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Hubble Space Telescope
The HubbleObserver Corner for August 2011

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Proposal ID = 12576
Principle Investigator = Paul Kalas, University of California - Berkeley
Title = "Orbit determination for Fomalhaut b and the origin of the
             debris belt halo"
Time Observed =  Aug 27, 2011 00:50:11 -  08:21:00
Instrument = WFC3/UVIS (the program also uses STIS) 


The direct imaging of a planet (Fomalhaut b) outside our own solar system is one of Hubble's greatest highlights. Since that discovery, Hubble has continued to monitor Fomalhaut b to better determine the shape of the orbit and other characteristics of the planetary system and the debris disk around this nearby (25 light years) star. The orientation of the telescope must be carefully chosen so that the planet does not land on various artifacts produced by the telescope and the WFC3 detector. The observations in proposal 12576 will continue over the next two cycles.

Paraphrasing from the abstract:

HST has a unique capability to detect tenuous debris disks and exosolar planets at optical wavelengths. Using the ACS/HRC in 2004-2006, we imaged the debris belt surrounding Fomalhaut, finding evidence for a planetary system in the structure of the belt, and then directly imaging a planet candidate, Fomalhaut b (Fom b). We also discovered a tenuous halo extending 30 AU beyond the previously measured outer belt edge. These grains may be driven outward by radiation pressure or dynamically perturbed by Fom b.

Using STIS observations, we propose a long-term GO program dedicated to the study of the orbit of Fom b and its interaction with this newly discovered halo. The goals are to constrain the orbital elements of Fom b and establish with confidence that it is bound. In addition, to pinpoint the origin of grains that comprise the belt halo, we propose to obtain the halo scattered light color by direct imaging in F336W and F814W using WFC3/UVIS. If the main belt and halo share the same color (as opposed to blue Rayleigh-scattering grains) then planetary dynamical perturbations will be suspected. The orientation is chosen so that the planet Fomalhaut b does not land on the saturation column of the star, the chip gap, or the diffraction spikes.

You can find most of this information and more on the HST Homepage by entering "12576" in the Prop. ID box.

Proposal ID = 12177
Principle Investigator = Pieter van Dokkum, Yale University
Title = "3D-HST: A Spectroscopic Galaxy Evolution Treasury"
Time Observed =  Aug 20, 2011 23:49:59
Target = GOODS-SOUTH-34
Instrument = WFC3/IR/GRISM


GRISM observations using the Wide Field Camera 3 (WFC3) represent a powerful new capability for Hubble. These allow a combination of both the imaging and spectroscopic observing modes, and have the ability to measure spectra for hundreds of objects from a single observation. A wide range of science projects are taking advantage of this new capability ranging from mapping the universe at intermediate and high redshift, as in this proposal, to observations of nearby objects like brown dwarfs and extrasolar planets.

This is a treasury program (i.e., > 100 orbits with strong "legacy" value for a range of other investigations). This particular observation represents the 35th and 36th orbits of the 136 allocated to this project.

Paraphrasing from the abstract:

The Hubble Space Telescope has given us a dazzling imaging legacy, which has enabled us to establish a broad picture across cosmic epochs of how galaxies came to be. Here we propose to extend this legacy with 3D-HST, a peerless near-IR spectroscopic program for studying the physical processes that shape galaxies in the distant Universe. 3D-HST will provide rest-frame optical spectra for a complete sample of ~9000 galaxies at 1

The survey also has immense legacy value as it provides spectra for all objects in the target fields: 3D-HST should reveal faint quasars at z~7-8 and identify the first spectroscopically-confirmed galaxies at z~9. The survey area will cover most of the Faber et al. Multiple Cycle Treasury Program (MCTP) imaging area, leveraging this 912-orbit WFC3 imaging investment and greatly enhancing the scientific returns from that program. The combination of the two surveys will provide a definitive imaging and spectroscopic dataset for studies of the distant Universe which will probably not be superseded until JWST.

You can find most of this information and more on the HST Homepage by entering "12177" in the Prop. ID box.

Another potentially useful link for investigating GRISM observations in more depth is:

Proposal ID = 12278
Principle Investigator = Thomas Ayres - University of Colorado at Boulder
Title = "Advanced Spectral Library Project: Cool Stars"
Time Observed =  Aug 14, 2011 05:56:25
Target = HD164058


Hubble observing time is highly oversubscribed; typically a factor of 6 to 9 in recent cycles. Because of this, Hubble is not often used for projects that can be carried out using ground-based telescope, for example building a large library of stellar spectra. However, ground-based telescopes have the limitation that they are not able to observe the UV portion of the spectrum.

The purpose of this proposal is to augment ground-based spectral libraries by providing the needed high signal-to-noise spectra for a sample of eight carefully selected late-type stars in the spectral range 1150 - 3100 Angstroms. This requires separate observations using a variety of gratings and detectors, which must then all be stitched together seamlessly into a single spectrum.

Paraphrasing from the abstract:

"Stars are the luminous backbone of the Universe, and without them, it would be a dull and dreary place indeed: no light, no heavy elements, no planets, no life. It also is safe to say that stellar spectroscopy is a cornerstone of astrophysics, providing much of what we know concerning temperatures and masses of stars, their compositions, planets, and the dynamics and evolution of the galaxies they inhabit. Hence, the proper interpretation of stellar spectra is fundamental to modern astronomy.

Unfortunately, the existing archive of Space Telescope Imaging Spectrograph rarely achieves the high S/N of the best ground-based spectra, and relatively few objects have the full wavelength coverage for which the powerful, highly multiplexed, second generation Hubble instrument was designed.

The main product of our Treasury program will be detailed stellar "atlases", based on advanced processing of the STIS echellegrams. Members of our broad collaboration will analyze these data for specific purposes, such as detection of rare species in sharp-lined F stars, properties and kinematics of local interstellar clouds, and dynamics of chromospheres, coronae, and winds of cool stars; but rapid public release (based on the "StarCAT" model) will enable many other investigations by a much wider community, for decades to come."

You can find most of this information and more on the HST Homepage by entering "12278" in the Prop. ID box.

Proposal ID = 12269
Principle Investigator = Claudia Scarlata, University of Minnesota - Twin Cities
Title = "The escape of Lyman-alpha photons in star-forming galaxies"
Time Observed = Aug 8, 2011 05:45:33  
Target = GALEX1420+5247
Instrument = COS/FUV/G160M


Lyman-α is the principle emission line for the Hydrogen atom, and hence is a critical diagnostic for both the discovery of the most distant star forming galaxies, and for understanding the physics that control the formation and evolution of galaxies. The emission line is in the UV part of the spectrum, making it difficult to observe from the ground, unless the galaxy is very distant and hence the UV light is shifted into the optical part of the spectrum. In addition, being located in the UV, much of the light is absorbed by dust, hence the "escape fraction" that penetrates the dust and reaches us is typically quite low.

This proposal takes a different approach than most to the study of Lyman-α emission in galaxies by using the excellent UV sensitivity of the Cosmic Origins Spectrograph (COS), and the fact that Hubble is above the UV-blocking atmosphere of the earth, to observe relatively nearby star forming galaxies (Z = 0.3) in order to measure the escape fraction.

Paraphrasing from the abstract:

"Our knowledge of the very high redshift Universe heavily depends upon the observation of the Lyman-α (Lyα) emission line for both spectroscopic confirmation and often the actual discovery of galaxies at very high redshifts. However, no comprehensive study of the astrophysics behind the Lyα production, transport, and escape fraction has so far been made, since the required supplementary observations are redshifted to inaccessible wavelengths for cosmological populations.

With the aim of characterizing the physics of Lyα escape from galaxies, our group has undertaken a major effort to followup a new well-defined sample of GALEX-selected z~0.3 Lyα emitters. Here, we propose to obtain FUV COS-G160M spectroscopy of 25 GALEX star-forming Lyα emitters for which we have already measured gas metallicity, nebular extinction, escape fraction of Lyα photons, and stellar masses. By investigating the physical mechanisms driving the Lyα output in a well-defined sample of low-z Lyα emitters, the proposed study will provide us with the necessary knowledge to interpret the observations in the more distant universe."

You can get more information about this proposal from the Program Status box on the HST Homepage, by entering "12269" in the Prop. ID box.

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