Fig. 1.
Amplitude spectrum of V458 Vul. The confidence levels of peaks in the
spectrum are shown by horizontal lines and per cents on the right
edge of the Figure.
Fig. 2. The light curve of V458 Vul folded with the
period of 0.58946 day (top). The light-decay trend is eliminated
to reduce data to plateau level. The light curve of a check star
folded with the same period to demonstrate the accuracy of
observations (middle). The averaged orbital light curve of V458 Vul
(bottom).
We analysed spectra of V458 Vul taken with SAO RAS 1-m reflector
on 2007 August 18.90 and October 18.68 UT (spectral range 3800-7530A,
resolution 8A). The date of the last spectrum coincides with
the date of the first X-ray detection by Swift. Our spectra confirm
the description of spectral evolution by T.N.Tarasova (IBVS #5807):
the features of FeII class nova were completely changed by ones
of He/N nova in the SSS phase. No signs of high excitation Fe ion
emission are seen in spectrum taken on October 18. HeII 4686A
emission is blended with CIII/NIII and HeI lines, but its intensity
is less than a half of Hbeta what gives the upper limit of the central
source temperature of 190000K. [Fe X] 6374A emission is very faint,
its detection is marginal.
Fig. 3. The light curve of V458 Vul drawn versus time. Horizontal line marks plateu, SSS - marks the first and the last detection of X-ray SuperSoft Source, digits 1-4 show the local maxima used to correct the orbital period.
Fig. 4. The spectra of V458 Vul taken on 2007 August 18 and
October 18. The line identifications are given.
Remark.
Dr. Albert Zijlstra (JBCA, Univ. of Manchester) reported about new
time-resolved optical spectroscopic observations of V458 Vul which
reveal radial velocity variations in the He II 5412 and 4686 A emission
lines with the period 0.06812255 (0.00000017) day (Rodriguez-Gil et al.
ArXiv:1006.1075). It is identified with the orbital period of the binary
system. T(0) = 2454652.52694 (8 x 10^-5). Period 0.58946 day and its
aliases determined by Goranskij et al. (ATel 1631) do not become apparent.
V458 Vul is therefore the planetary nebula central binary star with the
shortest period known.
We try to identify this period in our photometric observations. We have
two sets of extensive monitoring in the V band: JD 2454644 - 2454655
(612 obs.) and
JD 2455060 - 2455073 (415 obs.). These data were cleaned for slow trends
and low frequency noise. Period 0.06812255 day appears in the first
set with the amplitude 0.03 mag and roughly sinusoidal light curve,
and in the second set with the amplitude of 0.05 mag with a small
eclipse-like dip near the phase of T(0). The averaged light curves
are shown in the following Figure.
Figure. Mean light curves of V458 Vul calculated with the
period of 0.06812255 day.
Sources.
J.J.Drake, K.Page, J.Osborne, M.Bode, R.Corradi, P.Rodriguez-Gil,
J.Drew, P.Gaensicke, D.Steeghs, C.Knigge, J.Sokoloski,
ATel 1246,
2007.
J.J.Drake, K.Page, J.Osborne, A.Beardmore, J.-U.Ness, S.Starrfield,
G.Schwarz, M.Tsujimoto, M.Barlow, R.Wesson, M.Bode, R.Corradi,
P.Rodriguez-Gil, P.Gaensicke, D.Steeghs, C.Knigge, D.Takai, A.Zijlstra,
ATel 1603,
2007.
T.N.Tarasova, IBVS No.5807,
2007.
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photometric data collection (in ASCII codes; JD hel., V,B,U,R
in the columns of the table).