"Spectroscopy and photometry of the symbiotic star V4018 Sgr in outburst"

ATel #4403; U. Munari (INAF Astr. Obs. Padua), P. Valisa, S. Dallaporta
            (ANS Collaboration), E. O. Waagen, A. Henden (AAVSO Headquarters)

                    on 21 Sep 2012; 01:41 UT
Credential Certification: U. Munari (ulisse.munari@oapd.inaf.it)

Spectroscopy of the the symbiotic star V4018 Sgr (=AS 304), reported by
AAVSO observers to be in outburst (AAVSO Alert Notice 470), was obtained
with the 0.6m telescope of the Schiaparelli Observatory in Varese (Italy). 
A low resolution, absolutely fluxed 4000-8650 Ang spectrum (4.24 Ang/pix)
was recorded on Sept 13.90 UT.  It shows the spectrum of the M giant
overwhelmed by a blue continuum up to 6000 Ang, with only hydrogen Balmer
and weak HeI lines visible in emission.  The integrated absolute fluxes of
representative emission lines are [in units of 10^(-13) erg cm^2 sec^(-1)]
Hbeta = 34, HeI 5876 = 7.3, Halpha = 242, HeI 6678 = 5.0, and HeI 7065 =
6.0.  Only feeble traces of [OIII] 5007 and OI 8446 are detectable. 
Compared with quiescence spectra (cf.  Allen (1984, Proc.  ASA 5, 369;
Munari and Zwitter 2002, A&A 383, 188; Gutierrez-Moreno et al.  1999, PASP
111, 571), all high ionization emission lines are gone, in particular HeII
4686 Ang and [FeVII] 6087, which were at times rivalling in intensity with
Hbeta and HeI 5876, respectively.  A medium resolution spectrum of V4018 Sgr
was obtained on Sept 15.78 UT over the Halpha region (5312-6950 Ang, range
0.73 Ang/pix), and a low S/N Echelle spectrum (0.30 Ang/pix) of the same
region was obtained on Sept 20.76 UT.  No P-Cyg profiles affect the detected
emission lines.  HeI emission lines are very sharp, with a FWHM of 40
km/sec.  The Halpha emission line displays a simple Gaussian-like emission core,
characterized by a FWHM of 98 km/sec (corrected for instrumental resolution)
and an heliocentric radial velocity of +105 KM/sec, with the strong and
extended symmetric wings typical of symbiotic stars (cf.  Sekeras and Skopal
2012, BaltA 21, 196).  The heliocentric radial velocity of HeI emission
lines is +80 km/sec.  The 25 km/sec difference with Halpha, is close to the
22 km/sec difference found by van Winckel et al.  (1993, A&AS 102, 401), who
report the Halpha radial velocity to be +91 km/sec on 14 Sept 1989, while
Munari and Buson (1993, MNRAS ) measured +74 km/sec on 31 July 1988.  These
Halpha profiles for 1988-89 did not present the absorption which is now
apparent on the blue wing on Halpha on our Echelle spectrum for Sept 20.76,
characterized by a FWHM of 60 km/sec and an heliocentric radial velocity of
+49 km/sec.  The outburst state of V4018 Sgr is confirmed by ANS
Collaboration daily CCD photometry for Sept 13-20, which shows V4018 Sgr
stable around B=11.66, V=11.00, Rc=10.35, Ic=9.68.  These values are
remarkably close to those reported by Munari et al.  (1992, A&AS 93, 383)
for V4018 Sgr in June 1990, during the previous bright outburst: B=11.69,
V=11.19, Rc=10.64, Ic 9.87, J=8.59, H=7.71, K=7.40.  Jurdana-Sepic and
Munari (2010, PASP 122, 35) found V4018 Sgr even brighter, at B=11.2, on
Asiago archive plates exposed in May 1961.  For comparison, the median
values for quiescence reported by Henden and Munari (2008, Baltic Astronomy
17, 293) are B=14.38, V=13.29, Rc=12.12, Ic=10.69. At the time of the
previous outburst, Munari and Buson (1993, MNRAS 263, 267) obtained in 1992
low-res ultraviolet spectra with the IUE satellite that showed deep P-Cyg
absorptions at large outflow velocity (2200 +/- 400 km/sec), a rarity among
symbiotic stars.