- 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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Search Results
- 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.
- 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.
15404. 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.
- 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/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/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/AJ/123/840
- Title:
- VI photometry of variable stars in Fornax
- Short Name:
- J/AJ/123/840
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a search for variable stars in the Fornax dwarf galaxy covering an area of half a square degree. We have ~30 epochs of VI data. We found and determined periods for more than 500 RR Lyrae, 17 anomalous Cepheids, and six Population II Cepheids. In addition we have 85 candidate long-period variables, the majority of which were previously unknown. We estimate that the average metal abundance of RR Lyrae stars is [Fe/H]~=-1.6dex.
