473 research outputs found
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
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
Line-profile variations of stochastically excited oscillations in four evolved stars
Since solar-like oscillations were first detected in red-giant stars, the
presence of non-radial oscillation modes has been debated. Spectroscopic
line-profile analysis was used in the first attempt to perform mode
identification, which revealed that non-radial modes are observable. Despite
the fact that the presence of non-radial modes could be confirmed, the degree
or azimuthal order could not be uniquely identified. Here we present an
improvement to this first spectroscopic line-profile analysis. Aims: We aim to
study line-profile variations of stochastically excited solar-like oscillations
in four evolved stars to derive the azimuthal order of the observed mode and
the surface rotational frequency. Methods: Spectroscopic line-profile analysis
is applied to cross-correlation functions, using the Fourier Parameter Fit
method on the amplitude and phase distributions across the profiles. Results:
For four evolved stars, beta Hydri (G2IV), epsilon Ophiuchi (G9.5III), eta
Serpentis (K0III) and delta Eridani (K0IV) the line-profile variations reveal
the azimuthal order of the oscillations with an accuracy of ~1. Furthermore,
our analysis reveals the projected rotational velocity and the inclination
angle. From these parameters we obtain the surface rotational frequency.
Conclusions: We conclude that line-profile variations of cross-correlation
functions behave differently for different frequencies and that they provide
additional information in terms of the surface rotational frequency and
azimuthal order.Comment: Accepted for publication in Astronomy and Astrophysics, 9 pages, 10
figures and 3 tables. A version with figure 1 in full resolution can be
obtained upon request from first autho
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
An observational asteroseismic study of the pulsating B-type stars in the open cluster NGC 884
Recent progress in the seismic interpretation of field β Cep stars has resulted in improvements of the physical description in the stellar structure and evolution model computations of massive stars. Further asteroseismic constraints can be obtained from studying ensembles of stars in a young open cluster, which all have similar age, distance and chemical composition. We present an observational asteroseismic study based on the discovery of numerous multi-periodic and mono-periodic B-type stars in the open cluster NGC 884 (χ Persei). Our study illustrates the current status of ensemble asteroseismology of this young open cluste
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
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
PND41 Predicting EQ-5D Utility Scores from the Huntington quality of Life instrument (H-QOL-I)
Analysis of MERCATOR data Part I: variable B stars
We re-classified 31 variable B stars which were observed more than 50 times
in the Geneva photometric system with the P7 photometer attached to the
MERCATOR telescope (La Palma) during its first 3 years of scientific
observations. HD89688 is a possible beta Cephei/slowly pulsating B star hybrid
and the main mode of the COROT target HD180642 shows non-linear effects. The
Maia candidates are re-classified as either ellipsoidal variables or spotted
stars. Although the mode identification is still ongoing, all the
well-identified modes so far have a degree l = 0, 1 or 2.Comment: 4 pages, 3 figures. To appear in: Proceedings of JENAM 2005 'Distant
worlds', Communications in Asteroseismolog
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