Research Interests

I am interested in both the formation of planetary systems and their habitability. To address the first topic, I image and model circumstellar disks, and try to connect their observed structure back to the underlying planetary system. This work makes use of radio interferometers like the Submillimeter Array (SMA), the Atacama Large Millimeter/submillimeter Array (ALMA), the Jansky Very Large Array (JVLA), and the Australia Telescope Compact Array (ATCA). As a result, I am also interested in modeling dust and grain dynamics and the techniques of radio interferometry. To address habitability, I explore the multi-wavelength flaring properties of stars. I am currently leading a multi-wavelength monitoring campaign of Proxima Centauri with multiple ground- and space-based facilities including ALMA, HST, Evryscope, and several telescopes at Las Campanas Observatory.

Some Relevant Links

CfA Protoplanetary Disks Group
SMA Observer Center
Atacama Large Millimeter/submillimeter Array (ALMA) Data Archive
Karl G. Jansky Very Large Array
ATCA Users Guide

Some Recent Highlights

Detection of a Millimeter Flare from Proxima Centauri (arXiv:1802.08257)

We present new analyses of ALMA 12-m and ACA observations at 233 GHz (1.3 mm) of the Proxima Centauri system with sensitivities of 9.5 and 47 uJy/beam, respectively, taken from 2017 January 21 through 2017 April 25. These analyses reveal that the star underwent a significant flaring event during one of the ACA observations on 2017 March 24. The complete event lasted for approximately 1 minute and reached a peak flux density of 100+/-4 mJy, nearly a factor of 1000x brighter than the star's quiescent emission. At the flare peak, the continuum emission is characterized by a steeply falling spectral index with frequency, with alpha=-1.77+/-0.45, and a lower limit on the fractional linear polarization of |Q/I|=0.19+/-0.02. Since the ACA observations do not show any quiescent excess emission, we conclude that there is no need to invoke the presence of a dust belt at 1-4 AU. We also posit that the slight excess flux density of 101+/-9 uJy observed in the 12-m observations compared to the photospheric flux density of 74+/-4 μJy extrapolated from infrared wavelengths may be due to coronal heating from continual smaller flares, as is seen for AU Mic, another nearby, well-studied, M dwarf flare star. If this is true, then the need for warm dust at ~0.4 AU is also removed.

Some Press Coverage:

A Complete ALMA Map of the Fomalhaut Debris Disk (arXiv:1705.05867)

We present ALMA mosaic observations at 1.3 mm (223 GHz) of the Fomalhaut system with a sensitivity of 14 uJy/beam. These observations provide the first millimeter map of the continuum dust emission from the complete outer debris disk with uniform sensitivity, enabling the first conclusive detection of apocenter glow. We adopt a MCMC modeling approach that accounts for the eccentric orbital parameters of a collection of particles within the disk. The outer belt is radially confined with an inner edge of 136.3+/-0.9 AU and width of 13.5+/-1.8 AU. We determine a best-fit eccentricity of 0.12+/-0.01. Assuming a size distribution power law index of q=3.46+/-0.09, we constrain the dust absorptivity power law index to be between 0.9 and 1.5. The geometry of the disk is robustly constrained with inclination 65.6+/-0.3 deg, position angle 337.9+/-0.3, and argument of periastron 22.5+/-4.3. Our observations do not confirm any of the azimuthal features found in previous imaging studies of the disk with HST, SCUBA, and ALMA. However, we cannot rule out structures smaller than 10 AU in size or which only affect smaller grains. The central star is clearly detected with a flux density of 0.75+/-0.02 mJy, significantly lower than predicted by current photospheric models. We discuss the implications of these observations for the directly imaged Fomalhaut b and the inner dust belt detected at infrared wavelengths.

Some Press Coverage:

ALMA Measurements of Circumstellar Material in the GQ Lup System (arXiv:1611.06229)

We present ALMA observations of the GQ Lup system, a young Sun-like star with a substellar mass companion in a wide-separation orbit. These observations of 870 micron continuum and CO J=3-2 line emission with beam size ~0.3" (~45 AU) resolve the disk of dust and gas surrounding the primary star, GQ Lup A, and provide deep limits on any circumplanetary disk surrounding the companion, GQ Lup b. The circumprimary dust disk is compact with a FWHM of 59+/-12 AU, while the gas has a larger extent with a characteristic radius of 46.5+/-1.8 AU. By forward-modeling the velocity field of the circumprimary disk based on the CO emission, we constrain the mass of GQ Lup A to be M=(1.03+/-0.05) x (d/156 pc) M_Sun, where d is a known distance, and determine that we view the disk at an inclination angle of 60.5+/-0.5 deg and a position angle of 346+/-1 deg. The 3-sigma upper limit on the 870 micron flux density of any circumplanetary disk associated with GQ Lup b of less than 0.15 mJy implies an upper limit on the dust disk mass of less than 0.04 Earth masses for standard assumptions about optically thin emission. We discuss proposed mechanisms for the formation of wide-separation substellar companions given the non-detection of circumplanetary disks around GQ Lup b and other similar systems.