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A Special Case of an Error, in the Observed Time of a Star's Transit

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A Special Case of an Error, in the Observed Time of a Star's Transit 3 200 On a small Nebula close to M. 57. By E. E. Barnard. In examining the annular Nebula of Lyra (M. 57) P with the 36 inch on October inld,I noticed a rather con- spicuous nebula in the field with it, and north preceding. As I have seen no record of this object, I have measured its position referred to the centre of the Ring Nebula, or rather with reference to the small star in the middle of the ring. 0 October and the da and dd were measured and October 8 the position angle and distance. ... Neb. - M. 57 ‘893 da Ad . oct 2 -20615 +131:1 -202.9 8 ____+ 133.3 -204.7 f132.2 The Aa and Ad for October 8, being derived from the following position angle and distance : P. A. = 303?3 Dist. = 2421’8 This nebula is about 1j2‘ diameter. Not round. A little brighter in the middle. About 14‘~magnitude. Inclosed is a sketch of its position (diam. of field a’&). I have not shown all the stars that are easily seen in this field. f Mt. Hamilton 1893 Oct. 8. E. E. Barnard. A Special Case of an Error, in the observed Time of a Star’s Transit, which is a Function of the Star’g Magnitude. By J. M. Schatberle. I In January 1891 I received a letter from Professor screens superposed reduced the brightness by about four Auwers of Berlin in which he informed me that from and six magnitudes respectively. a discussion of a series of observations sent to him it The program adopted was as follows. appeared that I observed bright stars in transit earlier than Each star (B. J.) was observed over six wires sym- faint ones, and that the difference in time amounted to metrically situated with reference to the middle wire. If about or02 for every whole magnitude. the transits over the first three wires were observed with Several series of observations made for the special the screen, then the remaining three transits were observed purpose of investigating this particular subject plainly without the screen, and vice versa. demonstrated the general correctness of Dr. Auwers’ con- As only naked eye stars of known magnitude were clusions. to be used and as stars down to the tenth magnitude can In this special investigation it was necessary to eli- be readily observed only two compound screens were minate as far as practicable errors due to a change of required to obtain the desired range in magnitude. One conditions during the observations on different stars ; the compound screen was made of two sheets and the other work, therefore, was so planed that each star observed of three sheets superposed so that the brightness could be during its transit furnished all the data for obtaining an reduced about four and six magnitudes respectively. independent value of the desired quantity. During the star’s transit an Assistant, Professor Treat To reduce the brightness of a star of known magni- (at the time a special student here) with the screens in tude, wire screens were made use of. A single thickness readiness, would at a given signal cover or uncover the or sheet of the fine wire screen (manufactured by the objective, thus leaving the observer undisturbed at the Repsold’s) when placed directly in front of the meridian telescope. circle objective was found to reduce the brightness of the If the star was brighter than the third magnitude the stars about two magnitudes. Two and three of these compound screen containing three sheets was to be used; '31 3 200 132 if fainter than the third magnitude the screen containing three times of transit reduced to the middle wire when no two sheets was to be employed. The times of transit were screens were used, while is is the value for the transits recorded on the chronograph. observed with the screen. tn0 and m, are respectively In general I had no knowledge and made no estimate the true and the screen magnitudes of the star observed. of the actual magnitude of the star, only the reduced magni- For comparison the secant of the star's declination tude was observed and recorded. is given in the last column; so far as these observations In the table given below to denotes the mean of the show, no decided variation with the declination is apparent. Results from Meridian Circle Observations made June 25, 1891. Jumbe Magnitude (Is - fu) Star of -- sec a creem (nr, - #lo) -- - p Virginis 2 4.8 +of15 +oTo31 1 .oo 109 Virginis 2 5 .O 0.00 0.000 I .oo a Librae 3 6.9 +o. 15 +0.022 1.04 2 H. Urs. min. 2 2.5 +0.02 +0.008 2 *49 p Bootis 2 4.6 +0.07 +o.o15 1.13 c Librae 2 4.5 +0.16 +0.036 1.06 3 Serpentis 2 3.3 +o.rg 4-0.045 I .oo B Librae 3 1.1 +0.20 +0.028 1.01 vl Bootis 2 4.4 c0.09 +0.020 1.33 a Cor. Bor. 3 6.3 +O.II +0.027 I.1'2 9 Bootis 2 4.0 +0.03 +O.OO~ 1.32 y Cor. Bor. 3 5.1 +0.16 +0.028 1.12 I 2 H. Draconis 2 3.5 0.00 0.000 2.20 y Serpentis 3 6.0 +0.31 +o 05 1 1.04 Gr. 2296 2 3.1 +0.07 +o.o I9 1.14 4 Draconis 2 5 .O +0.12 +0.024 1.93 9 Herculis 2 4.6 -0.02 -0.004 1.42 8 Ophiuchi 3 6.2 +0.17 +0.027 1.00 E Ophiuchi 3 6.2 +0.2 I +0.034 I .oo z Herculis 2 5.4 +0.13 +0.024 1.45 o) Herculis 2 3.8 +0.16 +0.042 I .03 a Scorpii 3 6.4 +0.09 +o.o14 1.1 I 8 Herculis 3 6.8 +0.13 +o.o19 I .08 6 Ophiuchi 3 6.4 to.03 +0.005 1.02 tj Herculis 3 6.4 +0.34 +om53 1.29 d Herculis 3 6.0 + 0.04 +0.001 1'10 4 Ophiuchi 3 6.0 +o.16 +0.027 1.10 ,!? ,!? Draconis 3 6.5 +0.29 +0.045 I .64 a Ophiuchi 3 6.5 +0.08 +0.012 1.02 6 Serpentis 2 3.9 +0.06 +0.015 1.04 c Herculis 3 6. I +0.07 +O.OI I I .44 fl Ophiuchi 3 6. I +0.08 +0.013 I .oo p Herculis 3 6.3 +0.26 +0.041 1.13 6 Draconis 3 6.4 +0.08 +0.012 1.83 y Draconis 3 6.6 +0.25 +0.038 1.61 y Sagittarii 2 5.2 +o. I0 +0.019 1.16 p Sagittarii 2 4.1 0.00 0.000 1.07 Gr. 2533 2 3.8 40.14 4- 0.03 7 1-35 7 Serpentis 3 6.3 +0.26 +0.041 I .oo 109 Herculis 3 5.8 +0-35 +0.060 I .08 b Draconis 2 3.6 +o.os +o.o 14 1.93 a Lyrae 3 5.9 +o. 14 +0.024 1.28 I 10 Herculis 2 3.9 +O.OI +0.003 1.07 '33 3 200 I 34 Besides the actual errors in the times of transit, the The abstract numbers m* and m representing the variations of the individual values given in the next to the magnitudes of the stars whose right ascensions are a' last column are also due to erroneous estimations of the and a, the observed times of transit being t' and t screen magnitudes and to variations in the character of respectively. the field illumination of the telescope for different stars. The above expression refers to a constant illumi- If we give the same weight to all the above results nation of the field of view for stars of different magnitudes, the expression for the difference between the right as- since for a given star observed both with and without the censions of two stars observed by me becomes screen during its transit over the two sets of wires no a' - a = (t' - t) - or022 (m'- m) change of illumination was made. Lick Observatory, 1893 Sept. 18. _______ J. M .!hueberIe. Hydrogen Envelope of ne Star BD. +30?3639. The 9.3 magnitude star BD. +3003639 is surrounded C7e-a with wide slit by an extensive hydrogen envelope. This star is of the Wolf-Rayet type, and its spectrum is very rich in bright lines, about thirty having been observed by me between Hg wave lengths 656 and 426. The most striking features of the visual spectrum are the continuous spectrum, the bright 1-a with narrow slit line at 2. the bright blue band at R and the 5694, 4652 The same appearance is' noticeable in the faint Hy very bright hydrogen H@ line. When the apparatus is in and very faint Ha lines. It is not noticeable in the other focus for the different parts of the spectrum referred to, lines of this spectrum, nor has it been seen in the spectra the line at 2 is a very small round image of the 5694 of any other stars of this type. It is due to an envelope star ; the band at 1 is broad and lies wholly upon 4652 of incandescent hydrogen. Whether the large disc is wholly the narrow continuous spectrum : but the HB line, observed due to an unusually extensive atmosphere, or in part to with a narrow slit, is a long line extending a very ap- proximity to the solar system, will be tested by further preciable distance on each side of the continuous spectrum ; observations to be made here.
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