3,032 research outputs found
Equations Predicting Primary Productivity (Biomass) of Trees, Shrubs and Lesser Vegetation Based on Current Literature
BVRI Observations of the Optical Afterglow of GRB 990510
We present observations of the optical counterpart to the Gamma-Ray
Burst (GRB) 990510 obtained with the Las Campanas 1.0-m telescope between 15
and 48 hours after the burst. The temporal analysis of the data indicates
steepening decay, independent of wavelength, approaching asymptotically
at early times ( and at
late times, with the break time at . GRB 990510 is the
most rapidly fading of the well-documented GRB afterglows. It is also the first
observed example of broad-band break for a GRB optical counterpart. The optical
spectral energy distribution, corrected for significant Galactic reddening, is
well fitted by a single power-law with . However, when the
-band point is dropped from the fit, the power-law becomes , indicating a possible deviation from the power-law in the spectrum,
either intrinsic or due to additional extinction near the source or from an
intervening galaxy at . Broad-band break behavior broadly similar to
that observed in GRB 990510 has been predicted in some jet models of GRB
afterglows, thus supporting the idea that the GRB energy is beamed, at least in
some cases.Comment: submitted to the ApJ Letters, 13 pages, 5 tables, 3 figures;
additional data available at ftp://cfa-ftp.harvard.edu/pub/kstanek/GRB990510/
and through WWW at http://cfa-www.harvard.edu/cfa/oir/Research/GRB
The Optical Gravitational Lensing Experiment. Variable Stars in Globular Clusters - IV. Fields 104A-E in 47 Tuc
Five fields located close to the center of the globular cluster NGC 104=47
Tuc were surveyed in a search for variable stars. We present V-band light
curves for 42 variables. This sample includes 13 RR Lyr stars -- 12 of them
belong to the Small Magellanic Cloud (SMC) and 1 is a background object from
the galactic halo. Twelve eclipsing binaries were identified -- 9 contact
systems and 3 detached/semi-detached systems. Seven eclipsing binaries are
located in the blue straggler region on the cluster color-magnitude diagram
(CMD) and four binaries can be considered main-sequence systems. One binary is
probably a member of the SMC. Eight contact binaries are likely members of the
cluster and one is most probably a foreground star. We show that for the
surveyed region of 47 Tuc, the relative frequency of contact binaries is very
low as compared with other recently surveyed globular clusters. The sample of
identified variables also includes 15 red variables with periods ranging from
about 2 days to several weeks. A large fraction of these 15 variables probably
belong to the SMC but a few stars are likely to be red giants in 47 Tuc. VI
photometry for about 50 000 stars from the cluster fields was obtained as a by
product of our survey.Comment: Latex file, l-aa style, 10 pages, 7 ps figures included. Submitted to
A&A. Figure 8 available from
ftp://sirius.astrouw.edu.pl/pub/jka/47Tuc/fig8.ps.
Thermo-ecological cost (TEC) evaluation of metallurgical processes
Metallurgy represents a complex production system of fuel and mineral non-renewable resources transformation. The effectiveness of resource management in metallurgical chains depends on the applied ore grade and on the irreversibility of components of the system. TEC can be applied to measure the influence of metallurgy on the depletion of natural resources. The paper discusses the possibility of application of TEC in metallurgy and presents illustrative example concerning blast-furnace process
Are the Ogle Microlenses in the Galactic Bar?
The analysis of the first two years of OGLE data revealed 9 microlensing
events of the galactic bulge stars, with the characteristic time scales in the
range days, where . The optical depth to
microlensing is larger than , in excess of
current theoretical estimates, indicating a much higher efficiency for
microlensing by either bulge or disk lenses. We argue that the lenses are
likely to be ordinary stars in the galactic bar, which has its long axis
elongated towards us. A relation between and the lens masses remains
unknown until a quantitative model of bar microlensing becomes available. At
this time we have no evidence that the OGLE events are related to dark matter.
The geometry of lens distribution can be determined observationally when the
microlensing rate is measured over a larger range of galactic longitudes, like
, and the relative proper motions of the galactic bulge
(bar) stars are measured with the HST.Comment: 10 pages, 2 figures, revised version accepted for the publication in
ApJL, uses AAS LaTeX aaspp.sty macro, PostScript figures and PostScript
version of the paper available through anonymous ftp from
astro.princeton.edu, directory stanek/tau, or on reques
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