ATEL #4996                                                           ATEL #4996

Title:  The symbiotic star YY Her is in outburst
Author: U. Munari (INAF Padova-Asiago), S. Dallaporta, F. Castellani,
                R. Belligoli, G. Cherini, G. L. Righetti, M. Graziani, P. Valisa,
                A. Milani (ANS Collaboration)
Queries:        ulisse.munari@oapd.inaf.it
Posted: 22 Apr 2013; 09:19 UT
Subjects:Optical, Cataclysmic Variable, Nova

The symbiotic star YY Her is in outburst.  The last outburst phase ended
during 2006, and was characterized by three brightness maxima occourring
in early 2003, mid-2004 and late 2005, with a separation of about 500 days
among them.  The last of these maxima occoured on 20 Nov 2005 at B =
12.69, V=11.92, Ic=10.17.  After a flat quiescence period lasting 6 years,
a new outburst phase begun in 2011.  A first maximum was reached on 5 Dec
2011 at U=12.24, B=12.47, V=11.78, Rc=11.05 and Ic=10.16.  The current bright
phase is the second maximum of the new outburst chain phase.  On 15 April
2013, at maximum brightness, we measured YY Her at U=12.59, B=12.84,
V=12.11, Rc=11.30, Ic=10.31.  Interestingly, the separation between these
two recent maxima is again about 500 days, as it was for the chain of three
maxima during the 2003-2005 outburst phase.  Such a separation is quite
shorter than the 590 day orbital period established from the reflection
effect and the ellipsoidal modulation observed in quiescence.  A low
resolution spectrum (4000-8660 Ang, 4.26 Ang/pix) and an Echelle Halpha
profile of YY Her were obtained on 18 April 2013 with 0.6m telescope in
Varese and the Multi Mode Spectrograph.  Compared with our latest spectrum
in quiescence, obtained with the Asiago 1.22m telescope on 22 Oct 2012,
the integrated absolute flux of the HeII, HeI and Balmer emission lines has
increased by a factor of 2.0, and the flux ratios HeII 4686/Hbeta and HeI
5876/HeII 4686 have remained stable at 0.46 and 0.29, respectively.  The
flux of nebular [OIII] 5007, 4959 lines increased by 3.6 times, that of
auroral [OIII] 4363 by just 1.4 times.  The most striking change is the
great increase in intensity of the fluorescence pumped NIII blend at 4640
Ang, which in YY Her is usually absent or much weaker during quiescence.
The Halpha profile for the present and 2011 outbursts are nearly identical,
with a sharp absorption component superimposed to a narrow emission and
blue-shifted from its peak by 85 km/s.  The equivalent width of the Halpha
absorption component is reduced in comparison to quiescence conditions.
No obvious P-Cyg features are observed.