Open AccessOn the moving subfeatures in the Be star ζ Oph
Author(s) -
Balona L. A.,
Kambe E.
Publication year - 1999
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.1999.02770.x
Subject(s) - physics , astrophysics , instability strip , stars , amplitude , line (geometry) , mode (computer interface) , instability , azimuth , be star , star (game theory) , astronomy , cepheid variable , mechanics , geometry , optics , mathematics , computer science , operating system
We analyse a series of line profile observations of the He i 6678 line in ζ Oph. A period analysis on these data using the mode and moments of the line profile confirms the two previously known periods. We describe a new method of mode identification for pulsating stars in which the calculated profiles are directly fitted to observed profiles. The method yields the full set of pulsational parameters including the spherical harmonic degree, ℓ, and azimuthal number, m . Application of the method to these data confirms the mode identifications previously suggested for the two periodicities. We find that the derived pulsational parameters are physically realistic and conclude that non‐radial pulsation is the most likely explanation for the travelling subfeatures. However, a unique mode identification is still not possible – several non‐sectorial modes fit the data as well as the usually adopted sectorial identifications. The predicted photometric amplitudes are in good accord with upper limits derived from photometric observations. We conclude that ζ Oph is a star in the β Cep instability strip in which two modes of high degree (probably ℓ=4 and ℓ=8) are excited. We present an interpretation of these findings in which the cause of the low‐order line profile and light variations in periodic Be stars is corotating photospheric clouds, while the travelling subfeatures are incidental to the Be phenomenon and are a result of non‐radial pulsation.