Modelling the He I triplet absorption at 10830 Angstroms in the atmospheres of HD 189733 b and GJ 3470 b. (arXiv:2101.09393v2 [astro-ph.EP] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Lampon_M/0/1/0/all/0/1">M. Lampón</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lopez_Puertas_M/0/1/0/all/0/1">M. López-Puertas</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sanz_Forcada_J/0/1/0/all/0/1">J. Sanz-Forcada</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sanchez_Lopez_A/0/1/0/all/0/1">A. Sánchez-López</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Molaverdikhani_K/0/1/0/all/0/1">K. Molaverdikhani</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Czesla_S/0/1/0/all/0/1">S. Czesla</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Quirrenbach_A/0/1/0/all/0/1">A. Quirrenbach</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Palle_E/0/1/0/all/0/1">E. Pallé</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Caballero_J/0/1/0/all/0/1">J. A. Caballero</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Henning_T/0/1/0/all/0/1">Th. Henning</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Salz_M/0/1/0/all/0/1">M. Salz</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Nortmann_L/0/1/0/all/0/1">L. Nortmann</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Aceituno_J/0/1/0/all/0/1">J. Aceituno</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Amado_P/0/1/0/all/0/1">P. J. Amado</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bauer_F/0/1/0/all/0/1">F. F. Bauer</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Montes_D/0/1/0/all/0/1">D. Montes</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Nagel_E/0/1/0/all/0/1">E. Nagel</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Reiners_A/0/1/0/all/0/1">A. Reiners</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ribas_I/0/1/0/all/0/1">I. Ribas</a>
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, He(2$^{3}$S), absorption of highly
irradiated planets have been recently reported, which provide a new mean to
study 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(2$^{3}$S) absorption measurements and using a 1D hydrodynamic model coupled
with a non-LTE model for the He(2$^{3}$S) state. We also use the H density
derived from Ly$alpha$ observations to further constrain their temperatures,
T, mass-loss rates,$dot M$, 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, 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 XUV, 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 T of
12400$^{+400}_{-300}$ K, with very low mean molecular mass
(H/He=(99.2/0.8)$pm0.1$), almost fully ionised above 1.1 R$_p$, and with $dot
M$=(1.1$pm0.1$)$times$10$^{11}$ g/s. In contrast, the upper atmosphere of GJ
3470 b is highly extended and relatively cold, with a maximum T of 5100$pm900$
K, also with very low mean molecular mass (H/He=(98.5/1.5)$^{+1.0}_{-1.5}$),
not strongly ionised and with $dot M$=(1.9$pm1.1$)$times$10$^{11}$ g/s.
Furthermore, our results suggest that the upper atmospheres of giant planets
undergoing hydrodynamic escape tend to have very low mean molecular mass
(H/He$gtrsim$97/3).
Characterising the atmospheres of exoplanets is key to understanding their
nature and provides hints about their formation and evolution. High-resolution
measurements of the helium triplet, He(2$^{3}$S), absorption of highly
irradiated planets have been recently reported, which provide a new mean to
study their atmospheric escape. In this work, we study the escape of the upper
atmospheres of HD 189733 b and GJ 3470 b by analysing high-resolution
He(2$^{3}$S) absorption measurements and using a 1D hydrodynamic model coupled
with a non-LTE model for the He(2$^{3}$S) state. We also use the H density
derived from Ly$alpha$ observations to further constrain their temperatures,
T, mass-loss rates,$dot M$, 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, 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 XUV, 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 T of
12400$^{+400}_{-300}$ K, with very low mean molecular mass
(H/He=(99.2/0.8)$pm0.1$), almost fully ionised above 1.1 R$_p$, and with $dot
M$=(1.1$pm0.1$)$times$10$^{11}$ g/s. In contrast, the upper atmosphere of GJ
3470 b is highly extended and relatively cold, with a maximum T of 5100$pm900$
K, also with very low mean molecular mass (H/He=(98.5/1.5)$^{+1.0}_{-1.5}$),
not strongly ionised and with $dot M$=(1.9$pm1.1$)$times$10$^{11}$ g/s.
Furthermore, our results suggest that the upper atmospheres of giant planets
undergoing hydrodynamic escape tend to have very low mean molecular mass
(H/He$gtrsim$97/3).
http://arxiv.org/icons/sfx.gif
