Kepler-70

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Star
Kepler-70
AladinLite
Observation
dates equinox :  J2000.0 , epoch : J2000.0
Constellation swan
Right ascension 19 h 45 m 25.48 s
declination + 41 ° 05 ′ 33.9 ″
Apparent brightness 14.87 ± 0.02 mag
Typing
Known exoplanets 2
B − V color index −0.16 
U − B color index −0.91 
R − I index −0.29 
Spectral class sdB
Astrometry
parallax (0.78 ± 0.03)  mas
distance (4180 ± 160)  ly
(1.280)  pc
Proper movement 
Rec. Share: (7.18 ± 0.06)  mas / a
Dec. portion: (−3.13 ± 0.06)  mas / a
Physical Properties
Dimensions 0.496 ± 0.002  M ☉
radius 0.203 ± 0.007  R ☉
Luminosity

22.9 ± 3.1  L ☉

Effective temperature 27730 ± 270  K
Other names
and catalog entries
2MASS catalog 2MASS 2MASS J19452546 + 4105339 [1]
Other names KIC 5807616 • KPD 1943 + 4058 • CMC1 J194525.4 + 410533 • USNO-B1.0 1310-00349976 • KOI-55

Kepler-70 (also KIC 05807616 , KPD 1943 + 4058 , KOI-55 ) is a star in the constellation Swan with an apparent visual magnitude of 14.9 mag at a distance of around 4000  light years . It is a hot B-subdwarf that ended its phase as a red giant around 18 million years ago. The star is orbited by at least two exoplanets .

Planetary system

In 2011 two planets were discovered in a very close orbit around the star. The two planets Kepler-70 b and Kepler-70 c have masses of presumably less than one Earth mass and orbit it in only 5.76 and 8.23 ​​hours at a (projected) distance of 0.0060 and 0.0076  AU . The planets were indirectly detected in data from the Kepler Space Telescope through fluctuations in the star's pulsation period, with the changes in brightness of less than 0.01% being caused by starlight reflected from the planets.

The two planets are remarkable in that they should not have actually survived the star's red giant phase. Popular models suggest that planets orbiting their star in less than about 1 AU will be swallowed up by it when it inflates into a red giant.

According to the discoverers, Kepler-70 b and Kepler-70 c were gas giants like Jupiter that originally orbited their star on orbits further out. As the star swelled into a red giant, they were swallowed up by its shell. This slowed them down and continued to pull them inwards until they finally lost their gas envelopes. What remained are the small stone cores observed. This scenario is confirmed by model calculations, according to which the predecessors of the planets now observed must have had masses of about one Jupiter's mass.

It is possible that the development of the star was also influenced by the process. Hot sub-dwarfs are stars that burn helium in their core and only have a very thin shell of hydrogen . Normally, helium is fused by red giants surrounded by a massive hydrogen shell. Hot sub-dwarfs would then be the cores of red giants that have lost their shell. This occurs in closely interacting binary star systems , in which the companion transfers orbital angular momentum to the shell of the red giant, which is thereby accelerated and can be detached. However, many hot sub-dwarfs, including Kepler-70, are single stars. In this case, instead of a stellar companion, the planets could have caused the shell to detach.

It cannot be ruled out that the two planets are not remnants of the original system at all, but have only formed anew from the material repelled by the star afterwards. However, it is questionable whether the time of 18 million years would have been sufficient for this. According to another scenario, the two planets are fragments of a single, larger gas planet that was swallowed by the red giant's hull and ultimately torn apart by the star's tidal forces .

Kepler 70 planet
Planet
(order
from the star) 		Discovered Mass
( earth masses ) 		Radius
( earth radii ) 		Major semiaxis of
the railway
( AU ) 		Rotation time
( days ) 		Orbit inclination
( degree )
b 2011 0.440 0.759 0.0060 0.2401 65
c 2011 0.655 0.867 0.0076 0.34289 65

annotation

  1. ↑ In the discovery article by Charpinet et al. the two planets are referred to as KOI-55.01 and KOI-55.02 contrary to convention .

Web links

Individual evidence

  1. ↑ a b c d e f KPD 1943 + 4058. In: SIMBAD . Center de Données astronomiques de Strasbourg , accessed October 29, 2018 .
  2. ↑ a b c d e f g S. Charpinet et al .: A compact system of small planets around a former red-giant star. Nature, 480, 496 (2011). doi: 10.1038 / nature10631
  3. ↑ K.-P. Schröder, RC Smith: Distant future of the Sun and Earth revisited. Mon. Not. R. Astron. Soc., 386, 155 (2008). doi: 10.1111 / j.1365-2966.2008.13022.x , arxiv : 0801.4031
  4. ↑ J.-C. Passy, ​​M.-M. Mac Low, O. De Marco: On the Survival of Brown Dwarfs and Planets Engulfed by Their Giant Host Star. Astrophys. J., 759, L30 (2012). doi: 10.1088 / 2041-8205 / 759/2 / L30 , arxiv : 1210.0879
  5. ↑ E. Bear, N. Soker: A Tidally Destructed Massive Planet as the Progenitor of the Two Light Planets around the sdB Star KIC 05807616. Astrophys. J., 749, L14 (2012). doi: 10.1088 / 2041-8205 / 749/1 / L14 , arxiv : 1202.1168
  6. ↑ Nasa Exoplanet Archives