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RAGHAB: Roman Analysis for a Galactic Hunt for Astrometric Binaries
Program ID 19080
Science Category Stellar Physics
Program Type Analysis
Category Medium
Principal Investigator Soumyadeep Bhattacharjee
PI Institution California Institute of Technology
Co-Investigators
  • Kareem El-Badry (California Institute of Technology)
  • Cheyanne Shariat (California Institute of Technology)
  • Casey Lam (Carnegie Observatories)
  • Jiwon Han (Harvard-Smithsonian Center for Astrophysics)
  • Geoffrey Mo (California Institute of Technology)
  • Leonardo Betancourt-Chitnis (California Institute of Technology)
  • Natsuko Yamaguchi (California Institute of Technology)
  • Pranav Nagarajan (California Institute of Technology)
  • Maude Gull (California Institute of Technology)
  • Lisa Blomberg (California Institute of Technology)
Abstract AU-scale binaries with orbital periods of ~1000 days challenge our understanding of binary evolution and mass transfer. The recent success of the Gaia mission in fitting astrometric orbits has demonstrated the power of  astrometric wobble to find and characterize these systems. Gaia, however, cannot probe optically-faint sources and sources in crowded fields, making Roman an excellent complementary mission for galactic astrometry. We propose to perform non-single-star (NSS) astrometric model fits to the epoch astrometry data from two Roman surveys: GBTDS for the bulge and HLTDS for the halo. With unprecedented depth and angular resolution, Roman will provide Gaia-like precise astrometry for tens of millions of sources inaccessible to Gaia. Our NSS data products will contain 1) an efficient RUWE-like metric to identify sources with astrometry inconsistent with single-star motion, 2) acceleration solutions yielding significantly better parallax measurements for high-RUWE sources, and 3) Keplerian orbital solutions whenever possible. We have developed a pipeline to perform NSS analyses on Roman epoch-astrometry data. Our simulated observations predict that we will obtain orbital solutions for ~10 black hole, tens to hundreds of neutron star, and hundreds of white dwarf and brown dwarf companions to main-sequence and giant stars, comparable to the all-sky yields of Gaia. RUWE and acceleration solutions will discover an order of magnitude more such systems. Low mass M-dwarf stars too faint for Gaia are of special interest. The GBTDS-detected bulge sources will enable comparison with Gaia sources from the disk. We will promptly publish the first NSS catalog with two years of Roman data; future programs will apply the same piple to astrometry from the full primary mission.