Orbital Parameters Research Articles

Bayesian sensitivity of binary pulsars to ultra-light dark matter

Ultra-light dark matter perturbs the orbital motion of binary pulsars, in particular by causing peculiar time variations of a binary's orbital parameters, which then induce variations in the pulses' times of arrival. Binary pulsars have therefore been shown to be promising detectors of ultra-light dark matter. To date, the sensitivity of binary pulsars to ultra-light dark matter has only been studied for dark matter masses in a narrow resonance band around a multiple of the binary pulsar orbital frequency. In this study we devise a two-step, bayesian method that enables us to compute semi-analytically the sensitivity for all masses, also away from the resonance, and to combine several observed binaries into one global sensitivity curve. We then apply our method to the case of a universal, linearly-coupled, scalar ultra-light dark matter. We find that with next-generation radio observatories the sensitivity to the ultra-light dark matter coupling will surpass that of Solar-System constraints for a decade in mass around \(m eV \), even beyond resonance.

Neutron emission from a source moving in a gravitational field

This work is devoted to the problem of neutron field formation near elliptical orbits of space objects equipped with nuclear power plants. The high-energy part of the fission spectrum is not affected by the gravitational field. Radiation safety is ensured by the triad fair for a point source: activity-distance-time. The connection between space object orbit parameters and neutron flux density occurs for the thermal (near-thermal) part of the spectrum. The possibility of formation of a stable neutron trace in the volume of a «torus» around the orbit of a space object is considered. The paper presents theoretical and numerical evidence of the validity of the hypothesis put forward. The introduction considers the separation effect of Galileo's relativity principle in the case of rectilinear uniform motion of a point isotropic neutron source on a plane. The occurrence of angular asymmetry of the neutron distribution in a stationary coordinate system when their relative velocity is close to the transport velocity of the source is illustrated. Under these conditions, a significant velocity dispersion of initially monochromatic neutrons is also recorded. This expected fundamental kinematic effect determines the characteristic distribution of neutrons in the gravitational field when the source moves along the Kepler orbit. The solution of the problem is carried out in the velocity space. It is argued that if the distribution of neutrons in the velocity space is such that their velocities are collinear to the orbital velocity of the source, this indicates the existence of a neutron flux near the orbit. The problem is analysed on the example of one revolution of a hypothetical space station by simulation modelling. For this purpose, thermal neutron packets with isotropic angular distribution were generated at eight points of an elliptical orbit. The neutron and source velocity fluxes at the selected points of the orbit were compared in a coordinate system related to the earth. The obtained data made it possible to calculate the densities of neutron velocity fluxes to the front and rear hemispheres relative to the source orbital motion as a function of the polar angle, while the value of the determinant of the correlation matrix – an indicator of collinearity of neutron velocity vectors in the flux - was fixed. The results of the studies confirm the hypothesis put forward about the possibility of formation of a «trace» in the orbit of a thermal neutron source, which determines the need to take it into account as a significant component of radiation risk.

Helium in Exoplanet Exospheres: Orbital and Stellar Influences

Searches for helium in the exospheres of exoplanets via the metastable near-infrared triplet have yielded 17 detections and 40 nondetections. We performed a comprehensive reanalysis of published studies to investigate the influence of stellar X-ray and extreme-ultraviolet (XUV) flux and orbital parameters on the detectability of helium in exoplanetary atmospheres. We identified a distinct “orbital sweet spot” for helium detection, 0.03 to 0.08 au from the host star, where the majority of detections occurred. This sweet spot is influenced by the stellar luminosity and planet size. Notably, a lower ratio of XUV flux to mid-UV flux is preferred for planets compared to nondetections. We also found that helium detections occur for planets around stars with effective temperatures of 4400–6500 K (i.e., spectral type K and G stars), with a sharp gap between 5400 and 6000 K, where no detections occur. We also report an upper-limit efficiency of 6% for energy-limited atmospheric escape from our analysis. Additionally, our analysis of the cumulative XUV flux versus escape velocity shows planets with helium detections above the “cosmic shoreline,” where atmospheres are not thought to be present, suggesting the shoreline needs revision. The unexpected trends revealed in our meta-analysis can contribute to a better understanding of star–planet interaction and exosphere evolution.

The possible origin of three Apollo asteroids. 3200 Phaethon, 2005UD, and 1999YC

We study the possible dynamical background of three Apollo asteroids: 3200 Phaethon, 2005 UD, and 1999 YC. The source regions under consideration are the asteroid families (2) Pallas, in the outer belt, and two inner-belt families (329) Svea and (142) Polana. We also aim to explain some of the contradictions in the literature in regards to the origin of Phaethon. Our methodology relies on the precise dynamical mapping of several mean motion resonances (MMRs), which are considered the main transport channels. This approach allows the clear detection of chaotic structures in an MMR and efficent selection of test asteroids for diffusion. We tracked the orbital evolution of the selected particles over 5 million years and registered all their eventual entries into the orbital neighborhood of the asteroids 3200 Phaethon, 2005 UD and 1999 YC. We performed massive calculations for different orbital and integration parameters using Orbit9 and Rebound software packages. We observed possible connections between three targeted Apollo asteroids and asteroid families we considered as their sources. The (2) Pallas family has the highest chance of being the origin of targeted asteroids, and (142) Polana has the lowest. The amount of transported material largely depends on the integrator, the integration step, and even the choice of the initial epoch, though to a lesser extent. There is a systematic discrepancy between the results obtained with Orbit9 and Rebound regarding the efficiency of the transport, but they show good agreement over delivery times and dynamical maps. A non-negligible number of objects approached all three target asteroids, which could indicate that the breakup of the precursor body occurred during its dynamical evolution.

Estimation of orbital parameters from [formula omitted]-coverage for a space radio interferometer

Searching for a suitable very long baseline (VLBI) interferometer geometry is a key task in planning observations, especially imaging sessions. VLBI image quality is characterized by (u,v)-coverage. With one or more radio telescopes located in space, such a task becomes more complex. This paper presents a method of recovering the optimal orbital parameters for space radio telescopes having a given desired (u,v)-coverage. In turn, this task can be called the inverse of the task of searching for the optimal geometry and orbital configurations of space-ground and pure space VLBI interferometers.

Verification of Astrometrically Accelerating Stars from Hipparcos and Gaia. I. Methodology and Application to HIP 44842

A large number of candidate binary stars with apparent acceleration on the sky has emerged from analysis of astrometric data collected by the Hipparcos, Tycho-2, and Gaia space missions. Although the apparent acceleration can serve as a relatively reliable indicator of binarity, it provides scarce information about the orbital and physical parameters of the components. With an emphasis on the search for stellar-mass black holes and neutron stars hidden in binary systems, we start a broader effort to characterize the most promising candidates using follow-up ground-based observations. Accurate quantification of orbital and physical parameters of systems with dim or invisible companions requires combination of Hipparcos, Gaia, and precision spectroscopic measurements. In this paper, we review the necessary steps in this implementation and describe the improved Hipparcos–Gaia sample of long-term astrometric accelerations, which includes correction of sky-correlated systematic errors using the vector spherical decomposition method. As an example, we study one Hipparcos star with a large acceleration, HIP 44842, where the companion is revealed to be a normal main-sequence star.

Expected evolution of the binary system PTF J2238+743015.1

Binary systems harboring a low-mass CO WD and a He-rich donor are considered to be the possible progenitors of explosive events via He detonation, producing low-luminosity thermonuclear supernovae with a peculiar nucleosynthetic pattern. Recently, the binary system PTF J223857.11+743015.1 was proposed as a candidate for this kind of stars. We investigate the evolution of the PTF J223857.11+743015.1 system, which is composed of a 0.75\ CO WD and a 0.390\ subdwarf. We consider the rotation of the WD component. Using the FuNS code, we computed the evolution of the two stars simultaneously, taking into account the possible evolution of the orbital parameters, as determined by mass transfer between the components and by mass ejection from the system during episodes of Roche lobe overflow. We consider that the WD gains angular momentum due to accretion and we followed the evolution of the angular velocity profile as determined by angular momentum transport via convection and rotation-induced instabilities. As the donor H-rich envelope is transferred, the WD experiences recurrent very strong H-flashes triggering Roche lobe overflow episodes during which the entirety of the accreted matter is lost from the system. Due to mixing of chemicals by rotation-induced instabilities during the accretion phase, H-flashes occur inside the original WD. Hence, pulse by pulse, the mass of the accretor is reduced down to 0.7453\ Afterwards, when He-rich matter is transferred, He detonation does not occur in the rotating WD, which undergoes six very strong He-flashes and subsequent mass-loss episodes. Also in this case, due to rotation-induced mixing of the accreted layers with the underlying core, the WD is eroded. Later, as the mass-transfer rate from the donor decreases, a massive He buffer is piled up onto the accretor, which ends its life as a cooling WD. The binary system PTF J2238+743015.1 and all other binary systems with components of similar masses and similar orbital parameters are not good candidates as thermonuclear explosion progenitors.

New estimation of critical insolation–CO2 relationship for triggering glacial inception

Abstract. It has been previously proposed that glacial inception represents a bifurcation transition between interglacial and glacial states and is governed by the nonlinear dynamics of the climate–cryosphere system. To trigger glacial inception, the orbital forcing (defined as the maximum of summer insolation at 65° N and determined by Earth’s orbital parameters) must be lower than a critical level, which depends on the atmospheric CO2 concentration. While paleoclimatic data do not provide a strong constraint on the dependence between CO2 and critical insolation, its accurate estimation is of fundamental importance for predicting future glaciations and the effect that anthropogenic CO2 emissions might have on them. In this study, we use the novel Earth system model of intermediate complexity CLIMBER-X with interactive ice sheets to produce a new estimation of the critical insolation–CO2 relationship for triggering glacial inception. We perform a series of experiments in which different combinations of orbital forcing and atmospheric CO2 concentration are maintained constant in time. We analyze for which combinations of orbital forcing and CO2 glacial inception occurs and trace the critical relationship between them, separating conditions under which glacial inception is possible from those where glacial inception is not materialized. We also provide a theoretical foundation for the proposed critical insolation–CO2 relation. We find that the use of the maximum summer insolation at 65° N as a single metric for orbital forcing is adequate for tracing the glacial inception bifurcation. Moreover, we find that the temporal and spatial patterns of ice sheet growth during glacial inception are not always the same but depend on the critical insolation and CO2 level. The experiments evidence the fact that during glacial inception, ice sheets grow mostly in North America, and only under low CO2 conditions are ice sheets also formed over Scandinavia. The latter is associated with a weak Atlantic Meridional Overturning Circulation (AMOC) for low CO2. We find that the strength of AMOC also affects the rate of ice sheet growth during glacial inception.

Orbital evolution of LIGO/Virgo binaries in stellar clusters driven by cluster tides, stellar encounters, and general relativity

ABSTRACT Origin of LIGO/Virgo gravitational wave events may involve production of binaries with relativistic components in dense stellar systems – globular or nuclear star clusters – and their subsequent evolution towards merger. Orbital parameters of these binaries (the inner orbit) and their motion inside the cluster (the outer orbit) evolve due to both external agents – random encounters with cluster stars and cluster tides due to the smooth cluster potential – and the internal ones – various sources of dissipation and precession within the binary. We present a numerical framework – binary evolution in stellar clusters (besc) – that follows the evolution of the binary inner and outer orbits accounting for all these effects simultaneously, enabling efficient Monte Carlo studies. The secular effect of cluster tides is computed in the singly averaged approximation, without averaging over the outer binary orbit. As to stellar encounters, we include the effects of both close and distant flybys on the inner and outer orbits of the binary, respectively. Also, given our focus on the LIGO/Virgo sources, we include the general relativistic precession (which suppresses cluster tides at high eccentricities) and the gravitational wave emission (shrinking the binary orbit). We use besc to illustrate a number of characteristic binary evolutionary outcomes and discuss relative contributions of different physical processes. In particular, we find that stellar encounters often dominate over the cluster tides in the evolution of compact binaries. besc can also be used to study other objects in clusters, e.g. blue stragglers, hot Jupiters, X-ray binaries, etc.

Orbital variability of polarized X-ray radiation reflected from a companion star in X-ray binaries

The reflection of X-ray radiation produced near a compact object from its stellar companion contributes to the orbital variability of polarization in X-ray binaries. The X-rays are reflected mainly via Thomson scattering resulting in a high polarization. The orbital variability of the polarization strongly depends on the inclination and the orbital parameters allowing us to constrain them. To explore this phenomenon, we present analytical single-scattering models for the polarized reflection. We find that while diluted by the direct emission, the reflection can produce a polarization degree of about 1<!PCT!> in the case of a large reflection albedo. We fitted the orbital variations of the X-ray polarization observed by the Imaging X-ray Polarimetry Explorer from an accreting weakly magnetized neutron star "clocked burster" GS 1826$-$238 and found that the amplitude of the variations is too large to be primarily caused by the companion star. The polarized reflection is more significant if the compact object is obscured from the observer, and thus it should be more easily observable in certain high-inclination targets.

TOI-2374 b and TOI-3071 b: two metal-rich sub-Saturns well within the Neptunian desert

ABSTRACT We report the discovery of two transiting planets detected by the Transiting Exoplanet Survey Satellite (TESS), TOI-2374 b and TOI-3071 b, orbiting a K5V and an F8V star, respectively, with periods of 4.31 and 1.27 d, respectively. We confirm and characterize these two planets with a variety of ground-based and follow-up observations, including photometry, precise radial velocity monitoring and high-resolution imaging. The planetary and orbital parameters were derived from a joint analysis of the radial velocities and photometric data. We found that the two planets have masses of (57 ± 4) M⊕ or (0.18 ± 0.01) MJ, and (68 ± 4) M⊕ or (0.21 ± 0.01) MJ, respectively, and they have radii of (6.8 ± 0.3) R⊕ or (0.61 ± 0.03) RJ and (7.2 ± 0.5) R⊕ or (0.64 ± 0.05) RJ, respectively. These parameters correspond to sub-Saturns within the Neptunian desert, both planets being hot and highly irradiated, with Teq ≈ 745 K and Teq ≈ 1812 K, respectively, assuming a Bond albedo of 0.5. TOI-3071 b has the hottest equilibrium temperature of all known planets with masses between 10 and 300 M⊕ and radii less than 1.5 RJ. By applying gas giant evolution models we found that both planets, especially TOI-3071 b, are very metal-rich. This challenges standard formation models which generally predict lower heavy-element masses for planets with similar characteristics. We studied the evolution of the planets’ atmospheres under photoevaporation and concluded that both are stable against evaporation due to their large masses and likely high metallicities in their gaseous envelopes.

Initial orbit determination via artificial intelligence for too-short arcs

In the framework of Space Traffic Management (STM) the growing number of space debris and the consequent increased risk of collisions have become a topic of great interest. Moreover, the difficulty of detecting and characterizing a Resident Space Object (RSO) in terms of orbital parameters makes this research field very challenging. In most cases the available observations have a very short duration and an accurate estimation of the orbit is very difficult. This paper introduces the Initial Orbit Determination via Artificial intelligence (IODA) algorithm, a reliable and accurate orbit estimator combining metaheuristic and artificial intelligence frameworks to perform precise orbit determination from Very Short Arcs (VSAs). Starting from an initial orbit estimate derived through an Artificial Bee Colony (ABC) algorithm, a Physics Informed Extreme Learning Machine is employed to increase the accuracy of the predicted orbit. Results on simulated data have shown the robustness of the algorithm to random parameters initialization and a percentage of success of 89% of retrieving the reference orbit with an error under 1 km and 0.01 km/s on the initial target’s state.

The CARMENES search for exoplanets around M dwarfs. Revisiting the GJ 581 multi-planetary system with new Doppler measurements from CARMENES, HARPS, and HIRES

GJ\,581 is a nearby M dwarf known to host a packed multiple planet system composed of two super-Earths and a Neptune-mass planet. We present new orbital analyses of the GJ\,581 system, utilizing recent radial velocity (RV) data obtained from the CARMENES spectrograph combined with newly reprocessed archival data from the HARPS and HIRES spectrographs. Our aim was to analyze the post-discovery spectroscopic data of GJ\,581, which were obtained with CARMENES. In addition, we used publicly available HIRES and HARPS spectroscopic data to seek evidence of the known and disputed exoplanets in this system. We aimed to investigate the stellar activity of GJ\,581 and update the planetary system's orbital parameters using state-of-the-art numerical models and techniques. We performed a periodogram analysis of the available precise CARMENES, HIRES, and HARPS RVs and of stellar activity indicators. We conducted detailed orbital analyses by testing various orbital configurations consistent with the RV data. We studied the posterior probability distribution of the parameters fit to the data and we explored the long-term stability and overall orbital dynamics of the GJ\,581 system. We refined the orbital parameters of the GJ\,581 system using the most precise and complete set of Doppler data available. Consistent with the existing literature, our analysis confirms that the system is unequivocally composed of only three planets detectable in the present data, dismissing the putative planet GJ\,581\,d as an artifact of stellar activity. Our N-body fit reveals that the system's inclination is $i = $\,deg, which implies that the planets could be up to 30<!PCT!> more massive than their previously reported minimum masses. Furthermore, we report that the GJ\,581 system exhibits long-term stability, as indicated by the posterior probability distribution, characterized by secular dynamical interactions without the involvement of mean motion resonances.

Two-dimensional Eclipse Mapping of the Hot-Jupiter WASP-43b with JWST MIRI/LRS

We present eclipse maps of the two-dimensional thermal emission from the dayside of the hot-Jupiter WASP-43b, derived from an observation of a phase curve with the JWST MIRI/LRS instrument. The observed eclipse shapes deviate significantly from those expected for a planet emitting uniformly over its surface. We fit a map to this deviation, constructed from spherical harmonics up to order ℓmax=2 , alongside the planetary, orbital, stellar, and systematic parameters. This yields a map with a meridionally averaged eastward hot-spot shift of (7.75 ± 0.36)°, with no significant degeneracy between the map and the additional parameters. We show the latitudinal and longitudinal contributions of the dayside emission structure to the eclipse shape, finding a latitudinal signal of ∼200 ppm and a longitudinal signal of ∼250 ppm. To investigate the sensitivity of the map to the method, we fix the parameters not used for mapping and derive an “eigenmap” fitted with an optimized number of orthogonal phase curves, which yields a similar map to the ℓmax=2 map. We also fit a map up to ℓmax=3 , which shows a smaller hot-spot shift, with a larger uncertainty. These maps are similar to those produced by atmospheric simulations. We conclude that there is a significant mapping signal which constrains the spherical harmonic components of our model up to ℓmax=2 . Alternative mapping models may derive different structures with smaller-scale features; we suggest that further observations of WASP-43b and other planets will drive the development of more robust methods and more accurate maps.

Investigation of different strategies for access to space of small satellites on a defined LEO orbit

In recent years small satellites have shifted from being secondary items to dominate the space market thanks to, but not only, the development of the large LEO constellations. For small satellites to be highly effective, particularly when arranged in such constellations, each satellite has to be placed in a specific orbital plane and orbital position.Currently, three main options are available to reach a specific orbit. The first, more straightforward solution is to employ a dedicated launch with a small launch vehicle. Plenty of small launchers are in development around the world (with few already operational); however, their cost per kilogram is predicted to be much higher than for large launchers. The second possibility is the exploitation of a rideshare option, where the satellite is transported by a large launcher together with other payloads on a general predetermined orbit. Afterwards the satellite needs to be transferred to its designed orbit. This can be done in two ways: through the use of a satellite carrier (also called self-propelled dispenser) or with the satellite own propulsion system. In both last cases, the mass transported by the launcher into the release orbit is higher than the final one necessary for the nominal mission, impacting total costs.In this paper these three possibilities are compared considering the need to reach various specific orbits, starting from a different release one in the case of the rideshare options. First of all, the change in velocity for different orbital parameters (altitude, eccentricity, phase, argument of perigee, inclination, RAAN) is computed. Afterwards the propulsion mass budget is calculated.Everything else being equal, it is demonstrated mathematically that a dispenser is inherently less efficient than a group of autonomous satellites, particularly for the RAAN change and a large number of carried satellites. However, it is not always possible or convenient to provide small satellites, particularly the smallest ones (nanosats/cubesats/microsats) with comparable propulsion capabilities of a larger dispenser, making the latter still an attractive option in several situations. A cost analysis also shows that, particularly for sophisticated small satellites, when the final orbit is far from the release one, a dedicated small launch vehicle can be cost competitive with the nominally much cheaper large launcher.

Mapping Lava Flows on Venus Using SAR and InSAR: Hawaiʻi Case Study

AbstractWe explore the potential for repeat‐pass SAR Interferometry (InSAR) correlation to track volcanic activity on Venus' surface motivated by future SAR missions to Earth's sister planet. We use Hawai'i as a natural laboratory to test whether InSAR can detect lava flows assuming orbital and instrument parameters similar to that of a Venus mission. Hawai'i was chosen because lava flows are frequent, and well documented by the United States Geological Survey, and because Hawai'i is a SAR supersite, where space agencies have offered open radar data sets for analysis. These data sets have different wavelengths (L, C, and X bands), bandwidths, polarizations, look angles, and a variety of orbital baselines, giving opportunity to assess the suitability of parameters for detecting lava flows. We analyze data from ALOS‐2 (L‐band), Sentinel‐1 (C‐band), and COSMO‐SkyMed (X‐band) spanning 2018 and 2022. We perform SAR amplitude and InSAR correlation analysis over temporal baselines and perpendicular baselines similar to those of a Venus mission. Fresh lava flows create a sharp, noticeable decrease in InSAR correlation that persists indefinitely for images spanning the event. The same lava flows are not always visible in the corresponding amplitude images. Moreover, noticeable decorrelation persists in image pairs acquired months after the events due to post‐emplacement contraction of flows. Post‐emplacement effects are hypothesized to last longer on the Venusian surface, increasing the likelihood of detecting Venus lava flows using InSAR. We argue for further focus on repeat‐pass InSAR capabilities in upcoming Venus missions, to detect and quantify volcanic activity on Earth's hotter twin.

Properties of Galactic B[e] Supergiants. X. Refined Orbit and Fundamental Parameters of the HD 327083 Binary System

HD 327083 is a binary system that consists of two supergiant components and exhibits the B[e] phenomenon. In this paper, we report the determination of a new set of the system’s fundamental parameters using a combination of photometric and spectroscopic data as well as the Gaia EDR3 distance. We found that the orbital period of the system is 107.68 ± 0.02 days. The spectral line content implies the effective temperatures of ≈7000 K and 25,400 ± 1400 K, while the photometric variations are consistent with the radii of ≈106 R ⊙ and ≈10 R ⊙ for the cool and hot components, respectively. The absorption lines of the cool component show a radial velocity semiamplitude of 48.3 ± 1.7 km s−1, similar to that of the emission lines that originate around the hot component. The inclination of the system to the line of sight is 47−20+17 °. Modeling of the system's evolutionary history suggests that the components have masses of ∼12.5 M ⊙ and currently undergo mass transfer between them. This configuration, which takes in heating of the surface of the cool component by the radiation from the hot one, can reproduce the photometric and spectroscopic data and is in agreement with previous infrared observations of the circumbinary disk. The results of this study further confirm the hypothesis that the reason for the presence of the B[e] phenomenon in most objects is a consequence of the evolution of various binary systems.

Predicting Deep Moonquake Source Regions Using Their Temporal and Spatial Patterns and Machine Learning

AbstractIn the near future, lunar exploration should be enhanced by deploying a new seismic station on the farside of the Moon, the Farside Seismic Suite (FSS), a package of two seismometers recently selected by NASA to fly on a commercial lander. The new data should provide us with new insights into Moon's seismic activity, its interior, and composition. To fully benefit from the new data, we need to take advantage of the data acquired during the Apollo missions. The problem of relating new and old data is complex due to the single‐station nature of the future deployment. In this study, we tackle this issue by developing a machine learning model in the context of the deep moonquake (DMQ) classification problem. The DMQs form the largest group of detected events from Apollo data, and their source regions have been located and are known to exhibit temporal and spatial patterns connected with the monthly lunar tidal periods. Therefore, we propose to utilize a machine learning (ML) algorithm named random forest to identify DMQs source regions without using waveform information and only using the lunar orbital parameters related to DMQs time occurrences. We show that ML models perform well (with an accuracy >70%) when they are trained to classify 4 or fewer different source regions. This approach gives us a good first location approximation of the DMQs source regions and opens up a new approach to their location estimate when captured by the future FSS single‐station seismometers.

Non-evolutionary effects on period change in Magellanic Cepheids

Context. Period change studies offer a novel way to probe the evolution and dynamics of Cepheids. While evolutionary period changes have been well studied both observationally and theoretically, non-evolutionary period changes lack a systematic and quantitative description. Here, we deal with one such aspect of non-evolutionary period changes related to a crucial property, namely, the binarity-based nature of a Cepheid. With the advent of long-term photometry surveys covering Magellanic fields, the census of classical Cepheids in binary (or multiple) systems outside the Milky Way is timely. This may have implications for crucial aspects such as the period-luminosity relationship calibrations and our understanding of the nature of Cepheid companions. Aims. The overall objective is to have a quantitative understanding of the full picture of non-evolutionary period changes in Cepheids to develop a formalism to disentangle it from the secular evolutionary period change. In the first paper in the series, we aim to conduct a systematic search for non-evolutionary period changes to look for Cepheids in likely binary configurations and quantify their incidence rates in the Magellanic Clouds. Methods. We collected more than a decade-long time-series photometry from the publicly available, Optical Gravitational Lensing Experiment (OGLE) survey, with more than 7200 Cepheids altogether from the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC). Our sample contains both fundamental-mode and first-overtone mode Cepheids. Then, we calculate d the observed minus calculated (O–C) diagrams to reveal the light-travel time effect (LTTE). Finally, we calculated the minimum companion masses of the Cepheids and compared them with the predictions from Cepheid population synthesis results. Results. In our search, out of an overall sample of more than 7200 Cepheids, we found 52 candidate Cepheid binary systems in the LMC (30 fundamental and 22 first-overtone mode) and 145 in the SMC (85 fundamental and 60 first-overtone mode). The majority of the sample is characterized by orbital periods of 2000–4000 d and eccentricities of 0.2–0.5. Moreover, we report two candidates in each galaxy with the Cepheid likely existing with a giant companion. The incidence rate ratio for SMC to LMC calculated from our sample is in agreement with binary Cepheid population synthesis predictions. Conclusions. In our attempt to quantify the non-evolutionary period change connected with the LTTE, our systematic search has enriched the Cepheid binary sample by a factor of about 2 in both galaxies. The future spectroscopic follow-up can confirm the binarity nature of our sample and constrain the orbital parameters.

Enabling efficient satellite mission design with rule-based collision avoidance

The growing number of operational spacecraft in Earth's orbit entails an increasing operational effort for collision avoidance (COLA), particularly regarding the coordination of evasive measures. To reduce the associated workload, COLA operations should already be considered in the early planning phases of space missions. The Mission Analysis Software (MAS) is a web-based application developed within the ESA-funded CASCADE (Collision avoidance, satellite coordination assessment demonstration environment) project by OKAPI:Orbits and TU Darmstadt for this purpose. The software follows a data-driven approach to offer satellite operators, mission designers, service providers, agencies, and authorities two services: conjunction assessment and rule analysis. The conjunction assessment provides an estimation of the number and type of conjunctions to be expected on the targeted orbit and identifies frequently conjuncting parties for the current population of active satellites as well as for conceivable future scenarios. The rule analysis follows a rule-based approach to coordinate COLA between individual operators, allowing users to build custom hierarchical rule sets from pre-defined rule building blocks to achieve a desired split of effort between the conjunction parties. The MAS enables the assessment of the operational consequences for a chosen rule set, empowering users to reach bilateral agreements with identified frequently conjuncting parties to determine the obligation to take evasive measures for future conjunctions. The approach of the MAS allows for the pre-emptive reduction of the expected number of conjunctions enabling operators to optimize orbit parameters within their mission constraints as well as the automatization of COLA coordination during operations. Through this, the MAS optimizes propellant needs, mission time, and required workforce associated with COLA for space missions.This paper presents the MAS, showcasing the key features and use cases that have been developed closely with stakeholders and the European Space Agency. Furthermore, the data-based simulation approach of the MAS will be explained, covering the data sources and design choices for the conjunction detection and propagation module. The paper also presents the results of a preliminary rule analysis conducted for the population of active satellites in low Earth orbit as of April 2023. As an intermediate result of an on-going research activity involving the authoring entities, a major goal of this paper is to engage with satellite operators, mission designers, service providers, agencies, and authorities in order to tailor the results of the activity to their actual needs.