J/A+A/650/L17 HERMES spectra of Betelgeuse (Kravchenko+, 2021)
Atmosphere of Betelgeuse before and during the Great Dimming event revealed
by tomography.
Kravchenko K., Jorissen A., Van Eck S., Merle T., Chiavassa A.,
Paladini C., Freytag B., Plez B., Montarges M., Van Winckel H.
<Astron. Astrophys. 650, L17 (2021)>
=2021A&A...650L..17K 2021A&A...650L..17K (SIMBAD/NED BibCode)
ADC_Keywords: Stars, late-type ; Spectroscopy
Keywords: stars: atmospheres - supergiants - line: formation -
techniques: spectroscopic - radiative transfer
Abstract:
Despite being the best studied red supergiant star in our Galaxy, the
physics behind the photometric variability and mass loss of Betelgeuse
is poorly understood. Moreover, recently the star has experienced an
unusual fading with its visual magnitude reaching a historical
minimum. The nature of this event was investigated by several studies
where mechanisms like episodic mass loss and presence of dark spots in
the photosphere were invoked.
We aim at relating the atmospheric dynamics of Betelgeuse to its
photometric variability, with the main focus on the dimming event. We
use the tomographic method which allows us to probe different depths
in the stellar atmosphere and to recover the corresponding
disk-averaged velocity field. The method is applied to a series of
high-resolution HERMES observations of Betelgeuse. Variations in the
velocity field are then compared with photometric and spectroscopic
variations.
The tomographic method reveals that the succession of two shocks along
our line-of-sight (in February 2018 and January 2019), the second one
amplifying the effect of the first one, combined with underlying
convection or/and outward motion present at this phase of the 400 d
pulsation cycle, produced a rapid expansion of a portion of the
atmosphere of Betelgeuse and an outflow between October 2019 and
February 2020. This resulted in a sudden increase of molecular opacity
in the cooler upper atmosphere of Betelgeuse and, thus, in the
observed unusual decrease of the star's brightness.
Description:
The observations of Betelgeuse were performed with the high-resolution
fibre-fed cross-dispersed echelle spectrograph HERMES mounted on the
1.2m Mercator telescope at the Roque de Los Muchachos Observatory, La
Palma (Spain). The spectral resolution of HERMES is R=86000, and the
wavelength coverage is from 3800 to 9000Å. The spectra were
obtained between November 2015 and September 2020.
Objects:
------------------------------------------------
RA (2000) DE Designation(s)
------------------------------------------------
05 55 10.31 +07 24 25.4 alpha Ori = HR 2061
------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
data-obs.dat 149 37 Information on HERMES spectra
sp/* . 37 Individual spectra
--------------------------------------------------------------------------------
Byte-by-byte Description of file: data-obs.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 15 F15.7 d Obs.date Julian date of the observations
17- 24 I8 --- Name Unique HERMES spectrum number
26- 40 A15 --- FileName Name of spectrum file in subdirectory sp
42-149 A108 --- Com Comments
--------------------------------------------------------------------------------
Byte-by-byte Description of file: sp/*
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 14 E14.9 0.1nm lambda Wavelength
19- 36 E18.9 --- Flux ?=- Flux
--------------------------------------------------------------------------------
Acknowledgements:
This work is based on observations obtained with the HERMES
spectrograph, which is supported by the Fund for Scientific Research
of Flanders (FWO), Belgium, the Research Council of K.U. Leuven,
Belgium, the Fonds de la Recherche Scientifique (F.R.S.-FNRS),
Belgium, the Royal Observatory of Belgium, the Observatoire de
Geneve, Switzerland and the Thueringer Landessternwarte Tautenburg,
Germany.
From Kateryna Kravchenko, kkravchenko(at)mpe.mpg.de
(End) Patricia Vannier [CDS] 02-Feb-2021