[vsnet-alert 24538] ASASSN-20jl astrometry

[Denis Denisenko d.v.denisenko@gmail.com via vsnet-alert]

I have obtained six 60-sec unfiltered exposures of ASASSN-20jl with 0.25-m
f/3.4 iTelescope T05 reflector in Mayhill, NM on Aug. 15th at 05:00 UT.
Image scale: 1.65"/pixel
Reference catalog: Gaia
Astrometric solution RMS: dRA=0.11", dDE=0.12"

Measured position from the combined 3x60-sec image: 16 46 14.69 +17 00 17.3
Gaia DR2 position with the proper motion in 20 years taken into account: 16
46 14.684 +17 00 17.26
1/cos(delta)=1.045, delta(RA) in seconds of hour is 1.045/15*delta(RA) in
seconds of arc.

Strange as it is, but the position of ASASSN-20jl coincides within the
errors (0.1" in both coordinates) with the G2V-class star "that shouldn't
go into outburst".

Moreover, the FWHM value of ASASSN-20jl is exactly the same as those of
three 14.1-14.3m nearby stars, as measured in both Astrometrica and MaxIm
DL. Flatness is also the same for all 4 comparison stars. Were it a blend
of the background variable and the constant star 0.5-1.0" away, we would
have detected the ellipticity of the stellar image, but this is not the
case.

Note should be taken when performing the photometry. The star is currently
at 14.0-14.1m. If this is a combined light from the variable itself and the
G2V star with Gmag=14.53, then the true magnitude of the variable is about
15m. The superhumps are leveled out by the contribution of the constant
star. After the deblending for 14.53m, the superhumps amplitude should be
more than twice the value reported by Tonny Vanmunster in [vsnet-alert
24535] and [vsnet-alert 24537].

Denis Denisenko