[vsnet-chat 1804] Yellow Alert from Eta Carinae

[Bish Ishibashi <bish@astro.spa.umn.edu>]

This is not so much for an alert-type letter, so allow me to post
it here as a vschat material. 

As we noted in IAUC 7146, Eta Carinae has been increasing its 
brightness at a unusual rate in the optical wavebands. 
In a past few years, as reported by van Genderen et al.
(Astr. Astrophysics, 343, 847, 1999), the rate of increase 
in the Johnson V magnitude is about -0.05 to 0.1 mag per 
year; photometry done at CTIO and SAAO on 17 Apr 1999
by several groups (Humphreys at UMN, Hamuy at UA, Berdnikov
and Whitelock at SAAO, and Metcalfe UT Austin) shows the larger  
increase and gives an estimated V magnitude of 5.25, indicating
nearly the rate of change of a -0.3 mag per year since the end of
1997. This is by far the largest, and the most rapid brightening
of Eta Car in the recent history of this star. As Kris Davidson
likes to describe it, "the last time it was this bright, Jubal Early's
confederate army was raiding not far from the present site of Goddard
Space Flight Center, Maryland..." 

(Also many thanks to Danie Overbeek at SA for checking up the star
for us in a short notice!)

I understand, from Frasier's comment for a long ago, that Eta Carinae 
is a difficult star to observe for novice amateurs because of many 
reasons (1., the "homunculus" nebula is bright, and 2., the spectrum 
is strongly contaminated by EMISSION lines and appear reddish due to 
a strong H-Alpha emission line formed in the wind, perhaps, and etc). 
But, we still like to encourage any amateurs or professionals to 
"keep an eye on" Eta Carinae as much as prudent. Even though this is
not a SUDDEN event like supernovae or novae or the rate of increase
is not terribly alarming, something *unusual* apparently is happening
to the star once again. And, the more we have people looking at the star, 
the less we are likely to miss something more dramatic...

Anyhow, I hope this letter encourages many observers to take a 
quick look on this star. In a meantime, X-ray monitoring of Eta Carinae, 
with M. F. Corcoran as a P.I., will continue to observe this star
in hard X-ray radiation throughout 1999, and hopefully a year after that. 
Any coordinated observations are encouraged (please contact me for 
more details). 

Cheers, 

Bish Ishibashi
University of Minnesota 

PS. I am actually an X-ray astronomer -- so pardon me if I didn't  
    get/write the details correctly. I am not used to talking UVBRI
    -- I understand "eV" better...

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