747 research outputs found
Abundances in HD27411 and the helium problem in Am stars
We analyze a high-resolution spectrum of the A3m star HD27411. We compare
abundances derived from ATLAS9 model atmospheres with those using the more
computationally-intensive ATLAS12 code. We found very little differences in the
abundances, suggesting that ATLAS9 can be used for moderate chemical
peculiarity. Our abundances agree well with the predictions of diffusion
theory, though for some elements it was necessary to calculate line profiles in
non-thermodynamic equilibrium to obtain agreement. We investigate the effective
temperatures and luminosities of Am/Fm stars using synthetic Stromgren indices
derived from calculated spectra with the atmospheric abundances of HD27411. We
find that the effective temperatures of Am/Fm stars derived from Stromgren
photometry are reliable, but the luminosities are probably too low. Caution is
required when deriving the reddening of these stars owing to line blanketing
effects. A comparison of the relative proportions of pulsating and
non-pulsating Am stars with delta Scuti stars shows quite clearly that there is
no significant decrease of helium in the driving zone, contrary to current
models of diffusion.Comment: 10 pages, 8 figures, 6 tables, accepted for publication in MNRA
Metal-Rich SX Phe Stars in theKeplerField
High-resolution spectroscopic observations have been made for 32 of the 34 candidate SX Phe stars identified in the Kepler field by Balona & Nemec (2012). All available long- and short-cadence Q0-Q17 Kepler photometry has been analyzed for the 34 candidates. Radial velocities (RVs), space motions (U, V, W), projected rotation veloc-
ities (v sin i), spectral types, and atmospheric characteristics (Teff , log g, [M/H], vmic, etc.) were derived from ∼160 spectra taken with the ESPaDOnS spectrograph on the Canada-
France-Hawaii 3.6-m telescope and with the ARCES spectrograph on the Apache Point Observatory 3.5-m telescope. Two thirds of the stars are fast rotators with v sin i > 50 km/s, including four stars with v sin i > 200 km/s. Three of the stars have (negative) RVs > 250 km/s and retrograde space motions, and seven stars have total space motions > 400 km/s. All the spectroscopically measured SX Phe candidates have positions in a Toomre diagram that are consistent with being bona fide halo and thick-disk stars. Although several stars
show a marked metal weakness, the mean [Fe/H] of the sample is near 0.0 dex (σ ∼ 0.25
dex), which is considerably more metal-rich than is normally expected for a sample of Pop. II stars. Observed pulsation frequency modulations and optical time delays suggest that at least eight of the SX Phe stars are in binary systems, some of which show signif- icant RV variations. Six of the time-delay binaries have secondary masses ranging from
0.05 to 0.70 Mo and orbital periods in the range 9 to 1570 days. Another star appears to be an ellipsoidal variable with a 2.3-day orbital period; and two other systems have orbital
periods longer than the ∼4-year sampling interval of the Kepler data
Has a star enough energy to excite the thousand of modes observed with CoRoT?
The recent analyses of the light curves provided by CoRoT have revealed
pulsation spectra of unprecedented richness and precision, in particular,
thousands of pulsating modes, and a clear distribution of amplitudes with
frequency. In the community, some scientists have started doubting about the
validity of the classical tools to analyze these very accurate light curves.
This work provides the asteroseismic community with answers to this question
showing that (1) it is physically possible for a star to excite at a time and
with the observed amplitudes such a large number of modes; and (2) that the
kinetic energy accumulated in all those modes does not destroy the equilibrium
of the star. Consequently, mathematical tools presently applied in the analyses
of light curves can a priori be trusted. This conclusion is even more important
now, when a large amount of space data coming from Kepler are currently being
analyzed.
The power spectrum of different stellar cases, and the non-adiabatic code
GraCo have been used to estimate the upper limit of the energy per second
required to excite all the observed modes, and their total kinetic energy. A
necessary previous step for this study is to infer the relative radial
pulsational amplitude from the observed photometric amplitude, scaling our
linear pulsational solutions to absolute values. The derived upper limits for
the required pulsational energy were compared with 1) the luminosity of the
star; and 2) the gravitational energy. We obtained that both upper energy
limits are orders of magnitude smaller.Comment: 18 pages, 2 figures, accepted by ApJ Letters Dec 15, 200
Disfiguring Figures. The political potentiality of Marlene Monteiro Freitas’s choreographic work
Departing from the German philologist Erich Auerbach’s foundational study on the genealogy of figura—a concept that belonging to the three different fields of theology, rhetoric and visual arts has laid the foundations of the theories and practices of Western European representation—and following the reformulations by Freud, Gilles Deleuze, and Lyotard of this influential notion of figura as indeterminacy between form and process, the visible and the invisible, sensible and intelligible, the corporeal and the spiritual, this paper wishes to address how the choreographed figures of ambivalence, hybridity and metamorphosis in Marlene Monteiro Freitas’ works, namely, in her solo work ‘Guintche’, set the stage for a contemporary criticality of some of the structuring postulates of European modernity.info:eu-repo/semantics/publishedVersio
A new method for the spectroscopic identification of stellar non-radial pulsation modes. I. The method and numerical tests
We present the Fourier parameter fit method, a new method for
spectroscopically identifying stellar radial and non-radial pulsation modes
based on the high-resolution time-series spectroscopy of absorption-line
profiles. In contrast to previous methods this one permits a quantification of
the statistical significance of the computed solutions. The application of
genetic algorithms in seeking solutions makes it possible to search through a
large parameter space. The mode identification is carried out by minimizing
chi-square, using the observed amplitude and phase across the line profile and
their modeled counterparts. Computations of the theoretical line profiles are
based on a stellar displacement field, which is described as superposition of
spherical harmonics and that includes the first order effects of the Coriolis
force. We made numerical tests of the method on a grid of different mono- and
multi-mode models for 0 <= l <= 4 in order to explore its capabilities and
limitations. Our results show that whereas the azimuthal order m can be
unambiguously identified for low-order modes, the error of l is in the range of
pm 1. The value of m can be determined with higher precision than with other
spectroscopic mode identification methods. Improved values for the inclination
can be obtained from the analysis of non-axisymmetric pulsation modes. The new
method is ideally suited to intermediatley rotating Delta Scuti and Beta Cephei
stars.Comment: 12 pages, 14 figure
- …