N.G.C., 4846. a=19h 11m0; 8=-9° 14'; λ=288° 0'; B = +13° 7' This "stellar" nebula has a very small angular diameter. On the 3-prism spectrograms the nebular lines are very short. There is no evidence of inclination of the lines on either plate secured with 3-pr. 16-in. dispersion. N.G.C. 6778. a= 19h 13m1; 8: -1° 48′; λ= = 289° 32′ ; B The three lines recorded on all the plates have relative intensities N, N, Hẞ:: 10:32. : : N.G.C. 6781. a=19h 13m6; 8 = +6° 21'; λ=290° 55'; B = +28° 28' An exposure of 122 in July, 1915, recorded a trace of N,, but too under-exposed for satisfactory measurement. N.G.C. 6790. a=19h 17m9; 8+1° 19' ; λ=291° 17'; B = +23° 20' The diameter of this "stellar" nebula is very small. Three observations by Keeler gave a radial velocity of +48.4 km. The short stubby lines on the last two plates afford no certain evidence of inclination. The nebula is small and round, with a diameter of about 5.5 seconds of arc. On the two spectrograms, with the slit along diameters respectively west-east and north-south, no inclination of the nebular lines is shown. 3 The N line is recorded in good intensity. All of the spectrograms are on Seed Graflex plates, and a reliable estimate of relative intensities for Seed 30 plates cannot be given, but it would approximate N,N, Hẞ: N, :: 10:31:2. : 3 N.G.C. 6807. a= 19h 29m6; 8=+5° 29′; λ=295° 12′; ß=+27° 0′ This nebula is "stellar" and indistinguishable from a star on Crossley plates. The N, and N2 lines on the spectrogram of July 28 are longer than they should be from such a small object, due probably to drifting of the image on the slit. They do not show any inclination. On the last plate the N, line is S-shaped. The bright central section of this line, having a length of 0.10 mm., has an inclination of 3:52. The inclination is in the sense that a point 1" north of the center is receding with respect to the corresponding point south of the center with a velocity of 8.6 km. per second. With such a minute object it is impossible to say how much of the observed form of line may be due to irregularities of guiding, but for the present we regard the above result as evidence of rotation. B.D. +30° 3639. This is a well known object, 1893 Mr. Campbell observed and recently Mr. Wright, by 19h 30m8; 8 +30° 18′; λ: = 302° 10′; ß=+51° 15′ described in the Draper classification as a Wolf-Rayet star. In that the star possesses a hydrogen envelope about 5" in diameter, means of long exposures with an efficient spectrograph, has been able to show that the object gives exceedingly faint nebular bright lines N1, N2, etc. Wt. Slit -25.4* 1 90° -32.3 1 90° -33.0 1 90° -31 1 90° Hẞ strong, no trace of N, N2 ᎻᏰ Miss Hobe Hẞ -31.1 -30.4 1 90° 1 293° 57′; ß=+7° 2′ 2 3 The lines recorded have about the relative intensities N, : N, Hẞ: N, :: 10:31:2. Two observations by Keeler gave radial velocity -16.7 ±4.5 km. The image of this nebula is an oval (outside diameters 22" X 15"), with major axis in pa=10°. The regions along and at the ends of the longer axis of figure are much fainter than the eastern and western edges. The appearance of the nebular lines when the slit is placed respectively along the minor and major axes is shown in the accompanying illustrations, plate XXXVI, figure 57, a and b, which are drawings of the N, line on the spectrograms of September 7, 1916, and July 13, 1917. It will be noticed that the central section of the line corresponding to the part of the nebula within about 5 seconds of are of the nucleus is distinctly divided into two components, of which the one on the red side has slightly greater intensity. The separation of the two components, for the slit in both positions, is about 0.7 A; or, interpreting the displacement as due to the Doppler-Fizeau effect, the two components indicate a relative velocity of 42.4 km./sec. Apparently this phenomenon and the general form of the lines are of the same nature as those found for N.G.C. 2392. In Tables I and II are given Mr. Moore's measures of the relative velocities at different points on the nebular lines, indicated by the lettered points on the drawing, together with the distances of these points, in seconds of are, from the assumed center of the nebula. Table I contains the results for the two spectrograms, July 23, 1916, and July 13, 1917, secured with the slit coincident with the major axis. Table II gives the corresponding values for the lettered points (with primes) for the three spectrograms May 25, September 3, and September 7, 1916, obtained on the shorter axis of the nebula. The measures refer to the N, alone, except for the plates of July 23 34 Publ. A. S. P., 5, 204, 1893; Astron. and Astro-Physics, 12, 913, 1893. 35 Astroph. Jour., 40, 470, 1914. and September 7, for which N2 was also measured. The value given at the point o in each table is for the dark line, separating the two bright components. As in the case of N.G.C. 2392, the measures indicate relative motions between corresponding portions of the nebula on opposite sides of the nucleus, for both the major and minor axes, in the sense that the parts of the nebula 5 to 10 seconds of arc respectively south and east of the center are receding relatively to the corresponding portions north and west of the center. If rotational effects are present in this nebula, they appear to be concealed or combined with other phenomena, the nature of which is not clear. Pease and Adams, from five lines, obtained-8 km.36 in 1915. On the spectrogram of June 1, 1916, taken with the slit coincident with the major axis of the nebular image, the N1, N2, and Hẞ lines show a very small inclination, in the sense that the southeastern edge of the nebula is approaching us while the northwestern edge is receding. The extreme tips of the N, line turn back slightly, indicating a smaller rotational velocity for the 36 Publ. A. S. P., 27, 240, 1915. outer layers of the nebula. Measures of the maximum relative velocities for the N, and N2 lines, between points on the major axis in the southeast edge and the northwest edge of the nebula, were made by Campbell and Moore, as follows: Our results indicate a comparatively small rotational speed for this object. No inclination of the lines is shown on the spectrogram of September 17, 1916, secured with the slit placed along the minor axis. The sharpness and regularity of the nebular lines on both plates indicate that this object is in a comparatively quiescent state throughout. Plate XXXVII, figure 58, is a direct enlargement of the N, line on the spectrogram of June 1, 1916. There is a suspicion of inclination of the very short central section of the lines on the plate of 1916 August 5, but this is not confirmed by the spectrogram of 1917 July 7, for which the image was reversed 180° on the slit. No inclination is shown by the lines on the last plate. The lines are in fact too short for promising results as to rotation effects. 19h 55m3; 8 +22° 27′; λ =307° 1′; B: +42° 16' N.G.C. 6853. This is the "Dumb-bell" nebula. The slit was directed upon the brightest region37 in the SW quadrant. The intensities of the lines on the last two spectrograms are about as N1 : N2 : Hẞ N: 10:31:1. 1 2 |