MMT Binospec

Overview

This file summarizes several instrument specific items for the MMTO’s Binospec spectrograph.

Setups and Frame Typing

Unique configurations (setups) are defined by both the grating (dispname, FITS DISPERS1) and the slit mask (decker, FITS MASK). Frames taken with different masks therefore end up in separate setups (separate .pypeit files and calibration groups), so that slit traces, pixel flats, and wavelength solutions are never mixed across distinct slit-mask geometries.

Pixel flats, trace flats, and illumination flats require the incandescent flat lamp to be on (FITS INCAN = on), in addition to the arc lamp being off (HENEAR = off) and the screen deployed (SCRN = deployed). Exposures taken with INCAN = off are dark/noisy and are not auto-typed as flats.

Wavelength Calibration

Templates were created in 2023 that cover the usable range for each of the 3 gratings; the 1000 l/mm template was extended in 2026 to support red central wavelengths. All wavelengths are vacuum. The current template coverage is:

Grating	Template file	Range (Å)
270 l/mm	`mmt_binospec_270.fits`	3825 – 9216
600 l/mm	`mmt_binospec_600.fits`	4042 – 10047
1000 l/mm	`mmt_binospec_1000.fits`	3757 – 7211

For the 1000 l/mm grating, central wavelengths from roughly 4500 Å through 6450 Å are covered with full overlap on both detector sides. Settings near the blue end of the grating range (e.g. central wavelength ~4000 Å) extend slightly below the template’s blue limit but should still be usable, since full_template only requires sufficient overlap to anchor the cross-correlation; better test data are needed to confirm this corner.

Bad pixel mask

The static bad pixel mask is loaded from FITS files derived from the IDL pipeline calibration data (badpix_binospec.fits plus the hard-coded bad columns and detector trap regions defined in bino_mosaic.pro). This adds roughly 12,500 individual bad pixels per detector, along with bad columns and detector trap region masking, replacing the small set of hard-coded bad columns previously identified from 2019 flat and bias observations. The mask files are distributed with the package as static_calibs/mmt_binospec/bpm_binospec_det{1,2}.fits.gz.