Although several thousands of exoplanets have now been detected and characterized, observational biases have led to a paucity of long-period, low-mass exoplanets with measured masses and a ...corresponding lag in our understanding of such planets. In this paper we report the mass estimation and characterization of the long-period exoplanet Kepler-538b. This planet orbits a Sun-like star (V = 11.27) with M and R . Kepler-538b is a R⊕ sub-Neptune with a period of P = 81.73778 0.00013 days. It is the only known planet in the system. We collected radial velocity (RV) observations with the High Resolution Echelle Spectrometer (HIRES) on Keck I and High Accuracy Radial velocity Planet Searcher in North hemisphere (HARPS-N) on the Telescopio Nazionale Galileo (TNG). We characterized stellar activity by a Gaussian process with a quasi-periodic kernel applied to our RV and cross-correlation function FWHM observations. By simultaneously modeling Kepler photometry, RV, and FWHM observations, we found a semi-amplitude of m s−1 and a planet mass of M⊕. Kepler-538b is the smallest planet beyond P = 50 days with an RV mass measurement. The planet likely consists of a significant fraction of ices (dominated by water ice), in addition to rocks/metals, and a small amount of gas. Sophisticated modeling techniques such as those used in this paper, combined with future spectrographs with ultra high-precision and stability will be vital for yielding more mass measurements in this poorly understood exoplanet regime. This in turn will improve our understanding of the relationship between planet composition and insolation flux and how the rocky to gaseous transition depends on planetary equilibrium temperature.
Super-Earths belong to a class of planet not found in the Solar system, but which appear common in the Galaxy. Given that some super-Earths are rocky, while others retain substantial atmospheres, ...their study can provide clues as to the formation of both rocky and gaseous planets, and – in particular – they can help to constrain the role of photoevaporation in sculpting the exoplanet population. GJ 9827 is a system already known to host three super-Earths with orbital periods of 1.2, 3.6, and 6.2 d. Here, we use new HARPS-N radial velocity measurements, together with previously published radial velocities, to better constrain the properties of the GJ 9827 planets. Our analysis cannot place a strong constraint on the mass of GJ 9827 c, but does indicate that GJ 9827 b is rocky with a composition that is probably similar to that of the Earth, while GJ 9827 d almost certainly retains a volatile envelope. Therefore, GJ 9827 hosts planets on either side of the radius gap that appears to divide super-Earths into pre-dominantly rocky ones that have radii below ∼1.5Rꚛ, and ones that still retain a substantial atmosphere and/or volatile components, and have radii above ∼2Rꚛ. That the less heavily irradiated of the three planets still retains an atmosphere, may indicate that photoevaporation has played a key role in the evolution of the planets in this system.
The exoplanet population characterized by relatively short orbital periods (
P
< 100 d) around solar-type stars is dominated by super-Earths and sub-Neptunes. However, these planets are missing in ...our Solar System and the reason behind this absence is still unknown. Two theoretical scenarios invoke the role of Jupiter as the possible culprit: Jupiter may have acted as a dynamical barrier to the inward migration of sub-Neptunes from beyond the water iceline; alternatively, Jupiter may have considerably reduced the inward flux of material (pebbles) required to form super-Earths inside that iceline. Both scenarios predict an anti-correlation between the presence of small planets and that of cold Jupiters in exoplanetary systems. To test that prediction, we homogeneously analyzed the radial-velocity measurements of 38 Kepler and K2 transiting small planet systems gathered over nearly ten years with the HARPS-N spectrograph, as well as publicly available radial velocities collected with other facilities. We used Bayesian differential evolution Markov chain Monte Carlo techniques, which in some cases were coupled with Gaussian process regression to model non-stationary variations due to stellar magnetic activity phenomena. We detected five cold Jupiters in three systems: two in Kepler-68, two in Kepler-454, and a very eccentric one in K2-312. We also found linear trends caused by bound companions in Kepler-93, Kepler-454, and K2-12, with slopes that are still compatible with a planetary mass for outer bodies in the Kepler-454 and K2-12 systems. By using binomial statistics and accounting for the survey completeness, we derived an occurrence rate of 9.3
−2.9
+7.7
% for cold Jupiters with 0.3–13
M
Jup
and 1–10 AU, which is lower but still compatible at 1.3
σ
with the value measured from radial-velocity surveys for solar-type stars, regardless of the presence or absence of small planets. The sample is not large enough to draw a firm conclusion about the predicted anti-correlation between small planets and cold Jupiters; nevertheless, we found no evidence of previous claims of an excess of cold Jupiters in small planet systems. As an important byproduct of our analyses, we homogeneously determined the masses of 64 Kepler and K2 small planets, reaching a precision better than 5, 7.5, and 10
σ
for 25, 13, and 8 planets, respectively. Finally, we release the 3661 HARPS-N radial velocities used in this work to the scientific community. These radial-velocity measurements mainly benefit from an improved data reduction software that corrects for subtle prior systematic effects.
The GAPS programme at TNG Rainer, M.; Borsa, F.; Pino, L. ...
Astronomy and astrophysics (Berlin),
05/2021, Letnik:
649
Journal Article
Recenzirano
Odprti dostop
Context.
Transiting ultra-hot Jupiters are ideal candidates for studying the exoplanet atmospheres and their dynamics, particularly by means of high-resolution spectra with high signal-to-noise ...ratios. One such object is KELT-20b. It orbits the fast-rotating A2-type star KELT-20. Many atomic species have been found in its atmosphere, with blueshifted signals that indicate a day- to night-side wind.
Aims.
We observe the atmospheric Rossiter-McLaughlin effect in the ultra-hot Jupiter KELT-20b and study any variation of the atmospheric signal during the transit. For this purpose, we analysed five nights of HARPS-N spectra covering five transits of KELT-20b.
Methods.
We computed the mean line profiles of the spectra with a least-squares deconvolution using a stellar mask obtained from the Vienna Atomic Line Database (
T
eff
= 10 000 K, log
g
= 4.3), and then we extracted the stellar radial velocities by fitting them with a rotational broadening profile in order to obtain the radial velocity time-series. We used the mean line profile residuals tomography to analyse the planetary atmospheric signal and its variations. We also used the cross-correlation method to study a previously reported double-peak feature in the
FeI
planetary signal.
Results.
We observed both the classical and the atmospheric Rossiter-McLaughlin effect in the radial velocity time-series. The latter gave us an estimate of the radius of the planetary atmosphere that correlates with the stellar mask used in our work (
R
p+atmo
∕
R
p
= 1.13 ± 0.02). We isolated the planetary atmospheric trace in the tomography, and we found radial velocity variations of the planetary atmospheric signal during transit with an overall blueshift of ≈10 km s
−1
, along with small variations in the signal depth, and less significant, in the full width at half maximum (FWHM). We also find a possible variation in the structure and position of the
FeI
signal in different transits.
Conclusions.
We confirm the previously detected blueshift of the atmospheric signal during the transit. The FWHM variations of the atmospheric signal, if confirmed, may be caused by more turbulent condition at the beginning of the transit, by a variable contribution of the elements present in the stellar mask to the overall planetary atmospheric signal, or by iron condensation. The
FeI
signal show indications of variability from one transit to the next.
Ultra-short period (USP) planets are a class of exoplanets with periods shorter than one day. The origin of this sub-population of planets is still unclear, with different formation scenarios highly ...dependent on the composition of the USP planets. A better understanding of this class of exoplanets will, therefore, require an increase in the sample of such planets that have accurate and precise masses and radii, which also includes estimates of the level of irradiation and information about possible companions. Here we report a detailed characterization of a USP planet around the solar-type star HD 80653 ≡EP 251279430 using the K2 light curve and 108 precise radial velocities obtained with the HARPS-N spectrograph, installed on the Telescopio Nazionale
Galileo
. From the K2 C16 data, we found one super-Earth planet (
R
b
= 1.613 ± 0.071
R
⊕
) transiting the star on a short-period orbit (
P
b
= 0.719573 ± 0.000021 d). From our radial velocity measurements, we constrained the mass of HD 80653 b to
M
b
= 5.60 ± 0.43
M
⊕
. We also detected a clear long-term trend in the radial velocity data. We derived the fundamental stellar parameters and determined a radius of
R
⋆
= 1.22 ± 0.01
R
⊙
and mass of
M
⋆
= 1.18 ± 0.04
M
⊙
, suggesting that HD 80653 has an age of 2.7 ± 1.2 Gyr. The bulk density (
ρ
b
= 7.4 ± 1.1 g cm
−3
) of the planet is consistent with an Earth-like composition of rock and iron with no thick atmosphere. Our analysis of the K2 photometry also suggests hints of a shallow secondary eclipse with a depth of 8.1 ± 3.7 ppm. Flux variations along the orbital phase are consistent with zero. The most important contribution might come from the day-side thermal emission from the surface of the planet at
T
~ 3480 K.
ABSTRACT
We report on the detailed characterization of the HD 77946 planetary system. HD 77946 is an F5 (M* = 1.17 M⊙, R* = 1.31 R⊙) star, which hosts a transiting planet recently discovered by ...NASA’s Transiting Exoplanet Survey Satellite (TESS), classified as TOI-1778 b. Using TESS photometry, high-resolution spectroscopic data from HARPS-N, and photometry from CHEOPS, we measure the radius and mass from the transit and radial velocity observations, and find that the planet, HD 77946 b, orbits with period Pb = $6.527282_{-0.000020}^{+0.000015}$ d, has a mass of Mb = 8.38 ± 1.32 M⊕, and a radius of $R_{\rm b} = 2.705_{-0.081}^{+0.086}$R⊕. From the combination of mass and radius measurements, and the stellar chemical composition, the planet properties suggest that HD 77946 b is a sub-Neptune with a ∼1 per cent H/He atmosphere. However, a degeneracy still exists between water-world and silicate/iron-hydrogen models, and even though interior structure modelling of this planet favours a sub-Neptune with a H/He layer that makes up a significant fraction of its radius, a water-world composition cannot be ruled out, as with $T_{\rm eq}~= 1248^{+40}_{-38}~$K, water may be in a supercritical state. The characterization of HD 77946 b, adding to the small sample of well-characterized sub-Neptunes, is an important step forwards on our journey to understanding planetary formation and evolution pathways. Furthermore, HD 77946 b has one of the highest transmission spectroscopic metrics for small planets orbiting hot stars, thus transmission spectroscopy of this key planet could prove vital for constraining the compositional confusion that currently surrounds small exoplanets.
HD 179949 is an F8V star, orbited by a giant planet at ∼8 R
★ every 3.092 514 d. The system was reported to undergo episodes of stellar activity enhancement modulated by the orbital period, ...interpreted as caused by star-planet interactions (SPIs). One possible cause of SPIs is the large-scale magnetic field of the host star in which the close-in giant planet orbits.
In this paper we present spectropolarimetric observations of HD 179949 during two observing campaigns (2009 September and 2007 June). We detect a weak large-scale magnetic field of a few gauss at the surface of the star. The field configuration is mainly poloidal at both observing epochs. The star is found to rotate differentially, with a surface rotation shear of dΩ= 0.216 ± 0.061 rad d−1, corresponding to equatorial and polar rotation periods of 7.62 ± 0.07 and 10.3 ± 0.8 d, respectively. The coronal field estimated by extrapolating the surface maps resembles a dipole tilted at ∼70°. We also find that the chromospheric activity of HD 179949 is mainly modulated by the rotation of the star, with two clear maxima per rotation period as expected from a highly tilted magnetosphere. In 2009 September, we find that the activity of HD 179949 shows hints of low-amplitude fluctuations with a period close to the beat period of the system.
The GAPS programme at TNG Rainer, M.; Desidera, S.; Borsa, F. ...
Astronomy and astrophysics (Berlin),
08/2023, Letnik:
676
Journal Article
Recenzirano
Odprti dostop
Context.
The leading spectrographs used for exoplanets’ search and characterization offer online data reduction softwares (DRS) that yield, as an ancillary result, the full-width at half-maximum ...(FWHM) of the cross-correlation function (CCF) that is used to estimate the radial velocity of the host star. The FWHM also contains information on the stellar projected rotational velocity
v
eq
sin
i
★
, if appropriately calibrated.
Aims.
We wanted to establish a simple relationship to derive the
v
eq
sin
i
★
directly from the FWHM computed by the HARPS-N DRS in the case of slow-rotating solar-like stars. This may also help to recover the stellar inclination
i
★
, which in turn affects the exoplanets’ parameters.
Methods.
We selected stars with an inclination of the spin axis compatible with 90 deg by looking at exoplanetary transiting systems with known small sky-projected obliquity: for these calibrators, we can presume that
v
eq
sin
i
★
is equal to stellar equatorial velocity
v
eq
. We derived their rotational periods from photometric and spectroscopic time series and their radii from the spectral energy distribution (SED) fitting. This allowed us to recover their
v
eq
, which could be compared to the FWHM values of the CCFs obtained both with G2 and K5 spectral-type masks.
Results.
We obtained an empirical relation for each mask: this can be used to derive
v
eq
sin
i
★
directly from FWHM values for slow rotators (
FWHM
< 20 km s
−1
). We applied our relations to 273 exoplanet-host stars observed with HARPS-N, obtaining homogeneous
v
eq
sin
i
★
measurements. When possible, we compared our results with the literature ones to confirm the reliability of our work. We were also able to recover or constrain
i
★
for 12 objects with no prior
v
eq
sin
i
★
estimation.
Conclusions.
We provide two simple empirical relations to directly convert the HARPS-N FWHM obtained with the G2 and K5 mask to a
v
eq
sin
i
★
value. We tested our results on a statistically significant sample, and we found a good agreement with literature values found with more sophisticated methods for stars with log
ɡ
> 3.5. We also tried our relation on HARPS and SOPHIE data, and we conclude that it can be used as it is also on FWHM derived by HARPS DRS with the G2 and K5 mask, and it may be adapted to the SOPHIE data as long as the spectra are taken in high-resolution mode.
ABSTRACT We report the detections of a giant planet (MARVELS-7b) and a brown dwarf (BD) candidate (MARVELS-7c) around the primary star in the close binary system, HD 87646. To the best of our ...knowledge, it is the first close binary system with more than one substellar circumprimary companion that has been discovered. The detection of this giant planet was accomplished using the first multi-object Doppler instrument (KeckET) at the Sloan Digital Sky Survey (SDSS) telescope. Subsequent radial velocity observations using the Exoplanet Tracker at the Kitt Peak National Observatory, the High Resolution Spectrograph at the Hobby Eberley telescope, the "Classic" spectrograph at the Automatic Spectroscopic Telescope at the Fairborn Observatory, and MARVELS from SDSS-III confirmed this giant planet discovery and revealed the existence of a long-period BD in this binary. HD 87646 is a close binary with a separation of ∼22 au between the two stars, estimated using the Hipparcos catalog and our newly acquired AO image from PALAO on the 200 inch Hale Telescope at Palomar. The primary star in the binary, HD 87646A, has = 5770 80 K, log g = 4.1 0.1, and Fe/H = −0.17 0.08. The derived minimum masses of the two substellar companions of HD 87646A are 12.4 0.7 and 57.0 3.7 . The periods are 13.481 0.001 days and 674 4 days and the measured eccentricities are 0.05 0.02 and 0.50 0.02 respectively. Our dynamical simulations show that the system is stable if the binary orbit has a large semimajor axis and a low eccentricity, which can be verified with future astrometry observations.
Abstract
We present mass and radius measurements of K2-79b and K2-222b, two transiting exoplanets orbiting active G-type stars observed with HARPS-N and K2. Their respective 10.99 day and 15.39 day ...orbital periods fall near periods of signals induced by stellar magnetic activity. The two signals might therefore interfere and lead to an inaccurate estimate of exoplanet mass. We present a method to mitigate these effects when radial velocity (RV) and activity-indicator observations are available over multiple observing seasons and the orbital period of the exoplanet is known. We perform correlation and periodogram analyses on subsets composed of each target's two observing seasons, in addition to the full data sets. For both targets, these analyses reveal an optimal season with little to no interference at the orbital period of the known exoplanet. We make a confident mass detection of each exoplanet by confirming agreement between fits to the full RV set and the optimal season. For K2-79b, we measure a mass of 11.8 ± 3.6
M
⊕
and a radius of 4.09 ± 0.17
R
⊕
. For K2-222b, we measure a mass of 8.0 ± 1.8
M
⊕
and a radius of 2.35 ± 0.08
R
⊕
. According to model predictions, K2-79b is a highly irradiated Uranus analog and K2-222b hosts significant amounts of water ice. We also present a RV solution for a candidate second companion orbiting K2-222 at 147.5 days.
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