  High resolution spectroscopy (R > 20,000) is currently the only known method
to constrain the orbital solution and atmospheric properties of non-transiting
hot Jupiters. It does so by resolving the spectral features of the planet into
a forest of spectral lines and directly observing its Doppler shift while
orbiting the host star. In this study, we analyse VLT/CRIRES (R = 100,000)
L-band observations of the non-transiting giant planet HD 179949 b centred
around 3.5 microns. We observe a weak (3.0 sigma, or S/N = 4.8) spectral
signature of H2O in absorption contained within the radial velocity of the
planet at superior-conjunction, with a mild dependence on the choice of line
list used for the modelling. Combining this data with previous observations in
the K-band, we measure a detection significance of 8.4 sigma for an atmosphere
that is most consistent with a shallow lapse-rate, solar C/O ratio, and with CO
and H2O being the only major sources of opacity in this wavelength range. As
the two sets of data were taken three years apart, this points to the absence
of strong radial-velocity anomalies due, e.g., to variability in atmospheric
circulation. We measure a projected orbital velocity for the planet of KP =
(145.2 +- 2.0)kms^{-1} (1 sigma) and improve the error bars on this parameter
by ~70%. However, we only marginally tighten constraints on orbital inclination
(66.2 +3.7 -3.1 degrees) and planet mass (0.963 +0.036 -0.031 Jupiter masses),
due to the dominant uncertainties of stellar mass and semi-major axis. Follow
ups of radial-velocity planets are thus crucial to fully enable their accurate
characterisation via high resolution spectroscopy.
