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- ID:
- ivo://CDS.VizieR/J/AJ/118/2839
- Title:
- BV photometry of NGC 1866
- Short Name:
- J/AJ/118/2839
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new deep (down to V~24) photometry of a wide region (~6'x6') around the Large Magellanic Cloud globular cluster NGC 1866. Our sample is much larger (by more than a factor of 3) than any previous photometry and with a main sequence (MS) that may be considered complete, down to at least 3 mag below the brightest MS star; such an occurrence allows a meaningful and robust comparison with various theoretical scenarios produced by means of models computed with the evolutionary code FRANEC.
- ID:
- ivo://CDS.VizieR/J/AJ/112/1061
- Title:
- BV photometry of NGC 7099
- Short Name:
- J/AJ/112/1061
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- New BV CCD photometry for the bright stars in cluster fields centered on the core of NGC 7099 is presented. The morphology of the LF though the turnoff region is similar to that found in other metal-poor clusters in that the relative number of turnoff to giant stars is lower than predicted by canonical models. Comparisons with evolutionary sequences of horizontal branch stars suggest a reddening E(B-V)=0.06 and a distance modulus (m-M)_V=14.83. Isochrone fits to [Fe/H]=-2.03, [O/Fe]=+0.70 models are consistent with an age of at least 14 Gyr. The model LF for this age accurately predicts the brightness of the tip of the red giant branch (RGB) as well as the location of the break which signals the transition from the base of the RGB to the main sequence. There is an indication that the evolutionary pause on the RGB, which manifests itself as a bump in the LF, occurs one magnitude fainter than the models predict. The excess of HB stars with respect to giants is confirmed and implies a helium abundance Y=0.28, which is higher than that found in other metal-poor globular clusters from the R method. From a comparison with the metal-rich, blue horizontal branch cluster NGC 288, it is argued that age cannot by itself be the solution to the second parameter problem.
- ID:
- ivo://CDS.VizieR/J/MNRAS/243/492
- Title:
- BV Photometry of NGC 6791
- Short Name:
- J/MNRAS/243/492
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- CCD BV photometry to V=20.5 of stars in the old open cluster NGC 6791 is presented. Comparison with the theoretical isochrones of VandenBerg gives a cluster age in the range of 10 to 12.5Gyr, and an apparent distance modulus of 13.45mag, adopting a solar metallicity. This cluster is only marginally younger than Palomar 12, which is the youngest globular cluster known. A search for short-period variables in the cluster field led to the discovery of only one low-amplitude variable, probably belonging to the FK Com-type stars. A very blue star was detected which may be an extremely young white dwarf formed in the cluster.
- ID:
- ivo://CDS.VizieR/J/AJ/113/1045
- Title:
- BV photometry of NGC 3680
- Short Name:
- J/AJ/113/1045
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A new CCD BV color-magnitude diagram (CMD) has been derived for the intermediate age open cluster NGC 3680. The quality of photometry coupled with the best-to-date knowledge of cluster memberships allows for a detailed isochrone fit to the CMD. The theoretical isochrones have been constructed using the Yale Rotating Evolution Code (YREC) in its non-rotating mode and the OPAL opacities (circa 1991). Four sets of isochrones have been calculated: one for the standard stellar model calibrated to the Sun and three others for models with different amounts of convective overshoot at the edge of the convective core, namely, 0.15, 0.20, and 0.25H_p_, where H_p_ is the pressure scale height at the core edge. All four sets of theoretical isochrones were adjusted to an adopted distance modulus of V_0_-M_V_=10.20 and reddening E(B-V)=0.075 which leads to ages of 1.3+/-0.15, 1.5+/-0.15, 1.6+/-0.15, and 1.7+/-0.15Gyr, respectively The uncertainties in age mainly reflect a subjective decision in differentiating a good fit from a poorer one The model with a convective overshoot of 0.20H_p_ seems to yield the best fit to the sharply curved upper main sequence. Hence, the estimated age of NGC 3680 is 1.6+/-0.15Gyr. The adopted overshoot parameter ostensibly is uncertain by +/-0.05H_p_. For comparison, the same stellar models with overshoot of 0.25H_p_ were fit to the color-magnitude diagram of the cluster NGC 752, which is similar in age and composition to NGC 3680 The age estimate for NGC 752 is 1.6+/-0.2Gyr, assuming V_0_-M_V_=8.20 and E(B-V)=0.030 for the cluster.
- ID:
- ivo://CDS.VizieR/J/AJ/105/938
- Title:
- BV photometry of NGC 1850 (in LMC)
- Short Name:
- J/AJ/105/938
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper we examine the age and internal dynamics of the young binary LMC cluster NGC 1850 using BV CCD images and echelle spectra of 52 supergiants.
- ID:
- ivo://CDS.VizieR/J/A+A/431/1189
- Title:
- BV photometry of NGC 6822 variables
- Short Name:
- J/A+A/431/1189
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Deep B, V time-series photometry obtained with the ESO Very Large Telescope has been used to identify variable stars in the dwarf irregular galaxy NGC 6822. We surveyed a 6.8x6.8 arcmin area of the galaxy and detected a total number of 390 candidate variables with the optimal image subtraction technique (Alard C., 2000A&AS..144..363A). Light curves on a magnitude scale were obtained for 262 of these variables. Differential flux light curve are available for the remaining sample. We were able to determine periods and pulsation characteristics for 69 out of the 262 variables with light curves in magnitude scale, they include: 18 RR Lyrae stars (16 ab-type and 2 c-type), 45 Cepheids and 6 binary systems. We also tentatively calibrated 8 of the 128 objects with light curves on a differential flux scale on the assumption that they are ab-type RR Lyrae stars.
- ID:
- ivo://CDS.VizieR/J/MNRAS/350/679
- Title:
- BV photometry of NGC 300 variables
- Short Name:
- J/MNRAS/350/679
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have performed a search for variable stars in the Sculptor Group spiral galaxy NGC 300 using wide-field multi-epoch BV photometry up to a limiting magnitude V~23. Apart from the Cepheid variables in this galaxy already reported in an earlier paper by Pietrzynski et al. (2002, Cat. <J/AJ/123/789>) and the variable blue supergiants reported by Bresolin et al. (2002ApJ...567..277B), we have identified 26 additional periodic variables, with periods ranging from 0.2 to 190d, and 121 slow variables. Two of these newly discovered variables are Galactic foreground stars (one of them is a W UMa system), and three correspond to previously identified Wolf-Rayet stars. 16 stars are new Cepheids, and the other objects span a huge range in colours and represent a mixture of different types of luminous variables.
- ID:
- ivo://CDS.VizieR/J/A+A/483/253
- Title:
- BV photometry of NGC 2099 variables
- Short Name:
- J/A+A/483/253
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Rotation and solar-type magnetic activity are closely related to each other in main-sequence stars of G or later spectral types. The presence and level of magnetic activity depend on star's rotation, and rotation itself is strongly influenced by strength and topology of the magnetic fields. Open clusters represent especially useful targets to investigate the connection between rotation and activity. The open cluster NGC 2099 has been studied as a part of the RACE-OC project (Rotation and ACtivity Evolution in Open Clusters), which is aimed at exploring the evolution of rotation and magnetic activity in the late-type members of open clusters of different ages. We collected time series CCD photometric observations of this cluster in January 2004, and we determined the presence of periodicities in the flux variation related to the stellar rotation by Fourier analysis. We investigate the relations between activity manifestations, such as the light curve amplitude, and global stellar parameters. We have discovered 135 periodic variables, 122 of which are candidate cluster members. Determination of rotation periods of G- and K-type stars has allowed us to better explore the evolution of angular momentum at an age of about 500Myr. In our analysis, we have also identified 3 new detached eclipsing binary candidates among cluster members. A comparison with the older Hyades cluster (~625Myr) shows that the newly-determined distribution of rotation periods is consistent with the scenario of rotational braking of main-sequence spotted stars as they age. However, a comparison with the younger M34 cluster (~200Myr) shows that the G8-K5 members of these clusters have the same rotation period distribution. That is, G8-K5 members in NGC 2099 seem to have experienced no significant braking in the age range from ~200 to ~500Myr. Finally, NGC 2099 members have a smaller level of photospheric magnetic activity, as measured by light curve amplitude, than in younger stars of the same mass and rotation, suggesting that the activity level also depends on some other age-dependent parameters.
- ID:
- ivo://CDS.VizieR/J/AJ/97/1360
- Title:
- BV photometry of Palomar 12
- Short Name:
- J/AJ/97/1360
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present broadband B,V photometry for 1154 stars in the field of the Galactic globular cluster Palomar 12, based upon direct CCD images obtained with the Canada-France-Hawaii 3.6m and Cerro Tololo 4m telescopes. The overall zero points of our V magnitudes and B-V colors appear to be known to about +/-0.02mag and +/-0.01mag, and our magnitude- and color-scale errors are probably controlled to <0.01mag. Pal 12's main sequence shows an excess fringe of stars along its red edge which are probably binaries; the CM diagram also contains a small number of probable blue stragglers. The principal result of this paper is that the color-magnitude diagram of Pal 12 is anomalous, in the sense that we cannot fake all of its principal sequences lie near or between those of the well studied and presumably typical Galactic globular clusters 47 Tucanae and M5, even though it lies near or between them in overall heavy-element abundance. The simplest explanation is that Pal 12 is younger than the other two clusters by some 25-30%. Other explanations are also possible, although perhaps somewhat harder to believe. This result greatly strengthens the possibility that age differences are responsible, at least in part, for the anomalous properties of some of the outer-halo globular clusters. Spectroscopic indications are that Pal 12's chemical abundances should also strongly resemble those of the two Galactic globular clusters NGC 288 and NGC 362, which have also been claimed to show age differences in comparison with M5. However, attempts to derive ages for these clusters relative to M5 and Pal 12 are inconclusive, possibly due to some inconsistencies within the available data.
