Custom apertures?

jhargisjhargis Member, Administrator, Institute_Staff, Moderator_MAST, Admin_MAST Posts: 30 admin
What are Custom Aperture Files (CAF)?
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  • scflemingscfleming Member, Institute_Staff, Moderator_MAST, Admin_MAST Posts: 35
    The vast majority of Kepler observations are taken with one of the standard apertures. However, for bright stars, where there is saturation and bleeding along the CCD columns, multiple objects that can not be reasonably separated into individual apertures (e.g., a star cluster) and objects that do not appear in the KIC, a custom aperture is defined and used for the observation. These observations, called custom aperture observations or CAF observations, are handled differently from usual Kepler observations and are assigned a kepler_id greater than 100,000,000 (for example, 100001645).

    The following apply to different subsets of CAF observations.
    • For many CAF observations, the kepler_id changes from quarter to quarter, even if the target and investigation are the same.
    • For CAF observations of clusters, the kepler_id may remain the same for a number of quarters.
    • For CAF observations of multiple targets and non-KIC targets, the coordinates change from quarter to quarter, as they are the geometric center of the aperture.
    • For CAF observations of objects with KIC ids (usually bright stars), the coordinates in the archive are taken from the KIC and remain the same from quarter to quarter, although the kepler_ids may not.
    • For CAF observations of bright targets the kepler_id is supposed to change from quarter to quarter. However, kepler_id = 100001645 violates this rule.
    For the archive user, a cone search is an obvious tool for finding CAF observations. In the case of a target with different coordinates in each quarter, the difference in the coordinates needs to be considered when specifying the cone search radius. In the case of bright objects, say 16 Cyg, the coordinates provided by the resolver (SIMBAD at CFA, for example) may differ from those in the KIC and so require a larger search radius to find the observations. We recommend the user try a range of radii. The current default is 0.02 arcminutes.
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