The Relationship Between X‐Ray Radiance and Magnetic Flux

Pevtsov, Alexei A.; Fisher, G. H.; Acton, L. W.; Longcope, D. W.; Johns–Krull, Christopher M.; Kankelborg, C. C.; Metcalf, Thomas R.

doi:10.1086/378944

Cited by 264 publications

(369 citation statements)

References 24 publications

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“…In particular, the relationship between the coronal radiative flux density and the average surface magnetic flux density is nearly linear for solar active regions and for entire stars (e.g. Fisher et al 1998;Schrijver & Zwaan 2000) over 12 orders of magnitude in absolute magnetic flux (Pevtsov et al 2003). The X-ray emission from late-type stars in open clusters exhibits two kinds of dependences on stellar rotation (e.g.…”

Section: Introductionmentioning

confidence: 99%

X-ray emission regimes and rotation sequences in M 35

Gondoin

2013

A&A

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Context. Late-type stars in young open clusters show two kinds of dependence of their X-ray emission on rotation. They also tend to group into two main sub-populations that lie on narrow sequences in diagrams where their rotation periods are plotted against their (B − V) colour indices. A correlation between these two regimes of X-ray emission and the rotation sequences has been recently observed in the M 34 open cluster. Sun-like M 34 stars also show a drop of their X-ray to bolometric luminosity ratio by about one order of magnitude at a Rossby number of about 0.3. Aims. The present study looks for similar connections between X-ray activity and rotation in an other open cluster. The aim is to consolidate a model of X-ray activity evolution on the main sequence and to provide observational constraints on dynamo processes in the interiors of late-type stars. Methods. The paper compares XMM-Newton measurements of X-ray stellar emission in M 35 with X-ray luminosity distributions derived from rotation period measurements assuming either an X-ray regime transition at a critical Rossby number or a correlation between X-ray emission regimes and rotation sequences. Results. This second hypothesis could account for the low number of M 35 stars detected in X-rays. A model of X-ray activity evolution is proposed based on the correlation. One major output is that the transition from saturated to non-saturated X-ray emission occurs at Rossby numbers between about 0.13 and 0.4 for each star depending on its mass and initial period of rotation on the ZAMS. This prediction agrees with observations of stellar X-ray emission in M 34. It explains the large range of X-ray luminosities observed among Sun-like stars in young open clusters. Conclusions. I conclude that the correlation between X-ray emission regimes and rotation sequences could be a fundamental property of the early evolution of stellar magnetic activity on the main sequence. I argue that the angular momentum redistribution mechanism(s) responsible for the transition between rotation sequences could result in a changing mixture of dynamo processes occurring side by side, possibly including a turbulent dynamo at high rotation rate and an interface-type dynamo whose efficiency decreases progressively at later stage of stellar evolution when rotation dies away.

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Section: Introductionmentioning

confidence: 99%

X-ray emission regimes and rotation sequences in M 35

Gondoin

2013

A&A

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“…They argue that, as in the Sun, globally strong magnetic fields will violently reconnect, generating flares that lead to strong X-ray emission. Such a close coupling between stellar magnetic flux and X-ray luminosity has been demonstrated to extend over 12-13 orders of magnitude in L X (Pevtsov et al 2003). Soker & Zoabi find that for B Ã k 1 G on AGB stars, the expected X-ray luminosity is k10 4 times stronger than that of the Sun, if the reconnection rate per unit surface area is similar.…”

Section: Introductionmentioning

confidence: 89%

“…If N H k 10 22 cm À2 and AGB magnetic reconnection events yield circumstellar plasma conditions similar to those of the solar corona (T X $ 2 Â 10 6 K; e.g., Pevtsov et al 2003), then much of the resulting (soft) X-ray emission could be attenuated by the AGB envelopes and our nondetections would have less significance (Fig. 1).…”

Section: What Is T X For Tx Cam (And T Cas)?mentioning

confidence: 98%

“…1). However, while the correlation between magnetic flux and L X is quite robust (Pevtsov et al 2003), the relationship (if any) between stellar magnetic fields and the temperature of X-ray emission has yet to be established. For stars of spectral type F and later, it appears that X-ray emission softens monotonically with stellar age from pre-main-sequence (T Tauri) through main-sequence stages (Kastner et al 2003 and references therein).…”

Section: What Is T X For Tx Cam (And T Cas)?mentioning

confidence: 99%

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Constraining the X‐Ray Luminosities of Asymptotic Giant Branch Stars: TX Camelopardalis and T Cassiopeia

Kastner¹,

Soker²

2004

ApJ

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To probe the magnetic activity levels of asymptotic giant branch (AGB) stars, we used XMM-Newton to search for X-ray emission from two well-studied objects, TX Cam and T Cas. The former star displays polarized maser emission, indicating magnetic field strengths of B $ 5 G, and the latter is one of the nearest known AGB stars. Neither star was detected by XMM-Newton. We use the upper limits on EPIC (CCD detector) count rates to constrain the X-ray luminosities of these stars and derive L X < 10 31 ergs s À1 (<10 30 ergs s À1 ) for an assumed X-ray emission temperature T X ¼ 3Â10 6 K (10 7 K). These limits represent P10% (P1%) of the X-ray luminosity expected under models in which AGB magnetic fields are global and potentially play an important role in collimating and/or launching AGB winds. We suggest, instead, that the B field strengths inferred from maser observations are representative of localized magnetic clouds.

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“…Pevtsov et al [23] have shown that the average temperature of a star's corona is proportional to the strength of its magnetic field. This is clear from the Sun too, where the average coronal temperature is observed to be proportional to photospheric flux [24].…”

Section: Atmospheric Heating and Flaresmentioning

confidence: 99%

Astrophysical processes on the Sun

Parnell

2012

Phil. Trans. R. Soc. A.

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Over the past two decades, there have been a series of major solar space missions, namely Yohkoh, SOHO, TRACE, and in the past 5 years, STEREO, Hinode and SDO, studying various aspects of the Sun and providing images and spectroscopic data with amazing temporal, spatial and spectral resolution. Over the same period, the type and nature of numerical models in solar physics have been completely revolutionized as a result of widespread accessibility to parallel computers. These unprecedented advances on both observational and theoretical fronts have led to significant improvements in our understanding of many aspects of the Sun's behaviour and furthered our knowledge of plasma physics processes that govern solar and other astrophysical phenomena. In this Theme Issue, the current perspectives on the main astrophysical processes that shape our Sun are reviewed. In this Introduction, they are discussed briefly to help set the scene.

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The Relationship Between X‐Ray Radiance and Magnetic Flux

Cited by 264 publications

References 24 publications

X-ray emission regimes and rotation sequences in M 35

X-ray emission regimes and rotation sequences in M 35

Constraining the X‐Ray Luminosities of Asymptotic Giant Branch Stars: TX Camelopardalis and T Cassiopeia

Astrophysical processes on the Sun

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