Eta Carinae - Brightening??????

[Suzy]

I have rung the Sir Thomas Brisbane Planetarium and spoke with an astronomer regarding Eta Carinae brightening. He told me he will investigate it further and get back to me. Will keep you informed of the outcome.

[space oddity]

Bit early in the morning for maths, but need some extra info. Assuming Eta Carina is 7,500 LY away and earth is about 8.4 light minutes from the sun,eta carina's light is diluted 2.2 x 10 to the power 17 compared with our sun. The typical scenario is that a supernova shines as bright while it is exploding as the rest of the galaxy put together, gives 100 billion times the light of an average star 10 to the power 11 .This equates to the brightness 1/2.2 x 10 to the power 6. This is 15 orders of magnitude. Assuming the sun is an average star(this is the extra info needed- what is the percentage difference), this equates to mag 29-15 =mag- 14 at supernova, 2 mags brighter than the full moon.Depending on the amount of infra red, it could be spectacular but not blinding. Brightness will be akin to looking at the full moon through small to medium sized binoculars. I have to head off for work soon, so I will pass the batton on to the next person to fine tune the maths and iron out my assumtions.
Maybe Eta Carina will go supernova for the star party- what a" blast" that would be.

[space oddity]

Finally made it home after an unexpectedly busy day at work. The Sunday is to compensate for taking the weekend off and hopefully the Friday for the star party. Researching on the web, a supernova of eta carina if a type 1a should reach a peak magnitude of -4. Tycho's supernova of 1572 ,also at around 7,500 LY away reached a peak of -4. Looks like the early morning maths may have been up to 10 orders of magnitude off the money. Looking at the subject on the net, other calculations give -7 magnitude. Any way you look at it, it will be having us all licking our chops.

[PeterM]

Originally Posted by space oddity

Finally made it home after an unexpectedly busy day at work. The Sunday is to compensate for taking the weekend off and hopefully the Friday for the star party. Researching on the web, a supernova of eta carina if a type 1a should reach a peak magnitude of -4. Tycho's supernova of 1572 ,also at around 7,500 LY away reached a peak of -4. Looks like the early morning maths may have been up to 10 orders of magnitude off the money. Looking at the subject on the net, other calculations give -7 magnitude. Any way you look at it, it will be having us all licking our chops.

Tychos star is listed as a Type 1a event, that is the incineration of a White Dwarf exceeding 1.4 solar mass. The "new star" was recorded at the time as quite red and studies now suggest redder than normal, probably from the absorption of light by interstellar dust. Eta is estimated at 100-150 times solar mass and expected to be more likely a Hypernova, never a Type 1a - now that would be a "blast" you are right there.
How does this all affect the chalkboard?

PeterM.

[bojan]

I am still trying to find in various ANZ standards some data on safety levels for laser radiation, to be able to calculate (roughly) the effects of staring at -13m star through telescope and unaided eye.
It will happen, eventually (me finding the right standard, I mean).
But, for the star 0m the "solar constant" is 25nW/m2 (the previous result of 3.7 nW was based on Sun being -29, but is is actually -27.
10" telescope will collect 6.3nW

-13m in 10" telescope will have a power flux close to 940uW, almost 1mW !!

That is A LOT !! And definitely above safe level.

You can look at -13m star without aid, but through any telescope it can fry your retina (provided the image is focussed).

[Merlin66 (Ken)]

Isn't that about the same magnitude as a Full moon?

[bojan]

It is, but full Moon power output is spread over 0.5° diameter circle (on retina this is will be 0.05mm or so)
So power density on the retina can not exceed safe level, while star image (all that power concentrated on one small area) potentially could, because it will be concentrated on couple of cells only.
Also, I am presenting numbers for effects using 10" telescope. This will definitely be dangerous.

[Merlin66 (Ken)]

I understood the sun, moon, planets (faint galaxies)etc were integrated magnitudes?
http://en.wikipedia.org/wiki/Apparent_magnitude

[bojan]

Yes they are...

But again, it is about power density at the retina - how much power (in joules per second or W) is falling on the unit area (mm2) , and if this value is high, power can not be dissipated fast enough (factors here are thermal conductivity of the retina tissue, blood flow and so on) and the temperature in that spot goes up (until a thermal balance is achieved again).

In case of point-like source (star), all incoming light (power received by eye through the telescope) is focussed into one spot (or very small area.. better the optical system, smaller the focal point) so the power density could be very high and this could result in high temperatures (on that small area).

Sun and Moon are extended light sources, their images on the retina are relatively large and the power density (W/mm2) or illumination is much lower, so the thermal power is spread over larger area and is less dangerous (in Moon's case only of course), especially if higher magnifications are used.

All this is of course idealised case - my (rough) calculation is based on solar constant and assumption that all power is received and converted into heat, and I assumed the spectral density of eta when it blows up will be similar to Sun's light - which it won't, of course - I think the spectral peak will be in UV, so the thermal effect will be smaller (because of Earth's atmosphere).
Also, if any kind of filter is used at the telescope end, the effect will be diminished further .

[Steffen]

Originally Posted by bojan

Also, I am presenting numbers for effects using 10" telescope. This will definitely be dangerous.

If we don't close down this thread soon we'll end up having telescopes of 10" and larger banned in Australia…

Cheers
Steffen.

[bojan]

Originally Posted by Steffen

If we don't close down this thread soon we'll end up having telescopes of 10" and larger banned in Australia…

Cheers
Steffen.

You are probably right
Lets stop

[astroron (Ron)]

Originally Posted by bojan

You are probably right
Lets stop

The point of the Thread was lost in all this mathematical exercise
IS Eta Carina Brightening:que stion:

[bojan]

No. Or, not significantly I would say..
I took an image of eta in January this year.. and I checked it couple of nights ago, same area, same equipment, same exposure time.
Unfortunately, I made couple of mistakes during imaging session.. first stack was destroyed because the mount did not track.. then I repeated the photo session, but it seems I moved the focus ring, then I went in the house because the mosquitoes were quite hungry then the clouds rolled in and only then I noticed the images were badly out of focus..
But I was still able to compare the general appearance of photos between January and two days ago, and eta didn't look significantly brighter.

[Suzy]

The astronomer from the Sir Thomas Brisbane Planetarium rang me back. He said that during that period, Eta Carinae got brighter from Mag. 4.65 to 4.55. and has been steadily getting brighter. It's not significant - not quite half a mag. But he did say it could have experienced a spike. He further went on to say that if there is an occurrence it is not necessarily released to the public straight away.

[duncan]

I wonder what was meant about "what the public has been told is not all that's there" in Suzys' post.?
Cheers,
Duncan

[Suzy]

He meant that if there is an occurrence it is not necessarily released to the public straight away. I do not know the time frame when they hold and release information. Apologies for not making that clearer. I will edit, so it make more sense.

Also interesting to know that variable star observations are carried out only once a fortnight. I only just found this out.

[duncan]

Thanks for the explanation Suzy. Might be something really interesting on the horizon.
Cheers,
Duncan

[Octane (Humayun)]

I want to see this in a binoviewer hooked up to two 20" mirrors. Ooh, yes, that's the ticket.

H

[Shano592 (Shane)]

Wasn't there one of those on eBay about a year ago, H?

[RobF (Rob)]

I'm sure I've read recently about Eta brightening in recent years. Maybe it is the current S&T? Will have to check.

This is an interesting read:
http://www.astrosociety.org/pubs/mercury/9804/eta.html