I took higher resolution spectra of the supposed 41Hz HSTS roll mode tonight (see first attachment). There are 2 peaks, however only the first peak has any coherance with anything. The 2 peaks are at:
40.9375 Hz (lots of DARM-PRC-SRC coherence)
41.0117 Hz (no coherence with anything I looked at)
The second attachment shows the set of 41Hz peaks in 3 of the last lock stretches. I attempted to use the ASC signals to check for coherence with DARM, but:
- the OSEM sensors on the HSTS suspensions are too noise, so see no coherence
- there is coherence with BOTH SRC and PRC, unfortunately, so hard to pin point where
- there is coherence with SRC1 which talks to SRM - is it cross-coupling thru ASC/LSC?
- there is no coherence with SRC2 likely because it is a noisy detector (AS DC), so can't tell if the SRM and SR2 combination that it talks to contribute to the 41Hz
- PRC1 not plotted, no ASC drive there, but witnessed that there is no coherence there
- PRC2 goes to PR3, so while there is coherence there (not plotted) it is likely because it is cross-coupling from SRC to PRC
- IMC_TRANS_P not plotted, but witnessed no coherence, again too noisy of a detector?
This is also close to the third harmonic of the Roll modes as seen at 41.25Hz at LLO 20737 though this is probably only relevant to highly excited roll modes.
The 40.9375 Hz mode is consistent with the PR2 M2 to M2 TFs, where a 40.93 +- 0.01 Hz mode was seen. See log 21741.
And just to clarify. This is not a third harmonic. It is the third (and highest) of the three roll modes of the HAM small triple suspension (HSTS).