• The "o" band for Pan-STARRS and how to get it

    From Eric Flesch@21:1/5 to All on Sun Mar 28 16:00:06 2021
    Those who use Pan-STARRS data might bemoan the lack of a "u" band.
    There is a quick fix, of sorts -- the POSSI-O band which is centered
    on 4050A. While not exactly u, it is blueward of Pan-STARRS grizy,
    and overlaps the g band only about 33%. The POSS-I survey was done in
    the 1950's and it covers all sky down to declination -33, which means
    it overlaps the entire Pan-STARRS sky which is down to declination
    -30. POSSI-O can be calibrated to Pan-STARRS via the POSSI-E band
    which is just Cousins R.

    Lupton 2005 gives the following transform for SDSS r & i to Cousins R:

    R = r - 0.2936(r-i) - 0.1439

    and this works here because Pan-STARRS r & i are just the same as
    SDSS. So get the R-E offset and add it to O, and boom, you've got
    Pan-STARRS "o" to add to their "grizy" bands -- "ogrizy" now. This is
    for the brighter objects, as POSS-I is about 2 magnitudes less deep
    than Pan-STARRS.

    There is one issue remaining, though, and that is that the POSSI-O and
    POSSI-E bands must be correctly calibrated to each other.
    Unfortunately, the USNO-B has bad offsets there, and USNO was the only
    place which digitized the Galactic POSS-I plates. There is a history
    there, USNO-A1.0 was USNO's first release which digitized the entire
    POSS-I survey and it was well-calibrated. But shortly thereafter they
    released USNO-A2.0 for the purpose of better astrometry, but some
    nasty photometric offsets got introduced also, and the POSS-I coverage
    was only down to declination -12 (replaced by UKST southwards of
    there). These bad photometric offsets were passed onwards to the
    USNO-B catalog, unfortunately.

    A while ago I released the ASP catalog (2017,PASA,34,25) which
    presents the whole POSS-I data (375M sources) calibrated correctly to
    the USNO-A standard and also to the APM (which covered POSS-I away
    from the Galaxy) standard. The calibrations are shown on the web

    http://quasars.org/APM-USNOB-plate-calibration.txt for USNO-B, and http://quasars.org/APM-USNOA-plate-calibration.txt for USNO-A1.0

    So the ASP catalog gives the full POSS-I data with POSSI-O calibrated
    correctly (or at least better than anywhere else) to POSSI-E. So that
    data can be mined for "Pan-STARRS o", using the above technique.

    Eric Flesch

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