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Sofia-exes observations of betelgeuse during the great dimming of 2019/2020

Harper, Graham M. ; Dewitt, Curtis N. ; Richter, Matthew J. ; Guinan, Edward F. ; Wasatonic, Richard ; Ryde, Nils LU orcid ; Montiel, Edward J. and Townsend, Amanda J. (2020) In Astrophysical Journal Letters 893(1).
Abstract

In 2019 October Betelgeuse began a decline in V-band brightness that went beyond the minimum expected from its quasi-periodic ∼420 day cycle, becoming the faintest in recorded photometric history. Observations obtained in 2019 December with Very Large Telescope/SPHERE have shown that the southern half of the star has become markedly fainter than in 2019 January, indicating that a major change has occurred in, or near, the photosphere. We present Stratospheric Observatory for Infrared Astronomy (SOFIA) Echelon Cross Echelle Spectrograph (EXES) high spectral-resolution observations of [Fe II] 25.99 μm and [S I] 25.25 μm emission lines from Betelgeuse obtained during the unprecedented 2020 February V-band brightness minimum to investigate... (More)

In 2019 October Betelgeuse began a decline in V-band brightness that went beyond the minimum expected from its quasi-periodic ∼420 day cycle, becoming the faintest in recorded photometric history. Observations obtained in 2019 December with Very Large Telescope/SPHERE have shown that the southern half of the star has become markedly fainter than in 2019 January, indicating that a major change has occurred in, or near, the photosphere. We present Stratospheric Observatory for Infrared Astronomy (SOFIA) Echelon Cross Echelle Spectrograph (EXES) high spectral-resolution observations of [Fe II] 25.99 μm and [S I] 25.25 μm emission lines from Betelgeuse obtained during the unprecedented 2020 February V-band brightness minimum to investigate potential changes in the circumstellar flow. These spectra are compared to observations obtained in 2015 and 2017 when the V magnitude was typical of brighter phases. We find only very small changes in the gas velocities reflected by either of the line profiles, no significant changes in the flux to continuum ratios, and hence no significant changes in the [Fe ii]/[S i] flux ratios. There is evidence that absorption features have appeared in the 2020 continuum. The Alfvén wave-crossing time from the upper photosphere is sufficiently long that one would not expect a change in the large-scale magnetic field to reach the circumstellar [Fe ii] and [S i] line-forming regions, 3 < R (R ∗) < 20. However, the light-crossing time is of order a few hours and a reduction in luminosity may reduce the dust-gas heating rate and [O i] 63.19 μm emission, which has contributions from R > 20R ∗, where significant circumstellar oxygen-rich dust is observed.

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author
; ; ; ; ; ; and
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Astrophysical Journal Letters
volume
893
issue
1
article number
L23
publisher
IOP Publishing
external identifiers
  • scopus:85085115949
ISSN
2041-8205
DOI
10.3847/2041-8213/ab84e6
language
English
LU publication?
yes
id
a6a3686b-e9b1-476d-94ff-f9655538c71d
date added to LUP
2020-06-24 12:39:17
date last changed
2024-03-20 11:29:52
@article{a6a3686b-e9b1-476d-94ff-f9655538c71d,
  abstract     = {{<p>In 2019 October Betelgeuse began a decline in V-band brightness that went beyond the minimum expected from its quasi-periodic ∼420 day cycle, becoming the faintest in recorded photometric history. Observations obtained in 2019 December with Very Large Telescope/SPHERE have shown that the southern half of the star has become markedly fainter than in 2019 January, indicating that a major change has occurred in, or near, the photosphere. We present Stratospheric Observatory for Infrared Astronomy (SOFIA) Echelon Cross Echelle Spectrograph (EXES) high spectral-resolution observations of [Fe II] 25.99 μm and [S I] 25.25 μm emission lines from Betelgeuse obtained during the unprecedented 2020 February V-band brightness minimum to investigate potential changes in the circumstellar flow. These spectra are compared to observations obtained in 2015 and 2017 when the V magnitude was typical of brighter phases. We find only very small changes in the gas velocities reflected by either of the line profiles, no significant changes in the flux to continuum ratios, and hence no significant changes in the [Fe ii]/[S i] flux ratios. There is evidence that absorption features have appeared in the 2020 continuum. The Alfvén wave-crossing time from the upper photosphere is sufficiently long that one would not expect a change in the large-scale magnetic field to reach the circumstellar [Fe ii] and [S i] line-forming regions, 3 &lt; R (R <sub>∗</sub>) &lt; 20. However, the light-crossing time is of order a few hours and a reduction in luminosity may reduce the dust-gas heating rate and [O i] 63.19 μm emission, which has contributions from R &gt; 20R <sub>∗</sub>, where significant circumstellar oxygen-rich dust is observed.</p>}},
  author       = {{Harper, Graham M. and Dewitt, Curtis N. and Richter, Matthew J. and Guinan, Edward F. and Wasatonic, Richard and Ryde, Nils and Montiel, Edward J. and Townsend, Amanda J.}},
  issn         = {{2041-8205}},
  language     = {{eng}},
  month        = {{04}},
  number       = {{1}},
  publisher    = {{IOP Publishing}},
  series       = {{Astrophysical Journal Letters}},
  title        = {{Sofia-exes observations of betelgeuse during the great dimming of 2019/2020}},
  url          = {{http://dx.doi.org/10.3847/2041-8213/ab84e6}},
  doi          = {{10.3847/2041-8213/ab84e6}},
  volume       = {{893}},
  year         = {{2020}},
}