Cycle 15 Abstract Catalog Generated from Phase I Submissions April 19, 2006 ================================================================================ Proposal Category: GO Scientific Category: UNRESOLVED STELLAR POPULATIONS ID: 10785 Title: Luminosity Profiles of Extremely Massive Clusters in NGC 7252 PI: Nate Bastian PI Institution: University College London (UCL) The galactic merger remnant NGC 7252 represents one of the most extreme post- starburst environments in the local universe. During the disk-disk merger (~400 Myr ago) this galaxy produced the largest young massive star cluster population known, including two star clusters above 10^7 Msun, a factor of 100 more massive than typical globular clusters in the Milky Way. We propose ACS- HRC observations of 3 fields in NGC 7252 in order to explore the detailed properties, i.e. luminosity profiles, of these massive star clusters. These observations will be able to test massive cluster formation mechanisms (e.g. the cluster-merger scenario) as well as the possible tidal erosion and truncation of the outer regions of the clusters by the galactic potential. These observations will compliment our large on-going study, using archival HST data, of star cluster profiles outside the Local Group. The cluster population in NGC 7252 will extend our sample in cluster mass by an order of magnitude. ================================================================================ Proposal Category: GO Scientific Category: SOLAR SYSTEM ID: 10786 Title: Rotational state and composition of Pluto's outer satellites PI: Marc Buie PI Institution: Lowell Observatory We propose an intricate set of observations aimed at discovering the rotational state of the newly discovered satellites of Pluto, S/2005 P1 and S/2005 P2. These observations will indicate if the satellites are in synchronous rotation or not. If they are not, then the observations will determine the rotational period or provide tight constraints on the amplitude. The other primary goal is to extend the wavelength coverage of the colors of the surface and allow us to constrain the surface compositions of both objects. From these data we will also be able to significantly improve the orbits of P1 and P2, improve the measurement of the bulk density of Charon, and search for albedo changes on the surface of Pluto. ================================================================================ Proposal Category: GO Scientific Category: UNRESOLVED STELLAR POPULATIONS ID: 10787 Title: Modes of Star Formation and Nuclear Activity in an Early Universe Laboratory PI: Jane Charlton PI Institution: The Pennsylvania State University Nearby compact galaxy groups are uniquely suited to exploring the mechanisms of star formation amid repeated and ongoing gravitational encounters, conditions similar to those of the high redshift universe. These dense groups host a variety of modes of star formation, and they enable fresh insights into the role of gas in galaxy evolution. With Spitzer mid-IR observations in hand, we have begun to obtain high quality, multi-wavelength data for a well-defined sample of 12 nearby (<4500km/s) compact groups covering the full range of evolutionary stages. Here we propose to obtain sensitive BVI images with the ACS/WFC, deep enough to reach the turnover of the globular cluster luminosity function, and WFPC2 U-band and ACS H-alpha images of Spitzer-identified regions hosting the most recent star formation. In total, we expect to detect over 1000 young star clusters forming inside and outside galaxies, more than 4000 old globular clusters in >40 giant galaxies (including 16 early-type galaxies), over 20 tidal features, approximately 15 AGNs, and intragroup gas in most of the 12 groups. Combining the proposed ACS images with UV GALEX observations, ground-based H-alpha imaging, and HI data, we will conduct a detailed study of stellar nurseries, dust, and gas kinematics. To supplement and dramatically enhance this rich dataset, we also propose to obtain Chandra observations to investigate the high-energy phenomena associated with AGN and star formation activity. ================================================================================ Proposal Category: GO Scientific Category: RESOLVED STELLAR POPULATIONS ID: 10788 Title: Probing the Central Dark Mass Concentration of the Collapsed-Core Globular Cluster M15 PI: Haldan Cohn PI Institution: Indiana University System We plan to probe the central dark mass concentration in the collapsed-core globular cluster M15 by analyzing the structure of its central stellar cusp with the highest possible angular resolution. The rapid rise of M/L toward the center of M15 can be alternatively explained by a central concentration of several thousand compact remnants (heavy white dwarfs and neutron stars) or instead by the presence of an intermediate-mass black hole (IMBH) of a few thousand solar masses. We propose to obtain one orbit of ACS/HRC F555W (V) imaging to supplement the available ACS/HRC F435W (B) imaging from GO-10401. This will allow us (1) to improve the constraints on the radius of the as yet unresolved core and (2) to investigate the relation between cusp slope and stellar mass, the form of which depends on the size and mix of the remnant population and on whether or not an IMBH is present. We will compare the central cusp structure with predictions from both Fokker-Planck and GRAPE-6 N- body models, with and without IMBHs, to constrain the nature of the intriguing dark mass concentration. ================================================================================ Proposal Category: GO Scientific Category: UNRESOLVED STELLAR POPULATIONS ID: 10789 Title: The Role of Environment in the Formation of Dwarf Galaxies PI: Christopher Conselice PI Institution: University of Nottingham Clusters of galaxies contain an overdensity of dwarfs compared to the field. Within galaxy clusters there is also a correlation between the overdensity of dwarfs and local galaxy density, such that areas of lower galaxy density contain more dwarfs per giant. The origin of these 'extra' dwarfs is unknown, but a large fraction of them did not form through standard collapses early in the universe. Some dwarf ellipticals in clusters have metal rich and young (< 6 Gyr) stellar populations while others contain old metal poor populations, suggesting multiple formation mechanisms and time scales. We propose to test the idea that dwarfs descend from galaxies accreted into clusters during the past 8 Gyr by correlating ages and metallicities of dwarfs with their internal structures - spiral arms, bars, and disks. If dwarfs originate from more massive galaxies then these features should be common in metal rich and young dwarfs. On the other hand, if no correlation is found it would suggest that dwarfs form through in-situ collapses of gas in the intragalactic medium after the universe was reionized. ================================================================================ Proposal Category: GO Scientific Category: ISM AND CIRCUMSTELLAR MATTER ID: 10790 Title: Planetary Nebulae, Globular Clusters and Binary Mergers PI: Orsola De Marco PI Institution: American Museum of Natural History Four planetary nebulae (PNe) have been found within 130 of the 150 globular clusters (GCs) of our Galaxy. This might not seem like many, but stellar evolution predicts that the old populations of these clusters should contain no PN at all ================================================================================ Proposal Category: GO Scientific Category: HOT STARS ID: 10791 Title: Proper motion may nail counterpart of unique X-ray pulsar PI: Andrea DeLuca PI Institution: CNR, Istituto di Astrofisica Spaziale 1E 1207.4-5209 is one of the most puzzling X-ray compact sources in the Galaxy. Long known to be a radio-quiet Neutron Star (NS) embedded in a young (~7000 y) supernova remnant, it displays a unique phenomenology, including multiple cyclotron absorption features in its thermal X-ray spectrum, as well as a possible non-monotonous evolution of its 424 ms rotational period. A candidate optical counterpart (I~23.4) with very red colours (not consistent with the expected emission of a NS, but rather with a low-mass stellar companion, or a fossil disk) was singled out with HST/ACS in 2003, at the margin of the Chandra error box. In order to test the reality of such an association, we propose to take advantage of the high space velocities characteristics of NSs to search for the expected displacement (~150 mas in the NE direction) of the candidate counterpart over a 3 years time span. One orbit observation, either unveiling the displacement or ruling it out, will settle the problem of the optical identification of 1E1207.4-5209. We stress that a null result would also be important for the understanding of this source. ================================================================================ Proposal Category: GO Scientific Category: AGN/QUASARS ID: 10792 Title: Quasars at Redshift z=6 and Early Star Formation History PI: Matthias Dietrich PI Institution: The Ohio State University Research Foundation We propose to observe four high-redshift quasars (z=6) in the NIR in order to estimate relative Fe/Mg abundances and the central black hole mass. The results of this study will critically constrain models of joint quasar and galaxy formation, early star formation, and the growth of supermassive black holes. Different time scales and yields for alpha-elements (like O or Mg) and for iron result into an iron