Research Report for 2017

Professor Patrick Hartigan's research involved the formation of stars, stellar jets, laboratory astrophysics, emission nebulae, and the physics of shock waves in 2017. Press releases of selected research papers and a full list of publications are available on the Web.

Star Spots: With Rice professor C. Johns-Krull, Hartigan initiated a study of the light curves of young stars with the Kepler satellite. Although Kepler has lost two of its reaction wheels, it can still be used to obtain high precision, uninterrupted light curves over the course of a couple of months. This ability is a vast improvement from analogous ground-based studies, which suffer both from much higher noise and from gaps in the temporal coverage caused by daylight and weather. The preliminary data look quite interesting, with multiple flares as well as sinusoidal fluctuations. There should be enough flares detected to provide a good comparison with solar phenomenon. Young stars have particularly strong flaring activity, and this activity will affect how the atmospheres of newly-formed planets evolve.

Laboratory Experiments: Hartigan continued to lead a collaboration with scientists at the University of Michigan, University of Rochester, MIT, and Imperial College, to study shock waves in the laboratory. Funded by the DOE, one project uses the Omega laser to launch jets and observe what happens when strong shock waves intersect. A separate project explores what happens to shock waves in a plasma where magnetic field strengths are large. Rice graduate student Andy Liao finished his Ph.D. thesis work using numerical models to help design laboratory experiments of magnetized flows. Of particular interest are diagnostics of magnetic fields made possible with proton radiography. The experimental radiographs show how the flow sweeps up magnetic fields into concentrations that mark the locations of shocks in the flows. These fields serve as tracers to image areas of shock fronts with much better spatial resolution than is possible using simple optical cameras. Our team is currently analyzing additional data that use spatially-resolved Thomson scattering to follow the dynamics of the gas as it flows through a strong shock.

Massive Star Forming Regions/JWST: As part of a large work related to molecular hydrogen emission in the Carina star-formation region published in the Astronomical Journal in 2015, a group led by Hartigan noticed that there was a consistent offset between emission from molecular hydrogen and that from atomic hydrogen. Additional data on the CygOB2 and IC 1396 region confirm this result as a general characteristic of photodissociation regions. Rice undergraduate Scott Carlsten wrote his senior thesis on this topic (winning the Departmental Heaps Prize for it), and we will submit a paper that describes these results soon. Hartigan is a collaborator on one of the fifteen large proposals accepted in the first round for the James Webb Space Telescope (JWST). The proposal will study the Orion Bar region as a means to test a variety of instruments on the telescope.

ALMA and Gemini Studies of Photodissociation Regions: With Rice assistant professor Andrea Isella, Hartigan obtained deep maps of a bright region of photodissociation in the Carina Nebula at millimeter and sub-mm wavelengths with the Atacama Large Millimeter Array in Chile. The array has recently been configured to operate at high enough frequencies to observe emission from the 600-micron line of C I. Together with existing H2 observations and new ALMA CO and CS maps of the region, we now have the first high-resolution maps that trace gas from where it is molecular deep within the dark cloud, to its atomic stage, to where it becomes ionized at the dissociation front, a process which occurs in all regions of massive star formation. Additional high-resolution images should become available this spring, as a proposal led by Hartigan for time on the 8-meter Gemini adaptive optics imager was just accepted. The adaptive optics imager should provide the sharpest image ever of a photodissociation region, and will rival that achievable with the James Webb Space Telescope when it comes on-line. Part of the science here is to understand the interface shapes, and Hartigan has been working to devise a new analysis technique along those lines.

Hubble Observations of Stellar Jets: Hartigan is PI on one proposal accepted in the latest cycle for the Hubble Telescope, and Co-I on another. The first target is a fascinating example of a combination of a molecular and atomic shock front, where the cooling zones are well-resolved. The proposal uses a rare observational mode with HST that will allow us to measure electron densities at extraordinarily high spatial resolution. By comparing with previous images we will also be able to quantify any proper motions throughout the jet. The second proposal, led by B. Nisini in Rome, will use HST to image the regions very close to protostars in an attempt to learn how jets are launched. The new images can be combined with future studies with JWST that will probe even further through the dense, dusty disks that surround these systems.

Numerical Simulations of Jets and Shock Fronts: Hartigan collaborated with professor A. Frank and University of Rochester graduate student Eddie Hansen to develop models of magnetohydrodynamic flows of pulsed supersonic jets, and to investigate the intersection surfaces of overlapping bow shocks. A refereed paper from this work appeared in the Astrophysical Journal in 2017. Another effort, with collaborator John Raymond at the Center for Astrophysics, is to produce a large grid of radiative shock models that can be used by researchers to predict emission line ratios. These are particularly helpful for interpreting forbidden lines, as will be needed by many studies once the James Webb Space Telescope is operational.

Large Synoptic Survey Telescope and a future UV Space Telescope: Hartigan is part of the Transient and Variable Stars group of the Large Synoptic Survey Telescope, a facility under construction in Chile that will survey the entire sky visible from that location every three days. These data will usher in a new era of `time-domain astronomy', requiring astronomers to sort through vast amounts of data in a short time. The LSST subgroups are tasked with optimizing the time cadences for their objects, and Hartigan led a white paper on the subject related to young stars. The entire document is now available on-line.

Campus Observatory Activities: It was a another busy year at the campus observatory, with a great deal of public interest focused on the solar eclipse that cut across the US on August 21, 2017. The telescopes were set up on the campus quad to show the partial phases, and we distributed hundreds of eclipse glasses to those who attended. An interesting total lunar eclipse occurred on Jan 31, 2018, but the weather here was poor. A summary of all the lunar eclipses visible from the Houston area out to the year 2060 is available. We continue to provide regular public viewing opportunities througout the semester, and give general astronomy talks before each observing session. All the lectures and observing opportunities are free to the public.

The Rice University Campus Observatory (RUCO), located on the roof of the Brockman Physics building continues to be the workhorse for our undergraduate major and nonmajor courses. The facilities are used by students as part of their undergraduate training. After many decades of having equipment scattered in multiple locations, we have now consolidating our equipment in a single storage location and have a usable work room adjacent to the observatory site. Details about current observatory schedules can be found on the observatory website.

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Patrick Hartigan