1,432 research outputs found
The ARAUCARIA project. Discovery of Cepheid Variables in NGC 300 from a Wide-Field Imaging Survey
Based on observations of NGC 300, obtained with the Wide-Field Camera at the
2.2 m ESO/MPI telescope during 29 nights spread over a 5.3 month interval, 117
Cepheids and 12 Cepheid candidates were found which cover the period range from
115 to 5.4 days. We present a catalog which provides equatorial coordinates,
period, time of maximum brightness, and intensity mean B and V magnitudes for
each variable, and we show phased B and V light curves for all the Cepheids
found. We also present the individual B and V observations for each Cepheid in
our catalog. We find very good agreement between our photometry and that
obtained by Freedman et al. from ground-based CCD data for common stars. The
Cepheids delineate the spiral arms of NGC 300, and a couple of them were
detected very close to the center of the galaxy. From the color-magnitude
diagram of NGC 300 constructed from our data, we expect that our Cepheid
detection is near-complete for variables with periods larger than about 10
days. We present plots of the PL relations in the B and V bands obtained from
our data, which clearly demonstrate the presence of a Malmquist bias for
periods below about 10 days. A thorough discussion of the distance to NGC 300
will be presented in a forthcoming paper which will include the analysis of
photometry in longer-wavelength bands.Comment: 26 pages, Latex. Astronomical Journal in pres
Estimating the Undercoverage of a Sampling Frame due to Reporting Delays
One of the imperfections of a sampling frame is miscoverage caused by delays in recording real- life events that change the eligibility of population units. For example, new units generally appear on the frame some time after they came into existence and units that have ceased to exist are not removed from the frame immediately. We provide methodology for predicting the undercoverage due to delays in reporting new units. The approach presented here is novel in a business survey context, and is equally applicable to overcoverage due to delays in reporting the closure of units. As a special case, we also predict the number of new-born units per month. The methodology is applied to the principal business register in the UK, maintained by the Office for National Statistics. <br/
Analysis of scanner data for crop inventories
There are no author-identified significant results in this report
Analysis of scanner data for crop inventories
There are no author-identified significant results in this report
Spatial and spectral simulation of LANDSAT images of agricultural areas
A LANDSAT scene simulation capability was developed to study the effects of small fields and misregistration on LANDSAT-based crop proportion estimation procedures. The simulation employs a pattern of ground polygons each with a crop ID, planting date, and scale factor. Historical greenness/brightness crop development profiles generate the mean signal values for each polygon. Historical within-field covariances add texture to pixels in each polygon. The planting dates and scale factors create between-field/within-crop variation. Between field and crop variation is achieved by the above and crop profile differences. The LANDSAT point spread function is used to add correlation between nearby pixels. The next effect of the point spread function is to blur the image. Mixed pixels and misregistration are also simulated
Electrically induced tunable cohesion in granular systems
Experimental observations of confined granular materials in the presence of
an electric field that induces cohesive forces are reported. The angle of
repose is found to increase with the cohesive force. A theoretical model for
the stability of a granular heap, including both the effect of the sidewalls
and cohesion is proposed. A good agreement between this model and the
experimental results is found. The steady-state flow angle is practically
unaffected by the electric field except for high field strengths and low flow
rates.Comment: accepted for publication in "Journal of Statistical Mechanics: Theory
and Experiment
A transiting planet among 23 new near-threshold candidates from the OGLE survey - OGLE-TR-182
By re-processing the data of the second season of the OGLE survey for
planetary transits and adding new mesurements on the same fields gathered in
subsequent years with the OGLE telescope, we have identified 23 new transit
candidates, recorded as OGLE-TR-178 to OGLE-TR-200. We studied the nature of
these objects with the FLAMES/UVES multi-fiber spectrograph on the VLT. One of
the candidates, OGLE-TR-182, was confirmed as a transiting gas giant planet on
a 4-day orbit. We characterised it with further observations using the FORS1
camera and UVES spectrograph on the VLT. OGLE-TR-182b is a typical ``hot
Jupiter'' with an orbital period of 3.98 days, a mass of 1.01 +- 0.15 MJup and
a radius of 1.13 (+0.24-0.08) RJup. Confirming this transiting planet required
a large investment in telescope time with the best instruments available, and
we comment on the difficulty of the confirmation process for transiting planets
in the OGLE survey. We delienate the zone were confirmation is difficult or
impossible, and discuss the implications for the Corot space mission in its
quest for transiting telluric planets.Comment: 7 pages, submitted to Astronomy and Astrophysic
A Search for Distant Galactic Cepheids Toward l=60
We present results of a survey of a 6-square-degree region near l=60, b=0 to
search for distant Milky Way Cepheids. Few MW Cepheids are known at distances
>~ R_0, limiting large-scale MW disk models derived from Cepheid kinematics;
this work was designed to find a sample of distant Cepheids for use in such
models. The survey was conducted in the V and I bands over 8 epochs, to a
limiting I~=18, with a total of ~ 5 million photometric observations of ~ 1
million stars. We present a catalog of 578 high-amplitude variables discovered
in this field. Cepheid candidates were selected from this catalog on the basis
of variability and color change, and observed again the following season. We
confirm 10 of these candidates as Cepheids with periods from 4 to 8 days, most
at distances > 3 kpc. Many of the Cepheids are heavily reddened by intervening
dust, some with implied extinction A_V > 10 mag. With a future addition of
infrared photometry and radial velocities, these stars alone can provide a
constraint on R_0 to 8%, and in conjunction with other known Cepheids should
provide good estimates of the global disk potential ellipticity.Comment: 18 pages, 4 tables, 13 figures (LaTeX / AASTeX
OGLE-TR-211 - a new transiting inflated hot Jupiter from the OGLE survey and ESO LP666 spectroscopic follow-up program
We present results of the photometric campaign for planetary and
low-luminosity object transits conducted by the OGLE survey in 2005 season
(Campaign #5). About twenty most promising candidates discovered in these data
were subsequently verified spectroscopically with the VLT/FLAMES spectrograph.
One of the candidates, OGLE-TR-211, reveals clear changes of radial velocity
with small amplitude of 82 m/sec, varying in phase with photometric transit
ephemeris. Thus, we confirm the planetary nature of the OGLE-TR-211 system.
Follow-up precise photometry of OGLE-TR-211 with VLT/FORS together with radial
velocity spectroscopy supplemented with high resolution, high S/N VLT/UVES
spectra allowed us to derive parameters of the planet and host star.
OGLE-TR-211b is a hot Jupiter orbiting a F7-8 spectral type dwarf star with the
period of 3.68 days. The mass of the planet is equal to 1.03+/-0.20 M_Jup while
its radius 1.36+0.18-0.09 R_Jup. The radius is about 20% larger than the
typical radius of hot Jupiters of similar mass. OGLE-TR-211b is, then, another
example of inflated hot Jupiters - a small group of seven exoplanets with large
radii and unusually small densities - objects being a challenge to the current
models of exoplanets.Comment: 6 pages. Submitted to Astronomy and Astrophysic
The spin-orbit angle of the transiting hot jupiter CoRoT-1b
We measure the angle between the planetary orbit and the stellar rotation
axis in the transiting planetary system CoRoT-1, with new HIRES/Keck and
FORS/VLT high-accuracy photometry. The data indicate a highly tilted system,
with a projected spin-orbit angle lambda = 77 +- 11 degrees. Systematic
uncertainties in the radial velocity data could cause the actual errors to be
larger by an unknown amount, and this result needs to be confirmed with further
high-accuracy spectroscopic transit measurements.
Spin-orbit alignment has now been measured in a dozen extra-solar planetary
systems, and several show strong misalignment. The first three misaligned
planets were all much more massive than Jupiter and followed eccentric orbits.
CoRoT-1, however, is a jovian-mass close-in planet on a circular orbit. If its
strong misalignment is confirmed, it would break this pattern. The high
occurence of misaligned systems for several types of planets and orbits favours
planet-planet scattering as a mechanism to bring gas giants on very close
orbits.Comment: to appear in in MNRAS letters [5 pages
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