A Long-term Photometric Study of the Near-contact Binary RU Ursae Minoris

Abstract

New CCD photometric observations of the near-contact binary RU UMi were obtained from1999 December to 2000 April and later during 2003 March. All available times of minimum light, including our own measurements, have been examined and indicate that the orbital period of the system has experienced a continuous period decrease with a rate of ðdP =dtÞ obs ¼ À1:6 × 10 À8 d yr À1 . This period decrease cannot be explained trivially by mass transfer from the more massive primary to the less massive secondary, because our light-curve synthesis indicates that RU UMi is in a semidetached configuration with the primary star filling 95% of its inner Roche lobe and the secondary filling its limiting lobe completely. We present the case that the observed period change may be produced by a combination of AML due to magnetic braking with a rate of ðdP =dtÞ mb ¼ À1:0 × 10 À7 d yr À1 and of mass transfer from the secondary to the primary at a rate of _ M 2 ¼ À6:0 × 10 À8 M ⊙ yr À1 . Historical light curves of RU UMi over a 32-yr interval display variably asymmetrical secondary minima. From analyses of velocity and light curves and of the light curves alone, the light variations are best represented by a variable cool spot that has consistently existed on the inner hemisphere of the secondary component. There is a weak indication that the hot star is no longer a main sequence one.

Photometric Analysis of Eclipsing Binaries: Vy Umi, Ru Umi and GSC 04364-00648

“…We can explain it by the temporal evolution of the spot, when the spot parameters, such as diameter, temperature and position on the star's surface, are changing over decades. Our absolute parameters of components determined from the radial velocity solution are a little larger than presented in Lee et al (2008). On the other hand, the absolute parameters determined from GAIA parallax are smaller than previously determined and correspond to an A6V primary component and an evolved K5 star secondary.…”

“…The resulting parameters of its orbit are listed in Table 3. We did not detect any secular quadratic period changes in the data used in our analysis, which contradicts the findings of Zhu et al (2006) and Lee et al (2008).…”

“…Photometric analysis of BV R and TESS light curves confirmed previous findings that RU UMi is a near contact system with a secondary component that almost fulfills its Roche lobe. We were not able to find any satisfactory LC solution with spot(s) (not evenTESS LC) as was done by Lee et al (2008), although some wave-like variation is visible in the residuals in Figure 3. We can explain it by the temporal evolution of the spot, when the spot parameters, such as diameter, temperature and position on the star's surface, are changing over decades.…”

“…RU UMi has been studied in the past years by several authors. Recently, Lee et al (2008) analyzed period variations, fitted light-curve and determined absolute parameters of the components from the radial velocities solution. From their period analysis they concluded that long-term period changes can be caused by the combination of angular momentum loss (AML) and mass transfer from the less massive secondary to the more massive primary.…”

“…Zhu et al (2006) published O − C period analysis of up to date minima times observations and suggested a continuous period decrease at a rate dP/dt = −1.72 × 10 −8 d yr −1 caused by a transfer of matter from the secondary to the primary component. Lee et al (2008) explained the secular period decrease by angular momentum loss (AML) due to magnetic braking alone or, more convincingly, by a combination of AML and mass transfer from the less massive secondary to the more massive primary. The distance to the system is 283.0±1.2 pc (Babusiaux et al 2022).…”