20210617

Observing with HPF while the LFC is saturating

Until the LFC is back to normal, this is our plan of operation

1. Take normal HPF evening/morning cals (i.e., the ones including the LFC).

2. Turn on the Etaon lamp at the end of the evening cals so it is available during the night, with this command in the HPF Scripts window:

   ./hpf_TurnOn.sh Etalon
   

   or with this cal command on Zeus: (can be scheduled with an "at" job on Zeus)

   cal hpf -et_warmup
   

   Remember that it takes 10 minutes to warm up. autodisplay is currently displaying etalon cals even when using "-nocal", so it's a good chance to check that the lamp is on.

3. Do NOT observe any simultaneous LFC targets (HPFCOMPARISON=LFC) at night. We can't do those right now. There are some in UT programs 12 & 13 that show up in htopx. Do NOT observe them. Check the Hcomp column in htopx.

4. Do observe high-precision targets like normal. PIs have been informed of the situation and can defer their targets if needed.

5. Replace any pre-observation or post-observation LFC requests with Etalon cals. Sergey's target_setup is doing this automatically based on the "LFC/Etalon" setting in the HPF section of the top of the RA NR. You can check the iexp commands should include "-et" instead of "-lfc" like:

   [stevenj@zeus ~]$ target_setup 4647 W -to
   ......
   # INSTRUMENT:  HPF
   # SETUPMETHOD: DirectACAM (direct)
   
   The script will take 1 Etalon cal after
   
   iexp 4647 W -et 1
   

6. Take Etalon cals throughout the night to help with wavelength drift. Can use cal command:

   cal hpf -et 3
   

Message from Suvrath about this issue, Thursday 17 June 2021

The HPF laser frequency comb (LFC) has suffered a failure on Monday 14 Jun in its spatial light modulator compromising the flattening of the LFC spectrum. The LFC also underwent a deterministic frequency hop of 125MHz (~125m/s), induced by attempts to identify the issue, that has been fixed. A fix to the LFC is anticipated only on timescales of mid July. The HPF team feels that at a high confidence level using the HPF etalon for calibrations through the night will still enable nightly calibration precision to ~1m/s. Programs requiring RV precision at or better than 1m/s have the potential to be impacted and the PIs may wish to consider deferring their targets. Most programs should be largely unaffected, though precision RV reductions may take longer than normal. Targets needing "simultaneous calibration" with LFC can not be observed. As always there is always a risk at these extreme precisions that unanticipated effects may prevent 1m/s calibration, but our best estimate is that the HPF etalon will help us bridge through this gap till mid July without serious issues (though not without considerable work behind the scenes on our end).