UT Sep 22, 2023: Photometry of V347 Aur (and looking for Venus in daytime)

Michael Richmond
Sep 22, 2023

On the night of Sep 21/22, 2023, under good 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 variable seems stuck in its fall from the plateau.

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 and B filters, 60-second exposures
• images binned 4x4
• no guiding
• focus position
  • in V: 0.670 yields FWHM 1.7 at T = 49/9

Notes from the night:

• Opened after midnight. Col, but no wind. Maybe some very light cirrus early, appeared clear later.
• no Moon at all, so skies dark.
• Temperature dropped from 53/12 in the dome at 2:00 AM to 45/7 when I closed at around 5:00 AM. That's the lowest temperature so far this autumn.
• the astro lab class had used the 12-inch for visual observations on Wednesday evening and left the electric focuser at 0.166, so images on the ASI camera were way out of focus. I was able to bring them into focus using only the electric focuser, without touching the silver knob. Good.
• no sign of animal life

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).

Tonight's stacks were formed from 25 x 60 sec in V band and 61 x 60 in B band. The FWHM of these stacks was among the best I've seen -- 2.9 pixels in V, and 3.2 pixels in B. I used a photometric aperture of 5 pixels (6.0 arcsec).

(As a test, I tried measuring the V-band image using apertures of radius 3 pixels and 4 pixels as well. The resulting magnitudes of V347 Aur differed by 0.02 +/- 0.07 mag from the 5-pixel magnitude, so aperture size has no significant effect. Good)

I reported the following to AAVSO:

    JD             filter          mag
---------------------------------------------------
  2460209.79        V         14.96 +/- 0.07

  2460209.83        B         16.22 +/- 0.16

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

The variable didn't change much from two nights ago.

Looking for Venus in the daytime

This morning, Venus was very bright in the eastern sky: magnitude V = -4.75, according to Stellarium, at an elongation of 41 degrees from the Sun. This is very close to its maximum possible brightness, so I decided to try looking for it during the day. I was inspired by reading a passage from "Romance of the Planets" by Mary Proctor. You can read the passage yourself if you're curious.

At about 9:15 AM, I checked the position of Venus in the sky using Stellarium: about 40 degrees from the Sun and an altitude of 54 degrees. I walked outside, lay down in the shadow of the Carlson Building to block the Sun's direct light, and looked up into the sky.

• I could not find Venus with my naked eye
• I could not find Venus in a (poor) pair of binoculars
• I took several photos of the sky and inspected them later on a computer, but couldn't find it in the photos
• I DID find Venus by sweeping the sky with my 4.25-inch Astroscan telescope and 28-mm eyepiece. The planet was a bright, very small, crescent. I looked up from the eyepiece and tried to find the planet with my unaided eyes, using the telescope to guide me, but still couldn't see it.

I'd like to try this again some time.