1 Introduction

V4334 Sgr (Sakurai's Object), the "novalike object in Sagittarius'' discovered by Y. Sakurai on February 20, 1996 (Nakano et al. 1996) is a very rare example of extremely fast evolution of a star during a very late final helium-burning event (Duerbeck & Benetti 1996). During the first few months after discovery, Sakurai's Object increased in visual brightness to ${V} \sim 12^{\rm m}$. In 1997 it increased further to ${V} \sim 11^{\rm m}$. In March 1997 the first evidence of dust formation was seen (Kimeswenger et al. 1997; Kamath & Ashok 1999; Kerber et al. 2000). In early 1998 the optical brightness of Sakurai's Object decreased (dimming first reported by Liller et al. 1998), but then recovered. However, during the second half of 1998 an avalanche-like growth of the dusty envelope occurred, causing a rapid decrease in optical brightness and the complete visual disappearance of the star in 1999. At present essentially only thermal emission by dust can be observed (Geballe et al. 2002). Our view of the born again star has been completely obscurred by the dust it has produced.

Abundance analyses by Asplund et al. (1997, 1999) and Kipper & Klochkova (1997) have found peculiarities similar to those of R CrB-like stars. Asplund et al. (1999) estimate that the logarithmic abundances of hydrogen, helium and carbon in atmosphere of Sakurai's Object in October 1996 were -2.42, -0.02 and -1.62, respectively, with hydrogen only the third most abundant element by number. All of the above studies are based on optical spectra obtained in 1996. At that time the spectrum of Sakurai's Object resembled that of an F-supergiant; molecular bands were absent or very weak. Cooling of the photosphere of Sakurai's Object resulted in its optical spectrum during 1997 and 1998 resembling those of C-giants with very strong bands of CN and C₂ (Pavlenko et al. 2000). Modeling of some of these optical spectra have allowed estimates of the changes in $T_{\rm eff}$ and E_B-V to be made during this period of rapid evolution of the optical spectrum (Pavlenko et al. 2000; Pavlenko & Duerbeck 2001).

Modeling of near infrared (1-2.5 $\mu$m) spectra of Sakurai's Object is of interest for several reasons. In addition to providing comparisons with results obtained from the optical spectrum and tests of the reliability of molecular and atomic data, it allows accurate determination of the effective temperature and sensitive tests for emission by hot dust. Use of the 1-2.5 $\mu$m region for modeling is especially important after 1996, when the bulk of the photospheric flux shifted from the optical into this waveband.

In this paper we present and compare model 1-2.5 $\mu$m spectra with those of Sakurai's Object obtained during 1997, on UT April 21 and July 13 at the United Kingdom Infrared Telescope (UKIRT). The observed spectra together with observational details were presented by Eyres et al. (1998) and the July spectrum is also shown in Geballe et al. (2002). The resolutions of these spectra as presented here are 1.4 nm (0.0014 $\mu$m) at 1.02-1.35 $\mu$m and 2.8 nm (0.0028 $\mu$m) at 1.42-2.52 $\mu$m. Narrow spectral features in the 1.82-1.95 $\mu$m portions of these spectra are due to incomplete removal of strong telluric lines.