J/AJ/170/101ivo://CDS.VizieR/J/AJ/170/101CDSGuo D.-F.Li K.Liu F.Wang L.-H.Li H.-Z.Chen XuGao X.2026-06-12T12:10:00Z2026-06-12T12:54:20ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.freclipsing-binary-starsinfrared-photometryvisible-astronomyphotometrymultiple-starsIn this paper, we present photometric observations and period analysis of two totally eclipsing binaries with extremely low-amplitude light curves. Both binaries exhibit typical W Ursae Majoris-type light curves with total eclipses, allowing for the precise determination of the mass ratios. Light-curve solutions were derived using the Python package PHysics Of Eclipsing BinariEs in combination with a Markov Chain Monte Carlo framework. Both WISE J053525.4-200442 (hereafter J053525) and ASASSN-V J175200.35+361805.2 (hereafter J175200) are identified as shallow contact binaries with ultralow mass ratios. Specifically, J053525 exhibits a mass ratio of q~0.124 and a marginal contact degree of f~22%, while J175200 has q~0.027 and a contact degree of f~13%. Notably, J175200 represents the most extreme mass ratio observed in contact binaries to date. However, due to degeneracies between mass ratio and third-light contributions in purely photometric analyses, the derived mass ratios should be interpreted as lower limits, especially for J175200. The evolutionary states of these systems differ significantly. For J053525, a long-term period decrease is detected, with the orbital period derivative calculated as dP/dt=-1.99e-6day/yr. In contrast, J175200 shows a period increase: dP/dt=1.93e-7day/yr. These contrasting period trends may be indicative of ongoing mass transfer; however, alternative explanations such as third-body effects cannot be ruled out. Nevertheless, the combination of their ultralow mass ratios, shallow contact configurations, and apparent period evolution highlights their unique value in testing mass ratio theories and the thermal relaxation oscillation hypothesis.2025AJ....170..101Ghttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/AJ/170/101CatalogResearchIsServedByTAP VizieR generic servicerelated-toI/337 : Gaia DR1 (Gaia Collaboration, 2016)I/345 : Gaia DR2 (Gaia Collaboration, 2018)II/366 : ASAS-SN catalog of variable stars (Jayasinghe+, 2018-2020)J/AJ/106/2096 : Limb-darkening coefficients in binaries (Van Hamme 1993)J/ApJ/723/1469 : Flux calibrations and WZ Oph photometry (Wilson+, 2010)J/ApJS/208/9 : Intrinsic colors and temperatures of PMS stars (Pecaut+, 2013)J/ApJ/788/48 : X-ray through NIR photometry of NGC 2617 (Shappee+, 2014)J/ApJS/237/28 : WISE catalog of periodic variable stars (Chen+, 2018)J/AJ/158/104 : LL Com BVR bands phot. & times of light minimum (Hu+, 2019)J/AJ/159/189 : Eclipse timings for 9 contact binaries (Li+, 2020)J/ApJ/922/122 : BVRcIc LCs of two contact binaries (Li+, 2021)J/AJ/162/13 : Parameters estimation for 173 eclipsing binaries (Li+, 2021)J/ApJS/262/12 : Kepler P<2d close binaries (Kobulnicky+, 2022)J/AJ/164/202 : Extrem. Low Mass Ratio Contact Binar. I. 10 syst. (Li+, 2022)J/A+A/672/A176 : Mass-ratio distribution of contact binary stars (Pesta+, 2023)J/A+A/692/L4 : The lowest mass ratio contact binary (Li+, 2024)http://archive.stsci.edu/ : Mikulski Archive for Space Telescopes (MAST)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/AJ/170/101https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/AJ/170/101http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/AJ/170/101https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/AJ/170/101https://vizier.iucaa.in/viz-bin/votable?-source=J/AJ/170/101http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/AJ/170/101GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapOpticalInfrareddefaultJ/AJ/170/101/table1The times of minimum light for WISE J053525.4-200442recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintBJD[8443.9/10357.1] Barycentric Julian Date, BJD-2450000dtime.epochdoubleTelSource of observation; telescope used (1)meta.code;instr.telchare_BJD[1.3e-4/1.4e-3] Uncertainty in BJDdstat.error;time.epochdoubleMinLight curve minimum, two per phase (9 I, 9 II)meta.idcharEpoch[-5539.5/0] Epoch in cycles (see Equations 1 & 3)meta.number;time.periodfloatO-C[0/0.01] Residualdstat.fit.residualdoubleJ/AJ/170/101/table2The times of minimum light for ASASSN-V J175200.35+361805.2e_BJD[2e-4/2e-3] Uncertainty in BJDdstat.error;time.epochdoubleMinLight curve minimum, two per phase (23 I, 17 II)meta.idcharEpoch[-18832/4773.5] Epoch in cycles (see Equations 2 & 4)meta.number;time.perioddoubleO-C[-0.1/0.04] Residualdstat.fit.residualdoublerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintBJD[3137.6/10472.2] Barycentric Julian Date, BJD-2450000dtime.epochdoubleTelSource of observation; telescope used (1)meta.code;instr.telchar