Experimental Astronomy最新文献

Stellar spectral line indices are key tools for studying stellar physical properties and evolutionary processes, playing a significant role in inferring important stellar attributes such as Teff, [Fe/H], and logg. This paper proposes an automated method for measuring stellar spectral line indices, specifically targeting LAMOST-DR7 A-type stellar spectra. The method involves several key steps: spectral preprocessing, continuum normalization, baseline correction, baseline fitting, spectral line fitting, and line index calculation, all aimed at achieving accurate spectral line index measurements. Traditional methods often encounter significant errors when dealing with complex spectral backgrounds. In contrast, the proposed method incorporates a series of optimizations and has been validated for robustness through Monte Carlo simulations. Our observational results indicate that this method is highly feasible from the comparisons to the line indices officially released by LAMOST and those in the Lick spectral library. Further testing with simulated data further demonstrates the reliability of this approach. This method provides a promising tool for future astronomical observations and stellar evolution studies and holds broad application potential. It not only helps improve the accuracy of research into stellar physical properties but also offers a practical technical approach for analyzing the composition and evolutionary patterns of stellar populations in galaxies.

Estimation of the statistical significance of the peaks appearing in the spectra of various astronomical time series is essential for the detection of signals especially when they are contaminated by high levels of observational noise. In the present paper we consider a broader perspective which relies on two main aspects: (i) all the peaks have or may have significance and, therefore, (ii) we propose two complementary approaches to simultaneously supply estimates of the statistical significance of all the peaks of interest through Monte Carlo simulations. They are natural generalisations of the already used methods featured either by specificity in frequency or by specificity in amplitude/power of the peaks occurred in the spectrum. Three recently obtained radial velocity data on stars with orbiting exoplanets were used to illustrate these approaches: two G-type stars observed by the HARPS spectrograph (TOI-733, TOI-763) and an M-type star observed by the CARMENES spectrograph (Wolf 327). Some both interesting and useful features of the two considered statistical significances are also emphasised.

In order to improve the energy reconstruction accuracy of gamma-ray events observed by ground-based array experiments, this work propose a new energy estimator based on machine learning (ML) algorithm to determine the energies of gamma ray induced air showers in the energy range between 1 TeV and 10 PeV. We carry out a full Monte Carlo (MC) simulation using the Tibet air shower array and underground muon detector array, located at an altitude of 4,300 m above sea level. The MC simulated gamma-ray data are used to extract characteristic parameters depicting the air shower information, which are then fed into the ML model for training on both high-energy data sets ((E >sim 10) TeV) and low-energy data sets ((E < 10) TeV). In our simulation data tests, we found that the ML method showed significant advantages over traditional energy estimators (S50, (N_e), and (sum rho )), with improved energy resolution for both low and high energy datasets. Compared to the traditional estimator, the energy resolution improves by approximately 30% for the inner array events and 55% for the outer array events at (E < 10) TeV. At around 100 TeV, the energy resolution for large zenith angle events in the outer array improves by approximately 20%. This work also found that while the energy resolution of events falling the inside array can only be slightly improved, however, events outside array and at large zenith shower clear improvements. Moreover, it is particularly noteworthy that the ML method has little difference in the energy resolution of the inner and outer array events. The enhanced energy resolution achieved through the machine learning method for outer array events reduces the limitations imposed by the observation area, resulting in an approximately 30% improvement in statistical events. This method is suitable for ground-based array experiments in gamma-ray astronomy, and provides some technical support for further study of the primary gamma-ray energy reconstruction.

The primary scientific objective of the High Energy Burst Searcher (HEBS) is to serve as a crucial component of the global space monitoring network for high-energy celestial burst sources. HEBS aims to monitor the high-energy electromagnetic counterparts of gravitational wave events, as well as the high-energy radiation from rapid radio bursts, gamma-ray bursts, magnetar flares, and other high-energy celestial phenomena across the entire sky. This effort will provide essential data support for related physical research, including energy spectra, light curves, and positional information. The probe is deployed on the Satech-01 satellite and operates in a 500 km solar-synchronous orbit. HEBS is equipped with two types of detectors: the Gamma Ray Detector (GRD) and the Charged Particle Detector (CPD). The GRD employs lanthanum bromide crystals coupled with silicon photomultiplier (SiPM) technology, as well as sodium iodide crystals paired with SiPM technology, to detect X-rays and gamma rays in the energy range of 6 keV to 5.9 MeV. It enables the localization of gamma-ray bursts and other high-energy events through the coordinated detection of multiple probes oriented in different directions. The CPD utilizes plastic scintillator technology coupled with SiPM to detect charged particles within the energy range of 150 keV to 5 MeV. When combined with the GRD, it effectively identifies and distinguishes space particle events from actual celestial phenomena. The payload processor (Electronics Box, EBOX) features onboard triggering and positioning capabilities, transmitting trigger times and positional data via Beidou short messaging in quasi-real time. This information will guide other telescopes in conducting follow-up observations.

Over the decades, astronomical X-ray telescopes have utilized the Wolter type-1 optical design, which provides stigmatic imaging in axial direction but suffers from coma and higher-order aberrations for off-axis sources. The Wolter-Schwarzschild design, with stigmatic imaging in the axial direction, while suffering from higher-order aberrations, is corrected for coma, thus performing better than the Wolter type-1. The Wolter type-1 and Wolter-Schwarzschild designs are optimized for on-axis but have reduced angular resolution when averaged over a wide field of view, with the averaging weighted by the area covered in the field of view. An optical design that maximizes angular resolution at the edge of the field of view rather than at the center is more suitable for wide-field X-ray telescopes required for deep-sky astronomical surveys or solar observations. A Hyperboloid-Hyperboloid optical design can compromise axial resolution to enhance field angle resolution, hence providing improved area-weighted average angular resolution over the Wolter-Schwarzschild design, but only for fields of view exceeding a specific size. Here, we introduce a new optical design that is free from coma aberration and capable of maximizing angular resolution at any desired field angle. This design consistently outperforms Wolter-1, Wolter-Schwarzschild, and Hyperboloid-Hyperboloid designs when averaged over any field of view size. The improvement in performance remains consistent across variations in other telescope parameters such as diameter, focal length, and mirror lengths. By utilizing this new optical design, we also present a design for a full-disk imaging solar X-ray telescope.

The detection of Line-of-sight (LOS) velocity of coronal mass ejections (CMEs) is crucial for understanding and forecasting their propagation. The LOS velocity can be derived from the Sun-as-a-star extreme ultraviolet spectrograph based on the Doppler effect. However, the poor spectral resolution of existing instruments is not sufficient for detection. In the paper, we propose a dual-band Sun-as-a-star spectrograph with high spectral resolution for measuring the LOS velocity of CMEs. Based on a multilayer concave grating operating in a normal incident mode, we optimized the parameters of the spectrograph for the wavelength ranges of 18.3( sim )21.3 nm and 49.6( sim )52.9 nm. The spectral resolving power for these two ranges exceeds 1000 and 2000, respectively, which is about three times higher than that of the Extreme ultraviolet Variability Experiment onboard the Solar Dynamics Observatory. B(_4)C/Al and B(_4)C/Mo/Al multilayer structures were optimized to improve the diffraction efficiency across both bands simultaneously. We also evaluated the instrument performance by calculating the photon numbers. Additionally, we discussed the degradation of spectral resolution caused by the stability of satellite platform, determining that the stability should be better than ±7.2(^{prime prime })(( pm )0.002(^circ )) within the exposure time of 60 s. Our investigation provides a new way to observe Sun-as-a-star extreme ultraviolet spectrum.

Ground-based observations of spacecraft signals have been used to study space weather. However, single spacecraft measurements observed from the Earth have limitations in studying the structure and evolution of solar plasma as they are unable to differentiate spatial and temporal variations. To overcome this limitation and improve our understanding of interplanetary scintillation, we simultaneously observed radio signals transmitted by two co-orbiting spacecraft: the ESA Mars Express (MEX) and the Chinese National Space Administration Tianwen-1 (TIW-1). We conducted the observations from April to November 2021 using the University of Tasmania’s VLBI radio telescopes at 8.4 GHz. We employed the Planetary Radio Interferometer and Doppler Experiment (PRIDE) technique to determine the topocentric Doppler measurements and residual phase of the carrier signal. These observables were used to quantify the phase fluctuations of the spacecraft signals caused by solar wind and hydrodynamic turbulence in the interplanetary medium. The measured phase fluctuations RMS from both spacecraft show small differences which are caused by factors such as the spacecraft’s motion, onboard electronics, and variations in the uplink signal path through Earth’s ionosphere. These fluctuations decrease with solar elongation and correlate with solar radio flux at 10.7 cm (2800 MHz), indicating solar activity. The estimated total electron contents along MEX and TIW-1’s radio lines of sight are similar, with higher values at lower solar elongations. Simultaneous multi-spacecraft observations also enable RFI characterization, frequent spacecraft performance comparisons, and investigation of solar activity effects on spacecraft performance and scientific outcomes.

The Athena mission entered a redefinition phase in July 2022, driven by the imperative to reduce the mission cost at completion for the European Space Agency below an acceptable target, while maintaining the flagship nature of its science return. This notably called for a complete redesign of the X-ray Integral Field Unit (X-IFU) cryogenic architecture towards a simpler active cooling chain. Passive cooling via successive radiative panels at spacecraft level is now used to provide a 50 K thermal environment to an X-IFU owned cryostat. 4.5 K cooling is achieved via a single remote active cryocooler unit, while a multi-stage Adiabatic Demagnetization Refrigerator ensures heat lift down to the 50 mK required by the detectors. Amidst these changes, the core concept of the readout chain remains robust, employing Transition Edge Sensor microcalorimeters and a SQUID-based Time-Division Multiplexing scheme. Noteworthy is the introduction of a slower pixel. This enables an increase in the multiplexing factor (from 34 to 48) without compromising the instrument energy resolution, hence keeping significant system margins to the new 4 eV resolution requirement. This allows reducing the number of channels by more than a factor two, and thus the resource demands on the system, while keeping a 4’ field of view (compared to 5’ before). In this article, we will give an overview of this new architecture, before detailing its anticipated performances. Finally, we will present the new X-IFU schedule, with its short term focus on demonstration activities towards a mission adoption in early 2027

X-ray Polarimeter Satellite (XPoSat) is India’s first landmark mission dedicated to X-ray polarimetry, with the aim of measuring and studying X-rays emitted by bright astronomical objects such as black hole X-ray binaries, pulsar wind nebulae, and accretion-powered pulsars. Polar Satellite Launch Vehicle-C58 (PSLV-C58) launched the XPoSat mission on 1st January 2024, equipped with two significant, scientific instruments: XSPECT (X-ray Spectroscopy and Timing) and POLIX (POLarimeter Instrument in X-rays). With the launch of XPoSat, a new and important fourth dimension of polarization has been added. POLIX became the first in the world to provide measurements of polarization in 8–30 kilo electron Volt (keV) energy band. XSPECT is a spectroscopy payload responsible for providing timing and spectral information in 0.8–15 keV energy band of X-ray emissions from about 54 potential identified cosmic X-ray sources. Astronomical sources emitting X-rays are sites of strong gravity, and strong magnetic fields and have a variety of geometries for scattering, which are expected to give rise to polarization signatures in these sources. This article provides a comprehensive overview from mission specifications to mission design, mission planning, mission analysis, and mission operations aspects of spacecraft configuration, operations, and on-orbit operations of XPoSat mission with the science brought by the first-time flown payload in high energy bands, which will allow astronomers to explore materials under intense magnetic and gravitational fields. The challenges involved in planning and executing the mission operations with critical scenarios have also been highlighted.

Microwave SQUID Multiplexing ((mu )MUX) is a widely used technique in the low-temperature detectors community as it offers a high capacity for reading large-scale Transition-Edge Sensor (TES) arrays. This paper proposes a Sliding Flux Ramp Demodulation (SFRD) algorithm for (mu )MUX readout system. It can achieve a sampling rate in the order of MHz while maintaining a multiplexing ratio of about one thousand. Advancing of this large array readout technique makes it possible to observe scientific objects with improved time resolution and event count rate. This will be highly helpful for TES calorimeters in X-ray applications, such as X-ray astrophysics missions.