Rotation of Outflow

Figures 1.19 and 1.20 show that the outflow found in globule CB 26 is rotating. CB 26 is a Bok globule with bipolar NIR refrection nebulae between which a very young T Tauri star and $\sim 200$AU-scale high-density disk are observed (Fig.1.19). Figure 1.20 shows the map of intensity-weighted velocity (1st moment)

$$V_{\rm ave}=\frac{\int T(v)v dv}{\int T(v) dv},$$ (1.7)

where $T(v)$ represents the brightness temperature for line-of-sight velocity $v$. Left panel indicates clearly that the right part gas is departing from us while the left part is arriving. This means there exists a global volocity gradient perpendicular to the flow axis, or in other words, the rotation motion in which the rotation axis coincides with the symmetric axis. The rotation is toward the same direction of the high-density disk observed by $^{13}$CO (Launhardt & Sargent 2001). Right panel is an expecting intensity-weighted velocity distribution for a simple model $^{12}$CO ($J=2-1$),

$$V_r(r) = v_0\left(\frac{r}{r_0}\right),$$ (1.8)

$$V_{\rm rot} = V_{\rm Kep}\left(\frac{\varpi}{\varpi_0}\right)^{-1},$$ (1.9)

$$n(r) = n_0\left(\frac{r}{r_0}\right)^{-3},$$ (1.10)

$$T_{\rm K}(r) = T_0\left(\frac{r}{r_0}\right)^{-q},$$ (1.11)

in which we assume (i) the outflow is conical, (ii) gas element at $(\varpi, z)$ in cylindrical coordinate was launched from a Keplerlian disk at $\varpi_0$ conserving angular momentum, (iii) the radial expanding speed $V_r(r)$ is simply proportional to the distance from the central star $r$ (eq.[1.8]). The assumption (ii) leads to (eq.[1.9) as the rotation speed is inversely proportional to the distance from the rotation axis $\varpi=(r^2-z^2)^{1/2}$. (iv) Density and temperature distributions are assumed as the density decreases with the distance $r$ in proportion to $r^{-3}$ (eq.[1.10]), and the kinetic temperature decreases with the distance $r$ in proportion to $r^{-q}$ (eq.[1.10]).

Comparing with a simple model (right panel), such global rotation motion is seen evidently only when the outflow is observed from edge-on.

Figure 1.19: Globule CB 26 has an outflow which seems to be seen edge-on. Grey-scale indicates the K-band image of the bipolar refrection nebula. Red contours which show SMA 1.1 mm dust continuum emission indicate a high-density disk exists between two lobes of the bipolar nebula. Green contours represent the $^{12}$CO($J=2-1$) integrated intensity.

Figure 1.20: Intensity weighted velocity is shown (left). Right one is a model.