608 research outputs found
Reduction procedures for accurate analysis of MSX surveillance experiment data
Technical challenges of the Midcourse Space Experiment (MSX) science instruments require careful characterization and calibration of these sensors for analysis of surveillance experiment data. Procedures for reduction of Resident Space Object (RSO) detections will be presented which include refinement and calibration of the metric and radiometric (and photometric) data and calculation of a precise MSX ephemeris. Examples will be given which support the reduction, and these are taken from ground-test data similar in characteristics to the MSX sensors and from the IRAS satellite RSO detections. Examples to demonstrate the calculation of a precise ephemeris will be provided from satellites in similar orbits which are equipped with S-band transponders
Astrometric observations of Saturn's satellites from McDonald Observatory, 1972
Observations of Saturn's satellites were reduced by means of secondary reference stars obtained by reduction of Palomar Sky Survey (PSS) plates. This involved the use of 39 SAO stars and plate overlap technique to determine the coordinates of 59 fainter stars in the satellite field. Fourteen plate constants were determined for each of the two PSS plates. Comparison of two plate measurement and reduction techniques on the satellite measurements demonstrate the existence of a serious background gradient effect and the utility of microdensitometry to eliminate this error source in positional determinations of close satellites
Seasonal and interannual variability of North American isoprene emissions as determined by formaldehyde column measurements from space
Formaldehyde (HCHO) columns measured from space by solar UV backscatter allow mapping of reactive hydrocarbon emissions. The principal contributor to these emissions during the growing season is the biogenic hydrocarbon isoprene, which is of great importance for driving regional and global tropospheric chemistry. We present seven years (1995-2001) of HCHO column data for North America from the Global Ozone Monitoring Experiment (GOME), and show that the general seasonal and interannual variability of these data is consistent with knowledge of isoprene emission. There are some significant regional discrepancies with the seasonal patterns predicted from current isoprene emission models, and we suggest that these may reflect flaws in the models. The interannual variability of HCHO columns observed by GOME appears to follow the interannual variability of surface temperature, as expected from current isoprene emission models
Evidence for a black hole in the historical X-ray transient A 1524-61 (=KY TrA)
We present VLT spectroscopy, high-resolution imaging and time-resolved
photometry of KY TrA, the optical counterpart to the X-ray binary A 1524-61. We
perform a refined astrometry of the field, yielding improved coordinates for KY
TrA and the field star interloper of similar optical brightness that we locate
arcsec SE. From the spectroscopy, we refine the radial velocity
semi-amplitude of the donor star to km s by employing
the correlation between this parameter and the full-width at half-maximum of
the H emission line. The -band light curve shows an ellipsoidal-like
modulation with a likely orbital period of d (
h). These numbers imply a mass function M. The
KY TrA de-reddened quiescent colour is consistent
with a donor star of spectral type K2 or later, in case of significant
accretion disc light contribution to the optical continuum. The colour allows
us to place a very conservative upper limit on the companion star mass, M, and, in turn, on the binary mass ratio, . By exploiting the correlation between the binary inclination and the
depth of the H line trough, we establish deg. All these
values lead to a compact object and donor mass of
M and M, respectively, thus confirming the
black hole nature of the accreting object. In addition, we estimate a distance
toward the system of kpc.Comment: 7 pages, 5 figure
Defining and cataloging exoplanets: The exoplanet.eu database
We describe an online database for extra-solar planetary-mass candidates,
updated regularly as new data are available. We first discuss criteria for the
inclusion of objects in the catalog: "definition" of a planet and several
aspects of the confidence level of planet candidates. {\bf We are led to point
out the conflict between sharpness of belonging or not to a catalogue and
fuzziness of the confidence level.} We then describe the different tables of
extra-solar planetary systems, including unconfirmed candidates (which will
ultimately be confirmed, or not, by direct imaging). It also provides online
tools: histogrammes of planet and host star data, cross-correlations between
these parameters and some VO services. Future evolutions of the database are
presented.Comment: Accepted in Astronomy and Astrophysics (revised version
Instantons in the nonperturbative QCD vacuum
The influence of nonperturbative fields on instantons in quantum
chromodynamics is studied. Nonperturbative vacuum is described in terms of
nonlocal gauge invariant vacuum averages of gluon field strength.Effective
action for instanton is derived in bilocal approximation and it is demonstrated
that stochastic background gluon fields are responsible for infra-red (IR)
stabilization of instantons. Dependence of characteristic instanton size on
gluon condensate and correlation length in nonperturbative vacuum is found.
Comparison of obtained instanton size distribution with lattice data is made.Comment: 25 pages, 7 figures, 3 tables, RevTeX4, some corrections made and
references adde
On whether azimuthal isotropy and alongshelf translational invariance are present in low-frequency acoustic propagation along the New Jersey shelfbreak
Author Posting. © Acoustical Society of America, 2012. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 131 (2012): 1762-1781, doi:10.1121/1.3672644.To understand the issues associated with the presence (or lack) of azimuthal isotropy and horizontal (along isobath) invariance of low-frequency (center frequencies of 600 Hz and 900 Hz) acoustic propagation in a shelfbreak environment, a series of experiments were conducted under the Autonomous Wide-Aperture Cluster for Surveillance component of the Shallow Water 2006 experiment. Transmission loss data reported here were from two mobile acoustic sources executing (nearly) circular tracks transmitting to sonobuoy receivers in the circle centers, and from one 12.5 km alongshelf acoustic track. The circle radii were 7.5 km. Data are from September 8, 2006. Details of the acoustic and environmental measurements are presented. Simple analytic and computer models are used to assess the variability expected due to the ocean and seabed conditions encountered. A comparison of model results and data is made, which shows preliminary consistency between the data and the models, but also points towards further work that should be undertaken specifically in enlarging the range and frequency parameter space, and in looking at integrated transmission loss.Office of Naval Research Code 32
Strangeness Enhancement in and Interactions at SPS Energies
The systematics of strangeness enhancement is calculated using the HIJING and
VENUS models and compared to recent data on , and
collisions at CERN/SPS energies (). The HIJING model is used to
perform a {\em linear} extrapolation from to . VENUS is used to
estimate the effects of final state cascading and possible non-conventional
production mechanisms. This comparison shows that the large enhancement of
strangeness observed in collisions, interpreted previously as possible
evidence for quark-gluon plasma formation, has its origins in non-equilibrium
dynamics of few nucleon systems. % Strangeness enhancement %is therefore traced
back to the change in the production dynamics %from to minimum bias
and central collisions. A factor of two enhancement of at
mid-rapidity is indicated by recent data, where on the average {\em one}
projectile nucleon interacts with only {\em two} target nucleons. There appears
to be another factor of two enhancement in the light ion reaction relative
to , when on the average only two projectile nucleons interact with two
target ones.Comment: 29 pages, 8 figures in uuencoded postscript fil
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