ABSTRACT
We obtained high-resolution infrared spectroscopy and short-cadence photometry of the 600–800 Myr Praesepe star K2-100 during transits of its 1.67-d planet. This Neptune-size object, ...discovered by the NASA K2 mission, is an interloper in the ‘desert’ of planets with similar radii on short-period orbits. Our observations can be used to understand its origin and evolution by constraining the orbital eccentricity by transit fitting, measuring the spin-orbit obliquity by the Rossiter–McLaughlin effect, and detecting any extended, escaping the hydrogen–helium envelope with the 10 830 -Å line of neutral helium in the 2s3S triplet state. Transit photometry with 1-min cadence was obtained by the K2 satellite during Campaign 18 and transit spectra were obtained with the IRD spectrograph on the Subaru telescope. While the elevated activity of K2-100 prevented us from detecting the Rossiter–McLaughlin effect, the new photometry combined with revised stellar parameters allowed us to constrain the eccentricity to e < 0.15/0.28 with 90/99 per cent confidence. We modelled atmospheric escape as an isothermal, spherically symmetric Parker wind, with photochemistry driven by ultraviolet radiation, which we estimate by combining the observed spectrum of the active Sun with calibrations from observations of K2-100 and similar young stars in the nearby Hyades cluster. Our non-detection (<5.7 m Å) of a transit-associated He i line limits mass-loss of a solar-composition atmosphere through a T ≤ 10000 K wind to <0.3 M⊕ Gyr−1. Either K2-100b is an exceptional desert-dwelling planet, or its mass-loss is occurring at a lower rate over a longer interval, consistent with a core accretion-powered scenario for escape.
ABSTRACT
M dwarf stars are high-priority targets for searches for Earth-size and potentially Earth-like planets, but their planetary systems may form and evolve in very different circumstellar ...environments than those of solar-type stars. To explore the evolution of these systems, we obtained transit spectroscopy and photometry of the Neptune-size planet orbiting the ≈650-Myr-old Hyades M dwarf K2-25. An analysis of the variation in spectral line shape induced by the Doppler ‘shadow’ of the planet indicates that the planet’s orbit is closely aligned with the stellar equator ($\lambda =-1.7_{-3.7}^{+5.8}$ deg), and that an eccentric orbit found by previous work could arise from perturbations by another planet on a coplanar orbit. We detect no significant variation in the depth of the He i line at 1083 nm during transit. A model of atmospheric escape as an isothermal Parker wind with a solar composition shows that this non-detection is not constraining compared to escape rate predictions of ∼0.1 M⊕ Gyr−1; at such rates, at least several Gyr are required for a Neptune-like planet to evolve into a rocky super-Earth.
We present the confirmation and characterisation of GJ 3473 b (G 50–16, TOI-488.01), a hot Earth-sized planet orbiting an M4 dwarf star, whose transiting signal (
P
= 1.1980035 ± 0.0000018 d) was ...first detected by the Transiting Exoplanet Survey Satellite (TESS). Through a joint modelling of follow-up radial velocity observations with CARMENES, IRD, and HARPS together with extensive ground-based photometric follow-up observations with LCOGT, MuSCAT, and MuSCAT2, we determined a precise planetary mass,
M
b
= 1.86 ± 0.30
M
⊕
, and radius,
R
b
= 1.264 ± 0.050
R
⊕
. Additionally, we report the discovery of a second, temperate, non-transiting planet in the system, GJ 3473 c, which has a minimum mass,
M
c
sin
i
= 7.41 ± 0.91
M
⊕
, and orbital period,
P
c
= 15.509 ± 0.033 d. The inner planet of the system, GJ 3473 b, is one of the hottest transiting Earth-sized planets known thus far, accompanied by a dynamical mass measurement, which makes it a particularly attractive target for thermal emission spectroscopy.
ABSTRACT
We report the discovery of a resolved (0.9 arcsec) substellar companion to a member of the 1–5 Myr Taurus star-forming region. The host star (2M0437) is a single mid-M type (Teff ≈ 3100 K) ...dwarf with a position, space motion, and colour–magnitude that support Taurus membership, and possible affiliation with a ∼2.5-Myr-old subgroup. A comparison with stellar models suggests a 2–5 Myr age and a mass of 0.15–0.18M⊙. Although K2 detected quasi-periodic dimming from close-in circumstellar dust, the star lacks detectable excess infrared emission from a circumstellar disc and its H α emission is not commensurate with accretion. Astrometry based on 3 yr of AO imaging shows that the companion (2M0437b) is comoving, while photometry of two other sources at larger separation indicates that they are likely heavily reddened background stars. A comparison of the luminosity of 2M0437b with models suggests a mass of 3–5 MJUP, well below the deuterium burning limit, and an effective temperature of 1400–1500 K, characteristic of a late L spectral type. The H − K colour is redder than the typical L dwarf, but comparable to other directly detected young planets, e.g. those around HR 8799. The discovery of a super-Jupiter around a very young, very low-mass star challenges models of planet formation by either core accretion (which requires time) or disc instability (which requires mass). We also detected a second, comoving, widely separated (75 arcsec) object that appears to be a heavily extincted star. This is certainly a fellow member of this Taurus subgroup and statistically likely to be a bound companion.
Aims. The purpose of this paper is to detect and investigate the nature of long-term radial velocity (RV) variations of K-type giants and to confirm planetary companions around the stars. Methods. We ...have conducted two planet search programs by precise RV measurement using the 1.8 m telescope at Bohyunsan Optical Astronomy Observatory (BOAO) and the 1.88 m telescope at Okayama Astrophysical Observatory (OAO). The BOAO program searches for planets around 55 early K giants. The OAO program is looking for 190 G–K type giants. Results. In this paper, we report the detection of long-period RV variations of three K giant stars, HD 40956, HD 111591, and HD 113996. We investigated the cause of the observed RV variations and conclude the substellar companions are most likely the cause of the RV variations. The orbital analyses yield P = 578.6 ± 3.3 d, m sin i = 2.7 ± 0.6 MJ, a = 1.4 ± 0.1 AU for HD 40956; P = 1056.4 ± 14.3 d, m sin i = 4.4 ± 0.4 MJ, a = 2.5 ± 0.1 AU for HD 111591; P = 610.2 ± 3.8 d, m sin i = 6.3 ± 1.0 MJ, a = 1.6 ± 0.1 AU for HD 113996.
ABSTRACT
In the unloading compliance method developed for clamped single edge tension (SE(T)) specimens, six crack mouth opening displacement (CMOD)‐based compliance equations (i.e. a/W = f(BCE′)) ...were proposed for the crack length evaluation without clearly clarifying the corresponding predictive accuracies. In addition, the effective elastic modulus (Ee) that reflects the actual state of stress should also be introduced in the crack length evaluation for SE(T) specimens, because the actual state of stress in the remaining ligament of the test specimen is neither plane stress (E) nor plane strain (E′). In this study, two‐dimensional (2D) plane strain and three‐dimensional (3D) finite element analyses (FEAs) are carried out to investigate predictive accuracies of the six compliance equations. In both 2D and 3D FEA, specimens with a wide range of crack lengths and geometric configurations are included. For a given specimen, the value of Ee that presents the equivalent stress state in the remaining ligament is calculated on the basis of 3D FEA data. A set of formulae for the clamped SE(T) specimen is proposed that allows to evaluate Ee from the corresponding CMOD compliance. This approach is verified using numerical data. The observations of the numerical verification suggest that the use of Ee instead of E or E′ in CMOD‐based compliance equations markedly improves the accuracy of the predicted crack length for clamped SE(T) specimens.
We report the discovery of two exoplanets around the M dwarfs GJ 724 and GJ 3988 using the radial velocity (RV) method. We obtained a total of 153 3.5 m Calar Alto/CARMENES spectra for both targets ...and measured their RVs and activity indicators. We also added archival ESO/HARPS data for GJ 724 and infrared RV measurements from Subaru/IRD for GJ 3988. We searched for periodic and stable signals to subsequently construct Keplerian models, considering different numbers of planets, and we selected the best models based on their Bayesian evidence. Gaussian process (GP) regression was included in some models to account for activity signals. For both systems, the best model corresponds to one single planet. The minimum masses are 10.75
−0.87
+0.96
and 3.69
−0.41
+0.42
Earth-masses for GJ 724 b and GJ 3988 b, respectively. Both planets have short periods (
P <
10 d) and, therefore, they orbit their star closely (
a
< 0.05 au). GJ 724 b has an eccentric orbit (
e
= 0.577
−0.052
+0.055
), whereas the orbit of GJ 3988 b is circular. The high eccentricity of GJ 724 b makes it the most eccentric single exoplanet (to this date) around an M dwarf. Thus, we suggest a further analysis to understand its configuration in the context of planetary formation and architecture. In contrast, GJ 3988 b is an example of a common type of planet around mid-M dwarfs.
ABSTRACT
Studies of planetary systems of stars in star-forming regions and young clusters open a window on the formative stages of planetary evolution. We obtained high-cadence high-resolution ...infrared spectroscopy of the solar-mass Taurus association-member V1298 Tau during a transit of its 10R⊕-size ‘b’ planet. We measured the systemic radial velocity (RV) and find that the kinematics of V1298 Tau suggest an affiliation with a ≳6 Myr-old subgroup. A comparison of V1298 Tau and the nearby, co-moving star 2M0405 with stellar evolution models suggests an age of ∼10–25 Myr. We measured the projected spin-orbit angle of ‘b’ as $\lambda =15_{-16}^{+15}$ and $\lambda = 2_{-4}^{+12}$ degrees using the apparent RV shift and change in line profile, respectively, induced by the transient occultation of the rotating star by the planet. These values indicate a prograde orbit like that of the interior ‘c’ planet of V1298 Tau and point to a co-planar multiplanet system that formed within a disc. We also measured variation in the strength of the 1083 nm triplet of neutral orthohelium as a probe of any extended/escaping atmosphere around ‘b’. We detect a steady decrease in absorption over the transit that appears to arise from the star or its planetary system. While this variation could be ascribed to ‘b’ or possibly to the immediately preceding transit of ‘d’, we cannot rule out that this is due to rapid variation in the stellar disc-integrated flux in the triplet. The amplitude of variation (∼0.04 nm) is consistent with moderate estimates of atmospheric escape driven by XUV radiation from the central star.
Ti-(5–20)Nb-(0.5–1)O alloys (mass%) were investigated for developing low-cost biomedical α+β-type Ti alloy. Ti-(5, 10, 15, 20)Nb-(0.5, 0.75, 1)O alloys (mass%) were arc-melted and forged into bars. ...The forged alloy bars were heat-treated at 873 to 1373 K for 3.6 ks in an Ar atmosphere and quenched in iced water. β transus (
T
β
) of the Ti-Nb-O alloys decreased with increasing Nb content. An increase in the oxygen content led to an increase in
T
β
. After quenching, the formation of α′ martensite was observed in Ti-5Nb-
y
O alloys. An increase in the Nb content to 10 mass% led to the formation of α′ and α″ martensites. A further increase in the Nb content to 15 and 20mass% resulted in the formation of more α″ martensites. The boundary temperature for the formation of α′ and α″ martensite in the Ti-10Nb-
y
O alloys increased with increasing oxygen content, because oxygen enhances the Nb distribution to the β phase. The ultimate tensile strength of the Ti-
x
Nb-0.75O alloys heattreated to obtain the α-phase fraction (
f
α
) of 0.5 was over 1000 MPa, except for the Ti-15Nb-0.75O alloy. The total elongation decreased with increasing Nb content. The Ti-5Nb-0.75O alloy exhibited excellent strength-ductility balance as a low-cost α+β-type biomedical Ti alloy.
This paper presents a study on fracture mechanisms of polycarbonate (PC)/acrylonitrile-butadiene-styrene (ABS) (50/50) blends with different ABS types under a drop weight impact test (DWIT) using a ...circular sheet specimen. Formation of secondary crack indicated by a stress-whitening layer on the mid-plane of scattered specimens and secondary surface of fracture perpendicular to primary fracture surface were captured under scanning electron microscope (SEM). Although the both blends finally failed in brittle modes, SEM observation showed that their secondary fracture mechanisms were completely different. Observation through the thickness of the etched PC/ABS specimen samples using SEM also clearly showed that PC and ABS were immiscible. The immiscibility between PC and ABS was indicated by presence of their layer structures through the thickness of the blends. It was revealed that layer of ABS structure was influenced by size of rubber particle and this latter parameter then affected microstructure and fracture mechanisms of the blends. Impact-induced fracture mechanisms of the blends due to such microstructures are discussed in this paper. It was also pointed out that the secondary cracking was likely caused by interface delamination between PC and ABS layers in the core due to transverse shear stress generated during the impact test.
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