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 first light took place 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.