The type Ia supernova 2023vjh: A peculiar 1991bg-like supernova with unusually faint light curves

Kopsacheili, M, Galbany, L, Folatelli, G, Phillips, MM, Burns, CR, Stritzinger, MD, Miao, H-Y, Gonzalez-Banuelos, M, Garcia-Benito, R, Muller-Bravo, TE, Hsiao, EY, Auchettl, K, Anderson, JP, Ashall, C, Chen, T-W, Desai, DD, Huber, ME, de Jaeger, T, DerKacy, JM, Gromadzki, M et al (2026) The type Ia supernova 2023vjh: A peculiar 1991bg-like supernova with unusually faint light curves. Astronomy & Astrophysics, 713. ISSN 0004-6361

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Abstract

We present observations of the 1991 bg-like type Ia supernova (SN Ia) 2023 vjh associated with the elliptical galaxy MCG+04-10-013. Its light-curve shape parameters (∆m15(B) = 1.89 ± 0.01 mag and sBV = 0.45 ± 0.03) together with its spectroscopic evolution place it firmly within the class of fast-declining subluminous SNe Ia. The near-peak spectra show prominent features of Si II, Ca II, and Ti II consistent with a cool photosphere and place SN 2023 vjh within the ‘cool’ and extremely cool regions on the classification diagrams. In addition, the three late-phase near-infrared (NIR) spectra display the Ca II NIR triplet, Fe II, and Co II absorptions but no obvious H-band break. Although SN 2023 vjh falls in the same regions of the classification diagrams as other well-studied 91 bg-like events, it shows some deviation within this class. In particular, it is systematically fainter than predicted by explosion models and fainter than other well-studied 91 bg-like SNe. Light-curve fitting and colour-based analyses indicate a relatively large reddening (E(B − V)host ∼ 0.2–0.35 mag), which is unusual for 91 bg-like SNe. Yet the lack of detectable Na I D absorption in its spectra, along with its large projected distance from the centre of its passive host galaxy (6.8 kpc), suggests that interstellar extinction along the line of sight is minimal. SN 2023 vjh appears to be fainter than typical 91 bg-like SNe, and it could be affected by circumstellar material (CSM). Comparisons with explosion models and alternative extinction prescriptions show that including CSM-like extinction improves agreement in the blue bands, but residual discrepancies in the i-band may reflect limitations in the model.

Item Type:	Article
Uncontrolled Keywords:	supernovae: general; supernovae: individual: SN 2023vjh; supernovae: individual: 91bg-like SNe Ia; 5101 Astronomical Sciences; 51 Physical Sciences; 0201 Astronomical and Space Sciences; Astronomy & Astrophysics; 5101 Astronomical sciences; 5107 Particle and high energy physics; 5109 Space sciences
Subjects:	Q Science > QB Astronomy
Divisions:	Astrophysics Research Institute
Publisher:	EDP Sciences
Date of acceptance:	8 July 2026
Date of first compliant Open Access:	30 October 2026
Date Deposited:	30 Oct 2026 09:00
Last Modified:	30 Oct 2026 09:00
DOI or ID number:	10.1051/0004-6361/202660699
URI:	https://researchonline.ljmu.ac.uk/id/eprint/29773

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