Hot Jupiters accreting onto their parent stars: Effects on the stellar activity

AbstractSince soon after the discovery of hot Jupiters, it had been suspected that interaction of these massive bodies with their host stars could give rise to observable signals. We discuss the observational evidence for star-planet interactions (SPI) of tidal and magnetic origin observed in X-rays and FUV. Hot Jupiters can significantly impact the activity of their host stars through tidal and magnetic interaction, leading to either increased or decreased stellar activity – depending on the internal structure of the host star and the properties of the hosted planet. In HD 189733, X-ray and FUV flares are preferentially in a very restricted range of planetary phases. Matsakos et al. (2015) show, using MHD simulations, planetary gas can be liberated, forming a stream of material that gets compressed and accretes onto the star with a phase lag of 70-90 degrees. This scenario explains many features observed both in X-rays and the FUV (Pillitteri et al. 2015). On the other hand, WASP-18 – an F6 star with a massive hot Jupiter, shows no signs of activity in X-rays or UV. Several age indicators (isochrone fitting, Li abundance) point to a young age (~0.5 –1.0 Gyr) and thus significant activity was expected. In this system, tidal SPI between the star and the very close-in and massive planet appears to destroy the formation of magnetic dynamo and thus nullify the stellar activity.

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HD 189733 b: bow shock or no shock?

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833567 ◽

2018 ◽

Vol 619 ◽

pp. A96 ◽

Cited By ~ 3

Author(s):

S. Kohl ◽

M. Salz ◽

S. Czesla ◽

J. H. M. M. Schmitt

Keyword(s):

Time Series ◽

Neutral Hydrogen ◽

Periodic Variation ◽

Bow Shock ◽

Time Variability ◽

Stellar Activity ◽

Hot Jupiters ◽

Upper Limits ◽

In Transit ◽

Infrared Triplet

Context. Hot Jupiters are surrounded by extended atmospheres of neutral hydrogen. Observations have provided evidence for in-transit hydrogen Hα absorption as well as variable pre-transit absorption signals. These have been interpreted in terms of a bow shock or an accretion stream that transits the host star before the planet. Aims. We test the hypothesis of planetary-related Hα absorption by studying the time variability of the Hα and stellar activity-sensitive calcium lines in high-resolution TIGRE (Telescopio Internacional de Guanajuato Robótico Espectroscópico) spectra of the planet host HD 189733. Methods. In the framework of an observing campaign spanning several months, the host star was observed several times per week randomly sampling the orbital phases of the planet. We determine the equivalent width in the Hα and Ca IRT(calcium infrared triplet) lines, and subtract stellar rotationally induced activity from the Hα time series via its correlation with the IRT evolution. The residuals are explored for significant differences between the pre-, in-, and out-of-transit phases. Results. We find strong stellar rotational variation with a lifetime of about 20–30 days in all activity indicators, but the corrected Hα time series exhibits no significant periodic variation. We exclude the presence of more than 6.2 mÅ pre-transit absorption and 5.6 mÅ in-transit absorption in the corrected Hα data at a 99% confidence level. Conclusions. Previously observed Hα absorption signals exceed our upper limits, but they could be related to excited atmospheric states. The Hα variability in the HD 189733 system is dominated by stellar activity, and observed signals around the planetary transit may well be caused by short-term stellar variability.

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Tidal effects on stellar activity

Proceedings of the International Astronomical Union ◽

10.1017/s1743921317004045 ◽

2016 ◽

Vol 12 (S328) ◽

pp. 308-314

Author(s):

K. Poppenhaeger

Keyword(s):

Orbital Period ◽

Binary Systems ◽

Semimajor Axis ◽

Rotation Period ◽

Magnetic Activity ◽

Stellar Rotation ◽

Stellar Activity ◽

Tidal Interaction ◽

Hot Jupiters ◽

Orbital Periods

AbstractThe architecture of many exoplanetary systems is different from the solar system, with exoplanets being in close orbits around their host stars and having orbital periods of only a few days. We can expect interactions between the star and the exoplanet for such systems that are similar to the tidal interactions observed in close stellar binary systems. For the exoplanet, tidal interaction can lead to circularization of its orbit and the synchronization of its rotational and orbital period. For the host star, it has long been speculated if significant angular momentum transfer can take place between the planetary orbit and the stellar rotation. In the case of the Earth-Moon system, such tidal interaction has led to an increasing distance between Earth and Moon. For stars with Hot Jupiters, where the orbital period of the exoplanet is typically shorter than the stellar rotation period, one expects a decreasing semimajor axis for the planet and enhanced stellar rotation, leading to increased stellar activity. Also excess turbulence in the stellar convective zone due to rising and subsiding tidal bulges may change the magnetic activity we observe for the host star. I will review recent observational results on stellar activity and tidal interaction in the presence of close-in exoplanets, and discuss the effects of enhanced stellar activity on the exoplanets in such systems.

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The GAPS Programme at TNG

Astronomy and Astrophysics ◽

10.1051/0004-6361/201937369 ◽

2020 ◽

Vol 638 ◽

pp. A5 ◽

Cited By ~ 6

Author(s):

I. Carleo ◽

L. Malavolta ◽

A. F. Lanza ◽

M. Damasso ◽

S. Desidera ◽

...

Keyword(s):

Radial Velocity ◽

Near Infrared ◽

Semimajor Axis ◽

Young Stars ◽

Homogeneous Sample ◽

Stellar Activity ◽

Orbital Parameters ◽

Hot Jupiters ◽

Multi Band ◽

Hot Jupiter

Context. The existence of hot Jupiters is still not well understood. Two main channels are thought to be responsible for their current location: a smooth planet migration through the protoplanetary disk or the circularization of an initial highly eccentric orbit by tidal dissipation leading to a strong decrease in the semimajor axis. Different formation scenarios result in different observable effects, such as orbital parameters (obliquity and eccentricity) or frequency of planets at different stellar ages. Aims. In the context of the GAPS Young Objects project, we are carrying out a radial velocity survey with the aim of searching and characterizing young hot-Jupiter planets. Our purpose is to put constraints on evolutionary models and establish statistical properties, such as the frequency of these planets from a homogeneous sample. Methods. Since young stars are in general magnetically very active, we performed multi-band (visible and near-infrared) spectroscopy with simultaneous GIANO-B + HARPS-N (GIARPS) observing mode at TNG. This helps in dealing with stellar activity and distinguishing the nature of radial velocity variations: stellar activity will introduce a wavelength-dependent radial velocity amplitude, whereas a Keplerian signal is achromatic. As a pilot study, we present here the cases of two known hot Jupiters orbiting young stars: HD 285507 b and AD Leo b. Results. Our analysis of simultaneous high-precision GIARPS spectroscopic data confirms the Keplerian nature of the variation in the HD 285507 radial velocities and refines the orbital parameters of the hot Jupiter, obtaining an eccentricity consistent with a circular orbit. Instead, our analysis does not confirm the signal previously attributed to a planet orbiting AD Leo. This demonstrates the power of the multi-band spectroscopic technique when observing active stars.

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Stellar impact on disequilibrium chemistry and observed spectra of hot Jupiter atmospheres

Astronomy and Astrophysics ◽

10.1051/0004-6361/201937210 ◽

2020 ◽

Vol 639 ◽

pp. A48 ◽

Cited By ~ 1

Author(s):

D. Shulyak ◽

L. M. Lara ◽

M. Rengel ◽

N.-E. Nèmec

Keyword(s):

Extreme Ultraviolet ◽

Chemical Species ◽

Pressure Profile ◽

Temperature Inversion ◽

Chemical Kinetic ◽

Mixing Ratio ◽

Stellar Activity ◽

Hot Jupiters ◽

The Impact ◽

Hot Jupiter

Aims. We study the effect of disequilibrium processes (photochemistry and vertical transport) on mixing ratio profiles of neutral species and on the simulated spectra of a hot Jupiter exoplanet that orbits stars of various spectral types. We additionally address the impact of stellar activity that should be present, to various degrees, in all stars with convective envelopes. Methods. We used the VULCAN chemical kinetic code to compute number densities of species in irradiated planetary atmospheres. The temperature-pressure profile of the atmosphere was computed with the HELIOS code. We also utilized the τ-REx forward model to predict the spectra of planets in primary and secondary eclipses. In order to account for the stellar activity, we made use of the observed solar extreme ultraviolet (XUV) spectrum taken from Virtual Planetary Laboratory as a proxy for an active sun-like star. Results. We find large changes in the mixing ratios of most chemical species in planets orbiting A-type stars, which radiate strong XUV flux thereby inducing a very effective photodissociation. For some species, these changes can propagate very deep into the planetary atmosphere to pressures of around 1 bar. To observe disequilibrium chemistry we favor hot Jupiters with temperatures Teq = 1000 K and ultra-hot Jupiters, with Teq ≈ 3000 K,which also have temperature inversion in their atmospheres. On the other hand, disequilibrium calculations predict no noticeable changes in spectra of planets with intermediate temperatures. We also show that stellar activity similar to that of the modern Sun drives important changes in mixing ratio profiles of atmospheric species. However, these changes take place at very high atmospheric altitudes and thus do not affect predicted spectra. Finally, we estimate that the effect of disequilibrium chemistry in planets orbiting nearby bright stars could be robustly detected and studied with future missions with spectroscopic capabilities in infrared such as James Webb Space Telescope and ARIEL.

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A CORRELATION BETWEEN STELLAR ACTIVITY AND THE SURFACE GRAVITY OF HOT JUPITERS

The Astrophysical Journal ◽

10.1088/2041-8205/717/2/l138 ◽

2010 ◽

Vol 717 (2) ◽

pp. L138-L142 ◽

Cited By ~ 43

Author(s):

J. D. Hartman

Keyword(s):

Surface Gravity ◽

Stellar Activity ◽

Hot Jupiters

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Detection of Exomoons Inside the Habitable Zone

Proceedings of the International Astronomical Union ◽

10.1017/s1743921313012751 ◽

2012 ◽

Vol 8 (S293) ◽

pp. 168-170

Author(s):

Luis Ricardo M. Tusnski ◽

Adriana Valio

Keyword(s):

The Other ◽

Planetary Orbit ◽

Habitable Zone ◽

The Moon ◽

Stellar Activity ◽

Orbital Parameters ◽

Hot Jupiters ◽

Habitable Zones ◽

Observational Bias ◽

Host Stars

AbstractSince the discovery of the first exoplanets, those most adequate for life to begin and evolve have been sought. Due to observational bias, however, most of the discovered planets so far are gas giants, precluding their habitability. However, if these hot Jupiters are located in the habitable zones of their host stars, and if rocky moons orbit them, then these moons may be habitable. In this work, we present a model for planetary transit simulation considering the presence of moons around a planet. The moon orbit is considered to be circular and coplanar with the planetary orbit. The other physical and orbital parameters of the star, planet, and moon, can be adjusted in each simulation. It is possible to simulate as many successive transits as desired. Since the presence of spots on the surface of the star may produce a signal similar to that of the presence of a moon, our model also allows for the inclusion of starspots. The goal is to determine the criteria for detectability of moons using photometry with the CoRoT and Kepler telescopes taking into account the stellar activity.

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Observable Impacts of Exoplanets on Stellar Hosts – An X-Ray Perspective

Proceedings of the International Astronomical Union ◽

10.1017/s1743921317004161 ◽

2016 ◽

Vol 12 (S328) ◽

pp. 290-297

Author(s):

Scott J. Wolk ◽

Ignazio Pillitteri ◽

Katja Poppenhaeger

Keyword(s):

Magnetic Interaction ◽

Significant Activity ◽

X Rays ◽

Restricted Range ◽

Surface Shear ◽

Stellar Activity ◽

X Ray ◽

Hot Jupiters ◽

Magnetic Origin ◽

Host Stars

AbstractSoon after the discovery of hot Jupiters, it was suspected that interaction of these massive bodies with their host stars could give rise to observable signals. We discuss the observational evidence for star-planet interactions (SPI) of tidal and magnetic origin observed in X-rays. Hot Jupiters can significantly impact the activity of their host stars through tidal and magnetic interaction, leading to either increased or decreased stellar activity – depending on the internal structure of the host star and the properties of the hosted planet. We provide several examples of these interactions. In HD 189733, the strongest X-ray flares are preferentially seen in a very restricted range of planetary phases. Hot Jupiters, can also obscure the X-ray signal during planetary transits. Observations of this phenomena have led to the discovery of a thin upper atmospheres in HD 189733A. On the other hand, WASP-18 – an F6 star with a massive hot Jupiter, shows no signs of activity in X-rays or UV. Several age indicators (isochrone fitting, Li abundance) point to a young age (~0.5 – −1.0 Gyr) and thus significant activity was expected. In this system, tidal SPI between the star and the very close-in and massive planet appears to disrupt the surface shear layer and thus nullify the stellar activity.

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