MAROON-X has two arms, each with its own CCD and readout system. Typical exposures thus result in two FITS files, one from each camera.
The filename convention is:
YYYYMMDTHHMMSSZ_FFFFF_C_ TTTT.fits
YYYYMMDD UTC date at exposure start
HHMMSS UTC time at exposure start
FFFFF Spectral source in fiber 1-5 (D - Dark, E - Etalon, F - Flat, O - Object, S - Sky, T - ThAr arc)
C Camera arm (b - Blue, r - Red)
TTTT Exposure time in sec (for sub-second fraction see also fits header keyword EXPTIME)
Examples:
20200904T125018Z_SOOOE_r_0300.fits Science frame from the red arm, with sky background in sky fiber (#1), object (stellar) light in science fibers (#2, #3, and #4) and Etalon light in simultaneous calibration fiber (#5). Integration time 300s.
20200904T134908Z_DTTTT_b_0015.fits Calibration frame from the blue arm, with no light (dark) in sky fiber (#1), ThAr arc light in science fibers (#2, #3, and #4) and simultaneous calibration fiber (#5). Integration time 15s.
The FITS header of each raw file contains a snapshot of the status of all subsystems of MAROON-X. For data taken after August 18, 2020, the snapshot is taken at the beginning of the exposure. For data taken before August 18, 2020, the snapshot was taken at the time the FITS file was written. For these files the telescope status information might have been incorrect as the telescope might have slewed to the next target during CCD readout.
Note: The FITS header keyword EXPTIME hold the exposure time with sub-second accuracy.
Image data consists of a 16bit 4400x4400 array for both CCDs. The blue CCD is read from four taps (amplifiers), the red CCD from two taps (amplifiers).