Context.
Most of the currently known planets are small worlds with radii between that of the Earth and that of Neptune. The characterization of planets in this regime shows a large diversity in ...compositions and system architectures, with distributions hinting at a multitude of formation and evolution scenarios. However, many planetary populations, such as high-density planets, are significantly under-sampled, limiting our understanding of planet formation and evolution.
Aims.
NCORES is a large observing program conducted on the HARPS high-resolution spectrograph that aims to confirm the planetary status and to measure the masses of small transiting planetary candidates detected by transit photometry surveys in order to constrain their internal composition.
Methods.
Using photometry from the K2 satellite and radial velocities measured with the HARPS and CORALIE spectrographs, we searched for planets around the bright (
V
mag
= 10) and slightly evolved Sun-like star HD 137496.
Results.
We precisely estimated the stellar parameters,
M
*
= 1.035 ± 0.022
M
⊙
,
R
*
= 1.587 ± 0.028
R
⊙
,
T
eff
= 5799 ± 61 K, together with the chemical composition (e.g. Fe/H = −0.027 ± 0.040 dex) of the slightly evolved star. We detect two planets orbiting HD 137496. The inner planet, HD 137496 b, is a super-Mercury (an Earth-sized planet with the density of Mercury) with a mass of
M
b
= 4.04 ± 0.55
M
⊕
, a radius of R
b
= 1.31
−0.05
+0.06
R
⊕
, and a density of ρ
b
= 10.49
−1.82
+2.08
g cm
-3
. With an interior modeling analysis, we find that the planet is composed mainly of iron, with the core representing over 70% of the planet’s mass (M
core
/ M
total
= 0.73
−0.12
+0.11
). The outer planet, HD 137496 c, is an eccentric (
e
= 0.477 ± 0.004), long period (
P
= 479.9
−1.1
+1.0
days) giant planet (
M
c
sin
i
c
= 7.66 ± 0.11
M
Jup
) for which we do not detect a transit.
Conclusions.
HD 137496 b is one of the few super-Mercuries detected to date. The accurate characterization reported here enhances its role as a key target to better understand the formation and evolution of planetary systems. The detection of an eccentric long period giant companion also reinforces the link between the presence of small transiting inner planets and long period gas giants.
Context. M-type subdwarfs are metal-poor low-mass stars and are probes for the old populations in our Galaxy. Accurate knowledge of their atmospheric parameters and especially their composition is ...essential for understanding the chemical history of our Galaxy. Aims. The purpose of this work is to perform a detailed study of M-subdwarf spectra covering the full wavelength range from the optical to the near-infrared. It allows us to perform a more detailed analysis of the atmospheric composition in order to determine the stellar parameters, and to constrain the atmospheric models. The study will allow us to further understand physical and chemical processes such as increasing condensation of gas into dust, to point out the missing continuum opacities, and to see how the main band features are reproduced by the models. The spectral resolution and the large wavelength coverage used is a unique combination that can constrain the processes that occur in a cool atmosphere. Methods. We obtained medium-resolution spectra (R = 5000−7000) over the wavelength range 0.3−2.5 μm of ten M-type subdwarfs with X-shooter at VLT. These data constitute a unique atlas of M-subdwarfs from optical to near-infrared. We performed a spectral synthesis analysis using a full grid of synthetic spectra computed from BT-Settl models and obtained consistent stellar parameters such as effective temperature, surface gravity, and metallicity. Results. We show that state-of the-art atmospheric models correctly represent the overall shape of their spectral energy distribution, as well as atomic and molecular line profiles both in the optical and near-infrared. We find that the actual fitted gravities of almost all our sample are consistent with old objects, except for LHS 73 where it is found to be surprisingly low.
Context. Planets with radii of between 2 and 4 R ⊕ closely orbiting solar-type stars are of significant importance for studying the transition from rocky to giant planets, and are prime targets for ...atmospheric characterization by missions such as JWST and ARIEL. Unfortunately, only a handful of examples with precise mass measurements are known to orbit bright stars. Aims. Our goal is to determine the mass of a transiting planet around the very bright F6 star HD 73344 (Vmag = 6.9). This star exhibits high activity and has a rotation period that is close to the orbital period of the planet ( P b = 15.6 days). Methods. The transiting planet, initially a K2 candidate, is confirmed through TESS observations (TOI 5140.01). We refined its parameters using TESS data and rule out a false positive with Spitzer observations. We analyzed high-precision radial velocity (RV) data from the SOPHIE and HIRES spectrographs. We conducted separate and joint analyses of K2, TESS, SOPHIE, and HIRES data using the PASTIS software. Given the star’s early type and high activity, we used a novel observing strategy, targeting the star at high cadence for two consecutive nights with SOPHIE to understand the short-term stellar variability. We modeled stellar noise with two Gaussian processes: one for rotationally modulated stellar processes, and one for short-term stellar variability. Results. High-cadence RV observations provide better constraints on stellar variability and precise orbital parameters for the transiting planet: a radius of R b = 2.88 −0.07 +0.08 R ⊕ and a mass of M b = 2.98 −1.90 +2.50 M ⊕ (upper-limit at 3σ is <10.48 M ⊕ ). The derived mean density suggests a sub-Neptune-type composition, but uncertainties in the planet’s mass prevent a detailed characterization. In addition, we find a periodic signal in the RV data that we attribute to the signature of a nontransiting exoplanet, without totally excluding the possibility of a nonplanetary origin. This planetary candidate would have a minimum mass of about M c sin i c = 116.3 ± −13.0 +12.8 M ⊕ and a period of P c = 66.45 −0.25 +0.10 days. Dynamical analyses confirm the stability of the two-planet system and provide constraints on the inclination of the candidate planet; these findings favor a near-coplanar system. Conclusions. While the transiting planet orbits the bright star at a short period, stellar activity prevented us from precise mass measurements despite intensive RV follow-up. Long-term RV tracking of this planet could improve this measurement, as well as our understanding of the activity of the host star. The latter will be essential if we are to characterize the atmosphere of planets around F-type stars using transmission spectroscopy.
Aims. Since 2011, the SOPHIE spectrograph has been used to search for Neptunes and super-Earths in the northern hemisphere. As part of this observational program, 290 radial velocity measurements of ...the 6.4 V magnitude star HD 158259 were obtained. Additionally, TESS photometric measurements of this target are available. We present an analysis of the SOPHIE data and compare our results with the output of the TESS pipeline.Methods. The radial velocity data, ancillary spectroscopic indices, and ground-based photometric measurements were analyzed with classical and ℓ1 periodograms. The stellar activity was modeled as a correlated Gaussian noise and its impact on the planet detection was measured with a new technique.Results. The SOPHIE data support the detection of five planets, each with m sin i ≈ 6 M⊕, orbiting HD 158259 in 3.4, 5.2, 7.9, 12, and 17.4 days. Though a planetary origin is strongly favored, the 17.4 d signal is classified as a planet candidate due to a slightly lower statistical significance and to its proximity to the expected stellar rotation period. The data also present low frequency variations, most likely originating from a magnetic cycle and instrument systematics. Furthermore, the TESS pipeline reports a significant signal at 2.17 days corresponding to a planet of radius ≈1.2 R⊕. A compatible signal is seen in the radial velocities, which confirms the detection of an additional planet and yields a ≈2 M⊕ mass estimate.Conclusions. We find a system of five planets and a strong candidate near a 3:2 mean motion resonance chain orbiting HD 158259. The planets are found to be outside of the two and three body resonances.
Comets play a dual role in understanding the formation and evolution of the solar system. First, the composition of comets provides information about the origin of the giant planets and their moons ...because comets formed early and their composition is not expected to have evolved significantly since formation. They, therefore serve as a record of conditions during the early stages of solar system formation. Once comets had formed, their orbits were perturbed allowing them to travel into the inner solar system and impact the planets. In this way they contributed to the volatile inventory of planetary atmospheres. We review here how knowledge of comet composition up to the time of the Rosetta mission has contributed to understanding the formation processes of the giant planets, their moons and small icy bodies in the solar system. We also discuss how comets contributed to the volatile inventories of the giant and terrestrial planets.
The wealth of observational data about Jupiter and Saturn provides strong constraints to guide our understanding of the formation of giant planets. The size of the core and the total amount of heavy ...elements in the envelope have been derived from internal structure studies by Saumon & Guillot. The atmospheric abundance of some volatile elements has been measured in situ by the Galileo probe or by remote sensing. In this Letter, we show that, by extending the standard core accretion formation scenario of giant planets by Pollack et al. to include migration and protoplanetary disk evolution, it is possible to account for all of these constraints in a self-consistent manner.
We present an evolutionary turbulent model of the Saturn's subnebula consistent with recent core accretion formation models of Saturn. Our calculations are similar to those conducted in the case of ...the Jovian subnebula, and take into account the vertical structure of the disk, as well as the evolution of its surface density, as given by an α-disk model. Using the thermodynamic conditions of our model, we calculate the evolution of the CO2:CO:CH4 and N2:NH3 molar mixing ratios in the subnebula. We thus show that the carbon and nitrogen homogeneous gas-phase chemistry is inhibited in the subnebula. We also consider the role played by Fischer-Tropsch catalysis in the gas-phase conversions of CO and CO2 into CH4. We demonstrate that, even if a catalytically active zone is likely to exist in the early Saturn's subnebula, it does not alter the composition of volatiles ultimately trapped in the forming solids. We study two different formation scenarios of Titan. In each scenario, we provide observational tests that are compared with measurements made by the Huygens probe. In the first scenario, Titan is formed in a late and cold subnebula from planetesimals produced in Saturn's feeding zone that have been preserved from vaporization. In the second scenario, Titan is formed in a balmy and early subnebula. We show that the first scenario predicts a CO:CH4 molar mixing ratio orders of magnitude larger than the observed one in the atmosphere of Titan, and requires strong variations of water abundance in the solar nebula on short lengthscales, whose origin is not explained. On the contrary, the second scenario does not require such large variations of the abundance of water, and predicts abundances of volatile species in Titan similar to the observed ones.
Context. The multi-planetary system HD 106315 was recently found in K2 data. The planets have periods of Pb ~ 9.55 and Pc ~ 21.06 days, and radii of rb = 2.44 ± 0.17 R⊕ and rc = 4.35 ± 0.23 R⊕ . The ...brightness of the host star (V = 9.0 mag) makes it an excellent target for transmission spectroscopy. However, to interpret transmission spectra it is crucial to measure the planetary masses. Aims. We obtained high precision radial velocities for HD 106315 to determine the mass of the two transiting planets discovered with Kepler K2. Our successful observation strategy was carefully tailored to mitigate the effect of stellar variability. Methods. We modelled the new radial velocity data together with the K2 transit photometry and a new ground-based partial transit of HD 106315c to derive system parameters. Results. We estimate the mass of HD 106315b to be 12.6 ± 3.2 M⊕ and the density to be 4.7 ± 1.7 g cm-3, while for HD 106315c we estimate a mass of 15.2 ± 3.7 M⊕ and a density of 1.01 ± 0.29 g cm-3. Hence, despite planet c having a radius almost twice as large as planet b, their masses are consistent with one another. Conclusions. We conclude that HD 106315c has a thick hydrogen-helium gaseous envelope. A detailed investigation of HD 106315b using a planetary interior model constrains the core mass fraction to be 5–29%, and the water mass fraction to be 10–50%. An alternative, not considered by our model, is that HD 106315b is composed of a large rocky core with a thick H–He envelope. Transmission spectroscopy of these planets will give insight into their atmospheric compositions and also help constrain their core compositions.
The Texas Echelon cross Echelle Spectrograph (TEXES), mounted on NASA's Infrared Telescope Facility (IRTF), was used to map mid-infrared ammonia absorption features on both Jupiter and Saturn in ...February 2013. Ammonia is the principle reservoir of nitrogen on the giant planets, and the ratio of isotopologues (N/N) can reveal insights into the molecular carrier (e.g., as N2 or NH3) of nitrogen to the forming protoplanets, and hence the source reservoirs from which these worlds accreted. We targeted two spectral intervals (900 and 960cm-1) that were relatively clear of terrestrial atmospheric contamination and contained close features of NH3 and NH3, allowing us to derive the ratio from a single spectrum without ambiguity due to radiometric calibration (the primary source of uncertainty in this study). We present the first ground-based determination of Jupiter's N/N ratio (in the range from to ), which is consistent with both previous space-based studies and with the primordial value of the protosolar nebula. On Saturn, we present the first upper limit on the N/N ratio of no larger than for the 900-cm-1 channel and a less stringent requirement that the ratio be no larger than for the 960-cm-1 channel ( confidence). Specifically, the data rule out strong N-enrichments such as those observed in Titan's atmosphere and in cometary nitrogen compounds. To the extent possible with ground-based radiometric uncertainties, the saturnian and jovian N/N ratios appear indistinguishable, implying that N-enriched ammonia ices could not have been a substantial contributor to the bulk nitrogen inventory of either planet. This result favours accretion of primordial N2 on both planets, either in the gas phase from the solar nebula, or as ices formed at very low temperatures. Finally, spatially-resolved TEXES observations are used to derive zonal contrasts in tropospheric temperatures, phosphine and NH3 on both planets, allowing us to relate thermal conditions and chemical compositions to phenomena observed at visible wavelengths in 2013 (e.g., Jupiter's faint equatorial red colouration event and wave activity in the equatorial belts, plus the remnant warm band on Saturn following the 2010-11 springtime storm).
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