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The HubbleObserver Corner for November 2011

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Proposal ID = 12468
Principle Investigator = Keith Noll - NASA Goddard Space Flight Center
Title = "How Fast Did Neptune Migrate? A Search for Cold Red Resonant Binaries"
Time = Nov 24, 2011 03:38:18 - 04:30:49
Target(s) = 149349
Instrument(s) =  WFC3/UVIS

Background:

The first trans-Neptunian object (besides Pluto) was discovered in 1992. There are now over 1200 trans-Neptunian objects (TNOs)! The large number of objects allow astronomers the opportunity to study the evolution of Neptune orbits, since Neptune has the strongest gravitational influence on them. Many of the TNOs are found in what are called "resonant orbits" with Neptune. For example, an object in a 3:2 resonance will orbit the sun twice while Neptune orbits three time. The object therefore gets a small gravitational kick at the same point in its orbit, which acts to hold (capture) the object in that particular orbit. Objects in 3:2 resonance are called Plutinos, since Pluto itself belongs to this group. However, there are also less well defined resonances such as 3/5 and 4/7. If Neptune moved smoothy out in its orbit it would have been able to capture some TNOs in these orbits as well. This proposal will test this model.

Paraphrasing from the abstract:

"Cold Classical" TNOs share a unique set of physical properties that were acquired in their nascent environment in the protoplanetary disk. These objects are red, have high albedos, and a high fraction (>30%) are binaries with nearly equal mass components. They appear to be a relatively undisturbed remnant of the original protoplanetary disk and are concentrated in low inclination orbits between the 3:2 and 2:1 resonances at 39.4 and 47.7 AU. As Neptune migrated outwards in the first several hundred million years of the solar system, its mean-motion resonances moved through and were able to capture some of these objects. Identifying Cold Classicals trapped in resonances will allow us to discriminate between the two leading models for Neptune's migration. Smooth migration will result in measurable differences between resonances, fast migration (including transport by planetary scattering) will not. We propose to survey all Resonant transneptunian objects that have not yet been observed with HST to search for the distinctive physical markers of captured Cold Classicals.

You can find most of this information and more on the HST Homepage by entering "12468" in the Prop. ID box.


Proposal ID = 11616
Principle Investigator = Gregory Herczeg - Max-Planck-Institut fur
                         Extraterrestrische Physik                                 
Title = "The Disks, Accretion, and Outflows (DAO) of T Tau Stars"
Time = Nov 10, 2011 09:09:54 - 13:26:01
Target(s) = UX-TAU-A
Instrument(s) = COS/FUV, COS/NUV, STIS/CCD, STIS/NUV-MAMA

Background:

T Tauri stars are young, highly variable stars that are powered by their gravitational contraction rather than by nuclear fusion. They are found around molecular clouds that are actively forming stars. T Tauri stars have accretion disks which power strong outflows from their inner regions. Some T- Tauri stars have circumstellar disks further out, believed to be the precursors of protoplanetary disks (i.e., the progenitors of planetary systems). This proposal uses the two spectrographs on Hubble, the Cosmic Origins Spectrograph (COS) and the Space Telescope Imaging Spectrograph (STIS), to better understand the physical properties and evolution of T Tauri stars. This is an example of a "large" proposal (i.e., more 100 orbits).

Paraphrasing from the abstract:

Classical T Tauri stars undergo magnetospheric accretion, power outflows, and possess the physical and chemical conditions in their disks to give rise to planet formation. Existing high resolution FUV spectra verify that this spectral region offers unique diagnostics of these processes, which have the potential to significantly advance our understanding of the interaction of a star and its accretion disk. We propose to use HST/COS to survey the disks, outflows, and accretion of 32 T Tauri star in the FUV at high spectral resolution. A survey of this size is essential to establish how properties of accretion shocks, winds and disk irradiation depend on disk accretion rate. Specifically, our goals are to (1) understand the physical properties of the gas very near the accretion shock; (2) measure the opacity, velocity, and temperature at the base of the outflow to constrain outflow models using wind absorption features; and (3) characterize the radiation incident on disks and protoplanetary atmospheres.

You can find most of this information and more on the HST Homepage by entering "11616" in the Prop. ID box.


Proposal ID = 12546
Principle Investigator = Dr. R. Brent Tully, University of Hawaii
Title = "The Geometry and Kinematics of the Local Volume"
Time = Nov 2, 2011 02:10:42 - 03:07:44
Target(s) = ESO104-044
Instrument(s) = ACS

Background:

The measurement of distance is one of the most fundamental pieces of information about any astronomical object. Given a certain luminosity, is an object nearby, and therefore intrinsically faint, or is it very distant, and hence intrinsically bright? While there are a host of methods available for measuring the distance to a galaxy, many of them cannot be used for a given target. For example, if there are no Cepheid variables or Type 1a supernovae, these methods cannot be used. This proposal uses a method for measuring distance that can be used for nearly all nearby galaxies, namely the Tip of the Red Giant Branch (TRGB). The method relies on the fact that there is a characteristic maximum luminosity for red giant branch stars. Hubble observations already exist to measure the distance to most of the known galaxies within 4 Mpc. This proposal is designed to provide measurements of randomly sampled galaxies out to 10 Mpc, hence providing much better information about the distribution of galaxies in the nearby universe.

Paraphrasing from the abstract:

HST is uniquely capable of providing distances to nearby galaxies through measurement of the luminosities of stars at the Tip of the Red Giant Branch (TRGB). With accurate distances, we generate three-dimensional maps of the distribution of galaxies and decouple the expansion and peculiar components of line-of-sight velocities. Essentially all galaxies have RGB stars and the halo populations are free of host reddening. With a single orbit ACS observation in two filters a color-magnitude diagram can be constructed that reaches 1.4 mag fainter than the TRGB for a galaxy at 8 Mpc. The tremendous efficiency and accuracy of the TRGB method makes it possible to observe a large, complete volume-limited sample with a modest allocation of HST resources. Our immediate interests are (a) to study in detail the clustering properties of galaxies with distance resolution of 200 kpc, and (b) to map the local velocity field as a probe of the distribution of dark matter and dark energy. In addition, the program will provide an archival legacy of the stellar content of nearby galaxies to a level in the color-magnitude diagram at least as faint as M_I = -2.6.

You can find most of this information and more on the HST Homepage by entering "12546" in the Prop. ID box.


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