Electron and positron capture rates on 55Co in stellar matter

55co is not only present in abundance in presupernova phase but is also advocated to play a decisive role in the core collapse of massive stars. the spectroscopy of electron capture and emitted neutrinos yields useful information on the physical conditions and stellar core composition. b(gt) values to low-lying states are calculated microscopically using the pn-qrpa theory. our rates are enhanced compared to the reported shell model rates. the enhancement is attributed partly to the liberty of selecting a huge model space, allowing consideration of many more excited states in our rate calculations. unlike previous calculations the so-called brink？s hypothesis is not assumed leading to a more realistic estimate of the rates. the electron and positron capture rates are calculated over a wide temperature (0.01×109 - 30×109k) and density (10 - 1011 gcm-3) grid.