A Unified Model for Bipolar Outflows from Young Stars: Apparent Magnetic Jet Acceleration by Strong Toroidal Magnetization
We explore a new, efficient mechanism that can power toroidally magnetized jets up to two to three times their original terminal velocity after they enter a self-similar phase of magnetic acceleration. Underneath the elongated outflow lobe formed by a magnetized bubble, a wide-angle free wind, through the interplay with its ambient toroid, is compressed and accelerated around its axial jet. The extremely magnetic bubble can inflate over its original size, depending on the initial Alfvén Mach number MA of the launched flow. The shape-independent slope ∂vr /∂r = 2/3t is a salient feature of the self-similarity in the acceleration phase. Peculiar kinematic signatures are observable in the PV diagrams and can combine with other morphological signatures as probes for density-collimated jets arising in toroidally dominated magnetized winds. The apparent second acceleration is powered by the decrease of the toroidal magnetic field but operates far beyond the scales of the primary magnetocentrifugal launch region and the free asymptotic terminal state. Rich implications may connect the jets arising from the youngest protostellar outflows such as HH 211 and HH 212 and similar systems with parsec-scale jets across the mass and evolutionary spectra.
Schematic plots of the outflow lobes with magnetic acceleration for a case with a strong ambient magnetic field (left) and without an ambient magnetic field (right).The radial profile of self-similar acceleration close to the jet axis at θ = 0°.0446 is shown in self-similar coordinates vr/v0 vs. r/v0t for the cases of MA = 1.2, 1.5, 2, 3, 6, 18, and 30 winds (distinguished by line styles) with n = 1, 2, 4, and 6 toroids (distinguished by color hues). The inset shows the plot of vf/v0 as a function of MA (vf = v0(1+2/MA)). The vf/v0 values corresponding to the illustrated MA values are shown as red dots in the inset.
The 2D spatial profiles of log10(-C/b0) for winds of MA = 1.2, 1.5, 2, 3, 6, 18, 30 with n = 1, 2, 4, and 6 toroids and ambient poloidal field strengths of αb = 1 (left) and αb = 0 (right), in which b0 = sqrt(D0)v0/MA. The black contours are loci of vr/v0 = 1, and the gray contours are loci of –C/b0 = 1. The spatial axes are labeled in units of v0t. The horizontal ϖ axes have been exaggerated by factors of 3.5, 2.3, 1.4, and 1.0 for n = 1, 2, 4, and 6, respectively.
The 2D spatial profiles of log10(h/h0), a specific magnetic enthalpy within the acceleration region, for winds of MA = 1.2, 1.5, 2, 3, 6, 18, and 30 with n = 1, 2, 4, and 6 toroids and ambient poloidal field strengths of αb = 1 (left) and αb = 0 (right), in which h0 = v02/MA2. The black contours are loci of vr/v0 = 1, and the brown contours are loci of h/h0 = 1. The spatial axes are labeled in units of v0t. The horizontal ϖ axes have been exaggerated by factors of 3.5, 2.3, 1.4, and 1.0 for n = 1, 2, 4, and 6, respectively.
PV diagrams of column density (rescaled for logNH contrast) produced by winds with MA = 1.2, 1.5, 2, 3, 6, 18, and 30 (left to right) for the strongly magnetized αb = 1 (top) and nonmagnetized αb = 0 (bottom) toroids of n = 1, 2, 4, and 6 (top to bottom) at an inclination angle of 45°. The column density is integrated for material with vp > aambient.
The 2D spatial profiles of number density (nH, the left halves) and column density (NH, the right halves) for winds of MA = 1.2, 1.5, 2, 3, 6, 18, and 30; toroids of n = 1, 2, 4, and 6; ambient poloidal field strengths of αb = 1 (left) and αb = 0 (right). The horizontal ϖ axes have been exaggerated by factors of 3.5, 2.3, 1.4, and 1.0 for n = 1, 2, 4, and 6, respectively.
Related Publications
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 )
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 )
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), 116, Dec 20, 2020 [SCI] ( ADS | Fulltext )
Wang L-Y; Shang H; Krasnopolsky R; Chiang T-Y, “A Two-Temperature Model of Magnetized Protostellar Outflows”, ApJ: 815(1), 39, Dec 10, 2015 [SCI] ( ADS | Fulltext )
Shang H; Allen A; Li Z-Y; Liu C-F; Chou M-Y; Anderson J, “A Unified Model for Bipolar Outflows from Young Stars”, ApJ: 649(2), 845-855, Oct 1, 2006 [SCI] ( ADS | Fulltext )
