Attached is a pre-ER7 list of narrow lines seen above 5 Hz in recent H1 DARM data, along with spectra containing labels for the lines.
The spectra used for line-hunting are from 18 hours of DC-readout conditions on May 17. Most of the lines were also seen
in the early-May mini-run data, but are more exposed in the more sensitive May 17 data (see figure 1)
Notable combs / lines:
- Exact integers: 16.0000 Hz, 64.0000 Hz (distinctly louder than other 16-Hz lines), 81.0000 Hz, 1150.0000 Hz, 1672.0000 Hz, 1704.0000 Hz, 1880.0000 Hz, 1896.0000 Hz
- Nearly exact-integer combs:
- 3.9994 Hz (offset by ~2 Hz from zero, first visible harmonic at 13.9977 Hz -- these seem to correlate with a near 4-Hz comb starting at 2 Hz in EX magnetometers (and to a lesser degree in EY magnetometers), where the contamination in DARM at 10 Hz and below is presumably too faint to be seen in the rapidly rising DARM noise. A strong comb is apparent in PEM FScans.
- 99.9989 Hz (correlated with magnetometers in EX - see NoEMi and PEM FScans)
- Quad suspension violin modes with fundamentals near 500 Hz are not quite truly harmonic, but some of their upconversion is (see figure 2)
- Especially pervasive combs: 3.9994 Hz (34 harmonics), 16.0000 Hz (124 harmonics), 60.0 Hz (9 harmonics), 64.0000 Hz (31 harmonics), 36.9733 (54 harmonics), 59.9954 (6 harmonics), 99.9989 (13 harmonics)
- There are tentative identifications here of lines near 300 Hz and their harmonics as due to beam splitter violin modes, but their frequencies shifted by several mHz between the mini-run and the May 17 lock stretches, unlike the quad suspension violin modes which hardly moved at all (attributable to temperature?)
- Designated calibration line frequencies are shown on the spectra even when there is no apparent line (some not yet enabled?)
Notes:
- Because the binning in the spectra is 0.5 mHz (based on 30-minute FScan Hann-windowed SFTs), but the line widths in the plots are much larger, the spectra shown here look awful (but aren't). Dewhitening applies five poles at 1 Hz and five zeroes at 100 Hz.
- I didn't bother labeling the forest of bounce/roll-mode sidebands on the quad suspensions and their harmonics
- Although the 1150-Hz line seems well centered on the integer value, its energy is spread over several tenths of a Hz, unlike other integer-Hz lines
- Many line frequencies are give to four digits after the decimal point, but their statistical uncertainties are typically no better than a few tenths of a mHz, and based on changes between early and mid May, some lines have systematic drifts of O(mHz).
- With one exception, the quad violin mode fundamental frequencies were determined from the mini-run data, where they were more excited than on May 17. Those frequencies agree (independently) to within 2 mHz (in most cases, to better than 1 mHz) with the frequencies measured for individual test masses here. The one exception was that I had originally marked 504.1492 Hz as a mode in the mini-run, while the earlier study had found a mode instead at 501.254 Hz. Since the earlier measurements are guided by test-stand data, I am deferring to them and tagging 501.2544 Hz here, since I do see a line there in the mini-run data, albeit weaker than other modes.
Key to spectra labels:
b = Bounce modes
r = Roll modes
C = Calibration lines
L = Lock-in oscillator
M = Power Mains comb
N = Near to power mains comb
S = 64 Hz comb
s = 16 Hz comb
F = Near to 4 Hz (3.9994 Hz) comb
H = Near to 100 Hz (99.9989 Hz) comb
D = 59.3155 Hz comb
E = 36.9733 Hz comb
G = 75.23 Hz comb
Q = Quad violin modes
B = Beam splitter violin modes
x = Miscellaneous singlets
Figures:
1 - Superposition of 0-2000 Hz spectra for minirun (29.5 hours) and May 17 data (18 hours)
2 - Quad violin mode regions for first three harmonics (actual modes are non-harmonic, but some upconversion of fundamental is propagation harmonically)
3 - May 17 spectrum with labeled lines
Other attachments:
1 - Ascii list of narrow lines / combs found in 0-2000 Hz
2 - zipped tar file of 27 sub-band spectra (mostly 100-Hz wide)