0803 W. M. KECK OBSERVATORY CALIFORNIA ASSOCIATION FOR RESEARCH IN ASTRONOMY

Keck Engineering Time Proposal

Title: Increase angle tracking sensitivity and test on GCIRS7 Date of Observation: June 29, 2007 Lead: J. Woillez Other persons involved: J.U. Pott, P. Wizinowich Telescope(s) K1 + K2 Instrument(s) IF-V2 / MRI project Sky time Requested 1 hour on both telescopes Date(s) to avoid None Required conditions None

Purpose (Please describe succinctly the main purpose of the proposal: development project, general telescope engineering, instrument commissioning, problem trouble shooting, data quality, etc.):

The current setup for the interferometer allows angle tracking in H-band but with a poor limiting magnitude of H~7.2. We would like to investigate the replacement of the culprit, a dichroic mirror, that currently sends the H-band light to the fringe tracker rather than toward the angle tracker, with a H-band transmissive element that would increase the limiting magnitude to H~11.2.

Benefits: Possible observation of GCIRS7, a key object in the galactic center for the MRI project. Provide a better instrumental setup to observe new red objects in general (YSOs, AGNs…). Description (Please describe your night-time engineering plan; provide justification for the time request, and include figures, ECR description and other attachments if necessary):

Scheduled after a first regular half night of V2 engineering, this test would require replacing the fringe tracker dichroic mirrors with a new pair that would transmit the H-band light. A few minutes are expected for the duration of the replacement operation, and will have been tested in the day time. Other day tests on this new set of dichroics will have been performed to confirm the good behavior of the possibly impacted fringe tracker.

A valid test for this configuration is to conduct a calibrated measurement: 1. Measure fringe contrast on GCIRS7. a. Acquire GC guide star with AO. b. Acquire off-axis GCIRS7 (H=9) with the Angle Tracker in H-band (H<11.2). c. Acquire GCIRS7 with the Fringe Tracker and record data. 2. Measure fringe contrast on TBD calibrator. 3. Repeat 1. and 2. for consistency. 4. Time permitting, repeat with GCIRS16NE (H=10.9).

The figure bellow shows the location of the piece of optics to be replaced and the new transmission scheme between the fringe tracker and the angle tracker. Current setup Star New setup Star Light Light

H+K K Fringe Fringe Tracker J Tracker J+H

Angle Angle Tracker Tracker

Plan for data reduction, analysis, and reporting:

1. Report on H-band angle tracker throughput. Angle Tracker throughput will be measured in day time but reported as well.

2. Report on GCIRS7 visibility. A visibility for GCIRS7 will be produced with the standard Michelson Science Center data processing pipeline. Comparison with other engineering targets on that same night will give a good indicator on the performance. Final visibility measurement will be integrated in the MRI-related GC observations astrometric error budget.

Other resources needed:

None. Status and progress reports from previous use of engineering time: 0