The GAPS programme at TNG Guilluy, G.; Andretta, V.; Borsa, F. ...
Astronomy and astrophysics (Berlin),
07/2020, Letnik:
639
Journal Article
Recenzirano
Context.
Exoplanets orbiting very close to their parent star are strongly irradiated. This can lead the upper atmospheric layers to expand and evaporate into space. The metastable helium (He
I
) ...triplet at 1083.3 nm has recently been shown to be a powerful diagnostic to probe extended and escaping exoplanetary atmospheres.
Aims.
We perform high-resolution transmission spectroscopy of the transiting hot Jupiter HD 189733 b with the GIARPS (GIANO-B + HARPS-N) observing mode of the Telescopio Nazionale
Galileo
, taking advantage of the simultaneous optical+near infrared spectral coverage to detect He
I
in the planet’s extended atmosphere and to gauge the impact of stellar magnetic activity on the planetary absorption signal.
Methods.
Observations were performed during five transit events of HD 189733 b. By comparison of the in-transit and out-of-transit GIANO-B observations, we computed high-resolution transmission spectra. We then used them to perform equivalent width measurements and carry out light-curves analyses in order to consistently gauge the excess in-transit absorption in correspondence with the He
I
triplet.
Results.
We spectrally resolve the He
I
triplet and detect an absorption signal during all five transits. The mean in-transit absorption depth amounts to 0.75 ± 0.03% (25
σ
) in the core of the strongest helium triplet component. We detect night-to-night variations in the He
I
absorption signal likely due to the transit events occurring in the presence of stellar surface inhomogeneities. We evaluate the impact of stellar-activity pseudo-signals on the true planetary absorption using a comparative analysis of the He
I
1083.3 nm (in the near-infrared) and the H
α
(in the visible) lines. Using a 3D atmospheric code, we interpret the time series of the He
I
absorption lines in the three nights not affected by stellar contamination, which exhibit a mean in-transit absorption depth of 0.77 ± 0.04% (19
σ
) in full agreement with the one derived from the full dataset. In agreement with previous results, our simulations suggest that the helium layers only fill part of the Roche lobe. Observations can be explained with a thermosphere heated to ~12 000 K, expanding up to ~1.2 planetary radii, and losing ~1 g s
−1
of metastable helium.
Conclusions.
Our results reinforce the importance of simultaneous optical plus near infrared monitoring when performing high-resolution transmission spectroscopy of the extended and escaping atmospheres of hot planets in the presence of stellar activity.
The GAPS programme with HARPS-N at TNG Mancini, L.; Esposito, M.; Covino, E. ...
Astronomy and astrophysics (Berlin),
05/2018, Letnik:
613
Journal Article
Recenzirano
Context.
The measurement of the orbital obliquity of hot Jupiters with different physical characteristics can provide clues to the mechanisms of migration and orbital evolution of this particular ...class of giant exoplanets.
Aims.
We aim to derive the degree of alignment between planetary orbit and stellar spin angular momentum vectors and look for possible links with other orbital and fundamental physical parameters of the star-planet system. We focus on the characterisation of five transiting planetary systems (HAT-P-3, HAT-P-12, HAT-P-22, WASP-39, and WASP-60) and the determination of their sky-projected planet orbital obliquity through the measurement of the Rossiter–McLaughlin effect.
Methods.
We used HARPS-N high-precision radial velocity measurements, gathered during transit events, to measure the Rossiter–McLaughlin effect in the target systems and determine the sky-projected angle between the planetary orbital plane and stellar equator. The characterisation of stellar atmospheric parameters was performed by exploiting the HARPS-N spectra, using line equivalent width ratios and spectral synthesis methods. Photometric parameters of the five transiting exoplanets were re-analysed through 17 new light curves, obtained with an array of medium-class telescopes, and other light curves from the literature. Survey-time-series photometric data were analysed for determining the rotation periods of the five stars and their spin inclination.
Results.
From the analysis of the Rossiter–McLaughlin effect we derived a sky-projected obliquity of
λ
= 21.2° ± 8.7°, λ = −54°
−13°
+41°
,
λ
= −2.1° ± 3.0°,
λ
= 0° ± 11°, and
λ
= −129° ± 17° for HAT-P-3 b, HAT-P-12 b, HAT-P-22 b, WASP-39 b, and WASP-60 b, respectively. The latter value indicates that WASP-60 b is moving on a retrograde orbit. These values represent the first measurements of
λ
for the five exoplanetary systems under study. The stellar activity of HAT-P-22 indicates a rotation period of 28.7 ± 0.4 days, which allowed us to estimate the true misalignment angle of HAT-P-22 b,
ψ
= 24° ± 18°. The revision of the physical parameters of the five exoplanetary systems returned values that are fully compatible with those existing in the literature. The exception to this is the WASP-60 system, for which, based on higher quality spectroscopic and photometric data, we found a more massive and younger star and a larger and hotter planet.
We present 20 yr of radial velocity (RV) measurements of the M1 dwarf Gl15A, combining five years of intensive RV monitoring with the HARPS-N spectrograph with 15 yr of archival HIRES/Keck RV data. ...We have carried out an MCMC-based analysis of the RV time series, inclusive of Gaussian Process (GP) approach to the description of stellar activity induced RV variations. Our analysis confirms the Keplerian nature and refines the orbital solution for the 11.44-day period super Earth, Gl15A b, reducing its amplitude to 1.68
−0.18
+0.17
m s
−1
(
M
sin
i
= 3.03
−0.44
+0.46
M
⊕
), and successfully models a long-term trend in the combined RV dataset in terms of a Keplerian orbit with a period around 7600 days and an amplitude of 2.5
−1.0
+1.3
m s
−1
, corresponding to a super-Neptune mass (
M
sin
i
= 36
−18
+25
M
⊕
) planetary companion. We also discuss the present orbital configuration of Gl15A planetary system in terms of the possible outcomes of Lidov–Kozai interactions with the wide-separation companion Gl15B in a suite of detailed numerical simulations. In order to improve the results of the dynamical analysis, we have derived a new orbital solution for the binary system, combining our RV measurements with astrometric data from the WDS catalogue. The eccentric Lidov–Kozai analysis shows the strong influence of Gl15B on the Gl15A planetary system, which can produce orbits compatible with the observed configuration for initial inclinations of the planetary system between 75° and 90°, and can also enhance the eccentricity of the outer planet well above the observed value, even resulting in orbital instability, for inclinations around 0° and 15°−30°. The Gl15A system is the multi-planet system closest to Earth, at 3.56 pc, and hosts the longest period RV sub-Jovian mass planet discovered so far. Its orbital architecture constitutes a very important laboratory for the investigation of formation and orbital evolution scenarios for planetary systems in binary stellar systems.
ABSTRACT
We present a precise characterization of the TOI-561 planetary system obtained by combining previously published data with TESS and CHEOPS photometry, and a new set of 62 HARPS-N radial ...velocities (RVs). Our joint analysis confirms the presence of four transiting planets, namely TOI-561 b (P = 0.45 d, R = 1.42 R⊕, M = 2.0 M⊕), c (P = 10.78 d, R = 2.91 R⊕, M = 5.4 M⊕), d (P = 25.7 d, R = 2.82 R⊕, M = 13.2 M⊕), and e (P = 77 d, R = 2.55 R⊕, M = 12.6 R⊕). Moreover, we identify an additional, long-period signal (>450 d) in the RVs, which could be due to either an external planetary companion or to stellar magnetic activity. The precise masses and radii obtained for the four planets allowed us to conduct interior structure and atmospheric escape modelling. TOI-561 b is confirmed to be the lowest density (ρb = 3.8 ± 0.5 g cm−3) ultra-short period (USP) planet known to date, and the low metallicity of the host star makes it consistent with the general bulk density-stellar metallicity trend. According to our interior structure modelling, planet b has basically no gas envelope, and it could host a certain amount of water. In contrast, TOI-561 c, d, and e likely retained an H/He envelope, in addition to a possibly large water layer. The inferred planetary compositions suggest different atmospheric evolutionary paths, with planets b and c having experienced significant gas loss, and planets d and e showing an atmospheric content consistent with the original one. The uniqueness of the USP planet, the presence of the long-period planet TOI-561 e, and the complex architecture make this system an appealing target for follow-up studies.
We present an analysis of how bisectors of spectral lines vary, for a few stars observed during the high-accuracy radial-velocity planet survey ongoing at the Telescopio Nazionale Galileo (TNG) ...using the Galileo High Resolution Spectrograph (Spettrografo Alta Risoluzione Galileo, SARG), and discuss their relation with differential radial velocities. The iodine cell lines employed in the radial velocity measurements were used to improve the wavelength calibration and then removed before bisector analysis. The line bisectors were then computed from average absorption profiles obtained by cross-correlation of the stellar spectra with a mask made from suitable lines of a solar catalog. Bisector velocity spans were determined and the run of bisector velocity span against radial velocity was studied to search for correlations between line asymmetries and radial velocity variations. We present an analysis of spectra of HD 216122B that show a slight contamination likely to be due to a stellar companion, and an analysis of spectra of HD 76036A, a case where the line bisectors are useful for improving the RV measurements. These systems are part of a survey sample being observed with adaptive optics (AdOpt at the TNG since 2006) in an attempt to visually resolve stellar companions.
The GAPS Programme with HARPS-N at TNG Lanza, A. F.; Malavolta, L.; Benatti, S. ...
Astronomy and astrophysics (Berlin),
08/2018, Letnik:
616
Journal Article
Recenzirano
Aims
. Stellar activity is the ultimate source of radial-velocity (hereinafter RV) noise in the search for Earth-mass planets orbiting late-type main-sequence stars. We analyse the performance of ...four different indicators and the chromospheric index log
R
′
HK
in detecting RV variations induced by stellar activity in 15 slowly rotating (
υ
sin
i
≤ 5 km s
−1
), weakly active (log
R
′
HK
≤ −4.95) solar-like stars observed with the high-resolution spectrograph High Accuracy Radial velocity Planet Searcher for the Northern hemisphere (HARPS-N).
Methods
. We consider indicators of the asymmetry of the cross-correlation function (CCF) between the stellar spectrum and the binary weighted line mask used to compute the RV, that is the bisector inverse span (BIS), Δ
V
, and a new indicator
V
asy(mod)
together with the full width at half maximum (FWHM) of the CCF. We present methods to evaluate the uncertainties of the CCF indicators and apply a kernel regression (KR) between the RV, the time, and each of the indicators to study their capability of reproducing the RV variations induced by stellar activity.
Results
. The considered indicators together with the KR prove to be useful to detect activity-induced RV variations in ~47 ± 18 percent of the stars over a two-year time span when a significance (two-sided p-value) threshold of one percent is adopted. In those cases, KR reduces the standard deviation of the RV time series by a factor of approximately two. The BIS, the FWHM, and the newly introduced
V
asy(mod)
are the best indicators, being useful in 27 ± 13, 13 ± 9, and 13 ± 9 percent of the cases, respectively. The relatively limited performances of the activity indicators are related to the very low activity level and
υ
sin
i
of the considered stars. For the application of our approach to sun-like stars, a spectral resolution allowing
λ
/Δ
λ
≥ 10
5
and highly stabilized spectrographs are recommended.
HADES RV Programme with HARPS-N at TNG Perger, M.; García-Piquer, A.; Ribas, I. ...
Astronomy and astrophysics (Berlin),
2/2017, Letnik:
598
Journal Article
ABSTRACT We present the characterization of the two transiting planets around HD 152843 (TOI 2319, TIC 349488688) using an intensive campaign of HARPS-N radial velocities, and two sectors of TESS ...data. These data reveal a unique and fascinating system: HD 152843 b and c have near equal masses of around 9 $M_{\hbox{$\oplus $}}$ but differing radii of $3.05 \pm 0.11$$R_{\hbox{$\oplus $}}$ and $5.94 _{ - 0.16 } ^ { + 0.18 }$$R_{\hbox{$\oplus $}}$, respectively, and orbital periods of $11.62071 _{ - 0.000106 } ^ { + 9.6e-05 }$ and $19.502104 _{ - 8.5e-05 } ^ { + 7.4e-05 }$ d. This indicates that HD 152843 c is in the lowest fifth-percentile in density of the known exoplanet population, and has the longest orbital period among these low-density planets. Further, HD 152843 c’s radius places it in the ‘Saturn valley’, the observed lack of planets larger than Neptune, but smaller than Saturn. The orbital periods of these planets indicate they are near a $5:3$ mean motion resonance, indicating the possibility of transit timing variations, and hints at the possibility of interaction with a third planet at some point in the evolution of this system. Further, the brightness of the host star and the low density of HD 152843 c make it a key target for atmospheric characterization.
Orbital obliquity is thought to be a fundamental parameter in tracing the physical mechanisms that cause the migration of giant planets from the snow line down to roughly 102 au from their host ...stars. We are carrying out a large programme to estimate the spin-orbit alignment of a sample of transiting planetary systems to study what the possible configurations of orbital obliquity are and whether they correlate with other stellar or planetary properties. We determine the true and the projected obliquity of HAT-P-36 and WASP-11/HATP-10 systems, respectively, which are both composed of a relatively cool star and a hot Jupiter planet. We used the new spectroscopic and photometric data to revise the main physical parameters and measure the sky-projected misalignment angle of the two systems. In the case of HAT-P-36, we were also able to estimate an upper limit of its real obliquity, which turned out to be psi < 63 degrees.
Context.
Small rocky planets seem to be very abundant around low-mass M-type stars. Their actual planetary population is however not yet precisely understood. Currently, several surveys aim to expand ...the statistics with intensive detection campaigns, both photometric and spectroscopic.
Aims.
The HADES program aims to improve the current statistics through the in-depth analysis of accurate radial-velocity (RV) monitoring in a narrow range of spectral sub-types, with the precision needed to detect small planets with a few Earth masses.
Methods.
We analyse 106 spectroscopic HARPS-N observations of the active M0-type star GJ 685 taken over the past five years. We combine these data with photometric measurements from different observatories to accurately model the stellar rotation and disentangle its signals from genuine Doppler planetary signals in the RV data. We run an MCMC analysis on the RV and activity index time series to model the planetary and stellar signals present in the data, applying Gaussian Process regression technique to deal with the stellar activity signals.
Results.
We identify three periodic signals in the RV time series, with periods of 9, 24, and 18 d. Combining the analyses of the photometry of the star with the activity indexes derived from the HARPS-N spectra, we identify the 18 d and 9 d signals as activity-related, corresponding to the stellar rotation period and its first harmonic, respectively. The 24 d signal shows no relation to any activity proxy, and therefore we identify it as a genuine planetary signal. We find the best-fit model describing the Doppler signal of the newly found planet, GJ 685 b, corresponding to an orbital period
P
b
= 24.160
−0.047
+0.061
d and a minimum mass
M
P
sin
i
= 9.0
−1.8
+1.7
M
⊕
. We also study a sample of 70 RV-detected M-dwarf planets, and present new statistical evidence of a difference in mass distribution between the populations of single- and multi-planet systems, which can shed new light on the formation mechanisms of low-mass planets around late-type stars.
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