- ID:
- ivo://CDS.VizieR/J/A+A/469/529
- Title:
- UBVI photometry of NGC 6864
- Short Name:
- J/A+A/469/529
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We carry out and analyze new multi-color photometry of the Galactic globular cluster (GC) M75 in UBVI and focus on the brighter sequences of the color-magnitude diagram (CMD), with particular emphasis on their location in U-based CMD. Specifically, we study the level both of the horizontal (HB) and red giant branches (RGB) relative to the main-sequence turnoff (TO) in the U magnitude. Along with the presented photometry of M75, we use our collection of photometric data on GCs belonging to the metal-poor range, [Fe/H]zw<-1.1dex, obtained from observations with different equipment, but calibrated by standard stars situated in the observed cluster fields. We confirm our earlier finding, and extend it to a larger magnitude range. We demonstrate that Delta(U_TO_^BHB^) expressing the difference in U magnitude between the TO point and the level of the blue HB, near its red boundary, of the metal-poor GCs observed with the EMMI camera of the NTT/ESO telescope is about 0.4-0.5mag smaller as compared to GCs observed with the 100" telescope and 1.3m Warsaw telescope of the Las Campanas Observatory. At the same time, Delta(U_TO_^RGB^), the difference in U magnitude between the TO and RGB inflection (brightest) points, does not show such an apparent dependence on the characteristics of U filters used, but it depends on cluster metallicity. We have shown, for the first time, the dependence of the parameter Delta(U_TO_^RGB^) on [Fe/H] and have estimated its analytical expression, by assuming a linear relation between the parameter and metallicity. Its slope, Delta(U_TO_^RGB^)/Delta[Fe/H]~1.2mag/dex, is approximately a factor of two steeper than that of the dependence of the RGB bump position in the V magnitude on metallicity. The asymptotic giant branch (AGB) clump and features of the RGB luminosity function (LF) of M75 are also discussed. The observations were made on 3 nights, 9-12 October 1998, with the 1.3m Warsaw telescope.
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- ID:
- ivo://CDS.VizieR/J/A+A/497/371
- Title:
- UBVI photometry of NGC 3201
- Short Name:
- J/A+A/497/371
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper aims at further studying one of the nearby Galactic globular clusters (GCs), NGC 3201. It is known to experience notable irregular variability of reddening across its face. By relying on our previous studies and findings and by developing them, we focus on the brighter sequences of the color-magnitude diagram (CMD) and on the cluster's characteristics. We carried out and analyzed new multi-color photometry of NGC 3201 in UBVI reaching below the turnoff point in all passbands in a fairly large cluster field, about 14'x14'. To achieve more reliable results and conclusions, we reduced the negative impact of the irregularly varying reddening and contamination by field stars. With this aim we first estimated mean reddening in different zones of the studied cluster field and then took its variations into account, by reducing them to the same level. We estimated metallicity of NGC 3201 using a new metallicity indicator related to U-based CMDs, recently proposed by us. We find [Fe/H]zw=-1.54+/-0.12dex, which falls between extreme estimates of the cluster's metallicity obtained using different methods or indicators. Also, the location of the RGB bump on the branch corresponds to [Fe/H]zw=-1.46+/-0.15dex. We isolate 73 probable blue straggler (BS) candidates, the largest population found in NGC 3201 so far. They are more centrally concentrated than the lower red giants at the 99.2% level. Their position in the two-color diagram assumes that presumably none of them belongs to BSa of collisional origin. The luminosity function (LF) of the RGB and its features in the low part of the branch are examined and discussed. We also resolve some of the contradictory results of previous publications.
- ID:
- ivo://CDS.VizieR/J/A+A/516/A23
- Title:
- UBVI Photometry of NGC 1261
- Short Name:
- J/A+A/516/A23
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This work studies in more detail the stellar population, including its photometric properties and characteristics, in the rarely studied southern Galactic globular cluster NGC 1261. We focus on the brighter sequences of the cluster's color-magnitude diagram (CMD). Like in our previous works, we rely upon photometry in several passbands to achieve more reliable results and conclusions. We carried out and analyzed new multi-color photometry of NGC 1261 in UBVI reaching below the turnoff point in all passbands in a fairly extended cluster field, about 14'x14'. We found several signs of the inhomogeneity ("multiplicity") in the stellar population. The most prominent of them are: (1) the dependence of the radial distribution of sub-giant branch (SGB) stars in the cluster on their U magnitude, with brighter stars less centrally concentrated at the 99.9% level than their fainter counterparts; (2) the dependence of the location of red giant branch (RGB) stars in the U-(U-B) CMD on their radial distance from the cluster center, with the portion of stars bluer in the (U-B) color increasing towards the cluster outskirts. Additionally, the radial variation of the RGB luminosity function in the bump region is suspected. We assume that both the SGB stars brighter in the U and the RGB stars bluer in the (U-B) color are probably associated with blue horizontal branch stars, because of a similarity in their radial distribution in the cluster. We estimated the metallicity of NGC 1261 from the slope of the RGB in U-based CMDs and the location of the RGB bump on the branch. These metallicity indicators give [Fe/H]_ZW_=-1.34+/-0.16dex and [Fe/H]_ZW_=-1.41+/-0.10dex, respectively. We isolated 18 probable blue straggler candidates. They are more centrally concentrated than the lower red giants of comparable brightness at the 97.9% level. Their photometric characteristics imply that their majority is not consistent with the collisional origin. We also reliably isolated the asymptotic giant branch (AGB) clump and estimated the parameter Delta V_{ZAHB}_^{clump}^=1.01+/-0.06, that is the difference between the V-levels of the zero age HB and the clump.
- ID:
- ivo://CDS.VizieR/J/AJ/114/2381
- Title:
- UBVI photometry of NGC 7252
- Short Name:
- J/AJ/114/2381
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new U, B, V, and I images of the prototypical merger remnant NGC 7252 obtained with the WFPC2 instrument of the Hubble Space Telescope. The photometry reaches about 3 mag deeper than the previous observations with WF/PCI and we detect 499 cluster candidates, most of them previously undiscovered. We can distinguish three populations of star clusters. We confirm the existence of a very luminous, blue population of clusters with a narrow range in color. Comparisons with Bruzual & Charlot (1996, in preparation) models incorporating a Salpeter stellar IMF show that the mean ages of these clusters are 650Myr for [Fe/H]=0.0 and 750 Myr if [Fe/H]=-0.3. Therefore, these are the clusters that formed during the merger event. The upper limit to the effective radii of these objects is 4.8+/-0.4pc (for D=64.4Mpc, H_0_=75), suggesting that they have physical properties like Galactic globular clusters. The second population of clusters is associated with the inner disk. Their (U-B) colors and reddening-free Q values indicate that their light is dominated by O stars and that they have ages less than 10Myr. However, with <R_eff_>=8.3+/-0.6pc, these objects may be more like stellar associations and they may not survive for a significant time. Finally, there is also evidence for the presence of the most luminous of the old, metal-poor globular clusters that belonged to the progenitor galaxies. The cluster luminosity function is a single power law with slope {alpha}~-1.8 down to a limiting magnitude of V=26. The current specific cluster frequency is S_N_=0.6+/-0.3 for old clusters and young clusters with M>10^5^M_{sun}_, but after the remnant has faded for about 15Gyr S_N_ will have increased to about 2.5. The central disk is now resolved into much finer detail than in earlier WF/PCI observations and the light profile of the nuclear region is consistent with a single power law with slope {gamma}=-1.26+/-0.03. After both the main body and the cluster system of NGC 7252 have aged, for several Gyr it may have the properties of a field elliptical.
- ID:
- ivo://CDS.VizieR/J/A+AS/26/353
- Title:
- UBV observations in globular NGC 1904
- Short Name:
- J/A+AS/26/353
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The BV photometric investigation of the Southern globular cluster NGC 1904 was carried out using the 1m telescope of Cerro Las Campanas (CARSO, 2 nights in February 1973 and 2 nights in April 1973), and the 1m telescope at la Silla (ESO, 4 nights in February 1975). The identification of the stars was made by B. Skiff (Lowell Obs.) in October 2010.
- ID:
- ivo://CDS.VizieR/II/248
- Title:
- UBV photometry and proper motions in M13
- Short Name:
- II/248
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The first epoch plates of 8 globular clusters, available in the plate collection of the Pulkovo Observatory, were taken with the normal astrograph at the end of the last and beginning of this century. These plates had been measured previously by N. Gamalei [1948, IzPul, 141] in order to determine the proper motions of the clusters. From 40 to 62 stars were used for this purpose and these were assumed to be cluster members on the basis of their proximity to the cluster centers. The epoch differences ranged from 30 to 45 years. As this time interval has now increased considerably (by about a factor of two), it is planned to redetermine the proper motions of these clusters, using more precise criteria for the selection of stars belonging to the cluster. In the previous study (N. Gamalei [1948, IzPul, 141]) only a limited number of field reference stars were measured, and as more complete data on the cluster, cluster members and field stars is desirable all the star images on the plates in an area 80'x80' will be measured in the present program. For future studies of the orbits of galactic clusters it is important that the absolute proper motions be on one system and therefore special attention should be devoted to this problem. The present paper is a continuation of an investigation of M13 and deals with the determination of the proper motions and U, B, V magnitudes of separate stars and also a redetermination of the proper motions of the cluster. The U, B, V magnitudes of the majority of 923 stars with measured proper motions were found from plates (table 2) taken with the 2 meter Schmidt telescope at Tautenburg and kindly lent to us by Professor N. Richter. The photoelectric standards as given by Savedoff [1956AJ.....61..254S] (table 7) and also U B V magnitudes of six bright field stars (table 8) observed by Mayer were used for calibration. A comparison of the determined B and V magnitudes of stars within an area of about 10'x10' centered on the cluster with those obtained by other authors indicates that the probable external errors do not exceed +/-0.03mag (table 15). However as the photoelectric magnitudes of fainter field stars were not available, a slight systematic error may be present in the derived magnitudes of these stars. Data on the plates used for the determination of the proper motions were given in Kadla [1963AZh....40..691K]. The relative proper motion of M 13, redetermined on the basis of a larger number of cluster members (80 in all, measured on 4 pairs of plates with a mean epoch difference equal to 61.4 years) is found to be {mu}x=+0.0008", {mu}y=-0.0014" with a probable error of +/-0.0002".
- ID:
- ivo://CDS.VizieR/J/AJ/124/3255
- Title:
- UBV photometry in M15
- Short Name:
- J/AJ/124/3255
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this series of two papers, we describe a project with the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope (HST) to measure the line-of-sight velocities of stars in the central few arcseconds of the dense globular cluster M15. This first paper focuses on the observations and reduction of the data. We "scanned" the central region of M15 spectroscopically by consecutively placing the 0.1" HST/STIS slit at 18 adjacent positions. The spectral pixel size exceeds the velocity dispersion of M15. This puts the project at the limit of what is feasible with STIS, and exceedingly careful and complicated data reduction and analysis were required.
- ID:
- ivo://CDS.VizieR/J/AJ/84/1305
- Title:
- UBV photometry in NGC 6528
- Short Name:
- J/AJ/84/1305
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- On the basis of its color-magnitude diagram NGC 6528 is one of the two most metal-rich globular clusters that have so far been found in the Galaxy. Such a conclusion is consistent with Morgan's metallic line-strength classification of the integrated spectrum of this cluster. The reddening of NGC 6528 is estimated to be E(B-V)=0.52+/-0.07, from which R=6.1kpc and Z=-0.4kpc.
- ID:
- ivo://CDS.VizieR/J/AJ/100/1811
- Title:
- UBV photometry in Ruprecht 106
- Short Name:
- J/AJ/100/1811
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- UBV CCD photometry for about 2500 stars in the Galactic globular cluster Ruprecht 106 has been performed yielding the first color-magnitude diagram (CMD) for this object. The CMD extends down to about 2 mag fainter than the main-sequence turnoff (TO). The cluster possesses a remarkably flat horizontal branch which lies completely to the red of the instability strip. From the analysis of the CMD the following basic parameters have been determined: [Fe/H] = -1.09 and primordial helium abundance Yp = 0.20 0.05. A sizable, highly centrally concentrated population of blue stragglers has also been detected. The location and morphology of the mean ridge lines in the CMD of Ruprecht 106 have then been differentially compared with that of the metal-rich cluster 47 Tuc, NGC 362, a cluster of intermediate metallicity, and with two well-studied metal-poor clusters, M68 and NGC 6397. Significant differences in the positions of the TOs are apparent in the comparison with the metal-poor clusters. These differences can be explained if Ruprecht 106 is 4-5 Gyr younger than NGC 6397 and M68, although alternative, less straightforward explanations cannot be ruled out. The horizontal branch morphology fits perfectly into this picture using models with non-solar-scaled abundances ([O/Fe]>0.5), showing that two second parameters are at work in this cluster, i.e., age (the dominant) and O enhancement. If these findings are confirmed, Ruprecht 106 will turn out to be the first young metal-poor Galactic globular cluster discovered, with quite strong implications for the study of the collapse and enrichment of the Galactic halo.
- ID:
- ivo://CDS.VizieR/J/AJ/112/2020
- Title:
- UBV Photometry of globular cluster NGC1841
- Short Name:
- J/AJ/112/2020
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The observations were acquired in two nights, 1993 December 20-22, with the EMMI camera on the NTT telescope at ESO. The photometric limit is close to the cluster main-sequence turnoff; a comparison of the photometry with Walker (1990AJ....100.1532W) shows slight systematic differences . the present magnitudes being fainter by 0.03-0.05mag, and colors being bluer by 0.05mag. The estimated parameters of the populous globular cluster NGC 1841, located approximately 15deg from each of the Magellanic Clouds and probably dynamically associated with the LMC, are: [Fe/H] = -2.0 +/- 0.15 E(B-V) = 0.17 +/- 0.03 mag (m-M)_0_ = 18.26 +/- 0.11 mag (true distance modulus)
