Accretion Disks Around Young Stars: Hartigan and S. Kenyon (CfA) have used the Hubble Space Telescope to observe a sample of ~ 20 young stars with accretion disks with an objective prism on the ACS camera. While HST was collecting a spectrum of the ultraviolet light from 2000A through 4500A, Hartigan observed the same targets at optical wavelengths from Kitt Peak in Arizona, while Kenyon observed them in the near-IR at Mt. Hopkins. Together, this data set provides the first complete, simultaneous spectral coverage of accretion disks around young stars from the UV through the optical and out to the infrared (0.2 - 3.5 microns). In many cases were observed exactly simultaneously on the three telescopes. All spectra have been combined together, and we are constructing models to fit the total spectral energy distribution. The UV is crucial for understanding the mass accretion rate, while the optical is needed to observe the star and the infrared to see emission from the dust. The systems vary on timescales of days; ours will be the first study to eliminate this variable in modeling the systems. Rice graduate student Jacob Palmer has begun to develop an accretion column model that makes use of an existing MHD code with the goal to reproduce the observed spectral energy distributions.
Collimation Regions of Stellar Jets: One of the most intriguing recent observations of stellar jets has been that they appear to rotate as they emerge from their host star/disk systems. However, the observations, based on spectra from HST are extremely difficult to perform, and strain the limits of the instrumentation. A new instrumental configuration on the Keck telescope combines a higher resolution spectrograph than the one available on HST with adaptive optics technology. With a collecting area about 20 times that of HST, this combination is the best in the world for projects such as jet rotation that require both the highest possible spatial and spectral resolution. Together with Lynne Hillenbrand (Caltech), Hartigan obtained spectra of the jet in RW Aur in late 2006, and was able to resolve intrinsic emission line widths very close to the source. The analysis of these data are now complete, and are nearing publication. While no rotation is found, the data provide the most stringent constraints to date on the dynamics of jets as they emerge from their sources.
Extrasolar Planets and Star Spots: Hartigan continued a study with recent Rice Ph.D. Marcos Huerta, Rice faculty member Chris Johns-Krull, and Lisa Prato (Lowell), and Rice graduate students Yang and Mahmud to search for radial velocity perturbations that might be caused by planets around young stars. Sensitive searches for older planets have turned up many such objects, but finding them around young stars is difficult because starspots, which are common when stars are young, often mimic the radial velocity signatures of planets. Analysis of bisectors and radial velocities shows conclusively that some of the sample have significant starspot activity that affects radial velocities at the level of about 1 km/s. Results for several young stars were published in the Astrophysical Journal in the last year. We took additional data in several observing runs at Kitt Peak and McDonald Observatory in the last year and have more scheduled.
Laboratory Experiments: Hartigan continued a collaboration with scientists at Los Alamos, Rochester, and AWE to study shock waves in collimated jets using high-powered lasers. Funded by the DOE, the project uses the Omega laser to launch jets and observe how the flows respond to inhomogenous media. We completed two sets of laser shots this year, and two more years of this research have just been funded by DOE. The jet collides with a spherical obstacle at various offset distances, and we are exploring how the structure of the shocks that result from this collision vary with time and with distance. In January 2008 we began to explore shock waves in multiple ball targets as a step in the direction of understanding shocked, clumpy flows. A sample image taken by illuminating the jet with X-rays, shows the jet deflecting from the ball. A major paper that combines the numerical, experimental and astronomical observational work is nearing publication.
Rice Ph.D. graduate students Bobby Carver and Jacob Palmer are both involved with numerical coding projects related to the laboratory astrophysics work. Carver's project is to incorporate material properties into the AstroBEAR numerical code (an astrophysical MHD code) to enable it to model the laboratory experiments, and that work is also nearing completion. Palmer is working to improve the radiative cooling algorithm in the code so it can predict accurate emission line images, useful for studies of accretion disks as well.
Movies [new]: Another exciting observational aspect of the laboratory work is the approval of a substantial Hubble Space Telescope project to obtain a third epoch of emission line images for three famous stellar jets. The previous two epochs, taken roughly 5 and 10 years ago, show substantial motions and structural changes within the flows. The third epochs have now been taken, and we have been able to make spectacular movies of the motions in these flows. A paper on this material is in preparation.
Massive Star Forming Regions [new]: Together with Rice undergraduate Ilse Cleeves, Hartigan obtained time on the Kitt-Peak 4-meter telescope to use a new state-of-the-art infrared array called NewFIRM. The NewFIRM system has an extremely large field of view, which enables studies of extended regions of star formation that would have taken months to be done in a matter of days. Our application is to the star formation region Cygnus OB2, which is an extremely rich region that has been poorly-studied to date owing to its location behind large amounts of obscuring dust. However, in the infrared we see through this dust into the stellar nursery. The weather was good and we obtained a full set of observations on the region. The images are highly complex and will be challenging to reduce and analyze (part of Ilse's senior thesis), but the quality is excellent and the quick-look results make it clear that many discoveries await us in this data set.
Statistical Spectral Analysis [new]: Hartigan and Johns-Krull are helping to direct Rice graduate student Colleen Kenney (Statistics Dept) in an attempt to apply independent component analysis and blind-source separation algorithms to a series of existing spectra of young stars, with the goal of being able to identify specific physical components in the spectra. If successful, this research may go a long way towards clarifying how young stars accrete material from their surrounding disks.
Campus Observatory Activities: The Rice University Campus Observatory (RUCO), built in 2002, continued as the workhorse for our undergraduate major and nonmajor courses, including the lab course for undergraduate majors run by Hartigan in Spring 2007 and 2008, and a lab course for academs taught by Dufour. The telescope mount underwent a major overhaul over the summer and is once again operating well. The Department and RSI operated several open houses in 2008. Events held during commencement and homecoming were well-attended by Rice students, faculty, staff, and members of the Houston community. Our graduate students and undergraduate majors have helped out during all of the public nights, and we continue to involve our students in these types of activities. More details about current observatory schedules can be found on the observatory website.
