Browsing by Author "Rich, R. M."

Now showing 1 - 5 of 5
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    Deep HST photometry of NGC 6388
    (2006) Catelan, M.; Stetson, Peter B.; Pritzl, Barton J.; Smith, Horace A.; Kinemuchi, Karen; Layden, Andrew C.; Sweigart, Allen V.; Rich, R. M.
    Using the Hubble Space Telescope, we have obtained the first color-magnitude diagram (CMD) to reach the main-sequence turnoff of the Galactic globular cluster NGC 6388. From a comparison between the cluster CMD and that of 47 Tucanae, we find that the bulk of the stars in these two clusters have nearly the same age and chemical composition. On the other hand, our results indicate that the blue horizontal branch and RR Lyrae components in NGC 6388 are intrinsically overluminous, which must be due to one or more, still undetermined, noncanonical second parameter(s) affecting a relatively minor fraction of the stars in NGC 6388.
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    NEW DENSITY PROFILE AND STRUCTURAL PARAMETERS OF THE COMPLEX STELLAR SYSTEM TERZAN 5
    (2010) Lanzoni, B.; Ferraro, F. R.; Dalessandro, E.; Mucciarelli, A.; Beccari, G.; Miocchi, P.; Bellazzini, M.; Rich, R. M.; Origlia, L.; Valenti, E.; Rood, R. T.; Ransom, S. M.
    Terzan 5 is a globular cluster-like stellar system in the Galactic bulge which has been recently found to harbor two stellar populations with different iron content and probably different ages. This discovery suggests that Terzan 5 may be the relic of a primordial building block that contributed to the formation of the Galactic bulge. Here we present a re-determination of the structural parameters (center of gravity, density and surface brightness profiles, total luminosity, and mass) of Terzan 5, as obtained from the combination of high-resolution (ESO-MAD and Hubble Space Telescope ACS-WFC) and wide-field (ESO-WFI) observations. We find that Terzan 5 is significantly less concentrated and more massive than previously thought. Still it has the largest collision rate of any stellar aggregate in the Galaxy. We discuss the impact of these findings on the exceptional population of millisecond pulsars harbored in this stellar system.
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    Preparing for low surface brightness science with the Vera C. Rubin Observatory: Characterization of tidal features from mock images
    (2022) Martin, G.; Bazkiaei, A. E.; Spavone, M.; Iodice, E.; Mihos, J. C.; Montes, M.; Benavides, J. A.; Brough, S.; Carlin, J. L.; Collins, C. A.; Duc, P. A.; Gomez, F. A.; Galaz, G.; Hernandez-Toledo, H. M.; Jackson, R. A.; Kaviraj, S.; Knapen, J. H.; Martinez-Lombilla, C.; McGee, S.; O'Ryan, D.; Prole, D. J.; Rich, R. M.; Roman, J.; Shah, E. A.; Starkenburg, T. K.; Watkins, A. E.; Zaritsky, D.; Pichon, C.; Armus, L.; Bianconi, M.; Buitrago, F.; Busa, I; Davis, F.; Demarco, R.; Desmons, A.; Garcia, P.; Graham, A. W.; Holwerda, B.; Hon, D. S-H; Khalid, A.; Klehammer, J.; Klutse, D. Y.; Lazar, I; Nair, P.; Noakes-Kettel, E. A.; Rutkowski, M.; Saha, K.; Sahu, N.; Sola, E.; Vazquez-Mata, J. A.; Vera-Casanova, A.; Yoon, I
    Tidal features in the outskirts of galaxies yield unique information about their past interactions and are a key prediction of the hierarchical structure formation paradigm. The Vera C. Rubin Observatory is poised to deliver deep observations for potentially millions of objects with visible tidal features, but the inference of galaxy interaction histories from such features is not straightforward. Utilizing automated techniques and human visual classification in conjunction with realistic mock images produced using the NewHorizon cosmological simulation, we investigate the nature, frequency, and visibility of tidal features and debris across a range of environments and stellar masses. In our simulated sample, around 80 per cent of the flux in the tidal features around Milky Way or greater mass galaxies is detected at the 10-yr depth of the Legacy Survey of Space and Time (30-31 mag arcsec(-2)), falling to 60 per cent assuming a shallower final depth of 29.5 mag arcsec(-2). The fraction of total flux found in tidal features increases towards higher masses, rising to 10 per cent for the most massive objects in our sample (M-* similar to 10(11.5) M-circle dot). When observed at sufficient depth, such objects frequently exhibit many distinct tidal features with complex shapes. The interpretation and characterization of such features varies significantly with image depth and object orientation, introducing significant biases in their classification. Assuming the data reduction pipeline is properly optimized, we expect the Rubin Observatory to be capable of recovering much of the flux found in the outskirts of Milky Way mass galaxies, even at intermediate redshifts (z < 0.2).
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    The cluster Terzan 5 as a remnant of a primordial building block of the Galactic bulge
    (2009) Ferraro, F. R.; Dalessandro, E.; Mucciarelli, A.; Beccari, G.; Rich, R. M.; Origlia, L.; Lanzoni, B.; Rood, R. T.; Valenti, E.; Bellazzini, M.; Ransom, S. M.; Cocozza, G.
    Globular star clusters are compact and massive stellar systems old enough to have witnessed the entire history of our Galaxy, the Milky Way. Although recent results(1-3) suggest that their formation may have been more complex than previously thought, they still are the best approximation to a stellar population formed over a relatively short timescale (less than 1 Gyr) and with virtually no dispersion in the iron content. Indeed, only one cluster-like system (omega Centauri) in the Galactic halo is known to have multiple stellar populations with a significant spread in iron abundance and age(4,5). Similar findings in the Galactic bulge have been hampered by the obscuration arising from thick and varying layers of interstellar dust. Here we report that Terzan 5, a globular-cluster-like system in the Galactic bulge, has two stellar populations with different iron contents and ages. Terzan 5 could be the surviving remnant of one of the primordial building blocks that are thought to merge and form galaxy bulges.
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    Variable Stars in the Inner Region of NGC 6388
    (2005) Pritzl, B. J.; Stetson, P. B.; Smith, H. A.; Catelan, Marcio; Layden, A. C.; Kinemuchi, K.; Rich, R. M.; Sweigart, A. V.
    The metal-rich globular clusters NGC 6388 and NGC 6441 ([Fe/H] ∼-0.6) have unusual sloping blue horizontal branches that extend from a prominent red clump through the RR Lyrae instability strip to a well-populated blue tail. The RR Lyrae variables found from ground-based studies in these clusters have unusually long periods for their metallicities and may represent a new Oosterhoff group. As part of a Hubble Space Telescope Snapshot program we have obtained ACS images of the inner, compact region of NGC 6388 and use archival WFPC2 images to search for additional variable stars. Here we present the results of this variable star search. The properties of the newly discovered RR Lyrae variables will be used to further define the nature of these unusual globular clusters. We gratefully acknowledge financial support through the HST grant GO-09821.09-A.