ASKAP detection of periodic and elliptically polarized radio pulses from UV Ceti

ABSTRACT Active M dwarfs are known to produce bursty radio emission, and multiwavelength studies have shown that solar-like magnetic activity occurs in these stars. However, coherent bursts from active M dwarfs have often been difficult to interpret in the solar activity paradigm. We present Australian Square Array Pathfinder (ASKAP) observations of UV Ceti at a central frequency of 888 MHz. We detect several periodic, coherent pulses occurring over a time-scale consistent with the rotational period of UV Ceti. The properties of the pulsed emission show that they originate from the electron cyclotron maser instability, in a cavity at least 7 orders of magnitude less dense than the mean coronal density at the estimated source altitude. These results confirm that auroral activity can occur in active M dwarfs, suggesting that these stars mark the beginning of the transition from solar-like to auroral magnetospheric behaviour. These results demonstrate the capabilities of ASKAP for detecting polarized, coherent bursts from active stars and other systems.

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A theory of incoherent scattering of radio waves by a plasma

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1960.0212 ◽

1960 ◽

Vol 259 (1296) ◽

pp. 79-99 ◽

Cited By ~ 203

Keyword(s):

Cross Section ◽

Thermal Fluctuations ◽

Incoherent Scattering ◽

Doppler Broadening ◽

Radio Waves ◽

Central Frequency ◽

Resonance Effects ◽

Doppler Shifts ◽

The Mean ◽

Free Plasma

A theory is developed which describes the scattering of radio waves by the random thermal fluctuations of electron density in a collision-free plasma. The frequency spectrum, as well as the amplitude, of the scattered radiation is calculated. Particular attention is paid to the part of the spectrum which corresponds to small Doppler shifts, this being the region of greatest significance in connexion with the phenomenon of incoherent scattering from the ionosphere. The calculations are based on a generalized version of Nyquist’s noise theorem, and they lead to the following conclusions: (1) The mean scattering cross-section for the ionosphere is equal to that which would exist if each of the electrons scattered independently with a cross-section of one-half the classical Thomson cross-section. (2) The mean Doppler broadening of the scattered signal corresponds roughly to the speed of the ions rather than to that of the electrons. (3) The spectral shape of this signal is not Gaussian. There is a mild maximum in the spectrum away from the central frequency, as can be seen in figure 1. (4) Plasma resonance effects contribute only negligibly to the scattering for frequencies currently of interest.

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Solar activity and the mean global temperature

Environmental Research Letters ◽

10.1088/1748-9326/4/1/014006 ◽

2009 ◽

Vol 4 (1) ◽

pp. 014006 ◽

Cited By ~ 22

Author(s):

A D Erlykin ◽

T Sloan ◽

A W Wolfendale

Keyword(s):

Solar Activity ◽

Global Temperature ◽

The Mean

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Solar activity and its impact on the mid-latitude trough during geomagnetic storms

10.5194/egusphere-egu21-6457 ◽

2021 ◽

Author(s):

Dorota Przepiórka ◽

Barbara Matyjasiak ◽

Agata Chuchra ◽

Hanna Rothkaehl

Keyword(s):

Solar Activity ◽

Geomagnetic Activity ◽

Evolutionary History ◽

Geomagnetic Storms ◽

Magnetic Activity ◽

Topside Ionosphere ◽

Auroral Region ◽

Distinct Structure ◽

Highly Sensitive ◽

Rapid Changes

<p>Mid-latitude trough (MIT) is the distinct structure observed in Earth&#8217;s ionosphere at high latitudes especially at the nighttimes. The phenomenon is observed at both hemispheres. As it resides at the topside ionosphere in the sub-auroral region, its behaviour and properties are highly sensitive to the solar and geomagnetic activity. Generally as the geomagnetic activity is more pronounced the MIT is observed at lower latitudes, it also deepens and becomes much more distinct in comparison to the low magnetic activity periods. MIT responds as well to the rapid changes in geomagnetic conditions, as are the geomagnetic storms, mainly caused by the CMEs.&#160;</p><p>Based on the observations gathered by DEMETER data between 2005 and 2010 years&#160; we present a set of geomagnetic storm cases and how the MIT properties has been changing as the storm evolves. We also discuss how it corresponds to the current solar activity and their evolutionary history&#160; described by a set of different parameters.</p>

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Asteroseismology of the β Cephei Star 12 (DD) Lacertae

Symposium - International Astronomical Union ◽

10.1017/s0074180900238977 ◽

1998 ◽

Vol 185 ◽

pp. 379-382

Author(s):

W.A. Dziembowski ◽

M. Jerzykiewicz

Keyword(s):

Frequency Spectrum ◽

Recent Analysis ◽

Central Frequency ◽

The Mean ◽

The Asymmetry

The frequency spectrum in Fig. 1 shows that at least five pulsation modes are excited in DD Lac. Three frequencies, f1, f4, and f3, form an equidistant triplet. In addition to the value of the central frequency, f4, the triplet can be characterized by the mean separation, S = (f3 − f1)/2, and the asymmetry, Δf = f4 − (f1 + f3)/2. Taking the values of the frequencies from a recent analysis of all available data (Pigulski 1994), we get S = 0.15544 ± 0.00021 and Δf = −0.00014 ± 0.00029 d−1.

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The ionospheric heating beneath the magnetospheric cleft revisited

Annales Geophysicae ◽

10.5194/angeo-23-827-2005 ◽

2005 ◽

Vol 23 (3) ◽

pp. 827-830 ◽

Cited By ~ 4

Author(s):

G. W. Prölss

Keyword(s):

Magnetic Activity ◽

Topside Ionosphere ◽

Ionospheric Heating ◽

Superposed Epoch Analysis ◽

Theoretical Predictions ◽

Northern Winter ◽

The Mean ◽

Epoch Analysis ◽

Winter Hemisphere ◽

Prominent Peak

Abstract. A prominent peak in the electron temperature of the topside ionosphere is observed beneath the magnetospheric cleft. The present study uses DE-2 data obtained in the Northern Winter Hemisphere to investigate this phenomenon. First, the dependence of the location and magnitude of the temperature peak on the magnetic activity is determined. Next, using a superposed epoch analysis, the mean latitudinal profile of the temperature enhancement is derived. The results of the present study are compared primarily with those obtained by Titheridge (1976), but also with more recent observations and theoretical predictions.

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Model results for the ionospheric lower transition height over mid-latitude

Annales Geophysicae ◽

10.5194/angeo-22-2037-2004 ◽

2004 ◽

Vol 22 (6) ◽

pp. 2037-2045 ◽

Cited By ~ 20

Author(s):

J. Lei ◽

L. Liu ◽

W. Wan ◽

S.-R. Zhang

Keyword(s):

Solar Activity ◽

Theoretical Calculations ◽

Magnetic Activity ◽

Composition Analysis ◽

Time Asymmetry ◽

Quantitative Studies ◽

Semiannual Variation ◽

Lower Transition ◽

Ap Index ◽

Opposite Tendency

Abstract. Theoretical calculations of the ionospheric lower transition height (LTH), a level of equal O+ and molecular ion densities, were performed and compared with empirical models by Zhang et al. (1996). This paper represents a substantial extension of the prior work by including the AE-C data of ion composition analysis and by detailed quantitative studies of the LTH simulation, and by creating a new LTH empirical model based on our simulations. Results show that: (1) the calculated LTH, in general, is lowest near 11-13LT and reaches the diurnal maximum after midnight (about 01~02LT). The local time asymmetry becomes more evident in summer, when the time of minimum shifts to 16LT. (2) The simulated LTH presents a dominant, semiannual variation during nighttime, and a pronounced annual variation during daytime. (3) The simulated LTH increases with solar activity at night and decreases by day, while the standard IRI option has an opposite tendency at night in summer and equinox. Therefore, the day-night difference of simulated LTH significantly increases with solar activity. (4) Both daytime and nighttime LTHs, tend to increase with the increasing geomagnetic activity Ap index, with a mean slope about 0.1455km per Ap unit. (5) The diurnal variation of LTH is found to be more than 20 km, which is much larger than the seasonal variation under F107=100 and Ap=10. Thus, the diurnal and solar activity variations of LTH are more pronounced than its seasonal and magnetic activity variations.

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Magnetic activity in the HARPS M dwarf sample

Astronomy and Astrophysics ◽

10.1051/0004-6361/201527078 ◽

2017 ◽

Vol 600 ◽

pp. A13 ◽

Cited By ~ 59

Author(s):

N. Astudillo-Defru ◽

X. Delfosse ◽

X. Bonfils ◽

T. Forveille ◽

C. Lovis ◽

...

Keyword(s):

Monitoring Program ◽

Rotation Period ◽

Magnetic Activity ◽

Spectral Lines ◽

M Dwarfs ◽

Low Mass Stars ◽

The Galaxy ◽

Low Mass ◽

M Dwarf ◽

The Relationship

Context. Atmospheric magnetic fields in stars with convective envelopes heat stellar chromospheres, and thus increase the observed flux in the Ca ii H and K doublet. Starting with the historical Mount Wilson monitoring program, these two spectral lines have been widely used to trace stellar magnetic activity, and as a proxy for rotation period (Prot) and consequently for stellar age. Monitoring stellar activity has also become essential in filtering out false-positives due to magnetic activity in extra-solar planet surveys. The Ca ii emission is traditionally quantified through the R'HK-index, which compares the chromospheric flux in the doublet to the overall bolometric flux of the star. Much work has been done to characterize this index for FGK-dwarfs, but M dwarfs – the most numerous stars of the Galaxy – were left out of these analyses and no calibration of their Ca ii H and K emission to an R'HK exists to date. Aims. We set out to characterize the magnetic activity of the low- and very-low-mass stars by providing a calibration of the R'HK-index that extends to the realm of M dwarfs, and by evaluating the relationship between R'HK and the rotation period. Methods. We calibrated the bolometric and photospheric factors for M dwarfs to properly transform the S-index (which compares the flux in the Ca ii H and K lines to a close spectral continuum) into the R'HK. We monitored magnetic activity through the Ca ii H and K emission lines in the HARPS M dwarf sample. Results. The R'HK index, like the fractional X-ray luminosity LX/Lbol, shows a saturated correlation with rotation, with saturation setting in around a ten days rotation period. Above that period, slower rotators show weaker Ca ii activity, as expected. Under that period, the R'HK index saturates to approximately 10-4. Stellar mass modulates the Ca ii activity, with R'HK showing a constant basal activity above 0.6 M⊙ and then decreasing with mass between 0.6 M⊙ and the fully-convective limit of 0.35 M⊙. Short-term variability of the activity correlates with its mean level and stars with higher R'HK indexes show larger R'HK variability, as previously observed for earlier spectral types.

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Reflection of Solar Activity Dynamics in Radionuclide Data

Radiocarbon ◽

10.1017/s0033822200013631 ◽

1992 ◽

Vol 34 (2) ◽

pp. 207-212 ◽

Cited By ~ 5

Author(s):

A. V. Blinov ◽

M. N. Kremliovskij

Keyword(s):

Nonlinear Dynamics ◽

Solar Activity ◽

Numerical Methods ◽

Chaotic Behavior ◽

Magnetic Activity ◽

Data Sets ◽

Cosmogenic Nuclide ◽

Proxy Records ◽

Solar Magnetic Activity ◽

Activity Dynamics

Variability of solar magnetic activity manifested within sunspot cycles demonstrates features of chaotic behavior. We have analyzed cosmogenic nuclide proxy records for the presence of the solar activity signals. We have applied numerical methods of nonlinear dynamics to the data showing the contribution of the chaotic component. We have also formulated what kind of cosmogenic nuclide data sets are needed for investigations on solar activity.

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Persistent Active Longitudes in Sunspot Activity: Sun-as-a-Star Approach

Symposium - International Astronomical Union ◽

10.1017/s007418090018204x ◽

2004 ◽

Vol 219 ◽

pp. 128-132

Author(s):

S. V. Berdyugina ◽

I. G. Usoskin

Keyword(s):

Sunspot Group ◽

Active Regions ◽

Magnetic Activity ◽

Sunspot Activity ◽

Flip Flop ◽

The Past ◽

Highly Active ◽

Group Data ◽

Cool Stars ◽

The Mean

Using a new Sun-as-a-star approach we analyze sunspot group data for the past 120 years and reveal that sunspots are formed preferably in two persistent migrating active longitudes 180° apart. Their migration is determined by changes of the mean latitude of sunspots and the surface differential rotation. The two active regions periodically alternate being the dominant region with a period of about 3.7 years similar to the “flip-flop” phenomenon known in starspot activity. The fact that the Sun shows the same pattern of magnetic activity as highly active stars strengthens the solar paradigm for magnetic activity on cool stars.

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