104 research outputs found
NIR spectroscopy of the Sun and HD20010 - Compiling a new linelist in the NIR
Context: Effective temperature, surface gravity, and metallicity are basic
spectroscopic stellar parameters necessary to characterize a star or a
planetary system. Reliable atmospheric parameters for FGK stars have been
obtained mostly from methods that relay on high resolution and high
signal-to-noise optical spectroscopy. The advent of a new generation of high
resolution near-IR spectrographs opens the possibility of using classic
spectroscopic methods with high resolution and high signal-to-noise in the NIR
spectral window. Aims: We aim to compile a new iron line list in the NIR from a
solar spectrum to derive precise stellar atmospheric parameters, comparable to
the ones already obtained from high resolution optical spectra. The spectral
range covers 10 000 {\AA} to 25 000 {\AA}, which is equivalent to the Y, J, H,
and K bands. Methods: Our spectroscopic analysis is based on the iron
excitation and ionization balance done in LTE. We use a high resolution and
high signal-to-noise ratio spectrum of the Sun from the Kitt Peak telescope as
a starting point to compile the iron line list. The oscillator strengths (log
gf) of the iron lines were calibrated for the Sun. The abundance analysis was
done using the MOOG code after measuring equivalent widths of 357 solar iron
lines. Results: We successfully derived stellar atmospheric parameters for the
Sun. Furthermore, we analysed HD20010, a F8IV star, from which we derived
stellar atmospheric parameters using the same line list as for the Sun. The
spectrum was obtained from the CRIRES- POP database. The results are compatible
with the ones found in the literature, confirming the reliability of our line
list. However, due to the quality of the data we obtain large errors.Comment: 9 pages and 9 figure
New and updated stellar parameters for 71 evolved planet hosts. On the metallicity - giant planet connection
It is still being debated whether the well-known metallicity - giant planet
correlation for dwarf stars is also valid for giant stars. For this reason,
having precise metallicities is very important. Different methods can provide
different results that lead to discrepancies in the analysis of planet hosts.
To study the impact of different analyses on the metallicity scale for evolved
stars, we compare different iron line lists to use in the atmospheric parameter
derivation of evolved stars. Therefore, we use a sample of 71 evolved stars
with planets. With these new homogeneous parameters, we revisit the metallicity
- giant planet connection for evolved stars. A spectroscopic analysis based on
Kurucz models in local thermodynamic equilibrium (LTE) was performed through
the MOOG code to derive the atmospheric parameters. Two different iron line
list sets were used, one built for cool FGK stars in general, and the other for
giant FGK stars. Masses were calculated through isochrone fitting, using the
Padova models. Kolmogorov-Smirnov tests (K-S tests) were then performed on the
metallicity distributions of various different samples of evolved stars and red
giants. All parameters compare well using a line list set, designed
specifically for cool and solar-like stars to provide more accurate
temperatures. All parameters derived with this line list set are preferred and
are thus adopted for future analysis. We find that evolved planet hosts are
more metal-poor than dwarf stars with giant planets. However, a bias in giant
stellar samples that are searched for planets is present. Because of a colour
cut-off, metal-rich low-gravity stars are left out of the samples, making it
hard to compare dwarf stars with giant stars. Furthermore, no metallicity
enhancement is found for red giants with planets (\,dex) with
respect to red giants without planets.Comment: 22 pages, 10 figures, 12 tables, accepted to A&
SWEET-Cat: A catalogue of parameters for Stars With ExoplanETs I. New atmospheric parameters and masses for 48 stars with planets
Due to the importance that the star-planet relation has to our understanding
of the planet formation process, the precise determination of stellar
parameters for the ever increasing number of discovered extra-solar planets is
of great relevance. Furthermore, precise stellar parameters are needed to fully
characterize the planet properties. It is thus important to continue the
efforts to determine, in the most uniform way possible, the parameters for
stars with planets as new discoveries are announced. In this paper we present
new precise atmospheric parameters for a sample of 48 stars with planets. We
then take the opportunity to present a new catalogue of stellar parameters for
FGK and M stars with planets detected by radial velocity, transit, and
astrometry programs. Stellar atmospheric parameters and masses for the 48 stars
were derived assuming LTE and using high resolution and high signal-to-noise
spectra. The methodology used is based on the measurement of equivalent widths
for a list of iron lines and making use of iron ionization and excitation
equilibrium principles. For the catalog, and whenever possible, we used
parameters derived in previous works published by our team, using well defined
methodologies for the derivation of stellar atmospheric parameters. This set of
parameters amounts to over 65% of all planet host stars known, including more
than 90% of all stars with planets discovered through radial velocity surveys.
For the remaining targets, stellar parameters were collected from the
literature.Comment: Astronomy & Astrophysics, accepted for publicatio
The AMBRE Project: searching for the closest solar siblings
Finding solar siblings, that is, stars that formed in the same cluster as the
Sun, will yield information about the conditions at the Sun's birthplace. We
search for solar sibling candidates in AMBRE, the very large spectra database
of solar vicinity stars. Since the ages and chemical abundances of solar
siblings are very similar to those of the Sun, we carried out a chemistry- and
age-based search for solar sibling candidates. We used high-resolution spectra
to derive precise stellar parameters and chemical abundances of the stars. We
used these spectroscopic parameters together with Gaia DR2 astrometric data to
derive stellar isochronal ages. Gaia data were also used to study the
kinematics of the sibling candidates. From the about 17000 stars that are
characterized within the AMBRE project, we first selected 55 stars whose
metallicities are closest to the solar value (-0.1 < [Fe/H] < 0.1 dex). For
these stars we derived precise chemical abundances of several iron-peak, alpha-
and neutron-capture elements, based on which we selected 12 solar sibling
candidates with average abundances and metallicities between -0.03 to 0.03 dex.
Our further selection left us with 4 candidates with stellar ages that are
compatible with the solar age within observational uncertainties. For the 2 of
the hottest candidates, we derived the carbon isotopic ratios, which are
compatible with the solar value. HD186302 is the most precisely characterized
and probably the most probable candidate of our 4 best candidates. Very precise
chemical characterization and age estimation is necessary to identify solar
siblings. We propose that in addition to typical chemical tagging, the study of
isotopic ratios can give further important information about the relation of
sibling candidates with the Sun. Ideally, asteroseismic age determinations of
the candidates could solve the problem of imprecise isochronal ages.Comment: Accepted for publication in A&
Deriving precise parameters for cool solar-type stars. Optimizing the iron line list
Temperature, surface gravity, and metallicitity are basic stellar atmospheric
parameters necessary to characterize a star. We aim to improve the description
of the spectroscopic temperatures especially for the cooler stars where the
differences with the Infrared Flux Method are higher, as presented in previous
work. Our spectroscopic analysis is based on the iron excitation and ionization
balance, assuming Kurucz model atmospheres in LTE. The abundance analysis is
determined using the code MOOG. We optimize the line list using a cool star
with high resolution and high signal-to-noise spectrum, as a reference in order
to check for weak, isolated lines. We test the quality of the new line list by
re-deriving stellar parameters for 451 stars with high resolution and
signal-to-noise HARPS spectra, that were analyzed in a previous work with a
larger line list. The comparison in temperatures between this work and the
latest IRFM shows that the differences for the cooler stars are significantly
smaller and more homogeneously distributed than in previous studies for stars
with temperatures below 5000 K. We use the new line list to re-derive
parameters for some of the cooler stars that host planets. Finally, we present
the impact of the new temperatures on the [Cr I/Cr II] and [Ti I/Ti II]
abundance ratios that previously showed systematic trends with temperature.Comment: 11 pages, 14 figures, accepted to A&
The role of ground motion duration and pulse effects in the collapse of ductile systems
The seismic collapse capacity of ductile single‐degree‐of‐freedom systems vulnerable to P‐Δ effects is investigated by examining the respective influence of ground motion duration and acceleration pulses. The main objective is to provide simple relationships for predicting the duration‐dependent collapse capacity of modern ductile systems. A novel procedure is proposed for modifying spectrally equivalent records, such that they are also equivalent in terms of pulses. The effect of duration is firstly assessed, without accounting for pulses, by assembling 101 pairs of long and short records with equivalent spectral response. The systems considered exhibit a trilinear backbone curve with an elastic, hardening and negative stiffness segment. The parameters investigated include the period, negative stiffness slope, ductility and strain hardening, for both bilinear and pinching hysteretic models. Incremental dynamic analysis is employed to determine collapse capacities and derive design collapse capacity spectra. It is shown that up to 60% reduction in collapse capacity can occur due to duration effects for flexible bilinear systems subjected to low levels of P‐Δ. A comparative evaluation of intensity measures that account for spectral shape, duration or pulses, is also presented. The influence of pulses, quantified through incremental velocity, is then explicitly considered to modify the long records, such that their pulse distribution matches that of their short spectrally equivalent counterparts. The results show the need to account for pulse effects in order to achieve unbiased estimation of the role of duration in flexible ductile systems, as it can influence the duration‐induced reduction in collapse capacity by more than 20%
Chemical abundances and kinematics of 257G-, K-type field giants. Setting a base for further analysis of giant-planet properties orbiting evolved stars
We performed a uniform and detailed abundance analysis of 12 refractory elements (Na, Mg, Al, Si, Ca, Ti, Cr, Ni, Co, Sc, Mn, and V) for a sample of 257G- and K-type evolved stars from the CORALIE planet search programme. To date, only one of these stars is known to harbour a planetary companion. We aimed to characterize this large sample of evolved stars in terms of chemical abundances and kinematics, thus setting a solid base for further analysis of planetary properties around giant stars. This sample, being homogeneously analysed, can be used as a comparison sample for other planet-related studies, as well as for different type of studies related to stellar and Galaxy astrophysics. The abundances of the chemical elements were determined using an local thermodynamic equilibrium (LTE) abundance analysis relative to the Sun, with the spectral synthesis code moog and a grid of Kurucz ATLAS9 atmospheres. To separate the Galactic stellar populations, both a purely kinematical approach and a chemical method were applied. We confirm the overabundance of Na in giant stars compared to the field FGK dwarfs. This enhancement might have a stellar evolutionary character, but departures from LTE may also produce a similar enhancement. Our chemical separation of stellar populations also suggests a ‘gap' in metallicity between the thick-disc and high-α metal-rich stars, as previously observed in dwarfs sample from HARPS. The present sample, as most of the giant star samples, also suffers from the B − V colour cut-off, which excludes low-log g stars with high metallicities, and high-log g star with low [Fe/H]. For future studies of planet occurrence dependence on stellar metallicity around these evolved stars, we suggest to use a subsample of stars in a ‘cut-rectangle' in the log g-[Fe/H] diagram to overcome the aforementioned issu
Planets around evolved intermediate-mass stars III. Planet candidates and long-term activity signals in six open clusters
[abridged]The aim of this work is to search for planets around evolved stars,
with a special focus on stars more massive than 2\,M in light of
previous findings that show a drop in planet occurrence around stars above this
mass. We used \texttt{kima} to find the Keplerian orbits most capable of
explaining the periodic signals observed in RV data. We also studied the
variation of stellar activity indicators and photometry in order to discard
stellar signals mimicking the presence of planets. We present a planet
candidate in the open cluster NGC3680 that orbits the 1.64\,M star No.
41. The planet has a minimum mass of 5.13M\, and a period of 1155 days.
We also present periodic and large-amplitude RV signals of probable stellar
origin in two more massive stars (5.84 and 3.05\,M in the clusters
NGC2345 and NGC3532). Finally, using new data, we revise the RV signals of the
three stars analysed in our previous paper. We confirm the stellar origin of
the signals observed in NGC2423 No. 3 and NGC4349 No. 127. On the other hand,
the new data collected for IC4651 No. 9122 (1.79\,M) seem to support
the presence of a bona fide planet of 6.22M\, at a period of 744 days,
although more data will be needed to discard a possible correlation with the
CCF-FWHM. The targets presented in this work showcase the difficulties in
interpreting RV data for evolved massive stars. The use of several activity
indicators (CCF-FWHM, CCF-BIS, \ha), photometry, and long-term observations
(covering several orbital and stellar rotational periods) is required to
discern the true nature of the signals. However, in some cases, all this
information is insufficient, and the inclusion of additional data -- such as
the determination of magnetic field variability or RV points in the
near-infrared -- will be necessary to identify the nature of the discovered
signals.Comment: accepted in A&
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