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

TL;DR

V515 And is identified as an intermediate polar residing in the CV period gap. By combining high-cadence TESS photometry with DOT optical spectroscopy, the study precisely measures $P_{ m Omega} \approx 2.731~\mathrm{h}$, $P_{\omega} \approx 465.4721~\mathrm{s}$, and $P_{\omega-\nOmega} \approx 488.6067~\mathrm{s}$, and shows sector-to-sector switches between disc-fed and stream-fed accretion (disc-overflow). Two micronova-like outbursts are detected with peak luminosities near $2.7\times 10^{33}$ erg s$^{-1}$ and $1.9\times 10^{33}$ erg s$^{-1}$ and energies around $6\times 10^{37}$ erg and $3\times 10^{37}$ erg, implying localized thermonuclear activity under magnetic confinement. Optical spectra reveal strong Balmer and He II emission with an inverted Balmer decrement and variable He II, indicating an actively magnetically channeled inner accretion region and associated instabilities. These results reinforce the presence of magnetic CVs in the period gap and illustrate how accretion geometry and micronova-like bursts are modulated by mass-transfer rate and magnetic confinement.

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.

Figures (7)

• Figure 1: (a) TESS light curve of all sectors. (b) Zoomed-in section from sector 57 showing the two outbursts in shaded regions.
• Figure 2: TESS power spectra of different sectors and the combined dataset. The identified frequencies are marked with red vertical dashed lines. The green dashed line represents the 99% confidence level. The right panel shows the zoomed-in part near the ${\omega}$ and ${\omega-\Omega}$ frequencies.
• Figure 3: Trailing power spectra from TESS, binned using a 1-day moving window with a step size of 0.1 days. The ${\omega}$ , and ${\omega-\Omega}$ frequencies, along with their identified harmonics, are shown with dashed lines.
• Figure 4: Spin and beat phase folded light curves of V515 And for each observed sector.
• Figure 5: (a) and (b) Trailed spin and beat phase folded light curve of the entire dataset. (c) Variation of spin and beat pulse fraction.