X-Ray Observations of Characteristic Structures and Time Variations from the Solar Corona: Preliminary Results from SKYLAB

Vaiana, G. S.; Davis, John M.; Giacconi, R.; Krieger, A. S.; Silk, J. K.; Timothy, A. F.; Zombeck, Martin V.

doi:10.1086/181318

Cited by 153 publications

(67 citation statements)

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“…Since it turns out that the loop length are much smaller than the pressure scale height H, the assumption of constant pressure in the loops is justified. Characteristic loop size and temperature on V390 Aurigae are respectively 1.3 × 10 10 cm and 7.2 × 10 6 K. Solar corona observations by comparison show bright hot loops within active regions which reach maximum temperatures and electron densities above the neutral line of typically (3−4) × 10 6 K and 10 10 cm −3 (Vaiana et al 1973). In addition to these hot loops, on-disk images of the Sun show that neighboring active regions are often connected into complexes of activity by large looplike structures (van Speybroek et al 1970).…”

Section: Structure Of V390 Aurigae Coronamentioning

confidence: 90%

The corona of V390 Aurigae (HD 33798)

Gondoin

2003

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Abstract. V390 Aurigae (HD 33798) is a rapidly rotating, lithium rich, late-type giant whose distinctive characteristics include a high X-ray luminosity observed by the XMM-Newton space observatory. Series of lines of highly ionized Fe and several Lyman lines of hydrogen-like ions and triplet lines of helium-like ions are visible in the reflection grating spectra, most notably from O and Ne. X-ray emission from plasma at high temperature (T > 10 7 K) indicates intense flaring activity on this star. Analysis results suggest a scenario where the corona of V390 Aurigae is dominated by large magnetic structures similar in size to interconnecting loops between solar active regions but significantly hotter. The interaction of these structures could explain the permanent flaring activity on large scales that is responsible for heating plasma to high temperatures. The intense activity on V390 Aurigae is related to its evolutionary position at the bottom of the red giant branch. It is anticipated that the rotation of the star will spin-down in the future, thus decreasing the efficiency of its α − Ω dynamo with the suppressing of large scale magnetic structures in its corona.

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Section: Structure Of V390 Aurigae Coronamentioning

confidence: 90%

The corona of V390 Aurigae (HD 33798)

Gondoin

2003

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“…Coronal loops were observed for the first time in the 70s with the Skylab mission (Vaiana et al 1973). The images revealed that the corona is highly stratified in density and magnetic field, and coronal plasma is concentrated mostly in loops.…”

Section: Introductionmentioning

confidence: 98%

Torsional Alfvén waves in small scale current threads of the solar corona

Copil

Voitenko

Goossens

2010

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Context. The magnetic field structuring in the solar corona occurs on large scales (loops and funnels), but also on small scales. For instance, coronal loops are made up of thin strands with different densities and magnetic fields across the loop. Aims. We consider a thin current thread and model it as a magnetic flux tube with twisted magnetic field inside the tube and straight field outside. We prove the existence of trapped Alfvén modes in twisted magnetic flux tubes (current threads) and we calculate the wave profile in the radial direction for two different magnetic twist models. Methods. We used the Hall MHD equations that we linearized in order to derive and solve the eigenmode equation for the torsional Alfvén waves. Results. We show that the trapped Alfvén eigenmodes do exist and are localized in thin current threads where the magnetic field is twisted. The wave spectrum is discrete in phase velocity, and the number of modes is finite and depends on the amount of the magnetic field twist. The phase speeds of the modes are between the minimum of the Alfvén speed in the interior and the exterior Alfén speed. Conclusions. Torsional Alfvén waves can be guided by thin twisted magnetic flux-tubes (current threads) in the solar corona. We suggest that the current threads guiding torsional Alfvén waves, are subject to enhanced plasma heating due to wave dissipation.

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“…This simple analysis suggests the possible existence of two loop systems in the coronae of UZ Librae reminiscent of solar coronal loops. Indeed, solar corona observations show bright hot loops within active regions which reach maximum temperatures and electron densities above the neutral line of typically 3-4 × 10 6 K and 10 10 cm −3 (Vaiana et al 1973). In addition to these hot loops, on-disk images of the Sun show that neighboring active regions are often connected into complexes of activity by large loop-like structures (van Speybroek et al 1970).…”

Section: Discussionmentioning

confidence: 99%

X-ray spectroscopy of UZ Librae

Gondoin

2003

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Abstract. UZ Librae is the giant primary of a close binary system with extremely fast rotation and revolution. Its distinctive characteristics include an optical light curve with a large amplitude and a high X-ray luminosity. UZ Librae was observed twice at five months interval in August 2000 and January 2001 by the XMM-Newton space observatory. Serie of lines of highly ionized Fe and several lines of the Ly and He series are visible in the reflection grating spectra, most notably from C, O and Ne. The corresponding ions are associated with plasma components with temperature in the range 3-8 MK. Bremstrahlung emission from plasma at high temperature (T > 3 × 10 7 K) indicates an intense flaring activity on UZ Librae. This is also supported by a Ne abundance enhancement relative to oxygen reminiscent of abundance anomalies observed during stellar and solar flares. In contrast to oxygen and neon, the abundance of Fe in the corona of UZ Librae is determined to be a tenth of the solar photospheric value. We conjecture that the large fluid kinetic helicity induced by the rapid rotation of the star currently generates magnetic fields with two characteristic scales comparable with compact loops within solar active regions and with larger cooler loops interconnecting solar active regions. The X-ray emission of UZ Librae would be strongly enhanced not only due to the occurrence of these magnetic structures, but mainly due to their large surface coverage and to their permanent interactions responsible for heating UZ Librae plasma to high temperatures. A rotational modulation effect could have contributed to the luminosity variation between the two XMM-Newton observations since a large fraction of the X-ray emitting material might be located above large photospheric spots detected on Doppler images of the star.

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X-Ray Observations of Characteristic Structures and Time Variations from the Solar Corona: Preliminary Results from SKYLAB

Cited by 153 publications

References 0 publications

The corona of V390 Aurigae (HD 33798)

The corona of V390 Aurigae (HD 33798)

Torsional Alfvén waves in small scale current threads of the solar corona

X-ray spectroscopy of UZ Librae

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