Overview of Penprase Astrophysics Research

Astrophysics from Asteroids to Quasars! 

My research encompasses a wide variety of observational astrophysics. It can be summarized as the observational astrophysics of “everything from asteroids to quasars” – which is both spanning a wide range of alphabet and astronomical distance scales!  The breadth of the research is a response to opportunities that arise for students to engage in cutting-edge astrophysics using telescopes available to me. The telescopes include the observatories at Pomona College, which I have developed over 20 years into a network of telescopes ranging from 14″ Celestron Paramount systems to our 1-meter telescope at Table Mountain Observatory. Phil Choi, my colleague at Pomona has taken over the last of these resources, and added a very advanced capability – an advanced adaptive optics instrument known as KAPAO. In addition to those resources, I have access to a wide range of telescopes from my Caltech and Carnegie collaborations. Over the years this has led to a number of great opportunities for research at Las Campanas Observatories in Chile, and the Keck telescope in Hawaii, as well as official partnerships with those institutions resulting in summer undergraduate research opportunities (such as the Carnegie-Claremont Astrophysics program), and major instrument development (such as the Robo-AO and KAPAO projects, which linked Pomona and Caltech).


The Pomona College Table Mountain 1-meter Observatory in Wrightwood, CA


The twin 10.5-meter Keck telescopes at Mauna Kea, Hawaii


Since coming to Yale-NUS College in Singapore, my astrophysics research efforts have been focused on developing a local network of observational astronomers, who can respond quickly to transients and who can coordinate in solar system observations. To this end, I convened a research conference at Yale-NUS College which included astronomers from NARIT (Thailand), Lulin Observatory (Taiwan), SNU (Korea), as well as from the Malaysian national observatory, a Turkish research institute, and Pomona College in California. We were joined at that meeting by Glenn Orton from JPL and Chris Go from the Philippines, and they described opportunities for ground-based astronomers to support the NASA Juno mission during August of 2016 and beyond as the spacecraft encountered the planet. I am working closely with Glenn Orton and his JPL team and will be helping to lead some ground-based campaigns this summer to provide supporting high-resolution images for the Juno mission.



The CTIO 1.5-meter telescope with its CHIRON spectrograph


Figure from presentation of Jupiter observations as part of the NASA Juno ground-based observing campaign



Additional telescopic resources from Yale University open further opportunities for me at Yale-NUS. Through the generosity of our Dean of Faculty, and Yale-NUS College, I have been given access to a large block of telescope time with the Yale University SMARTS consortium telescopes at Cerro Tololo Interamerican Observatory (CTIO) in Chile. The main telescopes of interest for this are the 1.5-meter telescope, with its amazing high resolution spectrometer named CHIRON, and the 1.3-meter telescope, with a fantastic dual infrared and optical imager known as Andicam. With the CHIRON spectrograph, I am conducting a research project investigating the three-dimensional structure of the local interstellar medium, using bright O, B and A type stars at various distances to detect structures of interstellar medium from the presence of absorption lines of Ca II and Na I.  This work benefits from a large block of CHIRON spectroscopy, and a large sample of over 300 stars is being observed to construct maps of the local interstellar medium. With Andicam, I hope to assemble a gallery of images of radio galaxies in collaboration with Lakshmi Saripalli of the Raman Research Institute (Bangalore India). These images can be combined with radio data to determine rotation and precession of jets and black holes within active galaxies over time.



A map of our local interstellar medium, with positions of stars studied by CHIRON indicated


Detail of the HD 28497 sightline showing variable Na I D absorption











My ZTF connections at Caltech have opened up a wide range of opportunities for students interested in time-variable sources and newly discovered gamma-ray bursts, asteroids, and supernovae. As part of the ZTF team, I will be working at Caltech for the upcoming several summers. I am leading an undergraduate astronomy institute there, which brings 15-20 Pomona College, Caltech, and Yale-NUS College students together for an intensive week learning about time-domain astrophysics, observational astronomy, and detector design. During 2015 our group was able to visit the Palomar Observatory and the Mt. Wilson Observatory, with scheduled observing runs with the 200″ and 60″ telescopes!  We also had a fantastic institute dinner at the Atheneum, talks by leading Caltech astronomers and instrument scientists, tours of laboratories and a fun time exploring the Caltech campus. At Pomona College we had a night at the Brackett Observatory, toured the adaptive optics lab, looked at the new Millikan astronomy building and planetarium, and had hands-on clinics in data analysis from Phil Choi, Loredana Vertere. New funding from NSF has opened up opportunities for international undergraduate research internships with our ZTF PIRE grant, and I am looking forward to helping create an active network of global astrophysics with my collaborators here in Asia and with the Caltech groups.


Our group of students for the 2015 ZTF Summer Undergraduate Astronomy Institute


Schematic of new ZTF camera, funded by NSF $8.0 million grant, for which I am a co-I and lead on educational efforts.











My spectroscopic research focuses on remote diagnostics of outer space using spectra to measure element abundances, physical conditions, and chemistry of interstellar clouds, and distant star-forming galaxies. The research is dedicated to unlock some of the mysteries in the early universe which can be observed directly through careful study of the “fossil light” from quasars and gamma ray bursts, which have traveled for billions of years and carry fingerprints of millions of absorbing gas clouds in their light. These studies elucidate the mechanisms of condensation within the early universe of the first small galaxies, which appear in quasar spectra as “Damped Lyman Alpha systems” or DLAs. These small galaxies, often billions of light years away, contain within them signatures of the first stars, and their elemental abundances give clues to the masses of these stars. By studying the range of composition within these small galaxies we can constrain the masses of the first stars, which in turn is of interest to cosmology. There are many other interesting pieces of information locked within a quasar’s light. These thousands of absorption lines contain within them the history of the universe, and the formation of the first stars and elements heavier than Helium that ultimately became the Earth and us. Other project with these absorption lines include the Caltech Damped Lyman Alpha database, and a study of Deuterium within the DLA systems, and the evolution of D/H abundance in the early universe.



Schematic of light from a quasar impinging on an absorbing galaxy at high redshift (top) and resulting quasar spectrum (bottom) showing strong HI absorption known as a “DLA” and corresponding “metal” absorption lines.


Example of our spectra taken with the Keck telescope, showing a “low metallicity DLA” system which shows traces of some of the first C, O, and Si in the early universe.

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