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SN 2011gu in ngc7485 - 14 ottobre 2011

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SN 2011gu (A.R. 23 06 02.80, Dec. +34 06 36.7) scoperta il 14 ottobre 2011 nella galassia NGC 7485 (offset 22E 8N), magnitudine 17, tipo Ia.

SN scoperta da F. Martinelli, R. Mancini e F. Briganti all'osservatorio astronomico di Montecatini val di Cecina (Pisa).

NGC 7485 è una galassia S0 nella costellazione del Pegaso, distante 81 Mpc, magnitudine 14.1.

                                                  Electronic Telegram No. 2866
Central Bureau for Astronomical Telegrams
CBAT Director: Daniel W. E. Green; Hoffman Lab 209; Harvard University;
20 Oxford St.; Cambridge, MA 02138; U.S.A.
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SUPERNOVA 2011gu IN NGC 7485 = PSN J23060280+3406367
A. Dimai, Cortina d'Ampezzo, Italy, on behalf of the Italian Supernovae
Search Project (ISSP), reports the discovery by Fabio Martinelli, Riccardo
Mancini, and Fabio Briganti of an apparent supernova on unfiltered CCD images
(limiting mag about 19.0) taken with the 0.35-m telescope of the Montecatini
Valdicecina Observatory (Pisa, Italy) on Oct. 14.0299 UT (when the new object
was at mag about 18.0) and 14.9319 (when it was at mag about 17.6). The
variable is located at R.A. = 23h06m02s.80, Decl. = +34d06'36".7 (equinox
2000.0), which is 22" west and 8" north of the nucleus of NGC 7485. Nothing
is visible at this position on Palomar Sky Survey infrared, red, and blue
plates. The variable was designated PSN J23060280+3406367 when it was posted
at the Central Bureau's TOCP webpage and is here designated SN 2011gu based
on the spectroscopic confirmation reported below.
Additional CCD magnitudes for 2011gu (unfiltered unless otherwised noted):
1989 July 14, [21 (Digitized Sky Survey red plate; via Vitali Nevski, Vitebsk,
Belarus); 2011 Oct. 1, [19.5 (ISSP); 15.888, 17.4 (S. Leonini and L. M. Tinjaca
Ramirez, Siena, Italy; 0.53-m f/8.7 reflector + U47 camera at Montarrenti
Observatory); 15.9, 17.0 (A. Dimai, 0.28-m telescope, Col Drusci Observatory);
15.920, R = 17.5 (Federica Luppi, Luca Ghirotto, and Mirko Maffiolini, Varese,
Italy; 0.36-m f/7.9 reflector + Bessell R filter; position end figures 02s.81,
36".0; CMC-14 catalogue for reference stars; image posted at website URL
http://www.astrogeo.va.it/pub/TOCP/PSN_N7485.jpg); 16.117, 17.8 (Joseph
Brimacombe, Cairns, Australia; position end figures 02s.79, 36".7; image
posted at URL http://www.flickr.com/photos/43846774@N02/6250906523/); 16.913,
17.4 (C. Jacques and E. Pimentel, Belo Horizonte, Brazil; remotely using the
GRAS 07 telescope at Nerpio, Spain; limiting magnitude 18.5; position end
figures 02s.81, 36".2; UCAC2 reference stars; image posted at website URL
http://ceamig-rea.net/tocp/ngc7485_tocp.png); 16.758, 16.9 (Nick James,
Chelmsford, Essex, England; Celestron C11 telescope + ST9XE camera; position
end figures 02s.83, 36".0; UCAC-3 reference stars); 18.144, 17.8 (Brimacombe);
18.763, R = 17.3 (Nevski, 0.3-m reflector; position end figures 02s.82, 36".1;
UCAC-3 catalogue reference stars).

L. Magill, M. Fraser, and R. Kotak, Queen's University, Belfast; and A.
Pastorello, Osservatorio Astronomico di Padova, Istituto Nazionale di
Astrofisica, Universita di Padova, report that an optical spectrogram (range
390-1000 nm) of PSN J23060280+3406367 = SN 2011gu was obtained with the
William Herschel Telescope (+ ACAM) on Oct. 15.01 UT. The spectrum was
cross-correlated with a library of supernovae spectra using the "Gelato" code
(Harutyunyan et al. 2008, A.Ap. 488, 383). The best fit was with the peculiar
type-Ia supernova 1991bg at an epoch of 2 days post-maximum (Filippenko et al.
1992, A.J. 104, 1543); however, the blue end of the spectrum is relatively
noisy, and the Ti II trough that characterizes the SN-1991bg sub-class does
not seem to be as pronounced in 2011gu. The strength of the O I 777.4-nm
feature is comparable to that of SN 1991bg. An expansion velocity of 9000
km/s is measured from the Si II absorption feature found at 635 nm, corrected
for the expansion velocity of the host galaxy, NGC 7485 (5706 km/s; Wegner et
al. 1993, A.J. 105, 1251; via the NED website). The authors tentatively
identify a feature at the rest wavelength of NGC 7485 that is likely due to
Na I D lines (equivalent width of 31.5 nm), suggesting non-negligible
extinction within the host galaxy.

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

(C) Copyright 2011 CBAT
2011 October 20 (CBET 2866) Daniel W. E. Green