  A (sub-)millimeter line and continuum study of the class I protostar Elias 29
in the Rho Ophiuchi molecular cloud is presented, whose goals are to understand
the nature of this source, and to locate the ices that are abundantly present
along this line of sight. Within 15-60" beams, several different components
contribute to the line emission. Two different foreground clouds are detected,
an envelope/disk system and a dense ridge of HCO+ rich material. The latter two
components are spatially separated in millimeter interferometer maps. We
analyze the envelope/disk system by using inside-out collapse and flared disk
models. The disk is in a relatively face-on orientation (<60 degrees), which
explains many of the remarkable observational features of Elias 29, such as its
flat SED, its brightness in the near infrared, the extended components found in
speckle interferometry observations, and its high velocity molecular outflow.
It cannot account for the ices seen along the line of sight, however. A small
fraction of the ices is present in a (remnant) envelope of mass 0.12-0.33 Msun,
but most of the ices (~70%) are present in cool (T<40 K) quiescent foreground
clouds. This explains the observed absence of thermally processed ices
(crystallized H2O) toward Elias 29. Nevertheless, the temperatures could be
sufficiently high to account for the low abundance of apolar (CO, N2, O2) ices.
This work shows that it is crucial to obtain spectrally and spatially resolved
information from single-dish and interferometric molecular gas observations in
order to determine the nature of protostars and to interpret infrared ISO
satellite observations of ices and silicates along a pencil beam.
