UT Jul 15, 2021: Photometry of Nova Her 2021

Michael Richmond
Jul 15, 2021

On the night of Jul 14/15, 2021, under fair conditions, I acquired images of Nova Her 2021 = V1674 Her. One can find information about it at

• Astronomer's Telegram 14704
• Astronomer's Telegram 14723 (and references therein)
• AAVSO Alert Notice 745

Tonight, I switched from V-band to unfiltered images, because the target has faded; it was near V = 14.3 during tonight's run. I tried both 60-second and 150-second exposures. The longer ones are probably a bit better for the light curve of this object, but some of the calibration stars start to saturate.

Nova Her 2021 = V1674 Her

This object was discovered by Seiji Ueda (Kushiro, Hokkaido, Japan) on 2021 June 12.537 UT. It rose quickly, then fell quickly.

An update from Enrique de Miguel, from vsnet-chat:

You guys are doing a nice coverage of the recent nova V1674 Her. At this stage, with the nova event so recent and with so many non-trivial effects still going on, detecting periodicities is not straightforward. The alledged spin signal (~8.4 min) seems to be there, but the amplitude is very low in the optical range. If this is a true periodicity (which most likely is) it will presumably become more apparent as the ongoing fireworks fade away. A second signal is now becoming increasingly important at ~0.152 d (~3.66 h) which, if shown to be stable, points to the orbital signature of the binary. So if we want to define the orbital wave properly, runs as long as possible are really a must.

The main setup was:

• Meade 12-inch telescope
• no focal reducer, so working at f/10
• ATIK 11000 CCD camera
• clear filter, exptime 60 seconds for first 2.5 hours, then 150 seconds for the remainder of the night
• images binned 2x2
• guiding with 3-second exposures
• focus in clear
  • 1.104 yields FWHM = 2.3 at T = 78/25
  • 1.093 yields FWHM = 2.9 at T = 69/20
• camera ran at T = -18 C

Notes from the night:

• clouds passed through late in the run, ruining about an hour of data
• waxing crescent Moon didn't interfere with observations
• I mixed the 60-second and 150-second exposures in the analysis, and overall uncertainty was around 0.025 mag at V = 14.3. Not bad.
• I smelled the skunk both early and late in the evening, and heard bats chirping at one point.

The object is located at

  RA =  18:57:30.95    Dec = +16:53:39.6     (J2000)

A chart of the field is shown below. The size of the chart is about 31 x 26 arcminutes.

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

• this chart from the AAVSO
• this list of stars and photometry from AAVSO

I'll use star "E" to shift my instrumental magnitudes to the V-band scale. It has a V-band magnitude (according to AAVSO chart X26675JQ) of 12.221, and (B-V) = 0.608.

The faint star marked "var" shows variations of size roughly +/- 0.3 mag in a roughly sinusoidal pattern over the run. It's perhaps an eclipsing binary. The star has magnitude V ~ 13.5 and position

      RA = 18:57:04.13    Dec = +16:46:00.9     (J2000)
         = 284.26722          = +16.76692

You can use its entry in the APASS catalog to look it up in Vizier, and to serve as a cross-reference.

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

The sky value shows clouds coming late, then leaving a short time before dawn.

The FWHM graph below shows a pretty steady value, though it's a bit worse in the 150-second images. I used X aggr setting of 3 all night.

Using aperture photometry with a radius of 7 pixels in a V filter (binned 2x2, each pixel is 1.24 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 show that the floor was about 0.007 mag for the 60-sec and 150-sec data combined. The faint variable is the smaller outlier at mag = 3.25.

Note the large change in zeropoint when I switched from 60-second exposures (early) to 150-second (late).

Here is the light curve of the object and several field stars in the V filter; I've shifted the instrumental magnitudes so that star "E" = 000-BMD-913 on AAVSO chart X26675JQ has the value given by AAVSO as its V-band magnitude. The faint variable star is labelled as "X".

Note the low signal-to-noise of the target, due to its faintness.

I have submitted these measurements to the AAVSO, CBA, and VSNet.

You can download my measurements below. A copy of the header of the file is shown to explain the format.

# Measurements of Nova_Her_2021 made at RIT Obs, UT 2021 Jul 15, 
#    in fair conditions, 
#    by Michael Richmond, 
#    using Meade 12-inch LX200 and ATIK 11000. 
# Exposures 60 or 150 seconds long, clear filter. 
# Tabulated times are midexposure (FITS header time - half exposure length) 
#    and accurate only to +/- 1 second (??). 
# 'mag' is a differential magnitude based on ensemble photometry 
#    using a circular aperture of radius 7 pix = 8.8 arcseconds.  
#    which has been shifted so AAVSO 000-BMD-913 has mag=12.221 
#    which is its V-band magnitude according to AAVSO.  
# 
# UT_day             JD            HJD        mag    uncert
Jul15.08149     2459410.58149  2459410.58601  14.340  0.020 
Jul15.08235     2459410.58235  2459410.58687  14.325  0.019 
Jul15.08321     2459410.58321  2459410.58773  14.292  0.018 

• download ASCII text file, UT 2021 Jul 15, Nova Her 2021 = V1674 Her from RIT Obs

Last modified 7/15/2021 by MWR.