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

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.

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

Astronomy and Astrophysics ◽

10.1051/0004-6361/202039417 ◽

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).

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Ionisation fractions and mass-loss in O stars

Symposium - International Astronomical Union ◽

10.1017/s0074180900156967 ◽

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.

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

Symposium - International Astronomical Union ◽

10.1017/s0074180900204993 ◽

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.

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The Properties of Planetary Nebulae Nuclei: Stellar Winds

Symposium - International Astronomical Union ◽

10.1017/s0074180900170159 ◽

1993 ◽

Vol 155 ◽

pp. 85-85 ◽

Cited By ~ 1

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.

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The dichotomy of atmospheric escape in AU Mic b

Monthly Notices of the Royal Astronomical Society Letters ◽

10.1093/mnrasl/slaa127 ◽

2020 ◽

Vol 498 (1) ◽

pp. L53-L57

Author(s):

S Carolan ◽

A A Vidotto ◽

P Plavchan ◽

C Villarreal D’Angelo ◽

G Hazra

Keyword(s):

Mass Loss ◽

Stellar Wind ◽

Evaporation Rate ◽

Loss Rate ◽

Extreme Ultraviolet ◽

Mass Loss Rate ◽

Young Star ◽

Planetary Atmosphere ◽

The Other ◽

Atmospheric Escape

ABSTRACT Here, we study the dichotomy of the escaping atmosphere of the newly discovered close-in exoplanet AU Microscopii (AU Mic) b. On one hand, the high extreme-ultraviolet stellar flux is expected to cause a strong atmospheric escape in AU Mic b. On the other hand, the wind of this young star is believed to be very strong, which could reduce or even inhibit the planet’s atmospheric escape. AU Mic is thought to have a wind mass-loss rate that is up to 1000 times larger than the solar wind mass-loss rate ($\dot{\mathrm{ M}}_\odot$). To investigate this dichotomy, we perform 3D hydrodynamics simulations of the stellar wind–planetary atmosphere interactions in the AU Mic system and predict the synthetic Ly α transits of AU Mic b. We systematically vary the stellar wind mass-loss rate from a ‘no wind’ scenario to up to a stellar wind with a mass-loss rate of $1000~\dot{\mathrm{ M}}_\odot$. We find that, as the stellar wind becomes stronger, the planetary evaporation rate decreases from 6.5 × 1010 g s−1 to half this value. With a stronger stellar wind, the atmosphere is forced to occupy a smaller volume, affecting transit signatures. Our predicted Ly α absorption drops from $\sim 20{{\ \rm per\ cent}}$ in the case of ‘no wind’ to barely any Ly α absorption in the extreme stellar wind scenario. Future Ly α transits could therefore place constraints not only on the evaporation rate of AU Mic b, but also on the mass-loss rate of its host star.

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Wind and nebula of the M 33 variable GR 290 (WR/LBV)

Astronomy and Astrophysics ◽

10.1051/0004-6361/201732540 ◽

2018 ◽

Vol 617 ◽

pp. A51 ◽

Cited By ~ 1

Author(s):

Olga Maryeva ◽

Gloria Koenigsberger ◽

Oleg Egorov ◽

Corinne Rossi ◽

Vito Francesco Polcaro ◽

...

Keyword(s):

Interstellar Medium ◽

Mass Loss ◽

Loss Rate ◽

Mass Loss Rate ◽

Model Atmosphere ◽

General Context ◽

Thermodynamical Equilibrium ◽

Bolometric Luminosity ◽

Non Local ◽

Circumstellar Environment

Context. GR 290 (M 33/V532 = Romano’s Star) is a suspected post-luminous blue variable star located in M 33 galaxy that shows a rare Wolf–Rayet (WR) spectrum during its minimum light phase. In spite of many studies, its atmospheric structure, its circumstellar environment, and its place in the general context of massive stars’ evolution is poorly known. Aims. We present a detailed study of this star’s wind and mass loss, and a study of the circumstellar environment associated to the star. Methods. Long-slit spectra of GR 290 were obtained during its present minimum luminosity phase with the Gran Telescopio Canarias covering the ∼3600–7500 Å wavelength range together with contemporaneous photometry using B, V, R and I filters. The data were compared with non-local thermodynamical equilibrium (non-LTE) model atmosphere synthetic spectra computed with CMFGEN code and with models for ionized interstellar medium regions computed with CLOUDY code. Results. The current mV = 18.8 mag is the faintest at which this source has ever been observed. The non-LTE models indicate effective temperatures of Teff = 27 000–30 000 K at radius R2/3 = 27−21 R⊙ and mass-loss rate Ṁ = 1.5 × 10−5 M⊙yr−1. The terminal wind speed v∞ = 620 km s−1 is faster than ever before recorded, while the current luminosity L* = (3.1–3.7) × 105L⊙ is the lowest ever deduced. The star is overabundant in He and N and underabundant in C and O. It is surrounded by an unresolved compact H II region with dimensions ≤4 pc, from where H-Balmer, He I lines, and [O III] and [N II] are detected. In addition, we find emission from a more extended interstellar medium (ISM) region, which appears to be asymmetric, with a larger extent to the east (16–40 pc) than to the west. Conclusions. In the present long lasting visual minimum, GR 290 is in a lower bolometric luminosity state with higher mass-loss rate. The nearby nebular emission seems to suggest that the star has undergone significant mass loss over the past 104–105 yr and is nearing the end stages of its evolution.

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