2,939 research outputs found
Photometric Observations of the Eta Carinae 2009.0 Spectroscopic Event
We have observed Eta Carinae over 34 nights between 4th January 2009 and 27th
March 2009 covering the estimated timeframe for a predicted spectroscopic event
related to a suspected binary system concealed within the homunculus nebula. A
photometric minimum feature was confirmed to be periodic and comparison to a
previous event indicated that the period to within our error at 2022.6 +/-1.0
d. Using the E-region standard star system, the apparent V magnitudes
determined for the local comparison stars were HD303308 8.14+/-0.02, HD 93205
7.77 +/-0.03 and HD93162 8.22 +/-0.05. The latter star was found to be dimmer
than previously reported.Comment: 5 pages,4 figures, 1 tabl
Stochastic Variability of Luminous Blue Variables
Using the archives of the American Association of Variable Stars Observers
and our own data, we analyse the long-term variability of several well-studied
Luminous Blue Variables (LBVs) aiming on a general picture of stochastic
variability of these objects. The power density spectra of all the selected
objects may be generally described by a single power law contaminated by
observational noise at higher frequencies. The slopes of the power-law
component are close to p=2 (where PDS ~ f^{-p}, and f is frequency) for
strongly variable flaring objects like AG Car and significantly smaller (p~1.3)
for P Cyg where brightness variation amplitude is <~ 1 mag and dominated by
slow low-amplitude variability. The slope holds for about two orders of
magnitude in the frequency domain, though peaks and curvatures are present at f
~ 10^{-2}.. 10^{-3} d^{-1}. We show that pseudo-photosphere approach to
variability may explain the power-law shape of the variability spectrum at
higher frequencies. However, the observed spectra are actually rather "red"
than "brown": flux variations are correlated up to tens of years that is much
longer than the characteristic refreshment time scales of the
pseudo-photosphere. We propose that several stochastic noise components produce
the power spectra of LBV stars.Comment: 21 pages, 4 figures, 4 tables; accepted by New Astronom
Accretion onto the Companion of Eta Carinae During the Spectroscopic Event: III. the He II 4686 Line
We continue to explore the accretion model of the massive binary system eta
Carinae by studying the anomalously high He II 4686 line. The line appears just
before periastron and disappears immediately thereafter. Based on the He II
4686 line emission from O-stars and their modeling in the literature, we
postulate that the He II 4686 line comes from the acceleration zone of the
secondary stellar wind. We attribute the large increase in the line intensity
to a slight increase in the density of the secondary stellar wind in its
acceleration zone. The increase in density could be due to the ionization and
subsequent deceleration of the wind by the enhanced X-ray emission arising from
the shocked secondary wind further downstream or to accretion of the primary
stellar wind. Accretion around the secondary equatorial plane gives rise to
collimation of the secondary wind, which increases its density, hence enhancing
the He II 4686 emission line. In contrast with previous explanations, the
presently proposed model does not require a prohibitively high X-ray flux to
directly photoionize the He.Comment: ApJ, in pres
Database management and implementation for coal fire detection and monitoring in the Ruijgou Coalfield, Northwest China
Coal fire monitoring by aerospace remote sensing and GIS techniques is an advanced approach, which has been implemented in the
Rujigou coalfield, northwest China. A database of several different types of data, including remote sensing images, results of
geological surveys, etc., has been collected and assembled in a PC-based information system, which is being developed by the
International Institute for Aerospace Survey and Earth Sciences (ITC). This coal fire monitoring and management information
system (CoalMan) comprises of two main parts: one is the database with its management tools, and the tools for data processing
and analysis form the other. This paper first introduces the structure of the CoalMan information system, presents the data types
and contents of CoalMan database, then shows the data management methods. A complex data analysis package is outlined too, as
the core of the information system
Remote sensing of environmental pollution on teesside
A preliminary reconnaissance is being carried out to study the methods and procedures most useful for the detection of vegetation stress resulting from the various forms of environmental pollution, in the industrial area of Teesside, NE England, by means of a multiband remote sensing programme. Present results indicate the need for a carefully integrated programme of image analysis, as well as for field and laboratory methods. Sequential aerial multiband photography is an extremely useful technique for plotting the spread of industries and pollution with time, as well as for examining the changes in vegetation and land-use. Colour-infrared film is considered to be the single most useful remote sensing device for vegetation stress determination, as plants under stress are usually accompanied by a loss of infrared reflectance from the affected verdure. Image enhancement techniques are considered to be useful tools in delimiting certain areas under stress. The use of multiband photography, together with other remote sensing techniques, can greatly assist in the determination of areas of vegetation stress
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