Modeling the chemical evolution of Omega Centauri using three-dimensional hydrodynamical simulations

We present a hydrodynamical and chemical model for the globular cluster Omega Cen, under the assumption that it is the remnant of an ancient dwarf spheroidal galaxy (dSph), the bulk of which was disrupted and accreted by our Galaxy ~10 Gyr ago. We highlight the very different roles played by Type II and Type Ia supernovae (SNe) in the chemical enrichment of the inner regions of the putative parent dSph. While the SNe II pollute the interstellar medium rather uniformly, the SNe Ia ejecta may remain confined inside dense pockets of gas as long as succesive SNe II explosions spread them out. Stars forming in such pockets have lower alpha-to-iron ratios than the stars forming elsewhere. Owing to the inhomogeneous pollution by SNe Ia, the metal distribution of the stars in the central region differs substantially from that of the main population of the dwarf galaxy, and resembles that observed in Omega Cen. This inhomogeneous mixing is also responsible for a radial segregation of iron-rich stars with depleted [alpha/Fe] ratios, as observed in some dSphs. Assuming a star formation history of ~1.5 Gyr, our model succeeds in reproducing both the iron and calcium distributions observed in Omega Cen and the main features observed in the empirical alpha/Fe versus Fe/H plane. Finally, our model reproduces the overall spread of the color-magnitude diagram, but fails in reproducing the morphology of the SGB-a and the double morphology of the main sequence. However, the inhomogeneous pollution reduces (but does not eliminate) the need for a significantly enhanced helium abundance to explain the anomalous position of the blue main sequence. Further models taking into account the dynamical interaction of the parent dwarf galaxy with the Milky Way and the effect of AGB pollution will be required.Comment: 15 pages, 13 figures. MNRAS accepte

Human infrastructure can alter the ecosystem services provided by a migratory ungulate

Wild ungulates, through their movement over the landscape, provide key ecosystem functions. Environmental processes such as soil productivity, seed dispersal and carbon sequestration are significantly affected by the presence of large herbivores. However, with the loss of migratory routes due to expanding human infrastructure networks and climate change, landscapes that depend on the movement of these species may experience changes in ecosystem functionality. Nutrient translocation and deposition, which is an important service provided by large herbivores, is of particular interest in alpine agricultural landscapes. Human activities generally have a negative impact on the quality, quantity, and dynamics of soil nutrient in the landscape, particularly nitrogen. Wild ungulates, with their movement and space use, can offset some of these human impacts by restoring concentrations over the landscape. In this project, we aim to map the nitrogen (N) flow derived by large migrating ungulates in a fragmented Alpine ecosystem. To this end, we developed an Agent-Based Model to quantify animal-vectored subsidies balance, based on observed movement of 15 GPS-tracked red deer over two years, and parameterized with population parameters from local monitoring, and species-specific information from literature. Preliminary stoichiometric nutrient budget maps indicate that human infrastructure networks and land use are shaping the movement of red deer, resulting in hotspots of nitrogen intake and uptake. Barrier to movements, caused by anthropogenic land use, has the potential to alter ecosystem services provided by free-ranging animals, particularly important in an ever-changing Alpine environment

Multimodal Distributions along the Horizontal Branch

We report on HST/WFPC2 U,V and far-ultraviolet observations of two Galactic Globular Clusters (GGCs), NGC 6205 = M13 and NGC 6093 = M80. Both of these clusters have horizontal-branch (HB) tails that extend to the helium-burning main sequence, with the hottest stars reaching theoretical effective temperatures above 35,000 K. In both clusters, groups of stars are found to be separated by narrow gaps along the blue HB sequence. These gaps appear at similar locations in the color-magnitude diagrams of the two clusters. While stochastic effects may give rise to variations in the color distribution along the HB, the coincidence of gaps in different clusters effectively rules this out as the primary cause. The comparison among the clusters strongly suggests that there are separate physical processes operating during the earlier red-giant phase of evolution to produce mass loss.Comment: 13pp LaTeX, uses AAS Latex version 4. Includes 7 postscript figures. Postscript file available for download at http://www.astro.virginia.edu/~bd4

A High-Resolution Study of the HI Content of Local Group Dwarf Irregular Galaxy WLM

Dwarf irregular galaxies are unique laboratories for studying the interaction between stars and the interstellar medium in low mass environments. We present the highest spatial resolution observations to date of the neutral hydrogen content of the Local Group dwarf irregular galaxy WLM. We find that WLM's neutral hydrogen distribution is typical for a galaxy of its type and size and derive an HI mass of 6.3e7 Msun for WLM. In addition, we derive an HI extent for WLM of 30 arcmin, which is much less than the 45 arcmin extent found by Huchtmeier, Seiradakis, and Materne (1981). We show that the broken ring of high column density neutral hydrogen surrounding the center of WLM is likely the result of star formation propagating out from the center of the galaxy. The young stars and Ha emission in this galaxy are mostly correlated with the high column density neutral hydrogen. The gap in the central ring is the result of star formation in that region using up, blowing out, or ionizing all of the neutral hydrogen. Like many late-type galaxies, WLM's velocity field is asymmetric with the approaching (northern) side appearing to be warped and a steeper velocity gradient for the approaching side than for the receding side in the inner region of the galaxy. We derive a dynamical mass for WLM of 2.16e9 Msun.Comment: 38 pages, 15 figures, 5 tables, accepted by AJ, high resolution version at http://www.astro.wisc.edu/~kepley/kepley_wlm.p

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

Timing of Millisecond Pulsars in NGC 6752: Evidence for a High Mass-to-Light Ratio in the Cluster Core

Using pulse timing observations we have obtained precise parameters, including positions with about 20 mas accuracy, of five millisecond pulsars in NGC 6752. Three of them, located relatively close to the cluster center, have line-of-sight accelerations larger than the maximum value predicted by the central mass density derived from optical observation, providing dynamical evidence for a central mass-to-light ratio >~ 10, much higher than for any other globular cluster. It is likely that the other two millisecond pulsars have been ejected out of the core to their present locations at 1.4 and 3.3 half-mass radii, respectively, suggesting unusual non-thermal dynamics in the cluster core.Comment: Accepted by ApJ Letter. 5 pages, 2 figures, 1 tabl

Dynamical age differences among coeval star clusters as revealed by blue stragglers

Globular star clusters that formed at the same cosmic time may have evolved rather differently from a dynamical point of view (because that evolution depends on the internal environment) through a variety of processes that tend progressively to segregate stars more massive than the average towards the cluster centre. Therefore clusters with the same chronological age may have reached quite different stages of their dynamical history (that is, they may have different dynamical ages). Blue straggler stars have masses greater than those at the turn-off point on the main sequence and therefore must be the result of either a collision or a mass-transfer event. Because they are among the most massive and luminous objects in old clusters, they can be used as test particles with which to probe dynamical evolution. Here we report that globular clusters can be grouped into a few distinct families on the basis of the radial distribution of blue stragglers. This grouping corresponds well to an effective ranking of the dynamical stage reached by stellar systems, thereby permitting a direct measure of the cluster dynamical age purely from observed properties.Comment: Published on the 20 December 2012 issue of Natur

BRST operator quantization of generally covariant gauge systems

The BRST generator is realized as a Hermitian nilpotent operator for a finite-dimensional gauge system featuring a quadratic super-Hamiltonian and linear supermomentum constraints. As a result, the emerging ordering for the Hamiltonian constraint is not trivial, because the potential must enter the kinetic term in order to obtain a quantization invariant under scaling. Namely, BRST quantization does not lead to the curvature term used in the literature as a means to get that invariance. The inclusion of the potential in the kinetic term, far from being unnatural, is beautifully justified in light of the Jacobi's principle.Comment: 16 pages (LaTeX manuscript). Revised version (minor changes) to appear in Physical Review

Deep HST-WFPC2 photometry of NGC 288. II. The Main Sequence Luminosity Function

The Main Sequence Luminosity Function (LF) of the Galactic globular cluster NGC 288 has been obtained using deep WFPC2 photometry. We have employed a new method to correct for completeness and fully account for bin-to-bin migration due to blending and/or observational scatter. The effect of the presence of binary systems in the final LF is quantified and is found to be negligible. There is a strong indication of the mass segregation of unevolved single stars and clear signs of a depletion of low mass stars in NGC 288 with respect to other clusters. The results are in good agreement with the prediction of theoretical models of the dynamical evolution of NGC 288 that take into account the extreme orbital properties of this cluster.Comment: 16 pages, 6 .ps figures. Low resolution version of fig. 1; full resolution figure soon available at http://www.bo.astro.it/bap/BAPhome.html l. Latex. emulateapj5.sty macro included. Accepted for publication by The Astronomical Journa

Entangling oscillators through environment noise

We consider two independent bosonic oscillators immersed in a common bath, evolving in time with a completely positive, markovian, quasi-free (Gaussian) reduced dynamics. We show that an initially separated Gaussian state can become entangled as a result of a purely noisy mechanism. In certain cases, the dissipative dynamics allows the persistence of these bath induced quantum correlations even in the asymptotic equilibrium state.Comment: 14 pages, plain-Te