-mass ratio, q=0.15, while ES Cep has a relatively high-mass ratio, q=0.69, indicating that they lie in different evolutionary stages. ES Cep is likely a newly formed contact binary via a Case A mass transfer, while EP Cep is an evolved system and may be on the oscillations caused by the combined effect of the thermal relaxation oscillation and the variable angular momentum loss. For another system, V369 Cep, we found that it is a primary-filling near-contact binary. Both the semidetached configuration and the continuous decrease in the orbital period indicate that it is undergoing a mass transfer from the primary component to the secondary one. This conclusion is in agreement with the excess luminosity seen in the light curves on the ingress of the secondary minimum produced by the impact of the mass transfer. All of the results suggest that V369 Cep is evolving into contact, and a shallow-contact high-mass ratio system similar to ES Cep will be formed. Then, it will evolve into a low-mass ratio contact binary just like EP Cep, and finally merge into a rapidly rotating single star.
- ID:
- ivo://CDS.VizieR/J/A+A/471/515
- Title:
- V light curves of NGC 6791 variable stars
- Short Name:
- J/A+A/471/515
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This work presents a high-precision variability survey in the field of the old, super metal-rich open cluster NGC 6791. The data sample consists of more than 75,000 high-precision CCD time series measurements in the V band obtained mainly at the Canada-France-Hawaii Telescope, with additional data from S. Pedro Martir and Loiano observatories, over a time span of ten nights. The field covers an area of 42x28arcmin^2^. We have discovered 260 new variables and re-determined periods and amplitudes of 70 known variable stars. By means of a photometric evaluation of the membership in NGC 6791, and a preliminary membership based on the proper motions, we give a full description of the variable content of the cluster and surrounding field in the range 16<V<23.5. Accurate periods can be given for the variables with P<4.0d, while for ones with longer periods the limited time-baseline hampered precise determinations. We categorized the entire sample as follows: 6 pulsating, 3 irregular, 3 cataclysmic, 89 rotational variables and 61 eclipsing systems; moreover, we detected 168 candidate variables for which we cannot give a variability class since their periods are much longer than our time baseline. On the basis of photometric considerations, and of the positions of the stars with respect to the center of the cluster, we inferred that 11 new variable stars are likely members of the cluster, for 22 stars the membership is doubtful and 137 are likely non-members. We also detected an outburst of about 3 mag in the light curve of a very faint blue star belonging to the cluster and we suggest that this star could be a new U Gem (dwarf nova) cataclysmic variable.
- ID:
- ivo://CDS.VizieR/J/AJ/154/256
- Title:
- VLM stars and BDs in Upper Sco using Gaia DR1
- Short Name:
- J/AJ/154/256
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Our understanding of the brown dwarf population in star-forming regions is dependent on knowing distances and proper motions and therefore will be improved through the Gaia space mission. In this paper, we select new samples of very low-mass objects (VLMOs) in Upper Scorpius using UKIDSS colors and optimized proper motions calculated using Gaia DR1. The scatter in proper motions from VLMOs in Upper Scorpius is now (for the first time) dominated by the kinematic spread of the region itself, not by the positional uncertainties. With age and mass estimates updated using Gaia parallaxes for early-type stars in the same region, we determine masses for all VLMOs. Our final most complete sample includes 453 VLMOs of which ~125 are expected to be brown dwarfs. The cleanest sample is comprised of 131 VLMOs, with ~105 brown dwarfs. We also compile a joint sample from the literature that includes 415 VLMOs, out of which 152 are likely brown dwarfs. The disk fraction among low-mass brown dwarfs (M<0.05M_{sun}_) is substantially higher than in more massive objects, indicating that disks around low-mass brown dwarfs survive longer than in low-mass stars overall. The mass function for 0.01<M<0.1M_{sun}_ is consistent with the Kroupa Initial Mass Function. We investigate the possibility that some "proper motion outliers" have undergone a dynamical ejection early in their evolution. Our analysis shows that the color-magnitude cuts used when selecting samples introduce strong bias into the population statistics due to varying levels of contamination and completeness. Our understanding of the brown dwarf population in star-forming regions is dependent on knowing distances and proper motions and therefore will be improved through the Gaia space mission. In this paper, we select new samples of very low-mass objects (VLMOs) in Upper Scorpius using UKIDSS colors and optimized proper motions calculated using Gaia DR1. The scatter in proper motions from VLMOs in Upper Scorpius is now (for the first time) dominated by the kinematic spread of the region itself, not by the positional uncertainties. With age and mass estimates updated using Gaia parallaxes for early-type stars in the same region, we determine masses for all VLMOs. Our final most complete sample includes 453 VLMOs of which ~125 are expected to be brown dwarfs. The cleanest sample is comprised of 131 VLMOs, with ~105 brown dwarfs. We also compile a joint sample from the literature that includes 415 VLMOs, out of which 152 are likely brown dwarfs. The disk fraction among low-mass brown dwarfs (M<0.05M_{sun}_) is substantially higher than in more massive objects, indicating that disks around low-mass brown dwarfs survive longer than in low-mass stars overall. The mass function for 0.01<M<0.1M_{sun}_ is consistent with the Kroupa Initial Mass Function. We investigate the possibility that some "proper motion outliers" have undergone a dynamical ejection early in their evolution. Our analysis shows that the color-magnitude cuts used when selecting samples introduce strong bias into the population statistics due to varying levels of contamination and completeness.
- ID:
- ivo://CDS.VizieR/J/A+A/462/123
- Title:
- VLT/Flames spectroscopic data of NGC 6530
- Short Name:
- J/A+A/462/123
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Mechanisms regulating the evolution of pre-main sequence stars can be understood by studying stellar properties such as rotation, disk accretion, internal mixing and binarity. To investigate such properties, we studied a sample of 332 candidate members of the massive and populous star forming region NGC 6530. We want to select cluster members by using different membership criteria, to study the properties of pre-main sequence stars with or without circumstellar disks. We use intermediate resolution spectra including the LiI6707.8{AA} line to derive radial and rotational velocities, binarity and to measure the Equivalent Width of the lithium line; these results are combined with X-ray data to study the cluster membership. Optical-IR data and H{alpha} spectra, these latter available for a subsample of our targets, are used to classify CTTS and WTTS and to compare the properties of stars with and without disks. We find a total of 237 certain members including 53 binaries. The rotational velocity distributions of stars with IR excesses are statistically different from that of stars without IR excesses, while the fraction of binaries with disks is significantly smaller than that of single stars. Stars with evidence for accretion show circumstellar disks; youth of cluster members is confirmed by the lithium abundance consistent with the initial content. As indicated by the disk-locking picture, stars with disks have in general rotational velocities lower than stars without disks. Binaries in NGC 6530 seem have undergone a significant disk evolution.
- ID:
- ivo://CDS.VizieR/J/A+A/456/623
- Title:
- VLT-FLAMES survey of massive stars
- Short Name:
- J/A+A/456/623
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new observations of 470 stars using the Fibre Large Array Multi-Element Spectrograph (FLAMES) instrument in fields centered on the clusters NGC 330 and NGC 346 in the Small Magellanic Cloud (SMC), and NGC 2004 and the N11 region in the Large Magellanic Cloud (LMC). A further 14 stars were observed in the N11 and NGC 330 fields using the Ultraviolet and Visual Echelle Spectrograph (UVES) for a separate programme. Spectral classifications and stellar radial velocities are given for each target, with careful attention to checks for binarity. In particular, we have investigated previously unexplored regions around the central LH9/LH10 complex of N11, finding ~25 new O-type stars from our spectroscopy. We have observed a relatively large number of Be-type stars that display permitted Fe II emission lines. These are primarily not in the cluster cores and appear to be associated with classical Be-type stars, rather than pre main-sequence objects. The presence of the Fe II emission, as compared to the equivalent width of H{alpha}, is not obviously dependent on metallicity. We have also explored the relative fraction of Be- to normal B-type stars in the field-regions near to NGC 330 and NGC 2004, finding no strong evidence of a trend with metallicity when compared to Galactic results. A consequence of service observations is that we have reasonable time-sampling in three of our FLAMES fields. We find lower limits to the binary fraction of O- and early B-type stars of 23 to 36%. One of our targets (NGC 346-013) is especially interesting with a massive, apparently hotter, less luminous secondary component.
- ID:
- ivo://CDS.VizieR/J/A+A/437/467
- Title:
- VLT-FLAMES survey of massive stars
- Short Name:
- J/A+A/437/467
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We introduce a new survey of massive stars in the Galaxy and the Magellanic Clouds using the Fibre Large Array Multi-Element Spectrograph (FLAMES) instrument at the Very Large Telescope (VLT). Here we present observations of 269 Galactic stars with the FLAMES-Giraffe Spectrograph (R~=25000), in fields centered on the open clusters NGC 3293, NGC 4755 and NGC 6611. These data are supplemented by a further 50 targets observed with the Fibre-Fed Extended Range Optical Spectrograph (FEROS, R=48000).
