The evolution of nova V5558 Sgr during the decline stage

We report the spectroscopic follow-up of the nova V5558 Sgr carried out in 2008 and 2009 at the Loiano Observatory, Italy, during the decline stage, as a part of an ongoing monitoring campaign. The spectra suggest that V5558 Sgr has entered the nebular stage, as shown by the presence of high ionization lines, and confirm that it is very similar to the slow nova V723 Cas, as previously suggested. We have estimated the decline time by three magnitudes, 170 ± 2 days, typical of slow novae. We have revised the estimation of the absolute magnitude at maximum (−6.3 to −5.9) and the distance (1.3–1.6 kpc) of V5558 Sgr, in agreement with previous results. The revised white dwarf mass (0.58–0.63 M⊙) confirms that V5558 Sgr is a critical system whose mass is close to the lower limit to trigger the nova outburst.