STELLAR WIND INFLUENCE ON PLANETARY DYNAMOS

Abstract The GJ 436 planetary system is an extraordinary system. The Neptune-size planet that orbits the M3 dwarf revealed in the Lyα line an extended neutral hydrogen atmosphere. This material fills a comet-like tail that obscures the stellar disc for more than 10 hours after the planetary transit. Here, we carry out a series of 3D radiation hydrodynamic simulations to model the interaction of the stellar wind with the escaping planetary atmosphere. With these models, we seek to reproduce the $\sim 56\%$ absorption found in Lyα transits, simultaneously with the lack of absorption in Hα transit. Varying the stellar wind strength and the EUV stellar luminosity, we search for a set of parameters that best fit the observational data. Based on Lyα observations, we found a stellar wind velocity at the position of the planet to be around [250-460] km s−1 with a temperature of [3 − 4] × 105 K. The stellar and planetary mass loss rates are found to be 2 × 10−15 M⊙ yr−1 and ∼[6 − 10] × 109 g s−1, respectively, for a stellar EUV luminosity of [0.8 − 1.6] × 1027 erg s−1. For the parameters explored in our simulations, none of our models present any significant absorption in the Hα line in agreement with the observations.

Download Full-text

Monte Carlo simulations of fast Newtonian and mildly relativistic shock breakout from a stellar wind

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3125 ◽

2020 ◽

Vol 499 (4) ◽

pp. 4961-4971

Author(s):

Hirotaka Ito ◽

Amir Levinson ◽

Ehud Nakar

Keyword(s):

Monte Carlo ◽

Monte Carlo Simulations ◽

Stellar Wind ◽

Compact Star ◽

Strong Dependence ◽

Shock Velocity ◽

Light Curves ◽

Ultraviolet Emission ◽

Relativistic Shocks ◽

Strong Explosion

ABSTRACT Strong explosion of a compact star surrounded by a thick stellar wind drives a fast (>0.1c) radiation mediated shock (RMS) that propagates in the wind, and ultimately breaks out gradually once photons start escaping from the shock transition layer. In exceptionally strong or aspherical explosions, the shock velocity may even be relativistic. The properties of the breakout signal depend on the dynamics and structure of the shock during the breakout phase. Here we present, for the first time, spectra and light curves of the breakout emission of fast Newtonian and mildly relativistic shocks, that were calculated using self-consistent Monte Carlo simulations of finite RMS with radiative losses. We find a strong dependence of the νFν peak on shock velocity, ranging from ∼1 keV for vs/c = 0.1 to ∼100 keV for vs/c = 0.5, with a shift to lower energies as losses increase. For all cases studied the spectrum below the peak exhibits a nearly flat component (Fν ∼ ν0) that extends down to the break frequency below which absorption becomes important. This implies much bright optical/ultraviolet emission than hitherto expected. The computed light curves show a gradual rise over tens to hundreds of seconds for representative conditions. The application to SN 2008D/XRT 080109 and the detectability limits are also discussed. We predict a detection rate of about one per year with eROSITA.

Download Full-text

Chemical Abundances of Early Type Stars

Symposium - International Astronomical Union ◽

10.1017/s007418090011486x ◽

1998 ◽

Vol 188 ◽

pp. 224-225

Author(s):

S. Tanaka ◽

S. Kitamoto ◽

T. Suzuki ◽

K. Torii ◽

M.F. Corcoran ◽

...

Keyword(s):

Surface Layer ◽

Stellar Wind ◽

Nuclear Reactions ◽

X Rays ◽

Early Type ◽

Chemical Abundances ◽

X Ray ◽

Low Metallicity ◽

Early Type Stars

X-rays from early-type stars are emitted by the corona or the stellar wind. The materials in the surface layer of early-type stars are not contaminated by nuclear reactions in the stellar inside. Therefore, abundance study of the early-type stars provides us an information of the abundances of the original gas. However, the X-ray observations indicate low-metallicity, which is about 0.3 times of cosmic abundances. This fact raises the problem on the cosmic abundances.

Download Full-text

Evolution of O stars and the WR connection

Symposium - International Astronomical Union ◽

10.1017/s0074180900013838 ◽

1979 ◽

Vol 83 ◽

pp. 431-445 ◽

Cited By ~ 3

Author(s):

Peter S. Conti

Keyword(s):

Mass Loss ◽

Stellar Wind ◽

High Luminosity ◽

Loss Mechanism ◽

Evolutionary Scenario ◽

Processed Material ◽

Dominant Process ◽

Highly Evolved ◽

Loss Rates ◽

Enriched Composition

The stellar wind mass loss rates of at least some single Of type stars appear to be sufficient to remove much if not all of the hydrogen-rich envelope such that nuclear processed material is observed at the surface. This highly evolved state can then be naturally associated with classic Population I WR stars that have properties of high luminosity for their mass, helium enriched composition, and nitrogen or carbon enhanced abundances. If stellar wind mass loss is the dominant process involved in this evolutionary scenario, then stars with properties intermediate between Of and WR types should exist. The stellar parameters of luminosity, temperature, mass and composition are briefly reviewed for both types. All late WN stars so far observed are relatively luminous like Of stars, and also contain hydrogen. All early WN stars, and WC stars, are relatively faint and contain little or no hydrogen. The late WN stars seem to have the intermediate properties required if a stellar wind is the dominant mass loss mechanism that transforms an Of star to a WR type.

Download Full-text

Planetary Magnetic Fields and Habitability in Super Earths

Open Astronomy ◽

10.1515/astro-2018-0026 ◽

2018 ◽

Vol 27 (1) ◽

pp. 183-231 ◽

Cited By ~ 1

Author(s):

Pablo Cuartas-Restrepo

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Scaling Laws ◽

Thermal Evolution ◽

Solid Core ◽

Direct Influence ◽

Physical Processes ◽

Planetary Magnetic Fields ◽

Planetary Magnetic Field ◽

Planetary Dynamos

Abstract This work seeks to summarize some special aspects of a type of exoplanets known as super-Earths (SE), and the direct influence of these aspects in their habitability. Physical processes like the internal thermal evolution and the generation of a protective Planetary Magnetic Field (PMF) are directly related with habitability. Other aspects such as rotation and the formation of a solid core are fundamental when analyzing the possibilities that a SE would have to be habitable. This work analyzes the fundamental theoretical aspects on which the models of thermal evolution and the scaling laws of the planetary dynamos are based. These theoretical aspects allow to develop models of the magnetic evolution of the planets and the role played by the PMF in the protection of the atmosphere and the habitability of the planet.

Download Full-text

Physical Processes in Nebular Shells and the Interpretation of Nebular Spectra

Symposium - International Astronomical Union ◽

10.1017/s0074180900093694 ◽

1983 ◽

Vol 103 ◽

pp. 219-227

Author(s):

J. Patrick Harrington

Keyword(s):

Charge Transfer ◽

Simple Model ◽

Stellar Wind ◽

High Velocity ◽

Planetary Nebulae ◽

Geometrical Parameters ◽

Stellar Winds ◽

Physical Processes ◽

Rapid Cooling ◽

Particle Distributions

Computed models are now recognized as useful tools for interpretation of the spectra of planetary nebulae. However, even the most detailed models need geometrical parameters such as filling factors which are poorly determined by observations. Some effects may be seen more clearly by modeling the stratification than by just using total fluxes. A simple model for NGC 6720 is presented which reproduces the behavior of (Ne III) λ3869 observed by Hawley and Miller (1977), clearly showing the effects of charge transfer. The behavior of C II λ4267 remains puzzling. Finally, we comment on the interaction of high velocity stellar winds with nebular shells. Non-equilibrium particle distributions at the contact between the shocked stellar wind and the nebula may result in the rapid cooling of the shocked gas.

Download Full-text

Circumstellar environment of 55 Cancri

Astronomy and Astrophysics ◽

10.1051/0004-6361/201937186 ◽

2020 ◽

Vol 633 ◽

pp. A48 ◽

Cited By ~ 6

Author(s):

C. P. Folsom ◽

D. Ó Fionnagáin ◽

L. Fossati ◽

A. A. Vidotto ◽

C. Moutou ◽

...

Keyword(s):

Magnetic Field ◽

Stellar Wind ◽

Large Scale ◽

Rotation Axis ◽

Doppler Imaging ◽

Magnetic Pole ◽

Average Strength ◽

Detailed Understanding ◽

The Magnetic Field ◽

Circumstellar Environment

Context. 55 Cancri hosts five known exoplanets, most notably the hot super-Earth 55 Cnc e, which is one of the hottest known transiting super-Earths. Aims. Because of the short orbital separation and host star brightness, 55 Cnc e provides one of the best opportunities for studying star-planet interactions (SPIs). We aim to understand possible SPIs in this system, which requires a detailed understanding of the stellar magnetic field and wind impinging on the planet. Methods. Using spectropolarimetric observations and Zeeman Doppler Imaging, we derived a map of the large-scale stellar magnetic field. We then simulated the stellar wind starting from the magnetic field map, using a 3D magneto-hydrodynamic model. Results. The map of the large-scale stellar magnetic field we derive has an average strength of 3.4 G. The field has a mostly dipolar geometry; the dipole is tilted by 90° with respect to the rotation axis and the dipolar strength is 5.8 G at the magnetic pole. The wind simulations based on this magnetic geometry lead us to conclude that 55 Cnc e orbits inside the Alfvén surface of the stellar wind, implying that effects from the planet on the wind can propagate back to the stellar surface and result in SPI.

Download Full-text

EXTRASOLAR GIANT MAGNETOSPHERIC RESPONSE TO STEADY-STATE STELLAR WIND PRESSURE AT 10, 5, 1, AND 0.2 au

The Astrophysical Journal ◽

10.3847/0004-637x/827/1/77 ◽

2016 ◽

Vol 827 (1) ◽

pp. 77 ◽

Cited By ~ 6

Author(s):

Matt A. Tilley ◽

Erika M. Harnett ◽

Robert M. Winglee

Keyword(s):

Steady State ◽

Stellar Wind ◽

Wind Pressure

Download Full-text