UT Feb 22, 2021: Astrometry of Ross 248 and GX And

Michael Richmond
Feb 22, 2021

On the night of Feb 21/22, 2021, under poor conditions, I acquired images of

Due to a combination of clouds and the bright Moon, these images have a lower signal-to-noise ratio than usual, and the results have larger uncertainties. However, Ross 248 shows the same "jump" in RA as the UT Dec 11 measurements, but all other values are about as expected. Fine.


Ross 248

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:

Notes from the night:

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 dark current was normal this evening. I took two sets of 1.5-second darks, at 22:32 and 22:48 UT (5:32 and 5:48 PM local). The first set was taken when the sky was still relatively bright (after sunset), and the second when it was much darker. The pixel values were almost identical, but very slightly higher in the second set. Huh.

The sky value ROSE as the clouds increased. Ugh.

The number of objects detected.

The FWHM was okay.

Here are the positions I've measured so far. The most recent measurements (at bottom center, cyan) show a big scatter due to the poor conditions tonight.


GX And

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 direction, as we would expect from its known (large) proper motion. The big scatter in tonight's measurements (blue symbols at right edge of graph) is due to the poor conditions.


Last modified 2/22/2021 by MWR.