Electronic Telegram No. 5278 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 V6598 SAGITTARII = TCP J17525020-2024150 = NOVA SAGITTARII 2023 No. 3 Andrew Pearce, Nedlands, Western Australia, reports his discovery of a variable star (unfiltered mag 10.3) on three images obtained on July 15.459 UT with a Canon 800D digital camera (+ 85-mm-f.l. f/1.2 lens), providing the star's approximate position as R.A. = 17h52m50s.2, Decl. = -20d24'15" (equinox J2000.0). The provisional designation TCP J17525020-2024150 was automatically assigned to this variable when Pearce posted it to the Central Bureau's TOCP webpage. Pearce adds that nothing is visible at this position on three images taken on July 12.455 and 14.457 with the same instrumentation; he confirmed the presence of the variable visually on July 15.498 at mag 10.3. Pearce then obtained a more accurate CCD position (and magnitudes V = 10.24, B = 11.73) for TCP J17525020-2024150 on July 15.539 using a 0.35-m R-COP reflector at Perth Observatory, yielding position end figures 49s.30, 15".5 (Gaia DR2 star-catalogue positions, noting the proximity to a star of G-mag 18.9 (Gaia DR3 4118800145787192064) and also a star of G-mag 20.5 in the Pan-STARRS1 survey (star 83512682054115201). Additional CCD magnitudes of TCP J17525020-2024150 by Pearce: July 15.591, B = 12.08, V = 10.29, R = 9.07, I = 8.12 (0.43-m reflector at Siding Spring, NSW); 16.018, B = 12.77, V = 11.37, R = 9.78, I = 8.40 (0.50-m reflector at Rio Hurtado Valley, Chile); 16.469, B = 13.37, V = 11.79, R = 10.06, I = 8.81 (0.43-m reflector at Siding Spring). H. Yamaoka, National Astronomical Observatory of Japan, reports the independent discovery of TCP J17525020-2024150 at mag about 9.6 on July 15.522 UT by Yuji Nakamura (Kameyama, Mie, Japan) on four 6-s CMOS images (limiting mag about 13.0) obtained with a 135-mm-f.l. f/4 lens (the NAOJ received an email report from Nakamura on July 15.688), supplying position end figures 49s.26, 14".3. Nothing was detected in similar images (limiting mag about 12.5) taken on July 11.476. S. Korotkiy (Ka-Dar Observatory/ Astrovert), K. Sokolovsky (Sternberg Astronomical Institute, Moscow State University), and S. Ostapenko write that unfiltered CCD pre-discovery images of TCP J17525020-2024150 obtained on July 14.8 UT with two cameras attached to identical 135-mm-f.l. f/2.0 telephoto lenses yield mag 13.5 on July 14.778 and 13.1 on July 14.793. Sokolovsky adds that the position of TCP J17525020-2024150 is close to that of the magnetic cataclysmic variable IGR J17528-2022. E. Guido, M. Rocchetto, and A. Valvasori report that their CMOS images obtained with a "Telescope Live" 0.1-m f/3.56 astrograph located in Yass, NSW, Australia, on July 15.5 UT show TCP J17525020-2024150 at L-filtered mag 10.5 with position end figures 49s.30, 15".6 (UCAC4 catalogue reference stars for astrometry). They have posted an image at URL https://tinyurl.com/novasgr and an animation showing a comparison between their image and an archival Palomar Sky Survey plate at website URL https://tinyurl.com/novasgranim. 15.583, 10.4. K. Yoshimoto, Yamaguchi, Japan, provides position end figures 49s.30, 15".6 and the following CCD magnitudes for TCP J17525020-2024150 on July 15.585 UT remotely using an iTelescope 0.43-m f/6.8 reflector located at Siding Spring: B = 12.05, V = 10.34, I_c = 8.28. He has posted an image at website URL http://orange.zero.jp/k-yoshimoto/TCP_J17525020-2024150.jpg. CCD magnitudes for TCP J17525020-2024150 obtained by S. Kiyota (Kamagaya, Japan) with an iTelescope 0.5-m f/6.8 CDK reflector located at the "Deep Sky Chile" observatory in the Rio Hurtado Valley on July 16.305 UT: B = 11.97, V = 10.94, R_c = 9.58 and I_c = 8.35. Kiyota posted an image of the variable at URL https://meineko.com/ccd/TCP_J17525020-2024150.jpg. G. Masi writes that he obtained position end figures 49s.31, 15".6 and magnitude R = 9.4 on July 16.860 UT using a 0.36-m robotic telescope at the Virtual Telescope Project facility in Manciano, Italy. A low-resolution spectrogram obtained with the same telescope on July 16.867 (grating with 200 lines/mm; dispersion abaout 1.7 nm/pixel) shows a very strong H-alpha emission at 656.3 nm. Additional visual magnitude estimates of TCP J17525020-2024150: July 15.528 UT, 10.3 (Pearce); 15.907, 11.4 (A. Amorim, Florianopolis, Brazil); 16.462, 11.9 (Pearce); 16.924, 11.8 (Amorim; via E. O. Waagen, AAVSO); 17.469, 13.0 (N. Brown, Yanchep, W. Australia; via Waagen). Additional digital magnitudes of TCP J17525020-2024150 provided by E. O. Waagen, AAVSO: July 16.112, V = 11.53 (E. Gomez, Sylva, NC, USA); 16.175, I = 8.60, V = 11.35, B = 12.90 (F.-J. Hambsch, remotely with instrumentation located at Atacama, Chile); 16.176, R = 10.00 (Hambsch); 17.062, V = 12.63 (Gomez). O. Garde, Chabons, France, reports that the "Southern Spectroscopic Project Observatory Team" (2SPOT; S. Charbonnel, P. Le Du, L. Mulato, T. Petit, and Garde) obtained spectroscopy of TCP J17525020-2024150 on July 15.979 UT with a 0.305-m f/4 Newtonian reflector (+ Alpy 600 spectrograph; R = 570) that shows Balmer lines in very broad emission with a P-Cyg profile and a very red continuum. They also obtained echelle spectroscopy (range 390-7600 nm; R = 11000) with a "Deep Sky Chile" 0.30-m reflector on July 16.42, which they have posted at the following website URL: http://o.garde.free.fr/astro/NovaSgr2023graph.png. Analysis of their spectra by S. Shore (cf. URL https://www.astronomerstelegram.org/?read=16135) suggest that this is a classical nova in an early stage of expansion. The Balmer lines show radial velocities around -4100 km/s. E. Kazarovets writes that the permanent GCVS designation V6598 Sgr has been given 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 July 17 (CBET 5278) Daniel W. E. Green