[vsnet-alert 10190] Luminous V838 Mon-type transient in NGC 300

Howard E. Bond bond at stsci.edu
Fri May 16 09:59:12 JST 2008

Dear Colleagues,

The message below has been submitted for publication in the IAU Circulars,
regarding a luminous transient in the nearby southern galaxy NGC 300 discovered
by Berto Monard. For the reasons given, I believe the object may be similar to
V838 Monocerotis. Regular photometric and spectroscopic observations are
strongly recommended to southern observers, even though you will have to stay up
until just before dawn!

clear skies,
Howard E. Bond
Space Telescope Science Institute


H. E. Bond (STScI), F. M. Walter (Stony Brook U.), and J. Velasquez
(CTIO) write: A bright variable star (J2000: 00 54 34.16 -37 38 28.6)
that has appeared in the Sculptor Group galaxy NGC 300 was reported on
the CBAT Unconfirmed Observations Page by L.A.G. Monard, with the
following unfiltered CCD magnitudes: Apr. 24.16, 16.5; May 14.14, 14.2;
15.14, 14.2. The star is not visible on DSS images to limiting mag 20.5.
A spectrum (resolution 17.2 A), obtained on 2008 May 15.4 with the
SMARTS 1.5-m telescope at Cerro Tololo, shows emission lines of H-alpha,
H-beta, the Ca II triplet 8542-8498-8662, and, remarkably, strong
emission at the forbidden [Ca II] doublet 7291-7323. Ca II H & K are
seen in absorption. The Balmer lines are only slightly resolved at the
790 km/s velocity resolution of the spectra. The mean heliocentric
radial velocity of the features is about +430 km/s, probably consistent
with membership in NGC 300. At an optical absolute magnitude of -12.5,
the object is photometrically and spectroscopically not a classical
nova, LBV, or supernova. The spectrum is fairly similar to that of V838
Mon on 2002 Feb 13 (Wisniewski et al. 2003, ApJ, 588, 486, Fig 5), an
object suggested to represent the collision or merger of two stars. We
urge continued spectroscopic and photometric monitoring.

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