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Exploring protostellar disk formation via misaligned rotation axes and magnetic field, and their observable features. The streamlines on the column density maps show the direction of flows along the picture frame. The black lines over Stokes Q and U parameters depict the direction of magnetic field estimated from the polarization angles. We predict that we witness magnetically directed spiraling behavior by polarization observations (Väisälä et al. 2019).
Observational signatures of early disk formation by MHD models
The panel of two figures illustrate the synthetic gas column density and linear polarization component q along the line of sight, inclined 15 degrees from the midplane, for a very early disk forming from collapsing magnetic flow with the Perspective code developed by the CHARMS project. The early disk in the model shows a spiral-like shape, presumably created by the magnetic field aligned along the rotational plane of the original cloud, that is streaming into the central source. (Perspective code; CHARMS Project; Väisälä, Shang et al., 2018, in preparation)
An early disk in formation from collapsing magnetic flows
A sample picture based on the radiative transfer code Perspective exploring a very early stage disk formed within the MHD model of Li et al. (2014). The picture shows gas column density and linear polarization component q along the line of sight, inclined 15 degrees from the midplane. The early disk in the model shows a spiral-like shape, presumably created by the magnetic field aligned along the rotational plane of the original cloud. (Väisälä, Shang et al., a work in progress)
Polarization Calculation and Visualization from MHD Simulation Data
Distribution of the logarithm of the mass density ρ and velocity field (unit vectors) on the equatorial plane, for Models I (left panel, non-rotating) and J (right, rotating) that include both ambipolar diffusion and (enhanced) Ohmic dissipation for magnetic decoupling at small radii. Again, both models show filamentary structures in the inner protostellar accretion flow driven by magnetic interchange instability.
Protostellar Accretion Flows Destabilized by Magnetic Flux Redistribution
<b>Effects of temperature and magnetization on molecular outflows:</b> the structure of the base of outflows at 1000 yr is shown with different physical conditions. Panels (a) to (c) shows the Alfvénic Mach number from 6, 30, to 90 [decreasing magnetic field strength]; and (1) to (3) shows the wind temperature from 10 K, 400 K, to 2000 K [increasing wind temperature]. These corresponds to different plasma beta parameter (β<sub>plasma</sub> ≣ 8πa<sup>2</sup>ρ/B<sup>2</sup>) from 0.001 to 46. The central axial jet is less collimated and the shell structure is widened when β<sub>plasma</sub> increases. In these cases, the poloidal magnetic field in the toroid is not included.
Two-Temperature Model for Magnetized Protostellar Outflows
Snapshots of rotationally supported disks formed by introduced Hall effect in the MHD calculations, at a representative time of 2 x 10<sup>12</sup> sec.<br> <b>Left:</b> the edge-on view of the case with rotational axis and magnetic axis being parallel. The poloidal velocity field is shown in white arrows and the magnetic field lines in gray solid lines. The white solid lines indicate the radial infall sonic transition at –0.2 km s<sup>–1</sup>. The thick black dashed line indicates the positions where the material is 90% Keplerian supported.<br> <b>Right:</b> the face-on view of the case with rotational axis and magnetic axis being anti-parallel. Note that the Hall effect forces the inner part to rotate in a direction opposite to that of the outer part.
Disk Formation Enabled by the Hall Effect
Snapshots of 2D density distributions of models with different mangetization, at a representative time of 10<sup>12</sup> sec. The white solid lines indicate positions of the radial infall sonic transition at –0.2 km s<sup>–1</sup>, and the dark gray solid lines mark the positions with 100% Keplerian rotational support. The top panels show two close-to-extreme cases: the non-magnetic case with no magnetic breaking <b>(left)</b> and the ideal-MHD case where no rotationally supported disks form <b>(right)</b>. The bottom panels show magnetic cases but with enhanced resistivity. The case with 10<sup>20</sup> cm<sup>2</sup> s<sup>–1</sup> forms a rotationally supported disk on a scale of ~ 100 AU.
Disk Formation Enabled by Enhanced Resistivity
<b>The structure of the warping pseudodisk and rotationally supported disk:</b> close-in view of the turbulent model with persistent disk structure. The pseudodisk roughly corresponds to the red surfaces of ρ = 10<sup>−17</sup> g cm<sup>−3</sup> and the rotationally supported disk roughly corresponds to the blue surfaces of ρ = 10<sup>−16</sup> g cm<sup>−3</sup>. The warping can be seen in the folded red surfaces. The representation time is t = 8 × 10<sup>11</sup> s and the box is 1200 AU in size.
Disk Formation through Pseudodisk Warping and Reconnections in Turbulent Magnetized Cores
Snapshots of 2D density distributions of models <b>A</b> to <b>I</b>. From top to bottom, the angle of magnetic field and rotational axis changes from aligned to totally misaligned. From left to right, the magnetic field strength increased by lowering the effective mass-to-flux ratio. The 3D density and field line distributions show examples of different extents of misalignment and mass-to-flux ratios.
Disk Formation Enabled by Misalignment between Magnetic Fields and Rotation Axis
Chemical abundances at the time t = 1 Myr <b>(top)</b> and t = 3 Myr <b>(bottom)</b> as a function of z-coordinates <b>(left)</b> and of visual extinction <b>(right)</b> in our hydrochemical simulation. The solid and dashed lines represent results for PDR benchmark model V2 and for the reference model with a larger chemical network, respectively.
A hydrochemical hybrid code (KM2) and its benchmarks for a Photon-Dominated Region (PDR)
Krasnopolsky, Ruben
CompAS Project Scientist
photo of Krasnopolsky, Ruben
Office: ASMAB 1218
TEL: +886-2-2366-5407
FAX: +886-2-2367-7849
Email: ruben_replace2@_asiaa.sinica.edu.tw

Research Interests

Star formation, MHD simulations

Journal Papers affiliated with ASIAA

  1. Ai T-H; Liu C-F; Shang H; Johnstone D; Krasnopolsky R, "A Unified Model for Bipolar Outflows from Young Stars: Kinematic and Mixing Structures in HH 30" , ApJ: 964(2), id.147 (15 pp), Apr, 2024 [SCI] ( ADS | Fulltext )
  2. Hirotani K; Shang H; Krasnopolsky R; Nishikawa K, "Formation of Limb-brightened Radio Jets by Angle-dependent Energy Extraction from Rapidly Rotating Black Holes" , ApJ: 965(1), id.50 (11 pp), Apr, 2024 [SCI] ( ADS | Fulltext )
  3. Motoyama K; Krasnopolsky R; Shang H; Aida K; Sakane E, "An Efficient Algorithm for Astrochemical Systems Using Stoichiometry Matrices" , ApJS: 270(2), id.19 (11 pp), Jan, 2024 [SCI] ( ADS | Fulltext )
  4. Hirotani K; Shang H; Krasnopolsky R; Nishikawa K-I, "Two-dimensional Particle-in-Cell simulations of axisymmetric black hole magnetospheres: angular dependence of the Blandford-Znajek flux" , ApJ: 943(2), id.164 (19 pp.), Feb, 2023 [SCI] ( ADS | Fulltext )
  5. Shang H; Krasnopolsky R; Liu C-F, "A Unified Model for Bipolar Outflows from Young Stars: Apparent Magnetic Jet Acceleration" , ApJL: 945(1), id.L1 (21 pp), March, 2023 [SCI] ( ADS | Fulltext )
  6. Shang H; Liu C-F; Krasnopolsky R; Wang L-Y, "A Unified Model for Bipolar Outflows from Young Stars: Kinematic Signatures of Jets, Winds, and Their Magnetic Interplay with the Ambient Toroids" , ApJ: 944(2), id.230 (55 pp), Feb, 2023 [SCI] ( ADS | Fulltext )
  7. Väisälä MS; Shang H; Galli D; Lizano S; Krasnopolsky R, "Exploring the Formation of Resistive Pseudodisks with the GPU Code Astaroth" , ApJ: 959(1), id.32 (21pp), Dec, 2023 [SCI] ( ADS | Fulltext )
  8. Wang W; Väisälä MS; Shang H; Krasnopolsky R; Li Z-Y; Lam KH; Yuan F, "Magnetic Spirals in Accretion Flows Originated from Misaligned Magnetic Fields" , ApJ: 928(1), id.85 (23pp), March, 2022 [SCI] ( ADS | Fulltext )
  9. Hirotani K; Krasnopolsky R; Shang H; Nishikawa K-I; Watson M, "Two-dimensional Particle-in-Cell Simulations of Axisymmetric Black Hole Magnetospheres" , ApJ: 908(1), id.88 (19pp), Feb, 2021 [SCI] ( ADS | Fulltext )
  10. Krasnopolsky R; Ponce-Martinez MP; Shang H; Tseng Y-H; Yen CC, "Efficient Direct Method for Self-gravity in 3D, Accelerated by a Fast Fourier Transform" , ApJS: 252(2), id.14 (14pp), Feb, 2021 [SCI] ( ADS | Fulltext )
  11. Väisälä MS; Pekkilä J; Käpylä MJ; Rheinhardt M; Shang H; Krasnopolsky R, "Interaction of Large- and Small-scale Dynamos in Isotropic Turbulent Flows from GPU-accelerated Simulations" , ApJ: 907(2), id.83 (18pp.), Feb, 2021 [SCI] ( ADS | Fulltext )
  12. Zhao B; Caselli P; Li Z-Y; Krasnopolsky R; Shang H; Lam KH, "The Interplay between Ambipolar Diffusion and Hall Effect on Magnetic Field Decoupling and Protostellar Disc Formation" , MNRAS: 505(4), 5142-5163, Aug, 2021 [SCI] ( ADS | Fulltext )
  13. Shang H; Krasnopolsky R; Liu C-F; Wang L-Y, "A Unified Model for Bipolar Outflows from Young Stars: The Interplay of Magnetized Wide-angle Winds and Isothermal Toroids" , ApJ: 905(2), id.116 (52pp.), Dec, 2020 [SCI] ( ADS | Fulltext )
  14. Yen H-W; Zhao B; Koch P; Krasnopolsky R; Li Z-Y; Ohashi N; Shang H; Takakuwa S; Tang Y-W, "Transition from Ordered Pinched to Warped Magnetic Field on a 100 au Scale in the Class 0 Protostar B335" , ApJ: 893(1), id.54 (11pp.), Apr, 2020 [SCI] ( ADS | Fulltext )
  15. Zhao B; Caselli P; Li Z-Y; Krasnopolsky R; Shang H; et al., "Hall effect in protostellar disc formation and evolution" , MNRAS: 492(3), 3375-3395, Mar, 2020 [SCI] ( ADS | Fulltext )
  16. Suriano SS; Li Z-Y; Krasnopolsky R; ...; Shang H; et al., "The formation of rings and gaps in wind-launching non-ideal MHD discs: three-dimensional simulations" , MNRAS: 484(1), 107-124, Mar, 2019 [SCI] ( ADS | Fulltext )
  17. Vaisala M; Shang H; Krasnopolsky R; Liu S-Y; et al., "Time Evolution of 3D Disk Formation with Misaligned Magnetic Field and Rotation Axes" , ApJ: 873(2), id. 114 (22 pp.), Mar, 2019 [SCI] ( ADS | Fulltext )
  18. Yen H-W; Zhao B; Hsieh I-T; Koch P; Krasnopolsky R; Lee C-F; Li Z-Y; Liu S-Y; Ohashi N; Takakuwa S; Tang Y-W; et al., "JCMT POL-2 and ALMA Polarimetric Observations of 6000─100 au Scales in the Protostar B335: Linking Magnetic Field and Gas Kinematics in Observations and MHD Simulations" , ApJ: 871(2), id. 243 (18 pp.), Feb, 2019 [SCI] ( ADS | Fulltext )
  19. Girart JM; Fernández-López M; Li Z-Y; ...; Krasnopolsky R; ...; Rao R; et al., "Resolving the Polarized Dust Emission of the Disk around the Massive Star Powering the HH 80–81 Radio Jet" , ApJL: 856(2), L27, April, 2018 [SCI] ( ADS | Fulltext )
  20. Suriano SS; Li Z-Y; Krasnopolsky R; Shang H, "The formation of rings and gaps in magnetically coupled disk-wind systems: ambipolar diffusion and reconnection" , MNRAS: 477(1), 1239-1257, June, 2018 [SCI] ( ADS | Fulltext )
  21. Yen H-W; Zhao B; Koch PM; Krasnopolsky R; Li Z-Y; Ohashi N; Takakuwa S, "Constraint on ion-neutral drift velocity in the Class 0 protostar B335 from ALMA observations" , A&A: 615, id.A58 (11 pp.), July, 2018 [SCI] ( ADS | Fulltext )
  22. Zhao B; Caselli P; Li Z-Y; Krasnopolsky R, "Decoupling of magnetic fields in collapsing protostellar envelopes and disc formation and fragmentation" , MNRAS: 473(4), 4868-4889, Feb, 2018 [SCI] ( ADS | Fulltext )
  23. Suriano SS; Li ZY; Krasnopolsky R; Shang H, "Rings and gaps produced by variable magnetic disc winds and avalanche accretion streams - I. Axisymmetric resistive MHD simulations" , MNRAS: 468(4), 3850-3868, July, 2017 [SCI] ( ADS | Fulltext )
  24. Yen H-W; Koch PM; Takakuwa S; Krasnopolsky R; Ohashi N; et al., "Signs of Early-stage Disk Growth Revealed with ALMA" , ApJ: 834(2), 178, Jan, 2017 [SCI] ( ADS | Fulltext )
  25. Zhao B; Caselli P; Li Z-Y; Krasnopolsky R; Shang H; Nakamura F, "Protostellar disc formation enabled by removal of small dust grains" , MNRAS: 460(2), 2050-2076, Aug 1, 2016 [SCI] ( ADS | Fulltext )
  26. Motoyama K; Morata O; Shang H; Krasnopolsky R; Hasegawa T, "A hydrochemical hybrid code for astrophysical problems. I. Code verification and benchmarks for Photon-Dominated Region (PDR)" , ApJ: 808(1), 46, July, 2015 [SCI] ( ADS | Fulltext )
  27. Wang L-Y; Shang H; Krasnopolsky R; Chiang T-Y, "A Two-Temperature Model of Magnetized Protostellar Outflows" , ApJ: 815(1), 39, Oct 10, 2015 [SCI] ( ADS | Fulltext )
  28. Yen H-W; Takakuwa S; Koch PM; ...; Krasnopolsky R; Ohashi N, "No Keplerian Disk >10 AU around the Protostar B335: Magnetic Braking or Young Age?" , ApJ: 812(2), 129, Oct 20, 2015 [SCI] ( ADS | Fulltext )
  29. Lee CF; Hirano N; Zhang QZ; Shang H; Ho PTP; Krasnopolsky R, "ALMA Results of the Pseudodisk, Rotating Disk, and Jet in the Continuum and HCO+ in the Protostellar System HH 212" , ApJ: 786(2), 114, May, 2014 [SCI] ( ADS | Fulltext )
  30. Li Z-Y; Banerjee R; Pudritz RE; Jørgensen JK; Shang H; Krasnopolsky R; Maury A, "The Earliest Stages of Star and Planet Formation: Core Collapse, and the Formation of Disks and Outflows" , Protostars and Planets: VI, 173-194, 2014 ( ADS | Fulltext )
  31. Li ZY; Krasnopolsky R; Shang H; Zhao B, "On the Role of Pseudodisk Warping and Reconnection in Protostellar Disk Formation in Turbulent Magnetized Cores" , ApJ: 793(2), 130, Oct, 2014 [SCI] ( ADS | Fulltext )
  32. Li Z-Y; Krasnopolsky R; Shang H, "Does Magnetic-field-Rotation Misalignment Solve the Magnetic Braking Catastrophe in Protostellar Disk Formation?" , ApJ: 774(1), 82, Sept 1, 2013 [SCI] ( ADS | Fulltext )
  33. Krasnopolsky R; Li Z-Y; Shang H; Zhao B, "Protostellar Accretion Flows Destabilized by Magnetic Flux Redistribution" , ApJ: 757(1), 77, Sept 20, 2012 [SCI] ( ADS | Fulltext )
  34. Krasnopolsky R; Li Z-Y; Shang H, "Disk Formation in Magnetized Clouds Enabled by the Hall Effect" , ApJ: 733(1), 54, May 20, 2011 [SCI] ( ADS | Fulltext )
  35. Li Z-Y; Krasnopolsky R; Shang H, "Non-ideal MHD Effects and Magnetic Braking Catastrophe in Protostellar Disk Formation" , ApJ: 738(2), 180, Sept 10, 2011 [SCI] ( ADS | Fulltext )
  36. Zhao B; Li Z-Y; Nakamura F; Krasnopolsky R; Shang H, "Magnetic Flux Expulsion in Star Formation" , ApJ: 742(1), 10, Nov 20, 2011 [SCI] ( ADS | Fulltext )
  37. Krasnopolsky R; Li Z-Y; Shang H, "Disk Formation Enabled by Enhanced Resistivity" , ApJ: 716(2), 1541-1550, June 20, 2010 [SCI] ( ADS | Fulltext )
  38. Krasnopolsky R; Shang H; Li Z-Y, "Topologies of Current-Free Axisymmetric Magnetospheres in Star-Disk Systems" , ApJ: 703(2), 1863-1871, Oct 1, 2009 [SCI] ( ADS | Fulltext )
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