The Search for Giant Planets Around M Dwarfs: Using Gaia to Improve the Precision of RECONS Astrometry

We describe a project to construct a new astrometric pipeline to reanalyze the archive of more than 20 years of images taken during Cerro Tololo Inter-American Observatory Parallax Investigation (CTIOPI) at the CTIO/SMARTS 0.9m telescope. This effort will reach the sensitivity necessary to detect planets down to one Jupiter mass in long-period orbits around M dwarfs.

Among the over 1000 stars observed and continuing to be observed by CTIOPI are dozens of M dwarfs within 25 pc for which orbits have been mapped for stellar and brown dwarf companions. However, the current data reduction techniques do not yield the precision necessary to detect planets. We can improve the sensitivity to reach lower mass planets by using better knowledge from Gaia about the positions and minute proper motions of the distant background reference stars. Incorporating the currently available Gaia astrometry for reference stars would allow for a more robust correction of field distortion, differential color refraction, and centroiding, while also vastly diminishing the number of unknown parameters in the overall astrometric solution. If the single epoch astrometric uncertainties are reduced to about 0.5 mas from the current 1 to 5 mas it would then be possible to combine CTIOPI and Gaia data with nearly equal statistical weighing. The combined dataset would expand the time coverage, thus allowing for the detection of longer period planets than what Gaia alone can do. We predict that we will have the ability to detect Jupiter mass planets with periods as long as 30 years for about 100 mid and late M dwarfs, and with periods as long as 40 years for another 50. In total, we believe we can probe at least 231 M dwarfs for jovian-type planets.

This effort has been supported by the NSF through grants AST-1715551 and AST-2108373 via observations made possible by the SMARTS Consortium. S.B.D. acknowledges support from the Space Telescope Science Institute through the STScI Postdoctoral Fellowship Program.