Very Large Telescope Observations of the peculiar globular cluster NGC6712. Discovery of a UV, H-alpha excess star in the core

We present results from multi-band observations in the central region of the cluster NGC6712 with the ESO-Very Large Telescope. Using high resolution images we have identified three UV-excess stars. In particular two of them are within the cluster core, a few arcsec apart: the first object is star "S" which previous studies identified as the best candidate to the optical counterpart to the luminous X-ray source detected in this cluster. The other UV object shows clearcut H-alpha emission and, for this reason, is an additional promising interacting binary candidate (a quiescent LMXB or a CV). The presence of two unrelated interacting binary systems a few arcsec apart in the core of this low-density cluster is somewhat surprising and supports the hypothesis that the (internal) dynamical history of the cluster and/or the (external) interaction with the Galaxy might play a fundamental role in the formation of these peculiar objects.Comment: 15 pages, 3 figures. ApJL in pres

The giant, horizontal and asymptotic branches of galactic globular clusters. I. The catalog, photometric observables and features

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 alpha-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.Comment: 51 pages, 23 figures, AAS Latex, macro rtrpp4.sty included, accepted by A

Another Non-segregated Blue Straggler Population in a Globular Cluster: the Case of NGC 2419

We have used a combination of ACS-HST high-resolution and wide-field SUBARU data in order to study the Blue Straggler Star (BSS) population over the entire extension of the remote Galactic globular cluster NGC 2419. The BSS population presented here is among the largest ever observed in any stellar system, with more than 230 BSS in the brightest portion of the sequence. The radial distribution of the selected BSS is essentially the same as that of the other cluster stars. In this sense the BSS radial distribution is similar to that of omega Centauri and unlike that of all Galactic globular clusters studied to date, which have highly centrally segregated distributions and, in most cases, a pronounced upturn in the external regions. As in the case of omega Centauri, this evidence indicates that NGC 2419 is not yet relaxed even in the central regions. This observational fact is in agreement with estimated half-mass relaxation time, which is of the order of the cluster age.Comment: in press in the Ap

M75, a Globular Cluster with a Trimodal Horizontal Branch. I. Color-Magnitude Diagram

Deep UBVI photometry for a large field covering the distant globular cluster M75 (NGC 6864) is presented. We confirm a previous suggestion (Catelan et al. 1998a) that M75 possesses a bimodal horizontal branch (HB) bearing striking resemblance to the well-known case of NGC 1851. In addition, we detect a third, smaller grouping of stars on the M75 blue tail, separated from the bulk of the blue HB stars by a gap spanning about 0.5 mag in V. Such a group of stars may correspond to the upper part of a very extended, though thinly populated, blue tail. Thus M75 appears to have a trimodal HB. The presence of the "Grundahl jump" is verified using the broadband U filter. We explore the color-magnitude diagram of M75 with the purpose of deriving the cluster's fundamental parameters, and find a metallicity of [Fe/H] = -1.03 +/- 0.17 dex and -1.24 +/- 0.21 dex in the Carretta & Gratton (1997) and Zinn & West (1984) scales, respectively. We discuss earlier suggestions that the cluster has an anomalously low ratio of bright red giants to HB stars. A differential age analysis with respect to NGC 1851 suggests that the two clusters are essentially coeval.Comment: 19 pages, 15 figures, emulateapj5/apjfonts style. Astronomical Journal, in press. This version contains some very low-resolution figures, due to the size constraints of astro-ph. We strongly encourage the interested reader to download instead the preprint with full-resolution figures, which can be found at http://www.astro.puc.cl/~mcatelan

ROSAT HRI X-ray Observations of the Open Globular Cluster NGC 288

A ROSAT HRI X-ray image was obtained of the open globular cluster NGC 288, which is located near the South Galactic Pole. This is the first deep X-ray image of this system. We detect a Low Luminosity Globular Cluster X-ray source (LLGCX) RXJ005245.0-263449 with an X-ray luminosity of (5.5+-1.4)x10^32 ergs/s (0.1-2.0 keV), which is located very close to the cluster center. There is evidence for X-ray variability on a time scale of <~ 1 day. The presence of this LLGCX in such an open cluster suggests that dense stellar systems with high interaction rates are not needed to form LLGCXs. We also searched for diffuse X-ray emission from NGC 288. Upper limits on the X-ray luminosities are L_X^h < 9.5x10^32 ergs/s (0.52-2.02 keV) and L_X^s < 9.3x10^32 ergs/s (0.11-0.41 keV). These imply upper limits to the diffuse X-ray to optical light ratios in NGC 288 which are lower than the values observed for X-ray faint early-type galaxies. This indicates that the soft X-ray emission in these galaxies is due either to a component which is not present in globular clusters (e.g., interstellar gas, or a stellar component which is not found in low metallicity Population II systems), or to a relatively small number of bright Low Mass X-ray Binaries (LMXBs).Comment: The Astrophysical Journal in press. Minor revisions to improve presentation. 6 pages with 3 embedded Postscript figures in emulateapj.st

Blue Straggler Stars in Globular Clusters: a powerful tool to probe the internal dynamical evolution of stellar systems

This chapter presents an overview of the main observational results obtained to date about Blue Straggler Stars (BSSs) in Galactic Globular Clusters (GCs). The BSS specific frequency, radial distribution, chemical composition and rotational properties are presented and discussed in the framework of using this stellar population as probe of GC internal dynamics. In particular, the shape of the BSS radial distribution has been found to be a powerful tracer of the dynamical age of stellar systems, thus allowing the definition of the first empirical "dynamical clock".Comment: Chapter 5, in Ecology of Blue Straggler Stars, H.M.J. Boffin, G. Carraro & G. Beccari (Eds), Astrophysics and Space Science Library, Springe

Time asymmetries in quantum cosmology and the searching for boundary conditions to the Wheeler-DeWitt equation

The paper addresses the quantization of minisuperspace cosmological models by studying a possible solution to the problem of time and time asymmetries in quantum cosmology. Since General Relativity does not have a privileged time variable of the newtonian type, it is necessary, in order to have a dynamical evolution, to select a physical clock. This choice yields, in the proposed approach, to the breaking of the so called clock-reversal invariance of the theory which is clearly distinguished from the well known motion-reversal invariance of both classical and quantum mechanics. In the light of this new perspective, the problem of imposing proper boundary conditions on the space of solutions of the Wheeler-DeWitt equation is reformulated. The symmetry-breaking formalism of previous papers is analyzed and a clarification of it is proposed in order to satisfy the requirements of the new interpretation.Comment: 25 pages, 1 figur

Verrucomicrobiota are specialist consumers of sulfated methyl pentoses during diatom blooms

Marine algae annually sequester petagrams of carbon dioxide into polysaccharides, which are a central metabolic fuel for marine carbon cycling. Diatom microalgae produce sulfated polysaccharides containing methyl pentoses that are challenging to degrade for bacteria compared to other monomers, implicating these sugars as a potential carbon sink. Free-living bacteria occurring in phytoplankton blooms that specialise on consuming microalgal sugars, containing fucose and rhamnose remain unknown. Here, genomic and proteomic data indicate that small, coccoid, free-living Verrucomicrobiota specialise in fucose and rhamnose consumption during spring algal blooms in the North Sea. Verrucomicrobiota cell abundance was coupled with the algae bloom onset and accounted for up to 8% of the bacterioplankton. Glycoside hydrolases, sulfatases, and bacterial microcompartments, critical proteins for the consumption of fucosylated and sulfated polysaccharides, were actively expressed during consecutive spring bloom events. These specialised pathways were assigned to novel and discrete candidate species of the Akkermansiaceae and Puniceicoccaceae families, which we here describe as Candidatus Mariakkermansia forsetii and Candidatus Fucivorax forsetii. Moreover, our results suggest specialised metabolic pathways could determine the fate of complex polysaccharides consumed during algae blooms. Thus the sequestration of phytoplankton organic matter via methyl pentose sugars likely depend on the activity of specialised Verrucomicrobiota populations

The First Empirical Mass Loss Law for Population II Giants

Using the Spitzer IRAC camera we have obtained mid-IR photometry of the red giant branch stars in the Galactic globular cluster 47 Tuc. About 100 stars show an excess of mid-infrared light above that expected from their photospheric emission. This is plausibly due to dust formation in mass flowing from these stars. This mass loss extends down to the level of the horizontal branch and increases with luminosity. The mass loss is episodic, occurring in only a fraction of stars at a given luminosity. Using a simple model and our observations we derive mass loss rates for these stars. Finally, we obtain the first empirical mass loss formula calibrated with observations of Population II stars. The dependence on luminosity of our mass loss rate is considerably shallower than the widely used Reimers Law. The results presented here are the first from our Spitzer survey of a carefully chosen sample of 17 Galactic Globular Clusters, spanning the entire metallicity range from about one hundredth up to almost solar

Characterization of bipartite states using a single homodyne detector

We suggest a scheme to reconstruct the covariance matrix of a two-mode state using a single homodyne detector plus a polarizing beam splitter and a polarization rotator. It can be used to fully characterize bipartite Gaussian states and to extract relevant informations on generic states.Comment: 7 pages, 1 figur