[vsnet-chat 5001] (fwd) Re: [vsnet-obs 37562] Eta Carinae is not brighter

[Taichi Kato <tkato@kusastro.kyoto-u.ac.jp>]

From: "Stan Walker" <astroman@xtra.co.nz>
To: "Bish Ishibashi" <bish@space.mit.edu>, <varsao@fullzero.com.ar>,
        <fraser@trilobytes.com.au>, <pfwilliams@onaustralia.com.au>,
        <vsnet-chat@kusastro.kyoto-u.ac.jp>
Cc: <bish@space.mit.edu>
References: <200201080552.AAA13471@cxc.mit.edu>
Date: Thu, 10 Jan 2002 21:03:35 +1300
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Subject: [vsnet-chat 0] Re: [vsnet-obs 37562] Eta Carinae is not brighter
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Hi Bish and others,

A long time ago we began UBV measures of eta Carinae because some members of
the RASNZ VSS had reported a 'flare' of a half magnitude or so. This turned
out to be unreal - we think for the following reasons.

Now the numbers in the following might be a bit out but the result shouldn't
be too bad. If eta is at 1800 parsecs and if we're all observing the
Homunculus with a diameter of 8-10 arcseconds then the object has a radius
of maybe 8000 AU. The light travel time is roughly 64000 minutes or 45 days.
So the quasar logic applies in reverse - you shouldn't see quick
brightenings. Even if the brightness quadrupled the magnitude change would
be about 0.1 per 3 days. If eta turned into a supernova the surrounding
shell would ensure that the event was seen by us in slow motion.

Having said this, I would admit that I haven't a clue as to how to observe
this star visually and am really impressed that anyone tries. But Peter and
Sebastian seem to get results that are close to the pe values. I'm still
trying to get back my BVRI filters. Unfortunately they were being worked on
by Garry Nankivell whose tragic recent death is a sad blow to NZ's
astronomical optical developments. But we'll be in action shortly, I hope.

Regards,
Stan

----- Original Message -----
From: Bish Ishibashi <bish@space.mit.edu>
To: <varsao@fullzero.com.ar>; <fraser@trilobytes.com.au>;
<pfwilliams@onaustralia.com.au>; <vsnet-chat@kusastro.kyoto-u.ac.jp>
Cc: <bish@space.mit.edu>
Sent: Tuesday, January 08, 2002 6:52 PM
Subject: [vsnet-chat 4995] Re: [vsnet-obs 37562] Eta Carinae is not brighter


>
> Hiya all,
>
> first let me thank all of those who continuously monitor
> variable stars, not just eta Carinae. I think many of the
> professionals would agree that your efforts are priceless.
>
> Well so we are not sure whether eta Carinae has actually
> brightened up or not -- no one may not ever be able to
> confirm that definitely -- though all the recent measurements
> suggest that it seems to be at its nominal brightness.
> I wouldn't dismiss the possibility of a large amplitude
> fluctuation though for a brief period of time. In any case,
> we'll try to determine what happened here. My philosophy
> is that there is always an explanation for everything we
> see or feel. And we learn from it so that next time (or when
> eta Car actually goes off supernova) we will know exactly
> what we should do.
>
> Regardless the outcome, eta Carinae is about to face another
> predicted event phase in the year 2003.5. So it is crucial
> that we professionals have your -- every one of you -- input
> on how the star is behaving. So the hunting season is STILL
> open. And do not hesitate to contact me if you would see
> something strange or peculiar. We are [ok, at least I am] always
> here to listen to you.
>
> Good work, people!
>
> Bish Ishibashi from American Astronomical Society Meeting in D.C.
>
> --
>
> "Bish" K. Ishibashi, Ph.D.
>
> Massachusetts Institute of Technology
> Center for Space Research                 e  bish@space.mit.edu
> 77 Massachusetts Ave. NE80-6011
> Cambridge, MA 02139
>

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