scholarly journals A study of many-year spectral variability of the Ae Herbig star HD 36112

2021 ◽  
Vol 2 (1) ◽  
pp. 21-25
Author(s):  
M.I. Fursyak ◽  
O.V. Kozlova
Keyword(s):  
Emission Line ◽  
Equivalent Width ◽  
Time Scale ◽  
Probable Mechanism ◽  
Circumstellar Disk ◽  
High Dispersion ◽  
Circumstellar Envelope ◽  
Spectral Variability ◽  
Resonance Doublet

We present the results of long-term high-dispersion spectral observations (R = 20000) of the Ae Herbig star HD 36112 in the regions of the Ha emission line and the NaI D resonance doublet lines. They show that parameters of the Ha emission line demonstrate complicated variability on several time scales: 1) variability from night to night caused by inhomogeneity of the circumstellar envelope; 2) variability on a time scale of about 1200d characterized by a variation of the equivalent width, intensity, and other emission parameters; 3) variability on a time scale of more than 4000d observed as a many-year trend in variations of parameters of the Ha emission line. We associate these results with variability of physical and kinematic conditions in the inner regions of the accretion disk and wind. The most probable mechanism of this variability is a process of planet formation in the circumstellar disk.

scholarly journals Ubiquitous C IV 1550 Variability in B and Be Stars

1987 ◽  
Vol 92 ◽  
pp. 286-288 ◽  
Author(s):  
G. Sonneborn ◽  
M.P. Garhart ◽  
C.A. Grady
Keyword(s):  
Time Scale ◽  
High Dispersion ◽  
Be Stars ◽  
Line Profiles ◽  
Standard Star ◽  
B Stars ◽  
Short And Long Term ◽  
Resonance Transitions ◽  
Long Term Behavior

Studies of line profile variability of the ultraviolet 1550 Angstrom resonance transitions of C IV in Be stars (Sonneborn et al. 1986; Grady, et al. 1986a,b) have prompted an investigation into the short- and long-term behavior of the C IV lines in other types of B stars. We present examples of two well-studied Be stars, Omega Orionis and 66 Ophiuchi, and two non-Be stars, Beta Cephei and the standard star Zeta Cassiopeiae. Zeta Cas is also known to be a 53 Per variable (see Cox 1983). The IUE SWP high-dispersion spectra of Beta Cep and Zeta Cas have been obtained from the IUE archives. It has been known for some years that the C IV line profiles in Beta Cep vary in a time scale of several days (Fishel and Sparks, 1980). However, it came as a surprise to discover C IV variability in Zeta Cas. Available data allow us to set an upper limit of several months for the time scale of Zeta Cas C IV variability. The principal difference between the C IV variability in Be and non-Be stars appears to be the magnitude and velocity range of the effect.

scholarly journals Omicron Andromedae Photometry, Polarimetry, and a Tentative Model of the Light Variability

1987 ◽  
Vol 92 ◽  
pp. 456-459
Author(s):  
K. Oláh ◽  
H. Božić ◽  
P. Hadrava ◽  
J. Horn ◽  
P. Koubský ◽  
...  
Keyword(s):  
Emission Line ◽  
Time Scale ◽  
Periodic Variation ◽  
Basic Information ◽  
Tentative Model ◽  
History Of ◽  
To Come ◽  
Photoelectric Observations ◽  
Light Variability

Basic information about the star o and (HR 8762, HD 217675-6) is a bright (V=3.55m, B-V=-0.11m U-B=-0.50m) B6 III-Ve star. Its emission-line and shell spectrum is known to come and go on a time scale of years. In fact, the presence of a strong shell spectrum misled the authors of the HD catalogue to assign the star two HD numbers.o and is a prototype of Be rapid light variables in the sense that it has the longest record of photoelectric monitoring which goes back to 1915! The long history of attempts to understand the variations of this star has recently been summarized by Harmanec (1983). Collecting and analyzing all historical photoelectric observations, Harmanec (1984) concluded that the light variations of o And can be understood as a superposition of a long-term cyclic (8.5y) variation with an amplitude over 0.1m (the star being faintest at the recorded shell maxima) and a rapid periodic variation with a period of 1.571272 days.

scholarly journals Long-term variation in the short-period binary system WR46 (WN3P+?)

1999 ◽  
Vol 193 ◽  
pp. 263-264
Author(s):  
Pieter M. Veen ◽  
Arnout M. van Genderen ◽  
Albert F. Jones
Keyword(s):  
Binary System ◽  
Emission Line ◽  
Equivalent Width ◽  
Short Period ◽  
Term Variation ◽  
Period Decrease ◽  
Photometric Variation

We studied the short-period (P ≈ 6–8 hr) binary system WR46 using simultaneous photometry and spectroscopy. We show that the long-term photometric variation is accompanied by changes in the equivalent width of the He II Λ5411 emission line and by an apparent period decrease on the rising branch. Furthermore, the brightening of the object is repeating.

The long-term instability of the new generation hydrogen masers

2020 ◽  
pp. 35-38
Author(s):  
S.I. Donchenko ◽  
I.Y. Blinov ◽  
I.B. Norets ◽  
Y.F. Smirnov ◽  
A.A. Belyaev ◽  
...  
Keyword(s):  
Time Scale ◽  
Frequency Difference ◽  
Clock Frequency ◽  
Quantum Frequency ◽  
Frequency Standards ◽  
Quantum Frequency Standards ◽  
New Generation ◽  
Atomic Time

The latest changes in the algorithm for the formation of the international atomic time scale TAI are reported in terms of estimating the weights of the clocks involved in the formation of TAI. Studies of the characteristics of the long-term instability of new-generation hydrogen masers based on processing the results of the clock frequency difference with respect to TAI are performed. It has been confirmed that at present, new-generation hydrogen masers show significantly less long-term instability in comparison with quantum frequency standards ofsimilar and other types.

scholarly journals Ensemble Pulsar Time Study by Pulsar Timing Observations

2004 ◽  
Vol 218 ◽  
pp. 439-440
Author(s):  
Tinggao Yang ◽  
Guangren Ni
Keyword(s):  
Time Scale ◽  
Wavelet Decomposition ◽  
Time Study ◽  
Millisecond Pulsar ◽  
Millisecond Pulsars ◽  
Pulsar Time ◽  
Pulsar Timing ◽  
Timing Data ◽  
Gravitational Wave Background

Long term timing of multiple millisecond pulsars can contribute to the study of an ensemble pulsar time scale PTens. A wavelet decomposition algorithm (WDA) was applied to define a PTens using the available millisecond pulsar timing datA. The PTens obtained from WDA is more stable than those resulting from other algorithms. The Chinese 50 m radio telescope is specially designed for PTens study and detection of gravitational wave background via millisecond pulsars timing observations. A scheme for multiple millisecond pulsar timing and ensemble pulsar time study is discussed in some detail.

scholarly journals The Rate of Information Transfer of Naturalistic Stimulation by Graded Potentials

2003 ◽  
Vol 122 (2) ◽  
pp. 191-206 ◽  
Author(s):  
Mikko Juusola ◽  
Gonzalo G. de Polavieja
Keyword(s):  
Time Scale ◽  
Information Transfer ◽  
Bright Light ◽  
Scale Structure ◽  
Finite Duration ◽  
Adaptation Mechanisms ◽  
Short And Long Term ◽  
Signaling Strategies

We present a method to measure the rate of information transfer for any continuous signals of finite duration without assumptions. After testing the method with simulated responses, we measure the encoding performance of Calliphora photoreceptors. We find that especially for naturalistic stimulation the responses are nonlinear and noise is nonadditive, and show that adaptation mechanisms affect signal and noise differentially depending on the time scale, structure, and speed of the stimulus. Different signaling strategies for short- and long-term and dim and bright light are found for this graded system when stimulated with naturalistic light changes.

NGC 3516: The Long‐Term Variability of the Active Galactic Nucleus Emission‐Line and Absorption‐Line Regions

1999 ◽  
Vol 524 (2) ◽  
pp. 707-731 ◽  
Author(s):  
M. R. Goad ◽  
A. P. Koratkar ◽  
J. Kim‐Quijano ◽  
K. T. Korista ◽  
P. T. O'Brien ◽  
...  
Keyword(s):  
Emission Line ◽  
Absorption Line ◽  
Active Galactic Nucleus

scholarly journals Has erosion globally increased? Long-term erosion rates as a function of climate derived from the impact crater inventory

2018 ◽  
Author(s):  
Stefan Hergarten ◽  
Thomas Kenkmann
Keyword(s):  
Time Scale ◽  
Impact Crater ◽  
Regional Effect ◽  
Tropical Zone ◽  
Erosion Rates ◽  
Continental Scale ◽  
River Loads ◽  
The Impact

Abstract. Worldwide erosion rates seem to have increased strongly since the beginning of the Quaternary, but there is still discussion about the role of glaciation as a potential driver and even whether the increase is real at all or an artefact due to losses in the long-term sedimentary record. In this study we derive estimates of average erosion rates on the time scale of some tens of million years from the terrestrial impact crater inventory. This approach is completely independent from all other methods to infer erosion rates such as river loads, preserved sediments, cosmogenic nuclides and thermochronometry. Our approach yields average erosion rates as a function of present-day topography and climate. The results confirm that topography accounts for the main part of the huge variation of erosion on Earth, but also identifies a significant systematic dependence on climate in contrast to several previous studies. We found a fivefold increase in erosional efficacy from the cold regimes to the tropical zone and that temperate and arid climates are very similar in this context. Combining our results to a worldwide mean erosion rate we found that erosion rates on the time scale of some tens of million years are at least as high as present-day rates and suggest that glaciation has a rather regional effect with a limited impact at the continental scale.

Interferometric long-term stabilization of a delay line: a tool for pump–probe photoelectron–photoion-coincidence spectroscopy on the attosecond time scale

2008 ◽  
Vol 91 (2) ◽  
pp. 287-293 ◽  
Author(s):  
F.M. Böttcher ◽  
B. Manschwetus ◽  
H. Rottke ◽  
N. Zhavoronkov ◽  
Z. Ansari ◽  
...  
Keyword(s):  
Time Scale ◽  
Delay Line ◽  
Pump Probe ◽  
Coincidence Spectroscopy

scholarly journals LONG TERM MORPHOLOGICAL MODELLING

2011 ◽  
Vol 1 (32) ◽  
pp. 64
Author(s):  
Sten Esbjørn Kristensen ◽  
Rolf Deigaard ◽  
Martin Anders Taaning ◽  
Jørgen Fredsøe ◽  
Nils Drønen ◽  
...  
Keyword(s):  
Time Scale ◽  
Surf Zone ◽  
Coastal Structures ◽  
Model Concept ◽  
General Applicability ◽  
Shoreline Evolution ◽  
Realistic Representation ◽  
Morphological Modelling ◽  
Constant Shape

A morphological modelling concept for long term nearshore morphology is proposed and examples of its application are presented and discussed. The model concept combines parameterised representations of the cross-shore morphology, with a 2DH area model for waves, currents and sediment transport in the surf zone. Two parameterization schemes are tested for two different morphological phenomena: 1) Shoreline changes due to the presence of coastal structures and 2) alongshore migration of a nearshore nourishment and a bar by-passing a harbour. In the case of the shoreline evolution calculations, a concept often used in one-line modelling of cross-shore shifting of an otherwise constant shape cross-shore profile is applied for the case of a groyne and a detached breakwater. In the case of alongshore bar/nourishment migration an alternative parameterization is adopted. All examples are presented, analysed and discussed with respect to the question of realistic representation, time scale and general applicability of the model concept.

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