[vsnet-chat 2952] (fwd) [vsnet-survey 19] Re: Coords and IDs for ASAS variables

[Daisaku Nogami <nogami@satsuki.kusastro.kyoto-u.ac.jp>]

 Date: Sun, 21 May 2000 19:09:07 -0400 (EDT)
 From: bp@astro.Princeton.EDU
 Subject: [vsnet-survey 19] Re: Coords and IDs for ASAS variables

Dear Brian,

Thank you very much for your very important e-mail.  I was not aware that 
HV stars were not included in the GCVS, as I suppose Pojmanski would have
identified them.

I wonder what could be done in future in order to streamline the whole
process of discovery, cross identification, verification, archiving etc.
There are going to be more projects like ROTSE and ASAS aimed at mass
discovery of variables, or just monitoring the sky.  I keep discovering
new individuals or groups who have such (or related) goals. I have close
knowledge of only two projects: OGLE and ASAS, but I guess things may be
similar with the others.  OGLE is a small team (6 or 7 people), ASAS is
just a single person.  There is no way they can do everything.  I think
it is reasonable to have a division of labor, which works so well in
the non-astronomical world.  Note that the number of recognized variables
is likely to exceed 10^5 by the end of this year, and 10^6 in 2-3 years.
At least half of these will be found with instruments with a short focal
length.  It will not be practical to inspect every single star by hand.
I think it would be useful to develop some system to deal with all this.
The following is my personal, rather amateur suggestion.  I just do not
know what is already available.

I supose the search projects should make public domain the data.  It is 
not practical to put on line all the CCD pixel data, but it would be 
useful to present either a best image of each field, or better yet a
composite image made by co-adding a number of exposures to get high S/N.
This is being now done by the OGLE, to be made public domain later this
year.  The positions and magnitudes for all non variable stars in one
of the standard bands are useful too, as obtained with whatever photometric
package used by the project.  This has been done by the ASAS.  Finally,
the time series of photometric measurements of all variable objects found.
This has also been done by the ASAS.  There will always be some spurious 
variables and some real variables will be missed.  However, as the 
monitoring projects expand and continue their data acquisition activity,
and once there is redundancy between separate projects it will be much 
easier to verify variability.

I suppose it would be best if the cross identification was done by somebody
unrelated to a particular search project.  As your e-mail indicates you
have done a better job at cross identification than Pojmanski did.  Yet,
what Pojmanski did in this respect was time consuming for him, and cut
into his time in developing new instruments.  I think that in an ideal
world it would be the best to have different people specialize in different
tasks, as this is so much more efficient than trying to do everything by
oneself.

I wonder if there is a single truly general catalog of variable object:
stars, AGNs, etc.  Object identified mostly by their position and possibly
their magnitude.  There will always be some confusion.  While imaging
Baade's Window with a good ground based seeing below 1" the limit of the
DC photometry is set not by the photon statistics but crowding.  Using
image subtraction to detect AC signal the variable stars can be found e.g.
(microlensed stars) for which it is not clear at all what is the DC
source.  With the detection rate of microlensing events likely to go into
hundreds per year soon it is not realistic to follow up all of them with
the HST.  And there will be 10^5 - 10^6 variable stars of zillions of
types discovered soon in the crowded reagions of the Milky Way.  So,
untill we get all sky covered with better than HST resolution there will
be a problem of zillions of variables identified and even classified, but
without clear evidence what their DC brightness might be, as the images
will be strongly blended at the resolution limited by the atmospheric
seeing.

In any case I wonder: is there a truly general catalog of variable stars
which includes all variables that are known, with some flag indicating the
reliability of the particular object?  And is there a place where one
could find all reported photometric measurements to any of these stars?
My guess is that such a thing does not exist, though it may be available
in some scattered form.  Or I may be simply ignorant about the current
ststus of archiving variable objects data.  I would be nice to have an
easy way to find out what is already avaliable, and what has to be done.
At this time I am trying to help (at least to some extent) projects like
ASAS and OGLE, and I would like to streamline their process of discovering
variable objects and making results public domain.  It is obvious that
there is a need to classify all those variables, to properly archive the
results, to make the access user friendly.  I would be more than happy to
help those who would like to get all those steps done well.  There is
plenty of discussion about various virtual observatories, i.e. various
data archives.  I think a complete, user friendly archive of photometric
data for variable objects would be a wonderful example of a virtual
observatory.

Bohdan

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