Target Stars Research Articles

Exoplanets across galactic stellar populations with PLATO. Estimating exoplanet yields around FGK stars for the thin disk, thick disk, and stellar halo

The vast majority of exoplanet discoveries to date have occurred around stars in the solar neighbourhood, with chemical compositions comparable to that of the Sun. However, models suggest that planetary systems in different Galactic environments, with varying dynamical histories and chemical abundances, may exhibit distinct characteristics, which can help improve our understanding of planet formation processes. This study aims to assess the potential of the upcoming PLATO mission to investigate exoplanet populations around stars in diverse Galactic environments, specifically focusing on the Milky Way thin disk, thick disk, and stellar halo. We aim to quantify PLATO's ability to detect planets in each environment and determine how these observations could constrain planet formation models. Beginning with the all-sky PLATO Input Catalogue, we kinematically classified the 2.4 million FGK stars into their respective Galactic components. For the sub-sample of stars in the long-observation LOPS2 and LOPN1 PLATO fields, we estimated planet occurrence rates using the New Generation Planet Population Synthesis (NGPPS) dataset. Combining these estimates with a PLATO detection efficiency model, we predicted the expected planet yields for each Galactic environment during a nominal 2+2 year mission. Based on our analysis, PLATO is likely to detect at least 400 exoplanets around the alpha -enriched thick disk stars. The majority of those planets are expected to be super-Earths and sub-Neptunes with radii between 2 and 10 $R_ and orbital periods between 2 and 50 days, which is ideal for studying the link between the radius valley and stellar chemistry. For the metal-poor halo, PLATO is likely to detect between 1 and 80 planets with periods between 10 and 50 days, depending on the potential existence of a metallicity threshold for planet formation. The PLATO fields contain more than 3,400 potential target stars with Fe/H < -0.6, which will help improve our understanding of planets around metal-poor stars. We identified a specific target list of 47 (kinematically classified) halo stars in the high-priority, high-signal-to-noise PLATO P1 sample, offering prime opportunities in the search for planets in metal-poor environments. PLATO's unique capabilities and large field of view position it as a valuable tool for studying planet formation across the diverse Galactic environments of the Milky Way. By probing exoplanet populations around stars with a varying chemical composition, PLATO will provide helpful insights into the connection between stellar chemistry and planet formation.

X-Shooting ULLYSES: Massive stars at low metallicity. VI. Atmosphere and mass-loss properties of O-type giants in the Small Magellanic Cloud

Mass loss through a stellar wind is an important physical process that steers the evolution of massive stars and controls the properties of their end-of-life products, such as the supernova type and the mass of compact remnants. To probe its role in stellar evolution over cosmic time, mass loss needs to be studied as function of metallicity. For mass loss to be accurately quantified, the wind structure needs to be established jointly with the characteristics of small-scale inhomogeneities in the outflow, which are known as wind clumping. We aim to improve empirical estimates of mass loss and wind clumping for hot main-sequence massive stars, study the dependence of both properties on the metal content, and compare the theoretical predictions of mass loss as a function of metallicity to our findings. Using the model atmosphere code Fastwind and the genetic algorithm fitting method Kiwi-GA we analyzed the optical and ultraviolet spectra of 13 O-type giant to supergiant stars in the Small Magellanic Cloud galaxy, which has a metallicity of approximately one-fifth of that of the Sun. We quantified the stellar global outflow properties, such as the mass-loss rate and terminal wind velocity, and the wind clumping properties. To probe the role of metallicity, our findings were compared to studies of Galactic and Large Magellanic Cloud samples that were analyzed with similar methods, including the description of clumping. We find significant variations in the wind clumping properties of the target stars, with clumping starting at flow velocities $0.01 - 0.23$ of the terminal wind velocity and reaching clumping factors $f_ cl = 2 - 30$. In the luminosity ($ L / odot = 5.0 - 6.0$) and metallicity ($Z/Z_ odot = 0.2 - 1$) range we considered, we find that the scaling of the mass loss $ M $ with metallicity $Z$ varies with luminosity. At $ odot = 5.75$, we find $ M Z^m$ with $m = 1.02 0.30$, in agreement with pioneering work in the field within the uncertainties. For lower luminosities, however, we obtain a significantly steeper scaling of $m > 2$. The monotonically decreasing $m(L)$ behavior adds a complexity to the functional description of the mass-loss rate of hot massive stars. Although the trend is present in the predictions, it is much weaker than we found here. However, the luminosity range for which $m$ is significantly larger than previously assumed (at $ odot 5.4$) is still poorly explored, and more studies are needed to thoroughly map the empirical behavior, in particular, at Galactic metallicity.

X-Ray Emission of Nearby Low-mass and Sunlike Stars with Directly Imageable Habitable Zones

Stellar X-ray and UV radiation can significantly affect the survival, composition, and long-term evolution of the atmospheres of planets in or near their host star’s habitable zone (HZ). Especially interesting are planetary systems in the solar neighborhood that may host temperate and potentially habitable surface conditions, which may be analyzed by future ground- and space-based direct-imaging surveys for signatures of habitability and life. To advance our understanding of the radiation environment in these systems, we leverage ∼3 Ms of XMM-Newton and Chandra observations in order to measure three fundamental stellar properties at X-ray energies for 57 nearby FGKM stellar systems: the shape of the stellar X-ray spectrum, the luminosity, and the timescales over which the stars vary (e.g., due to flares). These systems possess HZs that will be directly imageable to next-generation telescopes such as the Habitable Worlds Observatory and ground-based Extremely Large Telescopes. We identify 29 stellar systems with L X/L bol ratios similar to (or less than) that of the Sun; any potential planets in the HZs of these stars therefore reside in present-day X-ray radiation environments similar to (or less hostile than) modern Earth, though a broader set of these targets could host habitable planets. An additional 19 stellar systems have been observed with the Swift X-ray Telescope; in total, only ∼30% of potential direct imaging target stars has been observed with XMM-Newton, Chandra, or Swift. The data products from this work (X-ray light curves and spectra) are available via a public Zenodo repository (doi:10.5281/zenodo.11490574).

Analyzing Stellar Spectra for PRV by Accurate Modeling and Retrieval of Telluric Absorption Features

Ground-based Precision Radial Velocity (PRV) measurements are inevitably impeded by contamination from telluric absorption features, particularly in the infrared region. Thus, it is crucial to improve modeling of the telluric absorption features down to the spectral noise level. As part of the efforts towards improved PRV measurements, we have taken an existing atmospheric trace gas retrieval algorithm (GFIT) and have successfully adapted it to fit the telluric absorption features in stellar spectra down to the spectral noise level (typically ∼1%). We have established a stellar spectral fitting processing pipeline, Stellar-GFIT, to analyze a series of stellar spectra observed by two spectrographs, PARVI (1.1–1.76 μm) commissioned at the Palomar Observatory (Palomar Mountain, CA) and iSHELL (1–5 μm) deployed on the IRTF (Mauna Kea, HI). For this, we have (1) implemented a Gaussian instrumental line shape function, (2) generated atmospheric models (consisting of temperature, pressure, and volume mixing ratios of all the known trace gases) for the particular observation sites and times, (3) employed the most up-to-date spectroscopic parameters in the target spectral regions, and finally (4) developed a series of spectral fitting intervals of ∼60 cm−1 width, i.e., micro-windows, customized to the individual orders of each spectrograph. Stellar-GFIT is also capable of handling non-telluric features, such as transitions from a gas cell placed in the starlight beam and stellar features if a model spectrum template is available for the target star. We present spectrum fits from the observations of various target stars and discuss the performance and advantages of our novel approach. One of the major strengths of Stellar-GFIT is an ability to adjust the abundance of atmospheric trace gases simultaneously with determining the stellar doppler shift, mitigating any adverse impacts of short-timescale variations of water vapor.

Closeby Habitable Exoplanet Survey (CHES). II. An Observation Strategy for the Target Stars

The Closeby Habitable Exoplanet Survey (CHES) constitutes a mission intricately designed to systematically survey approximately 100 solar-type stars located within the immediate proximity of the solar system, specifically within a range of 10 pc. The core objective of this mission is the detection and characterization of potentially habitable Earth-like planets or super-Earths within the habitable zone of these stars. The CHES mission obtains high-precision astrometric measurements of planets orbiting the target stars by observing angular distance variations between the target star and reference stars. As a result, we surveyed the relevant parameters of both target and reference stars in detail, conducting a thorough analysis and calculation of the required observation accuracy, the number of observations, and the priority assigned to each target star. Observational emphasis will be concentrated on targets considered of higher priority, ensuring the effectiveness of their observation capabilities. Through this approach, we formulate a 5 yr observation strategy that will cover all the target stars within a 6 month time frame. The strategy not only fulfills the required observing capability but also exhibits high efficiency simultaneously, providing an executable program for future mission. Over the span of the mission’s 5 yr duration, a cumulative observation time of 29,220 hr will be available. Approximately 86% of this, totaling 25,120 hr, is allocated for the observation of target stars. This allocation leaves approximately 4100 hr for extended scientific observation programs. We have also performed simulated observations based on this strategy and verified its observational capability for exoplanets.

Candidate Runaway Stars in the Cluster NGC 2180

The relative proper motions and tangential velocities of four stars from the cluster NGC 2180 are investigated using Gaia DR3 data. Our approach is to subtract the mean proper motion of the fields (the stars within a 1” radius around each target star) and the cluster from the motion of the target stars to calculate the relative proper motions with respect to their field and the cluster, respectively. From the relative proper motions of the target stars with respect to the field stars and the distance to the center of the cluster, we estimated the relative tangential velocities of our target stars. We use the astrometric excess noise information to filter the field stars from star-like objects, such as unresolved binaries. To eliminate foreground contaminations of the field stars used to figure out the relative proper motions of the target stars, we made a parallax cut, Color Magnitude Diagram (CMD) cut, and proper motion (PM) selection. The flight times of the target stars to the cluster NGC 2180 (kinematic ages) are calculated using angular separations from the cluster and their relative proper motions with respect to the cluster. All of the target stars have kinematic ages less than the age of the cluster. The stars, ID1 and ID3 have and with respect to their fields, which corresponds to the relative velocities respectively. These two stars could be runaways from the cluster because they have flight times from the cluster agreed with late ejection from the cluster and have larger proper. The remaining two stars, ID 2 and ID 4 have and with respect to the fields, which corresponds to the relative velocities and respectively, and could not be runaways as they have smaller proper motions, although their flight times to the cluster agreed with late ejection from the cluster.

An absence of binary companions to Wolf-Rayet stars in the Small Magellanic Cloud

To predict black hole mass distributions at high redshifts, we need to understand whether very massive single stars (M ≳ 40 M⊙) with low metallicities (Z) lose their hydrogen-rich envelopes, like their metal-rich counterparts, or whether a binary companion is required to achieve this. To test this, we undertook a deep spectroscopic search for binary companions of the seven known apparently single Wolf-Rayet (WR) stars in the Small Magellanic Cloud (SMC; where Z ≃ 1/5 Z⊙). For each of them, we acquired six high-quality VLT-UVES spectra spread over a time period of 1.5 years. By using the narrow N V lines in these spectra, we monitored radial velocity (RV) variations to search for binary motion. We find low RV variations of between 6 and 23 km/s for the seven WR stars, with a median standard deviation of 5 km/s. Our Monte Carlo simulations imply probabilities below ∼5% that any of our target WR stars have a binary companion more massive than ∼5 M⊙ with orbital periods of less than a year. We estimate that the probability that all our target WR stars have companions with orbital periods shorter than 10 yr is below ∼10−5 and argue that the observed modest RV variations may originate from intrinsic atmosphere or wind variability. Our findings imply that metal-poor massive stars born with M ≳ 40 M⊙ can lose most of their hydrogen-rich envelopes via stellar winds or eruptive mass loss, which strongly constrains their initial mass–black hole mass relation. We also identify two of our seven target stars (SMC AB1 and SMC AB11) as runaway stars with a peculiar RV of ∼80 km/s. Moreover, with all five previously detected WR binaries in the SMC exhibiting orbital periods of less than 20 d, a puzzling absence of intermediate-to-long-period WR binaries has emerged, with strong implications for the outcome of massive binary interactions at low metallicities.

Projection factor and radii of Type II Cepheids

Context. Type II Cepheids are old pulsating stars that can be used to trace the distribution of an old stellar population and to measure distances to globular clusters and galaxies within several megaparsecs, and by extension, they can improve our understanding of the cosmic distance scale. One method that can be used to measure the distances of Type II Cepheids relies on period-luminosity relations, which are quite widely explored in the literature. The semi-geometrical Baade-Wesselink technique is another method that allows distances of radially pulsating stars, such as Type II Cepheids, to be measured if the so-called projection factor is known. However, the literature concerning this parameter for Type II Cepheids is limited to just a few pioneering works. Aims. In determining projection factors for eight nearby short-period Type II Cepheids, also known as BL Her type stars, we aim to calibrate the Baade-Wesselink method for measuring distances for this class of stars. Methods. Using the surface brightness-colour relation version of the Baade-Wesselink technique, we determined the projection factors and radii of eight nearby BL Her type stars. We adopted accurate distances of target stars from Gaia Data Release 3. Time series photometry in the V and KS bands have been collected with two telescopes located at the RolfChini Cerro Murphy Observatory (former Cerro Armazones Observatory), while spectroscopic data have been obtained within dedicated programmes with instruments hosted by the European Southern Observatory. Results. The measured projection factors for the stars with good quality data are in the range between 1.21 and 1.36. The typical uncertainty of projection factors is 0.1. The mean value is 1.330 ± 0.058, which gives the uncertainty of ∼4%. The main sources of uncertainty on the p-factors are statistical errors of the Baade-Wesselink fit (related to the dispersion and coverage of light and radial velocity curves) and parallax. In the case of radii, the biggest contribution to the error budget comes from the KS band photometry’s systematic uncertainty and parallax. The determined radii allowed us to construct the period-radius relation for BL Her stars. Our period-radius relation is in good agreement with the previous empirical calibration, while two theoretical calibrations found in the literature agree with our relation within 2σ. We also confirm that BL Her and RR Lyr stars obey an apparent common period-radius relation.

Segmented parabolic adjustment of the FAST reflector utilizing spatial coordinate rotation transformation

Abstract Since the middle of the twentieth century, the advent of radio telescopes has brought a whole new way and approach to astronomical observation. For Arecibo-type radio telescopes, the tuning optimization of the active reflecting surface (working paraboloid) is the main factor affecting the reflectance calibration. In this study, leveraging the transformation of spatial coordinates through rotation, we introduce an innovative optimization model specifically for the segmented paraboloid of the Five-hundred-meter Aperture Spherical radio Telescope (Hereinafter referred to as FAST) designed by China astronomer and scientist Nan Rendong. This research constructs the equation for an ideal paraboloid and adjusts the working paraboloid to fit within specified constraints such as the orientation of the target star, the adjustment limit of the actuator, and the spatial coordinates. The study employs a combination of coarse and fine grid searches to identify and record the optimal adjustment scheme of the main cable nodes at different angles and the corresponding 2226 actuator coordinates and telescoping length, based on which we build a back propagation model to continuously modify the adjustment scheme. A combination of geometric simulation and Monte Carlo tests were also used for verification. Furthermore, we delve into the impact of variations between adjacent nodes of the modulating actuators, as well as potential longitudinal and radial changes. Compared to the conventional conditioning model, the segmented solution idealized paraboloid we created increases the original reflection efficiency from 77.92% to 95.56% in the working area of 300 m aperture, it will contributes to enhancing the overall performance of FAST.

Compact Spatial Heterodyne Spectrographs for Future Space-Based Observations: Instrument Modeling and Applications.

High-resolution spectroscopy employing spatial heterodyne spectrographs (SHS) holds significant promise for forthcoming space missions, building upon its established track record in science applications. Notably, it offers exceptional performance and cost- effectiveness in the ultraviolet-visual (UV-Vis) region compared to contemporary instruments. SHS instruments provide high-resolution capabilities and substantially larger etendues than similar resolving power instruments. This study introduces a comprehensive Python-based SHS model integrated with a user-friendly web scraping interface for target star selection, parameter generation, and 2D interferogram creation. Our SHS model demonstrates double the resolving power of a grating spectrometer and a throughput comparable to a Fourier transform spectrometer (FTS) but without moving parts, enhancing robustness for deployment in space. The interferogram processing algorithm includes flat-fielding, bias removal, apodization, and an inverse Fourier transform (IFT) for accurate spectrum retrieval. Despite bandwidth limitations due to resolving power constraints, SHS models excel in applications requiring high spectral resolution over narrow wavelength ranges, such as studying isotopic emission lines. The model provides optimization results and trade-offs for system parameters, ensuring precise spectral recovery with realistic signal-to-noise ratio (SNR) values. SHS is versatile and effective for various scientific applications, including investigating atomic and molecular emissions from comets, planetary atmospheres, the Earth's atmosphere, the Sun, and the interstellar medium (ISM). This research significantly contributes to expediting the development and deployment of SHS instruments, demonstrating their potential across numerous scientific domains.

In-Orbit Image Motion Compensation Technology for Long-Integration Time Space Cameras Using a Two-Axis Pointing Platform

Space cameras play a pivotal role in various fields, such as astronomical exploration. When operating in orbit, these cameras encounter the relative motion between the target and the camera during the exposure, resulting in image motion, which affects the imaging quality. Therefore, it is necessary to compensate for this image motion. This paper investigates the in-orbit image motion compensation (IMC) method for space cameras with a long integration time based on a two-axis pointing platform. Firstly, the mechanical design of the camera is introduced. Secondly, the in-orbit IMC model for the camera is analyzed, and the angular motion needed for compensating for the image motion by the two-axis pointing platform are derived. Factors influencing the compensation accuracy are also analyzed. The effectiveness of the IMC model is verified through simulations. Finally, the in-orbit experimental results indicate that the energy concentration of the target star images obtained exceeded 70%, demonstrating excellent performance in space cameras and effectively enhancing imaging quality using IMC technology.

Volume density maps of the 862 nm DIB carrier and interstellar dust. Hints on the role of carbon-rich ejecta from AGB stars

The carbonaceous macromolecules imprinting the numerous absorptions called diffuse interstellar bands (DIBs) in astronomical spectra are omnipresent in the Galaxy and beyond. They represent a considerable reservoir of organic matter. However, their chemical formulae, formation, and destruction sites remain unknown. Their spatial distribution and the local relation to other interstellar species is key to tracing their role in the lifecycle of organic matter. Volume density maps bring local instead of line-of-sight distributed information and allow for new diagnostics to be captured. We present the first large-scale volume (3D) density map of a DIB carrier and compare it with an equivalent map of interstellar dust. The DIB carrier map was obtained through hierarchical inversion of sim 202,000 measurements of the 8621 nm DIB obtained with the Gaia -RVS instrument. It covers about 4000 pc around the Sun in the Galactic plane. We built a dedicated interstellar dust map based on the extinction towards the same target stars. At the simeq 50 pc resolution of the maps, the shape of the 3D DIB distribution is found to be remarkably similar to the 3D distribution of dust. On the other hand, the DIB-to-dust local density ratio increases in low-dust areas. It is also increasing away from the disk, however, the minimum ratio is found to be shifted above the Galactic plane to Z=simeq +50pc. Finally, the average ratio is also surprisingly found to increase away from the Galactic Center. We suggest that the three latter trends may be indications of a dominant contribution of material from the carbon-rich category of dying giant stars to the formation of the carriers. Our suggestion is based on recent catalogs of asymptotic giant branch (AGB) stars and estimates of the mass fluxes of their C-rich and O-rich ejecta.

Optimization of polarization balance in beam splitter films for weak star simulator.

In the weak star simulator, the background stray light of the self-excited star image and the simulated target star light are mixed with each other, which is difficult to separate and reduces the simulation accuracy of the star position. Therefore, based on the polarized light tracing method, this paper explores the induction mechanism of the polarization effect of the weak star simulator on the background stray light field of the star map, and proposes a polarization balance optimization method for the beam splitter film. At the same time, the mapping model of star position simulation accuracy, polarization parameters of beam splitter and polarization stray light suppression degree is established. Based on this evaluation function, the polarization balance optimization process of beam splitter is constructed to reduce the influence of polarization effect of beam splitter on the background stray light field of star image. The simulation and experimental results show that the stray light suppression ability of the weak star simulator is improved by 2.1 times and the simulation accuracy of the star position is improved by 1.64 times after the polarization balance optimization of the beam splitter film.

TESS Light Curves of Cataclysmic Variables. IV. A Synoptic View of Eclipsing Old Novae and Novalike Variables

Based mainly on the months-long 2 minutes time-resolution light curves observed by the Transiting Exoplanet Survey Telescope (TESS) space mission of 48 eclipsing old novae and novalike variables (commonly referred to as NLs) selected from the Ritter & Kolb catalog, a synoptic view of some basic properties of these systems is provided. The supraorbital variations exhibit a large diversity of behavior. Data taken from the literature and many additional eclipse epochs measured in the TESS and in AAVSO light curves are used to update the orbital ephemerides of 21 targets. The large majority of these suffer period variations which defy current theoretical understanding. Orbital waveforms are constructed and, if possible, their variation over time is studied, revealing some common characteristics but also substantial differences between individual systems. The dependence of the eclipse depth on the out-of-eclipse flux reveals that in all systems a fraction of the light source responsible for the out-of-eclipse variations escapes eclipse and is probably located in the outer disk regions. In systems exhibiting superhumps, both eclipse width and epoch are modulated with the accretion disk precession period. This suggests an expansion and contraction of the eclipsed light source, as well as a periodic shift of its light center as a function of the accretion disk precession phase. The dependence of the orbital and superhump waveforms on the disk precession phase is also examined but does not lead to a consistent picture. Two cataclysmic variables are newly identified as eclipsing. Attention is drawn to specific peculiarities in some of the target stars.

PLATO’s signal and noise budget

ESA’s PLATO mission aims the detection and characterization of terrestrial planets around solar-type stars as well as the study of host star properties. The noise-to-signal ratio (NSR) is the main performance parameter of the PLATO instrument, which consists of 24 Normal Cameras and 2 Fast Cameras. In order to justify, verify and breakdown NSR-relevant requirements the software simulator PINE was developed. PINE models the signal pathway from a target star to the digital output of a camera based on physical models and considers the major noise contributors. In this paper, the simulator’s coarse mode is introduced which allows fast performance analyses on instrument level. The added value of PINE is illustrated by exemplary applications.

Increasing the raw contrast of VLT/SPHERE with the dark hole technique

Context. Imaging exoplanetary systems is essential to characterizing exoplanet atmospheres and orbits as well as circumstellar disks and to studying planet-disk interactions to understand the planet formation processes. Imaging exoplanets or circumstellar disks in the visible and near-infrared is challenging, however, because these objects are very faint relative to their star, even though only fractions of an arcsecond away. Coronagraphic instruments have already allowed the imaging of a few exoplanets, but their performance is limited by wavefront aberrations. Adaptive optics systems partly compensate for the Earth’s atmosphere turbulence, but they cannot fully control the wavefront. Some of the starlight leaks through the coronagraph and forms speckles in the astrophysical image. Focal plane wavefront control, used as a second stage after the adaptive optics system, has been proposed to minimize the speckle intensity within an area called the dark hole. Aims. We previously demonstrated the on-sky performance of dark hole techniques, pairwise probing coupled with electric field conjugation, using the apodized pupil Lyot coronagraph of the VLT/SPHERE instrument. In this paper, we probe their performance using the SPHERE four-quadrant phase mask coronagraph, and we demonstrate the interest of combining dark hole techniques and reference differential imaging. Methods. We used these dark hole techniques on-sky to create a dark hole in the narrow band around 1.7 |j.m observing HR 4796. We then recorded broadband images of HR 4796 and a reference star at the H band. Results. The dark hole techniques improved the H-band detection limit by a factor of three. The dark hole was stable from one star to a nearby star enabling reference differential imaging. Conclusions. This stability offers two new strategies of observation. First, one can quickly create a dark hole observing a bright star before pointing to a faint target star. Furthermore, one can couple dark hole techniques and reference differential imaging. A very interesting point is that the performance of these methods does not depend on the astrophysical signal.

Searching for gamma-ray emission from stellar flares

Abstract Flares from magnetically active dwarf stars should produce relativistic particles capable of creating γ-rays. So far, the only isolated main sequence star besides the Sun to have been detected in γ-rays is TVLM 513-46546. Detecting γ-ray flares from more dwarf stars can improve our understanding of their magnetospheric properties, and could also indicate a diminished likelihood of their planets’ habitability. In this work, we stack data from the Fermi Gamma-ray Space Telescope during a large number of events identified from optical and X-ray flare surveys. We report an upper limit of γ-ray emission from the population of flare stars. Stacking results towards control positions are consistent with a non-detection. We compare these results to observed Solar γ-ray flares and against a model of emission from neutral pion decay. The upper limit is consistent with Solar flares when scaled to the flare energies and distances of the target stars. As with Solar flares, the neutral pion decay mechanism for γ-ray production is also consistent with these results.

Abundances of Neutron-capture Elements in 62 Stars in the Globular Cluster Messier 15

M15 is a globular cluster with a known spread in neutron-capture elements. This paper presents abundances of neutron-capture elements for 62 stars in M15. Spectra were obtained with the Michigan/Magellan Fiber System spectrograph, covering a wavelength range from ∼4430 to 4630 Å. Spectral lines from Fe i, Fe ii, Sr i, Zr ii, Ba ii, La ii, Ce ii, Nd ii, Sm ii, Eu ii, and Dy ii were measured, enabling classifications and neutron-capture abundance patterns for the stars. Of the 62 targets, 44 are found to be highly Eu-enhanced r-II stars, another 17 are moderately Eu-enhanced r-I stars, and one star is found to have an s-process signature. The neutron-capture patterns indicate that the majority of the stars are consistent with enrichment by the r-process. The 62 target stars are found to show significant star-to-star spreads in Sr, Zr, Ba, La, Ce, Nd, Sm, Eu, and Dy, but no significant spread in Fe. The neutron-capture abundances are further found to have slight correlations with sodium abundances from the literature, unlike what has been previously found; follow-up studies are needed to verify this result. The findings in this paper suggest that the Eu-enhanced stars in M15 were enhanced by the same process, that the nucleosynthetic source of this Eu pollution was the r-process, and that the r-process source occurred as the first generation of cluster stars was forming.

Research on the de-tumbling method of magnetic moment variation of two stars based on the tangential formation

High-speed space debris threatens the safety of satellites in orbit, making the efficient removal of this debris an increasingly unavoidable necessity. By exploring the non-contact de-tumbling method for high-speed rotating targets, a de-tumbling technique is proposed. This method relies on leveraging the differential magnetic moments of two satellites arranged in tangential formation. Two single-coil electromagnetic satellites form a uniform magnetic field at the rotating targets, forming a tangential collinear distribution. The de-tumbling method of the simultaneous change of the magnetic moment of two satellites and the change of magnetic moment of one satellite and the other satellite is explored, and the de-tumbling effect is compared through numerical simulation. The simulation results indicate that the de-tumbling effect of the latter method is superior. Additionally, there is minimal variation observed in the relative distance between servicing stars and between servicing stars and target stars throughout the de-tumbling process.

SMART: Special-shaped Micro-lens Aimer for Real-time Targeting of multi-object telescopes

In the process of acquiring astronomical spectral data, the alignment accuracy between the fiber core in the focal plane and the image of the target star is crucial for multi-target telescopes. This work presents a Special-shaped Micro-lens Aimer for Real-time Targeting (SMART), which combines a special-shaped microlens and a fiber bundle to carry out online alignments and improve the injection efficiency of the fiber. The special-shaped microlens consists of a central plate and six side microlenses. The central plate transfers the signal to the science fiber without focal ratio degradation. The side microlenses focus the leakage light to the feedback fibers and return a misalignment signal. The experiment in the laboratory indicates that the SMART-T system can visually demonstrate the recognition of offsets. The SMART-P system is able to realize the alignment for a variety of seeing cases. Under the condition that the diameter of turbulent star image is 0.2 mm, the corrected injection efficiency is improved to 99.7% of the best injection efficiency of the science fiber. The re-centering accuracy is 0.01 mm.