Young accreting planets are excellent testbeds for planet formation theories and early evolutionary models. By directly imaging accreting planets, we can constrain the speed at which planets grow, investigate planet-disk interactions, and characterize young planet atmospheres. I find this tremendous wealth of information in young planet observations exciting.

However, newly formed planets (protoplanets) are at least a thousand times fainter than and only separated by a few resolution elements from their stars. To date, only two bona-fide protoplanets have been observed — PDS 70 b and c. The scarcity of young planet discoveries has become one of the primary limitations to advancing our knowledge of planet formation.

Motivated by efforts to use H-alpha emission (656 nm) from planetary accretion shock fronts as a tracer of active planet formation, I created a new technique to efficiently image young planets with Hubble Space Telescope’s Wide Field Camera 3 (HST/WFC3). My approach takes advantage of HST’s excellent point spread function (PSF) stability and a novel archival PSF library compiled by STScI to reveal the power of reference star differential imaging (RDI). This technique uses reference stars distinct from the science target to build a model of the host star’s PSF for removal of the contaminating starlight. Further, I spearheaded the analysis of a first-of-its-kind HST survey of 10 transition disk-bearing stars in the H-alpha wavelength to uncover a new candidate protoplanet — AB Aurigae b. Careful analysis showed that the H-alpha line-to-continuum ratio of AB Aur b was consistent with scattered light from the host star. Thus, disentangling the source of AB Aur b’s H-alpha emission would not only be crucial in understanding this candidate’s origin, but also for the interpretation of future discoveries of disk-embedded protoplanets.

Associated Papers:
(1) Sanghi, A., Zhou, Y., Bowler, B. P., 2022, AJ, 163, 119
(2) Zhou, Y., Sanghi, A., Bowler, B. P., et al., 2022, ApJL, 934, L13.

Giant planets (∼2-13 Jupiter masses) are the most favorable planet population for detailed spectroscopic characterization studies using the technique of direct imaging. To assemble more of these highly prized systems, the field of exoplanet imaging has pivoted towards conducting targeted searches by combining Gaia astrometry with archival Hipparcos astrometry to select stars exhibiting small changes in their proper motion (termed accelerating stars), consistent with being caused by a planet.

Kyle Franson, a graduate student at UT Austin, is leading a multi-facility high-contrast imaging survey of the most promising young, nearby accelerating stars to discover new long-period planet and brown dwarf companions. I am a member of the team and am contributing to the survey by performing complementary reductions of the acquired high-contrast imaging sequences using the technique of reference star differential imaging (RDI). I have created a multi-night and mutli-year reference library from the survey dataset and am implementing statistical frame selection strategies to optimize detection sensitivities.

The first discovery from this program is a 24 Jupiter mass brown dwarf companion around the accelerating Hyades (650 Myr) star HIP 21152. The second discovery from this program is a giant planet orbiting the young beta-Pictoris member AF Lep. At ~3.2 Jupiter masses, AF Lep b is the lowest-mass imaged planet with a dynamical mass measurement.

Associated Papers:
(1) Franson, K., Bowler, B. P., Bonavita, M., et al. (incl. Sanghi, A.), 2023, AJ, 165, 39.
(2) Franson, K., Bowler, B. P., Zhou, Y., et al. (incl. Sanghi, A.), 2023, ApJL, 950, L19.