UT Jul 26, 2020: Astrometry of Ross 248 and GX And

Michael Richmond
Jul 26, 2020

On the night of Jul 25/26, 2020, under fair conditions, I acquired images for astrometry of two nearby stars. One was Ross 248 , and the other GX And ; the latter is actually a double star, with two components separated by about 35 arcsec moving together.


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.

The main setup was:

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:

I ran the camera at the slightly-higher-than-normal temp of -18 C. Nothing out of the ordinary.

I took a series of 50 exposures of the field, using the R-band filter and an exposure time of 20 seconds.

Using the same techniques as described for earlier nights, I matched detected stellar positions to the Gaia DR2 catalog; as usual, I used a linear model and included all stars in the catalog.

I am continuing to use the box

cr=650 sc=1000 nr=1300 nc=1000
mentioned in the entry for Jun 28, 2020 to avoid vignetting and coma.

This is my tenth measurement of Ross 248. The small hints of motion, negative in both directions, are consistent with the expected path of the object.

The dispersion of the derived positions continues to be smaller than it was earlier in the summer. Good.


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:

I took two series of 50 exposures of the field, using the R-band filter and an exposure time of only 5 seconds.

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.


Last modified 7/26/2020 by MWR.