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

Abstract

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 $I_{\mathrm{V}}/I_{\mathrm{R}}$ and the absorption-core velocity over multiple orbital cycles, whereas the peak separation remains nearly constant at $\Delta V_r=78\pm 4$ km s${}^{-1}$. The heliocentric radial velocity measurements yield a systemic velocity of $\gamma =7.46\pm 0.64$ 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 Ȧ triplet ($W_{\lambda }=1.16\pm$ 0.02 Ȧ), corresponds to $\log (L/L_{\odot })\approx$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.

15 pages, 7 figures, 2 tables, accepted for publication in RA&A