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"Saunders, Nicholas"
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eleanor: An Open-source Tool for Extracting Light Curves from the TESS Full-frame Images
During its two-year prime mission, the Transiting Exoplanet Survey Satellite (TESS) will perform a time-series photometric survey covering over 80% of the sky. This survey comprises observations of 26 24° × 96° sectors that are each monitored continuously for approximately 27 days. The main goal of TESS is to find transiting planets around 200,000 pre-selected stars for which fixed aperture photometry is recorded every two minutes. However, TESS is also recording and delivering full-frame images (FFIs) of each detector at a 30-minutes cadence. We have created an open-source tool, eleanor, to produce light curves for objects in the TESS FFIs. Here, we describe the methods used in eleanor to produce light curves that are optimized for planet searches. The tool performs background subtraction; aperture and point-spread function photometry; decorrelation of instrument systematics; and cotrending using principal component analysis. We recover known transiting exoplanets in the FFIs to validate the pipeline and perform a limited search for new planet candidates in Sector 1. Our tests indicate that eleanor produces light curves with significantly less scatter than other tools that have been used in the literature. Cadence-stacked images, and raw and detrended eleanor light curves for each analyzed star will be hosted on Mikulski Archive for Space Telescopes, with planet candidates on ExoFOP-TESS as Community TESS Objects of Interest. This work confirms the promise that the TESS FFIs will enable the detection of thousands of new exoplanets and a broad range of time domain astrophysics.
Journal Article
Desert insurgency : archaeology, T.E. Lawrence, and the Arab revolt
In the desert sands of southern Jordan lies a once-hidden conflict landscape along the Hejaz Railway. Built at the beginning of the twentieth-century, this narrow-gauge 1,320 km track stretched from Damascus to Medina and served to facilitate participation in the annual Muslim Hajj to Mecca. The discovery and archaeological investigation of an unknown landscape of insurgency and counter-insurgency along this route tells a different story of the origins of modern guerrilla warfare, the exploits of T.E. Lawrence, Emir Feisal, and Bedouin warriors, and the dramatic events of the Arab Revolt of 1916-18. Ten years of research in this prehistoric terrain has revealed sites lost for almost 100 years: vast campsites occupied by railway builders; Ottoman Turkish machine-gun redoubts; Rolls Royce Armoured Car raiding camps; an ephemeral Royal Air Force desert aerodrome; as well as the actual site of the Hallat Ammar railway ambush. This unique and richly illustrated account from Nicholas Saunders tells, in intimate detail, the story of a seminal episode of the First World War and the reshaping of the Middle East that followed.
BOOK
Progression of Osteosarcoma from a Non-Metastatic to a Metastatic Phenotype Is Causally Associated with Activation of an Autocrine and Paracrine uPA Axis
Pulmonary metastasis is the major untreatable complication of osteosarcoma (OS) resulting in 10-20% long-term survival. The factors and pathways regulating these processes remain unclear, yet their identification is crucial in order to find new therapeutic targets. In this study we used a multi-omics approach to identify molecules in metastatic and non-metastatic OS cells that may contribute to OS metastasis, followed by validation in vitro and in vivo. We found elevated levels of the urokinase plasminogen activator (uPA) and of the uPA receptor (uPAR) exclusively in metastatic OS cells. uPA was secreted in soluble form and as part of the protein cargo of OS-secreted extracellular vesicles, including exosomes. In addition, in the tumour microenvironment, uPA was expressed and secreted by bone marrow cells (BMC), and OS- and BMC-derived uPA significantly and specifically stimulated migration of metastatic OS cells via uPA-dependent signaling pathways. Silencing of uPAR in metastatic OS cells abrogated the migratory response to uPA in vitro and decreased metastasis in vivo. Finally, a novel small-molecule inhibitor of uPA significantly (P = 0.0004) inhibited metastasis in an orthotopic mouse model of OS. Thus, we show for the first time that malignant conversion of OS cells to a metastatic phenotype is defined by activation of the uPA/uPAR axis in both an autocrine and paracrine fashion. Furthermore, metastasis is driven by changes in OS cells as well as in the microenvironment. Finally, our data show that pharmacological inhibition of the uPA/uPAR axis with a novel small-molecule inhibitor can prevent the emergence of metastatic foci.
Journal Article
The Possible Tidal Demise of Kepler’s First Planetary System
We present evidence of tidally-driven inspiral in the Kepler-1658 (KOI-4) system, which consists of a giant planet (1.1R J, 5.9M J) orbiting an evolved host star (2.9R ⊙, 1.5M ⊙). Using transit timing measurements from Kepler, Palomar/WIRC, and TESS, we show that the orbital period of Kepler-1658b appears to be decreasing at a rate Ṗ=131−22+20 ms yr−1, corresponding to an infall timescale P/Ṗ≈2.5Myr . We consider other explanations for the data including line-of-sight acceleration and orbital precession, but find them to be implausible. The observed period derivative implies a tidal quality factor Q⋆′=2.50−0.62+0.85×104 , in good agreement with theoretical predictions for inertial wave dissipation in subgiant stars. Additionally, while it probably cannot explain the entire inspiral rate, a small amount of planetary dissipation could naturally explain the deep optical eclipse observed for the planet via enhanced thermal emission. As the first evolved system with detected inspiral, Kepler-1658 is a new benchmark for understanding tidal physics at the end of the planetary life cycle.
Journal Article
Stellar Cruise Control: Weakened Magnetic Braking Leads to Sustained Rapid Rotation of Old Stars
Despite a growing sample of precisely measured stellar rotation periods and ages, the strength of magnetic braking and the degree of departure from standard (Skumanich-like) spin-down have remained persistent questions, particularly for stars more evolved than the Sun. Rotation periods can be measured for stars older than the Sun by leveraging asteroseismology, enabling models to be tested against a larger sample of old field stars. Because asteroseismic measurements of rotation do not depend on starspot modulation, they avoid potential biases introduced by the need for a stellar dynamo to drive starspot production. Using a neural network trained on a grid of stellar evolution models and a hierarchical model-fitting approach, we constrain the onset of weakened magnetic braking (WMB). We find that a sample of stars with asteroseismically measured rotation periods and ages is consistent with models that depart from standard spin-down prior to reaching the evolutionary stage of the Sun. We test our approach using neural networks trained on model grids produced by separate stellar evolution codes with differing physical assumptions and find that the choices of grid physics can influence the inferred properties of the braking law. We identify the normalized critical Rossby number Rocrit/Ro⊙ = 0.91 ± 0.03 as the threshold for the departure from standard rotational evolution. This suggests that WMB poses challenges to gyrochronology for roughly half of the main-sequence lifetime of Sun-like stars.
Journal Article
Role of intratumoural heterogeneity in cancer drug resistance: molecular and clinical perspectives
Drug resistance continues to be a major barrier to the delivery of curative therapies in cancer. Historically, drug resistance has been associated with over‐expression of drug transporters, changes in drug kinetics or amplification of drug targets. However, the emergence of resistance in patients treated with new‐targeted therapies has provided new insight into the complexities underlying cancer drug resistance. Recent data now implicate intratumoural heterogeneity as a major driver of drug resistance. Single cell sequencing studies that identified multiple genetically distinct variants within human tumours clearly demonstrate the heterogeneous nature of human tumours. The major contributors to intratumoural heterogeneity are (i) genetic variation, (ii) stochastic processes, (iii) the microenvironment and (iv) cell and tissue plasticity. Each of these factors impacts on drug sensitivity. To deliver curative therapies to patients, modification of current therapeutic strategies to include methods that estimate intratumoural heterogeneity and plasticity will be essential.
Journal Article
The Far Side of the Galactic Bar/Bulge Revealed through Semi-regular Variables
The Galactic bulge is critical to our understanding of the Milky Way. However, due to the lack of reliable stellar distances, the structure and kinematics of the bulge/bar beyond the Galactic center have remained largely unexplored. Here, we present a method to measure distances of luminous red giants using a period–amplitude–luminosity relation anchored to the Large Magellanic Cloud, with random uncertainties of 10%–15% and systematic errors below 1%–2%. We apply this method to data from the Optical Gravitational Lensing Experiment to measure distances to 190,302 stars in the Galactic bulge and beyond out to 20 kpc. Using this sample, we measure a distance to the Galactic center of R 0 = 8108 ± 106stat ± 93sys pc, consistent with direct measurements of stars orbiting Sgr A*. We cross-match our distance catalog with Gaia DR3 and use the subset of 39,566 overlapping stars to provide the first constraints on the Milky Way’s velocity field (V R , V ϕ , V z ) beyond the Galactic center. We show that the V R quadrupole from the bar’s near side is reflected with respect to the Galactic center, indicating that the bar is bisymmetric and aligned with the inner disk. We also find that the vertical height V Z map has no major structure in the region of the Galactic bulge, which is inconsistent with a current episode of bar buckling. Finally, we demonstrate with N-body simulations that distance uncertainty plays a factor in the alignment of the major and kinematic axes of the bar, necessitating caution when interpreting results for distant stars.
Journal Article
Discovery of a Jupiter Analog Misaligned to the Inner Planetary System in HD 73344
We present the discovery of a Jupiter-like planet, HD 73344 d ( md=2.55−0.46+0.56MJ , ad=6.70−0.26+0.25 au, ed=0.18−0.12+0.14 ) based on 27 yr radial velocity (RV) observations from ELODIE, Lick/Hamilton, SOPHIE, APF, and HIRES. HD 73344 also hosts a compact inner planetary system, including a transiting sub-Neptune, HD 73344 b (Pb = 15.61 days, rb=2.88−0.07+0.08R⊕ ), and a nontransiting Saturn-mass planet (Pc = 65.936 days, mcsinic=0.367−0.021+0.022MJ ). By analyzing TESS light curves, we identified a stellar rotation period of 9.03 ± 1.3 days. Combining this with vsini* measurements from stellar spectra, we derived a stellar inclination of 63.6∘−16.5+17.4 . Furthermore, by combining RVs and Hipparcos–Gaia astrometric acceleration, we characterized the three-dimensional orbit of the outer giant planet and constrained its mutual inclination relative to the innermost transiting planet to be 46° < ΔIbd < 134° (1σ) and 20° < ΔIbd < 160° (2σ), strongly disfavoring coplanar architectures. Our analytical calculations and N-body simulations reveal that the two inner planets are strongly coupled with each other and undergo nodal precession together around the orbital axis of the giant planet. During nodal precession, the orbital inclinations of inner planets oscillate with time and therefore become misaligned relative to the stellar spin axis. The formation of such systems suggests a history of planet–planet scattering or misalignment between the inner and outer components of protoplanetary disks. The upcoming release of Gaia Data Release 4 will uncover more systems similar to HD 73344, and enable the study of the flatness of exoplanet systems with a mixture of inner and outer planetary systems on a statistical level.
Journal Article
K Dwarf Radius Inflation and a 10 Gyr Spin-down Clock Unveiled through Asteroseismology of HD 219134 from the Keck Planet Finder
We present the first asteroseismic analysis of the K3 V planet host HD 219134 based on four consecutive nights of radial velocities collected with the Keck Planet Finder. We apply Gold deconvolution to the power spectrum to disentangle modes from side lobes in the spectral window and extract 25 mode frequencies with spherical degrees 0 ≤ ℓ ≤ 3. We derive the fundamental properties using five different evolutionary-modeling pipelines and report a mass of 0.763 ± 0.020 (stat) ± 0.007 (sys) M⊙, a radius of 0.748 ± 0.007 (stat) ± 0.002 (sys) R⊙, and an age of 10.151 ± 1.520 (stat) ± 0.810 (sys) Gyr. Compared to the interferometric radius 0.783 ± 0.005 R⊙, the asteroseismic radius is 4% smaller at the 4σ level—a discrepancy not easily explained by known interferometric systematics, modeling assumptions on atmospheric boundary conditions and mixing lengths, magnetic fields, or tidal heating. HD 219134 is the first main-sequence star cooler than 5000 K with an asteroseismic age estimate and will serve as a critical calibration point for stellar spin-down relations. We show that existing calibrated prescriptions for angular momentum loss, incorporating weakened magnetic braking with asteroseismically constrained stellar parameters, accurately reproduce the observed rotation period. Additionally, we revised the masses and radii of the super-Earths in the system, which support their having Earth-like compositions. Finally, we confirm that the oscillation amplitude in radial velocity scales as (L/M)1.5 in K dwarfs, in contrast to the (L/M)0.7 relation observed in G dwarfs. These findings provide significant insights into the structure and angular momentum loss of K-type stars.
Journal Article