1,102 research outputs found
Yields of Population III Supernovae and the Abundance Patterns of Extremely Metal-Poor Stars
The abundance patterns of extremely metal-poor (EMP) stars provide us with
important information on nucleosynthesis in supernovae (SNe) formed in a Pop
III or EMP environment, and thus on the nature of the first stars in the
Universe. We review nucleosynthesis yields of various types of those SNe,
focusing on core-collapse (black-hole-forming) SNe with various progenitor
masses, explosion energies (including Hypernovae), and asphericity. We discuss
the implications of the observed trends in the abundance ratios among iron-peak
elements, and the large C/Fe ratio observed in certain EMP stars with
particular attention to recently discovered hyper metal-poor (HMP) stars. We
show that the abundance pattern of the HMP stars with [Fe/H] < -5 and other EMP
stars are in good accord with those of black-hole-forming supernovae, but not
pair-instability supernovae. This suggests that black-hole-forming supernovae
made important contributions to the early Galactic (and cosmic) chemical
evolution. Finally we discuss the nature of First (Pop III) Stars.Comment: Published in "IAU Symp. 228: From Lithium to Uranium: Elemental
Tracers of Early Cosmic Evolution", ed. V. Hill, P. Francois, and F. Primas
(Cambridge University Press) 287-296 (2005
NH3 in the Galactic Center is formed in Cool Conditions
It is an open question why the temperature of molecular gas in the Galactic
center region is higher than that of dust. To address this problem, we made
simultaneous observations in the NH_3 (J,K) = (1,1), (2,2), and (3,3) lines of
the central molecular zone (CMZ) using the Kagoshima 6 m telescope. The
ortho-to-para ratio of NH_3 molecules in the CMZ is 1.5--3.5 at most observed
area. This ratio is higher than the statistical equilibrium value, and suggests
that the formation temperature of NH_3 is 11--20 K. This temperature is similar
to the dust temperature estimated from the submillimeter and infrared
continuum. This result suggests that the NH_3 molecules in the CMZ were
produced on dust grains with the currently observed temperature (11--20 K), and
they were released into the gas phase by supernova shocks or collisions of dust
particles. The discrepancy between warm molecular gas and cold dust can be
explained by the transient heating of the interstellar media in the CMZ
approximately 10^5 years ago when the NH_3 molecules were released from the
dust.Comment: 19 pages, 12 figures, accepted for PAS
Multi-Epoch VERA Observations of Sagittarius A*: I. Images and Structural Variability
We report the results of multi-epoch observations of Sgr A* with VLBI
Exploration of Radio Astrometry (VERA) at 43 GHz, carried out from 2004 to
2008. We detected a time variation of flux at 11 % level and intrinsic size at
19 %. In addition, comparisons with previous Very Long Baseline Array (VLBA)
results shows that Sgr A* underwent the flaring event at least longer than 10
days in May 2007. The intrinsic size of Sgr A* remained unchanged within 1
level from the size before/after the flaring event, indicating that
the brightness temperature of Sgr A* was increased. The flaring event occurred
within 31 d, which is shorter than the refractive time scale. Moreover it is
difficult to explain the increase in the spectral index at the flaring event by
the simple interstellar scattering model. Hence, the flaring event is most
likely associated with the changes in intrinsic properties of Sgr A*. We
considered the origin of the brightness temperature variation, and concluded
that the flaring event of Sgr A* could be explained by the continuous heating
of electrons, such as a standing shock in accretion flow.Comment: 13 pages, 7 figures, published in Publications of the Astronomical
Society of Japan (PASJ
VLBI Imagings of Kilo-parsec Knot in 3C 380
We investigate observational properties of a kilo-parsec scale knot in
radio-loud quasar 3C 380 by using two epoch archival data obtained by Very Long
Baseline Interferometry (VLBI) at 5 GHz on 1998 July and 2001 April. We succeed
in obtaining the highest spatial resolution image of the bright knot K1 located
at 732 milliarcseconds, or more than 20 kpc de-projected, downstream from the
nucleus three times better than previously obtained highest resolution image by
Papageorgiou et al. (2006). Our images reveal, with new clarity, "inverted
bow-shock" structure in K1 facing the nucleus and its morphology resembles a
conical shock wave. By comparing the two epoch images directly, we explore the
kinematics of K1 and obtain the upper limit of apparent velocity, 0.25 mas/yr
or 9.8 c of K1 for the first time. The upper limit of apparent velocity is
marginally smaller than superluminal motions seen in the core region. Further
new epoch VLBI observations are necessary to measure the proper motion at K1.Comment: 15 pages, 4 figures, accepted for publication in PAS
Experimental and Numerical Investigations of Annular Freejets
The structure of an axisymmetric freejet issuing from an annular orifice is described for the stagnation chamber to ambient pressure ratio of 13. The flowfield is numerically calculated. In the calculations, the physical plane is transformed to the computational one because of taking more grid points in the vicinity of the orifice. For two-dimensional calculations, the operator splitting method is used, and also the two-step Lax-Wendroff scheme is applied to each operator. To verify the computational data, laser interferometry is employed to determine the density in the freejet. The radially resolved densities are determined by means of the Abel inversion. The experimental results show a fairly good agreement with the computational results
Focus Issue on Male Infertility
Male infertility problems can occur when sperms are limited in number or function. In this paper, we describe the clinical evaluation of male infertility. A detailed history, physical examination, and basic semen analysis are required. In addition, ultrasound, karyotyping, and hormonal studies are needed to determine specific causes of infertility. In addition, the World Health Organization (WHO, 2009) has developed a manual to provide guidance in performing a comprehensive semen analysis. Among the possible reasons for male infertility, nonobstructive azoospermia is the least treatable, because few or no mature sperm may be produced. In many cases, men with nonobstructive azoospermia typically have small-volume testes and elevated FSH. Although treatment may not completely restore the quality of semen from men with subnormal fertility, in some cases a successful pregnancy can still be achieved through assisted reproductive technology
Astrometry of HO Masers in Nearby Star-Forming Regions with VERA --- IV. L1448C
We have carried out multi-epoch VLBI observations with VERA (VLBI Exploration
of Radio Astrometry) of the 22~GHz HO masers associated with a Class 0
protostar L1448C in the Perseus molecular cloud. The maser features trace the
base of collimated bipolar jet driven by one of the infrared counter parts of
L1448C named as L1448C(N) or L1448-mm A. We detected possible evidences for
apparent acceleration and precession of the jet according to the
three-dimensional velocity structure. Based on the phase-referencing VLBI
astrometry, we have successfully detected an annual parallax of the HO
maser in L1448C to be 4.310.33~milliarcseconds (mas) which corresponds to
a distance of 23218~pc from the Sun. The present result is in good
agreement with that of another HO maser source NGC~1333 SVS13A in the
Perseus molecular cloud, 235~pc. It is also consistent with the photometric
distance, 220~pc. Thus, the distance to the western part of the Perseus
molecular cloud complex would be constrained to be about 235~pc rather than the
larger value, 300~pc, previously reported.Comment: 15 pages, 5 figures, accepted for publication in PAS
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