[IAUC] CBET 1757: 20090406 : AX PERSEI

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                                                  Electronic Telegram No. 1757
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
M.S. 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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AX PERSEI
     U. Munari and A. Siviero, Istituto Nazionale di Astrofisica, Padova
Astronomical Observatory; and S. Dallaporta, G. Cherini, P. Valisa, F.
Castellani, A. Frigo, A. Vagnozzi, S. Bacci, G. Righetti, S. Moretti, and S.
Tomaselli, "Asiago Novae and Symbiotic Stars" (ANS) collaboration, report
that the symbiotic star AX Per is undergoing a brightening phase.  The
monitoring carried out with several ANS-collaboration telescopes recorded
AX Per to be still in quiescence at B = 12.56, B-V = +1.08, V-I_c = +3.03 on
2009 Feb. 28, when it started a rapid increase in brightness that took it to
B = 12.07, B-V = 0.86, V-I_c = 2.68 by Mar. 12, and to B = 11.55, B-V = +0.82,
V-I_c = +2.43 by Apr. 1.  Such a bright state has not been reached after
the major outburst that AX Per underwent between 1988 and 1992 (cf. IAUCs
4544, 4621, 4922, 4994).  Other major outbursts occurred around 1888, 1925,
1950, and 1978, according to the historical lightcurve compiled by Skopal et
al. (2001, A.Ap. 367, 199).  Absolute optical spectrophotometry of AX Per was
obtained during the recent event with the 0.60-m telescope of the Schiaparelli
Observatory in Varese and the 1.22-m telescope of the Asiago Astrophysical
Observatory.  The spectrum for 2009 Apr. 1 is characterized by a very strong
and high-ionization emission-line spectrum, superimposed on the M giant
absorption spectrum, which is veiled shortward of 500 nm by the blue continuum
from circumstellar nebular material.  On this Apr. 1 spectrum, the integrated
flux of H_beta emission is 6.3 x 10**(-12) erg cm**(-2) s**(-1), and the flux
ratios (H_beta):(He II 468.6-nm):(He I 587.6-nm):([O III] 500.7-nm) are
1.00:0.76:0.61:0.37; the corresponding average values in quiescence are 4.5 x
10**(-12) erg cm**(-2) s**(-1) and 1.00:0.47:0.27:0.13 (Mikolajewska and
Kenyon 1992, A.J. 103, 579).  Thus, the current event is characterized by a
large increase in both the intensity and ionization conditions of the
emission-line spectrum, with a larger fraction of the circumstellar gas being
ionized by the radiation field of a hotter and more luminous central source.
This extra nebular continuum is reponsible for the brightness increase and
"bluing" of the colors.  Quite similar photometric and spectroscopic
conditions characterized the short-duration flare that AX Per underwent about
one year before the onset of major 1988-1992 outburst, according to the data
presented by Mikolajewska and Kenyon (op.cit.).


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                         (C) Copyright 2009 CBAT
2009 April 6                     (CBET 1757)              Daniel W. E. Green