We investigate the effect on U,B,V magnitudes of the removal of emission lines from the spectra of some symbiotic stars and novae during their nebular phases. We approach this problem by the precise reconstruction of the composite UV/optical continuum and the line spectrum. The corrections ΔU, ΔB and ΔV are determined from the ratio of fluxes with and without emission lines. We demonstrate the effect for symbiotic nova V1016 Cyg during its nebular phase. We find that about 68%, 78% and 66% of the observed flux in the U, B and V filters is radiated in the emission lines. The effect should be taken into account before using the observed color indices of emission-line objects for diagnosis of their radiation in the continuum.
Open Astronomy is a peer-reviewed, fully open access online journal, that publishes research, reviews and news spanning all aspects of astronomy and astrophysics. Open Astronomy (formerly Baltic Astronomy) was founded by the Institute of Theoretical Physics and Astronomy (Lithuania) in 1992 and acquired by De Gruyter in 2016.