[vsnet-chat 558] Re: Eta Carinae periodicies

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

G'day Bish (and vsnetters),

   >I just joined in this mailing list and I am not sure how this chat place
   >really works.

Welcome aboard!  "vsnet-chat" is specially reserved for complaints about
clouds... ;)

Seriously, so far this year we have discussed:

various chart problems,
variable star sequences (and their problems),
the most suitable telescope for variables observing,
the behaviours of certain objects (Eta Car, WX Hyi, BL Lac, etc),
announced interesting Web pages and computer software,
asked all sorts of questions among ourselves,
organized observing campaigns,
reported on accidental discoveries,

..and much much more.  In effect, anything related to variable stars that is
not just a list of observations or an alert notice.


   >and today I saw a Dr. Farrell's reply to his remark.

I love receiving these instant Ph.D.'s! <G>


   >Let me to clarify what Augusto Damineli really meant
   >to tell in his paper. His initial prediction is that
   >every 5.52 years "high-excitation events," i.e.,
   >any events that are associated with high-temperature
   >gas or radiation, diminishes.

Perhaps he should call these "high-excitation minima" ?  The word "event" can
imply either a brightening _or_ a fading.


   >http://vsnet1.elsevier.
   >nl/journals/newast/jnl/articles/S1384107697000080/ ) currently
   >explain the periodicity with a binary model. If Eta Carinae is
   >indeed a binary, the minimum state in high- excitation event (the
   >maximum for the H-band or optical??) may last a longer than a month.

I had a quick read of that article on-line.  Ideally Eta Car should be monitored
every night from end of 1997 November to 1998 February.  According to the
article there is a lot of spectroscopic activity, but if anything shows up in
visual mags it is likely to be subtle.  And possibly masked by the "normal"
variations.

   >There will be also an article by Kris Davidson commenting on the
   >DCL paper, which will soon appear (pending on its acception) in New
   >Astronomy as well. If you want a copy of Kris's paper, I can have
   >him send it out electronically for anyone who wants it.

Yes please!


   >How often do you do photometry on Eta Carinae?

On clear nights, when there's not much Moonlight, and when Eta Car isn't behind
the neighbour's trees  :)

   >If so, I would like to see your result and see if the optical
   >photometry is in any way correlated with our X-ray monitoring of
   >Eta Carinae (we generally monitor weekly, but in the period of 1997
   >June 20th ot July 20th, we took X-ray data daily). Could you please
   >let me know if this is possible?

You would need a more complete lightcurve.  The best man to ask is our Director
(Frank Bateson) at the VSS RASNZ - varstar@voyager.co.nz.  He has all the
observations from my group, plus those from other observers (including the many
not on Internet).


   >And I searched the log of this mailing list and found that YOU were
   >the one who sent out that alert about Eta Carinae in last December.

Yes, it seemed to be getting more restless back then....

   >If it makes you happy, we X-ray astronomers also noted that the
   >hard X-ray flux from Eta began its gradual increase at about the
   >same time. Well, coincidence? Who knows?

They may indeed be related.  I shall digress for a moment:

Eta Car is surrounded by that vast shell of dust, and X-ray irradiation of many
silicates (and sulfides) causes them to flouresce!  For example, quartz (SiO2)
with about 1% of Mn (or some other transition metal) can show some lovely
colours under an X-ray beam.  Specimens I've seen have been green, white,
yellow, orange, violet, or any multi-combination of these colours.

UV radiation has a similar effect. A 250nm UV light (at night or underground) is
an old prospector's trick for finding flourescent silicates.  Sulfide
flourescence shows up with a 320nm UV light.  Have a chat to one of your local
mineralogists about X-ray/UV flourescence.

So how does all this relate to visual observation of Eta Car?  First of all, the
visual observer doesn't see the star, but the dust shell.  And secondly, any
flourescence induced by X-rays (and UV) will contribute some broadband peaks to
the visual spectrum of the shell.  Therefore an X-ray outburst might show up
visually too....


   >So far the STScI
   >refused twice our requests for using the HST/STIS to observe Eta
   >Carinae spectroscopically, because either they don't think it's
   >important or do not believe that this event will happen.

Even if you got HST time I suspect their Press Release would ignore all the
collaborators and previous work on this topic.  For example their recent
"discovery" of Mira's companion (VZ Cet, mentioned in many observer's guides!);
and not mentioning that the Mira observation was deliberately scheduled - with
the help of the AAVSO's lightcurve - for minimum light.

Their previous Eta Car image was described as showing detail for the first
time (!) in the Homunculus.  Even my small telescope shows the general
structure, and David Malin has done some remarkable ground-based photography of
this object.

I'm beginning to wonder if the HST Press Releases are written by someone who is
genuinely unaware of related researches; or if STScI are too proud to admit
their expensive baby needs "outside help" ?


   >partly our fault because we did such a poor PR on this event, and
   >therefore not many astronomers seems to be noticed or cared about

What about another IAUC?


   >1999 may occur in the Summer of (no I meant Winter of) 2003, when
   >Eta Carinae is probably unobservable from ground.

It is an evening object in winter.  For most southern observers, it will remain
visible (weather permitting) for 3-4 hours after sunset.




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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