Talk:LBV 1806-20

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[edit] Distance

It'd be interesting to see how far away from this star an earth like body would have to be to receive the same amount of light the Earth receives from the Sun. --BHC 20:00, 20 November 2006 (UTC)

To receive the same amount of light from the Sun, Earth needs to be placed a staggering 6325 AUs (0.1 light years!) away from this monster if it has a luminosity of 40 million suns, using the inverse square law. --Strangerguy 15:00, 15 April 2007 (UTC)

Neat, thanks --BHC 00:46, 27 April 2007 (UTC)

[edit] The Image

I know stars do get "bigger" as well as denser, but with all I've learned about astronomy, it seems to me that they're comparing "mass" more than size but representing it with size. I mean, if it's that big, so be it, but things supposedly get denser until they hit certain amounts of mass. For example, Jupiter would need to be 13 to 80 times more massive than it currently is in order to be a brown dwarf star, but it would (in theory) stay the same size and just get denser. Once it was big enough to be an actual star (ala the sun) it would definitely get bigger (fusion?), but then stars are known to be about ten or so solar masses and only slightly bigger than the sun. Also, some lower mass stars are many thousands of times bigger. I think one has something like 70 or 80 masses and is in the THOUSANDS of times bigger than the sun, but isn't anywhere near the most massive. If anyone could help out, it'd be much appreciated! 12.165.254.36 08:08, 21 August 2007 (UTC)

In reply to the inquiry above, the issue of size of stars is a rather complicated issue once one strays into either the territory of young stars still stabilizing their structure or old ones which are beginning to develop shell structures with different regions burning different fuels. The very fact that stars get large (form red giants) at this end stage is commonly argued with hand-waving and invocations of the Virial theorem in introductory classes -- but this simplification misses some (sometimes) critical physics. A paper circa 1985 treating the red giant issue in some detail spent dozens of pages on development of an analytical formulation to capture the essential physics. The result was to establish that it was not necessarily as simple as one would guess as to why evolved stars become red giants. In fact, stars with more primordial compositions are not always red giants/supergiants at the end of their life -- Supernova 1987A exploded as a *blue* supergiant (which is much smaller than a red supergiant). Don Barry, Cornell Astronomy.


[edit] V mag of 35

A V magnitude of 35? That's well beyond the detection limit of any current telescope - either this is a calculated value (which should be made clear), or someone is confused. The Eikenberry paper quotes AV of 35 ± 5 (which is visual extinction at V NOT the V magitude, which is itself a calculated value), SIMBAD does not know of the object and the Figer paper is silent on the matter (but does quote vLSR of 35, which is the velocity relative to the local standard of rest, again not V magnitude). Modest Genius talk 00:59, 25 September 2007 (UTC)

The V=35 number was apparently put in by someone else from an elementary calculation -- it's an inferred measure not directly mentioned in the Eikenberry et al. paper (of which I'm a co-author). That paper argues for an absolute magnitude in V of -10.6. Add to that the inferred distance modulus (15.9) and the extrapolated extinction in visual (29) and you get an apparent magnitude of 34.3. Of course, in reality this is meaningless -- that much extinction also means that scattering will destroy any morphological integrity to the field, if one even had a super-telescope outside the inner solar system where zodiacal light would swamp this miniscule intensity. Don Barry, Cornell Astronomy. —Preceding unsigned comment added by 132.236.6.98 (talk • contribs) 21:45, 29 October 2007
That's what I assumed had happened. However, I don't think we should be quoting such an unphysical back-of-the-envelope number in the article. Either we need to make it clear that it is a calculated and highly uncertain value, or quote at some other wavelength, or not quote a magnitude at all. I've commented out the relevant line, pending discussion. Edit: I also rephrased some of the text. Modest Genius talk 00:13, 31 October 2007 (UTC)
Then why not put in the apparent K magnitude? That is what was observed. Infrared colors may not be the most widely familiar measures to non-specialists, but they are the gold standard when one still wants to sample the continuum thermal emission of a heavily extincted hot object from a ground-based telescope. Don Barry. —Preceding unsigned comment added by 24.92.252.0 (talk) 12:32, 31 October 2007 (UTC)
I am the one who had put in the 35, but unfortunately I do not remember where that came from. I can't imagine that I would have done a naïve calculation though. A quick check of some obvious potential sources didn't turn up anything, so feel free to get rid of the 35 unless some justification turns up. Ardric47 (talk) 07:28, 28 November 2007 (UTC)

[edit] Limit of 120 solar masses

Do we have a citation for "Current star formation theories tell us that a star can have at most about 120 Solar masses"? --P3d0 (talk) 04:47, 2 January 2008 (UTC)

Difficult to determine precisely, but no stars are observed to have confirmed masses >~150. For references, how about the recent http://adsabs.harvard.edu/abs/2007ApJ...660.1480M (concluding a limit of between 100 and 200) or Don Figer's Nature paper http://adsabs.harvard.edu/abs/2005Natur.434..192F , which suggests 150.
However, that DOES seem misleading, since I know of no THEORETICAL limit - both of those papers infer a limit from observations, not theory. Modest Genius talk 21:20, 3 January 2008 (UTC)