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We explore the prospects for Twinkle to determine the atmospheric composition of the nearby terrestrial-like planet LTT 1445 Ab, including the possibility of detecting the potential biosignature ammonia (NH3). At a distance of 6.9 pc, this system is the second closest known transiting system and will be observed through transmission spectroscopy with the upcoming Twinkle mission. Although LTT 1445 Ab has been suggested to be a candidate for a Hycean world, constraints on the interior composition based on its mass and radius suggests that the planet lacks a substantial water layer, and thus the proposed Hycean scenario is disfavoured. We use PETITRADTRANS and a Twinkle simulator to simulate transmission spectra for the more likely scenario of a cold Haber world for which NH3 is considered to be a biosignature. We study the detectability under different scenarios: varying hydrogen fraction, concentration of ammonia, and cloud coverage. We find that ammonia can be detected at an ∼3σ level for optimal (non-cloudy) conditions with 25 transits and a volume mixing ration of 4.0 ppm of NH3. We provide examples of retrieval analysis to constrain potential NH3 and H2O in the atmosphere. Our study illustrates the potential of Twinkle to characterize atmospheres of potentially habitable exoplanets.

 

Most ultra-hot Jupiters (UHJs) show evidence of temperature inversions, in which temperature increases with altitude over a range of pressures. Temperature inversions can occur when there is a species that absorbs the stellar irradiation at a relatively high level of the atmospheres. However, the species responsible for this absorption remains unidentified. In particular, the UHJ KELT-20b is known to have a temperature inversion. Using high resolution emission spectroscopy from LBT/PEPSI we investigate the atomic and molecular opacity sources that may cause the inversion in KELT-20b, as well as explore its atmospheric chemistry. We confirm the presence of Fe i with a significance of 17σ. We also report a tentative 4.3σ detection of Ni i. A nominally 4.5σ detection of Mg i emission in the PEPSI blue arm is likely in fact due to aliasing between the Mg i cross-correlation template and the Fe i lines present in the spectrum. We cannot reproduce a recent detection of Cr i, while we do not have the wavelength coverage to robustly test past detections of Fe ii and Si i. Together with non-detections of molecular species like TiO, this suggests that Fe i is likely to be the dominant optical opacity source in the dayside atmosphere of KELT-20b and may be responsible for the temperature inversion. We explore ways to reconcile the differences between our results and those in literature and point to future paths to understand atmospheric variability.

 

Vortex fiber nulling (VFN) is a technique for detecting and characterizing faint companions at small separations from their host star. A near-infrared (∼2.3μm) VFN demonstrator mode was deployed on the Keck Planet Imager and Characterizer (KPIC) instrument at the Keck Observatory and presented earlier. In this Letter, we present the first VFN companion detections. Three targets, HIP 21543 Ab, HIP 94666 Ab, and HIP 50319 B, were detected with host–companion flux ratios between 70 and 430 at and within one diffraction beamwidth (λ/D). We complement the spectra from KPIC VFN with flux ratio and position measurements from the CHARA Array to validate the VFN results and provide a more complete characterization of the targets. This Letter reports the first direct detection of these three M dwarf companions, yielding their first spectra and flux ratios. Our observations provide measurements of bulk properties such as effective temperatures, radial velocities, and$v\sin i$, and verify the accuracy of the published orbits. These detections corroborate earlier predictions of the KPIC VFN performance, demonstrating that the instrument mode is ready for science observations.

 

Abstract Background In the CRISPR-Cas9 system, the efficiency of genetic modifications has been found to vary depending on the single guide RNA (sgRNA) used. A variety of sgRNA properties have been found to be predictive of CRISPR cleavage efficiency, including the position-specific sequence composition of sgRNAs, global sgRNA sequence properties, and thermodynamic features. While prevalent existing deep learning-based approaches provide competitive prediction accuracy, a more interpretable model is desirable to help understand how different features may contribute to CRISPR-Cas9 cleavage efficiency. Results We propose a gradient boosting approach, utilizing LightGBM to develop an integrated tool, BoostMEC (Boosting Model for Efficient CRISPR), for the prediction of wild-type CRISPR-Cas9 editing efficiency. We benchmark BoostMEC against 10 popular models on 13 external datasets and show its competitive performance. Conclusions BoostMEC can provide state-of-the-art predictions of CRISPR-Cas9 cleavage efficiency for sgRNA design and selection. Relying on direct and derived sequence features of sgRNA sequences and based on conventional machine learning, BoostMEC maintains an advantage over other state-of-the-art CRISPR efficiency prediction models that are based on deep learning through its ability to produce more interpretable feature insights and predictions. 

During mitosis, cells round up and utilize the interphase adhesion sites within the fibrous extracellular matrix (ECM) as guidance cues to orient the mitotic spindles. Here, using suspended ECM-mimicking nanofiber networks, we explore mitotic outcomes and error distribution for various interphase cell shapes. Elongated cells attached to single fibers through two focal adhesion clusters (FACs) at their extremities result in perfect spherical mitotic cell bodies that undergo significant 3-dimensional (3D) displacement while being held by retraction fibers (RFs). Increasing the number of parallel fibers increases FACs and retraction fiber-driven stability, leading to reduced 3D cell body movement, metaphase plate rotations, increased interkinetochore distances, and significantly faster division times. Interestingly, interphase kite shapes on a crosshatch pattern of four fibers undergo mitosis resembling single-fiber outcomes due to rounded bodies being primarily held in position by RFs from two perpendicular suspended fibers. We develop a cortex–astral microtubule analytical model to capture the retraction fiber dependence of the metaphase plate rotations. We observe that reduced orientational stability, on single fibers, results in increased monopolar mitotic defects, while multipolar defects become dominant as the number of adhered fibers increases. We use a stochastic Monte Carlo simulation of centrosome, chromosome, and membrane interactions to explain the relationship between the observed propensity of monopolar and multipolar defects and the geometry of RFs. Overall, we establish that while bipolar mitosis is robust in fibrous environments, the nature of division errors in fibrous microenvironments is governed by interphase cell shapes and adhesion geometries. 

Abstract With the launch of the JWST, we will obtain more precise data for exoplanets than ever before. However, these data can only inform and revolutionize our understanding of exoplanets when placed in the larger context of planet–star formation. Therefore, gaining a deeper understanding of their host stars is equally important and synergistic with the upcoming JWST data. We present detailed chemical abundance profiles of 17 FGK stars that will be observed in exoplanet-focused Cycle 1 JWST observer programs. The elements analyzed (C, N, O, Na, Mg, Si, S, K, and Fe) were specifically chosen as being informative to the composition and formation of planets. Using archival high-resolution spectra from a variety of sources, we perform an LTE equivalent width analysis to derive these abundances. We look to literature sources to correct the abundances for non-LTE effects, especially for O, S, and K, where the corrections are large (often >0.2 dex). With these abundances and the ratios thereof, we will begin to paint clearer pictures of the planetary systems analyzed by this work. With our analysis, we can gain insight into the composition and extent of migration of Hot Jupiters, as well as the possibility of carbon-rich terrestrial worlds. 

Abstract Extremely large telescopes (ELTs) provide an opportunity to observe surface inhomogeneities for ultracool objects including M dwarfs, brown dwarfs (BDs), and gas giant planets via Doppler imaging and spectrophotometry techniques. These inhomogeneities can be caused by star spots, clouds, and vortices. Star spots and associated stellar flares play a significant role in habitability, either stifling life or catalyzing abiogenesis depending on the emission frequency, magnitude, and orientation. Clouds and vortices may be the source of spectral and photometric variability observed at the L/T transition of BDs and are expected in gas giant exoplanets. We develop a versatile analytical framework to model and infer surface inhomogeneities that can be applied to both spectroscopic and photometric data. This model is validated against a slew of numerical simulations. Using archival spectroscopic and photometric data, we infer starspot parameters (location, size, and contrast) and generate global surface maps for Luhman 16B (an early T dwarf and one of our solar system’s nearest neighbors at a distance of ≈2 pc). We confirm previous findings that Luhman 16B’s atmosphere is inhomogeneous with time-varying features. In addition, we provide tentative evidence of longer timescale atmospheric structures such as dark equatorial and bright midlatitude to polar spots. These findings are discussed in the context of atmospheric circulation and dynamics for ultracool dwarfs. Our analytical model will be valuable in assessing the feasibility of using ELTs to study surface inhomogeneities of gas giant exoplanets and other ultracool objects. 

M dwarfs are common host stars to exoplanets but often lack atmospheric abundance measurements. Late-M dwarfs are also good analogs to the youngest substellar companions, which share similarT_eff∼ 2300–2800 K. We present atmospheric analyses for the M7.5 companion HIP 55507 B and its K6V primary star with Keck/KPIC high-resolution (R∼ 35,000)K-band spectroscopy. First, by including KPIC relative radial velocities between the primary and secondary in the orbit fit, we improve the dynamical mass precision by 60% and find$M_B={88.0}_{-3.2}^{+3.4}{M}_{\mathrm{Jup}}$, putting HIP 55507 B above the stellar–substellar boundary. We also find that HIP 55507 B orbits its K6V primary star with$a={38}_{-3}^{+4}$au ande= 0.40 ± 0.04. From atmospheric retrievals of HIP 55507 B, we measure [C/H] = 0.24 ± 0.13, [O/H] = 0.15 ± 0.13, and C/O = 0.67 ± 0.04. Moreover, we strongly detect¹³CO (7.8σsignificance) and tentatively detect${\mathrm{H}}_2^{18}\mathrm{O}$(3.7σsignificance) in the companion’s atmosphere and measure${}^{12}\mathrm{CO}{/}^{13}\mathrm{CO}={98}_{-22}^{+28}$and${\mathrm{H}}_2^{16}\mathrm{O}/{\mathrm{H}}_2^{18}\mathrm{O}={240}_{-80}^{+145}$after accounting for systematic errors. From a simplified retrieval analysis of HIP 55507 A, we measure${}^{12}\mathrm{CO}{/}^{13}\mathrm{CO}={79}_{-16}^{+21}$and${\mathrm{C}}^{16}\mathrm{O}/{\mathrm{C}}^{18}\mathrm{O}={288}_{-70}^{+125}$for the primary star. These results demonstrate that HIP 55507 A and B have consistent¹²C/¹³C and¹⁶O/¹⁸O to the <1σlevel, as expected for a chemically homogeneous binary system. Given the similar flux ratios and separations between HIP 55507 AB and systems with young substellar companions, our results open the door to systematically measuring¹³CO and${\mathrm{H}}_2^{18}\mathrm{O}$abundances in the atmospheres of substellar or even planetary-mass companions with similar spectral types.

 

By measuring the elemental abundances of a star, we can gain insight into the composition of its initial gas cloud— the formation site of the star and its planets. Planet formation requires metals, the availability of which is determined by the elemental abundance. In the case where metals are extremely deficient, planet formation can be stifled. To investigate such a scenario requires a large sample of metal-poor stars and a search for planets therein. This paper focuses on the selection and validation of a halo star sample. We select ∼17,000 metal-poor halo stars based on their Galactic kinematics, and confirm their low metallicities ([Fe/H] < −0.5), using spectroscopy from the literature. Furthermore, we perform high-resolution spectroscopic observations using LBT/PEPSI and conduct detailed metallicity ([Fe/H]) analyses on a sample of 13 previously-known halo stars that also have hot kinematics. We can use the halo star sample presented here to measure the frequency of planets and to test planet formation in extremely metal-poor environments. The result of the planet search and its implications will be presented and discussed in a companion paper by Boley et al.