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Ruoyi, Zhang
A Ph.D student majoring in astronomy

About

Ruoyi, Zhang

zry@mail.bnu.edu.cn ｜ Beijing, China

Education

2019.9 – present ｜ Department of Astronomy, Beijing Normal University ｜ Doctor
2023.12 – 2024.12 ｜ Max Planck Institute for Astronomy ｜ Visiting Ph.D student
2015.9 – 2019.6  ｜ Department of Astronomy, Beijing Normal University ｜ Bachelor

(Supervisor: Haibo, Yuan)

Research Interests

  • Interstellar dust
  • Diffuse interstellar bands (DIBs)
  • The large-scale structure of the Milky Way

Finished Projects

  1. Detections of Dust in the Outskirts of M31 and M33 (Published in ApJL)

    We using about 0.2 million stars selected from the LAMOST data and combining precise photometry and parallaxes from the Gaia DR2, we have constructed a two-dimensional foreground dust reddening map toward the M31 and M33 region. From our revealed map of extragalactic dust, we found the dust disks of M31 and M33 extend to about 2.5 times their optical radius. A large amount of dust is detected in the M31 halo out to over 100 kpc.

  2. Stellar Color Loci of Red Giant Stars in SDSS Stripe 82 (Published in Research in Astronomy and Astrophysics (RAA))

    We present the metallicity-dependent Sloan Digital Sky Survey (SDSS) stellar color loci of red giant stars, using a spectroscopic sample of red giants in the SDSS Stripe 82. With good photometry, photometric metallicities of red giants can be reliably determined to an accuracy of 0.2 – 0.25 dex, comparable to the precision achievable with low-resolution spectroscopy for a signal-to-noise ratio of 10. We also propose a new technique to discriminate between red giants and MS stars based on the SDSS photometry. The technique achieves completeness of ∼70 percent and efficiency of ∼80 percent in selecting metal-poor red giant stars of [Fe/H] ≤ –1.2.

  3. Empirical Temperature- and Extinction-Dependent Extinction Coefficients (Published in ApJS)

    We have obtained accurate dust reddening from far-ultraviolet to the mid-infrared for up to 5 million stars by the star-pair algorithm based on LAMOST stellar parameters along with GALEX, Pan-STARRS 1, Gaia, SDSS, 2MASS, and WISE photometric data. And we derived the empirical reddening coefficients for 21 colors both in the traditional (single-valued) way and as a function of \({\rm T_{eff}}\) and E(B-V). Comparisons with measurements in the literature show that the \({\rm T_{eff}}\) - and E(B-V)-dependent coefficients explain the discrepancies between different measurements naturally, i.e., using sample stars of different temperatures and reddening. A Python package extinction_coefficient is also provided for using the coefficients.

  4. An Rv Map of the Milky Way Revealed by LAMOST (Published in ApJS)

    By utilizing accurate color excess measurements from the optical to the mid-infrared range, we have derived \(R_{V}\) values for approximately three million stars from LAMOST DR7 using a forward-modeling technique. This extensive data set enables us to construct a comprehensive 2D \(R_{V}\) map of the Milky Way within the LAMOST footprint at a spatial resolution of ∼27.’5. Based on reliable sight lines of E(B−V)>0.1, we find that \(R_{V}\) exhibits a Gaussian distribution centered around 3.25 with a standard deviation of 0.25. The spatial variability of \(R_{V}\) in the Galactic disk exhibits a wide range, spanning from small scales within individual molecular clouds to large scales up to kiloparsecs. A striking correlation is observed between the distribution of \(R_{V}\) and molecular clouds. Notably, we observe lower \(R_{V}\) values within the regions of nearby molecular clouds compared to their surrounding areas. Furthermore, we have investigated the relationships between \(R_{V}\) and various parameters, including dust temperature, dust emissivity spectral index, column densities and ratios of atomic and molecular hydrogen, as well as the gas-to-dust ratio. We find that these relationships vary with the level of extinction. These analyses provide new insights into the properties and evolution of dust grains in diverse interstellar environments and also hold significant importance for achieving accurate extinction corrections.

Awards

  • 2021        National Scholarship of China
  • 2020, 2022, 2023   Academic First-class Scholarship (Beijing Normal University)

Publications

  1. Ruoyi, Z. and Haibo, Y., 2020. Detections of Dust in the Outskirts of M31 and M33. The Astrophysical Journal Letters, 905(2), p.L20.
  2. Zhang, R.Y., Yuan, H.B., Liu, X.W., Xiang, M.S., Huang, Y. and Chen, B.Q., 2021. Stellar loci IV. red giant stars. Research in Astronomy and Astrophysics, 21(12), p.319.
  3. Yang, L., Yuan, H., Zhang, R.Y., Niu, Z., Huang, Y., Duan, F. and Fang, Y., 2021. Correction to the photometric magnitudes of the Gaia Early Data Release 3. The Astrophysical Journal Letters, 908(2), p.L24.
  4. Yuan, H.B. and Zhang, R.Y., 2021. Application of Star-Pairing Method in the Large-Scale Sky Survey Era. Science Popularization in University, 15(2), p.59-61.
  5. Xu, S., Yuan, H., Zhang, R.Y., Li, H., Beers, T.C. and Huang, Y., 2022. Stellar Loci VI: An Updated Catalog of the Best and Brightest Metal-poor Stars. The Astrophysical Journal Supplement Series, 263(2), p.29.
  6. Zhang, R.Y. and Yuan, H., 2022. Empirical Temperature-and Extinction-dependent Extinction Coefficients for the GALEX, Pan-STARRS 1, Gaia, SDSS, 2MASS, and WISE Passbands. The Astrophysical Journal Supplement Series, 264(1), p.14.
  7. Yi, F., Haibo, Y., Ruoyi, Z., Jian, G. and Shuai, X., 2023. Empirical extinction coefficients for the Swift-UVOT optical-through-ultraviolet passbands. Monthly Notices of the Royal Astronomical Society, 525(2), pp.2701-2707.
  8. Xiao, K., Yuan, H., Huang, B., Zhang, R.Y., Yang, L. and Xu, S., 2023. Improvement of Pan-STARRS Photometric Calibration with LAMOST and Gaia. The Astrophysical Journal Supplement Series, 268(2), p.53.
  9. Zhang, R., Yuan, H. and Chen, B., 2023. An RV Map of the Milky Way Revealed by LAMOST. The Astrophysical Journal Supplement Series, 269(1), p.6.

Talks

  1. 7th Interstellar Physics and Chemistry Symposium🔗
    Study of the properties of DIBs based on LAMOST, APOGEE, and Gaia data
    Huaibei, China, Jul, 2019
  2. Chinese Astronomical Society 2020 Annual Academic Conference
    Detections of Dust in the Outskirts of M31 and M33
    Beijing, China, Oct, 2020
  3. 8th Interstellar Physics and Chemistry Symposium🔗
    Large-scale 3D distribution of DIB based on APOGEE and Gaia data
    Zhuhai, China, Jan, 2021
  4. 9th Interstellar Physics and Chemistry Symposium🔗
    Empirical temperature- and extinction-dependent extinction coefficients and 3D extinction law
    Yichang, China, Aug, 2022
  5. CSST 2022/23 Annual Scientific Meeting🔗
    On Precise Correction of the Milky Way Dust Extinction
    Beijing, China, Mar, 2023
  6. The 14th Zhang Heng Symposium of the Chinese Astronomical Society🔗
    On Precise Correction of the Milky Way Dust Extinction
    Wuhan, China, Apr, 2023
  7. 2023 LAMOST User Training Session
    On Precise Correction of the Milky Way Dust Extinction
    Beijing, China, Jun, 2023
  8. The 13th meeting on Cosmic Dust🔗
    On Precise Correction of the Milky Way Dust Extinction
    Kitakyushu, Japan, Jul, 2023
  9. Annual Conference on Molecular Clouds and Star Formation🔗
    An RV Map of the Milky Way Revealed by LAMOST
    Chongqing, China, Oct, 2023
  10. CSST 2024 Annual Scientific Meeting🔗
    An Empirical Extinction Curve Revealed by Gaia XP Spectra and LAMOST
    Hangzhou, China, May, 2024

Hobbies

Chinese calligraphy, movies, biology, and pure music (especially postrock and Ambient).