(cba:news) Var Cas 06, one more time - not yet a done deal!

[Joe Patterson]

Dear CBAers,

Anticipating your disappointment at seeing such a flat light curve, I 
forward to try to keep motivation high!  The only caveat is that you 
should not extend observations beyond about 1.8 airmasses - beyond 
which, differential extinction sort of kills.  (Very different from our 
usual targets, since we normally remove slow trends in searching for 
periodic effects)

We've invested a lot in GSC 3656-1399 as a comp now, so that really 
needs to be the one.  Careful about saturation...

joe





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The Astronomer's Telegram 
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Posted: Fri Nov 10 01:30:02 EST 2006 -- Mon Nov 13 01:30:00 EST 2006
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ATEL #942							     ATEL #942

Title:		VAR CAS 2006, A Nearby Microlens?
Author:	D. Spiegel et al. (Columbia U.)
Queries:	jop at astro.columbia.edu
Posted:	12 Nov 2006;  19:55  UT
Subjects:	Optical, X-ray, Microlensing Events, Transients, Variables,
		Stars

D. Spiegel, J. Patterson, E. Gotthelf, J. Sokoloski, N. Zimmerman, N.
Mirabal, Columbia U.; T. Krajci, CBA-New Mexico, R. Koff, CBA-Colorado;
P. de Ponthiere, CBA-Lesve; A. Oksanen, CBA-Finland; S. Dong, S. Gaudi,
L. Watson, Ohio State U.; R. Remillard, MIT Kavli Institute for Space 
Research.
Time-series photometry of the new transient in Cassiopeia (GSC 3656-1328,
see CBET #711) during November 1-10 with the telescopes of the Center for
Backyard Astrophysics (CBA) reveals no variability other than the timescale
of overall decay.  Snapshot BVRI magnitudes show no discernible change
in color, and continued spectral coverage is consistent with the A-star
description given by Munari et al. (CBET #718), with no emission components.
Study of the RXTE All-Sky-Monitor database shows no detections over the
10-year lifetime of RXTE, and a 5000 s observation with SWIFT on November
3 shows no 0.5-10 Kev flux to a limit of 10**-12 ergs cm-2 s-1.  These
observations are difficult to reconcile with any of the easy-to-imagine
theories for the transient's origin: a dwarf nova, an X-ray transient,
an erupting shell star.  But the properties and light curve can be 
acceptably
fit by a microlens interpretation (see also ATEL #931), despite the very
low optical depth to microlensing for such a nearby star (1 Kpc).  This
may provide an opportunity to study a nearby microlens, with observable
effects from parallax.  Continued photometric and spectroscopic observation
is vital to severely test this idea.  Archival searches of this region
during the pre-maximum phase (October 18-31) are especially critical, as
the existing data are sparse.  Since the transient appears to have reached
V=7.5, even images from very small cameras may be quite helpful.  Of
course, any evidence that GSC 3656-1328 is an intrinsic variable star is
even more crucial!

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Password Certification:  Joseph Patterson (jop at astro.columbia.edu)
http://www.astronomerstelegram.org/?read=942
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Your keywords: Radio, Millimeter, Sub-Millimeter, Far-Infra-Red, Infra-Red,
Optical, Ultra-Violet, X-ray, Gamma Ray, >GeV, Request for Observations,
A Comment, AGN, Asteroids, Binaries, Black Holes, Comets, Cosmic Rays,
Cataclysmic Variables, Globular Clusters, Gamma-Ray Bursts, Meteors, 
Microlensing
Events, Neutron Stars, Novae, Planets, Planets (minor), Pulsars, Quasars,
Soft Gamma-ray Repeaters, Solar System Objects, The Sun, Supernovae, 
Supernova
Remnants, Transients, Variables, Stars

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