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IAUC 2981: V1500 Cyg; 1975 YA

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                                                  Circular No. 2981
Central Bureau for Astronomical Telegrams
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.

     P. J. Young, Department of Astronomy, University of Texas at
Austin, writes: "This nova was examined visually with the 208-cm
Struve reflector at McDonald Observatory on July 6 (coude periscope
500 x) and July 8 (Cassegrain focus 1200 x) with excellent seeing
conditions on both occasions.  No associated nebulosity as large as
0".1 was observed with either scotopic or photopic vision when the
Airy disks, of size ~ 0".05, of the two twelfth-magnitude stars < 1'
north of the nova could be seen.  Spectroscopic scans by D. L.
Lambert at the coude focus of the 270-cm reflector indicate that 10
percent of the luminosity in the scotopic visual band is due to the
[O III] emission at 4959 A and 5007 A; this also accounts for 30 percent
of the luminosity seen in the photopic band with minor contributions
from H-alpha blended with [N II].  The scotopic visual magnitude
was 11.20, and photoelectric measurement yielded mean values V
12.00, B-V = +0.51, U-B = -0.25 (on July 8.353 UT; with cooled 8575
photomultiplier tube).  The absence of an observed nebulosity is in
conflict with the prediction that the gas shell should be ~ 0".4 in
diameter, assuming an expansion velocity of 1300 km/s, a distance
of 1.4 kpc and a roughly spherically-symmetric ejection."

     J. C. Kemp, R. J. Rudy and M. V. Sykes, Department of Physics,
University of Oregon, report: "Based on 12 cycles observed from 1
July to 25 July 1976 the current light curve has a peak-to-peak
amplitude of 0m.20 in unfiltered light (3500-5500 A).  The period of
variations is currently 0d.1384 with an epoch of the even minimum on
1976 July 16.333 UT.  The true orbital period might be twice the
period of light variations.  The even minima are rounded and
symmetrical, while the odd minima tend to show a slow drop and a rapid
rise.  The difference, if real, is obscured by random variability
and by progressive changes.  A careful search for the even/odd effect
is urged.  Power spectra of the rapid flickering (IAUC 2973)
show peaks at 122s and 196s, but it has not been established that
either of these is a real or persistent period."

1975 YA
     The following position has been obtained by R. E. McCrosky,
Harvard College Observatory, with the 155-cm reflector at the
Agassiz Station.  Measurer: C.-Y. Shao.

     1976 UT             R. A. (1950) Decl.
     May  29.26546    20 43 44.08   +13 55 20.5

1976 August 4                  (2981)              Zdenek Sekanina

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