AAVSO Special Notice #45: 1804-18 V5558 Sgr = Nova Sgr 2007

Coordinates: R.A. = 18h 10m 18.27s    Decl. = -18o 46' 52.1" (2000.0)

Further to AAVSO Special Notice #44, 1804-18 Nova Sgr 2007 has been given
the name V5558 Sgr by N. N. Samus, Institute of Astronomy, Russian Academy
of Sciences, according to IAU Circular 8832 (Daniel W. E. Green, ed.).

Spectroscopic information available to date and announced in Central
Bureau Electronic Telegram 934 (Daniel W. E. Green, ed.) indicates that
the exact nature of V5558 Sgr is not clear. T. Iijima, Astronomical
Observatory of Padova, Asiago, reports that medium-dispersion spectra taken
on Apr. 20.12 and 20.14 UT indicate that "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 obtained on Apr. 20.80 UT
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."

Recent observations reported to the AAVSO include:
Apr. 21.1042 UT, 9.9, W. Kriebel, Schierling/Walkenstetten, Germany;
21.1306, 9.6, M. Jacquesson, Sevigny-Waleppe, France;
21.1360, 9.9, P. Schmeer, Bischmisheim, Germany;
21.196, 10.0. A. Amorim, Florianopolis, Brazil (via CBET 934);
21.3236, 9.6, L. Shotter, Uniontown, PA;
22.0764, 9.8, S. Swierczynski, Dobczyce, Poland;
22.1174, 9.7, Jacquesson;
22.1350, 10.0, Schmeer;
22.2889, 9.8, M. Komorous, London, Ontario, Canada;
22.3563, 9.6, Shotter;
23.0625, 9.6, Swierczynski;
23.0917, 9.7, Kriebel;
23.1310, 10.0, Schmeer;
24.3451, 9.8, Komorous;
24.4020, 9.7, R. Campbell, Largo, FL;

As mentioned in Special Notice #44, a chart of the region may be drawn
using the coordinates above and VSP:
http://www.aavso.org/observing/charts/vsp/
Sequence and calibration work on this field continue.

Please continue to observe this extremely interesting object, and report
observations to the AAVSO as 1804-18 V5558 SGR. Be sure to include your
comparison star information.

Thank you and good observing!

This special notice was compiled by: Elizabeth O. Waagen
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