Detalles de publicación
PP 014030
The GAPS Programme with HARPS-N at TNG. III: The retrograde orbit of HAT-P-18b.
(1) Instituto de Astrof\'isica de Canarias, C/ V\'ia L\'actea, s/n, E38205 - La Laguna (Tenerife), Spain;
(2) Dep. de Astrof\'isica, Universidad de La Laguna, Avda. Astrof\'isico Francisco S\'anchez, s/n 38206 La Laguna, Tenerife, Spain;
(3) INAF -- Osservatorio Astronomico di Capodimonte, via Moiariello, 16, 80131 Naples, Italy;
(4) Max-Planck-Institut f\"ur Astronomie, K\"onigstuhl 17, D-69117 Heidelberg, Germany;
(5) Fundaci\'on Galileo Galilei - INAF, Rambla Jos\'e Ana Fernandez P\'erez, 7 38712 Bre\~na Baja, TF - Spain;
(6) Astrophysics Group, Keele University, Staffordshire,ST5 5BG, UK;
(7) INAF -- Osservatorio Astrofisico di Catania, via S. Sofia 78, 95123 Catania, Italy;
(8) Dipartimento di Fisica e Astronomia Galileo Galilei, Universit\`a di Padova, Vicolo dell'Osservatorio 2, I-35122, Padova, Italy;
(9) INAF -- Osservatorio Astrofisico di Torino, Via Osservatorio 20, I-10025, Pino Torinese, Italy;
(10) INAF -- Osservatorio Astronomico di Brera, Via E. Bianchi 46, 23807, Merate (LC), Italy;
(11) INAF -- Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio 5, 35122 Padova, Italy;
(12) INAF -- Osservatorio Astronomico di Palermo, Piazza del Parlamento, Italy 1, I-90134, Palermo, Italy;
(13) INAF -- IASF Milano, via Bassini 15, I-20133 Milano, Italy;
(14) INAF -- Osservatorio Astronomico di Trieste, Via Tiepolo 11, 34143 Trieste Italy
The measurement of the Rossiter-McLaughlin effect for transiting exoplanets
places constraints on the orientation of the orbital axis with respect to the stellar spin axis,
which can shed light on the mechanisms shaping the orbital configuration of planetary
systems.
Here we present the interesting case of the Saturn-mass planet HAT-P-18b,
which orbits one of the coolest stars for which the Rossiter-McLaughlin effect
has been measured so far.
We acquired a spectroscopic time-series, spanning a full transit, with the HARPS-N spectrograph
mounted at the TNG telescope. The very precise radial velocity measurements delivered by the HARPS-N pipeline were used to
measure the Rossiter-McLaughlin effect. Complementary new photometric observations of another full transit were
also analysed to obtain an independent determination of the star and planet parameters.
We find that HAT-P-18b lies on a counter-rotating orbit, the sky-projected angle between the stellar spin axis and the planet
orbital axis being $\lambda=132\pm15$ deg. By joint modelling of the radial velocity and photometric data we obtain new
determinations of the star ($M_\star=0.770 \pm 0.027$ M$_\odot$;
$R_\star=0.717 \pm 0.026$ R$_\odot$; $V\sin{I_\star}=1.58 \pm 0.18$ km s$^{-1}$)
and planet ($M_{\rm p}=0.196 \pm 0.008$ M$_{\rm J}$; $R_{\rm p}=0.947 \pm 0.044$ R$_{\rm J}$)
parameters. Our spectra provide for the host star an effective temperature $T_{\rm eff}=4870 \pm 50$ K,
a surface gravity of $\log g_\star=4.57 \pm 0.07 $ cm s$^{-2}$
and an iron abundance of [Fe/H] = $ 0.10 \pm 0.06$.
HAT-P-18b is one of the few planets known to transit a star with $T_{\rm eff} < 6250$ K
on a retrograde orbit. Objects such as
HAT-P-18b (low planet mass and/or relatively long orbital period) most likely have a weak tidal coupling with their parent stars, therefore
their orbits preserve any original misalignment. As such, they are ideal targets to study the causes of orbital
evolution in cool main-sequence stars.
places constraints on the orientation of the orbital axis with respect to the stellar spin axis,
which can shed light on the mechanisms shaping the orbital configuration of planetary
systems.
Here we present the interesting case of the Saturn-mass planet HAT-P-18b,
which orbits one of the coolest stars for which the Rossiter-McLaughlin effect
has been measured so far.
We acquired a spectroscopic time-series, spanning a full transit, with the HARPS-N spectrograph
mounted at the TNG telescope. The very precise radial velocity measurements delivered by the HARPS-N pipeline were used to
measure the Rossiter-McLaughlin effect. Complementary new photometric observations of another full transit were
also analysed to obtain an independent determination of the star and planet parameters.
We find that HAT-P-18b lies on a counter-rotating orbit, the sky-projected angle between the stellar spin axis and the planet
orbital axis being $\lambda=132\pm15$ deg. By joint modelling of the radial velocity and photometric data we obtain new
determinations of the star ($M_\star=0.770 \pm 0.027$ M$_\odot$;
$R_\star=0.717 \pm 0.026$ R$_\odot$; $V\sin{I_\star}=1.58 \pm 0.18$ km s$^{-1}$)
and planet ($M_{\rm p}=0.196 \pm 0.008$ M$_{\rm J}$; $R_{\rm p}=0.947 \pm 0.044$ R$_{\rm J}$)
parameters. Our spectra provide for the host star an effective temperature $T_{\rm eff}=4870 \pm 50$ K,
a surface gravity of $\log g_\star=4.57 \pm 0.07 $ cm s$^{-2}$
and an iron abundance of [Fe/H] = $ 0.10 \pm 0.06$.
HAT-P-18b is one of the few planets known to transit a star with $T_{\rm eff} < 6250$ K
on a retrograde orbit. Objects such as
HAT-P-18b (low planet mass and/or relatively long orbital period) most likely have a weak tidal coupling with their parent stars, therefore
their orbits preserve any original misalignment. As such, they are ideal targets to study the causes of orbital
evolution in cool main-sequence stars.