22h 24m3; α=

8= -21° 21'; λ

330° 0'; ẞ=—10° 35′

N.G.C. 7293.
This is a faint though very large nebula-the largest planetary known to exist.

Two observations by Keeler yielded a radial velocity of -11.4 ±4.8 km. N, is brighter in this nebula than Hẞ.

We have made no effort to determine absolute radial velocities from the spectrograms obtained when various auxiliary analyzing pieces, such as a -wave plate or a Fresnel rhomb, were in place over the slit, as we could not be sure that the collimator lens was fully or symmetrically illuminated under those conditions.

The non-monochromatic and complicated character of the bright lines in this nebula make it an unfavorable subject for accurate velocity determination.

On photographs with the Crossley reflector the image of this nebula appears as a somewhat irregular bright ring (17" X 14" outside diameters) with the longer axis in position angle about 45°, and this ring appears to be superimposed upon a faint oval (32′′ × 28"), only the brighter parts of which are effective in recording bright lines on our high dispersion spectrograms, corresponding to diameters of 24′′ to 26′′.

The forms and peculiar distribution of intensities of the lines when the slit is placed respectively along the minor axis, a diameter making an angle of 45° with this, and the major axis are shown in plate XL, figure 64, a, b, and c. These are drawings of the N, line as shown on spectrograms obtained with the 3-prism 32-inch spectrograph on the following dates: a, September 11, pa 318°; b, October 12, pa: 273°; and c, September 14, pa = 228°. The N1 lines on these spectrograms are reproduced (enlarged) in plate XXXIX, figure 65.

=

The nebular lines in the three positions of the slit are similar in appearance. All three show the peculiar curved shadings, especially in the portions originating in the bright inner ring, and the division of the central section into two components. Some variation in the relative intensity of the components is apparent as we pass from the major axis to the minor axis. For example, on the major axis (c) the red component is considerably stronger than the violet one southwest of the nucleus, while on the opposite side of the center the violet component is the stronger. Along the minor axis the red component is the stronger, except for a short distance near the inner edge of the northwest ring. In all three lines the stronger component appears to be the continuation of the same line from the ring.

A marked difference in the inclination of the central and outer sections of the lines is apparent. The line corresponding to the major axis (c), considered as a whole, has the form which we have described as that of the letter S. On the diagonal axis (b) the line is a more shallow S, while for the position coincident with the minor axis (a) no inclination of the line as a whole is observed.

In Table I, a, b, and c, are the measures made by Campbell and Moore at different points in the nebular lines of the best spectrograms obtained respectively on the major, minor, and diagonal axes. The results are given as the radial velocity at the particular point whose distance from the nucleus in seconds of arc is recorded in the first column. On the spectrograms of August 16 and September 14 the measures refer to the N, and N, lines, and on the others to the N, alone.

TABLE I

2

Fig. 64-Drawings of the N, line in N.G C. 7662 (Moore). (a) minor axis, 1916 Sept. 11; (b) diagonal axis, 1916 Oct. 12; (c) major axis, 1916 Sept. 14.