erosita-forum

Hi,

In the documentation for the "ebarycen" task (https://erosita.mpe.mpg.de/dr1/eSASS4DR ... n_doc.html), it looks like there isn't a parameter option to specify which JPL ephemeris to use (e.g. DE200, DE405, DE440, etc.). When I run the task, I notice that by default, a "PLEPHEM" header column is added with the value "JPL-DE200". However, for consistency with other instrument data and to maintain up-to-date standards, I am aiming to use the JPL-DE440 ephemeris. Is there a way to specify this for ebarycen?

Thanks very much in advance,
Joheen Chakraborty

Dear Joheen,

the "ebarycen" task uses the HEASOFT task "barycen" to compute the barycentric correction. Unfortunately, "barycen" has no option to choose the ephemeris file. However, after looking into the "barycen" source code (heasoft-6.29), I found that barycen uses the file ephemeris JPLEPH.405, but writes PLEPHEM = 'JPL-DE200' to the header of the output file.

It should also be mentioned that the event times in the eROSITA DR1 data are affected by clock drift of the SRG spacecraft clock. This can lead to errors in the absolute event timing of up to ~ 1sec. The clock drift and other timing errors will be corrected in future eROSITA data releases.

Regards,
Georg Lamer