  HD 140283 is a reference subgiant that is metal poor and confirmed to be a
very old star. The abundances of this type of old star can constrain the nature
and nucleosynthesis processes that occurred in its (even older) progenitors.
The present study may shed light on nucleosynthesis processes yielding heavy
elements early in the Galaxy. A detailed abundance analysis of a high-quality
spectrum is carried out, with the intent of providing a reference on stellar
lines and abundances of a very old, metal-poor subgiant. We aim to derive
abundances from most available and measurable spectral lines. The analysis is
carried out using high-resolution (R = 81 000) and high signal-to-noise ratio
(800 < S/N/pixel < 3400) spectrum, in the wavelength range 3700 - 10475,
obtained with a seven-hour exposure time, using the ESPaDOnS at the CFHT. The
calculations in LTE were performed with the OSMARCS 1D atmospheric model and
the spectrum synthesis code Turbospectrum, while the analysis in NLTE is based
on the MULTI code. We present LTE abundances for 26 elements, and NLTE
calculations for the species C I, O I, Na I, Mg I, Al I, K I, Ca I, Sr II, and
Ba II lines. The abundance analysis provided an extensive line list suitable
for metal-poor subgiant stars. The results for Li, CNO, alpha-, and iron peak
elements are in good agreement with literature. The newly NLTE Ba abundance,
along with a NLTE Eu correction and a 3D Ba correction from literature, leads
to [Eu/Ba] = +0.59 +/- 0.18. This result confirms a dominant r-process
contribution, possibly together with a very small contribution from the main
s-process, to the neutron-capture elements in HD 140283. Overabundances of the
lighter heavy elements and the high abundances derived for Ba, La, and Ce
favour the operation of the weak r-process in HD 140283.
