Estudio numérico de la interacción entre vientos estelares y planetarios

Tesis (Doctor en Astronomía)--Universidad Nacional de Córdoba, Facultad de Matemática, Astronomía, Física y Computación, 2016.En esta tesis se estudió, mediante simulaciones numéricas (hidrodinámicas y magnetohidrodinámicas), el escape atmosférico del exoplaneta HD 209458b y su interacción con el viento y la radiación estelar. Los resultados numéricos se comparan con el rasgo más distintivo de este sistema, las observaciones de tránsito en la línea de emisión Ly-α. Las mismas han sido exhaustivamente estudiadas y analizadas, confirmando la presencia de material neutro escapando del planeta. Para poder incluir la presencia de los campos magnéticos en los modelos, fue necesario adaptar el código numérico con el fin de resolver las ecuaciones de la MHD. Todos los modelos numéricos tienen en cuenta la gravedad del planeta y la estrella, la presión de radiación y los procesos radiativos involucrados. Como resultado principal, se logró restringir el valor de la tasa de pérdida de masa planetaria y los parámetros del viento estelar.In this thesis I studied, by means of numerical simulations (hydrodynamics and magnetohydrodynamics), the atmospheric escape of HD 209458b and his interaction with the stellar wind and radiation. The numerical results are compared with the most distinguished feature of this planetary system, the transits observations of the stellar emision Lyα line. This line have been extensively studied and analyzed, confirming the presence of neutral material escaping from the planet. In order to include in the models the presence of magnetic fields, the numerical code was adapted to resolve the MHD equations. All the numerical models take into account the gravity of the planet and the star, the radiation pressure and the radiative process involved. As a main result, it was possible to constrain the planetary mass loss rate and the stellar wind parameters

Magnetized winds and their influence in the escaping upper atmosphere of HD 209458b

Lyman a observations during an exoplanet transit have proved to be very useful to study the interaction between the stellar wind and the planetary atmosphere. They have been extensively used to constrain planetary system parameters that are not directly observed, such as the planetary mass-loss rate. In this way, Ly α observations can be a powerful tool to infer the existence of a planetarymagnetic field, since it is expected that the latterwill affect the escaping planetary material. To explore the effect that magnetic fields have on the Ly α absorption of HD 209458b, we run a set of 3D MHD simulations including dipolar magnetic fields for the planet and the star. We assume values for the surface magnetic field at the poles of the planet in the range of [0-5] G, and from 1 to 5 G at the poles of the star. Our models also include collisional and photo-ionization, radiative recombination, and an approximation for the radiation pressure. Our results show that the magnetic field of the planet and the star change the shape of the Ly α absorption profile, since it controls the extent of the planetary magnetosphere and the amount of neutralmaterial inside it. Themodel that best reproduces the absorption observed in HD 209458b (with canonical values for the stellar wind parameters) corresponds to a dipole planetary field of ≲ 1 G at the poles.Fil: Villarreal D'angelo, Carolina Susana. University of St. Andrews; Reino UnidoFil: Esquivel Salazar, José Alejandro. Universidad Nacional Autónoma de México. Instituto de Ciencias Nucleares; MéxicoFil: Schneiter, Ernesto Matías. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Sgró, Mario Agustín. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; Argentin

Hydrodynamical interaction of stellar and planetary winds: Effects of charge exchange and radiation pressure on the observed Ly α absorption

Lyman α observations of the transiting exoplanet HD 209458b enable the study of exoplanet exospheres exposed to stellar extreme ultraviolet (EUV) fluxes, as well as the interacting stellar wind properties. In this study we present 3D hydrodynamical models for the stellar-planetary wind interaction including radiation pressure and charge exchange, together with photoionization, recombination, and collisional ionization processes. Our models explore the contribution of the radiation pressure and charge exchange to the Ly α absorption profile in a hydrodynamical framework, and for a single set of stellar wind parameters appropriate for HD 209458. We find that most of the absorption is produced by the material from the planet, with a secondary contribution of neutralized stellar ions by charge exchange. At the same time, the hydrodynamic shock heats up the planetary material, resulting in a broad thermal profile. Meanwhile, the radiation pressure yields a small velocity shift of the absorbing material. While neither charge exchange nor radiation pressure provides enough neutrals at the velocity needed to explain the observations at -100 km s-1 individually, we find that the two effects combined with the broad thermal profile are able to explain the observations.Fil: Esquivel, A.. Universidad Nacional Autónoma de México. Instituto de Ciencias Nucleares; México. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Schneiter, Ernesto Matías. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; Argentina. Stockholms Universitet; SueciaFil: Villarreal D'angelo, Carolina Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Sgró, Mario Agustín. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Krapp, Leonardo Javier. Stockholms Universitet; Suecia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; Argentin

Magnetized winds and their influence in the escaping upper atmosphere of HD 209458b

CVD acknowledges STFC (ST/M001296/1) and the PhD fellowship from CONICET. MAS acknowledges support from the CONICET via an Assistant Research Fellowship. The authors want to thank the Centro de Simulación Computacional para Aplicaciones Tecnológicas - CONICET, where some of the test of the code was run. AE acknowledges support from CONACYT DGAPA-PAPIIT (UNAM) grants IN 109715 and IG 100516.Lyman a observations during an exoplanet transit have proved to be very useful to study the interaction between the stellar wind and the planetary atmosphere. They have been extensively used to constrain planetary system parameters that are not directly observed, such as the planetary mass-loss rate. In this way, Ly α observations can be a powerful tool to infer the existence of a planetarymagnetic field, since it is expected that the latterwill affect the escaping planetary material. To explore the effect that magnetic fields have on the Ly α absorption of HD 209458b, we run a set of 3D MHD simulations including dipolar magnetic fields for the planet and the star. We assume values for the surface magnetic field at the poles of the planet in the range of [0-5] G, and from 1 to 5 G at the poles of the star. Our models also include collisional and photo-ionization, radiative recombination, and an approximation for the radiation pressure. Our results show that the magnetic field of the planet and the star change the shape of the Ly α absorption profile, since it controls the extent of the planetary magnetosphere and the amount of neutralmaterial inside it. Themodel that best reproduces the absorption observed in HD 209458b (with canonical values for the stellar wind parameters) corresponds to a dipole planetary field of ≲ 1 G at the poles.Publisher PDFPeer reviewe

Slingshot prominence evolution for a solar-like star

Funding: UK STFC grant (ST/M001296/1) (CVD, MJ).Although the present-day Sun rotates too slowly to exhibit centrifugally supported ‘slingshot prominences’, at some time during its past it may have formed these clouds of cool gas and ejected them into the interplanetary medium. We determine the time period for this behaviour using a rotation evolution code to derive the properties of the formation and ejection of slingshot prominences during the lifetime of a star similar to our Sun. The mass, mass-loss rate, and rate of ejection of these prominences are calculated using the analytical expression derived in our previous work. We find that for stars with an initial rotation rate larger than 4.6Ω⊙⁠, about half of all solar mass stars, slingshot prominences will be present even after the star reaches the main-sequence phase. In a fast rotator, this means that prominences can form until the star reaches ∼800 Myr old. Our results also indicate that the mass and lifetime of this type of prominence have maximum values when the star reaches the zero-age main sequence at an age of ∼40 Myr for a solar mass star.Publisher PDFPeer reviewe

Evolution of helium triplet transits of close-in gas giants orbiting K-dwarfs

Atmospheric escape in exoplanets has traditionally been observed using hydrogen Lyman-$\alpha$ and H-$\alpha$ transmission spectroscopy, but more recent detections have utilised the metastable helium triplet at 1083$~$nm. Since this feature is accessible from the ground, it offers new possibilities for studying atmospheric escape. Our goal is to understand how the observability of escaping helium evolves during the lifetime of a highly irradiated gas giant. We extend our previous work on 1-D self-consistent hydrodynamic escape from hydrogen-only atmospheres as a function of planetary evolution to the first evolution-focused study of escaping hydrogen-helium atmospheres. Additionally, using these novel models we perform helium triplet transmission spectroscopy. We adapt our previous hydrodynamic escape model to now account for both hydrogen and helium heating and cooling processes and simultaneously solve for the population of helium in the triplet state. To account for the planetary evolution, we utilise evolving predictions of planetary radii for a close-in 0.3$~M_{\rm Jup}$ gas giant and its received stellar flux in X-ray, hard and soft EUV, and mid-UV wavelength bins assuming a K dwarf stellar host. We find that the helium triplet signature diminishes with evolution. Our models suggest that young ($\lesssim 150$~Myr), close-in gas giants ($\sim 1$ to $2~R_{\rm Jup}$) should produce helium 1083$~$nm transit absorptions of $\sim 4\%$ or $\sim 7\%$, for a slow or fast-rotating K dwarf, respectively, assuming a 2$\%$ helium abundance.Comment: 20 pages, 13 figures, 4 tables; accepted for publication in MNRA

Prominence formation and ejection in cool stars

We acknowledge STFC (ST/M001296/1) and H2020 (682393).The observational signatures of prominences have been detected in single and binary G and K type stars for many years now, but recently this has been extended to the M dwarf regime. Prominences carry away both mass and angular momentum when they are ejected and the impact of this mass on any orbiting planets may be important for the evolution of exoplanetary atmospheres. By means of the classification used in the massive star community, that involves knowledge of two parameters (the co-rotation and Alfvén radii, rK and rA), we have determined which cool stars could support prominences. From a model of mechanical support, we have determined that the prominence mass mp/M*=(EM/EG)(r*/rK)2F where EMB2⋆r3⋆ and EG=GM2⋆/r⋆ are magnetic and gravitational energies and F is a geometric factor. Our calculated masses and ejection frequencies (typically 1016−1017g and 0.4 d, respectively) are consistent with observations and are sufficient to ensure that an exoplanet orbiting in the habitable zone of an M dwarf could suffer frequent impacts.PostprintPeer reviewe

Benchmarking the power of amateur observatories for TTV exoplanets detection

We perform an analysis of ~80 000 photometric measurements for the following 10 stars hosting transiting planets:WASP-2, -4, -5, -52, Kelt-1, CoRoT-2, XO-2, TrES-1, HD 189733, GJ 436. Our analysis includes mainly transit light curves from the Exoplanet Transit Database, public photometry from the literature, and some proprietary photometry privately supplied by other authors. Half of these light curves were obtained by amateurs. From this photometry we derive 306 transit timing measurements, as well as improved planetary transit parameters. Additionally, for 6 of these 10 stars we present a set of radial velocity measurements obtained from the spectra stored in the HARPS, HARPS-N and SOPHIE archives using the HARPS- TERRA pipeline. Our analysis of these transit timing and radial velocity data did not reveal significant hints of additional orbiting bodies in almost all of the cases. In the WASP-4 case, we found hints of marginally significant TTV signals having amplitude 10-20 s, although their parameters are model dependent and uncertain, while radial velocities did not reveal statistically significant Doppler signals.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

Benchmarking the power of amateur observatories for TTV exoplanets detection

This document is the Accepted Manuscript version of the following article: Roman v. Baluev, et al, ‘Benchmarking the power of amateur observatories for TTV exoplanets detection’, Monthly Notices of the Royal Astronomical Society, Vol. 450(3): 3101-3113, first published online 9 May 2015. The version of record is available at doi: https://doi.org/10.1093/mnras/stv788 © 2015 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.We perform an analysis of ~80000 photometric measurements for the following 10 stars hosting transiting planets: WASP-2, -4, -5, -52, Kelt-1, CoRoT-2, XO-2, TrES-1, HD 189733, GJ 436. Our analysis includes mainly transit lightcurves from the Exoplanet Transit Database, public photometry from the literature, and some proprietary photometry privately supplied by other authors. Half of these lightcurves were obtained by amateurs. From this photometry we derive 306 transit timing measurements, as well as improved planetary transit parameters. Additionally, for 6 of these 10 stars we present a set of radial velocity measurements obtained from the spectra stored in the HARPS, HARPS-N, and SOPHIE archives using the HARPS-TERRA pipeline. Our analysis of these TTV and RV data did not reveal significant hints of additional orbiting bodies in almost all of the cases. In the WASP-4 case, we found hints of marginally significant TTV signals having amplitude 10-20 sec, although their parameters are model-dependent and uncertain, while radial velocities did not reveal statistically significant Doppler signals.Peer reviewe