HETDEX conflict calculator

    The 24-2 trimester of HETDEX observations will conclude the Guaranteed Time Observations approved by the HET Board of Directories. After the night of July 31st 2024, beginning in the 24-3 trimester, HETDEX will cease its dark time dominance with hundreds of hours of Pr0 time requiring careful planning for other science programs to avoid it. As such, the HET Object Observability calculator has been updated so that it does not include the HETDEX target conflicts by default, but allows the user to enable that feature if desired. The calendar is available as the usual location: https://www.het.astronomy.utexas.edu/HET/hetweb/ProgramPrep/hetdexcalendar.html

Collecting Efficiency

    We continue to work towards implementing a significant improvement to the Phase II Target Submission Language parameterization of sky transparency. Instead of requesting N/S/P conditions (0%/50%/90% transparency), users will soon request a minimum value of Collecting Efficiency (CE) for their observation, where:

    Collecting Efficiency  =  Sky Transparency * Primary Mirror Pupil Illumination

This will give users more detailed information and control over their data quality. There is documentation available to describe how to estimate CE for your targets and what types of values are reasonable to request: https://hydra.as.utexas.edu/?a=help&h=140
    Sky Transparency varies between 0.0 (fully cloudy) and 1.0 (fully clear) and Pupil Illumination varies between 0.5 (tracker at extreme edge) and 1.0 (tracker centered over the mirror), so CE varies from 0.0 to 1.0. Note that we also provide an online Filling Factor Calculator to determine the maximum pupil illumination available for a given declination and exposure time. Experienced users will be aware that longer exposures experience worse pupil illumination: at Dec=+45deg, a 10min exposure has an average pupil of 97% but a 30min exposure has only 91% pupil illumination. This impact should be considered carefully when requesting CE in the future!
    Beginning in 23-1, all observations reported on the "Objects Observed" tab on Hydra include the CE for each exposure. Users are strongly encouraged to use this opportunity to become familiar with the typical values of CE during regular observations.