[Aavso-photometry] What to use when there are no suitablecomparison stars in the field?

[arne]

Robin Leadbeater wrote:
> Hi Terry,
> 
>>  There is one star in
>> the field TYC 8794-1530-1 with a tycho V mag of 9.589 but this is
>> pretty bright compared to the variables. With a 60 sec exposure it
>> half fills the dynamic range of my CCD but the variables are still a
>> bit dim with a S/N giving errors of ~0.1 mag. It would be better to
>> double the exposure but this will make the tyco star not usable.
> 
> Assuming it is photon count rather than read noise which is limiting the S/N 
> how about summing  multiple exposures to increase dynamic range? It seemed 
> to work when I used to do photometry using an 8 bit camera.
> 
I should say that another alternative is to use the Tycho star, and
make your own comparison sequence by measuring the brightness of
other stars in the field.  You can even step down, say measuring the
11th magnitude stars with respect to the Tycho star, and then
measuring the 13th magnitude stars with respect to the 11th magnitude,
newly calibrated, ones.

Robin's technique works, and I've used it before, but it takes
more effort since you now have to stack before doing your photometry.
As long as you have stars of the proper magnitude in your frame, you
might as well get them calibrated and make use of them.

Whatever you do, if reporting the data to the AAVSO, identify which
stars were used as comparisons and what magnitude you were using
for them.
Arne