COMET NOTES Elizabeth Roemer U. S. Naval Observatory Flagstaff

Elizabeth Roemer U. S. Naval Observatory Flagstaff Station

The fourth new comet of 1963 was discovered on September 14 by Z. Pereyra of Córdoba, Argentina, and reported to Copen- hagen and Harvard by G. M. lannini of the Córdoba Observatory. Located not far from a Hydrae at the time of discovery, Comet Pereyra was of second magnitude and had a tail many degrees in length. Alan McClure, observing the new comet on the morning of September 16 with binoculars from Mount Pinos, north of Los Angeles, reported a narrow tail about 10° long and a total brightness of sixth magnitude. Many early observations and approxi- mate positions came from Smithsonian Baker-Nunn Satellite Tracking Stations around the world, while accurate positions were obtained by H. L. Giclas (Lowell), Stokes (Mount Stromlo), K. Tomita (Tokyo), M, Antal (Skalnaté Pleso), and J. A. Bruwer (Johannesburg). Similar orbits for Comet Pereyra were calculated by M. P. Candy, L. E. Cunningham, and by G. M. lannini, all of whom found a very small perihelion distance (0.005 a.u.) and angular elements much like those of the family of sun-grazing comets that includes the comets 1668, 1843 1, 18801, 1882 II, 1887 1, and 1945 VII. Perihelion passage occurred on August 23, and thus Comet Peryera was three weeks past perihelion and on the far side of the sun from the earth at the time of discovery. As Cun- ningham pointed out, Comet Pereyra might have been a very spectacular object under better observing conditions. Because of the rapid increase in heliocentric distance (2 a.u. by mid-November), Comet Pereyra faded very quickly after discovery. Although the comet was readily visible with modest optical aid on the morning of September 23 at Flagstaff, the brightness of the nuclear condensation was only magnitude 13.2 as esti- mated from plates exposed with the 40-inch reflector. The nucleus was only moderately well condensed on all plates exposed during September and October at Flagstaff and as seen with the 40-inch reflector. On November 9 a secondary condensation only a few

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seconds of arc from the primary nucleus was suspected. The primary nucleus was then of magnitude 17.2, with a faint, indistinct tail reaching to about 12' north of west on 30-minute exposures with the 40-inch telescope. When the long-sought P/d?Arrest was still unaccounted for at the end of the September dark run, B. G. Marsden quickly in- tegrated on a digital computer the motion of the comet from 1943 to 1963 and found a time of perihelion for 1963 about seven days later than had been suggested previously by other investigators. The very first plate taken on the new ephemeris showed the comet on October 9. The recovery was confirmed on October 12 and announced the following day. Two other periodic comets were recovered during September in more routine fashion, but both were very faint and stellar in appearance, and announcement was withheld until additional observations in October removed all possible doubt of identification. P/Arend-Rigaux, 1963 g, was first photographed on September 12 at Flagstaff, and additional observations were obtained on September 21, 23, 25, and October 18. Subsequent to the recovery, images that may be of P/Arend-Rigaux were recognized on a pair of plates taken on August 24. The brightness, corrected ap- proximately for extinction, was about 19.4 during September and October, all images being stellar in appearance. P/Encke, 1963 h, was photographed on September 24 and 25, and again on Octo- ber 12 to confirm identification of the star-like images of magnitude 20.2. Recovery with the 40-inch reñector some months before perihelion passage next June 3 compares favorably with the recovery by Cunningham with the 100-inch reflector some ten months before perihelion under very similar circumstances in 1953. Comet Kearns-Kwee, discovered with the 48-inch Schmidt at Palomar on August 17, was followed regularly during September, October, and November. The sharp, essentially stellar nuclear con^ densation remained within a few tenths of a magnitude of 16.5, but the faint, narrow tail west became somewhat more prominent. Because of an increasing deviation from the preliminary parabolic orbit, Marsden calculated an improved orbit on the basis of accurate positions between August 24 and October 11. The new orbit

was definitely elliptical, with an eccentricity of 0.47, period of 8.5 years, perihelion passage on December 9 at a heliocentric distance of 2.2 a.u., and an inclination of 9°. Marsden writes that P/Kearns-Kwee approached Jupiter within 0.05 a.u. in October 1961, and that prior to that time the comet moved in a larger and more nearly circular orbit. Only three comets, P/Brooks 2, P/Lexell, and P/Helfenzrieder are known to have passed closer to Jupiter. P/Johnson, 1963 c, which was at perihelion early in June, faded steadily as it continued under observation during the autumn. The nuclear condensation was nearly stellar in appearance on all plates, but the brightness faded from magnitude 17.7 on September 11 to 18.8 on November 9. On all plates a faint, narrow tail extended a fraction of a minute of arc north of east. Comet Ikeya faded very rapidly during September and Octo- ber, and apparently was fainter than 19th magnitude by October 23, when no image of the comet could be identified on a single 120-minute exposure with the 40-inch reflector at Flagstaff. On October 12 a weak but apparently stellar image of magnitude 19.2 had been recorded on a plate exposed for 100 minutes. P/Whipple, 1962 /, retained the sharpness of its nuclear condensation as it rose higher in the morning sky during September and October, but the brightness changed little from the 18.3 reported for the magnitude on August 27. On all plates there was a suspicion of a very faint, short tail west. P/Ashbrook-Jackson, 1962 e, which passed perihelion on Octo- ber 2 at a distance of 2.3 a.u. from the sun, was an easy evening object during September and October and even was visible with the 5-inch finder telescope at Flagstaff on September 11. The strong, sharp nuclear condensation was of magnitude 15.2 as esti- mated from photographs on September 11 but had faded to magnitude 15.6 on October 9. On most plates the nucleus was seen at the apex of a fan-shaped coma, but a 30-minute exposure on September 11 showed also a broad, faint tail curving west to a distance of 3'S. Comet Schwassmann-Wachmann 1 was active when photographed on October 25 at Flagstaff, the sharp nuclear condensation of magnitude 18.9 being surrounded by a sharply bounded

symmetrical coma CK8 in diameter. A denser wedge was embedded within the north side of the coma. Attempts were made to photograph P/Oterma on September 23 and on October 18 and 23, pairs of 120-minute exposures being obtained each night, but the comet was not recognized. The ex^- pected brightness at opposition early in October was about 20.7. Attempts were made also to photograph P/Tempel-Swift ac- cording to the prediction by Marsden referred to in the last Comet Notes, but no comet was found along the line of variation to about ±4 days in Τ and to 19th magnitude. A new elliptical orbit which includes perturbations has been computed by Marsden for Comet Humason, 1961 e. An orbit osculating near the date of perihelion on December 2, 1962, has a period of 2940 years, but the period of the orbit osculating in 1964 is some 200 years longer. The comet should be reobserved in Corvus before the end of 1963 and may be as bright as 13th magnitude.