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Eta Carinae brightest magnitude since 1863

Sebastian Otero's picture
Sebastian Otero
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Joined: 2010-09-19

Periastron passage of eta Car's companion is approaching and this week the system has reached V= 4.5 (on the scale that sets all historical data to the same zero point, there are different zero points according to the different sources because this star is particularly difficult to measure due to the surrounding nebula and emission lines).
Eta Carinae wasn't this bright since 1863, while fading from its huge historical outburst.
I could observe it visually last week almost 0.2 mag. brighter than a month ago (weather here has been awful).
An observation from OALP (Observatorio Astronomico de La Plata) here in Argentina from last night confirms the brightening at V= 4.45 which translates to V= 4.54 in the all-time/all-sources scale I have set.

http://etacar.fcaglp.unlp.edu.ar/plots/EtaPromVbig.png

Mideclipse should happen around August 13 and the eclipse should start by the end of July. The star usually brightens steadily before the eclipse starts but this brightening has been more rapid than in previous eclipses.

It is a good time to observe it!

Cheers,
Sebastian

So much for 5th magnitude and
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uis01
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Joined: 2010-07-25

So much for 5th magnitude and boring Sebastian. :)  Thanks for the note.

I'd add that while there is a dip in brightness around the time of what the best models predict is periasteron for this pair of stars that it isn't an eclipse per se.  Normally it is refferred to as the "spectroscopic event" or just "event."  For anyone interested in spectroscopy, the changes in even a low resolution spectrum are more dramatic than the changes in brightness.  

The event in this cycle happens close to the time of solar conjunction. :(  But it is still worth watching and easy for a visual observer to keep tabs on.  

I'll say that the time to really pay attention is when it come out from behind solar conjunction.  The most dramatic changes in brightness have normally followed the event.  Eta likes to suprprise and break patterns.  But if that pattern holds the star may end up going from a star that you have to take some time finding with the unaided eye to much brighter in the later half of this year.

Has the color changed notably?
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uis01
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Sebastian, I noticed on th light curve generator that over the past few years the mean of the visual observation of Eta have shifted relative to the reported V band measurements.  Has the color of Eta changed notably to the unaided human eye or is it still bright orangish?

 

Eta Car color and problems to estimate it
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Sebastian Otero
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Joined: 2010-09-19

Hi John,

No, the color has remained stable around B-V= 0.6 over the years (and I still see it orangish at the eyepiece). The star is still embebbed inside its nebula so real changes are hidden.
The problem is that such a star is very difficult to estimate because of different reasons:

* It is not a punctual source but a star+nebula. This makes it difficult to estimate correctly because you are comparing apples and oranges (here the "orange" would be eta Car, ha ha).
* Emission lines that affect the results depending on the detector/filter and with this I also mean each person's sensitivity. E.g. I see it ~0.15 mag. fainter than V.
* Atmospheric extinction. This star is very influenced by atmospheric extinction and I observe a seasonal variation due to this that I hace to correct on my own estimates. I don't see such a pronounced effect in other stars, maybe is due to its color and the sum of that and the other weirdities this star shows...

I also think that there is another major factor now: the star can be observed with the naked eye. However, it is in a crowded area. This means that people are switching from binoculars to naked eye and adding some field stars to the estimate in the process. This may well acount for a couple of tenths of a magnitude.
Some people will be observing it naked eye and some will be observing it with instruments.

There are too many factor affecting eta Car's results. I think it is the most interesting and also the most difficult star to observe. The key is trying to be consistent in the way you observe it in order to detect the changes that are taking place right now.

About the event, yes, the amplitude and duration of the "eclipse" (yes it is not a normal eclipse since it is not a star which is being hidden but probably opaque matter occulting the bright emisison caused by colliding winds) varies with wavelength and it is mostly an X-ray event, barely amounting to 0.1-0.15 mag. in the visual. I wish I could have X-ray eyes...
 

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