X-Ray Emission of Massive Stars and Their Winds

Rauw, Grégor

doi:10.1007/978-981-16-4544-0_79-1

Cited by 2 publications

(1 citation statement)

References 170 publications

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“…The second big difference between γ Cas and 59 Cyg only emerges in the X-ray domain. γ Cas is the prototype of a small (O(1%)) but still growing fraction of Be stars emitting very hard and highly variable thermal X-rays at a total flux level intermediate between Be-XRBs and the winds from highly evolved early-type stars (for a recent review see Rauw 2022). In 59 Cyg, X-rays have not been detected.…”

Section: Overviews Of γ Cas and 59 Cygmentioning

confidence: 99%

The historical active episodes of the disks around γ Cassiopeiae (B0.5 IVe) and 59 Cygni (B1 IVe) revisited

Baade,

Labadie-Bartz,

Rivinius

et al. 2023

A&A

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The observations of all known major activity phases of the disks around the classical Be stars γ Cas and 59 Cyg with low-mass companions are comprehensively reviewed and purely qualitatively evaluated again, though taking advantage of new insights gained over the past 25 yr into the physics of Be disks. Both stars have exhibited activity cycles in the violet-to-red (V/R) flux ratio of emission lines with two peaks. This activity is indistinguishable from those of the vast majority of Be stars and so probably were caused by one-armed (m = 1) disk oscillations. The anomalous high-activity phases from 1932 to 1942 in γ Cas and between 1972 and 1976 in 59 Cyg were distinguished from m = 1 density waves by large variations in the separations of pairs of emission peaks. In two consecutive cycles, shell phases during which the emission peaks were maximally separated alternated with single (blended) emission peaks. The amplitude in peak separation of more than a factor of two implies a high-amplitude variation in the disk aspect angle. When the peaks were blended and the disk was viewed closest to face-on, local maxima in visual brightness probably occurred in γ Cas, and the visibility of the stellar absorption lines was reduced, as is expected from increased free-bound emission into the line of sight (there is no time-resolved photometry for 59 Cyg from the event in the 1970s). In y Cas, the pre-event V/R variability (pre-event observations of 59 Cyg do not exist) was practically identical to m = 1 variability. In spite of the subsequent rapid rise in amplitude (up to ~4), the V/R variations connected smoothly in phase but may require an explanation involving the 3D structure of the disk. The phasing of single-peak and shell stages relative to the V/R activity was the same in both cycles of γ Cas, whereas this is not clear for 59 Cyg. During both high-activity cycles of γ Cas, but at different phases, transient additional pairs of emission lines appeared in γ Cas that were much sharper than the main ones and they also had different peak separations and V/R ratios. In the second instance, their velocities were up to ~+500 km s−1. The extremely rapid excitation of the activity phases and their short duration of only two cycles in both stars may indicate a resonant behavior of an unidentified nature. In both stars, the line emission was strongly developed at the onset of the high-activity phases but it basically disappeared at the end of them, and the disks may have been dynamically destroyed. The atypical disk variations were presumably triggered by enhanced interactions between a disk and companion star. In both systems, there seems to be less evidence for a mass-loss outburst than for a reduced mass-injection rate into the disk. The resulting lower viscous coupling between a disk and star would have facilitated the tilting of the disk.

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Section: Overviews Of γ Cas and 59 Cygmentioning

confidence: 99%

The historical active episodes of the disks around γ Cassiopeiae (B0.5 IVe) and 59 Cygni (B1 IVe) revisited

Baade,

Labadie-Bartz,

Rivinius

et al. 2023

A&A

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Discovery of extraordinary X-ray emission from magnetospheric interaction in the unique binary stellar system ϵ Lupi

Das

Petit

Naze

et al. 2023

Monthly Notices of the Royal Astronomical Society

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We report detailed X-ray observations of the unique binary system ε Lupi, the only known short-period binary consisting of two magnetic early-type stars. The components have comparably strong, but anti-aligned magnetic fields. The orbital and magnetic properties of the system imply that the magnetospheres overlap at all orbital phases, suggesting the possibility of variable inter-star magnetospheric interaction due to the non-negligible eccentricity of the orbit. To investigate this effect, we observed the X-ray emission from ε Lupiboth near and away from periastron passage, using the Neutron Star Interior Composition Explorer mission (NICER) X-ray Telescope. We find that the system produces excess X-ray emission at the periastron phase, suggesting the presence of variable inter-star magnetospheric interaction. We also discover that the enhancement at periastron is confined to a very narrow orbital phase range ($\approx 5~{{\%}}$ of the orbital period), but the X-ray properties close to periastron phase are similar to those observed away from periastron. From these observations, we infer that the underlying cause is magnetic reconnection heating the stellar wind plasma, rather than shocks produced by wind-wind collision. Finally, by comparing the behavior of ε Lupiwith that observed for cooler magnetic binary systems, we propose that elevated X-ray flux at periastron phase is likely a general characteristic of interacting magnetospheres irrespective of the spectral types of the constituent stars.

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X-Ray Emission of Massive Stars and Their Winds

Cited by 2 publications

References 170 publications

The historical active episodes of the disks around γ Cassiopeiae (B0.5 IVe) and 59 Cygni (B1 IVe) revisited

The historical active episodes of the disks around γ Cassiopeiae (B0.5 IVe) and 59 Cygni (B1 IVe) revisited

Discovery of extraordinary X-ray emission from magnetospheric interaction in the unique binary stellar system ϵ Lupi

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