79 research outputs found
Ejection of close-in super-Earths around low-mass stars in the giant impact stage
Earth-sized planets were observed in close-in orbits around M dwarfs. While
more and more planets are expected to be uncovered around M dwarfs, theories of
their formation and dynamical evolution are still in their infancy. We
investigate the giant impact growth of protoplanets, which includes strong
scattering around low-mass stars. The aim is to clarify whether strong
scattering around low-mass stars affects the orbital and mass distributions of
the planets. We perform -body simulation of protoplanets by systematically
surveying the parameter space of the stellar mass and surface density of
protoplanets. We find that protoplanets are often ejected after twice or three
times close-scattering around late M dwarfs. The ejection sets the upper limit
of the largest planet mass. Adopting the surface density scaling linearly with
the stellar mass, we find that as the stellar mass decreases less massive
planets are formed in orbits with higher eccentricities and inclinations. Under
this scaling, we also find that a few close-in protoplanets are generally
ejected. The ejection of protoplanets plays an important role in the mass
distribution of super-Earths around late M dwarfs. The mass relation of
observed close-in super-Earths and their central star mass is well reproduced
by ejection.Comment: accepted for publication in A&
Detection of planet candidates around K giants, HD 40956, HD 111591, and HD 113996
Aims. The purpose of this paper is to detect and investigate the nature of
long-term radial velocity (RV) variations of K-type giants and to confirm
planetary companions around the stars.
Methods. We have conducted two planet search programs by precise RV
measurement using the 1.8 m telescope at Bohyunsan Optical Astronomy
Observatory (BOAO) and the 1.88 m telescope at Okayama Astrophysical
Observatory (OAO). The BOAO program searches for planets around 55 early K
giants. The OAO program is looking for 190 G-K type giants.
Results. In this paper, we report the detection of long-period RV variations
of three K giant stars, HD 40956, HD 111591, and HD 113996. We investigated the
cause of the observed RV variations and conclude the substellar companions are
most likely the cause of the RV variations. The orbital analyses yield P =
578.6 3.3 d, sin = 2.7 0.6 , = 1.4
0.1 AU for HD 40956; P = 1056.4 14.3 d, sin = 4.4 0.4
, = 2.5 0.1 AU for HD 111591; P = 610.2 3.8 d,
sin = 6.3 1.0 , = 1.6 0.1 AU for HD 113996.Comment: 10 pages, 12 figures. Accepted for publication in Astronomy &
Astrophysic
Substellar Companions to Seven Evolved Intermediate-Mass Stars
We report the detections of substellar companions orbiting around seven
evolved intermediate-mass stars from precise Doppler measurements at Okayama
Astrophysical Observatory. o UMa (G4 II-III) is a giant with a mass of 3.1
M_sun and hosts a planet with minimum mass of m_2sini=4.1 M_J in an orbit with
a period P=1630 d and an eccentricity e=0.13. This is the first planet
candidate (< 13 M_J) ever discovered around stars more massive than 3 M_sun. o
CrB (K0 III) is a 2.1 M_sun giant and has a planet of m_2sini=1.5 M_J in a
187.8 d orbit with e=0.19. This is one of the least massive planets ever
discovered around ~2 M_sun stars. HD 5608 (K0 IV) is an 1.6 M_sun subgiant
hosting a planet of m_2sini=1.4 M_J in a 793 d orbit with e=0.19. The star also
exhibits a linear velocity trend suggesting the existence of an outer, more
massive companion. 75 Cet (G3 III:) is a 2.5 M_sun giant hosting a planet of
m_2sini=3.0 M_J in a 692 d orbit with e=0.12. The star also shows possible
additional periodicity of about 200 d and 1880 d with velocity amplitude of
~7--10 m/s, although these are not significant at this stage. nu Oph (K0 III)
is a 3.0 M_sun giant and has two brown-dwarf companions of m_2sini= 24 M_J and
27 M_J, in orbits with P=530.3 d and 3190 d, and e=0.126 and 0.17,
respectively, which were independently announced by Quirrenbach et al. (2011).
The ratio of the periods is close to 1:6, suggesting that the companions are in
mean motion resonance. We also independently confirmed planets around k CrB (K0
III-IV) and HD 210702 (K1 IV), which had been announced by Johnson et al.
(2008) and Johnson et al. (2007a), respectively. All of the orbital parameters
we obtained are consistent with the previous results.Comment: 21 pages, 14 figures, accepted for publication in PAS
A Double Planetary System around the Evolved Intermediate-Mass Star HD 4732
We report the detection of a double planetary system orbiting around the
evolved intermediate-mass star HD 4732 from precise Doppler measurements at
Okayama Astrophysical Observatory (OAO) and Anglo-Australian Observatory (AAO).
The star is a K0 subgiant with a mass of 1.7 M_sun and solar metallicity. The
planetary system is composed of two giant planets with minimum mass of
msini=2.4 M_J, orbital period of 360.2 d and 2732 d, and eccentricity of 0.13
and 0.23, respectively. Based on dynamical stability analysis for the system,
we set the upper limit on the mass of the planets to be about 28 M_J (i>5 deg)
in the case of coplanar prograde configuration.Comment: 12 pages, 7 figures, accepted for publication in Ap
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