Atmospheric Heating and Wind Acceleration in Cool Evolved Stars

Airapetian, Vladimir; Cuntz, M.

doi:10.1007/978-3-319-09198-3_5

Cited by 3 publications

(1 citation statement)

References 142 publications

(258 reference statements)

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“…If the same mechanisms are responsible for the heating in giant stars, then the expected X-ray flux would be ∼10 29 erg s −1 (Toriumi & Airapetian 2022), which is contradicted by the absence of coronal emission signatures in γ Cru and has 2 orders of magnitude greater X-ray flux than is observed from the corona in γ Dra. While nanoflares are likely the dominating mechanism for the coronal heating in the Sun, Alfvén wave heating is likely the dominant factor in giants (Airapetian et al 2010Airapetian & Cuntz 2015).…”

Section: Discussionmentioning

confidence: 99%

The Advanced Spectral Library: The Evolution of Chromospheric Wind Characteristics from Noncoronal to Hybrid Giant Stars*

Nielsen

Airapetian

Carpenter

et al. 2023

ApJ

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The Hubble Space Telescope (HST)/Space Telescope Imaging Spectrograph treasury program Advanced Spectral Library enables investigations of the characteristics and dynamics of the wind and chromosphere of cool stars using high-quality spectral data. This paper shows how the wind features change with spectral class when transferring across the Linsky–Haisch dividing line by comparing the noncoronal M3.5 giant γ Cru with the K5 hybrid γ Dra. We compare the presence of high-ionization diagnostics in the two objects in addition to the prominent wind spectrum in predominantly singly ionized species. We study the intrinsic strength and variation of the numerous Fe ii profiles observed in the near-ultraviolet HST spectrum that are sensitive to the wind opacity, turbulence, and flow velocity. The Fe ii relative strengths and wavelength shifts between the absorption and emission components reflect the acceleration of the wind from the base of the chromosphere. Furthermore, we have modeled the wind spectra using the SEI code to derive terminal velocities, wind acceleration, and mass-loss rates. Our results indicate that the chromosphere is denser when moving toward the hybrid objects. The derived average mass-loss rates in the two objects are similar but with a significantly greater terminal wind velocity and acceleration in the hybrid star. We present the analysis of the outflowing wind characteristics when transitioning from the cool noncoronal objects toward the warmer objects with chromospheric emission from a hotter environment.

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Section: Discussionmentioning

confidence: 99%

The Advanced Spectral Library: The Evolution of Chromospheric Wind Characteristics from Noncoronal to Hybrid Giant Stars*

Nielsen

Airapetian

Carpenter

et al. 2023

ApJ

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Impact of space weather on climate and habitability of terrestrial-type exoplanets

Airapetian

Barnes

Cohen

et al. 2019

International Journal of Astrobiology

187

141

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The search for life in the Universe is a fundamental problem of astrobiology and modern science. The current progress in the detection of terrestrial-type exoplanets has opened a new avenue in the characterization of exoplanetary atmospheres and in the search for biosignatures of life with the upcoming ground-based and space missions. To specify the conditions favourable for the origin, development and sustainment of life as we know it in other worlds, we need to understand the nature of global (astrospheric), and local (atmospheric and surface) environments of exoplanets in the habitable zones (HZs) around G-K-M dwarf stars including our young Sun. Global environment is formed by propagated disturbances from the planet-hosting stars in the form of stellar flares, coronal mass ejections, energetic particles and winds collectively known as astrospheric space weather. Its characterization will help in understanding how an exoplanetary ecosystem interacts with its host star, as well as in the specification of the physical, chemical and biochemical conditions that can create favourable and/or detrimental conditions for planetary climate and habitability along with evolution of planetary internal dynamics over geological timescales. A key linkage of (astro)physical, chemical and geological processes can only be understood in the framework of interdisciplinary studies with the incorporation of progress in heliophysics, astrophysics, planetary and Earth sciences. The assessment of the impacts of host stars on the climate and habitability of terrestrial (exo)planets will significantly expand the current definition of the HZ to the biogenic zone and provide new observational strategies for searching for signatures of life. The major goal of this paper is to describe and discuss the current status and recent progress in this interdisciplinary field in light of presentations and discussions during the NASA Nexus for Exoplanetary System Science funded workshop ‘Exoplanetary Space Weather, Climate and Habitability’ and to provide a new roadmap for the future development of the emerging field of exoplanetary science and astrobiology.

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Density asymmetry and wind velocities in the orbital plane of the symbiotic binary EG Andromedae

Shagatova¹,

Skopal²,

Kundra³

et al. 2023

A&A

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Context. Non-dusty late-type giants without a corona and large-scale pulsations represent objects that do not fulfil the conditions under which standard mass-loss mechanisms can be applied efficiently. Despite the progress during the past decades, the driving mechanism of their winds is still unknown. Aims. One of the crucial constraints of aspiring wind-driving theories can be provided by the measured velocity and density fields of outflowing matter. The main goal of this work is to match the radial velocities of absorbing matter with a depth in the red giant (RG) atmosphere in the S-type symbiotic star EG And. Methods. We measured fluxes and radial velocities of ten Fe I absorption lines from spectroscopic observations with a resolution of ≈30 000. At selected orbital phases, we modelled their broadened profiles, including all significant broadening mechanisms. Results. The selected Fe I absorption lines at 5151–6469 Å originate at a radial distance ≈1.03 RG radii from its centre. The corresponding radial velocity is typically ≈1 km s−1, which represents a few percent of the terminal velocity of the RG wind. The high scatter of the radial velocities of several km s−1 in the narrow layer of the stellar atmosphere points to the complex nature of the near-surface wind mass flow. The average rotational velocity of 11 km s−1 implies that the rotation of the donor star can contribute to observed focusing the wind towards the orbital plane. The orbital variability of the absorbed flux indicates the highest column densities of the wind in the area between the binary components, even though the absorbing neutral material is geometrically more extended from the opposite side of the giant. This wind density asymmetry in the orbital plane region can be ascribed to gravitational focusing by the white dwarf companion. Conclusions. Our results suggest that both gravitational and rotational focusing contribute to the observed enhancement of the RG wind towards the orbital plane, which makes mass transfer by the stellar wind highly efficient.

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Atmospheric Heating and Wind Acceleration in Cool Evolved Stars

Cited by 3 publications

References 142 publications

The Advanced Spectral Library: The Evolution of Chromospheric Wind Characteristics from Noncoronal to Hybrid Giant Stars*

The Advanced Spectral Library: The Evolution of Chromospheric Wind Characteristics from Noncoronal to Hybrid Giant Stars*

Impact of space weather on climate and habitability of terrestrial-type exoplanets

Density asymmetry and wind velocities in the orbital plane of the symbiotic binary EG Andromedae

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