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

[Taichi Kato <tkato>]

(fwd) Call for Observations : GC vars (Greaves)

Date: Wed, 14 Jun 2000 13:49:25 +0000
From: JG <jgts@jgws.totalserve.co.uk>
Subject: Call for Observations : GC vars [chat]

There are a number of amateurs worldwide who use sophisticated
telescopic and CCD equipment to generate time series photometry as well
as high precision astrometry.  Of these, many are also capable of
understanding and using packages like DAOPHOT and MUNIDOS or similar.
Though "absolute" photometry, rather than differential photometry, is
often problematic, datasets like GSC 1.2, USNO Ax and the recent UCAC1
mean that the astrometry done can be of professional standard, as
practiced by some.

There are several known "novae" in globular clusters, including T Sco in
M80, N Oph 1938 in M14, possibly N Sgr 1943 [V1148 Sgr] in NGC 6553 and
possibly another that I can't remember.

There are quite a few suspected xray selected CVs in globular clusters,
but these are usually magnetic or similar CVs, not expected to give UG
type outbursts.

Astrophysically [ie tidal dynamically], binary or close stars in
globular clusters seem to end up as blue stragglers at one end of the
schemes, or LMXBs at the other [or even millisecond pulsars], but not
all globular clusters are "relaxed", and there is scope for the
existence of UG stars.

A handful of suspect UG stars are known of, and like the above mentioned
novae, these have mostly been stumbled across by sheer accident.  And
although they have been few and far between, this is an apparent
sparsity, for these globulars have been rarely studied systematically to
photometric standard.

On the other hand, it is possible that the SAI [Sternberg Astronomical
Institute] may be intending to correct a short fall in globular cluster
variable information, with regards identity, position and
characteristics, as they have done with extragalactic variables.  This
will not be easy, and may call for new obserations, due to deficiencies
in the literature.

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.

As the "robots" take over variable and asteroid discovery and follow up,
with even opportunistic high speed time series photometry to be
automated in a few years time, some of the better equipped amateurs may
find themselves needing something different to do in a few years anyway!

Of course, it is okay for me to sit here on my opinions suggesting this,
without having/being able to do anything about it myself, but it should
be noted that globulars have been much ignored in this regard for quite
some time.  Recently some _handful_ professionals have been using modern
techniques and equipment to chase up and revise old results, but much
that is in the literature is still based on old survey plate images,
with little CCD astrometry/photometry.

So, what do folk reckon?  Worth a campaign re the brighter/easier
objects?

If the above is a bit flawed in places, I'm sure Taichi Kato, Brian
Skiff and one or two others will correct the sheer gaffs in the
argument.

Just remember that globular clusters have never been monitored
adequately neither in terms of equipment nor in the time domain with
respect to UG type behaviour.  If they exist, any organised survey
campaign could stumble across a few almost incidentally.


Well, just thinking out loud I suppose...


Cheers

John

John Greaves
UK

VSNET Home Page

Return to Daisaku Nogami

---

vsnet-adm@kusastro.kyoto-u.ac.jp