Study of Negative and Positive Superhumps in ER Ursae Majoris

Abstract

We carried out the photometric observations of the SU UMa-type dwarf nova ER UMa during 2011 and 2012, which showed the existence of persistent negative superhumps even during the superoutburst. We performed two-dimensional period analysis of its light curves by using a method called "least absolute shrinkage and selection operator" (Lasso) and "phase dispersion minimization" (PDM) analysis, and we found that the period of negative superhumps systematically changed between a superoutburst and the next superoutburst. The trend of the period change can beinterpreted as reflecting the change of the disk radius. This change of the disk radius is in good agreement with the predicted change of the disk radius by the thermal-tidal instability (TTI) model. The normal outbursts within a supercycle showed a general trend that the rising rate to maximum becomes slower as the next superoutburst approaches. The change can be interpreted as the consequence of the increased gas-stream flow onto the inner region of the disk as the result of the tilted disk. Some of the superoutbursts were found to be triggered by a precursor normal outburst when the positive superhumps appeared to develop. The positive and negative superhumps co-existed during the superoutburst. The positive superhumps were prominent only during four or five days after the supermaximum, while the signal of the negative superhumps became strong after the middle phase of the superoutburst plateau. A simple combination of the positive and negative superhumps was found to be insufficient in reproducing the complex profile variation. We were able to detect the developing phase of positive superhumps (stage A superhumps) for the first time in ER UMa-type dwarf novae. Using the period of stage A superhumps, we obtained a mass ratio of 0.100(15), which indicates that ER UMa is on the ordinary evolutional track of CVs.

PASJ accepted

References in corpus (5)

• New Method to Estimate Binary Mass Ratios by Using Superhumps
• Study of Superoutbursts and Superhumps in SU UMa Stars by the Kepler Light Curves of V344 Lyrae and V1504 Cygni
• Survey of Period Variations of Superhumps in SU UMa-Type Dwarf Novae. V: The Fifth Year (2012-2013)
• A Further Study of Superoutbursts and Superhumps in SU UMa Stars by the Kepler Light Curves of V1504 Cygni and V344 Lyrae
• GALEX J194419.33+491257.0: An Unusually Active SU UMa-Type Dwarf Nova with a Very Short Orbital Period in the Kepler Data

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• Survey of Period Variations of Superhumps in SU UMa-Type Dwarf Novae. VI: The Sixth Year (2013-2014)
• Survey of Period Variations of Superhumps in SU UMa-Type Dwarf Novae. VIII: The Eighth Year (2015-2016)
• Exploring the tilted accretion disc of AQ Men with TESS
• Nine New Cataclysmic Variable Stars with Negative Superhumps
• Evolution of negative superhumps, quasi-periodic oscillations and outbursts in the Z Cam-type dwarf nova AH Her
• RZ Leonis Minoris Bridging between ER Ursae Majoris-Type Dwarf Nova and Novalike System
• Dwarf Nova EZ Lyncis Second Visit to Instability Strip
• The 2015 superoutburst of QZ Virginis: Detection of growing superhumps between the precursor and main superoutburst
• On the Colour Variations of Negative Superhumps
• Detection of the Supercycle in V4140 Sagittarii: First Eclipsing ER Ursae Majoris-like Object
• Fuse and IUE Spectroscopy of the Prototype Dwarf Nova ER Ursa Majoris During Quiescence