Spectroscopic Detection of Pulsations in the Candidate <i>δ</i> Scuti Star V845 Mon

Abstract We present time-resolved spectroscopy of the candidate δ Scuti blue straggler star V845 Mon, to verify its δ Scuti nature and characterize its pulsation properties. Nine low-resolution spectra were obtained over three consecutive nights using ESO Faint Object Spectrograph and Camera (v.2) at the New Technology Telescope. Radial velocities were measured from the H β line, yielding a spectroscopic period of 0.0548 ± 0.001 day from a Lomb–Scargle periodogram and a semi-amplitude of 18.55 ± 3.65 km s −1 . The systemic velocity of 77.15 ± 3.19 km s −1 is consistent within 2.2 σ of the cluster radial velocity, confirming membership. The spectroscopic period is consistent with the second overtone, while the TESS photometric period (0.0921day) is dominated by the fundamental mode. The ratio between radial velocity and photometric amplitudes (∼180 km s −1 mag −1 ) indicates radial pulsation, with a displacement of 1.6% ± 0.32% of the stellar radius, confirming V845 Mon as a high-amplitude δ Scuti star.