scholarly journals The Geometrical Structure of Activity in the AR Lac System

1983 ◽  
Vol 6 ◽  
pp. 650-650
Author(s):  
Gibor Basri ◽  
David Gibson ◽  
Fredrick Walter
Keyword(s):  
Solar Activity ◽  
Time Scales ◽  
Geometrical Structure ◽  
Good Reason ◽  
Stellar Rotation ◽  
Stellar Activity ◽  
Reasonable Time ◽  
X Ray ◽  
Short Period

Although solar activity is seen to exhibit a very inhomogeneous and convoluted set of structures, and we have good reason to expect that stellar activity is also very structured, it is naturally quite difficult to resolve such structures on other stars. One of the best opportunities for doing so is afforded by an active eclipsing system of short period, in which both the eclipses and stellar rotation serve to cover and uncover features on reasonable time scales. AR Lac is the nearest and most suitable such system, it is an RSCVn system comprised of an active G dwarf and active K subgiant with a two day period. We report here on simultaneous X-ray and UV coverage of an eclipse in this system obtained with the Einstein and IUE observations. More details are given in reports in IAU Coll. No. 71 and IAU Symp. No. 102.

scholarly journals The burst of solar and geomagnetic activity in August–September 2005

2009 ◽  
Vol 27 (3) ◽  
pp. 1019-1026 ◽  
Author(s):  
A. Papaioannou ◽  
H. Mavromichalaki ◽  
E. Eroshenko ◽  
A. Belov ◽  
V. Oleneva
Keyword(s):  
Solar Activity ◽  
Solar Cycle ◽  
Geomagnetic Activity ◽  
Neutron Monitor ◽  
Cosmic Ray ◽  
High Energy ◽  
X Ray ◽  
Cycle Minimum ◽  
Short Period ◽  
Ray Density

Abstract. During the August–September 2005 burst of solar activity, close to the current solar cycle minimum, a significant number of powerful X-ray flares were recorded, among which was the outstanding X17.0 flare of 7 September 2005. Within a relatively short period (from 22 August to 17 September) two severe magnetic storms were also recorded as well as several Forbush effects. These events are studied in this work, using hourly mean variations of cosmic ray density and anisotropy, derived from data of the neutron monitor network. During these Forbush effects the behavior of high energy cosmic ray characteristics (density and anisotropy) is analyzed together with interplanetary disturbances and their solar sources, and is compared to the variations observed in geomagnetic activity. A big and long lasting (~6 h) cosmic ray pre-decrease (~2%) is defined before the shock arrival on 15 September 2005. The calculated cosmic ray gradients for September 2005 are also discussed.

scholarly journals Disentangling between stellar activity and planetary signals

2010 ◽  
Vol 6 (S273) ◽  
pp. 281-285 ◽  
Author(s):  
Isabelle Boisse ◽  
François Bouchy ◽  
Guillaume Hébrard ◽  
Xavier Bonfils ◽  
Nuno Santos ◽  
...  
Keyword(s):  
Orbital Period ◽  
Rotational Period ◽  
Stellar Rotation ◽  
Stellar Activity ◽  
Short Period ◽  
Stellar Photosphere ◽  
Low Mass ◽  
Host Stars

AbstractPhotospheric stellar activity (i.e. dark spots or bright plages) might be an important source of noise and confusion in the radial-velocity (RV) measurements. Radial-velocimetry planet search surveys as well as follow-up of photometric transit surveys require a deeper understanding and characterization of the effects of stellar activities to disentangle it from planetary signals.We simulate dark spots on a rotating stellar photosphere. The variations of the RV are characterized and analyzed according to the stellar inclination, the latitude and the number of spots. The Lomb-Scargle periodograms of the RV variations induced by activity present power at the rotational period Prot of the star and its two-first harmonics Prot/2 and Prot/3. Three adjusted sinusoids fixed at the fundamental period and its two-first harmonics allow to remove about 90% of the RV jitter amplitude. We apply and validate our approach on four known active planet-host stars: HD 189733, GJ 674, CoRoT-7 and ι Hor. We succeed in fitting simultaneously activity and planetary signals on GJ674 and CoRoT-7. We excluded short-period low-mass exoplanets around ι Hor. Our approach is efficient to disentangle reflex-motion due to a planetary companion and stellar-activity induced-RV variations provided that 1) the planetary orbital period is not close to that of the stellar rotation or one of its two-first harmonics, 2) the rotational period of the star is accurately known, 3) the data cover more than one stellar rotational period.

scholarly journals Wavelet analysis of the long-term activity of V833 Tau

2020 ◽  
Vol 495 (4) ◽  
pp. 3788-3794 ◽  
Author(s):  
R Stepanov ◽  
N I Bondar’ ◽  
M M Katsova ◽  
D Sokoloff ◽  
P Frick
Keyword(s):  
Solar Activity ◽  
Wavelet Analysis ◽  
Time Scales ◽  
Best Practice ◽  
Dynamo Theory ◽  
Theoretical Understanding ◽  
Stellar Activity ◽  
Order Of Magnitude ◽  
Consistent Method ◽  
Photometric Monitoring

ABSTRACT The bulk of available stellar activity observations is frequently checked for the manifestation of signs in comparison with the known characteristic of solar magnetic modulation. The problem is that stellar activity records are usually an order of magnitude shorter than available observations of solar activity variation. Therefore, the resolved time-scales of stellar activity are insufficient to decide reliably that a cyclic variation for a particular star is similar to the well-known 11-yr sunspot cycles. As a result, recent studies report several stars with double or multiple cycles which serve to challenge the underlying theoretical understanding. This is why a consistent method to separate ‘true’ cycles from stochastic variations is required. In this paper, we suggest that a conservative method, based on the best practice of wavelet analysis previously applied to the study of solar activity, for studying and interpreting the longest available stellar activity record – photometric monitoring of V833 Tau for more than 100 yr. We find that the observed variations of V833 Tau with time-scales of 2–50 yr should be comparable with the known quasi-periodic solar mid-term variations, whereas the true cycle of V833 Tau, if it exists, should be of about a century or even longer. We argue that this conclusion does not contradict the expectations from the stellar dynamo theory.

Interfacial properties of GaSb/InAs superlattices

1993 ◽  
Vol 51 ◽  
pp. 826-827
Author(s):  
M. E. Twigg ◽  
B. R. Bennett ◽  
J. R. Waterman ◽  
J. L. Davis ◽  
B. V. Shanabrook ◽  
...  
Keyword(s):  
Gaas Substrate ◽  
Molecular Beam ◽  
Infrared Detector ◽  
Interfacial Properties ◽  
Ex Situ ◽  
X Ray Diffraction ◽  
Absorption Coefficients ◽  
X Ray ◽  
Short Period ◽  
High Optical Absorption

Recently, the GaSb/InAs superlattice system has received renewed attention. The interest stems from a model demonstrating that short period Ga1-xInxSb/InAs superlattices will have both a band gap less than 100 meV and high optical absorption coefficients, principal requirements for infrared detector applications. Because this superlattice system contains two species of cations and anions, it is possible to prepare either InSb-like or GaAs-like interfaces. As such, the system presents a unique opportunity to examine interfacial properties.We used molecular beam epitaxy (MBE) to prepare an extensive set of GaSb/InAs superlattices grown on an GaSb buffer, which, in turn had been grown on a (100) GaAs substrate. Through appropriate shutter sequences, the interfaces were directed to assume either an InSb-like or GaAs-like character. These superlattices were then studied with a variety of ex-situ probes such as x-ray diffraction and Raman spectroscopy. These probes confirmed that, indeed, predominantly InSb-like and GaAs-like interfaces had been achieved.

scholarly journals Properties of Faint X-ray Activity of XTE J1908+094 in 2019

Galaxies ◽  
2021 ◽  
Vol 9 (2) ◽  
pp. 25
Author(s):  
Debjit Chatterjee ◽  
Arghajit Jana ◽  
Kaushik Chatterjee ◽  
Riya Bhowmick ◽  
Sujoy Kumar Nath ◽  
...  
Keyword(s):  
Black Hole ◽  
Temporal Analysis ◽  
Power Density Spectrum ◽  
Periodic Oscillations ◽  
Telescope Array ◽  
Density Spectrum ◽  
X Ray ◽  
Black Hole Candidate ◽  
Short Period ◽  
Spectral State

We study the properties of the faint X-ray activity of Galactic transient black hole candidate XTE J1908+094 during its 2019 outburst. Here, we report the results of detailed spectral and temporal analysis during this outburst using observations from Nuclear Spectroscopic Telescope Array (NuSTAR). We have not observed any quasi-periodic-oscillations (QPOs) in the power density spectrum (PDS). The spectral study suggests that the source remained in the softer (more precisely, in the soft–intermediate) spectral state during this short period of X-ray activity. We notice a faint but broad Fe Kα emission line at around 6.5 keV. We also estimate the probable mass of the black hole to be 6.5−0.7+0.5M⊙, with 90% confidence.

scholarly journals From Femtoseconds to Hours–Measuring Dynamics over 18 Orders of Magnitude with Coherent X-rays

2021 ◽  
Vol 11 (13) ◽  
pp. 6179
Author(s):  
Felix Lehmkühler ◽  
Wojciech Roseker ◽  
Gerhard Grübel
Keyword(s):  
Time Scales ◽  
Free Electron Laser ◽  
Photon Correlation Spectroscopy ◽  
Signal To Noise Ratio ◽  
Coherent Scattering ◽  
Correlation Spectroscopy ◽  
X Rays ◽  
Photon Correlation ◽  
X Ray ◽  
Scattering Technique

X-ray photon correlation spectroscopy (XPCS) enables the study of sample dynamics between micrometer and atomic length scales. As a coherent scattering technique, it benefits from the increased brilliance of the next-generation synchrotron radiation and Free-Electron Laser (FEL) sources. In this article, we will introduce the XPCS concepts and review the latest developments of XPCS with special attention on the extension of accessible time scales to sub-μs and the application of XPCS at FELs. Furthermore, we will discuss future opportunities of XPCS and the related technique X-ray speckle visibility spectroscopy (XSVS) at new X-ray sources. Due to its particular signal-to-noise ratio, the time scales accessible by XPCS scale with the square of the coherent flux, allowing to dramatically extend its applications. This will soon enable studies over more than 18 orders of magnitude in time by XPCS and XSVS.

scholarly journals Transient absorption spectroscopy using high harmonic generation: a review of ultrafast X-ray dynamics in molecules and solids

2019 ◽  
Vol 377 (2145) ◽  
pp. 20170463 ◽  
Author(s):  
Romain Geneaux ◽  
Hugo J. B. Marroux ◽  
Alexander Guggenmos ◽  
Daniel M. Neumark ◽  
Stephen R. Leone
Keyword(s):  
Time Scales ◽  
Harmonic Generation ◽  
Absorption Spectroscopy ◽  
Transient Absorption ◽  
High Harmonic ◽  
High Harmonic Generation ◽  
Transient Absorption Spectroscopy ◽  
Spectroscopic Techniques ◽  
X Rays ◽  
X Ray

Attosecond science opened the door to observing nuclear and electronic dynamics in real time and has begun to expand beyond its traditional grounds. Among several spectroscopic techniques, X-ray transient absorption spectroscopy has become key in understanding matter on ultrafast time scales. In this review, we illustrate the capabilities of this unique tool through a number of iconic experiments. We outline how coherent broadband X-ray radiation, emitted in high-harmonic generation, can be used to follow dynamics in increasingly complex systems. Experiments performed in both molecules and solids are discussed at length, on time scales ranging from attoseconds to picoseconds, and in perturbative or strong-field excitation regimes. This article is part of the theme issue ‘Measurement of ultrafast electronic and structural dynamics with X-rays’.

Combined HREELS, Raman and X-ray diffraction study of short-period GaAsAlAs superlattices

1996 ◽  
Vol 368 (1-3) ◽  
pp. 185-189 ◽  
Author(s):  
T Tsuruoka ◽  
Y Uehara ◽  
S Ushioda ◽  
T Kojima ◽  
Y Sugiyama
Keyword(s):  
Diffraction Study ◽  
X Ray Diffraction ◽  
X Ray ◽  
Short Period

scholarly journals Magnetic assessment and modelling of the Aramis undulator beamline

2018 ◽  
Vol 25 (3) ◽  
pp. 686-705 ◽  
Author(s):  
M. Calvi ◽  
C. Camenzuli ◽  
R. Ganter ◽  
N. Sammut ◽  
Th. Schmidt
Keyword(s):  
Magnetic Properties ◽  
Magnetic Measurement ◽  
Hall Probe ◽  
Measurement Equipment ◽  
Series Production ◽  
Close Collaboration ◽  
X Ray ◽  
Short Period ◽  
Reduction Methods ◽  
Paul Scherrer

Within the SwissFEL project at the Paul Scherrer Institute (PSI), the hard X-ray line (Aramis) has been equipped with short-period in-vacuum undulators, known as the U15 series. The undulator design has been developed within the institute itself, while the prototyping and the series production have been implemented through a close collaboration with a Swiss industrial partner, Max Daetwyler AG, and several subcontractors. The magnetic measurement system has been built at PSI, together with all the data analysis tools. The Hall probe has been designed for PSI by the Swiss company SENIS. In this paper the general concepts of both the mechanical and the magnetic properties of the U15 series of undulators are presented. A description of the magnetic measurement equipment is given and the results of the magnetic measurement campaign are reported. Lastly, the data reduction methods and the associated models are presented and their actual implementation in the control system is detailed.

Time-scales to reach chemical equilibrium in ices at snowline distance around compact objects: the influence of accretion mass in the central object

2021 ◽  
Vol 503 (2) ◽  
pp. 2973-2978
Author(s):  
G A Carvalho ◽  
S Pilling
Keyword(s):  
Time Scales ◽  
Chemical Equilibrium ◽  
Accretion Rate ◽  
Radiation Reaction ◽  
Compact Objects ◽  
Compact Stars ◽  
X Ray ◽  
Accretion Rates ◽  
Central Compact Objects ◽  
Astrophysical Ices

ABSTRACT In this work, we analyse soft X-ray emission due to mass accretion on to compact stars and its effects on the time-scale to reach chemical equilibrium of eventual surrounding astrophysical ices exposed to that radiation. Reaction time-scales due to soft X-ray in water-rich and pure ices of methanol, acetone, acetonitrile, formic acid, and acetic acid were determined. For accretion rates in the range $\dot{m}=10^{-12}\!-\!10^{-8}\,{\rm M}_\odot$ yr−1 and distances in the range 1–3 LY from the central compact objects, the time-scales lie in the range 10–108 yr, with shorter time-scales corresponding to higher accretion rates. Obtained time-scales for ices at snow-line distances can be small when compared to the lifetime (or age) of the compact stars, showing that chemical equilibrium could have been achieved. Time-scales for ices to reach chemical equilibrium depend on X-ray flux and, hence, on accretion rate, which indicates that systems with low accretion rates may not have reached chemical equilibrium.

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