Open Access. Powered by Scholars. Published by Universities.®
Physical Sciences and Mathematics Commons™
Open Access. Powered by Scholars. Published by Universities.®
- Institution
Articles 1 - 15 of 15
Full-Text Articles in Physical Sciences and Mathematics
The Acs Survey Of Galactic Globular Clusters Xiv: Bayesian Single-Population Analysis Of 69 Globular Clusters, R. Wagner-Kaiser, Ted Von Hippel, A. Sarajedini, D. C. Stenning, D. A. Van Dyck, Et Al.
The Acs Survey Of Galactic Globular Clusters Xiv: Bayesian Single-Population Analysis Of 69 Globular Clusters, R. Wagner-Kaiser, Ted Von Hippel, A. Sarajedini, D. C. Stenning, D. A. Van Dyck, Et Al.
Publications
We use Hubble Space Telescope (HST) imaging from the ACS Treasury Survey to determine fits for single population isochrones of 69 Galactic globular clusters. Using robust Bayesian analysis techniques, we simultaneously determine ages, distances, absorptions, and helium values for each cluster under the scenario of a \single" stellar population on model grids with solar ratio heavy element abundances. The set of cluster parameters is determined in a consistent and reproducible manner for all clusters using the Bayesian analysis suite BASE-9. Our results are used to re-visit the age-metallicity relation. We find correlations with helium and several other parameters such as …
Stellar Fossils: Globular Clusters As Probes Of The Galaxy, Shane L. Larson
Stellar Fossils: Globular Clusters As Probes Of The Galaxy, Shane L. Larson
Public Talks
No abstract provided.
A Fast X-Ray Disk Wind In The Transient Pulsar Igr J17480-2446 In Terzan 5, Jon M. Miller, Dipankar Maitra, Edward M. Cackett, Sudip Bhattacharyya, Tod E. Strohmayer
A Fast X-Ray Disk Wind In The Transient Pulsar Igr J17480-2446 In Terzan 5, Jon M. Miller, Dipankar Maitra, Edward M. Cackett, Sudip Bhattacharyya, Tod E. Strohmayer
Physics and Astronomy Faculty Research Publications
Accretion disk winds are revealed in Chandra gratings spectra of black holes. The winds are hot and highly ionized (typically composed of He-like and H-like charge states) and show modest blueshifts. Similar line spectra are sometimes seen in "dipping" low-mass X-ray binaries (LMXBs), which are likely viewed edge-on; however, that absorption is tied to structures in the outer disk, and blueshifts are not typically observed. Here, we report the detection of blueshifted He-like Fe XXV (3100 ± 400 km s-1) and H-like Fe XXVI (1000 ± 200 km s-1) absorption lines in a Chandra/HETG spectrum of …
The Acs Survey Of Galactic Globular Clusters. Vii. Relative Ages, Antonio Marín-Franch, Antonio Aparicio, Giampaolo Piotto, Alfred Rosenberg, Brian Chaboyer
The Acs Survey Of Galactic Globular Clusters. Vii. Relative Ages, Antonio Marín-Franch, Antonio Aparicio, Giampaolo Piotto, Alfred Rosenberg, Brian Chaboyer
Dartmouth Scholarship
The ACS Survey of Galactic globular clusters is a Hubble Space Telescope Treasury program designed to provide a new large, deep, and homogeneous photometric database. Based on observations from this program, we have measured precise relative ages for a sample of 64 Galactic globular clusters by comparing the relative position of the clusters' main-sequence (MS) turnoffs, using MS fitting to cross-compare clusters within the sample. This method provides relative ages to a formal precision of 2%-7%. We demonstrate that the calculated relative ages are independent of the choice of theoretical model. We find that the Galactic globular cluster sample can …
The Acs Survey Of Galactic Globular Clusters. Vi. Ngc 6366: A Heavily Stripped Galactic Globular Cluster, Nathaniel E. Q. Paust, Antonio Aparicio, Giampaolo Piotto, I. Neill Reid, Jay Anderson, Ata Sarajedini, Luigi R. Bedin, Brian Chaboyer
The Acs Survey Of Galactic Globular Clusters. Vi. Ngc 6366: A Heavily Stripped Galactic Globular Cluster, Nathaniel E. Q. Paust, Antonio Aparicio, Giampaolo Piotto, I. Neill Reid, Jay Anderson, Ata Sarajedini, Luigi R. Bedin, Brian Chaboyer
Dartmouth Scholarship
We have used observations obtained as part of the Hubble Space Telescope/ACS Survey of Galactic globular clusters (GCs) to construct a color-magnitude diagram for the bulge cluster, NGC 6366. The luminosity function derived from those data extends to M F606W ~ 9, or masses of ~0.3 M ☉. Unlike most GCs, the mass function peaks near the main-sequence turnoff with significantly fewer low-mass stars even after correction for completeness and mass segregation. Using a multimass King model, we extrapolate the global cluster behavior and find the global mass function to be poorly matched by a power law, with …
The Acs Survey Of Galactic Globular Clusters. Iii. The Double Subgiant Branch Of Ngc 1851, A. P. Milone, L. R. Bedin, G. Piotto, J. Anderson, I. R. King, A. Sarajedini, A. Dotter, B. Chaboyer, A. Marin Franch, S. Majewski, A. Aparicio, M. Hempel, N. E.Q Paust, I. N. Reid, A. Rosenberg, M. Siegel
The Acs Survey Of Galactic Globular Clusters. Iii. The Double Subgiant Branch Of Ngc 1851, A. P. Milone, L. R. Bedin, G. Piotto, J. Anderson, I. R. King, A. Sarajedini, A. Dotter, B. Chaboyer, A. Marin Franch, S. Majewski, A. Aparicio, M. Hempel, N. E.Q Paust, I. N. Reid, A. Rosenberg, M. Siegel
Dartmouth Scholarship
Photometry with the Hubble Space Telescope Advanced Camera for Surveys (HST 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 ~1 Gyr. We discuss other anomalies in NGC 1851 that 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 …
The Dartmouth Stellar Evolution Database, Aaron Dotter, Brian Chaboyer, Darko Jevremović, Veselin Kostov
The Dartmouth Stellar Evolution Database, Aaron Dotter, Brian Chaboyer, Darko Jevremović, Veselin Kostov
Dartmouth Scholarship
The ever-expanding depth and quality of photometric and spectroscopic observations of stellar populations increase the need for theoretical models in regions of age-composition parameter space that are largely unexplored at present. Stellar evolution models that employ the most advanced physics and cover a wide range of compositions are needed to extract the most information from current observations of both resolved and unresolved stellar populations. The Dartmouth Stellar Evolution Database is a collection of stellar evolution tracks and isochrones that spans a range of [Fe/H] from –2.5 to +0.5, [α/Fe] from –0.2 to +0.8 (for [Fe/H] ≤ 0) or +0.2 (for …
Globular Clusters In The Outer Galactic Halo: Am-1 And Palomar 14, Aaron Dotter, Ata Sarajedini, Soung-Chul Yang
Globular Clusters In The Outer Galactic Halo: Am-1 And Palomar 14, Aaron Dotter, Ata Sarajedini, Soung-Chul Yang
Dartmouth Scholarship
AM-1, at ~120 kpc, and Palomar 14 (Pal 14), at ~70 kpc, are two of the most distant Galactic globular clusters (GCs) known. We present Hubble Space Telescope Wide Field Planetary Camera 2 photometry of AM-1 and Pal 14 that reveals unprecedented depth and detail in the color-magnitude diagrams of these two clusters. Absolute and relative age measurements confirm that both are younger than the inner halo GC M 3 by 1.5-2 Gyr assuming all three clusters have similar compositions. Thus AM-1 and Pal 14 join Pal 3, Pal 4, and Eridanus as distant GCs with red horizontal branches (HBs) …
The Acs Survey Of Galactic Globular Clusters: M54 And Young Populations In The Sagittarius Dwarf Spheroidal Galaxy, Michael H. Siegel, Aaron Dotter, Steven R. Majewski, Ata Sarajedini, Brian Chaboyer, David L. Nidever, Jay Anderson, Antonio Martin-French, Alfred Rosenberg, Luigi R. Bedin, Antonio Aparicio, Ivan King, Giampolo Piotto, I. Neill Reid
The Acs Survey Of Galactic Globular Clusters: M54 And Young Populations In The Sagittarius Dwarf Spheroidal Galaxy, Michael H. Siegel, Aaron Dotter, Steven R. Majewski, Ata Sarajedini, Brian Chaboyer, David L. Nidever, Jay Anderson, Antonio Martin-French, Alfred Rosenberg, Luigi R. Bedin, Antonio Aparicio, Ivan King, Giampolo Piotto, I. Neill Reid
Dartmouth Scholarship
As part of the ACS Survey of Galactic Globular Clusters, we present new Hubble Space Telescope photometry of the massive globular cluster M54 (NGC 6715) and the superposed core of the tidally disrupted Sagittarius (Sgr) dSph galaxy. Our deep (F606W ~ 26.5), high-precision photometry yields an unprecedentedly detailed color-magnitude diagram showing the extended blue horizontal branch and multiple main sequences of the M54+Sgr system. The distance and reddening to M54 are revised using both isochrone and main-sequence fitting to (m - M)0 = 17.27 and E(B - V) = 0.15. Preliminary assessment finds the …
A Chandra X-Ray Observation Of The Globular Cluster Terzan 1, E. M. Cackett, R. Wijnands, C. O. Heinke, D. Pooley, W. H. G. Lewin, J. E. Grindlay, P. D. Edmonds, P. G. Jonker, J. M. Miller
A Chandra X-Ray Observation Of The Globular Cluster Terzan 1, E. M. Cackett, R. Wijnands, C. O. Heinke, D. Pooley, W. H. G. Lewin, J. E. Grindlay, P. D. Edmonds, P. G. Jonker, J. M. Miller
Physics and Astronomy Faculty Research Publications
We present a ~19-ks Chandra Advanced CCD Imaging Spectrometer (ACIS)-S observation of the globular cluster Terzan 1. 14 sources are detected within 1.4arcmin of the cluster centre with two of these sources predicted to be not associated with the cluster (background active galactic nuclei or foreground objects). The neutron star X-ray transient, X1732-304, has previously been observed in outburst within this globular cluster with the outburst seen to last for at least 12yr. Here, we find four sources that are consistent with the ROSAT position for this transient, but none of the sources are fully consistent with the position of …
From Canonical To Enhanced Extra Mixing In Low‐Mass Red Giants: Tidally Locked Binaries, Pavel A. Denissenkov, Brian Chaboyer, Ke Li
From Canonical To Enhanced Extra Mixing In Low‐Mass Red Giants: Tidally Locked Binaries, Pavel A. Denissenkov, Brian Chaboyer, Ke Li
Dartmouth Scholarship
Stellar models that incorporate simple diffusion or shear-induced mixing are used to describe canonical extra mixing in low-mass red giants of low and solar metallicity. These models are able to simultaneously explain the observed Li and CN abundance changes along the upper red giant branch (RGB) in field low-metallicity stars and match photometry, rotation, and 12C/13C ratios for stars in the old open cluster M67. The shear mixing model requires that main-sequence (MS) progenitors of upper RGB stars possessed rapidly rotating radiative cores and that specific angular momentum was conserved in each of their mass shells during …
Theoretical Uncertainties In Red Giant Branch Evolution: The Red Giant Branch Bump, Stephan R. R. Bjork, Brian Chaboyer
Theoretical Uncertainties In Red Giant Branch Evolution: The Red Giant Branch Bump, Stephan R. R. Bjork, Brian Chaboyer
Dartmouth Scholarship
A Monte Carlo simulation exploring uncertainties in standard stellar evolution theory on the red giant branch of metal-poor globular clusters has been conducted. Confidence limits are derived on the absolute V-band magnitude of the bump in the red giant branch luminosity function (MV,b) and the excess number of stars in the bump, Rb. The analysis takes into account uncertainties in the primordial helium abundance, abundance of α-capture elements, radiative and conductive opacities, nuclear reaction rates, neutrino energy losses, the treatments of diffusion and convection, the surface boundary conditions, and color transformations. The uncertainty in …
The Effect Of The Galactic Spheroid On Globular Cluster Evolution, C Murali, Md Weinberg
The Effect Of The Galactic Spheroid On Globular Cluster Evolution, C Murali, Md Weinberg
Astronomy Department Faculty Publication Series
We study the combined effects of relaxation, tidal heating and binary heating on globular cluster evolution, exploring the physical consequences of external effects and examining evolutionary trends in the MilkyWay population. Our analysis demonstrates that heating on circular and low-eccentricity orbits can dominate cluster evolution. The results also predict rapid evolution on eccentric orbits either due to strong relaxation caused by the high densities needed for tidal limitation or due to efficient bulge shocking of low density clusters. The combination of effects leads to strong evolution of the population as a whole. For example, within the solar circle, tidally-limited 105M⊙ …
Globular Cluster Evolution In M87 And Fundamental Plane Ellipticals, C Murali, Md Weinberg
Globular Cluster Evolution In M87 And Fundamental Plane Ellipticals, C Murali, Md Weinberg
Astronomy Department Faculty Publication Series
The globular cluster population in M87 has decreased measurably through dynamical evolution caused by relaxation, binary heating and time-dependent tidal perturbation. For fundamental plane ellipticals in general, cluster populations evolve more rapidly in smaller galaxies because of the higher mass density. A simple evolutionary model reproduces the observed trend in specific frequency with luminosity for an initially constant relationship. Fits of theoretically evolved populations to M87 cluster data from McLaughlin et al. (1994) show the following: 1) dynamical effects drive evolution in the initial mass and space distributions and can account for the large core in the spatial profile as …
Evolution Of The Galactic Globular Cluster System, C Murali, Md Weinberg
Evolution Of The Galactic Globular Cluster System, C Murali, Md Weinberg
Astronomy Department Faculty Publication Series
We study the dynamical evolution of disk and halo globular clusters in the Milky Way using a series of Fokker-Planck calculations combined with parametric statistical models. Our sample of 113 clusters with velocity data is predicted to descend from an initial population of 250 clusters, implying more than a factor of two decrease in population size due to evolution. Approximately 200 of these clusters are in a halo component and 50 in a disk component. The estimated initial halo population follows a coreless R−3.38 density profile in good agreement with current estimates for the distribution of halo field stars. The …