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17131. VLBI suvey around B0218+357 at 90cm
ID:
ivo://CDS.VizieR/J/ApJ/673/78
Title:
VLBI suvey around B0218+357 at 90cm
Short Name:
J/ApJ/673/78
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report on the first wide-field, very long baseline interferometry (VLBI) survey at 90cm. The survey area consists of two overlapping 28deg^2^ fields centered on the quasar J0226+3421 and the gravitational lens B0218+357. A total of 618 sources were targeted in these fields, based on identifications from Westerbork Northern Sky Survey (WENSS) data. Of these sources, 272 had flux densities that, if unresolved, would fall above the sensitivity limit of the VLBI observations. A total of 27 sources were detected as far as 2{deg} from the phase center. The results of the survey suggest that at least 10% of moderately faint (S~100mJy) sources found at 90 cm contain compact components smaller than ~0.1"-0.3" and stronger than 10% of their total flux densities.
17132. V light curves of EP Cep, ES Cep, and V369 Cep
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.
17133. V light curves of NGC 6791 variable stars
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.
17134. V light curves of variable stars in NGC 6229
ID:
ivo://CDS.VizieR/J/ApJ/102/17
Title:
V light curves of variable stars in NGC 6229
Short Name:
J/ApJ/102/17
Date:
21 Oct 2021
Publisher:
CDS
Description:
Improved distance moduli for the two globular clusters NGC 5634 and NGC 6229 are derived from a photometric investigation of their cluster-type variables. The resulting values are m-M=16.91+/-0.04 for NGC 5634 and m-M=17.53+/-0.02 for NGC 6229. Both globular clusters are of less than average luminosity.
17135. VLM stars and BDs in Upper Sco using Gaia DR1
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.
17136. VLT and ACS observations in RDCS J1252.9-2927
ID:
ivo://CDS.VizieR/J/ApJ/663/164
Title:
VLT and ACS observations in RDCS J1252.9-2927
Short Name:
J/ApJ/663/164
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present results from an extensive spectroscopic survey, carried out with VLT FORS, and from an extensive multiwavelength imaging data set from the HST Advanced Camera for Surveys and ground-based facilities, of the cluster of galaxies RDCS J1252.9-2927.
17137. VLT/Flames spectroscopic data of NGC 6530
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.
17138. VLT-FLAMES survey of massive stars
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.
17139. VLT-FLAMES survey of massive stars
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).
17140. VLT-FLAMES survey of massive stars
ID:
ivo://CDS.VizieR/J/A+A/466/277
Title:
VLT-FLAMES survey of massive stars
Short Name:
J/A+A/466/277
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present an analysis of high-resolution FLAMES spectra of approximately 50 early B-type stars in three young clusters at different metallicities, NGC 6611 in the Galaxy, N 11 in the Large Magellanic Cloud (LMC) and NGC 346 in the Small Magellanic Cloud (SMC). Using the TLUSTY non-LTE model atmospheres code, atmospheric parameters and photospheric abundances (C, N, O, Mg and Si) of each star have been determined. These results represent a significant improvement on the number of Magellanic Cloud B-type stars with detailed and homogeneous estimates of their atmospheric parameters and chemical compositions. The relationships between effective temperature and spectral type are discussed for all three metallicity regimes, with the effective temperature for a given spectral type increasing as one moves to a lower metallicity regime. Additionally the difficulties in estimating the microturbulent velocity and the anomalous values obtained, particularly in the lowest metallicity regime, are discussed. Our chemical composition estimates are compared with previous studies, both stellar and interstellar with, in general, encouraging agreement being found.

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