- ID:
- ivo://CDS.VizieR/J/AJ/133/2737
- Title:
- NGC 3610 globular clusters HST BVI photometry
- Short Name:
- J/AJ/133/2737
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Advanced Camera for Surveys on board the Hubble Space Telescope has been used to obtain deep, high-resolution images of the giant elliptical galaxy NGC 3610, a well-established remnant of a dissipative galaxy merger. These observations supersede previous, shallower observations that revealed the presence of a population of metal-rich globular clusters of intermediate age (~1.5-4Gyr). We detect a total of 580 cluster candidates, 46% more than from the previous WFPC2 images. The new photometry strengthens the significance of the previously found bimodality of the color distribution of clusters.
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- ID:
- ivo://CDS.VizieR/J/AJ/140/2101
- Title:
- NGC 5128 globular clusters photometry
- Short Name:
- J/AJ/140/2101
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new photometry for 323 of the globular clusters in NGC 5128 (Centaurus A), measured for the first time in the g'r'i'z' filter system. The color indices are calibrated directly to standard stars in the g'r'i'z' system and are used to establish the fiducial mean colors for the blue and red (low and high metallicity) globular cluster sequences. We also use previously published spectroscopically measured abundances to establish the conversion between the most metallicity-sensitive colors ((g'-r')_0_,(g'-i')_0_) and metallicity, [Fe/H].
- ID:
- ivo://CDS.VizieR/J/AJ/134/494
- Title:
- NGC 5128 globular clusters UBVRICMT1 phot. & RV
- Short Name:
- J/AJ/134/494
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A new kinematic and dynamic study of the halo of the giant elliptical galaxy NGC 5128 is presented. From a spectroscopically confirmed sample of 340 globular clusters and 780 planetary nebulae, the rotation amplitude, rotation axis, velocity dispersion, and total dynamical mass are determined for the halo of NGC 5128.
- ID:
- ivo://CDS.VizieR/J/MNRAS/437/1609
- Title:
- NGC 2808 HB stars abundances
- Short Name:
- J/MNRAS/437/1609
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an abundance analysis of 96 horizontal branch (HB) stars in NGC 2808, a globular cluster exhibiting a complex multiple stellar population pattern. These stars are distributed in different portions of the HB and cover a wide range of temperature. By studying the chemical abundances of this sample, we explore the connection between HB morphology and the chemical enrichment history of multiple stellar populations. For stars lying on the red HB, we use GIRAFFE and UVES spectra to determine Na, Mg, Si, Ca, Sc, Ti, Cr, Mn, Fe, Ni, Zn, Y, Ba and Nd abundances. For colder, blue HB stars, we derive abundances for Na, primarily from GIRAFFE spectra. We were also able to measure direct non-local thermodynamic equilibrium He abundances for a subset of these blue HB stars with temperature higher than ~9000K. Our results show that: (i) HB stars in NGC 2808 show different content in Na depending on their position in the colour-magnitude diagram, with blue HB stars having higher Na than red HB stars; (ii) the red HB is not consistent with a uniform chemical abundance, with slightly warmer stars exhibiting a statistically significant higher Na content; and (iii) our subsample of blue HB stars with He abundances shows evidence of enhancement with respect to the predicted primordial He content by {Delta}Y=+0.09+/-0.01+/-0.05 (internal plus systematic uncertainty). Our results strongly support theoretical models that predict He enhancement among second-generation(s) stars in globular clusters and provide observational constraints on the second-parameter governing HB morphology.
- ID:
- ivo://CDS.VizieR/J/A+A/565/A100
- Title:
- NGC 288 hot horizontal branch stars abundances
- Short Name:
- J/A+A/565/A100
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- NGC 288 is a globular cluster with a well-developed blue horizontal branch covering the u-jump that indicates the onset of diffusion. It is therefore well suited to study the effects of diffusion in blue horizontal branch (HB) stars. We compare observed abundances with predictions from stellar evolution models calculated with diffusion and from stratified atmospheric models. We verify the effect of using stratified model spectra to derive atmospheric parameters. In addition, we investigate the nature of the overluminous blue HB stars around the u-jump. We defined a new photometric index sz from uvby measurements that is gravity-sensitive between 8000K and 12000K. Using medium-resolution spectra and Stroemgren photometry, we determined atmospheric parameters (Teff, logg) and abundances for the blue HB stars. We used both homogeneous and stratified model spectra for our spectroscopic analyses. The atmospheric parameters and masses of the hot HB stars in NGC 288 show a behaviour seen also in other clusters for temperatures between 9000K and 14000K. Outside this temperature range, however, they instead follow the results found for such stars in {omega} Cen. The abundances derived from our observations are for most elements (except He and P) within the abundance range expected from evolutionary models that include the effects of atomic diffusion and assume a surface mixed mass of 10^-7^M_{sun}_. The abundances predicted by stratified model atmospheres are generally significantly more extreme than observed, except for Mg. When effective temperatures, surface gravities, and masses are determined with stratified model spectra, the hotter stars agree better with canonical evolutionary predictions. Our results show definite promise towards solving the long-standing problem of surface gravity and mass discrepancies for hot HB stars, but much work is still needed to arrive at a self-consistent solution.
- ID:
- ivo://CDS.VizieR/J/AJ/146/57
- Title:
- NGC 6402. I. BV photometry
- Short Name:
- J/AJ/146/57
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present BV photometry of the Galactic globular cluster NGC 6402 (M14), based on 65 V frames and 67 B frames, reaching two magnitudes below the turnoff level. This represents, to the best of our knowledge, the deepest color-magnitude diagram (CMD) of NGC 6402 available in the literature. Statistical decontamination of field stars as well as differential reddening corrections are performed in order to derive a precise ridgeline and hence physical parameters of the cluster. We discuss previous attempts at deriving a reddening value for the cluster, and argue in favor of a value E(B-V)=0.57+/-0.02, which is significantly higher than indicated by either the Burstein & Heiles or Schlegel et al. (corrected according to Bonifacio et al.) interstellar dust maps. Differential reddening across the face of the cluster, which we find to be present at the level of {Delta}E(B-V){approx}0.17mag, is taken into account in our analysis. We measure several metallicity indicators based on the position of the red giant branch (RGB) in the cluster CMD. These give a metallicity of [Fe/H]=-1.38+/-0.07 on the Zinn & West scale and [Fe/H]=-1.28+/-0.08 on the new Carretta et al. (UVES) scale. We also provide measurements of other important photometric parameters for this cluster, including the position of the RGB luminosity function "bump" and the horizontal branch morphology. We compare the NGC 6402 ridgeline with that of NGC 5904 (M5) derived by Sandquist et al., and find evidence that NGC 6402 and M5 have approximately the same age to within the uncertainties, although the possibility that M14 may be slightly older cannot be ruled out.
- ID:
- ivo://CDS.VizieR/J/MNRAS/468/2816
- Title:
- NGC6397 low-mass variable stars
- Short Name:
- J/MNRAS/468/2816
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have conducted a photometric survey of the globular cluster NGC 6397 in a search for variable stars. We obtained ~11h of time-resolved photometric images with one European Southern Observatory-Very Large Telescope using the FOcal Reducer and low dispersion Spectrograph imager distributed over two consecutive nights. We analysed 8391 light curves of stars brighter than magnitude 23 with the 465-nm filter, and we identified 412 variable stars, reaching ~4.8+/-0.2 per cent of variability with time-scales between 0.004 and 2d, with amplitudes variation greater than +/-0.2mag.
- ID:
- ivo://CDS.VizieR/J/A+A/623/A159
- Title:
- NGC6530 member parameters from Gaia-ESO survey
- Short Name:
- J/A+A/623/A159
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In very young clusters, stellar age distribution is the empirical proof of the duration of star formation (SF) and of the physical mechanisms involved in the process. We derived accurate stellar ages for the cluster NGC6530, associated with the Lagoon Nebula to infer its SF history. We use the Gaia-ESO survey observations and Gaia DR2 data, to derive cluster membership and fundamental stellar parameters. We identified 652 confirmed and 9 probable members. The reddening inferred for members and non-members allows us to distinguish MS stars and giants, in agreement with the distances inferred from Gaia DR2 data. The foreground and background stars show a spatial pattern that traces the 3D structure of the nebular dust component. We derive stellar ages for 382 confirmed cluster members and we find that the gravity-sensitive gamma index distribution for M stars is correlated with stellar age. For all members with Teff<5500K, the mean logarithmic age is 5.84 (units of years) with a dispersion of 0.36dex. The age distribution of stars with accretion and/or disk (CTTSe) is similar to that of stars without accretion and without disk (WTTSp). We interpret this dispersion as evidence of a real age spread since the total uncertainties on age determinations, derived from Monte Carlo simulations, are significantly smaller than the observed spread. This conclusion is supported by the evidence of a decreasing of the gravity-sensitive gamma index as a function of stellar ages. The presence of the age spread is also supported by the spatial distribution and the kinematics of old and young members. In particular, members with accretion and/or disk, formed in the last 1Myr, show evidence of subclustering around the cluster center, in the Hourglass Nebula and in the M8-E region, suggesting a possible triggering of star formation events by the O-type star ionization fronts.
- ID:
- ivo://CDS.VizieR/J/MNRAS/355/608
- Title:
- NGC 4649 (M60) globular clusters
- Short Name:
- J/MNRAS/355/608
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present Sloan g and i imaging from the Gemini Multi-object Spectrograph (GMOS) instrument on the Gemini North telescope for the globular cluster (GC) system around the Virgo galaxy NGC 4649 (M60). Our three pointings, taken in good seeing conditions, cover an area of about 90 square arcmin. We detect 2151 unresolved sources. Applying colour and magnitude selection criteria to this source list gives 995 candidate GCs. Our source list is greater than 90 per cent complete to a magnitude of i=23.6, and has little contamination from background galaxies. We find fewer than half a dozen potential ultracompact dwarf galaxies around NGC 4649.
- ID:
- ivo://CDS.VizieR/J/MNRAS/420/1333
- Title:
- NGC 5024 (M53) RR Lyrae VI light curves
- Short Name:
- J/MNRAS/420/1333
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the discovery of amplitude and phase modulations typical of the Blazhko effect in 22 RRc and nine RRab type RR Lyrae stars in NGC 5024 (M53). This brings the confirmed Blazhko variables in this cluster to 23 RRc and 11 RRab stars, which represent 66 and 37 per cent of the total population of RRc and RRab stars in the cluster, respectively, making NGC 5024 the globular cluster with the largest presently known population of Blazhko RRc stars. We place a lower limit of 52 per cent on the overall incidence rate of the Blazhko effect among the RR Lyrae population in this cluster. New data have allowed us to refine the pulsation periods. The limitations imposed by the time span and sampling of our data prevent reliable estimations of the modulation periods. The amplitudes of the modulations range between 0.02 and 0.39mag. The RRab and RRc are neatly separated in the colour-magnitude diagram, and the RRc Blazhko variables are on average redder than their stable counterparts; these two facts may support the hypothesis that the horizontal branch (HB) evolution in this cluster is towards the red and that the Blazhko modulations in the RRc stars are connected with the pulsation mode switch.
