NOFS 1.8-meter Spectrograph

The U.S. Naval Observatory intends to acquire a new, robotically-controlled spectrograph system, which includes a Nasmyth-mounted front-end and a fiber-fed optical bench setup, to be mounted to the USNO Flagstaff Station (NOFS) 1.8-meter Keck outrigger telescope. This spectrograph will enable regular spectroscopic monitoring of USNO mission-critical targets, such as ICRF quasars and bright/double stars. The spectrograph system will meet the following design requirements: A 3-arcsecond diameter target fiber with at least one 3-arcsecond sky background fiber. Fiber acquisition module to center the target within the fiber. Built-in spectroscopic calibration lamps, arc and flat field lamps. Precision guider system with generous field of view (> ~ 25 sq. arcmin) for operations in low-density sky regions. Filter wheel with 11 or more standard-size filter slots for direct imaging capability in standard passbands (UBVRcIc, Sloan ugriz, Pan-STARRS y ). Precision color-insensitive focuser. Switching time between imaging and spectroscopy of less than 10 seconds. High quantum efficiency (QE) spectrograph detector: > 80% QE between ~ 3800 and 9000 - Detector within minimal red-light fringing. Detector operating temperature of -100C for minimal noise; Peltier and liquid cooling system to achieve this temperature. One low-resolution diffraction grating (l/Dl ~ 500) with spectral bandwidth across full QE range of detector. Operable on bright stars within range of 3 < V < 6. One medium-resolution diffraction grating (l/Dl ~ 2000) with spectral bandwidth of at least 3000 . Must be able to integrate down to S/N > ~ 5 in continuum for quasar-like spectrum at a Sloan r mag of ~ 20 within 2 hours. One high-resolution diffraction grating (l/Dl ~ 10,000 - 12,000) with bandwidth of 100 to 200 - in order to obtain radial velocity measures to a precision of 1 km/s in solar-type stars and star systems. Absolute position encoding for all moving hardware. Design and fabrication of a mechanism to rotate the tertiary mirror of the 1.8-m telescope between two positions facing instrument ports on either fork. If this option is too costly, a pickoff mirror is acceptable using the primary instrument port in front of the laser guider star adaptive optics system. Lightweight and rigid construction, low thermal expansion for minimal flexion. Stray-light mitigation within front-end and optical bench. Front-end mass within 150 kg. De-rotator for Nasmyth focus of telescope, which is on an alt-az mount. Ability to safely cable/fiber wrap around a full range of azimuth during operations. Ability to operate on moving targets, such as satellites and asteroids. Control cabinet with UPS. Includes encoders, electronics and control system with interface option to Linux computer for automated operation. Python-scriptable Fully robotic: no need for an on-site operator/technician for any spectrograph operations or switching between spectrograph use and other instruments. Spectrograph shall be operable from USNO NOFS and USNO DC. Instrument failures requiring operator intervention (not including routine maintenance) shall not occur more often than once per two weeks, on average. Science and calibration data shall adhere to the most recent version of the Flexible Image Transport System (FITS) standard (e.g., 4.0), readable and writeable using common FITS manipulation software (e.g., IRAF, Astropy, etc.), with all FITS standard-compliant keywords required to determine, at minimum, the following information: Start/stop/midpoint time of observation to available precision. Exposure time in seconds. Time system (i.e., UTC in ISOT format and MJD) Telescope name Telescope site name Telescope site latitude and longitude Telescope pointing right ascension/declination to available precision. Set detector temperature Actual detector temperature Coordinates of the spectral fibers in right ascension/declination to available precision. Coordinate system (i.e., ICRS) Airmass or zenith angle Image type (target/science, lamp/calibration, bias, flat, dark. etc.) Filter wheel position All information required to optimally calibrate the spectrum. Any weather information available to the acquisition software Comment keywords for any other reportable information.