ETC Frequently Asked Questions

Q. Why do I get a blank output page?
A. Several types of errors cause the ETC to stop the calculation before completion. One common example is when the ETC is asked to normalize the flux to a certain value when the flux in the input spectrum is zero. Given the large parameters space for the ETC, there can be several such errors. Since the ETC does not track all such errors, it sometimes gives a blank output page. However, the problem usually lies in one of the input parameters, so you should double check the input parameters before asking for help from the STScI help desk.

Q. What is the ID number?
A. The ID number serves two purposes. First, it serves to cross-identify your output page with the corresponding plots and second, some of the information is temporarily stored under that particular ID in an internal directory, allowing the STIS team to identify any potential problems more easily. Users should provide the ID when reporting problems with a particular calculation.

Q. If I am supplying my own user-input spectrum, does the spectrum have to cover the whole wavelength range of the observation?
A. No. This was a limitation of the earlier version of the ETC; but the ETC has been enhanced so that the user-input spectrum does not have to cover the entire wavelength range of the observations. However, you must make sure that you normalize the spectrum at a wavelength where your input spectrum has some flux, and that you normalize within the wavelength range of observations.

Q. What does CR-SPLIT=1 mean?
A. The CR-SPLIT number is the number of exposures. The total time of the number of CR-SPLIT exposures will equal the specified integration time. So CR-SPLIT=1 means that the total number of exposures for the specified integration time is 1.

Q. Is the CR-SPLIT option only for the CCDs?
A. Yes. The CCD observations are CR-split to correct for cosmic rays. Also, in the case of the CCD detector, the full-well limit is a consideration which is affected by the number of CR-SPLITs. None of these apply to the MAMAs. So the CR-SPLIT option is valid ONLY for the CCD. If used in the case of MAMA observations, the CR-SPLIT number is simply ignored.

Q. What kind of MAMA pixels are used in the ETC?
A. The ETC always uses low-res (25 x 25 micron) MAMA pixels.

Q. What is the allowed range of redshifts if I use the template QSO spectrum provided by the ETC?
A. This depends on the wavelength of the observation. The 'rest' wavelength of the template QSO spectrum ranges from 800 to 6000A. So the redshift has to be in the range so that the redshifted wavelength range covers the entire wavelength range of the observation. Otherwise, the ETC will give a blank output page.

Q. Can the ETC redshift the other 'template' spectra for me?
A. No. The redshift option is applicable only to the QSO spectrum. If you need to redshift other spectra, you need to provide the redshifted spectrum.