Substellar companion around a hot subdwarf star

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Substellar companion around a hot subdwarf star

Post by Edasich on 10th August 2009, 6:03 am

Discovery of a close substellar companion to the hot subdwarf star HD 149382 - The decisive influence of substellar objects on late stellar evolution

Substellar objects, like planets and brown dwarfs orbiting stars, are by-products of the star formation process. The evolution of their host stars may have an enourmous impact on these small companions. Vice versa a planet might also influence stellar evolution as has recently been argued.Here we report the discovery of a 8-23 Jupiter-mass substellar object orbiting the hot subdwarf HD 149382 in 2.391 days at a distance of only about five solar radii. Obviously the companion must have survived engulfment in the red-giant envelope. Moreover, the substellar companion has triggered envelope ejection and enabled the sdB star to form. Hot subdwarf stars have been identified as the sources of the unexpected ultravoilet emission in elliptical galaxies, but the formation of these stars is not fully understood. Being the brightest star of its class, HD 149382 offers the best conditions to detect the substellar companion. Hence, undisclosed substellar companions offer a natural solution for the long-standing formation problem of apparently single hot subdwarf stars. Planets and brown dwarfs may therefore alter the evolution of old stellar populations and may also significantly affect the UV-emission of elliptical galaxies.

Reading the article, more likely a superplanet rather a brown dwarf.
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Re: Substellar companion around a hot subdwarf star

Post by Sirius_Alpha on 10th August 2009, 9:18 am

How does a super-Jovian or brown dwarf (or anything) survive to a 2.391-day orbit around an sdB?

Any other way planets migrate other than by disks?
Could somehow the object orbiting through the extended envelope have caused the star to quickly end its enlarge phase? The drag would have lowered the orbit of the object.

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Re: Substellar companion around a hot subdwarf star

Post by Edasich on 10th August 2009, 11:26 am

Jean Schneider worried to come back from holidays to update EPE with this detection *LOL* Laughing

http://exoplanet.eu/star.php?st=HD+149382

Mass within Superjovian regime. bounce
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Re: Substellar companion around a hot subdwarf star

Post by Lazarus on 10th August 2009, 1:09 pm

Sirius_Alpha wrote:How does a super-Jovian or brown dwarf (or anything) survive to a 2.391-day orbit around an sdB?

Any other way planets migrate other than by disks?
Could somehow the object orbiting through the extended envelope have caused the star to quickly end its enlarge phase? The drag would have lowered the orbit of the object.
Seems to be a case of engulfment in the red giant envelope. Extreme mass ratio between star and planet means mass transfer is unstable, so doesn't form an accretion disc around the planet, but a common envelope. Planet would possibly have gained mass during the inspiral. (Indeed in the paper about the HW Virginis system, it is noted that the red dwarf companion could potentially be a former brown dwarf that became a star by accreting some of the primary's envelope during the red giant stage).

Very interesting evidence that planetary systems can have significant effects on the evolution of their parent stars, and perhaps even the spectrum of entire galaxies...
HD 149382 b provides evidence that substellar companions can decisively change the evolution of stars, as they trigger extensive mass loss. They could be responsible for the formation of the single hot subdwarf population. These stars are not only numerous in our Galaxy, but also make elliptical galaxies shine in ultraviolet light.
One other thing to notice is the detection method: the other planet known around a single sdB star, V391 Peg b, was discovered by timing of pulsations, while this one was an RV detection - HD 149382 does not seem to be a pulsating sdB star.
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Re: Substellar companion around a hot subdwarf star

Post by Sirius_Alpha on 10th August 2009, 8:13 pm

I'm not 100% sure how they were able to determine the inclination of the star. I looked over the paper, but wasn't able to follow.

I was also surprised by the cleanness of the RV curve. I would've expected much more noise.

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