COMMISSION 27 OF THE I. A. U.
          INFORMATION BULLETIN ON VARIABLE STARS
                      Number 1981

                                    Konkoly Observatory
                                    Budapest
                                    1981 June 22

                                    HU ISSN 0374-0676



    PHOTOMETRY AND DISTANCE OF NOVA CORONA AUSTRINA 1981


   Photometry of Nova CrA (I.A.U. Circular 3590) (alpha = 18h40.6m, 
delta = -37d33' [1981], l = 358d, b = -14. 4d) was carried out on the
S.A.A.O. 0.5m and 1.0m telescopes during a three-week period shortly 
after discovery. UBV and V(RI)_KC were obtained on two photometers 
equipped with an EMI6256 and an EMI9659 photomultiplier
tube, respectively. The results appear in Table I.


                   Table I


   2444000     V         B-V     U-B     V-R    V-I
    703.63    8.87      -0.33   -0.91    1.05   1.07
    704.56    8.98      -0.38   -0.92    1.02   0.97
    706.68    9.25      -0.38   -0.96    1.03   0.82
    712.58    9.88      -0.50   -0.98    0.87   0.46
    713.62    9.93      -0.52   -0.94    --     --
    715.64   10.06      -0.59   -0.95    0.78   0.39
    720.55   10.60      -0.70   -1.05    --     --


Formal errors are <~.01 except for the 5th and 7th U-B points
where they are ~.015. However, the transformation to the standard
system is no doubt very rough because of the probable extreme
differences between the nova spectrum and those of normal 
calibrating stars. This is demonstrated by the consistent shift of
V(blue tube) - V(red tube) - 0.176, dispersion 0.012. The tabulated
V magnitude corresponds to an average of the two tubes,
or to V(blue tube) minus one-half the average shift on two nights
when only blue tube data were available. Mr. J. D. Laing contributed 
the last epoch observation with the 1.0m; the rest are 0.5m
by the author.
  A straight-line fit of magnitude versus time is fair except for
V-I. We obtain,


	V = 8.539 + (JD - 2444700.) x0.1009
	B = 8.284 + (JD - 2444700.) x0.0801


  Kozai and Kosai (I.A.U. Circular 3950) reported the time of
discovery as JD2444697.25. Gilmore (I.A.U. Circular 3951) provided
evidence that eruption had not yet occurred as of 2.20 days
earlier. With these limits on the time of maximum, together with
the van den Bergh (1965) nova parallax


	M_pg (max) = -11.9 + (3.2 +- 0.3)log t_2



the Bahcall-Soneira (1980) space reddening model (based on Sandage's
(1972) modified cosec b law and an obscuring layer in the Galactic
plane of z scale height 100 pc) 


	A_B(r) = 0.83(1 - exp(-2.5r)),


and a distance scale of R_0 = 9 kpc, we obtain the distance to the
nova and its Galactocentric (R,z) position given in Table II.



                  Table II
t discovery
-t maximum^(d) r(kpc)    R(kpc)     z(kpc)
  0.0           8.5       2.2        2.1
  1.1           8.2       2.3        2.0
  2.2           7.9       2.4        2.0


The parallax-based uncertainty on the distance is typically
+-1.6 kpc, that on z, +-0.4kpc. The nova apparently is located in
the proximity of the central Galactic bulge.
  One caution on this analysis is in order, however. The announcing 
circular provisionally gave two V magnitudes of 7.0
(2444697.25) and 7.4 (2444701.27), which fit the slope but are
1.25 magnitudes brighter than the S.A.A.O. extrapolated line. If
these two data points were confirmed, then the above analysis
would yield r = 4.8-4.4 kpc, R = 4.5-4.8 kpc, and z = 1.2-1.1 kpc
in place of Table II.



				JOHN A. R. CALDWELL
				South African Astronomical
				Observatory
				7935 Cape Town, R.S.A.





References:
Bahcall, J. N., and Soneira, R. M., 1980, Ap. J. Suppl. 44, 73. [BIBCODE 1980ApJS...44...73B ]
van den Bergh, S., 1965, in Landolt-Bornstein ed. H.H. Voigt
  (Berlin-Springer Verlag) p. 644.
Gilmore, A.C., 1981, I.A.U. Circ. 3591. [BIBCODE 1981IAUC.3591....1G ]
Kozai, Y. and Kosai, H., Cragg, T., 1981, I.A.U. Circ. 3590. [BIBCODE 1981IAUC.3590....1K ]
Sandage, A., 1972, Ap. J. 178, 1. [BIBCODE 1972ApJ...178....1S ]