Instrument: ARIES + MMTAO · Sensor: IR wavefront sensor
Overview
The third night of this AO engineering run focused on closing the loop at higher mode counts than previous nights, refining the alignment, and acquiring on-sky data for an ASU science target and a photometric reference for Suresh’s gain comparison.
At the start of the night there were lingering alignment issues from Night 2, so we budgeted time to revisit the bootstrap sequence before pushing to high mode counts.
Planned sequence
- Improve pupil alignment
- Confirm alignment on the IR wavefront sensor
- Check and select flat files
- Close loop — bootstrap from 3 modes up to maximum achievable
- Observe ASU science target
Night log
Coma and alignment
Significant coma was present in the WFS signal at the start of the night. This appeared to originate on the wavefront sensor side and was propagating into ARIES. The coma level pushed the hexapod near its travel limit, which caps how much we can correct going forward. A full realignment of both the AO system and ARIES is warranted before the next run — there is something mechanically misaligned upstream.
Silver lining: ARIES performs better when the hexapod is within limits, so a proper realignment should yield a meaningful improvement to Strehl.
Flat selection
We tried several flat configurations. None showed a clear advantage over the others, so we settled on the 35 μm gap flat and used it for the remainder of the night. This will be our reference for the run.
WFS alignment
After the alignment iteration, the four pupils on the WFS were better centered and the slope maps looked more symmetric. The improvement was visible by eye.
Bootstrap
Redid the 3-mode and 20-mode loops, going back and forth between mode counts to bring the mirror to a position where the WFS could robustly pick up the surface. The iterative bootstrap was slower than ideal but ultimately got the mirror into the right regime.
Science target — MASCARA-1 b
| Parameter | Value |
|---|---|
| V magnitude | 8.3 |
| K magnitude | 7.7 |
| IR WFS Detector signal | ~200 counts (~1% of detector) |
Summary and follow-up
The coma and hexapod limit situation is the most pressing issue.
The 32-minute loop run at 50 modes is encouraging — the system is stable when it’s up. The wild coil events are shorter and less frequent than early in the run, suggesting the system is warming up to a more thermally stable state.