UT Dec 13, 2020: Astrometry of Ross 248

Michael Richmond
Dec 13, 2020

On the night of Dec 12/13, 2020, under poor conditions, through on-and-off clouds, I acquired images of

• Ross 248 (astrometry for capstone project)

These measurements confirm that the position of Ross 248 has "jumped" in RA as a result of re-focusing with the telescope's silver focus knob. Sigh.

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:

• Meade 12-inch telescope
• no focal reducer, so working at f/10
• ATIK 11000 CCD camera
• R filter, 20-second exposures
• focus in R at 1.350, yielding FWHM 2.0 pixel
• images binned 2x2
• no guiding

Notes from the night:

• low clouds covered the sky when I arrived. I waited for a hole, started taking images, then had to close and wait for another 1.5 hours to finish the set
• no Moon
• temperature was warm: around 48 F / 9 C at start (6:55 PM), and 49 F / 9 C at end (9:18 PM).

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 35 of the 63 images I acquired (those in the second 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), and the "jump" to the left from about -350 to -500 milliarcseconds.

Last modified 12/13/2020 by MWR.