[vsnet-campaign 29] Re: XTE J1118+480 ASCA-VSNET campaign

[Taichi Kato <tkato>]

Re: [vsnet-campaign 25] Re: XTE J1118+480 ASCA-VSNET campaign

Dr. Sostero,

> About XTE J1118+480: it would be great for us to collect data with
> sampling time better than 5 sec, but unfortunately the problem is that
> with stars at V=13 or fainter, we are approaching the noise background
> limit of our electronics. The photometer we are currently operating, is
> based on an old 1P21 photomultiplier tube and electronics, that is very
> "noisy".
> 
> For this reason I consider more safe to use an integrating time of 10
> sec. According our experience, this is the only way to reach an accuracy
> of the order of 0.05magn for such "faint" objects. Otherwise the risk is
> to measure electronic background noise and not flickering.

    If conditions allow (and if it won't affect you operation), you may
choose "white-light" (without a filter) high-speed photometry.  This will
provide you roughly double photons.

    While the choice is upon you and your observing condition, I must
remind all high-speed photometrists (using photomultiplier tubes rather
than CCDs) that we don't need to get signal-to-noise ratio in _individual_
integrations (i.e. several seconds).  What is more important is the
signal-to-noise ratio in the summed (or phased, correlated ...)
observations (maybe hours long).  This is something like pulsar photometry.
Photomultiplier tubes will have greater advantage in such occasions!

Regards,
Taichi Kato

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