Kap CrB : Planet(s?) and resolved disk around a subgiant star

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Kap CrB : Planet(s?) and resolved disk around a subgiant star

Post by Sirius_Alpha on 28th February 2013, 10:20 pm

In 2007, Kappa Coronae Borealis was announced to have a planetary companion.
http://arxiv.org/abs/0711.4367

Now there's evidence for a second planet and a resolved disk.

Spatially Resolved Images of Dust Belt(s) Around the Planet-hosting Subgiant Kappa CrB
http://arxiv.org/abs/1302.7000

We present Herschel spatially resolved images of the debris disc orbiting the subgiant Kappa CrB. Not only are these the first resolved images of a debris disc orbiting a subgiant, but Kappa CrB is a rare example of an intermediate mass star where a detailed study of the structure of the planetary system can be made, including both planets and planetesimal belt(s). The only way to discover planets around such stars is to observe 'retired' A stars, which are cooler and slower rotators compared to their main-sequence counterparts. A planetary companion has already been detected orbiting the subgiant Kappa CrB, with revised parameters of m sin i = 2.1MJ and apl = 2.8AU (Johnson et al. 2008a). We present additional Keck I HIRES radial velocity measurements that provide evidence for a second planetary companion, alongside Keck II AO imaging that places an upper limit on the mass of this companion. Modelling of our Herschel images shows that the dust is broadly distributed, but cannot distinguish between a single wide belt (from 20 to 220AU) or two narrow dust belts (at around 40 and 165AU). Given the existence of a second planetary companion beyond approximately 3AU it is possible that the absence of dust within approximately 20AU is caused by dynamical depletion, although the observations are not inconsistent with depletion of these regions by collisional erosion, which occurs at higher rates closer to the star.


Last edited by Sirius_Alpha on 9th April 2013, 10:30 am; edited 1 time in total

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Re: Kap CrB : Planet(s?) and resolved disk around a subgiant star

Post by Shellface on 28th February 2013, 11:00 pm

hmmm…

Well… the debris disk occurence around A-type stars is on the order of 1/5, if I recall correctly - much larger than the 1/20 or so of solar-type stars. And if those disks can stick around until the star hops up to the horizontal branch…

As for the velocity trend? Doesn't seem to be there considering the 2007 Lick data and 2012 OAO data. could really do with the updated datasets, but considering that the OAO data goes back an orbit further than the Lick data, the non-detection of the trend may be an indication of non-linearity…

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Re: Kap CrB : Planet(s?) and resolved disk around a subgiant star

Post by Sirius_Alpha on 9th April 2013, 10:30 am

Press release.
https://www.ras.org.uk/news-and-press/224-news-2013/2241-retired-star-found-with-planets-and-debris-disc

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Re: Kap CrB : Planet(s?) and resolved disk around a subgiant star

Post by Sirius_Alpha on 19th June 2013, 10:31 pm

NPOI Observations of the Exoplanet Host kappa Coronae Borealis and Their Implications for the Star's and Planet's Masses and Ages
http://arxiv.org/abs/1306.4322

We used the Navy Precision Optical Interferometer to measure the limb-darkened angular diameter of the exoplanet host star kappa CrB and obtained a value of 1.543 +/- 0.009 mas. We calculated its physical radius (5.06 +/- 0.04 R_Sun) and used photometric measurements from the literature with our diameter to determine kappa CrB's effective temperature (4788 +/- 17 K) and luminosity (12.13 +/- 0.09 L_Sun). We then placed the star on an H-R diagram to ascertain the star's age (3.42 +0.32/-0.25 Gyr) and mass (1.47 +/- 0.04 M_Sun) using a metallicity of [Fe/H] = +0.15. With this mass, we calculated the system's mass function with the orbital elements from a variety of sources, which produced a range of planetary masses: m_p sin i = 1.61 to 1.88 M_Jup. We also updated the extent of the habitable zone for the system using our new temperature.

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