Low-Resolution Spectroscopy of the Recurrent Nova T Pyxidis at its Early Stage of the 2011 Outburst

Abstract

We present our observational results of the recurrent nova T Pyx at its early stage of the 2011 outburst, using a low-resolution spectrograph ($ R$$ \approx$ 400) attached to a 28 cm telescope. The total number of nights of our observation was 11, among which 9 nights were during the pre-maximum stage. As a result, we obtained a detailed evolutional feature of this recurrent nova on the way to its maximum light. At first, on the earliest three nights (25–21 days before maximum), broad and prominent emission lines, such as Balmer series, He I, He II, N II, N III, and O I together with the P Cyg profile, are seen on the spectra. The blueshifted absorption minima of H$ \alpha$ yields a maximum expansion velocity of approximately 2200 km s$ ^{-1}$ , and the velocity gradually decreases. Then, helium and nitrogen lines are weakened day by day. After that (18 days before maximum light), Fe II (multiplets) lines emerge on the spectra. These lines are then strengthened day by day, and the P Cyg profiles also become more prominent. Accordingly, the expansion velocities turn to gradual increase. In addition, during the pre-maximum stage, the nova spectral type of T Pyx is thought to evolve from the He$ /$ N type to the Fe II one.