Experimental Astronomy最新文献

Eastern Anatolia Observatory (DAG), located at 39.78 degrees North latitude (N) and 41.23 degrees East longitude (E) with 3170 m altitude above the sea level in the east part of Türkiye, having the first 4m class infrared (IR) telescope. DAG telescope is not only the largest telescope in Türkiye but also the most important telescope in the northern hemisphere because it also covers a large observational gap thanks to its location over the World. The atmospheric conditions of the DAG site have a major impact on the quality of observations in ground-based astronomy. The atmospheric conditions of an observatory site being effective and important for both optical and infrared observations is a key parameter in assessing the performance of astronomic observations and observatory sites. In this study, as an observatory site, a detailed long-term atmospheric and astronomical analysis of DAG site were presented for near-infrared observations, especially. Within the scope of basic atmospheric and astronomical parameters, it has been revealed that the DAG site is an observatory site with a great astronomical observation potential, due to its location, robust infrastructure, astronomical and atmospheric properties originating from geography.

The grazing-incidence optics with Wolter-I type geometry is commonly used in X-ray astronomy. The manufacturing technologies are still under development for future space missions to fulfill the stringent performance requirements with reduced weight and cost, e.g. the planned enhanced X-ray Timing and Polarimetry Mission. To improve the manufacturing process, it is necessary to study the relationship between metrological characterization and angular resolution via ray-optics or wave-optics models. The model calculations produce inconsistent results depending on the characteristics of wide-band surface errors, which require validation before their application in the Wolter-I type optics. In this work, two samples of the single-reflection mirrors with an elliptical shape are produced to validate the models. The first sample uses the Aluminum alloy substrate and the second sample uses the Aluminum alloy coated with Nickel-Phosphorous as the substrate. Tungsten is coated on both substrates to increase the X-ray reflectivity. The metrological characterization is inspected using the Fizeau interferometer and 3D optical profiler. The X-ray calibration of the mirror is performed in the 100-m X-ray Test Facility of Institute of High Energy Physics using the Color X-ray Camera. Both ray-optics and wave-optics models are validated in a wide scope of applications from smooth to relatively rough surfaces. The proper treatments of the metrological data are required as input to the model calculations: the post-fit distribution of figure errors, the micro-roughness defined in a specific frequency band, and the smoothed power spectral density of the surface errors. The validated models can be further applied in Wolter-I optics to predict mirror performances or to provide precision processing requirements.

The magnetic field strength and its topology play an important role in understanding the formation, evolution, and dynamics of the solar corona. Also, it plays a significant role in addressing long-standing mysteries such as coronal heating problem, origin and propagation of coronal mass ejections, drivers of space weather, origin and acceleration of solar wind, and so on. Despite having photospheric magnetograms for decades, we do not have reliable observations of coronal magnetic field strengths today. To measure the coronal magnetic field precisely, the spectropolarimetry channel of the Visible Emission Line Coronagraph (VELC) on board the Aditya-L1 mission is designed. Using the observations of coronal emission line Fe XIII [10747Å ], it is possible to generate full Stokes maps (I, Q, U, and V) that help in estimating the Line-of-Sight (LOS) magnetic field strength and to derive the magnetic field topology maps of solar corona in the Field of View (FOV) (1.05 – 1.5 R(_{odot })). In this article, we summarize the instrumental details of the spectropolarimetry channel and detailed calibration procedures adopted to derive the modulation and demodulation matrices. Furthermore, we have applied the derived demodulation matrices to the observed data in the laboratory and studied their performance.

In the universe, there are up to 2 trillion galaxies with different features ranging from the number of stars, light spectrum, age, or visual appearance. Consequently, automatic classifiers are required to perform this task; furthermore, as shown by some related works, while greater the number of classes considered, the performance of the classifiers tends to decrease. This work is focused on the morphological classification of galaxies. They can be associated with a subset of 10 classes arranged in a hierarchy derived from the Hubble sequence. The proposed method, Bayesian and Convolutional Neural Networks (BCNN), is composed of two main modules. The first module is a convolutional neural network trained with the images of galaxies, and its predictions feed the second module. The second module is a Bayesian network that evaluates the hierarchy and helps to improve the prediction accuracy by combining the predictions of the first module through probabilistic inference over the Bayesian network. A collection of galaxies sourced from the Principal Galaxies Catalog and the APM Equatorial Catalogue of Galaxies are used to perform the experiments. The results show that BCNN performed better than five CNNs in multiple evaluation measures, reaching the scores 83% in hierarchical F-measure, 78% in accuracy, and 67% in exact match evaluation.

The primary objective of this study is to employ Multi-Criteria Decision Analysis (MCDA) and Geographical Information System (GIS) techniques to identify and assess potential sites for astronomical observations in Antarctica. Our study focuses on the development of the Suitability Index for Astronomical Sites in Antarctica (SIASA). This index is formulated by merging data from satellites and models, providing extensive temporal and spatial coverage over two decades. To assess its suitability, we employed a combination of MCDA and GIS techniques, allowing us to evaluate various data, including cloud cover (CC), precipitable water vapor (PWV) levels, elevation, atmospheric temperature and wind speed. Our analysis confirmed the exceptional characteristics of Antarctica: An average of 361 cloud-free days per year, exceptionally low PWV values (0 mm), and an average elevation of 2.300 meters. The stable atmospheric wind profile further enhances its suitability for astronomical observations. Long-term trends and correlations of the data were also studied. SIASA values identified the eastern and inner parts of the Transatlantic Mountains as highly favorable for astronomical observations, while the coastal areas were considered less suitable. The best sites cover 10% of Antarctica in all SIASA scenarios, with Dome A, Ridge A and Dome F having the highest values of all stations. These findings hold considerable importance in planning future astronomical sites on the continent.

The spiral structure is an important morphology within galaxies, providing information on the formation, evolution, and environment of spiral galaxies. The number of spiral arms is one of the important parameters to describe the morphology of spiral galaxies. In this project, we study the classification of spiral galaxies by the number of spiral arms based on deep learning algorithms. The data set for this project consists of eligible samples from Galaxy Zoo 2 and Galaxy Zoo DECaLS. To better identify the texture features of the spiral arms, we designed a convolutional neural network model incorporating Gabor filter (Gabor Residual Filtering Convolutional Net, GReFC-Net), and used other networks for 3 and 4-way classifications. In the 3-way case, the GReFC-Net algorithm achieves the highest precision, recall, F1-score, and AUC value, which are 96.25%, 96.23%, 96.21%, and 0.9937. In the 4-way case, the GReFC-Net algorithm has the highest recall, F1-score and AUC value, which are 95.57%, 95.42% and 0.9957. The interpretability of GReFC-Net is analyzed by the SHAP method, and the results show that the network can identify the spiral arm structure of spiral galaxies well. It can be seen that the GReFC-Net algorithm can be effectively applied to the automatic measurement task of spiral arm structure in a large number of spiral galaxies.

In this study, we have presented the results of the precipitable water vapor (PWV) for the Eastern Anatolia Observatory (in Turkish: Doğu Anadolu Gözlemevi, the acronym is DAG) site in Erzurum, Türkiye. The DAG has Türkiye’s largest and the first near infrared (NIR) telescope with a mirror diameter of 4 meters at the altitude of 3170 m. The DAG telescope is going to take the first light in the end of summer 2024. This study is focused on the examining of the precipitable water vapor data for the NIR observations at the DAG. In this context, the NWC SAF Total Precipitable Water (TPW) data obtained by both the satellite based and the radiosonde balloon validated with six radiosonde stations were examined by temporal, vertical and horizontal analyses for the DAG site between June 2019 to December 2020. The results obtained from these analyzes indicate that the mean and median TPW values at the DAG site were approximately 7 mm and the minimum and maximum values were 0.59 mm and 24.12 mm, respectively. The monthly median TPW values at the DAG site varied between approximately 3-10 mm, with a decreasing trend from June to January and an increase in the first seven months of 2020. These results also indicate that the TPW data obtained by its 15 minutes temporal resolution, aligns closely with the radiosonde measurements. Furthermore, the values of PWV at both lower and upper levels of the atmosphere are minimal while the values increase slightly in the middle layer of the atmosphere. As a result, the effective monitoring of the PWV in a site would result in the generation of higher quality astronomical IR observations and be important in terms of the optimum operating cost for an observatory.

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.

The enhanced X-ray Timing and Polarimetry mission (eXTP) is a next-generation flagship X-ray astronomy satellite currently in phase-B study. The large Area Detector (LAD) on board eXTP contains 40 modules, each consisting of a set of 4(times )4 large area SDDs and 4(times )4 collimators, and has a designed effective area of 3.0 m(^2) at 8 keV and a Field of View (FoV) of 1(^circ ). To achieve such a large effective area, the collimator’s Open Area Ratio (OAR) should be greater than 70%. In this paper, we introduce the measurement methods used to determine the OAR and the rocking curve (angular response) of the LAD collimator at the 100-m X-ray Test Facility (100XF) of the Institute of High Energy Physics (IHEP) in Beijing, and report the results of the collimators manufactured under different conditions. The measured OARs of the collimators are usually smaller than the theoretical values by a few percent, which is due to the non-uniformity and irregularity of the pores. The measured rocking curves are usually broader than the theoretical triangular curves, and the lower the energy of the incident X-ray the broader the rocking curve. This broadening of the rocking curve is the result of reflection on the inner wall of the pores. Our results also show that increasing the etching time in the manufacturing of the collimators can increase the OARs but does not change significantly the shape of the rocking curves.

The spectroscopy focusing array is one of the four main scientific instruments of the enhanced X-ray Timing and Polarimetry mission, tasked with spectral and timing observation in the energy range 0.5-10 keV. An engineering model of the spectroscopy focusing array with a 4 mirror shells assembly and a focal plane detector using commercial detectors has now been developed. To evaluate the performance, the spectral and timing calibration of the engineering model has been held in the 100-m X-ray Test Facility. A multi-target X-ray source with multiple emission lines is used to calibrate the spectral performance. A timing X-ray source based on a grid controlled X-ray tube has been utilized for the timing calibration. The timing X-ray source can generate X-ray pulses to measure the response time distribution, and can also simulate the pulsar lightcurves to examine the detection ability for pulsars. The energy-channel relation and energy resolution are determined through spectral calibration. The energy resolution at 5.95 keV is 142 eV, now. According to the timing calibration, the mean response time of the engineering model is 1.55 (upmu )s, the full width at half maximum of the response time distribution is 0.45 (upmu )s, and the engineering model has sufficient ability to detect the profile of millisecond pulsars.