[vsnet-chat 3090] Re: (fwd) Call for Observations : GC vars (Greaves)

[Taichi Kato <tkato>]

Re: [vsnet-chat 3087] (fwd) Call for Observations : GC vars (Greaves)

> SO: those suitably equipped who get bored between the appearance of
> unexpected outbursts of superhumping CVs, or apparitions of challenging
> NEOs in need of astrometric follow up observations, or similar, may
> consider doing fresh astrometry and photometry on globular variables.
> Especially if they find they've automated and learnt their current
> practices to such a level that it is no longer a real challenge.
> 
> Some of this would be new/challenging work... ...many of even the
> brightest GC vars have little known positions, ill determined epochs and
> approximate periods [indeed for some it is not certain whether the
> period is the quoted one or twice that value, etc].  "Absolute" Johnson
> or similar passband photometry is _not_ necessary for epoch and period
> determination in most if not all cases: differential photometry will
> usually suffice especially given sufficient coverage.

   The main difficulty in observing globular clusters using small equipment
is the high density of stars.  The high surface brightness of the core
also limits the exposure time (if the center is included).  If images are
taken after overcoming these difficulties, observers will meet further
difficulty of notorious photometry of crowded star fields (I wonder whether
MUNIDOS can do this).  These globular clusters have several stars within
a pixel, so it is usually hopeless to make meaningful photometry close
to the core.  On the other hand, amateur CCD equipemnt can perform a good
job in observing the outskirts of globulars.  Monitoring for known and new
UG variables are within the capability.  No difficulties, except for distant
faint ones, exist in photometry of bright pulsating variables, since many
of which are already observable visually.

Regards,
Taichi Kato

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