[vsnet-chat 551] Eta Carinae: Will it brighten-up this December?

[Fraser Farrell <fraserf@dove.net.au>]

G'day all,


Toshihito ISHIDA wrote:
  >I cannot check the recent light curve of Eta Carinae on vsnet web site,
  >because my computer network environment is poor.  I believe that this
  >star is still not experienced the next brightening from Damineli's letter.

How bright is it expected to be?  And for how long?  I have not seen Daminelli's
paper.

Eta Car has been showing small irregular fluctuations between visual magnitudes
5.4 and 5.8 (on a timescale of days) all this year.  Its behaviour last year was
similar, although it tended more to the 5.4 than the 5.8 in my opinion.

No meaningful period is apparent from my database; and a simple straight
line-of-best-fit suggests an overall slight fading (<0.1 mag) since the end of
1995.  Previous to this time, Eta Car was brightening at about 0.1-0.2 magnitude
per year, again with many small irregular variations.  I suspect some of the
variation is not from the star, but from the dust shell ("Homunculus")
surrounding it.

I would not recommend Eta Car to beginner observers.   Although the comparison
star sequence is good, the brilliant nebula NGC 3372 prevents any of these stars
being seen against a truly uniform background. This nebula is a complex and
beautiful object covering several square degrees of sky. Unfortunately (for us)
it includes all of the comparison stars now being used! Also, Eta Car (actually
its dust shell) is strongly red-orange in colour so the usual problems of
Moonlight + red stars can occur.


If Daminelli is only expecting a 0.1-0.2 mag brightening, we may not notice it
until we analyse our observations after the event.  If he is predicting a repeat
of 1843 or 1920 I shall keep my sunglasses on while observing :)

I am wondering if Daminelli's spectral variation mechanism is related to Eta
Car's recently announced X-ray variablity??


At this time of year, Eta Car is getting low in the southwest at sunset, and
spends much of the night on the southern horizon (for observers around 35
degrees south).  During September it is on the horizon almost all night; but
in early October it moves into the morning sky.  Observers in southern New
Zealand see Eta Car as an easy circumpolar object all year.


  >I'm afraid that the mechanism of the major bright-up on 1843 may not be
  >the same as that of the minor one.  However, although they might not the
  >same,  we will get information on the present status of this star.
  >And from this information, we may get a new insight to the major bright-up,
  >and we may make a prediction which star will be "the next Eta Carinae".

The prediction we are _really_ hoping to test is "when is SN Eta Car going to
happen?"  I will need to photometrically calibrate my car headlights first!



cheers,
Fraser Farrell

http://vsnet.dove.net.au/~fraserf/   email: fraserf@dove.net.au
traditional: PO Box 332, Christies Beach, SA  5165, Australia

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