COMMISSION 27 OF THE I. A. U.
          INFORMATION BULLETIN ON VARIABLE STARS
                       NUMBER 686

                                           Konkoly Observatory
                                           Budapest
                                           1972 June 20


EXTRAGALACTIC CaII ABSORPTION LINES IN THE SPECTRA OF THE SUPERNOVA IN NGC 5253


The Supernova in NGC 5253 discovered by Kowal has been observed at Cerro
Tololo Interamerican Observatory in Chile. We secured several spectroscopic
plates with the 60 inch reflecting telescope. The grating spectrograph
combination we used gives a reciprocal dispersion of 39 A/mm. Figure 1
displays a densitometric tracing of the plate C-2613 showing the continuum
energy distribution (on linear intensity scale) of the supernova. It shows
features of H and K CaII absorption lines of galactic origin; also a
red-shifted system of H and K lines are suspected in Fig. 1. Figure 2 shows a
densitometric tracing of the H and K lines where the red-shifted system is
clearly seen. Micrometric measurements with a Gartner machine of these
lines give the results listed in Table 1. The radial velocities obtained for
the stronger pair (K_1 and H_1) of interstellar galactic origin give a radial
velocity of -5+-3 km/s, while the red shifted pair gives +427+-6 km/s.

                           [FIGURE 1]

The equivalent widths of the lines were measured on the plates C-2595, C-2613,
and C-2621. Calibration plates were taken with a spot sensitometer at lambda
4950 A (Delta lambda/2=130). The mean values obtained are: WK_1=0.445,
WK_2=0.105, WH_1=0.361, WH_2=0.078, in Angstrom units. From these values the
doublet ratios (DR) are: (DR)_1=1.23 and (DR)_2=1.35. From the theoretical
curves of growth of Stromgren (1948) and Munch (1957) as given by Munch 
(1968) we obtain:

(NL)_1=1.8*10^13cm^-2           (NL)_2=2.8*10^12cm^-2
(Log W/b)_1=0.42                (Log W/b)_2=0.30
(Log tau_0)_1=0.52              (Log tau_0)_2=0.26,

from Stromgren's curve, and
                                                           [FIGURE 2]

(NL)_1=2.6*10^13cm^-2           (NL)_2=3.1*10^12cm^-2
(Log W/n)_1=0.75                (Log W/n)_2=0.60
(Log tau_0)_1=+1.0              (Log tau_0)_2=+0.61,

from the Munch's curve of growth.

The above values indicate that the red-shifted absorption lines are formed in
the interstellar gas of NGC 5253, being the amount of matter involved smaller
by a factor ~10 as compared with that which forms the galactic absorption. The
turbulence parameters are also smaller for NGC 5253 indicating again a thinner
absorbing layer as compared with the galactic plane.

The observed red-shift in NGC 5253 at the place of the supernova is in
agreement with the velocity distribution in NGC 5253 (Sersic, 1972).

A complete study will be published elsewhere.

Tale 1.

Radial velocities reduced to the sun (Km/2-s).

Plate     Date          K_1    K_2     H_1     H_2
          1972
         May, UT

C-2595   26, 0h 00m      0    +427     -11    +408
  2613   29, 1  45     -11     442     - 7     420
  2614   29, 2  46     - 5     428     -10     417
  2615   29, 3  54     - 1     448     - 5     413
  2616   29, 5  07     + 6     434     - 5     438

References:

Munch, G. 1957, Ap.J., 125, 42. [BIBCODE 1957ApJ...125...42M ]
Munch, G. 1968, in Nebulae and Interstellar Matter, Ed. B.M. Middlehurst
   and L. Aller, Ch. 8, The University Chicago Press.
Sersic, J.L. 1972, Private. comm.
Stromgren, B. 1948, Ap.J. 108, 242. [BIBCODE 1948ApJ...108..242S ]


June, 1972
Observatorio Astronomico and
I.M.A.F., Cordoba, Argentina.

R.F. SISTERO and M.F. CASTORE DE SISTERO
Visiting Astronomers at Cerro Tololo Interamerican Observatory, which is
operated by AURA under contract with the N.S.F.