arXiv subjects

Antonio Claret

Publications and source records attributed to Antonio Claret.

18 recordsLinked to original sources

arXiv2022

Rapidly rotating stars and their transiting planets: KELT-17b, KELT-19Ab, and KELT-21b in the CHEOPS and TESS era

Rapidly rotating early-type main-sequence stars with transiting planets are interesting in many aspects. Unfortunately, several astrophysical effects in such systems are not well understood yet. Therefore, we performed a photometric mini-survey of three rapidly rotating stars with transiting planets, namely KELT-17b, KELT-19Ab, and KELT-21b, using the Characterising Exoplanets Satellite (CHEOPS), complemented with Transiting Exoplanet Survey Satellite (TESS) data, and spectroscopic data. We aimed at investigating the spin-orbit misalignment and its photometrical signs, therefore the high-quality light curves of the selected objects were tested for transit asymmetry, transit duration variations, and orbital precession. In addition, we performed transit time variation analyses, obtained new stellar parameters, and refined the system parameters. For KELT-17b and KELT-19Ab we obtained significantly smaller planet radius as found before. The gravity-darkening effect is very small compared to the precision of CHEOPS data. We can report only on a tentative detection of the stellar inclination of KELT-21, which is about 60 deg. In KELT-17b and KELT-19Ab we were able to exclude long-term transit duration variations causing orbital precession. The shorter transit duration of KELT-19Ab compared to the discovery paper is probably a consequence of a smaller planet radius. KELT-21b is promising from this viewpoint, but further precise observations are needed. We did not find any convincing evidence for additional objects in the systems.

astro-ph.EP↗

arXiv2020

The ExoTETHyS package: Tools for Exoplanetary Transits around Host Stars

We present here the first release of the open-source python package ExoTETHyS, which aims to provide a stand-alone set of tools for modeling spectro-photometric observations of the transiting exoplanets. In particular, we describe: (1) a new calculator of stellar limb-darkening coefficients that outperforms the existing software by one order of magnitude in terms of light-curve model accuracy, i.e., down to <10 parts per million (ppm); (2) an exact transit light-curve generator based on the entire stellar intensity profile rather than limb-darkening coefficients. New tools will be added in later releases to model various effects in exoplanetary transits and eclipsing binaries. ExoTETHyS is a reference package for high-precision exoplanet atmospheric spectroscopy with the upcoming JWST and ARIEL missions.

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arXiv2019

Orbital Decay in a 20 Minute Orbital Period Detached Binary with a Hydrogen Poor Low Mass White Dwarf

We report the discovery of a detached double white dwarf binary with an orbital period of $\approx20.6\,\rm minutes$, PTF J053332.05+020911.6. The visible object in this binary, PTF J0533+0209B, is a $\approx 0.17\,M_\odot$ mass white dwarf with a helium-dominated atmosphere containing traces of hydrogen (DBA). This object exhibits ellipsoidal variations due to tidal deformation, and is the visible component in a single-lined spectroscopic binary with a velocity semi-amplitude of $K_B=618.7\pm6.9 \, \rm km \, s^{-1}$. We have detected significant orbital decay due to the emission of gravitational radiation, and we expect that the Laser Interferometer Space Antenna (LISA) will detect this system with a signal to noise of $8.4^{+4.2}_{-3.0}$ after four years of operation. Because this system already has a well determined orbital period, radial velocity semi-amplitude, temperature, atmospheric composition, surface gravity, and orbital decay rate, a LISA signal will help fully constrain the properties of this system by providing a direct measurement of its inclination. Thus, this binary demonstrates the synergy between electromagnetic and gravitational radiation for constraining the physical properties of an astrophysical object.

astro-ph.SR↗

arXiv2019

Updating the theoretical tidal evolution constants: Apsidal motion and the moment of inertia

The theoretical apsidal motion constants are key tools to investigate the stellar interiors in close eccentric binary systems. In addition, these constants and the moment of inertia are also important to investigate the tidal evolution of close binary stars as well as of exo-planetary systems. The aim of the paper is to present new evolutionary models, based on the MESA package, that include the internal structure constants (k$_2$, k$_3$, and k$_4$), the radius of gyration, and the gravitational potential energy for configurations computed from the pre-main-sequence (PMS) up to the first ascent giant branch or beyond. The calculations are available for the three metallicities [Fe/H]= 0.00, -0.50, and -1.00, which take the recent investigations in less metallic environments into account. This new set of models replaces the old ones, published about 15 years ago, using the code GRANADA. Core overshooting was taken into account using the mass-f$_{ov}$ relationship, which was derived semi-empirically for models more massive than 1.2 M$_{\odot}$. The differential equations governing the apsidal motion constants, moment of inertia, and the gravitational potential energy were integrated simultaneously through a fifth-order Runge-Kutta method with a tolerance level of 10$^{-7}$. The resulting models (from 0.8 up to 35.0 M$_{\odot}$) are presented in 54 tables for the three metallicities, containing the usual characteristics of an evolutionary model (age, initial masses, log T$_{\rm eff}$, log g, and log L), the constants of internal structure (k$_2$, k$_3$, and k$_4$), the radius of gyration $β,$ and the factor $α$ that is related with the gravitational potential energy.

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arXiv2019

The dependence of convective core overshooting on stellar mass: reality check, and additional evidence

Overshooting from the convective cores of stars more massive than about 1.2 M(Sun) has a profound impact on their subsequent evolution. And yet, the formulation of the overshooting mechanism in current stellar evolution models has a free parameter (f[ov] in the diffusive approximation) that remains poorly constrained by observations, affecting the determination of astrophysically important quantities such as stellar ages. In an earlier series of papers we assembled a sample of 37 well-measured detached eclipsing binaries to calibrate the dependence of f[ov] on stellar mass, showing that it increases sharply up to a mass of roughly 2 M(Sun), and remains constant thereafter out to at least 4.4 M(Sun). Recent claims have challenged the utility of eclipsing binaries for this purpose, on the basis that the uncertainties in f[ov] from the model fits are typically too large to be useful, casting doubt on a dependence of overshooting on mass. Here we reexamine those claims and show them to be too pessimistic, mainly because they did not account for all available constraints --- both observational and theoretical --- in assessing the true uncertainties. We also take the opportunity to add semi-empirical f[ov] determinations for 13 additional binaries to our previous sample, and to update the values for 9 others. All are consistent with, and strengthen our previous conclusions, supporting a dependence of f[ov] on mass that is now based on estimates for a total of 50 binary systems (100 stars).

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arXiv2018

Limb and gravity-darkening coefficients for the TESS satellite at several metallicities, surface gravities, and microturbulent velocities

We present new gravity and limb-darkening coefficients for a wide range of effective temperatures, gravities, metallicities, and microturbulent velocities. These coefficients can be used in many different fields of stellar physics as synthetic light curves of eclipsing binaries and planetary transits, stellar diameters, line profiles in rotating stars, and others. The limb-darkening coefficients were computed specifically for the photometric system of the space mission TESS and were performed by adopting the least-square method. In addition, the linear and bi-parametric coefficients, by adopting the flux conservation method, are also available. On the other hand, to take into account the effects of tidal and rotational distortions, we computed the passband gravity-darkening coefficients $y(λ)$ using a general differential equation in which we consider the effects of convection and of the partial derivative $\left(\partial{\ln I(λ)}/{\partial{\ln g}}\right)_{T_{\rm eff}}$. To generate the limb-darkening coefficients we adopt two stellar atmosphere models: ATLAS (plane-parallel) and PHOENIX (spherical, quasi-spherical, and $r$-method). The specific intensity distribution was fitted using five approaches: linear, quadratic, square root, logarithmic, and a more general one with four terms. These grids cover together 19 metallicities ranging from 10$^{-5}$ up to 10$^{+1}$ solar abundances, 0 $\leq$ log g $\leq$ 6.0 and 1500 K $\leq$ T$_{\rm eff}$ $\leq$ 50000 K. The calculations of the gravity-darkening coefficients were performed for all plane-parallel ATLAS models.

astro-ph.SR↗

arXiv2018

A new method to compute limb-darkening coefficients for stellar atmosphere models with spherical symmetry: the space missions TESS, Kepler, Corot, and MOST

One of the biggest problems we can encounter while dealing with the limb-darkening coefficients for stellar atmospheric models with spherical symmetry is the difficulty of adjusting both the limb and the central parts simultaneously. In particular, the regions near the drop-offs are not well reproduced for most models, depending on Teff, log g, or wavelength. Even if the law with four terms is used, these disagreements still persist. Here we introduce a new method that considerably improves the description of both the limb and the central parts and that will allow users to test models of stellar atmospheres with spherical symmetry more accurately in environments such as exoplanetary transits, eclipsing binaries, etc. The method introduced here is simple. Instead of considering all the $μ$ points in the adjustment, as is traditional, we consider only the points until the drop-off ($μ_{cri}$) of each model. From this point, we impose a condition ${I(μ)}/{I (1)} = 0$. All calculations were performed by adopting the least-squares method. The resulting coefficients using this new method reproduce the intensity distribution of the PHOENIX spherical models (COND and DRIFT) quite well for the photometric systems of the space missions {\sc TESS}, {\sc KEPLER}, {\sc COROT}, and {\sc MOST}. The calculations cover the following ranges of local gravity and effective temperatures: 2.5 $\leq$ log g $\leq$ 6.0 and 1500 K $\leq$ T$_{\rm eff}$ $\leq$ 12000 K. The new spherical coefficients can easily be adapted to the most commonly used light curve synthesis codes.

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arXiv2018

The dependence of convective core overshooting on stellar mass: Additional binary systems and improved calibration

Many current stellar evolution models assume some dependence of the strength of convective core overshooting on mass for stars more massive than 1.1-1.2 solar masses, but the adopted shapes for that relation have remained somewhat arbitrary for lack of strong observational constraints. In previous work we compared stellar evolution models to well-measured eclipsing binaries to show that, when overshooting is implemented as a diffusive process, the fitted free parameter f(ov) rises sharply up to about 2 solar masses, and remains largely constant thereafter. Here we analyze a new sample of eight binaries selected to be in the critical mass range below 2 solar masses where f(ov) is changing the most, nearly doubling the number of individual stars in this regime. This interval is important because the precise way in which f(ov) changes determines the shape of isochrones in the turnoff region of 1-5 Gyr clusters, and can thus affect their inferred ages. It also has a significant influence on estimates of stellar properties for exoplanet hosts, on stellar population synthesis, and on the detailed modeling of interior stellar structures, including the calculation of oscillation frequencies that are observable with asteroseismic techniques. We find that the derived f(ov) values for our new sample are consistent with the trend defined by our earlier determinations, and strengthen the relation. This provides an opportunity for future series of models to test the new prescription, grounded on observations, against independent observations that may constrain overshooting in a different way.

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arXiv2017

The dependence of convective core overshooting on stellar mass: semi-empirical determination using the diffusive approach with two different element mixtures

Convective core overshooting has a strong influence on the evolution of stars of moderate and high mass. Studies of double-lined eclipsing binaries and stellar oscillations have renewed interest in the possible dependence of overshooting on stellar mass, which has been poorly constrained by observations so far. Here we have used a sample of 29 well-studied double-lined eclipsing binaries in key locations of the H-R diagram to establish the explicit dependence of f(ov) on mass, where f(ov) is the free parameter in the diffusive approximation to overshooting. Measurements of the masses, radii, and temperatures of the binary components were compared against stellar evolution calculations based on the MESA code to infer semi-empirical values of f(ov) for each component. We find a clear mass dependence such that f(ov) rises sharply from zero in the range 1.2--2.0 solar masses, and levels off thereafter up to the 4.4 solar mass limit of our sample. Tests with two different element mixtures indicate the trend is the same, and we find it is also qualitatively similar to the one established in our previous study with the classical step-function implementation of overshooting characterized by the free parameter alpha(ov). Based on these measurements we infer an approximate relationship between the two overshooting parameters of alpha(ov)/f(ov) = 11.36 +/- 0.22, with a possible dependence on stellar properties.

astro-ph.SR↗

arXiv2017

Detection of titanium oxide in the atmosphere of a hot Jupiter

As an exoplanet transits its host star, some of the light from the star is absorbed by the atoms and molecules in the planet's atmosphere, causing the planet to seem bigger; plotting the planet's observed size as a function of the wavelength of the light produces a transmission spectrum. Measuring the tiny variations in the transmission spectrum, together with atmospheric modelling, then gives clues to the properties of the exoplanet's atmosphere. Chemical species composed of light elements$-$such as hydrogen, oxygen, carbon, sodium and potassium$-$have in this way been detected in the atmospheres of several hot giant exoplanets, but molecules composed of heavier elements have thus far proved elusive. Nonetheless, it has been predicted that metal oxides such as titanium oxide (TiO) and vanadium oxide occur in the observable regions of the very hottest exoplanetary atmospheres, causing thermal inversions on the dayside. Here we report the detection of TiO in the atmosphere of the hot-Jupiter planet WASP-19b. Our combined spectrum, with its wide spectral coverage, reveals the presence of TiO (to a confidence level of 7.7σ), a strongly scattering haze (7.4σ) and sodium (3.4σ), and confirms the presence of water (7.9σ) in the atmosphere.

astro-ph.EP↗

arXiv2016

The dependence of convective core overshooting on stellar mass

Convective core overshooting extends the main-sequence lifetime of a star. Evolutionary tracks computed with overshooting are quite different from those that use the classical Schwarzschild criterion, which leads to rather different predictions for the stellar properties. Attempts over the last two decades to calibrate the degree of overshooting with stellar mass using detached double-lined eclipsing binaries have been largely inconclusive, mainly due to a lack of suitable observational data. Here we revisit the question of a possible mass dependence of overshooting with a more complete sample of binaries, and examine any additional relation there might be with evolutionary state or metal abundance Z. We use a carefully selected sample of 33 double-lined eclipsing binaries strategically positioned in the H-R diagram, with accurate absolute dimensions and component masses ranging from 1.2 to 4.4 solar masses. We compare their measured properties with stellar evolution calculations to infer semi-empirical values of the overshooting parameter alpha(ov) for each star. Our models use the common prescription for the overshoot distance d(ov) = alpha(ov) Hp, where Hp is the pressure scale height at the edge of the convective core as given by the Schwarzschild criterion, and alpha(ov) is a free parameter. We find a relation between alpha(ov) and mass that is defined much more clearly than in previous work, and indicates a significant rise up to about 2 solar masses followed by little or no change beyond this mass. No appreciable dependence is seen with evolutionary state at a given mass, or with metallicity at a given mass despite the fact that the stars in our sample span a range of a factor of ten in [Fe/H], from -1.01 to +0.01.

astro-ph.SR↗

arXiv2015

Capella (alpha Aurigae) revisited: New binary orbit, physical properties, and evolutionary state

Knowledge of the chemical composition and absolute masses of Capella are key to understanding the evolutionary state of this benchmark binary system comprising two giant stars. Previous efforts, including our own 2009 study, have largely failed to reach an acceptable agreement between the observations and current stellar evolution models, preventing us from assessing the status of the primary. Here we report a revision of the physical properties of the components incorporating recently published high-precision radial velocity measurements, and a new detailed chemical analysis providing abundances for more than 20 elements in both stars. We obtain highly precise (to about 0.3%) masses of 2.5687 +/- 0.0074 and 2.4828 +/- 0.0067 solar masses, radii of 11.98 +/- 0.57 and 8.83 +/- 0.33 solar radii, effective temperatures of 4970 +/- 50 K and 5730 +/- 60 K, and independently measured luminosities based on the orbital parallax (78.7 +/- 4.2 and 72.7 +/- 3.6 solar luminosities). We find an excellent match to stellar evolution models at the measured composition of [Fe/H] = -0.04 +/- 0.06. Three different sets of models place the primary star firmly at the end of the core helium-burning phase (clump), while the secondary is known to be evolving rapidly across the Hertzprung gap. The measured lithium abundance, the C/N ratio, and the 12C/13C isotopic carbon abundance ratio, which change rapidly in the giant phase, are broadly in agreement with expectations from models. Predictions from tidal theory for the spin rates, spin-orbit alignment, and other properties do not fare as well, requiring a 40-fold increase in the efficiency of the dissipation mechanisms in order to match the observations.

astro-ph.SR↗

arXiv2013

Absolute properties of the eclipsing binary system AQ Serpentis: A stringent test of convective core overshooting in stellar evolution models

We report differential photometric observations and radial-velocity measurements of the detached, 1.69-day period, double-lined eclipsing binary AQ Ser. Accurate masses and radii for the components are determined to better than 1.8% and 1.1%, respectively, and are M1 = 1.417 +/- 0.021 MSun, M2 = 1.346 +/- 0.024 MSun, R1 = 2.451 +/- 0.027 RSun, and R2 = 2.281 +/- 0.014 RSun. The temperatures are 6340 +/- 100 K (spectral type F6) and 6430 +/- 100 K (F5), respectively. Both stars are considerably evolved, such that predictions from stellar evolution theory are particularly sensitive to the degree of extra mixing above the convective core (overshoot). The component masses are different enough to exclude a location in the H-R diagram past the point of central hydrogen exhaustion, which implies the need for extra mixing. Moreover, we find that current main-sequence models are unable to match the observed properties at a single age even when allowing the unknown metallicity, mixing length parameter, and convective overshooting parameter to vary freely and independently for the two components. The age of the more massive star appears systematically younger. AQ Ser and other similarly evolved eclipsing binaries showing the same discrepancy highlight an outstanding and largely overlooked problem with the description of overshooting in current stellar theory.

astro-ph.SR↗

arXiv2013

The internal structure of neutron stars and white dwarfs, and the Jacobi virial equation. II

In a previous paper we have shown that the function Γ(M, EOS)=αβ_{GR}/Λ^{0.9}(R) is constant (~ 0.4) for pre main-sequence stars (PMS), white dwarfs (WD) and for some neutron star (NS) models, where α_{GR} and β_{GR} are the form-factors of the gravitational potential energy and of the moment of inertia. To investigate the structural evolution of another type of celestial bodies, we use the MESA code to extend these calculations to gaseous planets. We show that this function is conserved for all models during the whole planetary evolution and is independent of the planet mass. We also analyse the cases for which this function is not conserved during some stellar evolutionary phases. For the PMS to the WD cooling sequences, we have found a connection between the strong variations of Γ(M, EOS) during the intermediary evolutionary phases and the specific nuclear power. A threshold for the specific nuclear power was determined. Below this limit this function is invariant (~ 0.4) for these models, i.e., at the initial and final stages (PMS and WD). Concerning NS, we study the influence of the equation of state (EOS) on this function and refine the exponent of the auxiliary function Λ(R) to be ~ 0.8. It is shown that the function Γ(M, EOS) is also invariant (~ 0.4) and is independent of the EOS and of the stellar mass. Therefore, we confirm that regardless of the final products of the stellar evolution, NS or WD, they recover the initial value of Γ(M, EOS) ~ 0.4 acquired at the PMS. Finally, we have introduced a macroscopic stability "criterion" for neutron star models based on the properties of the relativistic product αβ_{GR}.

astro-ph.HE↗

arXiv2012

Absolute Properties of the Triple Star CF Tauri

CF Tau is now known to be an eclipsing triple star with relatively deep total and annular eclipses. New light and radial velocity curves as well as new times of minima were obtained and used for further modeling of the system. Very accurate (better than 0.9%) masses and radii of the eclipsing pair are determined from analysis of the two new light curves, the radial velocity curve, and the times of minimum light. The mass and luminosity of the distant third component is accurately determined as well. Theoretical models of the detached, evolved eclipsing pair match the observed absolute properties of the stars at an age of about 4.3 Gy and [Fe/H] = -0.14.

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arXiv2009

Absolute properties of the highly eccentric eclipsing binary star LV Herculis

We report extensive spectroscopic and differential V-band photometric observations of the 18.4-day detached double-lined eclipsing binary LV Her (F9V), which has the highest eccentricity (e = 0.613) among the systems with well-measured properties. We determine the absolute masses and radii of the components to be M1 = 1.193 +/- 0.010 M(Sun), M2 = 1.1698 +/- 0.0081 M(Sun), R1 = 1.358 +/- 0.012 R(Sun), and R2 = 1.313 +/- 0.011 R(Sun), with fractional errors of 0.9% or better. The effective temperatures are 6060 +/- 150 K and 6030 +/- 150 K, respectively, and the overall metallicity is estimated to be [m/H] = +0.08 +/- 0.21. A comparison with current stellar evolution models for this composition indicates an excellent fit for an age between 3.8 and 4.2 Gyr, with both stars being near the middle of their main-sequence lifetimes. Full integration of the equations for tidal evolution is consistent with the high eccentricity, and suggests the stars' spin axes are aligned with the orbital axis, and that their rotations should be pseudo-synchronized. The latter prediction is not quite in agreement with the measured projected rotational velocities.

astro-ph.SR↗

arXiv2009

The Rossiter-McLaughlin effect of CoRoT-3b & HD189733b

We present radial-velocity sequences acquired during three transits of the exoplanet HD 189733b and one transit of the CoRoT-3b. We applied a combined Markov-Chain Monte Carlo analysis of spectroscopic and photometric data on these stars, to determine a full set of system parameters including the project spin-orbit misalignement angle of HD 189733b to an unprecedented precision via the Rossiter-McLaughlin effect: beta = 0.85 degrees (+0.32 -0.28) . This small but non-zero inclination of the planetary orbit is important to understand the origin of the system. On CoRoT-3b, results seem to point towards a non-zero inclination as well with beta = 37.6 degrees (+10.0 -22.3), but this remains marginal. Systematic effects due to non-gaussian cross-correlation functions appear to be the main cause of significant residuals that prevent an accurate determination of the projected stellar rotation velocity V sin(I) for both stars.

astro-ph.EP↗

arXiv2009

Binary orbit, physical properties, and evolutionary state of Capella (alpha Aurigae)

We report extensive radial-velocity measurements of the two giant components of the detached, 104-day period binary system of Capella. Our highly accurate three-dimensional orbital solution based on all existing spectroscopic and astrometric observations including our own yields much improved masses of 2.466 +/- 0.018 M_Sun and 2.443 +/- 0.013 M_Sun for the primary and secondary (relative errors of 0.7% and 0.5%). Improved values are derived also for the radii (11.87 +/- 0.56 R_Sun and 8.75 +/- 0.32 R_Sun), effective temperatures (4920 +/- 70 K and 5680 +/- 70 K), and luminosities (79.5 +/- 4.8 L_Sun and 72.1 +/- 3.6 L_Sun). The distance is determined to be 13.042 +/- 0.028 pc. Capella is unique among evolved stars in that, in addition to all of the above, the chemical composition is known, including the overall metallicity [m/H], the carbon isotope ratio 12C/13C for the primary, and the lithium abundance and C/N ratios for both components. The latter three quantities are sensitive diagnostics of evolution, and change drastically for giants as a result of the deepening of the convective envelope during the first dredge-up. The secondary is crossing the Hertzprung gap, while the primary is believed to be in the longer-lived core-helium burning phase. However, we find that current stellar evolution models are unable to match all of the observations for both components at the same time, and at a single age, for any evolutionary state of the primary. Similar problems are found when testing the rotational synchronization, spin axis alignment, and orbital circularization of the system against tidal theory. We conclude that our understanding of the advanced stages of stellar evolution is still very incomplete. [Abridged]

astro-ph.SR↗