220 research outputs found
Fundamental properties of solar-like oscillating stars from frequencies of minimum : II. Model computations for different chemical compositions and mass
The large separations between the oscillation frequencies of solar-like stars
are measures of stellar mean density. The separations have been thought to be
mostly constant in the observed range of frequencies. However, detailed
investigation shows that they are not constant, and their variations are not
random but have very strong diagnostic potential for our understanding of
stellar structure and evolution. In this regard, frequencies of the minimum
large separation are very useful tools. From these frequencies, in addition to
the large separation and frequency of maximum amplitude, Y\i ld\i z et al.
recently have developed new methods to find almost all the fundamental stellar
properties. In the present study, we aim to find metallicity and helium
abundances from the frequencies, and generalize the relations given by Y\i ld\i
z et al. for a wider stellar mass range and arbitrary metallicity () and
helium abundance (). We show that the effect of metallicity is {
significant} for most of the fundamental parameters. For stellar mass, for
example, the expression must be multiplied by (Z/Z_{\sun})^{0.12}. For
arbitrary helium abundance, M \propto (Y/Y_{\sun})^{0.25} . Methods for
determination of and from pure asteroseismic quantities are based on
amplitudes (differences between maximum and minimum values of \Dnu) in the
oscillatory component in the spacing of oscillation frequencies. Additionally,
we demonstrate that the difference between the first maximum and the second
minimum is very sensitive to . It also depends on and small separation between the frequencies. Such a dependence leads us
to develop a method to find (and ) from oscillation frequencies. The
maximum difference between the estimated and model values is about 14 per
cent. It is 10 per cent for .Comment: 8 pages, 13 figures; published in MNRAS (2015
Comparison of Gaia and asteroseismic distances
Asteroseismology provides fundamental properties (mass, radius and effective
temperature) of solar-like oscillating stars using so-called scaling relations.
These properties allow the computation of the asteroseismic distance of stars.
We compare the asteroseismic distances with the recently released Gaia
distances for 74 stars studied in Y{\i}ld{\i}z et al. There is a very good
agreement between these two distances; for 64 of these stars, the difference is
less than 10 per cent. However, a systematic difference is seen if we use the
effective temperature obtained by spectroscopic methods; the Gaia distances are
about 5 per cent greater than the asteroseismic distances.Comment: 4 pages, 4 figures, accepted by MNRA
On the structure and evolution of planets and their host stars effects of various heating mechanisms on the size of giant gas planets
It is already stated in the previous studies that the radius of the giant
planets is affected by stellar irradiation. The confirmed relation between
radius and incident flux depends on planetary mass intervals. In this study, we
show that there is a single relation between radius and irradiated energy per
gram per second (), for all mass intervals. There is an extra increase in
radius of planets if is higher than 1100 times energy received by the
Earth (). This is likely due to dissociation of molecules. The tidal
interaction as a heating mechanism is also considered and found that its
maximum effect on the inflation of planets is about 15 per cent. We also
compute age and heavy element abundances from the properties of host stars,
given in the TEPCat catalogue (Southworth 2011). The metallicity given in the
literature is as [Fe/H]. However, the most abundant element is oxygen, and
there is a reverse relation between the observed abundances [Fe/H] and [O/Fe].
Therefore, we first compute [O/H] from [Fe/H] by using observed abundances, and
then find heavy element abundance from [O/H]. We also develop a new method for
age determination. Using the ages we find, we analyse variation of both radius
and mass of the planets with respect to time, and estimate the initial mass of
the planets from the relation we derive for the first time. According to our
results, the highly irradiated gas giants lose 5 per cent of their mass in
every 1 Gyr.Comment: 15 pages, 13 figures, 3 tables. Accepted by MNRA
Asteroseismic Investigation of 20 Planet and Planet-Candidate Host Stars
Planets and planet candidates are subjected to great investigation in recent
years. In this study, we analyse 20 planet and planet-candidate host stars at
different evolutionary phases. We construct stellar interior models of the host
stars with the MESA evolution code and obtain their fundamental parameters
under influence of observational asteroseismic and non-asteroseismic
constraints. Model mass range of the host stars is 0.74-1.55 .
The mean value of the so-called large separation between oscillation
frequencies and its variation about the minima show the diagnostic potential of
asteroseismic properties. Comparison of variations of model and observed large
separations versus the oscillation frequencies leads to inference of
fundamental parameters of the host stars. Using these parameters, we revise
orbital and fundamental parameters of 34 planets and four planet candidates.
According to our findings, radius range of the planets is 0.35-16.50
. The maximum difference between the transit and revised
radii occurs for Kepler-444b-f is about 25 per cent.Comment: 9 pages, 7 figures, 6 table
Fundamental properties of Kepler and CoRoT targets -- IV. Masses and radii from frequencies of minimum and their implications
Recently, by analysing the oscillation frequencies of 90 stars, Yildiz,
\c{C}elik Orhan & Kayhan have shown that the reference frequencies (, and ) derived from glitches due to He
{\scriptsize II} ionization zone have very strong diagnostic potential for the
determination of their effective temperatures. In this study, we continue to
analyse the same stars and compute their mass, radius and age from different
scaling relations including relations based on , and . For most of the stars, the masses computed using
and are very close to each other. For 38
stars, the difference between these masses is less than 0.024 .
The radii of these stars from and are even
closer, with differences of less than 0.007 . These stars may be
the most well known solar-like oscillating stars and deserve to be studied in
detail. The asteroseismic expressions we derive for mass and radius show slight
dependence on metallicity. We therefore develop a new method for computing
initial metallicity from this surface metallicity by taking into account the
effect of microscopic diffusion. The time dependence of initial metallicity
shows some very interesting features that may be important for our
understanding of chemical enrichment of Galactic Disc. According to our
findings, every epoch of the disc has its own lowest and highest values for
metallicity. It seems that rotational velocity is inversely proportional to 1/2
power of age as given by the Skumanich relation.Comment: 19 pages, 12 figure
Properties of 42 Solar-type Kepler Targets from the Asteroseismic Modeling Portal
Recently the number of main-sequence and subgiant stars exhibiting solar-like
oscillations that are resolved into individual mode frequencies has increased
dramatically. While only a few such data sets were available for detailed
modeling just a decade ago, the Kepler mission has produced suitable
observations for hundreds of new targets. This rapid expansion in observational
capacity has been accompanied by a shift in analysis and modeling strategies to
yield uniform sets of derived stellar properties more quickly and easily. We
use previously published asteroseismic and spectroscopic data sets to provide a
uniform analysis of 42 solar-type Kepler targets from the Asteroseismic
Modeling Portal (AMP). We find that fitting the individual frequencies
typically doubles the precision of the asteroseismic radius, mass and age
compared to grid-based modeling of the global oscillation properties, and
improves the precision of the radius and mass by about a factor of three over
empirical scaling relations. We demonstrate the utility of the derived
properties with several applications.Comment: 12 emulateapj pages, 9 figures, 1 online-only extended figure, 1
table, ApJS accepted (typo corrected in Eq.8
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