Hints, Tips and FAQ
version: 2003-01-15 oh
This page lists various hints, tips, and frequently asked questions. If you don't find a reply to your problem, pls contact us.
- Conversion of ESO headers to IRAF compatible headers
- Active Optics and Image Analysis
- Observations at Zenith and Alt-Az Mount
Conversion of ESO FITS headers to IRAF compatible headers
The FITS files produced by ESO instruments make extensive use of the hierachical keywords. Some image processing systems, including IRAF, cannot deal with them. To convert these keywords (e.g. from HIERARCH ESO TEL AIRM START to AIRMASS ) use the hierarch28 program developped by N. Devillard. This program, together with a series of other useful FITS-related programs, is available at http://archive.eso.org/saft. (They are part of the ECLIPSE package, and therefore directly available at the telescope and on any scisoft machine). Alternatively, ESO has developped a set of tools to deal more generically with the FITS headers, the FITS Translation Utility, or FTU, which is available from http://archive.eso.org/ftu .
NTT: Active Optics and Image Analysis
- An image analysis should be performed at the beginning of night (not necessarilly on the first object, e.g. if the latter is a standard star).
- An image analysis should be performed when the seeing is better than ~1.2", and that the telescope moved by more than ~10-15deg in altitude when from the zenith and more than 20-30deg when close to the zenith.
- Whenever possible, the image analysis should be ran in parallel with the observations. If the conditions are very stable, the corrections can be sent to the optics automatically, during the integrations. When the conditions are not optimal, the Telescope Operator will check the results of the analysis before applying them.
- An image analysis takes 3-6min in general
See the NTT active optics page
NTT: Observations at Zenith and Alt-Az Mount
The NTT has an Alt-Az mount; as a consequence, the singularity for the pointing is at Zenith, and not at the pole as it is on traditional equatorial mounts. When observing very close to the Zenith, the telescope, building, and instrument rotators have to rotate very fast to track the object. This will result in a poor image quality, unaccurate pointing and tracking, objects getting out of the slit, etc. In the worst cases, presetting too close to the Zenith can also crash the system.
To avoid any problem:
- Never, ever point within 5deg from the Zenith (-32
- Never, ever observe within 5deg from the Zenith (-32
- In the -32 to -27 dec range, do NOT observe within 15min from the meridian
- in the -50 to -10 dec range, be aware that you may get bad surprises within 15deg from the meridian.
So, adjust your program taking this into account.
As a compensation, the NTT does not have a 6h limit on the hour angle, as on equatorial mounts: you can point below the pole at 12h HA.