Â鶹ÒùÔº

Using the Very Large Telescope (VLT), Chilean astronomers have observed a cataclysmic variable known as V1425 Aql. As a result, they have found that this system hosts an arc-shaped nova shell. The finding is presented in a research paper on the arXiv preprint server.

Cataclysmic variables (CVs) are binary star systems consisting of a white dwarf accreting material from a normal star companion. They irregularly increase in brightness by a large factor, then drop back down to a quiescent state. Dwarf novae (DNe), or U Geminorum variables, are the most populous subtype of CVs and show frequent and dramatic outbursts of typically 2–8 mag.

Polars are a subclass of cataclysmic variables distinguished from other CVs by the presence of a very strong magnetic field in their white dwarfs. In some CVs, accretion occurs through a truncated accretion disk when the white dwarf is moderately magnetic. These systems are known as intermediate polars (IPs).

V1425 Aql is a DN whose nova eruption was observed in February 1995, when it reached a maximum brightness of 8.0 mag. Subsequent observations of V1425 Aql after the eruption detected two strong periodicities, one at 6.14 hours, and a second at 1.44 hours, which were attributed to the orbital motion and to the spin of the white dwarf, respectively. This suggests that the system is likely an intermediate polar hosting a weak magnetic white dwarf.

However, more recent studies of V1425 Aql were not able to detect any X-ray emissions coming from the system, putting the magnetic nature of the white dwarf into question. Moreover, it was found that the system has a peculiar nova shell, which is a remnant of a nova eruption in a CV. This shell deviates from other features of this type as it consists of at least two different components: an inner symmetric shell, and an outer asymmetric shell. The outer shell appears to be expanding faster than the inner one.

Therefore, in order to shed more light on the properties and origin of the unusual nova shell in V1425 Aql, a team of astronomers led by Lientur Celedón of the University of Valparaíso in Chile decided to investigate this system using VLT's Multi-Unit Spectrograph Explorer (MUSE), which is an integral field spectrograph.

MUSE observations found that the outer shell has an arc-shaped structure that partially encircles the inner shell, which is more spherical. Such a structure is unexpected, as nova shells usually showcase cone or plume geometry.

Furthermore, the observations detected Balmer, oxygen, nitrogen, and helium emission lines in the spectra of V1425 Aql's nova shell. It turned out that the outer ejecta is only visible in the so-called forbidden lines, while the inner shell shows a mix between allowed and forbidden transitions.

The analysis of the collected spectra revealed clumpy structures within the shell, which may appear to share the same axes in the sky as the outer ejecta. However, further observations are required in order to confirm this, and as the shell expands, these clumps should be more evident.

Trying to explain the origin of the unusual structure of the nova shell in V1425 Aql, the authors of the paper assume that a magnetic white dwarf may be the reason behind it. However, given that the magnetic nature of the white dwarf in this system is unconfirmed, they cannot draw final conclusions about the true mechanism responsible for the observed shell geometry.

© 2025 Science X Network