479 research outputs found
Probing the parameter space of HD 49933: a comparison between global and local methods
We present two independent methods for studying the global stellar parameter
space (mass M, age, initial chemical composition X_0, Z_0) of HD 49933 with
seismic data. Using a local minimization and an MCMC algorithm, we obtain
consistent results for the determination of the stellar properties: M = 1.1 -
1.2 M_solar, Age ~ 3.0 Gyr, Z_0 ~ 0.008. A description of the error ellipses
can be defined using Singular Value Decomposition techniques, and this is
validated by comparing the errors with those from the MCMC method.Comment: to be published in JPC
Variation in the frequency separations with activity and impact on stellar parameter determination
Frequency separations used to infer global properties of stars through
asteroseismology can change depending on the strength and at what epoch of the
stellar cycle the p-mode frequencies are measured. In the Sun these variations
have been seen, even though the Sun is a low-activity star. In this paper, we
discuss these variations and their impact on the determination of the stellar
parameters (radius, mass and age) for the Sun. Using the data from maximum and
minimum activity, we fitted an age for the Sun that differs on average by 0.2
Gyr: slightly older during minimum activity. The fitted radius is also lower by
about 0.5% for the solar effective temperature during minimum.Comment: to be published in JPCS to be published in JPC
Duplicate retention in signalling proteins and constraints from network dynamics
Both single-gene and whole-genome duplications (WGD) are well documented in various organisms (Brenner et al., 1995; Zhang, 2003; Vogel & Chothia, 2006), and it is estimated that single-gene duplication
Constraining the properties of delta Scuti stars using spectroscopic eclipsing binary systems
Many stars exhibit stellar pulsations, favoring them for asteroseismic
analyses. Interpreting the oscillations requires some knowledge of the
oscillation mode geometry (spherical degree, radial and azimuthal orders). The
delta Scuti stars (1.5 - 2.5 M_sol) often show just one or few pulsation
frequencies. Although this may promise a successful seismological analysis, we
may not know enough about either the mode or the star to use the oscillation
frequency to improve the determination of the stellar model, or probe the
star's structure. For the observed frequencies to be used successfully as
seismic probes of these objects, we need to concentrate on stars for which we
can reduce the number of free parameters in the problem, such as binary systems
or open clusters. We investigate how much our understanding of a delta Scuti
star is improved when it is in a detached eclipsing binary system instead of
being a single field star. We use singular value decomposition to explore the
precision we expect in stellar parameters (mass, age and chemical composition)
for both cases. We examine how the parameter uncertainties propagate to the
luminosity - effective temperature diagram and determine when the effort of
obtaining a new measurement is justified. We show that for the single star, a
correct identification of the oscillation mode is necessary to produce strong
constraints on the stellar model properties, while for the binary system the
observations without the pulsation mode provide the same or better constraints
on the stellar parameters. In the latter case, ...Comment: emulateapj 16 pages, accepted Ap
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