Rivilla, V. M.V. M.RivillaFONTANI, FRANCESCOFRANCESCOFONTANIBELTRAN SOROLLA, MARIA TERESAMARIA TERESABELTRAN SOROLLAVasyunin, A.A.VasyuninCaselli, P.P.CaselliMartín-Pintado, J.J.Martín-PintadoCESARONI, RiccardoRiccardoCESARONI2021-02-192021-02-1920160004-637Xhttp://hdl.handle.net/20.500.12386/30476Phosphorus is a crucial element in biochemistry, in particular the P-O bond, which is key in the formation of the backbone of deoxyribonucleic acid. So far, PO has only been detected toward the envelope of evolved stars, but never toward star-forming regions. We report the first detection of PO toward two massive star-forming regions, W51 e1/e2 and W3(OH), using data from the IRAM 30 m telescope. PN has also been detected toward the two regions. The abundance ratio PO/PN is 1.8 and 3 for W51 and W3(OH), respectively. Our chemical model indicates that the two molecules are chemically related and are formed via gas-phase ion-molecule and neutral-neutral reactions during cold collapse. The molecules freeze out onto grains at the end of the collapse and desorb during the warm-up phase once the temperature reaches ∼35 K. Similar abundances of the two species are expected during a period of ∼5 × 10<SUP>4</SUP> yr at the early stages of the warm-up phase, when the temperature is in the range 35-90 K. The observed molecular abundances of 10<SUP>-10</SUP> are predicted by the model if a relatively high initial abundance of 5 × 10<SUP>-9</SUP> of depleted phosphorus is assumed.STAMPAenArticle10.3847/0004-637X/826/2/1612-s2.0-84982274191000381977900061https://iopscience.iop.org/article/10.3847/0004-637X/826/2/1612016ApJ...826..161RFIS/05 - ASTRONOMIA E ASTROFISICA