Radial velocity study of the roAp star HR 3831

Abstract

We present results of 566 high‐dispersion echelle spectra of the roAp star HR 3831. We obtain radial velocities of different ions by cross‐correlation with suitable templates. The inhomogeneous abundance distribution results in different rotational velocity curves for different ions. We confirm the large pulsational amplitude in doubly ionized rare‐earth ions. In addition we show that, whereas Hα has a large pulsational velocity amplitude, the pulsational velocity amplitudes in Hβ and Hγ are below the detection limit. This supports the idea that the pulsational amplitude is a function of height and that there is a layer enriched with rare earths in the upper atmosphere. We present a list of lines where the pulsational velocity is the largest. In the radial velocities of the Nd iii line we are able to resolve the two frequencies of highest amplitude seen in the light variations. Co‐added spectra indicate that one of these frequencies is an axisymmetric mode [possibly (ℓ, m) = (2, 0)] and the other a non‐axisymmetric mode [possibly (2, −2)]. This confirms recent observations of non‐axisymmetric modes in roAp stars. We suggest that the presence of non‐axisymmetric modes is simply a consequence of the departure of the eigenfunction from a pure spherical harmonic inclined to the rotational axis and is not related to the Coriolis force. Hence the frequency splitting is precisely equal to the rotational frequency, as observed. Whereas the light variations show strong harmonics, these are not present in the radial velocities.

Multi-element abundance Doppler imaging of the rapidly oscillating Ap star HR 3831

“…In particular, the latter two studies convincingly demonstrated that previous claims of the detection of pulsations in the lines of iron-peak and light elements (Kanaan & Hatzes 1998) stem from an incorrect line identification and that all instances of high-amplitude pulsational variability in the spectra of γ Equ, α Cir and HR 3831 are invariably associated with pulsations in REE lines, such as Pr , Nd  and Nd . This discovery was confirmed by follow up time-resolved spectroscopic investigations in wide spectral regions and in other roAp stars (Balona 2002;Balona & Zima 2002;Kurtz et al 2003).…”

“…Some authors (e.g., Kanaan & Hatzes 1998;Baldry et al 1998b;Balona 2002) suggested that high-amplitude pulsations of REE lines are explainable by accumulation of these elements at the magnetic poles, where pulsational fluctuations are expected to attain maximum amplitudes for the oblique = 1 pulsator model. Yet before the present work no DI maps of roAp stars were available.…”

“…Non-radial pulsations in HR 3831 have been extensively studied photometrically (see Kurtz et al 1997 and references therein) and were recently detected with time-resolved spectroscopic observations (Baldry et al 1998b;Kochukhov & Ryabchikova 2001b;Balona 2002). The main photometric pulsational characteristics of this roAp star are well described by the oblique pulsator model (Kurtz 1982).…”

Eigenfunctions of Axisymmetric p-modes in The Presence of A Dipole Magnetic Field: Observational Consequences

“…Line-profile variations (LPVs) have been detected in some roAp stars (Kochukhov & Ryabchikova 2001a,b;Balona 2002). Fig.…”

Line profile variations in γ Equ: A puzzle

“…have been reported (Savanov, Malanushenko, & Ryabchikova 1999;Kochukhov & Ryabchikova 2001a,b;Balona & Zima 2002;Kochukhov et al 2002;Balona 2002;Balona & Laney 2003;. Kochukhov & Ryabchikova (2001a) found spectacular line profile variations (LPV) for 7 Equ in lines of Nd III and Pr III.…”