4,290 research outputs found
Aerothermal modeling program
Some significant features of the approach adopted for the combustor aerothermal modeling program are described. The individual computerized models utilized in the aero design approach are characterized. The preliminary design module provides the overall envelope definition of the burner. The diffuser module provides the detailed contours of the diffuser and combustor cowl region, as well as the pressure loss characteristics into each of the individual flow passages into the dome and around the combustor. The flow distribution module provides the air entry quantities through each of the aperatures and the overall pressure drop. The heat transfer module provides detailed metal temperature distribution throughout the metal structure as input to stress and life analysis that are not part of the aerothermo design effort. Finally, the internal flow module, INTFLOW, is described and the approach for model evaluation using laboratory data is discussed
Focal Plane Wavefront Sensing using Residual Adaptive Optics Speckles
Optical imperfections, misalignments, aberrations, and even dust can
significantly limit sensitivity in high-contrast imaging systems such as
coronagraphs. An upstream deformable mirror (DM) in the pupil can be used to
correct or compensate for these flaws, either to enhance Strehl ratio or
suppress residual coronagraphic halo. Measurement of the phase and amplitude of
the starlight halo at the science camera is essential for determining the DM
shape that compensates for any non-common-path (NCP) wavefront errors. Using DM
displacement ripples to create a series of probe and anti-halo speckles in the
focal plane has been proposed for space-based coronagraphs and successfully
demonstrated in the lab. We present the theory and first on-sky demonstration
of a technique to measure the complex halo using the rapidly-changing residual
atmospheric speckles at the 6.5m MMT telescope using the Clio mid-IR camera.
The AO system's wavefront sensor (WFS) measurements are used to estimate the
residual wavefront, allowing us to approximately compute the rapidly-evolving
phase and amplitude of speckle halo. When combined with relatively-short,
synchronized science camera images, the complex speckle estimates can be used
to interferometrically analyze the images, leading to an estimate of the static
diffraction halo with NCP effects included. In an operational system, this
information could be collected continuously and used to iteratively correct
quasi-static NCP errors or suppress imperfect coronagraphic halos.Comment: Astrophysical Journal (accepted). 26 pages, 21 figure
Modeling giant extrasolar ring systems in eclipse and the case of J1407b: sculpting by exomoons?
The light curve of 1SWASP J140747.93-394542.6, a 16 Myr old star in the
Sco-Cen OB association, underwent a complex series of deep eclipses that lasted
56 days, centered on April 2007. This light curve is interpreted as the transit
of a giant ring system that is filling up a fraction of the Hill sphere of an
unseen secondary companion, J1407b. We fit the light curve with a model of an
azimuthally symmetric ring system, including spatial scales down to the
temporal limit set by the star's diameter and relative velocity. The best ring
model has 37 rings and extends out to a radius of 0.6 AU (90 million km), and
the rings have an estimated total mass on the order of . The ring
system has one clearly defined gap at 0.4 AU (61 million km), which we
hypothesize is being cleared out by a exosatellite orbiting
around J1407b. This eclipse and model implies that we are seeing a
circumplanetary disk undergoing a dynamic transition to an
exosatellite-sculpted ring structure and is one of the first seen outside our
Solar system.Comment: 13 pages, 6 figures, 3 tables. Accepted for publication in ApJ. Data
and computer code for model at: http://github.com/mkenworthy/exoring
Infrared Variability of the Gliese 569B System
Gliese 569B is a multiple brown dwarf system whose exact nature has been the
subject of several investigations over the past few years. Interpretation has
partially relied on infra-red photometry and spectroscopy of the resolved
components of the system. We present seeing limited Ks photometry over four
nights, searching for variability in this young low mass substellar system. Our
photometry is consistent with other reported photometry, and we report the
tentative detection of several periodic signals consistent with rotational
modulation due to spots on their surfaces. The five significant periods range
from 2.90 hours to 12.8 hours with peak to peak variabilities from 28 mmag to
62 mmag in the Ks band.
If both components are rotating with the shortest periods, then their
rotation axes are not parallel with each other, and the rotation axis of the Bb
component is not perpendicular to the Ba-Bb orbital plane. If Bb has one of the
longer rotational periods, then the Bb rotation axis is consistent with being
parallel to the orbital axis of the Ba-Bb system.Comment: 22 pages, 7 figures, accepted for publication in the Astrophysical
Journa
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