378 research outputs found
TOI-5126: a hot super-Neptune and warm Neptune pair discovered by TESS and CHEOPS
No full textWe present the confirmation of a hot super-Neptune with an exterior Neptune companion orbiting a bright (V = 10.1 mag) F-dwarf identified by the Transiting Exoplanet Survey Satellite (TESS). The two planets, observed in sectors 45, 46, and 48 of the TESS extended mission, are 4.74+−001416 and 3.86+−001617 R with 5.4588385+−0000000720000070 and 17.8999+−0000130018 d orbital periods, respectively. We also obtained precise space-based photometric follow-up of the system with ESA’s CHaracterising ExOplanets Satellite to constrain the radius and ephemeris of TOI-5126 b. TOI-5126 b is located in the ‘hot Neptune Desert’ and is an ideal candidate for follow-up transmission spectroscopy due to its high-predicted equilibrium temperature (Teq = 1442+−4046 K) implying a cloud-free atmosphere. TOI-5126 c is a warm Neptune (Teq = 971+−2731 K) also suitable for follow-up. Tentative transit timing variations have also been identified in analysis, suggesting the presence of at least one additional planet, however this signal may be caused by spot-crossing events, necessitating further precise photometric follow-up to confirm these signals
An ultrahot Neptune in the Neptune desert
No full text© 2020, The Author(s), under exclusive licence to Springer Nature Limited. About 1 out of 200 Sun-like stars has a planet with an orbital period shorter than one day: an ultrashort-period planet1,2. All of the previously known ultrashort-period planets are either hot Jupiters, with sizes above 10 Earth radii (R⊕), or apparently rocky planets smaller than 2 R⊕. Such lack of planets of intermediate size (the ‘hot Neptune desert’) has been interpreted as the inability of low-mass planets to retain any hydrogen/helium (H/He) envelope in the face of strong stellar irradiation. Here we report the discovery of an ultrashort-period planet with a radius of 4.6 R⊕ and a mass of 29 M⊕, firmly in the hot Neptune desert. Data from the Transiting Exoplanet Survey Satellite3 revealed transits of the bright Sun-like star LTT 9779 every 0.79 days. The planet’s mean density is similar to that of Neptune, and according to thermal evolution models, it has a H/He-rich envelope constituting 9.0−2.9+2.7% of the total mass. With an equilibrium temperature around 2,000 K, it is unclear how this ‘ultrahot Neptune’ managed to retain such an envelope. Follow-up observations of the planet’s atmosphere to better understand its origin and physical nature will be facilitated by the star’s brightness (Vmag = 9.8)
HD 183579b: a warm sub-Neptune transiting a solar twin detected by TESS
No full textWe report the discovery and characterization of a transiting warm sub-Neptune planet around the nearby bright (V = 8.75 mag, K = 7.15 mag) solar twin HD 183579, delivered by the Transiting Exoplanet Survey Satellite (TESS). The host star is located 56.8 +/- 0.1 pc away with a radius of R-* = 0.97 +/- 0.02R(circle dot) and a mass of M-* = 1.03 +/- 0.05M(circle dot). We confirm the planetary nature by combining space and ground-based photometry, spectroscopy, and imaging. We find that HD 183579b (TOI-1055b) has a radius of R-p = 3.53 +/- 0.13R(circle plus) on a 17.47 d orbit with a mass of M-p = 11.2 +/- 5.4M(circle plus) (3 sigma mass upper limit of 27.4M(circle plus)). HD 183579b is the fifth brightest known sub-Neptune planet system in the sky, making it an excellent target for future studies of the interior structure and atmospheric properties. By performing a line-by-line differential analysis using the high-resolution and signal-to-noise ratio HARPS spectra, we find that HD 183579 joins the typical solar twin sample, without a statistically significant refractory element depletion
A Measure of Detachment: Richard Hofstadter and the Progressive Historians
No full textThis thesis argues that Richard Hofstadter's innovations in historical method arose as a critical response to the Progressive historians, particularly to Charles Beard. It argues that Hofstadter's first two books were demonstrations of the inadequacy of Progressive methodology, while his third book (the Age of Reform) was a demonstration of the potential of his new way of doing history.Histor
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Experimental analysis and computational simulation of unilateral transtibial amputee walking to evaluate prosthetic device design characteristics and amputee gait mechanics
No full texttextOver one million amputees are living in the United States with major lower limb loss (Ziegler-Graham et al. 2008). Lower limb amputation leads to the functional loss of the ankle plantar flexor muscles, which are important contributors to body support, forward propulsion, and leg swing initiation during walking (Neptune et al. 2001; Liu et al. 2006). Effective prosthetic component design is essential for successful rehabilitation of amputees to return to an active lifestyle by partially replacing the functional role of the ankle muscles. The series of experimental and computer simulation studies presented in this research showed that design characteristics of energy storage and return prosthetic ankles, specifically the elastic stiffness, significantly influence residual and intact leg ground reaction forces, knee joint moments, and muscle activity, thus affecting muscle output. These findings highlight the importance of proper prosthetic foot stiffness prescription for amputees to assure effective rehabilitation outcomes. The research also showed that the ankle muscles serve to stabilize the body during turning the center of mass. When amputees turn while supported by their prosthetic components, they rely more on gravity to redirect the center of mass than active muscle generation. This mechanism increases the risks of falling and identifies a need for prosthetic components and rehabilitation focused on increasing amputee stability during turning. A proper understanding of the effects of prosthetic components on amputee walking mechanics is critical to decreasing complications and risks that are prevalent among lower-limb amputees. The presented research is an important step towards reaching this goal.Mechanical Engineerin
TOI-3862 b: A dense super-Neptune deep in the hot Neptune desert
No full textContext . The structure and evolution of close-in exoplanets are shaped by atmospheric loss and migration processes, which give rise to key population features such as the hot Neptune desert, ridge, and savanna – regions of the period-radius space whose boundaries offer critical insights into planetary formation and survival. Aims . As part of the KESPRINT collaboration, we selected the TESS transiting planet candidate TOI-3862.01 for radial velocity follow-up to confirm its planetary nature and characterize its mass and bulk properties. This planet candidate is of particular interest due to its position in the middle of the hot Neptune desert, making it a valuable probe for testing theories of planet migration and atmospheric loss. Methods . We confirmed the planetary nature and determined the mass of TOI-3862.01 (hereinafter TOI-3862 b) by performing a joint fit with both transit and radial velocity data, precisely characterizing the bulk properties of this planet. Results . TOI-3862b is a super-Neptune on a 1.56-day orbit around a Sun-like star with an effective temperature of 5300±50 K. It has a mass of 53.7 −2.9 +2.8 M ⊕ and a radius of 5.53 ± 0.18 R ⊕ , corresponding to a density of 1.7±0.2 g/cm 3 . This places it among the rare population of hot and dense super-Neptune desert planets. Conclusions . TOI-3862b, residing deep in the hot Neptune desert, represents a rare occurrence in an otherwise sparsely populated region, offering a valuable opportunity to probe the processes that may allow planets to survive in such environments
TOI-2498 b: A hot bloated super-Neptune within the Neptune desert
No full textWe present the discovery and confirmation of a transiting hot, bloated
Super-Neptune using photometry from TESS and LCOGT and radial velocity
measurements from HARPS. The host star TOI-2498 is a V = 11.2, G-type
(T = 5905 12K) solar-like star with a mass of 1.12 0.02
M and a radius of 1.26 0.04 R. The planet, TOI-2498
b, orbits the star with a period of 3.7 days, has a radius of 6.1 0.3
R, and a mass of 35 4 M. This results in a density
of 0.86 0.25 g cm. TOI-2498 b resides on the edge of the Neptune
desert; a region of mass-period parameter space in which there appears to be a
dearth of planets. Therefore TOI-2498 b is an interesting case to study to
further understand the origins and boundaries of the Neptune desert. Through
modelling the evaporation history, we determine that over its 3.6 Gyr
lifespan, TOI-2498 b has likely reduced from a Saturn sized planet to its
current radius through photoevaporation. Moreover, TOI-2498 b is a potential
candidate for future atmospheric studies searching for species like water or
sodium in the optical using high-resolution, and for carbon based molecules in
the infra-red using JWST.Comment: 13 pages, 11 figures, accepted for publication in MNRA
TOI-333b: A Neptune-desert planet around an F7V star
No full textObservations have shown that planets similar to Neptune are rarely found orbiting Sun-like stars with periods up to ∼4 days. This defines the so-called Neptune desert region. The detection of each individual planet in this region therefore holds a high value by providing detailed insights into the formation and evolution of this population. We report the detection of TOI-333b, a Neptune-desert planet with a mass, radius, and bulk density of 20.1 ± 2.4 M
⊕
, 4.26 ± 0.11 R
⊕
, and 1.42 ± 0.21 g cm
−3
. The planet orbits an F7V star every 3.78 d, whose mass, radius, and effective temperature are of 1.2 ± 0.1 M
⊙
, 1.10 ± 0.03 R
⊙
, and 6241
−62
+73
K, respectively. TOI-333bis likely younger than 1 Gyr, which is supported by the doublet Li line around 6707.856 Å and its comparison to Li abundances in open clusters with well-constrained ages. The planet is expected to host only a 8.5
−8.3
+10.9
% gas-to-core mass ratio for an H/He envelope. On the other hand, models of irradiated ocean worlds predict a 20
−10
+11
% H
2
O mass fraction with a core fraction of 35
−23
+20
%. We therefore expect that the internal composition of TOI-333bis dominated by a pure rocky composition with almost no H/He envelope, or a rocky world with almost equal mass fraction of water. Finally, TOI-333bis more massive and larger than 77% and 82% of its Neptune-desert counterparts, and its host ranks among the hottest known stars for Neptune-desert planets. This makes this system a unique laboratory for studying the evolution of these planets around hot stars.</p
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Compensatory strategies in walking due to musculoskeletal disorders and changes in gait mode
No full textThe objectives of this study were to theoretically identify the necessary compensatory strategies to overcome specific musculoskeletal disorders in walking and to determine differences in gait mechanics between overground and treadmill walking. Body segment kinematic data and ground reaction force (GRF) data were collected from healthy subjects walking at 1.5 m/s. A detailed musculoskeletal model and muscle-actuated forward dynamic simulations that emulated the experimental data were analyzed to quantify compensatory strategies due to altered musculoskeletal properties. The musculoskeletal properties of interest were altered individually, with the strength of each muscle group decreased by 50%, hip joint stiffness increased by 20% and maximum contraction velocity decreased by 30%. Dynamic optimization was then used to identify the compensatory strategies necessary to restore the nominal walking mechanics for each perturbation. Increased soleus (SOL) work output was the primary compensatory strategy for decreased knee and hip extensor and hip flexor strength, increased hip joint stiffness and decreased maximum contraction velocity, which are functional deficits commonly observed in older adult populations. In addition, increased gastrocnemius (GAS) work output was an important compensatory strategy for decreased hip flexor and SOL strength. Thus, rehabilitation and preventative exercise programs may consider focusing on increasing or maintaining plantar flexor strength, which appears critical to maintaining normal walking mechanics in older adult populations. To determine any differences in gait mechanics between overground and treadmill walking, GRF and electromyography (EMG) were collected from healthy subjects during each gait mode. The purpose of this study was to test the hypothesis that there would be no difference between gait modes in the generation of anterior/posterior (A/P) propulsion. To test the hypothesis, the GRF and impulses were compared between overground and treadmill walking collected from 11 healthy young adults to determine if there were any significant differences (p < 0.05). The hypothesis was not supported. The results indicated that the horizontal and vertical peak GRFs and propulsion impulses were significantly lower (p < 0.05) during treadmill walking compared to overground walking. Examination of individual subject EMG data revealed that muscle activity did change between gait modes and reflected the changes observed in the GRF data. Therefore, the differences between the GRFs and impulses in overground versus treadmill walking observed in this study should be noted when using a treadmill to analyze gait in healthy or clinical populationsMechanical Engineerin
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The influence of load carriage and foot stiffness on knee joint loading and metabolic cost during amputee walking
No full textIndividuals experience sudden load changes during activities of daily living. This added weight places an increased demand on the muscles providing body support, forward propulsion and balance control. For non-amputees, the mechanical output from the ankle muscles are seamlessly modulated to meet the altered demands of load carriage. However, for individuals with a lower-limb amputation, the stiffness properties of standard-of-care prosthetic feet are constant and do not change with varying load conditions. Thus, lower limb amputees often develop gait asymmetries to compensate for the loss of ankle muscles, which may be exacerbated by load carriage. These asymmetries may increase the risk for developing overuse injuries and osteoarthritis in the intact knee as well as elevate the metabolic cost of walking relative to non-amputees. Unfortunately, it is not well understood how prosthetic foot stiffness and load carriage technique influences joint loading asymmetries during amputee gait. The purpose of this study was to use a forward dynamics simulation framework to assess the influence of load carriage technique and prosthetic foot stiffness on knee joint loading and metabolic cost during amputee gait. Forward dynamics simulations were generated to track experimental amputee walking data for each loading condition (unloaded, with a backpack, and with a frontpack) and prosthetic foot condition (four commercially available elastic energy storage and return (ESAR) feet). The results of these simulations showed that amputees rely on their intact limb as a compensatory strategy to meet the increased demands of carrying a load. Carrying the load in a backpack was found to reduce metabolic cost but increase intact knee joint loading. When varying prosthetic foot stiffness, there was no consistent effect on metabolic cost or knee joint loading in any of the three loading conditions. Future work should focus on designing prosthetic components that help reduce the joint loading asymmetry and elevated metabolic cost during load carriage for lower limb amputees. In addition, the tradeoff between metabolic cost and joint loading should be considered when determining the appropriate load carriage technique.Mechanical Engineerin
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