K Dwarfs Research Articles

Air-drying causes an alteration in density fractionation of soil materials from organic horizons containing volcanic ash

Density fractionation is commonly used to isolate organic matter in soils based on organo-mineral associations. Not only mineral horizons but also organic horizons contain mineral components. Soil samples for density fractionation are sometimes air-dried or freeze-dried, which can introduce unexpected biases in the results. In this study, we compared the density fraction distributions in wet, air-dried, and freeze-dried organic horizon samples rich in reactive Al and Fe minerals. On Mt. Chokai, a volcano in northern Japan, samples were collected from organic horizons from three representative vegetation types: K1 (dwarf pine and dwarf bamboo at the summit), K2 (dwarf bamboo on the back slope), and K3 (snow meadow with predominantly Poaceae at the foot slope). Wet, air-dried, and freeze-dried samples were subjected to sequential density fractionation using cutoff values of 1.6 and 1.8 g cm–3. We then determined the mass, organic carbon, and total nitrogen distributions in the isolated fractions. Air-drying altered the mass, organic carbon, and total nitrogen distribution of each density fraction. Although we observed differences in the mass distributions of the freeze-dried and wet samples in the snow meadow samples (K3), the mass distributions in the K1 and K2 samples did not change significantly between the freeze-dried and wet samples. Therefore, freeze-drying is recommended as a pretreatment to minimize the effects of drying on density fractionation, particularly for soil samples with no drying history, high organic matter content, and/or high levels of reactive Al and Fe minerals.

Detailed mapping of the Galactic disc structure in the solar neighbourhood through LAMOST K dwarfs

ABSTRACT The Galactic disc is one of the main components of the Milky Way, which contributes most of the luminosity. Its structure is essential for understanding the formation and evolution of the Milky Way. Using 174 443 K-type dwarf stars observed by both Large Sky Area Multi-Object Fiber Spectroscopic Telescope and Gaia Data Release 3, we study the disc density profile in the local volume within 1200 pc. In the azimuthal dimension, we find strong asymmetric signal of the thin disc. The surface density and the scale height of the southern disc significantly change versus the azimuthal angle at the same Galactocentric distance R. Meanwhile, in the vertical dimension, the scale height of the northern disc has quite different trend than that of the southern one. The scale height of the southern disc shows a decreasing trend with ϕ ∼ −2.5°, and change to an increasing one with ϕ ∼ 5.0°. Meanwhile, the scale height of the northern disc has a consistently smaller increase. Finally, we divide the entire sample into three subsamples based on metallicity and all three subsamples show significant non-axisymmetric and north–south asymmetric signals in the Galactic disc. Furthermore, we find that the scale height of the metal-poor ([Fe/H] < −0.4 dex) subsample in the northern disc is greater than that of the metal-rich ([Fe/H] > −0.1 dex) subsample. However, in the southern disc, the scale height exhibits varying relationships across different metallicity slices.

Volatile blooms of Aleurodicus rugioperculatus Martin infested coconut and banana leaves attracting parasitoid Encarsia guadeloupae Viggiani

Invasive whitefly species in coconut plantations have become a matter of concern in the last half a decade as they cause direct and indirect infestation on the palms. The Rugose spiralling whitefly (RSW), Aleurodicus rugioperculatus Martin infestation was high on Cocos nucifera L. (coconut) followed by Dypsis lutescens (H. Wendl.) (Butterfly palm) and Annona squamosa L. (custard apple). The coconut varieties Malayan Yellow Dwarf and Chowghat Orange Dwarf were observed with higher infestation index while that of West coast tall was the lowest. Higher RSW parasitization levels were observed on Musa paradisiaca L. (banana) and Canna indica L. (Indian shot), with 85.96 and 71.59% parasitization, respectively. Identification of volatile organic compounds (VOCs) between healthy and RSW-infested coconut plants revealed the emission of 56 VOCs from the healthy coconut plant and 47 VOCs from RSW infested plant. 22 VOCs were common in both samples, and 25 VOCs were unique to RSW-infested coconut plants. The presence of 42 VOCs was identified from the headspace extracts of RSW-infested bananas. Differences in the VOCs emitted from RSW-infested banana and coconut plants revealed higher emission of terpenoids like β-Caryophyllene, (E, Z)-2,6-dimethyl-2,4,6-Octatriene, Humulene, α-Pinene, Farnesane, α-Copaene and β-cis-Ocimene from RSW infested banana plants that proved to be more attractive to the parasitoid. Identifying specific blends of volatile compounds influencing Encarsia guadeloupae Viggiani could help to augment the parasitotic for RSW management in coconut plantations.

Per se performance of elite coconut genotypes and hybrids for economic quality traits and oil yield

The present study was conducted at Coconut Research Station, Aliyarnagar Tamil Nadu state of India. The experimental trees comprised of five tall coconut genotypes viz., IC 610370, IC 610371, IC 610372, IC 610374 and IC 610379 West Coast Tall (Check), and the hybrids viz., Chowghat Orange Dwarf x Aliyar 1 (COD x ALR1), Chowghat Orange Dwarf x West Coast Tall (COD x WCT), Aliyar 1 x Malayan Green Dwarf (ALR1 x MGD), Malayan Green Dwarf x Aliyar 1 (MGD x ALR), Kenthali Dwarf x Aliyar 1 (KTD x ALR1) and Veppankulam Hybrid Coconut VHC 2 (Check hybrid - released from Veppankulam Coconut Research Station, Tamil Nadu Agricultural University, Tamil Nadu, India). Coconut palms of uniform size were taken from the chosen genotypes and hybrids for recording the observation. All the coconut genotypes and hybrids showed variation in yield, nut characters, and quality traits. The results of the present study revealed that the genotype IC 610370 and the hybrid COD x WCT recorded maximum values for all the recorded traits. This was followed by the genotype IC 610371 and the hybrid COD x ALR1.

Characterization of mother palms and novel techniques to produce elite seedlings of coconut var. Chowghat Orange Dwarf

Characterization of mother palms and novel techniques to produce elite seedlings of coconut var. Chowghat Orange Dwarf

TOI-332 b: a super dense Neptune found deep within the Neptunian desert

ABSTRACT To date, thousands of planets have been discovered, but there are regions of the orbital parameter space that are still bare. An example is the short period and intermediate mass/radius space known as the ‘Neptunian desert’, where planets should be easy to find but discoveries remain few. This suggests unusual formation and evolution processes are responsible for the planets residing here. We present the discovery of TOI-332 b, a planet with an ultra-short period of 0.78 d that sits firmly within the desert. It orbits a K0 dwarf with an effective temperature of 5251 ± 71 K. TOI-332 b has a radius of $3.20^{+0.16}_{-0.12}$ R⊕, smaller than that of Neptune, but an unusually large mass of 57.2 ± 1.6 M⊕. It has one of the highest densities of any Neptune-sized planet discovered thus far at $9.6^{+1.1}_{-1.3}$ g cm−3. A 4-layer internal structure model indicates it likely has a negligible hydrogen-helium envelope, something only found for a small handful of planets this massive, and so TOI-332 b presents an interesting challenge to planetary formation theories. We find that photoevaporation cannot account for the mass-loss required to strip this planet of the Jupiter-like envelope it would have been expected to accrete. We need to look towards other scenarios, such as high-eccentricity migration, giant impacts, or gap opening in the protoplanetary disc, to try and explain this unusual discovery.

TOI-1416: A system with a super-Earth planet with a 1.07 d period

TOI-1416 (BD+42 2504, HIP 70705) is a V =10 late G- or early K-type dwarf star. TESS detected transits in its Sectors 16, 23, and 50 with a depth of about 455 ppm and a period of 1.07 days. Radial velocities (RVs) confirm the presence of the transiting planet TOI-1416 b, which has a mass of 3.48 ± 0.47 M⊕ and a radius of 1.62 ± 0.08 R⊕, implying a slightly sub-Earth density of 4.50−0.83+0.99 g cm−3. The RV data also further indicate a tentative planet, c, with a period of 27.4 or 29.5 days, whose nature cannot be verified due to strong suspicions of contamination by a signal related to the Moon’s synodic period of 29.53 days. The nearly ultra-short-period planet TOI-1416 b is a typical representative of a short-period and hot (Teq ≈ 1570 K) super-Earth-like planet. A planet model of an interior of molten magma containing a significant fraction of dissolved water provides a plausible explanation for its composition, and its atmosphere could be suitable for transmission spectroscopy with JWST. The position of TOI-1416 b within the radius-period distribution corroborates the idea that planets with periods of less than one day do not form any special group. It instead implies that ultra-short-period planets belong to a continuous distribution of super-Earth-like planets with periods ranging from the shortest known ones up to ≈30 days; their period-radius distribution is delimited against larger radii by the Neptune Desert and by the period-radius valley that separates super-Earths from sub-Neptune planets. In the abundance of small, short-periodic planets, a notable plateau has emerged between periods of 0.6–1.4 days, which is compatible with the low-eccentricity formation channel. For the Neptune Desert, its lower limits required a revision due to the increasing population of short-period planets; for periods shorter then 2 days, we establish a radius of 1.6 R⊕ and a mass of 0.028 Mjup (corresponding to 8.9 M⊕) as the desert’s lower limits. We also provide corresponding limits to the Neptune Desert against the planets’ insolation and effective temperatures.

X-ray flashes from the low-mass X-ray binary IGR J17407−2808

IGR J17407−2808 is an enigmatic and poorly studied X-ray binary that was recently observed quasi-simultaneously with NuSTAR and XMM-Newton. In this paper we report the results of this observational campaign. During the first 60 ks of observation, the source was caught in a relatively low emission state characterised by a modest variability and an average flux of ∼8.3 × 10−13 erg cm−2 s−1 (4−60 keV). Subsequently, IGR J17407−2808 entered a significantly more active emission state that persisted for the remaining ∼40 ks of the NuSTAR observation. During this state, IGR J17407−2808 displayed several fast X-ray flares of ∼1 − 100 s in duration and featuring profiles with either single or multiple peaks. The source flux in the flaring state reached values as high as ∼2 × 10−9 erg cm−2 s−1 (4−60 keV), leading to a measured dynamic range during the NuSTAR and XMM-Newton campaign of ≳103. We also analysed available archival photometric near-infrared data for IGR J17407−2808 in order to improve the constraints available so far on the nature of the donor star hosted in this system. Our analysis shows that the donor star can be either a rare K or M-type sub-subgiant, a K-type main sequence or subgiant star. Our findings support the classification of IGR J17407−2808 as a low-mass X-ray binary. We discuss the X-ray behaviour of the source as recorded by NuSTAR and XMM-Newton in view of this revised classification.

An insight into pollen morphology and evaluation of pollen viability, germination and mineral composition of some coconut (Cocos nucifera L.) genotypes

• Pollen morphology of eight coconut accessions differed in origin, stature, breeding behaviour and tolerance to abiotic stresses were characterised with scanning electron microscope. • Variations in pollen size, shape and exine ornamentation pattern was observed between the coconut genotypes. • Pollen physiological features such as pollen viability, germination and pollen tube length and pollen nutrient composition were evaluated for the eight coconut genotypes. • The results obtained revealed differences in pollen morphological features which can potentially be used for cultivar identification and the information on pollen viability, germination and pollen mineral contents amongst genotypes can support conservation and crop improvement studies of the genotypes. The micro-morphological characteristic of the pollen grain is one of the most important diagnostic traits use for identification and characterization of plants even to the accession levels. In this study, pollen grains characterization of eight different coconut ( Cocos nucifera L.) accessions were carried out. Morphometric observations and structure analysis of the pollen grains were performed using light and scanning electron microscopy. The variation in length and width observed ranged from 55.06 -71.25 µm and 24.38 -36.27 µm amongst the accessions. The pollen grains exhibited an ellipsoidal to elliptical shape with the exine ornamentation ranging from granulate to reticulate. Pollen viability, germination and pollen tube length were significantly different amongst the tested accessions. While pollen viability varied from 92.35 to 96.5%, germination rate and pollen tube length (after 2 h) ranged from 16.05 - 31.59% and 234.95 μm to 414.96 μm respectively. Pollen mineral composition from different accessions also varied significantly with Malayan Orange Dwarf (MOD) recording higher phosphorus (0.93%), calcium (0.64%) and magnesium (0.38%) content while highest potassium (1.01%), sodium (0.71%), iron (149.35 ppm) zinc (119.59 ppm) and boron (45.05 ppm) content was noticed in San Ramon Tall (SNRT). This investigation highlights the fact that these pollen morphological features could be potentially used for differentiating the selected accessions thereby supporting their conservation and crop improvement studies.

A dense mini-Neptune orbiting the bright young star HD 18599

ABSTRACT Very little is known about the young planet population because the detection of small planets orbiting young stars is obscured by the effects of stellar activity and fast rotation, which mask planets within radial velocity and transit data sets. The few planets that have been discovered in young clusters generally orbit stars too faint for any detailed follow-up analysis. Here, we present the characterization of a new mini-Neptune planet orbiting the bright (V = 9) and nearby K2 dwarf star, HD 18599. The planet candidate was originally detected in TESS light curves from sectors 2, 3, 29, and 30, with an orbital period of 4.138 d. We then used HARPS and FEROS radial velocities, to find the companion mass to be 25.5$\pm$4.6 $M_{\oplus }$. When we combine this with the measured radius from TESS of 2.70$\pm$0.05 $R_{\oplus }$, we find a high planetary density of 7.1$\pm$1.4 g cm$^{-3}$. The planet exists on the edge of the Neptune Desert and is the first young planet (300 Myr) of its type to inhabit this region. Structure models argue for a bulk composition to consist of 23 per cent H$_2$O and 77 per cent Rock and Iron. Future follow-up with large ground- and space-based telescopes can enable us to begin to understand in detail the characteristics of young Neptunes in the galaxy.

Universal Scaling Laws for Solar and Stellar Atmospheric Heating: Catalog of Power-law Index between Solar Activity Proxies and Various Spectral Irradiances

The formation of extremely hot outer atmospheres is one of the most prominent manifestations of magnetic activity common to late-type dwarf stars, including the Sun. It is widely believed that these atmospheric layers, the corona, transition region, and chromosphere, are heated by the dissipation of energy transported upwards from the stellar surface by the magnetic field. This is signified by the spectral line fluxes at various wavelengths, scaled with power-law relationships against the surface magnetic flux over a wide range of formation temperatures, which are universal to the Sun and Sunlike stars of different ages and activity levels. This study describes a catalog of power-law indices between solar activity proxies and various spectral line fluxes. Compared to previous studies, we expanded the number of proxies, which now includes the total magnetic flux, total sunspot number, total sunspot area, and the F10.7 cm radio flux, and further enhanced the number of spectral lines by a factor of 2. This provides the data to study in detail the flux–flux scaling laws from the regions specified by the temperatures of the corona (log(T/K) = 6–7) to those of the chromosphere (log(T/K) ∼ 4), as well as the reconstruction of various spectral line fluxes of the Sun in the past, F-, G-, and K-type dwarfs, and the modeled stars.

Constraining the Physical Properties of Stellar Coronal Mass Ejections with Coronal Dimming: Application to Far-ultraviolet Data of ϵ Eridani

Coronal mass ejections (CMEs) are a prominent contributor to solar system space weather and might have impacted the Sun’s early angular momentum evolution. A signal diagnostic of CMEs on the Sun is coronal dimming: a drop in coronal emission, tied to the mass of the CME, that is the direct result of removing emitting plasma from the corona. We present the results of a coronal dimming analysis of Fe xii 1349 Å and Fe xxi 1354 Å emission from ϵ Eridani (ϵ Eri), a young K2 dwarf, with archival far-ultraviolet observations by the Hubble Space Telescope’s Cosmic Origins Spectrograph. Following a flare in 2015 February, ϵ Eri’s Fe xxi emission declined by 81 ± 5%. Although enticing, a scant 3.8 minutes of preflare observations allows for the possibility that the Fe xxi decline was the decay of an earlier, unseen flare. Dimming nondetections following each of three prominent flares constrain the possible mass of ejected Fe xii-emitting (1 MK) plasma to less than a few × 1015 g. This implies that CMEs ejecting this much or more 1 MK plasma occur less than a few times per day on ϵ Eri. On the Sun, 1015 g CMEs occur once every few days. For ϵ Eri, the mass-loss rate due to CME-ejected 1 MK plasma could be < 0.6 , well below the star’s estimated 30 mass-loss rate (wind + CMEs). The order-of-magnitude formalism we developed for these mass estimates can be broadly applied to coronal dimming observations of any star.

GC-MS-based metabolomics reveals dynamic changes in the nutritionally important metabolites in coconut meat during nut maturation

Coconut is an economically important tropical palm fruit. Among various coconut products, the endosperm (coconut meat) is a rich source of several nutritionally rich metabolites.The coconut fruit typically takes 10–12 months to attain commercial maturity. Although metabolite profile of coconut meat vary during nut development and maturation because of transformation of liquid endosperm into solid endosperm, there are as such no reports describing the real dynamics of these changes. Therefore, in this work, we applied gas chromatography-mass spectrometry (GC-MS)-based metabolomics technology to identify the alteration in the metabolite levels during nut development. Metabolite profile was carried out from 'Chowghat Orange Dwarf ' (COD) and 'Malayan YellowDwarf' (MYD) varieties of coconut at three critical nut development stages. We identified a total of 43 and 40 metabolites from 'COD' and 'MYD', variety, respectively. By employing the partial least squares-discriminant analysis we identified specific fatty acids as important biomarker metabolites for actual prediction of nut maturity stages. These results show several patterns of variation in metabolite composition and level, especially in the primary metabolites, during the process of nut maturation. These fundamental metabolomic profile data will be very useful for understanding the appropriate nut maturity stages and their corresponding nutritional value.

Physicochemical characterization and fatty acid profiles of testa oils from various coconut (Cocos nucifera L.) genotypes.

Cocos nucifera (L.) is an important plantation crop with immense but untapped nutraceutical potential. Despite its bioactive potential, the biochemical features of testa oils of various coconut genotypes are poorly understood. Hence, in this study, the physicochemical characteristics of testa oils extracted from six coconut genotypes - namely West Coast Tall (WCT), Federated Malay States Tall (FMST), Chowghat Orange Dwarf (COD), Malayan Yellow Dwarf (MYD), and two Dwarf × Dwarf (D × D hybrids) viz., Cameroon Red Dwarf (CRD) × Ganga Bondam Green Dwarf (GBGD) and MYD × Chowghat Green Dwarf (CGD) - were analyzed. The proportion of testa in the nuts (fruits) (1.29-3.42%), the proportion of oil in the testa (40.97-50.56%), and biochemical components in testa oils - namely proxidant elements Fe (34.17-62.48 ppm) and Cu (1.63-2.77 ppm), and the total phenolic content (6.84-8.67 mg GAE/100 g), and phytosterol content (54.66-137.73 mg CE/100 g) varied depending on the coconut genotypes. The saturated fatty acid content of testa oils (67.75 to 78.78%) was lower in comparison with that of coconut kernel oils. Similarly, the lauric acid (26.66-32.04%), myristic (18.31-19.60%), and palmitic acid (13.43-15.71%,) content of testa oils varied significantly in comparison with the coconut kernel oils (32-51%, 17-21% and 6.9-14%, respectively). Liquid chromatography-mass spectrometry (LC-MS) analysis revealed the presence of 18 phenolic acids in coconut testa oil. Multivariate analysis revealed the biochemical attributes that defined the principal components loadings. Hierarchical clustering analysis of the genotypes showed two distinct clusters. This study reveals the genotypic variations in the nutritionally important biochemical components of coconut testa oils. The relatively high concentration of polyunsaturated fatty acids (PUFA) and polyphenol content in testa oils warrant further investigation to explore their nutraceutical potential. © 2022 Society of Chemical Industry.

Study on Biometrics of Selected Coconut Varieties for the Development of a Drone Spraying and Harvesting System for Coconut Palms

Background: Coconut palm (Cocos nucifera) is a significant cash crop in the humid tropics of India. The quality, variety and types of coconut palm vary from one place to other. Nowadays, the lack of skilled climbers for tree climbing is a serious problem experienced by coconut farmers. The adoption of drone technology in coconut cultivation is considered to enhance the productivity of coconut. The current study aimed to study the biometrics of different varieties of coconut trees to design and develop a drone-based spraying and harvesting system which suits all types of coconut palms. Methods: The major parameters influencing drone spraying and harvesting design are crop, machine and meteorological parameters. The crop parameters for the palms were measured by using standard techniques. The prominent varieties include West coast tall, Coconut - ALR (CN) 1, Coconut - ALR (CN) 3, Chowghat orange dwarf, Chowghat green dwarf, Malaysian yellow dwarf, East coast tall and Chandra Kalpa were selected. The biometric data were observed from the randomly selected healthy coconut trees. Result: The eight major coconut varieties were selected and their biometric data was observed. It was concluded that the observations aided in deciding the design of the drone components as well as the spraying and harvesting mechanism suitable for coconut palms.

Study on Nutrient Removal (NPK) from Different Parts of Chowghat Orange Dwarf (COD) and West Coast Tall (WCT) Cultivars of Coconut

Aims: This research was carried out to study the nutrients removal by different parts of coconut. This palm takes up a lot of nutrients from the ground for growth and development. Removal of nutrients varies from different components of palm. Hence this was carried to study the nutrient removal by different parts of coconut to improve growth. &#x0D; Study Design: The study was carried out in Factorial Randomized Block Design (FRBD) with 2 factors (A and B) and 4 replications.&#x0D; Place and Duration of Study: This study was carried out at Coconut Orchard Department of Plantation and Spices Horticultural College &amp; Research Institute Tamil Nādu Agricultural University Coimbatore during 2021-2022.&#x0D; Methodology: Here the major nutrient (NPK) removal of two varieties Chowghat Orange Dwarf (COD) and West Coast Tall (WCT) were estimated. The nutrient removal was estimated by collecting plant sample before fertilizer application(initial) and 3rd and 6th months after fertilizer application. These samples were dried powdered and analysed with respective procedures and instruments.&#x0D; Results: The result revealed that the removal of nutrients from parts of coconut is increased from initial (without fertilizer application) to 3rd and 6th months after fertilizer application in both Chowghat Orange Dwarf (COD) and West Coast Tall (WCT). There is more removal of potassium compared to nitrogen and phosphorus. The percentage of nutrients removed was 13.52,18.69,21.22 during initial, 3rd month and 6th month in COD as such 16.22,19.8,22.44 in WCT respectively. Comparing with Chowghat Orange Dwarf (COD) and West Coast Tall (WCT) removes more nutrients.&#x0D; Conclusion: The present study revealed that there was enormous removal of potassium from both varieties Chowghat Orange Dwarf (COD) and West Coast Tall (WCT). So, there is a need to increase in the potassium fertilizer application from normal recommended dose or potassium enriched nutrient application is recommended.

A Coronagraph with a Sub-λ/D Inner Working Angle and a Moderate Spectral Bandwidth

Future high-contrast imaging spectroscopy with a large segmented telescope will be able to detect atmospheric molecules of Earth-like planets around G- or K-type main-sequence stars. Increasing the number of target planets will require a coronagraph with a small inner working angle (IWA), and wide spectral bandwidth is required if we enhance a variety of detectable atmospheric molecules. To satisfy these requirements, in this paper, we present a coronagraphic system that provides an IWA less than 1λ 0/D over a moderate wavelength band, where λ 0 is the design-center wavelength and D denotes the full width of the rectangular aperture included in the telescope aperture. A performance simulation shows that the proposed system approximately achieves a contrast below 10−10 at 1λ 0/D over the wavelengths of 650–750 nm. In addition, this system has a core throughput ≥10% at input separation angles of ∼0.7–1.4λ 0/D; to reduce telescope time, we need prior information on the target’s orbit by other observational methods to a precision higher than the width of the field of view. For some types of aberration including tilt aberration, the proposed system has a sensitivity less than ever-proposed coronagraphs that have IWAs of approximately 1λ 0/D. In future observations of Earth-like planets, the proposed coronagraphic system may serve as a supplementary coronagraphic system dedicated to achieving an extremely small IWA.

Magnetic field evolution of the K2 dwarf V471 Tau

ABSTRACT Observations of the eclipsing binary system V471 Tau show that the time of the primary eclipses varies in an apparent periodic way. With growing evidence that the magnetically active K2 dwarf component might be responsible for driving the eclipse timing variations (ETVs), it is necessary to monitor the star throughout the predicted ∼35 yr activity cycle that putatively fuels the observed ETVs. We contribute to this goal with this paper by analysing spectropolarimetric data obtained with ESPaDOnS at the Canada–France–Hawaii Telescope in 2014 December and 2015 January. Using Zeeman–Doppler Imaging, we reconstruct the distribution of brightness inhomogeneities and large-scale magnetic field at the surface of the K2 dwarf. Compared to previous tomographic reconstructions of the star carried out with the same code, we probe a new phase of the ETVs cycle, offering new constraints for future works exploring whether a magnetic mechanism operating in the K2 dwarf star is indeed able to induce the observed ETVs of V471 Tau.

Efficient modeling of correlated noise

The radial velocity method is a very productive technique used to detect and confirm extrasolar planets. The most recent spectrographs, such as ESPRESSO or EXPRES, have the potential to detect Earth-like planets around Sun-like stars. However, stellar activity can induce radial velocity variations that dilute or even mimic the signature of a planet. A widely recognized method for disentangling these signals is to model the radial velocity time series, jointly with stellar activity indicators, using Gaussian processes and their derivatives. However, such modeling is prohibitive in terms of computational resources for large data sets, as the cost typically scales as the total number of measurements cubed. Here, we present S+LEAF 2, a Gaussian process framework that can be used to jointly model several time series, with a computational cost that scales linearly with the data set size. This framework thus provides a state-of-the-art Gaussian process model, with tractable computations even for large data sets. We illustrate the power of this framework by reanalyzing the 246 HARPS radial velocity measurements of the nearby K2 dwarf HD 138038, together with two activity indicators. We reproduce the results of a previous analysis of these data, but with a strongly decreased computational cost (more than two order of magnitude). The gain would be even greater for larger data sets.

NEID Rossiter–McLaughlin Measurement of TOI-1268b: A Young Warm Saturn Aligned with Its Cool Host Star

Abstract Close-in gas giants present a surprising range of stellar obliquity, the angle between a planet’s orbital axis and its host star’s spin axis. It is unclear whether the obliquities reflect the planets’ dynamical history (e.g., aligned for in situ formation or disk migration versus misaligned for high-eccentricity tidal migration) or whether other mechanisms (e.g., primordial misalignment or planet–star interactions) are more important in sculpting the obliquity distribution. Here we present the stellar obliquity measurement of TOI-1268 (TIC-142394656, V mag ∼ 10.9), a young K-type dwarf hosting an 8.2 day period, Saturn-sized planet. TOI-1268’s lithium abundance and rotation period suggest the system age between the ages of the Pleiades cluster (∼120 Myr) and the Prasepe cluster (∼670 Myr). Using the newly commissioned NEID spectrograph, we constrain the stellar obliquity of TOI-1268 via the Rossiter–McLaughlin effect from both radial velocity and Doppler tomography signals. The 3σ upper bounds of the projected stellar obliquity ∣λ∣ from both models are below 60°. The large host star separation (a/R ⋆ ∼ 17), combined with the system’s young age, makes it unlikely that the planet has realigned its host star. The stellar obliquity measurement of TOI-1268 probes the architecture of a young gas giant beyond the reach of tidal realignment (a/R ⋆ ≳ 10) and reveals an aligned or slightly misaligned system.