Photometric Analysis of TCP J20171288$+$1156589 -- WZ Sge Type Dwarf Nova with Delayed Ordinary Superhumps Emergence

TL;DR

TCP J20171288+1156589 is a WZ Sge-type dwarf nova that exhibited a large-amplitude outburst with an unusual delay between early and ordinary superhumps. A multi-telescope, time-resolved photometric campaign identifies early superhump periods near $P_{orb}$ and a later ordinary superhump period of $P_{ord}=0.0616$ d, from which a mass ratio of $q\approx0.06$ and a white-dwarf mass of $M_{WD}\approx1.0\,M_{\odot}$ are inferred. Colour evolution analysis yields $E(B-V)\approx0.18$, a disk-temperature trajectory from $\sim15{,}000$ K to $\sim10{,}000$ K, and a distance of $d\approx850$ pc. The resulting parameter set and the pronounced SH-delay provide new insights into disk-instability physics under extreme mass ratios and expand the phenomenology of SH evolution in WZ Sge stars.

Abstract

We present the results of photometric analysis of WZ Sge type dwarf nova TCP J20171288$+$1156589. This object exhibited an outburst with a large amplitude of $>7.9$ magnitudes and was observed for over a month. The photometric evolution of the superoutburst was atypical for WZ Sge-type dwarf novae. Periodogram analisys reveals early superhumps with the most probable period of $0.0611\pm0.0001$ days during the initial decline. After a plateau phase of approximately 11 days, ordinary superhumps (likely stage B) emerged with a period of $0.0616\pm0.0001$ days, corresponding to a superhump excess of $ε=0.008$ correspondingly. This delay in the onset of ordinary superhumps is an unusual feature among WZ Sge stars. We evaluated the main parameters of the system: mass ratio $q=M_{RD}/M_{WD}=0.06\pm0.005$, yielding component masses of $M_{WD}\sim1.0\pm0.15M_{\odot}$ for the white dwarf and $M_{RD}=0.06\pm0.01M_{\odot}$ for the donor. The estimated distance to the system is $\sim850$ pc, and the binary separation is $a=0.67\pm0.03R_{\odot}$.

Figures (8)

• Figure 1: Finding charts for TCP J2017: left panel indicates TCP J2017 (marked as var) and comparison stars; right panel shows combined colour image, TCP J2017 is marked with an arrow and has a noticeable blue colour.
• Figure 2: Full lightcurve of TCP J2017. Data points are represented as circles and photometric limits - as triangles.
• Figure 3: Periodogram of the light curve of TCP J2017 for the first 4 nights. Peaks corresponding to probable periods of early superhumps are marked.
• Figure 4: Profiles of early superhumps of TCP J2017, folded with period $0.0576\pm0.0001$ days (upper panels) and $0.0611\pm0.0001$ (lower pannels): first 4 nights (left panels) and other nights of primary decline phase (right panels). Data points are green circles, the average profile is shown by black connected dots.
• Figure 5: Colour index curves for TCP J2017 (upper panel). $V$ passband light curve is shown in the lower panel.