Re: HD 145913

[Michael Koppelman <lolife@bitstream.net>]

On Friday, May 9, 2003, at 01:30 PM, Arne Henden wrote:

>  I usualy also recommend apertures around 5x fwhm diameter
> when trying to do accurate photometry of bright objects, so you
> might experiment with aperture size and see what happens.


Why is this? Take a look at my radial profile:

http://www.lolife.com/astronomy/hd145913/rad_prof.jpg

There is nothing going on (that I can see) after 4 or 5 pixels. You are 
suggesting a radius (in this case) of 7 pixels or so. Seems like I 
would get a lot more noise and a lot less signal in that case.

Also, check out this BVR plot:

http://www.lolife.com/astronomy/hd145913/hd145913_bvr.jpg

The apparent rise in B is probably due to redder comp stars. My airmass 
was 2.7 at the start of the run and 1.42 at the end and I have no 
suitable comp stars that match the color of my program star. I'll 
probably abandon B on this star and stick to VRI.

Cheers,
Michael Koppelman