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

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: K1 = 121 ± 4 km s−1 and K2 = 152 ± 2 km s−1 and its mass functions MWsin 3i = 0.30 ± 0.01 M⊙ and MRsin 3i = 0.24 ± 0.02 M⊙, while its binary separation is given by asin i = 1.39 ± 0.02 R⊙. The orbital period Porb = 0.25812 ± 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 Horne et al. (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○ ± 2○. Nonetheless, should the donor be a ZAMS star, we obtain that the inclination is between i = 43○ and i = 44○. We also present Doppler tomography of Hα and Hβ, 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 Hα and Hβ 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.

Evolution of Negative Superhumps, Quasiperiodic Oscillations, and Outbursts in the Z Cam-type Dwarf Nova AH Her

“…(2021; error = 3.2 × 10 −4 days). The differences between our determined orbital period and theirs are all within the uncertainty of Echevarría et al (2021). In addition, the orbital period we obtained is based on a large number of photometric data from TESS and has an important reference value.…”

“…The orbital period of AH Her was accurately determined by Horne et al (1986) to be P orb = 0.258116(4) days based on the radial-velocity analysis (spectroscopic observations in 1980 and 1981). Echevarría et al (2021) also performed radialvelocity analysis (spectroscopic observations in 2013) and obtained an orbital period of P orb = 0.25812(32) days. The time interval between the two spectroscopic observations is about 30 yr, but the difference in the orbital period is within the uncertainty, which proves that the orbital period of AH Her is relatively stable.…”

“…Based on spectroscopic observations, Bruch (1987) estimated that the spectral type of the secondary star might be K5. Echevarría et al (2021) performed photometric and spectroscopic observations combined with a radial-velocity analysis for AH Her, and the orbital period was determined as P orb = 0.25812 ± 0.00032 days in general agreement with Horne et al (1986), although Horne et al (1986)ʼs orbital period is more accurate.…”