Experimental Astronomy最新文献

In this paper, the wavefront perturbation method based on power detection of radio sources is used to measure the surface error of the Tianma radio telescope. By measuring the surface errors at different elevation angles, a surface compensation model to correct gravitational deformation is established. Observation results shows that the efficiency reduction caused by the gravitational deformation can be effectively compensated by loading this model on the active surface, especially at high and low elevations. A dual-beam calibration scheme is further used to remove atmospheric background fluctuations, which significantly improves data quality at lower elevations. The form and order of the perturbation modes and data processing are optimized to improve measurement accuracy. This paper presents the first attempt to apply the wavefront perturbation method to large radio telescopes and demonstrates its capacity and effectiveness in telescope runtime surface measurement and maintenance.

In an ideal germanium detector, fully-absorbed monoenergetic (gamma )–rays will appear in the measured spectrum as a narrow peak, broadened into a Gaussian of width determined only by the statistical properties of charge cloud generation and the electronic noise of the readout electronics. Multielectrode detectors complicate this picture. Broadening of the charge clouds as they drift through the detector will lead to charge sharing between neighboring electrodes and, inevitably, low-energy tails on the photopeak spectra. We simulate charge sharing in our germanium cross strip detectors in order to reproduce the low-energy tails due to charge sharing. Our goal is to utilize these simulated spectra to develop an analytical fit (shape function) for the spectral lines that provides a robust and high-quality fit to the spectral profile, reliably reproduces the interaction energy, noise width, and the number of counts in both the true photopeak and the low-energy tail, and minimizes the number of additional parameters. Accurate modeling of the detailed line profiles is crucial for both calibration of the detectors as well as scientific interpretation of measured spectra.

Time series reconstruction of astronomical catalogues is an important part of data archiving and a basis for time-domain astronomical analysis in the era of time-domain astronomy. As the field of view and sampling frequency of various time-domain telescopes increase, the amount of data to be processed becomes larger and larger. How to optimize the spatial and temporal efficiency of this process with the aid of computer technology becomes a hot issue. To address the problem of spatial efficiency, in this paper, we propose a time series data compression algorithm based on the negative database and dynamic programming, and on this basis, we design a multi-level storage and access query architecture for hot data and non-hot data, which greatly compresses the storage space of data while ensuring the query efficiency. To address the issue of time efficiency, this paper proposes a spatio-temporal data partitioning and layout algorithm suitable for distributed architecture, whose nested round-robin strategy has a wide range of load balancing effects on different spatial locations, temporal locations, and different ranges of temporal data queries, which can effectively ensure the execution efficiency of the distributed system. Experimental results show that the proposed optimization algorithm can keep the system at a low load skewness level of about 4% and save about 83% of storage space.

We use synthetic model spectra to investigate the potential of near-ultraviolet (3000-4050 Å) observations of massive O-type stars. We highlight the He I (lambda )3188 and He II (lambda )3203 pair as a potential temperature diagnostic in this range, supported by estimates of gravity using the high Balmer series lines. The near-ultraviolet also contains important metallic lines for determinations of chemical abundances (oxygen in particular) and estimates of projected rotational velocities for O-type spectra. Using the model spectra we present performance estimates for observations of extragalactic massive stars with the Cassegrain U-Band Efficient Spectrograph (CUBES) now in construction for the Very Large Telescope. The high efficiency of CUBES will open-up exciting new possibilities in the study of massive stars in external galaxies. For instance, CUBES will provide new insights into the physical properties of O-type stars, including oxygen abundances, in metal-poor irregular galaxies at (sim )1 Mpc from integrations of just 2-3 hrs. Moreover, CUBES will bring quantitative spectroscopy of more distant targets within reach for the first time, such as the O-type star (V (sim ) 21.5 mag) in Leo P (at 1.6 Mpc) in only half a night of observations.

The Ariel Space Mission aims to observe a diverse sample of exoplanet atmospheres across a wide wavelength range of 0.5 to 7.8 microns. The observations are organized into four Tiers, with Tier 1 being a reconnaissance survey. This Tier is designed to achieve a sufficient signal-to-noise ratio (S/N) at low spectral resolution in order to identify featureless spectra or detect key molecular species without necessarily constraining their abundances with high confidence. We introduce a P-statistic that uses the abundance posteriors from a spectral retrieval to infer the probability of a molecule’s presence in a given planet’s atmosphere in Tier 1. We find that this method predicts probabilities that correlate well with the input abundances, indicating considerable predictive power when retrieval models have comparable or higher complexity compared to the data. However, we also demonstrate that the P-statistic loses representativity when the retrieval model has lower complexity, expressed as the inclusion of fewer than the expected molecules. The reliability and predictive power of the P-statistic are assessed on a simulated population of exoplanets with H(_2)-He dominated atmospheres, and forecasting biases are studied and found not to adversely affect the classification of the survey.

PRATUSH – Probing ReionizATion of the Universe using Signal from Hydrogen – is a proposed cosmology experiment to detect the global red-shifted 21-cm signal from the Cosmic Dawn and Epoch of Reionization (CD/EoR). PRATUSH orbiting the Moon will seek to precisely measure the low-frequency radio sky-spectrum over 40 to 200 MHz. The scientific observations would be made in the radio-quiet region when in the farside of the Moon, and the data would be transmitted back to Earth when in the near-side. PRATUSH was proposed to the Indian Space Research Organization (ISRO) during a call for proposals in the announcement of opportunity for science payloads in 2018. PRATUSH is in the pre-project studies phase. Here we present a mission concept and baseline design of the proposed payload optimized to operate over the Cosmic Dawn signal band of 55 - 110 MHz. Starting with a description of the fundamental design principles followed, we discuss the PRATUSH baseline design and sensitivity. We further enumerate the challenges that are common to most PRATUSH like experiments, which have been proposed to seek a detection of the CD/EoR signal in orbit in the lunar farside. Due to the highly sensitive nature of the measurement, PRATUSH is designed to operate as a solo experiment with a dedicated spacecraft. Our simulations, assuming a mission lifetime of two years, estimate that PRATUSH would have the sensitivity required to detect the CD signal predicted by the standard models with varying degrees of confidence.A concept model of PRATUSH is under development, which is expected to lead to the engineering model followed by flight model subject to mission approval.

This article presents the design and implementation of a soft X-ray polarized calibration platform based on Bragg’s Law and Fresnel’s Law, which is used to calibrate low-energy polarization detector(LPD/POLAR-2) that has potential deployment onboard the China Space Station. The platform is equipped with versatile equipment that can generate both completely and partially polarized X-ray beams, and provides precise control over the diffraction angle, achieving the desired polarization degree. It covers the 3–8 keV energy band, with a high fraction of monochromatic light (>93%)(The proportion of monochromatic light is defined as the ratio of the number of photons falling within three times the sigma of the target peak centre value to the total photons.) and good monochromaticity(In this article, we evaluate the monochromaticity of the polarized source using the Full Width at Half Maximum (FWHM) of its all-in-one peak.), and is suitable for calibrating LPD’s large-field-of-view soft X-ray polarization detector using its vertically incident and obliquely incident polarized X-rays. The completely and partially polarized X-ray beams generated at 8.0 keV by the calibration platform are used to test the polarization measurement capabilities of the soft X-ray polarized detector and verify the linearity between the calibration source’s polarization and the measurable modulation of the polarimeter.

An observation simulator is established for the Spectroscopy Focusing Array (SFA) and Polarimetry Focusing Array (PFA) onboard the planned enhanced X-ray Timing and Polarimetry observatory (eXTP). It consists of photon generation, imaging, detection, and event readout to generate data products, which can be analyzed by the standard astronomical analysis software. It is used to simulate a few astronomical sources to estimate and understand the impact of the payload and platform design configurations on the scientific goals of eXTP, including the background estimation of the central pixel in SFA, position dependence of silicon drift detector signals and its impacts, and pointing jitter requirements. The joint data analysis of the SFA and PFA payloads shows that the PFA image can help estimate the impact of nearby sources on the target source and select the proper pixels for the background estimation of the central pixel in SFA. The spectral and timing study of the millisecond pulsar depicts that the position dependence of silicon drift detector signals itself has an insignificant impact on the results. The type-C low-frequency quasi-periodic oscillations of black holes ranging from 0.01 Hz to 30 Hz are considered to raise the pointing jitter requirements of the telescope. In this case, the stability of the telescope should be less than 12(^{prime prime }) to avoid any spurious modulation signal. These examples demonstrate the necessity of an end-to-end observation simulator in the space mission, which will be further tested and improved by the ground segment in a wider range of applications.

In an effort to map our meteor showers, a total of 76,765 meteoroids were triangulated by the United Arab Emirates Astronomical Camera Network between 01 January 2017 and 31 December 2021 as part of the global Cameras for Allsky Meteor Surveillance network. The calculated meteoroid orbits were analyzed by a newly developed user-friendly software to identify potential new meteor showers. The software is designed to run in three different modes that assign orbits to either a known shower, to any of the previously reported meteor showers listed in the IAU Working List of Meteor Showers, while the remainder of orbits are linked to find newly defined meteor showers using one of three Discriminant-criterion methods. 12 new meteors showers were identified and added to the IAU Working List, most of which identify the hitherto unknown debris streams of Jupiter-family comets.

POLAR-2, a plastic scintillator based Compton polarimeter, is currently under development and planned for a launch to the China Space Station in 2025. It is intended to shed a new light on our understanding of Gamma-Ray Bursts by performing high precision polarization measurements of their prompt emission. The instrument will be orbiting at an average altitude of 383 km with an inclination of 42° and will be subject to background radiation from cosmic rays and solar events. In this work, we tested the performance of plastic scintillation bars, EJ-200 and EJ-248M from Eljen Technology, under space-like conditions, that were chosen as possible candidates for POLAR-2. Both scintillator types were irradiated with 58 MeV protons at several doses from 1.89 Gy(corresponding to about 13 years in space for POLAR-2) up to 18.7 Gy, that goes far beyond the expected POLAR-2 life time. Their respective properties, expressed in terms of light yield, emission and absorption spectra, and activation analysis due to proton irradiation are discussed. Scintillators activation analyses showed a dominant contribution of β + decay with a typical for this process gamma-ray energy line of 511 keV.