Hubble's Variable Nebula

Analysis

Glenlea Astronomical Observatory, University of Manitoba

From previous studies

R Mon is a massive Herbig Ae/Be star surrounded by an optically thick accretion disk. It varies by more than 4 magnitudes in brightness.
Strong polar winds collimate at P.A. 350 degrees to clear a narrow "throat" through the accetion disk. This throat is about 75 AU wide (0.1") and 45 AU north of R Mon and is the source of most of R Mon's light in the visible spectrum.
Infalling envelope material is collimated into long filaments which are carried northward by this wind.
This ejected material has formed the reflection nebula NGC 2261.
The nebula is thought to be a thin (<800 AU) walled parabolic shell. Its major axis is aligned along P.A. 350 degrees and inclined 20 degrees toward us. R Mon is at its base.
Visible and near infrared light escaping through the "throat" illuminates the walls of the nebula. The walls are transparent at wavelengths greater than 4 microns.
Rotating steamers of dust, formed 1-2 AU from R Mon, cast shadows onto the walls of the nebula as they rise through the "throat".
The proper motion velocities of some shadows exceed the speed of light. The bright part of the nebula (all that can be easily seen in most of the images at this site) is approximately 0.2 light-years wide (east-west) and 0.4 light-years long (north-south).

From this study

The nebula continues to change in brightness over a period of days and weeks. This includes

From image subtraction, it was found that the shadows move away from and/or at right-angles to R Mon in a counterclockwise direction. This is the same direction as seen in the Lampland images, however, the shadow transit seen in this study had much greater northward velocity than the shadow transits seen in the Lampland series.
Large parts of the nebula did not change during this study, especially the fainter northern parts. In particular, images taken 50+ years ago show many of the same features seen today.
Shadow transit structure suggests that the shape of the reflection nebula is more complex than a simple parabolic shell.
From image subtraction, highly structured changes in brightness were detected over large, irregularly illuminated areas. This suggests that the source of the shadows is also highly structured.