UT Jul 14, 2020: Astrometry of Ross 248 and GX And; no occultation by (256) Anna

Michael Richmond
Jul 14, 2020

On the night of Jul 13/14, 2020, under good 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.

I also attempted to observe the occultation of a star (TYC 1188-651-1) by asteroid (256) Anna, but saw no dip in the star's light at the expected time. I was slightly outside the predicted path, so no big surprise.

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:

• Meade 12-inch telescope
• no focal reducer, so working at f/10
• ATIK 11000 CCD camera
• R filter, 20-second exposures
• images binned 2x2
• no guiding
• focus in R at 0.620, FWHM = 3.4 pixels
• camera ran at T = -20 C

Notes from the night:

• waning moon low in East, not very important
• sky mostly clear, but a few wisps of cirrus
• temperature was comfortable -- it was 64 F/16 C when I closed at 4:43 AM
• Comet C/2020 F3 (NEOWISE) was surprisingly easy to see low on the northern horizon, even though it was over the lights of Rochester. I could see the tail very faintly with my naked eye, and clearly with binoculars. The comet was barely visible to my eyes at 4:45 AM, but disappeared by 4:52 AM.
• quite a flock of bats fluttered over the lawn before dawn, hunting insects. Thanks, Bats!

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 usual temperature of -20 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

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

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 one 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.

No occultation by (256) Anna

This morning, the International Occultations Timing Association predicted that the path of the occultation of TYC 1188-651-1 by asteroid (256) Anna would sweep very close to Rochester. We were just a bit east of the predicted shadow, but only by about two sigma, so I thought I'd try to observe it.

My plan was to put the Watec video camera on the small white finder telescope, run the video through the Kiwi OSD device, digitize the video, and record the results on my laptop. However, there were some problems -- not the least of which was that I didn't allow enough time for this project.

• the Watec camera's video signal looked very noisy -- covered with "snow". I hooked it up to the same 12-volt DC power cord that I use for the Orion Starshoot integrating camera; maybe I need to use a different power supply.
• so, I replaced the Watch with the Orion Starshoot, keeping its integration time at the usual 256 fields. I was able to see the target easily, together with a comparison star of similar brightness just to the west; there were plenty of brighter stars visible elsewhere in the field as well.
• the Kiwi OSD unit failed to acquire a GPS lock: it consistently displayed the error message RS232 or 1PPS absent. I suspect that the phone-jack connector in the Kiwi box for the GPS antenna has a loose or broken connection. I'll have to look inside.
• I didn't have time to set up the video digitizing unit and my laptop, so I simply sent the video to the TV monitor and watched it visually.
• I used the short-wave radio to listen to WWV time signals; they faded in and out, but it was good enough to get a time to a second or two.

I watched from 07:40:00 to 07:43:00, and saw no dip in brightness. Oh, well. You can find a copy of my report here:

• Excel spreadsheet with report for IOTA

I should pratice setting everything up a night in advance next time.

Last modified 7/14/2020 by MWR.