- ID:
- ivo://CDS.VizieR/J/A+A/351/526
- Title:
- NGC 2172 CCD BVI photometry
- Short Name:
- J/A+A/351/526
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new CCD photometry for the young LMC cluster NGC 2172, giving B, V, I magnitudes for more than 600 stars within 70" from the cluster center, down to -approximately- V=21mag. After correction for completeness and field stars contamination, we discuss the cluster HR diagram and the MS luminosity function in the light of current evolutionary theories and in connection with the problem of cluster age.
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Search Results
- ID:
- ivo://CDS.VizieR/J/PASP/117/22
- Title:
- NGC 6318 CCD BVI photometry
- Short Name:
- J/PASP/117/22
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present CCD BVI photometry for the southern open cluster NGC 6318. The sample consists of 9876 stars measured in an area of 13.6'x13.6', extending down to V~21.5mag. Star counts carried out within and outside the cluster region allowed us to estimate the cluster angular radius as 8'.
- ID:
- ivo://CDS.VizieR/J/ApJS/71/25
- Title:
- NGC 1866 CCD photometry
- Short Name:
- J/ApJS/71/25
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The first part of this paper is devoted to a new CCD investigation of stars in the field of the LMC cluster NGC 1866. Two main frames have been analyzed, one covering the cluster's central region and the other covering an area about 10' from the cluster's center, and data has been collected for 2207 objects. On this basis, a C-M diagram has been derived, which shows a well-developed blue sequence reaching a limiting magnitude of about V=21mag together with the already known sequence of the cluster's He-burning giants. A new feature in our data is represented by the evidence for a second group of less luminous giants clumping around V=19mag, which we interpret as field He-burning giants. The second part of the paper is devoted to a comparison of these data with theoretical calculations. On the basis of new evolutionary tracks we find that the composition Y=0.28, Z=0.02 already used by Becker and Mathews (1983ApJ...270..155B) offers an adequate fitting of the observed range in color spanned by cluster He giants. Theoretical isochrones for this composition have been produced and are compared with the observed distribution of cluster stars. A good agreement with the observed C-M diagram is achieved for a cluster age of the order of t=100Myr, whereas field stars appear to be significantly older, with ages of about 500 Myr or more. The distribution of cluster stars is studied, and both the luminosity function of the blue sequence (BS) and number of He giants relative to BS stars are examined. We find that both these cluster characteristics can be reproduced with a Salpeter slope for the initial mass function, overcoming previous difficulties raised by suggestions of a serious disagreement between theory and observations in this cluster. The Appendix reports data for the evolutionary models and for the corresponding isochrones, covering both the H- and He-burning phases
- ID:
- ivo://CDS.VizieR/J/A+A/355/138
- Title:
- NGC 6994 CCD photometry
- Short Name:
- J/A+A/355/138
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- BVRI CCD photometry of 144 stars in the region of NGC 6994: positions, V magnitudes, (B-V), (V-R) and (V-I) colors.
- ID:
- ivo://CDS.VizieR/J/other/ApSS/361.126
- Title:
- NGC 6819 CCD UBV photometry
- Short Name:
- J/other/ApSS/361
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of CCD UBV observations of the open cluster NGC 6819. We calculated the stellar density profile in the cluster's field to determine the structural parameters of NGC 6819. Using the existing astrometric data, we calculated the probabilities of the stars being physical members of the cluster, and used these objects in the determination of the astrophysical parameters of NGC 6819. We inferred the reddening and metallicity of the cluster as E(B-V)=0.130+/-0.035mag and [Fe/H]=+0.051+/-0.020dex, respectively, using the U-B vs B-V two-colour diagram and UV excesses of the F-G type main-sequence stars. We fit the colour-magnitude diagrams of NGC 6819 with the PARSEC isochrones and derived the distance modula, distance and age of the cluster as mu_V=12.22+/-0.10mag, d=2309+/-106pc and t=2.4+/-0.2Gyr, respectively. The parameters of the galactic orbit estimated for NGC 6819 indicate that the cluster is orbiting in a slightly eccentric orbit of e=0.06 with a period of P_orb_=142Myr. The slope of the mass function estimated for the cluster is close to the one found for the stars in the solar neighbourhood.
- ID:
- ivo://CDS.VizieR/J/other/ApSS/355.267
- Title:
- NGC 6811 CCD UBVRI photometry
- Short Name:
- J/other/ApSS/355
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of CCD UBVRI observations of the open cluster NGC 6811 obtained on 18th July 2012 with the 1m telescope at the TIBITAK National Observatory (TUG). Using these photometric results, we determine the structural and astrophysical parameters of the cluster. The mean photometric uncertainties are better than 0.02 mag in the V magnitude and B-V, V-R, and V-I colour indices to about 0.03mag for U-B among stars brighter than magnitude V=18. Cluster member stars were separated from the field stars using the Galaxia model of Sharma et al. (2011ApJ...730....3S) together with other techniques. The core radius of the cluster is found to be r_c_=3.60arcmin. The astrophysical parameters were determined simultaneously via Bayesian statistics using the colour-magnitude diagrams V versus B-V, V versus V-I, V versus V-R, and V versus R-I of the cluster. The resulting most likely parameters were further confirmed using independent methods, removing any possible degeneracies. The colour excess, distance modulus, metallicity and the age of the cluster are determined simultaneously as E(B-V)=0.05+/-0.01mag, {mu}=10.06+/-0.08mag, [M/H]=-0.10+/-0.01dex and t=1.00+/-0.05Gyr, respectively. Distances of five red clump stars which were found to be members of the cluster further confirm our distance estimation.
- ID:
- ivo://CDS.VizieR/J/PASP/110/1318
- Title:
- NGC 7789 CCD VI photometry
- Short Name:
- J/PASP/110/1318
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A V, V-I-diagram for the intermediate-age open cluster NGC 7789 has been derived from CCD observations of more than 15,000 stars within ~18' of the cluster center. From the brightest giants and blue stragglers at V~11 to the faintest lower main-sequence stars that were observed (at V~21, M_V_~9), the color-magnitude diagram is well defined. A prominent clump of core helium-burning stars is evident at V=13.0, and the upper end of the main sequence shows a fairly pronounced curvature to the red, which is indicative of significant convective core overshooting. Indeed, comparisons with up-to-date stellar models show that it is not possible to explain the observed morphology in the vicinity of the turnoff unless the overshooting is quite extensive. Interestingly, if sufficient overshooting is assumed in order to match the main-sequence data, it is not possible to reproduce the cluster's extended giant branch unless the cluster age is at least 1.6 Gyr (assuming a metallicity in the range -0.2<=[FeMH]<=0.0). This, in turn, requires that the cluster have an apparent distance modulus m-M_V_<=12.2. Thus, sometime within the past few hundred million years, the ignition of helium burning in NGC 7789 has switched from a quiescent to an explosive ("flash") phenomenon, and the length of the cluster's red giant branch has been steadily increasing with the passage of time since then. From main-sequence fits to models that have been carefully normalized to the Sun, we infer a reddening 0.35<=E(V-I)<=0.38.
- ID:
- ivo://CDS.VizieR/J/A+A/543/A131
- Title:
- NGC1316 globular cluster candidates photometry
- Short Name:
- J/A+A/543/A131
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalog of point-like sources around NGC 1316, which forms the photometric database for our paper. This catalogue basically is a selection from a larger photometric database. The selection criteria are specified in the paper. The catalog contains coordinates, R magnitudes with uncertainties, C-R colors and their uncertainties as well as "sharp" and "chi" values from DAOPHOT II. The coordinates are for identification purposes only. Depending on the position, deviations of up to 1 arcsec may occur. See the paper for validity limits of the photometric calibration, particularly for very red colors.
- ID:
- ivo://CDS.VizieR/J/A+A/641/A51
- Title:
- NGC 2516 membership list
- Short Name:
- J/A+A/641/A51
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We wish to measure the cool star rotation period distribution for the Pleiades-age rich open cluster NGC 2516 and use it to determine whether cluster-to-cluster variations exist in otherwise identical open clusters. We obtained 42d-long time-series CCD photometry of NGC 2516 in the V and Ic filters using the Yale 1m telescope at CTIO and performed a number of related analyses, including PSF-based time-series photometry. Our data are complemented with additional information from several photometric datasets, literature radial velocities, and Gaia DR2 astrometry. All available data are used to construct an integrated membership list for NGC 2516, containing 844 stars in our ~1 degree field of view. We derived 308 rotation periods for late-F to mid-M cluster members from our photometry. We identified an additional 247 periodic M dwarf stars from a prior study as cluster members, and used these to construct a 555-star rotation period distribution for NGC 2516. The colour-period diagram (in multiple colours) has almost no outliers and exhibits the anticipated triangular shape, with a diagonal slow rotator sequence that is preferentially occupied by the warmer stars along with a flat fast rotator sequence that is preferentially populated by the cooler cluster members. We also find a group of extremely slowly rotating M dwarfs (10d<P<23d), forming a branch in the colour-period diagram which we call the 'extended slow rotator sequence'. This, and other features of the rotational distribution can also be found in the Pleiades, making the colour-period diagrams of the two clusters nearly indistinguishable. A comparison with the well-studied (and similarly aged) open cluster M 35 indicates that the cluster's rotational distribution is also similarly indistinguishable from that of NGC 2516. Those for the open clusters M 50 and Blanco 1 are similar, but data issues for those clusters make the comparisons somewhat more ambiguous. Nevertheless, we demonstrate the existence of a representative zero-age main sequence (ZAMS) rotational distribution and provide a simple colour-independent way to represent it. We perform a detailed comparison of the NGC 2516 rotation period data with a number of recent rotational evolution models. Using X-ray data from the literature, we also construct the first rotation-activity diagram for solar-type stars in NGC 2516, one that we find is essentially indistinguishable from those for the Pleiades and Blanco 1. The two clusters NGC 2516 and Pleiades can be considered twins in terms of stellar rotation and related properties (and M 35, M 50, and Blanco 1 are similar), suggesting that otherwise identical open clusters also have intrinsically similar cool star rotation and activity distributions.
- ID:
- ivo://CDS.VizieR/J/AJ/115/130
- Title:
- NGC 925 & NGC 1637 supergiants VRI CCD photometry
- Short Name:
- J/AJ/115/130
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- V, R, and I CCD images obtained with the Canada-France-Hawaii Telescope are used to investigate the bright stellar content of the barred spiral galaxies NGC 925 and NGC 1637. Not counting objects located in H II regions, we detect 295 supergiants in NGC 925 and 266 in NGC 1637. Comparisons with theoretical isochrones indicate that massive star formation in NGC 925 has been ongoing for at least a few tens of millions of years. Most of the supergiants in NGC 925 are younger than 20Myr and have masses between 10 and 60M_{sun}_. The majority of supergiants in NGC 1637 appear to be younger than 40Myr and have initial masses between 8 and 60 M_{sun}_. The luminosity functions of supergiants in both galaxies follow power laws with exponents d(logn)/d(logV)=0.50+/-0.05 for NGC 925 and 0.62+/-0.04 for NGC 1637. These values are shallower than what is seen in most spiral galaxies, although there are some exceptions. Archival Hubble Space Telescope images of NGC 925 are used to assess the effects of blending on our photometric measurements. We conclude that crowding could cause a flattening of the luminosity function and bias the brightnesses of the most luminous stars. The brightest red supergiants are used to estimate the distance moduli of these galaxies. After applying corrections for blending, we find that {mu}_0_=29.67 for NGC 925 and {mu}_0_=29.47 for NGC 1637, corresponding to linear distances of 8.6^+1.1^_-1.0_ and 7.8^+1.0^_-0.9_Mpc, respectively. The distance computed for NGC 925 is in good agreement with that recently derived from Cepheids.
