158 research outputs found
Beryllium Abundances of Solar-Analog Stars
An extensive beryllium abundance analysis was conducted for 118 solar analogs
(along with 87 FGK standard stars) by applying the spectrum synthesis technique
to the near-UV region comprising the Be II line at 3131.066 A, in an attempt to
investigate whether Be suffers any depletion such as the case of Li showing a
large diversity. We found that, while most of these Sun-like stars are
superficially similar in terms of their A(Be) (Be abundances) around the solar
value within ~ +/- 0.2dex, 4 out of 118 samples turned out strikingly
Be-deficient (by more than ~2 dex) and these 4 stars belong to the group of
lowest v_e sin i (projected rotation velocity). Moreover, even for the other
majority showing an apparent similarity in Be, we can recognize a tendency that
A(Be) gradually increases with an increase in v_e sin i. These observational
facts suggest that any solar analog star (including the Sun) generally suffers
some kind of Be depletion during their lives, where the rotational velocity (or
the angular momentum) plays an important role in the sense that depletion tends
to be enhanced by slower rotation. Hence, our findings require that the
occasionally stated view "G-type dwarfs with T_eff ~< 6000 K are essentially
homogeneous in Be with their original composition retained" should be revised.
Also, our analysis indicates that the difference of ~0.2 dex in A(Be) between
the solar photosphere and the meteorite really exists, implying that "UV
missing opacity" is irrelevant at least for this Be II line.Comment: 18 pages, 12 figures, 3 tables and 3 electronic tables (included as
ancillary files), accepted for publication in Publ. Astron. Soc. Japan (2011,
Vol. 63, No. 4
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
High energy resolution hard X-ray and gamma-ray imagers using CdTe diode devices
We developed CdTe double-sided strip detectors (DSDs or cross strip
detectors) and evaluated their spectral and imaging performance for hard X-rays
and gamma-rays. Though the double-sided strip configuration is suitable for
imagers with a fine position resolution and a large detection area, CdTe diode
DSDs with indium (In) anodes have yet to be realized due to the difficulty
posed by the segmented In anodes. CdTe diode devices with aluminum (Al) anodes
were recently established, followed by a CdTe device in which the Al anodes
could be segmented into strips. We developed CdTe double-sided strip devices
having Pt cathode strips and Al anode strips, and assembled prototype CdTe
DSDs. These prototypes have a strip pitch of 400 micrometer. Signals from the
strips are processed with analog ASICs (application specific integrated
circuits). We have successfully performed gamma-ray imaging spectroscopy with a
position resolution of 400 micrometer. Energy resolution of 1.8 keV (FWHM: full
width at half maximum) was obtained at 59.54 keV. Moreover, the possibility of
improved spectral performance by utilizing the energy information of both side
strips was demonstrated. We designed and fabricated a new analog ASIC, VA32TA6,
for the readout of semiconductor detectors, which is also suitable for DSDs. A
new feature of the ASIC is its internal ADC function. We confirmed this
function and good noise performance that reaches an equivalent noise charge of
110 e- under the condition of 3-4 pF input capacitance.Comment: 6 pages, 10 figures, accepted for publication in IEEE Transactions on
Nuclear Scienc
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