22 research outputs found
Signatures of rocky planet engulfment in HAT-P-4. Implications for chemical tagging studies
Aims. To explore the possible chemical signature of planet formation in the
binary system HAT-P-4, by studying abundance vs condensation temperature Tc
trends. The star HAT-P-4 hosts a planet detected by transits while its stellar
companion does not have any detected planet. We also study the Lithium content,
which could shed light on the problem of Li depletion in exoplanet host stars.
Conclusions. The exoplanet host star HAT-P-4 is found to be ~0.1 dex more metal
rich than its companion, which is one of the highest differences in metallicity
observed in similar systems. This could have important implications for
chemical tagging studies, disentangling groups of stars with a common origin.
We rule out a possible peculiar composition for each star as lambda Boo, delta
Scuti or a Blue Straggler. The star HAT-P-4 is enhanced in refractory elements
relative to volatile when compared to its stellar companion. Notably, the
Lithium abundance in HAT-P-4 is greater than in its companion by ~0.3 dex,
which is contrary to the model that explains the Lithium depletion by the
presence of planets. We propose a scenario where, at the time of planet
formation, the star HAT-P-4 locked the inner refractory material in
planetesimals and rocky planets, and formed the outer gas giant planet at a
greater distance. The refractories were then accreted onto the star, possibly
due to the migration of the giant planet. This explains the higher metallicity,
the higher Lithium content, and the negative Tc trend detected. A similar
scenario was recently proposed for the solar twin star HIP 68468, which is in
some aspects similar to HAT-P-4. We estimate a mass of at least Mrock ~ 10
Mearth locked in refractory material in order to reproduce the observed Tc
trends and metallicity.Comment: 5 pages, 6 figures, A&A Letters accepte
High-precision analysis of binary stars with planets. I. Searching for condensation temperature trends in the HD 106515 system
We explore the probable chemical signature of planet formation in the
remarkable binary system HD 106515. The A star hosts a massive long-period
planet with 9 MJup detected by radial velocity. We also refine stellar and
planetary parameters by using non-solar-scaled opacities when modeling the
stars. Methods. We carried out a simultaneous determination of stellar
parameters and abundances, by applying for the first time non-solar-scaled
opacities in this binary system, in order to reach the highest possible
precision. Results. The stars A and B in the binary system HD 106515 do not
seem to be depleted in refractory elements, which is different when comparing
the Sun with solar-twins. Then, the terrestrial planet formation would have
been less efficient in the stars of this binary system. Together with HD
80606/7, this is the second binary system which does not seem to present a
(terrestrial) signature of planet formation, and hosting both systems an
eccentric giant planet. This is in agreement with numerical simulations, where
the early dynamical evolution of eccentric giant planets clear out most of the
possible terrestrial planets in the inner zone. We refined the stellar mass,
radius and age for both stars and found a notable difference of 78% in R
compared to previous works. We also refined the planet mass to mp sini = 9.08
+/- 0.20 MJup, which differs by 6% compared with literature. In addition, we
showed that the non-solar-scaled solution is not compatible with the classical
solar-scaled method, and some abundance differences are comparable to NLTE or
GCE effects specially when using the Sun as reference. Then, we encourage the
use of non-solar-scaled opacities in high-precision studies such as the
detection of Tc trends.[abridged]Comment: 9 pages, 10 figures, A&A accepted. arXiv admin note: text overlap
with arXiv:1507.0812
KELT-17: a chemically peculiar Am star and a hot-Jupiter planet
Context. The detection of planets orbiting chemically peculiar stars is very
scarcely known in the literature. Aims. To determine the detailed chemical
composition of the remarkable planet host star KELT-17. This object hosts a
hot-Jupiter planet with 1.31 MJup detected by transits, being one of the more
massive and rapidly rotating planet hosts to date. We aimed to derive a
complete chemical pattern for this star, in order to compare it with those of
chemically peculiar stars. Methods. We carried out a detailed abundance
determination in the planet host star KELT-17 via spectral synthesis. Stellar
parameters were estimated iteratively by fitting Balmer line profiles and
imposing the Fe ionization balance, using the program SYNTHE together with
plane-parallel ATLAS12 model atmospheres. Specific opacities for an arbitrary
composition and microturbulence velocity vmicro were calculated through the
Opacity Sampling (OS) method. The abundances were determined iteratively by
fitting synthetic spectra to metallic lines of 16 different chemical species
using the program SYNTHE. The complete chemical pattern of KELT-17 was compared
to the recently published average pattern of Am stars. We estimated the stellar
radius by two methods: a) comparing the synthetic spectral energy distribution
with the available photometric data and the Gaia parallax, and b) using a
Bayesian estimation of stellar parameters using stellar isochrones. Results. We
found overabundances of Ti, Cr, Mn, Fe, Ni, Zn, Sr, Y, Zr, and Ba, together
with subsolar values of Ca and Sc. Notably, the chemical pattern agrees with
those recently published of Am stars, being then KELT-17 the first exoplanet
host whose complete chemical pattern is unambiguously identified with this
class. The stellar radius derived by two different methods agrees to each other
and with those previously obtained in the literature.Comment: 5 pages, 8 figures, 2 tables, A&A accepte
ζ1 + ζ2 Reticuli binary system: a puzzling chromospheric activity pattern
We perform, for the first time, a detailed long-term activity study of the binary system ζ Ret. We use all available HARPS spectra obtained between the years 2003 and 2016. We build a time series of the Mount Wilson S index for both stars, then we analyse these series by using Lomb-Scargle periodograms. The components ζ1 Ret and ζ2 Ret that belong to this binary system are physically very similar to each other and also similar to our Sun, which makes it a remarkable system. We detect in the solar-analogue star ζ2 Ret a long-term activity cycle with a period of ?10 yr, similar to the solar one (?11 yr). It is worthwhile to mention that this object satisfies previous criteria for a flat star and for a cycling star simultaneously. Another interesting feature of this binary system is a high ?0.220 dex difference between the average log (R^´ }_HK) activity levels of both stars. Our study clearly shows that ζ1 Ret is significantly more active than ζ2 Ret. In addition, ζ1 Ret shows an erratic variability in its stellar activity. In this work, we explore different scenarios trying to explain this rare behaviour in a pair of coeval stars, which could help to explain the difference in this and other binary systems. From these results, we also warn that for the development of activity-age calibrations (which commonly use binary systems and/or stellar clusters as calibrators) the whole history of activity available for the stars involved should be taken into account.Fil: Flores, M. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Instituto de Ciencias Astronómicas, de la Tierra y del Espacio. Universidad Nacional de San Juan. Instituto de Ciencias Astronómicas, de la Tierra y del Espacio; ArgentinaFil: Saffe, Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Instituto de Ciencias Astronómicas, de la Tierra y del Espacio. Universidad Nacional de San Juan. Instituto de Ciencias Astronómicas, de la Tierra y del Espacio; ArgentinaFil: Buccino, Andrea Paola. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Jaque Arancibia, Marcelo Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Instituto de Ciencias Astronómicas, de la Tierra y del Espacio. Universidad Nacional de San Juan. Instituto de Ciencias Astronómicas, de la Tierra y del Espacio; ArgentinaFil: González, J F. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Instituto de Ciencias Astronómicas, de la Tierra y del Espacio. Universidad Nacional de San Juan. Instituto de Ciencias Astronómicas, de la Tierra y del Espacio; ArgentinaFil: Nuñez, N E. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Instituto de Ciencias Astronómicas, de la Tierra y del Espacio. Universidad Nacional de San Juan. Instituto de Ciencias Astronómicas, de la Tierra y del Espacio; ArgentinaFil: Jofré, E. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba; Argentin
X-ray, UV, and optical observations of the accretion disk and boundary layer in the symbiotic star RT Crucis
Compared to mass transfer in cataclysmic variables, the nature of accretion in symbiotic binaries in which red giants transfer material to white dwarfs (WDs) has been difficult to uncover. The accretion flows in a symbiotic binary are most clearly observable, however, when there is no quasi-steady shell burning on the WD to hide them. RT Cru is the prototype of such non-burning symbiotics, with its hard (δ-type) X-ray emission providing a view of its innermost accretion structures. In the past 20 yr, RT Cru has experienced two similar optical brightening events, separated by ∼ 4000 days and with amplitudes of ΔV ∼ 1.5 mag. After Swift became operative, the Burst Alert Telescope (BAT) detector revealed a hard X-ray brightening event almost in coincidence with the second optical peak. Spectral and timing analyses of multi-wavelength observations that we describe here, from NuSTAR, Suzaku, Swift/X-Ray Telescope (XRT) + BAT + UltraViolet Optical Telescope (UVOT) (photometry) and optical photometry and spectroscopy, indicate that accretion proceeds through a disk that reaches down to the WD surface. The scenario in which a massive, magnetic WD accretes from a magnetically truncated accretion disk is not supported. For example, none of our data show the minute-time-scale periodic modulations (with tight upper limits from X-ray data) expected from a spinning, magnetic WD. Moreover, the similarity of the UV and X-ray fluxes, as well as the approximate constancy of the hardness ratio within the BAT band, indicate that the boundary layer of the accretion disk remained optically thin to its own radiation throughout the brightening event, during which the rate of accretion onto the WD increased to 6.7 × 10-9M· yr-1 (d/2 kpc)2. For the first time from a WD symbiotic, the NuSTAR spectrum showed a Compton reflection hump at E > 10 keV, due to hard X-rays from the boundary layer reflecting off of the surface of the WD; the reflection amplitude was 0.77 ± 0.21. The best fit spectral model, including reflection, gave a maximum post-shock temperature of kT = 53 ± 4 keV, which implies a WD mass of 1.25 ± 0.02 M·. Although the long-term optical variability in RT Cru is reminiscent of dwarf-novae-type outbursts, the hard X-ray behavior does not correspond to that observed in well-known dwarf nova. An alternative explanation for the brightening events could be that they are due to an enhancement of the accretion rate as the WD travels through the red giant wind in a wide orbit, with a period of about ∼4000 days. In either case, the constancy of the hard X-ray spectrum while the accretion rate rose suggests that the accretion-rate threshold between a mostly optically thin and thick boundary layer, in this object, may be higher than previously thought.Fil: Luna, Gerardo Juan Manuel. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Mukai, K.. National Aeronautics and Space Administration; Estados UnidosFil: Sokoloski, J. L.. Columbia University; Estados UnidosFil: Lucy, A. B.. Columbia University; Estados UnidosFil: Cusumano, G.. Istituto Nazionale di Astrofisica; ItaliaFil: Segreto, A.. Istituto Nazionale di Astrofisica; ItaliaFil: Jaque Arancibia, Marcelo Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Instituto de Ciencias Astronómicas, de la Tierra y del Espacio. Universidad Nacional de San Juan. Instituto de Ciencias Astronómicas, de la Tierra y del Espacio; ArgentinaFil: Nuñez, Natalia Edith. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Instituto de Ciencias Astronómicas, de la Tierra y del Espacio. Universidad Nacional de San Juan. Instituto de Ciencias Astronómicas, de la Tierra y del Espacio; ArgentinaFil: Puebla, R. E.. Universidad Central del Ecuador; EcuadorFil: Nelson, T.. University of Pittsburgh at Johnstown; Estados UnidosFil: Walter, F. M.. Columbia University; Estados Unido
Evaluation et cartographie du risque d'incendie de foret dans le massif des Maures. Rapport final
SIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : GR 1467 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc
Discovery of an activity cycle in the solar analog HD 45184
Context. Most stellar activity cycles similar to that found in the Sun have been detected by using the chromospheric Ca i
Using non-solar-scaled opacities to derive stellar parameters
Aims. In an effort to improve spectroscopic methods of stellar parameters determination, we implemented non-solar-scaled opacities in a simultaneous derivation of fundamental parameters and abundances. We wanted to compare the results with the usual solar-scaled method using a sample of solar-type and evolved stars.
Methods. We carried out a high-precision determination of stellar parameters and abundances by applying non-solar-scaled opacities and model atmospheres. Our sample is composed of 20 stars, including main sequence and evolved objects. The stellar parameters were determined by imposing ionization and excitation equilibrium of Fe lines, with an updated version of the FUNDPAR program, together with plane-parallel ATLAS12 model atmospheres and the MOOG code. Opacities for an arbitrary composition and vmicro were calculated through the opacity sampling (OS) method. We used solar-scaled models in the first step, and then continued the process, but scaled to the abundance values found in the previous step (i.e. non-solar-scaled). The process finishes when the stellar parameters of one step are the same as in the previous step, i.e. we use a doubly iterated method.
Results. We obtained a small difference in stellar parameters derived with non-solar-scaled opacities compared to classical solar-scaled models. The differences in Teff, log g, and [Fe/H] amount to 26 K, 0.05 dex, and 0.020 dex for the stars in our sample. These differences can be considered the first estimation of the error due to the use of classical solar-scaled opacities to derive stellar parameters with solar-type and evolved stars. We note that some chemical species could also show an individual variation greater than those of the [Fe/H] (up to ~0.03 dex) and varying from one species to another, obtaining a chemical pattern difference between the two methods. This means that condensation temperature Tc trends could also present a variation. We include an example showing that using non-solar-scaled opacities, the solution found with the classical solar-scaled method indeed cannot always verify the excitation and ionization balance conditions required for a model atmosphere. We discuss in the text the significance of the differences obtained when using solar-scaled versus non-solar-scaled methods.
Conclusions. We consider that the use of the non-solar-scaled opacities is not mandatory in every statistical study with large samples of stars. However, for those high-precision works whose results depend on the mutual comparison of different chemical species (such as the analysis of condensation temperature Tc trends), we consider its application to be worthwhile. To date, this is probably one of the most precise spectroscopic methods for stellar parameter derivation
Testing the accretion scenario of lambda Boo stars
Our aim is to test the accretion scenario of lambda Boo stars. This model
predicts that a binary system with two early-type stars passing through a
diffuse cloud should both display the same superficial peculiarity. We carried
out a detailed abundance determination of three multiple systems hosting a
candidate lambda Boo star: the remarkable triple system HD 15164/65/65C and the
binary systems HD 193256/281 and HD 198160/161. The abundance analysis of HD
15164/65/65C shows a clear lambda Boo object (HD 15165) and two objects with
near solar composition (HD 15164 and 15165C). Notably, the presence of a lambda
Boo star (HD 15165) together with a near solar early-type object (HD 15164) is
difficult to explain under the accretion scenario. Also, the solar-like
composition derived for the late-type star of the system (HD 15165C) could be
used, for the first time, as a proxy for the initial composition of the lambda
Boo stars. Then, by reviewing abundance analysis of all known binary systems
with candidate lambda Boo stars from literature and including the systems
analyzed here, we find no binary/multiple system having two clear "bonafide"
lambda Boo stars, as expected from the accretion scenario. The closer
candidates to show two lambda Boo-like stars are HD 84948, HD 171948 and HD
198160; however, in our opinion they show mild rather than clear lambda Boo
patterns. Our results brings little support to the accretion scenario. Then,
there is an urgent need of additional binary and multiple systemsto be analyzed
through a detailed abundance analysis.[abridged]Comment: A&A accepted, 14 pages, 9 Figures, 9 Table
Chemical analysis of early-type stars with planets
Aims. Our goal is to explore the chemical pattern of early-type stars with planets, searching for a possible signature of planet formation. In particular, we study a likely relation between the λ Boötis chemical pattern and the presence of giant planets.
Methods. We performed a detailed abundance determination in a sample of early-type stars with and without planets via spectral synthesis. Fundamental parameters were initially estimated using Strömgren photometry or literature values and then refined by requiring excitation and ionization balances of Fe lines. We derived chemical abundances for 23 different species by fitting observed spectra with an iterative process. Synthetic spectra were calculated using the program SYNTHE together with local thermodynamic equilibrium ATLAS12 model atmospheres. We used specific opacities calculated for each star, depending on the individual composition and microturbulence velocity vmicro through the opacity sampling method. The complete chemical pattern of the stars were then compared to those of λ Boötis stars and other chemically peculiar stars.
Results. We compared the chemical pattern of the stars in our sample (13 stars with planets and 24 stars without detected planets) with those of λ Boötis and other chemically peculiar stars. We have found four λ Boötis stars in our sample, two of which present planets and circumstellar disks (HR 8799 and HD 169142) and one without planets detected (HD 110058). We have also identified the first λ Boötis star orbited by a brown dwarf (ζ Del). This interesting pair, the λ Boötis star and brown dwarf, could help to test stellar formation scenarios. We found no unique chemical pattern for the group of early-type stars bearing giant planets. However, our results support, in principle, a suggested scenario in which giant planets orbiting pre-main-sequence stars possibly block the dust of the disk and result in a λ Boötis-like pattern. On the other hand, we do not find a λ Boötis pattern in different hot-Jupiter planet host stars, which does not support the idea of possible accretion from the winds of hot-Jupiters, recently proposed in the literature. As a result, other mechanisms should account for the presence of the λ Boötis pattern between main-sequence stars. Finally, we suggest that the formation of planets around λ Boötis stars, such as HR 8799 and HD 169142, is also possible through the core accretion process and not only gravitational instability