2020A&A...634L...4D


Query : 2020A&A...634L...4D

2020A&A...634L...4D - Astronomy and Astrophysics, volume 634, L4-4 (2020/2-1)

The high-energy environment and atmospheric escape of the mini-Neptune K2-18 b.

DOS SANTOS L.A., EHRENREICH D., BOURRIER V., ASTUDILLO-DEFRU N., BONFILS X., FORGET F., LOVIS C., PEPE F. and UDRY S.

Abstract (from CDS):

K2-18 b is a transiting mini-Neptune that orbits a nearby (38 pc), cool M3 dwarf and is located inside its region of temperate irradiation. We report on the search for hydrogen escape from the atmosphere K2-18 b using Lyman-α transit spectroscopy with the Space Telescope Imaging Spectrograph instrument installed on the Hubble Space Telescope. We analyzed the time-series of fluxes of the stellar Lyman-α emission of K2-18 in both its blue- and redshifted wings. We found that the average blueshifted emission of K2-18 decreases by 67%±18% during the transit of the planet compared to the pre-transit emission, tentatively indicating the presence of H atoms escaping vigorously and being blown away by radiation pressure. This interpretation is not definitive because it relies on one partial transit. Based on the reconstructed Lyman-α emission of K2-18, we estimate an EUV irradiation in the range 101-102erg/s/cm2 and a total escape rate on the order of 108g/s. The inferred escape rate suggests that the planet will lose only a small fraction (<1%) of its mass and retain its volatile-rich atmosphere during its lifetime. More observations are needed to rule out stellar variability effects, confirm the in-transit absorption, and better assess the atmospheric escape and high-energy environment of K2-18 b.

Abstract Copyright: © ESO 2020

Journal keyword(s): stars: individual: K2-18 - stars: chromospheres - planets and satellites: atmospheres - ISM: kinematics and dynamics

VizieR on-line data: <Available at CDS (J/A+A/634/L4): orbit1.dat orbit2.dat orbit3.dat orbit4.dat>

Simbad objects: 13

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Number of rows : 13
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2023
#notes
1 * pi. Men c Pl 05 37 09.8851202601 -80 28 08.831347245           ~ 77 0
2 NAME LP 424-4b Pl 07 59 05.8395618539 +15 23 29.240025256           ~ 259 1
3 * rho01 Cnc e Pl 08 52 35.8113282132 +28 19 50.956901366           ~ 519 1
4 NAME L 320-124b Pl 10 14 51.7783473599 -47 09 24.189733387           ~ 141 0
5 HD 97658b Pl 11 14 33.1613362847 +25 42 37.391912066           ~ 185 1
6 K2-18b Pl 11 30 14.5176249117 +07 35 18.257210626           ~ 122 0
7 K2-18 PM* 11 30 14.5177445592 +07 35 18.255348492   15.01 13.50 13.24   dM2.5 79 0
8 Ross 905 PM* 11 42 11.0933350978 +26 42 23.650782778   12.06 10.613 10.272 8.24 M3V 592 1
9 Ross 905b Pl 11 42 11.0933874353 +26 42 23.658083337           ~ 739 1
10 NAME NGP reg 12 51 26.275 +27 07 41.70           ~ 1131 0
11 BD+41 3306 PM* 19 19 00.5489000285 +41 38 04.582441681 10.01 9.67 8.86 8.18 7.66 K0V 261 0
12 TRAPPIST-1 LM* 23 06 29.3684948589 -05 02 29.037301866     18.798 16.466 14.024 M7.5e 812 0
13 HD 219134b Pl 23 13 16.9747821012 +57 10 06.076520993           ~ 92 0

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2023.02.01-07:08:02

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