BVRcIc light curves, period and spectroscopic study of a low mass-ratio contact binary HV Aqr

New BVRcIc light curves of the short period binary system, HV Aqr, are presented. Photometric solutions were derived using the 2015 version of Wilson–Devinney code. The characteristics of complete eclipses showing in the light curves enable us to determine high-precision photometric parameters of the binary system. We have derived q=0.159 from our observations and q=0.149 from the TESS data. The degree of contact is f=56.21% and f=49.58% from our observations and TESS data, respectively. Based on all available times of light minimum, we analyzed the long-term period changes. A decrease rate of dP/dt=−1.29×10−7 days/yr was determined. The continuous period decrease can be explained by mass transfer from the primary component to the secondary and angular momentum loss via magnetic braking. A conservative mass transfer rate of 2.17×10−8M⊙yr−1 was derived. As the orbital period decreases, its contact of degree will become deeper and it will evolve into a single rapid-rotating star finally.