- ID:
- ivo://CDS.VizieR/J/A+A/566/A39
- Title:
- UBVI photometry of Melotte 66
- Short Name:
- J/A+A/566/A39
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Multiple generations of stars are routinely encountered in globular clusters, but no convincing evidence has been found in Galactic open clusters up to date. In this paper we use new photometric and spectroscopic data to search for multiple stellar population signatures in the old, massive open cluster, Melotte 66. The cluster is know to have a red giant branch wide in color, which could be an indication of metallicity spread. Also the main sequence is wider than what expected from photometric errors only. This evidence might be associated either with differential reddening or with binaries. Both hypothesis have, however, to be evaluated in detail before recurring to the presence of multiple stellar populations. New, high-quality, CCD UBVI photometry have been acquired to this aim, together with high-resolution spectroscopy of seven clump stars, complemented with literature data, thus doubling the number of clump stars member of the cluster for which high-resolution spectroscopy is available. All this new material is carefully analyzed in search for any manifestation, either spectroscopic or photometric, of multiple populations among the cluster stars. Our photometric study confirms that the width of the main sequence close to the turn off point is entirely accounted for by binary stars and differential reddening, with no need to advocate more sofisticated scenarios, like metallicity spread or multiple main sequences. By constructing synthetic color-magnitude diagrams, we infer that the binary fraction has to be as large as 30%, and their mass ratio in the range 0.6-1.0. As a by-product of our simulations, we provide new estimates of the cluster fundamental parameters. We measure a reddening E(B-V)=0.15+/-0.02, and confirm the presence of a marginal differential reddening. The distance to the cluster is 4.7^+0.2^_-0.1_kpc, and the age is 3.4+/-0.3Gyr, somewhat younger and better constrained than previous estimates. Our detailed abundance analysis reveals that, overall, Melotte 66 looks like a typical object of the old thin disk population, with no significant spread in any of the chemical species we could measure. Finally, we perform a photometric study of the blue straggler star population, and argue that their number in Melotte 66 has been significantly over-estimated in the past. The analysis of their spatial distribution supports the scenario they are most probably primordial binaries.
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Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/441/L36
- Title:
- UBVI photometry of NGC4337
- Short Name:
- J/MNRAS/441/L36
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Galactic open clusters do not survive long in the high-density regions of the inner Galactic disc. Inside the solar ring only 11 open clusters are known with ages older than 1Gyr. We show here, basing on deep, high-quality photometry, that NGC 4337, contrary to earlier findings, is indeed an old open cluster. The cluster is located very close to the conspicuous star cluster Trumpler 20, as well misclassified in the past, and that has received so much attention in recent years. NGC 4337 shows a significant clump of He-burning stars which was not detected previously. Its beautiful colour-magnitude diagram is strikingly similar to the one of the classical old open clusters IC 4651, NGC 752, and NGC 3680, and this suggests similar age and composition. A spectroscopic study is much needed to confirm our findings. This, in turn, would also allow us to better define the inner disc radial abundance gradient and its temporal evolution. To this aim, a list of clump star candidates is provided.
- 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.
- ID:
- ivo://CDS.VizieR/J/A+A/466/931
- Title:
- UBVI photometry of NGC 1901
- Short Name:
- J/A+A/466/931
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Observations indicate that present-day star formation in the Milky Way disk takes place in stellar ensembles or clusters rather than in isolation. Bound, long-lived stellar groups are known as open clusters. They gradually lose stars and are severely disrupted in their final evolutionary stages, leaving an open cluster remnant made up of a few stars. In this paper, we study in detail the stellar content and kinematics of the poorly populated star cluster NGC 1901. This object appears projected against the Large Magellanic Cloud. The aim of the present work is to derive the current evolutionary status, binary fraction, age, and mass of this stellar group. These are fundamental quantities to compare with those from N-body models in order to study the most general topic of star cluster evolution and dissolution. The analysis is performed using wide-field photometry in the UBVI pass-band, proper motions from the UCAC.2 catalog, and 3 epochs of high-resolution spectroscopy, as well as results from extensive N-body calculations. The star group NGC 1901 is found to be an ensemble of solar metallicity stars, 400+/-100Myr old, with a core radius of 0.23pc, a tidal radius of 1.0pc, and a location at 400+/-50pc from the Sun. Out of 13 confirmed members, only 5 single stars have been found. Its estimated present-day binary fraction is at least 62%. The calculated heliocentric space motion of the cluster is not compatible with possible membership in the Hyades stream. Our results show that NGC 1901 is a clear prototype of an open cluster remnant characterized by a high value of the binary fraction and a significant depletion of low-mass stars. In light of numerical simulations, this is compatible with NGC 1901 being what remains of a larger system initially made of 500-750 stars.
- ID:
- ivo://CDS.VizieR/J/AJ/108/585
- Title:
- UBVI photometry of NGC 6791
- Short Name:
- J/AJ/108/585
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have investigated the reddening and metallicity of NGC 6791 using photoelectric and Charge Coupled Devices (CCD) photometry at the KPNO 0.9m telescope. The reddenings to 31 photoelectrically measured stars in the direction of the cluster were determined individually yielding a mean E(B-V)=0.10+/-0.02. Broadband UBVI CCD images were taken with a 512x512 CCD and included deep frames on the center, plus a 3x3 mosaic of the cluster.
- 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+A/385/471
- Title:
- UBVI photometry of NGC 7036 and NGC 7772
- Short Name:
- J/A+A/385/471
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present CCD UBVI observations obtained in the field of the two previously unstudied dissolving open cluster candidates NGC 7036 and NGC 7772. Our analysis suggests that both the objects are Open Cluster Remnants (OCR). NGC 7036 is an open cluster remnant with a core radius of about 3-4 arcmin. We derive for the first time estimates of its fundamental parameters. We identify 17 likely members that define a group of stars at 1kpc from the Sun, with a low reddening E(B-V)~0.1, and with an age of about 3-4Gyr. As for NGC 7772, we identify 14 likely members, that define a group of stars with a very low reddening (E(B-V)~0.03), are 1.5Gyr old and are located about 1.5kpc from the Sun.
- ID:
- ivo://CDS.VizieR/J/A+A/387/479
- Title:
- UBVI photometry of NGC 133 and NGC 1348
- Short Name:
- J/A+A/387/479
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present CCD UBVI observations obtained in the field of the previously unstudied northern open clusters NGC 133 and NGC 1348. We argue that NGC 133 is a heavily contaminated cluster, for which we identify 13 candidate members down to V=14.50mag on the basis of the position in the two-color Diagram. Membership has been checked against proper motions from Tycho 2, whenever available. The cluster turns out to have a reddening E(B-V)=0.60+/-0.10mag, to be 630+/-150pc distant from the Sun, and to have an age less than 10Myrs. NGC 1348 is a more reddened clusters (E(B-V)=0.85+/-0.15mag) for which we isolate 20 members. The cluster lies at a distance of 1.9+/-0.5kpc away from the Sun, and has an age greater than 50Myrs. Observations were carried out with the AFOSC camera at the 1.82m Copernico telescope of Cima Ekar (Asiago, Italy), in the photometric night of December 18, 2001.
