2017A&A...602A.106B


Query : 2017A&A...602A.106B

2017A&A...602A.106B - Astronomy and Astrophysics, volume 602A, 106-106 (2017/6-1)

Strong H I Lyman-α variations from an 11 Gyr-old host star: a planetary origin?

BOURRIER V., EHRENREICH D., ALLART R., WYTTENBACH A., SEMAAN T., ASTUDILLO-DEFRU N., GRACIA-BERNA A., LOVIS C., PEPE F., THOMAS N. and UDRY S.

Abstract (from CDS):

Kepler-444 provides a unique opportunity to probe the atmospheric composition and evolution of a compact system of exoplanets smaller than the Earth. Five planets transit this bright K star at close orbital distances, but they are too small for their putative lower atmosphere to be probed at optical/infrared wavelengths. We used the Space Telescope Imaging Spectrograph instrument on board the Hubble Space Telescope to search for the signature of the planet's upper atmospheres at six independent epochs in the Lyman-α line. We detect significant flux variations during the transits of both Kepler-444 e and f (∼20%), and also at a time when none of the known planets was transiting (∼40%). Variability in the transition region and corona of the host star might be the source of these variations. Yet, their amplitude over short timescales (∼2-3h) is surprisingly strong for this old (11.2±1.0Gyr) and apparently quiet main-sequence star. Alternatively, we show that the in-transit variations could be explained by absorption from neutral hydrogen exospheres trailing the two outer planets (Kepler-444 e and f). They would have to contain substantial amounts of water to replenish hydrogen exospheres such as these, which would reveal them to be the first confirmed ocean planets. The out-of-transit variations, however, would require the presence of an as-yet-undetected Kepler-444 g at larger orbital distance, casting doubt on the planetary origin scenario. Using HARPS-N observations in the sodium doublet, we derived the properties of two interstellar medium clouds along the line of sight toward Kepler-444. This allowed us to reconstruct the stellar Lyman-α line profile and to estimate the extreme-UV (XUV) irradiation from the star, which would still allow for a moderate mass loss from the outer planets after 11.2Gyr. Follow-up of the system at XUV wavelengths will be required to assess this tantalizing possibility.

Abstract Copyright: © ESO, 2017

Journal keyword(s): planetary systems - stars: individual: Kepler-444 - planets and satellites: atmospheres - techniques: spectroscopic - techniques: spectroscopic

Simbad objects: 16

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Number of rows : 16
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 HD 166 BY* 00 06 36.7840068588 +29 01 17.412693890   6.88   5.6   G8 335 1
2 NAME LIC Cld 04 41 +31.           ~ 277 0
3 HD 33793 PM* 05 11 40.5898395497 -45 01 06.361734876 11.624 10.433 8.853 7.9 6.899 M1VIp 315 0
4 WASP-12b Pl 06 30 32.7966788910 +29 40 20.266334158           G0 689 1
5 * rho01 Cnc e Pl 08 52 35.8113282132 +28 19 50.956901366           ~ 513 1
6 * rho01 Cnc b Pl 08 52 35.8113282132 +28 19 50.956901366           ~ 249 1
7 HD 97658 PM* 11 14 33.1612754184 +25 42 37.390358520 9.049 8.569 7.714 7.259 6.835 K1V 156 1
8 HD 97658b Pl 11 14 33.1613362847 +25 42 37.391912066           ~ 182 1
9 Ross 905 PM* 11 42 11.0933350978 +26 42 23.650782778   12.06 10.613 10.272 8.24 M3V 587 1
10 Ross 905b Pl 11 42 11.0933874353 +26 42 23.658083337           ~ 732 1
11 BD+41 3306e Pl 19 19 00.5488384064 +41 38 04.581624991           ~ 33 0
12 BD+41 3306f Pl 19 19 00.5488384064 +41 38 04.581624991           ~ 27 0
13 BD+41 3306 PM* 19 19 00.5489000285 +41 38 04.582441681 10.01 9.67 8.86 8.18 7.66 K0V 257 0
14 HD 189733 BY* 20 00 43.7129433648 +22 42 39.073143456 9.241 8.578 7.648 7.126 6.68 K2V 820 1
15 HD 189733b Pl 20 00 43.7130382888 +22 42 39.071811263           ~ 1304 1
16 HD 209458b Pl 22 03 10.7729598762 +18 53 03.548248479           ~ 1723 1

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2022.11.27-09:38:25

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