Spectroscopy and photometry of HR Lyr (Nova Lyr 1919) during one of its mysterious dimming episodes
ATel #9418; U. Munari (INAF Padova), A. Siviero, P. Ochner (Univ. Padova); S. Dallaporta (ANS Collaboration)
on 27 Aug 2016; 14:17 UT
Credential Certification: U. Munari (email@example.com)
Subjects: Optical, Cataclysmic Variable, Nova
An alert posted to the BAA-VSS newsgroup on Aug 24 by J. Shears informs
about a new excursion down to V~17 of old nova HR Lyr (Nova Lyr 1919). A few
other such episodes were catch by Honeycutt et al (2014, AJ 147, 105) in
their intensive 1991-2012 V-band monitoring of HR Lyr, usually between V=15.5 and 16.0.
Apparently no multi-color photometric or spectroscopic observations obtained
during one such dimming episode have been published, which contributes to
the uncertainty about their causes.
We have obtained BVRI photometry of HR Lyr on Aug 25.94 UT with the Asiago
Schmidt 67/92cm telescope, and measured V=16.98, B-V=+0.31, V-Rc=+0.36 and
V-Ic=+0.86 (+/- 0.01 on all of them) on the Landolt (2013, AJ 146, 131)
system of standards at +50 dec. This confirms the low state HR Lyr is
currently undergoing and founds its color slightly redder than the average
B-V=+0.13 listed by Bruch (1984, A&AS 56, 441).
We have obtained a 3300-8000 Ang spectrum (dispersion 2.31 Ang/pix) of HR
Lyr on Aug 26.93 UT with the Asiago 1.22m telescope. The spectrum is
characterized by a smooth bluish continuum with superimposed strong emission
lines. Hydrogen Balmer lines are visible in emission down to at least H13
(3734 Ang). Most prominent HeI emission lines are 7065, 6678, 5876, 5016
and 4922 Ang. The intensity of HeII 4686 is 0.32 times that of Hbeta. In
units of 10(-15) erg cm-2 s-1, the integrated flux of Halpha, Hbeta, HeI
5876, HeII 4686 emission lines is 10.5, 6.0, 1.0, 1.8, respectively, and
their E.W. 22.1, 8.4, 1.8, 2.5 Ang, respectively. The spectral appearance
of HR Lyr during a dimming episode is therefore quite different from that
exhibited during normal quiescence, when a featureless blue continuum
dominates the optical spectrum with no trace of emission lines (Humason
1938, ApJ 88, 228; Kraft 1964, ApJ 139, 457; Williams 1983, ApJS 53, 523).
A weak emission in Halpha has been reported for several quiescence epochs by
Honeycutt et al (2014), who measured an average E.W.=6.6 Ang. During the
current episode, the E.W. of Halpha emission has therefore more than
tripled, as if the dimming affects the underlying blue continuum but not
the emission lines.