Others in the group have replied with excellent descriptions of what the 25 mag per arcsec squared measurement embodies so I won't duplicate that effort again.
The HYPERLEDA catalogue stores the major and minor axis data in a rather non-user friendly manner. I will try to explain how to extract meaningful data from the catalogue. First, the major axis diameter is stored as the base 10 logarithm (log10) of the diameter expressed in 0.1 arcminute increments. (Yeah, it is wacky). To extract the actual major axis diameter, take the inverse log10 of the database value, then divide by 10 to get the diameter in arcminutes. Based on the language/method you use to perform this conversion, you may or may not have an inverse log10 function. If not, simply raise 10, using a power function, to the value found in the database. This is the equivalent of the inverse log10 function. Ok, so that was the easy one! The minor axis diameter is stored as the log10 of the ratio between the major axis and the minor axis (major axis diameter divided by the minor axis diameter or major/minor). To extract the actual minor axis, take the inverse log10 of the value in the database to get the ratio then divide the major axis diameter by the ratio to get the minor axis diameter. I highly doubt that CatGen is going to be able to compute these conversions using its simple scripting schema (I do not know this for sure as I have never tried). Your probably looking at performing a conversion on the data before running it through CatGen to create your catalog. On a side note, the data you downloaded from the CDS is over five years old. This may or may not be important to the specific purpose for which you are attempting to build a CatGen catalog. Regards, Jeff Burton --- In [email protected], "klauslms" <[EMAIL PROTECTED]> wrote: > > Thank you for answering. > My problem is how to compute this measure in catgen to get the > necessary data. I have downloaded this catalog last week: HYPERLEDA. > I. Catalog of galaxies(Paturel+, 2003 here: > http://cdsarc.u-strasbg.fr/viz-bin/Cat?VII/237 ; besides thank´s Mr. > Burton for his actual version! > Kind regards > Charlyms >
