What was the absolute magnitude of Eta Carinae in 1843?

Ask questions, find resources, browse the virtual shelves.
Post Reply
User avatar
Ann
4725 Å
Posts: 13369
Joined: Sat May 29, 2010 5:33 am

What was the absolute magnitude of Eta Carinae in 1843?

Post by Ann » Tue Jan 01, 2013 6:52 pm

In 1843, Eta Carinae became the second brightest star in the sky, with an apparent magnitude of -0.8, despite being several thousand light-years away.

How bright was Eta Carinae intrinsically? To answer the question, we need to make several assumptions. Let's assume that Eta Carinae was located 8,000 light-years from the Earth. Let's assume that the light that reached the Earth from the star was completely unaffected by reddening (which is impossible, but never mind). Let's not worry about the bolometric (total) luminosity of the star in 1843, which is probably hard to estimate, since there were presumably no measurements done of the brightness of the star in different wavelengths back in 1843. Let's just assume that a magnitude of -0.8 corresponded to the "visual" magnitude of the star, whatever we mean by that.

If we make all these assumptions, how bright was Eta Carinae intrinsically (and visually) back in 1843? Let's compare it with the Sun, whose absolute magnitude in V (visual) light is +4.84.

Ann
Color Commentator

User avatar
owlice
Guardian of the Codes
Posts: 8406
Joined: Wed Aug 04, 2004 4:18 pm
Location: Washington, DC

Re: What was the absolute magnitude of Eta Carinae in 1843?

Post by owlice » Tue Jan 01, 2013 7:17 pm

Ann, do you already have an answer to your question?
A closed mouth gathers no foot.

User avatar
Chris Peterson
Abominable Snowman
Posts: 18102
Joined: Wed Jan 31, 2007 11:13 pm
Location: Guffey, Colorado, USA
Contact:

Re: What was the absolute magnitude of Eta Carinae in 1843?

Post by Chris Peterson » Tue Jan 01, 2013 7:48 pm

Ann wrote:If we make all these assumptions, how bright was Eta Carinae intrinsically (and visually) back in 1843? Let's compare it with the Sun, whose absolute magnitude in V (visual) light is +4.84.
I'd ignore the distance, and just look at absolute magnitudes.

Currently, Eta Carina's absolute magnitude is -7, which is 11.8 magnitudes brighter than the Sun, or about 50,000 times brighter. At its last major outburst, its absolute magnitude was -12.4 (5.4 magnitudes brighter than today), or some 7.5 million times brighter than the Sun. Visually it would have had the same brightness as Canopus (Alpha Carina), which would have created a striking pair; Canopus is white, while the apparent color of Eta Carina under outburst probably isn't known, although white or blue-white would seem likely.
Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
https://www.cloudbait.com

User avatar
Ann
4725 Å
Posts: 13369
Joined: Sat May 29, 2010 5:33 am

Re: What was the absolute magnitude of Eta Carinae in 1843?

Post by Ann » Wed Jan 02, 2013 4:41 am

Thanks, Chris! Yes, ignoring distances and just looking at absolute magnitudes makes very good sense.

Ann
Color Commentator

Wayne
Ensign
Posts: 77
Joined: Tue Apr 12, 2005 10:27 am
Location: UK
Contact:

Re: What was the absolute magnitude of Eta Carinae in 1843?

Post by Wayne » Sat Jan 19, 2013 7:16 pm

I actually work out a BV absolute magnitude of -16.8 for Eta Carinae's 1843 outburst. This weighs in at around ten million solar. This compares quite well with some supernovae.

Post Reply