Thu, 13 May 2021
These two images of the star system STF1879 illustrate some properties of telescope and camera used to capture them. Only the two stars A and B are gravitationally bound. Parallax measurements show that A and B are 44 parsecs away while C and D are much further away.
The first image, exposed for 1 second at gain 65 on the ZWO ASI183MM shows the four stars A-D listed for the system in the Washington Double Star catalog. From SIMBAD one can find that the magnitude of star C is greater 13, 13.23 in visual light. Star A is magnitude 7.72, so star A is about 160 times a bright as star C, and the dynamic range of the camera is over 5 magnitudes as the image of A is not saturated.
The second image was exposed for 20 milliseconds at gain 65 and shows the separation of A and B. These two stars are about 75 AU apart -- dwarf planet Eris is about 68 AU from our Sun -- and revolve about each other in about 250 years.
The second image also hints at limits of 20 millisecond exposures with this rig (~0.3 square meters of light gathering mirror effectively focused at 5 meters). At magnitude 13.2 star C is close to the limit of detection with 1 second exposures, so the detection limit for 20 milliseconds should decrease by about 4.2 magnitudes to about magnitude 9. For example, we wouldn't expect to be able to detect star D at magnitude 11.6, and, indeed, we cannot.
posted at: 17:56 | path: | permanent link to this entry