Affiliation
American Association of Variable Star Observers (AAVSO)
Fri, 07/22/2022 - 19:01
The AAVSSO Extended File Format states that the Date field in a variable star report should be the midpoint of the observation. However, I see that VPHOT apparently pulls in from the FITS header the start time of the observation instead of the midpoint.
Comments?
Thanks.
Dennis Conti
Dennis:
I do not think you are correct. The JD in the AEFF report is the mid point of the exposure. This has been checked many times.
You would need to share an image (MZK) and send me the report (kenmenstar@gmail.com) and explain exactly what you did.
Ken
Ken,
I just sent you via regular email an image used to create a VPHOT-generated AAVSO report, which I also included in the email I sent you. You will see that it appears VPHOT picked up the start time and not the mid-obs time from the FITS header.
Thanks for looking into this.
Dennis
There is a switch in the Telescope Profile where you tell VPhot what time to expect from the fits header.
It is normally Start of Observation, in which case VPhot will figure out the middle of the exposure for you.
If that specification is Mid-point of exposure then it would simply use the datetime found in the Fits header, believing all is well.
Might this be the problem?
George
Hi George,
Ken helped me resolve the issue, which was this: I specified mid-exposure time in the telescope setup since mid-exposure time was explicitly in the FITS header - inserted by AstroImageJ. But, since VPHOT did not recognize the AIJ keyword (JD_UTC), it took the DATE-OBS value as if it were the midpoint. I changed by telescope setup to start-exposure and VPHOT then correctly took 1/2 the exposure time, added it to my DATE-OBS and computed the midpoint.
Thanks,
Dennis