Research Report for 2019

Professor Patrick Hartigan's research involved the formation of stars, stellar jets, emission nebulae, the physics of shock waves, and time-domain astronomy in 2019. A full list of publications is available on the Web, as are overview pages that describe research areas of young stars and stellar jets.

Massive Star Forming Regions/JWST: Hartigan is leading a project to obtain orbital parameters for newly-discovered young eclipsing binaries in the Carina massive star formation region. Eclipsing binaries are the most reliable way to test pre-main-sequence evolutionary tracks because the primary and secondary must have the same ages. The eclipsing binary data allows us to measure the radii and temperatures of each star accurately, making it possible to find their individual ages. Only a handful of young eclipsing binaries are known, so new discoveries of these objects are an important constraint to the theory. In 2019, we acquired three nights of spectra with the 4-m SOAR telescope in Chile, and we have 6 more nights assigned in 2020.

Hartigan is a collaborator on one of the fifteen large proposals accepted in the first round for the James Webb Space Telescope (JWST; O. Berne PI). The proposal will study the Orion Bar region as a means to test a variety of instruments on the telescope once it launches.

Stellar Jets: Hartigan is currently actively involved with two projects that use the Hubble Space Telescope. The first of these imaged the stellar jet HH 7-11 to determine electron densities and excitations everywhere along the flow with the spatial resolution of HST. This science could only be done by employing a rarely-used set of filters on the WFC3 camera that isolate individual emission lines. The images reveal a remarkable cavity evacuated by the flow, and show that the jet punches through sheets of material as it propagates and then deflects to the side in response to these encounters. The end of the flow is fascinating example of a combination of a molecular and atomic shock front, where the cooling zones are well-resolved. By comparing with previous images we were able to watch how the shock waves moved in real time, a great aid for interpreting the dynamics. A paper on these results was published in 2019 in the Astrophysical Journal.

The second proposal, led by B. Nisini in Rome, uses HST to image the regions very close to protostars in an attempt to learn how jets are launched. The images were acquired in 2019, and are of high quality. These images can be combined with future studies with JWST that will probe even further through the dense, dusty disks that surround these systems.

Hartigan is leading a study of the HH 32 jet with data taken from the Keck image slicer. The new data explore the spatial and velocity characteristic of the blue part of the spectrum of a stellar jet for the first time. The resulting data cubes include Fe, Ca, Mg, H, O, and N, and contain a wealth of new information about the outflow, shock waves, and entrainment.

Physical conditions within the HH 7 shock complex as observed by HST (from Hartigan et al 2019).

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. Graduate student Maxwell Hummel is studying the cores in the Carina region with these data.

In a parallel project, we acquired additional high-resolution infrared images with the 8-meter Gemini adaptive optics imager. These images are the sharpest ever of a photodissociation region, and 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.

Images of the Western Wall in Carina: left - optical/IR composite ; right - ALMA continuum and CO map of a dense core

Numerical Simulations of Jets and Shock Fronts: Hartigan is collaborating with professor A. Frank at the University of Rochester to study cooling instabilities in strongly-shocked flows. The project compares numerical simulations with various cooling curves to determine whether or not dense clumps observed in laboratory experiments of colliding flows come from the onset of cooling instabilities. Hartigan is working 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.

Time Domain Studies: For the observing season 2019A, Hartigan led a team that successfully acquired a full month of time on the Blanco NOAO 4-m telescope in Chile to study variability in the Carina star formation region with the Dark Energy Camera (DECam). This imager has a full field of view of over 2 degrees, and is ideal for monitoring light variations of the thousands of young stars present in this region. Variability holds clues to many aspects of the star formation process, including rotational properties, obscuration by dusty envelopes, starspot coverage, accretion and flares. Results from the project will presage what the Large Synoptic Survey telescope may accomplish in this arena.

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. Hartigan and Co-PI Rosario led a white paper on the subject related to young stars. The entire document is now available on-line.

Campus Observatory Activities: 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. 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. There was a lot of excitement from the public about the lunar eclipse in January 2019, and we had lovely views of the event at Rice. A summary of all the lunar eclipses visible from the Houston area out to the year 2060 is available. Hartigan hosted an open house in December, where we discussed the discoveries of what appear to be interstellar objects passing through our solar system, comet Borisov and small body Oumuamua. Details about current observatory schedules can be found on the observatory website.

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Patrick Hartigan