28 research outputs found
Exploring the water and carbon monoxide shell around Betelgeuse with VLTI/AMBER
We present the results of the analysis of our recent interferometric
observations of Betelgeuse, using the AMBER instrument of the VLTI. Using the
medium spectral resolution mode () we detected the presence of the
water vapour and carbon monoxide (CO) molecules in the H and K bands. We also
derived the photospheric angular diameter in the continuum. By analysing the
depth of the molecular lines and the interferometric visibilities, we derived
the column densities of the molecules, as well as the temperature and the size
of the corresponding regions in the atmosphere of Betelgeuse (the MOLsphere)
using a single shell model around the photosphere. Our results confirm the
findings by Perrin \et al\ (\cite{Perrin2004}) and Ohnaka \et al\
(\cite{Ohnaka2011}) that the HO and CO molecules are distributed around
Betelgeuse in a MOLsphere extending to approximately 1.3 times the star's
photospheric radius.Comment: Betelgeuse Workshop, November 2012, Paris. To be published in the
European Astronomical Society Publications Series, 2013, Editors: Pierre
Kervella, Thibaut Le Bertre \& Guy Perri
The convection of close red supergiant stars observed with near-infrared interferometry
Our team has obtained observations of the photosphere of the two closest red
supergiant stars Betelgeuse ( Ori) and Antares ( Sco) using
near infrared interferometry. We have been monitoring the photosphere of
Betelgeuse with the VLTI/PIONIER instrument for three years. On Antares, we
obtained an unprecedented sampling of the visibility function. These data allow
us to probe the convective photosphere of massive evolved stars.Comment: 5 pages, 3 figures. Published in the proceedings of the Physics Of
Evolved Stars conference, dedicated to the memory of Olivier Chesneau (Nice,
France, 2015
Properties of the CO and HO MOLsphere of the red supergiant Betelgeuse from VLTI/AMBER observations
Context. Betelgeuse is the closest red supergiant (RSG); therefore, it is
well suited for studying the complex processes in its atmosphere that lead to
the chemical enrichment of the interstellar medium. Aims. We intend to
investigate the shape and composition of the close molecular layer (also known
as the MOLsphere) that surrounds the star. This analysis is part of a wider
program that aims at understanding the dynamics of the circumstellar envelope
of Betelgeuse. Methods. On January and February 2011, Betelgeuse was observed
using the Astronomical Multi-BEam combineR (AMBER) instrument of the Very Large
Telescope Interferometer (VLTI) in the H and K bands. Using the medium spectral
resolution of the instrument (R 1500), we were able to investigate the
carbon monoxide band heads and the water-vapor bands. We used two different
approaches to analyse our data: a model fit in both the continuum and
absorption lines and then a fit with a Radiative HydroDynamics (RHD)
simulation. Results. Using the continuum data, we derive a uniform disk
diameter of ~mas, a power law type limb-darkened disk diameter
of ~mas and a limb-darkening exponent of .
Within the absorption lines, using a single layer model, we obtain parameters
of the MOLsphere. Using a RHD simulation, we unveil the convection pattern in
the visibilities. Conclusions. We derived a new value of the angular diameter
of Betelgeuse in the K band continuum. Our observations in the absorption lines
are well reproduced by a molecular layer at 1.2 stellar radii containing both
CO and HO. The visibilities at higher spatial frequencies are matching a
convection pattern in a RHD simulation.Comment: 13 pages, 11 figures, accepted for publication in Astronomy &
Astrophysics; Language editin
An edge-on translucent dust disk around the nearest AGB star L2 Puppis - VLT/NACO spectro-imaging from 1.04 to 4.05 microns and VLTI interferometry
As the nearest known AGB star (d=64pc) and one of the brightest (mK-2), L2
Pup is a particularly interesting benchmark object to monitor the final stages
of stellar evolution. We report new lucky imaging observations of this star
with the VLT/NACO adaptive optics system in twelve narrow band filters covering
the 1.0-4.0 microns wavelength range. These diffraction limited images reveal
an extended circumstellar dust lane in front of the star, that exhibits a high
opacity in the J band and becomes translucent in the H and K bands. In the L
band, extended thermal emission from the dust is detected. We reproduce these
observations using Monte-Carlo radiative transfer modeling of a dust disk with
the RADMC-3D code. We also present new interferometric observations with the
VLTI/VINCI and MIDI instruments. We measure in the K band an upper limit to the
limb-darkened angular diameter of theta_LD = 17.9 +/- 1.6 mas, converting to a
maximum linear radius of R = 123 +/- 14 Rsun. Considering the geometry of the
extended K band emission in the NACO images, this upper limit is probably close
to the actual angular diameter of the star. The position of L2 Pup in the
Herzsprung-Russell diagram indicates that this star has a mass around 2 Msun
and is probably experiencing an early stage of the asymptotic giant branch. We
do not detect any stellar companion of L2 Pup in our adaptive optics and
interferometric observations, and we attribute its apparent astrometric wobble
in the Hipparcos data to variable lighting effects on its circumstellar
material. We however do not exclude the presence of a binary companion, as the
large loop structure extending to more than 10 AU to the North-East of the disk
in our L band images may be the result of interaction between the stellar wind
of L2 Pup and a hidden secondary object. The geometric configuration that we
propose, with a large dust disk seen almost edge-on, appears particularly
favorable to test and develop our understanding of the formation of bipolar
nebulae.Comment: 16 pages, 15 figure
Spatially Resolved Ultraviolet Spectroscopy of the Great Dimming of Betelgeuse
The bright supergiant, Betelgeuse (Alpha Orionis, HD 39801) experienced a
visual dimming during 2019 December and the first quarter of 2020 reaching an
historic minimum 2020 February 713. During 2019 September-November, prior to
the optical dimming event, the photosphere was expanding. At the same time,
spatially resolved ultraviolet spectra using the Hubble Space Telescope/Space
Telescope Imaging Spectrograph revealed a substantial increase in the
ultraviolet spectrum and Mg II line emission from the chromosphere over the
southern hemisphere of the star. Moreover, the temperature and electron density
inferred from the spectrum and C II diagnostics also increased in this
hemisphere. These changes happened prior to the Great Dimming Event. Variations
in the Mg II k-line profiles suggest material moved outwards in response to the
passage of a pulse or acoustic shock from 2019 September through 2019 November.
It appears that this extraordinary outflow of material from the star, likely
initiated by convective photospheric elements, was enhanced by the coincidence
with the outward motions in this phase of the 400 day pulsation cycle.
These ultraviolet observations appear to provide the connecting link between
the known large convective cells in the photosphere and the mass ejection event
that cooled to form the dust cloud in the southern hemisphere imaged in 2019
December, and led to the exceptional optical dimming of Betelgeuse in 2020
February.Comment: 11 pages, 8 figures, Astrophysical Journal, accepte
Towards a coherent view of mass loss in Betelgeuse from the photosphere to the interstellar medium
International audienc
Towards a coherent view of mass loss in Betelgeuse from the photosphere to the interstellar medium
International audienc
A study of the red supergiant Betelgeuse at high angular resolution
International audienc