Apparent discrepancy in BJD

Posted by Davidgp on Mar 21, 2018; 4:05pm
URL: http://astroimagej.170.s1.nabble.com/Apparent-discrepancy-in-BJD-tp982.html

I am new to AIJ and from answers on this website I have been able to insert into the Measurement Table, BJD times in the format BJD_TDB_MOBS.  Previously I had always used the Iowa State University (ISU) website for converting from JD_UTC to BJD_TDB and so decided to cross check.  In doing so I get a difference of ~1.89s +/-0.03s taken over 61 observations.  I used the same Simbad coordinates for V*NY Vir (RA 13:38:48.15; Dec -02:01:49.1) in both MP Coordinate Converter and the ISU webpage.  Likewise I used the same observatory coordinates (Long -110:23:53.18; Lat +31:39:56.08) for both with altitude set to zero for both.  Exposure time was 15s.  I am unable to find the cause of this difference but wondered if it was related to the definition of BJD_TDB_MOBS.  As an example I get 2458190.882506 and 2458190.882483 for ISU and AIJ respectively.