- ID:
- ivo://CDS.VizieR/J/MNRAS/474/2479
- Title:
- Orbital parameters of globular clusters
- Short Name:
- J/MNRAS/474/2479
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a study of the effects of collisional dynamics on the formation and detectability of cold tidal streams. A semi-analytical model for the evolution of the stellar mass function was implemented and coupled to a fast stellar stream simulation code, as well as the synthetic cluster evolution code EMACSS for the mass evolution as a function of a globular cluster orbit. We find that the increase in the average mass of the escaping stars for clusters close to dissolution has a major effect on the observable stream surface density. As an example, we show that Palomar 5 would have undetectable streams (in an SDSS-like survey) if it was currently three times more massive, despite the fact that a more massive cluster loses stars at a higher rate. This bias due to the preferential escape of low-mass stars is an alternative explanation for the absence of tails near massive clusters, than a dark matter halo associated with the cluster. We explore the orbits of a large sample of Milky Way globular clusters and derive their initial masses and remaining mass fraction. Using properties of known tidal tails, we explore regions of parameter space that favour the detectability of a stream. A list of high-probability candidates is discussed.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/AJ/128/3019
- Title:
- Pal 13 blue stragglers and main-sequence binaries
- Short Name:
- J/AJ/128/3019
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present high-precision VI photometry of stars from the middle of the giant branch to about 5mag below the main-sequence turnoff in the globular cluster Palomar 13 based on images obtained with the Keck II 10m telescope. We tabulate a complete sample of blue stragglers in the cluster out to about 18 core radii.
- ID:
- ivo://CDS.VizieR/J/A+A/419/533
- Title:
- Pal 13 UBV, proper motions and radial velocities
- Short Name:
- J/A+A/419/533
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Recently, combining radial velocities from Keck/HIRES echelle spectra with published proper motion membership probabilities, Cote et al. (2002ApJ...574..783C) observed a sample of 21 stars, probable members of Palomar 13, a globular cluster in the Galactic halo. Their projected velocity dispersion sigma_p_=2.2+/-0.4km/s gives a mass-to-light ratio M/L_V_=40^+24^_-17_, about one order of magnitude larger than the usual estimate for globular clusters. We present here radial velocities measured from three different CCD frames of commissioning observations obtained with the new ESO/VLT instrument FLAMES (Fibre Large Array Multi Element Spectrograph). From these data, now publicly available, we measure the homogeneous radial velocities of eight probable members of this globular cluster. A new projected velocity dispersion sigma_p_=0.6-0.9+/-0.3km/s implies Palomar 13 mass-to-light ratio M/L_V_=3-7, similar to the usual value for globular clusters. We discuss briefly the two most obvious reasons for the previous unusual mass-to-light ratio finding: binaries, now clearly detected, and more homogeneous data from the multi-fibre FLAMES spectrograph.
- ID:
- ivo://CDS.VizieR/J/AJ/159/254
- Title:
- Parameters for 453 metal-poor stars in NGC5139
- Short Name:
- J/AJ/159/254
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The most massive and complex globular clusters in the Galaxy are thought to have originated as the nuclear cores of now tidally disrupted dwarf galaxies, but the connection between globular clusters and dwarf galaxies is tenuous with the M54/Sagittarius system representing the only unambiguous link. The globular cluster Omega Centauri ({omega}Cen) is more massive and chemically diverse than M54, and is thought to have been the nuclear star cluster of either the Sequoia or Gaia-Enceladus galaxy. Local Group dwarf galaxies with masses equivalent to these systems often host significant populations of very metal-poor stars ([Fe/H]<-2.5), and one might expect to find such objects in {omega}Cen. Using high-resolution spectra from Magellan-M2FS, we detected 11 stars in a targeted sample of 395 that have [Fe/H] ranging from -2.30 to -2.52. These are the most metal-poor stars discovered in the cluster, and are five times more metal-poor than {omega}Cen's dominant population. However, these stars are not so metal-poor as to be unambiguously linked to a dwarf galaxy origin. The cluster's metal-poor tail appears to contain two populations near [Fe/H]~-2.1 and -2.4, which are very centrally concentrated but do not exhibit any peculiar kinematic signatures. Several possible origins for these stars are discussed.
- ID:
- ivo://CDS.VizieR/J/A+A/618/A15
- Title:
- Parameters of EHB stars in {omega} Cen
- Short Name:
- J/A+A/618/A15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The presence of extreme horizontal branch (EHB) and blue hook stars in some Galactic globular clusters (GGCs) constitutes one of the remaining mysteries of stellar evolution. While several evolutionary scenarios have been proposed to explain the characteristics of this peculiar population of evolved stars, their observational verification has been limited by the availability of spectroscopic data for a statistically significant sample of such objects in any single GGC. In this first paper, we focus on {omega} Centauri, a peculiar, massive GGC that hosts multiple stellar populations. We use non-LTE model atmospheres to derive atmospheric parameters (Teff, log g and N(He)/N(H)) and spectroscopic masses for 152 EHB stars in the cluster. We also search for close binaries among these stars based on radial velocity variations. The majority of our sample consists of sdOB stars that have roughly solar or super-solar atmospheric helium abundances. It is these objects that constitute the blue hook at V>18.5mag in the {omega} Cen colour-magnitude diagram.
- ID:
- ivo://CDS.VizieR/J/MNRAS/450/2692
- Title:
- Parameters of galactic globular clusters
- Short Name:
- J/MNRAS/450/2692
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use our Galactic Globular Cluster Catalog (G2C2) photometry for 111 Galactic globular clusters (GCs) in g and z, as well as r and i photometry for a subset of 60 GCs and u photometry for 22 GCs, to determine the structural parameters assuming King models. In general, the resulting core radii are in good comparison with the current literature values. However, our half-light radii are slightly lower than the literature. The concentrations (and therefore also the tidal radii) are poorly constrained mostly because of the limited radial extent of our imaging. Therefore, we extensively discuss the effects of a limited field of view on the derived parameters using mosaicked Sloan Digital Sky Survey data, which do not suffer from this restriction. We also illustrate how red giant branch (RGB) stars in cluster cores can stochastically induce artificial peaks in the surface brightness profiles. The issues related to these bright stars are scrutinized based on both our photometry and simulated clusters. We also examine colour gradients and find that the strongest central colour gradients are caused by central RGB stars and thus not representative for the cluster light or colour distribution. We recover the known relation between the half-light radius and the Galactocentric distance in the g band, but find a lower slope for redder filters. We did not find a correlation between the scatter on this relation and other cluster properties. We find tentative evidence for a correlation between the half-light radii and the [Fe/H], with metal-poor GCs being larger than metal-rich GCs. However, we conclude that this trend is caused by the position of the clusters in the Galaxy, with metal-rich clusters being more centrally located.
- ID:
- ivo://CDS.VizieR/J/ApJ/590/797
- Title:
- Parameters of galactic globular clusters
- Short Name:
- J/ApJ/590/797
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The relations between the luminosities M_V_, the metallicities [Fe/H], the Galactocentric radii R, and the central concentration indices c of Galactic globular clusters are discussed. It is found that the most luminous clusters rarely have collapsed cores. The reason for this might be that the core collapse timescales for such populous clusters are greater than the age of the Galaxy. Among those clusters for which the structure has not been modified by core collapse, there is a correlation between central concentration and integrated luminosity, in the sense that the most luminous clusters have the strongest central concentration. The outermost region of the Galaxy with R>10kpc was apparently not able to form metal-rich ([Fe/H]>-1.0) globular clusters, whereas such clusters (of which Ter 7 is the prototype) were able to form in some nearby dwarf spheroidal galaxies. It is not yet clear how the popular hypothesis that globular clusters were initially formed with a single power-law mass spectrum can be reconciled with the observation that both (1) Galactic globular clusters with R>80kpc and (2) the globulars associated with the Sagittarius dwarf appear to have bimodal luminosity functions. Presently available data hint at, but are not yet able to establish, the existence of a radial metallicity gradient for metal-poor globular clusters with [Fe/H]<-1.0.
- ID:
- ivo://CDS.VizieR/J/A+A/547/A109
- Title:
- Parameters of HB stars in {omega} Cen
- Short Name:
- J/A+A/547/A109
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze the reddening, surface helium abundance and spectroscopic mass of 115 blue horizontal branch (HB) and blue hook (BH) stars in {omega} Centauri (NGC5139), spanning the cluster HB from the blue edge of the instability strip (T_eff_=8000K) to BH objects with T_eff_~50000K.
- ID:
- ivo://CDS.VizieR/J/ApJ/791/107
- Title:
- Parameters of NGC 5139 SGBs stars
- Short Name:
- J/ApJ/791/107
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- {omega} Centauri is a peculiar globular cluster formed by a complex stellar population. To investigate it, we studied 172 stars belonging to the five SGBs that we can identify in our photometry, in order to measure their [Fe/H] content as well as estimate their age dispersion and the age-metallicity relation. The first important result is that all of these SGBs have a distribution in metallicity with a spread that exceeds the observational errors and typically displays several peaks that indicate the presence of several subpopulations. We were able to identify at least six of them based on their mean [Fe/H] content. These metallicity-based subpopulations are seen to varying extents in each of the five SGBs. Taking advantage of the age sensitivity of the SGB, we showed that, first of all, at least half of the subpopulations have an age spread of at least 2 Gyr. Then, we obtained an age-metallicity relation that is the most complete to date for this cluster. Interpretation of the age-metallicity relation is not straightforward, but it is possible that the cluster (or what we can call its progenitor) was initially composed of two populations with different metallicities. Because of their age, it is very unlikely that the most metal-rich derives from the most metal-poor by some kind of chemical evolution process, so they can be assumed to be two independent primordial objects, or perhaps two separate parts of a single larger object, that merged in the past to form the present-day cluster.
- ID:
- ivo://CDS.VizieR/J/AJ/135/1459
- Title:
- Period of M15 variable stars
- Short Name:
- J/AJ/135/1459
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new BVI CCD photometry for variables in the globular cluster M15. Our photometry was obtained using both the image subtraction package ISIS and DAOPHOT/ALLFRAME. The data were acquired in 2001 on two observing runs on 11 observing nights using the 2m telescope of the Bulgarian National Astronomical Observatory "Rozhen" with a Photometrics CCD camera. For 39 previously known variables, we present a period for the first time, and improved periods were obtained for many previously known variables. Fourteen new variables are reported. We present updated Bailey diagrams for the cluster, and discuss its Oosterhoff classification. Although many of M15's RRab pulsators fall at an intermediate locus between Oosterhoff types I and II (OoII) in the Bailey diagram, we argue that M15 is indeed a bona fide OoII globular cluster.
