ar X iv : a st ro - p h / 04 01 42 3 v 1 2 1 Ja n 20 04 The multiple spectroscopic and photometric periods of DI Cru ≡ WR 46 1

In an effort to determine the orbital period of the enigmatic star DI Cru ≡ WR 46 ≡ HD 104994, we made photometric and spectroscopic observations of this object between 1996 and 2002. Both photometric and spectroscopic characteristics are quite complex. The star is highly variable on short (few hours) as well as on long (few months) time-scales. The optical spectrum is rich in strong emission lines of high ionization species such as He II, N IV, N V and O VI. Weak emission of C III and Hβ is also present. Emission lines have been compiled and identified from the ultraviolet to the infrared. In the UV, emission of O V and N IV is also observed, together with very weak emission of C IV. The N V 4603+19Å/He II 4686Å line ratios vary by a significant amount from night to night. Temporal Variance Spectrum – TVS – analysis shows that the He II 4686Å line has P Cyg-like variable absorption, while N V 4603/19Å lines have a strong and broad variable component due to the continuum fluorescence from a source (stellar atmosphere/optically thick wind) of variable temperature. We also show that the object has variable degree of ionization, probably caused by wind density variation. The star presents multiple periods in radial velocity and photometry. We derived, from our data, a main radial velocity period of 0.3319 d with an amplitude of K = 58 km s. This period is similar to the value found by Marchenko et al. (2000). When at intermediate brightness level, this period is also seen in the photometric measurements. When the star is at bright phase, the photometric variations do not present the same period. Photometric periods ranging from 0.154 to 0.378 d are present, consistent with observations reported by other authors. Besides the 0.3319 d period other spectroscopic periods are also seen. On distinct epochs, the periods are different; Marchenko et al. (2000) interpreted the 0.3319 d period as the orbital one. Although we do not discard this possibility, the true binary nature (e.g. long term coherence or detection of a secondary star) has not yet been demonstrated. DI Cru is a Population I WR object. Given the similarities (e.g. multiple periods likely due to non-radial oscillations), it could be interpreted as a luminous counterpart of the qWR star HD 45166. Subject headings: stars: individual (DI Cru) — stars: Wolf-Rayet — stars: peculiar — binaries: spectroscopic — stars: oscillations Instituto de Astronomia, Geof́ısica e Ciências Atmosféricas, Universidade de São Paulo, CP 9638, 01065-970 São Paulo, Brazil Based on observations made at Observatório do Pico dos Dias/LNA, Brazil, and at the 1.5m ESO telescope at La Silla, Chile.