Long-term high-resolution spectroscopic monitoring of the evolved metal-poor binary PS Gem

We present results of long-term high-resolution spectroscopic monitoring of the extremely low-metallicity star PS Gem (=HD 52961), associated with IRAS 07008+1050. The spectra were obtained with the 6-meter BTA telescope at a resolving power of R=60000 during 1997--2025, providing a homogeneous dataset spanning nearly three decades. Quantitative measurements of the H alpha two-peaked profile reveal repeatable phase-dependent variations of the peak-intensity ratio I V/I R and the absorption-core velocity over multiple orbital cycles, whereas the peak separation remains nearly constant at V r = 78 plus or minus 4 km s-1. The heliocentric radial velocity measurements yield a systemic velocity of gamma=7.46 plus or minus 0.64 km s-1 and an orbital semi-amplitude of K=2.49 km s-1. No significant long-term secular drift is observed over the monitoring interval. The stellar luminosity, estimated from the equivalent width of the OI 7773. A triplet (W lambda=1.16 plus or minus 0.02. A), corresponds to (L/L) about 3.5. The average radial velocity of diffuse interstellar bands is consistent with the location of PS Gem in the Local Arm. These observations provide rare multi-decade time-domain constraints on the dynamical behavior of this evolved metal-poor star.