Chinese Astronomy and Astrophysics最新文献

Firstly, four types of BeiDou dual-frequency combined common-view time transferring modes were briefly introduced. The software rnx2cgg, supporting the new signals in BeiDou-3 not included in CGGTTS V2E (Common GNSS (Global Navigation Satellite System) Generic Time Transfer Standard Version 2 Extended), was developed for converting RINEX (Receiver Independent Exchange Format) to CGGTTS. Secondly, the BeiDou timing error models were comprehensively analyzed, including SISRE (Signal-In-Space Ranging Error), pseudorange measurement noise, and DCB (Differential Code Bias). Then, the common-view weighting function was mathematically determined based on the error modes. Finally, the performances of single-station timing and between-station common-view were analyzed with the time transfer experiments between BSNC (Beijing Satellite Navigation Center) and MGEX (The Multi-GNSS Experiment and Pilot Project) stations. The experiments show that, the closure error of the whole link from ground to space is better than 2 ns. The BeiDou common-view noise is about 0.7 ns, corresponding to the time transferring stability of $1\times {10}^{-9}/\tau$ in short and medium term over long distance.

Satellite galaxies are powerful probes of galaxies formation. Recent studies have pointed out that when the central galaxy is an elliptical galaxy, there are more satellite galaxies than spiral galaxies. In order to explore this difference, we used the data constructed from TNG300-1 of the Next Generation Illustris Simulations set. We select the central galaxies within ${10}^{10}{M}_{\odot }·h^{-1}\le M_c\le {10}^{12}{M}_{\odot }·h^{-1}$ in stellar mass. At the same time, central galaxies in this range are divided into spirals and ellipticals according to the bulge-to-total mass ratio (B/T). Through the usage of statistical methods, we found that when the mass distribution of the halos is controlled (the halo mass distribution is exactly the same between spirals and ellipticals), there is still a new difference in the distribution of satellite galaxies. However, the satellites of the spirals are significantly more than ellipticals. This conclusion is contrary to observations. The main reason for this difference is that the satellite galaxies of spirals contain more cold gas, which makes the satellites of spirals more efficient in star formation.

The direct-imaging exploration can obtain comprehensive physical information of exoplanets, which is a key technology to search for extraterrestrial life in the future. In this paper, based on our recent high-contrast imaging data of ground-based telescope, the newly discovered multi-star candidates are presented. In the early stage, combined with the ability of high-contrast imaging equipment for the exoplanets in the ground-based system, we select about 1000 targets from published works which are compiled using the catalogs released by Gaia. These targets are distributed in different young star clusters. Recently, we used Hale Telescope at Palomar Observatory to carry out high-contrast imaging observation on 42 of the above targets in the K-band. Most of the observed targets are 7.5–14 in the V-band. In 2019, after two rounds of observation, we discover six multi-star system candidates. It is however difficult to find out whether these targets are single-star or multi-star systems in Gaia DR2 (Data Release 2) catalog and Gaia EDR3 (early Data Release 3) catalog.

We searched the quasi-periodic variability in the light curve of blazar 3C 66A in the optical V band. The data used in this paper are from Shanghai Astronomical Observatory (ShAO), AAVSO (The American Association of Variable Star Observers), and Steward Observatory respectively, with a total coverage of $\sim$18 years (from 2003 to 2021). Two methods were employed to search for the possible quasi-periodic variability in the resulting optical light curve of the source. The Jurkevich method yielded two possible periods of (850 $\pm$ 90) d ($\sim$2.3 yr) and (1150 $\pm$ 140) d ($\sim$3.2 yr). While the Lomb-Scargle Periodogram, with the red noise considered, yielded two possible periods of (869 $\pm$ 70) d and (1111 $\pm$ 90) d, which are consistent with the results of the Jurkevich method. The significance level of the two periods calculated using the PSRESP (power spectra response) method is $>$ 99% and $>$ 95% for the two possible periods, respectively. We compared our results with previous researches, and found that the period around 2.3 yr is stable in the historical light curve of 3C 66A, while the later one is more likely a transient phenomenon which is only present in the high state of the source.

We use the results of high resolution numerical simulations to fix the theoretical model of high redshift quasars (QSOs) ionizing and heating neutral gas, and predict the signal characteristics and signal/noise (S/N) ratios for Five-hundred-meter Aperture Spherical Telescope (FAST) to observe the 21 cm radiation around QSO. Our conclusions are summarized as: (1) the 21 cm frequency spectrum under the FAST field has full HII region for the QSO at $z=8$ and with luminosity similar to ULAS J1120+0641, while has only a small trough for the QSO at $z=10$ and with low luminosity; (2) the effect of Finite Light Travel Time (FLTT) obviously changes the 21 cm frequency spectrum of high redshift QSOs, makes the transition curve at lower frequency much steeper than that at higher frequency; (3) the FAST telescope can observe the 21 cm radiation of high redshift QSO with very high S/N ratio as high as $\sim 12$, thus can identify the HII regions and the FLTT effect.

Light variation is one of the most significant observation features of Blazar, some of which are quasi periodic. The analysis of Blazar’s variability periodicity can provide important information for explaining the internal physical structure of its central black hole and accretion disk. In this paper, benefited from the advantages of empirical mode decomposition (EMD) and auto-regressive (AR) model spectrum estimation methods, a combined variability periodicity analysis method is proposed based on the EMD-AR spectrum. First, EMD is used to decompose the observed data to obtain the modal components, and the correlation coefficient between them and the original light variation curve are calculated. Then, the variability periodicity of the components with a high correlation is estimated and summed. Finally, the light variation period of Blazar is calculated by using the power spectrum. The principle and application steps of EMD-AR spectrum method are discussed, and the observational data of quasar 3C 273 from 1887 to 2016 are analyzed with this method. The long time scale periods of object 3C 273 were 21.23, 13.51, 11.02, 5.51, 4.69, 3.79, and 2.76 yr, which were in good agreement with that reported in the literature. The short time scale periods were (30$\pm$1), (15$\pm$ 0.3), (7.5 $\pm$ 0.2), (10 $\pm$ 0.1), (5 $\pm$ 0.6) and (6 $\pm$ 0.4), and (3 $\pm$ 0.5) min. There is an approximate period-doubling relationship among these possible periods, which has not been reported before, and may provide reference for further research.

In this paper, by comparing the optical spectra of Sloan Digital Sky Survey (SDSS), Keck LRIS (Low-Resolution Imaging Spectrograph), and Baryon Oscillation Spectroscopic Survey (BOSS), a preliminary study has been done on the properties of the accretion disk of the double-peaked broad line radio quasar B3 1637+436A. The continuum of the SDSS spectrum of B3 1637+436A (May 21, 2001) and the Keck spectrum (June 28, 2003) is not significantly different, while the continuum of the BOSS spectrum (June 17, 2018) is about 1.2 magnitudes lower than the SDSS spectrum in the V band. The H$\alpha$ emission lines of the three spectra have a clear double-peaked broad line profile. Like the continuum, the double-peaked broad line profile is also considered to come from the accretion disk. By fitting the disk model of the double-peaked profile of H$\alpha$ on the three spectra, we found that the double-peaked H$\alpha$ profile of the BOSS spectrum can be well fit with a single disk model, and the emission line region lies about 900–3000 gravitational radius away from the central black hole. The double-peaked profiles of SDSS and Keck’s H$\alpha$ need to be fit with two disk models. The corresponding accretion disk emission area has two regions, one of which (“The outer disk”) is similar to BOSS, and the other emission region (“The inner disk”) is located within the range of about 400–900 gravitational radius, which is much smaller than the outer disk. Combining the characteristics of variations of the continuum spectrum, we believe that the disappearance of the inner disk is the main reason for the variation between the SDSS/Keck spectrum and the BOSS spectrum.

Radio frequency interference (RFI) is one of the main challenges in the search of radio targets and their accurate analysis. The efficient RFI detection and mitigation techniques are required in the radio data processing. Existing RFI mitigation algorithms typically fall into three categories: component decomposition methods, threshold-based methods, and machine learning methods. The threshold-based algorithms are widely used in real applications because of its clear principle, simple structure, and easily implementation. Especially, the SumThreshold method is becoming more concerned for its good performance in RFI detection. Therefore, this work investigates the principles and algorithm of SumThreshold, and discusses its characteristics and applicability.

China plans to establish a lunar orbital VLBI (Very Long Baseline Interferometer) station around 2025, which will carry a space passive hydrogen maser as the time and frequency reference. Since it is the first time to use a space passive hydrogen maser for VLBI observation, its feasibility needs to be studied and verified. Therefore, we carried out VLBI observations using the space passive hydrogen maser as the frequency reference. In the experiment, the active hydrogen atomic clock and space passive hydrogen maser were used as the frequency standard, and the alternate VLBI observations of China’s Mars probe TW1 (Tianwen 1) were carried out using the 25 m radio telescope at Sheshan, Shanghai, and other VLBI stations. The results of data processing and analysis show that the standard deviation of VLBI residual group delay based on both active hydrogen atomic clock and space passive hydrogen maser are within 0.5 ns, which indicates that the space passive hydrogen maser can meet the accuracy requirements of VLBI measurement for deep space exploration, and verify its feasibility as the frequency standard of lunar orbital VLBI stations.

Wide field, high sensitivity, high resolution, wide bandwidth, and polarization components are constantly pursued by CO molecular line surveys at millimeter wavelengths. Several key science cases that could be focused on by future large-scale molecular surveys have been identified upon the current progress of molecular surveys. A conceptual design for the new-generation multi-beam receiver system is proposed. Combined with the latest technical progress, the key technical solutions to realize the scheme are explained. The new design aims at a receiving scale of 100 beams. Following the newly developed hybrid planar integration technology, a new dual polarization receiving function is realized while inheriting the sideband separation mixing mode. On the basis of multi-line receiving configuration, each receiving sideband is expanded to 8 GHz. Judged from the existing technologies and the newest progress, this conceptual design scheme is fully achievable. Compared with the existing millimeter wave multi-beam receiving equipment, the comprehensive receiving capacity of the new generation millimeter wave multi-beam receiving system is estimated to increase by a factor of 89–178. This design is expected to bring another evolutionary progress for millimeter wave multi-beam receiving capability.