scholarly journals Stellar activity and coronal heating: an overview of recent results

2015 ◽  
Vol 373 (2042) ◽  
pp. 20140259 ◽  
Author(s):  
Paola Testa ◽  
Steven H. Saar ◽  
Jeremy J. Drake
Keyword(s):  
Magnetic Activity ◽  
Coronal Heating ◽  
Complementary Information ◽  
Stellar Activity ◽  
X Ray ◽  
Solar Observations ◽  
Term Evolution ◽  
Wide Range ◽  
Stellar Magnetic Fields

Observations of the coronae of the Sun and of solar-like stars provide complementary information to advance our understanding of stellar magnetic activity, and of the processes leading to the heating of their outer atmospheres. While solar observations allow us to study the corona at high spatial and temporal resolution, the study of stellar coronae allows us to probe stellar activity over a wide range of ages and stellar parameters. Stellar studies therefore provide us with additional tools for understanding coronal heating processes, as well as the long-term evolution of solar X-ray activity. We discuss how recent studies of stellar magnetic fields and coronae contribute to our understanding of the phenomenon of activity and coronal heating in late-type stars.

scholarly journals Swift/XRT, Chandra, and XMM–Newton observations of IGR J17091–3624 as it returns into quiescence

2020 ◽  
Vol 497 (1) ◽  
pp. 1115-1126
Author(s):  
M Pereyra ◽  
D Altamirano ◽  
J M C Court ◽  
N Degenaar ◽  
R Wijnands ◽  
...  
Keyword(s):  
Black Hole ◽  
Neutron Star ◽  
Time Scales ◽  
Strong Evidence ◽  
Spectral Properties ◽  
X Ray ◽  
Term Evolution ◽  
Wide Range ◽  
Low Mass

ABSTRACT IGR J17091–3624 is a low-mass X-ray binary (LMXB), which received wide attention from the community thanks to its similarities with the bright black hole system GRS 1915+105. Both systems exhibit a wide range of highly structured X-ray variability during outburst, with time-scales from few seconds to tens of minutes, which make them unique in the study of mass accretion in LMXBs. In this work, we present a general overview into the long-term evolution of IGR J17091–3624, using Swift/XRT observations from the onset of the 2011–2013 outburst in 2011 February till the end of the last bright outburst in 2016 November. We found four re-flares during the decay of the 2011 outburst, but no similar re-flares appear to be present in the latter one. We studied, in detail, the period with the lowest flux observed in the last 10 yr, just at the tail end of the 2011–2013 outburst, using Chandra and XMM-Newton observations. We observed changes in flux as high as a factor of 10 during this period of relative quiescence, without strong evidence of softening in the spectra. This result suggests that the source has not been observed at its true quiescence so far. By comparing the spectral properties at low luminosities of IGR J17091–3624 and those observed for a well-studied population of LMXBs, we concluded that IGR J17091–3624 is most likely to host a black hole as a compact companion rather than a neutron star.

scholarly journals Stellar X-Ray Emission as an Indicator of Stellar Magnetic Activity

1983 ◽  
Vol 102 ◽  
pp. 165-186 ◽  
Author(s):  
G. S. Vaiana
Keyword(s):  
Dynamic Range ◽  
Magnetic Activity ◽  
Coronal Emission ◽  
X Ray ◽  
Surface Magnetic Field ◽  
Solar Observations ◽  
Wide Range ◽  
Field Activity ◽  
The Mean ◽  
Stellar Magnetic Activity

An overview of recent Einstein Observatory observations and theoretical modeling of stellar x-ray emission is presented, with particular emphasis upon the role such studies can play furthering our understanding of stellar magnetic activity. We argue that solar observations can be used to show that coronal emission is morphologically related to surface magnetic field activity; to establish a quantitative link between the observed soft x-ray flux and the mean surface (photospheric) magnetic flux; and, in sum, to demonstrate that soft x-ray emission is a sensitive diagnostic for the presence of surface magnetic fields, uncomplicated by radiative transfer effects and the resulting coupling to the underlying atmosphere (which may introduce unwanted correlations with spectral type and luminosity class). Recent analyses of stellar x-ray observations from the Einstein Observatory have focused on the interpretation of stellar coronal emission and possibly-related surface magnetic activity within the framework of our understanding of solar activity; including “loop” models of stellar coronae, observations of coronal emission variability on a wide range of time scales (which provide information on the morphology of the emitting plasma), and observations and modeling of low-resolution spectroscopic x-ray observations (which test the applicability of solar modeling). These recent results, which I review, all reenforce the argument that stellar coronal emission constitutes an excellent probe for studying stellar magnetic activity over a wide dynamic range, one which may prove to be uniquely suited to studying such activity in distant (and hence faint) sources.

scholarly journals How the planetary research helps to the stellar dynamo understanding

2012 ◽  
Vol 8 (S294) ◽  
pp. 471-475
Author(s):  
I. Boisse ◽  
M. Oshagh ◽  
C. Lovis ◽  
N. C. Santos ◽  
X. Dumusque ◽  
...  
Keyword(s):  
Planetary System ◽  
Magnetic Activity ◽  
Doppler Imaging ◽  
Habitable Zone ◽  
Stellar Activity ◽  
Term Variation ◽  
Solar Type ◽  
Low Mass ◽  
Stellar Dynamo

AbstractMost of the exoplanet science is dependent on the stellar knowledge. One of them that has to be understood is the magnetic activity when we search for planets with radial velocity or photometry measurements. The main shape of stellar activity and spots properties have to be understood, for example, to choose the best targets to search for low-mass planets in the habitable zone or to derive the accurate parameters of a planetary system. With that aim, we show in this presentation how these studies lead to give clues on spots latitudes and on the long term variation of stellar activity. The properties of magnetic activity on the low rotators solar-type stars are not easily reachable by other techniques (spectropolarimetry or Doppler imaging) and these studies should be used to constrain theories of stellar dynamo.

scholarly journals Long-term stellar variability

2009 ◽  
Vol 5 (S264) ◽  
pp. 136-145 ◽  
Author(s):  
Isabella Pagano
Keyword(s):  
Magnetic Loop ◽  
Magnetic Activity ◽  
Electromagnetic Spectrum ◽  
X Ray ◽  
Cool Star ◽  
Optical Region ◽  
Balmer Lines ◽  
Sun Spots

AbstractStars with significant subsurface convection zones develop magnetic loop structures that, arising from the surface upward to the external atmospheres, cause flux variability detectable throughout the whole electromagnetic spectrum. In fact, diagnostics of magnetic activity are in radio wavelengths, where gyrosincrotron radiation arises from the quiescent and flaring corona; in the optical region, where important signatures are the Balmer lines, the Ca ii IRT and H&K lines; in the UV and X ray domains, the latter mainly due to coronal thermal plasma. The zoo of different magnetic features observed for the Sun – spots, faculae, flares, CMEs – are characterized by different temporal evolution and energetics, both in quantity and quality. As a consequence, the time scale of variability, the amount of involved energy and the quality of the involved photons are used as fingerprints in interpreting the observed stellar variability in the framework of the solar-stellar analogy. Here I review main results from long-term multiwavelength observations of cool star atmospheres, with emphasis to similarities and differences with the solar case.

scholarly journals Accretion and outflow in V404 Cyg

2019 ◽  
Vol 488 (1) ◽  
pp. 1356-1365 ◽  
Author(s):  
J Casares ◽  
T Muñoz-Darias ◽  
D Mata Sánchez ◽  
P A Charles ◽  
M A P Torres ◽  
...  
Keyword(s):  
Mass Transfer ◽  
Black Hole ◽  
Radiation Pressure ◽  
Decay Time ◽  
Total Mass ◽  
Key Factors ◽  
X Ray ◽  
Term Evolution ◽  
Inner Parts

ABSTRACT We study the optical evolution of the 2015 outburst in V404 Cyg, with emphasis on the peculiar nebular phase and subsequent decay to quiescence. From the decay time-scale of the Balmer emission associated with the nebula, we measure an outflow mass Mwind ≃ 4 × 10−6 M⊙. Remarkably, this is ∼100 times larger than the accreted mass and ∼10 per cent of the total mass stored in the disc. The wind efficiency must therefore be significantly larger than previous estimates for black hole transients, suggesting that radiation pressure (in addition to other mechanisms such as Compton-heating) plays a key role in V404 Cyg. In addition, we compare the evolution of the 2015 and 1989 outbursts and find not only clear similarities (namely a large luminosity drop ∼10 d after the X-ray trigger, followed by a brief nebular phase) but also remarkable differences in decay time-scales and long-term evolution of the H α profile. In particular, we see evidence for a rapid disc contraction in 2015, consistent with a burst of mass transfer. This could be driven by the response of the companion to hard X-ray illumination, most notably during the last gigantic (super-Eddington) flare on 2015 June 25. We argue that irradiation and consequential disc wind are key factors to understand the different outburst histories in 1989 and 2015. In the latter case, radiation pressure may be responsible for the abrupt end of the outburst through depleting inner parts of the disc, thus quenching accretion and X-ray irradiation. We also present a refined orbital period and updated ephemeris.

Investigation of the coronal heating through phase relation of solar activity indexes

2020 ◽  
Vol 37 ◽  
Author(s):  
K. J. Li ◽  
J. C. Xu ◽  
Z. Q. Yin ◽  
J. L. Xie ◽  
W. Feng
Keyword(s):  
Solar Wind ◽  
Solar Activity ◽  
Phase Relation ◽  
Large Scale ◽  
Solar Rotation ◽  
Rotation Period ◽  
Magnetic Activity ◽  
Coronal Heating ◽  
Small Scale

Abstract The coronal heating problem is a long-standing perplexing issue. In this study, 13 solar activity indexes are used to investigate their phase relation with the sunspot number (SSN). Only three of them are found to statistically significantly lag the SSN (large-scale magnetic activity) by about one solar rotation period; the three indexes are total solar irradiance (TSI), the modified coronal index, and the solar wind velocity; the former two indexes may represent the long-term variation of energy quantity of the heated photosphere and corona, respectively. The Mount Wilson Sunspot Index (MWSI) and the Magnetic Plage Strength Index (MPSI), which reflect the large- and small-scale magnetic field activities, respectively, are also utilised to investigate their phase relations with the three indexes. The three indexes are found to be much more intimately related to MPSI than to MWSI, and MWSI statistically significantly leads TSI by about one rotation period. The heated corona is found to pulse perfectly in step with the small-scale magnetic activity rather than the large-scale magnetic activity; furthermore, combined with observations, our statistical evidence should thus attribute coronal heating firmly to small-scale magnetic activity phenomena, such as spicules, micro-flares, nano-flares, and others. The photosphere and the corona are synchronously heated, which should seemingly prefer magnetic reconnection heating to wave heating. In the long term, such a coronal heating way is inferred effective. Statistically, it is also small-scale magnetic activity phenomena that produce TSI enhancement. Coronal heating and solar wind acceleration are found to be synchronous, as standard models require.

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