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IAUC 6724: 1997dd; Cep X-4

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                                                 Circular No. 6724
Central Bureau for Astronomical Telegrams
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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SUPERNOVA 1997dd IN NGC 6060
     S. Nakano, Sumoto, Japan, reports the discovery of an apparent
supernova (V = 16.4) by Masakatsu Aoki (Tsukioka Cho, Toyama) on
ten CCD frames (limiting mag about 17.5) taken with a 0.43-m f/6
reflector around Aug. 20.535 UT.  SN 1997dd is located at R.A. =
16h05m46s.32, Decl. = +21o29'14".3 (equinox 2000.0), which is 79"
west and 9" north of the center of NGC 6060.  Confirming frames
were taken by Aoki on Aug. 21, and nothing was visible at this
location on his frames taken on May 26, June 14 and 27, July 21,
and Aug. 3 and 10.  P. Garnavich and R. Kirshner, Harvard-
Smithsonian Center for Astrophysics, report that K. Stanek obtained
CCD images on Aug. 26.18 with the Whipple Observatory's 1.2-m
reflector, showing SN 1997dd at position end figures 46s.33, 14".2
(+/- 0".4), and magnitudes R about 17.2, B about 17.9 (measured
with respect to the USNO A1.0 magnitudes of the star at position
end figures 52s.60, 31'26".8).

     J. M. Bonnet-Bidaud, Service d'Astrophysique, Centre d'Etudes
de Saclay; and M. Mouchet, Observatoire de Paris, report:  "Long-
slit spectra (375-725 nm; resolution 1.3 nm) of the proposed
optical identification of the transient 66-s x-ray pulsar Cep X-4 =
GS 2138+56 (IAUC 6698, 6711), obtained on July 29 and 30 at Haute-
Provence Observatory, show features typical of x-ray Be binaries.
Superimposed on a weak emission from the IC 1396 nebula, strong
H-alpha (equivalent width 4.5 nm) and H-beta (EW 0.3 nm) lines are
seen in emission with the other Balmer lines in absorption.
Significant interstellar absorption features are also detected,
including a strong Na I doublet (589 nm) and diffuse bands at 443,
578, and 628 nm.  Considering a wide range of spectral types from
B7 to O9, dereddening of the spectra yields E_(B-V) = 1.0-1.2,
corresponding to an absorption of N_H = (7-8) x 10E21 atoms cmE-2
for a typical gas/dust ratio.  This is in very good agreement with
the x-ray column density (7.8 +/- 1.9) x 10E21 atoms cmE-2 derived
by Schulz et al. (1995, A.Ap. 295, 413) and confirms the
identification.  Assuming a mean interstellar density of 1 hydrogen
atom cmE-3, the deduced distance is 2300-2700 pc.  A similar value
of 3000 pc is independently derived from the strong Na line (EW 0.3
nm), if assumed fully interstellar.  At this distance, the x-ray
quiescent luminosity is 2 x 10E33 erg sE-1, comparable to x-ray
Be-binary low states."

                      (C) Copyright 1997 CBAT
1997 August 26                 (6724)            Daniel W. E. Green

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