[IAUC] CBET 862: 20070228 : SUPERNOVA 2007Y IN NGC 1187

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                                                  Electronic Telegram No. 862
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
M.S. 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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SUPERNOVA 2007Y IN NGC 1187
     G. Folatelli, Las Campanas Observatory (LCO), together with N.
Morrell, M. Phillips, and M. Hamuy, on behalf of the Carnegie Supernova
Project, report spectroscopic observations of SN 2007Y (cf. CBET 845,
IAUC 8813) obtained on Feb. 19.04 and 25.02 UT with the 2.5-m du Pont
telescope (+ WFCCD spectrograph) at LCO.  The spectra show that 2007Y is
a type-Ib/c supernova of peculiar evolution, in most aspects resembling
the case of SN 2005bf at early stages (see Folatelli et al. 2006, Ap.J.
641, 1039).
     The first spectrum is similar to that of SN 2005bf at 32 days before
maximum light, showing strong absorptions due to Fe II, Ca II, and other
metals.  In particular, the Ca II infrared triplet absorption component
at about 820 nm is remarkably strong.  Another absorption is seen at
about 620 nm, which may be identified as Si II or H-alpha, the latter
requiring higher expansion velocities.  Assuming the NED recession
velocity of 1390 km/s for the host galaxy (from Koribalski et al. 2004,
A.J. 128, 16), a comparison with synthetic spectra obtained using the
SYNOW code (Fisher 2000, Ph.D. thesis, University of Oklahoma) allows us
to identify a photospheric velocity of about 7000 km/s.  The match of Ca
II and Fe II lines improves by adding a high-velocity component appearing
beyond 15000 km/s, which would support the identification of the feature
at 620 nm as H-alpha at similarly high velocities.  The high-velocity
components of Ca II and Fe II are not as strong as the ones shown by SN
2005bf.  Through the same analysis, a strong absorption trough seen
around 420 nm is explained by a mixture of Fe II, Ti II, Mg II, and Sc
II.  The presence of a weak component of He I cannot be ruled out.
     The second spectrum resembles the spectra of SN 2005bf at 27 and 24
days before maximum.  The Ca II infrared triplet absorption has
significantly weakened, although a high-velocity component persists.  The
trough at 420 nm has also weakened, and the overall slope of the continuum
appears bluer, suggesting an increase in temperature.  The absorption at
about 620 nm has also become weaker, while the presence of He I appears
slightly more evident.  Acquisition images, obtained with the WFCCD
spectrograph prior to each of the spectra, were used to measure B- and
V-band photometry of SN 2007Y relative to a field star located 111".8 east
and 41".8 north of the supernova; these measurements indicate that 2007Y
brightened by about 1 magnitude in V, and its B-V color became bluer by
about 0.3 mag between Feb. 19 and 25.


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                         (C) Copyright 2007 CBAT
2007 February 28                 (CBET 862)               Daniel W. E. Green