arXiv subjects

Fangyu Xu

Publications and source records attributed to Fangyu Xu.

4 recordsLinked to original sources

arXiv2026

Observations of a Solar Jet Triggered by Reconnection between Super-penumbral Fibrils and a Mini-filament

Coronal jets are highly dynamic phenomena in the solar atmosphere, yet their driving mechanisms remain an active topic of investigation. In this paper, we report a coronal jet triggered by the interaction between super-penumbral fibrils and a mini-filament, based on coordinated observations from the New Vacuum Solar Telescope (NVST), the Chinese H$\alpha$ Solar Explorer (CHASE), and the Solar Dynamics Observatory (SDO). The fibrils were anchored between the negative-polarity region of a sunspot and an emerging positive-polarity region associated with a moving magnetic feature (MMF). As the positive polarity migrated outward, the fibrils elongated and interacted with the mini-filament, one of whose footpoints was rooted in pre-existing negative-polarity fields. Intense brightenings at the interaction site, together with changes in the connectivity of the mini-filament footpoint from the pre-existing negative polarity to the sunspot, indicate the occurrence of magnetic reconnection. The event produced a narrow hot jet accompanied by a broader cool component. The cool plasma exhibited a clockwise rotation, providing evidence for the transfer of magnetic twist during reconnection. Persistent magnetic flux cancellation was observed before and during the jet eruption. These observations demonstrate that small-scale magnetic structures, such as MMFs, can significantly influence mini-filament eruptions and highlight the important role of flux cancellation in triggering coronal jet activity.

astro-ph.SR↗

arXiv2026

Machine Learning-based Separation of the He I 10830{\AA} Chromospheric Signal: Quantitative Analysis of Chromosphere-Corona Intensity in the Quiet Sun

The He I 10830{\AA} line, a crucial optically thin chromospheric line, is frequently used to study coronal heating and vertical coupling across the chromosphere-corona interface. However, its images are severely contaminated by the strong photospheric background signal, hindering the analysis of fine chromospheric structures. Given the morphological differences between the Active Region (AR) and the Quiet Sun (QS), we proposed separating the He I 10830{\AA} chromospheric signal using two deep learning CNN models. Our model utilizes TiO images and cross-band learning to infer the He I 10830{\AA} photospheric background. The output is combined with an exponential absorption model to achieve quantitative analysis of the pure chromospheric component. Joint analysis of Solar Dynamics Observatory (SDO) data and the separated QS structures reveals a strong spatial negative correlation between chromospheric He I 10830{\AA} intensities(R approx -0.84 in 304{\AA} ), and significant layered coupling with EUV (171, 193, and 304{\AA}) radiation. Furthermore, strong He I 10830{\AA} absorption areas are highly correlated with regions of strong magnetic fields, while 171{\AA} radiative enhancement areas extend to the strong magnetic field edges and the mixed-polarity regions. These findings quantify the radiation intensity relationship between He I 10830{\AA} and EUV bands in the Quiet Sun. It also demonstrates the differences in heating characteristics between unipolar and mixed-polarity magnetic fields.

astro-ph.SR↗

arXiv2024

Locating heating channels of the solar corona in a plage region with the aid of high-resolution 10830 Å filtergrams

In this paper, with a set of high-resolution He I 10830 Å filtergrams, we select an area in a plage, very likely an EUV moss area, as an interface layer to follow the clues of coronal heating channels down to the photosphere. The filtergrams are obtained from the 1-meter aperture New Vacuum Solar Telescope (NVST). We make a distinction between the darker and the brighter regions in the selected area and name the two regions enhanced absorption patches (EAPs) and low absorption patches (LAPs). With well-aligned, nearly simultaneous data from multiple channels of the AIA and the continuum of the HMI on board SDO, we compare the EUV/UV emissions, emission measure, mean temperature, and continuum intensity in the two kinds of regions. The following progress is made: 1) The mean EUV emissions over EAPs are mostly stronger than the corresponding emissions over LAPs except for the emission at 335 Å. The UV emissions at 1600 and 1700 Å fail to capture the difference between the two regions. 2) In the logarithmic temperature range of 5.6-6.2, EAPs have higher EUV emission measure than LAPs, but they have lower mean coronal temperature. 3) The mean continuum intensity over EAPs is lower. Based on the above progress, we suggest that the energy for coronal heating in the moss region can be traced down to some areas in intergranular lanes with enhanced density of both cool and hot material. The lower temperature over the EAPs is due to the greater fraction of cool material over there.

astro-ph.SR↗

arXiv2020

The estimate of sensitivity for large infrared telescopes based on measured sky brightness and atmospheric extinction

In order to evaluate the ground-based infrared telescope sensitivity affected by the noise from the atmosphere, instruments and detectors, we construct a sensitivity model that can calculate limiting magnitudes and signal-to-noise ratio ($S/N$). The model is tested with tentative measurements of $\rm M'$-band sky brightness and atmospheric extinction obtained at the Ali and Daocheng sites. We find that the noise caused by an excellent scientific detector and instruments at $-135^\circ \rm C$ can be ignored compared to the $\rm M'$-band sky background noise. Thus, when $S/N=3$ and total exposure time is 1 second for 10 m telescopes, the magnitude limited by the atmosphere is $13.01^{\rm m}$ at Ali and $12.96^{\rm m}$ at Daocheng. Even under less-than-ideal circumstances, i.e., the readout noise of a deep cryogenic detector is less than $200e^-$ and the instruments are cooled to below $-87.2^\circ \rm C$, the above magnitudes decrease by $0.056^{\rm m}$ at most. Therefore, according to observational requirements with a large telescope in a given infrared band, astronomers can use this sensitivity model as a tool for guiding site surveys, detector selection and instrumental thermal-control.

astro-ph.IM↗