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Fergal Mullally renamed We_targeted_GD1212_a.tex to Observations, Extractions and Detrending.tex
about 10 years ago
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We observed GD1212 (GJ\,4355, WD\,2336$-$079, Catalogue number 60017836) for a total of 283 hours using the \kepler spacecraft in two-wheel mode. With only two working reaction wheels, the spacecraft pointing can not be stabilised in three axes. By pointing the boresight close to the plane of the spacecraft's orbit \citep[within about a degree of the ecliptic][]{Howell14}, the unconstrained spacecraft roll is placed in equilibrium with respect to the solar pressure, the dominant external force exerted on the spacecraft. This is an unstable equilibrium , and the pointing needs to be corrected every 3-6 hours by firing the thrusters. No data is lost during a thruster firing (known as a reset), but the change in attitude causes a strong jump in the measured flux from the star. The spacecraft rolls by no more than 25 arcsec (check this) between resets, which corresponds to motion of a star at the extreme edge of the field of view by no more than 1 pixel.
We can point a single field for up to 80 days, before the angle of the sun with respect to the solar panels exceeds allowed limits. \citet{Putnam14} provides further details of the capabilities and limitations two wheel operation.
%Resats -- I don't think I need to talk about these
%Each one looses 1 LC and 27 SC.
We collected data from 2014-01-17 19:17 UTC to 2014-01-20 09:34, and 2014-02-04 12:57 to 2014-02-13 12:44 in SC. Each exposure is 58.8 seconds. Our observing was interrupted for 15 days by a safe mode and subsequent fault analysis. In contrast to the primary mission where only small masks were placed around each star, GD1212 data was collected using a 50x50 pixel ``super aperture''. We expect the aperture size used in two wheel mode will decrease as our confidence in the spacecraft pointing ability increases. The observed pixels were processed through the CAL module of the \kepler pipeline \citep{Quintana10} to produce target pixel files (TPFs). Light curve files were not produced for this commissioning data. TPF data for all stars observed during this engineering run are available at the MAST Kepler archive \footnote{\url{http://archive.stsci.edu/kepler}}.
Describe processing, detrending, filtering; Tom B.?
