J1152 is an unusual long-period dwarf nova with recurring eclipses, observations find

Astronomers from the South African Astronomical Observatory (SAAO) and elsewhere have conducted photometric and spectroscopic observations of a cataclysmic variable system designated SRGA J115215.0−510656. Results of the new observations, published April 29 on the arXiv pre-print server, indicate that the investigated system is an unusual long-period dwarf nova.

CVs and DNe

Cataclysmic variables (CVs) are binary star systems consisting of a white dwarf primary accreting matter from a normal star companion. They irregularly increase in brightness by a large factor, then drop back down to a quiescent state. These binaries have been found in many environments, such as the center of the Milky Way galaxy, the solar neighborhood, and within open and globular clusters.

Given that in CVs, mass transfer from the companion star often occurs through an accretion disk around the white dwarf and, in some cases, thermal instability in the disk triggers an outburst known as a dwarf nova (DN). These novae are the type of CVs that undergo semi-periodic outbursts. Some DNe only experience regular 2–5 mag outbursts (U Gem type) while others display additional features.

Nearby CV candidate explored by astronomers

SRGA J115215.0−510656, or J1152 for short, was first identified in X-rays in 2021 and classified as a CV candidate. The system is located some 2,086 light years away and has an X-ray luminosity at a level of 100 nonillion erg/s.

Recently, a team of astronomers led by SAAO’s Nikita Rawat has utilized the South African Large Telescope (SALT) and the Sutherland Observatory to perform photometry and spectroscopy of J1152, hoping to shed more light on its nature. Their observations were complemented by data from NASA’s Transiting Exoplanet Survey Satellite (TESS).

“In this paper, we present the first detailed investigation of the optical properties of J1152, making use of archival data from TESS, along with ground-based photometric and spectroscopic observations,” the researchers write.

Eclipses and outbursts

The observations found that J1152 experiences deep, recurring eclipses consistent with a high-inclination geometry and an orbital period of approximately 10.46 hours. Moreover, it exhibits clear outbursts with an average amplitude of approximately 1.6 mag and a recurrence timescale of roughly 40–60 days.

The morphology of J1152’s eclipses during outburst is consistent with a possible “inside-out” type outburst and supports classification of the system as a dwarf nova of the U Gem type. The absolute magnitude of J1152 at the outburst turned out to be 4.0 mag, which is in agreement with the values given for long orbital period DNe by previous studies.

By analyzing the outburst spectrum of J1152, the astronomers found that it is consistent with dense, optically thick gas in a disk wind. This finding places J1152 among the growing number of DNe in which disk wind accretion plays a key dynamical role.

The nature of J1152

When it comes to the nature of the two components of J1152, the results of observations suggest that the donor star most likely has a spectral type K3 and is moderately inflated, while the secondary star is mildly evolved.

“SRGA J115215.0−510656 appears to be a rare and compelling example of a bright, long-period dwarf nova whose optical properties are influenced by disk-wind processes during outburst,” the authors of the paper conclude.

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