Context. The Gl 486 system consists of a very nearby, relatively bright, weakly active M3.5V star at just 8 pc with a warm transiting rocky planet of about 1.3 R⨁ and 3.0 M⨁. It is ideal for both ...transmission and emission spectroscopy and for testing interior models of telluric planets.
Aims. To prepare for future studies, we aim to thoroughly characterise the planetary system with new accurate and precise data collected with state-of-the-art photometers from space and spectrometers and interferometers from the ground.
Methods. We collected light curves of seven new transits observed with the CHEOPS space mission and new radial velocities obtained with MAROON-X at the 8.1m Gemini North telescope and CARMENES at the 3.5m Calar Alto telescope, together with previously published spectroscopic and photometric data from the two spectrographs and TESS. We also performed near-infrared interferometric observations with the CHARA Array and new photometric monitoring with a suite of smaller telescopes (AstroLAB, LCOGT, OSN, TJO). This extraordinary and rich data set was the input for our comprehensive analysis.
Results. From interferometry, we measure a limb-darkened disc angular size of the star Gl 486 at θLDD = 0.390 ± 0.018 mas. Together with a corrected Gaia EDR3 parallax, we obtain a stellar radius R* = 0.339 ± 0.015 R⨀. We also measure a stellar rotation period at Prot = 49.9 ± 5.5 days, an upper limit to its XUV (5–920 Å) flux informed by new Hubble/STIS data, and, for the first time, a variety of element abundances (Fe, Mg, Si, V, Sr, Zr, Rb) and C/O ratio. Moreover, we imposed restrictive constraints on the presence of additional components, either stellar or sub-stellar, in the system. With the input stellar parameters and the radial-velocity and transit data, we determine the radius and mass of the planet Gl 486 b at Rp = 1.343+0.063-0.062 R⨀ and Mp = 3.00+0.13-0.13 M⨁, with relative uncertainties of the planet radius and mass of 4.7% and 4.2%, respectively. From the planet parameters and the stellar element abundances, we infer the most probable models of planet internal structure and composition, which are consistent with a relatively small metallic core with respect to the Earth, a deep silicate mantle, and a thin volatile upper layer. With all these ingredients, we outline prospects for Gl 486 b atmospheric studies, especially with forthcoming James Webb Space Telescope (Webb) observations.
Powder metallurgy is a promising processing path to produce high entropy alloys (HEA) with improved mechanical properties. According to this, a bulk CoCrFeMnNi alloy was milled with a wide range of ...conditions. It was shown that a powder which is micronic, approximately spherical and with nanometric crystallites could be produced by a cryo-milling which was followed by a short duration planetary milling. Next, this powder was fully densified by spark plasma sintering. According to X-ray diffraction, the single phase of the bulk alloy remains stable during both milling and sintering. However, carbides and oxides precipitate during sintering, as shown by scanning electron microscopy coupled with energy dispersive spectroscopy. Electron backscattered diffraction evidences that those precipitates limit the growth of grains. By nanoindentation measurements, it was shown that preparing a CoCrFeMnNi HEA by milling and sintering significantly increases the hardness compared to conventional processing by melting and casting. Moreover, the different strengthening contributions were calculated and analyzed. It revealed that grains have a strengthening contribution as described by the Hall & Petch law, contrary to crystallites.
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•A micronic and nearly spherical CoCrFeMnNi powder is produced by a two-step milling.•This powder is fully densified by spark plasma sintering.•The single phase of the bulk alloy remains stable during milling and sintering.•Carbides and oxides limit the growth of grains.•Grains are strengthening, contrary to crystallites.
Abstract
We present
K
-band interferometric observations of the PDS 70 protoplanets along with their host star using VLTI/GRAVITY. We obtained
K
-band spectra and 100
μ
as precision astrometry of ...both PDS 70 b and c in two epochs, as well as spatially resolving the hot inner disk around the star. Rejecting unstable orbits, we found a nonzero eccentricity for PDS 70 b of 0.17 ± 0.06, a near-circular orbit for PDS 70 c, and an orbital configuration that is consistent with the planets migrating into a 2:1 mean motion resonance. Enforcing dynamical stability, we obtained a 95% upper limit on the mass of PDS 70 b of 10
M
Jup
, while the mass of PDS 70 c was unconstrained. The GRAVITY
K
-band spectra rules out pure blackbody models for the photospheres of both planets. Instead, the models with the most support from the data are planetary atmospheres that are dusty, but the nature of the dust is unclear. Any circumplanetary dust around these planets is not well constrained by the planets’ 1–5
μ
m spectral energy distributions (SEDs) and requires longer wavelength data to probe with SED analysis. However with VLTI/GRAVITY, we made the first observations of a circumplanetary environment with sub-astronomical-unit spatial resolution, placing an upper limit of 0.3 au on the size of a bright disk around PDS 70 b.
Cepheid stars play a considerable role as extragalactic distances indicators, thanks to the simple empirical relation between their pulsation period and their luminosity. They overlap with that of ...secondary distance indicators, such as Type Ia supernovae, whose distance scale is tied to Cepheid luminosities. However, the period-luminosity (P-L) relation still lacks a calibration to better than 5%. Using an original combination of interferometric astrometry with optical and ultraviolet spectroscopy, we measured the geometrical distance pc of the 3.33 day period Cepheid V1334 Cyg with an unprecedented accuracy of 1%, providing the most accurate distance for a Cepheid. Placing this star in the P-L diagram provides an independent test of existing P-L relations. We show that the secondary star has a significant impact on the integrated magnitude, particularly at visible wavelengths. Binarity in future high-precision calibrations of the P-L relations is not negligible, at least in the short-period regime. Subtracting the companion flux leaves V1334 Cyg in marginal agreement with existing photometric-based P-L relations, indicating either an overall calibration bias or a significant intrinsic dispersion at a few percent level. Our work also enabled us to determine the dynamical masses of both components, (Cepheid) and (companion), providing the most accurate masses for a Galactic binary Cepheid system.
We present results for the inflated super-Neptune HATS-8b from the Michigan Optical Planetary Spectra Survey (MOPSS). This program is aimed at creating a database of optical planetary transmission ...spectra all observed, reduced, and analyzed with a uniform method for the benefit of enabling comparative exoplanet studies. HATS-8b orbits a G dwarf and is a low-density super-Neptune with a radius of 0.873 RJup, a mass of 0.138 MJup, and a density of 0.259 g cm−3. Two transits of HATS-8b were observed in 2017 July and August with the Inamori-Magellan Areal Camera and Spectrograph (IMACS) instrument on the Magellan Baade 6.5 m telescope. We find an enhanced scattering slope on each night that agree within 2.3 . This slope is stronger than one due only to Rayleigh scattering and cannot be fully explained by unocculted starspots. We explore the impact of condensates on the scattering slope and determine that MnS particulates smaller than 10−2 m can explain up to 80% of our measured slope if the planet is warmer than equilibrium, or 50% of the slope at the equilibrium temperature of the planet for a low mean molecular weight atmosphere. The scattering slope that we observe is thus beyond even the most extreme haze case we consider. We suggest further follow up on this target and host star to determine if the temporal variation of the slope is primarily due to stellar or planetary effects, and to better understand what these effects may be.
Context.
Methods used to detect giant exoplanets can be broadly divided into two categories: indirect and direct. Indirect methods are more sensitive to planets with a small orbital period, whereas ...direct detection is more sensitive to planets orbiting at a large distance from their host star. This dichotomy makes it difficult to combine the two techniques on a single target at once.
Aims.
Simultaneous measurements made by direct and indirect techniques offer the possibility of determining the mass and luminosity of planets and a method of testing formation models. Here, we aim to show how long-baseline interferometric observations guided by radial-velocity can be used in such a way.
Methods.
We observed the recently-discovered giant planet
β
Pictoris c with GRAVITY, mounted on the Very Large Telescope Interferometer.
Results.
This study constitutes the first direct confirmation of a planet discovered through radial velocity. We find that the planet has a temperature of
T
= 1250 ± 50 K and a dynamical mass of
M
= 8.2 ± 0.8
M
Jup
. At 18.5 ± 2.5 Myr, this puts
β
Pic c close to a ‘hot start’ track, which is usually associated with formation via disk instability. Conversely, the planet orbits at a distance of 2.7 au, which is too close for disk instability to occur. The low apparent magnitude (
M
K
= 14.3 ± 0.1) favours a core accretion scenario.
Conclusions.
We suggest that this apparent contradiction is a sign of hot core accretion, for example, due to the mass of the planetary core or the existence of a high-temperature accretion shock during formation.
Aims. We aim to demonstrate that the presence and mass of an exoplanet can now be effectively derived from the astrometry of another exoplanet. Methods. We combined previous astrometry of β Pictoris ...b with a new set of observations from the GRAVITY interferometer. The orbital motion of β Pictoris b is fit using Markov chain Monte Carlo simulations in Jacobi coordinates. The inner planet, β Pictoris c, was also reobserved at a separation of 96 mas, confirming the previous orbital estimations. Results. From the astrometry of planet b only, we can (i) detect the presence of β Pictoris c and (ii) constrain its mass to 10.04 −3.10 +4.53 M Jup . If one adds the astrometry of β Pictoris c, the mass is narrowed down to 9.15 −1.06 +1.08 M Jup . The inclusion of radial velocity measurements does not affect the orbital parameters significantly, but it does slightly decrease the mass estimate to 8.89 −0.75 +0.75 M Jup . With a semimajor axis of 2.68 ± 0.02 au, a period of 1221 ± 15 days, and an eccentricity of 0.32 ± 0.02, the orbital parameters of β Pictoris c are now constrained as precisely as those of β Pictoris b. The orbital configuration is compatible with a high-order mean-motion resonance (7:1). The impact of the resonance on the planets’ dynamics would then be negligible with respect to the secular perturbations, which might have played an important role in the eccentricity excitation of the outer planet.
The reconstruction of the flow behind a backward-facing step at a Reynolds number of 60,000 using linear stochastic estimation (LSE) and modified LSE (with or without multi-time-delay) is ...investigated. In particular, the turbulent spatial integral length scales estimated for several sensor configurations are studied. The estimation of the proper orthogonal decomposition (POD) modes is also performed in order to show the limitations of the SE for complex flows, for which taking into account only a few POD modes may not be enough to represent the flow dynamics. The importance of the sensor locations on the estimation is also emphasized, and the opportunity to use a sensor location optimization algorithm is investigated.
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