Achieving Sub-Millimagnitude Precision from the Ground: the Capabilities of ARCTIC and the LHS 1140 System
As TESS observes most stars for only 28 days, many TESS planetary candidates will require future observations by other facilities in order to be properly vetted. Ground-based observations of these candidates can reject false positives, update mid-transit times, refine planetary parameters, and provide long-term monitoring of interesting systems. Ground-based telescopes achieve these science goals in part due to their larger size compared to TESS's 0.1m diameter lens. However, most observations from the ground struggle to achieve precisions better than 1 millimagnitude. The new CCD imager ARCTIC, installed on the 3.5m Apache Point Observatory Telescope, attains extreme precision by combining its large collecting area (1000× larger than TESS) with a diffuser that spreads the stellar PSF into a stable top-hat. We test the performance of this instrument by observing multiple transits of LHS 1140b and LHS 1140c. LHS 1140 is a nearby M-dwarf orbited by two rocky, near Earth-sized planets, including one in the habitable zone. This system therefore presents a unique opportunity to study two rocky planets in very different temperature regimes around the same star. Our observations double the number of published LHS 1140b and 1140c transits, and we use these to update the ephemeris and better constrain the planetary parameters. We find ARCTIC achieves a RMS of 150ppm on LHS 1140 for data binned to 20 minute timescales. Based on our success with the LHS 1140 system, we predict that ARCTIC will prove a useful instrument for future TESS follow-up on both smaller and fainter planet candidates as TESS moves into the northern hemisphere this year.
AAS/Division for Extreme Solar Systems Abstracts
- Pub Date:
- August 2019