Spectroscopic classification and BVRI photometry of ASASSN-21eh as a classical nova

ATel #14488; U. Munari (INAF Padova), A. Vagnozzi, S. Dallaporta, P. Valisa (ANS Collaboration)
on 27 Mar 2021; 09:03 UT
Credential Certification: U. Munari (ulisse.munari@oapd.inaf.it)

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The transient ASASSN-21eh has been discovered on 2021 March 25.29 UT at g=11.54 mag by the ASAS-SN survey (Shappee et al. 2014, ApJ 788, 48). At coordinates 18:49:05.05 -19:02:04.2 it matches the position of a rather blue g=20.0 star in the PanSTARRS PS1 sky survey (Chambers et al. 2016 arXiv 16120.5560) with no counterpart in the 2MASS JHK survey (Cutri et al. 2003, yCat 2246).

We have obtained BVRI photometry of ASASSN-21eh with ANS Collaboration telescopes ID 0310 and 1301, against a local photometric sequence extracted from APASS DR8. The results are given in the Table:

2021 UT	B	V	R	I
Mar 26.166	11.465	11.132	10.879	10.658
Mar 27.149	10.641	10.242	9.997	9.776

A high resolution spectrum of ASASSN-21eh (6470-6630 Ang, 0.169 Ang/px) has been obtained on March 27.179 UT with a 50cm telescope operated for ANS Collaboration in Stroncone (Italy), under poor sky conditions. The spectrum shows a broad emission in Halpha (FWHM=1800 km/s) flanked by a deep P-Cyg absorption (FWHM=1120 km/s), blue shifted by 860 km/s with respect to the photo-center of the emission component.

On the base of the large photometric amplitude (approaching 10 mag) and the recorded Halpha profile, we classify ASASSN-21eh as a classical nova, still rising in brightness (0.9 mag in the last 24 hours) and of rather blue colors (B-V=+0.40, V-R=+0.25, V-I=+0.47) suggesting a very low interstellar reddening. By comparing with our photometry, it could be suggested that ASASSN-21eh was discovered during passage at pre-maximum halt.