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Pöllmann, Lorenz

doi:10.1007/978-3-658-32209-0

Cited by 5 publications

(7 citation statements)

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“…3. This high-emission event culminated in December 2020 -January 2021 as independently reported by Pollmann (2021). Between 1973 varied between −20 Å and −50 Å with irregular cycles on timescales of about 10 years (Miroshnichenko et al 2002).…”

Section: Emission Line Variabilitysupporting

confidence: 63%

“…These lines are most likely formed in the inner parts of the disc (Stee et al 1998), and the relative impact of a change in disc radius on the EW will thus be more modest compared to Hα, which forms over a much wider region. Moreover, for the He  λ 6678 line, we observe a rather large dispersion of the EW data, due to fluctuations occurring on short timescales (see also Pollmann 2021). These rapid variations might result from nonradial pulsations and/or migrating sub-features that were previously observed in high-cadence time series of this line (Smith 1995).…”

Section: Emission Line Variabilitysupporting

confidence: 62%

“…These rapid variations might result from nonradial pulsations and/or migrating sub-features that were previously observed in high-cadence time series of this line (Smith 1995). Alternatively, they could reflect ongoing mass injection from the star into the disc, which would mostly affect the conditions in the innermost part of the disc where the He  λ 6678 line is formed (Pollmann 2021). Yet, even in those lines, we can find a clear signature of a change in the circumstellar envelope of γ Cas during the high-emission event.…”

Section: Emission Line Variabilitymentioning

confidence: 66%

“…Smoothed particle hydrodynamics simulations of Be HMXBs (Martin et al 2014;Martin & Franchini 2019, 2021 and equal-mass Be + B binaries (Suffak et al 2022) indicate that Be discs that are inclined with respect to the orbital plane may get tilted away from the equatorial plane, precess about the orbital axis, and undergo Kozai-Lidov oscillations. These dynamical interactions with the companion act on timescales that are an order of magnitude longer than the orbital period.…”

Section: Doppler Tomographymentioning

confidence: 99%

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The X-ray Emission ofγCassiopeiae During the 2020–2021 disc eruption

Rauw

Nazé

Motch

et al. 2022

A&A

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Context. γ Cas is known for its unusually hard and intense X-ray emission. This emission could trace accretion by a compact companion, wind interaction with a hot sub-dwarf companion, or magnetic interaction between the star and its Be decretion disc. Aims. These various scenarios should lead to diverse dependences of the hard X-ray emission on disc density. To test these scenarios, we collected X-ray observations of γ Cas during an episode of enhanced disc activity that took place around January 2021. Methods. We investigate the variations in the disc properties using time series of dedicated optical spectroscopy and existing broadband photometry. Equivalent widths and peak velocity separations are measured for a number of prominent emission lines. Epochdependent Doppler maps of the Hα, Hβ, and He  λ 5876 emission lines are built to characterise the emission regions in velocity space. We analyse four XMM-Newton observations obtained between January 2021 and January 2022 at key phases of the episode of enhanced disc activity. Archival XMM-Newton, Chandra, MAXI, and RXTE-ASM data are also used to study the long-term correlation between optical and X-ray emission. Results. Optical spectroscopy unveils a clear increase in the radial extent of the emission regions during the episode of enhanced disc activity, whilst no increase in the V-band flux is recorded. Our Doppler maps do not reveal any stable feature in the disc resulting from the putative action of the companion on the outer parts of the Be disc. Whilst the hard X-ray emission is found to display the usual level and type of variability, no specific increase in the hard emission is observed in relation to the enhanced disc activity. However, at two occasions, including at the maximum disc activity, the soft X-ray emission of γ Cas is strongly attenuated, suggesting more efficient obscuration by material from a large flaring Be disc. In addition, there is a strong correlation between the long-term variations in the X-ray flux and the optical variations in the V-band photometry. Conclusions. The observed behaviour of γ Cas suggests no direct link between the properties of the outer regions of the Be disc and the hard X-ray emission, but it favours a link between the level of X-ray emission and the properties of the inner part of the Be disc. These results thus disfavour an accretion or colliding wind scenario.

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Section: Emission Line Variabilitysupporting

confidence: 63%

Section: Emission Line Variabilitysupporting

confidence: 62%

Section: Emission Line Variabilitymentioning

confidence: 66%

Section: Doppler Tomographymentioning

confidence: 99%

See 2 more Smart Citations

The X-ray Emission ofγCassiopeiae During the 2020–2021 disc eruption

Rauw

Nazé

Motch

et al. 2022

A&A

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“…Despite these trends, there is considerable diversity in disk strength and variability among early-type Be stars. For example, the disk of γ Cas (B0.5Ve) has been built up at a relatively steady rate over a few decades and as of 2021 is relatively massive (Pollmann 2021). On the other hand, HD 49330 has the same spectral type as γ Cas but is highly variable as the stellar mass ejection turns on and off over months/years (Huat et al 2009).…”

Section: The Be and Bn Populations And Sample Selectionmentioning

confidence: 99%

Ultraviolet Spectropolarimetry with Polstar: on the origin of rapidly rotating B stars

Jones¹,

Labadie-Bartz²,

Nazé³

et al. 2021

Preprint

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The proposed MIDEX mission, Polstar, will provide high resolution UV spectroscopy and spectropolarimetry and offers a unique opportunity to study massive stars in this wavelength range with unprecedented detail. We demonstrate that these observations will provide critical new knowledge of several types of massive stars (specifically the B-emission stars and the Bn stars). We will determine accurate stellar parameters including their rotation rates and variation of surface temperature associated with stellar oblateness. Our work will allow us to detect binary companions and determine binary orbital properties. Binary population synthesis predictions will allow us to determine the fraction of these stars that are spun up due to binary interaction compared to single star evolution. These rapidly rotating stars have the potential to probe mass loss and the mixing of chemical elements which affects their evolution and ultimately the evolution of their surroundings.

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Bist du allein? Vereinzelung als Herausforderung und Chance für die Vermarktung von Kunst und Kultur

Kastner

2022

Neue Wege Für Die Kultur?

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Kulturmarketing

Abstract: Die Deutsche Nationalbibliothek verzeichnet diese Publikation in der Deutschen Nationalbibliografie; detaillierte bibliografische Daten sind im Internet über http://dnb.d-nb.de abrufbar.

Cited by 5 publications

References 0 publications

The X-ray Emission ofγCassiopeiae During the 2020–2021 disc eruption

The X-ray Emission ofγCassiopeiae During the 2020–2021 disc eruption

Ultraviolet Spectropolarimetry with Polstar: on the origin of rapidly rotating B stars

Bist du allein? Vereinzelung als Herausforderung und Chance für die Vermarktung von Kunst und Kultur

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