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N.G.C. 246. a = 0" 42m0; 8 = —12° 25' Campbell and Paddock, using a 1-prism spectroscope and a slit fully 1 mm. wide, were just able to see a bright N, line in the spectrum of this faint planetary nebula. It is too faint to photograph for radial velocity: the 3-prism 6-inch combination would probably require fifty hours or more to record N, in measurable strength.
N.G.C2 1644. a = P 6^2; 8 = —73° 44'; A = 311° 0'; /3 = —65° 51' This is the only bright-line nebula known to exist in the Lesser Magellanic Cloud.
N.G.C. 604 (598). a = V 28I',9; 8 = +30° 16' This is classified as a separate object in the New General Catalogue, but it is in reality a prominent detail in the well known spiral nebula N.G.C. 598, Messier 33. N.G.C. 604 is 10' n. f. the nucleus of N.G.C. 598. We include it here because the spectrum of the detail contains the nebular bright lines. These were apparently first observed by Vogel." Pease and Adams in 1915 made spectrographic observations of N.G.C. 604 with the 60-inch reflector, exposure 34L£ hours. The bright lines recorded, N„ H/3, and Hy, yielded a radial velocity of —278 km. per sec.10 Slipher obtained —263 km. from the bright lines in N.G.C. 598, probably referring to the detail of structure catalogued as N.G.C. 604."
N.G.C. 650-651. a = l" 36m0; 8 = +51° 4'; A = 43° 28'; /3= +37° 44' The New General Catalogue describes this object as two separate nebulae, of the same right ascension, but differing V in declination, with No. 651 north of No. 650; and so they do appear to visual observers. We accordingly secured three spectrograms of each object before Dr. Curtis's Crossley photograph showed that they are but the two brighter lobes of one large planetary nebula. After receiving the 6-inch Brashear camera lens we obtained an additional spectrogram of each lobe, to increase the accuracy of the results. The first four observations quoted below are of No. 650 and the second four are of No. 651. N, and N- have their usual relative intensities. H/3 is not visible on any of the plates.
"Schemer's Spectralanalyse der Gestirne, p. 254, 1890.
io Publ. A. S. P., 28, 34, 1916.
u Proc. Amer. Phil. Soc., 56, 406, 1917.
The lines N„ N2 , H/3 have about their usual relative intensities, 10 :3 :1.
N.G.C. 1068. a = 2" 37^6; & = —0" 27' This is not a planetary nebula. It is a spiral nebula, included here because it contains green bright bands corresponding to the green bright lines characteristic of planetaries, in addition to the usual absorption spectrum of spirals, as Fath discovered'2 in 1908 with the slitless spectrograph of the Crossley reflector. Dr. Slipher, in 1914, from both the bright bands and the dark lines, obtained a radial velocity of +1100 km. per sec. for this object.13 Following Slipher's announcement, we observed the bright bands as below.
Gr. M. T.
1914 Nov. 12.8 Dec. 31.8
1915 Oct. 5.4
N, v. ft. and diffuse
There is no advantage in using dispersion higher than the 1-pr. 5-in. combination supplies, as the bright bands are fully 30 Angstroms wide, with intensities decreasing gradually each way from their centers.
In 1915, with a spectrograph attached to the 60-inch reflector, Pease, Adams, and Miss Harwell observed the N, and N2 bright bands in this nebula and obtained a radial velocity of +765 km.14
Gr. M. T.
1913 Aug. 30.99
lit. pr. 16 in. Haynes
Miss Hobe 1-lt. pr. 16-in. Haynes
Miss Hobe 1-pr. 16-in. Haynes
1914 Feb. 8.71
1-pr. 16 in.
Sept. 4.93 5.0 3-pr. 16-in.
i* Lick Obs. Bull, 5, 73, 1908.
"Pop. Antron., 23, 23, 1915; Proc. Amer. Phil. Hoc., 56, 40b, 191/.
"Publ. A. S. P., 27, 133, 1915.
H/3 not visible
N, v. ft.
The last two spectrograms were taken with the slit of the spectrograph placed along the major axis of the nebular image, which is a faint minute oval disk (about 8" X 6"). On both plates the Int! line is somewhat under-exposed, but it shows definite evidence of inclination. Our measures of the angle of inclination of the N, line are briefly summarized in the following table:
These results are evidence that a point on the major axis of the nebula 3 or 4 seconds of arc south of the center is receding with reference to the corresponding point north of the center about 5.4 km. per sec.
N.G.C. 1501. a = 3h 58m4; 8 = +60° 39'; A = 71° 21'; / 3 = +39° 9'
N.G.C. 1514. a = 4h 2m9; 8 = +30° 30' Professor Pickering reported in 1879, and again in Annals H.C.O., 33, 144, 1900, that this is a bright-line nebula. Moore, Paddock, and Selga, using the 36-inch refractor in 1914, saw one bright line (probably NJ in the spectrum, but it is too faint to photograph for radial velocity.
The last two spectrograms were taken with the slit placed on the longer axis of the bright oval ring (about 20" X 17"). On the plate of November 12, 1916, the N, line appears slightly S-shaped, but is not sufficiently exposed to permit measurement of relative velocities at different points of the line. The appearance of the N, line on the spectrogram of November 22, 1917, is shown in plate XXVII, figure 5, which is a reproduction of a drawing of this line. In order to show more clearly the broken form of the line, the horizontal scale is four times that of the vertical scale. The width of the line has not been correspondingly increased, which amounts in effect to assuming that the line is monochromatic. That this assumption is approximately true will be seen by comparing its width with that of the reference line of helium, of about the same intensity as the nebular line, at the upper right edge of the cut. In the following table are collected the radial velocities from the measures made by Messrs. Campbell and Moore at the points a, b, o, c, d, along the N, line, as indicated on the right of the drawing.
* Campbell measured the inclination of the line be and the radial velocity at o, from which the velocities at b and c were computed.
The results indicate that a point on the major axis 4.4 seconds of arc southwest of the center is receding with respect to the corresponding point northeast of the nucleus with a velocity of 4.4 km./sec. The brighter portion of the line corresponding to the northeast section of the ring is bent back, indicating a slower rotational speed than for the central section be. At the point a, however (the brightest part of the whole line), corresponding to the southwest part of the ring, the line is broadened toward the red, and this conceals to some extent the simple phenomenon observed in the northeast portion of the ring.
Our high-dispersion spectrograms do not record the lines of the faint outer disk (42" X 37") shown on the Crossley photographs of this nebula.
N.G.C2 2105. a = 4h 49-^9; 8 = —69° 21'; A = 328° 58'; /3 = —82° 53' This is a round planetary nebula, diameter 5", magnitude 10.5, situated in the Greater Magellanic Cloud. A 10th magnitude star is about 20" W and 8" S of the nebula.
N.G.C. 1714. a = 4" 52'!,0; 8 = —67° 6'; A = 347° 30'; p = —83° 18' This nebula is planetary in form, with no prominent nucleus, but it appears uniformly brighter toward the center. It is about 8" in diameter and 10th magnitude. Faint nebulosity extends at least 20" north preceding. It is in the Greater Magellanic Cloud.