151 research outputs found
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
Substellar Companions to Evolved Intermediate-Mass Stars: HD 145457 and HD 180314
We report the detections of two substellar companions orbiting around evolved
intermediate-mass stars from precise Doppler measurements at Subaru Telescope
and Okayama Astrophysical Observatory. HD 145457 is a K0 giant with a mass of
1.9 M_sun and has a planet of minimum mass m_2sini=2.9 M_J orbiting with period
of P=176 d and eccentricity of e=0.11. HD 180314 is also a K0 giant with 2.6
M_sun and hosts a substellar companion of m_2sin i=22 M_J, which falls in
brown-dwarf mass regime, in an orbit with P=396 d and e=0.26. HD 145457 b is
one of the innermost planets and HD 180314 b is the seventh candidate of
brown-dwarf-mass companion found around intermediate-mass evolved stars.Comment: 16 pages, 4 figures, accepted for publication in PAS
Planetary Companions to Evolved Intermediate-Mass Stars: 14 Andromedae, 81 Ceti, 6 Lyncis, and HD 167042
We report on the detection of four extrasolar planets orbiting evolved
intermediate-mass stars from a precise Doppler survey of G and K giants at
Okayama Astrophysical Observatory. All of the host stars are considered to be
formerly early F-type or A-type dwarfs when they were on the main sequence. 14
And (K0 III) is a clump giant with a mass of 2.2 M_solar and has a planet of
minimum mass m_2sin i=4.8 M_Jup in a nearly circular orbit with a 186 day
period. This is one of the innermost planets around evolved intermediate-mass
stars and such planets have only been discovered in clump giants. 81 Cet (G5
III) is a clump giant with 2.4 M_solar hosting a planet of m_2sin i=5.3 M_Jup
in a 953 day orbit with an eccentricity of e=0.21. 6 Lyn (K0 IV) is a less
evolved subgiant with 1.7 M_solar and has a planet of m_2sin i=2.4 M_Jup in a
899 day orbit with e=0.13. HD 167042 (K1 IV) is also a less evolved star with
1.5 M_solar hosting a planet of m_2sin i=1.6 M_Jup in a 418 day orbit with
e=0.10. This planet was independently announced by Johnson et al. (2008, ApJ,
675, 784). All of the host stars have solar or sub-solar metallicity, which
supports the lack of metal-rich tendency in planet-harboring giants in contrast
to the case of dwarfs.Comment: 23 pages, 6 figures, accepted for publication in PAS
A Substellar Companion to the Intermediate-Mass Giant 11 Com
We report the detection of a substellar companion orbiting the
intermediate-mass giant star 11 Com (G8 III). Precise Doppler measurements of
the star from Xinglong station and Okayama Astrophysical Observatory (OAO)
revealed Keplerian velocity variations with an orbital period of 326.03 +/-
0.32 days, a semiamplitude of 302.8 +/- 2.6 m/s, and an eccentricity of 0.231
+/- 0.005. Adopting a stellar mass of 2.7 +/- 0.3 M_solar, the minimum mass of
the companion is 19.4 +/- 1.5 M_Jup, well above the deuterium burning limit,
and the semimajor axis is 1.29 +/- 0.05 AU. This is the first result from the
joint planet search program between China and Japan aiming at revealing
statistics of substellar companions around intermediate-mass giants. 11 Com b
emerged from 300 targets of the planet search program at OAO. The current
detection rate of a brown dwarf candidate seems to be comparable to that around
solar-type stars within orbital separations of 3 AU.Comment: 19 pages, 4 figures, accepted by Ap
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