261 research outputs found
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
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
Dynamical Spot Evolution in HD 11753
Our recent studies of HD 11753, a late B-type star showing a HgMn peculiarity for the first time revealed the presence of a fast dynamical evolution of chemical spots on the surface of this chemically peculiar early-type star. These observations suggest a hitherto unknown physical process operating in stars with outer radiative envelopes. Furthermore, we have also discovered existence of magnetic fields on HgMn stars that were up to now considered non-magnetic. Here we will discuss the dynamical spot evolution in HD 11753 in detail, and also summarize our new results on the magnetic fields of the AR Aur binary system
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
Magnetic field geometry and chemical abundance distribution of the He-strong star CPD -57 3509
The magnetic field of CPD -57 3509 was recently detected in the framework of
the BOB (B fields in OB stars) collaboration. We acquired low-resolution
spectropolarimetric observations of CPD -57 3509 with FORS2 and high-resolution
UVES observations randomly distributed over a few months to search for
periodicity, to study the magnetic field geometry, and to determine the surface
distribution of silicon and helium. We also obtained supplementary photometric
observations at a timeline similar to the spectroscopic and spectropolarimetric
observations. A period of 6.36d was detected in the measurements of the mean
longitudinal magnetic field. A sinusoidal fit to our measurements allowed us to
constrain the magnetic field geometry and estimate the dipole strength in the
range of 3.9-4.5kG. Our application of the Doppler imaging technique revealed
the presence of He I spots located around the magnetic poles, with a strong
concentration at the positive pole and a weaker one around the negative pole.
In contrast, high concentration Si III spots are located close to the magnetic
equator. Further, our analysis of the spectral variability of CPD -57 3509 on
short time scales indicates distinct changes in shape and position of line
profiles possibly caused by the presence of beta Cep-like pulsations. A small
periodic variability in line with the changes of the magnetic field strength is
clearly seen in the photometric data.Comment: 11 pages, 5 tables, 7 figures, accepted for publication in MNRA
The CoRoT B-type binary HD50230: a prototypical hybrid pulsator with g-mode period and p-mode frequency spacings
B-type stars are promising targets for asteroseismic modelling, since their
frequency spectrum is relatively simple.
We deduce and summarise observational constraints for the hybrid pulsator,
HD50230, earlier reported to have deviations from a uniform period spacing of
its gravity modes. The combination of spectra and a high-quality light curve
measured by the CoRoT satellite allow a combined approach to fix the position
of HD50230 in the HR diagram.
To describe the observed pulsations, classical Fourier analysis was combined
with short-time Fourier transformations and frequency spacing analysis
techniques. Visual spectra were used to constrain the projected rotation rate
of the star and the fundamental parameters of the target. In a first
approximation, the combined information was used to interpret multiplets and
spacings to infer the true surface rotation rate and a rough estimate of the
inclination angle.
We identify HD50230 as a spectroscopic binary and characterise the two
components. We detect the simultaneous presence of high-order g modes and
low-order p and g-modes in the CoRoT light curve, but were unable to link them
to line profile variations in the spectroscopic time series. We extract the
relevant information from the frequency spectrum, which can be used for seismic
modelling, and explore possible interpretations of the pressure mode spectrum.Comment: 26 pages, 12+6 figures, accepted for publication in Astronomy and
Astrophysic
Detection of gravity modes in the massive binary V380 Cyg from Kepler spacebased photometry and high-resolution spectroscopy
We report the discovery of low-amplitude gravity-mode oscillations in the
massive binary star V380 Cyg, from 180 d of Kepler custom-aperture space
photometry and 5 months of high-resolution high signal-to-noise spectroscopy.
The new data are of unprecedented quality and allowed to improve the orbital
and fundamental parameters for this binary. The orbital solution was subtracted
from the photometric data and led to the detection of periodic intrinsic
variability with frequencies of which some are multiples of the orbital
frequency and others are not. Spectral disentangling allowed the detection of
line-profile variability in the primary. With our discovery of intrinsic
variability interpreted as gravity mode oscillations, V380 Cyg becomes an
important laboratory for future seismic tuning of the near-core physics in
massive B-type stars.Comment: 5 pages, 4 figures, 2 tables. Accepted for publication in MNRAS
Letter
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