The STIS Exposure Time Calculators currently available on the Web have a large range of options for the input spectra. However, except in the specific case of a user input spectrum where the user can provide a sufficient number of points in the spectrum, the ETC does not have full information on the width of the emission and absorption features in the spectrum. As a result, in specific cases where (i) the source is extended, (ii) the line width is smaller than the wavelength resolution of the observation, and (iii) the wavelength step in the input spectrum is larger than the wavelength resolution, the supplied information is insufficient to calculate the countrates accurately at all wavelengths. In such cases, the calculated countrates (and signal-to-noise ratio) can be inaccurate around the emission lines. In order to correctly calculate the countrates and signal-to-noise ratio, additional information on the width of the line is necessary and the calculations must take the line width parameter into account. This is now being handled by the new Emission Line Tool (ELT) in the STIS spectroscopic ETC. The ELT has been integrated into the Spectroscopic ETC, providing a new section on the input form for the user to input line center, flux and FWHM for up to three emission lines.
American Astronomical Society Meeting Abstracts #192
- Pub Date:
- May 1998