1,149 research outputs found
Modeling low order aberrations in laser guide star adaptive optics systems
When using a laser guide star (LGS) adaptive optics (AO) system, quasi-static aberrations are observed between the measured wavefronts from the LGS wavefront sensor (WFS) and the natural guide star (NGS) WFS. These LGS aberrations, which can be as much as 1200 nm RMS on the Keck II LGS AO system, arise due to the finite height and structure of the sodium layer. The LGS aberrations vary significantly between nights due to the difference in sodium structure. In this paper, we successfully model these LGS aberrations for the Keck II LGS AO system. We use this model to characterize the LGS aberrations as a function of pupil angle, elevation, sodium structure, uplink tip/tilt error, detector field of view, the number of detector pixels, and seeing. We also employ the model to estimate the LGS aberrations for the Palomar LGS AO system, the planned Keck I and the Thirty Meter Telescope (TMT) LGS AO systems. The LGS aberrations increase with increasing telescope diameter, but are reduced by central projection of the laser compared to side projection
The Mass, Orbit, and Tidal Evolution of the Quaoar-Weywot System
Here we present new adaptive optics observations of the Quaoar-Weywot system.
With these new observations we determine an improved system orbit. Due to a
0.39 day alias that exists in available observations, four possible orbital
solutions are available with periods of , , , and
days. From the possible orbital solutions, system masses of
kg are found. These observations provide an
updated density for Quaoar of 2.7-5.0{g cm^{-3}}. In all cases, Weywot's
orbit is eccentric, with possible values . We present a
reanalysis of the tidal orbital evolution of the Quoaor-Weywot system. We have
found that Weywot has probably evolved to a state of synchronous rotation, and
have likely preserved their initial inclinations over the age of the Solar
system. We find that for plausible values of the effective tidal dissipation
factor tides produce a very slow evolution of Weywot's eccentricity and
semi-major axis. Accordingly, it appears that Weywot's eccentricity likely did
not tidally evolve to its current value from an initially circular orbit.
Rather, it seems that some other mechanism has raised its eccentricity
post-formation, or Weywot formed with a non-negligible eccentricity.Comment: Accepted to Icarus, Nov. 8 201
A high-Resolution Catalog of Cometary Emission Lines
Using high-resolution spectra obtained with the Hamilton echelle spectrograph at Lick Observatory, we have constructed a catalog of emission lines observed in comets Swift-Tuttle and Brorsen-Metcalf. The spectra cover the range between 3800 Å and 9900 Å with a spectral resolution of λ/Δλ~42000. In the spectra, we catalog 2997 emission lines of which we identify 2438. We find cometary lines due to H, O, C_2, CN, NH_2, C_3, H_2O^+, CH, and CH^+. We list 559 unidentified lines compiled from the two spectra and comment on possibilities for their origins
Non-detection of the OH Meinel system in comet P/Swift-Tuttle
We report a search for emissions from the OH Meinel system in high-resolution near-infrared spectra of comet P/Swift-Tuttle. Because of the large cometary heliocentric velocity and high resolution of the spectrograph, the cometary lines should be well separated from the bright OH sky lines. Contrary to the findings of Tozzi et al. (1994) - who report seeing cometary OH at intensities comparable to the sky emissions in their low-resolution spectra - we find no OH in these spectra with an upper limit of 5% the value of the night sky lines. The non-detection of these cometary lines is consistent with theoretical calculations of expected emission strengths from prompt and fluorescent emission from cometary OH
Discovery of Temperate Latitude Clouds on Titan
Until now, all the clouds imaged in Titan's troposphere have been found at far southern latitudes (60°-90° south). The occurrence and location of these clouds is thought to be the result of convection driven by the maximum annual solar heating of Titan's surface, which occurs at summer solstice (2002 October) in this south polar region. We report the first observations of a new recurring type of tropospheric cloud feature, confined narrowly to ~40° south latitude, which cannot be explained by this simple insolation hypothesis. We propose two classes of formation scenario, one linked to surface geography and the other to seasonally evolving circulation, which will be easily distinguished with continued observations over the next few years
Quasi-static aberrations induced by laser guide stars in adaptive optics
Laser Guide Star Adaptive Optics (LGS AO) systems use the return from an artificial guide star to measure the wavefront aberrations in the direction of the science object. We observe quasi-static differences between the measured wavefront and the wavefront aberration of the science object. This paper quantifies and explains the source of the difference between the wavefronts measured using an LGS and a natural guide star at the W. M. Keck Observatory, which can be as high as 1000 nm RMS
On in situ Determination of Earth Matter Density in Neutrino Factory
We point out that an accurate in situ determination of the earth matter
density \rho is possible in neutrino factory by placing a detector at the magic
baseline, L = \sqrt{2} \pi / G_{F} N_{e} where N_{e} denotes electron number
density. The accuracy of matter density determination is excellent in a region
of relatively large theta_{13} with fractional uncertainty \delta \rho / \rho
of about 0.43%, 1.3%, and \lsim 3% at 1 sigma CL at sin^2 2theta_{13}=0.1,
10^{-2}, and 3 x 10^{-3}, respectively. At smaller theta_{13} the uncertainty
depends upon the CP phase delta, but it remains small, 3%-7% in more than 3/4
of the entire region of delta at sin^2 2theta_{13} = 10^{-4}. The results would
allow us to solve the problem of obscured CP violation due to the uncertainty
of earth matter density in a wide range of theta_{13} and delta. It may provide
a test for the geophysical model of the earth, or it may serve as a method for
stringent test of the MSW theory of neutrino propagation in matter once an
accurate geophysical estimation of the matter density is available.Comment: 21 pages, 4 figures, version to appear in PR
A Slowly Precessing Disk in the Nucleus of M31 as the Feeding Mechanism for a Central Starburst
We present a kinematic study of the nuclear stellar disk in M31 at infrared
wavelengths using high spatial resolution integral field spectroscopy. The
spatial resolution achieved, FWHM = 0."12 (0.45 pc at the distance of M31), has
only previously been equaled in spectroscopic studies by space-based long-slit
observations. Using adaptive optics-corrected integral field spectroscopy from
the OSIRIS instrument at the W. M. Keck Observatory, we map the line-of-sight
kinematics over the entire old stellar eccentric disk orbiting the supermassive
black hole (SMBH) at a distance of r<4 pc. The peak velocity dispersion is
381+/-55 km/s , offset by 0.13 +/- 0.03 from the SMBH, consistent with previous
high-resolution long-slit observations. There is a lack of near-infrared (NIR)
emission at the position of the SMBH and young nuclear cluster, suggesting a
spatial separation between the young and old stellar populations within the
nucleus. We compare the observed kinematics with dynamical models from Peiris &
Tremaine (2003). The best-fit disk orientation to the NIR flux is [,
, ] = [-33 +/- 4, 44 +/- 2, -15 +/-
15], which is tilted with respect to both the larger-scale galactic
disk and the best-fit orientation derived from optical observations. The
precession rate of the old disk is = 0.0 +/- 3.9 km/s/pc, lower than
the majority of previous observations. This slow precession rate suggests that
stellar winds from the disk will collide and shock, driving rapid gas inflows
and fueling an episodic central starburst as suggested in Chang et al. (2007).Comment: accepted by Ap
- …