42,664 research outputs found
Parametric bootstrap approximation to the distribution of EBLUP and related prediction intervals in linear mixed models
Empirical best linear unbiased prediction (EBLUP) method uses a linear mixed
model in combining information from different sources of information. This
method is particularly useful in small area problems. The variability of an
EBLUP is traditionally measured by the mean squared prediction error (MSPE),
and interval estimates are generally constructed using estimates of the MSPE.
Such methods have shortcomings like under-coverage or over-coverage, excessive
length and lack of interpretability. We propose a parametric bootstrap approach
to estimate the entire distribution of a suitably centered and scaled EBLUP.
The bootstrap histogram is highly accurate, and differs from the true EBLUP
distribution by only , where is the number of parameters
and the number of observations. This result is used to obtain highly
accurate prediction intervals. Simulation results demonstrate the superiority
of this method over existing techniques of constructing prediction intervals in
linear mixed models.Comment: Published in at http://dx.doi.org/10.1214/07-AOS512 the Annals of
Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical
Statistics (http://www.imstat.org
HD 174884: a strongly eccentric, short-period early-type binary system discovered by CoRoT
Accurate photometric CoRoT space observations of a secondary seismological
target, HD 174884, led to the discovery that this star is an astrophysically
important double-lined eclipsing spectroscopic binary in an eccentric orbit (e
of about 0.3), unusual for its short (3.65705d) orbital period. The high
eccentricity, coupled with the orientation of the binary orbit in space,
explains the very unusual observed light curve with strongly unequal primary
and secondary eclipses having the depth ratio of 1-to-100 in the CoRoT 'seismo'
passband. Without the high accuracy of the CoRoT photometry, the secondary
eclipse, 1.5 mmag deep, would have gone unnoticed. A spectroscopic follow-up
program provided 45 high dispersion spectra. The analysis of the CoRoT light
curve was performed with an adapted version of PHOEBE that supports CoRoT
passbands. The final solution was obtained by simultaneous fitting of the light
and the radial velocity curves. Individual star spectra were derived by
spectrum disentangling. The uncertainties of the fit were derived by bootstrap
resampling and the solution uniqueness was tested by heuristic scanning. The
results provide a consistent picture of the system composed of two late B
stars. The Fourier analysis of the light curve fit residuals yields two
components, with orbital frequency multiples and an amplitude of about 0.1
mmag, which are tentatively interpreted as tidally induced pulsations. An
extensive comparison with theoretical models is carried out by means of the
Levenberg-Marquardt minimization technique and the discrepancy between models
and the derived parameters is discussed. The best fitting models yield a young
system age of 125 million years which is consistent with the eccentric orbit
and synchronous component rotation at periastron.Comment: 15 pages, 12 figures. Accepted for publication by A&
Observational evidence for a metal rich atmosphere on the super-Earth GJ1214b
We report observations of two consecutive transits of the warm super-Earth
exoplanet GJ1214b at 3.6 and 4.5 microns with the Infrared Array Camera
instrument on-board the Spitzer Space Telescope. The two transit light curves
allow for the determination of the transit parameters for this system. We find
these paremeters to be consistent with the previously determined values and no
evidence for transit timing variations. The main investigation consists of
measuring the transit depths in each bandpass to constrain the planet's
transmission spectrum. Fixing the system scale and impact parameters, we
measure R_p/R_star=0.1176 (+0.0008/-0.0009) and 0.1163 (+0.0010/-0.0008) at 3.6
and 4.5 microns, respectively. Combining these data with the previously
reported MEarth Observatory measurements in the red optical yields constraints
on the GJ1214b's transmission spectrum and allows us to rule-out a cloud-free,
solar composition (i.e., hydrogen-dominated) atmosphere at 4.5 sigma
confidence. This independently confirms a recent finding that was based on a
measurement of the planet's transmission spectrum using the VLT. The Spitzer,
MEarth, and VLT observations together yield a remarkably flat transmission
spectrum over the large wavelength domain spanned by the data. Consequently,
cloud-free atmospheric models require more than 30% metals (assumed to be in
the form of H2O by volume to be consistent with all the observations.Comment: Accepted for publication in ApJL. 13 pages, 3 figures, 1 tabl
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