9,221 research outputs found
JVN observations of H2O masers around the evolved star IRAS 22480+6002
We report on the H2O maser distributions around IRAS 22480+6002 (=IRC+60370)
observed with the Japanese VLBI Network (JVN) at three epochs spanning 2
months. This object was identified as a K-type supergiant in 1970s, which was
unusual as a stellar maser source. The spectrum of H2O masers consists of 5
peaks separated roughly equally by a few km/s each. The H2O masers were
spatially resolved into more than 15 features, which spread about 50 mas along
the east--west direction. However, no correlation was found between the proper
motion vectors and their spatial distributions; the velocity field of the
envelope seems random. A statistical parallax method applied to the observed
proper-motion data set gives a distance of 1.0+-0.4 kpc for this object, that
is considerably smaller than previously thought. The distance indicates that
this is an evolved star with L~5800 Lsun. This star shows radio, infrared, and
optical characteristics quite similar to those of the population II post-AGB
stars such as RV Tau variables.Comment: 7 pages, 5 figures, PASJ 60, No. 1 (2008 Feb. 25 issue) in press.
High res. figures available at ftp://ftp.nro.nao.ac.jp/nroreport/no657.pdf.g
Local Spin Susceptibility of the S=1/2 Kagome Lattice in ZnCu3(OD)6Cl2
We report single-crystal 2-D NMR investigation of the nearly ideal spin S=1/2
kagome lattice ZnCu3(OD)6Cl2. We successfully identify 2-D NMR signals
originating from the nearest-neighbors of Cu2+ defects occupying Zn sites. From
the 2-D Knight shift measurements, we demonstrate that weakly interacting Cu2+
spins at these defects cause the large Curie-Weiss enhancement toward T=0
commonly observed in the bulk susceptibility data. We estimate the intrinsic
spin susceptibility of the kagome planes by subtracting defect contributions,
and explore several scenarios.Comment: 4 figures; published in PR-B Rapid Communication
77Se NMR Investigation of the K(x)Fe(2-y)Se(2) High Tc Superconductor (Tc=33K)
We report a comprehensive 77Se NMR study of the structural, magnetic, and
superconducting properties of a single crystalline sample of the newly
discovered FeSe-based high temperature superconductor K(x)Fe(2-y)Se(2) (Tc=33K)
in a broad temperature range up to 290 K. We will compare our results with
those reported for FeSe (Tc=9K) and FeAs-based high Tc systems.Comment: Final versio
VLBI Observations of Water Masers in the Circumstellar Envelope of IRC+60169
Water masers around an AGB star, IRC+60169, were observed at four epochs
using the Japanese VLBI networks. The distribution of the maser features is
limited in a thick-shell region, which has inner and outer expansion velocities
of 7 km/s and 14 km/s at radii of 25 mas and 120 mas, respectively. The
distribution of the red-shifted features exhibits a ring-like structure, the
diameter of which is 30 mas, and corresponds to the inner radius of the maser
shell. This implies that dense gas around the star obscures red-shifted
emission. Although a position--radial velocity diagram for the maser features
is consistent with a spherical shell model, the relative proper motions do not
indicate an expansion motion of the shell. A remarkable property has been found
that is a possible periodic change of the alignment pattern of water maser
spots.Comment: 9 pages including 7 figures, to appear in PASJ, Vol. 54, No.
NMR Characterization of Sulphur Substitution Effects in the K(x)Fe(2-y)Se(2-z)S(z) high Tc Superconductor
We present an NMR study of the effect of S substitution in the high Tc
superconductor K(x)Fe(2-y)Se(2-z)S(z) in a temperature range up to 250 K. We
present NMR Knight shift and nuclear spin-lattice relaxation rate 1/T1 data,
and compare our results to that of the non-substituted system K(x)Fe(2-y)Se(2).Comment: Typos fixed, figure replace
A Measurement of Proper Motions of SiO Maser Sources in the Galactic Center with the VLBA
We report on the high-precision astrometric observations of maser sources
around the Galactic Center in the SiO J=1--0 v=1 and 2 lines with the VLBA
during 2001 -- 2004. With phase-referencing interferometry referred to the
radio continuum source Sgr A*, accurate positions of masers were obtained for
three detected objects: IRS 10 EE (7 epochs), IRS 15NE (2 epochs), and SiO 6
(only 1 epoch). Because circumstellar masers of these objects were resolved
into several components, proper motions for the maser sources were derived with
several different methods. Combining our VLBA results with those of the
previous VLA observations, we obtained the IRS 10EE proper motion of 76+-3 km
s^{-1} (at 8 kpc) to the south relative to Sgr A*. Almost null proper motion of
this star in the east--west direction results in a net transverse motion of the
infrared reference frame of about 30+-9 km s^{-1} to the west relative to Sgr
A*. The proper-motion data also suggests that IRS 10EE is an astrometric binary
with an unseen massive companion.Comment: High-res. figures are available at
ftp://ftp.nro.nao.ac.jp/nroreport/no656.pdf.gz . PASJ 60, No. 1 (2008) in
pres
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