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To gain insight into the physical conditions and kinematics of the warm(100-1000 K) gas around the red hyper-giant VY CMa, we performed sensitive highspectral resolution observations of molecular lines in the sub-mm/FIR using theHIFI instrument of the Herschel Space Observatory. We observed CO, H2O, andother molecular species, sampling excitation energies from a few tens to a fewthousand K. These observations are part of the Herschel Guaranteed Time KeyProgram HIFISTARS. We detected the J=6-5, J=10-9, and J=16-15 lines of 12CO and13CO at about 100, 300, and 750K above the ground state (and the 13CO J=9-8line). These lines are crucial for improving the modelling of the internallayers of the envelope around VY CMa. We also detected 27 lines of H2O and itsisotopomers, and 96 lines of species such as NH3, SiO, SO, SO2 HCN, OH andothers, some of them originating from vibrationally excited levels. Three lineswere not unambiguously assigned. Our observations confirm that VY CMa'senvelope must consist of two or more detached components. The molecularexcitation in the outer layers is significantly lower than in the inner ones,resulting in strong self-absorbed profiles in molecular lines that areoptically thick in this outer envelope, for instance, low-lying lines of H2O.Except for the most abundant species, CO and H2O, most of the molecularemission detected at these sub-mm/FIR wavelengths arise from the central partsof the envelope. The spectrum of VY CMa is very prominent in vibrationallyexcited lines, which are caused by the strong IR pumping present in the centralregions. Compared with envelopes of other massive evolved stars, VY CMa'semission is particularly strong in these vibrationally excited lines, as wellas in the emission from less abundant species such as H13CN, SO, and NH3.

HIFISTARS Herschel/HIFI observations of VY Canis Majoris. Molecular-line inventory of the envelope around the largest known star