http://tinyurl.com/irms-etc
(DOWNLOAD).
Please see installation instructions below.
The IRMS exposure time calculator (ETC) has preliminarily been adopted from the MOSFIRE ETC given the similarities in their technical specifications. The MOSFIRE ETC was written by Gwen Rudie to facilitate the computation of exposure time for an observation given a desired signal-to-noise ratio (SNR), and vice versa. The principle modes involve computations of SNR based on a specific line of interest ("Line Flux") or on the full continuum band ("Magnitude"). The user may also indicate whether AO mode was to be used for the intended observations, and the appropriate AO PSF will be chosen. The inputs to the ETC include the wavelength bands, slit width, angular extent, line flux or full band magnitude information, the desired SNR or an input exposure time, etc. as demonstrated on the left side of the ETC's graphical user interface (GUI) in the figure below:
Installation Guide
The IRMS ETC is primarily a GUI widget coded in IDL. A preliminary version can be downloaded from http://tinyurl.com/irms-etc, or
here. This
guide walks you through running the code on a working IDL
installation with the astronomy library 'ASTROLIB'. However, it
should also be able to run with IDL virtual machine which does not
require an IDL license. For more details please refer to the
installation guide of the MOSFIRE ETC.
After you download and unzipped the tar file, check and make sure that the mandatory directories are present: the bin directory contains the main codes of the ETC that must be compiled prior to starting up the ETC; the mosfire, Mauna_Kea_sky, MosfireSkySpec, MosfireSpecEff, and NFIRAOS directories all contain relevant data files regarding MOSFIRE and TMT/AO characteristics on which the IRMS ETC are based.
Be sure to set the 'MOSFIRE_XTCALC' environment variable to the path where you put the directories. Start up an IDL session, and start running the ETC by first compiling the following:
IDL> .r events_XTcalc.pro
IDL> .r XTcalc_irms.pro
IDL> .r run_XTcalc.pro
IDL> run_XTcalc
Changes to the MOSFIRE ETC
For the IRMS ETC, we have adopted the MOSFIRE ETC code but incorporated the following important changes to account for differences between observations from the two instruments and telescopes: the effective area of the telescope (e.g. a factor of ~8 larger), the slit width (e.g. a factor of ~4 narrower), pixel scale (e.g. a factor of ~3 finer), dispersion pixel size (e.g. ~60% smaller), and detector readnoise (e.g. a factor of 3 lower). Estimates of the Mauna Kea sky background, throughput curves, and linearity limits have been temporarily adopted from MOSFIRE, while the atmospheric transparency spectra were taken from the Gemini Observatory website. Once an observed throughput spectrum is taken with IRMS and the reflectance of the TMT mirrors measured, this will need to be updated in the ETC.
As IRMS will operate behind NFIRAOS, improvement on the sensitivity based on adaptive optics needs to be taken into account. Point spread function (PSF) models from NFIRAOS have been simulated by the TMT AO team for the J, H, and K bands and have been incorporated in the calculations to the first order. In AO mode, a fixed off-axis PSF is convolved with the line or spectrum of interest before SNR or required exposure time is computed. In future implementation of the ETC, different AO models reflecting the degree off-axis of the target and effect from slit orientation may be incorporated.