59 research outputs found
Chemical abundances of 1111 FGK stars from the HARPS-GTO planet search sample. III. Sulfur
Context. Elemental abundances are of prime importance to help us reconstruct
the origin and evolution of stars and galaxies in our Universe. Sulfur
abundances have not been as heavily studied as other elements, so some details
regarding its behaviour are still unclear. Aims. We aim to investigate [S/Fe]
ratios in stars of the solar neighbourhood in order to analyse the chemical
evolution of sulfur and probe for possible differences in abundances of planet
host and non-planet host stars. Methods. We use the code MOOG to perform
spectral synthesis and derive v*sin(i) values and [S/Fe] ratios for 719 FGK
stars with high-resolution (R~115000) and high-quality spectra from the
HARPS-GTO program. We find the best fit and corresponding parameter values by
performing chi-square minimisation of the deviation between synthetic profiles
and observational spectra. Results. Our results reveal that sulfur behaves as a
typical alpha-element, with low abundances in young thin disk stars and high
abundances in old thick disk stars, following what was expected from our
understanding of the Galactic chemical evolution (GCE). Nevertheless, further
studies into the abundances of sulfur in very metal-poor stars are required as
our sample only derived sulfur abundances to stars with metallicity as low as
[Fe/H]=-1.13 dex. High-alpha metal rich stars are more enhanced in sulfur
compared to their thin disk counterparts at the same metallicity. We compare
our results to GCE models from other authors in the [S/Fe] vs. [Fe/H] plane.
The [S/Fe]-age relationship is a good proxy for time, just like it is the case
with other alpha-elements. We report no differences in the abundances of sulfur
between stars with and without planetary companions in the metallicity range
[Fe/H] >= -0.3 dex.Comment: 11 pages, 10 figures. Paper has been accepted for publication in
Astronomy & Astrophysic
Volatiles and refratories in solar analogs: no terrestial planet connection
We have analysed very high-quality HARPS and UVES spectra of 95 solar
analogs, 24 hosting planets and 71 without detected planets, to search for any
possible signature of terrestial planets in the chemical abundances of volatile
and refractory elements with respect to the solar abundances. We demonstrate
that stars with and without planets in this sample show similar mean abundance
ratios, in particular, a sub-sample of 14 planet-host and 14 "single" solar
analogs in the metallicity range 0.14<[Fe/H]<0.36. In addition, two of the
planetary systems in this sub-sample, containing each of them a
super-Earth-like planet with masses in the range ~ 7-11 Earth masses, have
different volatile-to-refratory abundance ratios to what would be expected from
the presence of a terrestial planets. Finally, we check that after removing the
Galactic chemical evolution effects any possible difference in mean abundances,
with respect to solar values, of refratory and volatile elements practically
dissappears.Comment: 2 pages, 2 figures, to appear in the proceedings of the 276th IAU
Symposium "The Astrophysics of Planetary Systems
Volatiles and refratories in solar analogs: No terrestial planet connection
We have analysed very high-quality HARPS and UVES spectra of 95 solar analogs, 24 hosting planets and 71 without detected planets, to search for any possible signature of terrestial planets in the chemical abundances of volatile and refractory elements with respect to the solar abundances. We demonstrate that stars with and without planets in this sample show similar mean abundance ratios, in particular, a sub-sample of 14 planet-host and 14 "single” solar analogs in the metallicity range 0.14 < [Fe/H] < 0.36. In addition, two of the planetary systems in this sub-sample, containing each of them a super-Earth-like planet with masses in the range ~ 7-11 Earth masses, have different volatile-to-refratory abundance ratios to what would be expected from the presence of a terrestial planets. Finally, we check that after removing the Galactic chemical evolution effects any possible difference in mean abundances, with respect to solar values, of refratory and volatile elements practically dissappear
Chemical clues on the formation of planetary systems
Theoretical studies suggest that C/O and Mg/Si are the most important elemental ratios in determining the mineralogy of terrestrial planets. The C/O ratio controls the distribution of Si among carbide and oxide species, while Mg/Si gives information about the silicate mineralogy. We find mineralogical ratios quite different from those of the Sun, showing that there is a wide variety of planetary systems which are not similar to Solar System. Many of planetary host stars present a Mg/Si value lower than 1, so their planets will have a high Si content to form species such as MgSiO3. This type of composition can have important implications for planetary processes like plate tectonics, atmospheric composition or volcanism. Moreover, the information given by these ratios can guide us in the search of stars more probable to form terrestrial planet
Enhanced lithium depletion in Sun-like stars with orbiting planets
The surface abundance of lithium on the Sun is 140 times less than
protosolar, yet the temperature at the base of the surface convective zone is
not hot enough to burn Li. A large range of Li abundances in solar type stars
of the same age, mass and metallicity is observed, but theoretically difficult
to understand. An earlier suggestion that Li is more depleted in stars with
planets was weakened by the lack of a proper comparison sample of stars without
detected planets. Here we report Li abundances for an unbiased sample of
solar-analogue stars with and without detected planets. We find that the
planet-bearing stars have less than 1 per cent of the primordial Li abundance,
while about 50 per cent of the solar analogues without detected planets have on
average 10 times more Li. The presence of planets may increase the amount of
mixing and deepen the convective zone to such an extent that the Li can be
burned.Comment: 13 pages, 2 figure
Determination of stellar parameters for Ariel targets: a comparison analysis between different spectroscopic methods
Ariel has been selected as the next ESA M4 science mission and it is expected to be launched in 2028. During its 4-year mission, Ariel will observe the atmospheres of a large and diversified population of transiting exoplanets. A key factor for the achievement of the scientific goal of Ariel is the selection strategy for the definition of the input target list. A meaningful choice of the targets requires an accurate knowledge of the planet hosting star properties and this is necessary to be obtained well before the launch. In this work, we present the results of a bench-marking analysis between three different spectroscopic techniques used to determine stellar parameters for a selected number of targets belonging to the Ariel reference sample. We aim to consolidate a method that will be used to homogeneously determine the stellar parameters of the complete Ariel reference sample. Homogeneous, accurate and precise derivation of stellar parameters is crucial for characterising exoplanet-host stars and in turn is a key factor for the accuracy of the planet properties
A compositional link between rocky exoplanets and their host stars
Stars and planets both form by accreting material from a surrounding disk.
Because they grow from the same material, theory predicts that there should be
a relationship between their compositions. In this study, we search for a
compositional link between rocky exoplanets and their host stars. We estimate
the iron-mass fraction of rocky exoplanets from their masses and radii and
compare it with the compositions of their host stars, which we assume reflect
the compositions of the protoplanetary disks. We find a correlation (but not a
1:1 relationship) between these two quantities, with a slope of >4, which we
interpret as being attributable to planet formation processes. Super-Earths and
super-Mercuries appear to be distinct populations with differing compositions,
implying differences in their formation processes.Comment: Authors' version of the manuscript. Published in Scienc
TESS asteroseismology of the known red-giant host stars HD 212771 and HD 203949
International audienc
TOI-332 b: a super dense Neptune found deep within the Neptunian desert
To date, thousands of planets have been discovered, but there are regions of the orbital parameter space that are still bare. An example is the short period and intermediate mass/radius space known as the ‘Neptunian desert’, where planets should be easy to find but discoveries remain few. This suggests unusual formation and evolution processes are responsible for the planets residing here. We present the discovery of TOI-332 b, a planet with an ultra-short period of 0.78 d that sits firmly within the desert. It orbits a K0 dwarf with an effective temperature of 5251 ± 71 K. TOI-332 b has a radius of R⊕, smaller than that of Neptune, but an unusually large mass of 57.2 ± 1.6 M⊕. It has one of the highest densities of any Neptune-sized planet discovered thus far at g cm−3. A 4-layer internal structure model indicates it likely has a negligible hydrogen-helium envelope, something only found for a small handful of planets this massive, and so TOI-332 b presents an interesting challenge to planetary formation theories. We find that photoevaporation cannot account for the mass-loss required to strip this planet of the Jupiter-like envelope it would have been expected to accrete. We need to look towards other scenarios, such as high-eccentricity migration, giant impacts, or gap opening in the protoplanetary disc, to try and explain this unusual discovery
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