[IAUC] CBET 965: 20070516 : V5558 SAGITTARII

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                                                  Electronic Telegram No. 965
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
     U. Munari and A. Siviero, Istituto Nazionale di Astrofisica, Padova
Astronomical Observatory; and S. Dallaporta and P. Valisa, ANS (Asiago Novae
and Symbiotic stars) Collaboration, report that, since its discovery on Apr.
14.78 UT (cf. IAUC 8832), V5558 Sgr = N Sgr 2007 has been steadily
increasing in brightness while keeping almost constant colors.  Their CCD
photometric monitoring began on Apr 21.126, when the nova was measured at
B = 10.52, B-V = +0.84, V-I_c = +1.22.  In the following weeks, it showed a
linear increase in brightness at a mean rate of -0.031 mag/day in B until
maximum was eventually reached at B = 9.78 and B-V = +0.87 around May 12.0,
after which the nova begun to slowly decline.  On May 16.106, the nova was
measured at B = 9.84 and B-V = +0.89, V-I_c = +1.56.  Since discovery, the
colors have become redder by 0.0016 mag/day in B-V, and 0.014 mag/day in
V-I_c.  The authors' latest absolutely fluxed spectra were obtained on May
11.082 (range 390-730 nm, resolution 0.35 nm) and May 11.115 (range 616.2-
682.0 nm, resolution 0.078 nm), with echelle spectroscopy on May 8.112
(range 430-730 nm, resolving power 24000).  These spectroscopic observations
show conspicuous changes in comparison with early reports.  Spectra obtained
around Apr. 20 by T. Iijima and by Naito et al. (cf. CBET 934) were
dominated by a featureless continuum with strong Balmer and He I emission
lines, all with P-Cyg profiles.  He I lines are now gone, and strong Fe II
emission lines (multiplets 27, 28, 37, 38, 42, 49, 74) have emerged instead,
still superimposed on a relatively flat continuum.  Si II (multiplet 2) is
also present in emission with a P-Cyg profile.  The FWHM and equivalent
width of H_beta emission were 500 km/s and 3.4 nm on Apr. 20; now they have
declined to 205 km/s and 2.23 nm, respectively.  The velocity separation
between emission and absorption components of P-Cyg profiles were 450 km/s
on Apr. 20; now it has declined to about 260 km/s for Balmer lines and 200
km/s for Fe II lines.  If the Apr. 20 spectra did not allow a firm conclusion
about the nature of the object, the current spectra look much like those of a
classical nova at maximum light, with low expansion velocity and belonging to
Fe II class.  The integrated emission line flux ratio H_alpha:H_beta:H_gamma
is 6.30:1.00:0.38.  The H_alpha integrated flux was 1.25 x 10**(-10) erg
cm**(-2) s**(-1) at the time of maximum brightness on May 12.  The
interstellar Na I D1 and D2 lines show two marginally resolved components at
heliocentric radial velocities -16 and +6 km/s; they seems to show the same
0.039-nm equivalent width, which would correspond to a total reddening of
E(B-V) = 0.18 + 0.18 = 0.36, following Munari and Zwitter (1997, A.Ap. 318,
269) calibration for the Na I D2 line.  Higher-S/N and -resolution echelle
observations of the interstellar lines are required to more firmly derive
the reddening affecting this nova.  Diffuse interstellar bands are observed
at 443.0, 578.0, 579.7, 628.4, 637.9, and 661.4 nm.
     Visual magnitude estimates for V5558 Sgr, provided in part by E. O.
Waagen from AAVSO data:  Apr. 22.135 UT, 10.0 (P. Schmeer, Bischmisheim,
Germany); 23.131, 10.0 (Schmeer); 24.385, 9.7 (R. King, Duluth, MN, U.S.A.);
25.397, 9.7 (R. Campbell, Largo, FL, U.S.A.); 26.066, 9.7 (S. Swierczynski,
Dobczyce, Poland); 27.069, 9.3 (H.-G. Purucker, Erlangen, Germany);
28.078, 9.6 (W. Kriebel, Schierling/Walkenstetten, Germany); 28.796, 9.6
(H. Matsuyama, Kanimbla, Queensland, Australia); 29.346, 9.6 (M. Komorous,
London, Ontario, Canada); 30.090, 9.6 (F. Vohla, Altenburg, Germany);
May 1.118, 9.9 (K. Wenzel, Grossostheim, Germany); 2.040, 9.3 (Swierczynski);
2.765, 9.4 (Matsuyama); 3.249, 9.4 (Komorous); 3.823, 9.6 (Matsuyama);
4.044, 9.3 (Swierczynski); 4.804, 9.2 (Matsuyama); 5.347, 9.3 (L. Shotter,
Uniontown, PA, U.S.A.); 6.762, 9.1 (Matsuyama); 8.209, 9.4 (Komorous);
9.374, 9.1 (Shotter); 9.765, 9.3 (Matsuyama); 11.218, 9.4 (Komorous);
12.965, 9.1 (Purucker); 13.380, 8.9 (Shotter); 13.792, 9.1 (Matsuyama);
15.017, 9.2 (Swierczynski); 15.769, 9.1 (Matsuyama).
     Waagen also communicates the following AAVSO CCD magnitudes of V5558
Sgr.  R magnitudes, made by M. Nicholson, Daventry, England, unless noted
otherwise:  Apr. 24.4214 UT, 8.85; 25.4469, 8.75; 26.4014, 8.69; 27.3954,
8.73; 28.7854, 8.63 (G. Di Scala, Sydney, NSW, Australia); May 1.3974, 8.63;
10.4658, 8.33; 11.3875, 8.33; 12.3450, 8.28.  V magnitudes, by Nicholson
unless otherwise noted:  Apr. 24.4222, 9.57; 24.4229, 9.49 (S. Dvorak,
Clermont, FL, U.S.A.); 25.4201, 9.38 (Dvorak); 25.4476, 9.42; 26.4021, 9.40;
27.3961, 9.48; 28.7854, 9.34 (Di Scala); 29.4073, 9.33 (Dvorak); 30.4173,
9.28 (Dvorak); May 1.3982, 9.34; 2.4168, 9.22 (Dvorak); 3.4136, 9.18
(Dvorak); 4.4142, 9.18 (Dvorak); 8.2555, 8.96 (Dvorak); 10.4131, 9.02
(Dvorak); 10.4665, 9.03; 11.3882, 9.02; 12.3458, 8.96; 12.4131, 8.93
(Dvorak).  B magnitudes, by Nicholson unless otherwise noted:  Apr. 24.4229,
10.35; 25.4218, 10.20 (Dvorak); 25.4484, 10.21; 26.4028, 10.25; 27.3968,
10.30; 28.7854, 10.22 (Di Scala); 29.4095, 10.17 (Dvorak); May 1.3989, 10.16;
2.4196, 10.05 (Dvorak); 4.4163, 10.05 (Dvorak); 8.2575, 9.81 (Dvorak);
10.4137, 9.88 (Dvorak); 10.4673, 9.86; 11.3890, 9.84; 12.3465, 9.79.


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                         (C) Copyright 2007 CBAT
2007 May 16                      (CBET 965)               Daniel W. E. Green