V515 And: An Intermediate Polar in the Period Gap Exhibiting Outbursts

TL;DR

This study combines TESS and spectroscopic data to analyze V515 And, an intermediate polar in the period gap, revealing accretion mode changes, outbursts likely due to micronovae, and confirming its orbital and spin periods.

Contribution

First comprehensive time-series and spectral analysis of V515 And in the period gap, demonstrating accretion mode transitions and identifying micronova-like outbursts.

Findings

V515 And has an orbital period of 2.73116 hours.

The system exhibits outbursts lasting about a day with high luminosities.

The source shows evidence of magnetic accretion and micronova-like bursts.

Abstract

Using long-term observations from the Transiting Exoplanet Survey Satellite (TESS) along with spectroscopic observations from the 3.6 m Devasthal Optical Telescope (DOT), we present a comprehensive time-series and spectral analysis of the intermediate polar V515 And. Our analysis reveals that V515 And resides within the period gap, with the detection of its orbital period of 2.73116 h. Additionally, we confirm the earlier findings of the spin and beat periods to be 465.4721 s and 488.6067 s, respectively. The time-resolved timing analysis reveals that V515 And undergoes changes in its accretion geometry, not only between different TESS sectors but also within individual sector observations. The system exhibits a transition in the dominant accretion mode, switching between disc-fed and stream-fed accretion. In the TESS light curve, we identify two successive outburst-like episodes, each persisting for roughly a day and reaching peak luminosities of $2.7\times10^{33}$ and $1.9\times10^{33}$ erg s$^{-1}$. Our analysis suggests that these bursts belong to the recently proposed class of micronovae. The optical spectrum of V515 And is characterised by strong Balmer and He II emission lines and shows an inverse Balmer decrement indicating the magnetic nature of the source.