Characterizing the masses, radii, and compositions of small planets orbiting M dwarfs is key to understanding their formation and identifying the best targets for atmospheric follow-up with facilities such as JWST. We present the characterization of two planetary systems orbiting the M dwarfs TOI-4336 A (M3.5V) and TOI-4342 (M0V), each hosting two transiting planets previously validated with TESS and ground-based observations. We refined the photometry of the TOI-4342 system using TESS and LCOGT data, and characterized the host stars with NIRPS and ESPRESSO spectroscopy. High-precision ESPRESSO radial velocities (RVs) allowed us to constrain the planetary masses and investigate their potential compositions. The TOI-4336 A system is composed of a sub-Neptune with a period of 16.34 days, a radius of 2.14 ± 0.08 ̊e, and a mass of 3.33 ± 0.36 along with an inner super-Earth on a 7.59-day orbit with a radius of 1.25 ± 0.07 ̊e and a mass of 1.55 ± 0.13 The TOI-4342 system hosts two sub-Neptunes of similar sizes (2.33 ± 0.09 ̊e and 2.35 ± 0.09 ̊e), with periods of 5.54 and 10.69 days. Their masses are measured to be 7.3 ± 1.3 and 4.8 ± 1.4 respectively. The RVs also reveal a planet candidate around TOI-4342, most likely non-transiting, with a period of 47.5 days and a minimum mass of 17.8 ± 3.0 With precise radii and masses, we derived bulk densities and explored possible compositions. The TOI-4336 A sub-Neptune and super-Earth have densities of 1.87 ± 0.30 and 4.35 ± 0.79 g cm -3 $, while the two similar-sized sub-Neptunes in TOI-4342 show distinct densities of 3.18 ± 0.67 and 2.01 ± 0.63 g cm^-3. Using an inference model, we find that TOI-4336 A b, TOI-4342 b, and TOI-4342 c have an atmosphere mass fraction (AMF) of ∼ 3.7%, ∼ 1.8%, and ∼ 2.9%, respectively, while the super-Earth TOI-4336 A c could contain ∼ 2% of water or have a core-to-mass fraction (CMF) of $∼ 31%. All four planets are excellent targets for future atmospheric characterization with JWST, and their multi-planet nature makes them especially interesting for comparative planetology. Notably, TOI-4336 A b stands out as one of the best-known targets in its size and temperature regime, with a transmission spectroscopy metric (TSM) of 138, comparable to benchmark planets such as K2-18 b and LHS 1140 b. Its inner sibling, TOI-4336 A c, may also be of interest for emission spectroscopy and exploring the “cosmic shoreline”, similarly to the Rocky Worlds DDT JWST program.

This work involves detailed numerical research on tri-hybrid nanofluid flow that takes place between two gyrating disks with integrated effects of the magnetic field, Joule heating, thermal radiation, as well as, homogeneous-heterogeneous reactions. The main equations have solved through bvp4c approach in dimensionless from. It has found in this work that the stretching factor at the bottom disk increases the axial flow, and the radial flow exhibits a twofold action. Axial and tangential velocities are directly proportional to Reynolds number but inversely proportional to the effects of the magnet whereas radial velocity is a mixed proportion. The rotational factor of tangential flow increases. Thermal profiles increase as Eckert, Reynolds, magnetic and radiation parameters increase. The concentration undergoes a decreasing trend when the homogeneous factors, heterogeneous factors and Schmidt numbers are increased and an increasing trend when Reynolds number is increased. There is great congruence in comparative results and Nusselt and Sherwood number are measured in tables and are used to determine the heat and mass transfer. This study contains useful information on how to optimize reactive thermal systems using rotating geometries and multimodal nanofluids, and can find its applications in energy systems and chemical reactors as well as innovative cooling technologies.

Wakes generated by upstream turbines in an offshore wind farm severely reduce the efficiency and power output of downstream turbines. Wind farm layout optimization offers a way to alleviate these negative impacts, where the main challenge lies in accurate and efficient evaluation across a vast number of potential configurations. Analytical wake models are crucial tools for this optimization, owing to their superb ability to efficiently predict wake distributions. This paper evaluates and discusses recent advances and persistent challenges in analytical wake modelling for layout optimization of wind farms. While the Jensen model remains efficient for discrete searches, the models capturing radial velocity gradients have become a preferred choice for high-fidelity optimization designs. Advanced models show the transition to full wakes to cover near-wake characteristics and complex inflow conditions. Motion corrections and physically based superposition methods improve the performance evaluation of floating offshore wind farms. Multi-objective optimization frameworks balance energy production and fatigue life by the integration of turbulence modelling. However, the increasing scale of modern wind turbines, the dynamic complexity of floating offshore wind farms, the clustering, and the model validation of large-scale wind farms present significant challenges to the applicability of these models. This paper highlights these emerging limitations in optimization problems, clarifying that addressing the gaps in these specific areas is essential for the development of high-fidelity optimizations and the design of future large-scale offshore wind turbine clusters.

Abstract We present a kinematical study of the outer halo ( r GC ∼ 60–160 kpc) of the Milky Way (MW) based on spectroscopy of 55 RR Lyrae stars using the Echelle Spectrograph and Imager instrument on the Keck II telescope. Our spectroscopic targets were selected from three photometric surveys: NGVS, DES, and Pan-STARRS 1. We derive center-of-mass radial velocities with uncertainties of 6–35 km s −1 . The halo velocity dispersion measured with our sample is 70 ± 7 km s −1 . The velocity field shows a possible dipole-like structure, with redshifted northern and blueshifted southern hemispheres. Fitting a MW–Large Magellanic Cloud (LMC) dipole perturbation model yields a weak/marginal dipole signal, with an amplitude of − 3 0 − 20 + 16 km s −1 and an apex direction ( l , b ) = ( − 38 . 2 − 31.5 + 42.4 , − 41 . 3 − 23.8 + 27.9 ) deg, along with a bulk compression velocity of −16 ± 11 km s −1 . While limited by sky coverage and sample size, our results are consistent with the presence of LMC-induced disequilibrium in the distant halo beyond 100 kpc. Aside from the 55 RR Lyrae stars, our spectroscopic analysis reveals that 10 additional phometrically selected RR Lyrae candidates are, in fact, quasar/blazar contaminants; this provides a cautionary tale about the presence of such contaminants in sparsely sampled photometric surveys. Our study demonstrates that single-epoch spectroscopy of RR Lyrae stars is a viable method for probing the kinematics of the outer halo, and future surveys like Rubin/LSST and the Dark Energy Spectroscopic Instrument (DESI-II) have the potential to significantly advance this effort.

Solar granulation properties have long been known to be affected by the presence of a magnetic field, which in turn affects the convective blueshift associated with magnetic regions. Their dependence on magnetic flux is, however, still poorly constrained. We studied how the properties of the convective blueshift in faculae and network structures depends on their size and magnetic flux at different positions on the solar disc. We studied the velocity shifts at small (pixel) and intermediate (several granule) spatial scales. Finally, our aim was to validate that simple laws applied to complex structure configurations are sufficient to describe the observed disc-integrated radial velocities in a realistic way. We analysed two series of HMI/SDO dopplergrams and magnetograms, which provide insights at different scales, to identify the Doppler shift associated with each structure and its properties. They were then used to evaluate their impact on radial velocity variability. We confirm the dominant role of the magnetic flux on the Doppler shift and dependence on distance from disc centre. However, we observe a saturation for large magnetic fluxes, as well as an unexpectedly large shift for the smallest network structures compared to that of the larger network structures. This may be due to the small-scale properties of the flows around the flux tubes or to the flux tube properties. The quiet network strongly contributes to the long-term radial velocity variability, but also exhibits significant rotational modulation. Despite the diversity of properties from network to faculae, simple models to describe the convective blueshift are sufficient to capture the main properties of radial velocity variability in the solar case.

Abstract By using the 1 m telescope of Yunnan Observatories and the 0.5 m telescope of Ho Koon Nature Education cum Astronomical Centre, China, we had obtained eight transit light curves for the exoplanetary system WASP-36 and three for the exoplanetary system XO-3 between 2010 and 2021. By means of the Markov Chain Monte Carlo technique, we have jointly analyzed these light curves and the relative Transiting Exoplanet Survey Satellite light curves to refine the physical parameters of both systems. Through combining the new mid-transit times with the published ones and the ones from the Exoplanet Transit Database website, we have derived transit timing variation (TTV) patterns of the two systems. By analyzing the TTV signals, we find that WASP-36’s TTV favors the apsidal precession model while XO-3’s TTV agrees to the orbital decay model. However, detailed physical analyses demonstrate that the two mechanisms are not the origin of the observed TTVs. Considering that the observed TTVs are induced by perturbers in the systems, based on dynamic simulations, we have constrained the mass of hypothetical perturbers by combining the rms values of both TTVs and radial velocity curve residuals. When the hypothetical perturbing planets are near mean-motion resonance with the transiting planets, the systems could potentially harbor Earth-mass perturbing planets capable of reproducing the observed TTV signals.

Abstract In addition to comprehensive surveys of the Milky Way (MW) bulge, disk, and halo, the Apache Point Galactic Evolution Experiment (APOGEE) project observed seven dwarf spheroidal satellites (dSphs) of the MW: Carina, Sextans, Sculptor, Draco, Ursa Minor, Bootes 1, and Fornax. APOGEE radial velocities, stellar parameters, and Gaia EDR3 proper motions are used to identify member stars from the targets in the vicinity of each dwarf; for seven dwarfs, new member stars are identified. To properly analyze the abundance patterns of these galaxies, a novel procedure was developed to determine the measurable upper limits of the APOGEE chemical abundances as a function of the effective temperature and the spectral signal-to-noise ratio. In general, the APOGEE abundance patterns of these galaxies (limited to [Fe/H] > −2.5) agree with those found in high-resolution optical studies in the literature after abundance offsets are applied. Most of the galaxies studied here have abundance patterns that are distinctly different from the majority of stars found in the MW halo, suggesting that these galaxies contributed little to the MW halo above [Fe/H] > −2.0. From these abundance patterns, we also find that these dSphs tend to follow two types of chemical evolution paths: episodic and continuous star formation, a result that is broadly consistent with previous photometric studies of the star formation histories (SFHs) of these galaxies. We explore whether mass and/or environment have an impact on whether a galaxy has an episodic or continuous SFH, finding tentative evidence that, in addition to the galaxy’s mass, proximity to a larger galaxy and the cessation of star formation may drive the overall shape of the chemical evolution.

Abstract We introduce a new photometric catalog of RR Lyrae (RRL) variables (∼300,000) mainly based on data available in public datasets. We also present the largest and most homogeneous spectroscopic dataset of RRLs and blue horizontal branch (BHB) stars ever collected. This includes radial velocity measurements (∼16,000) and iron abundances (Δ S method for 8140 RRLs, plus 547 from literature). Elemental abundances based on high-resolution spectra are provided for 487 RRLs and 64 BHB stars. We identified candidate RRLs associated with the main Galactic components and their iron distribution function (IDF) becomes more metal rich when moving from the halo ([Fe/H] = −1.56) to the thick disk (TCD; [Fe/H] = −1.47) and thin disk (TND; [Fe/H] = −0.73). Furthermore, halo RRLs and RRLs in retrograde orbits are α enhanced ([ α /Fe]=0.27, σ = 0.18), while TCD RRLs are either α enhanced ([Fe/H] ≤ −1.0) or α poor ([Fe/H] > −1.0), and TND RRLs are mainly α poor ([ α /Fe] = −0.01, σ = 0.20). We also identified RRLs associated with the main stellar streams—Gaia–Sausage–Enceladus (GSE); Sequoia, Helmi, and Sagittarius—and we found that their IDFs are quite similar to halo RRLs. However, GSE RRLs lack the metal-poor/metal-rich tails and their α -element distribution is quite compact. The iron radial gradient in Galactocentric distance for TND, TCD, and halo RRLs is negative and it decreases from −0.026, to −0.010, and to −0.002 dex kpc −1 . The iron radial gradient based on dry halo (halo without substructures) RRLs is, within the errors, equal to the global halo. We also found a strong similarity between iron and [ α /Fe] radial gradients of Milky Way RRLs and M31 globular clusters throughout the full range of galactocentric distances covered by the two samples.

Abstract We study classical motion in the inverse-square cylindrical potential U(ρ) ∝ 1/ρ 2 . After the two-body reduction, a single dimensionless parameter η-combining interaction strength and axial angular momentum-fully sets the dynamics. This splits the motion into three regimes. For η < 1 the motion is unbound: trajectories have a unique closest approach and an analytic deflection that depends only on the impact parameter. At the threshold η = 1 the effective potential vanishes: generic paths are scale-invariant spirals with constant radial speed, while the special case E = 0 gives neutrally stable circles. For η > 1 the trajectory plunges to the center after one turning point, in a finite collapse time. We provide closed-form orbits, normalized PGFPlots/TikZ figures, and order-of-magnitude estimates that connect atom-optics and magnetostatic realizations directly to η.

Abstract Based on the spectral data from the LAMOST Medium-Resolution Spectroscopic Survey (LAMOST-MRS) DR11-v1.1, combined with a publicly available open cluster catalog, we built a large-sample database of open clusters with medium-resolution spectroscopic parameters. This sample encompasses radial velocity measurements from medium-resolution spectroscopy for 1,033 open clusters, among which 446 clusters further offer metallicity profiles and abundance distributions for dozens of chemical elements. Based on this comprehensive dataset, we performed statistical analyses on key parameters of open clusters, including radial velocities, metallicities, and chemical element abundances. Notably, when the star cluster radial velocities are compared with results from the high-resolution spectroscopic survey (APOGEE), the mean difference is constrained within 1 km s$^{-1}$, with a standard deviation less than 10 km s$^{-1}$. For metallicity [Fe/H] comparisons with published high-resolution literature values, the average discrepancy falls in the range of 0.02 - 0.04 dex, accompanied by a standard deviation of 0.06 - 0.08 dex. These findings demonstrate that open cluster properties derived by LAMOST-MRS exhibit reliable precision, making them suitable as probes for in-depth investigations into the chemical evolution of the Milky Way. Finally, we have compiled a catalog of 1,033 open clusters, complemented by parameter lists for approximately 7,000 member stars - all including their LAMOST-MRS spectroscopic parameters. This dataset provides a valuable resource for advancing galactic astrophysics research.

Abstract We identify and correct for small but coherent instrumental drifts in 7 yr of radial velocity (RV) data from the EXtreme PREcision Spectrograph (EXPRES). The systematics are most notable for the six months before and after 2022 January, when EXPRES experienced larger temperature variations, and we see a systematic trough-to-peak amplitude of 2.8 m s −1 in the radial velocities. This is large enough to mimic or obscure planetary signatures. To isolate and correct these effects, we develop a suite of diagnostics that track two-dimensional échellogram shifts, scalings, and rotation, as well as line bisector spans derived from laser frequency comb lines. By combining these empirical tracers with instrument telemetry in a multidimensional regression, we reduce the EXPRES instrument trend traced with solar RVs from an rms of 1.32–0.43 m s −1 , a 67% improvement, and the aggregate of 12 chromospherically quiet stars shows a 26% reduction in velocity scatter. Our injection/recovery simulations further demonstrate a doubling in sensitivity to low-amplitude planetary signals after correction. When applied to the stellar time series of ρ Coronae Borealis ( ρ CrB), the correction removes a spurious planet d signal, restoring the integrity of the data. These results highlight the need for long-term monitoring and multidimensional calibration diagnostics on the path toward true centimeter-per-second precision in next-generation extreme precision RV instruments.

Non-invasive measurement of basic physiological parameters, such as blood flow and temperature, has long been crucial for daily healthcare and the early screening of cardiovascular diseases. This study aims to integrate multimodal human data with a one-dimensional arterial tree model and a lumped-parameter tissue heat transfer model to assess personalized cardiovascular hemodynamics. By matching the measured radial pressure and flow velocity waveforms of the subjects, we obtained personalized peripheral impedance and pulse wave velocities, and first predicted personalized central aortic pressure for validation of the one-dimensional (1D) cardiovascular model. The 1D cardiovascular model was further coupled with a lumped-parameter heat transfer model to investigate the interplay between blood flow and skin temperature. Skin blood perfusion and tissue layer thickness in the facial and upper limb regions were predicted based on the integrated thermo-blood flow model and the measured skin temperatures of the subject's nose tip and fingertip. We finally explored variations in cardiovascular blood flow under local heating and drowsy conditions using the developed model, based on the measured peripheral skin temperatures. The results demonstrate that the coupled cardiovascular-tissue heat transfer model effectively simulates the subjects' blood flow waveforms and skin temperature, supporting the use of non-invasive pulse wave collection devices to predict and calibrate central aortic pressure. This approach enhances our understanding of the mechanisms by which skin temperature reflects peripheral blood flow dynamics.

Abstract Spaceborne synthetic aperture radar (SAR) has been widely used to observe tropical cyclone (TC) wind forcing on the sea surface. Beyond its capability to retrieve wind fields, SAR also provides a unique mapping of one‐dimensional sea surface velocity along the radar line‐of‐sight via the Doppler centroid anomaly. This study utilizes Sentinel‐1 acquisitions over two representative TC cases, Maria (2017) and Cimaron (2018), to examine the relationship between Doppler velocity and the SAR‐derived wind field. For Maria, the spatial distribution of closely follows the radial wind speed projected onto the radar line‐of‐sight , exhibiting a distinct quadrant asymmetry in this case. The ratio of to is approximately 8% in the front right quadrant but decreases to 4% in the rear left quadrant. This asymmetry is attributed to the influence of ocean swell, as supported by analytical model simulations. Following swell enhances wind‐driven surface velocity in the front quadrant, whereas opposing swell suppresses the wind‐induced motion in the rear. In the case of Cimaron, Doppler velocity effectively delineates the Kuroshio Current, a feature not detectable in radar backscattering observations. These two case studies emphasize the added value of SAR‐derived Doppler velocity as a complementary constraint on wind–wave–current interactions under extreme TC conditions. The results illustrate how SAR Doppler observations can inform interpretation of surface velocity variability under TC forcing, while broader generalization across storm events shall require statistical analysis of a larger data set.

Abstract The increasing presence of unmanned aerial vehicles (UAVs) in urban environments presents challenges for reliable detection due to clutter caused by buildings, infrastructure, and other static structures. Conventional Doppler‐based radar methods often struggle in such conditions, particularly when UAVs exhibit low radial velocities. This paper presents a non‐Doppler scattering‐point framework for UAV detection, based on a frequency‐modulated continuous wave (FMCW) radar system operating in the X‐band (9.950–10.026 GHz). The system utilizes a rotating platform for azimuth scanning and applies azimuth‐range mapping combined with adaptive DBSCAN clustering and β ‐expanded convex hull boundary estimation to reduce false detections from static clutter. Experimental validation was conducted in a controlled urban setting with multiple buildings and varied UAV trajectories. The method was evaluated across several elevation angles, demonstrating consistent detection performance and improved distinction between UAV detections and points caused by environmental clutter. These results support the use of FMCW radar and spatial clustering techniques as an effective alternative to Doppler‐independent methods for UAV monitoring in complex environments.

Beta Pictoris is a young nearby A5V star, about 20 Myr old, that is embedded in a prominent debris disc. For the past 40 years, variable absorption features, produced by the gaseous tails of exocomets transiting the star, have been observed in the stellar spectrum. Yet, despite the large number of observations available, the origin and dynamical evolution of the exocomets remain poorly understood. Here we present new spectroscopic observations of Space Telescope and the High Accuracy Radial Velocity Planet Searcher. We report the detection of three strong exocomet signatures at low radial velocities (-7.5, $+2.5,$ and $+10$ km/s) from a large set of lines from various species and excitation levels. We show that the three exocometary tails have different excitation states, indicating that they are located at different distances from the star. Using a detailed modelling of the excitation state of the transiting gas, which includes both radiative and collisional excitation, we derived the transit distance of the three exocometary gaseous tails to be 0.88 ± 0.08,, 4.7 ± 0.3,, and 1.52 ± 0.15,au. These values are much larger than previous estimates, which generally placed the transient features within 0.2,au. This reveals that gaseous tails produced by exocomets sublimating close to the star can expand and migrate over large distances while still remaining detectable in absorption spectroscopy. Our study provides a new method for measuring the transit distance of exocomets based on excitation modelling; this complements the acceleration method, which is only applicable to high-velocity objects. obtained on April 29, 2025, with the Hubble

Galactic globular clusters are a very important tool in explaining the characteristics of the Milky Way. Therefore it is essential to determine the kinematical and dynamical properties of the new star cluster candidates, especially at the low-latitude regions that suffer from heavy extinction and crowding. In this work, we report the first spectroscopic analysis for seven recently identified star cluster candidates: CWNU 4193, FSR 1700, Garro 02, Patchick 98, FSR 1767, Mercer 08, and BH 140. Our aim is to determine the kinematical properties, such as the mean cluster radial velocity , and the dynamical properties, such as the orbital parameters and the global dynamical mass, of these clusters in order to spectroscopically confirm the nature of these seven stellar systems. We collected the high-resolution infrared spectra of 33 candidate members of these clusters using the WINERED spectrograph mounted on the Magellan Clay 6.5 m telescope. Using the WINERED spectra, we measured the radial velocity of each individual star to confirm its membership in the clusters. From the confirmed members, we derived the mean cluster radial velocity of each cluster. In addition, for these clusters, we computed the orbital elements using the model and estimated their GravPot16 global dynamical masses based on the virial theorem. As a result, we confirmed enough member stars (from three to seven stars per cluster) to reliably derive the mean cluster radial velocity and compute the orbital parameters of the clusters CWNU 4193, FSR 1700, Garro 02, and BH 140. For clusters CWNU 4193, FSR 1700, and BH 140, the number of confirmed members also allowed us to estimate their global dynamical masses. Therefore, we successfully derived key kinematical and dynamical properties for four of the most obscured star clusters in the Milky Way.

Abstract We present 22 sets of light curves and one radial velocity curve for the W UMa-type total eclipse contact binary system V2790 Ori, derived by combining all available public photometric data, the photometric data in previous studies, and our own spectroscopic and decade-long photometric observations. Our simultaneous analysis of the light curves and radial velocity curve shows that V2790 Ori is a W-subtype contact binary with a mass ratio of q = 0.322(±0.001) and a shallow contact degree of 14.8(±0.6)%. The orbital period analysis based on 445 eclipsing minima reveals a secular decrease at a rate of P ̇ = − 3.18 ( ± 0.75 ) × 1 0 − 8 days yr − 1 , superimposed with a cyclic variation with an amplitude of A = 8.98(±2.19) × 10 −4 days and a period of P 3 = 7.44(±0.52) yr. The secular decrease is caused by angular momentum loss via magnetic braking, while the cyclic period variation is explained by the light-travel time effect due to a third body, which is likely to be a brown dwarf. Furthermore, our analysis indicates a mass transfer from the more massive component to the less massive one at a rate of 1.22(±0.29) × 10 −8 M ⊙ yr −1 . A model with a cool spot on each component was adopted to fit the O’Connell effect observed in the light curves. Since the O’Connell effect varies over time, we identified a solar-like magnetic activity cycle with a period of approximately 5.4 yr by analyzing the magnitude difference (Δ m ) at the two light maxima and the O’Connell effect ratio. In addition, evolutionary analysis suggests that V2790 Ori is a newly formed contact binary that evolved from a detached phase into the present contact configuration.

It has recently been suggested that the magnitude of the interaction between galaxies could be measured from the level of kinematic disturbance of their outer regions with respect to the innermost ones. In this work, I proved that the outer northeastern region of the Small Magellanic Cloud (SMC), a relatively recent stellar structure with a tidal origin from the interaction with the Large Magellanic Cloud (LMC), is imprinted by a residual velocity pattern. I obtained mean radial velocities RVs) of star clusters formed in situ from GEMINI GMOS spectra, which, added to derived mean proper motions and heliocentric distances, allowed me to compute their 3D space-velocity components. These space velocities are different from those that the clusters would have if they instead rotated with the galaxy in an orderly fashion; i.e., their residual velocities are larger than the upper limit for an object pertaining to the SMC's main body rotation disk. The level of kinematic disturbance depends on the SMC rotation disk adopted; galaxy rotation disks traced using relatively old objects are discouraged. The resulting kinematic disturbance arises in younger and older stellar populations, so the epoch of close interaction between both Magellanic Clouds cannot be uncovered on the basis of the kinematics behavior of stellar populations in the outer SMC regions.

The Canis Major (CMa) star-forming region, a remote molecular cloud complex within the recently discovered Radcliffe Wave, remains under-explored in the literature. We revisit the stellar census in the CMa region, characterizing its stellar population, kinematics, and age using recent astrometric and photometric data from the third data release of the Gaia space mission (Gaia DR3). We conducted a membership analysis of Gaia DR3 sources across a 16 deg2 field encompassing the youngest subgroups in CMa. This new stellar census, combined with spectroscopic observations, allowed us to investigate the structure, kinematics, and age of this region. We identified 1 531 objects as members of the CMa region, confirming 401 previously known members and introducing 1,130 new candidate members. These objects have magnitudes ranging from 10 to 18 mag in the G band from Gaia DR3. We identified two subgroups of CMa stars in our sample labelled as Cluster A and Cluster B. They are located at roughly the same distance A = 1,150^ +79 _ -88 pc and d_ B = 1,183^ +103 _ -108 pc) and exhibit similar space motions that can be derived thanks to the precise radial velocities obtained in this study. The subgroups have a mean isochronal age of about 2-3 Myr. However, based on infrared photometry we show that Cluster A has a higher fraction of disc-bearing stars suggesting that it could be somewhat younger than Cluster B. Our analysis provides new insights into the stellar population of the Canis Major region, by identifying new members, characterizing their kinematics, and assessing their evolutionary stages. Future studies incorporating additional data from upcoming Gaia data releases, multi-wavelength and high-resolution spectroscopic observations will be essential to further advance our understanding of the history of star formation in this region.

Abstract [HP99] 159 is remarkable as the first supersoft X-ray source (SSS) identified with an evolved helium star donor. With a likely orbital period of 1.164 d or 2.327 d, the origin of the SSS component is controversial, with the two current models being either steady He-burning on the white dwarf surface, or that it is a helium nova in the decaying phase. To help resolve this issue we present extensive new long-term spectroscopy (with SALT) and photometry (at SAAO and with OGLE) of [HP99] 159 which (a) supports 2.327 d as the orbital period, and (b) finds only a small He ii radial velocity modulation. The latter is surprising as it implies a very low inclination system, whereas our light curve modelling suggests i ∼ 50○, and hence that the He ii must be produced in outflowing material further above, or beyond, the disc. We find that the decaying nova model cannot fit our OGLE light curve and the observed SSS flux level. [HP99] 159 has been essentially constant as an SSS over several decades, implying a sustained high level of mass-transfer from its He star donor, making it the only confirmed single-degenerate scenario SN Ia progenitor. We have updated the known SSS binary parameters and find a clear ∼1.5 mag difference in their MV when compared to the MV − Σ properties of LMXBs, likely due to the larger irradiated areas and more luminous donors.