Affiliation
British Astronomical Association, Variable Star Section (BAA-VSS)
Thu, 07/18/2024 - 20:10
I remember that there is a routine in VPhot to cope with close companions.
RU Peg has one which (for optimal settings of aperture, for my first obs) sits on the inner sky annulus circle.
I just wondered if I should try to get the intruder in one region or the other.
Thanks
Kevin
Hi Kevin,
Don't worry about it if the star is in the sky annulus. The sky-determining algorithm rejects stars that are in the annulus (think median filtering, though it is usually more complex than that).
Arne
Kevin:
1. You may recall from your vphot course that I don't like to simply give an answer so you may ignore my questions/comments if you want to! ;-)
2. What is measured in the 'inner circle' (aperture)? What is measured in the 'gap'? What is measured in the outer 'sky annulus'?
3. Look at the vphot 'star profile'. Can you see the neighbor in the profile? How close (radius) is it to the target? Does the star plot vs radius reach a background level on either side of the companion if you can see it? IOW, is the companion on the target downslope or completely separate from the target? Could you adjust/shrink the inner aperture? Would that help?
4. Do you think some flux from the target may be found in the 'gap'? Does that matter? Do you think some of the flux from the companion may be found in the inner circle/aperture? Does that matter? Might this extra flux impact the target magnitude or not?
5. As you hinted at 'remembering', Arne told you that there is an algorithm in VPhot to remove the impact of stars in the sky annulus. It's an iterative 3 std deviation rejection.
6. Rather than 'wondering' what happens when you place the companion in the 'gap' OR the 'sky annulus', why don't you try both and see what happens to the target magnitude?
Ken