Hα detection in KELT-9b - an extended hydrogen envelope of the hottest exoplanet

Fei Yan (Postdoctoral Fellow)

Max-Planck-Institute for Astronomy, Heidelberg, Germany

F. Yan & Th. Henning, 2018, Nature Astronomy, 2, 714–718

Hα detection in exoplanets

difficulties:

Large number of excited atoms needed (unlike Lyα)

Hα detection in exoplanets

difficulties:

Large number of excited atoms needed (unlike Lyα) Stellar Hα source is complicated

Hα image of the Sun

Ehrenreich, 2018, Nature Astronomy, 2, 703

KELT-9b: the hottest exoplanet

The host star: A0 type star, T ~ 10,000 K, V = 7.56 The planet: gas gaint Teq ~ 4000 K

( Gaudi et al. 2017, Nature, 546, 514–518)

Observation:

DDT proposal to Calar Alto Observatory: two transits with CARMENES: 2017-08-06 and 2017-09-21

CARMENES: new high resolution spectrograph (R ~ 94, 600)

Both observations were under partially cloudy weather

In transit

Date reduction:

Date reduction:

•  Rebin the two nights data with 0.01 phase step. •  18 residual spectra obtained.

Date reduction:

Planetary orbital motion ( -91 km/s to +91 km/s during transit)

Date reduction: Ph

ase

In transit

•  Rebin the two nights data with 0.01 phase step. •  18 residual spectra obtained.

fast rotating: Vsini = 111.4 km/s Spin–orbit alignment: -85 degree

Stellar line variation:

Rossiter–McLaughlin (RM) effect

Model the stellar line variation:

Model: RM effect + CLV (center-to-limb variation) effect

CLV effect: Yan et al. 2017, A&A

Light curve (of equivalent width):

Well resolved Hα line profile:

(1) Absorption depth: 1.15% (transit depth: 0.68%) (2) Gaussian sigma: 21.7 km/s (optically thick)

1.15%

21.7km/s

Interpretation:

1.15% line depth 1.64 Rplanet Extended atmosphere close to the Roche lobe

Interpretation:

1.15% line depth 1.64 Rplanet Extended atmosphere close to the Roche lobe Atmosphere probably escaping dramatically

Individual night:

repeatable and stable

Conclusions:

•  We detected strong Hα absorption in the atmosphere of hottest exoplanet with CARMENES.

•  The planet has an extended atmosphere close to its Roche lobe, indicating an escaping atmosphere.

•  The planetary orbital RV was directly measured with a single line.

Fei Yan @ HoRES, Nice, France, Oct. 2018

F. Yan & Th. Henning, 2018, Nature Astronomy, 2, 714–718