Classical Echelle Spectrograph for the Apache Point Observatory 3.5-m Telescope

I am working with collaborators at JHU and NMSU on the design of a new, classical, optical echelle spectrograph for the Apache Point Observatory 3.5-m Telescope.  Our vision is to replace the venerable ARCES spectrograph, in service for 20 years, with a new instrument using the latest innovations in high-resolution spectrograph design to provide maximal throughput across the wavelength range of 350 nm --- 1000 nm.

As of Fall 2023 we have a robust conceptual design for a spectrograph with baseline resolution R ~ 32,000 for a 1.7 arcsec slit (4.5 pixel sampling).  Featuring a white pupil design, the instrument would have dedicated blue and red arms with prism cross-dispersion and refractive cameras.  The slit length is approx. 6 arcsec.

A slit change mechanism would also allow the use of a 1.3 arcsec slit to be used along with a high-speed tip-tilt image stabilization mechanism in the fore-optics.  The tip-tilt system would minimize PSF broadening from sources such as telescope vibration, tracking errors, and, to a lesser extent, atmospheric tip-tilt.  This slit would provide resolution R ~ 40,000.   A "Bowen-Walraven" two-slit image slicer would also be available to provide resolution R ~ 64,000.  The fore-optics will also include an Atmospheric Dispersion Corrector, Slit Viewer, and dedicated Calibration System.

Radial Velocity Upgrades to APOGEE Spectrographs

For SDSS-V, we have recently commissioned multiple external upgrades, pioneered by the Penn State precision radial velocity instrumentation group, to both APOGEE spectrographs to improve the instrument radial velocity precision from approx. 100 m/sec to 30 m/sec.  The upgrades, described in Wilson et al. 2022, consist of: 

• Fabry-Perot Interferometric calibration sources to provide a picket fence of spectral lines with uniform spacing and intensity for precision wavelength calibration.
• Back Pressure Regulators control the back pressure seen by the internal LN₂ tanks to help isolate the tanks from varying atmospheric pressure.  This stabilizes the internal temperatures of the cryogenically cooled instruments.
• Octagonal Fibers in series with the fibers going to the instrument from the telescope to minimize motion of the near-field image at the ends of the fibers inside the instrument at the pseudo-slit.