NIRSPEC Status (Updated March. 2023)

NIRSPEC returns to Service as of March 1st, 2023

February's warm-and-pump service is now completed. NIRSPEC is now cold again and back in service for science operations.

Warm and Pump service happening for NIRSPEC in Feb 2023, Back in Service March 1, 2023

NIRSPEC is presently offline as it undergoes its annual service to remove trace amounts of water inside the dewar that has diffused through the O-rings over the past 12 months. Current temperature and pressure plots can be viewed here.

NIRSPEC back in Service with Routine Science Operations since March 11, 2022

The February service mission was mostly successful. The new Kband filter (so called "Kband-new") is performing very well and is now the preferred filter to use for all Kband science (e.g. instead of "NIRSPEC-7" or "K" or "Kprime", which are still available). Recent engineering tests on sky verified a total measured throughput increase (instrument + telecope + sky) of 10%. Those throughputs and other info have been updated on the NIRSPEC sensitivity page here.

We have re-installed the 24" x 0.720" slit, which now takes the place of the pinhole array that is no longer needed. The pinhole array had been installed in the slit wheel for the NIRSPEC upgrade activities, used to assess and optimize the focus at the SPEC detector.

Unfortunately, the efforts to mitigate the previous thermal light leak were not successful. The elevated thermal background is still present. The illumination pattern shown below is of a 30 minute SPEC exposure with the cold blank in beam. This "dark" frame shows structure that does not change for a given instrument configuration, and is therefore easily removed in a standard Beam A minus Beam B subtracted pair. The overall effect for spectroscopy is then a modest increase in the noise as per the elevated effective dark current, now measured at 1.7 e-/s in the regions with the highest thermal background (i.e. near top and center of detector). Note, this increased background will only dominate at wavelegnths shorter than 2.3 microns where the thermal background from the sky is lower.

NIRSPEC Now Cooling, Back in Service March 11, 2022

Following the open dewar service in early Feb. 2022, NIRSPEC is now cooling, and expected to resume science operations in March.

NIRSPEC open dewar service mission completed in Feb. 2022

NIRSPEC was warmed and opened up in early February to install new (better optimized) FEU stops for KPIC-FIU operations. We also installed a new K-band filter (named "Kband-new") which will have a significant improvement to the throughout (~97% compared with ~80% ) and built-in blocking all the way out to 5 microns (thus not needing the THIN blocker). The new filter replaces the H2 narrowband filter, which was not used for science. We took steps to address the small thermal light leak that is getting into the SPEC detector housing somehow, resulting in the elevated (quasi) dark current. We also re-installed the 0.720"x24" slit used for spectrophotometry in high resolution mode with the longer slit. Getters were removed, baked out for 30 hours at 100C, then re-installed before closing up the dewar.

Routine Science Operations Now Proceeding with Upgraded NIRSPEC

Following the successful upgrade of NIRSPEC, a variety of science programs over the past semester have benefited from the increased wavelength grasp and enhanced sensitivity delivered by the new Teledyne H2RG detector. Equipped with a new Linux based control system that delivers a stable user control environment, server crashes are now a relic of the past.

A key improvement to the user interface is a python-based image display and slit acquisition tool called Ginga. Slit viewing camera (SCAM) images are displayed with a green overlay showing the active slit in use, along with the corresponding slit center and nod positions (yellow circles). Acquiring a target in the slit can be accomplished by a single click within the display. Small adjustments (i.e. single or fractional pixels) to the target position is another useful plugin tool available through Ginga. Other ready tools include display cuts, histogram plots, point source fits, and more programmable options tailored to the needs our observers.

Ginga is also used separately as a quick look display and analysis of spectra being taken by the H2RG science detector (SPEC), with background subtraction display tools and easy access to previous frames via a thumbnail tab. As with Ginga SCAM, brightness, contrast, and zoom functions are all controlled through buttons from the lower tool bar.

Finally, in a service mission February 2019, we successfully restored the operation of NIRSPEC’s internal rotator to provide tracking of objects at a fixed position angle on the sky. In fact, the coupling between the rotator gear and the motor drive shaft worm was improved, which significantly reduced the vibration imparted to the gratings while the rotator is tracking. The result is that the cross disperser and echelle gratings are now much less influenced by the motion of the rotator, improving the stability by more than a factor five.

NIRSPEC Post-Upgrade Notes

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