Obscured clusters. II. GLIMPSE-C02 – A new metal rich globular cluster in the Milky Way (original) (raw)
Related papers
A deep near-infrared view of the Galactic globular cluster 2 MASS GC 02
Astronomy and Astrophysics, 2007
Context. We have obtained deep infrared images and K-band spectra of the Galactic globular cluster 2 MASS GC 02. A variable star search has also been carried out. Aims. Some basic physical properties of the cluster, such as metallicity, reddening, distance modulus and radial velocity, are derived. Methods. These measurements are based on an analysis of the J − K s versus K s color-magnitude diagram of the cluster. Spectroscopically derived metallicities and radial velocities of 15 stars are presented. In addition, periods and amplitudes are provided for five RR Lyrae stars discovered in the field. Results. The cluster is moderately metal-rich and has a relatively high radial velocity. Its horizontal branch appears to be predominantly red, though our photometry cannot rule out the presence of a blue component as seen in NGC 6388 and NGC 6441. Similar to these two clusters, the detected RR Lyrae stars in GC 02 have anomalously long periods for the cluster's moderately high metallicity, which suggests that it too is an Oosterhoff type III cluster. Conclusions. Comparison with the existing kinematic and abundance information for the Galactic globular clusters shows that GC 02 most probably belongs to the bulge sub population, although an inner halo association cannot be ruled out.
Globular cluster system and Milky Way properties revisited
Astronomy and Astrophysics, 2006
Updated data of the 153 Galactic globular clusters are used to readdress fundamental parameters of the Milky Way, such as the distance of the Sun to the Galactic center, bulge and halo structural parameters and cluster destruction rates. We build a reduced sample, decontaminated of the clusters younger than 10 Gyr, those with retrograde orbits and/or evidence of relation to dwarf galaxies. The reduced sample contains 116 globular clusters that are tested whether formed in the primordial collapse. The 33 metal-rich globular clusters ([Fe/H] ≥ −0.75) of the reduced sample extend basically to the Solar circle and distribute over a region with projected axial-ratios typical of an oblate spheroidal, ∆x : ∆y : ∆z ≈ 1.0 : 0.9 : 0.4. Those outside this region appear to be related to accretion. The 81 metal-poor globular clusters span a nearly spherical region of axial-ratios ≈ 1.0 : 1.0 : 0.8 extending from the central parts to the outer halo, although several clusters in the external region still require detailed studies to unravel their origin as accretion or collapse. A new estimate of the Sun's distance to the Galactic center based on symmetries of the spatial distribution of 116 globular clusters is provided with an uncertainty considerably smaller than in previous determinations using globular clusters, R O = 7.2±0.3 kpc. The metal-rich and metalpoor radial-density distributions flatten for R GC ≤ 2 kpc and are well represented over the full Galactocentric distance range both by a power-law with a core-like term and Sérsic's law; at large distances they fall off as ∼ R −3.9 . Both metallicity components appear to have a common origin, which is different from that of the dark matter halo. Structural similarities of the metal-rich and metalpoor radial distributions with the stellar halo are consistent with a scenario where part of the reduced sample was formed in the primordial collapse, and part was accreted in an early period of merging. This applies to the bulge as well, suggesting an early merger affecting the central parts of the Galaxy. The present decontamination procedure is not sensitive to all accretions (especially prograde) during the first Gyrs, since the observed radial density profiles still preserve traces of the earliest merger(s). We estimate that the present globular cluster population corresponds to ≤ 23±6% of the original one. The fact that the volume-density radial distributions of the metal-rich and metal-poor globular clusters of the reduced sample follow both a core-like power-law and Sérsic's law indicates that we are dealing with spheroidal subsystems in all scales.
Unveiling the nature of 12 new low-luminosity Galactic globular cluster candidates
Astronomy & Astrophysics, 2022
Context. The Galactic globular cluster system is incompletely known, especially in the low-latitude regions of the Galactic bulge and disk. We report the physical characterisation of 12 star clusters in the Milky Way, most of which are explored here for the first time. Aims. Our primary aim is determining their main physical parameters, such as reddening, extinction, metallicity, age, total luminosity, mean cluster proper motions (PMs), and distances, in order to reveal the physical nature of these clusters. Methods. We study the clusters using optical and near-infrared (NIR) datasets. In particular, we use the Gaia Early Data Release 3 (EDR3) PMs in order to perform a PM decontamination procedure and build final catalogues with probable members. We match the Gaia EDR3 with the VISTA Variables in the Vía Láctea extended (VVVX) survey and the Two Micron All-Sky survey (2MASS) in the NIR, in order to construct complete NIR and optical colour-magnitude diagrams (CMDs) and investigate t...
The Astronomical Journal, 1999
A catalog including a set of the most recent Color Magnitude Diagrams (CMDs) is presented for a sample of 61 Galactic Globular Clusters (GGCs). We used this data-base to perform an homogeneous systematic analysis of the evolved sequences (namely, Red Giant Branch (RGB), Horizontal Branch (HB) and Asymptotic Giant Branch (AGB)). Based on this analysis, we present: (1) a new procedure to measure the level of the ZAHB (V ZAHB ) and an homogeneous set of distance moduli obtained adopting the HB as standard candle; (2) an independent estimate for RGB metallicity indicators and new calibrations of these parameters in terms of both spectroscopic ([Fe/H] CG97 ) and global metallicity ([M/H], including also the α−elements enhancement). The set of equations presented can be used to simultaneously derive a photometric estimate of the metal abundance and the reddening from the morphology and the location of the RGB in the (V, B − V )-CMD. (3) the location of the RGB-Bump (in 47 GGCs) and the AGB-Bump (in 9 GGCs). The dependence of these features on the metallicity is discussed. We find that by using the latest theoretical models and the new metallicity scales the earlier discrepancy between theory and observations (∼ 0.4 mag) completely disappears.
FORS2/VLT survey of Milky Way globular clusters
Astronomy & Astrophysics, 2014
Context. Globular clusters trace the formation and evolution of the Milky Way and surrounding galaxies, and outline their chemical enrichment history. To accomplish these tasks it is important to have large samples of clusters with homogeneous data and analysis to derive kinematics, chemical abundances, ages and locations. Aims. We obtain homogeneous metallicities and α-element enhancement for 51 Galactic bulge, disc, and halo globular clusters that are among the most distant and/or highly reddened in the Galaxy's globular cluster system. We also provide membership selection based on stellar radial velocities and atmospheric parameters. The implications of our results are discussed. Methods. We observed R ∼ 2000 spectra in the wavelength interval 456-586 nm for over 800 red giant stars in 51 Galactic globular clusters. We applied full spectrum fitting with the code ETOILE together with libraries of observed and synthetic spectra. We compared the mean abundances of all clusters with previous work and with field stars. We used the relation between mean metallicity and horizontal branch morphology defined by all clusters to select outliers for discussion. Results. [Fe/H], [Mg/Fe], and [α/Fe] were derived in a consistent way for almost one-third of all Galactic globular clusters. We find our metallicities are comparable to those derived from high-resolution data to within σ = 0.08 dex over the interval −2.5 < [Fe/H] < 0.0. Furthermore, a comparison of previous metallicity scales with our values yields σ < 0.16 dex. We also find that the distribution of [Mg/Fe] and [α/Fe] with [Fe/H] for the 51 clusters follows the general trend exhibited by field stars. It is the first time that the following clusters have been included in a large sample of homogeneous stellar spectroscopic observations and metallicity derivation: BH 176, Djorg 2, Pal 10, NGC 6426, Lynga 7, and Terzan 8. In particular, only photometric metallicities were available previously for the first three clusters, and the available metallicity for NGC 6426 was based on integrated spectroscopy and photometry. Two other clusters, HP 1 and NGC 6558, are confirmed as candidates for the oldest globular clusters in the Milky Way. Conclusions. Stellar spectroscopy in the visible at R ∼ 2000 for a large sample of globular clusters is a robust and efficient way to trace the chemical evolution of the host galaxy and to detect interesting objects for follow-up at higher resolution and with forthcoming giant telescopes. The technique used here can also be applied to globular cluster systems in nearby galaxies with current instruments and to distant galaxies with the advent of ELTs.
Discovery of a New Low-Latitude Milky Way Globular Cluster Using GLIMPSE
The Astronomical Journal, 2005
Spitzer Space Telescope imaging from the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) reveals a previously unidentified low-latitude rich star cluster near l=31.3 • , b=-0.1. Near-infrared JHK' photometry from the Wyoming Infrared Observatory indicates an extinction of A V ≃ 15 ± 3 mag for cluster members. Analysis of 13 CO features along the same sightline suggests a probable kinematic distance of 3.1 -5.2 kpc. The new cluster has an angular diameter of ∼ 1 − 2 pc, a total magnitude corrected for extinction of m K 0 = 2.1, and a luminosity of M K ≃ −10.3 at 3.1 kpc. In contrast to young massive Galactic clusters with ages <100 Myr, the new cluster has no significant radio emission. Comparison to theoretical K-band luminosity functions indicates an age of at least several Gyr and a mass of at least 10 5 M ⊙ . Unlike known old open clusters, this new cluster lies in the inner Galaxy at R GC ≃ 6.1 kpc. We designate this object "GLIMPSE-C01" and present evidence that it is a Milky Way globular cluster passing through the Galactic disk. We also identify a region of star -2formation and fan-shaped outflows from young stellar objects in the same field as the cluster. The cluster's passage through the Galactic molecular layer may have triggered this star formation activity.
Near Infrared Photometry of New Galactic Globular Clusters GC 01 and GC 02
Symposium - International Astronomical Union
We present a preliminary report on the first deep near infrared photometry of 2MASS GC 01 and 2MASS GC 02 - new Galactic globular cluster candidates, discovered by the 2MASS. The red giant branch slopes yielded [Fe/H]=-0.42 ± 0.15 dex and [Fe/H]=-0.66 ± 0.17 dex, respectively for GC 01 and GC 02. We estimated the reddening towards GC 01 and GC 02: E(B - V) = 5.36 ± 0.20, and E(B - V) = 4.55 ± 0.17. The calculated distance moduli to the clusters are: (m - M)0 = 13.53 ± 0.27 and (m - M)0 = 14.53 ± 0.31 for GC 01 and GC 02. Our best fit for the radial surface brightness profile of GC 02 yields: lg(rc) = 1.40, lg(rh) = 1.54, lg(rt) = 1.31, and c=1.60. CC 01 is less concentrated: lg(rc) = 1.63, lg(rh) = 1.7, lg(rt) = 1.25, and c=1.41.
Three Galactic globular cluster candidates
Astronomy & Astrophysics, 2011
The census of Galactic globular clusters (GCs) is still incomplete, and about ten new objects are supposed to await discovery, hidden behind the crowded and reddened regions of the Galactic bulge and disk. We investigated the nature of three new GC candidates, discovered in the frames collected by the Vista Variables in the Via Lactea (VVV) near-infrared survey. They will be called VVV CL002, VVV CL003, and VVV CL004. We studied the results of point-spread-function near-infrared photometry from VVV data for the three objects and their surrounding fields, the proper motion information available in the literature and, when possible, we derived the cluster parameters by means of calibrated indices measured on the color-magnitude diagrams. The evidence shows that VVV CL002 is a newly discovered, small, moderately metal-rich (Fe/H -0.4) Galactic GC. It is located at a Galactocentric distance of 0.7+-0.9 kpc, and it could be one of the nearest GC to the Galactic center. Its characteristics are more similar to those of low-mass, Palomar-like GCs than to more classical, old, and massive bulge GCs. VVV CL003 is the first star cluster discovered in the Galactic disk on the opposite side of the center with respect to the Sun, at a Galactocentric distance of ~5 kpc. Its high metallicity (Fe/H -0.1) and location point to an open cluster, but a GC cannot be excluded. VVV CL004, on the contrary, is most probably only a random clump of field stars, as indicated by both its low statistical significance and by the impossibility to distinguish its stars from the surrounding field population. We claim the detection of i) a new Galactic GC, deriving an estimate of its basic parameters; ii) a stellar aggregate, probably an open cluster, in the disk directly beyond the Galactic center; and iii) an overdensity of stars, most probably an asterism.
Confirmation of a New Metal-poor Globular Cluster in the Galactic Bulge
The Astrophysical Journal
We use deep near-IR photometry of the VISTA Variables in the Vía Láctea (VVV) Survey and deep DECam Plane Survey (DECaPS) optical photometry to confirm the physical reality of the candidate globular cluster (GC) Minni 22, which is located in the Galactic bulge. This object, which was detected as a high density region in our maps of bulge red giants, is now confirmed as a real GC based on the optical and near-IR color-magnitude diagrams. We also recover three known fundamental mode (ab type) RR Lyrae stars within 2 arcmin of the cluster center. The presence of RR Lyrae stars also seems to confirm Minni 22 as a bonafide old and metal-poor GC. We estimate a cluster reddening E J Ks 0.6-= () mag and determine its heliocentric distance D=7.4±0.3 kpc. The optical and near-IR color-magnitude diagrams reveal well-defined red giant branches in all cases, including a red giant branch bump at Ks=13.30±0.05 mag. The comparison with theoretical isochrones yields a mean metallicity of [Fe/H]=−1.3±0.3 dex, and age of t∼11.2 Gyr. This is a good example of a new low-luminosity (M V =−6.2 mag) GC found in the central bulge of the Milky Way. After discussing the different ways to confirm the existence of bulge GC candidates, we find that one of the best methods is to use the CMDs from the combination of the DECaPS + VVV photometries.
Observational Properties of Globular Clusters in Dwarf Galaxies
EAS Publications Series, 2011
We analyse evolutionary parameters of globular clusters in dwarf galaxies obtained in our medium-resolution spectroscopic observations, and their connection with the properties of the host galaxies. We find that 1) the metallicity spread in globular cluster systems is wider for larger galaxies; 2) metal-rich clusters are young and preferentially found in galaxies more massive than ∼10 9 M ; 3) intermediateage globular clusters in early-type dwarf galaxies are richer in metals than star clusters representing dynamically cold gas-rich environments in dwarf irregulars; 4) the age-metallicity relation is special for each galaxy, and depends not only on its mass, but also on some other factors, probably environmental conditions.