HET Beginning-Trimester Report
  Third Period of 2023
August 1 - November 30

This report is primarily to give updates to PIs on recent changes/improvements and to summarize the determination of time allocations for the 22-3 trimester.



Updates on recent changes/improvements:

MOONDOWN TSL keyword

    As of the 23-2 trimester (1-April 2023) we have been using the new TSL keyword "MOONDOWN" which is used to request that the moon be below the horizon during the entire visit (and that the visit be completed within the dark portion of the night between 18-deg twilights). In the past, SKYBRIGHT_X (where X = g, r, or i) of exactly 21.0 was an indication that the moon should be below the horizon. Starting in 23-2 we are treating the sky surface brightness keywords literally.

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:










Commissioning, Engineering, and Guaranteed Time allocations


The HET Board granted the following allocations for the 23-3 period:



 





Breakdown of how science hours for TACs at each partner were determined:



quantity
 Aug
(hrs)
 Sep
(hrs)
 Oct
(hrs)
 Nov
(hrs)
 Total
(hrs)
18deg-18deg times
 243.93
 268.10
 306.58
 318.17
 1136.78
Weather loss frac. 0.44
 0.46
 0.35
 0.37
Efficiency loss frac.
(align+PRs)
 0.07
 0.07
 0.07
 0.07
"Clear science" time
 127.04
 134.64
 185.33
 186.41
 633.42
Com/Eng/GTO time
 *time granted by Board



185
"Allowed" hours
given to TACs
for science



415.22
*with correction factor based on typical fraction actually utilized



 

Hours allowed for each TAC as determined Jun 9, 2023:


Partner
 Share
 Time deficit
correction
 Total hours
allowed
Allocated
as of Aug 6
(excl. Pr4)
Goettingen
 0.03860
 +2.76
 20.07
 20.1
Munich
 0.05724
 +3.72
 29.39
 29.4
PSU
 0.24897
 -18.54
 93.10
 89.1
UT
 0.65518
 +12.06
 295.86*
 295.3
*includes 10h removed for TESLA

Corrections were applied using 20% of the cumulative deficits in time balance between the partners. As of Apr 1 2023, those time deficits were:
  UT:   20.1h deficit
  PSU: 30.9h surplus
  M:     6.2h deficit
  G:     4.6h deficit
Actual time usage is carefully monitored to ensure equitable balance between the partners; these corrected allocations should help improve this balance over the long-term.
 
Note that effective 1-Dec 2022, TACs may allocate up to 13.3% at P0*, 20% at P1*, 33.3% at P2 and 33.3% at P3; P4 allocations are not restricted. Priorities of Com/Eng/GTO time are assigned by the HET Board.

*In September 2022 the HET Board approved a proposal (available here) from the Users Committee to temporarily change the fractional time allocations at each priority. After the HETDEX guaranteed time observations are completed, the priority breakdowns will return to the previously adopted fractions.








SJ, 6 Aug 2023