63 research outputs found
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
The Infrared Imaging Spectrograph (IRIS) for TMT: optical design of IRIS imager with "Co-axis double TMA"
IRIS (InfraRed Imaging Spectrograph) is one of the first-generation
instruments for the Thirty Meter Telescope (TMT). IRIS is composed of a
combination of near-infrared (0.84--2.4 m) diffraction limited imager and
integral field spectrograph. To achieve near-diffraction limited resolutions in
the near-infrared wavelength region, IRIS uses the advanced adaptive optics
system NFIRAOS (Narrow Field Infrared Adaptive Optics System) and integrated
on-instrument wavefront sensors (OIWFS). However, IRIS itself has challenging
specifications. First, the overall system wavefront error should be less than
40 nm in Y, z, J, and H-band and 42 nm in K-band over a 34.0 34.0
arcsecond field of view. Second, the throughput of the imager components should
be more than 42 percent. To achieve the extremely low wavefront error and high
throughput, all reflective design has been newly proposed. We have adopted a
new design policy called "Co-Axis double-TMA", which cancels the asymmetric
aberrations generated by "collimator/TMA" and "camera/TMA" efficiently. The
latest imager design meets all specifications, and, in particular, the
wavefront error is less than 17.3 nm and throughput is more than 50.8 percent.
However, to meet the specification of wavefront error and throughput as built
performance, the IRIS imager requires both mirrors with low surface
irregularity after high-reflection coating in cryogenic and high-level Assembly
Integration and Verification (AIV). To deal with these technical challenges, we
have done the tolerance analysis and found that total pass rate is almost 99
percent in the case of gauss distribution and more than 90 percent in the case
of parabolic distribution using four compensators. We also have made an AIV
plan and feasibility check of the optical elements. In this paper, we will
present the details of this optical system.Comment: 18 pages, 14 figures, Proceeding 9908-386 of the SPIE Astronomical
Telescopes + Instrumentation 201
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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