5,123 research outputs found
An evaluation of aft-end ignition for solid propellant rocket motors
Performance evaluation of solid propellant rocket motor ignition to determine igniter design and parameters to avoid overpressurizatio
Gust penetration loads and elastic vehicle response for Saturn 5 launch vehicles
Analysis of gust penetration loads and associated elastic vehicle response of Saturn 5 launch vehicles AS-505 through AS-508 penetrating sinusoidal gust
An algorithm for correcting CoRoT raw light curves
We introduce the CoRoT detrend algorithm (CDA) for detrending CoRoT stellar
light curves. The algorithm CDA has the capability to remove random jumps and
systematic trends encountered in typical CoRoT data in a fully automatic
fashion. Since enormous jumps in flux can destroy the information content of a
light curve, such an algorithm is essential. From a study of 1030 light curves
in the CoRoT IRa01 field, we developed three simple assumptions which upon CDA
is based. We describe the algorithm analytically and provide some examples of
how it works. We demonstrate the functionality of the algorithm in the cases of
CoRoT0102702789, CoRoT0102874481, CoRoT0102741994, and CoRoT0102729260. Using
CDA in the specific case of CoRoT0102729260, we detect a candidate exoplanet
around the host star of spectral type G5, which remains undetected in the raw
light curve, and estimate the planetary parameters to be Rp=6.27Re and P=1.6986
days.Comment: 8 pages, 13 figure
A Physical Limit to the Magnetic Fields of T Tauri Stars
Recent estimates of magnetic field strengths in T Tauri stars yield values
--. In this paper, I present an upper limit to the
photospheric values of by computing the equipartition values for different
surface gravities and effective temperatures. The values of derived from
the observations exceed this limit, and I examine the possible causes for this
discrepancy
- A tool for multiband light curve modeling of planetary transits and stellar spots
Several studies have shown that stellar activity features, such as occulted
and non-occulted starspots, can affect the measurement of transit parameters
biasing studies of transit timing variations and transmission spectra. We
present , which we designed to model multiband transit
light curves showing starspot anomalies, inferring both transit and spot
parameters. The code follows a pixellation approach to model the star with its
corresponding limb darkening, spots, and transiting planet on a two dimensional
Cartesian coordinate grid. We combine with an MCMC
framework to study and derive exoplanet transmission spectra, which provides
statistically robust values for the physical properties and uncertainties of a
transiting star-planet system. We validate 's performance
by analyzing eleven synthetic light curves of four different star-planet
systems and 20 transit light curves of the well-studied WASP-41b system. We
also investigate the impact of starspots on transit parameters and derive
wavelength dependent transit depth values for WASP-41b covering a range of
6200-9200 , indicating a flat transmission spectrum.Comment: 17 pages, 22 figures; accepted for publication in Astronomy &
Astrophysic
Spectropolarimetry of the Classical T Tauri Star TW Hydrae
We present high resolution (R ~ 60,000) circular spectropolarimetry of the
classical T Tauri star TW Hydrae. We analyze 12 photospheric absorption lines
and measure the net longitudinal magnetic field for 6 consecutive nights. While
no net polarization is detected the first five nights, a significant
photospheric field of Bz = 149 \pm 33 G is found on the sixth night. To rule
out spurious instrumental polarization, we apply the same analysis technique to
several non-magnetic telluric lines, detecting no significant polarization. We
further demonstrate the reality of this field detection by showing that the
splitting between right and left polarized components in these 12 photospheric
lines shows a linear trend with Lande g-factor times wavelength squared, as
predicted by the Zeeman effect. However, this longitudinal field detection is
still much lower than that which would result if a pure dipole magnetic
geometry is responsible for the mean magnetic field strength of 2.6 kG
previously reported for TW Hya. We also detect strong circular polarization in
the He I 5876 and the Ca II 8498 emission lines, indicating a strong field in
the line formation region of these features. The polarization of the Ca II line
is substantially weaker than that of the He I line, which we interpret as due
to a larger contribution to the Ca II line from chromospheric emission in which
the polarization signals cancel. However, the presence of polarization in the
Ca II line indicates that accretion shocks on Classical T Tauri stars do
produce narrow emission features in the infrared triplet lines of Calcium.Comment: One tar file. The paper has 22 pages, 5 figures. Accepted by AJ on
Sep 10, 200
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