The main goal of the HATPI instrument is to provide high cadence high-precision light curves for all stars brighter than 14th magnitude covering 3/4th of the visible sky from Las Campanas Observatory in Chile. This will enable the detection and characterization of exoplanets ranging from super-Earths to hot-Jupiters in orbit around these bright stars, and studies of variable stars at time-scales ranging from minutes to years.
HATPI is expected to discover ~200 long period and/or small radius planets, many of which would not be found by other surveys, including some within the habitable zones of their host stars, and some beyond the snow line (a distance from the host star of great importance in planet formation theories). No other current or upcoming survey has significant sensitivity to these long period planets, which will be prime targets for detailed characterization with major observatories currently under development, including the James Webb Space Telescope (NASA's replacement for the Hubble Space Telescope), and extremely large ground-based telescopes. In particular, HATPI will greatly increase our chances of discovering a transiting terrestrial planet in the habitable zone of a bright star.
HATPI will discover hundreds of thousands of new variable stars. For these, it will securely measure rotation periods for ~100,000 stars across the HR diagram and in diverse stellar environments, thus placing constraints on their ages via gyrochronology.
Based on initial results of experiments (see plots above) with prototype HATPI instrument holder units (IHUs) attached to existing HATSouth telescope stations, and carried out over much of 2015 and 2016, we expect to reach a best case precision of better than 2.5 milli-mag for 9th magnitude stars using the usual 30 second cadence of the instrument. If light curves are binned to one hour cadence, the precision improves to better than 0.5 milli-mag at the same magnitude. We expect to improve further upon these initial results once the full instrument comes online.
Over time, HATPI will build up an extremely deep wide-field view of 3/4th of the sky allowing the detection of faint large-scale features. Below, we show examples of one and eight hour co-added deep stacks from single-lens HATPI IHU testing for the region near the Lagoon and Trifid Nebulae in Sagittarius. Click the images to get the full 2048 x 2048 pixel (13 x 13 degree) frames.
HATPI will provide high-cadence and high-precision light curves for numerous transients. It will be uniquely sensitive to bright, very short duration events such as stellar flares, relativistic outbursts and rapidly evolving transients. We estimate that HATPI will provide 10% precision (at 30 second cadence) light curves for about 10 bright supernovae (SN) per year, reasonable light curves at 1 hour cadence for 165 SN/yr, and at least one valid measurement for ~500 SN/yr. For galactic novae, based on statistics for the past 15 years, HATPI will provide unique, better than 5% precision (at 30 seconds) light curves for about 8 novae per year out of the 10 observed. Based on statistics from the Swift satellite, the annual rate of gamma ray burst afterglows peaking at V magnitudes brighter than 14 is ~60 per year. Presently, only ~3 per year are observed. We expect HATPI to observe > 5 of these per year, thus doubling the rate.
HATPI will be capable of exploring the bright transient sky at timescales as short as 30 seconds; it may therefore find new classes of transient objects. We expect that additional science will be yielded by the high precision and high cadence light curves.
The figures below show a movie and a light curve generated from subtracted frames cut out to show a postage stamp of the recent nova Sagittarii 2015 3. This was in a field being monitored by the HATPI prototype IHUs before and during its outburst phase in Fall 2015. We will make such stamps publicly available for any part of the sky observed by HATPI within hours of the initial observations, allowing interested astronomers and citizen-scientists to track down any bright transient occuring in the Southern Hemisphere's night sky. We will also provide an alert system to bring these transients to the attention of observers quickly, thus aiding in their spectroscopic follow-up observations to determine these objects' fundamental properties.
The extensive temporal and sky coverage of HATPI will also allow us to observe thousands of inner and outer solar system asteroids and minor planets. We will be able to obtain light curves and rotation periods for most of these as well as track their orbits. HATPI will be the most sensitive Southern hemisphere facility for finding potentially hazardous near-Earth asteroids. Below is an example of such an object, the near-Earth asteroid 2004 BL86 originally found in 2004 by the LINEAR survey. This object happened to be present in test frames being taken by HATPI IHUs during its closest approach to Earth in January 2015.