We present the results of a deep radio observation of the globular cluster NGC 2808. We show that there are no sources detected within the core of the cluster, placing constraints on both the pulsar population of the cluster and the mass of a possible intermediate mass black hole in NGC 2808. We compare the results for this cluster with other constraints on intermediate mass black holes derived from accretion measures. With the exception of G1 in M~31 which has previously shown radio emission, even with considerably more conservative assumptions, only the clusters with the poorest of observational constraints are consistent with falling on the $M_{BH}-σ$ relation. This result is interpreted in terms of the fundamental differences between galaxies and globular clusters.
We have obtained spectra for 103 published globular cluster candidates in the Sculptor Group galaxies NGC 253 and NGC 55. On the basis of radial velocities and digitized plate images, 14 globular clusters are identified in NGC 253 and one probable globular cluster is identified in NGC 55. The majority of the objects in the sample appear to be background galaxies. We have obtained and analysed COSMOS plate scans of NGC 253 and NGC 55 and use these along with the spectroscopically identified clusters to define new samples of globular cluster candidates in the two galaxies which should have reduc…
We present VI photometry of the metal-poor inner halo globular clusters NGC6293 and NGC6541 using the planetary camera of the WFPC2 on board HST. Our color-magnitude diagrams of the clusters show well-defined BHB populations, consistent with their low metallicities and old ages. NGC6293 appears to have blue straggler stars in the cluster's central region. We discuss the interstellar reddening and the distance modulus of NGC6293 and NGC6541 and obtain E(B-V) = 0.40 and (m-M)_0 = 14.61 for NGC6293 and E(B-V) = 0.14 and (m-M)_0 = 14.19 for NGC6541. Our results confirm that NGC6293 and NGC6541 are…
We combine near-infrared photometry obtained with the VLT/ISAAC instrument and archival HST/WFPC2 optical images to determine VIK magnitudes and colours of globular clusters in two early-type galaxies, NGC 3115 and NGC 4365. The combination of near-IR and optical photometry provides a way to lift the age-metallicity degeneracy. For NGC 3115, the globular cluster colours reveal two major sub-populations, consistent with previous studies. By comparing the V-I, V-K colours of the NGC 3115 globular clusters with SSP models, we find that the colour difference between the two >10 Gyr old major sub-p…
In this third paper of our series on near-IR and optical photometry of globular cluster systems in early-type galaxies we concentrate on the photometric results for NGC 5846 and NGC 7192, two group ellipticals, and on a first comparison between the globular cluster systems investigated so far. In NGC 5846 the colour-colour diagram shows clear bi-modality in (V-K), which is confirmed by a KMM test. The mean colour of both peaks were estimated to be (V-K) =2.57+/-0.06 (blue) and (V-K)=3.18+/-0.06 (red). The situation in NGC 7192 is different, in that the colour-colour diagram gives no evidence f…
We present near-infrared photometry of the globular cluster systems of the early-type galaxies NGC 4472, NGC 4594, NGC 3585, and NGC 5813. We combine these near-infrared data, obtained with PANIC at the Magellan Baade 6.5m telescope, with archival optical HST and FORS/VLT data, and use the optical to near-infrared colors to constrain the ages and metallicities of the globular clusters around the target galaxies. For NGC 4472 we have the most extensive near-infrared and optical photometric dataset. These colors show that the NGC 4472 globular cluster system has a broad metallicity distribution …
We discuss the Oosterhoff classification of the unusual, metal-rich globular clusters NGC 6388 and NGC 6441, on the basis of new evolutionary models computed for a range of metallicities. Our results confirm the difficulty in unambiguously classifying these clusters into either Oosterhoff group, and also question the view that RR Lyrae stars in Oosterhoff type II globular clusters can all be evolved from a position on the blue zero-age horizontal branch.
The millisecond pulsars discovered in globular clusters are diagnostic tools for studying the dynamics of the clusters, the intracluster ionized gas and the evolution of the binaries embedded in the cluster. In the first two years of a search at 1.4 GHz in progress at the Parkes radio telescope 12 new millisecond pulsars have been discovered in 6 globular clusters in which no pulsars were previously known. The scientific fall-back of these discoveries is here discussed for the case of two globular clusters: NGC 6397 and NGC 6752.
We present a study of the globular cluster systems of two edge-on spiral galaxies, NGC4565 and NGC5907, from WFPC2 images in the F450W and F814W filters. The globular cluster systems of both galaxies appear to be similar to the Galactic globular cluster system. In particular, we derive total numbers of globular clusters of N_{GC}(4565)= 204+/-38 {+87}{-53} and N_{GC}(5907)=170+/-41 {+47}{-72} (where the first are statistical, the second potential systematic errors) for NGC4565 and NGC5907, respectively. This determination is based on a comparison to the Milky Way system, for which we adopt a t…
The presence of two globular cluster subpopulations in early-type galaxies is now the norm rather than the exception. Here we present two more examples for which the host galaxy appears to have undergone a recent merger. Using multi-colour Keck imaging of NGC 1052 and NGC 7332 we find evidence for a bimodal globular cluster colour distribution in both galaxies, with roughly equal numbers of blue and red globular clusters. The blue ones have similar colours to those in the Milky Way halo and are thus probably very old and metal-poor. If the red GC subpopulations are at least solar metallicity, …
Some of the properties of the globular clusters in NGC 5128 are compared to those of Galactic globular clusters. Assuming the color- metallicity relations that hold for Galactic globular clusters then the metal-poor clusters in NGC 5128 that have [Fe/H] < -1.80 are significantly fainter than are the more metal-rich globulars in that galaxy. No such metallicity dependent luminosity difference is observed among the globular clusters associated with the Milky Way. Furthermore the NGC 5128 cluster sample contains two objects that, on the basis of their observed colors, appear to be super metal-poo…
The Fornax cluster galaxies NGC 1399 and NGC 1404 are ideal for studying the effects of a cluster environment on globular cluster systems. Here we present new optical imaging of these two galaxies from both the Hubble Space Telescope's Wide Field and Planetary Camera 2 and the Cerro Tololo Inter-American Observatory's 1.5m telescope. The combination of both data sets provides unique insight on the spatial and colour distribution of globular clusters. From B-I colours, we find that both galaxies have a broad globular cluster metallicity distribution that is inconsistent with a single population…
We present high-quality near-Infrared photometry of four Bulge metal-rich globular clusters, namely: NGC 6304, NGC 6569, NGC 6637 and NGC 6638. By using the observed Colour-Magnitude Diagrams we derived a photometric estimates of the cluster reddening and distance. We performed a detailed analysis of the Red Giant Branch, presenting a complete description of morphologic parameters and evolutionary features (Bump and Tip). Photometric estimates of the cluster metallicity have been obtained by using the updated set of relations (published by our group) linking the metal abundance to a variety of…
We report the first results of an ongoing spectroscopic survey of blue horizontal branch stars in the metal-rich ([Fe/H] ~ -0.5) globular clusters NGC 6388 and NGC 6441. Based on data obtained with the ESO-New Technology Telescope (NTT), we provide gravities and temperatures for four stars in NGC 6388 and three stars in NGC 6441. These results are marginally inconsistent with the predictions of canonical evolutionary theory, but disagree strongly with all non-canonical scenarios that explain the sloped horizontal branches seen in the colour-magnitude diagrams of these clusters.
The distribution of stars in the outer part of the sparse globular cluster NGC 5466 provides evidence for possible tidal mass loss after a recent disk-shock near the solar circle.
We investigate the kinematics of a combined sample of 74 globular clusters around NGC 1399. Their high velocity dispersion, increasing with radius, supports their association with the gravitational potential of the galaxy cluster rather than with that of NGC 1399 itself. We find no evidence for rotation in the full sample, although some indication for rotation in the outer regions. The data do not allow us to detect differences between the kinematics of the blue and red sub-populations of globular clusters. A comparison between the globular cluster systems of NGC 1399 and those of NGC 1404 and…
We present radial and rotation (v sini) velocity measurements, from UVES+VLT high resolution spectra of 61 stars in the blue horizontal branches (HB) of the Galactic globular clusters NGC 1904 (M79), NGC 2808, NGC 6093 (M80), and NGC 7078 (M15). The data reduction and the velocity determination, based on cross-correlation techniques, are discussed in detail. Most of this database has been used by Recio-Blanco et al. (2002) in their analysis of the rotation velocity properties of blue HB stars. Here we present additional data for NGC 2808. We confirm the results of the previous paper, in partic…
We have carried out spectrophotometry in the range 3600--9700Å~ of five globular clusters in NGC 5128 for which previous photometric studies suggested a high metal content. We compare the equivalent widths of a set of metallic features of the NGC 5128 clusters with those of well-studied Galactic and M31 globular clusters. This enables us to derive a reliable ranking and estimate of the metallicity for the NGC 5128 clusters. The reddening is obtained from the comparison of the continuum distribution of the observed clusters with those of reference clusters. The present spectroscopic study clari…
I present multiband optical and UV Hubble Space Telescope photometry of the two Galactic globular clusters NGC6388 and NGC6441, in order to investigate the nature of the physical mechanism(s) responsible for the existence of an extended blue tail and of a slope in the horizontal branch. Further evidence that the horizontal branch tilt cannot be interpreted as an effect of differential reddening is provided, while I show that a possible solution of the puzzle is to assume that a small fraction of the stellar population in the two clusters is strongly helium enriched.
We report the discovery of a sizeable, previously unknown variable star population in the Sagittarius dwarf spheroidal globular clusters NGC 5634, Arp 2 and Terzan 8. Location, preliminary pulsation periods and B-band light curves in relative flux units are provided for all these stars.
NGC 3311, the central cD galaxy in the Hydra cluster, was previously thought to host the most metal-rich globular cluster system known. Ground-based Washington photometry had indicated the almost complete absence of the population of globular clusters near [Fe/H] ~ -1 dex, normally dominant in the metallicity distribution functions of giant elliptical galaxies. Lacking the normal metal-poor globular cluster population, NGC 3311 was an outstanding exception among galaxies, not easily understood under any of the current globular cluster formation scenarios. Our HST/WFPC2 data yield normal globul…
We present a preliminary analysis of HST-WFPC2 observations of globular cluster systems in the two brightest galaxies, UGC 9799 (cD) and NGC 1129 (non-cD), located in the center of rich clusters.
We detect stars from the Hipparcos and Tycho Catalogues in the field of view of observations with the ROSAT HRI of three globular clusters. We use the positions of these stars to reduce the systematic error in the positions of X-ray sources in the clusters to ~2'' for omega Cen and NGC6752, and 1'' for NGC6397. We detect three X-ray sources in the core of omega Cen, and four in the core of NGC6752; the data for the center of NGC6397 may be fitted with five or six sources. Outside the cores, but within the half-mass radius of the clusters, we detect two sources in omega Cen, one in NGC6397 and …
We present the chemical compositions for eight bright giants in the globular cluster NGC 1851. Our analysis reveals large star-to-star abundance variations and correlations of the light elements O, Na, and Al, a feature found in every well studied globular cluster. However, NGC 1851 also exhibits large star-to-star abundance variations of the s-process elements Zr and La. These s-process elements are correlated with Al, and anticorrelated with O. Furthermore, the Zr and La abundances appear to cluster around two distinct values. A recent study revealed a double subgiant branch in NGC 1851. Our…
Using the NIRSPEC spectrograph at Keck II, we have obtained infrared echelle spectra covering the range 1.5-1.8 micron for the moderately reddened bulge globular clusters NGC 6342 and NGC 6528, finding [Fe/H]= -0.60 and -0.17 dex, respectively. We measure an average alpha-enhancement of approx +0.33 dex in both clusters, consistent with previous measurements on other metal rich bulge clusters, and favoring the scenario of a rapid bulge formation and chemical enrichment. We also measure very low 12C/13C isotopic ratios (approx 5 in NGC 6342 and approx 8 in NGC 6528), suggesting that extra-mixin…
At the distance of NGC 5128 (3.6 \pm 0.2 Mpc) it is possible to resolve globular clusters with high resolution imaging from the ground, thus allowing the globular cluster candidate selection primarily through their morphological properties. I report the discovery of 71 globular clusters in NGC 5128 on VLT UT1+FORS1 images, including the faintest members (Mv ~ -5) known to date in this galaxy as well as 5 previously known clusters. U- and V-band photometry has been measured for all the candidates and the luminosity function, spanning -10.1<Mv<-4.9 and -9.3<Mu<-3.3, constructed. These are the de…
We present 8 bright globular clusters and/or objects of less familiar nature which we found in the course of scrutinizing the globular cluster system of NGC 1399. These objects are morphologically striking, either by their sizes or by other structural properties. Some of them may be candidates for stripped dwarf galaxy nuclei, emphasizing the possible role of accretion in the NGC 1399 cluster system. They are all highly interesting targets for further deep spectroscopy or HST-imaging. Since these objects have been found within an area of only 42 arcmin**2, we expect many more still to be detec…
We present a Washington C and Kron-Cousins R photometric study of the globular cluster system of NGC 1399, the central galaxy of the Fornax cluster. A large areal coverage of 1 square degree around NGC 1399 is achieved with three adjoining fields of the MOSAIC II Imager at the CTIO 4-m telescope. Working on such a large field, we can perform the first indicative determination of the total size of the NGC 1399 globular cluster system. The estimated angular extent, measured from the NGC 1399 centre and up to a limiting radius where the areal density of blue globular clusters falls to 30 per cent…
We present low-resolution Keck spectroscopy for the globular cluster H VIII in the Local Group dIrr galaxy NGC 6822. We find the metallicity of the cluster to be [Fe/H]= -1.58 +/- 0.28 and the age of the cluster to be 3-4 Gyr, slightly older than but consistent with previous age estimates. H VIII seems to be more metal-poor than most intermediate-age globular clusters in the Local Group, and appears most similar to the anomalous Small Magellanic Cloud clusters Lindsay 113 and NGC 339.
Accurate photometry with HST/ACS shows that the main sequence of the globular cluster NGC 2808 splits into three separate branches. The three MS branches may be associated with complexities of the cluster's horizontal branch and of its abundance distribution. We attribute the MS branches to successive rounds of star formation, with different helium abundances; we discuss possible sources of helium enrichment. Some other massive globulars also appear to have complex populations; we compare them with NGC 2808.
We present multi-colour broad band CCD photometric observations of a few thousands of stars located region of the galactic globular clusters NGC 1904 and NGC 6341. These observations are used to generate their deep colour magnitude diagrams (CMDs) to study overall morphologies of sub giant, red giant, asymptotic giant and horizontal branches. We also determine the main sequence morphology of the NGC 6341. A comparison of their CMDs with the theoretical isochrones given by Demarque et al. (1996) indicates an age of 14 and 16 Gyr for NGC 1904 and NGC 6341 GGCs respectively. We present a new meth…
We have applied Alard's image subtraction method (ISIS v2.1) to the observations of the globular clusters NGC 6388 and NGC 6441 previously analyzed using standard photometric techniques (DAOPHOT, ALLFRAME). In this reanalysis of observations obtained at CTIO, besides recovering the variables previously detected on the basis of our ground-based images, we have also been able to recover most of the RR Lyrae variables previously detected only in the analysis of Hubble Space Telescope WFPC2 observations of the inner region of NGC6441. In addition, we report five possible new variables not found in…
The giant early-type merger remnant galaxy NGC 1316 is an ideal probe for studying the long-term effects of a major merger on its globular cluster (GC) system, given its spectroscopically derived merger age of 3 Gyr which we reported in a recent paper. Here we report several pieces of photometric evidence showing that the second-generation GCs in NGC 1316 are at an evolutionary phase in between that of luminous GCs found in younger merger remnants such as (e.g.) NGC 7252 and that of `red' GCs found in `normal, old' ellipticals. The observation that massive, second-generation GCs formed during …
We have analyzed archival HST/WFPC2 time-series data of the central parts of globular clusters M13, M30 and NGC 6712 in search of variable objects. Among a total of 21 identified variables there are 15 new discoveries. The sample includes nine RR Lyr stars, two SX Phe stars and seven W UMa-type contact binaries. One object is preliminarily classified as a detached eclipsing binary and another as an ellipsoidal variable.
The Antlia galaxy cluster is the third nearest galaxy cluster after Virgo and Fornax. We used the wide-field MOSAIC camera of the 4-m CTIO telescope to search in the brightest cluster galaxies for globular cluster systems, which were detected in the two larger ellipticals -- NGC 3258 and NGC 3268. These galaxies each contain several thousand clusters; NGC 3258 more than NGC 3268. The color distributions of the globular cluster systems are clearly bimodal. The peak colors agree with those of other ellipticals. The radial number density profiles of the globular cluster systems are indistinguisha…
We present measurements of ages, metallicities, and [alpha/Fe] ratios for 16 globular clusters (GC) in NGC 147, NGC 185, and NGC 205 and of the central regions of the diffuse galaxy light in NGC 185, and NGC 205. Our results are based on spectra obtained with the SCORPIO multi-slit spectrograph at the 6-m telescope of the Russian Academy of Sciences. We include in our analysis high-quality HST/WFPC2 photometry of individual stars in the studied GCs to investigate the influence of their horizontal branch (HB) morphology on the spectroscopic analysis. All our sample GCs appear to be old (T>8 Gyr…
We have derived ages and metallicities from co-added spectra of 131 globular clusters associated with the giant elliptical galaxy NGC 4472. Based upon a calibration with Galactic globular clusters, we find that our sample of globular clusters in NGC 4472 span a metallicity range of approximately -1.6 <= [Fe/H] <= 0 dex. There is evidence of a radial metallicity gradient in the globular cluster system, which is steeper than that seen in the underlying starlight. Determination of the absolute ages of the globular clusters is uncertain, but formally, the metal-poor population of globular clusters…
Bimodality is a common feature of globular cluster (GC) color distributions in galaxies. Although it is well known that the GC system of the Milky Way is bimodal in metallicity, this has yet to be directly demonstrated for an elliptical galaxy. We use Lick index measurements from the literature to derive metallicities for 47 GCs in the giant Virgo elliptical galaxy NGC 4472. The resulting distribution shows clear evidence for two metallicity subpopulations of GCs.
We present abundances of C, N, O, F, Na, and Fe in six giant stars of the tidally disrupted globular cluster NGC 6712. The abundances were derived by comparing synthetic spectra with high resolution infrared spectra obtained with the Phoenix spectrograph on the Gemini South telescope. We find large star-to-star abundance variations of the elements C, N, O, F, and Na. NGC 6712 and M4 are the only globular clusters in which F has been measured in more than two stars, and both clusters reveal F abundance variations whose amplitude is comparable to, or exceeds, that of O, a pattern which may be pr…
We studied the properties of the globular cluster systems of five early--type galaxies in the Fornax galaxy cluster: NGC 1374, NGC 1379, NGC 1387, NGC 1427, and the central giant elliptical NGC 1399. From the investigation of their number of globular clusters, specific frequency, color distribution, surface density profile, and spatial distribution, we conclude that our faint ellipticals have no more globular clusters than spirals of the same mass, and neither differ in their other properties. For these galaxies there is no need to imply a different formation scenario of the globular cluster s…
We present a chemical abundance study of three inner old halo clusters NGC 6287, NGC 6293, and NGC 6541, finding [Fe/H] = -2.01 +/- 0.05, -1.99 +/- 0.02, and -1.76 +/- 0.02, respectively, and our metallicity measurements are in good agreement with previous estimates. The mean alpha-element abundances of our program clusters are in good agreement with other globular clusters, confirming previous results. However, the individual alpha-elements appear to follow different trends. The silicon abundances of the inner halo clusters appear to be enhanced and the titanium abundances appear to be deplet…
We use CTIO 4-m Mosaic II images taken with the Washington $CM$ and Harris $R$ filters to identify candidate globular clusters in the six major galaxies of the Sculptor group: NGC 45, NGC 55, NGC 247, NGC 254, NGC 300, and NGC 7793. From follow-up spectroscopy with Hydra-CTIO, we find 19 new globular clusters in NGC 55, NGC 247, NGC 253, and NGC 300, bringing the total number of known Sculptor group globular clusters to 36. The newly discovered clusters have spectroscopic ages consistent with those of old Milky Way globular clusters, and the majority are metal-poor. Their luminosity function c…
Radial velocities of 468 globular clusters around NGC 1399, the central galaxy in the Fornax cluster, have been obtained with FORS2 and the Mask Exchange Unit (MXU) at the ESO Very Large Telescope. This is the largest sample of globular cluster velocities around any galaxy obtained so far. The mean velocity uncertainty is 50 km/sec. This data sample is accurate and large enough to be used in studies of the mass distribution of NGC 1399 and the properties of its globular cluster system. Here we describe the observations, the reduction procedure, and discuss the uncertainties of the resulting ve…
We study the properties of the globular cluster system of the ``old'' merger NGC 5018. We detect a relatively poor globular cluster system, that can be divided into at least two populations based on colors: a small population of blue clusters, aged between several hundred Myr to 6 Gyr, the formation of which was probably induced by the last interaction in the galaxy group; and one (possibly two) population(s) of old(er) clusters that can be associated with the original galaxy(ies). (...)
Galactic globular clusters harbour binary systems that are detected as faint X-ray sources. These close binaries are thought to play an important role in the stability of the clusters by liberating energy and delaying the inevitable core collapse of globular clusters. The inventory of close binaries and their identification is therefore essential. We present XMM-Newton observations of two Galactic globular clusters: NGC 2808 and NGC 4372. We use X-ray spectral and variability analysis combined with ultra-violet observations made with the XMM-Newton optical monitor and published data from the H…
We present new data on the globular cluster system of the elliptical galaxy NGC 3923 which show that it has the most globular clusters per unit luminosity of any non-cluster elliptical yet observed, with $S_N=6.4 \pm1.4$. NGC 3923 is also among the brightest ellipticals outside of a galaxy cluster for which the number of globular clusters has been determined. Our observation of a large number of clusters per unit luminosity (high $S_N$ value) for a bright elliptical in a sparse environment is consistent with the suggestion of Djorgovski \& Santiago that the number of globular clusters is a pow…
Photometry with HST's ACS reveals that the subgiant branch (SGB) of the globular cluster NGC 1851 splits into two well-defined branches. If the split is due only to an age effect, the two SGBs would imply two star formation episodes separated by $\sim$ 1 Gyr. We discuss other anomalies in NGC 1851 which could be interpreted in terms of a double stellar population. Finally, we compare the case of NGC 1851 with the other two globulars known to host multiple stellar populations, and show that all three clusters differ in several important respects.
We report the abundance analysis of one red giant branch star in the metal-poor outer halo globular cluster NGC 5694. We obtain [Fe/H] = -1.93, based on the ionized lines, and our metallicity measurement is in good agreement with previous estimates. We find that [Ca+Ti/2Fe] and [Cu/Fe] of NGC 5694 are about 0.3 -- 0.4 dex lower than other globular clusters with similar metallicities, but similar to some LMC clusters and stars in some dwarf spheroidal galaxies. Differences persist, however, in the abundances of neutron capture elements. The unique chemical abundance pattern and the large Galact…
We present a deep VLT photometry in the regions surrounding the two dominant galaxies of the Antlia cluster, the giant ellipticals NGC 3258 and NGC 3268. We construct the luminosity functions of their globular cluster systems (GCSs) and determine their distances through the turn-over magnitudes. These distances are in good agreement with those obtained by the SBF method. There is some, but not conclusive, evidence that the distance to NGC 3268 is larger by several Mpc. The GCSs colour distributions are bimodal but the brightest globular clusters (GCs) show a unimodal distribution with an inter…
We present velocity dispersion measurements of 14 globular clusters in NGC 5128 (Centarus A) obtained with the MIKE echelle spectrograph on the 6.5m Magellan Clay telescope. These clusters are among the most luminous globular clusters in NGC 5128 and have velocity dispersions comparable to the most massive clusters known in the Local Group, ranging from 10 - 30 km/s. We describe in detail our cross-correlation measurements, as well as simulations to quantify the uncertainties. These 14 globular clusters are the brightest NGC 5128 globular clusters with surface photometry and structural paramet…
We compare the properties of the globular clusters around NGC 1399, NGC 1404 and NGC 1380, the three brightest early-type galaxies in the center of the Fornax galaxy cluster. The globular cluster systems are qualitatively very similar, pointing to similar mechanisms of formation. However, NGC 1399 host a factor of 10 more globular clusters, while being only 0.3-0.4 mag brighter, than the other two galaxies. Further, the kinematics of the globular clusters around NGC 1399 favor the association of a large fraction of them with the galaxy cluster rather than with the giant elliptical. Globular cl…
The two brightest elliptical galaxies in the Eridanus A group, NGC 1400 and NGC 1407, have been observed in both the Washington T_1 and Kron-Cousins I filters to obtain photometry of their globular cluster systems (GCSs). This group of galaxies is of particular interest due to its exceptionally high M/L value, previously estimated at ~3000h, making this cluster highly dark-matter-dominated. NGC 1400's radial velocity (549 km/s) is extremely low compared to that of the central galaxy of Eridanus A (NGC 1407 with $v_\odot$ = 1766 km/s) and the other members of the system, suggesting that it is a…
We present time-series VI photometry of the metal-rich globular cluster NGC 6316. Our color-magnitude diagrams show a predominantly red-clump horizontal branch morphology with no evidence of the blue extensions seen in NGC 6388 and NGC 6441. Our data are in good agreement with published estimates of the reddening and metallicity provided the cluster has an absolute distance modulus of 15.50 mag. We have discovered more than one dozen long-period variable stars in our field of view, and argue that at least seven of them are members of NGC 6316. We have also discovered four RR Lyrae variables, a…
We present the results of a search for variable stars in the central part of the globular cluster NGC 6752. The monitored sample included 160 BHB and 107 EHB stars, respectively. A total of 17 variables were detected of which 14 are new identifications. Five variables are BHB/EHB stars. We report also on identification of a detached eclipsing binary being likely a member of the cluster. Moreover, we detected an outburst of a dwarf nova located in the cluster core.
The central part of the globular cluster NGC 288 was surveyed in a search for short-period variable stars. We obtained the V-band light curves for 4 SX Phe stars and 2 RR Lyrae variables, five of which are new discoveries. All SX Phe stars belong to blue stragglers. We present a color-magnitude diagram including stars from the tip of red giant branch to the level of the main-sequence turnoff. Three likely hot subdwarfs were located on the extension of the blue horizontal branch of the cluster.
We present BVI photometry of the globular cluster NGC 6642 using the SOI imager at the SOAR Telescope. The Colour Magnitude Diagrams (CMD) reach $\approx$1.5mag in V below the main sequence turn-off. A comparison of the overall sequences, and in particular the Red Giant Branch slope of NGC 6642 with that of M~5 indicates that the two clusters must have a similar metallicity of [Fe/H]$\approx$-1.3. We also obtain for NGC 6642 a reddening E(B-V)=0.42$\pm$0.03, and a distance from the Sun of d$_{\odot}$=7.2$\pm$0.5 kpc. Therefore NGC 6642 is a moderately metal-poor globular cluster, spatially loc…
As part of a large HST project to study the formation and evolution of rich star clusters in the Large Magellanic Cloud, we present results for the Galactic bulge metal-rich globular cluster NGC6553. HST observations using WFPC2, NICMOS and STIS were obtained for this cluster. The primarily reason for studying NGC6553 is to allow the possibility to transform our NICMOS and STIS magnitudes directly into stellar masses. This is particularly important for determining the low mass end of the IMF. NGC 6553 was chosen because its metallicity, [Fe/H]$=-0.22\pm 0.05$, is representative of the metallic…
The structure of a very bright (MV = -10.9) globular cluster in NGC 1023 is analyzed on two sets of images taken with the Hubble Space Telescope. From careful modeling of King profile fits to the cluster image, a core radius of 0.55+/-0.1 pc, effective radius 3.7+/-0.3 pc and a central V-band surface brightness of 12.9+/-0.5 mag / square arcsec are derived. This makes the cluster much more compact than Omega Cen, but very similar to the brightest globular cluster in M31, G1 = Mayall II. The cluster in NGC 1023 appears to be very highly flattened with an ellipticity of about 0.37, even higher t…
A globular cluster ~15 My old that contains 5x10^5 Msun of stars inside an 11 pc radius has been found in the nearby spiral galaxy NGC 6946, surrounded by clouds of dust and smaller young clusters inside a giant circular bubble 300 pc in radius. At the edge of the bubble is an arc of regularly-spaced clusters that could have been triggered during the bubble's formation. The region is at the end of a spiral arm, suggesting an origin by the asymmetric collapse of spiral arm gas. The globular is one of the nearest examples of a cluster that is similar to the massive old globulars in the Milky Way…
Using the NIRSPEC spectrograph at Keck II, we have obtained infrared echelle spectra covering the 1.5-1.8 micron range for giant stars in the massive bulge globular clusters NGC6440 and NGC6441. We report the first high dispersion abundance for NGC6440, [Fe/H]=-0.56+/-0.02 and we find [Fe/H]=-0.50+/-0.02 for the blue HB cluster NGC6441. We measure an average $α$-enhancement of ~+0.3 dex in both clusters, consistent with previous measurements of other metal rich bulge clusters, and favoring the scenario of a rapid bulge formation and chemical enrichment. We also measure very low 12C/13C isotopi…
We analyse Keck spectra of 24 candidate globular clusters (GCs) associated with the spiral galaxy NGC 2683. We identify 19 bona fide GCs based on their recession velocities, of which 15 were suitable for stellar population analysis. Age and metallicity determinations reveal old ages in 14 out of 15 GCs. These old GCs exhibit age and metallicity distributions similar to that of the Milky Way GC system. One GC in NGC 2683 was found to exhibit an age of ~3 Gyr. The age, metallicity and alpha-element abundance of this centrally located GC are remarkably similar to the values found for the galactic…
