Planets diving in Mira giants' photospheres

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Planets diving in Mira giants' photospheres

Post by Edasich on 6th December 2008, 10:48 am

A (relatively) old paper, from 2003, discussing about the possibility of exoplanets around Mira-type variable stars as an explanation of (part of) their variability.

Mira Variables explained by a planetary companion interaction: A means to drop the pulsation paradigm?

If you cannot download the paper, ask me. I have the fulltext.

If I've read right, assuming orbital periods equal to host star's variability period, we could have jovian planets laying between 1 and 5.2 AUs. But host stars can be >>200 Solar radii wide and thus reach orbital zones. Nevertheless this would imply a peculiar kind of orbit, where planets "dive" in stellar photospheres causing period decreases in stellar variability, I think.
Planetary atmospheres should be extremely ionized, yielding very bloated planetary radii around 2 Jupiter radii wide or even more. pale

If I'm wrong, please correct me ;p

More from Rudnitskij, G. M - Effects of a Close Low-mass Companion on the Spectrum and Light Curve of a Mira-type Star:

The case of a close binary system, containing a red giant and a compact low-mass object (`planet'), is considered. The `planet' is orbiting within the inner layers of the red-giant circumstellar envelope. Its supersonic motion engenders a conical shock wave, which ionises gas and creates a small HII region within the envelope. This hot spot, too, is moving across the red giant disc, causing appearance and disappearance of emission lines in the optical spectrum. If the optical depth of the dust in the envelope is large enough, then the short-wave radiation from the shock may be unobservable, and longer-wave optical emission lines will be the only observational manifestation of the embedded compact companion. This model is proposed as an alternative to the pulsation-driven shocks as sources of optical emissions in Miras, because recent radio continuum data (Knapp et al. 1995, Reid and Menten 1997, Chapman and Rudnitskij 1998) suggest that such shocks are probably much weaker than it was believed, and their velocities do not exceed ~15-20 km.s^{-1}. The effects of a hot spot migrating over the disc of the red giant may also explain asymmetry in brightness distributions over the discs of some Miras (Bedding et al. 1997, Lattanzi et al. 1997), peculiarities in the light curves and in the velocity structure of emission line profiles of Mira-type variables
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Re: Planets diving in Mira giants' photospheres

Post by marasama on 6th December 2008, 7:31 pm

Could/Might lead to recycled planets or recycled brown dwarfs.

The accretion of brown dwarfs and planets by giant stars - II. Solar-mass stars on the red giant branch
- RGS phase mass loss -> planet aquires materials -> recycled planet
- RGS phase mass loss -> planet aquires materials to push over ~13Mj -> recycled brown dwarf
http://adsabs.harvard.edu/abs/1999MNRAS.308..1133

RGS = Red Giant Star

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Re: Planets diving in Mira giants' photospheres

Post by Sirius_Alpha on 6th December 2008, 9:10 pm

marasama wrote:- RGS phase mass loss -> planet aquires materials to push over ~13Mj -> recycled brown dwarf

Interesting. The paper describing the planets at HW Virginis proposes that this may have occurred for the inner planet.

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