||PHASES: A Project to Perform Absolute Spectrophotometry from Space
||472, New Quests in Stellar Astrophysics III: A Panchromatic View of Solar-like Stars, With and Without Planets
||del Burgo, C.; Vather, D.; Allende Prieto, C.; Murphy, N.
||This paper presents the current status of the opto-mechanical design of PHASES (Planet Hunting
and AsteroSeismology Explorer Spectrophotometer), which is a project to develop a
space-borne telescope to obtain absolute flux calibrated spectra of bright stars.
The science payload is intended to be housed in a micro-satellite launched into a
low-earth Sun-synchronous orbit with an inclination to the equator of 98.7°
and a local time ascending node LTAN of 6:00 AM.
PHASES will be able to measure micromagnitude photometric variations due to
stellar oscillations/activity and planet/moon transits. It consists of a 20 cm
aperture modified Baker telescope feeding two detectors: the tracking detector
provides the fine telescope guidance system with a required pointing stability
of 0.2″, and the science detector performs spectrophotometry in the
wavelength range 370–960 nm with a resolving power between 200 and 900.
The spectrograph is designed to provide 1% RMS flux calibrated spectra
with signal-to-noise ratios > 100 for stars with V < 10 in short integration times.
Our strategy to calibrate the system using A type stars is explained.
From comparison with model atmospheres it would be possible to determine the stellar
angular diameters with an uncertainty of approximately 0.5%. In the case of a star
hosting a transiting planet it would be possible to derive its light curve, and then
the planet to stellar radius ratio. Bright stars have high precision Hipparcos parallaxes
and the expected level of accuracy for their fluxes will be propagated to the
stellar radii, and more significantly to the planetary radii.
The scientific drivers for PHASES give rise to some design challenges, which are
particularly related to the opto-mechanics for extreme environmental conditions.
The optical design has been developed with the primary goal of avoiding
stray light reaching the science detector. Three different
proposals for the opto-mechanical design are under investigation.