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- ID:
- ivo://CDS.VizieR/J/ApJ/797/15
- Title:
- HST/WFC3 observations in 4 metal-poor GCs of Fornax
- Short Name:
- J/ApJ/797/15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use measurements of nitrogen abundances in red giants to search for multiple stellar populations in the four most metal-poor globular clusters (GCs) in the Fornax dwarf spheroidal galaxy (Fornax 1, 2, 3, and 5). New imaging in the F343N filter, obtained with the Wide Field Camera 3 on the Hubble Space Telescope, is combined with archival F555W and F814W observations to determine the strength of the NH band near 3370{AA}. After accounting for observational errors, the spread in the F343N-F555W colors of red giants in the Fornax GCs is similar to that in M15 and corresponds to an abundance range of {Delta}[N/Fe]~2dex, as observed also in several Galactic GCs. The spread in F555W-F814W is, instead, fully accounted for by observational errors. The stars with the reddest F343N-F555W colors (indicative of N-enhanced composition) have more centrally concentrated radial distributions in all four clusters, although the difference is not highly statistically significant within any individual cluster. From double-Gaussian fits to the color distributions, we find roughly equal numbers of "N-normal" and "N-enhanced" stars (formally ~40% N-normal stars in Fornax 1, 3, and 5 and ~60% in Fornax 2). We conclude that GC formation, in particular, regarding the processes responsible for the origin of multiple stellar populations, appears to have operated similarly in the Milky Way and in the Fornax dSph. Combined with the high ratio of metal-poor GCs to field stars in the Fornax dSph, this places an important constraint on scenarios for the origin of multiple stellar populations in GCs.
- ID:
- ivo://CDS.VizieR/J/ApJ/804/71
- Title:
- HST/WFC3 observations of stars in M15
- Short Name:
- J/ApJ/804/71
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We examine the radial distributions of stellar populations in the globular cluster (GC) M15, using Hubble Space Telescope/Wide Field Camera 3 (WFC3) photometry of red giants in the nitrogen-sensitive F343N-F555W color. Surprisingly, we find that giants with "primordial" composition (i.e., N abundances similar to those in field stars) are the most centrally concentrated within the WFC3 field. We then combine our WFC3 data with Sloan Digital Sky Survey u,g photometry and find that the trend reverses for radii >~1' (3pc) where the ratio of primordial to N-enhanced giants increases outward, as already found by Lardo et al. (2011A&A...525A.114L). The ratio of primordial to enriched stars thus has a U-shaped dependency on radius with a minimum near the half-light radius. N-body simulations show that mass segregation might produce a trend resembling the observed one, but only if the N-enhanced giants are ~0.25M_{sun}_ less massive than the primordial giants, which requires extreme He enhancement (Y>~0.40). However, such a large difference in Y is incompatible with the negligible optical color differences between primordial and enriched giants, which suggest {Delta}Y<~0.03 and thus a difference in turn-off mass of {Delta}M<~0.04M_{sun}_ between the different populations. The radial trends in M15 are thus unlikely to be of dynamical origin and presumably reflect initial conditions, a result that challenges all current GC formation scenarios. We note that population gradients in the central regions of GCs remain poorly investigated and may show a more diverse behavior than hitherto thought.
- ID:
- ivo://CDS.VizieR/J/A+A/624/A25
- Title:
- HST WFC3 photometry of NGC 2419
- Short Name:
- J/A+A/624/A25
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new deep imaging of the central regions of the remote globular cluster NGC 2419, obtained with the F343N and F336W filters of the Wide Field Camera 3 on board the Hubble Space Telescope. The new data are combined with archival imaging to constrain nitrogen and helium abundance variations within the cluster. We find a clearly bimodal distribution of the nitrogen-sensitive F336W-F343N colours of red giants, from which we estimate that about 55% of the giants belong to a population with about normal (field-like) nitrogen abundances (P1), while the remaining 45% belong to a nitrogen-rich population (P2). On average, the P2 stars are more He-rich than the P1 stars, with an estimated mean difference of {Delta}Y~=0.05, but the P2 stars exhibit a significant spread in He content and some may reach {Delta}Y~=0.13. A smaller He spread may also be present for the P1 stars. Additionally, stars with spectroscopically determined low Mg abundances ([Mg/Fe]<0) are generally associated with P2. We find the P2 stars to be slightly more centrally concentrated in NGC 2419 with a projected half-number radius of about 10% less than for the P1 stars, but the difference is not highly significant (p~=0.05). Using published radial velocities, we find evidence of rotation for the P1 stars, whereas the results are inconclusive for the P2 stars, which are consistent with no rotation as well as the same average rotation found for the P1 stars. Because of the long relaxation time scale of NGC 2419, the radial trends and kinematic properties of the populations are expected to be relatively unaffected by dynamical evolution. Hence, they provide constraints on formation scenarios for multiple populations, which must account not only for the presence of He spreads within sub-populations identified via CNO variations, but also for the relatively modest differences in the spatial distributions and kinematics of the populations.
- ID:
- ivo://CDS.VizieR/J/AJ/140/631
- Title:
- HST WFC3/UVIS photometry of omega Cen core
- Short Name:
- J/AJ/140/631
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We used archival multi-band Hubble Space Telescope observations obtained with the Wide Field Camera 3 in the UV-optical channel to present new important observational findings on the color-magnitude diagram (CMD) of the Galactic globular cluster omega Centauri. The ultraviolet (UV) WFC3 data have been coupled with available WFC/ACS optical-band data. The new CMDs, obtained from the combination of colors coming from eight different bands, disclose an even more complex stellar population than previously identified. This paper discusses the detailed morphology of the CMDs.
- ID:
- ivo://CDS.VizieR/J/PAZh/22/847
- Title:
- Identification and coordinates in M4
- Short Name:
- J/PAZh/22/847
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Accurate equatorial coordinates have been determined for 54 variable stars in the globular cluster M 4=NGC 6121.
- ID:
- ivo://CDS.VizieR/J/PAZh/21/509
- Title:
- Identification and coordinates in M5
- Short Name:
- J/PAZh/21/509
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Accurate equatorial coordinates have been determined for 143 variable and suspected variable stars in the globular cluster M5=NGC 5904. For 28 stars, identifications with Kustner (1933VeUSB..26....1K) catalogue were found for the first time.
- ID:
- ivo://CDS.VizieR/J/PAZh/23/454
- Title:
- Identification and coordinates in M 53
- Short Name:
- J/PAZh/23/454
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Equatorial coordinates have been determined for 61 variables in the northern globular cluster M 53 and for 12 variables in the southern globular cluster NGC 2808 with accuracy sufficient for reliable identifications. A number of errors have been revealed in publications on variable starts in M 53.
- ID:
- ivo://CDS.VizieR/J/PAZh/20/693
- Title:
- Identification and coordinates in NGC 5272
- Short Name:
- J/PAZh/20/693
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Equatorial coordinates of variable stars in the globular cluster M3 (NGC 5272) and its nearest surroundings, mainly measured on a plate taken with The Zeiss-1000 telescope, are presented. Positions in a homogeneous system are presented for the first time for objects from the Catalogue of variable stars in globular clusters as well as for GCVS and NSV catalogue stars.
- ID:
- ivo://CDS.VizieR/J/MNRAS/374/399
- Title:
- Infrared star clusters with |b|<20{deg}
- Short Name:
- J/MNRAS/374/399
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We used star density maps obtained from the Two-Micron All-Sky Survey (2MASS) to obtain a sample of star clusters in the entire Galactic Plane with |b|<20{deg}. A total of 1788 star cluster candidates are identified in this survey. Among those are 681 previously known open clusters and 86 globular clusters. A statistical analysis indicates that our sample of 1021 new cluster candidates has a contamination of about 50 per cent. Star cluster parameters are obtained by fitting a King profile to the star density. These parameters are used to statistically identify probable new globular cluster candidates in our sample. A detailed investigation of the projected distribution of star clusters in the Galaxy demonstrates that they show a clear tendency to cluster on spatial scales in the order of 12-25pc, a typical size for molecular clouds.
