- ID:
- ivo://CDS.VizieR/J/AJ/122/2569
- Title:
- VI photometry of NGC 288, 362 and 1851
- Short Name:
- J/AJ/122/2569
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present deep V, I photometry of the globular clusters NGC 288, 362, and 1851 obtained during a single observational run under strictly homogeneous conditions. We use the bimodal horizontal branch (HB) of NGC 1851 as a "bridge" to obtain the optimum relative match between the HBs of NGC 288 and NGC 362. In this way we can effectively remove the uncertainties associated with distance, reddening, and inhomogeneities in the absolute calibration, thus obtaining a very robust, purely differential estimate of the age difference between these two clusters. According to the bridge test, NGC 288 is found to be older than NGC 362 by 2+/-1Gyr. The observations were carried out during the nights of 1997 January 2 and 3 at the 2.2 m ESO/MPI telescope at La Silla (Chile), with the EFOSC2 camera equipped with a Loral/Lesser 2048x2048 pixel CCD. The pixel scale is 0.26"/pix, and the effective field of view is 8x8arcmin^2^. The gain is 1.63 e^-^ADU^-^, and the readout noise is 6.3 e^-^rms. The seeing conditions were average during the January 2 night (~1.3") when the NGC 1851 and NGC 288 observations were carried out, and they worsened (~2") during the second night when we observed NGC 362.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/AJ/132/2171
- Title:
- VI photometry of NGC 6293 and NGC 6541
- Short Name:
- J/AJ/132/2171
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present VI photometry of the metal-poor inner halo globular clusters NGC 6293 and NGC 6541 using the WFPC2 on board the Hubble Space Telescope (HST). Our color-magnitude diagrams of the clusters show well-defined blue horizontal-branch populations, consistent with their low metallicities and old ages. NGC 6293 appears to have blue straggler stars in the cluster's central region. We discuss the interstellar reddening and the distance modulus of NGC 6293 and NGC 6541 and obtain E(B-V)=0.40 and (m-M)_0_=14.61 for NGC 6293 and E(B-V)=0.14 and (m-M)_0_=14.19 for NGC 6541. Our results confirm that NGC 6293 and NGC 6541 are clearly located in the Galaxy's central regions (R_GC_<=3kpc).
- ID:
- ivo://CDS.VizieR/J/ApJS/116/263
- Title:
- VI photometry of open clusters
- Short Name:
- J/ApJS/116/263
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- New CCD VI photometric data for 10 template open clusters with accurately determined fundamental parameters are presented. From the observed V versus V-I diagrams of the clusters, fiducial sequences have been defined and transformed into the M_v_ versus (V-I)_0_ diagram by averaging sequences of template open clusters with similar ages. The resulting composite Mv versus (V-I)_0_ diagram presents a homogeneous set of empirical isochrones in the age range between 5Myr and 4Gyr. These empirical isochrones show an overall very good agreement with those computed from stellar evolutionary models. Theoretical isochrones with moderate overshooting fit the observed main sequences better than the canonical ones for clusters older than 600Myr. The present set of empirical isochrones will be useful for the study of faint reddened open clusters
- 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.
- ID:
- ivo://CDS.VizieR/J/AJ/125/1261
- Title:
- VI photometry of Sextans A Cepheids
- Short Name:
- J/AJ/125/1261
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have identified 82 short-period variable stars in Sextans A from deep Wide Field Planetary Camera 2 observations. All the periodic variables appear to be short-period Cepheids, with periods as small as 0.8 days for fundamental mode Cepheids and 0.5 days for first-overtone Cepheids. These objects have been used, along with measurements of the red giant branch (RGB) tip and red clump, to measure a true distance modulus to Sextans A of {mu}0=25.61+/-0.07, corresponding to a distance of d=1.32+/-0.04Mpc. Comparing distances calculated by these techniques, we find that short-period Cepheids (P<2-days) are accurate distance indicators for objects at or below the metallicity of the Small Magellanic Cloud. As these objects are quite numerous in low-metallicity star-forming galaxies, they have the potential for providing extremely precise distances throughout the Local Group. We have also compared the relative distances produced by other distance indicators. We conclude that calibrations of RR Lyrae stars, the RGB tip, and the red clump are self-consistent, but that there appears to be a small dependence of long-period Cepheid distances on metallicity. Finally, we present relative distances of Sextans A, Leo A, IC 1613, and the Magellanic Clouds.
- ID:
- ivo://CDS.VizieR/J/MNRAS/327/1116
- Title:
- VI photometry of Sombrero globular clusters
- Short Name:
- J/MNRAS/327/1116
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We explore the rich globular cluster (GC) system of the nearby Sa galaxy M104, the "Sombrero" (NGC 4594), using archive Wide Field Planetary Camera 2 data. The GC colour distribution is found to be bimodal at the >99 per cent confidence level, with peaks at (V-I)0=0.96+/-0.03 and 1,21+/-0.03. The inferred metallicities are very similar to those of GCs in our Galaxy and M31. However, the Sombrero reveals a much enhanced number of red (metal-rich) GCs compared to other well-studied spirals. Because the Sombrero is dominated by a huge bulge and only has a modest disc, we associate the two subpopulations with the halo and bulge components, respectively. Thus our analysis supports the view that the metal-rich GCs in spirals are associated with the bulge rather than with the disc. The Sombrero GCs have typical effective (half-light) radii of ~2pc with the red ones being ~30 per cent smaller than the blue ones. We identify many similarities between the GC system of the Sombrero and those of both late-type spirals and early-type galaxies. Thus both the GC system and the Hubble type of the Sombrero galaxy appear to be intermediate in their nature.
- ID:
- ivo://CDS.VizieR/J/ApJ/736/24
- Title:
- VI photometry of sources in the halo of NGC253
- Short Name:
- J/ApJ/736/24
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have obtained Magellan/IMACS and HST/ACS imaging data that resolve red giant branch stars in the stellar halo of the starburst galaxy NGC 253. The HST data cover a small area, and allow us to accurately interpret the ground-based data, which cover 30% of the halo to a distance of 30kpc, allowing us to make detailed quantitative measurements of the global properties and structure of a stellar halo outside of the Local Group. The geometry of the halo is significantly flattened in the same sense as the disk, with a projected axis ratio of b/a~0.35+/-0.1. The total stellar mass of the halo is estimated to be M_halo ~2.5+/-1.5x10^9^M_{sun}_, or 6% of the total stellar mass of the galaxy, and has a projected radial dependence that follows a power law of index -2.8+/-0.6, corresponding to a three-dimensional power law index of ~-4. The total luminosity and profile shape that we measure for NGC 253 are somewhat larger and steeper than the equivalent values for the Milky Way and M31, but are well within the scatter of model predictions for the properties of stellar halos built up in a cosmological context. Structure within the halo is seen at a variety of scales: there is small kpc-scale density variation and a large shelf-like feature near the middle of the field. The techniques that have been developed will be essential for quantitatively comparing our upcoming larger sample of observed stellar halos to models of halo formation.
- ID:
- ivo://CDS.VizieR/J/MNRAS/360/185
- Title:
- VI photometry of the Leo II galaxy
- Short Name:
- J/MNRAS/360/185
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present V and I photometry of a 9.4'x9.4' field centered on the dwarf spheroidal galaxy Leo II. The Tip of the Red Giant Branch is identified at I^TRGB^=17.83+/-0.03 and adopting <[M/H]>=-1.53+/-0.2 from the comparison of RGB stars with Galactic templates, we obtain a distance modulus (m-M)_0=21.84+/-0.13, corresponding to a distance D=233+/-15kpc. Two significant bumps have been detected in the Luminosity Function of the Red Giant Branch. The fainter bump (B1, at V=21.79+/-0.05) is the RGB bump of the dominant stellar population while the brightest one (B2, at V=21.36+/-0.05) may be identified as the Asymptotic Giant Branch Clump of the same population. The luminosity of the main RGB bump (B1) suggest that the majority of RGB stars in Leo II belongs to a population that is >~4Gyr younger than the classical Galactic globular clusters. The stars belonging to the He-burning Red Clump are shown to be significantly more centrally concentrated than RR Lyrae and Blue Horizontal Branch stars, probing the existence of an age/metallicity radial gradient in this remote dwarf spheroidal.
- ID:
- ivo://CDS.VizieR/J/A+AS/120/153
- Title:
- VI photometry of Ton 2 cluster
- Short Name:
- J/A+AS/120/153
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Ton 2 is among the less-known Galactic globular clusters. We present for the first time colour magnitude diagrams in the V, I bands. We used the ESO NTT telescope under an excellent seeing of 0.6". The horizontal branch is red and close to the red giant branch, tilted by some differential reddening. The horizontal branch morphology and the red giant branch curvature suggest a metallicity similar to that of 47 Tucanae. We derive a reddening of E(B-V)=1.26 and a distance d_{sun}_=6.4kpc. Therefore, Ton 2 is =~2.0kpc from the Galactic center, and it appears to belong to the bulge population, being however only moderately metal rich.
- ID:
- ivo://CDS.VizieR/J/A+AS/118/303
- Title:
- VI Photometry of variables in NGC 2243
- Short Name:
- J/A+AS/118/303
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Tables 3-13 contain V and I band light curves for 6 variables reported in the paper. Tables 14 and 15 contain VI photometry presented in Figs. 5 and 9, respectively.
