Relative motions of fragments of the split comets

ICARUS 3 8 , 3 0 0 - - 3 1 6

(1979)

Relative Motions of Fragments of the Split Comets III. A Test of Splitting and Comets with Suspected Multiple Nuclei ZDENEK

SEKANINA

Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts 02138

Received September 20, 1978; revised November 27, 1978 A test based on a model of split comets that assumes the motions of cometary fragments to be determined primarily by outgassing is devised to establish whether or not an allegedly multiple comet has in fact split. The test is first applied to 18 suspects for which quantitative descriptions of multiplicity and some supportive evidence have been published. It is found that only 6 of them are clear-cut cases of split comets (Sawerthal 1888 I, Campbell 1914 IV, Whipple-Fedtke-Tevzadze 1943 I, Honda 1955 V, Wild 1968 III, and Tago-Sato-Kosaka 1969 IX), although there is a good chance that another 2 (Davidson 1889 IV and Periodic Giacobini 1896 V) broke up as well. About half of these secondary nuclei turn out to be shortlived companions (with decelerations relative to the principal nuclei between 0.0004 and 0.0008 the solar attraction), but minor fragments (decelerations from 0.0010 to 0.0050), which are particularly difficult to detect, are suggested to break off from parent nuclei most frequently. For Comet Tago-Sato-Kosaka we find that the breakup coincided with a flare-up reported by several visual observers and with a sudden increase in the thermal flux from the comet. No split comet appears to exist among 15 reported cases for which unconfirmed quantitative descriptions of multiplicity are available. Numerous qualitative remarks on "granulated" nuclei by early visual observers are disregarded. I. THE THEORY

angle of the c o m p a n i o n relative to the principal mass determines the time t~; the distance of separation at a given position angle, yields the m a g n i t u d e of ~. Thus, in principle, a single differential m e a s u r e of the c o m p a n i o n provides b o t h parameters. Note, however, t h a t while the position angle is sufficient to derive t~, the s e p a r a t i o n distance by itself supplies no useful i n f o r m a tion whatsoever. W i t h the single exception of C o m e t W i r t a n e n 1957 VI, P a p e r I d e m o n s t r a t e d a good deal of correspondence b e t w e e n this m o d e l a n d the o b s e r v a t i o n s of the well-known split comets. I n a follow-up paper (Sekanina, 1978a ~ P a p e r I I ) the model has been generalized t o include the velocity of s e p a r a t i o n in the differentialcorrection procedure. This option has n o t

A recent m o d e l of split c o m e t s (Sekanina, 1977; hereafter called P a p e r I) has been developed on the premise t h a t f r a g m e n t s of a c o m e t g r a d u a l l y s e p a r a t e at a rate t h a t is d e t e r m i n e d b y the m o m e n t u m f r o m outgassing. T h e net differential force is t h u s of t h e same n a t u r e as the n o n g r a v i t a tional effects in c o m e t a r y motions, q u a n t i t a t i v e l y i n t e r p r e t e d b y W h i p p l e (1950) a n d extensively studied b y M a r s d e n (1972). T h e relative m o t i o n of two such f r a g m e n t s is expressed in t e r m s of only t w o p a r a m eters: the t i m e of splitting t~ a n d the differential force ~. R e f e r r i n g the m o t i o n of the less massive c o m p o n e n t to t h a t of the more massive one, the model predicts the force to be a deceleration. T h e position 300

0019-1035/79/050300-17502.00/0 Copyright O 1979 by Academic Press, Inc. All rights of reproduction in any form reserved.

MOTIONS O F THE SPLIT COMETS, III only settled the problem with Comet Wirtanen, but has also removed slight systematic trends in the residuals of other extensively observed split comets. The results of Papers I and II show that ts a~d ~ are the main dynamical characteristics of the split comets and that, with rare exceptions, the impulse at breakup is essentially negligible. Even for Comet Wirtanen the basic model (Solution SD in Paper II) offers a fair approximation to the best t, and ~ from the improved theory. The original, two-parameter version of the model is used in this study to formulate a quantitative test of splitting for comets with suspected multiple nuclei. II. A TEST OF SPLITTING The term "split comet" is used as a synonym to a term "double/multiple comet" (or a "double~multiple nucleus"), although the existence of quasistable, gravitationally locked multiple nuclei is at least remotely possible (Sekanina, 1978b). Each secondary nucleus of a split comet is assumed to be a single fragment of the parent nucleus and large enough to appear, at least from time to time, as an independent comet. Our experience suggests that the following conditions are pertinent to the configurations and other properties of the fragments : (i) The condition of a separation at rest implies that, following the conservation of momentum law, the less massive component (companion) should lie in the orbit plane and on the convex side of the orbit of the more massive (principal) nucleus, restricted to a sector that is confined by the prolonged radius vector RV and the reverse orbital-velocity vector - V . In terms of the position angle P relative to the principal nucleus this condition reads P ( - V ) < P(companion) < P(RV),

(1)

when the Earth is to the "north" of the comet's orbit plane, from where the comet

301

is seen to orbit the Sun counterclockwise; and P(RV) < P(eompanion) < P(--V)

(2)

when the Earth is to the "south" of the plane. This criterion is particularly restrictive for observations made before perihelion, although the range of allowed position angles always spans less than 180 ° . Only at times of the Earth's transit through the comet's orbit plane is this test either of very limited use or none whatsoever, depending on the configuration of the comet relative to the Earth and the Sun. (ii) Only objects with decelerations ~ 500 units (1 unit = 10-'~ the solar attraction) qualify as companions. There is a tendency for the companions to group into three categories by deceleration: (a) persistent companions, for which 1 ~< ~ ~< 10 units; (b) short-lived companions, for which 10 <<-~ < 100 units; and (c) rarely observed minor fragments, for which 100 < ~/~ 500 units. Decelerations 0 <= ~, < 1 unit have so far been found only for the Sun-grazing comets, where the effect of the deceleration could not be properly discriminated from that of the tranverse component of the separation velocity (Paper II). This same effect most probably also accounts for the single known case of < 0 (companion A to Comet 1882 II, cf. Paper I). Decelerations higher than ~500 units have invariably been shown to refer to other phenomena that might on occasions look like nuclei but physically differ from them distinctly (cf. P/Halley in Section I I I ; also Section IV). (iii) Consistent with criterion (ii) should be the companion's endurance, defined as the interval of time from splitting, t,, to the final observation, tf, corrected for the variable heliocentric distance (cf. Paper I). It follows that, when expressed in equivalent days (e.d.), i.e., days at 1 AU from the Sun, the endurance is equal to

E ~ A.f/p 11~,

(3)

302

ZDENEK SEKANINA

where As~ is the heliocentric arc of orbit (deg) swept by the comet between t, and t~ and p is the semilatus rectum of the orbit (AU). Persistent companions typically have E ~> 100 e.d., short-lived companions 10 < E < 100 e.d., and minor fragments E ~ 20 e.d. (iv) Another condition required for persisten~ companions is the existence of confirming observations that give consistent t~ and ~. Because of the highly erratic brightness behavior of most short-lived companions and minor fragments, it appears fair to exempt these objects from the requirement of confirming observations, if the available observation is deemed trustworthy. III. COMETS WITH SUSPECTED MULTIPLE NUCLEI ON MORE THAN ONE OCCASION In early days of visual observations of comets, journals were literally flooded with reports of multiple or "granulated" nuclei. This peculiar structure, sometimes further described as a multitude of intermittently "flashing" or "sparkling" bright spots in the immediate proximity of each other, is probably a combined effect of scintillation in the Earth's atmosphere, physiological properties of the human eye, and also psychological factors. Since their thinking was influenced by the naive notion of a cometary nucleus as a swarm of loose, independent particles, many 19th- and early 20th-century observers must have believed that the granulation was a true cometary phenomenon that provided observational evidence for the "model." Characteristically, no details on the granulated nuclei were ever offered, and a list of such accounts is obviously worthless. Two or more distinctly separated condensations have been reported considerably less frequently. In the following we examine the cases with quantitative descriptions and some supportive evidence (such as observations made by an experienced observer; consistent reports by independent

observers; confirming plates in the case of photographic observations; etc.). Where possible, images of such comets have been carefully inspected by the author on photographs, on loan from the Yerkes Observatory, taken by the late G. Van Biesbroeck between 1922 and 1963. A critical assessment of observational evidence on each candidate is complemented by the test of splitting. The results for the newly recognized split comets are presented in Table I, where the columns list, respectively: the comet's designation, the relative deceleration ~ (in units of 10-6 the solar attraction); the time of splitting relative to the time of perihelion passage t, - T; the most probable date of splitting ts, the distances from the Sun r~ and the ecliptic zs at ts; the endurance E (in equivalent days) of the companion; the number of observations Nobs; the interval of observation; the observed range of separation; the mean residual from the least-squares solution to t8 and ~,; and remarks. Comet Donati 1858 V I was seen double by Winnecke (1859) on four nights in October 1858. The test of~ splitting is decisively negative: the position angle lies outside of the allowed range by 20 to 30 ° and the separation increases much too rapidly. No other reports are available. Periodic Comet Brorsen 1868 I was reported by Vogel (Bruhns, 1868) to display several condensations in the coma on May 8, 1868. His description and drawing of the comet on May 14 indicate several bright spots in the southern preceding section of the coma, at position angles relative to the central condensation that closely match the direction of the reverse orbital-velocity vector. This suggests (see Paper I) that if the comet did indeed split, it must have happened long before 1868. Unfortunately, observational evidence is too inconclusive for a more definite statement. We are unable to find confirming reports in 1868, although numerous qualitative accounts of

-5.9 -14.9 ~ +IO --187 -I-20

+ 30.8 - 740 + 125

+50

228 1.04 79

65

ts - T (days)

11.9 7.0 ~220 -41

7 (units)

Mar. Mar. July Apr. Aug.

11 2 29 24 25

1970 F e b . 9

1943 M a r . 9 1953 J u l y 1968 A u g . 3

1888 1888 ~ 1889 1890 1914

D a t e ts (ET)

1.20

1.43 8.2 2.92

0.71 0.76 ~1.05 2.36 0.82

r~ (AU)

M o s t probable

+0.20

t0.44 -- 3 . 5 + 1.33

--0.12 --0.28 ~ --0.02 +0.35 --0.59

zB (AU)

16

13 170 11

96 113 ~27 47 41

E (e.d.)

2

5 5 2

6 3 6 3 5

N~

M a r . 30--May 11 M a r . 30-Apr. 16 A u g . 3--Sept. 2 Sept. 26-28 Sept. 18-Oct. 6

1970 M a r . 14

1943 M a r . 31-Apr. 9 1955 Sept. 2 1 ~ c t . 19 1968 N o v . 23

1888 1888 1889 1896 1914

I n t e r v a l of observation

4

10--16 5--7 4

3-15 3--6 up to ~ -19-30

R a n g e of observed separations (arcsec)

--

:t:0.51 ±0.69 --

±0.86 +0.14 ----

Mean residual (arcsec)

3, 4

7 8 3, 4

1 2 3 3, 4, 5 3, 6

Remarks°

o Remarks : I . Solution I (see Section I I I ) . M e a n errors: =I=I.7 u n i t in v, ~-2.7 d a y s in is. 2. Solution I I (see Section I I I ) . M e a n errors: ± 0 . 5 unit in "r. 4-1.4 days in tB. 3. N o t a least-squares solution. 4. Separation parameter(s) based on a single published m e a s u r e of position angle a n d / o r separation distance. 5. Separation unknown. Deceleration in units is equal to 14 t i m e s the Sept. 26-28 separation distance in arcsec. M e a n error in ts e s t i m a t e d a t =I=6 days. 0. M e a n errors e s t i m a t e d a t ~ I 0 units in 7, 4-3 d a y s in ts. A least-squares solution based on the Sept. 18, O c t . 6 positions gives 7 = 4 4 . 4 4- 4 . 8 units, tB - T ffi + 2 0 . 9 -4- 1.2 days, m e a n residual =t:1:04. 7. M e a n errors: :t:16 units in ~., :t:0.8 d a y in t~. 8. M e a n errors: -~0.15 u n i t in ~, -~260 days in t,.

1889 I V D a v i d s o n 1896 V P / G i a c o b i n i 1914 I V Campbell 1943 I WhippleFedtke-Tevzadze 1955 V H o n d a 1968 I I I Wild 1969 I X Tago-SatoKosaka

1888 I Sawerthal

Comet

TABLE I R E L A T I V E M O T I O N S OF F R A G M E N T S O F T H E S P L I T C O M E T S

N

©

©

Z

©

304

ZDENEK SEKANINA

a multiple nucleus refer to the comet's 1857 apparition (Bruhns, 1857; Rfimker, 1857; Schmidt, 1857; Secchi, 1858; Winnecke, 1863). This comet is known to be one of the long-lost comets with very erratic dynamical behavior (Marsden and Sekanina, 1971). Periodic Comet Pons-Winnecke 1869 I was also observed to exhibit more than one condensation in the coma. MSller (1870) remarked on two condensations on April 28 and 29, 1869, on four to five condensations on April 30, and again on two condensations in early September. A double nucleus was also reported by Weiss (1870) on June 12, and less definite comments on a multiple structure of the central condensation in April were made by SchSnfeld (1869) and by Winnecke (1869). MSller's observations, the only semiquantitative data secured, fail to pass the test of splitting. Periodic Comet Tempel 2 1873 I I was reported by Schulhof (1874) to have a multiple nucleus for most of July 1873, and by Tempel (1873) on at least one day in July. None of Schulhof's semiquantitatire descriptions of the configuration of the condensations complies with the conditions for splitting. Tempel's account was only qualitative. Comet Brooks 1886 I I I does not seem to be a strong suspect either. We were able to find only two remarks on a secondary condensation. Between May 4 and 12, 1886, Pechfile (1886) commented on a nebulous streak issuing from a nucleus, following it along the parallel (i.e., at position angle 90°), and terminating in a second, somewhat blurred nucleus, from which emanated a fan-shaped tail. His measures referred to the preceding nucleus. On May 7 Luther (1889) reported an intermittently visible secondary condensation that preceded the nucleus. Since Luther's and Pechfile's May 7 measures referred the comet to the same star, the two positions could easily be compared. We find

that Pechfile and Luther bisected the same nucleus (to within 1.6 arcsec), in which case the secondary condensations reported by them were clearly two different features. On the same night two other observers failed to detect either condensation: Engelhardt (1886) mentioned a disk-shaped nucleus, while Knorre (1887) noted and measured a sharp tip from which the tail emanated, but could not see any nucleus. Since Knorre's measures systematically show right ascension about 5 arcsec greater than those by Pechfile and by Luther, it is likely that Knorre's sharp tip was identical with Pechtile's second nucleus, a feature that does not satisfy the conditions for splitting. Luther's secondary condensation might have been a minor fragment (Section II), although a knot in the tail appears to offer a more probable explanation. Comet Sawerthal 1888 1 was undoubtedly a split comet. The duplicity had been first suspected by Charlois (1888a,b) on March 20 and 22, 1888. Relative positions of the two components were later measured by Cruls (1888a, b), by Engelhardt (1888a), and also by Pechfile (1889). In a number of instances observers reported only incomplete positional data [-Anguiano (1889), Charlois (1888a-c), Engelhardt (1888a,b), Hill (1888a,b), who also communicated the confirmation of the double nucleus by Barnard3 or qualitative descriptions of the duplicity or suspected duplicity (Becker, 1889 ; Franz, 1890 ; Hill, 1889 ; Leavenworth and Gummere, 1889; Stone, 1888). The companion, preceding the principal nucleus, was consistently reported to be distinctly the fainter of the two masses. Charlois (1888c), Cruls (1888a,b), and Wutschichowski (1888) gave fragmentary accounts of a third condensation. Scores of other observers saw the nucleus elongated. These observations refer to dates between late March and the end of April, and to scattered dates in mid-May and the first half of June. Luther (1891) suspected two nuclei on June 24, but the reported separa-

305

MOTIONS OF THE SPLIT COMETS, I I I TABLE I I RELATIVE POSITIONSOF THE COMPANIONTO COMET SAWERTHAL (REDUCED TO EQUINOX 1950.0) Date 1888 UT

Separation Obs

Mar.

20.21 •

--

22.19 ~

-2".96 3.79 3 5

30.33 Apr.

3.34 5.54 6.15

--

16.12

5 6.3 --

16.12 18.16 20.09

--

11.07

15

19.05 a June

-

CI

O

CII

--1.2

--

--

--1.8 --0.54 --+{-0.7

--1.3 --0.02 --+3.8

--

--

2.02 b

.

5.04

--

--

--

7

--20.9

--12.8

24.98

~

.

-

--

--1.2

--

-

----0".01 +0.05 -1.2 +0.7

--

4

13.54

-

--+0.~63 +0.50 --0.9 +1.0

--

7.15 10.44

May

o

.

Observer

Position angle

.

Obs

o -- CI

0 -- cH

239?8 239.8 242.9 243.4 -247.4

--6?6 -7.0 --6.3 --7.3 ---4.5

+171 +{-0.3 -0.6 --2.3 -0.0

248.9

--3.4

+1.0

--

--

--

255.3

+0.3

+3.7

257.9 255.0 249.9 254.5 270.0

+1.8 --1.1 --7.1 --3.3 +{-4.3

+4.9 +2.0 --4.2 --0.6 +5.1

271.6

+3.3

+3.7

270

--2

--2

271.1

--1.6

--2.0

--6

--7

~-~270

Charlois Charlois Cruls Cruls Hill Pechiile Pechtile Anguiano Hill Pechfile Engelhardt Charlois Charlois Pechiile Engelhardt Engelhardt Charlois Luther

a Duplicity suspected. b Nucleus elongated. t i o n is u t t e r l y i n c o n s i s t e n t w i t h t h e r e s t of the measures. I n T a b l e I, S o l u t i o n I is b a s e d o n all six available positions, Solution II disregards t h e m e a s u r e s b y P e c h i i l e (1889), w h o s e separations were only approximate. Table II indicates that the preferred Solution II is m u c h m o r e c o n s i s t e n t w i t h t h e b u l k of position-angle measures. Comet Davidson 1889 I V w a s o b s e r v e d b y R i c c 6 (1890) t o h a v e a d o u b l e n u c l e u s on s e v e r a l n i g h t s b e t w e e n A u g u s t 3 a n d 11, 1889. U n t i l A u g u s t 8 t h e s e p a r a t i o n b e t w e e n t h e t w o c o m p o n e n t s b e c a m e , in his 2 5 - c m r e f r a c t o r , m o r e d i s t i n c t e v e r y day, the fainter but larger condensation following. T h e o n l y o t h e r m e n t i o n of d u p l i c i t y c o m e s f r o m R e n z (1891), who, u s i n g a 38-cm t e l e s c o p e , n o t i c e d a s e c o n d a r y n u c l e u s on A u g u s t 28 a n d a g a i n on S e p t e m b e r 2. O b s e r v i n g w i t h t h e L i c k O b s e r v a t o r y ' s 3 0 - c m e q u a t o r i a l , B a r n a r d (1890a,

1892) d i d n o t r e p o r t a n y s e c o n d a r y cond e n s a t i o n on A u g u s t 6 (nor d i d R i c c 5 on t h a t d a t e ) , 22, a n d 28. R i c c S ' s a c c o u n t s of t h e d o u b l e n u c l e u s are too definite to disregard. They contain a f a i r a m o u n t of i n f o r m a t i o n on t h e posit i o n a n g l e b u t n o t on t h e s e p a r a t i o n . R e n z e s t i m a t e d t h e s e p a r a t i o n o n l y c r u d e l y on S e p t e m b e r 2 a n d n o t e d t h a t t h e t w o cond e n s a t i o n s were l o c a t e d in t h e t a i l axis 5 d a y s earlier. T h e p o s i t i o n a n g l e of t h e tail, i n t e r p o l a t e d f r o m o b s e r v a t i o n s on A u g u s t 20 ( R e n z , 1891) a n d 30 (Le C a d e t , 1889), is r e a s o n a b l y c o n s i s t e n t w i t h R i c c S ' s m e a sures. T h e s p l i t t i n g s h o u l d h a v e o c c u r r e d s o m e 10 t o 13 d a y s a f t e r p e r i h e l i o n , a n d t h e d e c e l e r a t i o n is f o u n d t o be v e r y high, m o r e t h a n 200 u n i t s ( T a b l e I). A n e p h e m e r i s b a s e d on t h i s m o d e l s h o w s t h a t for R i c c S ' s observations the distance between the components should have expanded from ~3 a r c s e c on A u g u s t 3 t o ~ 1 7 a r c s e c on

306

ZDENEK SEKANINA

August 11, a conspicuous increase in separation. On the last date Ricc5 commented on the comet passing by a star, at which time the double nucleus and the star " . . . made a configuration of three equally bright masses arranged in a straight line, all embedded in the nebulosity." From the apparent direction of motion of the comet, the implied position angle of the companion is 129 or 309 °, the first value being in good agreement with those on preceding nights. We identified the star, measured its position on older H a r v a r d plates, and found t h a t at the time of the closest approach the star was at position angle 309 ° and 16 arcsec distant from the preceding nucleus. Since an observer is likely to comment on a straight-line configuration of three objects when t h e y are approximately equidistant, it is probably a good guess t h a t on August 11 the two components of the comet were -~16 arcsec apart, which would indeed be in excellent agreement with our working model. We feel t h a t Ricc5 and Renz did refer to the same companion, and t h a t gathered evidence, however fragmentary, tends to favor the existence of a split nucleus, consisting of two components very uneven in mass. Comet (;iacobini 1896 V, a single-apparition short-period comet, was observed by Perrotin (1896) on September 26-28, 1896, to have an extremely faint companion in the immediate vicinity of the main nucleus at position angle 225 ° . The detection, made with the 76-cm equatorial of the Nice Observatory, appears to have been confirmed independently by Hussey and Perrine (1897) on September 30 and October 1, although their remarks on the observations with the Lick Observatory's 91-cm refractor are cautious and are not accompanied by positional information. The calculations show t h a t the position angle of the companion should have changed rapidly with time. The Nice observations tie in fairly well with a report by Sy (1896) of the nucleus elongated at 160 °, as observed

with a smaller telescope on September 10. We feel t h a t a splitting of this comet long before perihelion (Table I) should be considered a distinct possibility. No quantitative data are available on the separation. The secondary nucleus was probably a short-lived companion. This statement appears to be supported by the calculated endurance (Table I), and it offers a reasonable range of separations, 1 to 7 arcsec, for the time of the Nice observations. This comet has never been recovered, although extensive searches were conducted in 1903 (Campbell, 1903; Wolf, 1903). Periodic Comet Halley 1910 I I was reported to have more than one condensation in the coma on a number of occasions near and after perihelion. Such accounts refer primarily to the second half of April 1910 (Innes, 1910a,b; Bobrovnikoff, 1931) and to late M a y and early June (Comas Sol~, • 1910 ; Innes, 1910b ; Rheden, 1910 ; Jaschke, 1911; Bobrovnikoff 1931). While m a n y of these secondary nuclei showed the same properties as the primary nucleus (jets, streamers, etc.), the available positional information does not suggest any systematic pattern characteristic of genuine companion nuclei and appears to refer to unrelated phenomena. Bobrovnikoff (1931) showed t h a t features taken by visual observers for secondary nuclei could often be identified with jets or local condensations within the jets on high-resolution photographs and t h a t studies of sequences of such photographs indicated rapid motions with repulsive accelerations ~,---104-10 ~ units. Changes in the jets could sometimes be detected on photographs taken during the same night. More persistent jets were rare but not nonexistent. In summary, one should agree with the statement b y Bobrovnikoff t h a t Comet Halley "was often on the verge of disruption but never broke in two . . . . " Comet Brooks 1911 V is another unlikely candidate. An account of a double nucleus was due to Doberck (1912), an experienced

MOTIONS OF THE SPLIT COMETS, III TABLE III POSITIONS OF THE N U C L E I OF COMET CAMPBELL FROM PLATES T A K E N BY W . H . PICKERING AT THE AREQUIPA STATION OF THE HARVARD COLLEGE OBSERVATORY D a t e 1914 U T

Nucleus

R.A. (1950.0) Decl. (1950.0)

Sept. 18.37303

Principal Companion

4h25m19.~43 4 25 17.09

-- 57°10'15 .~2 --57 10 12.5

double-star observer. He commented on a distinct companion preceding the main nucleus at a distance of only 2 arcsec on October 1, 1911 and also remarked on several "alternately bright" nuclei on September 18. Although an elongated nucleus was reported on several occasions in late September and for most of October (Chofardet, 1912; Gonnessiat, 1912; Nijland and van der Bilt, 1912 ; Schiller, 1912 ;

307

Graft and Thiele, 1913; Bohlin, 1932), the observed directions of the elongation axis are inc6mpatible with the position of the Doberck companion. P a r t l y because of a fairly large scatter in the observed position angles of the long axis of the nucleus, these data are only marginally consistent with the conditions for splitting. Accepting approximately t~ - T ~-~ --40 days (i.e., ts ~--- 1911 Sept. 18) and assuming t h a t the actual separation of the components was roughly one-half the length of the observed elongated nucleus, we find "t "~ 7 units, i.e., the inferred secondary nucleus should be rather a persistent one. Yet numerous observations in November and later indicated t h a t the elongation vanished and never developed into two separate condensations. Comet Campbell 191~ I V was observed double when passing near the E a r t h in late

i/i:iii:::i: ¸ ii

1914 "FV

1943 I

FIG. 1. Comet Campbell (1914 IV) photographed by W. H. Pickering with the 61-cm Bruce telescope at the Harvard College Observatory's Arequipa Station on September 18, 1914, apparently the first successful photographic observation of a double comet (courtesy of Harvard College Observatory); and Comet Whipple-Fedtke-Tevzadze (1943 I) exposed by G. Van Biesbroeck with the 208-cm Struve reflector of the McDonald Observatory on March 31, 1943 (courtesy of Yerkes Observatory). North is up, east to the left. The scales are 7.5 arcsec m m -1 for Comet Campbell, 2.5 arcsec m m -1 for Comet Whipple-Fedtke-Tevzadze.

308

ZDENEK SEKANINA

S e p t e m b e r a n d early October 1914. The duplicity was observed visually b y Innes a n d Wood (1919) a n d both visually a n d photographically b y L u n t (1919). Photographs t a k e n b y L. Campbell with the 20-cm Bache telescope of the H a r v a r d Obs e r v a t o r y at the Arequipa Station (Pickering, 1915) had neither a sufficient resolution nor accurate enough guiding to show the companion. However, inspection of the O b s e r v a t o r y ' s plate collection has revealed t h a t on the discovery night three photographs were t a k e n by W. H. Pickering with the 61-cm Bruce telescope and t h a t of these a 10-min exposure had guiding (very difficult on account of the comet's diffuseness, fast motion, a n d unavailability of ephemeris) good enough to show distinctly a faint companion. The positions of both c o m p o n e n t s have now been measured, and the results are listed in Table I I I . The c o m e t ' s image on the Pickering plate, reproduced in Fig. 1, a p p e a r s to be the first successful photographic detection of a double comet. The rapidly changing g e o m e t r y resulted in a fast a p p a r e n t r o t a t i o n of the companion

around the principal nucleus (reaching 23 ° per d a y on S e p t e m b e r 26), a favorable circumstance for the determination of the time of splitting. The position angle measured on the Arequipa p h o t o g r a p h was linked with those from the visual observations at Cape a n d J o h a n n e s b u r g to indicate t h a t the comet m u s t have split before discovery. The trial-and-error fit listed in Table I represents the position-angle measurements (Table IV) more satisfactorily t h a n a least-squares solution based on the S e p t e m b e r 18 a n d October 6 positions, the only two with consistent separation distances. The companion was clearly fainter t h a n the principal nucleus, and no reports of it came after mid-October, when the comet became accessible to northernhemisphere observers. Comet N e w m a n 1932 V I I was found b y Schmitt (1932a) to be a c c o m p a n i e d b y a distant satellite on June 25, 1932 (separation ~075). T h e companion, known as C o m e t 1932h, was detected again, both visually and photographically, on J u n e 29 but not on J u l y 1, 3, and 4 (Schmitt, 1932b, c). I n the meantime, Davidson

TABLE IV RELATIVE POSITIONS OF THE COMPANION TO COMET CAMPBELL (REDUCED TO EQUINOX 1950.0)

Date 1914 UT

Sept. 18.37 20.89 21.86 21.87 27.74 28.81 Oct. 6.85 10.75

Separation

Position angle

Obs

Calc

Obs

Calc

19.~2 ---20-4-30 --

20~1 20.8 20.0 20.0 12.1 13.7 29.2 32.6

27871 --(315±) 50± 75± 118.4 --

275?0 298.9 309.8 309.9 53.2 73.7 119.0 122.9

a Condensed remarks: 1. Double nucleus on photograph; the secondary is faint and diffused. 2. Wide double nucleus ; components in common motion. 3. On photograph the secondary is diffused and elongated. 4. Two nuclei; the fainter is north preceding. 5. Nucleus double.

Observer

Pickering Lunt Lunt Innes, Wood Innes, Wood Innes, Wood Lunt Lunt

Remarksa

MOTIONS OF THE SPLIT COMETS, III TABLE V

309

in Table I. The deceleration indicates that the companion belonged to the category of minor fragments. No effect of a separation velocity could be detected. Although this comet is known to have experienced two major outbursts (with amplitudes 195o.o) ~1.5 magnitude), the breakup could be Date 1943 UT Separation Position Exposure correlated with only a minor surge in angle (rain) brightness, which, according to Beyer (1948), commenced on March 5 and peaked Mar. 31.41 9.s8 209° ½ 12 days later; after correction for heliApr. 1.37 10.6 206 ½ ocentric distance its amplitude was less 2.37 11.8 2O5 ½ 3.44 12.6 203 ½ than 0.5 magnitude. 9.32 16.2 201 ½ Comet Pajdu~dkovd 1951 I I was observed visually by Beyer (1955) to have (1932a) reported that this comet was ap- a triple nucleus on six occasions between parently observed by Steavenson on July 1, March 3 and 26, 1951. The position angles and further positions, from July 6 and 7, of the supposed companions are within were communicated by Delporte (1932a), several degrees of the direction of the prowho also discovered a third, asteroidal ob- longed radius vector, the separations rangject (Delporte, 1932b, Delporte et al., 1932). ing from 0.2 to 1 arcmin. A test of splitting On the other hand, searches by Schorr is decisively negative: the time of separa(1932) and by Struve (1932) in the same tion varies from observation to observation, period of time were negative, and Davidson and the deceleration is on the order of l0 s (1932b) found it impossible to calculate a units or more. Photographs taken by Van Keplerian orbit from the positions by Biesbroeck (1953) on March 5 and 10 show Schmitt and by Delporte. While Kobold a bright jet 1 arcmin long in the direction of (1932) and Crommelin (1933) speculated the "companions." Comet Vozdrovd 1954 V I I I was photothat 1932h could have separated from 1932 VII, we are unable to fit any of the graphed double at Kazan (Martynov and five published positions of 1932h on this Usmanova, 1954) on five nights in late August and early September 1954. From assumption. Comet Whipple-Fedtke-Tevzadze 1943 I, the description the condensations were according to a description by Van Bies- apparently nearly equal in brightness. broeck (1944), displayed a secondary nu- Although we found that they pass the cleus on April 3, 1943. All his plates taken test of splitting, an equally good, if not a with the 208-cm reflector at the McDonald better, fit could be achieved on the assumpObservatory around this date have now tion that they were images of a single been reexamined, and the companion was nucleus displaced in the direction of the clearly recognized on four consecutive comet's motion by imperfect guiding of nights from March 31 to April 3. It was the telescope. In the critical period of time fairly sharply condensed on March 31 the comet's declination was more than + 8 0 ° and the Kazan exposures were rather (Fig. 1), became more diffuse on the following nights, and faded to near the long (20 to 30 min). Indeed, no duplicity was reported by any other observer in the plate limit by April 9. The results of our measures are listed same period of time (Mitani, 1954; Steavenin Table V, and the separation parameters son, 1954; Van Biesbroeck, 1957; KresKk from a least-squares solution, are given and Antal, 1966). Examination of Van

RELATIVE POSITIONS OF THE COMPANION TO COMET WHIPPLE--FEDTKE--TEvzADZE ON PLATES TAKEN BY G. VAN BIESBROECK WITH THE 208-CM REFLECTOR OF THE McDONALD OBSERVATORY (EQUINOX

310

ZDENEK SEKANINA

Biesbroeck's plates confirms the presence of a single nucleus. This and the fact t h a t either of the two " c o m p o n e n t s " satisfies the orbit of the comet less well t h a n does their optical center (mean residuals of -4-8'.'2 and -4-7'.'4 for " c o m p o n e n t s " I and II, respectively, versus =t=2.~1 for the center) suggest strongly t h a t there were technical problems with the Kazan observations. Comet Honda 1955 V had two distinct nuclei, nearly equal in brightness, when photographed by Roemer (1955) on September 21, 1955. She reported their relative position on this date and remarked t h a t the southeastern component (the companion) was fading rapidly during the following two weeks. The duplicity was also noticed by Van Biesbroeck (1957) on September 13 and 28 and October 6 and suspected by Mitani (1956) on several dates between September 21 and October 16. In our examination of all plates of the comet taken by Van Biesbroeck we found that the companion was clearly seen only on October 19, while its image was barely measurable on two other dates (Table VI). Our measures are inconsistent with the positions published by Van Biesbroeck but could be linked by least squares with the Roemer position to calculate the separation parameters in Table I. Although the time of splitting is very uncertain, the comet must have broken up at a large heliocentric distance long before perihelion. The two nuclei should have been widely separated,

up to about 45 arcsec, during the close approach of the comet to the E a r t h in midAugust. Nevertheless, no definite traces of the duplicity could be detected on any of the August plates exposed by Van Biesbroeck at Yerkes. Apparently, the companion was then too faint to show up; only a distinct elongation of the main mass in the predicted direction of the companion is seen on some of these photographs. Comet Wild 1968 I I I was found by Roemer (1969) to have a double nucleus on two plates taken on N o v e m b e r 23, 1968. The test of splitting is positive and the available approximate position of the companion suggests a separation some 2.5 months before discovery (Table I). Comet Tago-Sato-Kosaka 1969 I X was also observed double by Roemer (Marsden, 1971). Plates t a k e n on March 14, 1970 showed a faint companion, whose approximate position suggests a breakup around F e b r u a r y 9, 1970. Considering t h a t the calculated time of separation varies with the position angle at a rate of ~ 1 . 3 day per degree, there appears to be a remarkable coincidence between the breakup and a flare-up of the comet t h a t was reported by a number of observers to have taken place around F e b r u a r y 6. In Fig. 2 the intrinsic brightness variations around the critical date, as reported by visual observers (Beyer, 1972; Bortle, 1970; Sugano, 1970), are compared with photoelectric V measures by Kiselev (1973a) and with

TABLE VI R E L k T I V E POSITIONS OF THE COMPANION TO COMET HONDA ON PLATES TAKEN BY G. VAN BIESBROECK WITH THE 61-CM REFLECTOR OF THE Y E R K E S OBSERVATORY AND THE 208-CM REFLECTOR OF THE M c D o N A L D OBSERVATORY (EQUINOX 1950.0)

Date 1955 UT

Separation

Position angle

Exposure (vain)

Sept. 28.06a Oct. 11.12 ~ 19.11 19.12

7~.1 4.8 5. O 5.0

126° 123 114 117

2 ½ 1 8

a Measures on this date uncertain.

Observatory Yerkes McDonald

McDonald McDonald

MOTIONS OF THE SPLIT COMETS, III I

I

I

311

I

Z

l-

COMET

I

w

® %° laJ

n\

/

X

•

\

•.b.u ®""'..

•

10.2/,/,,m

Z ~'~ 5 /

2 X

\ \

°'°°.o°°°%°

¢0

\

~

\

I

r_42......... ......

I

I

I

I

6

II

FEBRUARY

.-

ha

\ =\ fE W :I:

"-~

E

:L

°o,..

P_

4 ,:I

b--tM

®/

o

--I

BEYER WENSKE BORTLE SUGANO KISELEV

\

"°°"..° ] o° 0

• 0 • 0 ®

\

/

®

.-I

55

1969

®

•..~ I=-

TAGO-SATO-KOSAKA

t~

°-°.o

I 16

I 21

ci

1970

Fio. 2. A flare-up of Comet Tago-Sato-Kosaka (1969 IX) in February 1970. Visual magnitude estimates by Beyer, Wenske, Bottle, and Sugano are compared with photovisual observations by Kiselev (diaphragm 8.6 aremin) and with thermal-flux measures by Kleinmann et al. at 10.2 #m (diaphragm 0.6 arcmin). The dotted curve is an inverse-fourth-power law of heliocentric distance r.

scaled thermal-flux measures at 10.2 ~m (Kleinmann et al., 1971), corrected for the aperture effect (using the law by Gatley et al., 1974) and the geocentric distance. Riives (1975) reported t h a t photographically the amplitude of the flare-up reached 1.4 magnitude and t h a t the appearance and development in the coma of a round halo, expanding at a rate of 1.1 km sec -~, indicated t h a t the outburst began on F e b r u a r y 6.4 UT. R o e m e r (1970) remarked t h a t the event was associated with conspicuous jet activity, observed both visually and photographically on F e b r u a r y 7. The flare-up was not, however, accompanied by a n y significant changes in B-V, the polarization (Kiselev, 1973a,b), or the flux distribution of the comet between 5 and 22 ~m (Kleinm a n n et al., 1971). Along with Comet West 1976 VI (Sekanina and Farrell, 1978) Comet Tago-Sato-Kosaka has offered us a

rare opportunity to learn about explosivetype events that appear to be related to the splitting of a cometary nucleus. To summarize, of the 18 comets examined in this section a splitting has been documented positively for only 6 comets, 1888 I, 1914 IV, 1943 I, 1955 V, 1968 III, and 1969 I X ; rather a good chance of breakup is suggested for 2 comets, 1889 IV and 1896 V; and a splitting either did not occur or was highly doubtful in the 10 remaining cases. Ironically, 3 of the comets for which evidence points heavily against b r e a k u p - 1910 II, 1951 II, and 1954 V I I I - - w e r e in the past classified as split comets in at least two independent studies (Stefanik, 1966; Konopleva, 1967; Pittich, 1971; Golubev, 1975, 1976), while 1943 I, 1914 IV, and 1896 V were always missed. We find t h a t the comets with secondary condensations t h a t are well documented a n d / o r de-

312

ZDENEK SEKANINA

tected with large telescopes pass the test of splitting, while the failure to do so is strongly correlated with poorly established observational evidence on the companions. This fact m a y serve to underscore the importance of high-quality observations as well as to reinforce the soundness of the applied model of split comets. With 1943 I and 1889 I V we now have at least three and possibly five cases of minor fragments (~, > 100 units). The others are fragments C of 1899 I, B of 1905 IV, and perhaps also B of 1860 I (Paper I). These objects should be no more t h a n several tens of meters in diameter. Considering the difficulties of their detection both visually (cf. Perrine, 1900 ; Barnard, 1908, 1932) and photographically (Van Biesbroeck, 1944; this paper), t h e y must often escape our attention and m a y in fact represent rather a common c o m e t a r y phenomenon. At least three of the secondary nuclei studied in the present paper should be classified as short-lived companions, while only two appear to be persistent ones (cf. Section II). This contrasts with the results of Papers I and I I (where of the total of

20 secondary nuclei of well-observed split comets 7 were short lived and 10 persistent), obviously because more enduring companions are likely to be better observed. An inspection of a recent list of cometary orbits (Marsden et al., 1978) shows t h a t a majority of the split (or probably split) comets investigated in this paper are " o l d " in the O o r t - S c h m i d t (1951) sense. Only one comet has a formally hyperbolic original orbit, one is a fairly new comet in the O o r t - S c h m i d t classification, and one is a single-apparition short-period comet. One nearly parabolic comet does not have an orbit determined well enough to distinguish between " n e w " and "old." Compared with the split comets in Paper I, the fraction of the "old" comets is now clearly greater. IV. UNCONFIRMED OBSERVATIONS OF MULTIPLICITY AND POSSIBLE CAUSES FOR FALSE REPORTS For a large number of comets duplicity or multiplicity of the nucleus was noticed or suspected on only one occasion. Ignoring reports in which no information was

TABLE VII UNCONFIRMED REPORTS OF SECONDARY CONDENSATIONS

Comet

1881 III Great Comet (Tebbutt) 1890 V Periodic d'Arrest 1891 V Periodic Tempel~Swift 1898 X Brooks 1901 I Great Comet (Viscara) 1905 VI Brooks 1906 VI Periodic Metcalf 1912 II Gale 1918 I Periodic Encke 1918 IV Periodic Borrelly 1943 I Whipple-Fedtke-Tevzadze 1948 XI Eclipse Comet 1963 III Alcock 1968 V Whitaker-Thomas 1968 VII Bally-Clayton

More condensations observed Date UT

Mode

1881 June 11 1890 Nov. 7 1891 Jan. 21 1898 Nov. 10 1901 May 15 1906 Apr. 17 1906 Nov. 22 1912 Sept. 17 1918 Jan. 14 1918 Sept. 5 1943 Mar. 29a 1948 Dec. 2 1963 June 23 1968 June 29 1968 Sept. 12

Vis. Vis. Vis. Phot. Vls. Vis. Vis. Vis. Phot. Vis. Phot. Vis. Phot. Phot. Vis.

Reference

Gould (1881) Stone and Parrish (1891) Spitaler (1892) Keeler (1898) Gill (1901) Wirtz (1906) Esclangon (1906) Wood (1919) Schorr (1918) Parask~vopoulos (1922) Arend (1943) Wilson (1949) Waterfield (1963) Waterfield (1968) Young (1968)

a This feature is different from that photographed by Van Biesbroeck (Section III).

MOTIONS OF THE SPLIT COMETS, III provided on the position(s) of the companion(s), we tested only those observations t h a t included position-angle data. For these comets the date of the observed multiple appearance, the mode of observation (visual or photographic), and the reference are listed in Table V I I . The test of splitting was negative in all these instances except for the secondary condensations near comets 1891 V, 1948 X I , a n d 1963 I I I (the innermost one). T h e case of C o m e t 1891 V is, however, inconclusive, as the observation was m a d e nearly edge~on to the comet's orbit plane (the E a r t h ' s cometocentric latitude <1°). The alleged splitting of C o m e t 1948 X I has been virtually disproved by Hirst (1954), who reported a single nucleus on six exposures t a k e n at the Cape on the critical night. For 1963 I I I R o e m e r and Lloyd (1966) noticed on high-resolution plates only a spine in the direction of the reported seco n d a r y condensations. I n s u m m a r y , we are inclined to conclude t h a t none of the suspects listed in Table V I I did in fact split. E v e n an experienced observer can be deceived into believing a comet to be multiple. T h e existing records of comet observations, only a small fraction of which can be examined quantitatively, d e m o n s t r a t e t h a t there are at least three m a j o r categories of causes for false reports of split comets: (a) coma or tail p h e n o m e n a whose appearance resembles secondary nuclei, (b) optical defects a n d i n s t r u m e n t a l a n d other technical problems, a n d (c) h u m a n errors. The first category a p p e a r s to be rather a frequent cause for false alarm. We already m e n t i o n e d t h a t visual observers working with small telescopes can easily confuse short jets or other bright features in the c o m e t a r y head with genuine secondary nuclei. The same is also true for knots and local condensations in the plasma tail, as d e m o n s t r a t e d b y the controversy surrounding C o m e t 1943 I (Arend, 1943; Brunner-Hager, 1943). The second category covers a v a r i e t y of

313

optical effects caused b y diverse unfavorable circumstances during observation a n d resulting in comet-like ghost images in the field of the telescope [-see Esclangon's (1906) report on his observation of C o m e t 1906 V I I . As for photographic observations, plate flaws ['see Keeler's (1898) comm e n t s on C o m e t - 1 8 9 8 X ] and guiding problems (Comet 1954 V I I I ) a p p e a r to be the m o s t likely causes. Finally, the third category encompasses such errors as confusing a secondary condensation of a comet with a nebula [-see B a r n a r d ' s (1890b) c o m m e n t s on an observation of C o m e t 1889 V b y Brooks (1889)J or with a star image i m m e r s e d in the coma of a slowly moving comet ['Engelh a r d t (1889) on C o m e t 1889 I ] ; or mistaking blurred star images near the horizon for comet condensations [-see Gould's (1881) alleged observation of C o m e t 1881 I I I a n d the following controversy ( T e b b u t t , 1882a; Gould, 1882; T e b b u t t , 1882b)]. ACKNOWLEDGMENTS I wish to thank Dr. L. M. Hobbs, Director, Yerkes Observatory, for granting me permission to examine comet photographs made by the late Dr. G. Van Biesbroeck between 1922 and 1963; and Dr. K. M. Cudworth, Yerkes Observatory, for his expert advice on the Observatory's plate collection. I also appreciate the help of Dr. E. Roemer and Mr. C. D. Vesely, Lunar and Planetary Laboratory, with regard to Van Biesbroeek's observing books, and Dr. Roemer's critical comments. This study was supported by the Planetary Atmospheres Program of the National Aeronautics and Space Administration under Grant NSG 7082. The travel to the Yerkes Observatory was made possible by a grant from the Fluid Research Funds of the Secretary of the Smithsonian Institution. REFERENCES

ANOUIANO, A. (1889). Observatorio Astron6mico National Mexicano de Tacubaya. 0bservaeiones de asteroids y eometas. Astron. Nachr. 122, 225-228. AREND,S. (1943). Comet Whipple-Fedtke (1942g). 1.4 U Circ. No. 944.

BARNARD,E. E. (1890a). Comet e 1889 (Davidson). Astron. J. 9, 66-67. BARNARD,E. E. (1890b). Physical and micrometrical

314

ZDENEK SEKANINA

observations of the companions to Comet 1889 V (Brooks). Astron. Nachr. 125, 177-196. BArnYARD, E. E. (1892). Filar-micrometer observations of Comet 1889 IV. Astron. J. 11, 75. BARNARD,E. E. (1908). Secondary nucleus to Comet b 1906 (Kopff's, March 3). Astron. J. 25, 83-84. BARNARD,E. E. (1932). Observations of comets (I). Astron. J. 41, 145-152. BECKER, E. (1889). Beobachtungen des Cometen 1888, I. Astron. Nachr. 120, 67-70. BEYER, M. (1948). Physische Beobachtungen yon Kometen. VI. Astron. Nachr. 275, 237-250. BEYZR, M. (1955). Physische Beobachtungen yon Kometen. IX. Astron. Nachr. 282, 145-167. BZYER, M. (1972). Physische Beobachtungen yon Kometen. XVII. Astron. Nachr. 293, 241-257. BOBROVNIKOFF, N. T. (1931). Halley's Comet in its apparition of 1909-1911. Publ. Lick Obs. 17, 309-482. BOH~N, K. (1932), Gelegentliche Beobachtungen an Meteoriten, Sternschnuppen und Kometen, 19111931. Astron. Nachr. 245, 369-374. BOR?LE, J. E. (1970). Comet Tago-Sato-Kosaka (1969g). I A U Circ. No. 2218. BROOKS, W. R. (1889). Comet Brooks (d 1889). S/d. Mess. 8, 363-364. BRUHNS, C. (1857). Verbesserte Elemente des periodischen Cometen (II. 1857), nebst Bemerkungen fiber seine Helligkeit und die Beschaffenheit seines Lichtes. Astron. Nachr. 45, 187-192. BRUHNS, C. (1868). Beobachtungen yon Planeten und Cometen auf der Leipziger Sternwarte. Astron. Nachr. 72, 275-286. BRUNNER-HAGER, W. (1943). Comet WhippleFedtke and Object Arend. I A U Circ. No. 950. CA~PRELL, W. W. (1903). Komet 1896 V (Giacobini) und Fayescher Komet. Astron. Nachr. 163, 351352. CHARLOm, A. (1888a). Beobachtungen des Cometen 1 8 8 8 . . . (Sawerthal). Astron. Nachr. 119, 27-28. CHARLOIS, A. (1888b). Observations de la com~te Sawerthal, falter ~ l'observatoire de Nice. Compt. Rend. 106, 1000-1001. CHARLOIS, A. (1888c). Observations des plan~tes (144), (223), (272), (275), (276), (277) et de la combte Sawerthal. Bull. Astron. 5, 345-347. C~OFAm)ET, P. (1912). Observations de com~tes. Astron. Nachr. 192, 9-16. COMAS SOL)[, J. (1910). In: Mittcilungen vom Halleyschen Kometen. Astron. Nachr. 185, 69-78. CROMMELIN, A. C. D. (1933). Comets. Mon. Not. Roy. Astron. Soc. 93, 272-275. CRULS, L. (1888a). Observations de la combte 1888 . . . (Sawerthal). Astron. Nachr. 119, 155-156. CRULS, L. (1888b). Observations de la com~te a 1888. Compt. Rend. 107, 316-319.

DAVIDSON, M. (1932a). New comet. Brit. Astron. Assoc. Circ. No. 120. DAVIDSON, M. (1932b). Comet Schmitt (1932h). I A U Circ. No. 394. DELPORTE, E. (1932a). Comet Schmitt (1932h). I A U Circ. No. 392. DELPORTE, E. (1932b). Comet Newman (1932f). 1.4 U Circ. No. 392.

DELPORTE, E., BOURGEOIS, P., AREND, S., RmAUX, F., AND LAUOIER, S. (1932). Observations photographiques de petites plan~tes. II. Astrographe Zeiss. Bull. Astron. Obs. Roy. Belg. 1, 146-152. DOSERCK, W. (1912). Observations of comets. Astron. Nachr. 190, 221-224. ENGE~XRDT, B. (1886). Beobachtungen des Cometen 1886 . . . (Brooks 2). Astron. Nachr. 114, 317-318. ENGE~ARDT, B. (1888a). Beobachtungen des Cometen 1888 . . . (Sawertha]). Astron. Nachr. 119, 79-80. ENOELUARDT,B. (1888b). Beobachtungen des Cometen 1888 I. Astron. Nachr. 119, 301-304. ENGELHARDT, B. (1889). Beobachtungen des Cometen Barnard 1888 Sept. 2. Astron. Nachr. 120, 47-48. ESCLANGON, E. (1906). Observations de la com~te 1906h faites au grand dquatorial de l'Observatoire de Bordeaux. Compt. Rend. 143, 870-871. FRANZ, J. (1890). Beobachtungen von Cometen und Planeten am KSnigsberger Heliometer. Astron. Nachr. 124, 187-190. GATLEY, I., BECKLIN, E. E., NEUGEBAUER,G., AND WERNER, M. W. (1974). Infrared observations of Comet Kohoutek (1973f). Icarus 23, 561-565. GILL, D. (1901). Observations of Comet 1901. I. Astron. Nachr. 156, 203-208. GOLUBEV, V. A. (1975). Splitting of cometary nuclei. I. A catalogue of split comets. Probl. Kosm. Fiz. 10, 23-34. (In Russian.) GOLUBEV, V. A. (1976). Splitting of cometary nuclei. II. Some properties of split comets. Probl. Kosm. Fiz. 11, 76-83. (In Russian.) GONNESSIAT, F. (1912). Observations de com~tes. Astron. Nachr. 191, 357-360. GOULD, B. A. (1881). Letter to the Editor. Astron. Nachr. 100, 113-116. GOULD, B. A. (1882). Letter to the Editor. Astron. Nachr. 102, 145-148. GRAFF, K., AND THIELE, H. (1913). Beobachtungen yon Kometen, Planeten und Fixsternen. Astron. Nachr. 194, 257-272. HILL, C. B. (1888a). Comet a 1888. Sid. Mess. 7, 221. HILL, C. B. (1888b). Double nucleus and Comet a 1888. Sid. Mess. 7, 262-263. HILL, C. B. (1889). Observations of Comet 1888 I (Sawerthal). Astron. Nachr. 120, 323-326. HIRST, W. P. (1954). The definitive orbit of the

MOTIONS OF T H E SPLIT COMETS, III Eclipse Comet 1948l. Mon. Not. Astron. Soc. South Africa 13, 31-40. HUSSEY, W. J., ANDPERRINE, C. D. (1897). Observations of Comet d 1896 (Giacobini). Astron. J. 17, 29. INNES, R. T. A. (1910a). Fortgesetzte Beobachtungen und Mitteilungen vom HaUeyschen Kometen. Astron. Nachr. 185, 55-60. INNES, R. T. A. (1910b). Observations of Halley's Comet, 1910. Transvaal Obs. Circ. No. 4, 23-35. INNES, R. T. A., AND WOOD, H. E. (1919). Micrometer observations made at the Union Observatory, Johannesburg. Comet 1914 (e) Lunt. Union Obs. Circ. 1, 171-173. JASCHKE, H. (1911). Bemerkungen zu den Beobachtungen des Halleyschen Kometen. Astron. Nachr. 188, 99-104. KEELER, J. E. (1898). Photographs of Comet i, 1898 (Brooks), made with the Crossley reflector of the Lick Observatory. Astrophys. J. 8, 287-290. KISELEV, N. N. (1973a). The photoelectric observations of magnitude and color of the comet 1969 IX. Komet. Meteor. No. 22, 3-4. (In Russian.) KXSELEV, N. N. (1973b). The electropolarimetry of the comets Tago-Sato-Kosaka 1969 IX and Bennett 1970 II. Komet. Meteor. No. 22, 5-7. (In Russian.) KLEINMANN,D. E., LEE, T., LOW,F. J., ANDO'DELL, C. R. (1971). Infrared observations of comets 1969g and 1969i. Astrophys. J. 165, 633-636. KNORRE, V. (1887). Beobachtungen yon Cometen und kleinen Planeten. Astron. Nachr. 117, 169-198. KOBOLD, H. (1932). Mitteilungen tiber Kometen. Astron. Nachr. 246, 325-326. KONOPLEVA, V. P. (1967). Active processes in cometary nuclei. In Active Processes in Comets (V. P. Konopleva, Ed.), pp. 57-68. Naukova Dumka, Kiev. (In Russian.) KRES.(K, L., AND ANTAL, M. (1966). Observations of comets at the Skalnat6 Pleso Observatory, 1946-1963. Contr. Astron. Obs. Skalnat$ Pleso 3, 113-146. LEAVENWORTH,F. P., AND GUMMERE,H. V. (1889). Filar-micrometer observations of Comet 1888a. Astron. J. 8, 39. LE CADET, G. (1889). Observations de la eom~te Davidson, faites ~ l'6quatorial coudd de l'observatoire de Lyon. Compt. Rend. 109, 65. LUNT, J. (1919). Micrometer observations made at the Royal Observatory, Cape of Good Hope. Comet 1914 (e) Lunt. Union Obs. Circ. 1,171-173. LUTHER, W. (1889). Beobaehtungen yon Cometen und kleinen Planeten. Astron. Nachr. 120, 113-136. LUTHER, W. (1891). Beobachtungen von Cometen und kleinen Planeten. Astron. Nachr. 127, 49-76. MARSDEN, B. G. (1971). Comets in 1970. Quart. J. Roy. Astron. Soc. 12, 244-273. MARSDEN, B. G. (1972). Nongravitational effects on comets: The current status. In The Motion, Evo-

315

lution of Orbits, and Origin of Comets (G. A. Chebotarev, E. I. Kazimirehak-Polonskaya, and B. G. Marsden, Eds.), pp. 135-143. Reidel, Dordrecht. MARSDEN, B. G., AND SEKANINA,Z. (1971). Comets and nongravitational forces. IV. Astron. J. 76, 1135-1151. MARSDEN, B. G., SEKANINA, Z., AND EVERHART, E. (1978). New osculating orbits for 110 comets and analysis of original orbits for 200 comets. Astron. J. 83, 64-71. MARTYNOV, D. J., AND USMANOVA,F. K. (1954). Observations of comet Vozarova 1954f at the Engelhardt Astronomical Observatory. Astron. Circ. USER No. 155, 3-4. (In Russian.) MITANI, T. (1954). Comet Vozarova (1954f). HarD. Announc. Card No. 1273. MITANI, T. (1956). Observations of comets. I A U Circ. No. 1538. MtiLLER, A. (1870). Beobaehtungen des periodischen Cometen yon Winnecke auf der Sternwarte zu Lund. Astron. Nachr. 75, 201-202. NIJLAND, A. A., AND VAN DER BILT, J. (1912). Beobachtungen yon Kometen am Utrechter Refraktor. Astron. Nachr. 191, 137-146. OORT, J. H., AND SCHMIDT, U . (1951). Differences between new and old comets. Bull. Astron. Inst. Neth. 11, 259-269. PARASK~VOPOULOS, J. (1922). Observations de la com~te Borrelly faites ~ l'Observatoire d'Ath~nes avec l'Equatorial Doridis (Gautier 0~.40). J. Obs. 5, 14. PECHi~LE, C. F. (1886). Cometenbeobachtungen. Astron. Nachr. 115, 385-392. PECHtYLE, C. F. (1889). Beobachtungen angestellt auf der Kopenhagener Sternwarte. Astron. Nachr. 122, 137-144. PERRINE, C. D. (1900). Observations of Comet 1899 I. Astron. J. 20, 186-187. PERROTIN, J. (1896). Sur la com~te pdriodique Giacobini. Compt. Rend. 123, 925-928. PXCKERINO, E. C. (1915). Campbell's comet, 1914e. HarD. Obs. Circ. No. 187. PITTICH, E. (1971). Space distribution Of the splitting and outbursts of comets. Bull. Astron. Inst. Czech. 22, 143-153. RENZ, F. (1891). Beobachtungen des Cometen 1889 IV. Astron. Nachr. 128, 169-174. RHEDEN, J. (1910). In: Weitere Mitteilungen vom Halleyschen Kometen. Astron. Nachr. 185, 241244. Riccb, A. (1890). Osservazioni della Cometa 1889 IV. Astron. Nachr. 123, 205-208. RIIVES, V. (1975). Photometry of Comets 1969 IX (Tago-Sato-Kosaka) and 1970 XV (Abe). Publ. Tartu Astrophys. Obs. 43, 208-215. ROEMER, E. (1955). Comet notes. Publ. Astron. Soc. Pacific 67, 424-426.

316

ZDENEK SEKANINA

ROEMER, E. (1969). Comet notes. Publ. Astron. Soc. Pacific 81, 79-81. ROEMER, E. (1970). Comet notes. Publ. Astron. Soc. Pacific 82, 356-366. ROEMER, E. AND LLOYD, R. E. (1966). Observations of comets, minor planets, and satellites. Astron. J. 71,443-457. Rt?MKER, G. (1857). Beobachtungen des Brorsen'schen Cometen auf der Hamburger Sternwarte. Astron. Nachr. 45, 277-278. SCHILLER, K. (1912). Kometenbeobachtungen am 29 cm Refraktor der Sternwarte Bothkamp. Astron. Nachr. 190, 329-336. SCHMIDT, J. F. J. (1857). Beobachtungen auf der Sternwarte zu Olmiitz. Astron. Nachr. 46, 145-156. SCHMITT, A. (1932a). New Comet Schmitt (1932h). I A U Circ. No. 389. SCHMI~r, A. (1932b). Comet Schmitt (1932h). I A U Circ. No. 392. SCHMITT, A. (1932e). Positions de combtes obtenues l'Equatorial photographique de l'Observatoire d'Alger. J. Obs. 15, 115. SCHONFELD, E. (1869). Beobachtungen des Winnecke'schen Cometen yon kurzer Umlaufszeit. Astron. Nachr. 74, 235-236. SCHORR, R. (1918). Beobachtungen des Enckeschen Kometen 1917c. Astron. Nachr. 207, 21-24. SCHORR, R. (1932). Comet Schmitt (1932h). I A U Circ. No. 391. SCHULHOF, L. (1874). Planeten- und CometenBeobachtungen, angestellt auf der Wiener Sternwarte. Astron. Nachr. 83, 177-198. SECCHI, A. (1858). Osservazioni della cometa IV. 1857 e della II. 1857 fatte all' osservatorio del Collegio Romano. Astron. Nachr. 47, 13-14. SEKANINA, Z. (1977). Relative motions of fragments of the split comets. I. A new approach. Icarus 30, 574-594. SEKANINA, Z. (1978a). Relative motions of fragments of the split comets. II. Separation velocities and differential decelerations for extensively observed comets. Icarus 33, 173-185. SEKANINA, Z. (1978b). The split comets: Gravitational interaction between the fragments. In Dynamics of the Solar System (R. L. Duncombe, Ed.). Reidel, Dordrecht, in press. SEKANINA, Z., AND FARRELL, J. A. (1978). Comet West 1976 VI: Discrete bursts of dust, split nucleus, flare-ups, and particle evaporation. Astron. J. 83, 1675-1680. SPITALER, R. (1892). Beobachtungen yon Cometen a m grossen Refractor der Wiener Sternwarte. Astron. Nachr. 129, 355-360. STEAVENSON, W. H. (1954). Comet Vozarova (1954f). I A U Circ. No. 1469. STEFANIK, R. P. (1966). On thirteen split comets. Mem. Soc. Roy. Sci. Libge, Sdr. 5. 12, 29-32.

STONE, E. J. (1888). Observations of Comet a 1888 (Sawerthal), made at the Radcliffe Observatory, Oxford. Mon. Not. Roy. Astron. Soc. 48, 345-347. STONE, 0., AND PARRISH, N. M. (1891). Filarmicrometer observations of Comet d 1890 (d'Arrest). Astron. J. 10, 167. STRUVE, G. (1932). Comet Schmitt (1932h). I A U Circ. No. 391. SUGANO, M. (1970). Comet Tago-Sato-Kosaka (1969g). I A U Circ. No. 2218. SY, F. (1896). Observations de la com~te Giacobini, faites, ~ l'observatoire d'Alger, ~ l'dquatorial coudd de 0.=318. Compt. Rend. 123, 481-482. TEBBUTT, J. (1882a). Letter to the Editor. Astron. Nachr. 161, 171-174. TEBBUTT, J. (1882b). Dr. Gould's observation of Comet 1881 III on June 11. Astron. Nachr. 103, 311-312. TEMPEL, W. (1873). Letter to the Editor. Astron. Nachr. 82, 113-116. VAN BIESBROECK,G. (1944). Observations of comets with the 82-inch reflector of the McDonald Observatory. Astron. J. 50, 183-184. VAN BIESBROECK, G. (1953). Observations of comets. Astron. J. 58, 79-87. VAN BIESBROECK, G. (1957). Observations of comets. Astron. J. 62, 191-197. WATERFIELD, R. L. (1963). Comet Alcock (1963b). I A U Circ. No. 1836. WATERFIELD, a. L. (1968). Comet WhitakerThomas (1968b). I A U Circ. No. 2084. WEISS, E. (1870). Kreismikrometer-Beobachtungen am 6-zSlligen Refractor der Sternwarte in Wien. Astron. Nachr. 75, 273-282. WHIPPLE, F. L. (1950). A comet model. I. The acceleration of Comet Encke. Astrophys. J. 111, 375-394. WILSON, R. H., JR. (1949). Observations of Comet 1948/. Astron. J. 54, 167. WINNECKE, A. (1859). Der grosse Comet yon 1858. Astron. Nachr. 50, 305-318. WINNECKE, h. (1863). Beobachtungen des Cometen Brorsen 1857. Astron. Nachr. 59, 67-70. WINNECKE, A. (1869). Letter to the Editor. Astron. Nachr. 74, 13-16. WlRTZ, C. W. (1906). Beobachtungen yon Kometen. Astron. Nachr. 172, 185-190. WOLF, M. (1903). Photographische Aufnahmen yon kleinen Planeten und Kometen. Astron. Nachr. 163, 175-176. WOOD, H. E. (1919). Comet Gale, 1912(a). Union Obs. Circ. 1, 7-8. WUTSCHICHOWSKY, L. (1888). Beobachtungen des Cometen 1888 I (Sawerthal). Astron. Nachr. 119, 191-192. YOUNG,J. W. (1968). Comet Bally-Clayton (1968d). I A U Circ. No. 2096