| 1. |
- Chen, Yajie, et al.
(författare)
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Application of a Magnetic-field-induced Transition in Fe x to Solar and Stellar Coronal Magnetic Field Measurements
- 2023
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Ingår i: Research in Astronomy and Astrophysics. - : IOP Publishing. - 1674-4527. ; 23:2
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Tidskriftsartikel (refereegranskat)abstract
- Magnetic fields play a key role in driving a broad range of dynamic phenomena in the atmospheres of the Sun and other stars. Routine and accurate measurements of the magnetic fields at all the atmospheric layers are of critical importance to understand these magnetic activities, but in the solar and stellar coronae such a measurement is still a challenge due to the weak field strength and the high temperature. Recently, a magnetic-field-induced transition (MIT) of Fe x at 257.26 Å has been proposed for the magnetic field measurements in the solar and stellar coronae. In this review, we present an overview of recent progresses in the application of this method in astrophysics. We start by introducing the theory underlying the MIT method and reviewing the existing atomic data critical for the spectral modeling of Fe x lines. We also discuss the laboratory measurements that verify the potential capability of the MIT technique as a probe for diagnosing the plasma magnetic fields. We then continue by investigating the suitability and accuracy of solar and stellar coronal magnetic field measurements based on the MIT method through forward modeling. Furthermore, we discuss the application of the MIT method to the existing spectroscopic observations obtained by the Extreme-ultraviolet Imaging Spectrometer onboard Hinode. This novel technique provides a possible way for routine measurements of the magnetic fields in the solar and stellar coronae, but still requires further efforts to improve its accuracy. Finally, the challenges and prospects for future research on this topic are discussed.
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| 2. |
- Liu, Beibei, et al.
(författare)
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A tale of planet formation : From dust to planets
- 2020
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Ingår i: Research in Astronomy and Astrophysics. - : IOP Publishing. - 1674-4527. ; 20:10
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Tidskriftsartikel (refereegranskat)abstract
- The characterization of exoplanets and their birth protoplanetary disks has enormously advanced in the last decade. Benefitting from that, our global understanding of the planet formation processes has been substantially improved. In this review, we first summarize the cutting-edge states of the exoplanet and disk observations. We further present a comprehensive panoptic view of modern core accretion planet formation scenarios, including dust growth and radial drift, planetesimal formation by the streaming instability, core growth by planetesimal accretion and pebble accretion. We discuss the key concepts and physical processes in each growth stage and elaborate on the connections between theoretical studies and observational revelations. Finally, we point out the critical questions and future directions of planet formation studies.
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| 3. |
- Ghosh, Rana, et al.
(författare)
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Phenol in High-mass Star-forming Regions
- 2022
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Ingår i: Research in Astronomy and Astrophysics. - : IOP Publishing. - 1674-4527. ; 22:6
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Tidskriftsartikel (refereegranskat)abstract
- Phenol, which belongs to the C6H6O isomeric group, is the simplest molecule in the family of alcohol of the aromatic series. Although phenol has yet to be detected in the interstellar medium, a tentative identification was reported toward the Orion KL hot core using the IRAM-30 m line survey. To explore some more species of this isomeric group, we consider ten species to study the fate of their astronomical detection. It is noticed that phenol is the most energetically favorable isomer of this group. In contrast, propargyl ether is the least favorable (having relative energy similar to 103 kcal mol(-1) compared to phenol) species of this group. So far, the studies associated with the formation of phenol are heavily concentrated on combustion chemistry. Here, we suggest a few key reactions (C6H6 + OH -> C6H5 + H2O, C6H6 + O -> C6H5OH, C6H6 + H -> C6H5 + H-2, and C6H5 + OH -> C6H5OH + h nu) for the formation of phenol. All these pathways are included in a large gas-grain chemical network to study its formation in high mass star-forming regions and dark cloud environments. It is noticed that the phenyl (-C6H5) formation by the ice-phase hydrogen abstraction reaction of benzene (i.e., C6H6 + OH -> C6H5 + H2O if allowed at similar to 10 K) could serve as the starting point for the formation of phenol in the gas phase by radiative association reaction C6H5 + OH -> C6H5OH + h nu. The gas-phase reaction C6H6 + O -> C6H5OH significantly contributes to the formation of phenol, when the ice-phase reaction C6H6 + OH -> C6H5 + H2O is not considered at low temperature. Band 4 ALMA archival data of a hot molecular core, G10.47+0.03, are analyzed. It yields an upper limit on phenol abundance of 5.19 x 10(-9). Our astrochemical model delivers an upper limit on phenol abundance of similar to 2.20 x 10(-9) in the hot molecular core, whereas its production in the dark cloud is not satisfactory.
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| 4. |
- Fan, Jin, et al.
(författare)
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Development of wideband orthomode transducers for FAST cryogenic receiver system
- 2020
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Ingår i: Research in Astronomy and Astrophysics. - : IOP Publishing. - 1674-4527. ; 20:5
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Tidskriftsartikel (refereegranskat)abstract
- This paper describes the design, construction, and performance of the wideband orthomode transducers (OMTs) for the L- (1.2-1.8 GHz), the S- (2-3 GHz) and the P- (0.56-1.12 GHz) band receiver systems of the Five-hundred-meter Aperture Spherical radio Telescope (FAST). These OMTs operate at the cryogenic temperature of 70K to reduce their thermal noise contribution to the receiver chains. The development on the FAST L- and S-band quad-ridged waveguide (QRWG) OMTs is carried out based on the theoretical mode analysis. In view of the miniaturization of FAST cryogenic receiver system at P-band, a novel wideband compact bowtie dipole OMT is designed with an octave bandwidth as well as a length of only quarter wavelength. The proposed L-, S- and P-band OMTs are designed and optimized by using Ansys High Frequency Structure Simulator (HFSS), and then manufactured, tested at room temperature. Measurement of FAST cryogenic receiver system noise is also performed with the L-, S- and P-band OMTs installed. The measured results fully comply with the design specifications.
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| 5. |
- Liu, Hao, et al.
(författare)
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X-ray spectral evolution in an X-ray changing-look AGN NGC 1365 with variable column density
- 2021
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Ingår i: Research in Astronomy and Astrophysics. - : IOP Publishing. - 1674-4527. ; 21:8
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Tidskriftsartikel (refereegranskat)abstract
- X-ray changing-look active galactic nuclei (CL AGNs) are a subpopulation of AGNs, whose line-of-sight column densities increase/decrease within several years. The physical mechanism for the variation of column density is unclear. We reduce the X-ray data from XMM-Newton and NuSTAR observations for a CL AGN NGC 1365 with strong variation of column densities. The X-ray spectrum quickly softens as the X-ray luminosity increases and optical-to-X-ray spectral index also increases as increasing of optical luminosity. These results support that NGC 1365 also undergoes strong spectral evolution as that recently suggested for the optically selected CL AGNs with reappearance/disappearance of broad emission lines. Therefore, the variation of column density may be driven by the variable disk winds during the strong evolution of disk/corona.
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| 6. |
- Zhao, W., et al.
(författare)
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The jet of fsrq pks 1229-02 and its misidentification as a γ-ray agn
- 2019
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Ingår i: Research in Astronomy and Astrophysics. - : IOP Publishing. - 1674-4527. ; 19:12
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Tidskriftsartikel (refereegranskat)abstract
- Flat-spectrum radio quasar PKS 1229-02 with a knotty and asymmetric radio morphology was identified as the optical and radio counterpart of a γ-ray source. In this paper, we study the properties (e.g. morphology, opacity, polarization and kinematics) of the jet in PKS 1229-02 using radio interferometry. With our results, we find that the knotty and asymmetric morphology of this source may probably shaped by the interaction between its anterograde jet and the nonuniform dense ambient medium. By reproducing a Spectral Energy Distribution of PKS 1229-02 with the obtained kinematic parameters, we find that the relativistic beaming effect in PKS 1229-02 is not strong enough to produce the reported γ-ray emission, i.e. PKS 1229-02 may not be a γ-ray AGN. The misidentification may probably be due to the poor spatial resolution of the γ-ray detector of the previous generation.
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