The spectrum of Sakurai's Object

This diagramme shows the average of two spectra of Sakurai's Object which recently appeared in the southern constellation of Sagittarius (The Archer). They were taken by Wilhelm Hoff, visiting astronomer at the ESO La Silla Observatory from the Astrophysikalisches Institut Jena (Germany). The spectrum shown here has been flux- [erg/s/cm2/A 10e-16] and wavelength- [Angstrom] calibrated.

This spectrum served to determine the very unusual nature of the star which was recently found by Japanese amateur astronomer Yukio Sakurai to undergo a brightening. The following description of the spectrum is adapted from the text published on IAU Circular 6325 (February 26, 1996) by S. Benetti, H. W. Duerbeck, and W. C. Seitter (ESO) and T. Harrison (New Mexico State University, USA):

`CCD spectrograms (439-702 nm, resolution 0.28 nm) of this object taken on Feb. 24.4 and 25.4 UT with the ESO 1.52-m telescope (+ Boller Chivens spectrograph) show a pure absorption-line spectrum with lines of He I, C I, C II, N I, O I, Si II, and faint lines of H. The lines are resolved (FWHM 90-100 km/s), the average heliocentric radial velocity is +108 km/s, and the strong interstellar Na I D lines have a radial velocity of +3 km/s. The slow brightness evolution, and the C-rich and H-poor spectrum, make this object the first candidate for a star undergoing its final helium flash since the eruption of V605 Aql in 1919 (cf. Seitter 1989, IAU Symp. 131, p. 315).'