Talk:R Doradus

One solar mass?!?

The article says this star has a mass approximately equal to that of the sun. I don't believe this -- after all, it's a giant star, while our sun isn't. RobertAustin 15:55, 7 January 2007 (UTC)

Nevermind. Some additional research convinced me that the article is, in fact, correct. RobertAustin 16:13, 7 January 2007 (UTC)

But some explanation might be in order. I won't put it in the article because I'm relying on my own general knowledge rather than sources I can cite. The article says it's a red giant. That means it's in its death throes. The thermonuclear reactions change because the composition has changed. The new reactions are faster and hotter, and the outer parts of the star swell tremendously. Note this irony. The surface temperature will be a lot cooler; a red star is significantly cooler than a yellow one. The total energy output will be several zeroes greater. But it will be distributed over a hugely greater surface area. The sun will reach that stage--I believe it's projected in about 10 billion years. I've heard variously that Mercury and maybe Venus will be swallowed up and the oceans and atmosphere on Earth will be boiled away, or that Earth would be swallowed up, too. 140.147.160.78 19:44, 16 January 2007 (UTC)Stephen Kosciesza

The figures don't seem to add up. The anomaly I've put in because there is such a huge discrepancy when you do the maths yourself. If the star was 6500 times more (visually) luminous than the Sun in to the at only 200 light years away, it would be the second brightest star in the sky. It isn't. If this is to do with infrared, I still would like to know more and why it is not emitting as a typical blackbody. Also the idea of a 1 solar mass star blowing up to 370x is vastly greater to what is predicted for the Sun at 1 solar mass. Another discrepancy. Personally, I would like to see another angular measure to confirm or refute the ESO/Bedding et al findings.Jonolewis (talk) 17:24, 29 August 2009 (UTC)jonolewis

Keep in mind that R Dor is a Mira variable, which means an asymptotic giant branch star rather than a red giant branch one. It's ~1.1 Solar masses now - post-main sequence stars tend to undergo quite a bit of mass loss on the RGB and AGB. It's predicted that the Sun will only be somewhere in the 0.52-0.6 Solar mass range by the time of its AGB ascent, so R Dor being this big now actually isn't surprising. As for the brightness discrepancy, it's not unusual for Miras to experience large amounts of extinction in visible light due to circumstellar gas and dust.203.57.211.237 (talk) 14:06, 17 November 2016 (UTC)

The diameter of R Doradus in kilometers

Note how the press release of Note 1 contain inconsistent data for the diameter: "The measured size implies that it has a physical diameter of 370 +- 50 times that of the Sun, or well over 250 million km!". The diameter of the sun is 1.392 million km. 370 times that is 515 million kilometers, not "well over 250 million km" (ok, very well over). The source of the press release can be found at [1] and gives the size only as 370 +- 50 times that of the Sun. Shirifan 22:40, 27 March 2007 (UTC)

It's just confusing radius and diameter. Half of 515 million is 257.5 million. That's 370 Suns either way. Sagittarian Milky Way 09:52, 5 April 2007 (UTC)

Assessment comment

The comment(s) below were originally left at Talk:R Doradus/Comments, and are posted here for posterity. Following several discussions in past years, these subpages are now deprecated. The comments may be irrelevant or outdated; if so, please feel free to remove this section.

As of 5/27/08, the article says that R Doradus has MV (absolute visual magnitude) of 6.97. This cannot be right. It's a fairly large Mira red giant, and must be around MV 0, with the bolometric magnitude maybe -1 or -2. ````

Last edited at 03:40, 28 May 2008 (UTC). Substituted at 03:43, 30 April 2016 (UTC)