scholarly journals Properties of Circumstellar Dust in Symbiotic Miras

2006 ◽  
Vol 2 (S240) ◽  
pp. 596-604
Author(s):  
D. Kotnik-Karuza ◽  
T. Jurkic ◽  
M. Friedjung
Keyword(s):  
Temperature Distribution ◽  
Systematic Study ◽  
Light Curves ◽  
Circumstellar Dust ◽  
Symbiotic Stars ◽  
Time Intervals ◽  
Dust Temperature ◽  
Long Time ◽  
Long Term Variations

AbstractWe present a study of the properties of circumstellar dust in symbiotic Miras during sufficiently long time intervals of minimal obscuration. The publishedJHKLmagnitudes of o Ceti, RX Pup, KM Vel, V366 Car, V835 Cen, RR Tel and R Aqr have been collected. In order to investigate their long-term variations, we removed the Mira pulsations to correct their light curves. Assuming spherical temperature distribution of the dust in the close neighbourhood of the Mira, the DUSTY code was used to solve the radiative transfer in order to determine the dust temperature and its properties in each particular case.The preliminary results of this systematic study of dust envelopes in symbiotic stars with Miras as cool components provide information on nature of dust in these objects.

scholarly journals Long-Term Variations of the Compact Radio Source Sgr A∗ at the Galactic Center

1989 ◽  
Vol 136 ◽  
pp. 535-541 ◽  
Author(s):  
Jun-Hui Zhao ◽  
R. D. Ekers ◽  
W. M. Goss ◽  
K. Y. Lo ◽  
Ramesh Narayan
Keyword(s):  
Radio Source ◽  
Flux Density ◽  
High Velocity ◽  
Galactic Center ◽  
Light Curves ◽  
Radio Flux ◽  
Compact Radio Source ◽  
Sgr A ◽  
Long Term Variations

We investigate the long-term flux density variations of the compact radio source Sgr A∗ at the galactic center by combining recent VLA observations with previous Green Bank interferometer data. We present radio flux density light-curves for Sgr A∗ at 20, 11, 6 and 3.7 cm from 1974 to 1987. Long-term variability with a timescale of at least 5 years is seen at 20 cm and there is evidence for more rapid variations at the shorter wavelengths. The variability timescales at 20, 11 and 6 cm fit the λ2 scaling predicted by the theory of refractive scintillation suggesting that the variability could be due to this cause. However, the timescales are relatively short, implying an unusually high velocity in the scattering screen. The modulation index of the variability is large and relatively independent of wavelength.

Photometry of Variable Stars, and System Transformability Over Long Time Intervals

2003 ◽  
Vol 12 (4) ◽  
Author(s):  
C. Sterken
Keyword(s):  
Fundamental Problem ◽  
Variable Stars ◽  
Time Intervals ◽  
Multi Wavelength ◽  
Long Time ◽  
Photometric Monitoring ◽  
Made In

AbstractThe fundamental problem of long-term photometric monitoring of variable stars and of multi-wavelength photometric campaigns is the problem of bringing the data to a common standard. Such homogenization can be achieved only when the measurements are made in photometric systems that are truly transformable. This fundamental problem is of a technical nature, and photometric observers, sometimes, are not aware of the problems. This frequently leads to over-interpretation of the data.

scholarly journals Modeling of Circumstellar Dust by the DUSTY Code

2011 ◽  
Vol 7 (S282) ◽  
pp. 247-250
Author(s):  
Tomislav Jurkić ◽  
Dubravka Kotnik-Karuza
Keyword(s):  
Near Infrared ◽  
Dynamical Behaviour ◽  
Light Curves ◽  
Young Stellar Objects ◽  
Numerical Code ◽  
Circumstellar Dust ◽  
Be Stars ◽  
Stellar Objects ◽  
Near Ir ◽  
Dust Temperature

AbstractWe present a circumstellar dust model around the symbiotic Mira RR Tel obtained by modeling the near-infrared JHKL magnitudes and ISO spectra. In order to follow the evolution of infrared colours in time, the published JHKL magnitudes were corrected by removing the Mira pulsations. The RR Tel light curves show three obscuration events in the near-IR. Using the simultaneously available JHKL magnitudes and ISO spectra in three different epochs, we obtained SEDs in the near- and mid-IR spectral region (1-20 μm) in epochs with and without obscuration.The DUSTY numerical code was used to solve the radiative transfer and to determine the circumstellar dust properties of the inner dust regions around the Mira, assuming a spherical dust temperature distribution in its close neighbourhood. The physical properties of the dust, mass loss and optical depth during intervals with and without obscuration have been obtained. Both JHKL and ISO observations during the obscuration period can be reproduced with a spherical dust envelope, while ISO spectra outside obscuration show a different behaviour. The dynamical behaviour of the circumstellar dust was obtained by modeling the JHKL magnitudes observed during the span of more than 30 years.The DUSTY code was also successfully applied in the modeling of circumstellar dust envelopes of young stellar objects, such as Herbig Ae/Be stars.

scholarly journals Errors of Observation in Double-Star Work

1971 ◽  
Vol 5 ◽  
pp. 133-135
Author(s):  
W. D. Heintz
Keyword(s):  
Noise Level ◽  
Double Star ◽  
Astronomical Observation ◽  
Time Interval ◽  
The Past ◽  
Visual Binary ◽  
Long Time ◽  
Observational Errors ◽  
Long Term Variations

Astronomical observation frequently is focused on minute quantities, and on digging information even from below the 'noise level'. In all cases of long-term variations, such as visual binary motions, measurements over a long time interval have to be combined. All of this requires a knowledge of the observational errors in the past and present. We usually are not at liberty to discard old observations since we cannot repeat them at any later time desired. Visual observations leave no re-measurable records, so we have to take the word of the observer, and make the best of it.

Errors of Observation in Double-Star Work

1965 ◽  
Vol 5 ◽  
pp. 132-135
Author(s):  
W. D. Heintz
Keyword(s):  
Noise Level ◽  
Double Star ◽  
Astronomical Observation ◽  
Time Interval ◽  
The Past ◽  
Visual Binary ◽  
Long Time ◽  
Observational Errors ◽  
Long Term Variations

Astronomical observation frequently is focused on minute quantities, and on digging information even from below the ‘noise level’. In all cases of long-term variations, such as visual binary motions, measurements over a long time interval have to be combined. All of this requires a knowledge of the observational errors in the past and present. We usually are not at liberty to discard old observations since we cannot repeat them at any later time desired. Visual observations leave no re-measurable records, so we have to take the word of the observer, and make the best of it.

scholarly journals Quasi–periodic Outburst Activity of Novae at Minimum

1990 ◽  
Vol 122 ◽  
pp. 48-49 ◽  
Author(s):  
M. Della Valle ◽  
M. Calvani
Keyword(s):  
Forthcoming Paper ◽  
Light Curves ◽  
Complete Analysis ◽  
Evolutionary Models ◽  
Time Intervals ◽  
Unequally Spaced ◽  
Solar Type ◽  
Analyse Data ◽  
Larger Sample

AbstractIn this paper we present the statistical analysis of historical light curves of 8 old novae, performed through a Fourier analysis on ~ 1600 no-equispaced (in the time) observations published by Steavenson between 1921 and 1953. The results seems to support the existence of a semiregular variability on typical timescales of 50d ÷ 100d and amplitude of ~ 0.3 ± 0.1 magnitudes.At present the largest body of data concerning the photometric behaviour of novae at minimum, is due to the pioneering works by Steavenson (1920→1950) and also to Robinson’s compilation (1975) of 33 preeruption lightcurves of novae.Besides testing the evolutionary models, such as the Hibernation Scenario (Shara et al. 1986), the importance of very long term observations of novae at minimum, has been recently pointed out by Bianchini (1987) and Warner (1988) in close connection to the possible detection of solar-type cycles of activity of the secondary. In spite of these considerations an interesting body of ~ 1000 homogenous observations of 5 posteruption lightcurves provided by Steavenson between 1920 to 1950 (published on M.N.R.A.S) has been neglected and only recently recovered (Delia Valle 1988).The aim of our analysis is:a)to verify possible presence of Dwarf Nova activityb)to confirm on the basis of a larger sample of objects, the existence of semiregular variability as observed in Q Cyg 1876 (Shugarov 1983) and v841 Oph (Della Valle and Rosino 1987).In this contribute we present only the preliminary results of our Fourier’s analysis, performed by adopting the procedure suggested by Deeming (1975) to analyse data taken at unequally spaced time intervals, whereas a more complete analysis will be presented in a forthcoming paper.

scholarly journals The Later Evolution of the Contact Binaries AP Leo, AK Her, AB And and AM Leo

2002 ◽  
Vol 187 ◽  
pp. 331-336
Author(s):  
L. Li ◽  
Z. Han ◽  
F. Zhang
Keyword(s):  
Light Curve ◽  
Rapid Change ◽  
Cataclysmic Variables ◽  
Light Curves ◽  
Common Envelope ◽  
Physical Mechanisms ◽  
Contact Binaries ◽  
The Common ◽  
Long Term Variations

AbstractA detailed study of the periods and light curves of binaries AK Her, AP Leo, AB And and AM Leo is presented. Based on the study of the O – C curves, we find that the period variation of each system contains several components with different frequencies, and we suggest that the periodical variations in the periods are likely influenced by different mechanisms. Based on the study of the light curve changes, we find that the light curves exhibit two kinds of variations: rapid variations and long-term variations. We investigate the physical mechanisms which may underlie the variations of the period and the light curve of each system and obtain some new conclusions. According to the characteristics of the rapid light variation in these systems, we suggest that the rapid change in the light curve is probably caused by pulsation of the common envelope, and that the mechanism(s) causing the pulsation may be mass transfer through the inner Lagrangian point L1 or its variation. Finally, the evolutionary trends of these systems are discussed, and we suggest that these systems may be progenitors of cataclysmic variables.

LONG-TERM BEHAVIOUR OF LARGE MECHANICAL SYSTEMS WITH RANDOM INITIAL DATA

2002 ◽  
Vol 02 (04) ◽  
pp. 533-562 ◽  
Author(s):  
R. KUPFERMAN ◽  
A. M. STUART ◽  
J. R. TERRY ◽  
P. F. TUPPER
Keyword(s):  
Heat Bath ◽  
Time Intervals ◽  
Random Initial Data ◽  
Empirical Measures ◽  
Long Time Behaviour ◽  
Auto Correlation ◽  
Long Time ◽  
Large Systems ◽  
Ergodic Behaviour

We study the long-time behaviour of large systems of ordinary differential equations with random data. Our main focus is a Hamiltonian system which describes a distinguished particle attached to a large collection of heat bath particles by springs. In the limit where the size of the heat bath tends to infinity, the trajectory of the distinguished particle can be weakly approximated, on finite time intervals, by a Langevin stochastic differential equation. We examine the long-term behaviour of these trajectories, both analytically and numerically. We find ergodic behaviour manifest in both the long-time empirical measures and in the resulting auto-correlation functions.

A Chemical Reaction Network to Generate Random, Power-Law-Distributed Time Intervals

2017 ◽  
Vol 23 (4) ◽  
pp. 518-527
Author(s):  
Patrick Krauss ◽  
Holger Schulze ◽  
Claus Metzner
Keyword(s):  
Power Law ◽  
Reaction System ◽  
Reaction Network ◽  
Basic Function ◽  
Time Intervals ◽  
Lévy Walks ◽  
Straight Line ◽  
New Directions ◽  
Long Time

In Lévy walks (LWs), particles move with a fixed speed along straight line segments and turn in new directions after random time intervals that are distributed according to a power law. Such LWs are thought to be an advantageous foraging and search strategy for organisms. While complex nervous systems are certainly capable of producing such behavior, it is not clear at present how single-cell organisms can generate the long-term correlated control signals required for a LW. Here, we construct a biochemical reaction system that generates long-time correlated concentration fluctuations of a signaling substance, with a tunable fractional exponent of the autocorrelation function. The network is based on well-known modules, and its basic function is highly robust with respect to the parameter settings.

scholarly journals Elimination of long-term variations from chaotic light curves

2013 ◽  
Vol 334 (9) ◽  
pp. 984-987
Author(s):  
E. Plachy ◽  
Z. Kolláth
Keyword(s):  
Light Curves ◽  
Long Term Variations
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