V1405 Cas Nova 2021: About the nature of a multi-maxima nova

TL;DR

This study analyzes the unusual multi-maxima brightness behavior of Nova V1405 Cas 2021 by examining spectral line variations and brightness fluctuations, suggesting multiple eruptions or density changes in the nova's envelope.

Contribution

It provides new insights into the correlation between spectral line properties and brightness variations during the nova's abnormal activity phase.

Findings

Secondary maxima in brightness and spectral line equivalent width occurred 6-14 days apart.

Maxima of equivalent width lagged behind brightness maxima by 6-14 days.

Results suggest multiple eruptions or density increases in the nova envelope.

Abstract

CONTEXT: The Nova V1405 Cas, which erupted on 18 March 2021, showed a pre-maximum phase of almost two months. After the main maximum, during several month the nova only weakened slightly and showed clear fluctuations in brightness. AIMS: The aim of this work is to investigate the relationship between brightness and half-width (FWHM) and equivalent width (EW) of the H-alpha emission line, and from this to infer possible causes for the abnormal behavior of the Nova. METHODS: Magnitudes and spectra from online databases were used, the H-alpha line of the spectra was measured and 2-day normal values were formed in order to establish a temporal comparison. RESULTS: After the main maximum, during the period investigated by JD 2459292 to 2459305 at intervals of 2-5 weeks secondary maxima with different characteristics. The maxima of the equivalent width were 6-14 days after the respective brightness maxima. The maxima are interpreted as subsequent outbreaks of the nova. Possibly these are subsequent weaker eruptions of the nova or other mechanisms that lead to an increase in density in the envelope.