6.3. How to use the HDA
6.3.1 What to do after querying the database and identifying the images or spectra of interest?
First, check the instrument's calibration screen to see if it is necessary to recalibrate the data with newer (and possibly better) calibration files. Not only the reference files might have changed, but also the algorithms used to create the calibration code. If the program had indeed changed, it will be necessary to decide the impact of this change based in the use you will give to the observations. This information can be found in the HST Data Handbook, the instrument manual or the WWW pages with instrument information (http://www.stsci.edu/instruments).
The absolute calibration of all observations taken with HST uses a scale based in the white dwarf scale.
In the case of the very early observations (between 1990-92) the aperture position listed in the header is not accurate. To verify and, if necessary, correct them it is possible to use the jitter files or using an image from the Digitized Sky Survey.
Other information of interest about the data is listed in Table 25.
|information||can be found at:|
|WF/PC and WFPC2|
|do superflats exist?||list in the WWW instrument pages|
|precise exposure time||header, HST Data Handbook (DHB)|
|light diffusion problem?||ISR FOS-127, HDB, Instrument Handbook (IHB)|
|background problem?||ISR FOS-114, IHB, DHB|
|GIMP correction applied?||header (observation date)|
|precise valor de FPKTTIME||IHB|
|precise value of EXPSTART||header, DHB|
|wavelength calibration||SPYBAL information (header or Phase II listing)|
Several tasks need to be completed before analyzing the data. It is recommended to extract all files related to an observation, even the engineering ones; i.e., the whole dataset. With all this information it is possible to reconstruct what happened during the observation. For example, the number of recentering events, which guide stars were used to point the telescope, any parallel observations obtained at the same time and the comments about the calibration and quality of the data. More information about these files can be found in the HST Data Handbook.
As explained above, it is very desirable to always check StarView's calibration screen and the instrument pages (http://www.stsci.edu/instruments). The Advisories section in them is a must read! It contains invaluable information about certain characteristics of the instruments and their data. Other items that can be found in the instrument pages are the latest edition of the instrument's handbook, Frequently Asked Questions, Instrument Science Reports and all the Space Telescope Analysis News issues. Other information of interest about the data can be found in the Instrument Science Reports. Table 26 is an example of this information.
Finally, it is also wise to read the contents and latest news posted in the STSDAS page (http://www.stsci.edu/stsdas.html). In these pages, not only the latest version of the software can be found, but also several other documents, handbooks and user's guides. This page has a link to the IRAF page, where the latest versions and documents can be found.