分类： 天文学 >> 天文学 提交时间： 2023-02-19
Pengfei Jiang
Lang Cui
Jun Yang
Bo Zhang
Shuangjing Xu
Fengchun Shu
Wu Jiang
Wen Chen
Guanghui Li
Bo Xia
Stuart Weston
Sergei Gulyaev
Hongmin Cao
Xiang Liu
Tao An
摘要： AR Scorpii (AR Sco), the only-known radio-pulsing white dwarf binary, shows unusual pulsating emission at the radio, infrared, optical and ultraviolet bands. To determine its astrometric parameters at the radio band independently, we conducted multi-epoch Very Long Baseline Interferometry (VLBI) phase-referencing observations with the European VLBI Network (EVN) at 5 GHz and the Chinese VLBI Network (CVN) plus the Warkworth 30-metre telescope (New Zealand) at 8.6 GHz. By using the differential VLBI astrometry, we provide high-precision astrometric measurements on the parallax ($\pi=8.52_{-0.07}^{+0.04}$ mas), and proper motion ($\mu_{\alpha}=9.48_{-0.07}^{+0.04}$ mas yr$^{-1}$, $\mu_{\delta}=-51.32_{-0.38}^{+0.22}$ mas yr$^{-1}$). The new VLBI results agree with the optical Gaia astrometry. Our kinematic analysis reveals that the Galactic space velocities of AR Sco are quite consistent with that of both intermediate polars (IPs) and polars. Combined with the previous tightest VLBI constraint on the size, our parallax distance suggests that the radio emission of AR Sco should be located within the light cylinder of its white dwarf.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Nobuyuki Sakai
Bo Zhang
Shuangjing Xu
Daisuke Sakai
Yoshiaki Tamura
Takaaki Jike
Taehyun Jung
Chungsik Oh
Jeong-Sook Kim
Noriyuki Kawaguchi
Hiroshi Imai
Wu Jiang
Lang Cui
Soon-Wook Kim
Pengfei Jiang
Tomoharu Kurayama
Jeong Ae Lee
Kazuya Hachisuka
Dong-Kyu Jung
Bo Xia
摘要： We aim to reveal the structure and kinematics of the Outer-Scutum-Centaurus (OSC) arm located on the far side of the Milky Way through very long baseline interferometry (VLBI) astrometry using KaVA, which is composed of KVN (Korean VLBI Network) and VERA (VLBI Exploration of Radio Astrometry). We report the proper motion of a 22 GHz H$_{2}$O maser source, which is associated with the star-forming region G034.84$-$00.95, to be ($\mu_{\alpha} \rm{cos}\delta$, $\mu_{\delta}$) = ($-$1.61$\pm$0.18, $-$4.29$\pm$0.16) mas yr$^{-1}$ in equatorial coordinates (J2000). We estimate the 2D kinematic distance to the source to be 18.6$\pm$1.0 kpc, which is derived from the variance-weighted average of kinematic distances with LSR velocity and the Galactic-longitude component of the measured proper motion. Our result places the source in the OSC arm and implies that G034.84$-$00.95 is moving away from the Galactic plane with a vertical velocity of $-$38$\pm$16 km s$^{-1}$. Since the H I supershell GS033+06$-$49 is located at a kinematic distance roughly equal to that of G034.84$-$00.95, it is expected that gas circulation occurs between the outer Galactic disk around G034.84$-$00.95 with a Galactocentric distance of 12.8$^{+1.0}_{-0.9}$ kpc and halo. We evaluate possible origins of the fast vertical motion of G034.84$-$00.95, which are (1) supernova explosions and (2) cloud collisions with the Galactic disk. However, neither of the possibilities are matched with the results of VLBI astrometry as well as spatial distributions of H II regions and H I gas.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Pengfei Jiang
Lang Cui
Jun Yang
Bo Zhang
Shuangjing Xu
Fengchun Shu
Wu Jiang
Wen Chen
Guanghui Li
Bo Xia
Stuart Weston
Sergei Gulyaev
Hongmin Cao
Xiang Liu
Tao An
摘要： AR Scorpii (AR Sco), the only-known radio-pulsing white dwarf binary, shows unusual pulsating emission at the radio, infrared, optical and ultraviolet bands. To determine its astrometric parameters at the radio band independently, we conducted multi-epoch Very Long Baseline Interferometry (VLBI) phase-referencing observations with the European VLBI Network (EVN) at 5 GHz and the Chinese VLBI Network (CVN) plus the Warkworth 30-metre telescope (New Zealand) at 8.6 GHz. By using the differential VLBI astrometry, we provide high-precision astrometric measurements on the parallax ($\pi=8.52_{-0.07}^{+0.04}$ mas), and proper motion ($\mu_{\alpha}=9.48_{-0.07}^{+0.04}$ mas yr$^{-1}$, $\mu_{\delta}=-51.32_{-0.38}^{+0.22}$ mas yr$^{-1}$). The new VLBI results agree with the optical Gaia astrometry. Our kinematic analysis reveals that the Galactic space velocities of AR Sco are quite consistent with that of both intermediate polars (IPs) and polars. Combined with the previous tightest VLBI constraint on the size, our parallax distance suggests that the radio emission of AR Sco should be located within the light cylinder of its white dwarf.
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