Star Image Research Articles

On-Orbit Geometric Distortion Correction on Star Images through 2D Legendre Neural Network

The star tracker is a prerequisite device to realize high-precision attitude determination for a spacecraft. However, due to the errors in optical lens machining, optical path assembly, and temperature alternation, optical instruments suffer from some amount of optical geometric distortion, resulting in declining star tracker accuracy. The on-orbit distortion correction of star images is indispensable for precise performance. In this paper, a novel single-layer 2D Legendre neural network (2DLNN) to automatically correct the geometric distortion of the star tracker is proposed. An offline training method grounded on batch star images and an online training algorithm based on sequential star images are designed, respectively. The 2DLNN realizes the ground-based and on-orbit online correction of optical geometric distortion for the star tracker. The 2DLNN features self-learning, lifelong learning, and good adaptability. The single-layer neural network is simple, quick convergence, which is suitable for on-orbit implementation. The simulations demonstrate that the average distortion error can be reduced to less than 0.04 px after ground-based training. In the earth-orientation mode of the LEO satellite, the on-orbit sequential training algorithm can converge in 2500 star images under 1 frame/s. The proposed 2DLNN can achieve high-precision correction at the sub-pixel level, effectively improving the star tracker’s attitude determination accuracy.

Effect of proton beam irradiation on the tracking efficiency of CMOS image sensors

A star tracker provides accurate space positioning and reference for satellites, intercontinental strategic missiles, and other spacecrafts. However, the main imaging unit of the star sensor – the image sensor – is affected by the space radiation environment and, in turn, affects the precision with which the star is located by the star tracker. In this study, the parameter degradation of a CMOS image sensor (CIS) after proton irradiation with different fluences was investigated. An outfield test platform for star map collection was built using the star sensor lens and image collection system. The influence of dark current, dark-current nonuniformity, and photo-response nonuniformity of the irradiated CIS on the star diagonal distance measurement error and star-point centroid position detection accuracy was studied. The results showed that with increasing proton fluences, the CIS noise increased, leading to an increase in the error in the measured diagonal distance of the star and a decrease in the star’s position detection accuracy. Among these parameters, the dark current plays the greatest role in influencing the measurement accuracy of the star tracker. Furthermore, when a tracker is exposed to space radiation with fluences that are same as those used in this experiment, it is beneficial to reduce the integration time. This reduction in the time will decrease the noise and improve the position measurement accuracy.

Local Correction of the Light Position Implemented on an FPGA Platform for a 6 Meter Telescope

The low-frequency component of the distortions caused by both the atmospheric turbulence and the behavior of the telescope itself has been studied. A corrector for the position of the center of the star image has been developed and is being used in front of the high-resolution Echelle spectrograph on the 6 m telescope of the Special Astrophysical Observatory, Russian Academy of Sciences. To speed up the calculations and to increase the bandwidth, a laser beam angular stabilization system based on an FPGA platform is considered. The system consists of two tip-tilt mirrors and two quadrant photodiodes. The FPGA analyzes the signals from the photodiodes, calculates and then applies the voltages to the piezo-driven tip-tilt mirrors to minimize the displacement of the beam on the photodiodes. The stabilization system was developed as a part of the adaptive optical system to improve the efficiency of the high-resolution Echelle spectrograph.

Star Identification Based on Radial Triangle Mapping Matrix

In this paper, a novel star image recognition algorithm is proposed based on a voting scheme that utilizes a radial triangle mapping matrix pattern. Inspired by the radial and cyclic algorithm, the radial triangle mapping matrix pattern is rotation-invariant, and does not rely on a location star, which provides a new idea for the construction of rotation-invariant patterns. The algorithm is based on a geometric voting scheme in which the radial triangle group is considered as the basic voting element. The database optimization is used to reduce the memory requirement and improve the query efficiency by extracting the nonzero value of the pattern. During the identification period, the voting scheme can vote for the candidate stars through the radial triangles, which improves the robustness towards the noise. The proposed algorithm exhibits a 98.41% identification rate with 2.0-pixel standard deviation of position noises and 0.3-Mv magnitude noises. The experimental results of the simulation star image and real star image show that the proposed algorithm is quite more robust towards position noise, magnitude noise, and false star noise when compared with other comparing algorithms.

Disk Evolution Study through Imaging of Nearby Young Stars (DESTINYS): A Panchromatic View of DO Tau’s Complex Kilo-astronomical-unit Environment

While protoplanetary disks are often treated as isolated systems in planet formation models, observations increasingly suggest that vigorous interactions between Class II disks and their environments are not rare. DO Tau is a T Tauri star that has previously been hypothesized to have undergone a close encounter with the HV Tau system. As part of the DESTINYS ESO Large Programme, we present new Very Large Telescope (VLT)/SPHERE polarimetric observations of DO Tau and combine them with archival Hubble Space Telescope (HST) scattered-light images and Atacama Large Millimeter/submillimeter Array (ALMA) observations of CO isotopologues and CS to map a network of complex structures. The SPHERE and ALMA observations show that the circumstellar disk is connected to arms extending out to several hundred astronomical units. HST and ALMA also reveal stream-like structures northeast of DO Tau, some of which are at least several thousand astronomical units long. These streams appear not to be gravitationally bound to DO Tau, and comparisons with previous Herschel far-IR observations suggest that the streams are part of a bridge-like structure connecting DO Tau and HV Tau. We also detect a fainter redshifted counterpart to a previously known blueshifted CO outflow. While some of DO Tau’s complex structures could be attributed to a recent disk–disk encounter, they might be explained alternatively by interactions with remnant material from the star formation process. These panchromatic observations of DO Tau highlight the need to contextualize the evolution of Class II disks by examining processes occurring over a wide range of size scales.

Could Fleabag be a Parisienne? Camille Cottin’s Star Image and a New French Femininity

This article discusses Camille Cottin’s star image, considering more specifically what was at stake in her 2019 performance in Mouche, the French remake of British tragicomedy TV series Fleabag created by Phoebe Waller-Bridge. The framework of this remake and the transposition of Cottin in the character played by Waller-Bridge offers a discussion on the representation of female sexuality and gender through the main character of Mouche and Fleabag. It argues that the nexus of Cottin’s gendered stardom both meets and transgresses the ideals of the cinematic type of the Parisienne, which may lead to think that Cottin was the perfect fit to be the French version of Fleabag. However, as Mouche, her persona gestures toward the projection of a female subjectivity that escapes inscription into the French cultural imagination and social practices. Drawing from theories of the abject and the female grotesque as a subversive strategy to challenge gendered expectations in Fleabag, this article sheds light on how effectively this is transposed to Cottin’s version of the character. It also considers how the strategy of breaking the fourth wall, which creates a personalised connection with the character of Fleabag, mimics the personalised and intimate connection to celebrities that social media now offers. The article suggests that Cottin’s on-screen persona competes with her star image, threatening to eradicate the space of spectatorial jouissance necessary for the processes of cinematic identification and intimate connection.

(In)Visible Woman

This critical reflection examines the growing career of actor Ruth Madeley, and her visibility in the industry as an ambulatory wheelchair user, exploring the impact of ‘cripping up,’ on casting practice, and its lasting effects on disabled actors, screen representation and the community they strive to represent. Madeley’s rise to prominence offers the opportunity to explore the significance of casting disabled actors, and the value of seeing and being seen. Her success indicates a shift toward greater inclusivity and diversity, but the sustained casting of disabled actors remains exceptional rather than commonplace. Drawing upon analysis of three high profile roles in Years and Years, Don't Take My Baby, Verisimilitude, and The Watch, alongside interviews and related paratexts, I explore how Madeley’s disability is negotiated and the tension this creates within her star image. With reference to scholarship on stardom, performance, and disability studies, I argue that Madeley is extraordinary in her ordinariness. She is highly visible, and yet, invisible. Her work dismantles entrenched yet ableist narratives where disabled characters are presented as little more than ‘inspiration porn’, reflected in Madeley’s pursuit of roles where disabled people and their lives are represented as rich and complex, thereby challenging perceptions of disabled characters and their life experiences. What does Madeley’s career tell us about the industry’s progression since Daniel Day-Lewis’ Oscar-winning portrayal of writer Christy Brown in My Left Foot? And, as Madeley herself has commented, what is left to do in terms of how we represent disabled lives on screen?

A “very politically correct, wholesome family show”: Jane Seymour’s white, heterosexual femininity in Dr. Quinn, Medicine Woman

In January 1993, the US television station CBS premiered a new TV drama about Michaela Quinn—a Boston doctor who moved alone to the Colorado frontier to establish her medical practice. Seymour’s biography played a critical role in the initial promotion of the show. The character of Dr. Quinn, as Seymour played her, was a feminist in the Hillary Rodham Clinton vein, and the show’s drama primarily revolved around Quinn’s gender deviance and issues arising from white patriarchy. Given this progressive, feminist bent, it’s surprising that the show resonated with conservative audiences and, in U.S. syndication, found a home on evangelical Christian networks such as PAX-TV and INSP. Combining media analysis, cultural analysis, and biographical research, this article analyzes how Jane Seymour’s star image and biography enabled Dr. Quinn to interrogate and challenge gender roles while also working to bolster the show’s position as “family values” TV. Ultimately, this analysis reveals the powerful role a star’s biography can play in disseminating ideas to diverse, sometimes potentially resistant, audiences.

From Friends to “The Girl Friend”: the Early Evolution of Jennifer Aniston’s Star Image

In the more than twenty-five years since the spectacular success of the iconic television sitcom/cultural phenomenon Friends (NBC, 1994-2004), the ensemble program’s six actors have parlayed that visibility into careers of varying success on network and cable television, streaming platforms, and the film industry. One of them, Jennifer Aniston, has managed to maintain a consistently visible star image which continues to resonate with fans and critics alike. In her nearly thirty-year career Aniston has successfully transitioned from her role on the small screen to starring roles in feature films, and most recently gaining critical and popular attention (as well as a Screen Actor’s Guild award) for her role in The Morning Show on the Apple + streaming service. While scholars have already considered work from her late and post-Friends career, this article examines her breakout role as the appealing and attractive Rachel Green as an effective vehicle for the transition into her early film roles (1997-1998). Through an analysis of various texts and paratexts, the article traces the roots of the actress’ early star image and argues that understanding Aniston as capable of playing both erotically charged objects of desire as well as fully agential desiring subjects is key to explaining her early star image.

Follow‐up observations of the binary system γ Cep

AbstractWe present follow‐up imaging and spectroscopic observations of the exoplanet host star γ Cep A, and of its low‐mass stellar companion γ Cep B. We used the lucky‐imager AstraLux at the Calar Alto observatory to follow the orbital motion of the companion around its primary, whose radial velocity (RV) was determined with spectra of the star, taken with the Échelle spectrograph FLECHAS at the University Observatory Jena. We measured the astrometry of the companion relative to the exoplanet host star in all AstraLux images and determined its apparent SDSS i′‐band photometry, for which we obtained mag. Using stellar evolutionary models and the Gaia parallax of the exoplanet host star, we derived the mass of γ Cep B to be 0.39 ± 0.03 M⊙. This is in good agreement with the mass of the companion that we derived from its near‐infrared photometry given in the literature. With the detection limit reached in our AstraLux images, we explored the detection space of potential additional companions in the γ Cep binary system. In the background limited region at angular separations larger than 5 arcsec (or 69 au of projected separation) companions down to 0.11 M⊙ are detectable around the bright exoplanet host star. The radial field of view, fully covered by our AstraLux observations, exhibits a radius of 11.2 arcsec. This allows the detection of companions with projected separations up to 155 au. However, except for γ Cep B, no additional companions could be imaged with AstraLux around the exoplanet host star. We redetermined the orbital solution of the γ Cep binary system with the new AstraLux astrometry of γ Cep B and the additional radial velocities of γ Cep A, obtained from our FLECHAS spectroscopy of the star, combined with astrometric and RV data from the literature. The determined Keplerian orbital elements were used to derive the system parameters and to calculate specific future ephemeris for this intriguing exoplanet host binary star system.

The incredible, ageless Reeves: aging celebrity, aging fans, and nostalgia

ABSTRACT As a star, Keanu Reeves is timeless. As a celebrity, ageless. Drawing on Jerslev and Petersen’s (eds, 2018) special issue of Celebrity Studies, this article reads Reeves’ star image through the lens of research on ageing celebrities, and ageing fans. While his iconic action roles centre Reeves as an ageing, yet ageless celebrity, the memeification of Reeves has been essential to his resurgent star image with younger fans. As a star notoriously private about his personal life, Reeves’ first public appearance with partner Alexandra Grant in November 2019, and the subsequent shock at the ‘age appropriate’ pairing (rather than the more common image of ageing male star, much younger starlet) added another layer to the discourse around ageing male stars. Finally, Reeves’ reprisal of his role as Ted ‘Theodore’ Logan in Bill and Ted Face the Music (BATFTM) (2020) speaks both to his age/lessness and star image, in addition to the nostalgia of his ageing fans. In sum, this paper will interrogate Reeves’ star image as an atypical representation of ageing celebrity masculinity – and how this contributes to his ongoing appeal to ageing fans.

A Framework of High-precision State Estimation for Approaching, Orbiting, and Touching an Asteroid

High-precision state estimation lies at the core of asteroid exploration. This paper investigates the high-precision state estimation methods in asteroid approaching, orbiting, and touching phases. The system and measurement models are established, and state estimation strategies are designed respectively for each phase. In the approaching phase, the star image is used to directly determine the relative orbit of the spacecraft to the target asteroid. To improve the optical state estimation precision, a deceleration-orientation-deceleration strategy is developed. In the orbiting phase, coupled orbit-attitude estimation is realized based on the terrain features of the asteroid, and the effect of dynamic error on the accuracy of state estimation is analysed. Then, a decoupled orbit-attitude state estimation method is developed to avoid the affection of dynamic error. In the touching phase, lidar measurement is used to determine the relative orbit and attitude of the spacecraft with respect to the landing spot. Based on the triple-stage state estimation framework proposed in this paper, the relative state error of the spacecraft converges from 100km level to 1mm level.

FASHION, CINEMA, AND GERMAN-AMERICAN PROPAGANDA IN 1930s BUCHAREST

This paper explores how Bucharest’s cinema-going public perceived the Nazi influence on Hollywood in the 1930s. The aim is to identify how Nazi propaganda was disseminated and consumed in interwar Bucharest and its similarities to the idea of glamour, relevant both to fashion and cinema. Considering the links between Goebbels’ propaganda machine and certain entities or individuals in Hollywood, US cinematography becomes a more complex medium of dissemination beyond a mere promoter of modernity’s technological and consumerist ideas. Romania’s situation in the 1930s, especially the increasing leaning towards the extreme right then inform movie star image, particularly through a gendered lens, as perfect tools for propagandists. The interwar cinema-centered Romanian discourse involves a triple filtration, through Hollywood, Berlin, and Bucharest, as a complex depiction of the Romanian public’s ideals and views. To illustrate these points, I will analyze relevant written and visual texts from the interwar era, including fiction, memoirs, essays, nationally and locally spread cinema-centered and general periodicals, postcards, or photographs. The interdisciplinary research will include cultural studies (fashion, media, cinema, gender), history, and discourse analysis. This innovative perspective on fashion and cinema in an interwar Romanian context adds to the existing knowledge by opening new research topics and subjects in the fields of fashion studies and Romanian studies.

Star–Galaxy Image Separation with Computationally Efficient Gaussian Process Classification

Abstract We introduce a novel method for discerning optical telescope images of stars from those of galaxies using Gaussian processes (GPs). Although applications of GPs often struggle in high-dimensional data modalities such as optical image classification, we show that a low-dimensional embedding of images into a metric space defined by the principal components of the data suffices to produce high-quality predictions from real large-scale survey data. We develop a novel method of GP classification hyperparameter training that scales approximately linearly in the number of image observations, which allows for application of GP models to large-size Hyper Suprime-Cam Subaru Strategic Program data. In our experiments, we evaluate the performance of a principal component analysis embedded GP predictive model against other machine-learning algorithms, including a convolutional neural network and an image photometric morphology discriminator. Our analysis shows that our methods compare favorably with current methods in optical image classification while producing posterior distributions from the GP regression that can be used to quantify object classification uncertainty. We further describe how classification uncertainty can be used to efficiently parse large-scale survey imaging data to produce high-confidence object catalogs.

Специфика реализации системы оппозиций пейзажной образности в рассказах о детстве И. С. Шмелева 1906–1912 гг.

This article examines the features of how the system of semantic oppositions of landscape images is objectified in the stories about childhood by the writer of the Russian expatriate community Ivan Sergeevich Shmelev, created in 1906-1912. The research material constitutes the works The Sergeant, On Urgent Business, One Night, Gingerbread (the Doctor’s Story), Festive Heroes, Stars, Timid Silence, related to the pre-emigration period of the author’s ouevre. The aim of the work is to consider the artistic principle of antinomy, actualizing a wide range of images, including images of ‘happy childhood’, mellow autumn, night landscape, idyllic summer panoramic landscape, autumn melancholy landscape, ‘sacred’ landscape, spilt innocent blood. All together, they recreate a rich motivic spectrum containing motifs of abundance, spaciousness, peace, blissful silence, contrasted with a dead, graceless silence. The theme of the rebellious revolutionary city in the stories is interspersed with the theme of harmonious unity, opposing the discordant life of man and nature, as well as the themes of death, unjust murder and human cruelty. In the works of I. S. Shmelev, the theme of the unity of children and nature is closely connected with the poetization of the Russian landscape, paintings-images of a rapid children’s run, combined with aerial imagery and the theme of human talent, bestowed by God. In the structure of the artistic space of the stories, a contrasting idea of the ‘inner’ fertile home space filled with children’s light, warmth, love, and the ‘outer’ cold, dark space bearing torment and death is realized. Biblical allusions, closely related to the images of stars, among which the image of the Christmas Star stands out, and the Christmas chronotope, are associated with the meaning of the higher, spiritual sphere and the theme of death.

Space Debris Automation Detection and Extraction Based on a Wide-field Surveillance System

Abstract Wide-field telescopes with long exposure times have stronger space target detection capabilities. However, complex background sky conditions will still cause a series of difficulties in detecting space debris, such as a large number of star points, a large amount of noise, and the discontinuity and nonlinearity of the target. We propose a space debris automatic extraction channel with a high detection rate and low computational cost to solve these difficulties. We apply an improved median filter for noise elimination and then the double-structure morphological filter algorithm used to suppress the background of the star image to eliminate star points and noise. Then, the guided filter was used to eliminate residual noise, and star points were used to reduce the impact on the target. Finally, the improved Hough transform was also applied to detect the target in the image. Our automatic extraction algorithm is used in real astronomical star maps, including different orbiting satellites (star-tracking mode). These images were obtained by using a 280 mm diameter telescope, which was located in Changchun Observatory. The experimental results demonstrated the effectiveness of the extraction algorithm in this study. It can effectively detect and track space targets in a long-exposure wide-field surveillance system and has high positioning accuracy and low computational complexity, which solves the problem of space debris extraction under a complex background.

Accurate Ground-based Astrometry of Naked-eye Stars: The United States Naval Observatory Bright-star Astrometric Database

Abstract We present the United States Naval Observatory (USNO) Bright-star Astrometric Database (UBAD), a current-epoch high-accuracy astrometric catalog. The catalog consists of 364 bright northern hemisphere stars, including all but five such stars with either V < 3.5 or with I < 3.2 and V < 6, as well as a large fraction of slightly fainter stars; 36 of the brightest catalog stars are not included in Gaia Early Data Release 3 (EDR3). Observations were conducted with the USNO Flagstaff Station Kaj Strand 61 inch Astrometric Reflector. Target stars were imaged through a small 12.5 mag neutral-density spot, while the remainder of the stars in the field of view were unattenuated. This allowed for unsaturated images of the bright target stars to be calibrated directly against much fainter reference stars from Gaia EDR3. The median position errors are 1.9 mas in both R.A. and decl. at the catalog epoch of 2017.0, with 90% of catalog stars having errors less than 2.6 mas; systematic errors are 1–3 mas. Combining UBAD observations with Hipparcos-2 positions yields proper motions with median errors of 0.045 and 0.049 mas yr−1 in R.A. and decl., respectively, with 90% of stars having errors less than 0.1 mas yr−1; systematic errors are about 0.1 mas yr−1. Single-frame accuracy for positions of the target stars is typically 5–6 mas. Gaia EDR3 astrometry for these bright stars, which are heavily saturated in the Gaia observations, is validated over the magnitude range 2 ≲ G ≲ 6.

Two-mirror aplanatic telescopes with a flat field

A complete description is given of two-mirror telescopes with a flat medial focal surface, on which the images of stars are circles of least confusion. Particular attention is paid to aplanats, since their field of view is noticeably larger than that of classical systems. Two sets of appropriate solutions correspond to Schwarzschild and Gregorian telescopes. As a result, it becomes possible to use flat light detectors with wide-field two-mirror telescopes. New designs are of particular interest when as few reflective surfaces as possible are required, which is typical for space exploration and non-optical observations.

A stellar energy extraction method based on exponential intra-pixel sensitivity model

The stability and accuracy of stellar energy extraction are important factors affecting the accuracy of in-orbit radiation calibration based on stars. However, the point spread function (PSF) and the intra-pixel sensitivity (IPS) of the infrared detector will have a great influence on the stability and accuracy of the point target energy extraction. To solve the above problems, this paper proposes a stellar energy extraction method based on an exponential intra-pixel sensitivity model. First, reconstruct the background image based on the multi-frame images to remove the influence of the instrument background. Then, each pixel was divided into 10 × 10 sub-pixels, and the value of each sub-pixel was obtained by fitting the target response value with a two-dimensional Gaussian function. Then, the exponential intra-pixel sensitivity model was established to obtain the IPS value of each sub-pixel, and the target response was deconvolved with the established IPS model. Finally, the star energy is obtained by the aperture photometry method. According to the simulation results, the accuracy of the proposed method is 0.4%, which is 15.6% higher than that without the IPS model; the stability of the proposed method is 0.5%, which is 5.6% higher than that without the IPS model. According to the experimental results using infrared star images observed in orbit, the accuracy of the proposed method is better than 3%, which is 13% higher than that without the IPS model; the stability of the proposed method is better than 3%, which is 5% higher than that without the IPS model. This method can provide a useful reference for the high-accuracy on-orbit star calibration of a large-aperture infrared remote sensing camera in space.

An Adaptive Space Target Detection Algorithm

In space target monitoring system, due to the interference of noise, stray light and the limitations of the image acquisition system, there are nonuniform background and smear phenomena in star images. Moreover, there are also a large number of background stars in star images. All these factors lead to the difficulty of space target detection. In order to improve the detection performance, an adaptive space target detection algorithm is proposed in this letter. Firstly, in order to suppress the complex background interference in the star image, a window adaptive bidirectional one-dimensional (1-D) median filtering method is proposed, whose window size is set based on the maximum star size in the first star image. Then, background correction is performed by bidirectional 1-D median filter. Secondly, in order to improve the reliability of space target segmentation, an improved inter-frame difference method is proposed, which consists of two parts: 1) the bright line residue is eliminated based on a horizontal 1-D median filter; 2) the target segmentation threshold is adaptively set based on the Kalman filter method. Compared with existing algorithms, our proposed method can detect space targets quickly with low false alarm rate and high detection rate under complex background conditions.