TCP J17490276-2324066 (=ASASSN 24fb) is a highly reddened nova, of the FeII class, caught close to maximum brightness

ATel #16727; U. Munari (INAF Padova), A. Farina (UniPD), A. Maitan, S. Dallaporta, V. Andreoli (ANS Collaboration)
on 21 Jul 2024; 07:16 UT
Credential Certification: U. Munari (ulisse.munari@oapd.inaf.it)

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TCP J17490276-2324066 has been discovered by K. Itagaki on 2024 Juy 20.476 UT. It coincides with ASASSN 24fb discovered by the ASAS-SN survey on 2024 July 17.05 UT at a reported V=12.43 mag. Refined coordinates listed in CBAT-TOCP (averaging on end figures 02s.735, 05".5) coincides within 0.384 arcsec with a Gaia DR3 star of G=20.8 mag (no BP, RP listed).

We have obtained BVRI transformed photometry of the transient with ANS Collaboration telescopes ID 0310 and 2202, with the results listed in the table below. The local photometric sequence has been extracted from the APASS DR8 survey, and the quote errors include quadratically the transformation uncertainty from color equations.

UT	ID	B	V	R	I
July 20.855	2202	13.000 +/-0.013	11.315 +/-0.011	10.176 +/-0.019	9.059 +/-0.011
July 20.862	0310	12.958 +/-0.013	11.316 +/-0.010	10.197 +/-0.010	9.124 +/-0.010

Low resolution spectra (3600-8000 Ang, dispersion 2.31 Ang/pix) of TCP J17490276-2324066 have been recorded between July 20.851 and 20.909 UT with the Asiago 1.22m + B&C spectrograph. They are dominated by a very red continuum, in fine agreement with the V-J=+2.2 photometric color index in the table above, with superimposed broad emission lines of the Balmer series and FeII multiplets. The strongest FeII multiplets in emission are 55, 74, and 49 (all with P-Cyg absorption components), with multiplets 42 and 48 present at a significant lower intensity. No HeI lines are present and OI 7772 is present in weak emission and displays the strongest P-Cyg aborption of all, with a structurated profile, at an overall velocity -790 km/s and FWHM=560 km/s.

The Halpha has a FWHM=1560 km/s with a sharp P-Cyg absorption of FWHM=530 km/s placed on its blue wing at velocity of -625 km/s with respect to the emission component, which is rather Guassian in shape. The integrated absolute flux of the Halpha emission component is 9.12E-12 erg/cm2/s. The Halpha/Hbeta flux ratio is 8.8.

Overall, TCP J17490276-2324066 appears to be a classical nova, of the FeII type, caught close to maximum brightness, and suffering from a large reddening, possibly amounting to E(B-V)=1.5 mag as supported by the very strong interstellar atomic lines and diffuse interstellar bands, and the large Halpha/Hbeta ratio.