Yun-Ao Xiao

Yun-Ao Xiao

National Astronomical Observatories, Chinese Academy of Sciences (NAOC)

A20, Datun Road, Chaoyang District, Beijing 100012, China

Tel: +44-7526 328476

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Pages

Posts

Future Blog Post

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Blog Post number 4

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Blog Post number 3

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Blog Post number 2

less than 1 minute read

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Blog Post number 1

less than 1 minute read

Published:

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education

portfolio

publications

submits

Star Proper Motions Based on Two-epoch Observations from the SDSS and DESI Imaging Surveys

Submitted to Astronomical Journal, first author, 2024

In this study, we present the construction of a new proper motion catalog utilizing the photometric data from the Sloan Digital Sky Survey (SDSS) and Dark Energy Spectroscopic Instrument (DESI) imaging surveys, with a median time baseline of about 13 years. To mitigate systematic errors, the DESI galaxy positions are employed to establish a reference frame and to correct the position-, magnitude-, and color-dependent discrepancies between SDSS and DESI imaging datasets. Spanning 12,589 square degrees, the catalog encompasses about 206.6 million non-Gaia objects down to m_r ~ 23. Based on 734k quasars, the assessment of the global systematic errors in the DESI-SDSS proper motion catalog yields values of 0.14 mas yr^-1 for $\mu\alpha$ and 0.11 mas yr^-1 for $\mu\delta$. The catalog exhibits a precision surpassing 3.7 mas yr^-1, albeit varying with position, color, and magnitude. An additional evaluation employing approximately 5,300 distant star samples yields an overall precision of approximately 3.0 and 2.9 mas yr^-1 for $\mu\alpha$ and $\mu\delta$, respectively. Further comparisons with proper motions from SDSS Stripe 82 reveal a strong consistency between the two datasets. As a practical application, we utilize fainter non-Gaia objects in our catalog to update the proper motions of 17 star clusters. The resulting proper motions for these clusters exhibit excellent consistency with those derived from Gaia data. Our proper motion measurements, characterized by a deeper limiting magnitude, stand as a valuable complement to the Gaia dataset. The catalog is publicly available at https://www.scidb.cn/s/YzaIv2.

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CSST Large Scale Structure Analysis Pipeline: III. Emission-line Redshift Measurement for Slitless Spectra

Submitted to Monthly Notices of the Royal Astronomical Society, participate, 2024

The China Space Station Telescope (CSST) is a forthcoming space-based optical telescope designed to co-orbit with the Chinese Space Station. With a planned slitless spectroscopic survey spanning a broad wavelength range of 255 − 1000 nm and a spectral resolution exceeding 200, the CSST holds significant potential for cosmic large-scale structure analysis. In this study, we focus on redshift determinations from slitless spectra through emission line analysis within the CSST framework. Our tailored redshift measurement process involves identifying emission lines in one-dimensional slitless spectra, aligning observed wavelengths with their rest-frame counterparts from prominent galaxy emissions, and calculating wavelength shifts to determine redshifts accurately. To validate our redshift measurement algorithm, we leverage simulated spectra generated by the CSST emulator for slitless spectroscopy. The outcomes demonstrate a remarkable redshift completeness exceeding 85 per cent for emission line galaxies (ELGs), alongside an purity surpassing 83 per cent. The redshift uncertainty remains impressively below 0.001. Notably, when concentrating on galaxies with more than three matched emission lines, both the completeness of ELGs and the purity of measurable galaxies can reach 97 per cent. Furthermore, we explore the influence of parameters like magnitude, spectral signal-to-noise ratio, and redshift on redshift completeness and purity. The discussion also delves into redshift degeneracies stemming from emission-line matching confusion. Our developed redshift measurement process will be applied to extensive simulated datasets and forthcoming CSST slitless spectroscopic observations for further cosmological and extragalactic analyses.

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Changing-look Active Galactic Nuclei from the Dark Energy Spectroscopic Instrument. II. Statistical Properties from the First Data Release

Submitted to Astrophysical Journal Supplement Series, participate, 2024

We present the identification of changing-look active galactic nuclei (CL-AGNs) from the Dark Energy Spectroscopic Instrument First Data Release and Sloan Digital Sky Survey Data Release 16 at z ≤ 0.9. To confirm the CL-AGNs, we utilize spectral flux calibration assessment via an [O III]-based calibration, pseudo-photometry examination, and visual inspection. This rigorous selection process allows us to compile a statistical catalog of 561 CL-AGNs, encompassing 527 $\text{H}\beta$, 149 $\text{H}\alpha$, and 129 Mg II CL behaviors.
In this sample, we find:
1. A 283:278 ratio of turn-on to turn-off CL-AGNs.
2. The critical value for CL events is confirmed around Eddington ratio ~ 0.01.
3. A strong correlation between the change in the luminosity of the broad emission lines (BEL) and variation in the continuum luminosity, with Mg II and Hβ displaying similar responses during CL phases.
4. The Baldwin-Phillips-Terlevich diagram for CL-AGNs shows no statistically significant difference from the general AGN catalog.
5. Five CL-AGNs are associated with asymmetrical mid-infrared flares, possibly linked to tidal disruption events.
Given the large number of CL-AGNs and the stochastic sampling of spectra, we propose that some CL events are inherently due to typical AGN variability during low accretion rates, particularly for CL events of the singular BEL. Finally, we introduce a Peculiar CL phase, characterized by a gradual decline over decades in the light curve and the complete disappearance of entire BEL in faint spectra, indicative of a real transition in the accretion disk.

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talks

teaching

Astronomical Data Reducation, Teaching Assistant

Graduate course, University of Chinese Academy of Sciences, School of Astronomy and Space Science, 2024

This course introduces the basic observational equipment and methods used in astrophysical observations across various electromagnetic wave bands from a practical observational perspective. It aims to train graduate students in astronomy to understand the acquisition and processing of observational data in modern astrophysics, promote the organic integration of astronomical observation with mathematical and physical knowledge, and expand students’ knowledge in astrophysics. The course covers practical astrophysical methods, including data acquisition, processing, and analysis, with each topic featuring hands-on assignments for data processing. This training is designed to develop essential research skills for graduate students in astronomy and lay a solid professional foundation for their future research in astrophysics. I work with Prof. Hu Zou, responsible for teaching photometric and spectral observations in the optical and infrared bands.
As a teaching assistant, my primary role is to guide students through practical optical observations and the processing of optical data. This includes hands-on training in data acquisition, calibration, and various analysis methods, ensuring students gain valuable experience in reducing and interpreting astronomical data effectively.