UT Aug 09, 2023: Photometry of V347 Aur

Michael Richmond
Aug 10, 2023

On the night of Aug 08/09, 2023, under mediocre conditions, I acquired images of V347 Aur as part of our optical monitoring program. All data was taken with the 12-inch telescope and ASI camera. The results were fair.

V347 Aur has faded in the past two days, roughly to its quiescent level. Hmmmm.

V347 Aur

V347 Aur is a young stellar object (YSO) which undergoes semi-periodic outbursts. I'm part of a team of astronomers who have applied for (and received) time on the XMM-Newton X-ray telescope to study this object in the fall of 2023. We have organized an observing campaign with the AAVSO to monitor the object in the optical in order to determine when the outburst begins -- if it begins! Our prediction is some time in mid-August, 2023.

These observations involved:

• Meade 12-inch telescope
• no focal reducer, so working at f/10
• ASI 6200MM CMOS camera
• V filter, 20-second exposures (reduced from 30 seconds to decrease the number of frames with trails)
• images binned 4x4
• no guiding
• focus position:
  • in V: 0.339 yields FWHM 2.2 at T = 64/17

Notes from the night:

• Opened after midnight. When I arrived, thin clouds over part of the sky and very high humidity. I acquired a small number of images before clouds covered the sky completely -- but then they disappeared after a short time and the sky was mostly clear until dawn.
• waning crescent Moon in the East, not far from Jupiter
• no sign of skunks
• switching to a 20-second exposure time was a good idea; fewer of the images need to be discarded

The position of the variable star is

   RA =  04:56:57.02   Dec = +51:30:50.9

At quiesence, it has magnitude V = 16-ish, but can rise to V = 12 in an outburst.

• chart of V347 Aur field from AAVSO

Here's a chart from the DSS2 Red plates, 0.6 degrees on a side.

The picture below, based on a stack of images taken on UT Jul 23, 2023, shows the area in the red box above. The variable is at its quiescent level in this image.

I've marked the location of several comparison stars.

  star       AAVSO ID            B          V         
------------------------------------------------------
   B            140              15.134    14.001                           

   C            127              13.617    12.660

   D            154              17.491    15.361
--------------------------------------------------------------------------

 

Here's a picture of the guider TV when pointed at the field (pointed slightly to the left of the variable, actually).

In this run, I took over 216 images of the field, but many of those were ruined by clouds; the first half of the run was more affected. The last hour, on the other hand, when the field was higher in the sky, was not bad. I chosed "good" images by requiring that my software could find at least 100 stars in each image; there were a total of 95 which met that criterion. I combined all of them together via a median technique to create a single image with effective exposure time (95 x 20 s = 1900 s = 31.7 minutes), which I used for subsequent analysis.

I reported the following to AAVSO:

    JD             filter          mag
---------------------------------------------------
  2460165.86        V         15.62 +/- 0.16

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

Hmmm. The variable has returned to its quiescent level, after having increased by nearly one magnitude a couple of days ago. Curious.

The current (two days later) light curve indicates that the star has started to brighten _again_; I hope to check it myself tonight.