11,346 research outputs found
Improved control system power unit for large parachutes
Improved control system power unit drives the control surfaces of very large controllable parachutes. The design features subassemblies for determining control surface position and cable loading, and protection of the load sensor against the possibility of damage during manipulation
Winch having cable position and load indicators Patent
Design and characteristics of device for showing amount of cable payed out from winch and load impose
The Most Detailed Picture Yet of an Embedded High-mass YSO
High-mass star formation is not well understood chiefly because examples are
deeply embedded, relatively distant, and crowded with sources of emission.
Using VLA and VLBA observations of water and SiO maser emission, we have mapped
in detail the structure and proper motion of material 20-500 AU from the
closest high-mass YSO, radio source-I in the Orion KL region. We observe
streams of material driven in a rotating, wide angle, bipolar wind from the
surface of an edge-on accretion disk. The example of source-I provides strong
evidence that high-mass star formation proceeds via accretionComment: typo corrected and word added to abstract 6 pages including 4 B&W
figures. To appear in the Proceeding of IAU Symposium 221, Star Formation at
High Angular Resolution, Editors M. Burton, R. Jayawardhana & T. Bourke,
Astronomical Society of the Pacifi
Large-Scale Asymmetries in the Transitional Disks of SAO 206462 and SR 21
We present Atacama Large Millimeter/submillimeter Array (ALMA) observations
in the dust continuum (690 GHz, 0.45 mm) and 12CO J=6-5 spectral line emission,
of the transitional disks surrounding the stars SAO 206462 and SR 21. These
ALMA observations resolve the dust-depleted disk cavities and extended gaseous
disks, revealing large-scale asymmetries in the dust emission of both disks. We
modeled these disks structures with a ring and an azimuthal gaussian, where the
azimuthal gaussian is motivated by the steady-state vortex solution from Lyra &
Lin (2013). Compared to recent observations of HD 142527, Oph IRS 48, and LkHa
330, these are low-contrast (< 2) asymmetries. Nevertheless, a ring alone is
not a good fit, and the addition of a vortex prescription describes these data
much better. The asymmetric component encompasses 15% and 28% of the total disk
emission in SAO 206462 and SR 21 respectively, which corresponds to a lower
limit of 2 MJup of material within the asymmetry for both disks. Although the
contrast in the dust asymmetry is low, we find that the turbulent velocity
inside it must be large (~20% of the sound speed) in order to drive these
azimuthally wide and radially narrow vortex-like structures. We obtain
residuals from the ring and vortex fitting that are still significant, tracing
non-axisymmetric emission in both disks. We compared these submillimeter
observations with recently published H-band scattered light observations. For
SR 21 the scattered light emission is distributed quite differently from the
submillimeter continuum emission, while for SAO 206462 the submillimeter
residuals are suggestive of spiral-like structure similar to the near-IR
emission.Comment: ApJL, in press. 6 pages, 3 figures, 2 table
Discrete local altitude sensing device Patent
Device for use in descending spacecraft as altitude sensor for actuating deceleration retrorocket
Imaging the Ionized Disk of the High-Mass Protostar Orion-I
We have imaged the enigmatic radio source-I (Orion-I) in the Orion-KL nebula
with the VLA at 43 GHz with 34 mas angular resolution. The continuum emission
is highly elongated and is consistent with that expected from a nearly edge-on
disk. The high brightness and lack of strong molecular lines from Orion-I can
be used to argue against emission from dust. Collisional ionization and H-minus
free-free opacity, as in Mira variables, require a central star with >10^5
Lsun, which is greater than infrared observations allow. However, if
significant local heating associated with accretion occurs, lower total
luminosities are possible. Alternatively, photo-ionization from an early B-type
star and p+/e- bremsstrahlung can explain our observations, and Orion-I may be
an example of ionized accretion disk surrounding a forming massive star. Such
accretion disks may not be able to form planets efficiently.Comment: 16 pages, 1 table, 3 figure
Searching for circumplanetary disks around LkCa 15
We present Karl G. Jansky Very Large Array (VLA) observations of the 7 mm
continuum emission from the disk surrounding the young star LkCa 15. The
observations achieve an angular resolution of 70 mas and spatially resolve the
circumstellar emission on a spatial scale of 9 AU. The continuum emission
traces a dusty annulus of 45 AU in radius that is consistent with the dust
morphology observed at shorter wavelengths. The VLA observations also reveal a
compact source at the center of the disk, possibly due to thermal emission from
hot dust or ionized gas located within a few AU from the central star. No
emission is observed between the star and the dusty ring, and, in particular,
at the position of the candidate protoplanet LkCa 15 b. By comparing the
observations with theoretical models for circumplanetary disk emission, we find
that if LkCa~15~b is a massive planet (>5 M_J) accreting at a rate greater than
1.e-6 M_J yr^{-1}, then its circumplanetary disk is less massive than 0.1 M_J,
or smaller than 0.4 Hill radii. Similar constraints are derived for any
possible circumplanetary disk orbiting within 45 AU from the central star. The
mass estimate are uncertain by at least one order of magnitude due to the
uncertainties on the mass opacity. Future ALMA observations of this system
might be able to detect circumplanetary disks down to a mass of 5.e-4 M_J and
as small as 0.2 AU, providing crucial constraints on the presence of giant
planets in the act of forming around this young star.Comment: Accepted for publication on Ap
Solar system constraints on the Dvali-Gabadadze-Porrati braneworld theory of gravity
A number of proposals have been put forward to account for the observed
accelerating expansion of the Universe through modifications of gravity. One
specific scenario, Dvali-Gabadadze-Porrati (DGP) gravity, gives rise to a
potentially observable anomaly in the solar system: all planets would exhibit a
common anomalous precession, dw/dt, in excess of the prediction of General
Relativity. We have used the Planetary Ephemeris Program (PEP) along with
planetary radar and radio tracking data to set a constraint of |dw/dt| < 0.02
arcseconds per century on the presence of any such common precession. This
sensitivity falls short of that needed to detect the estimated universal
precession of |dw/dt| = 5e-4 arcseconds per century expected in the DGP
scenario. We discuss the fact that ranging data between objects that orbit in a
common plane cannot constrain the DGP scenario. It is only through the relative
inclinations of the planetary orbital planes that solar system ranging data
have sensitivity to the DGP-like effect of universal precession. In addition,
we illustrate the importance of performing a numerical evaluation of the
sensitivity of the data set and model to any perturbative precession.Comment: 9 pages, 2 figures, accepted for publication in Phys. Rev.
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