693 research outputs found
A new seismic analysis of Alpha Centauri
Models of alpha Cen A & B have been computed using the masses determined by
Pourbaix et al. (2002) and the data derived from the spectroscopic analysis of
Neuforge and Magain (1997). The seismological data obtained by Bouchy and
Carrier (2001, 2002) do help improve our knowledge of the evolutionary status
of the system. All the constraints are satisfied with a model which gives an
age of about 6 Gyr for the binary.Comment: to be published in Astronomy and Astrophysic
Seismic modelling of the Cep star HD\,180642 (V1449\,Aql)
We present modelling of the Cep star HD\,180642 based on its
observational properties deduced from CoRoT and ground-based photometry as well
as from time-resolved spectroscopy. We investigate whether present-day
state-of-the-art models are able to explain the full seismic behaviour of this
star, which has extended observational constraints for this type of pulsator.
We constructed a dedicated database of stellar models and their oscillation
modes tuned to fit the dominant radial mode frequency of HD\,180642, by means
of varying the hydrogen content, metallicity, mass, age, and core overshooting
parameter. We compared the seismic properties of these models with those
observed. We find models that are able to explain the numerous observed
oscillation properties of the star, for a narrow range in mass of
11.4--11.8\,M and no or very mild overshooting (with up to 0.05 local
pressure scale heights), except for an excitation problem of the ,
p mode. We deduce a rotation period of about 13\,d, which is fully
compatible with recent magnetic field measurements. The seismic models do not
support the earlier claim of solar-like oscillations in the star. We instead
ascribe the power excess at high frequency to non-linear resonant mode coupling
between the high-amplitude radial fundamental mode and several of the low-order
pressure modes. We report a discrepancy between the seismic and spectroscopic
gravity at the level.Comment: 10 pages, 2 Tables, 6 Figures. Accepted for publication in Astronomy
and Astrophysic
An asteroseismic study of the beta Cephei star beta Canis Majoris
We present the results of a detailed analysis of 452 ground-based
high-resolution high S/N spectroscopic measurements spread over 4.5 years for
beta Canis Majoris with the aim to determine the pulsational characteristics of
this star, and to use them to derive seismic constraints on the stellar
parameters. We determine pulsation frequencies in the SiIII 4553 Angstrom line
with Fourier methods. We identify the m-value of the modes by taking into
account the photometric identifications of the degrees l. To this end we use
the moment method together with the amplitude and phase variations across the
line profile. The frequencies of the identified modes are used for a seismic
interpretation of the structure of the star. We confirm the presence of the
three pulsation frequencies already detected in previous photometric datasets:
f_1 = 3.9793 c/d (46.057 microHz), f_2 = 3.9995 c/d (46.291 microHz) and f_3 =
4.1832 c/d (48.417 microHz). For the two modes with the highest amplitudes we
unambiguously identify (l_1,m_1) = (2,2) and (l_2,m_2) = (0,0). We cannot
conclude anything for the third mode identification, except that m_3 > 0. We
also deduce an equatorial rotational velocity of 31 +/- 5 Km/s for the star. We
show that the mode f_1 must be close to an avoided crossing. Constraints on the
mass (13.5 +/- 0.5 Msun), age (12.4 +/- 0.7 Myr) and core overshoot (0.20 +/-
0.05 H_P) of beta CMa are obtained from seismic modelling using f_1 and f_2.Comment: Accepted for publication in A&
An asteroseismic study of the beta Cephei star 12 Lacertae: multisite spectroscopic observations, mode identification and seismic modelling
We present the results of a spectroscopic multisite campaign for the beta
Cephei star 12 (DD) Lacertae. Our study is based on more than thousand
high-resolution high S/N spectra gathered with 8 different telescopes in a time
span of 11 months. In addition we make use of numerous archival spectroscopic
measurements. We confirm 10 independent frequencies recently discovered from
photometry, as well as harmonics and combination frequencies. In particular,
the SPB-like g-mode with frequency 0.3428 1/d reported before is detected in
our spectroscopy. We identify the four main modes as (l1,m1) = (1, 1), (l2,m2)
= (0, 0), (l3,m3) = (1, 0) and (l4,m4) = (2, 1) for f1 = 5.178964 1/d, f2 =
5.334224 1/d, f3 = 5.066316 1/d and f4 = 5.490133 1/d, respectively. Our
seismic modelling shows that f2 is likely the radial first overtone and that
the core overshooting parameter alpha_ov is lower than 0.4 local pressure scale
heights.Comment: 16 pages, 11 figures, accepted in MNRA
Abundance analysis, spectral variability, and search for the presence of a magnetic field in the typical PGa star HD19400
The aim of this study is to carry out an abundance determination, to search
for spectral variability and for the presence of a weak magnetic field in the
typical PGa star HD19400. High-resolution, high signal-to-noise HARPS
spectropolarimetric observations of HD19400 were obtained at three different
epochs in 2011 and 2013. For the first time, we present abundances of various
elements determined using an ATLAS12 model, including the abundances of a
number of elements not analysed by previous studies, such as Ne I, Ga II, and
Xe II. Several lines of As II are also present in the spectra of HD19400. To
study the variability, we compared the behaviour of the line profiles of
various elements. We report on the first detection of anomalous shapes of line
profiles belonging to Mn and Hg, and the variability of the line profiles
belonging to the elements Hg, P, Mn, Fe, and Ga. We suggest that the
variability of the line profiles of these elements is caused by their
non-uniform surface distribution, similar to the presence of chemical spots
detected in HgMn stars. The search for the presence of a magnetic field was
carried out using the moment technique and the SVD method. Our measurements of
the magnetic field with the moment technique using 22 Mn II lines indicate the
potential existence of a weak variable longitudinal magnetic field on the first
epoch. The SVD method applied to the Mn II lines indicates =-76+-25G on
the first epoch, and at the same epoch the SVD analysis of the observations
using the Fe II lines shows =-91+-35G. The calculated false alarm
probability values, 0.008 and 0.003, respectively, are above the value 10^{-3},
indicating no detection.Comment: 13+6 pages, 14 figures, 6+1 tables, including the online-only
material, accepted for publication in MNRA
CoRoT high-precision photometry of the B0.5 IV star HD 51756
OB stars are important constituents for the ecology of the Universe, and
there are only a few studies on their pulsational properties detailed enough to
provide important feedback on current evolutionary models. Our goal is to
analyse and interpret the behaviour present in the CoRoT light curve of the
B0.5 IV star HD 51756 observed during the second long run of the space mission,
and to determine the fundamental stellar parameters from ground-based
spectroscopy gathered with the CORALIE and HARPS instruments after checking for
signs of variability and binarity, thus making a step further in mapping the
top of the Beta Cep instability strip. We compare the newly obtained
high-resolution spectra with synthetic spectra of late O-type and early B-type
stars computed on a grid of stellar parameters. We match the results with
evolutionary tracks to estimate stellar parameters. We use various time series
analysis tools to explore the nature of the variations present in the light
curve. Additional calculations are carried out based on distance and historical
position measurements of the components to impose constraints on the binary
orbit. We find that HD 51756 is a wide binary with both a slow (v sin i \approx
28 km s^-1) and a fast (v sin i \approx 170 km s^-1) early-B rotator whose
atmospheric parameters are similar (T_eff \approx 30000 K and log g \approx
3.75). We are unable to detect pulsation in any of the components, and we
interpret the harmonic structure in the frequency spectrum as sign of
rotational modulation, which is compatible with the observed and deduced
stellar parameters of both components. The non-detection of pulsation modes
provides a feedback on the theoretical treatment, given that non-adiabatic
computations applied to appropriate stellar models predict the excitation of
both pressure and gravity modes for the fundamental parameters of this star.Comment: Accepted for publication in Astronomy and Astrophysics on 14/01/2011,
11 pages, 9 figures, 4 table
Teach Me To Smile
https://digitalcommons.library.umaine.edu/mmb-vp/6656/thumbnail.jp
New spectroscopic and polarimetric observations of the A0 supergiant HD92207
Our recent search for the presence of a magnetic field in the bright early
A-type supergiant HD92207 using FORS2 in spectropolarimetric mode revealed the
presence of a longitudinal magnetic field of the order of a few hundred Gauss.
However, the definite confirmation of the magnetic nature of this object
remained pending due to the detection of short-term spectral variability
probably affecting the position of line profiles in left- and right-hand
polarized spectra. We present new magnetic field measurements of HD92207
obtained on three different epochs in 2013 and 2014 using FORS2 in
spectropolarimetric mode. A 3sigma detection of the mean longitudinal magnetic
field using the entire spectrum, _all=104+-34G, was achieved in
observations obtained in 2014 January. At this epoch, the position of the
spectral lines appeared stable. Our analysis of spectral line shapes recorded
in opposite circularly polarized light, i.e. in light with opposite sense of
rotation, reveals that line profiles in the light polarized in a certain
direction appear slightly split. The mechanism causing such a behaviour in the
circularly polarized light is currently unknown. Trying to settle the issue of
short-term variability, we searched for changes in the spectral line profiles
on a time scale of 8-10min using HARPS polarimetric spectra and on a time scale
of 3-4min using time series obtained with the CORALIE spectrograph. No
significant variability was detected on these time scales during the epochs
studied.Comment: 10 pages, 11 figures, 2 tables, accepted for publication in
Astronomische Nachrichte
Multisite spectroscopic seismic study of the beta Cep star V2052 Oph: inhibition of mixing by its magnetic field
We used extensive ground-based multisite and archival spectroscopy to derive
observational constraints for a seismic modelling of the magnetic beta Cep star
V2052 Ophiuchi. The line-profile variability is dominated by a radial mode
(f_1=7.14846 d^{-1}) and by rotational modulation (P_rot=3.638833 d). Two
non-radial low-amplitude modes (f_2=7.75603 d^{-1} and f_3=6.82308 d^{-1}) are
also detected. The four periodicities that we found are the same as the ones
discovered from a companion multisite photometric campaign (Handler et al.
2012) and known in the literature. Using the photometric constraints on the
degrees l of the pulsation modes, we show that both f_2 and f_3 are prograde
modes with (l,m)=(4,2) or (4,3). These results allowed us to deduce ranges for
the mass (M \in [8.2,9.6] M_o) and central hydrogen abundance (X_c \in
[0.25,0.32]) of V2052 Oph, to identify the radial orders n_1=1, n_2=-3 and
n_3=-2, and to derive an equatorial rotation velocity v_eq \in [71,75] km
s^{-1}. The model parameters are in full agreement with the effective
temperature and surface gravity deduced from spectroscopy. Only models with no
or mild core overshooting (alpha_ov \in [0,0.15] local pressure scale heights)
can account for the observed properties. Such a low overshooting is opposite to
our previous modelling results for the non-magnetic beta Cep star theta Oph
having very similar parameters, except for a slower surface rotation rate. We
discuss whether this result can be explained by the presence of a magnetic
field in V2052 Oph that inhibits mixing in its interior.Comment: 12 pages, 6 figures and 5 tables; accepted for publication in MNRAS
on 2012 August 1
First HARPSpol discoveries of magnetic fields in massive stars
In the framework of the Magnetism in Massive Stars (MiMeS) project, a
HARPSpol Large Program at the 3.6m-ESO telescope has recently started to
collect high-resolution spectropolarimetric data of a large number of Southern
massive OB stars in the field of the Galaxy and in many young clusters and
associations. In this Letter, we report on the first discoveries of magnetic
fields in two massive stars with HARPSpol - HD 130807 and HD 122451, and
confirm the presence of a magnetic field at the surface of HD 105382 that was
previously observed with a low spectral resolution device. The longitudinal
magnetic field measurements are strongly varying for HD 130807 from -100
G to 700 G. Those of HD 122451 and HD 105382 are less variable with
values ranging from -40 to -80 G, and from -300 to -600 G,
respectively. The discovery and confirmation of three new magnetic massive
stars, including at least two He-weak stars, is an important contribution to
one of the MiMeS objectives: the understanding of origin of magnetic fields in
massive stars and their impacts on stellar structure and evolution.Comment: 4 pages, 2 figures, accepted for publication in A&A Lette
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