On the night of Dec 10/11, 2020, under mediocre conditions, I acquired images of
The big news tonight is that I found the measured position of Ross 248 "jumped" in RA by a significant amount, relative to previous measurements and its expected motion. I suspect this is the result of changing the focus of the telescope several nights ago during tests with a different camera. Details below.
This is one of the stars that a capstone student may study over the next year in a project involving parallax. Ross 248 is a relatively faint red star surrounded by many other stars of similar brightness, so it's a good candidate for high-precision parallax measurements.
These observations involved:
The object is (currently) near position
RA = 23:41:55.27 Dec = +44:10:06.38 (J2000)
A chart of the field is shown below. The size of the chart is about 41 x 27 arcminutes. The noisy area at right (West) is the shadow of the guider's pickoff mirror.
I've marked the location of several comparison stars.
star UCAC4 B V r ------------------------------------------------------------------------- A UCAC4 671-120730 12.617 10.689 B UCAC4 671-120688 C UCAC4 671-120749 10.987 10.663 P kappa And 4.06 4.14 --------------------------------------------------------------------------
I took a photo of the finder TV's screen when pointing to Ross 248; this could be a useful reference for the future:
The skies were cloudy tonight, so I used only 33 of the 70 images I acquired (those taken in the first half of the run).
The number of objects detected.
The FWHM.
Here are the positions I've measured so far. Note the clear motion to the south-east (lower-left).
Note the jump in RA: the lowest group of green points sits about 150 milliarcsec in RA relative to the rest. On the night of Dec 8/9, I was practicing for the upcoming conjunction of Jupiter and Saturn by placing a different camera than usual (the Orion Starshoot) at the Cass focus of the 12-inch telescope. In order to bring light to a focus on it, I used the silver knob to modify the focus by a significant amount. Tonight, I used the silver knob again to move the focus back for the Atik camera, but it is possible that these motions caused the primary mirror to tilt slightly. A small tilt, in turn, might modify the astrometric measurements.
I'll keep monitoring Ross 248, and see if future measurements are consistent with a one-time jump in RA (and possibly Dec) on this night.
Like Ross 248, GX And is a nearby (binary) star which will be the target of a parallax project in the coming year. One of the two components is bright -- about mag V = 8 -- so one must use short exposures to prevent it from saturating the detector. That may mean that this system isn't as easy to measure as Ross 248 or some others.
The object is currently close to this position:
RA = 00:18:28.4 Dec = +44:01:31 (J2000)
but it does have a very high proper motion.
A chart of the field is shown below. The size of the chart is about 41 x 27 arcminutes. The noisy area at right (West) is the shadow of the guider's pickoff mirror.
The two components of the GX And binary sit inside the box. I've marked the location of several comparison stars as well.
star UCAC4 B V r ----------------------------------------------------------- A 671-001473 9.939 9.790 B 670-001639 9.413 8.472 C 671-001509 12.712 11.421 11.001 -----------------------------------------------------------
I took a photo of the finder TV's screen when pointing to GX And; this could be a useful reference for the future:
Using the same techniques as described for earlier nights, I matched detected stellar positions to the Gaia DR2 catalog.
The target is clearly moving in the positive RA and Dec directions, as we would expect from its known (large) proper motion.
These measuerements do NOT show the same "jump" in RA as those of Ross 248. That's a bit puzzling. I checked images of the two stars: they appear at roughly the same pixel coordinates. So one would expect a one-time shift to affect both equally. Strange ...
Last modified 11/21/2020 by MWR.