Multiperiodic pulsations in the Be stars NW Ser and V1446 Aql

TL;DR

This study presents detailed photometric analysis of two Be stars, NW Ser and V1446 Aql, revealing multiple pulsation frequencies and suggesting they exhibit hybrid pulsation modes, including g-modes and possibly p-modes.

Contribution

The paper provides the first detailed frequency analysis of NW Ser and V1446 Aql, identifying multiple pulsation modes and proposing their hybrid nature combining β Cephei and SPB characteristics.

Findings

Both stars exhibit multiple significant pulsation frequencies.

Detection of g-modes and potential p-modes suggests hybrid pulsation behavior.

Stars show rapid amplitude variations likely due to beating phenomena.

Abstract

Aims: We present accurate photometric time series of two Be stars: NW Ser and V1446 Aql. Both stars were observed at the Observatorio de Sierra Nevada (Granada) in July 2003 with an automatic four-channel Str\"omgren photometer. We also present a preliminary theoretical study showing that the periodic variations exhibited by these stars can be due to pulsation. Methods: An exhaustive Fourier analysis together with a least-square fitting has been carried out on the time series for all four Str\"omgren bands. Several independent frequencies and non-periodic trends explain most of the variance. A theoretical non-adiabatic code applied to stellar models for these stars shows that g-modes are unstable. Results: Both stars show rapid variations in amplitude, probably due to a beating phenomenon. Four significant frequencies have been detected for each star. Comparison of the observed amplitude ratios for each pulsational frequency with those calculated from theoretical pulsation codes allows us to estimate the pulsation modes associated with the different detected frequencies. NW Ser seems also to show unstable p-modes and thus could be one of the newly discovered $\beta$ Cephei and SPB hybrid stars. Further spectroscopic observations are planned to study the stability of the detected frequencies.