Astronomy & Astrophysics

All Figures

$\begin{figure} \par\includegraphics[width=8cm,clip]{ms3553f1.eps}\end{figure}$ Figure 1: Grain charge as a function of time along the trajectories of a sample of 0.01 $\mu$ m grains chosen from those used in the calculations of the grain velocity distributions. The trajectories have the same initial point in space (time t=0) but different initial velocities. The trajectories are calculated in reverse time direction and end when the grains reach the distant region in space within which the phase space distribution function for the grains is assumed known. Note that the charge on the grains (which does not differ from the local value of the equilibrium charge by more than 0.01 percent) does not vary much in the transition region.
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[width=7.5cm,clip]{ms3553f2.eps}\end{figure}$ Figure 2: Simulated distributions of grain impact speed |v| outside the heliopause (distance from the Sun 150 AU, observer speed 60 km s^-1 relative to Sun, direction of motion offset from the apex by 15 $^\circ$ perpendicular to the magnetic field) for the case of sharp bow shock and the IS field inclined at 45 $^\circ$ relative to ${\vec V}_{\rm LISM}$ . The stacked curves correspond to grain sizes from 0.001 $\mu$ m to 0.15 $\mu$ m as indicated in the figure. The dashed lines show the results if the grain trajectories passing very close to the heliopause are included. The grain velocity distribution in the ISM was assumed to be a Maxwellian (in plasma frame) of width 3 km s^-1, independent of the grain size. The simulated distributions for small size grains are wide, reflecting Larmor rotation. For 0.001 $\mu$ m grains (for which the Larmor rotation time $T_{\rm L}$ is much smaller than the flow time $T_{\rm f}$ through the transition region) and for 0.01 $\mu$ m grains (for which $T_{\rm f}/T_{\rm L}\sim$ 5) the distributions are very similar. This holds also for 0.015 $\mu$ m grains. For 0.02 $\mu$ m grains, the Larmor rotation time is close to the flow time: $T_{\rm f}/T_{\rm L}\sim$ 1 and the distributions become size-dependent. For large size grains (0.075, 0.10 and 0.15 $\mu$ m) the distributions approach another size-independent form, with single peak at the LISM velocity.
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[width=7.5cm,clip]{ms3553f3.eps}\end{figure}$ Figure 3: As previous figure, but for the case of no bow shock and the IS field perpendicular to the LISM velocity. The distributions are narrow and singly peaked. They are independent of the grain size for the cases of small and large grains. There is a transition region where the average impact velocity shifts from the one corresponding to local plasma velocity (small grains) to the LISM velocity (large grains). The distributions for the case of inclined field are similar.
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[width=7.8cm,clip]{ms3553f4.eps}\end{figure}$ Figure 4: Simulated distribution over impact directions (the case of sharp bow shock) for small (a=0.01 $\mu$ m) grains as seen by the detector with a field-of-view of ( $\pm$ 30 $^\circ$ )² situated outside the heliopause at the distance of 150 AU from the Sun, and moving radially in the direction offset from the apex by 15 $^\circ$ perpendicular to the magnetic field, at the speed of 60 km s^-1. The ring distribution is visible. The magnetic field in the LISM is inclined at 45 $^\circ$ to the LISM velocity. Its projection onto the instrument field-of-view is along the horizontal axis.
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[width=7.8cm,clip]{ms3553f5.eps}\end{figure}$ Figure 5: Simulated impact direction distribution for 0.01 $\mu$ m grains for the case of sharp bow shock, with the magnetic field in the LISM perpendicular to the LISM velocity. In this case the grains do not acquire significant parallel velocity. The Larmor ring is seen side-on.
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[width=8.4cm,clip]{ms3553f6.eps}\end{figure}$ Figure 6: Simulated impact direction distribution (the case of no bow shock, field inclined at 45 $^\circ$ ) for 0.01 $\mu$ m grains. The grain velocity distribution in the LISM is assumed to be a Maxwellian with the half-width of 2 km s^-1.
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[width=7.3cm,clip]{ms3553f7.eps}\end{figure}$ Figure 7: The $V_\parallel$ distributions of the grains along a magnetic field line (the case of the perpendicular field). The distributions shown are for a set of 20 equally spaced points along a field line passing close to the outside surface of the heliopause (see the insert). The maximum field intensity corresponds to the middle of the stack. Note the streams of the grains moving in opposite directions away from the region of high magnetic field, and the density enhancements.
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[width=7.6cm,clip]{ms3553f8.eps}\end{figure}$ Figure 8: As previous figure, but for the case of inclined field. Note the reflected streams of the grains reaching $V_\parallel =0$ .
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[width=7.8cm,clip]{ms3553f5.eps}\end{figure}$	Figure 5: Simulated impact direction distribution for 0.01 $\mu$ m grains for the case of sharp bow shock, with the magnetic field in the LISM perpendicular to the LISM velocity. In this case the grains do not acquire significant parallel velocity. The Larmor ring is seen side-on.
Open with DEXTER

$\begin{figure} \par\includegraphics[width=8.4cm,clip]{ms3553f6.eps}\end{figure}$	Figure 6: Simulated impact direction distribution (the case of no bow shock, field inclined at 45 $^\circ$ ) for 0.01 $\mu$ m grains. The grain velocity distribution in the LISM is assumed to be a Maxwellian with the half-width of 2 km s^-1.
Open with DEXTER

$\begin{figure} \par\includegraphics[width=7.6cm,clip]{ms3553f8.eps}\end{figure}$	Figure 8: As previous figure, but for the case of inclined field. Note the reflected streams of the grains reaching $V_\parallel =0$ .
Open with DEXTER