Photometric and Spectroscopic Studies of Four Low Mass-ratio Contact Binaries with Period Longer than 0.7 days

TL;DR

This study presents a coordinated photometric and spectroscopic analysis of four long-period, low-mass-ratio A-type contact binaries, combining NEXT photometry with archival multi-survey data and LAMOST spectroscopy. The authors model light curves with the Wilson–Devinney code, assess third-light and spots to explain O'Connell effects, and use O–C analyses to infer ongoing mass transfer for three systems, with one showing no long-term period changes. A new log–log $P$–$a$ relation for long-period CBs is derived from a sample of 44 systems, enabling more reliable absolute parameters than Gaia-based estimates under RUWE/extinction constraints. The results place these systems in a broader context of 217 CBs, revealing that longer-period CBs have distinct $M$–$R$ and $M$–$L$ properties, are typically undergoing mass transfer, and remain dynamically stable, offering insights into the formation and evolution of this class.

Abstract

Photometric and spectroscopic studies of four long-period low mass-ratio contact binaries, V0508 And, V0844 Aur, V0699 Cep, and NSVS 6259046, are performed. V0508 And, V0844 Aur, and V0699 Cep are found to be A-type low-mass-ratio medium-contact binaries, while NSVS 6259046 is found to be an A-type deep-contact binary. O - C analysis indicates no long-term variation in V0844 Aur. However, the orbital periods of the other three targets are increasing. We conclude that V0844 Aur, V0699 Cep and NSVS 6259046 are magnetically active, as evidenced by the presence and variable nature of the O'Connell effect in these systems. By analyzing the LAMOST spectroscopic data, we find out that NSVS 6259046 and V0508 And exhibit no chromospheric activity on the dates the LAMOST spectra were taken, while the low signal-to-noise ratio in LAMOST data for V0844 Aur prevents us from obtaining reliable results. We discover that V0699 Cep is an early-type contact binary with chromospheric activity. Their initial masses and ages are calculated. All four systems are determined to be currently stable. We collect 217 contact binaries with both spectroscopic and photometric observations, and compare the differences between short-period and long-period systems in terms of mass-luminosity relation and mass-radius relation, using 0.7 days as the period boundary.

Figures (9)

• Figure 1: The relation between mass ratio $q$ and mean residual $\varSigma$ generated by the W-D program for the NEXT light curves, the mass ratios are ranging from 0.06 to 5.00.
• Figure 2: This figure presents a comparison between the observed (symbols) and theoretical (solid lines) light curves generated by the W-D program for the NEXT, TESS, ASAS-SN, SuperWASP and ZTF light curves. The residuals of the fit are also displayed.
• Figure 3: (Continued)
• Figure 4: The upper illustration shows the $O - C$ diagram and the lower illustration refers to the residuals. Eclipsing times are from NEXT, ASAS-SN, CRTS, TESS, SuperWASP, ZTF, $O - C$ Gateway and 2024NewA..11202270A.
• Figure 5: The normalized observed, synthesized, and subtracted spectra near the location of $H_{\alpha}$ observed by LAMOST.