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Spectroscopic confirmation of TCP J18385851-0351482 as a classical nova

ATel #17292; Alexander Tarasenkov (INASAN/SAI MSU), Andrey Tatarnikov, Alexandr Dodin, Marina Burlak, Natalia Ikonnikova (SAI MSU), Sergey Shugarov (AISAS/SAI MSU), Vladimir Belousov, Stanislav Korotkiy (Astroverty, Ka-Dar), Elias Aydi (TTU), Kirill Sokolovsky (UIUC)
on 19 Jul 2025; 02:13 UT
Credential Certification: Kirill Sokolovsky (kirx@scan.sai.msu.ru)

Subjects: Optical, Nova

We report spectroscopic classification of the optical transient TCP J18385851-0351482 found by the New Milky Way Survey (Sokolovsky, Korotkiy & Lebedev 2014, ASPC, 490, 395) at unfiltered magnitude 12 on 2025-07-17.9085 UTC. The transient was also detected by the Zwicky Transient Facility (Masci et al. 2019, PASP, 131, 018003) as ZTF25abbsdyb at g=14.41 on 2025-07-17.2329. The forced photometry with the ASAS-SN Sky Patrol (Shappee et al. 2014, ApJ, 788, 48; Kochanek et al. 2017, PASP, 129, 104502) server reveals the first significant detection on 2025-07-15.9858 at g=15.8.

TCP J18385851-0351482 was observed on 2025-07-18.846 with the 2.5 m telescope at the Caucasian Mountain Observatory of the Sternberg Astronomical Institute (Lomonosov Moscow State University) using the Transient Double-beam Spectrograph (Potanin et al. 2020, AstL, 46, 836) covering 3550-5700 A at R~1300 (blue arm) and 5700-7450 A at R~2400 (red arm). The spectrum displays red continuum and P Cyg lines, including H_alpha and H_beta. The peak-to-trough velocity of H_alpha is ~560 km/s. In addition to the Balmer lines we identify Fe II lines of the (42), (48), and (49) multiplets. We interpret the spectrum as that of a classical nova before maximum light affected by interstellar reddening.

Photometric observations of TCP J18385851-0351482 were obtained using three telescopes: the 0.6m Zeiss-600 telescope (FLI ML 3041 CCD) at Stara Lesna Observatory of the Astronomical Institute, Slovak Academy of Sciences; the 0.6m ASA RC600 reflector (Andor iKon-L CCD) at the Caucasian Mountain Observatory of the Sternberg Astronomical Institute; and the 0.5m Astrosib RC500 telescope (ZWO ASI6200MM Pro CMOS) at Kislovodsk observatory of INASAN, Russian Academy of Sciences, yielding the following preliminary results:

 
2025-07-18.8348 V=12.10 B-V=2.36 V-R=1.88 V-I=3.19 SAI  
2025-07-18.8764 V=12.09 B-V=2.18 V-R=1.86 V-I=3.33 AISAS  
2025-07-18.8776 V=11.94 B-V=2.01 V-R=1.92 V-I=3.40 INASAN  

The magnitudes were calibrated using the APASS stars in the field, but not transformed to the standard system. The new unfiltered observations with the NMW camera show the nova at the same brightness as the previous night:

 
2025-07-18.7704 CV=11.9  
2025-07-18.8132 CV=12.0  

We also used images from the AISAS, SAI, and INASAN photometric telescopes to measure the astrometric position of the nova with respect to Gaia DR3 stars: 18:38:58.47 -03:51:49.4 J2000 which coincides within 0.1" with the position of ZTF25abbsdyb.

2.5m CMO SAI spectrum of TCP J18385851-0351482