Re: HD 145913

[Arne Henden <aah@nofs.navy.mil>]

Michael Koppelman wrote:
>> My guess is that Mira's photometric estimate is in
>> error or not being used correctly.
> 
> 
> Why? I've heard people talk of errors being (S/N)^-1, which in this case 
> would be like 0.00125. The 1-sigma in the comp star is 0.0045. That puts 
> 3-sigma at 0.01. The thing is damn bright -- even a hack like me can get 
> OK results with enough signal, don't you think? ;)
> 
   Once you get to this signal level, you need to worry about systematic
effects such as how good your flatfielding is.  Also, the quoted errors
tend to be ~Poisson, so your comp star can look good but your variable
can be quite a bit worse if it is fainter, on a bad part of the chip,
etc.  The flickering can be real, but when you start making assumptions
about low-level variations, you have to test those assumptions in many
different ways to ensure they are correct.  Kato-san already mentioned
how the power spectrum of flickering should look like, for example.
Arne

> The TASS data has a few points which look errant and a lot of points 
> with a flag of 1. If you delete all of those you still get a standard 
> deviation of 0.017 and and amplitude of 0.105, which is much more 
> variation than I was able to demonstrate. Maybe it's worth another look.
> 

   I don't know where Tom's saturation level is; this might be close.
However, your time series was not long enough to confirm or deny the
4.8hr period in any case.  Since you've started on this star, you
might as well carry it to completion and try to get a longer time
series.
Arne