Research NoteThe spectrum of V4334 Sgr (Sakurai's object) in August, 1998

Abstract

Abstract. Theoretical spectral energy distributions are computed for a grid of hydrogen-deficient and carbonrich model atmospheres with a range in T eff of 4000−5500 K and log g of 1.0−0.0, using the technique of opacity sampling, and taking into account continuous, atomic line and molecular band absorption. The energy distributions are compared with the spectrum of V4334 Sgr (Sakurai's object) of August 12, 1998 in the wavelength interval 300−1000 nm. This comparison yields an effective temperature of V4334 Sgr of T eff = 5250 ± 200 K, and a value for the interstellar plus circumstellar reddening of EB−V = 1.3 ± 0.1.

Models of infrared spectra of Sakurai's Object (V4334 Sgr) in 1997

“…photosphere). That may explain the similarity of T eff obtained in this paper for July 1997 and that found in August 1998 by Pavlenko & Duerbeck (2001). The decreased optical brightness of Sakurai's Object in 1998 was mainly caused by development of the dust envelope (Kimeswenger 1999).…”

“…We note that Duerbeck (2002) did not find evidence for dust in the optical spectra from 1997. On the other hand, the fits by Pavlenko & Duerbeck (2001) to the observed SEDs at optical wavelengths indicate that E B−V had increased by 0.6 (from 0.7 to 1.3) from April 1997 to August 1998. However, the August 1998 data were best fit using T eff = 5250 ± 200 K, the same value as for July 1997 in this paper.…”

Sakurai's Object (V4334 Sgr): evolution of the dust shell from 1999 to 2001

“…2. We note that the temperature of the central object in our modelling is not well constrained [it was taken to be 5200 K (Pavlenko & Duerbeck 2001; Pavlenko 2002) for all data from 1999 onwards] and the dusty output is not very sensitive to the precise nature of the central star (see ); the apparent increase of R * with time should not therefore be taken too literally.…”

“…We therefore used the radiatively driven wind option in dusty , as used for the modelling of objects such as AGB stars in which the envelope expansion is driven by radiation pressure on the dust grains. The radiation source used was a single blackbody with the temperature being estimated from the results of Asplund et al (1999) and Pavlenko & Duerbeck (2001); the temperature of the star fell from ∼7000 K in 1996 to an almost constant 5200 K from 1998 onwards (Pavlenko 2002). We have also run the dusty models with blackbody central sources having different temperatures, and with a hydrogen‐deficient model atmosphere provided by Dr M. Asplund (private communication), the difference in the resultant output parameters and model spectra is less than 5 per cent for temperatures in the range 5200–6000 K.…”

The interstellar extinction to V4334 Sgr (Sakurai's object)

“…Pavlenko & Duerbeck 2001;Pavlenko & Geballe 2002), while values based on observations of the PN are somewhat model-dependent. We note that the E(B − V) reported here is based on the only method that uses the direct observation of the foreground material and as such must be one of the most secure.…”