Electronic Telegram No. 5498
Central Bureau for Astronomical Telegrams
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V7991 SAGITTARII = NOVA SAGITTARII 2025 No. 1 = TCP J18265456-2719122
     K. Itagaki, Yamagata, Japan, reports the discovery by Yukio Sakurai
(Mito, Japan) of an apparent nova (mag 9.2) on three unfiltered frames
(limiting mag 10.1) taken on Jan. 26.861 UT with a Nikon D7500 digital camera
(+ 180-mm-f.l. f/2.8 lens).  The variable star's position was given as R.A. -
18h26m54s.56, Decl. = -27d19'12".2 (equinox J2000.0), and it was automatically
assigned the preliminary designation TCP J18265456-2719122 when Itagaki posted
it to the Central Bureau's TOPC webpage.  Sakurai's discovery image has been
posted by Itagaki at website URL http://k-itagaki.jp/images/sakurai-Sgr.jpg.
Itagaki has posted what appears to be his own CCD image of the variable star
at mag 8.8, taken on Jan. 27.882 also with a 180-mm-f.l. f/2.8 camera lens,
at URL http://k-itagaki.jp/images/sakurai-PNV.jpg; he provides position end
figures 54s.54, 11".6.
     A. Pearce, Nedlands, Western Australia, reports that CCD images taken on
Jan. 27.861 UT with a 0.05-m f/5 refractor yield magnitudes V = 9.03, TB =
10.22, and TR = 8.60 for TCP J18265456-2719122; TB is a "tri-color B
magnitude" from a color camera, and TG is the green channel (he finds that the
green channel is very close to Johnson V, but the TB channel is not as close
to Johnson B).  He measured position end figures 54s.51, 12".1 using Gaia DR2
star-catalogue positions; Pearce adds that this is within 0".12 of the star
Gaia 4051881016197528192 (G mag 20.3).  Additional V magnitudes from Pearce
for TCP J18265456-2719122:  Jan. 28.866, 9.37; 29.873, 9.90; 30.863, 10.10;
31.858, 10.22; Feb. 1.853, 10.04; 2.853, 9.96.  Additional TB magnitudes:
Jan. 28.866, 10.11; 29.873, 10.33; 30.863, 10.72; 31.858, 10.79; Feb. 1.853,
10.65; 2.853, 10.31.
     K. Yoshimoto, Yamaguchi, Japan, reports that he obtained a CMOS image of
TCP J18265456-2719122 on Jan. 28.375 UT remotely with a "Deep Sky Chile"
0.25-m f/3.8 Newtonian astrograph (+ Luminance filter) that yields V mag 8.99,
noting a "slightly red color", with position end figures 54s.54, 12".0; he
posted his image at the following website URL:
http://orange.zero.jp/k-yoshimoto/TCP_J18265456-2719122_20250128.jpg.
     E. Aydi et al. have reported that spectroscopy obtained on Jan. 31 (no
time provided) of TCP J18265456-2719122 with the 4.1-m Southern Astrophysical
Research (SOAR) Telescope at Cerro Pachon in Chile show strong, broad emission
lines of H I, Fe II, O I, and Na II, with the Balmer lines having FWZI around
6000 km/s, adding that this appears to be a classical nova past peak optical
brightness (cf. website URL https://www.astronomerstelegram.org/?read=17012).
     E. Kazarovets writes that the permanent GCVS designation V7991 Sgr has
been assigned to this nova.


NOTE: These 'Central Bureau Electronic Telegrams' are sometimes
      superseded by text appearing later in the printed IAU Circulars.

                         (C) Copyright 2025 CBAT
2025 February 3                  (CBET 5498)              Daniel W. E. Green