A long-standing and profound problem in
astronomy is the difficulty in obtaining deep near-infrared
observations from the ground due to the extreme brightness and
variability of the night sky at these wavelengths. The atmospheric
emission at 1.0 – 1.7 um arises almost entirely from a forest of
extremely bright, very narrow OH emission lines that vary on
timescales of minutes. Infrared astronomers have long envisaged the
prospect of selectively removing these lines, while retaining high
throughput between the lines. Such a filter has now been realized at
1.5 – 1.7 um by members of our team; it is called PRAXIS and was
tested on the AAT. The unique approach of PRAXIS relies on using fiber
Bragg gratings (FBGs). These gratings are fabricated by imposing
variations of the refractive index along individual optical
fibers. Here we seek to apply this same technology to commission the
Maryland OH Suppression Infrared System (MOHSIS, pronounced “Moses”) for
the Rapid IMAger-Spectrometer (RIMAS), a new near-infrared imager-spectrometer
for the 4.3-meter Lowell Discovery Telescope (LDT). MOHSIS + RIMAS will
become one of the premier instruments for deep near-infrared
spectroscopy. The ∼40× lower sky brightness of this instrument over
conventional spectrographs will result in an effective ∼6× gain in
sensitivity to faint sources. This is a project
with low risk: (i) MOHSIS uses the same proven technology as PRAXIS;
(ii) RIMAS is based on a simple double-beam design and on schedule for
first light in summer 2025; (iii) Our team has extensive experience in
designing, building, and commissioning instruments on large telescopes
and spacecraft missions.
This project wil train graduate and undergraduate astronomy students
in scientific practices at the interface of photonics and
astronomy. It will be the subject of a PhD thesis at Maryland. These
students will participate in the design, fabrication, integration,
testing, and commissioning of MOHSIS, the GRB science, and extensive
user support. This user support will help maximize the scientific
output of this instrument, benefiting students and researchers at
Maryland and all LDT partner institutions. This project fits the
definition of transformative research: as the first photonic OH
suppression systm in the world with simultaneous J + H coverage,
MOHSIS has the potential to change the way NIR spectroscopy is done
from the ground and be a pathfinder to major new instrumentation and
scientific discoveries.