Is ACP correctly putting BJD in fits? And use or not the _MOBS?

[gboyle]

HI
ACP version 8.1 now puts additional fields in fits, including BJD and other time/airmass figures.
They seem to be in there when I look at them when the files come out of ACP but when I process in AIJ and open the measurements table in AIJ these fields show "NaN" until I update the fields using the co-ordinate converter function.
Is there something wrong with the ACP values or do I need to change something so that they are read correctly - am just looking to take advantage of the automation and limit manual processes where available!

Also should I be using BJD or BJD_MOBS - am not sure what the latter is..!

Thanks
Gavin

[karenacollins]

Hi Gavin,

For FITS header values to be extracted by Multi-aperture properly, the associated FITS header keyword names need to appear exactly as they are in the FITS files in the comma separated list of the aperture settings panel as shown below. Also, the option "List the following FITS keywords ..." needs to be selected.

Note that if you are using DP to calibrate your data, and if you have "General" "FITS Header Updates" enabled, some of the ACP values may be overwritten by AIJ.

To avoid that, either deselect the above feature, or use the "wrench" FITS Header Settings" option to specify alternate header keyword names or disable individual keywords that are being calculated by other software. Whatever you change them to, you need to specify the new names in the comma separated list above if you want them to show up in the measurements table after a photometry run.

By the way, AIJ calculates BJD in the TDB reference frame (see Eastman et al. 2010), rather than the UTC reference frame. The resulting time format BJD_TDB is the one used by most of the transiting exoplanet community, so I would recommend letting AIJ calculate that if ACP does not. Note that in the latest released version of AIJ, there is an error in the default keyword name for BJD_TDB. Please replace the default value of BJD_UTC with BJD_TDB as shown above.

I expect BJD_MOBS is BJD at mid exposure time, but that doesn't specify the UTC or TDB time base. The MOBS part is usually understood to be the case, so it is preferred to use a key keyword name of BJD_UTC or BJD_TDB to indicated specifically what the time format is (there is currently over a minute of difference between the two).

Karen