Observed and modeled light curves for V 717 Andromedae. The blue curve shows B-band, green, V -band, and red, R-band; the purple curve shows the Check Star. Black lines represent the white dwarf modeled light curves for each band. The curves have been shifted vertically for clarity. Credit: arXiv (2025). DOI: 10.48550/arxiv.2509.23278
Astronomers from Australia and Serbia have performed multi-band photometric observations of a binary star known as V717 Andromedae. The observations yielded crucial information regarding the properties of V717 Andromedae, finding that it is an active low mass ratio contact binary system. The new findings are detailed in a research paper Sept. 27 on the arXiv preprint server.
Contact binaries consist of two stars orbiting so closely that they share a common gaseous envelope. The components of such systems often have similar effective temperatures and luminosities, regardless of their respective masses.
V717 Andromedae was initially identified as a contact binary in 2013. The source reached a magnitude of 13.4 mag in the V-band, and its orbital period was measured to be approximately 0.317 days.
However, given that no dedicated observations of V717 Andromedae have been conducted to date, very little is known about its nature. That is why a team of astronomers led by Surjit Wadhwa of Western Sydney University in Australia decided to use the 1.4 m Milanković telescope in Serbia to investigate this system. Their study was complemented by archival data from various astronomical surveys.
The observations carried out by Wadhwa's team provided essential information regarding the physical properties of the two stars in V717 Andromedae.
"The geometric light curve solution combined with distance and extinction estimates are used to derive absolute parameters for the system," the researchers explained.
It turned out that the primary star in the system has a radius of about 1.14 solar radii and its mass is comparable to that of the sun. The secondary star is about two times smaller and has a mass of approximately 0.197 solar masses. Therefore, these findings make V717 Andromedae an extreme low mass ratio system.
The observations found that the primary and secondary stars of V717 Andromedae are separated by about 2.13 solar radii and have effective temperatures of 5,895 and 5,813 K, respectively. The distance to the system was measured to be 2,811 light years.
Furthermore, the collected data indicate that V717 Andromedae does not show signs of the so-called O'Connell effect—one of the markers of enhanced chromospheric and coronal activity in contact binaries. However, the astronomers report that there are a number of other markers strongly suggesting the system is chromospherically active, such as calcium II infrared triplet (CaII IRT) lines.
The study also found that the predicted instability mass ratio range for V717 Andromedae is approximately 0.065-0.060. Thus, the mass ratio for V717 Andromedae, at a level of 0.197, means that the system is stable and not a potential merger candidate.
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More information: S. S. Wadhwa et al, V717 Andromedae: An Active Low Mass Ratio Contact Binary, arXiv (2025).
Journal information: arXiv
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