Abstract
ABSTRACT A transient in the Local Group dwarf irregular galaxy NGC 6822 (Barnard’s Galaxy) was discovered on 2017 August 2 and is only the second classical nova discovered in that galaxy. We conducted optical, near-ultraviolet, and X-ray follow-up observations of the eruption, the results of which we present here. This ‘very fast’ nova had a peak V-band magnitude in the range −7.41 > MV > −8.33 mag, with decline times of t2,V = 8.1 ± 0.2 d and t3,V = 15.2 ± 0.3 d. The early- and late-time spectra are consistent with an Fe ii spectral class. The H α emission line initially has a full width at half-maximum intensity of ∼2400 km s−1 – a moderately fast ejecta velocity for the class. The H α line then narrows monotonically to ∼1800 km s−1 by 70 d post-eruption. The lack of a pre-eruption coincident source in archival Hubble Space Telescope imaging implies that the donor is a main-sequence, or possibly subgiant, star. The relatively low-peak luminosity and rapid decline hint that AT 2017fvz may be a ‘faint and fast’ nova.
Highlights
Classical novae (CNe) belong to the class of accreting binaries known as cataclysmic variables
NGC 6822 has a Galactic longitude and latitude of = 25.4◦ and b = −18.4◦, respectively (Mateo 1998). This results in that galaxy being affected by a modest amount of foreground Milky Way extinction
In this paper we present observations and analysis of AT 2017fvz, the second nova observed in the Local Group dwarf irregular galaxy NGC 6822
Summary
Classical novae (CNe) belong to the class of accreting binaries known as cataclysmic variables. Through Roche lobe overflow or the stellar wind of an evolved donor, hydrogenrich material from the donor streams, usually via an accretion disc (Warner 1995), on to the WD where severe heating and compression take place. Given favourable conditions, this results in a thermonuclear runaway (TNR) within the accreted envelope on the WD with a proportion of that envelope subsequently ejected – the nova eruption (Starrfield, Sparks & Truran 1976). This results in the emission of a large amount of X-rays typically peaking in the range 30–50 eV
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