# MN Draconis - peculiar, active dwarf nova in the period gap

## TL;DR

This study presents extensive observations of MN Draconis, a peculiar dwarf nova in the period gap, revealing its supercycle length increase and unique superhump behavior, which challenge existing models of dwarf nova outbursts.

## Contribution

The paper provides the first detailed analysis of MN Draconis in the period gap, including its supercycle length increase and superhump characteristics, expanding understanding of SU UMa systems.

## Key findings

- Detected four superoutbursts and several normal outbursts.
- Derived supercycle length of 74 days, increasing over 12 years.
- Calculated orbital period of approximately 0.0994 days.

## Abstract

Context: We present results of an extensive world-wide observing campaign of MN Draconis. Aims: MN Draconis is a poorly known active dwarf nova in the period gap and is one of the only two known cases of period gap SU UMa objects showing the negative superhumps. Photometric behaviour of MN Draconis poses a challenge for existing models of the superhump and superoutburst mechanisms. Therefore, thorough investigation of peculiar systems, such as MN Draconis, is crucial for our understanding of evolution of the close binary stars. Methods: To measure fundamental parameters of the system, we collected photometric data in October 2009, June-September 2013 and June-December 2015. Analysis of the light curves, $O-C$ diagrams and power spectra was carried out. Results: During our three observational seasons we detected four superoutburts and several normal outbursts. Based on the two consecutive superoutbursts detected in 2015, the supercycle length was derived P_sc = 74 +/- 0.5 days and it has been increasing with a rate of P_dot = 3.3 x 10^(-3) during last twelve years. Based on the positive and negative superhumps we calculated the period excess epsilon = 5.6% +/- 0.1%, the period deficit epsilon_ = 2.5% +/- 0.6%, and in result, the orbital period P_orb = 0.0994(1) days (143.126 +/- 0.144 min). We updated the basic light curve parameters of MN Draconis. Conclusions: MN Draconis is the first discovered SU UMa system in the period gap with increasing supercycle length.