Electronic Telegram No. 5224
Central Bureau for Astronomical Telegrams
Mailing address:  Hoffman Lab 209; Harvard University;
 20 Oxford St.; Cambridge, MA  02138; U.S.A.
e-mail:  cbatiau@eps.harvard.edu (alternate cbat@iau.org)
URL http://www.cbat.eps.harvard.edu/index.html
Prepared using the Tamkin Foundation Computer Network


V6596 SAGITTARII = TCP J17562787-1714548 = NOVA SAGITTARII 2023
     Several observers have reported independent discoveries of a new nova.
The first report received by the Central Bureau was from Yukio Sakurai (Mito,
Ibaraki-ken, Japan), who found the new star (mag 9.6) on three unfiltered
digital frames (limiting mag 12.1) taken on Feb. 19.823 UT with a Nikon D7100
camera (+ 180-mm-f.l. f/2.8 lens), providing the following position:  R.A. =
17h56m27s.87, Decl. = -17d14'54".8 (equinox J2000.0).  Sakurai notes that
nothing was visible at this position on three frames (limiting mag 12.8)
taken on Feb. 17.816 with the same instrumentation.  When S. Nakano (Central
Bureau) posted these observations to the Central Bureau's TOCP webpage, it
was automatically assigned the provisional designation TCP J17562787-1714548.
     Hideo Nishimura, Kakegawa, Shizuoka-ken, Japan, reported his independent
discovery of this object (at mag 10.8) to Nakano and to H. Yamaoka (National
Astronomical Observatory of Japan), finding it on an image (limiting mag 14)
taken on Feb. 19.804 UT with a Canon EOS 6D digital camera (+ 200-mm-f.l. f/3
lens) at position end figures 27s.89, 53".2, and noting that nothing was
visible at this position on three frames (limiting mag about 15) taken on
Feb. 17.849 using the same instrumentation.  Nishimura's image can be viewed
at website URL https://y2.nao.ac.jp/index.php/s/7od8X3zY2PKEA5w.
     Andrew Pearce, Nedlands, W. Australia, also found TCP J17562787-1714548
independently at unfiltered mag 10.5 on Feb. 18.834 UT on three images
obtained with a Canon 800D camera (+ 85-mm-f.l. f/1.2 lens), adding that
nothing was visible at this position on images taken on Feb. 16.839 (limiting
mag 11.5).  Pearce measured position end figures 27s.90, 53".7 (Gaia DR2
catalogue for reference stars) from a CCD image obtained on Feb. 20.126 with
a 0.5-m f/6.8 reflector at the Skygems Observatory in Namibia, finding
unfiltered magnitude 10.5.  Pearce notes that his position seems to coincide
with an 18th-magnitude star (Gaia 4144602552564272000).  He also estimated
visual magnitude 11.5 on Feb. 20.846.
     Additional CCD magnitudes for TCP J17562787-1714548 reported to the
Central Bureau:  Feb. 20.358 UT, B = 11.71, V = 11.18, R_c = 9.80, I_c = 9.26
(S. Kiyota, Kamagaya, Japan; remotely using an iTelescope 0.34-m f/6.8
telescope at "Deep Sky Chile", Rio Hurtado Valley, Chile); 20.827, 10.95 (T.
Noguchi, Katori, Japan, 0.23-m f/10 Schmidt-Cassegrain reflector; position end
figures 27s.91, 53".5; unfiltered image posted at URL
http://park8.wakwak.com/~ngc/images/TCPinSgr_20230220.jpg); 21.402, B = 12.86
(Pearce, from CCD images obtained remotely using a  0.5-m reflector at Rio
Hurtado Valley); 21.403, V = 12.32 (Pearce); 21.523, V = 11.88 (F. Romanov,
Yuzhno-Morskoy, Nakhodka, Russia, from CCD images obtained remotely using an
iTelescope 0.50-m f/6.8 reflector at the Utah Desert Remote Observatory,
Great Basin Desert, Beryl Junction, UT, USA); Feb. 21.524, B = 12.65
(Romanov); 21.525, R_c = 10.72 (Romanov); 21.526, I_c = 10.32 (Romanov);
21.527, V = 11.88 (Romanov); 21.528, B = 12.62 (Romanov); 21.529, R_c = 10.72
(Romanov); 21.530, I_c = 10.32 (Romanov).  Romanov has posted a color image
composed of three 60-s exposures each with V, B, and R_c filters at website
URL https://www.flickr.com/photos/filipp-romanov/52702897703/.  E. O. Waagen,
AAVSO, forwards the following additional photometry from Pearce for TCP
J17562787-1714548:  Feb. 20.364, B = 12.07; 20.365, V = 11.39; 20.367, V =
11.38; 20.368, B = 12.08.
     Pearce forwards a spectroscopic report for TCP J17562787-1714548 from
H. Barker (Rutherford Street Observatory, Nelson, New Zealand), who obtained
a low-resolution (R about 500) spectrogram on Feb 20.676 UT using a 25-cm
Newtonian telescope (+ JTW L200 littrow spectrograph); the spectrum shows a
reddened continuum and strong emission with a heavily broadened base in
hydrogen Balmer lines and in He I lines at 447.1 (weak), 501.6, 667.8, and
706.5 nm, all consistent in width with H-alpha.  No profiles show P-Cyg
absorption.  The H-alpha HWZI velocity is 5500 km/s.  The Balmer ratio
H_beta/H_alpha ratio seems to be consistent with the Lyman lines still being
optically thick, but the lack of absorption suggests a low ejecta mass.  The
H-alpha line shows emission peaks at -2060, 1740, and 4200 km/s; the red wing
is blended with He I 667.8-nm, typical of a complex, possibly axisymmetric
ejection.  The spectral features and radial velocity are consistent with the
object being a very rapidly evolving nova after visual maximum, possibly a
recurrent nova or an ONe-type system.
     N. Samus writes that the permanent GCVS designation V6596 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 2023 CBAT
2023 February 22                 (CBET 5224)              Daniel W. E. Green