- ID:
- ivo://CDS.VizieR/J/A+A/432/851
- Title:
- Distance of 72 Galactic globular clusters
- Short Name:
- J/A+A/432/851
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present distance modulus and reddening determinations for 72 Galactic globular clusters from the homogeneous photometric database of Piotto et al. (2002, cat. <J/A+A/391/945>), calibrated to the HST flight F439W and F555W bands. The distances have been determined by comparison with theoretical absolute magnitudes of the ZAHB. For low and intermediate metallicity clusters, we have estimated the apparent Zero Age Horizontal Branch (ZAHB) magnitude from the RR Lyrae level. For metal rich clusters, the ZAHB magnitude was obtained from the fainter envelope of the red HB. Reddenings have been estimated by comparison of the HST colour-magnitude diagrams (CMD) with ground CMDs of template clusters with low reddening. The homogeneity of both the photometric data and the adopted methodological approach allowed us to obtain highly accurate relative cluster distances and reddenings. Our results are also compared with recent compilations in the literature. Description:
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/619/A13
- Title:
- 28 distant globular clusters CaT metallicities
- Short Name:
- J/A+A/619/A13
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In an earlier paper we presented the first part of a project to obtain metallicities and radial velocities of Galactic globular clusters from multiobject spectroscopy of their member stars using the ESO Very Large Telescope. In this paper we add metallicities and radial velocities for a new sample of 28 globular clusters, including in particular globular clusters in the MW halo and the Galactic bulge. Together with our previous results, this study brings the number of globular clusters with homogeneous measurements to ~69% of those listed in the W. Harris' catalogue. As in our previous work, we have used the CaII triplet lines to derive metallicities and radial velocities. For most of the clusters in this study, this is the first analysis based on spectroscopy of individual member stars. The metallicities derived from the CaII triplet are then compared to the results of our parallel study based on spectral fitting in the optical region and the implications for different calibrations of the CaII triplet line strengths are discussed.
- ID:
- ivo://CDS.VizieR/J/ApJ/689/919
- Title:
- Dynamical evolution of globular clusters
- Short Name:
- J/ApJ/689/919
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We test the hypothesis that metal-poor globular clusters form within disk galaxies at redshifts z>3. We calculate the orbits of model clusters in the time-variable gravitational potential of a Milky Way-sized galaxy, using the outputs of a cosmological N-body simulation. We find that at present the orbits are isotropic in the inner 50kpc of the Galaxy and preferentially radial at larger distances. All clusters located outside 10kpc from the center formed in satellite galaxies, some of which are now tidally disrupted and some of which survive as dwarf galaxies. Mergers of the progenitors lead to a spheroidal spatial distribution of model clusters, although it is more extended than that of Galactic metal-poor clusters and has a somewhat shallower power-law slope of the number density profile, {gamma}~2.7. The combination of two-body relaxation, tidal shocks, and stellar evolution drives the evolution of the cluster mass function from an initial power law to a peaked distribution, in agreement with observations. However, not all initial conditions and not all evolution scenarios are consistent with the observed mass function of the Galactic globular clusters. We find that our best-fitting models require the average cluster density, M/R^3^_h_, to be constant initially for clusters of all mass and to remain constant with time. However, these models do not explain the observed decrease of the mean density with galactocentric distance. Both synchronous formation of all clusters at a single epoch (z=4) and continuous formation over a span of 1.6Gyr (between z=9 and 3) are consistent with the data. For both formation scenarios, we provide online catalogs of the main physical properties of model clusters.
- ID:
- ivo://CDS.VizieR/J/ApJ/347/251
- Title:
- Dynamics of Globular Cluster M15
- Short Name:
- J/ApJ/347/251
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The velocity dispersion as a function of radius in the globular cluster M15 is derived from measurements of 120 individual stars between 0.1' and 4.6' of the cluster center, and from the integrated light of the central cusp. The stellar measurements, with an individual accuracy of 1 km/s, indicate a mean cluster velocity of -107.1+/-0.9 km/s, and a mean velocity dispersion of 9.0+/-0.6 km/s. The velocity dispersion inside 1' varies with radius. The dispersion of the 27 stars within 20" is 14.2+/-1.9 km/s, while that of the 30 stars between 0.5' and 1.2' is 8.4+/-1.4 km/s. The cusp itself appears to have a dispersion of at least 25 km/s. Except for its greater velocity broadening, the spectrum of the integrated light of the cusp is indistinguishable from that formed by superposition of the individual M15 giant spectra, demonstrating that the excess light at the center is due primarily to the normal M15 population. The increase of the dispersion toward the center is not consistent with truncated isothermal (King-Michie) models, for which the velocity dispersion is nearly constant within a few core radii and then falls steeply beyond. The observed behaviour is difficult to reconcile as well with current post-core collapse models, which are also isothermal and whose central energy sources are modest. It is indicative of a nonthermal energy distribution with substantial heating in the central regions; this is consistent with a central black hole of about 1000 M_{sun}_.
- ID:
- ivo://CDS.VizieR/J/AJ/106/1508
- Title:
- Dynamics of globular cluster NGC 362
- Short Name:
- J/AJ/106/1508
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper we have examined the internal dynamics of the globular cluster NGC 362 using a combination of V-band CCD images and echelle spectra of the member red giants. A V-band surface brightness profile (SBP) was constructed from the CCD images, and, after it was determined that the cluster is not post core-collapse, fit with single- and multi-pass King-Michie (KM) models. We found that for small values of the mass function slope, x, anisotropic models were favored while for steeper mass functions isotropic orbits provided superior fits. The total cluster luminosity is 1.70 +/- 0.1 x 10^5 L(Vsun) [assumes (m-M)0 = 14.77]. A total of 285 stellar spectra were obtained of 215 stars for radial velocity determinations. Three stars were obvious nonmembers and four showed strong evidence for radial velocity variations; these latter stars are probably members of binary systems with periods less than a few years. The true cluster binary fraction was determined from simulations to be 0.15 for circular orbits or 0.27 for orbits with a distribution function f(e) = e (e is eccentricity). This relatively high binary detection frequency may indicate that NGC 362 is overabundant in binaries compared to other clusters. The 208 remaining stellar velocities showed no sign of rotation and had kinematics which were incompatible with KM models having isotropic orbits and luminosity profiles consistent with the SBP. Therefore, the best agreement with both the kinematic data and the SBP were for shallow mass functions x = 0.0-0.5 and intermediate amounts of anisotropy in the velocity dispersion tensor. In this best-fit range, the derived cluster mass is M = 2.5-3.5x10^5 Msun for a global mass-to-light ratio of M/L(V) = 1.5-2.0 Msun/L(Vsun). This low value for x is in disagreement with the correlation between x and the height above the Galactic disk seen for a sample of other clusters. The results are also different from the sharp turnup in the low mass end of mass functions derived from the deep luminosity functions of three other globular clusters.
- ID:
- ivo://CDS.VizieR/J/A+A/459/391
- Title:
- Dynamics of NGC 4636 globular cluster system
- Short Name:
- J/A+A/459/391
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first dynamical study of the globular cluster system of NGC 4636. It is the southernmost giant elliptical galaxy of the Virgo cluster and is claimed to be extremely dark matter dominated, according to X-ray observations. Globular clusters are used as dynamical tracers to investigate, by stellar dynamical means, the dark matter content of this galaxy. Several hundred medium resolution spectra were acquired at the VLT with FORS 2/MXU. We obtained velocities for 174 globular clusters in the radial range 0.90'<R<15.5', or 0.5-9R_e_ in units of effective radius. Assuming a distance of 15Mpc, the clusters are found at projected galactocentric distances in the range 4 to 70kpc, the overwhelming majority within 30kpc. The measured line-of-sight velocity dispersions are compared to Jeans-models.
- ID:
- ivo://CDS.VizieR/J/other/Obs/136.168
- Title:
- Early observations of M13 variables
- Short Name:
- J/other/Obs/136.
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In 1900 E.E. Barnard published 37 visual observations of Variable 2 (V2) in the globular cluster M13 made in 1899 and 1900. A review of Barnard's notebooks revealed he made many additional brightness estimates up to 1911, and he had also recorded the variations of V1 starting in 1904. These data provide the earliest-epoch light curves for these stars and thus are useful for studying their period changes. This paper presents Barnard's observations of the M13 variables along with their derived heliocentric Julian dates and approximate V magnitudes. These include 231 unpublished observations of V2 and 94 of V1. How these data will be of value for determining period changes by these stars is described.
- ID:
- ivo://CDS.VizieR/J/MNRAS/122/363
- Title:
- Eggen PV photometry in NGC 7492
- Short Name:
- J/MNRAS/122/363
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Photometry of NGC 7492, a very faint, well resolved cluster, shows that it has a colour-magnitude relation similar in form to that of a typical globular cluster. A well defined but sparsely populated red giant branch is present, along with a horizontal branch, blue stars, and variables. The distance modulus, 17.17, and the distance 27.2kpc., are obtained. The colour excess appears to be negligible. The integrated photographic absolute magnitude is -4.84. The star density in the cluster is unusually low, being approximately 0.06 stars per cubic parsec for stars brighter than +2.5 absolute magnitude. For a description of the PV photometric system, see e.g. <GCPD/31>
- ID:
- ivo://CDS.VizieR/J/AJ/118/1245
- Title:
- Elemental abundances in five stars in M54
- Short Name:
- J/AJ/118/1245
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Chemical abundances in five stars in M54, a globular cluster associated with the Sagittarius dwarf galaxy, have been determined using high-resolution echelle spectra. We find the cluster to have [Fe/H] = -1.55 and possibly halo-normal abundance patterns, although the [O/Fe] and [{alpha}/Fe] ratios lie between solar and the normal halo values. One star shows the combination of low oxygen and enhanced Na and Al, symptomatic of deep mixing of ON-cycle and other proton-capture products; a second star shows a lesser degree of O depletion unaccompanied by Na and Al excesses. In the cluster Eu is also enhanced, indicating that about 30% of the Ba in the cluster is due to the r-process. In general, M54 is similar to globulars of comparable metallicity in the inner Galactic halo, despite its clear association with the Sagittarius dwarf spheroidal.
- ID:
- ivo://CDS.VizieR/J/AJ/127/373
- Title:
- Elemental abundances of 3 red giants in Ter 7
- Short Name:
- J/AJ/127/373
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Chemical abundances in three giants in Terzan 7, a globular cluster associated with the Sagittarius dwarf galaxy, have been determined using high-resolution spectra obtained with the UVES spectrograph on the ESO 8.2m Kueyen telescope. We find the overall metallicity of the stars to be [Fe/H]=-0.61+/-0.07, which is slightly higher than that previously evaluated from photometry and used for the age determination of this cluster. This metallicity yields an age of about 6Gyr, which is slightly lower than derived from previous estimates. The relative abundance ratios of various chemical elements to iron lie between those of its host galaxy's metal-poor and metal-rich stars and reveal an intriguing similarity to the pattern seen in the Large Magellanic Cloud.
