784 research outputs found
Failure Mechanism of True 2D Granular Flows
Most previous experimental investigations of two-dimensional (2D) granular
column collapses have been conducted using three-dimensional (3D) granular
materials in narrow horizontal channels (i.e., quasi-2D condition). Our recent
research on 2D granular column collapses by using 2D granular materials (i.e.,
aluminum rods) has revealed results that differ markedly from those reported in
the literature. We assume a 2D column with an initial height of h0 and initial
width of d0, a defined as their ratio (a =h0/d0), a final height of h , and
maximum run-out distance of d . The experimental data suggest that for the low
a regime (a <0.65) the ratio of the final height to initial height is 1.
However, for the high a regime (a >0.65), the ratio of a to (d-d0)/d0, h0/h ,
or d/d0 is expressed by power-law relations. In particular, the following
power-function ratios (h0/h=1.42a^2/3 and d/d0=4.30a^0.72) are proposed for
every a >0.65. In contrast, the ratio (d-d0)/d0=3.25a^0.96 only holds for 0.65<
a1.5. In addition,
the influence of ground contact surfaces (hard or soft beds) on the final
run-out distance and destruction zone of the granular column under true 2D
conditions is investigated.Comment: 8 page
Direct detection of exoplanet host star companion γ Cep B and revised masses for both stars and the sub-stellar object
Context. The star γ Cep is known as a single-lined spectroscopic triple system at a distance of 13.8 pc, composed of a K1 III-IV primary star with V = 3.2 mag, a stellar-mass companion in a 66-67 year orbit (Torres 2007, ApJ, 654, 1095), and a substellar companion with M_p sin i = 1.7 M_(Jup) that is most likely a planet (Hatzes et al. 2003, ApJ, 599, 1383).
Aims. We aim to obtain a first direct detection of the stellar companion, to determine its current orbital position (for comparison with the spectroscopic and astrometric data), its infrared magnitude and, hence, mass.
Methods. We use the Adaptive Optics camera CIAO at the Japanese 8 m telescope Subaru on Mauna Kea, Hawaii, with the semi-transparent coronograph to block most of the light from the bright primary γ Cep A, and to detect at the same time the faint companion B. In addition, we also used the IR camera Ω Cass at the Calar Alto 3.5 m telescope, Spain, to image γ Cep A and B by adding up many very short integrations (without AO).
Results. γ Cep B is clearly detected on our CIAO and Ω Cass images. We use a photometric standard star to determine the magnitude of B after PSF subtraction in the Subaru image, and the magnitude difference between A and B in the Calar Alto images, and find an average value of K = 7.3 ± 0.2 mag. The separations and position angles between A and B are measured on 15 July 2006 and 11 and 12 Sept. 2006, B is slightly south of west of A.
Conclusions. By combining the radial velocity, astrometric, and imaging data, we have refined the binary orbit and determined the dynamical masses of the two stars in the γ Cep system, namely 1.40 ± 0.12 M_☉ for the primary and 0.409 ± 0.018 M_☉ for the secondary (consistent with being a M4 dwarf). We also determine the minimum mass of the sub-stellar companion to be M_p sin i = 1.60 ± 0.13 M_(Jup)
Direct detection of exoplanet host star companion gamma Cep B and revised masses for both stars and the sub-stellar object
The star gamma Cep is known as a single-lined spectroscopic triple system at a distance of 13.8 pc, composed of a K1 III-IV primary star with V = 3.2 mag, a stellar-mass companion in a 66--67 year orbit (Torres 2006), and a substellar companion with M_p sin i = 1.7 M_Jup that is most likely a planet (Hatzes et al. 2003). We aim to obtain a first direct detection of the stellar companion, to determine its current orbital position (for comparison with the spectroscopic and astrometric data), its infrared magnitude and, hence, mass. We use the Adaptive Optics camera CIAO at the Japanese 8m telescope Subaru on Mauna Kea, Hawaii, with the semi-transparent coronograph to block most of the light from the bright primary gamma Cep A, and to detect at the same time the faint companion B. In addition, we also used the IR camera Omega-Cass at the Calar Alto 3.5m telescope, Spain, to image gamma Cep A and B by adding up many very short integrations (without AO). gamma Cep B is clearly detected on our CIAO and Omega-Cass images. We use a photometric standard star to determine the magnitude of B after PSF subtraction in the Subaru image, and the magnitude difference between A and B in the Calar Alto images, and find an average value of K = 7.3 \pm 0.2 mag. The separations and position angles between A and B are measured on 15 July 2006 and 11 and 12 Sept 2006, B is slightly south of west of A. By combining the radial velocity, astrometric, and imaging data, we have refined the binary orbit and determined the dynamical masses of the two stars in the gamma Cep system, namely 1.40 \pm 0.12 M_sun for the primary and 0.409 \pm 0.018 M_sun for the secondary (consistent with being a M4 dwarf). We also determine the minimum mass of the sub-stellar companion to be M_p sin i = 1.60 \pm 0.13 M_Jup
A New Galactic Extinction Map of the Cygnus Region
We have made a Galactic extinction map of the Cygnus region with 5' spatial
resolution. The selected area is 80^\circ to 90^\circ in the Galactic longitude
and -4^\circ to 8^\circ in the Galactic latitude. The intensity at 140 \mum is
derived from the intensities at 60 and 100 \mum of the IRAS data using the
tight correlation between 60, 100, and 140 \mum found in the Galactic plane.
The dust temperature and optical depth are calculated with 5' resolution from
the 140 and 100 \mum intensity, and Av is calculated from the optical depth. In
the selected area, the mean dust temperature is 17 K, the minimum is 16 K, and
the maximum is 30 K. The mean Av is 6.5 mag, the minimum is 0.5 mag, and the
maximum is 11 mag. The dust temperature distribution shows significant spatial
variation on smaller scales down to 5'. Because the present study can trace the
5'-scale spatial variation of the extinction, it has an advantage over the
previous studies, such as the one by Schlegel, Finkbeiner, & Davis, who used
the COBE/DIRBE data to derive the dust temperature distribution with a spatial
resolution of 1^\circ. The difference of Av between our map and Schlegel et
al.'s is \pm 3 mag. A new extinction map of the entire sky can be produced by
applying the present method.Comment: 27 pages, 14 figures, accepted for publication in Ap
V1647 Orionis (IRAS 05436-0007) : A New Look at McNeil's Nebula
We present a study of the newly discovered McNeil's nebula in Orion using the
JHKs-band simultaneous observations with the near-infrared (NIR) camera SIRIUS
on the IRSF 1.4m telescope. The cometary infrared nebula is clearly seen
extending toward north and south from the NIR source (V1647 Orionis) that
illuminates McNeil's nebula. The compact nebula has an apparent diameter of
about 70 arcsec. The nebula is blue (bright in J) and has a cavity structure
with two rims extending toward north-east and north-west. The north-east rim is
brighter and sharp, while the north-west rim is diffuse. The north-east rim can
be traced out to ~ 40 arcsec from the location of the NIR source. In contrast,
no cavity structure is seen toward the south, although diffuse nebula is
extended out to ~ 20 arcsec. New NIR photometric data show a significant
variation in the magnitudes (> 0.15 mag) of the source of McNeil's nebula
within a period of one week, that is possibly under the phase of eruptive
variables like FUors or EXors.Comment: 13 pages, 5 figures in JPEG format. Accepted for the publication in
PASJ Letter
Interferometric Observations of the T Tauri Stars in the MBM 12 Cloud
We have carried out a millimeter interferometric continuum survey toward 7
YSOs in the MBM 12 cloud. Thermal emissions associated with 2 YSOs were
detected above the 3- level at 2.1 mm, and one also showed a 1.3 mm
thermal emission. Another object was marginally detected at 2.1 mm. Spectral
energy distributions of the YSOs are well fitted by a simple power-law disk
model. Masses of the circumstellar disks are estimated to be an order of 0.05
M_{\sun}. The circumstellar disks in the MBM 12 cloud have properties in
common with the disks in nearby star-forming regions, in terms of disk
parameters such as a disk mass, as well as an infrared excess.Comment: 9 pages, 3 figures, accepted by ApJ Letter
Possible Molecular Spiral Arms in the Protoplanetary Disk of AB Aur
The circumstellar dust disk of the Herbig Ae star AB Aur has been found to
exhibit complex spiral-like structures in the near-IR image obtained with the
Subaru Telescope. We present maps of the disk in both 12CO (3-2) and dust
continuum at 345 GHz with the SMA at an angular resolution of 1.0"x0.7" (144AU
x 100AU). The continuum emission traces a dust disk with a central depression
and a maximum overall dimension of 450AU (FWHM). This dust disk exhibits
several distinct peaks that appear to coincide with bright features in the
near-IR image, in particular the brightest inner spiral arm. The CO emission
traces a rotating gas disk of size 530AU x 330AU with a deprojected maximum
velocity of 2.8km/s at 450AU. In contrast to the dust disk, the gas disk
exhibits an intensity peak at the stellar position. Furthermore, the CO
emission in several velocity channels traces the innermost spiral arm seen in
the near-IR. We compare the observed spatial-kinematic structure of the CO
emission to a simple model of a disk in Keplerian rotation, and find that only
the emission tracing the main spiral arm clearly lies outside the confines of
our model. This emission has a net outward radial motion compared with the
radial velocity predicted by the model at the location of the main spiral arms.
The disk of AB Aur is therefore quite different from the Keplerian disks seen
around many Herbig Ae stars. The spiral-like structures of the disk with
non-Keplerian motions we revealed in 12CO (3-2), together with the central
depression of the dust disk, may be explained to be driven by the possible
existence of a giant planet forming in the disk.Comment: 21 pages, 6 figures. Accepted by ApJ on Mar 14, 200
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