Astrophysics Brown Bag Lunch Talk 10/18/2021: Speakers Catherine Clark (Northern Arizona University) And Gourav Khullar (University Of Chicago)

Monday October 18, 2021 12:00 pm
TBA in person or via Zoom

Monday, October 18

12:00 – 12:30pm

Catherine Clark, Northern Arizona University/Lowell Observatory

Looking out for the Little Guys: Measuring M-dwarf Multiplicity with Speckle Imaging

Abstract: The M-dwarfs have been established as the most favorable targets for exoplanet detection and characterization. However, unresolved stellar companions can contaminate the light curve, resulting in underestimated planet radii, skewed planet radius distributions and occurrence rates, incorrect characterization of both stars’ properties, and a bias against detecting Earth-sized planets with transit surveys such as TESS. We therefore present the first results from the POKEMON (Pervasive Overview of Kompanions of Every M-dwarf in Our Neighborhood) survey, the largest speckle multiplicity survey produced to-date of the objects that comprise over 70% of the stars in our galaxy: the M-dwarfs. POKEMON is a volume-limited survey through M9 that inspected, at diffraction-limited resolution, every M-dwarf out to 15pc, with additional brighter targets to 25pc. We utilized the Differential Speckle Survey Instrument (DSSI) at the 4.3m Lowell Discovery Telescope, along with the NN-Explore Exoplanet Stellar Speckle Imager (NESSI) on the 3.5-m WIYN telescope to carry out this survey. Using these instruments, we have discovered 30+ new companions to nearby M-dwarfs. We also report results from our speckle follow-up of M-dwarf TESS Objects of Interest (TOIs), which used DSSI, NESSI, and the two speckle imagers at Gemini North and Gemini South. This work has enabled us to compare the multiplicity rate and orbital period distribution of planet-hosting M-dwarfs with the non-planet-hosting POKEMON stars.

Bio: I received my B.S. from the University of Michigan, where I studied Astronomy and Astrophysics, as well as Spanish. I moved to Flagstaff, Arizona, in 2017 to pursue my PhD in Astronomy and Planetary Science at Northern Arizona University. I work as a Graduate Research Assistant at Lowell Observatory, where I investigate M-dwarf multiplicity with various high-resolution imaging techniques. I plan to defend my dissertation next year.




Gourav Khullar, University of Chicago

Synthesizing Stellar Populations in Galaxy Clusters and High-Redshift Lensed Galaxies

Abstract: In this talk, I describe my work to characterize stellar populations in massive galaxies at two different epochs — redshifts ~0.5 and ~5. As part of a multi-wavelength effort within the South Pole Telescope (SPT) Galaxy Clusters collaboration, we use spectrophotometric observations of member galaxies in clusters to answer the question: on what timescales do galaxies that end up in clusters form their stars, and does the cluster sample matter when studying these properties? We use a mass-limited cluster sample — the SPT-GMOS Survey and the SPT Hi-z Cluster Survey — to constrain star formation histories, stellar masses, and formation redshifts of 900 passive galaxies in clusters across 0.3 < z < 1.5 via rest-frame optical age indicators, as a function of cluster environment and mass. On the other ‘end’ of the redshift scale, I describe the work of the COOL-LAMPS collaboration, and share the discovery and characterization of COOL J1241+2219, a lensed galaxy at z = 5.04 that is the brightest galaxy known at z > 5 (with zAB mag of 20.5). This galaxy was discovered as part of COOL-LAMPS — ChicagO Optically-selected strong Lenses – Located At the Margins of Public Surveys — initiated to find strongly lensed systems in recent ground-based public imaging survey data, consisting primarily of a team of undergraduate students. We characterize the lensed galaxy using ground-based spectrophotometric data to constrain its stellar mass and star formation rate. We aim to compare COOL J1241+2219 and other massive galaxies in the z > 5 Universe, with today’s brightest cluster galaxies. With existing spectrophotometric data from Magellan, SMA and Gemini Telescopes, and upcoming data across wavelengths with JWST (Cycle 1 GO Program), HST, Chandra, VLA, and NOEMA, COOL J1241+2219 is on its way to become the most well-studied galaxy in the early universe.

Bio: I am a PhD Candidate at the Dept of Astronomy & Astrophysics, and Kavli Institute for Cosmological Physics (KICP), at the University of Chicago. I work on studying high-redshift galaxy clusters, star formation histories in cluster members and strong gravitationally lensed galaxies. I use optical and infrared spectroscopic data facilities like the Magellan, Gemini Telescopes, Nordic Optical Telescope and Hubble, and am the PI of a JWST Cycle 1 program to study COOL J1241+2219, the brightest galaxy in the early Universe. I am part of the South Pole Telescope, COOL-LAMPS, Sloan Giant Arcs Survey (SGAS) and Astrobites collaborations.



Event Contact

Josh Borrow