Friday, January 16, 2009

Bad Gain Exponents

I'm trying to calibrate some archival VLA HI data from 1989 and FILLM keeps giving me scary messages about BAD GAIN EXPONENTS, e.g.,

MCCHED: 0/02:34:45.0 12 x 12 BAD GAIN EXPONENT 26

AIPS seems to really not like this. The source table of the resulting data file only contains the first source observed, which is not right. I'm was going to be more aggressive about the FILLM selection parameters to avoid the bad times, but was wondering if anyone else has encountered this?

EDIT: After playing with the TIMERANG keyword for FILLM, it seems like this is a problem with how AIPS is reading in the file. Everytime I change the TIMERANG keyword, the data with the BAD GAIN EXPONENTS changes to the earliest data in the file. Weird.


Adrienne said...

I was wondering about bad gain exponents as well (in VLA+EVLA data) and was pointed at this page (last paragraph) as a possible explanation:

However I haven't actually tracked it down, and don't know if that's the problem. I don't know why it would be the first scan ALL the time.

amanda said...

Hi Adrienne,

Thanks for posting the email. I had found it, but hadn't had time to edit the post. I've calibrated the data and it seems to be fine. I'm wondering if the error messages are set to cutoff after a certain number of errors to avoid too much output on the MSGSRV.