New radial velocity observations of AH Her: evidence for material outside the tidal radius

TL;DR

This study presents new radial velocity data for AH Her during a deep quiescent state, revealing material outside the tidal radius and providing insights into the system's orbital parameters and emission line behavior.

Contribution

The paper provides the first detailed spectroscopic analysis during a deep quiescent state, including radial velocities, mass functions, and Doppler tomography, highlighting material outside the tidal radius.

Findings

Radial velocity semi-amplitudes: K1=121 km/s, K2=152 km/s.

Orbital period determined as 0.25812 days.

Emission regions are outside the tidal radius and at an unstable position.

Abstract

Spectroscopic observations of AH Herculis during a deep quiescent state are put forward. We found the object in a rare long minima, allowing us to derive accurately the semi-amplitudes: $K_1 =121 \pm \, 4$ \kms\ and $K_2 =152 \pm 2$ \kms\ and its mass functions $M_W{ \sin }^{ 3 }i=0.30 \pm 0.01$ M$_{\odot}$ and $M_R{ \sin }^{ 3 }i=0.24 \pm 0.02$ M$_{\odot}$, while its binary separation is given by $a \sin i =1.39 \pm 0.02$~R$_{\odot}$. The orbital period $P_{orb}$~=~ 0.25812~$\pm~0.00032$~days was found from a power spectrum analysis of the radial velocities of the secondary star. These values are consistent with those determined by \citet{Horne:1986}. Our observations indicate that K5 is the most likely spectral type of the secondary. We discuss why we favour the assumption that the donor in AH Her is a slightly evolved star, in which case we find that the best solution for the inclination yields $i = 48^\circ \pm 2^\circ$. Nonetheless, should the donor be a ZAMS star, we obtain that the inclination is between $ i = 43^\circ$ and $i = 44^\circ$. We also present Doppler tomography of H$\alpha$ and H$\beta$, and found that the emission in both lines is concentrated in a large asymmetric region at low velocities, but at an opposite position to the secondary star, outside the tidal radius and therefore at an unstable position. We also analyse the H$\alpha$ and H$\beta$ line profiles, which show a single broad peak and compare it with the previous quiescent state study which shows a double-peaked profile, providing evidence for its transient nature.