- ID:
- ivo://CDS.VizieR/J/ApJ/507/655
- Title:
- VI photometry of new Cepheids in NGC 2541
- Short Name:
- J/ApJ/507/655
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the detection of Cepheids and a new distance to the spiral galaxy NGC 2541, based on data obtained with the Wide Field Planetary Camera 2 on board the Hubble Space Telescope (HST). A total of 25 exposures (divided into 13 epochs) were obtained using the F555W filter (transformed to Johnson V), and nine exposures were obtained (divided into five epochs) using the F814W filter (transformed to Cousins I). Photometric reduction of the data is performed using two independent packages, DoPHOT and DAOPHOT II/ALLFRAME, which give very good agreement in the measured magnitudes. A total of 34 bona fide Cepheids, with periods ranging from 12 to over 60 days, are identified based on both sets of photometry. By fitting V and I period-luminosity relations, apparent distance moduli are derived assuming a Large Magellanic Cloud distance modulus and mean color excess of {mu}_LMC_=18.50+/-0.10mag and E(B-V)=0.10mag, respectively. Adopting A(V)/E(V-I)=2.45, we obtain a true distance modulus to NGC 2541 of {mu}_0_=30.47+/-0.11 (random) +/-0.12 (systematic) mag (D=12.4+/-0.6 [random] +/-0.7 [systematic] Mpc), and a total (Galactic plus internal) mean color excess E(B-V)=0.08+/-0.05 (internal error) mag.
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- ID:
- ivo://CDS.VizieR/J/A+A/507/803
- Title:
- VI photometry of new M53 variables
- Short Name:
- J/A+A/507/803
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the variable star content of the globular cluster M53 to compute the physical parameters of the constituting stars and the distance of the cluster. Covering two adjacent seasons in 2007 and 2008, new photometric data are gathered for 3048 objects in the field of M53. By using the OIS (optimal image subtraction) method and subsequently TFA (trend filtering algorithm), we search for variables in the full sample by using discrete Fourier transformation and box-fitting least squares method. We select variables based on the statistics related to these methods combined with visual inspection. We identified 12 new variables (2 RR Lyrae stars, 7 short periodic stars - 3 of them are SX Phe stars - and 3 long-period variables). No eclipsing binaries were found in the present sample. Except for the 3 (hitherto unknown) Blazhko RR Lyrae (two RRab and an RRc) stars, no multiperiodic variables were found. We showed that after proper period shift, the PLC (period-luminosity-color) relation for the first overtone RR Lyrae sample tightly follows the one spanned by the fundamental stars. Furthermore, the slope is in agreement with that derived from other clusters. Based on the earlier Baade-Wesselink calibration of the PLC relations, the derived reddening-free distance modulus of M53 is 16.31+/-0.04mag, corresponding to a distance modulus of 18.5mag for the Large Magellanic Cloud. From the Fourier parameters of the RRab stars we obtained an average iron abundance of -1.58+/-0.03 (error of the mean). This is ~0.5dex higher than the overall abundance of the giants as given in the literature and derived in this paper from the three-color photometry of giants. We suspect that the source of this discrepancy (observable also in other, low-metallicity clusters) is the lack of a sufficient number of low-metallicity objects in the calibrating sample of the Fourier method.
20873. VI photometry of NGC 5634
- ID:
- ivo://CDS.VizieR/J/AJ/124/915
- Title:
- VI photometry of NGC 5634
- Short Name:
- J/AJ/124/915
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first (V, V-I) color-magnitude diagram (CMD) for the poorly studied globular cluster NGC 5634. The CMD shows a steep red giant branch (RGB) and a predominantly blue horizontal branch (HB): both these characteristics suggest a low metal content for this cluster. The data were obtained at the 3.52 m Italian Telescopio Nazionale Galileo (Roque de los Muchachos, La Palma, Canary Islands, Spain), using the LSR DoLoRes Camera equipped with a 2048x2048 pixel thinned and back-illuminated Loral CCD array.
20874. VI photometry of NGC 6426
- ID:
- ivo://CDS.VizieR/J/AJ/112/1054
- Title:
- VI photometry of NGC 6426
- Short Name:
- J/AJ/112/1054
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A color-magnitude diagram of the globular cluster NGC 6426 has been constructed from photometry in the V and I passbands. The cluster has the steep giant branch indicative of a very metal-poor composition. Following the technique of Sarajedini (1994AJ....107..618S), we derive [Fe/H]=-2.31+/-0.10 and E(V-I)=0.54+/-0.03 [E(B-V)=0.40+/-0.02] from a comparison with the giant branches of other globular clusters. These values are very close to the ones obtained from photometry of the cluster's integrated light, and the weighted means of our results and the previous ones are [Fe/H]=-2.28+/-0.09 and E(B-V)=0.41+/-0.02. The mean V magnitude of the horizontal branch (HB) at the instability strip is 18.12+/-0.05, from which we estimate that NGC 6426 lies 17.4kpc from the Sun, 11.5kpc from the galactic center, and 4.9kpc from the galactic plane. NGC 6426 resembles NGC 5466 and M68 in both [Fe/H] and HB morphology. The HB of NGC 6426 overlaps the one in M15 from the red HB to M15's gap in the blue HB, but there is no evidence of significant numbers of faint blue HB stars in NGC 6426 that are analogous to the ones constituting the "extended HB" in M15.
20875. VI photometry of NGC 6397
- ID:
- ivo://CDS.VizieR/J/A+A/425/509
- Title:
- VI photometry of NGC 6397
- Short Name:
- J/A+A/425/509
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We used VLT-FORS1 data to obtain photometry for stars located within 10 arcmin from the center of the cluster NGC 6397. The data taken in service mode in 1999 (field2, RA=17 41 03.5, DE=-53 45 36) and in 2000 (field1, RA=17 41 14.3, DE=-53 44 27.6) were retrieved electronically from the ESO-STECF archive (proposals: 63.H-0721(A) and 65.H-0531(B)). The resulting V, V-I photometry reachs a limiting magnitude of V~27. As our fields were affected by a large number of saturated stars and, as the photometric procedures can include those peaks in the final photometric catalogue, we decided to eliminate from the catalogue the spurious identifications before performing the data analysis. In this way, a total of 15081 and 11161 objects were detected, respectively, in the fields f1 and f2. We used the 7059 objects in common between these two fields to optimize our photometry by computing a weighted average between the values of the magnitudes of a given star in each catalogue and to transform the frame coordinates to a common coordinate system referred to the field f2. At the end of this procedure an homogeneous set of instrumental magnitudes, color and position were obtained for a total of 19228 objects.
20876. VI photometry of NGC 2157
- ID:
- ivo://CDS.VizieR/J/AJ/115/592
- Title:
- VI photometry of NGC 2157
- Short Name:
- J/AJ/115/592
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have carried out Wide Field Planetary Camera 2 V- and I-band imaging of the young LMC cluster NGC 2157. Construction of a color-magnitude diagram and isochrone fitting yield an age of {tau}=10^8^yr, a reddening E(B-V)=0.1, and a distance modulus of 18.4mag. Our data cover the mass range 0.75M_{sun}_<=m<=5.1M_{sun}_. We find that the cluster mass function changes significantly from the inner regions to the outer regions, becoming steeper (larger number of low-mass stars relative to high-mass stars) at larger radii. The age of NGC 2157 is comparable to its two-body relaxation timescale only in the cluster core. The observed steepening of the mass function at larger radii is therefore most likely an initial condition of the cluster stars. Such initial conditions are predicted in models of cluster star formation in which dissipative processes act more strongly upon more massive stars.
- 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.
- 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.
