[vsnet-chat 870] Re: Magnitudes, sequences, etc

[Taichi Kato <tkato>]

Bruce Sumner wrote:

> Unfortunately many people who should know 
> better are using GSC magnitudes as sequence stars. Don't fall into 
> that trap - they are garbage. And the USNO A1.0 catalogue, which 
> is extremely useful for the production of deep charts ( I use it 
> regularly), is useless for the final accurate magnitude sequence.

   Well, commercial programs like Astrometrica automatically produce
photometric results, which substantial number of amateurs report as
"photometric observations".  They are usually derived from GSC (or USNO)
magnitudes.  It's an unavoidable fact.  I now become adopting these
magnitudes, if the constant set of comparisons are used by the same observer,
as representing differential variability of the object.

   One thing some people mention is that these magnitudes look to have
become officially "accepted" by IAUCs (unfiltered CCD magnitudes, sequence
GSC).  This tendency seems to be reinforcing (or even recommending) the
usage of GSC as comparison stars, and unfiltered CCD as photometric device
-- now getting regarded as "IAUC standard".  (The due increase of the number
of people interested in CCD photometry is truly welcomed, though).

> BUT these folk are ALL professional 
> astronomers . Where are you amateurs who could help. In particular is 
> there someone in the southern hemishere who would like to get 
> involved. You will gain the undying appreciation of fellow variable 
> star observers for your work.

   From my experience with amateurs, there may be at least three main
reasons.

1) The lack (and cost) of readily available "standard" filters.  Standard
   filters are often expensive, not so easily attached as an eyepiece.
   Some amateurs (like Kiyota-san) uses a specially ordered set (I believe),
   but is a rere exception.  Filters introduce additional problems to
   otherwise intact, well-bahaving CCD system, as represented by the
   difficulties getting high-quaility flat fields, difficulties in cleaning
   the whole optics (filters often introduce dusts).

2) The lack of photometry-oriented easy softwares.  There are already too
   many "tips" even for aperture photometry, and standard photometry.
   It's usually a more difficult task for amateurs to get reliable photometry
   than astrometry.  All-sky photometry is even more difficult.

3) Some astronomy, in which amateurs are interested, doesn't always require
   filters.  Unfiltered time-series photometry is usually enough for analyzing
   periodic signals.  Unfiltered images can go deep.  It's not a wonder
   if people don't dare to buy an expensive filter set, and dare to reduce
   photons.

4) (This may only apply to the Japanese life style..)  Amateur observers have
   little time to spend for observation.  Returning home - rash to the
   telescope and start cooling the CCD (one may have to drive hard further
   to get a "night" or a "place" to set the telescope; there is often no
   room for backyard in Japanese houses).  How could one do with a free
   time of an hour or so..?

Regards,
Taichi Kato

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