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The HubbleObserver Corner for January 2012

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Proposal ID = 12181
Principle Investigator = Dr. Drake Deming  -  University of Maryland 
Title = "The Atmospheric Structure of Giant Hot Exoplanets"
Time = Jan 17, 2012 02:45:15	- 08:30:06
Target =  COROT-1
Instrument = WFC3/IR

Background:

When Hubble was launched, probably nobody was thinking it might one day provide an opportunity to measure the constituents of the atmospheres of planets outside our own solar system. However the discovery of giant hot exoplanets orbiting close to their stars makes eclipses, as viewed from the Earth, relatively frequent. The high precision photometry from Hubble, and more recently Spitzer, makes it possible to observe the very small dips in the luminosity of the star as it blocks the light from the star. Some of the light from the star goes through the atmosphere of the planet before it reaches us, leaving tell-tale absorption signatures when a spectrum of the star taken during the eclipse is subtracted from a spectrum taken when the star is not eclipsed. This observing technique is called transmission spectroscopy. CoRoT (COnvection, ROtation, and Planetary Transits) is a French/ESA space mission designed to study extrasolar planets and asteroseismology. This particular target, COROT-1, was the first extrasolar planet discovered by the CoRot spacecraft in 2007.

Paraphrasing from the abstract:

Characterization of close-in giant exoplanets has proceeded rapidly over the past few years, due largely to Spitzer and HST observations in transiting systems. Low resolution thermal emission spectra of over two dozen planets have been measured by Spitzer, and HST observations of a few key planets have indicated unusual molecular abundances via transmission spectroscopy. However, current models for the atmospheric structure of these worlds exhibit degeneracies wherein different combinations of temperature and molecular abundance profiles can fit the same Spitzer data for each planet. Fortunately, the advent of the IR capability on HST/WFC3 allows us to solve this major problem in exoplanet science. We propose to inaugurate a Large HST program that is scientifically complementary to Spitzer, Kepler, and CoRoT exoplanet results.

We will obtain transmission spectroscopy of the 1.4-micron water band in a sample of 13 planets, using the G141 grism on WFC3. Among the abundant molecules, only water absorbs at this wavelength, and our measurement of water abundance will enable us to break the degeneracies in the Spitzer results with minimal model assumptions. We will also use the G141 grism to observe secondary eclipses for 7 very hot giant exoplanets at 1.5-microns, including several bright systems in the Kepler and CoRoT fields. Kepler and CoRoT teams will thereby be able to subtract the thermal contribution from their increasingly precise measurements of optical eclipses, and measure, or place extremely stringent limits on the albedo of these exotic worlds.

You can find most of this information and more on the HST Homepage by entering "12181" in the Prop. ID box.


Proposal ID = 12786
Principle Investigator = Dr. Andrew J. Levan  -  The University of Warwick 
Title = "Searching for the nature of the ultra-long transient GRB 111209A"
Time = Jan 13, 2012 08:58:04 - 11:41:17
Target =  GRB111209A
Instrument = WFC3/IR, WFC3/UVIS

Background:

Gamma Ray Bursts (GRBs) come in a variety of flavors, with typical durations ranging from tens of milliseconds to several minutes. The distribution appears to be bimodal with short-burst GRBs (< 1 second) believed to originate from the merger of binary neutron stars (or a neutron star + black hole), while long-burst GRBs (> 2 seconds) appear to be associated with supernova events with the star collapsing to form a neutron star or black hole. There are also very rare events lasting longer, such as the "Christmas day GRB" that went off Dec 25, 2010 and lasted 28 minute. Two very different models have been suggested for this event. The first model consists of a merger between a neutron star and a companion star that has just entered the red giant phase. The second model is a collision between a comet and a neutron star. On December 9, 2011, GRB 111209A was observed with a 2 hour duration. The proposers submitted a "Target of Opportunity" proposal to observe the environment of this unique event with Hubble roughly a month after it was first observed. Many GRBs (including GRB 111209A) are observed to be in host galaxies which provides a means of determining the distance and hence the total energy of the event. This has demonstrated that GRBs are the most luminous events known in the universe since the Big Bang.

Paraphrasing from the abstract:

We propose observations of the exceptional long duration transient GRB 111209A. Its long-lived gamma- and X-ray emission mark it apart from other GRBs, and are very similar to those of the Christmas day burst 2010, whose origin remains under debate, culminating in the publication of two competing scenarios in Nature earlier this month. Unlike the Christmas day burst, our deep VLT and Gemini spectroscopy has unveiled the redshift of GRB 111209A, and allows us to launch a comprehensive campaign to understand its origin. Does it originate from a massive star collapse akin to long GRBs? Is it related to Galactic nuclei, as suggested for some other long lived gamma-ray transients discovered in 2011? By utilizing the exquisite HST PSF we will obtain a precise position of the afterglow with respect to its host galaxy. Coupled with this we will use the unique ability of WFC3 grism's to obtain good S/N across the 1 micron region to search at the expected peak of any supernova, and hence provide spectroscopic evidence for the presence (or absence) of an associated supernova. Ultimately these observations may show conclusively what these long duration transients are, and link them into the diverse populations of high energy transients that are now being uncovered.

You can find most of this information and more on the HST Homepage by entering "12786" in the Prop. ID box.


Proposal ID = 12238
Principle Investigator = Dr. William Harris
Title = "Supermassive Star Clusters in Supergiant Galaxies: 
           Tracing the Enrichment of the Earliest Stellar Systems"
Time = Jan 9, 2012 15:06:04 - 21:54:59
Target =  ESO038-G076
Instrument = ACS/WFC, WFC3/UVIS

Background:

Globular clusters provide the best fossil record of the early universe. Our own galaxy has roughly 160 globular clusters, making it difficult to study a variety of newly found correlations (listed in the abstract below), or to sample the extremes in the population, especially the rare supermassive globular clusters. The central galaxies in rich galaxy clusters (cD galaxies) are much more massive than our own Milky Way galaxy, and hence have much richer populations of globular clusters; in many cases numbering in the tens of thousands. This proposal aims to use this property of these unique galaxies to obtain a much larger sample of globular clusters. The 7 galaxies in this sample will provide a larger database than the ACS Virgo Cluster Survey (proposal 9401 - see https://www.astrosci.ca/users/VCSFCS/Home.html) of 100 elliptical and SO galaxies, albeit at larger distances which will preclude studying the fainter clusters.

Paraphrasing from the abstract:

The cD-type Brightest Cluster Galaxies contain the richest globular cluster systems (GCSs) that exist. Surprisingly, we know little about these systems beyond the globular cluster populations in the nearby cDs M87 (Virgo) and NGC 1399 (Fornax), and these two cases no longer provide adequate tests of the new phenomena now being uncovered, such as the correlation between GC mass and metallicity, the strikingly different formation efficiencies of metal-poor and metal-rich clusters, the galaxy-to-galaxy differences in GC mass distribution, and connections to Ultra-Compact Dwarfs and dE nuclei. We propose to image 7 cD-type systems within 200 Mpc that are representative of the very biggest galaxies known (Mv < -23). These lie in far richer Abell-cluster environments than we could ever probe in Virgo, Fornax, or nearer systems. We will use ACS/WFC and WFC3 to image their GCSs down to the turnover point of the GC luminosity function, using the B and I filters. Our complete survey will produce luminosities, metallicities, and spatial distribution functions for more than 35, 000 GCs, the largest GC database in existence and an order of magnitude larger than even the recent Virgo Cluster Survey.

You can find most of this information and more on the HST Homepage by entering "12238" in the Prop. ID box.


Proposal ID = 12187
Principle Investigator = Luis C. Ho,  Carnegie Institution of Washington
Title = "A New Sample of Circumnuclear Gas Disks for Measuring Black 
            Hole Masses in Spiral Galaxies"
Time = Jan 1, 2012 18:07:33 - 23:17:48
Target =  IC-356
Instrument = STIS/CCD

Background:

It is now known that most, and perhaps all galaxies have a massive black hole (BH) at their center, as shown by the increase in the random velocities of stars in the inner regions of galaxies. These random velocities are called the stellar velocity dispersion. A surprising discovery based on such measurements is that there is a tight correlation between the mass of the black hole (M) and the stellar velocity dispersion in the bulge of the galaxy (sigma). This is called the M-sigma relation. The tightness of the relation demonstrates that the formation of black holes is linked to the formation of the galaxy as a whole; one of the most important results of the past decade. Another way to measure the mass of a black hole is to determine how fast gas is rotating around it. This is more likely to be possible in a gas-rich spiral galaxy (i.e., a late type galaxy) than in a gas-poor elliptical galaxy (i.e., an early type galaxy). The goal of this proposal is to increase the sample of spiral galaxies with BH mass determinations, hence providing insight into the formation of spiral and elliptical galaxies and how they are related.

Paraphrasing from the abstract:

The correlation between central black hole (BH) mass and bulge stellar velocity dispersion has become a fundamental tool to investigate the link between BH growth and galaxy formation. However, the current BH census in nearby galaxies is highly biased toward early-type galaxies. It is important to increase the number of direct BH mass measurements along the spiral sequence, not only to better delineate the M-sigma relation but also to verify tentative claims that the scatter and zero point of the relation may vary with galaxy morphology and the formation history of the bulge. With these goals in mind, we carried out an ACS/WFC narrow-band (F658N) imaging survey of nearby S0-Sbc galaxies to identify circumnuclear Halpha disks suitable for follow-up STIS spectroscopy. We found 6 good new candidates of circumnuclear gas disks in spiral galaxies. STIS G750M spectra will be obtained for each source using three parallel slits to map out the gas kinematics in the inner portion of the nuclear disks: We will perform dynamical modeling to measure the central BH masses. If successful, this study will provide a significant increase in the current sample of spirals with secure BH masses, with important ramifications for improving and refining the M-sigma relation.

You can find most of this information and more on the HST Homepage by entering "12187" in the Prop. ID box.


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