Abstract. We present the results of our analysis of a high resolution (R 30 000) infrared spectrum of V4334 Sgr (Sakurai's Object) around the first overtone CO bands, obtained in 1998 July. The 12 CO and 13 CO bands are well-resolved, and we compute synthetic hydrogen-deficient model atmosphere spectra to determine the 12 C/ 13 C ratio. We find 12 C/ 13 C 4 ± 1, consistent with the interpretation of V4334 Sgr as an object that has undergone a very late thermal pulse.

We compare high-resolution infrared observations of the CO 2-0 bands in the 2.297-2.310 µm region of M dwarfs and one L dwarf with theoretical expectations. We find a good match between the observational and synthetic spectra throughout the 2000-3500 K temperature regime investigated. None the less, for the 2500-3500 K temperature range, the temperatures that we derive from synthetic spectral fits are higher than expected from more empirical methods by several hundred kelvin. In order to reconcile our findings with the empirical temperature scale, it is necessary to invoke warming of the model atmosphere used to construct the synthetic spectra. We consider that the most likely reason for the back-warming is missing high-temperature opacity due to water vapour. We compare the water vapour opacity of the Partridge-Schwenke line list used for the model atmosphere with the output from a preliminary calculation by Barber & Tennyson. While the Partridge-Schwenke line list is a reasonable spectroscopic match for the new line list at 2000 K, by 4000 K it is missing around 25 per cent of the water vapour opacity. We thus consider that the offset between empirical and synthetic temperature scales is explained by the lack of hot water vapour used for computation of the synthetic spectra. For our coolest objects with temperatures below 2500 K, we find best fits when using synthetic spectra which include dust emission. Our spectra also allow us to constrain the rotational velocities of our sources, and these velocities are consistent with the broad trend of rotational velocities increasing from M to L.

Context. The recurrent nova RS Ophiuchi undergoes nova eruptions every ∼10−20 years as a result of thermonuclear runaway on the surface of a white dwarf close to the Chandrasekhar limit. Both the progress of the eruption and its aftermath depend on the (poorly known) composition of the red giant in the RS Oph system. Aims. Our aim is to understand better the effect of the giant secondary on the recurrent nova eruption. Methods. Synthetic spectra were computed for a grid of M-giant model atmospheres having a range of effective temperatures 3200 < T eff < 4400 K, gravities 0 < log g < 1 and abundances −4 < [Fe/H] < 0.5, and fit to infrared spectra of RS Oph as it returned to quiescence after its 2006 eruption. We have modelled the infrared spectrum in the range 1.4−2.5 μm to determine metallicity and effective temperature of the red giant. Results. We find T eff = 4100 ± 100 K, log g = 0.0 ± 0.5, [Fe/H] = 0.0 ± 0.5, [C/H] = −0.8 ± 0.2, [N/H] = +0.6 ± 0.3 in the atmosphere of the secondary, and demonstrate that inclusion of some dust "veiling" in the spectra cannot improve our fits.

Context. We report results from lithium abundance determinations using high resolution spectral analysis of the 107 metal-rich stars from the Calan-Hertfordshire Extrasolar Planet Search programme. Aims. We aim to set out to understand the lithium distribution of the population of stars taken from this survey. Methods. The lithium abundance taking account of non-local thermodynamical equilibrium effects was determined from the fits to the Li I 6708 Å resonance doublet profiles in the observed spectra. Results. We find that a) fast rotators tend to have higher lithium abundances; b) log N(Li) is higher in more massive and hot stars; c) log N(Li) is higher in stars of lower log g; d) stars with the metallicities >0.25 dex do not show the lithium lines in their spectra; e) most of our planet hosts rotate slower; and f) a lower limit of lithium isotopic ratio is 7 Li/ 6 Li > 10 in the atmospheres of two stars with planets (SWP) and two non-SWP stars. Conclusions. Measurable lithium abundances were found in the atmospheres of 45 stars located at distances of 20−170 pc from the Sun, for the other 62 stars the upper limits of log N(Li) were computed. We found well defined dependences of lithium abundances on T eff , V sin i, and less pronounced for the log g. In case of V sin i we see two sequences of stars: with measurable lithium and with the upper limit of log N(Li). About 10% of our targets are known to host planets. Only two SWP have notable lithium abundances, so we found a lower proportion of stars with detectable Li among known planet hosts than among stars without planets. However, given the small sample size of our planet-host sample, our analysis does not show any statistically significant differences in the lithium abundance between SWP and stars without known planets.