Subject: ARC echelle

From: Jon Holtzman

Submitted: Fri, 17 Aug 2012 17:28:18 -0600

Message number: 1284 (previous: 1283, next: 1285 up: Index)

One of the tasks for the 3.5m summer shutdown this year was to install a new grating in the echelle, and this was successfully accomplished.

The main driver for this was to improve throughput, as we identified an alternative master grating that should have provided a minimum of 30-50% throughput improvement. Based on initial internal calibration data, however, it does not appear that we are seeing a significant improvement in throughput.  We are in the process of trying to figure out why this is and hope to have additional information in the coming weeks.

A side result of the new grating installation is that the location of traces and, especially, wavelengths, on the chip have changed significantly, so old calibration files for extraction and wavelength calibration will not be applicable to the new configuration. We do have initial reference files for trace location and wavelength calibration for use with IRAF reduction scripts; we are still confirming the applicability of these across multiple nights and will make them publically available as soon as possible, but users in the near future can certainly contact me or APO to get the initial versions if desired.

Because of the shifts, all echelle users need to be aware about the new configuration!

Depending on additional information we may get about overall throughput and possible explanations, it is uncertain whether there will be future changes to the current configuration.

Jon Holtzman, Instrument Scientist
Mark Klaene, Site Operations Manager



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