SMITHSONIAN

CONTRIBUTIONS

to

ASTROPHYSICS

Smithsonian Institution

Astrophysical Observatory

Number 12

Two Computerized

Stream Searches

Among Meteor Orbits:

1. Among 865 Precise

Photographic Orbits;

2. Among 2401

Photographic Orbits

By Bertil-Anders Lindblad

Smithsonian Institution Press

SMITHSONIAN CONTRIBUTIONS TO

ASTROPHYSICS

NUMBER 12

Bertil-Anders Lindblad TwO Computerized

Stream Searches

Among Meteor Orbits:

1. Among 865 Precise

Photographic Orbits;

2. Among 2401

Photographic Orbits

SMITHSONIAN INSTITUTION PRESS

CITY OF WASHINGTON

1971
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Contents

Page

1. A Stream Search Among 865 Precise Photographic Meteor Orbits . 1

2. A Computerized Stream Search Among 2401 Photographic Meteor

Orbits 14

in

Bertil-Anders Lindblad 1. A Stream Search

Among 865 Precise

Photographic Meteor

Orbits

Introduction

Meteors are generally divided into two classes

—shower meteors and sporadic meteors. About

a dozen major showers occur every year. These

showers, or streams, are conspicuous in any list

of visually observed or photographed meteors,

and virtually all their members are readily

identifiable. If the shower radiant is diffuse or

the hourly rate is low, however, it is not easy

to recognize a meteor stream.

The division into stream metors and sporadic

meteors is, to a certain extent, arbitrary. The

classifications hitherto used for stream identification are based primarily on geocentric quantities such as radiants, velocities, and dates of

occurrence. When, in addition, detailed orbital

information is available for individual meteors,

the above methods of classification are supplemented or superseded by methods based on comparisons of sets of orbital elements. The use of

the orbital elements has the advantage that

these parameters are more fundamental, having

regard to the initial formation of a stream.

Owing to inherent differences among the individual members of a meteor stream, the investigator who makes a stream search is faced

with the difficult problem of rejecting suspected

stream members when the orbital elements exBertil-Anders Lindblad, Lund Observatory, Lund,

Sweden.

hibit too large a deviation from some assumed

mean set of orbital elements. The rejection level

adopted as well as the assumed set of mean

elements is necessarily somewhat subjective,

being largely based on the investigator's a

priori knowledge of the dispersion within the

stream.

It is difficult to recognize members of a previously unknown stream or members of a

stream not well represented in the sample under

study. The problem of stream identification becomes increasingly difficult in large samples

owing to the amount of labor involved and also

to the possibility of spurious associations among

different sets of orbital elements. The expected

existence in the near future of very large collections of fairly precise meteor orbits determined by photographic and radio methods

makes it necessary to introduce a quantitative

criterion for stream membership as well as an

automatic method of stream search suitable for

computer analysis.

The D-criterion of stream membership

Southworth and Hawkins (1963) present a

study they made of the statistics of meteor

streams. The study is based on a quantitative

measure of orbit similarity, which the authors

call the D-criterion. Their method depends on

the principle of intercomparison of two sets of

orbital elements. Let A and B represent two

individual meteors to be tested for orbit simi-
SMITHSONIAN CONTRIBUTIONS TO ASTROPHYSICS

larity. Let the orbital elements be represented

by the five quantities q, e, i, ft, and ir, where, as

usual, qf = a(l-e ) is the perihelion distance,

e the eccentricity, i the inclination, ft the longitude of the ascending node, and TT = co + ft the

longitude of perihelion, measured from the

vernal equinox.

Let IAB be the angle between the orbital

planes and TTAB the difference between the longitudes of perihelion measured from the intersection of the orbital planes. Further, let the

differences of angular orbital elements be measured by their chords, i.e., by twice the sine of

half the angle. A quantitative measure of orbit

similarity (or difference) is then given by the

expression

[D{A,B)Y= (eB-eAy+ (qB-qA)

2

±-(«A + eB) 2 (i)

where--- (eA + eB) is a weight function. The

last two terms in equation (1) are related to the

orbital elements as follows:

(

+ sin (A sin iB(2 sin

 B

 ~

 Aj (2)

and

ttAH = COB - (oA + 2 arc sin

lA + IB . ftfl - ClA

cos—^—sin ^— sec

IAB\

2 / * (3)

2 " 2

In the definition of D, the difference in

perihelion distance is substituted for the semimajor axis a as a measure or orbit size, because

the perihelion distance is well determined by

observations and exhibits a small range of

values. This is particularly important in the

analysis of photographic meteor data, which

often contain a high percentage of nearly parabolic orbits.

Having acquired a quantitative measure of

orbit similarity, let us proceed to the definition

of a meteor stream. A criterion of stream membership may be based on either of the following

two definitions:

1. As previously, a stream may be defined

by a comparison of the orbital elements of an

individual member N with the corresponding

elements of a mean orbit M. Let D(M, N) have

the same mathematical form as D(A,B) of

equation (1). A stream may then be defined as

all those meteors N whose difference D(M, N)

from the mean orbit M is less than a certain

prescribed amount Z)max.

2. A stream may be defined by serial association between the members. Two meteors A

and B are said to be associated if D(A, B) does

not exceed a standard value Ds. A stream may

then be defined as a group of meteors in which

every member is associated with one or more of

the other members.

ADOPTED METHOD OF STREAM SEARCHING.—Of

the two definitions mentioned above, the latter

has the advantage of not demanding any a priori

knowledge of the orbit of a meteor stream and

is therefore suitable for a computer search for

streams. A computer program based on the concept of serial associations has been worked out

by South worth. The method of stream search

consists essentially of labeling the meteors in a

sample, in some order, and computing first the

orbital difference D(A, N) between a meteor A

and all the other meteors in the sample, and

second the orbital differences between meteor B

and the other members, etc. As soon as a pair is

detected by the condition D<DS, where the

standard value of Ds has been prescribed in

advance, these two meteors are said to form a

stream. Eventually more meteors will be included in the stream by the continued comparison process. When the computer has run

through the entire process, there will appear

several groups or chains of meteors, each of

which may be considered a stream. The program then numbers the streams and computes

a mean orbit M for each of these streams, the

difference D(M, N) between each stream member N and this mean orbit, the equatorial coordinates (a, 8) of the mean radiant, and the mean

geocentric velocity of the stream.

A difficulty encountered in the study of large

data samples is that the above method of serial

association sometimes produces a long chain, or
NUMBER 12

string, of meteors wherein consecutive meteors

exhibit a high degree of orbit similarity, but

where the first and last meteor in the chain

exhibit very little resemblance to each other

or to the stream mean. This case reveals its

presence through the very large D(M, N) values

exhibited by most members of the "stream." If

a mean D(M, N) is computed for all members of

the stream, its value will greatly exceed the

prescribed value of Ds. To overcome this difficulty, the numerical value of Ds

 has to be adjusted to the size of the sample under study.

Present investigation

Southworth and Hawkins (1963) applied the Dcriterion to a sample of 360 meteor orbits. The

data represented a random sample of meteors

photographed from two stations by the Harvard

Super-Schmidt meteor cameras (Hawkins and

Southworth, 1958). In the present paper, the

study is extended to include 865 precise photographic two-station orbits of the Harvard

Meteor Program. The purpose of the investigation was twofold: to study how the numerical

value of Ds should be adjusted to fit a larger

sample, and to present the streams detected by

the new stream search together with a short

discussion of their orbital properties.

The 865 meteors comprised 139 small-camera

orbits published by Whipple (1954), 313 SuperSchmidt meteor orbits published by Hawkins

and Southworth (1961), and 413 Super-Schmidt

meteor orbits listed by Jacchia and Whipple

(1961). Of the published small-camera orbits,

5 were excluded because of incomplete data. Of

the 360 orbits in the random sample of SuperSchmidt meteors, 47 were excluded since they

are already included in the 413 orbits listed by

Jacchia and Whipple.

The orbital elements and other relevant data

for each meteor were available on cards, together with the shower (or sporadic) classification proposed by the original investigator. A

few meteors originally classified as sporadic

have in subsequent papers been reclassified

as shower meteors; these reclassifications are

listed in various papers of the Harvard Meteor

Program (Wright, Jacchia, and Whipple, 1957;

Hawkins, Southworth, and Stienon, 1959; McCrosky and Posen, 1959) and were taken into

account in this analysis.

APPLICATION OP STREAM SEARCH TO KNOWN

STREAMS.—Once a computer procedure for

stream searching has been established, it remains to determine the rejection level, i.e., the

numerical value of Ds that should be used in the

search. Southworth and Hawkins adopted the

rejection level Ds=0.20, because when D(A, B)

was computed for all possible pairs within each

of the recognized meteor showers in their survey, the value of D(A, B) never exceeded 0.20.

They noted that the rejection level Ds would

have to be decreased in a sample larger than

that under study (360 meteors). The authors

predicted that Da should vary inversely as

the fourth root of the sample size. Hence,

Z>s=0.20

/360\"

V8657 -°*

161 would be an appropriate value to use in the present study.

To avoid prejudicing our choice, we decided

to run independent stream searches at several

levels of Ds. The 865 sets of orbital elements

were therefore tested for stream membership at

the rejection levels D,=0.20, 0.15, and 0.10.

The results of these searches are given below.

The first stream search revealed that at the

rejection level D,=0.20 it was not possible to

single out the previously known meteor streams

of low inclination. To illustrate the difficulties

encountered in the search, we mention that one

meteor stream of low inclination extended from

July to December and included the a Capricornids, the x Orionids, the Andromedids, and

the Northern and Southern Taurids. In a similar manner, the Virginid stream combined with

a group of 88 sporadic meteors to form one

vast, low-inclination meteor stream extending

from February through June. These results

clearly indicate that the value of the rejection

level Ds had been set too high. Although no

further use is made of the search at Ds=0.20,

it may be mentioned that at this rejection level

the stream search singled out all the previously

known meteor showers of moderate and high

inclination.

The results of the search at £>,=0.15 are presented in Table 1. The first column gives the

arbitrary stream number assigned by the computer program to the shower, the second the
SMITHSONIAN CONTRIBUTIONS TO ASTROPHYSICS

TABLE 1.—Previously known streams detected by stream search at Dg = 0.15

New

nember

Total no.

at D_ = 0. 15 Nc

by stream

Harvard

2

14

18

52

23

36

40

13

22

45

65

71

72

74

76

79

80

82

84

87

88

a Capricornids

X Orionids

Andromedids

Northern i Aquar

Virginids

Northern Tauridi

Southern i Aquar

Northern 6 Aqua:

Southern 6 Aquai

Geminids

Draconids

K Cygnids

Quadrantids

Lyrids

Perseids

<r Hydrids

Leonids

Orionids

Total

ids

i

ids

rids

ids

18

3

3

2

2

3

30

19

2

1

2

5

1 1

50

2

8

14

5

27

4

5

17

2 3 :

3419 8075

0828 1934 10247

2961 3886 5124 9416

2630

3784 8098 8307

9507

4513

2643 4472

6093 6105

1910 10531

1089 2049 2801 4216

8348

2328

1898 2179

2691 4974 5063 5183

5210 5231

name of the shower, and the third the number

of shower meteors, according to conventional

classification, that were retained by the stream

search. The fourth column lists the number of

new members detected by the search. The fifth

column in the table gives the total number of

members in a stream as defined by the computer

program. The last two columns list previous

shower members that were rejected in the

computer search.

Table 1 lists 19 previously recognized meteor

streams for which more than one meteor existed

in the sample. Inspection of Table 1 reveals that,

with one exception, the computer program successfully identified and singled out the known

meteor streams. The Andromedid shower, however, was split up into two showers, and the

very diffuse Southern i-Aquarid stream into

three separate components. The one apparent

failure occurred in the vast Taurid meteor

complex, where the stream search at Z)s=0.15

did not separate the Northern and Southern

Taurid meteor streams. The Taurid meteor

shower is of very long duration, and it has presented considerable difficulties to conventional

shower-identification techniques. The northern

and southern branches of this stream may, however, be easily separated by inspection of the

orbital elements, since the line of nodes is

shifted by 180° (Whipple, 1938; Wright and

Whipple, 1950).

The results of the stream search at Ds=0.10

are summarized in Table 2. Although most of

the known showers were still identified by the

search, as many as 71 previous members were

rejected and only 3 new ones added. We therefore concluded that the rejection level Ds=0.10

imposed too stringent requirements on stream

membership. Two streams disappeared entirely.

The Taurid shower was split up into three components, while the North 8 Aquarids and the

K Cygnids were split up into two separate

showers. It is, however, interesting to note that

at this level the Southern 8-Aquarid stream

suffered no losses and that the Quadrantid and

Geminid streams were essentially intact. This

indicates a high degree of orbit similarity

within these showers.
NUMBER 12

TABLE 2.—Previously known streams detected by stream search at D§ = 0.10

Substrear

no.

27

9

34

-

-

20

22

17

8

38

44

41

42

45

49

50

51

52

54

56

59

60

n

Name

a Capricornids

X Orionids

Andromedids

Northern i Aquai

Virginids

Southern Taurid.

Northern Taurid

Southern i Aquar

Northern 6 Aqua

Southern G Aquai

Geminids

Draconids

K Cygnids

Quadrantids

Lyrids

Perseids

0- Hydrids

Leonids

Orionids

Total

ids

5

i d s

rids

ids

Previous

m

9

3

2

-

-

15

9

18

2

2

11

50

2

2

4

14

4

25

3

4

16

198

New

8

-

-

-

-

1

-

-

-

-

-

-

-

-

1

-

3

Total no.

9

3

2

-

-

15

9

19

2

2

3

1 1

50

2

1

2

1

201

Previous members

rejected by

st earn search

9

-

-

4

6

1 1

1

6

-

1

1

4

2

3

7

2

3

7

71

DISCUSSION—The results of the above three

tests clearly illustrate the rather arbitrary

character of a computer stream search and

stress the need for a more precise definition

of a meteor stream.

The best Z>-value to use in the present search

was estimated as follows. Consider a large data

sample already studied for streams. The computer search will reject some previously recognized members and include some "new"

members. Since the number of new and rejected

members varies from stream to stream, the

value of Ds chosen should be such that the total

number of rejections approximately equals the

total number of new members. This approach

gives us the best agreement with the conventional method of stream classification.

Table 1 indicates that among the known

photographic streams, the search program at

Z>,=0.15 rejected 36 previous members and

added 29 new ones. We hence consider Ds=0.15

to be very nearly the optimum value of Ds for

use in the present sample. A detailed inspection

of the rejected meteors revealed that there are

often good reasons, according to conventional

classification methods, for a rejection. Of the

36 previous members that were rejected in our

search, 17 were either hyperbolic meteors or

were classified by the original investigators as

very doubtful members. If these objects are

excluded from the list of previously known

shower members, we find a net loss of 19 previous members and a gain of 29 new members.

In view of the above considerations, Z),=0.15

is adopted as the rejection level. This empirically determined value of Ds

 is in good agreement

with the value (0.161) based on the inverse

fourth-root relation referred to earlier.

Further results of stream search at D8 = 0.15

In addition to the 19 streams (21 computer

streams) listed in Table 1, the computer search

at Ds=0.15 produced an additional 59 meteor

streams. The most significant of these are listed

in Tables 3, 4, and 5. The identification and discussion of these new streams are the subject

of the rest of this report.

COMPARISON WITH STREAM SEARCH OF MCCROSKY AND POSEN.—The existence of numer-
SMITHSONIAN CONTRIBUTIONS TO ASTROPHYSICS

ous weak meteor showers in the Harvard

photographic data has become evident through

several investigations. A study of 2529 SuperSchmidt meteor trails obtained during the

period from February 1952 through July 1954

has been made by McCrosky and Posen (1961).

Of the meteors photographed during this period,

2181 were reduced by an approximate, graphical

method to yield radiants, velocities, and orbits.

A stream search based on conventional methods revealed seven new photographic showers

(McCrosky and Posen, 1959). Three of the

minor showers found by McCrosky and Posen

also appear as separate showers in our data

TABLE 3.—Comparison with new streams detected by McCrosky and Posen

Strean

42

48

86

90

Rema

The Q

The u

In the

1

r k s

Vir,

P e g

corr

aVirj

« Peg

Coma

EGen

ginids

asids

ipilati

Nair

jinid.

asidi

. Ber

ninid

a r e

a r e

on of

l e

i (Ms

1

enici

s

inclu

ident

tabl

i y )

e d s

d e d

ical

e 3,

P r

inou

with .

only

-

1

-

2

r cr-Leonid

our a Pegai

meteors co

N

stri

sids

rnrr

e w

.

3

2

2_

7

i a r

•• ( t

l o r

n (t.

a b h

i to

able

> 4).

t h e

T c

4 ) .

s u r

>tal l

stre

-

4

2

2

9

v e y

Pre-

-

-

1

z.

1

of McCrosky a

c t e

,nd

•d by

Posi

:h

1918

»n and our

ey have bee

(Table 3). Another stream listed by these authors, the a Virginid, is included in the cr-Leonid

stream found by Southworth and Hawkins and

discussed below. Hence, of the seven showers

found by McCrosky and Posen, four also appear

in our smaller data sample.

Very little information is available on the recurrent nature of these minor streams. In one

case (fi Pegasids), all four members of the

stream were observed on two consecutive nights

in the same year. Hence, some caution should

perhaps be exercised in considering these minor

streams as regular, recurrent phenomena.

COMPARISON WITH STREAM SEARCH OF SOUTHWORTH AND HAWKINS.—Southworth and Hawkins (1963) list 24 previously unknown meteor

streams. Since their entire sample of 360

meteors is included in our data, it is of interest

to compare the results of the two surveys.

Of the 24 possible new streams found by

Southworth and Hawkins, 16 appear as separate streams in our search. These streams are

listed in Table 4, together with the shower

names proposed by Southworth and Hawkins.

It should be noted that changes in the membership of these streams are very frequent. In a

few cases, these changes shift the position of the

radiant by several degrees. It would therefore

perhaps be appropriate to rename a few of

these streams. In order to avoid confusion in

the nomenclature, however, we have refrained

from changing the original designations listed

in Table 4.

Table 4 includes three showers that appear

in the stream search of McCrosky and Posen,

and are therefore listed in Table 3 as well: the

e-Geminid stream bears the same name in both

lists, the fi Pegasids of McCrosky and Posen

are associated with our a Pegasids, and their

a Virginids are included in our <r Leonids.

The inclusion of additional data in a second

stream search may result in new stream members being detected in either of the following

two ways: (1) a meteor orbit not previously

studied may be classified as a shower member,

and (2) a meteor orbit previously studied and

rejected may be accepted in the second search

because of the inclusion of new members in the

shower. It is interesting to note that the second

method of acquisition at Ds=0.15 has operated
NUMBER 12

TABLE 4.—Possible new streams detected by Southworth and

Hawkins and found in present search

Stream

3

15

19

20

21

29

32

42

48

54

60

66

67

75

77

90

*Of the

Cyclic

p Gerr

H Oph

X Gen

| Ori

4- Urs

e Oph

a Peg

u Urs

6 Her

T Her

<t> Boo

Y Boo

)JL Dra

EGen

Total

new me

Pre

Name mer

Is

linids

Luchids

ninids

onids

:ae Majorids

iuchids

nids

asids

ae Majorids

culids

culids

tids

tids

conids (June)

linids

mbers one is from

5

4

2

1

3

2

5

10

3

2

1

1

2

2

3

3

49

the s

New

1

2

1

2

2

1

17

1

3

1

7*

.

1

-

39

mailer sample

Total no.

in stream

at Ds = 0. 15

6

6

3

3

3

4

6

27

4

5

2

8

2

3

3

_J5

88

used by Southvs

Pr

rej

No.

-

1

3

-

-

-

17

6

1

2

1

1

-

3

_ ;

35

f

orth and

ected by stream

search

8294

6069 6098 6102

4012 6376 6458

6460 6484 6784

6803 6826 6885

6929 6992 7033

7056 12690 12752

10168 10193

4432 4627 4842

8828 8844 9208

7661

8510 8699

7920

12462

3346 7790 12592

Hawkins.

in the case of only one meteor shower, the

T Herculid, where it added one new member

to the stream.

Southworth and Hawkins estimated that

about half their newly found streams were

spurious associations. It is convenient to divide

the 24 new streams listed in Table 2 of their

study (1963, pp. 268-272) into two groups

according to the number of meteors in each

stream. Of their new streams with 4 members

or more, all 7 are verified by the present survey.

In their shower list there are 7 streams with 3

members and 10 streams with 2 members. Of

these minor streams, 6 of the former and 3 of

the latter were detected in the present survey

as well. Thus, approximately half their minor

streams do not appear in the new search.

Hence, with admittedly some simplification of

the argument, we regard these streams as

unverified. The disappearance of these minor

streams is nearly always the result of a reclassification of the individual members as sporadic

meteors.

The largest stream found by Southworth and

Hawkins, and in the present study, is the

o--Leonid stream. In our data the activity of this

shower extends from 18 March to 14 June and

the stream consists of 27 members, of which 21

show a value of D(M, N) larger than 0.15, i.e.,

larger than the adopted value of Ds. The mean

value of D(M, N) is 0.275. Inspection of Tables

4 and 6 reveals that the new stream search has

drastically altered the membership list of this

shower. It has also shifted the radiant by more

than 20°, placing it in the constellation of Virgo

instead of Leo. In view of these facts, we agree

with Southworth and Hawkins that it is necessary to consider this shower a composite one.

The correct interpretation of this stream must

await further stream search in a much larger

sample of precise orbits.

The next largest stream appearing in Table 4

is the T Herculid, with 8 members. Its activity

extends from 1 to 24 June and there is no pronounced date of maximum activity. Only 3

members show a value of D(M, N) larger than

0.15, while the mean value of D(M, N) is 0.128.

The degree of orbit similarity within this

stream resembles that found in such wellrecognized showers as the Northern 8 Aquarids

and K Cygnids.

NEW STREAMS FOUND IN PRESENT SEARCH.—
8 SMITHSONIAN CONTRIBUTIONS TO ASTROPHYSICS

Summing up, the present study revealed 19

previously recognized meteor showers detected

by conventional stream-identification techniques

(Table 1), as well as 17 new minor showers

discovered by McCrosky and Posen and by

South worth and Hawkins (Tables 3 and 4).

In addition, our search produced 42 new

minor photographic "showers" each with from

2 to 7 members. Of these new streams, however,

37 have only 2 or 3 members each. In accordance

with our previous findings, we now reject new

streams with only 2 or 3 members on the belief

that there is at least a 50-percent probability

that they are spurious groupings in the data.

Accordingly, we list in Table 5 as new photographic showers discovered by our search only

those streams that have 4 or more members.

The new photographic streams found by us

have been compared with various lists of meteor

radiants published by visual observers. The A

Virginids are identical with the a Virginids of

Mclntosh (1935), while the e Piscids appear to

be related to the Piscid shower listed by Denning (1899) and Hoffmeister (1948). The 0

Librids are identical with x Scorpiids listed by

Mclntosh. The a-Virginid shower is a very

prominent one in the radiant list of Mclntosh

(1935). It is interesting to note that several

of our rejected two- or three-member streams

have radiants that appear to be related to the

TABLE 5.—Possible new streams detected by present search

Na of str

Solar longitude

(I960) K R (km/sec)

K Aquarids 18Sept-12Oct 175"-19H°

X. Virginids 2 3 March-22 Apr il 2 - 31

8 Librids 23 May-7 June 61 - 76

£ Piscids 2-12 Oct 188 -198

6 Cetids 27 Sept-12 Nov 183 -229

341 - 3

208 -14

238 -14

1 5 7

TABLE 6.—Orbital elements of new photographic streams (equinox 1950.0)

Stream

3

10

15

16

17

25

29

32

38

42

48

54

66

Ns

Cyclidf

K Aqua

p Gerni

X Virgi

8 Libri

C Pise

+ Ursa.

6 Ophii

6 Cetid

a Pegat

•me

i

rids

nids

nids

ds

ids

e Major

jchids

ids

lids

u Ursae Major

T Hereulids

ids

ids

Duration of stream

10 Apr. -19 Oct.

18 Sept. -12 Oct.

15-27 Jan.

23 March-22 Apr.

23 May-7 June

2-12 Oct.

27 Feb. -21 Apr.

21 May-16 June

27 Sept. -12 Nov.

18 March-14 June

11-12 Nov.

21 May-5 June

1-24 June

a

1. 01

2. 94

2.66

2. 32

2. 63

2. 19

1. 84

2. 67

1. 67

2. 56

3. 29

2. 93

2. 90

e

0. 087

0.705

0. 710

0.861

0. 713

0. 749

0.489

0.839

0. 528

0. 683

0.697

0.653

0.660

i

. ' 9

2. 1

3. 5

2. 8

3. 3

0. 7

8 . 0

4. 4

5. 5

3. 1

7. 5

16. 7

20. 7

«

83°0

229.2

243. 4

119.4

249. 1

274. 0

212. 1

108. 7

68. 2

239.7

199. 0

170. 5

203. 6

52°

185.

301.

196.

70.

194.

6.

257.

27.

31.

229.

66.

80.

1

9

4

8

5

8

5

0

7

8

6

3

8

135.M

55. 1

184. 8

316.2

319. 6

108. 8

218. 6

5. 7

95. 9

271. 5

68. 6

236. 8

284. 4

Q R

61°

341

110

208

238

15

162

265

21

195

344

174

236

6 R

28°

- 3

29

- 1 4

- 1 4

7

43

- 2 7

- 5

1

22

67

41

Harvard sc

4084

12440

1514

0815

6286

1937

7333

2863

4728

8974

1920

3327

7895

4659

4952

4432

1988

12193

•rial n

7199

4624

6179

3210 7073

10384 10439

7744

4774

9030

6927

7726

7899

4996

7788

8800

0

7326

4679

6245

71 14

12342

8888

7179 10173

7808

5047

1068 3246 3303

6915 6971 7040

7067 7135 7158

7218 7240 7303

7372 7388 7480

7514 7520 7664

7750 11825 11856

5370

3307

7767

2024

7820

5373

3312

3346

7882

5375

3344

7871

9323

4111

7056

7184

7324

7494

7734

5396

7745

4103 4125

12399 12711
NUMBER 12

a-Virginid radiant. The e-Piscid stream is

described by Denning as a very well-defined

shower chiefly active in September and October.

ORBITAL ELEMENTS OP NEW STREAMS.—The

mean orbital elements of all new photographic

meteor showers with four or more members

are summarized in Table 6. The table includes

revised orbital elements of the eight showers

detected by Southworth and Hawkins and verified by the present search, as well as the five

additional showers detected by us.

For a meteor stream of small inclination, a

large dispersion in i will result in meteors being

observed simultaneously at both ascending and

descending nodes. The stream members thus fall

into two groups, the line of nodes differing by

180°. In the computation of the mean orbital

elements for such a stream (Table 6), negative

inclinations are introduced for one group, and

fl and o) are changed by 180°.

NUMBER OP METEORS IN STREAMS.—Inspection of Tables 1, 3, 4, and 5 shows that a total

of 378 meteors in 41 showers were classified by

us as stream meteors. Of an additional 82

meteors in 37 minor streams with only 2 or 3

members, it is estimated that about half may

be real stream meteors. It is hence concluded

that very nearly 45 percent of the meteor orbits

could definitely be classed as streams, while a

further 5 percent could probably be classed as

members of minor streams. Thus at the rejection level Ds=0.15, very nearly half the meteor

population is composed of streams.

Relation between D(M,N) and orbital energy

After a meteor particle has been ejected from a

parent comet, a number of perturbing forces

act on it. These forces, both gravitational and

nongravitational, will over a period of time

produce substantial changes in the initial orbit.

The cometary debris is thus dispersed into a

series of orbits that exhibit a smaller or larger

degree of similarity. This group of orbits we

call a meteor stream, and the degree of similarity or dispersion is measured by the D-criterion.

During stream dispersion, the orbital energy

of the various individual stream members will

be changed. The orbital energy of an elliptical

orbit is given by the quantity—I/a, where a is

the semimajor axis. As a convenient measure

of the scatter of orbital energy within a meteor

stream, we now introduce the standard deviation of I/a computed for all orbits belonging to

the stream. This quantity may be used as an index of stream dispersion without making any

assumptions as to the nature of the dispersing

forces.

The standard deviation of I/a was computed

for all streams detected by the search at

Ds = 0.15. In Figure 1A we have plotted ar (I/a)

against mean D(M, N) for the 10 major

showers with more than 9 members in our

sample (Table 1). The corresponding quantities

are plotted in Figure 1B for all streams with 4

or more members (Tables 1, 3, 4, and 5). As a

fiducial point, the corresponding quantities for

the Draconid shower are also included in the

diagrams. A high correlation between the two

measures of orbital scatter is evident. Since

the D-criterion does not directly include the

semimajor axis, this correlation is very encouraging. The evidence produced in the present

investigation thus confirms that the D-criterion

is a very useful measure of the amount of perturbation that will transform one orbit into

another.

Velocity-elongation diagram

The mean geocentric velocity and the mean

apparent elongation of the radiant from the

earth's apex were computed for all streams

detected in our search. Datum points for the

previously known photographic showers listed

in Tables 1 and 3 are plotted in the velocityelongation diagram (Figure 2). The continuous

curve in the diagram represents the theoretical

relation between geocentric velocity and elongation assuming parabolic velocity at the earth's

perihelion. Inspection of Figure 2 will show that

comparatively few datum points appear in the

lower right-hand part of the diagram. These

points are all fairly near the parabolic curve.

They represent meteor streams that are moving

in retrograde orbits and whose members thus

make head-on collisions with the earth's

atmosphere.

The majority of meteor streams in the diagram cluster along a curve, which branches off
10 SMITHSONIAN CONTRIBUTIONS TO ASTROPHYSICS

0.15

0.00 0.05 0.10 0.15

MEAN VALUE OF D

0.20 0.25

FIGURE 1.—Scatter of

orbital energy vs mean

D(M^N): A, major

photographic meteor

streams; B, all photographic streams with

four or more members.

FIGURE 2.—Velocityelongation diagram for

previously known

photographic streams.

X

140

120

1OO

80

60

40

20

•

> —i 1

§ 1 1 1 1

PREVIOUSLY KNOWN STREAMS

\ •

\

10 30 40 SO 6 0

GEOCENTRIC VELOCITY (ka/sac)

70 80 VG
NUMBER 12 11

FIGURE 3.—Velocity-elongation diagram for new photographic streams.

20 30 40 SO 60

GEOCENTRIC VELOCITY (IM/MC )

70

FIGURE 4.—Velocity-elongation diagram for the meteor associations of Jacchia and Whipple.

30 4 0 50 60

GEOCENTRIC VELOCITY Ikai/stc)

70
12 SMITHSONIAN CONTRIBUTIONS TO ASTROPHYSICS

from the parabolic limiting curve at approximately A=60° and is displaced by about 5

km/sec with respect to the curve. It is evident

from considerations of the geometry involved

that members of the meteor streams plotted in

the upper left-hand part of the diagrams are

moving in direct, low-inclination orbits. These

meteors are approaching the earth from the

anti-apex direction and are catching up with

us at relatively low velocities.

The velocity-elongation diagram for streams

listed in Tables 4 and 5 is shown in Figure 3,

from which it is apparent that the new streams

detected by the two computer searches are, with

only one exception, all of the low-inclination,

low-velocity type mentioned above. Meteors belonging to these showers are obviously more

difficult to observe, since only fairly large

meteor masses will produce sufficient luminosity

to be detected. Their shower identification is

also difficult to establish, since the low geocentric velocity implies a diffuse radiant. It is

therefore not surprising that these streams do

not generally show up in the radiant lists of

visual observers.

Meteor associations

Jacchia and Whipple (1961) attempted to classify into a number of groupings, or associations,

meteor orbits not belonging to a recognized

stream. The classification was based on orbital

similarity. Of the 552 meteor orbits common to

our study and that of Jacchia and Whipple, 161

were arranged in groupings or associations. A

comparison of these associations with the unidentified streams in our search reveals five cases

where the streams and associations have identical members and an additional five cases where

an entire association (of Jacchia and Whipple)

is included in one of our minor streams. These

identifications, however, mainly involve streams

and associations with only two or three members. Too much weight should therefore not

be attached to them.

Although good agreement between the associations of Jacchia and Whipple and the minor

streams of the computer search occurs in only

a few cases, the statistical properties of these

two groups are very similar. In the velocityelongation diagram (Figure 4), we have plotted

datum points for all the associations listed by

Jacchia and Whipple and having three or more

members in our sample. A comparison of Figures 3 and 4 clearly shows that the new streams

found by either principle of classification have

a tendency to cluster in the upper left-hand part

of the velocity-elongation diagram.

Acknowledgments

This investigation was carried out mainly during two visits to the Harvard College Observatory and Smithsonian Astrophysical Observatory in 1963 and 1965. For the investigations,

Drs. G. S. Hawkins, L. G. Jacchia, and R. B.

Southworth very kindly placed at my disposal

complete card sets of their meteor data. Their

constant help and advice are gratefully acknowledged. The assistance of Mrs. S. Rosenthal has

been invaluable in the reduction work.

This work has been supported in part by the

National Aeronautics and Space Administration

under contract NSR 09-015-033 to the Smithsonian Astrophysical Observatory and contract

NASr-158 to the Harvard College Observatory

and by the National Science Foundation under

grants G20135 and G388 to the Harvard College

Observatory.

References

Denning, W. F.

1899. General Catalogue of the Radiant Points of

Meteoric Showers and of Fireballs and Shooting

Stars Observed at More Than One Station.

Memoirs of the Royal Astronomical Society of

London, 53: 203-292

Hawkins, G. S., and R. B. Southworth

1958. The Statistics of Meteors in the Earth's Atmosphere. Smithsonian Contributions to Astrophysics, 2 (11) : 349-364.

1961. Orbital Elements of Meteors. Smithsonian

Contributions to Astrophysics, 4 (3): 85-95.

Hawkins, G. S., R. B. Southworth, and F. Stienon

1959. Recovery of the Andromedids. Astronomical

Journal, 64 (5) : 183-188.

Hoffmeister, C.

1948. Meteorstrome. Leipzig, Verlag Johann Ambrosius Barth.
NUMBER 12 13

Jacchia, L. G., and F. L. Whipple

1961. Precision Orbits of 413 Photographic Meteors.

Smithsonian Contributions to Astrophysics, 4

(4) : 97-129.

McCrosky, R. E., and A. Posen

1959. New Photographic Meteor Showers. Astronomical Journal, 64 (1) : 25-27.

1961. Orbital Elements of Photographic Meteors.

Smithsonian Contributions to Astrophysics, 4

(2) : 15-84.

Mclntosh, R. A.

1935. An Index to Southern Meteor Showers. Monthly Notices of the Royal Astronomical Society,

95 (8): 709-718.

Southworth, R. B., and G. S. Hawkins

1963. Statistics of Meteor Streams. Smithsonian

Contributions to Astrophysics, 7: 261-285.

Whipple, F. L.

1938. Photographic Meteor Studies I. Proceedings

of the American Philosophical Society, 79 (4) :

499-548.

1954. Photographic Meteor Orbits and Their Distribution in Space. Astronomical Journal, 59

(6): 201-217.

Wright, F. W., L. G. Jacchia, and F. L. Whipple

1957. Photographic i-Aquarid Meteors and Evidence

for the Northern 8 Aquarids. Astronomical

Journal, 62 (7) : 225-233.

Wright, F. W., and F. L. Whipple

1950. The Photographic Taurid Meteors. Technical

Report 6, Harvard Reprint Series, n-35, 44

pages.

Abstract

A search for meteor streams was made among 865 precise photographic meteor orbits

collected in the Harvard Meteor Program. An automatic computer program was

utilized. In all, 80 meteor streams were detected. Of these, 21 represent 19 previously

known, well-studied photographic meteor showers and 17 represent new meteor streams

found by McCrosky and Posen and by Southworth and Hawkins. Five previously unstudied photographic streams with four or more members were discovered. Of these,

three were identified with streams reported by visual observers.

Of the remaining streams, 8 have 3 members and 29 have only 2 members. About

half the 2- and 3-member streams are believed to be spurious. A comparison of these

streams with the meteor associations of Jacchia and Whipple indicate similar statistical

properties, but few individual agreements are noticed.
Bertil-Anders Lindblad 2. A

Stream Search

Among 2401

Photographic

Meteor Orbits

Introduction

The existence of a large number of weak meteor

showers has been inferred by several observers

from their numerous visual observations. Until

recently, the photographic meteor data have not

been sufficient to confirm or to refute these

observations. The large samples now available

of meteor orbits determined from photographic

or radio data make a renewed study of the

minor streams desirable.

New criteria for the definition of a meteor

stream and computer techniques for meteorstream detection have recently been proposed

by South worth and Hawkins (1963) and by

Southworth (1968). Successful application of

these techniques to radio meteor orbits has been

reported by Hawkins, Southworth, and Rosenthai (1964), Elford, Hawkins, and Southworth

(1964), and Forti (1968), and to photographic

meteor orbits by Southworth and Hawkins

(1963) and Lindblad (1970).

PREVIOUS STUDY.—Lindblad (1970) used the

computer stream-detection technique in the

analysis of a sample of 865 precisely reduced

photographic orbits collected in the Harvard

Meteor Program. The technique successfully

detected and sorted out all the previously known

Bertil-Anders Lindblad, Lund Observatory, Lund,

Sweden.

14

photographic meteor streams for which more

than one member was available in the sample.

In addition, eight new meteor streams of more

than four members were delineated. All these

new streams were of low geocentric velocity

and low inclination.

Present investigation

McCrosky and Posen (1961) have given fundamental data for 2529 photographic meteors recorded by the Baker Super-Schmidt cameras of

the Harvard Meteor Program. The sample studied constituted about 70 percent of all meteors

photographed from February 1953 to July 1954.

It is the largest sample of photographic meteor

orbits hitherto available and thus provides valuable material for a study of meteor streams. Of

the meteors studied, 2059 were reduced by the

graphical method (McCrosky, 1957). The sample included 355 meteor orbits reduced by Jacchia by a more accurate technique, as well as

115 meteors without orbital information.

PREVIOUS SEARCHES IN THE SAMPLE.—McCrosky and Posen (1961) identified and listed

a number of meteors belonging to the familiar

major showers. In an earlier study of essentially

the same data, McCrosky and Posen (1959) had

compared radiants, velocities, and dates and
NUMBER 12 15

found seven new minor photographic streams.

Of these, only two could be identified with previously known visual meteor streams. Since a

stream search using classical methods of classification is very laborious, no exhaustive search

was made in the McCrosky and Posen sample.

Subsequently, Terent'eva (1965,1968) analyzed

a very large collection of photographic data,

including those from the McCrosky and Posen

sample.

PURPOSE OF PRESENT SEARCH.—Using the Dcriterion for stream membership (Southworth

and Hawkins, 1963), the present study concerns

an exhaustive search among the orbits given by

McCrosky and Posen. It differs from the previous stream search by Lindblad (pages 1-13)

in that the data sample is larger but, at the

same time, the errors in the orbital elements are

larger. The errors in velocities and radiants,

nevertheless are smaller than those obtained in

visual meteor programs. Therefore, we felt that

a stream search in the McCrosky and Posen

sample would supply valuable new information

about minor meteor streams and thus provide

students with an up-to-date list of minor meteor

streams and their orbits. If most of the more

prominent showers reported by visual observers

could be detected in the photographic data, the

accuracy of the older visual data would be

confirmed.

DATA PREPARATION.—Of the 2529 meteors

listed by McCrosky and Posen, 115 were

omitted, since no orbital information was available. An additional 13 meteors with orbital

eccentricities e>2.0 were also rejected. The

sample under study thus consisted of 2401

meteors whose orbital elements were available

on cards, together with the shower classification originally proposed by the authors. In the

preparation of the input for the computer

stream search, the cards were sorted in order

of increasing inclination. Inclinations t=90°.0

were not accepted by the program and were

therefore altered to i=89°.9. No other modifications were made in the original data.

D-criterion for stream membership

The computer stream-detection technique of

Southworth and Hawkins (1963) is based on

the intercomparison of different sets of orbital

elements. In the search, each meteor orbit in a

sample is compared with all others in the sample

to find groups of similar orbits. This approach

is particlarly useful for detecting minor streams

since only a few orbits are necessary for

delineating a stream.

The use of a computer has two advantages:

a large collection of data can be handled, and

the search is objective. But the rejection level

Ds must be set by the investigator, and firm

rules must be laid down for this choice.

DETERMINATION OF REJECTION LEVEL DS.—

Southworth and Hawkins (1963) proposed that

the rejection level Ds should vary inversely with

the fourth root of sample size. For a sample of

360 precise photographic orbits, they used

Ds=0.20. If N is sample size, we therefore have

Ds=0.20x

/360\*

VNT/ ' (1)

Equation (1) has been tested by the present

author on several data samples of precise photographic orbits. In general, agreement with conventional shower classification is good if Ds

 is

assigned a value slightly lower than that given

by equation (1). The following approximate

rule may be recommended:

Z)s=0.80xAf~%- (2)

It may be necessary to use a somewhat smaller

value of Ds if the orbital data have appreciable

observational or reductional errors.

For AT=2401, equation (1) gives D,=0.125,

while equation (2) gives D,=0.114. In a first

test run of the McCrosky and Posen sample,

£>s=0.12 was used. It was found, however, that

at this rejection level several low-inclination

meteor streams were not clearly separated. A

new search at Ds-0.115 gave the desired separation for most of these streams, and this

value was therefore adopted.

Discussion of stream search

The sample of orbits was divided by the search

at Z>,=0.115 into 1049 stream meteors and 1352

sporadic meteors. Thus, 43 percent of the meteor

population was in streams. The percentage of

stream meteors and associations, as defined by
16 SMITHSONIAN CONTRIBUTIONS TO ASTROPHYSICS

TABLE la.—Durations, radiants, and geocentric velocities

of previously known photographic meteor streams

Provisional

42

52

60

110

61

62

76

78

92

105

108

122

109

171

186

196

2 02

216

217

220

221

223

228

230

231

Stream name

Northern 6 Arietids

Southern Virginids

Southern i Aquarids

Southern i Aquarids

Southern Taurids

Northern Taurids

Northern Virginids

Northern x Orionids

Northern I Aquarids

Piscids

Pegasids

a Capricornids

a Capricornids

Southern x Orionids

Northern 6 Aquarids

Geminids

Southern 6 Aquarids

Draconids

Quadrantids

Lyrids

Hyperbolic Perseids

Perseids

a Hydrids

Orionids

Hyperbolic Orionids

E Geminids

Duration

Dec 8-Jan 2

March 12-27

July 1 9-Aug 6

Aug 5-22

Sept 19-Nov 21

Feb 18-March 12

Dec 4—13

Aug 21-Sept 20

Aug 31-Nov 2

Oct 29-Nov 12

July 15-Aug 10

Aug 4-9

Dec 7-14

Aug 5-25

Dec 4-16

July 21-Aug 8

Oct 9

Jan 2-3

April 21-22

Aug 9-13

Aug 8-15

Dec 13-15

Oct 16-Nov 7

Oct 14-29

Oct 16-27

QR

54

185

320

348

40

173

83

354

10

344

3 04

317

85

347

1 11

340

2 76

229

271

-

46

129

95

-

102

6 R

25

- 2

-15

- 1 0

13

5

26

1

6

19

- 1 0

- 7

16

1

32

-16

49

49

34

-

57

1

16

-

27

VG

17

28

35

41

31

36

28

31

27

16

25

28

28

40

37

43

21

42

47

-

60

59

67

-

70

conventional methods of classification based on

geocentric quantities, is normally about 50 percent. Previous computer stream search have

given very nearly the same percentage (Lindblad, 1970). The lower stream contribution

found here is probably due to the larger errors

in the orbital elements.

The number of streams at Ds=0.115 was 198.

In an endeavor to present the data in some

orderly fashion, we shall first list streams previously detected by conventional techniques and

then those previously detected by other computer searches, and finally, several new streams

that have been identified with visual streams.

Several new comet-meteor associations will also

be presented.

PREVIOUSLY KNOWN PHOTOGRAPHIC STREAMS.

—Tables la and lb present radiants and orbits

of 21 previously known photographic meteor

streams detected in the search. The mean orbital

elements do not differ appreciably from those

published in other lists of meteor stream orbits

determined by the Harvard Meteor Program

(McCrosky and Posen, 1959; Jacchia, 1963). It

follows that orbital data obtained by the graphical reduction procedure of McCrosky and Posen

are sufficiently accurate for use in a computer

stream search.

It should be observed that the mean radiant

and geocentric velocity listed by the computer

program are obtained directly from the mean

orbit of the stream. These quantities may therefore differ slightly from those obtained by averaging of individual meteor data.

The showers listed in Tables la and lb may be

regarded as well confirmed. They have been
NUMBER 12 17

TABLE lb.—Orbital elements of previously known photographic streams

Northern 6 Arietids

52

60

110

61

So uthern

Southern

So

Nc

uthe rn

uthe rn

irtherr

Virgi:

i Aqu

I Aqu

Tauri

i Taur:

nid

a ri

a ri

ds

ids

s

d

d

0. 857

0.431

0. 266

0. 119

0. 330

2. 420

2. 027

3. 967

3. 662

1. 991

0.634

0. 783

0. 925

0. 959

0. 828

2*1

0. 3

0. 0

12.6

3. 3

228.0 262.6

287. 0

121 5

143. 9

118. 8

356. 4

304. 0

321. 8

28. 7

130.6

283.4

65. 5

105.7

147. 5

5527 5552 5573 5752 5772 5878 5953 5970

6023 9438 9486 9498 9841 9895

6786 6816 10353

3355 3406 3407 8235

3619 3658 3784 8178 8318 8410 8483 8624

4455

4732

4866

4999

5176

5347

5429

8855

9004

9104

92 38

9314

4498 4507

4747 4754

4883 4891

5003 5019

5180 5195

5353 5371

5499 5511

8886 8945

9015 9016

9121 9150

9240 9246

9328 9331

4546 4556

4764 4819

4907 4912

5022 5074

5244 5257

5380 5388

8796 8803

8954 8956

9037 9041

9158 9182

4574

4830

4928

5115

5298

5417

8811

8971

9063

9185

926 5

4666 4701

4832 4862

4966 4975

5124 5147

5341 5346

5419 5425

8836 8849

8990 8998

9074 9077

9210 9216

62

76

78

92

No

No

No

Pi i

rthern

rthe rn

rthern

Jcids

V

X

t

irgi

O ri

Aqu

nids

onids

arids

0. 234

0. 472

0. 326

0. 525

2.

2

2.

2.

637

220

000

864

0.

0.

0.

0.

912

787

830

808

3. 5 308. 0 333. 8

2. 5 281. 0 258. 3

4. 0 299. 7 161. 4

1, 5 273.6 190. 1

281.8

179. 3

101. 1

103. 7

6496 6798 10200 12237

5620 5886 9400 9674

3663 3886 4516

3864 4369 4391 4476 4478 4505 4520 4531

4544 4582 4605 4684 4728 4767 4774 4839

4967 4977 4987 5064 8767 8777 8790 8800

8830 8832 8838 8872 8899 8922 8930 9030

9134

105

108

122

1 0 9

171

186

Pegasids

a Capric

a Capric

Southern

Nor the rr.

Geminid!

ornids

ornids

X Orionids

i 6 Aquarids

i

0. 966

0. 592

0.497

0.471

0. 085

0. 140

3. 512

2. 524

2. 573

2. 387

2. 102

1. 466

0. 718

0.760

0. 807

0.790

0.956

0. 902

6. 8

7. 1

8. 7

6. 9

20. 7

23. 2

200. 2

267.9

279. 0

100. 6

330.8

324.2

227. 0

125. 4

133. 4

79. 1

140. 5

260. 2

67.2

33. 3

52. 4

179. 7

111.3

224.4

5367

3379

3411

8334

8146

5529

3573

8610

5533

5624

5673

5711

5785

5891

5926

5991

9451

9725

5370

3382

3416

8668

8147

5537

3574

5543

5637

5677

5714

5789

5893

5928

6 005

9454

9742

5373

3385

8026

8368

5795

3610

5 566

5640

5681

5720

5797

5897

5933

6 021

9510

9749

5396

3386

8063

9416

4219

5581

5644

5683

5729

5814

5899

5939

8645

9547

9771

9107

3387

8148

9488

8168

5601

5648

5690

5734

5817

5901

5946

9390

9611

11401

3405

8149

966!

8210

5605

5655

5701

5759

5824

591 1

5152

9418

96 56

3408

822 5

9745

8371

5614

5659

5705

5764

5862

5917

5964

9421

9709

34 10

8304

1677

844 1

56 18

566 7

5709

5777

5868

5922

5980

9425

9719

196 Southern 6 Aquarids

202 Draconids

216 Quadrantids

217 Lyrids

220 Hyperbolic Perseids

221 Perseids

223 <r Hydrids

228 Orionids

230 Hyperbolic Orionids

0. 999

0.974

0. 879

0.958

3. 330

2.612

25. 812

-30. 601

0. 700

0.618

0. 956

1. 065

25. 0

72. 4

177. 0

170. 5

196. 0

282. 8

0.

0.

2 3 0

5 7 0

1 1 .

16.

525

7 2 0

0.

0.

9 8 0

931

78.6 217.2 31.6

113. 0 153. 4 138. 6

113.2 147 9 138.7

125. 0 124 0 82. 0

163.9 83 4 29.2

164. 1 75. 0 28. 0

13. 0

93. 3

248. 8

292. 0

206. 0

1 12. 6

3360 3399 3421 3424 3447 3450 3463 3472

3487 8187 8238 8254 8344

9902 9907 9928 9942 9945 9946 9952 9954

9962 9964 9966 9974 9975 9980 9983 9986

9988

3217 3218 3271 7444 7447

8374 8418 8431 8435 8437 8492 8494 8501

8516 8532 8536

8324 8330 8348 8383 8401 8420 8424 8444

8452 8463 8469 8496 8512 8518 8555 8567

8599 8658 8719 8726

5001 5006 5015 5023 5039 5076 5079 5083

5093 5101 5112 5119 5127 5129 5183 5185

5208 5210 5282 9090 9097 9099 9258

4789 4811 4876 4922 4936 5013 5041

5097 5102 5140 5145 5153 5155 5157

5165 5196 5260 5327 9079

5095

5163

173. 0 236 7 207 5 4889 5063 5309 9082
18 SMITHSONIAN CONTRIBUTIONS TO ASTROPHYSICS

discussed in the literature and will therefore

only be briefly commented on here. It will be

seen that the Southern i Aquarids and a Capricornids are split into one July and one August

stream. The Perseids and the Orionids are

divided into an elliptical and a hyperbolic

branch. This division is obviously a spurious

result caused by the large errors in the graphical

reduction procedure. The Piscid stream (no. 92)

is included in Tables la and lb since it was

originally believed that this stream was related

to the Andromedids. The Andromedid stream

has recently been shown to be much more extensive than formerly believed (Hawkins, Southworth, and Stienon, 1959); however, the fairly

high geocentric velocity and early date of appearance of stream 92 preclude the possibility

of a relation to the Andromedids. Stream 92

includes all members of a previously detected

shower: the € Piscids (Lindblad, 1971).

A number of streams were split into a northern and a southern branch. This phenomenon

had previously been detected in the Harvard

data for the Taurids, t Aquarids, and 8 Aquarids. Our study indicates a similar splitting of

the x Orionids. In the case of the Virginid

stream the precision of the orbital data is not

sufficient to decide if the observed separation

into two branches is significant. The 8-Arietid

stream (McCrosky and Posen, 1959) also consists of a northern and a southern branch. Only

two members of the southern branch are present

in the McCrosky and Posen sample, however,

and the computer search incorporated these in

the northern branch. Of their 47 new meteor

associations, Jacchia and Whipple (1961) list

4 more cases of a northern and a southern

stream component. In the stream catalog of

TABLE 2a.—Durations, radiants, and geocentric velocities of streams detected in previous

computer searches (Southworth-Hawkins = Listed in "Statistics of Meteor Streams";

Lindblad 865 = Listed in "A Stream Search Among 865 Precise Photographic Meteor

Orbits")

Provisional

8

20

45

83

85

90

98

102

119

126

137

152

160

167

168

188

191

2 03

Stream name

<r Leonids

K Aquarids

^ Ophiuchids

Northern X. Virginids

Southern X Virginids

p Geminids

6 Ophiuchids

Southern x Geminids

X Scorpiids

8 Cetids

Northern x Geminids

u Ursae Majorids

v Ursae Majorids

9 Herculids

T Herculids

<|> Bootids

a Bootids

Y Bootids

Duration

March 21-May 13

Sept 11-28

Aug 10

April 4-15

May 5-6

Jan 15-23

June 4-16

Jan 23-Feb 7

May 27-June 20

Oct 19-21

Jan 19-21

May 7-June 5

April 10-13

Aug 6-9

May 19-June 14

April 16-May 12

April 14-May 12

April 13-15

a R

195

338

267

210

210

112

266

122

246

22

127

184

188

26 0

228

240

218

215

8 R

- 5

- 5

-14

- 1 0

- 1 8

31

- 2 8

13

-12

-11

34

47

59

30

40

51

19

36

V G

20

20

15

32

25

21

30

21

23

19

23

16

15

18

18

16

23

25

Identification

Southworth-Hawkins

Hoffmeister's Virginids

Mclntosh 103 (6 Virginids)

Lindblad 865-10

Denning 268

Mclntosh 299

Southworth-Hawkins

Mclntosh 182

Lindblad 865-16

Mclntosh 114

Lindblad 865-16

Southworth-Hawkins

Southworth-Hawkins

Mclntosh 184

Southworth-Hawkins

Lindblad 865-17 (6 Librids)

Mclntosh 147

Lindblad 865-38

Mclntosh 28?

Southworth-Hawkins

Southworth-Hawkins

Southworth-Hawkins

Southworth-Hawkins

Southworth-Hawkins

Comet 1930 VI

Southworth-Hawkins

Southworth-Hawkins

Denning 169?

Southworth-Hawkins
NUMBER 12 19

Terent'eva (1965, 1968), several more cases are

reported. In nearly all cases, we have to deal

with low-inclination orbits, in which there is a

shift of 180° in the argument of perihelion a>

and in the longitude of the ascending node ft

between the two branches, the radiants moving

nearly parallel to the ecliptic, one south of it

and the other north.

It should be mentioned that the computer

search failed to separate the northern and southern branches of the Taurid meteor stream. A

similar result was obtained in the previous

search of 865 orbits.

STREAMS DETECTED IN PREVIOUS SEARCHES.—

Tables 2a and 2b list 18 new photographic

meteor streams that first were detected in the

computer searches of Southworth and Hawkins

(1963) and Lindblad (1971) and now are confirmed in this study.

In the previous study of 865 orbits, 13 possible new photographic meteor streams were

listed in Table 6 (page 8). These were considered to be the most significant of the newly

detected streams. It is encouraging to note that

12 of these were also detected in this study

as separate streams (Table 2a). The single

exception was the e-Piscid stream, which, as

previously mentioned, was included in our Piscid stream (no. 92). Hardly any doubt can

therefore exist about the reality of the streams

listed in Tables 2a and 2b. A comparison with

the radiant lists of Denning (1899) and Mclntosh (1935) gave a number of identifications

with visually observed showers. These are listed

in Table 2a.

In the comparison, a critical attitude was

taken toward the radiants listed by Denning.

His belief in long-persisting stationary radiants

often led him to combine unrelated stream

radiants in an arbitrary way. Denning's radiants were therefore accepted only if on inspection of the radiant list a short, well-defined

period of stream activity was found. As an additional criterion, Denning's remarks as to the velocity classification (slow, fast) were compared,

when available, with the photographically

determined velocity.

On comparison of our new streams with the

previous computer search listings, it was found

that the mean radiant had sometimes shifted by

TABLE 2b.—Orbital elements of streams previously detected by computer searches

N o .

8

2 0

4 5

83

85

9 0

98

102

119

126

137

152

1 6 0

167

168

1 8 8

191

2 0 3

S tr

.Leo ,

K Aqua

H Ophi

Northe

Southe

pGem

6 Ophi

Southe

earn name

a d s

rids

uchids

rn \ Virgin

rn V Virgin!

inids

uchids

rn x Gemin

X Scorpiids

0 Cetit

Northe

u Ursa

+ Ursa

0 Here

T Here

4> Boot

a Boot

Y Boot

Is

rn x Gemir

ie Majorids

ie Majorids

ulids

ulids

i d s

i d s

i d s

i d s

i d s

i d s

lids

q

0.753

0.814

0. 980

0. 343

0.686

0. 708

0.405

0.693

0.679

0.783

0. 595

0. 998

0. 984

1. 005

0. 970

0. 949

0. 753

0. 818

a

2. 349

3. 196

2. 420

2.630

6. 705

2. 197

2. 797

2. 390

3. 112

1. 760

1. 830

3. 893

1. 805

3. 113

2.695

1.248

2. 647

3. 790

e

0.663

0. 744

0. 595

0. 870

0. 895

0.673

0. 852

0. 710

0. 767

0. 555

0.675

0. 740

0.455

0.667

0.633

0.2 37

0. 706

0. 775

>

0. 7

1.8

2. 5

2. 0

3. 5

5. 0

4.7

4. 0

6.0

8. 5

9. 5

12. 3

14.0

16.7

18 6

19 3

18. 0

27.0

u

247.5

235.6

204. 5

295. 0

72.0

252.3

108. 0

72.0

256.7

67. 0

268. 5

186. 7

203. 0

194. 3

204.2

225. 8

246 9

235.5

a

28 2

178. 0

137. 0

19 5

224. 5

297. 7

258. 0

130. 5

73. 9

27. 0

300. 0

59. 3

21. 5

135. 0

71. 9

40. 5

36 2

24. 0

-

275.7

53.6

341.5

314. 5

296.5

190. 0

6.0

202.5

330.6

94. 0

2 08. 5

246. 0

224. 5

329. 3

276. 1

266 3

283. 1

259. 5

3015

7303

11190

4292

8394

7073

11912

6162

7726

6329

7754

12436

4918

626 0

7529

7179

8244

3335

12161

3212

3239

7261

3246

7336

11955

4432

8415

7333

11947

6179

7782

6393

7823

12478

4997

6296

7694

7265

836 3

4103

12355

7379

7291

7331

Ha i vmrd s

7058 7133

7356 7372

11976

4492

6338

78 08

4624

7899

erial no

7158

7480

4679

7924 10584 12138

12508 12517

7745

8369

7201

7520

7240 7287

7664 10406

12341 12368

4106 4108 4112 7692

12378 12398 12470

7485

7385

Till

7439

7651

7 506

11848

76 4 3

7820 12142

12513

11174 11863
20 SMITHSONIAN CONTRIBUTIONS TO ASTROPHYSICS

several degrees. This occurred particularly

among minor streams with only a few members

in the sample under study. In future discussions, a number of these streams should therefore be renamed. To simplify identification,

however, most of the provisional stream names

used in previous papers have been retained in

Tables 2a and 2b.

Again a number of streams are split by the

search into a northern and a southern branch.

In Table 2b, we note this for the A Virginids

and x Geminids. The existence of two A-Virginid

branches is, however, somewhat open to doubt

on account of the large differences in g and a.

An inspection of the argument of perihelion o>

and longitude of node ft of the individual stream

members shows that two branches also exist in

the ovLeonid and x-Scorpiid streams. The

southern branch of the x Scorpiids was identified with the visual w

2

-Scorpiid shower (Mclntosh no. 146), the northern branch, with the

visual x-Scorpiid shower (Mclntosh no. 147).

The largest new stream detected in previous

computer searches is a rather poorly defined

one radiating from Leo and Virgo during the

period February-May. This stream is often

referred to as the o- Leonid since Southworth

and Hawkins (1963) found a mean radiant

near a- Leonis. Although the computer search

did not distinguish between the two components, an inspection of the argument of perihelion of individual members showed that the

stream is composite, with one northern and one

southern branch. The northern branch, with

activity in March-May, has a mean radiant near

$ Virginis. The southern branch, with activity

in April and May, has a mean radiant near ^

Virginis. Activity in February and March from

a radiant near 8 Leonis (Table 3a) adds

additional complexity to the picture.

NEW PHOTOGRAPHIC STREAMS.—After identification of the well-confirmed photographic

streams (Tables 1 and 2), a large number of

previously unknown streams remained to be

studied. Of these, 108 had 2 members, and 43

had 3 members. We feel that about half of these

streams are chance associations. Unfortunately,

there is no way of concluding which streams are

spurious. We therefore rejected all except those

for which an identification with a well-studied

visual shower was immediately obvious. These

identifications are listed in Tables 3a and 3b.

A total of 18 streams that had 4 or more

members each and that were not already listed

in Tables 1 and 2 remained. Attempts to identify these possible new photographic streams

with previously observed visual streams by

Denning and Mclntosh were successful in some

cases. These identifications are listed in Tables

3a and 3b. Remaining nonidentified streams

have been rejected.

The photographic 5-Leonid stream is active

at the same time as the Leonid-Virginid stream.

The 8-Leonid radiant is identical with a prominent radiant of the same name in Denning's

catalog. Our photographic /i-Sagittarid stream

is identical with a major shower of the same

name listed by Mclntosh (1935). A study of the

orbit suggests an association with Comet Lexell.

The a Lyrids and £ Draconids are listed as

prominent showers by Denning. They are active

at the same time as the K Cygnids and are often

confused with this shower. An alternative interpretation of the two a-Scorpiid streams is to

consider them as southern branches of the

0-Ophiuchid stream (no. 123). In a similar way

the o Serpentids may be interpreted as a northern branch of the 6 Ophiuchids (no. 98).

In our search, the Cyclid stream was incorporated into a vast agglomerate of short-period,

low-inclination orbits (stream 1, with 61 members). Inspection of radiant coordinates and

orbital elements of individual members of this

stream revealed very large scatter. Stream 1

was therefore rejected. A subsequent substream

search at D = 0.10 produced a Cyclid stream

with 15 members, the orbital elements of which

are similar to those given by Southworth and

Hawkins (1963).

Hoffmeister'g ecliptical streams

Inspection of radiant catalogs published by

visual observers suggests a rather confused

grouping of radiants all along the ecliptic. An

attempt to systematize this picture has been

made by Hoffmeister (1948), who reported that

a major contribution to the meteor-stream complex came from a few short-period, low-inclination streams. These were referred to as the
NUMBER 12 21

"ecliptical streams." Hoffmeister listed six three, listed in Table 4, have not been previously

ecliptical streams, of which three, the 8-Aqua- recognized as photographic streams. A comrid, Taurid, and Geminid, are now well-estab- parison with our Tables 1-3 produced the poslished photographic streams. The remaining sible identifications listed in Table 4.

TABLE 3a.—Durations, radiants, and geocentric velocities

of new photographic streams

2 1

2 8

31

59

81

7 3

123

1 2 9

1 4 4

1 4 b

1 7 4

2 04

2 0 7

2 2 5

2 3 2

6 Leonic

6 Cancr

Piscids

Q Scorpi

a Scorpi

\J. Sagitt;

* Ophiu

a Trian;

K Virgir

o Se rpei

n Serpei

a Lyrid:

£ Dracc

Lyncids

£, Arieti

I s

i d s

i d s

i d s

iriids

chids

gulids

lids

itids

itids

S

,nids

id s

F e

J a i

S e ,

Ms

A p

J m

M a

N o

A p

J u i

J u i

A u

A u

b 5-March 19

113-21

Dt 25-Oct 19

ty 9-12

ril 1 1-May 5

ne 22-July 6

iy 3-8

v 7-12

ril 13-May 12

ne 9-2 5

ne 2 5-July 3

g 4-13

g 20-25

Sept 27-28

A u g 13-2 5

1 5 9

126

26

2 4 7

235

268

2 4 7

2 2

22 1

2 7 4

2 7 8

282

2b 9

1 1 0

4 9

1 9

2 0

14

- 2 4

- 2 1

- 1 5

- 1 8

3 0

- 5

- 1 1

- 2

4 2

5 9

4 8

14

23

2 3

2 9

3 5

3 4

2 3

3 8

2 1

2 9

3 0

2 5

2 3

2 4

66

71

Denning 120 or 129

Denning 100

Denning 17 (r| Arietids)

Mclntosh 157

Denning 190?

Mclntosh 173

Denning 204 (u Ophiucids)

Comet 1770 I

Mclntosh 160

Denning 20

Denning 166?

Mclntosh 178

Denning 2 04 (u Ophiucids)

Mclntosh 191

Denning 211

Denning 219

Denning 198

Denning 84?

Denning 154?

TABLE 3b.—Orbital elements of new photographic streams

2 8

31

59

81

7 3

1 2 3

1 2 9

1 4 4

1 4 6

1 7 4

2 0 4

2 07

2 2 5

2 32

6 Cai

Pise

a Sec

ncrids

i d s

>rpiids

a Scorpiids

fi Sag• ittariids

$ Ophiuchids

a Tr

l± Vii

o Se)

n Se

a Ly

I Di

Lync

C Ar

iangulids

rginids

rpentids

rpentids

rids

•aconids

i d s

ietids

0.448

0.399

0.212

0. 189

0.680

0. 133

0.784

0.477

0. 430

0.606

0. 958

1. 015

0. 770

0. 973

2.273

2. 062

2.235

2. 097

2. 862

2. 170

3.257

3. 116

2.895

2. 165

3. 437

2. 820

76.970

17. 905

0. 800

0. 797

0. 905

0. 893

0. 757

0. 937

0. 757

0. 831

0. 847

0. 715

0. 720

0. 640

0. 990

0. 945

0. 3

3 . 4

3. 5

2. 3

5. 5

10. 0

9. 7

9. 9

13. 0

15. 5

29. 7

33. 0

136. 5

172. 5

282.6

290. 8

132. 0

136. 7

257. 5

322. 0

238. 0

280. 0

284. 2

268. 5

207. 7

183. 5

152. 5

19. 5

2 % . 4

199.-1

229. 5

216. 3

95. 3

44. 0

227. 5

35. 0

85. 8

97. 0

134. 7

149. 5

184. 5

326. 0

219. 0

129.9

1. 5

353. 0

352. 8

6. 0

105. 5

315. 0

10. 0

5. 5

342. 4

333. 0

337. 0

345. 5

2982 4012 6391 6399 6440 6458 6460 6467

6484 6766 6776 6915 6918 6940 6971 6995

10164 10168 10193 10208 10270 10303

12690 12773

6069 6081 6176 6189 6254 6258 6292

4560 4793 4854 4856 4870 4938 8952 9025

9070

7610 12 089

7248 7474 11935

4147 4169 4175 7944

7575 11832 11903

5335 5339 5382 5392

3021 3250 7272 7348 7583 7622 12076

4143 4181 12541 12576

12713 12864

8143 8227 8476

3633 3813

4622 4683

3804 8526
22

SMITHSONIAN CONTRIBUTIONS TO ASTROPHYSICS

TABLE 4. Comparison of Hoffmeister's ecliptical streams and new photographic streams

Name

Virginids (Hoffmeister)

er Leonids (8)

Piscids (Hoffmeister)

Northern i Aquarids (78)

Piscids (31)

Sco-Sgr system (Hoffmeister)

6 Ophiuchids (98)

Duration of

stream

March 1-May 10

March 21-May 13

Aug 16-Oct 8

Aug 21-Sept 20

Sept 25-Oct 19

April 2 0-July 30

June 4-16

q

0.48

0.75

0.40

0. 33

0.40

0.47

0.41

a

1. 53

2. 35

1.43

2. 00

2. 06

1. 77

2.80

e

0. 69

0.66

0. 72

0. 83

0. 80

0. 73

0.85

i

If

0.

3.

4.

3.

6.

4.

9

7

5

0

4

0

7

286°

248

296

300

291

106

108

n

13°

28

169

161

199

263

258

•

299°

276

105

101

130

9

6

•

200°

195

0

354

26

2 7 0

266

6

- 6°

- 5

+ 4

+ 1

14

- 3 0

- 2 8

VG

2 0

31

29

30

The identity between Hoffmeister's Virginid

and our Leonid-Virginid stream is of particular

interest. Table 4 compares our mean LeonidVirginid orbit with the visual Virginid orbit

determined by Hoffmeister (1948). The radiant

at a = 195°, 8 = -5° differs but little from the

visual Virginid radiant reported by him. The

period of activity, 21 March-13 May, is also in

agreement with his data. Hoffmeister's orbit

was based on visual estimates of velocities. In

view of the uncertainties inherent in this

method, the discrepancies in q and a must be

regarded as not significant.

Hoffmeister's Scorpius-Sagittarius system

closely resembles our 0-Ophiuchid stream. Inspection of Table 4 shows good agreement in all

orbital elements. His Piscid stream is more difficult to identify. Our Northern i-Aquarid

stream probably is a September apparition of

the Piscids, while our Piscid stream 31 probably represents an October display of Hoffmeister's stream. Another possibility is that our

Piscid stream (no. 92) is identical with Hoffmeister's Piscids.

Comet-meteor associations

Hasegawa (1958) has published a general index

of the expected theoretical radiant points of

meteors associated with comets. A comparison

of our new meteor-stream radiants with the

theoretical radiants yielded several probable

associations. Orbital elements of meteor streams

and associated comets are compared in Table 5.

One new stream, the /u-Sagittariid, moves in an

orbit similar to that of Comet 1770 I (Lexell).

Since the comet orbit crosses the earth's

orbit twice, two meteor showers can occur, one

in June-July and one in December. The nearest

TABLE 5.—Comet-meteor associations found in McCrosky and Posen sample

Name

u Sagittariidi

Comet Lexell (1770 I)

T Herculid.

Schwassmann-Wachmann (3)

(1930 VI)

Monocerot.d.

Comet Mellish (1917 I)

; Arietids

Schmidt-Temple (1862 II)

Observed/

predicted

date

June 22-July 6

July 5

May 19-June 14

June 8

Dec 12-17

Dec 15

Aug 13-25

Aug 21

q

0.680

0.674

0.970

1. 011

0. 175

0. 190

0.973

0. 981

a

2.

3.

2.

3

52.

17.

862

153

695

09

24

64

905

e

0. 757

0. 786

0. 6 33

0. 672

0. 994

0. 993

0. 945

1. 000

i

5.*

1.

18

17.

31.

22

172.

172.

5

6

6

4

5

7

5

1

u

257°

224.

204.

192.

131.

121.

19.

27.

5

3

2

3

0

3

5

2

Si

95°

132.

71.

76.

82.

87.

326.

32 7.

3

0

9

8

5

5

0

8

T,

352*8

356. 3

276. 1

269. 1

213. 5

2 08. 8

345. 5

355. 0

a

268°

272

228

218

104

103

4 9

49

6

-15*

-21

40

45

10

9

14

13

V G

23

21

18

14

42

4 0

71

72
NUMBER 12 23

approach to the earth's orbit does not occur at

the node but at node -32° and node -60°, respectively. Table 5 shows that the /x-Sagittariid

stream is detected at node -37°, in agreement

with predictions. The December apparition is

not detected in our study, probably because the

radiant is too far south. Tentative associations

between Comet 1770 I and various minor meteor

streams of June and December have been proposed by several authors (Terent'eva, 1964;

Nilsson, 1963, 1964). However, none of these

streams agrees very well with the orbit of

Comet 1770 I.

A tentative association between the r-Herculid stream and Comet 1930 VI (SchwassmannWachmann) has been proposed by Southworth

and Hawkins (1963). The larger data sample

now available has made it possible to delineate

clearly the r-Herculid orbit. Inspection of Table

5 suggests good agreement in all orbital elements, and the proposed comet-meteor relation

may now be considered very probable. The

meteor stream associated with Comet 1930 VI

was observed visually in Japan in 1930 (Nakamura, 1930). The computed radiant and orbit

of this stream agree reasonably well with our

T-Herculid orbit.

Two members of the December Monocerotid

stream are present in the McCrosky-Posen meteor sample (meteors 6040 and 9557). A comparison of the mean Monocerotid orbit with

Comet 1917 I (Mellish) indicates close correspondence in all orbital elements, and this

association must now be regarded as fairly certain. Our identification of the Monocerotids

with Comet 1917 I receives support from the

tentative connection suggested by Whipple

(1954) between this comet and Harvard meteors 2313 and 2405.

A fourth comet-meteor association, the i/»

Arietids with Comet 1862 II (Schmidt-Temple),

is fairly probable, although the meteor-stream

orbit is based on only two photographic meteors. Particular attention is here drawn to the

very small earth-comet orbit distance of 0.028

a. u.

Porter (1952) gives a list of 19 theoretical

radiants for 17 ecliptical comet orbits, observed

after 1700, that approach the earth's orbit to

within 0.1 a. u. Of these radiants, 11 can easily

be seen from the Northern Hemisphere, and 8

of these correspond to well-known meteor showers. The detection of the /i-Sagittariid, T-Herculid, and Monocerotid photographic meteor

streams add three more comet-meteor associations to Porter's 1952 list, leaving only one

comet (1743 I) without observed meteors.

Acknowledgments

Part of this study was carried out during a stay

at the Smithsonian Astrophysical Observatory.

I thank Dr. R. E. McCrosky for placing at my

disposal cards of the basic orbital data, Dr. R. B.

Southworth for permission to use his computer

search program, and Mrs. S. Rosenthal for help

in the data reduction. I am indebted to the

Swedish Natural Science Council for a travel

grant. This work was also supported in part by

contract NSR 09-015-033 from the National

Aeronautics and Space Administration.

References

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1899. General Catalogue of the Radiant Points of

Meteoric Showers and of Fireballs and Shooting Stars Observed at More than One Station.

Memoirs of the Royal Astronomical Society,

53:203-292.

Elford, W. G., G. S. Hawkins, and R. B. Southworth

1964. The Distribution of Sporadic Meteor Radiants.

Harvard-Smithsonian Radio Meteor Project,

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Forti, G.

1968. On the Width of the Geminid Shower at Faint

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1958. General Index List. Theoretical Radiant Points

of Meteors Associated with Comets. Documentation des Observateurs, volume 11, bulletins

1, 4, 8, and 11.

Hawkins, G. S., R. B. Southworth, and S. Rosenthal

1964. Preliminary Analysis of Meteor Radiants and

Orbits. Harvard-Smithsonian Radio Meteor

Project, Research Report 7, 32 pages.

Hawkins, G. S., R. B. Southworth, and F. Stienon

1959. Recovery of the Andromedids. Astronomical

Journal, 64 (5): 183-188.

Hoffmeister, C.

1948. Meteorstrome. Leipzig, Verlag Johann Ambrosius Barth.
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Jacchia, L.

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774-798. Chicago, University of Chicago Press.

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(4) : 97-129.

Lindblad, B. A.

1971. A Stream Search Among 865 Precise Photographic Meteor Orbits. Smithsonian Contributions to Astrophysics, 12 [in this volume].

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McCrosky, R. E., and A. Posen

1959. New Photographic Meteor Showers. Astronomical Journal, 64 (1) : 25-27.

1961. Orbital Elements of Photographic Meteors.

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of Comet Schwassmann-Wachmann. Monthly

Notices of the Royal Astronomical Society, 91:

204-209.

Nilsson, C. S.

1963. A Possible Association Between the Lost Comet

Lexell 1700 I and a Minor Meteor Shower in

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Abstract

A computer stream search has been made among 2401 photographic meteor orbits. The

resulting meteor streams are presented in tabular form. For known photographic

streams, the mean orbital elements, as determined by the search, are similar to those

previously obtained by conventional methods of stream classification.

Many new photographic meteor streams have been detected by the search. Some have

been identified with visual showers listed by Denning, Mclntosh, and Hoffmeister. The

extensive Leonid-Virginid photographic stream is identified with Hoffmeister's Virginid

stream. Identifications with other ecliptical currents reported by Hoffmeister are also

suggested.

Several streams are split into a northern and a southern branch, with their orbital

planes symmetrical with respect to the plane of the ecliptic.

Four streams move in orbits similar to those of well-known comets: the n Sagittariid

is associated with Comet Lexell (1770 I), the r Herculid very probably with comet

Schwassman-Wachmann (1930 VI), the December Monocerotid with Comet Mellish

(1917 I), and the f Arietid with Comet Schmidt-Temple (1862 II). Porter's list of

comets approaching the earth's orbit to within 0.1 a.u. gives the first three mentioned

meteor-cometary associations as predicted but not observed. The addition of these three

to the list implies that ten of eleven theoretical radiants listed by Porter as observable

in the Northern Hemisphere have now been detected.

-&U.S. GOVERNMENT PRINTING OFFICE: 1971 O 4O4-7O8