ETC and Sensitivity
A first generation Microsoft-Excel Exposure Time Calculator [ETC] for point sources is available for ARCoIRIS based on commissioning observations immediately after the installation of the instrument on the Blanco telescope. The calculator is based on exposures of bright A0V telluric calibrator stars observed in 8-okta clear skies with seeing ~1.0" (see example spectrum below). Users should input their source magnitude, desired exposure time and number of co-adds, with resulting example spectra and S/N estimates returned based on Fowler16 sampling. The ETC is known to work with LibreOffice 4.3 running under a Fedora-21 LiNuX distribution, Microsoft Office 2010 on a Windows 7 platform, as well as Microsoft Excel 2008 on a Mac OS X distribution. Observing overheads are ~10 minutes per field, which allows for telescope slewing, on-slit centering, setting up of AB or ABBA (or slew to off-slit background box), or any user-specified nod positions, and guide star selection.