[vsnet-sdor 48] (fwd) To people interested in eta Carinae

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

From: "Sebastian Otero" <varsao@fullzero.com.ar>
Date: Sat, 15 Jun 2002 02:18:24 -0300
Subject: [vsnet-chat 5353] To people interested in eta Carinae

Dear colleagues:

Eta Carinae is probably the most spectacular variable star of all.
Its mean brightness has been rising slowly since a long time.
In 1999 it brightened in a way that was unexpected for most of the people
(up to V= 5.1)
This brightening was widely commented, but it wasn't the one.
If we take the 1999 and 2000 brightenings as a whole big event, then in
August 2001 we had another maximum that was actually brighter than the
previous one.
The star probably reached 5.0.
Now eta Carinae is rising again. The recent minimum was 0.1 mag. brighter
than the last one so if the star follows the same pattern as in the 2001
brightening, we might have an interesting show by the end of August (again)
with eta Carinae being probably -and finally- brighter than 5.0.
However, DON'T TAKE this as an alert or something that is worth taking a
look tomorrow (as has happened in the past).
The brightness changes are slow, so it's only a reminder in order not to
forget that we'll have a good oportunity to understand what is happening to
the star and what the causes of these brightenings are.

I have prepared a webpage with my lightcurve of eta Carinae, including
PEP(V) mostly from Harry Williams and Stan Walker:
http://ar.geocities.com/varsao/Curva_Eta_Carinae.htm

You also might think that this yearly cycle is a result of atmospheric
extinction, but eta Car is currently overhead and no problem of that kind is
likely to exist.
Only observations will tell.
To visual observers, there are several ways to look at eta Carinae and eache
of them will give different results.
If you have a dark sky and don't use any instrument but your own eyes,
you'll see star+nebulosity+open cluster that surrounds it.
That combination gives a result ~0.2 mag. brighter than the PEP(V) values
from Auckland which I will take as the "right" ones.
Observation with low power binoculars will give a result similar to the
PEP(V) data.
And finally if we use a telescope, besides not having the advantage of the
comparison stars being placed in the same field of view, we will be
resolving part of the Homunculus and that will end up with a fainter result
for the star.

Type of vision involved also plays a role. I use direct vision for most of
my estimates and that ends up with a result that probably doesn't include
most of the Homunculus scattered light.
The PEP(V) values include a part of it and that is why they are always ~0.15
mag. brighter.

Then, it would be proper not to look at the star with the naked eye unless
it gets too bright, when contribution from the nearby stars will not be
important.

So, let's stay tuned...

Regards,
Sebastian.







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