J/A+A/667/A111 High-resolution spectra of Achernar (Kervella+, 2022)
The binary system of the spinning-top Be star Achernar.
Kervella P., Borgniet S., Domiciano de Souza A., Merand A., Gallenne A.,
Rivinius Th., Lacour S., Carciofi A., Moser Faes D., Le Bouquin J.-B.,
Taormina M., Pilecki B., Berger J.-P., Bendjoya P., Klement R., Millour F.,
Janot-Pacheco E., Spang A., Vakili F.
<Astron. Astrophys. 667, A111 (2022)>
=2022A&A...667A.111K 2022A&A...667A.111K (SIMBAD/NED BibCode)
ADC_Keywords: Stars, bright ; Stars, double and multiple ; Spectra, optical
Keywords: stars: individual: Achernar - techniques: high angular resolution -
techniques: interferometric - techniques: radial velocities -
binaries: visual
Abstract:
Achernar, the closest and brightest classical Be star, presents
rotational flattening, gravity darkening, occasional emission lines
due to a gaseous disk, and an extended polar wind. It is also a member
of a close binary system with an early A-type dwarf companion.
We aim to determine the orbital parameters of the Achernar system and
to estimate the physical properties of the components. Methods. We
monitored the relative position of Achernar B using a broad range of
high angular resolution instruments of the VLT/VLTI (VISIR, NACO,
SPHERE, AMBER, PIONIER, GRAVITY, and MATISSE) over a period of
13 years (2006-2019). These astrometric observations are complemented
with a series of ∼750 optical spectra for the period from 2003 to
2016.
We determine that Achernar B orbits the primary Be star on a
seven-year period, eccentric orbit (e=0.7255±0.0014) which brings
the two stars within 2au at periastron. The mass of the Be star is
found to be mA=6.0±0.6M☉ for a secondary mass of
mB=2.0±0.1M☉ (the latter was estimated from modeling). We find
a good agreement of the parameters of Achernar A with the evolutionary
model of a critically rotating star of 6.4M☉ at an age of 63Ma.
The equatorial plane of the Be star and the orbital plane of the
companion exhibit a relative inclination of 30°. We also identify
a resolved comoving low-mass star, which leads us to propose that
Achernar is a member of the Tucana-Horologium moving group.
The proximity of Achernar makes this star a precious benchmark for
stellar evolution models of fast rotators and intermediate mass
binaries. Achernar A is presently in a short-lived phase of its
evolution following the turn-off, during which its geometrical
flattening ratio is the most extreme. Considering the orbital
parameters, no significant interaction occurred between the two
components, demonstrating that Be stars may form through a direct,
single-star evolution path without mass transfer. Since component A
will enter the instability strip in a few hundred thousand years,
Achernar appears to be a promising progenitor of the Cepheid binary
systems.
Description:
This data set comprises approximately 700 optical spectra for the
period from 2003 to 2016. They were collected using the BESO, BeSS,
CHIRON, CORALIE, FEROS, HARPS, PUCHEROS, and UVES instruments. The
spectra are provided in the form of standard FITS files, with the
continuum flux normalized to unity.
Objects:
-------------------------------------------------
RA (2000) DE Designation(s)
-------------------------------------------------
01 37 42.85 -57 14 12.3 Achernar = * alf Eri
-------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
list.dat 142 706 List of spectra
fits/* . 706 Individual fits spectra
--------------------------------------------------------------------------------
Byte-by-byte Description of file: list.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 11 F11.8 deg RAdeg Right ascension (ICRS) at Epoch=J1991.25
13- 24 F12.8 deg DEdeg Declination (ICRS) at Epoch=J1991.25
26- 36 F11.5 d MJD Modified Julian date
38- 47 A10 "date" Date Calendar date
49- 56 A8 --- Inst Spectrograph
58- 64 A7 --- Range Spectral range
66- 71 F6.2 --- S/N Signal-to-noise ratio
73- 78 I6 --- SpecRes Spectral resolution
80- 86 F7.2 0.1nm blambda Minimum wavelength (Angstroem)
88- 94 F7.2 0.1nm Blambda Maximum wavelength (Angstroem)
96- 99 F4.2 0.1nm dlambda Wavelength step (Angstroem)
101-104 I4 Kibyte size Size of FITS file
106-142 A37 --- FileName FITS file name
--------------------------------------------------------------------------------
Acknowledgements:
Pierre Kervella, pierre.kervella(at)observatoiredeparis.psl.eu
(End) Pierre Kervella [Obs. de Paris], Patricia Vannier [CDS] 09-Sep-2022