[IAUC] CBET 934: 20070422 : V5558 SAGITTARII

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                                                  Electronic Telegram No. 934
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
M.S. 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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V5558 SAGITTARII
     T. Iijima, Astronomical Observatory of Padova, Asiago, reports that
medium-dispersion spectra (range 360-760 nm, resolution 1000) of V5558
Sgr (cf. IAUC 8832) were taken on Apr. 20.12 and 20.14 UT at Asiago
Astrophysical Observatory with a Boller-and-Chivens spectrograph mounted
on the 1.22-m reflector.  The spectra show prominent narrow emission lines
of H I and He I (e.g., equivalent width -3.4 nm and FWHM = 480 km/s for
H_beta, and -0.50 nm and 360 km/s for He I 587.6-nm).  Weak emissions of
some Fe II lines of multiplets 37, 42, and 49 were seen, and Mg II, Si II,
and probably N II were also noticed in emission.  Most of the prominent
emission lines were accompanied by a weak absorption component blueshifted
by 400-500 km/s with respect to the line center of the emission body.
This object could be a rather peculiar classical nova in the pre-maximum
stage.
     H. Naito and K. Matsuda, Nishi-Harima Astronomical Observatory; and H.
Yamaoka, Kyushu University, report that a low-resolution spectrum (range
410-670 nm; resolution 1500 at H_alpha) of V5558 Sgr was obtained on Apr.
20.80 UT with the 2.0-m NAYUTA telescope (+ MALLS), showing a smooth
continuum with emission lines of the Balmer series and P-Cyg profiles of
He I 492.2-nm (+ Fe II 492.4-nm), 501.50nm (+ Fe II 492.4-nm), 504.8-nm,
587.6-nm, 667.8-nm, and Fe II 516.9-nm.  The expansion velocity, derived
from the FWHM of the Balmer series (H_alpha, H_beta, H_gamma), is 500, 520,
and 540 km/s, respectively.  Notable Na I D absorption lines suggest that
our view of the nova suffers some reddening.  The overall feature of the
spectrum does not resemble that of a classical nova, but with the
amplitude (> 10 mag) of outburst and the absence of a pre-outburst
counterpart in the infrared or x-ray regions, it could be very remarkable
object.
     Visual magnitude estimate of V5558 Sgr by A. Amorim, Florianopolis,
Brazil:  Apr. 21.196 UT, 10.0.


NOTE: These 'Central Bureau Electronic Telegrams' are sometimes
      superseded by text appearing later in the printed IAU Circulars.

                         (C) Copyright 2007 CBAT
2007 April 22                    (CBET 934)               Daniel W. E. Green