High Orbital Inclination Research Articles

Optimal Trajectories of Diffractive Sail to Highly Inclined Heliocentric Orbits

Recent literature indicates that the diffractive sail concept is an interesting alternative to the more conventional reflective solar sail, which converts solar radiation pressure into a (deep space) thrust using a thin, lightweight highly reflective membrane, usually metalized. In particular, a diffractive sail, which uses a metamaterial-based membrane to diffract incoming solar rays, is able to generate a steerable thrust vector even when the sail nominal plane is perpendicular to the Sun–spacecraft line. This paper analyzes the optimal transfer performance of a diffractive-sail-based spacecraft in a challenging heliocentric scenario that is consistent with the proposed Solar Polar Imager mission concept. In this case, the spacecraft must reach a near-circular (heliocentric) orbit with a high orbital inclination with respect to the Ecliptic in order to observe and monitor the Sun’s polar regions. Such a specific heliocentric scenario, because of the high velocity change it requires, is a mission application particularly suited for a propellantless propulsion system such as the classical solar sail. However, as shown in this work, the same transfer can be accomplished using a diffractive sail as the primary propulsion system. The main contribution of this paper is the analysis of the spacecraft transfer trajectory using a near-optimal strategy by dividing the entire flight into an approach phase to a circular orbit of the same radius as the desired final orbit but with a smaller inclination, and a subsequent cranking phase until the desired (orbital) inclination is reached. The numerical simulations show that the proposed strategy is sufficiently simple to implement and can provide solutions that differ by only a few percentage points from the optimal results obtainable with a classical indirect approach.

On the Co-orbital Motion of Any Inclination

The co-orbital motion occurs when a celestial body (e.g. an asteroid) shares the same semimajor axis with the perturbing object (e.g. a planet), and thus they are in a 1:1 mean motion resonance. Trojan asteroids in the tadpole orbits around planets in the Solar System are these co-orbital objects. The motion and origin of some Trojan asteroids, particularly those on high-inclination orbits, are still not fully understood. In this paper, a newly developed perturbation function expansion, which is applicable to the 1:1 resonance, is used to investigate the co-orbital motion in three-dimensional space. The position of the resonance center and the resonance width are calculated for different initial orbital elements, and the relationship between the orbital types and the initial orbital elements is analyzed. The results obtained by the analytical method are compared with and verified by the results from numerical simulations. A panorama of the co-orbital motion in the wide orbital elements space is obtained.

Spectroscopy of the binary TNO Mors–Somnus with the JWST and its relationship to the cold classical and plutino subpopulations observed in the DiSCo-TNO project

Context. Trans-Neptunian objects (TNOs) are remnants of small icy bodies from planetary formation that orbit in the region beyond Neptune. Within the population of TNOs, Trans-Neptunian binaries (TNBs) provide a valuable opportunity to test the models of the formation and evolution of planetesimals in the trans-Neptunian region. Various theories have been proposed to describe the observed separations between binary components, their relative sizes, and other orbital parameters. The colors of TNOs have been used to trace the dynamical history of the outer Solar System and the colors of TNB components provide tests for formation theories. However, spectral information for the components of small TNBs, crucial information that could validate formation mechanisms, has until now remained elusive. Aims. The main goal of this work is to characterize the near-infrared spectral properties of the TNB plutino (341520) Mors–Somnus, the only TNB with resolved components in the James Webb Space Telescope (JWST) Large Cycle 1 General Observer program “DiSCo-TNOs” (PID 2418; PI: Pinilla-Alonso). The secondary goal is to use the surface compositions of the individual components of the Mors–Somnus system to probe formation and dynamical evolution in the outer Solar System through comparison to the surface properties of the cold classical and plutino (3:2 resonant) dynamical groups. Methods. To achieve these goals, we measured the spectral slope of the continuum and identified absorption bands in the individual spectra of Mors and Somnus, as well as in those of the cold classicals and plutinos obtained with the NIRSpec Integral Field Unit (IFU) and the PRISM/CLEAR disperser (0.6–5.3 μm), and compared these results to shed light on the dynamical evolution of the Mors–Somnus binary. Results. The spectra of Mors and Somnus are similar and indicate the presence of complex organic materials, CO2, CO, OH-compounds, and tentative nitrogen-rich materials. We find a high degree of compositional diversity in the plutino population, a group of TNOs that likely formed elsewhere and moved to their current orbits during the migration of Neptune, while the cold classical TNOs, which likely formed in situ, appear more homogeneous. Conclusions. The very wide separation between the components, their nearly equal sizes, and the high orbital inclination of the system suggest this plutino binary is a survivor of the primordial population of objects beyond 30 au. The similarities found between the spectral features of the plutinos Mors and Somnus and those of all of the cold classical TNOs in the DiSCo-TNOs sample as well as the high degree of compositional heterogeneity found in the plutino population provide compositional evidence for evaluation of Neptune’s migration in the trans-Neptunian region early on in the history of the Solar System.

Large constellations for fast acquisition and delivery of information: Design and analysis by stereographic projection onto the equatorial plane

SummaryRecent space projects are designed by satellite constellations with a large number of spacecraft, a global character (i.e., from equatorial to high inclination orbits), and the possibility to transfer information to different satellites of the constellation (inter satellite link) in order to deliver the information to the ground as soon as possible. To cope with a large number of parameters, a fast tool for constellation design, performance evaluation and networking strategies is needed. The aim of this paper is to obtain the performance of any constellation in less than 1 s, even when the number of satellites in the constellation and the duration of the analysis is large (e.g., more than 200 satellites in a period of some days). The proposed algorithm is based on analytical formulae obtained by using the stereographic projection on the equatorial plane of the satellite orbits and the projection of the target and ground station orbits. It is believed that the two‐dimensional projection proposed here can offer some advantages with respect to the spatial analysis of satellite orbits and their ground tracks, such as the reduction in time required to calculate station/satellite and satellite/satellite encounter conditions, and the clear and simple representation of the motion of the satellite of the constellation and of the ground stations of interest.

Hβspectroscopy of the high-inclination black hole transientSwiftJ1357.2−0933 during quiescence

SwiftJ1357.2−0933 is a transient low-mass X-ray binary hosting a stellar-mass black hole. The source exhibits optical dips and very broad emission lines during both outburst and quiescence, which are thought to be the result of a high orbital inclination. We present phase-resolved spectroscopy obtained with the 10.4 m Gran Telescopio Canarias (GTC). The spectra focus on the Hβspectral region during X-ray quiescence. The emission line is exceptionally broad (full width at half maximum,FWHM > 4000 Å), in agreement with previous studies focused on Hα. A two-Gaussian fit to the prominent double-peaked profile reveals a periodic variability in the centroid position of the line. We also produced a diagnostic diagram aimed at constraining additional orbital parameters. Together, they allow us to independently confirm the orbital period of the system using a new dataset obtained five years after the previous outburst. However, our estimates for both the systemic velocity and the radial velocity semi-amplitude of the black hole reveal larger values than those found in previous studies. We argue that this could be explained by the precession of the disc and the presence of a hotspot. We found evidence of a narrow inner core in the double-peaked Hβemission profile. We studied its evolution across the orbit, finding that it is likely to result from the occultation of inner material by the outer rim bulge, further supporting the high orbital inclination hypothesis.

Quantifying the global solar wind-magnetosphere interaction with the Solar-Terrestrial Observer for the Response of the Magnetosphere (STORM) mission concept

Much of what we know about the solar wind’s interaction with the Earth’s magnetosphere has been gained from isolated in-situ measurements by single or multiple spacecraft. Based on their observations, we know that reconnection, whether on the dayside magnetopause or deep within the Earth’s magnetotail, controls the bulk flow of solar wind energy into and through the global system and that nightside activity provides the energized particles that power geomagnetic storms. But by their very nature these isolated in-situ measurements cannot provide an instantaneous global view of the entire system or its cross-scale dynamics. To fully quantify the dynamics of the coupled solar wind-magnetosphere requires comprehensive end-to-end global imaging of the key plasma structures that comprise the magnetosphere which have spatial resolutions that exceeds anything possible with multi-point or constellation situ measurements. Global, end-to-end, imaging provides the pathway to understanding the system as a whole, its constituent parts, and its cross-scale processes on a continuous basis, as needed to quantify the flow of solar wind energy through the global magnetospheric system. This paper describes how a comprehensively-instrumented single spacecraft in a high-altitude, high-inclination orbit coupled with ground-based instruments provides the essential observations needed to track and quantify the flow of solar wind energy through the magnetosphere. This includes observations of the solar wind plasma and magnetic field input, the magnetopause location in soft X-rays, the auroral oval in far ultraviolet, the ring current in energetic neutrals, the plasmasphere in extreme ultraviolet, the exosphere in Lyman-α, and the microstructure of the nightside auroral oval from ground-based all sky cameras.

On the observed excess of large Mars-crossers in high-inclination orbits

Mars-crossing asteroids (MCAs) constitute a population of transient bodies coming from the asteroid belt that end up in the near-Earth region or are ejected hyperbolically. We analyze the dynamical evolution of a sample of 1066 MCAs with absolute magnitudes H<16 for 800 Myr. We find that the sample can be split in two groups: the high-inclination group (i≳15°) and the low-inclination group (i≲15°). Asteroids of the first group generally have much longer dynamical lifetimes than those of the latter group. We focus our attention on the largest members of the MCAs in high-i orbits which seem to be in excess relative to those of smaller sizes. We followed in particular the dynamical evolution of (132) Aethra – the largest MCA – and 9 clones for an extended period of 2 Gyr. We found that Aethra and all its clones remain in a stable orbit for the whole studied period. Despite Aethra partially crosses Mars’s orbit, no close encounters with this planet are registered (within a Hill radius) which is due to the Kozai mechanism by which the oscillations of Aethra’s perihelion distance are coupled with the precession of the argument of perihelion. Given its size, the Yarkovsky mechanism, that causes a size-dependent drift in the semimajor axis, is probably too small to drive Aethra’s semimajor axis to an unstable zone in the asteroid belt on a Gyr timescale. Long dynamical lifetimes (at least several hundreds Myr) are also found for other large MCAs (D≳10 km) in high-i orbits, which also share Aethra-like dynamics. Their long dynamical lifetimes may explain their observed excess in comparison with what would be expected from the extrapolation of the size distribution of smaller members of the population, whose dynamics may be affected by the Yarkovsky mechanism that destabilizes their orbits and shortens their lifetimes. By contrast, there are very few large MCAs in the low-i population, which suggests an insufficient replenishment rate of big bodies in low-i orbits. The time scale to shift big fragments produced in catastrophic collisions to unstable zones of the main asteroid belt by the Yarkovsky mechanism may very likely be too long in comparison with the dynamical lifetimes of low-i MCAs. The frequency of collisions of the Earth with any of the large MCAs is estimated to be of one every several hundreds Myr and it will most likely move on a low-i orbit.

Sun Sailing Polar Orbiting Telescope (SunSPOT): A solar polar imaging mission design

Although the Sun has been a focus of space-based research for several decades, there are still many open questions. One severe gap in solar physics knowledge is the lack of detailed, long-term observations of the solar polar regions to explore the origins of the Sun’s magnetism and other connected phenomena.To fill this gap, this paper presents a feasibility study of a mission concept for a solar polar orbiting imaging mission called the Sun Sailing Polar Orbiting Telescope (SunSPOT). SunSPOT utilizes a doppler magnetograph instrument to observe the polar magnetic structure and a large deployable solar sail to reach high inclination orbit. The mission concept is derived from two science objectives investigating the formation of solar active regions and the solar dynamo. These objectives are aligned with the science goals formulated by the National Research Council (NRC) in the 2013 Decadal Survey in Solar and Space Physics and their science closure is shown in the Science Traceability Matrix. The mission and spacecraft design are explained, including a cost and risk analysis, with a special focus on the requirements and risks of the solar sail propulsion system. While the solar sail presents a significant design challenge and financial risk to this and other proposed solar polar missions, it is a necessity to achieve the orbit required for closure of decadal science goals. Although originally conceived of as a Discovery-class mission fitting within a $600 M budget, the solar sail pushes the cost beyond this threshold.The work presented here is the outcome of the NASA Heliophysics Mission Design School (HMDS) 2020 hosted by the NASA Jet Propulsion Laboratory.

X-Ray Observation of the Roche-lobe-filling White Dwarf plus Hot Subdwarf System ZTF J213056.71+442046.5

ZTF J213056.71+442046.5 is the prototype of a small class of recently discovered compact binaries composed of a white dwarf and a hot subdwarf that fills its Roche lobe. Its orbital period of only 39 minutes is the shortest known for the objects in this class. Evidence for a high orbital inclination (i = 86°) and for the presence of an accretion disk has been inferred from a detailed modeling of its optical photometric and spectroscopic data. We report the results of an XMM-Newton observation carried out on 2021 January 7. ZTF J213056.71+442046.5 was clearly detected by the Optical Monitor, which showed a periodic variability in the UV band (200–400 nm), with a light curve similar to that seen at longer wavelengths. Despite accretion on the white dwarf at an estimated rate of the order of 10−9 M ⊙ yr−1, no X-rays were detected with the EPIC instrument, with a limit of ∼1030 erg s−1 on the 0.2–12 keV luminosity. We discuss possible explanations for the lack of a strong X-ray emission from this system.

Near-UV Reddening Observed in the Reflectance Spectrum of High-inclination Centaur 2012 DR30

Abstract Centaurs with high orbital inclinations and perihelia (i &gt; 60°; q ≳ 5 au) are a small group of poorly understood minor planets that are predicted to enter the giant planet region of the solar system from the inner Oort Cloud. As such, they are one of the few samples of relatively unaltered Oort Cloud material that can currently be directly observed. Here we present two new reflectance spectra of one of the largest of these objects, 2012 DR30, in order to constrain its color and surface composition. Contrary to reports that 2012 DR30 has variable optical color, we find that consistent measurements of its spectral gradient from most new and published data sets at 0.55–0.8 μm agree with a spectral gradient of S ′ ≃ 10 % ± 1 % / 0.1 μ m within their uncertainties. The spectral variability of 2012 DR30 at near-UV/blue and near-IR wavelengths, however, is still relatively unconstrained; self-consistent rotationally resolved follow-up observations are needed to characterize any spectral variation in those regions. We tentatively confirm previous detections of water ice on the surface of 2012 DR30, and we also consistently observe a steady steepening of the gradient of its spectrum from λ ∼ 0.6 μm toward near-UV wavelengths. Plausible surface materials responsible for the observed reddening may include ferric oxides contained within phyllosilicates and aromatic refractory organics.

Study on the asteroidal spin characteristics in the Hungaria region

AbstractHungaria region locates the inner edge of asteroidal main belt with the high orbital inclination and is surrounded by several resonances, in which more small asteroids (size less than 11 km) reside. We estimate the spin states for eight fast (rotation period ) rotators in this region based on the dense photometric data and discover that seven of them are in the retrograde spin state. By the analysis on the distributions of spin characteristics, 35 out of 59 Hungaria region members exhibit a tendency—their obliquities distribute in the range larger than , and especially, most of them clustering significantly in the interval of . Meanwhile, it is also noted that the Hungaria region asteroids with the fast spin (rotation period ) show more significant clustering characteristic.

Lunar cratering asymmetries with high lunar orbital obliquity and inclination of the Moon

Accurate estimation of cratering asymmetry on the Moon is crucial for understanding Moon evolution history. Early studies of cratering asymmetry have omitted the contributions of high lunar obliquity and inclination. Here, we include lunar obliquity and inclination as new controlling variables to derive the cratering rate spatial variation as a function of longitude and latitude. With examining the influence of lunar obliquity and inclination on the asteroids population encountered by the Moon, we then have derived general formulas of the cratering rate spatial variation based on the crater scaling law. Our formulas with addition of lunar obliquity and inclination can reproduce the lunar cratering rate asymmetry at the current Earth-Moon distance and predict the apex/ant-apex ratio and the pole/equator ratio of this lunar cratering rate to be 1.36 and 0.87, respectively. The apex/ant-apex ratio is decreasing as the obliquity and inclination increasing. Combining with the evolution of lunar obliquity and inclination, our model shows that the apex/ant-apex ratio does not monotonically decrease with Earth-Moon distance and hence the influences of obliquity and inclination are not negligible on evolution of apex/ant-apex ratio. This model is generalizable to other planets and moons, especially for different spin-orbit resonances.

Micro Satellite Orbital Boost by Electrodynamic Tethers.

In this manuscript, a method for maneuvering a spacecraft using electrically charged tethers is explored. The spacecraft’s velocity vector can be modified by interacting with Earth’s magnetic field. Through this method, a spacecraft can maintain an orbit indefinitely by reboosting without the constraint of limited propellant. The spacecraft-tether system dynamics in low Earth orbit are simulated to evaluate the effects of Lorentz force and torques on translational motion. With 500-meter tethers charged with a 1-amp current, a 100-kg spacecraft can gain 250 m of altitude in one orbit. By evaluating the combined effects of Lorenz force and the coupled effects of Lorentz torque propagation through Euler’s moment equation and Newton’s translational motion equations, the simulated spacecraft-tether system can orbit indefinitely at altitudes as low as 275 km. Through a rare evaluation of the nonlinear coupling of the six differential equations of motion, the one finding is that an electrodynamic tether can be used to maintain a spacecraft’s orbit height indefinitely for very low Earth orbits. However, the reboost maneuver is inefficient for high inclination orbits and has high electrical power requirement. To overcome greater aerodynamic drag at lower altitudes, longer tethers with higher power draw are required.

Designing Low-Thrust Transfers to High-Inclination Science Orbits via Hybrid Optimization

Placing a small satellite into a high-inclination orbit with respect to the ecliptic plane may offer a low-cost option for opportunistic and targeted observations of the polar regions of the Sun or the zodiacal dust cloud of the solar system. In this paper, dynamical systems theory and hybrid optimization techniques are integrated into a cohesive framework to design low-thrust trajectories for a small satellite to reach a highly out-of-ecliptic science orbit near the Sun–Earth equilibrium point. Propellant-optimal low-thrust trajectories with a specific geometry are designed and studied across a variety of engine and power models within a low-thrust-enabled circular restricted three-body problem. The geometry of the trajectories is then varied during the initial guess construction process to support a preliminary study of the tradeoff between flight time and propellant mass usage.

Evidence for Multiple Accretion Events in the Gaia-Sausage/Enceladus Structures

Abstract We present evidence that multiple accretion events are required to explain the origin of the Gaia-Sausage and Enceladus (GSE) structures, based on an analysis of dynamical properties of main-sequence stars from the Sloan Digital Sky Survey Data Release 12 and Gaia Data Release 2. GSE members are selected to have eccentricity (e) &gt; 0.7 and [Fe/H] &lt; −1.0, and separated into low and high orbital-inclination (LOI/HOI) groups. We find that the LOI stars mainly have e &lt; 0.9 and are clearly separable into two groups with prograde and retrograde motions. The LOI stars exhibit prograde motions in the inner-halo region and strong retrograde motions in the outer-halo region (OHR). We interpret the LOI stars in these regions to be stars accreted from two massive dwarf galaxies with low-inclination prograde and retrograde orbits, affected to different extents by dynamical friction due to their different orbital directions. In contrast, the majority of the HOI stars have e &gt; 0.9, and exhibit a globally symmetric distribution of rotational velocities (V ϕ ) near zero, although there is evidence for a small retrograde motion for these stars (V ϕ ∼ −15 km s−1) in the OHR. We consider these stars to be stripped from a massive dwarf galaxy on a high-inclination orbit. We also find that the LOI and HOI stars on highly eccentric and tangential orbits with clear retrograde motions exhibit different metallicity peaks at [Fe/H] = −1.7 and −1.9, respectively, and argue that they are associated with two low-mass dwarf galaxies accreted in the OHR of the Galaxy.

Launch Vehicle Rendezvous to Catalogued Orbital Debris while Injecting into Highly-Inclined Orbits

Introduction. A constant increase in the amount of space debris already constitutes a significant threat to satellites in nearEarth orbits, starting with the trajectory of their launch vehicle injection. Problem Statement. Design and development of various modern methods of protection against space debris requires knowledge of the statistical characteristics of the distribution of the kinematic parameters of the simultaneous motion of a launch vehicle injecting satellite and a group of space debris objects in the area of its trajectory. Purpose. Development of a mathematical model of a launch vehicle rendezvous with a group of observable orbital debris while injecting a satellite into near-earth orbits with an altitude of up to 2100 km and an inclination from 45 to 90 degrees. Materials and Methods. The following methods are used in the research: analysis, synthesis, comparison, simulation modeling, statistical processing of experimental results, approximation, correlation analysis, and the least squares method. Results. The simultaneous motion of a launch vehicle and a group of space debris objects has been studied. The distributions of relative distance, relative velocity, angle of encounter, and moments of time of approach of a launch vehicle to a group of the observed space debris at a relative distance of less than 5 km have been obtained. The dependence of the average rendezvous concentration on the distribution of space debris across the average altitude of the orbit and the inclination of the target orbit of the launch vehicle has been determined. The dependence of the average probability of rendezvous in the launch on the inclination of the target orbit, the number of orbital debris, and the relative distance of the rendezvous has been determined. Conclusions. The obtained mathematical model of rendezvous of a launch vehicle with a group of observed orbital debris can be used while designing means of cleaning the near-Earth space and systems to protect modern satellite launch vehicles from orbital debris. In addition, the results of the research can be used to assess the impact of unobserved orbital debris on the flight of a launch vehicle.

The obscured X-ray binaries V404 Cyg, Cyg X–3, V4641 Sgr, and GRS 1915+105

Aims. V404 Cyg, Cyg X–3, V4641 Sgr, and GRS 1915+105 are among the brightest X-ray binaries and display complex behavior in their multiwavelength emission. Except for Cyg X–3, the other three sources have large accretion disks, and there is evidence of a high orbital inclination. Therefore, any large-scale geometrical change in the accretion disk can cause local obscuration events. On the other hand, Cyg X–3 orbits its Wolf-Rayet companion star inside the heavy stellar wind obscuring the X-ray source. We study here whether the peculiar X-ray spectra observed from all four sources can be explained by local obscuration events. Methods. We used spectra obtained with the Nuclear Spectroscopic Telescope Array and Rossi X-ray Timing Explorer to study the spectral evolution of the four luminous hard X-ray sources. We fit the time-averaged spectra, and also time-resolved spectra in case of V404 Cyg, with two physically motivated models describing either a scenario where all the intrinsic emission is reprocessed in the surrounding matter or where the emitter is surrounded by a thick torus with variable opening angle. Results. We show that the X-ray spectra during specific times are very similar in all four sources, likely arising from the high-density environments where they are embedded. The fitted models suggest that a low-luminosity phase preceding an intense flaring episode in the 2015 outburst of V404 Cyg is heavily obscured, but intrinsically very bright (super-Eddington) accretion state. Similar spectral evolution to that of V404 Cyg is observed from the recent X-ray state of GRS 1915+105 that presented unusually low luminosity. The modeling results point to a geometry change in the (outflowing) obscuring matter in V404 Cyg and GRS 1915+105, which is also linked to the radio (jet) evolution. Within the framework of the models, all sources display obscured X-ray emission, but with different intrinsic luminosities ranging from lower than 1% of the Eddington luminosity up to the Eddington limit. This indicates that different factors cause the obscuration. This work highlights the importance of taking the reprocessing of the X-ray emission in the surrounding medium into account in modeling the X-ray spectra. This may well take place in other sources as well.

The violent collisional history of aqueously evolved (2) Pallas

Asteroid (2) Pallas is the largest main-belt object not yet visited by a spacecraft, making its surface geology largely unknown and limiting our understanding of its origin and collisional evolution. Previous ground-based observational campaigns returned different estimates of its bulk density that are inconsistent with one another, one measurement1 being compatible within error bars with the icy Ceres (2.16 ± 0.01 g cm−3)2 and the other3 compatible within error bars with the rocky Vesta (3.46 ± 0.03 g cm−3)4. Here we report high-angular-resolution observations of Pallas performed with the extreme adaptive optics-fed SPHERE imager5 on the Very Large Telescope. Pallas records a violent collisional history, with numerous craters larger than 30 km in diameter populating its surface and two large impact basins that could be related to a family-forming impact. Monte Carlo simulations of the collisional evolution of the main belt correlate this cratering record to the high average impact velocity of ~11.5 km s−1 on Pallas—compared with an average of ~5.8 km s−1 for the asteroid belt—induced by Pallas’s high orbital inclination (i = 34.8°) and orbital eccentricity (e = 0.23). Compositionally, Pallas’s derived bulk density of 2.89 ± 0.08 g cm−3 (1σ uncertainty) is fully compatible with a CM chondrite-like body, as suggested by its spectral reflectance in the 3 μm wavelength region6. A bright spot observed on its surface may indicate an enrichment in salts during an early phase of aqueous alteration, compatible with Pallas’s relatively high albedo of 12–17% (refs. 7,8), although alternative origins are conceivable. High-resolution observations of the third largest asteroid, (2) Pallas, from SPHERE unveil a heavily cratered surface, probably due to Pallas’s inclined and eccentric orbit, a density almost equal to carbonaceous chondrites and hint at surficial salt-enriched spots.

A Shapiro delay detection in the pulsar binary system PSR J1811–2405

ABSTRACT This paper presents the first detection of Shapiro delay from the binary millisecond pulsar PSR J1811–2405. We report a 11σ measurement of the orthometric amplitude, h3 = 6.8(6) × 10−7, and a 16σ measurement of the orthometric ratio, ς = 0.81(5). Given the relatively high orbital inclination, i = 79(2)°, of this binary system, we obtain constraints on the companion mass of $m_{\rm {c}}=0.31^{+0.08 }_{ -0.06}\, \mathrm{M}_{\odot }$. The pulsar mass is currently less well constrained, with a value of $2.0^{+0.8 }_{ -0.5}\, \mathrm{M}_{\odot }$. The companion mass and the orbital period are in agreement with the prediction made by previous numerical calculations of the evolution of compact binary systems. From a study of the polarization, we find that the orbital inclination angle is ∼100° and that PSR J1811–2405 is an orthogonal rotator. In addition, the μs-level timing precision together with its narrow profile makes PSR J1811–2405 a good candidate for inclusion in the pulsar timing arrays being used to detect nHz gravitational waves.

A detailed non-LTE analysis of LB-1: Revised parameters and surface abundances

Context. It has recently been proposed that LB-1 is a binary system at 4 kpc consisting of a B-type star of 8 M⊙ and a massive stellar black hole (BH) of 70 M⊙. This finding challenges our current theories of massive star evolution and formation of BHs at solar metallicity. Aims. Our objective is to derive the effective temperature, surface gravity, and chemical composition of the B-type component in order to determine its nature and evolutionary status and, indirectly, to constrain the mass of the BH. Methods. We use the non-LTE stellar atmosphere code FASTWIND to analyze new and archival high-resolution data. Results. We determine (Teff, log g) values of (14 000 ± 500 K, 3.50 ± 0.15 dex) that, combined with the Gaia parallax, imply a spectroscopic mass, from log g, of 3.2+2.1−1.9 M⊙ and an evolutionary mass, assuming single star evolution, of 5.2+0.3−0.6 M⊙. We determine an upper limit of 8 km s−1 for the projected rotational velocity and derive the surface abundances; we find the star to have a silicon abundance below solar, and to be significantly enhanced in nitrogen and iron and depleted in carbon and magnesium. Complementary evidence derived from a photometric extinction analysis and Gaia yields similar results for Teff and log g and a consistent distance around 2 kpc. Conclusions. We propose that the B-type star is a slightly evolved main sequence star of 3–5 M⊙ with surface abundances reminiscent of diffusion in late B/A chemically peculiar stars with low rotational velocities. There is also evidence for CN-processed material in its atmosphere. These conclusions rely critically on the distance inferred from the Gaia parallax. The goodness of fit of the Gaia astrometry also favors a high-inclination orbit. If the orbit is edge-on and the B-type star has a mass of 3–5 M⊙, the mass of the dark companion would be 4–5 M⊙, which would be easier to explain with our current stellar evolutionary models.