The complex organic molecular content in the L1517B starless core

Recent observations of the pre-stellar core L1544 and younger starless L1498 have revealed that complex organic molecules (COMs) are enhanced in gas phase toward their outer intermediate-density shells. Our goal is to determine level chemical complexity L1517B, which seems than L1498, compare it with other two previously studied cores see if there a evolution within cores. We carried out 3 mm high-sensitivity positions L1517B core: core's centre position where methanol emission peaks (at distance $\sim$5000 au from centre). reveal lower number COMs COM precursors detected respect L1544, also show abundances. Besides methanol, we only CH$_3$O, H$_2$CCO, CH$_3$CHO, CH$_3$CN, CH$_3$NC, HCCCN, HCCNC. Their measured abundances $\sim$3 times larger peak centre, mimicking behaviour found more evolved L1498. propose differences observed between three consequence evolution, being less one, followed by L1544. Chemical these increase over time, N-bearing forming first O-bearing at later stage as result catastrophic depletion CO.