Re: Gas planet found orbiting dying red giant star closer than Earth orbits Sun

Bluuuue Rajah wrote:
The article doesn't say how far away HD 102272 is, or what is its diameter. If it's close by, an accurate measurement might be made for it's size, which can be used to calibrate the model that describes the expansion of main sequence stars into red giants.

Actually the article did mention that the star is 1200 ly's away in Leo. But it was mentioned at the very end of the article.

That the star did not envelop it's exoplanet suggests that, whatever was the mass of HD 102272 before it went giant, it did not have enough fuel to expand as large as the sun will, so it must be of a lighter spectral class than the sun. The existing model can be used to extrapolate backwards in time to a pseudo-measurement of HD 102272's mass and spectral class before it went giant, and therefore, its position on the Hertzprung-Russell Diagram.

Since the sun is a G2 star, this one must be smaller, meaning that it must be either G1, G0, K or M. I don't know the threshold for a star to become a red giant, but it almost certainly doesn't include the M class, and also maybe not the lower ranges of the K class. Of course, all this assumes that HD 102272 was a main sequence star before it became a red giant, but AFAIK, that's a reliable assumption, since becoming a red giant is a normal evolutionary process for main sequence stars.

I did a search and it's listed as a K0 star.

HD 102272 c - Wikipedia, the free encyclopedia
http://en.wikipedia.org/wiki/HD_102272_c

Also, note that the article says that the exoplanet is inside the equivalent orbit of Venus, not that of Earth, meaning that the star may have been a *lot* smaller than the sun, when it was on the main sequence.

That's quite likely.

Yousuf Khan
.

Relevant Pages