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7881. VI photometry of M33 star clusters
ID:
ivo://CDS.VizieR/J/A+A/366/498
Title:
VI photometry of M33 star clusters
Short Name:
J/A+A/366/498
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have detected 102 star clusters in M 33, from 35 deep Hubble Space Telescope (HST) WFPC2 fields taken from our program and from the HST archive. Twenty-eight fields have V and I band imaging, and an additional seven fields are imaged in a single V filter. Eighty-two of the clusters were previously unknown. Integrated photometry reveals that 25 clusters have (V-I) colors typical of those found in Galactic globular clusters (only ten of these objects were previously known). Our discovery of 15 new globular cluster candidates increases previous estimates of the old cluster population in M 33 by ~60%. An additional eleven objects (only two were previously known) have colors expected for intermediate age clusters. The new clusters have a range of ages from 6 million years to >15Gyrs, and masses between 10^2^M_{sun}_-10^6^M_{sun}_, although these parameters are estimated from only one color.
7882. VI photometry of new Cepheids in NGC 3198
ID:
ivo://CDS.VizieR/J/ApJ/514/614
Title:
VI photometry of new Cepheids in NGC 3198
Short Name:
J/ApJ/514/614
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report the detection of Cepheid variable stars and a new distance to the Sc spiral NGC 3198. NGC 3198 is one of 25 galaxies that have been observed with the WFPC2 of the Hubble Space Telescope (HST) for the purpose of measuring Cepheid distances. Eighteen of these galaxies were targeted by the HST Key Project on the Extragalactic Distance Scale, whose objective is to calibrate a variety of secondary distant indicators and determine the Hubble constant to an accuracy of 10%. NGC 3198 was selected as part of this sample because its type and orientation make it very suitable as a Tully-Fisher calibrator. The WFPC2 data are comprised of 13 epochs in F555W ({~}V) and five epochs in F814W ({~}I). Two different crowded-field photometry packages (DAOPHOT/ALLFRAME and DoPHOT) were used. The magnitudes derived from these two packages agree to within a few percent. We identified 78 Cepheid candidates in the period range from eight to >50 days, of which 52 were selected for establishing the distance modulus. Period-luminosity relations were constructed in Johnson V and Kron-Cousins I by transforming the F555W and F814W to the standard system. We adopted a distance modulus of {mu}_o_=18.50{+/-}0.10 mag and mean reddening of E(B-V)=0.10 mag to the Large Magellanic Cloud Cepheids and found a true distance modulus to NGC 3198 of {mu}_o_=30.80{+/-}0.16 (random) {+/-}0.12 (systematic) mag. This modulus corresponds to a distance of 14.5 Mpc, with random and systematic errors of {+/-}1.2 and {+/-}0.9 Mpc, respectively.
7883. VI photometry of new Cepheids in NGC 3319
ID:
ivo://CDS.VizieR/J/ApJ/523/540
Title:
VI photometry of new Cepheids in NGC 3319
Short Name:
J/ApJ/523/540
Date:
21 Oct 2021
Publisher:
CDS
Description:
The distance to NGC 3319 has been determined from Cepheid variable stars as part of the Hubble Space Telescope Key Project on the Extragalactic Distance Scale. Thirteen and four epochs of observations, using filters F555W (V) and F814W (I), respectively, were made with the Wide Field Planetary Camera 2. Thirty-three Cepheid variables between periods of 8 and 47 days were discovered. Adopting a Large Magellanic Cloud distance modulus of 18.50{+/-}0.10 mag and extinction of E(V-I)=0.13 mag, a true reddening-corrected distance modulus (based on an analysis employing the ALLFRAME software package) of 30.78 {+/-}0.14 (random) {+/-}0.10 (systematic) mag and the extinction of E(V-I)=0.06 mag were determined for NGC 3319. This galaxy is the last galaxy observed for the HST H_o_ Key Project.
7884. VI photometry of new Cepheids in NGC 4725
ID:
ivo://CDS.VizieR/J/ApJ/512/48
Title:
VI photometry of new Cepheids in NGC 4725
Short Name:
J/ApJ/512/48
Date:
21 Oct 2021
Publisher:
CDS
Description:
The distance to NGC 4725 has been derived from Cepheid variables as part of the Hubble Space Telescope Key Project on the Extragalactic Distance Scale. Thirteen F555W (V) and four F814W (I) epochs of cosmic-ray-split Wide Field and Planetary Camera 2 observations were obtained. Twenty Cepheids were discovered, with periods ranging from 12 to 49 days. Adopting a Large Magellanic Cloud distance modulus and extinction of 18.50{+/-}0.10 mag and E(V-I)=0.13 mag, respectively, a true reddening-corrected distance modulus (based on an analysis employing the ALLFRAME software package) of 30.50{+/-}0.16 (random) {+/-}0.17 (systematic) mag was determined for NGC 4725. The corresponding of distance of 12.6{+/-}1.0 (random) {+/-}1.0 (systematic) Mpc is in excellent agreement with that found with an independent analysis based upon the DoPHOT photometry package. With a foreground reddening of only E(V-I)=0.02, the inferred intrinsic reddening of this field in NGC 4725, E(V-I)=0.19, makes it one of the most highly reddened fields encountered by the HST Key Project to date.
7885. VI photometry of new Cepheids in NGC 2541
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.
7886. VI photometry of new M53 variables
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.
7887. 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.
7888. 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.
7889. 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.
7890. 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.