scholarly journals Modelling the He I triplet absorption at 10 830 Å in the atmospheres of HD 189733 b and GJ 3470 b

2021 ◽  
Vol 647 ◽  
pp. A129
Author(s):  
M. Lampón ◽  
M. López-Puertas ◽  
J. Sanz-Forcada ◽  
A. Sánchez-López ◽  
K. Molaverdikhani ◽  
...  
Keyword(s):  
High Resolution ◽  
Mass Loss ◽  
Molecular Mass ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Upper Atmosphere ◽  
Maximum Temperature ◽  
Comparable Rate ◽  
Radial Outflow ◽  
Triplet Absorption

Characterising the atmospheres of exoplanets is key to understanding their nature and provides hints about their formation and evolution. High resolution measurements of the helium triplet absorption of highly irradiated planets have been recently reported, which provide a new means of studying their atmospheric escape. In this work we study the escape of the upper atmospheres of HD 189733 b and GJ 3470 b by analysing high resolution He I triplet absorption measurements and using a 1D hydrodynamic spherically symmetric model coupled with a non-local thermodynamic model for the He I triplet state. We also use the H density derived from Lyα observations to further constrain their temperatures, mass-loss rates, and H/He ratios. We have significantly improved our knowledge of the upper atmospheres of these planets. While HD 189733 b has a rather compressed atmosphere and small gas radial velocities, GJ 3470 b, on the other hand with a gravitational potential ten times smaller, exhibits a very extended atmosphere and large radial outflow velocities. Hence, although GJ 3470 b is much less irradiated in the X-ray and extreme ultraviolet radiation, and its upper atmosphere is much cooler, it evaporates at a comparable rate. In particular, we find that the upper atmosphere of HD 189733 b is compact and hot, with a maximum temperature of 12 400−300+400 K, with a very low mean molecular mass (H/He = (99.2/0.8) ± 0.1), which is almost fully ionised above 1.1 RP, and with a mass-loss rate of (1.1 ± 0.1) × 1011 g s−1. In contrast, the upper atmosphere of GJ 3470 b is highly extended and relatively cold, with a maximum temperature of 5100 ± 900 K, also with a very low mean molecular mass (H/He = (98.5/1.5)−1.5+1.0), which is not strongly ionised, and with a mass-loss rate of (1.9 ± 1.1) × 1011 g s−1. Furthermore, our results suggest that upper atmospheres of giant planets undergoing hydrodynamic escape tend to have a very low mean molecular mass (H/He ≳ 97/3).

scholarly journals Modelling the He I triplet absorption at 10 830 Å in the atmosphere of HD 209458 b

2020 ◽  
Vol 636 ◽  
pp. A13 ◽  
Author(s):  
M. Lampón ◽  
M. López-Puertas ◽  
L. M. Lara ◽  
A. Sánchez-López ◽  
M. Salz ◽  
...  
Keyword(s):  
Absorption Spectrum ◽  
High Resolution ◽  
Mass Loss ◽  
Loss Rate ◽  
Extreme Ultraviolet ◽  
Mass Loss Rate ◽  
Measured Absorption ◽  
Non Local ◽  
Mean Molecular Weight ◽  
Triplet Absorption

Context. HD 209458 b is an exoplanet with an upper atmosphere undergoing blow-off escape that has mainly been studied using measurements of the Lyα absorption. Recently, high-resolution measurements of absorption in the He I triplet line at 10 830 Å of several exoplanets (including HD 209458 b) have been reported, creating a new opportunity to probe escaping atmospheres. Aims. We aim to better understand the atmospheric regions of HD 209458 b from where the escape originates. Methods. We developed a 1D hydrodynamic model with spherical symmetry for the HD 209458 b thermosphere coupled with a non-local thermodynamic model for the population of the He I triplet state. In addition, we performed high-resolution radiative transfer calculations of synthetic spectra for the helium triplet lines and compared them with the measured absorption spectrum in order to retrieve information about the atmospheric parameters. Results. We find that the measured spectrum constrains the [H]/[H+] transition altitude occurring in the range of 1.2 RP–1.9 RP. Hydrogen is almost fully ionised at altitudes above 2.9 RP. We also find that the X-ray and extreme ultraviolet absorption takes place at effective radii from 1.16 to 1.30 RP, and that the He I triplet peak density occurs at altitudes from 1.04 to 1.60 RP. Additionally, the averaged mean molecular weight is confined to the 0.61–0.73 g mole−1 interval, and the thermospheric H/He ratio should be larger than 90/10, and most likely approximately 98/2. We also provide a one-to-one relationship between mass-loss rate and temperature. Based on the energy-limited escape approach and assuming heating efficiencies of 0.1–0.2, we find a mass-loss rate in the range of (0.42–1.00) ×1011 g s−1 and a corresponding temperature range of 7125–8125 K. Conclusions. The analysis of the measured He I triplet absorption spectrum significantly constrains the thermospheric structure of HD 209458 b and advances our knowledge of its escaping atmosphere.

scholarly journals Ionisation fractions and mass-loss in O stars

1987 ◽  
Vol 122 ◽  
pp. 449-450
Author(s):  
Raman K. Prinja ◽  
Ian D. Howarth
Keyword(s):  
High Resolution ◽  
Mass Loss ◽  
Column Density ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Terminal Velocity ◽  
Stellar Radius ◽  
Left Part ◽  
Hr Diagram

The most sensitive indicators of mass-loss for stars in the upper left part of the HR diagram are the UV P Cygni profiles observed in the resonance lines of common ions such as N V, Si IV, and C IV. We present here some results from a study of these lines in the high resolution IUE spectra of 197 Ï stars. Profile fits were carried out in the manner described by Prinja & Howarth (1986) for all unsaturated P Cygni resonance doublets. The parameterisations adopted enable the product of mass-loss rate (Ṁ) and ion fraction (qi) to be determined at a given velocity, such that Ṁ qi°C Ni R* v∞, where Ni is the column density of the observed ion i, v∞ is the terminal velocity, and R⋆ is the stellar radius. The accompanying figures illustrate the behaviour of Ṁ qi (evaluated at 0.5 v∞) for N V and C IV.

scholarly journals The runaway supergiant HD 188209 (O9.5Iab): a binary or a pulsating star?

1999 ◽  
Vol 193 ◽  
pp. 69-70
Author(s):  
Garik Israelian ◽  
Artemio Herrero ◽  
E. Santolaya-Rey ◽  
A. Kaufer ◽  
F. Musaev ◽  
...  
Keyword(s):  
Time Series ◽  
High Resolution ◽  
Mass Loss ◽  
Radial Velocity ◽  
Loss Rate ◽  
State Of The Art ◽  
Mass Loss Rate ◽  
Fundamental Parameters ◽  
Binary Nature ◽  
Period 2

We report radial velocity studies of photospheric absorption lines from spectral time series of the late O-type runaway supergiant HD 188209. Radial velocity variations with a quasi-period ∼ 2 days have been detected in high-resolution echelle spectra and most probably indicate that the supergiant is pulsating. Night-to-night variations in the position and strength of the central emission reversal of the Hα profile have been observed. The fundamental parameters of the star have been derived using state-of-the-art plane-parallel and unified non-LTE model atmospheres, these last including the mass-loss rate. The binary nature of this star is not suggested either from Hipparcos photometry or from radial-velocity curves.

scholarly journals On the thermal atmospheric escape of π Men c

2021 ◽  
Author(s):  
E. S. Kalinicheva ◽  
◽  
V. I. Shematovich ◽  
Ya. N. Pavlyuchenkov ◽  
◽  
...  
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Upper Atmosphere ◽  
One Dimensional ◽  
Atmospheric Escape ◽  
Self Consistent ◽  
Atmospheric Mass ◽  
Suprathermal Particles

In this work we present the results of the modeling of exoplanet pi Men c upper atmosphere, produced using the previously developed one-dimensional self-consistent aeronomic model. The model used takes into account the contribution of suprathermal particles, which significantly refines the heating function of the atmosphere. The hight profiles of temperature, velocity and density were obtained, the atmospheric mass-loss rate was calculated. The presence of two hight-scales in the structure of the atmosphere was found: the first corresponds to a relatively dense stationary atmosphere, the second to a more rarefied corona.

scholarly journals The Properties of Planetary Nebulae Nuclei: Stellar Winds

1993 ◽  
Vol 155 ◽  
pp. 85-85 ◽  
Author(s):  
L. Bianchi ◽  
G. De Francesco
Keyword(s):  
High Resolution ◽  
Mass Loss ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Planetary Nebulae ◽  
Forthcoming Paper ◽  
Continuum Emission ◽  
Stellar Winds ◽  
High Gravity ◽  
Wind Characteristics

We present IUE observations of some nuclei of Planetary Nebulae. From these data we derive the stellar photospheric parameters (Teff Lbol, log g), and the wind characteristics (velocity, mass loss rate). Teff, R∗, Lbol are derived from UV low resolution spectra, combining optical and radio data, from Bianchi (1988) or from new IUE data, with the same method (fit of the UV continuum with model atmospheres for high gravity stars, after correcting for reddening and for the contribution of continuum emission by the nebular gas). P Cygni profiles from IUE high resolution spectra are fitted with the SEI method and V∞ is derived. The non-LTE ionisation in the wind and the mass loss rate are computed as in Bianchi et al. (1986). Details are given in a forthcoming paper. The results for a first group of objects are given in the Table below.

scholarly journals The Molecular Envolope of Mira

1989 ◽  
Vol 120 ◽  
pp. 306-306
Author(s):  
P. Planesas ◽  
R. Bachiller ◽  
J. Martín-Pintado ◽  
V. Bujarrabal
Keyword(s):  
Mass Loss ◽  
Molecular Mass ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Circumstellar Envelope ◽  
Main Component

We have mapped the CO J = 2 → 1 and J = 1 → 0 emission of the circumstellar envelope of Mira. Emission in both transitions extends to a distance of ~ 4 x 1016cm from the star. In the inner 2 x 1016cm the lines show the presence of three velocity components. The main component has the intermediate velocity and extends over the whole envelope. From this component we have estimated a mass loss rate of 3 x 107M⊙yr-1 and a total molecular mass of 1.2 x 10-3M⊙. We have shown that, from our data, the only reliable explanation for the lowest and highest velocity components is that they are due to an outflow located within the envelope.

scholarly journals Three-dimensional hydrodynamic simulations of the upper atmosphere of π Men c: Comparison with Lyα transit observations

2020 ◽  
Vol 639 ◽  
pp. A109
Author(s):  
I. F. Shaikhislamov ◽  
L. Fossati ◽  
M. L. Khodachenko ◽  
H. Lammer ◽  
A. García Muñoz ◽  
...  
Keyword(s):  
Mass Loss ◽  
Stellar Wind ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Three Dimensional ◽  
High Energy ◽  
Planetary Atmosphere ◽  
Upper Atmosphere ◽  
Energy Emission ◽  
High Energy Emission

Context. π Men c is the first planet to have been discovered by the Transiting Exoplanet Survey Satellite. It orbits a bright, nearby star and has a relatively low average density, making it an excellent target for atmospheric characterisation. The existing planetary upper atmosphere models of π Men c predict significant atmospheric escape, but Lyα transit observations indicate the non-detection of hydrogen escaping from the planet. Aims. Our study is aimed at constraining the conditions of the wind and high-energy emission of the host star and reproducing the non-detection of Lyα planetary absorption. Methods. We modelled the escaping planetary atmosphere, the stellar wind, and their interaction employing a multi-fluid, three-dimensional hydrodynamic code. We assumed a planetary atmosphere composed of hydrogen and helium. We ran models varying the stellar high-energy emission and stellar mass-loss rate, and, for each case, we further computed the Lyα synthetic planetary atmospheric absorption and compared it with the observations. Results. We find that a non-detection of Lyα in absorption employing the stellar high-energy emission estimated from far-ultraviolet and X-ray data requires a stellar wind with a stellar mass-loss rate about six times lower than solar. This result is a consequence of the fact that, for π Men c, detectable Lyα absorption can be caused exclusively by energetic neutral atoms, which become more abundant with increasing velocity or density of the stellar wind. By considering, instead, that the star has a solar-like wind, the non-detection requires a stellar ionising radiation about four times higher than estimated. The reason for this is that despite the fact that a stronger stellar high-energy emission ionises hydrogen more rapidly, it also increases the upper atmosphere heating and expansion, pushing the interaction region with the stellar wind farther away from the planet, where the planet atmospheric density that remains neutral becomes smaller and the production of energetic neutral atoms less efficient. Conclusions. Comparing the results of our grid of models with what is expected and estimated for the stellar wind and high-energy emission, respectively, we support the idea that it is likely that the atmosphere of π Men c is not hydrogen-dominated. Therefore, future observations should focus on the search for planetary atmospheric absorption at the position of lines of heavier elements, such as He, C, and O.

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