COMMISSION 27 OF THE I. A. U.
        INFORMATION BULLETIN ON VARIABLE STARS
                     NUMBER 505

                             Konkoly Observatory
                             Budapest
                             1971 January 9


    THE SPECTRUM OF THE JULY 1970 SUPERNOVA IN M 101

      On the nights of August 5th and 6th, 1970, we 
obtained two well exposed spectra of the supernova in M 101
discovered by Lovas (I.A.U.C. 2269). Two underexposed plates
were taken later. All of the exposures (see Table for 
details) were made on blue-sensitive plates taken with the
60-90 cm Burrell Schmidt.



   Exposure data for supernova plates
-----------------------------------------
UT date  exposure A/mm         Remarks
 1970      time   at H_gamma
-----------------------------------------
 Aug 5.07   12m   1300
 Aug 6.07   30     580
Aug 25.11   30     580 badly underexposed
Aug 26.11   30     580 faint
-----------------------------------------



      The Figure is a density tracing of the spectrum of
August 6, in which the prominent emission features are
Identified. The spectrum is clearly that of a type II supernova, 
as all of the bands also appear in the spectra of
ordinary novae. Although it is difficult to be quantitative,
the gradient of the continuum energy distribution was
clearly less than that of an F star used for comparison
purposes. Changes in the appearance of the spectrum were
not marked over the time interval covered by our data.
There was only a general fading of about 0.5 to 1.0 magnitudes 
between the first and last plates, as estimated from
a comparison with neighboring stars.
     We have also measured the expansion velocity of the
shell from the widths of Hbeta and Hgamma. Because of the small
size of the spectrum and the rather low contrast, we have
measured the widths in three ways: with a measuring engine,
with an 0.1 mm scale, and with a ruler on the tracings. The
results for Hbeta are in good agreement, but those for Hgamma show
a spread of 50micron (out of 200micron). This scatter is no doubt
due to the slow change of density on the red side of Hgamma
seen in the tracing. The seeing disc of the star has a
negligible effect upon the true widths of these lines for
all reasonable assumptions about the size of the seeing
disc and the true line profile. Accordingly we have 
calculated an expansion velocity by simple averaging of the

                     [FIGURE 1]

measured widths. The mean velocity corresponding to the
line half widths is 3700 km/sec with a formal standard 
deviation of 130 km/sec.



                     FRANCIS STIENON
                     THOMAS WDOWIAK

                Warner and Swasey Observatory
               Case Western Reserve University,
                    Cleveland, Ohio