The symbiotic star Hen 2-468 is undergoing a rare and bright outburst
ATel #6841; U. Munari (INAF-Padova), S. Dallaporta and F. Castellani (ANS Collaboration)
on 21 Dec 2014; 11:46 UT
Credential Certification: U. Munari (ulisse.munari@oapd.inaf.it)
Subjects: Optical, Cataclysmic Variable, Nova, Variables
The symbiotic star Hen 2-468 (V2428 Cyg) is on a fast rise toward a bright outburst, brighter than the only previously recorded active phase for this star during 1980-1984. A reflection/heating effect with an orbital period of 774 days modulates the quiescent brightness of Hen 2-468 between B~15.8 and B~16.9 (Munari and Jurdana-Sepic 2002, A&A 386, 237) suggesting a large orbital inclination. We are intensively monitoring the star since 2007 without seasonal gaps. Our last photometric measurement was obtained on 2014 Dec 20.7 UT when we measured Hen 2-468 at B=14.39, V=13.21, Rc=12.37 and Ic=11.08. Hen 2-468 is now ~2.4 mag brighter in B than when it started the steep (~0.05 mag in B-band per day) rise in brightness around 2014 Nov 1 when we measured the star at B=16.75, V=14.90, Rc=13.43 and Ic=11.58. In quiescence, the emission line spectrum of Hen 2-468 (cf. Munari and Zwitter 2002, A&A 383, 188) is characterized by high ionization and high density conditions with no significant nebular lines, HeII 4686 vastly larger than HeI and of an intensity similar to Hbeta, and a strong symbiotic band at 6825 Ang (Raman scattering of OVI by neutral hydrogen). On our last spectrum, obtained on 2014 Dec 18.75 UT with the Asiago 1.22m telescope (range 3350-7980 Ang, dispersion 2.31 Ang/pix), all emission lines are gone, only Halpha and Hbeta remain visible, and a strong bluer continuum veils the TiO bands of the M giant well into the Rc band. Compared to 2014 Oct 17, the Hbeta integrated flux has increased nearly three times, from 2.73x10(-14) to 7.60x10(-14) erg cm(-2) s(-1) and the Halpha/Hbeta ratio has declined from 19.4 to 12.8.
