UT Dec 03, 2020: Astrometry of Ross 248 and GX And, photometry of Nova Per 2020 in V

Michael Richmond
Dec 8, 2020

On the night of Dec 02/03, 2020, under fair and then bad conditions, I acquired images of three different targets:

• Ross 248 (astrometry for capstone project)
• GX And (astrometry for capstone project)
• Nova Per 2020 (5.5 hours in V)

I initially tried taking images of Nova Per 2020 in BVRI, as I had done three nights earlier, but the filterwheel repeatedly "froze" when trying to move; details below.

By mistake, I analyzed all the data before removing the "vertical stripe" pattern from the images. I saved the results, then removed the stripes and re-reduced all the data. Comparing the results, I found

• no significant difference in position of Ross 248 and GX And
• no significant difference in photometry of Nova Per 2020

Nova Per 2020

This bright nova was discovered on Nov 25, 2020, so it is just a few days old at this point. One can find discussions of its properties and pointers to additional information at

• AAVSO forum for Nova Per 2020

It's quite bright, sitting at around V = 8.5 at the current time.

These measurements involved

• Meade 12-inch telescope
• no focal reducer, so working at f/10
• ATIK 11000 CCD camera
• V filter, 5-second exposures
• focus in R (same as V) at 1.604, yielding FWHM 3.5 pixel
• images binned 2x2
• no guiding

Notes from the night:

• bright full Moon rose in the East early in the evening, made the entire sky bright during the observations
• temperature at start (5:44 PM) 42 F / 5 C, dropping at end (2:07 AM) 31 F / -1 C.
• as I took domeflats, early in the evening, an error message appeared: "Atik Server not running". I had to quit and re-start MaximDL, but things were fine after that
• around 8:24 PM, just after I started observing Nova Per with a sequence of RVBI, the filterwheel stopped moving as it tried to switch from "B" to "I". I unplugged the power and USB cords to the filterwheel, then re-plugged them. The filterwheel responded normally at first, but then froze again when trying to move from "B" to "I". Perhaps the temperature was so cold that something shrank too much? In any case, I switched to taking pictures in V-band only, so that the filterwheel wouldn't have to move.
• added a 10-second delay between images, to avoid a monstrously large dataset
• at end of run, while shutting things down, I noticed that several of the programs which run during data collection (putty, Stellarium, etc.) produced error messages of the form "Putty has stopped working." I didn't notice any errors during the observations. Curious.

The object is located at

  RA =  04:29:18.85    Dec = +43:54:23.0   (J2000)

A chart of the field is shown below. The size of the chart is about 34 x 27 arcminutes.

I've marked the location of several comparison stars as well.

  star       AAVSO               B          V          r
-----------------------------------------------------------

   A        000-BNS-437        12.456     11.867        

   B        000-BNS-438        13.169     12.458        

   C        000-BNS-439        13.383     12.680            

-----------------------------------------------------------

 

I took a photo of the finder TV's screen when pointing to Nova Per 2020; this could be a useful reference for the future:

The sky value shows that the sky was clear for the first four hours of the run, but clouds came and went through the last hour or so.

I used an aperture of 7 pix = 8.7 arcsec for photometry in V-band.

Using aperture photometry with a radius of 7 pixels in V-band (binned 2x2, each pixel is 1.25 arcsec, so a radius of 8.7 arcsec), I measured the instrumental magnitudes of a number of reference stars and the target. Following the procedures outlined by Kent Honeycutt's article on inhomogeneous ensemble photometry, I used all stars available in each image to define a reference frame, and measured each star against this frame.

Sigma-vs-mag plots in V-band show that the floor was about 0.010 mag with 5-second exposures; the relatively large value is due to the influence of clouds.

The effect of the clouds was quite variable near the end of the run, so I was able to make some measurements during relatively clear patches.

Here are light curves of the nova and the field stars in V-band. The nova rises very slightly over the 5.5-hour observing run.

I have submitted measurements in V-band to the AAVSO.

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 1.604, yielding FWHM 3.5 pixel
• images binned 2x2
• no guiding

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 sky value shows no sign of clouds.

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).

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 and Dec directions, as we would expect from its known (large) proper motion.

Last modified 11/21/2020 by MWR.