[vsnet-alert 24540] Re: ASASSN-20jl astrometry

[Tonny Vanmunster tonny.vanmunster@gmail.com via vsnet-alert]

Dear Denis,

W.r.t. your comment on superhumps amplitude: please note that the star is currently (Aug 14.86 UT) at V = 14.4 and not 14.0-14.1. I reconfirm that the amplitude measured in my observations is between 0.03 and 0.04 mag.

Best regards
Tonny


-----Original Message-----
From: vsnet-alert [mailto:vsnet-alert-bounces at ooruri.kusastro.kyoto-u.ac.jp] On Behalf Of Denis Denisenko d.v.denisenko at gmail.com via vsnet-alert
Sent: zaterdag 15 augustus 2020 8:11
To: 
Subject: [vsnet-alert 24538] ASASSN-20jl astrometry

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