significant HPF downtime planned for 22-2 trimester

[Steven Janowiecki]

Dear HET PIs,

I'm writing to let you know about some planned HPF downtime this summer which we anticipate will affect HET observations in the 22-2 trimester. This downtime will allow critical maintenance and engineering work on the HPF detector - see Suvrath's email at the end of this message for full details. The need for this downtime was first realized last Thursday and now that we have more details I wanted to share it with the full HET community as our plans move forward.

Even if you're not an HPF user, keep reading since this will have some affect on your programs as well.

HPF is used for ~47% of HET's annual science observations (nearly 100% during bright time), so this will cause a significant impact. Furthermore, HPF users should be warned that this will be a velocity break in your long-term RV-monitoring programs. After this work the RV zeropoints will change, since the physical hardware will have warmed/cooled. Some HPF programs may want to consider a push to complete their observations before this break, and possibly include that justification in your 22-2 proposals.

Detailed plans are still being made, and as we've seen over the past 23 months no plan is ever final until it actually happens. But for planning purposes, this is a rough schematic of the expected down-time as we currently expect it:

++ late May: HPF goes offline for vacuum pumping warmup

++ HPF is fully unavailable for science for ~3 weeks as pumping and electronics work continue

++ While HPF cools for 6-8 weeks, limited low-precision observations (chemistry/abundances) may be possible, although the data quality will not be as high as when the detector is fully cooled.

Effectively this means that all 22-2 high-precision HPF RV observations should be planned for the time period of Apr 1st to May ~20th.

I will share with the partner TACs a detailed breakdown of the 22-2 science time we expect to have available with HPF and the time available without HPF, to help everyone allocate programs appropriately balanced to the time available. LRS2-R bright-time observers should seriously consider proposing for targets which can be observed during June/July bright time, when there will be little competition in the queue.

This plan is still only a plan, so we'll keep everyone informed as necessary if the details evolve. Please let me know if you have any questions about this, or have potential projects/observations that could make use of this unusual bright time opportunity (no idea too crazy! seriously).

Steven

=============
Suvrath Mahadevan (HPF PI)  reports:
"When we designed HPF we built it with sufficient charcoal reserves in
the getters to be able to maintain vacuum levels and quality for at
least 3 years.  This summer we will be at 4 years- and other than some
minor issues operations have been very stable so far! (hope you feel the
same). Some days ago we have begun seeing indications that the pressure
is indeed creeping up. The MKS vacuum gauge has begun to switch between
its low and high modes. The rising pedestal issue in the H2RG  is also a
concern, and while we have a current workaround, good for a few months,
its cause has not been identified. If its issues are caused by the
deteriorating vacuum, a pump-down would reveal that issue (and
potentially fix it). If not- this would point to a significant issue
with the ASIC/Detector which would require a much more complicated
intervention in the future. Either way -- we need to know.
    We have concluded today, after looking at all the data, that we need
to plan on an HPF pump-down in the late May/June time period (exact
timeline is tentative) to begin to resolve these issues."