Chinese Astronomy and Astrophysics最新文献

This paper describes the method of using the optical telescope to assist the Tianma 13 m radio telescope for pointing measurement and establishing the pointing error correction model. For small-aperture telescopes, there are few target sources for pointing and calibration, and it is difficult to establish a pointing model by radio method to cover the whole sky area. The Tianma 13 m radio telescope of Shanghai Astronomical Observatory is used to conduct optical-assisted pointing measurement research. A set of optical pointing system was installed on the back frame of Tianma 13 m antenna, which obtained a repeatable measurement accuracy better than 3”. In addition, through the analysis of the factors affecting the antenna pointing, a pointing error correction model containing 8 error terms, as well as the optical axis and electrical axis deviation models were established. The pointing model was brought into the antenna servo control system to cross-scan the calibration target radio source, and a pointing error of about 5” was obtained. This research can provide a reference method for high-precision pointing modeling.

Instrumental polarization is a vital factor for the accurate measurements of the solar magnetic field. It is necessary to optimize the optical design of the large solar telescope to obtain high accuracy solar magnetic field information. In this paper, an optimal design scheme based on four-mirror polarization compensation optics for the 8-meter giant solar telescope is presented. The polarization effect of pupil and field of view are analyzed by the polarization ray tracing programming, the telescope motion and wavelength properties of the field-effect are investigated detailedly. The result shows that, in the near infrared waveband which includes the magnetic sensitive spectral lines of He I 1.083 $\mu$m and Fe I 1.565 $\mu$m, the polarization-free field size is 0.91${}^{\prime }$, and the polarization-free field size in the visible band is 0.5${}^{\prime }$, in which the instrumental polarization of telescope is smaller than $2\times {10}^{-4}$.

The heliospheric radio emissions are the strongest radio emissions phenomenon in the solar system, with a radiation power of at least ${10}^{13}$ W, which can provide important physical information of high energy electron beam and magnetic plasma structure near the heliospheric boundary. Since the first detection by the Voyager spacecraft in 1983, those radio emissions have widely and continuously attracted much attention from researchers. There are generally two types of the heliospheric radio emissions: instantaneous or drifting emission with relatively high frequency, and continuous emission or non-drifting emission with relatively low frequency. Usually, both types of emissions start from about 2 kHz. For the drifting emission, it has the characteristic of drifting toward high frequency, the drifting rate is about 1–3 kHz/yr, the frequency range is 1.8–3.6 kHz, and the duration is about 100–300 days. For the non-drifting emission, it has no obvious frequency drift, the frequency range is 1.8–2.6 kHz, and the duration is about 3 yr. It is generally believed that the heliospheric radio emissions are related to shock. In this paper, the possible source region of the radio emissions, the emission mechanisms, and the source of shock related to the emissions are introduced. Furthermore, the existing scientific problems and the future perspectives on the research of heliospheric radio emissions are discussed.

Solar physics specializes the study of the fundamental processes occurred in the Sun and their influences on the interplanetary space. It deals with detailed measurements that are possible only for our closest star which is a natural plasma laboratory with multi-scale processes taking place. In addition, solar activities have a high impact on the space weather and habitability of the Earth, major solar eruptive events such as solar flare and coronal mass ejection have harmful effects on communication systems, satellites, power grid, and so forth. The study of the Sun not only helps us to understand the universe, the solar-terrestrial relationship, and the planetary habitability, but also serves national strategies in space and aerospace security. In the 21st century, there has been considerable progress in solar physics due to the development of detecting the Sun from space. In this paper, recent space exploration development trends of solar physics are examined both at home and abroad, key fields of the future space exploration development of solar physics in China are summarized, the disciplinary layout is optimized, and high-quality development of solar physics is promoted.

Using the multi-spectral lines from ALMA (Atacama Large Millimeter/submillimeter Array) with high-resolution ($\sim$ 0.2${}^{″}$–0.7${}^{″}$) and the continuum data, this work studies the physical properties of the nuclear region of nearby galaxy NGC 1068. The spectral lines include CO (1-0), CO (2-1), CO (3-2), HCN (1-0), HCO${}^{+}$ (1-0), HCN (3-2), HCO${}^{+}$ (3-2), HCN (4-3) and HCO${}^{+}$ (4-3). The CND (CircumNuclear Disk) shows an asymmetric ring structure with a size of $\sim$ 300 pc in the velocity-integrated intensity images. All the molecular lines of the CND show stronger emission at the eastern knot (E-knot) than the western knot (W-knot) of the CND. Furthermore, the E-knot shows larger velocities than the W-knot, which indicates that there is significant rotational pattern in the CND. The dense gas fraction (traced by the different transitions of HCN or HCO${}^{+}$ to CO (1-0) integrated intensity ratios) and dense gas ratio (HCN/HCO${}^{+}$) are higher at the E-knot, implying that the E- and W-knots have different physical environments or chemical compositions. The HCN emission in the CND show enhancement compared with HCO${}^{+}$, which could be affected by the AGN (Active Galactic Nucleus) radiation and starburst activity. The CO (3-2)/CO (1-0) integrated intensity ratio is a significant indicator of gas excitation. CO (3-2)/CO (1-0) ratios show much higher values at the E-knot, suggesting that there is molecular excitation enhancement caused by the extreme physical environment. Compared with the fluxes of HCN (4-3) and HCO${}^{+}$ (4-3) from the single-dish telescope JCMT (James Clerk Maxwell Telescope), the ALMA missing fluxes of dense molecular gas on 1 kpc scale are about 10%–20%. The spectral lines show that the flux ratios between E-knot and W-knot are $\sim$ 1.8–3.9. These differences shown between E-knot and W-knot may be associated with the AGN feedback. In addition, the CO (2-1), CO (1-0) and HCO${}^{+}$ (1-0) spectra show absorption features in the position of AGN. This absorption could be caused by the strong background of continuum emissions, and the gas inflow around the AGN can produce self-absorption in spectra.

As well known, more than 99% of the observable matter in the universe is plasma, and the plasma astrophysics studies various physical processes and phenomena occurring in cosmic plasmas, from small-scale collective interaction processes and energy transforming mechanisms in particle kinetics to the state of large-scale structure of cosmic objects and their eruptive phenomena. The present paper reviews the important role of the plasma astrophysics in the development of the modern astronomy as well as the formation of the modern plasma cosmology based on the history of the cosmic evolution, the formation of large-scale structures, and eruptive phenomena of cosmic objects. In addition, the unique function of satellite in situ exploring researches in space plasmas to act as the natural laboratory for the plasma astrophysics is further elaborated.

GRS 1915+105 is a galactic low-mass X-ray binary. Its energy spectra and black hole spin have been extensively studied. Since 2018 June, it has declined into a low-flux X-ray level, occasionally interrupted by multi-wavelength flares. Using the data of Insight-HXMT (Insight-Hard X-ray Modulation Telescope) satellite from August 30 to Oct 13, 2020, the energy spectra characteristics of GRS 1915+105 is investigated. The results show that the energy spectra can be well fitted with a Comptonized multi-temperature blackbody model. The evolution of the hardness-intensity diagram during the outburst remains in the soft state. Adopting new dynamical parameters of GRS 1915+105 (including the black hole mass $M$, the Sun mass $M_{\odot }$, the inclination angle $i$, and the distance $D$): $M=12.4_{-1.8}^{+2.0}$ $M_{\odot }$, $i={60}^{\circ }\pm 5^{\circ }$, $D=8.6_{-1.6}^{+2.0}$ kpc, the group obtains a lower limit of the black hole spin, $a_{*}>0.9990$, confirming that GRS 1915+105 is an extremely-spinning black hole. Considering the effects of a local absorber, the group adds the absorption component “tbpcf” into the model. Its equivalent hydrogen column density reaches ${10}^{23}$ cm${}^{-2}$, which is consistent with the characteristics of “Compton-thick”.

Collisionless magnetic reconnection, which converts the magnetic energy into the kinetic energy of plasma particles via the heating or acceleration, has been believed widely to be able to explain various eruptive phenomena such as solar flares and geomagnetic storms. However, the microphysical mechanism of anomalous resistivity in the collisionless magnetic reconnection is still an unsolved fundamental problem. Among the many physical mechanisms of anomalous resistivity generation, chaos-induced resistivity based on the chaos of the charged particle orbits near the magnetic neutral point is not the most popular formation mechanism, but its microscopic physical picture is the clearest. This paper first briefly reviews the early research and physical model of the chaos-induced resistivity in collisionless magnetic reconnection region, introduces the recent research progress of the chaos-induced resistivity, and expounds the future research direction of the chaos-induced resistivity.

Type Ia supernovae (SNe Ia) originate from thermonuclear explosions of carbon-oxygen white dwarfs at masses approaching the Chandrasekhar limit, and are widely used as standard candles for cosmological distances. However, the progenitor system and explosion mechanism of SNe Ia are still unclear. The circumstellar environment of SNe Ia has received increasing attention in recent decades. The distance and other geometric properties of the circumstellar material provide essential clues for exploring the physical origin of SNe Ia. At the same time, the scattering of circumstellar dust can produce observable effects on the light curve, spectrum, and polarization during the late phase of SNe Ia. The spectroscopically normal SNe Ia can be classified into two categories: normal-velocity and high-velocity ones. The high-velocity SNe Ia have an apparent blue excess within a few months after the maximum brightness. This blue excess can be fitted by circumstellar dust scattering. Meanwhile, fitting the late-phase spectrum or imaging polarization of SNe Ia can constrain the grain size or the geometric distribution of circumstellar dust, respectively. The result indicates that multi-epoch image polarimetry during the late phase of SNe Ia is a crucial probe to reveal the characteristics of circumstellar dust.

In the smooth mass distribution model, the critical curve represents a line with magnification divergence on the image plane in a strong gravitational lensing system. Considering the microlensing effects caused by discrete masses, the magnification map in the source plane exhibits a complex structure, which offers a promising way for detecting dark matter. However, simulating microlensing near the critical curve poses challenges due to magnification divergence and the substantial computational demands involved. To achieve the required simulation accuracy, direct inverse ray-shooting would require significant computational resources. Therefore we applied a GPU-based code optimized with interpolation method to enable efficient computation on a large scale. Using the GPU of NVIDIA Tesla V100S PCIe 32GB, it takes approximately 7000 seconds to calculate the effects of around 13,000 microlenses for a simulation involving ${10}^{13}$ emitted rays. Then we generated 80 magnification maps, and select 800 light curves for a statistical analysis of microcaustic density and peak magnification.