Precise masses for the transiting planetary system HD 106315 with HARPS

WYTTENBACH, A.; TRIAUD, A. H. M. J.; SEFAKO, R.; OSBORN, H. P.; MELO, C.; VIGAN, A.; LENDL, M.; SOUSA, S. G.; HÉBRARD, G.; SANTOS, N. C.; FARIA, J. P.; NEAL, J. J.; EHRENREICH, D.; LOVIS, C.; DÍAZ, R. F.; JACKMAN, J.; COLLIER CAMERON, A.; FOXELL, E.; BOUCHY, F.; FAEDI, F.; BENTO, J.; DUMUSQUE, X.; ADIBEKYAN, V.; DEMANGEON, O.; BRUGGER, B.; COCHRAN, W. D.; LILLO-BOX, J.; BONOMO, A. S.; BARRADO, D.; ARMSTRONG, D. J.; DELGADO MENA, E.; GOSSELIN, H.; UDRY, S.; SHPORER, A.; POLLACCO, D.; MOUSIS, O.; LIGI, R.; HOJJATPANAH, S.; FIGUEIRA, P.; ESPINOZA, N.; DOYLE, A.; DELEUIL, M.; BROWN, D. J. A.; BOISSE, I.; ARMSTRONG, J. D.; SANTERNE, A.; BAYLISS, D.; BARROS, S. C. C.

ASTRONOMY AND ASTROPHYSICS

EDP SCIENCES S A

Lugar: Paris; Año: 2017 vol. 608

0004-6361

Context. The multi-planetary system HD 106315 was recently found in K2data. The planets have periods of Pb 9.55 and Pc 21.06 days, and radii of rb = 2.44 ± 0.17R⊕ and rc = 4.35 ± 0.23R⊕ . The brightness of the host star (V = 9.0 mag)makes it an excellent target for transmission spectroscopy. However, tointerpret transmission spectra it is crucial to measure the planetarymasses. Aims: We obtained high precision radial velocities for HD106315 to determine the mass of the two transiting planets discoveredwith Kepler K2. Our successful observation strategy was carefullytailored to mitigate the effect of stellar variability. Methods:We modelled the new radial velocity data together with the K2 transitphotometry and a new ground-based partial transit of HD 106315c toderive system parameters. Results: We estimate the mass of HD106315b to be 12.6 ± 3.2 M⊕ and the density tobe 4.7 ± 1.7 g cm-3, while for HD 106315c we estimatea mass of 15.2 ± 3.7 M⊕ and a density of 1.01± 0.29 g cm-3. Hence, despite planet c having a radiusalmost twice as large as planet b, their masses are consistent with oneanother. Conclusions: We conclude that HD 106315c has a thickhydrogen-helium gaseous envelope. A detailed investigation of HD 106315busing a planetary interior model constrains the core mass fraction to be5-29%, and the water mass fraction to be 10-50%. An alternative, notconsidered by our model, is that HD 106315b is composed of a large rockycore with a thick H-He envelope. Transmission spectroscopy of theseplanets will give insight into their atmospheric compositions and alsohelp constrain their core compositions.