What was the absolute magnitude of Eta Carinae in 1843?

[Ann]

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

[owlice]

Ann, do you already have an answer to your question?

[Chris Peterson]

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.

[Ann]

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

Ann

[Wayne]

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.