T. A. Smecker-Hane

University of California, Irvine, Irvine, California, United States

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Publications (85)158.48 Total impact

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    ABSTRACT: We present results of two-color VR photometry of the intermediate polar RXS J1803. The data were aquired using the Korean 1-m telescope located at Mt. Lemmon, USA. Different "high" and 'low" luminosity states, similar to other intermediate polars, were discovered. No statistically significant variability of the color index with varying luminosity was detected. The orbital variability was found to be not statistically significant. Spin maxima timings were determined, as well as the photometric ephemeris for the time interval of our observations. The spin period variations, caused by interaction of the accretion structure with the rotating magnetic white dwarf, were also detected. These variations are of complicated character, and their study requires further observations. We determine the color transformation coefficients for our photometric systems, and improve on the secondary photometric standards.
    Journal of the Korean Astronomical Society 01/2011; 44:89-96. · 0.91 Impact Factor
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    ABSTRACT: The outer regions of disc galaxies are becoming increasingly recognized as key testing sites for models of disc assembly and evolution. Important issues are the epoch at which the bulk of the stars in these regions formed and how discs grow radially over time. To address these issues, we use Hubble Space Telescope Advanced Camera for Surveys imaging to study the star formation history (SFH) of two fields at 9.1 and 11.6 kpc along M33's northern major axis. These fields lie at ∼ 4 and 5 V-band disc scalelengths and straddle the break in M33's surface brightness profile. The colour–magnitude diagrams (CMDs) reach the ancient main-sequence turn-off with a signal-to-noise ratio of ∼ 5. From detailed modelling of the CMDs, we find that the majority of stars in both fields combined formed at z < 1. The mean age in the inner field, S1, is ∼ 3 ± 1 Gyr and the mean metallicity is [M/H]∼− 0.5 ± 0.2 dex. The SFH of S1 unambiguously reveals how the inside-out growth previously measured for M33's inner disc out to extends out to the disc edge at . In comparison, the outer field, S2, is older (mean age ∼ 7 ± 2 Gyr), more metal-poor (mean [M/H]∼− 0.8 ± 0.3 dex), and contains ∼ 30 times less stellar mass. These results provide the most compelling evidence yet that M33's age gradient reverses at large radii near the disc break and that this reversal is accompanied by a break in stellar mass surface density. We discuss several possible interpretations of this behaviour including radial stellar mixing, warping of the gaseous disc, a change in star formation efficiency and a transition to another structural component. These results offer one of the most detailed views yet of the peripheral regions of any disc galaxy and provide a much needed observational constraint on the last major epoch of star formation in the outer disc.
    Monthly Notices of the Royal Astronomical Society 12/2010; 410(1):504 - 516. · 5.52 Impact Factor
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    Tammy A. Smecker-Hane, R. Kuzio de Naray
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    ABSTRACT: The COSMOS program is a month-long, residential, summer program for talented high school students held at four University of California campuses (Davis, Irvine, Santa Cruz, and San Diego). Since the program's inception in 2000, we have offered the Astronomy & Astrophysics Cluster in the UCI COSMOS program. Our high school students take classes and laboratories in astronomy & astrophysics and complete a research project in small groups under the supervision of faculty and teaching assistants. Students take data for their research projects with telescopes at the UCI Observatory or use data that we already have obtained at other observatories in the course of our research. In this poster, we discuss the curriculum, the research projects, highlighting one of the newest labs we developed involving measuring dark matter with galaxy rotation curves, and discuss many of the lessons we have learn working with these talented students over the past 10 years.
    01/2010;
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    ABSTRACT: We will present the results of a spectroscopic survey of red giant stars in the Local Group spiral galaxy M33, including evidence for the existence of a thick disk and stellar halo. Surface photometry of M33 is well-fit by a single exponential disk (Teig 2007), however, this does not exclude the existence of a thick disk with a similar scale length. Since M33's systemic velocity significantly overlaps the velocities of Milky Way dwarfs, radial velocity measurements are not sufficient to separate foreground dwarfs from bona fide M33 stars. Instead, we used our photometric observations in V, I, and the narrow-band DDO51 filters to identify M33 stars. We use the DEIMOS multi-object spectrograph on the Keck 10-meter telescope to obtain spectra surrounding the CaII triplet of absorption lines. We have analyzed the radial velocities of 443 confirmed M33 red giant stars from 7 fields along the major and minor axes of the galaxy. In addition to a stellar thin disk with a velocity dispersion of 24 km/s, we detect a population of stars along the major axis that are shifted toward M33's systemic velocity. These stars represent a stellar thick disk, rotating slower than the HI gas. We also find 11 stars with velocities very different from the rotating disk that are members of a stellar halo. This halo makes up 8% of the stars in our fields, with a velocity dispersion of 54 km/s. In addition to these kinematic measurements, we will also present chemical abundance information for individual red giant stars throughout M33.
    05/2009;
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    ABSTRACT: If a galaxy cluster is effectively in dynamical equilibrium, then all galaxy populations within the cluster must have distributions in velocity and position that individually reflect the same underlying mass distribution, although the derived virial masses can be quite different. Specifically, within the Canadian Network for Observational Cosmology cluster sample, the virial radius of the red galaxy population is, on the average, a factor of 2.05 ± 0.34 smaller than that of the blue population. The red galaxies also have a smaller rms velocity dispersion, a factor of 1.31 ± 0.13 within our sample. Consequently, the virial mass calculated from the blue galaxies is 3.5 ± 1.3 times larger than from the red galaxies. However, applying the Jeans equation of stellar hydrodynamic equilibrium to the red and blue subsamples separately gives statistically identical cluster mass profiles. This is strong evidence that these clusters are effectively equilibrium systems and therefore demonstrates empirically that the masses in the virialized region are reliably estimated using dynamical techniques.
    The Astrophysical Journal 01/2009; 476(1):L7. · 6.73 Impact Factor
  • Tammy A. Smecker-Hane, B. Marsteller, A. Cole, J. Bullock, J. S. Gallagher
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    ABSTRACT: We report on results of new deep imaging obtained with the Hubble Space Telescope (HST) Advance Camera for Surveys (ACS) that show the Leo I dwarf Spheroidal (dSph) galaxy has a much larger population of ancient (>10 Gyr old) stars than previously determined with shallower WFPC2 imaging (Gallart et al. 1999, Dolphin 2003), as well as the previously identified component of intermediate-aged stars. Our new imaging is much deeper, which allows us to unambiguously identify the main sequence turnoffs of the ancient population and constrain the star formation rate at the epoch of the formation of the "first stars'' in this galaxy. We will determine the galaxy's star formation rate as a function of time from the observed density of stars in the color-magnitude diagram by comparing with Padova stellar evolutionary models (Girardi et al. 2000). We compare and contrast the star formation histories of the Leo I dSph, which is currently devoid of any gas, with that of the gas-rich Leo A dIrr galaxy. The two are very different in that the dSph formed most of its stars early and the dIrr formed most of its stars later, however both have been actively forming stars over most of the age of the universe.
    01/2009;
  • Proceedings of the International Astronomical Union 01/2009; 254.
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    ABSTRACT: We are quantifying the kinematics of the stellar populations (thin disk, thick disk and halo) of the nearby spiral galaxy M33. Photometry from tet{hoo_ferg06} shows M33's inner region is well-fit by a single exponential disk with a scale length of 0.1° (1.4 kpc) out to a radius of 0.6°, although individual stars observed well outside a radius of 1.0° are potential members of a thick disk or halo. We are using the DEIMOS spectrograph at the Keck II 10-meter telescope to obtain spectra surrounding the CaII near-infrared triplet lines for ˜1000 individual red giant stars throughout M33. We derived radial velocities for 331 stars to date from five fields along the major and minor axes of the galaxy, with typical 1-sigma random errors of 10 km/s. Of these stars, 234 are probable M33 red giants rather than foreground Milky Way dwarfs based on our photometric observations made in the narrow-band DDO51 filter. In addition to a thin disk with a velocity dispersion of 15 km/s around the HI disk, we also see a component with a large velocity dispersion of 47 km/s. This dispersion is much larger than the 17 km/s dispersion seen in young disk clusters tep{hoo_chan02} and the 9 km/s dispersion found in the HI disk tep{hoo_warner73}, suggesting the existence of a thick disk and stellar halo that make up 30% and 4% of the total number of stars in these fields, respectively.
    01/2009;
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    Andrew McWilliam, Tammy A. Smecker-Hane
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    ABSTRACT: We present copper abundances for 14 red giant stars in the Sagittarius dwarf spheroidal galaxy (Sgr dSph), showing that [Cu/Fe] is deficient by ~0.5 dex, relative to the Galactic trend. This is most easily understood as due to an enhanced contribution of iron peak nucleosynthesis products from Type Ia supernovae (SNe Ia). The deficient [Cu/Fe] ratios might also be the result of a metallicity-dependent yield from SNe Ia, similar to previous conclusions for Mn, although SN Ia nucleosynthesis predictions suggest a negligible Cu yield. The enhanced SN Ia products, suggested by our low [Cu/Fe] ratios, fit a leaky box chemical evolution scenario for the Sgr dSph, where ejecta from the old, metal-poor, population overwhelmed nucleosynthesis products from younger generations, resulting in young stars with uncharacteristic compositions. The only other system known to have unusually low [Cu/Fe] is the Galactic globular cluster ω Cen, which, like the Sagittarius dwarf galaxy, has strong enhancements of s-process elements. Thus, our copper abundances lend support to the idea that ω Cen is the remaining nucleus of an accreted dwarf galaxy.
    The Astrophysical Journal 12/2008; 622(1):L29. · 6.73 Impact Factor
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    ABSTRACT: Using WFPC2 on board the Hubble Space Telescope, we have created deep color-magnitude diagrams in the V and I passbands for approximately 105 stars in a field at the center of the LMC bar and another in the disk. The main-sequence luminosity functions (LFs) from 19 ≤ V ≤ 23.5, the red clump and horizontal branch morphologies, and the differential Hess diagram of the two fields all strongly imply that the disk and bar have significantly different star formation histories (SFHs). The disk's SFH has been relatively smooth and continuous over the last ~15 Gyr, while the bar's SFH was dominated by star formation episodes at intermediate ages. Comparison of the LF against predictions based on Padova theoretical stellar evolution models and an assumed age-metallicity relationship allows us to identify the dominant stellar populations in the bar with episodes of star formation that occurred from 4 to 6 and 1 to 2 Gyr ago. These events accounted for ~25% and ~15%, respectively, of its stellar mass. The disk field may share a mild enhancement in SF for the younger episode, and thus we identify the 4 to 6 Gyr episode with the formation of the LMC bar.
    The Astrophysical Journal 12/2008; 566(1):239. · 6.73 Impact Factor
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    ABSTRACT: We introduce the SMC in space and time, a large coordinated space and ground-based program to study star formation processes and history, as well as variable stars, structure, kinematics and chemical evolution of the whole SMC. Here, we present the Colour-Magnitude Diagrams(CMDs) resulting from HST/ACS photometry, aimed at deriving the star formation history (SFH) in six fields of the SMC. The fields are located in the central regions, in the stellar halo, and in the wing toward the LMC. The CMDs are very deep, well beyond the oldest Main Sequence Turn-Off, and will allow us to derive the SFH over the entire Hubble time. Comment: 5 pages, 2 figures, Conference Proceeding for IAU Symposium 255: Low-Metallicity Star Formaion: From the First Stars to Dwarf Galaxies
    Proceedings of the International Astronomical Union 08/2008;
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    Andrew A. Cole, Tammy A. Smecker-Hane, and John S. Gallagher III
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    ABSTRACT: We report new metallicity determinations for 39 red giants in a 220 arcmin2 region, 18 southwest of the bar of the Large Magellanic Cloud. These abundance measurements are based on spectroscopy of the Ca II infrared triplet. We have carefully considered the effects of abundance ratios, the physics of Ca II line formation, the variation of red clump magnitude, and the contamination by foreground stars in our abundance analyses. The metallicity distribution function (MDF) shows a strong peak at [Fe/H] = -0.57 ± 0.04; a tail to abundances at least as low as [Fe/H] ≈ -1.6 brings the average abundance down to [Fe/H] = -0.64 ± 0.02. Half the red giants in our field fall within the range -0.83 ≤ [Fe/H] ≤ -0.41. The MDF appears to be truncated at [Fe/H] ≈ -0.25; the exact value of the maximum abundance is subject to ~0.1 dex uncertainty in the calibration of the Ca II IR triplet for young, metal-rich stars. We find a striking contrast in the shape of the MDF below [Fe/H] ≤ -1 between our inner disk field and the distant outer field studied by Olszewski: red giants deficient by more than a factor of 10 in heavy elements relative to the Sun are extremely scarce in the inner disk of the LMC. Our field star sample does not reproduce the full MDF of the LMC star clusters but seems similar to that of the intermediate-age (1–3 Gyr) clusters. We have also obtained abundance estimates using Strömgren photometry for ≈103 red giants in the same field. Photometry is the only practical way to measure abundances for the large numbers of stars necessary to lift age-metallicity degeneracy from our high-precision color-magnitude diagrams. The Strömgren measurements, which are sensitive to a combination of cyanogen and iron lines, correlate well with the Ca II measurements, but a metallicity-dependent offset is found. The offset may be due either to variations in the elemental abundance ratios due to galactic chemical evolution or to a metal-dependent mixing mechanism in RGB stars. An empirical relation between photometric and spectroscopic abundance estimates is derived. This will allow photometric abundance measurements to be placed on a consistent metallicity scale with spectroscopic metallicities, for very large numbers of stars.
    The Astronomical Journal 12/2007; 120(4):1808. · 4.97 Impact Factor
  • M. Teig, T. Smecker-Hane, M. Hood
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    ABSTRACT: Our goal is to reliably separate foreground Milky Way dwarfs from M33 red giants via photometry in order to study M33's stellar populations (thin disk, thick disk and/or halo). Our technique is based on the gravity sensitivity of the MgI triplet lines and MgH absorption band at lambda&ap;5100 Å in stars with F to K spectral types. The strengths of these lines are quantified photometrically using the narrow-band DDO51 filter. The (V-I) vs (DDO51-V) colors essentially map onto the theoretical temperature-gravity plane, allowing for clean separation between dwarfs and giants of the same temperature for stars with 1&lap;(V-I)&lap;2. Using the the KPNO 4m telescope and MOSAIC camera, we have obtained photometry for four fields in M33, extending to ˜1°. M33's distance of 794 kpc tep{mjt_mifilt:trgb} and exponential disk scale length of 1.4 kpc tep{mjt_ferg:disk} suggest that the ˜800 candidate M33 stars we observe beyond 0.67° are probably halo/thick disk stars. Our data are also being used to select targets in our spectroscopic companion work.
    12/2007;
  • T. L. Bosler, T. A. Smecker-Hane, P. B. Stetson
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    ABSTRACT: The photometry and astrometry for Leo I and II were obtained as part of a larger program to provide homogeneous photometry for star clusters and nearby resolved galaxies (e.g. Stetson, Hesser & Smecker-Hane 1998, Cat. ; Stetson 2000PASP..112..925S). The present photometry is based upon a large database of CCD images acquired by ourselves and collaborators, images obtained from the archives of the Canada-France-Hawaii Telescope and the Isaac Newton Group and images privately donated by other astronomers. (4 data files).
    VizieR Online Data Catalog. 11/2007;
  • Shimonee Kadakia, T. Smecker-Hane, T. Bosler
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    ABSTRACT: We determine the chemical abundances of 19 red giant branch stars in the Galactic globular cluster NGC 2419. Lying at a distance of 84.2 kpc and a galactocentric distance of 91.5 kpc, NGC 2419 is the fourth brightest globular cluster in the Milky Way with a total magnitude of M_V = -9.6 mag, which is significantly brighter than M_V = -7.5 mag, the typical peak of the globular cluster luminosity functions in external galaxies. Our results will give an insight of whether NGC 2419 is in fact a globular cluster or a core of a disrupted galaxy that merged with the Milky Way. We have used IRAF to reduce spectra we have taken with the DEIMOS spectrograph on the the Keck I 10-meter telescope. Using the strengths of the Ca II triplet absorption lines at approximately 8600 Angstrom, we will determine the chemical abundance of each star. If the chemical abundances differ by significantly more than the observational errors would predict then we can conclude the cluster is a remnant of the core of a galaxy that merged with the Milky Way and not a normal globular cluster, because most globular clusters formed quickly from a well mixed gas cloud, and thus their stars have nearly identical ages and chemical compositions. We gratefully acknowledge financial support from a UROP grant to SK and NSF grant AST-0307863 to TSH. These data were obtained at the Keck Observatory, operated by the California Inst. of Technology, Univ. of California and NASA and made possible by generous financial support from the W.M. Keck Foundation.
    05/2007;
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    Tammy L. Bosler, Tammy A. Smecker-Hane, Peter B. Stetson
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    ABSTRACT: We have obtained spectra of 102 red giant branch (RGB) stars in the Leo I dwarf spheroidal galaxy (dSph) and 74 RGB stars in the Leo II dSph using LRIS on the Keck I 10-meter Telescope. We report on the calcium abundances [Ca/H] derived from the strengths of the Ca II triplet absorption lines at 8498, 8542, 8662 angstroms in the stellar spectra using a new Ca II triplet calibration to [Ca/H]. The two galaxies have different average [Ca/H] values of -1.34 +/- 0.02 for Leo I and -1.65 +/- 0.02 for LeoII with intrinsic abundance dispersions of 1.2 and 1.0 dex, respectively. The typical random and total errors in derived abundances are 0.10 and 0.17 dex per star. For comparison to existing literature, we also converted our Ca II measurements to [Fe/H] on the scale of Carretta and Gratton (1997) though we discuss why this may not be the best determinant of metallicity; Leo I has a mean [Fe/H] = -1.34 and Leo II has a mean [Fe/H] = -1.59. The metallicity distribution function of Leo I is approximately Gaussian in shape with an excess at the metal-rich end, while that of Leo II shows an abrupt cutoff at the metal-rich end. The lower mean metallicity of Leo II is consistent with the fact that it has a lower luminosity, hence lower total mass, than Leo I; thus the evolution of Leo II may have been affected more by mass lost in galactic winds. We compare our observed metallicity distribution functions to those inferred by Dolphin (2002) from modelling of deep CMDs obtained with the Hubble Space Telescope. The models predict a median metallicity that is systematically more metal-rich than observed, by 0.36 dex in the Leo I dSph, and by 0.49 dex in the Leo II dSph. We show that differences this large are not likely caused by non-solar [Ca/Fe] in the dSph stars.
    Monthly Notices of the Royal Astronomical Society 09/2006; · 5.52 Impact Factor
  • Matthew J. Teig, T. Smecker-Hane, M. Hood
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    ABSTRACT: Our goal is to reliably separate foreground Milky Way dwarfs from M33 red giants via photometry to study M33's stellar populations (disk/halo). This cannot be done using radial velocities alone due to the large overlap between M33's stars and Milky Way foreground stars. Our technique is based on the gravity-sensitivity of the MgI triplet and MgH absorption band at lambda&ap;5100Å in F-K stars (Clark & McClure 1979). The strengths of these lines are quantified photometrically by the difference in magnitude between the V-band, which measures the stellar continuum, and the narrow-band DDO51 filter (lambdacentral=5100Å width=150Å). A (V-I, 51-V) color-color plot essentially maps onto the theoretical temperature-gravity plane, allowing for clean separation between dwarfs and giants of the same temperature for stars with 1
    06/2006;
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    ABSTRACT: The advent of the new class 8 meters telescopes allows for the first time the detailed study of numerous stars of galaxies other than our own. The Large Magellanic Cloud is one of the most interesting targets due to its proximity and its relatively face-on disk, permitting to separate populations pertaining to the different structures of the galaxy. We have used FLAMES (the Fibre Large Array Multi Element Spectrograph) at the VLT-UT2 telescope to obtain spectra of a large sample of stars from the Inner Disk of the LMC, $\sim$2 kpc from the center of the galaxy. We investigate the chemical abundances of iron-peak elements, heavy and light $s$-process elements, Cu, Na, Sc and $\alpha$-elements for a sample of red giant stars. Metallicities for the sample stars range from [Fe/H] = $-$1.76 to $-$0.02. LMC inner disk stars show a definitely different chemical pattern when compared to galactic stars of the same metallicity.
    05/2006;
  • M. Teig, T. Smecker-Hane, M. Hood
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    ABSTRACT: Our goal is to quantify the kinematics and chemical abundances of the stellar populations (thin disk and thick disk and/or halo) of the nearby spiral galaxy M33 in order to test sophisticated models of galaxy formation. We are using the DEIMOS spectrograph at the Keck II 10-meter telescope to obtain spectra surrounding the Ca II near-infrared triplet lines for approximately 1000 red giant stars throughout M33's disk and halo. From the spectra we will measure the radial velocities and chemical abundances of the stars and distinguish the separate stellar populations. One critical step in our project is our use of V, I, and DDO51-band imaging to separate M33 red giants from foreground Milky Way dwarf stars, because the radial velocities of these stars overlap significantly. Our imaging has been done using the Kitt Peak National Observatory 4-meter telescope and MOSAIC camera. A star's flux in the DDO51 filter (centered at 5100 Å; width of 150 Å) is a measure of the strength of the Mg I lines that are highly dependent on the star's surface gravity. Thus when plotted in a (V-I) vs. (DDO51-V) diagram, most M33 red giants are easily discriminated from foreground Galactic dwarfs. We will present photometric results from a field located SE of M33's core along the minor axis, the first of four fields that we have observed. We also will show fiducials from globular and open star clusters that illustrate this technique's lack of metallicity dependence, and thus its power. We gratefully acknowledge financial support from grants NSF AST-0307863 and STScI/NASA GO-9837 to Tammy Smecker-Hane.
    12/2004;
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    Andrew McWilliam, Tammy A. Smecker-Hane
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    ABSTRACT: We outline the results of a study of the chemical composition of 14 stars in the Sagittarius dwarf spheroidal galaxy (Sgr dSph). For the Sgr dSph stars with [Fe/H]>-1 the abundances are highly unusual, showing a striking enhancement in heavy s-process elements, increasing with [Fe/H], deficiencies of the alpha- elements (O, Si, Ca, and Ti), deficiencies of Al and Na, and deficiencies of the iron-peak elements Mn and Cu. Our abundances suggest that the composition of the metal-rich Sgr dSph stars is dominated by the ejecta of an old, metal-poor population, including products of AGB stars and type Ia supernovae (SN). We suggest two scenarios to explain the observations: Prolonged chemical evolution in a galaxy experiencing significant mass-loss, and chemical enrichment in a system with a large burst of star-formation, followed by a quiescent period of many Gry. The Galactic globular cluster Omega Cen, and the Fornax dwarf galaxy show similar abundance patterns, which suggests that those systems evolved similar to the Sgr dSph.
    10/2004;

Publication Stats

1k Citations
158.48 Total Impact Points

Institutions

  • 1996–2011
    • University of California, Irvine
      • Department of Physics and Astronomy
      Irvine, California, United States
  • 1999
    • University of Wisconsin, Madison
      • Department of Astronomy
      Madison, MS, United States
  • 1998
    • CSU Mentor
      Long Beach, California, United States
  • 1997
    • University of Cambridge
      • Institute of Astronomy
      Cambridge, England, United Kingdom
  • 1992
    • Johns Hopkins University
      • Department of Physics and Astronomy
      Baltimore, Maryland, United States