Title: The GAPS Programme with HARPS-N at TNG. XIII. The orbital obliquity of three close-in massive planets hosted by dwarf K-type stars: WASP-43, HAT-P-20 and Qatar-2,
Abstract: In the framework of the GAPS project, we are conducting an observational
programme aimed at the determination of the orbital obliquity of known
transiting exoplanets. The targets are selected to probe the obliquity against
a wide range of stellar and planetary physical parameters. We exploit
high-precision radial velocity (RV) measurements, delivered by the HARPS-N
spectrograph at the 3.6m Telescopio Nazionale Galileo, to measure the
Rossiter-McLaughlin (RM) effect in RV time-series bracketing planet transits,
and to refine the orbital parameters determinations with out-of-transit RV
data. We also analyse new transit light curves obtained with several 1-2m class
telescopes to better constrain the physical fundamental parameters of the
planets and parent stars. We report here on new transit spectroscopic
observations for three very massive close-in giant planets: WASP43b, HATP20b
and Qatar2b orbiting dwarf K-type stars with effective temperature well below
5000K. We find lambda = 3.5pm6.8 deg for WASP43b and lambda = -8.0pm6.9 deg for
HATP20b, while for Qatar2, our faintest target, the RM effect is only
marginally detected, though our best-fit value lambda = 15pm20 deg is in
agreement with a previous determination. In combination with stellar rotational
periods derived photometrically, we estimate the true spin-orbit angle, finding
that WASP43b is aligned while the orbit of HATP20b presents a small but
significant obliquity (Psi=36 _{-12}^{+10} deg). By analyzing the CaII H&K
chromospheric emission lines for HATP20 and WASP43, we find evidence for an
enhanced level of stellar activity which is possibly induced by star-planet
interactions.