Physical studies of asteroids

ICARUS 74, 4 5 4 - 4 7 1

(1988)

Physical Studies of A s t e r o i d s XVII. JHK Photometry of Selected Main-Belt and Near-Earth Asteroids 1 G E R H A R D H A H N AND C L A E S - I N G V A R L A G E R K V I S T Astronomiska Observatoriet, Box 515, S-751 20 Uppsala, Sweden

Received June 2, 1987; revised October 22, 1987 JHK photometry of 74 main-belt and 3 near-Earth asteroids has been performed. We interpret our data together with previously published JHK measurements, in all a sample of 151 asteroids, and present the results in J-H vs H-K diagrams for all taxonomic types. We find a very wide range in J-H for M-type asteroids and a distinct separation for the S and A classes, as well as a less well pronounced division for D-type asteroids. For some 10 asteroids we propose new types or changes in the classification using JHK colours and the newly available IRAS albedo data (D. Matson 1986, in Infrared Astronomical Satellite Asteroid and Comet Survey: Preprint Version N o . 1, Section III-1, pp. 1-83, Jet Propulsion Laboratory Publication D-3698). For near-Earth asteroids (NEA) a wide spread is found in the JHK diagram, covering practically all types of asteroids. A comparison with JHK colors for active and low-activity comets is made, showing that at least two N E A , 2100 Ra-Shalom and 1979 V A , have JHK colors similar to cometary dust. Three N E A , 1627 Ivar, 2368 Beltrovata, and 1986 D A , have almost identical JHK colors resembling those of D-type asteroids. © 1988AcademicPress,Inc.

INTRODUCTION Infrared J H K p h o t o m e t r y has shown to be a powerful tool to get information about the composition of asteroids (see, e.g., Veeder et al. 1982, 1983a). This technique can also be used as a c o m p l e m e n t to phot o m e t r y in the visual and other wavelength regions for the classification of asteroids and is especially important for the study of fainter and small asteroids, where other methods, such as, e.g., C V F spectroscopy, fail because of brightness limitations. We have carried out an observing program o v e r a period of 2 years in order to enlarge the sample of J H K data of asteroids of all taxonomic and dynamical types. Particular emphasis has been given to possible observations of near-Earth asteroids for which only a very limited n u m b e r of data t Based on observations collected at the European Southern Observatory, ESO, La Silla, Chile.

have been available so far. We have also included previously published J H K data in our discussion, which brings the sample to 151 asteroids. OBSERVATIONS All o b s e r v a t i o n s were done with the l-m telescope at the E u r o p e a n Southern Observatory (ESO), L a Silla, Chile. The J H K L M p h o t o m e t e r and a liquid-nitrogen-cooled InSb detector was used ( K r e y s a 1979, Danks 1979). This system has a wobbling flat mirror which provides sky chopping through any angle up to +3.5 arcmin on the sky. A c h o p p e r throw of 20 arcsec at a frequency of 7 H z and a 15-arcsec diaphragm were typically used. The standard broadband J H K filters at effective wavelengths J = 1.25 ~ m , H = 1.63 p~m, K = 2.8/~m were used. The m e a s u r e m e n t s were obtained in a n u m b e r of cycles A B B A (A = sky + object, B = sky) of 5 sec integration time per step, until an internal a c c u r a c y of 0.5 (for the 454

0019-1035/88 $3.00 Copyright © 1988 by Academic Press. Inc.

JHK PHOTOMETRY

standard stars) and 1% (for the asteroids) was reached.A minimum of two cycles was measuredfor all objects; no more than eight cycles = 160set per filter were integrated, which gavefor the faintest asteroids(J - 11 mag) errors of less than 5%. Normally, each asteroid was measuredtwice during the night. For someobjects an attempt was madeto get IR lightcurves. A few asteroids could only be observedonce (cf. Table I), which renders a lower weight for the obtained colors. DATA REDUCTIONS

Normally, 7-13 standard stars, mainly from Koornneef (1983), were observed eachnight, in a total of 130measurements. These standardstars do in principle define our photometric system. The errors, as determined from the difference between the catalog and the observed values for the standardstars, as given by

E= d w - Q2

n-l ’ are in J = 0.04, in H = 0.02, and in K = 0.02. In this photometric system the colors of an A0 star are zero in all filters. We also measuredtwo different solar analog stars, representingthe solar colors in our system: BD + 8’2015(J-H = 0.36 -+ 0.04, H-K = 0.07 2 0.02)and HD 105590(J-H = 0.31 * 0.04, H-K = 0.07 + 0.02). From the standard star measurements extinction coefficients for each night were determined. The mean extinction coefficients for La Silla are 0.08 in J, 0.06 in H, and 0.11in K (cf. Engels et al. 1981),which agree rather well with our values, but for the K filter we found somewhatlower values. The reduction of the data and the transformation to the standardsystem was performedby a specially developedroutine for IR photometric reductions in use at ES0 (Bouchet 1987). RESULTS

The results are presented in Table I, where all individual observationsas well as

OF ASTEROIDS

455

the mean J-H and H-K colors for each asteroid and the number of observationsare given. The classificationsare from Tholen (1984,1987private communication). In order to enlargethe number of asteroids we have for the discussion included data from Veeder et al. (1981, 1982, 1983a, 1983b, 1984), Hartmann et al. (1982), Chapman and Morrison (1976),Johnsonet al. (1975), Leake et al. (1978),McCheyneet al. (1985) Green et al. (1985),and Tedesco and Gradie (1987).With Veeder et al. (1982,1983a) we have observations of nine asteroids in common and thus a possibility to ensure that the data are in the same system. The correlations between the J-H and H-K in the two systems are satisfactory (cf. Elias et al. 1982)and we have chosento reduce all data from Veeder et al. to our system. The correctionsare normally very small, of the order of a few hundredths of magnitudes. Only for some of the very red asteroids the corrections are somewhat larger, amounting to more than 0.1 mag (cf. Fig. 1 with Fig. 1 in Veeder et al. (1983a)).Also for the data from Chapman and Morrison (1976),Leake et al. (1978),Hartmann et al. (1982),and McCheyne et al. (1985)transformations with similar correlations were made.Thesereductionsinfluencein no way the results of the following discussion. In Table II we give the relations between the various photometric systems and ours. The various columns give the coefficients and their errors as derived from a linear least-squaresolution, followed by the correlation coefficient, the numberof asteroids in common, and a reference.For few data found in the literature no such transformations were possiblebecausethere were too few objects in common, but the general agreementseemedsatisfactory (cf. Tables III and VI). We thus have J-H and H-K data for 151asteroidsto be usedin the discussion. For those asteroidsfor which data from different sources were available, a mean value was calculated and plotted in the diagrams.The JHK colors for asteroids not measuredby us but found in the litera-

HAHN AND LAGERKVIST

456

TABLE I J H K PHOTOMETRY OF ASTEROIDS

Asteroid

Type

Date (UT)

J

H

K

2 Pallas 2 2 2

B

1985 1985 1985 1985

Nov Nov Nov Nov

26.285 26.331 27.310 28.240

6.97 6.96 6.99 6.96

6.72 6.71 6.71 6.70

6.67 6.66 6.66 6.64

4 Vesta 4

V

1985 M a r 1985 M a r

6.317 6.320

5.29 5.28

5.03 5.03

5.04 5.04

6 Hebe 6 6 6

S

1986 1986 1986 1986

Mar Mar Mar Mar

1.270 2.315 3.335 3.373

8.97 9.09 9.02 9.04

8.65 8.71 8.66 8.66

8.60 8.64 8.58 8.60

7 Iris 7 7 7

S

1986 1986 1986 1986

Mar Mar Mar Mar

1.279 2.324 3.342 3.379

8.75 8.84 8,80 8,80

8.36 8.38 8.38 8.37

8.29 8.31 8.29 8.30

I0 Hygiea 10

C

1985 Sep 23.335 1985 Sep 24.256

9.04 9.72

9.36

8.39 9.19

16 Psyche 16

M

1985 N o v 26.237 1985 N o v 28.234

8.08 8.11

7.75 7.74

7.61 7.59

18 Thetis 18 18 18 18 18 18

S

1985 1985 1986 1986 1986 1986 1986

N o v 26.325 N o v 27.317 Mar 1.032 Mar 1.086 M a r 2.042 Mar 3.026 M a r 3.055

7.97 7.93 9.01 8.78 9.01 8.95 8.98

7.64 7.57 8.68 8.47 8.59 8.57 8.58

7.57 7,50 8.61 8.41 8.52 8.51 8.52

22 Kalliope

M

1985 Sep 23.084

9.81

9.43

9.23

23 Thalia 23 23 23

S

1986 1986 1986 1986

Mar Mar Mar Mar

1.290 1.347 2.333 3.352

9.86 9.88 9.98 9.93

9.53 9.53 9.56 9.55

9.51 9.46 9.49 9.48

24 T h e m i s 24 24 24

C

1986 1986 1986 1986

Mar Mar Mar Mar

1.098 2.079 3.066 3.121

9.96 10.14 10.14 10.10

9.67 9.75 9.76 9.75

9.52 9.58 9.60 9.63

29 Amphitrite 29

S

1985 M a r 1985 M a r

6.389 6.393

9.43 9.42

9.08 9.07

9.03 9.03

32 P o m o n a

S

1985 Mar

6.073

9.57

9.20

9.12

34 Circe 34 34

C

1985 N o v 26.145 1985 N o v 27.119 1985 N o v 28.094

11.00 11.13 11.12

10.78 10.79 10.79

10.66 10.68 10.66

J-H

H-K

n

0.26

0.05

4

0.25

-0.01

2

0,36

0.06

4

0.42

0.07

4

0.43:

0.17

2

0.35

0.14

2

0.36

0.07

7

0.38

0.20

!

0.37

0.06

4

0.35

0.15

4

0.35

0.04

2

0.37

0.08

1

0.30

0.12

3

JHK PHOTOMETRY OF ASTEROIDS

457

TABLE l--Continued

Asteroid

Type

Date (UT)

J

H

K

35 Leukothea 35

C

1985 Mar 1985 Mar

8.346 8.355

11.55 11.58

11.25 11.27

11.05 11.07

37 Fides 37 37 37 37

S

1986 Mar 1986 Mar 1986 Mar 1986 Mar 1986 Mar

1.188 2.201 2.244 3.208 3.245

9.67 10.00 9.79 9.74 9.84

9.36 9.66 9.41 9.39 9.49

9.34 9.60 9.37 9.32 9.47

40 Harmonia 40 40 40

S

1986 Mar 1986 Mar 1986 Mar 1986 Mar

1.304 1.361 2.346 3.364

9.73 9.82 9.94 9.82

9.40 9.50 9.52 9.46

9.32 9.45 9.47 9.39

41 Daphne 41

C

1985 Mar 1985 Mar

6.266 6.270

8.83 8.84

8.51 8.51

8.41 8.41

44 N y s a 44

E

1985 Mar 1985 Mar

6.307 6.311

9.06 9.06

8.77 8.77

8.67 8.69

45 Eugenia 45 45 45 45

FC

1985 Nov 27.348 1986 Mar 1.055 1986 Mar 2.054 1986 Mar 3.308 1986 Mar 3.093

10.96 10.65 10.77 10.71 10.70

10.58 10.36 10.34 10.33 10.34

10.43 10.19 10.15 10.12 10.19

48 Doris 48 48 48 48

CG

1986 Mar 1986 Mar 1986 Mar 1986 Mar 1986 Mar

1.078 2.067 2.091 3.079 3.108

10.19 10.39 10.38 10.37 10.36

9.93 10.01 10.02 10.05 10.04

9.87 9.97 9.98 9.99 10.00

51 N e m a u s a 51 51

CU

1985 Mar 1985 Mar 1985 Mar

6.030 7.032 7.037

9.76 9.77 9.79

9.33 9.32 9.34

9.21 9.23 9.22

55 Pandora 55

M

1985 Mar 1985 Mar

8.323 8.332

11.63 11.61

11.31 11.30

10.99 11.04

59 Elpis

CP

1985 Sep 24.016

10.06

9.69

9.50

63 Ausonia 63

S

1985 Nov 27.056 1985 Nov 28.140

9.86 10.05

9.39 9.62

9.32 9.61

65 Cybele 65

P

1985 Nov 26.225 1985 Nov 28.216

10.99 10.98

10.68 10.63

10.61 10.53

68 Leto 68 68 68

S

1986 1986 1986 1986

t0.65 10.96 10.76 10.78

10.27 10.48 10.30 10.30

10.23 10.41 10.25 10.23

Mar Mar Mar Mar

1.243 2.292 3.288 3.324

J-H

H-K

n

0.31

0.20

2

0.35

0.04

5

0.36

0.06

4

0.32

0.10

2

0.29

0.09

2

0.37

0.17

5

0.33

0.05

5

0.44

0.11

3

0.31

0.29

2

0.37

0.19

1

0.45

0.04

2

0.33

0.08

2

0.45

0.06

4

458

HAHN

AND LAGERKVIST

T A B L E I--Continued

Asteroid

Type

Date (UT)

J

H

K

69 Hesperia 69

M

1985 Mar 1985 M a r

6.331 6.341

10.64 10.63

10.27 10.27

10.10 10.12

70 P a n o p a e a

C

1 9 8 5 N o v 27.212

10.58

10.26

10.21

78Diana 78 78

C

1986Mar 1986Mar 1986Mar

1.150 2.152 3.159

9.27 9.43 9.38

8.97 9.08 9.06

8.91 9.00 8.96

80 Sappho 80

S

1985Mar 1985Mar

6.105 6.112

10.37 10.36

9.93 9.93

9.87 9.89

83 Beatrix 83 83

EMP

1986Mar 1986Mar 1986Mar

1.137 2.124 3.148

10.09 10.18 10.20

9.76 9.80 9.82

9.64 9.67 9.69

87 Sylvia

P

1985 Sep 24.287

10.40

10.05

9.85

88 Thisbe 88 88

CF

1985Mar 1985 Mar 1985Mar

6.285 6.295 7.227

10.63 10.68 10.72

10.29 10.31 10.31

10.12 10.12 10.11

97Klotho 97 97

M

1986Mar 1986Mar 1986Mar

1.261 2.306 3.300

10.90 11.09 ll.01

10.59 10.69 10.65

10.56 10.60 10.56

103 Hera 103 103 103 103

S

1986 Mar 1986Mar 1986Mar 1986Mar 1986Mar

l.ll2 1.123 2.105 2.138 3.136

10.27 10.26 10.39 10.35 10.36

9.94 9.93 10.00 9.96 9.99

9.88 9.88 9.94 9,93 9,94

l l 0 Lydia ll0 110 110 110

M

1985 Sep 1985 N o v 1985 N o v 1985Nov 1985 N o v

24.330 26.106 27.068 27.077 28.040

10.78 10.18 10.24 10.22 10.39

10.38 9.87 9.85 9.83 9.99

10.24 9.75 9.70 9.69 9.86

115 T h y r a

S

1985 Sep 24.133

8.61

8.21

8.17

124 Alkeste 124 124 124 124 124 124 124 124 124 124 124

S

1984 Dec 27.056 1984 D e c 2 7 . 0 6 5 1984Dec 27.184 1984 Dec 27.195 1984Dec 27.261 1984 Dec 27.269 1984 Dec 28.066 1984 Dec 28.074 1 9 8 4 D e c 28.147 1984 Dec 28.159 1 9 8 6 M a r 1.216 1 9 8 6 M a r 2.216

11.17 11.26 11.27 11.35

10.83 10.82 10.91

11.18 11.24 11.21 11.18 11.17 10.26 10.43

10.87 10.86 10.87 10.84 10.86 10.83 9.94 10.05

10.81 10.75 10.75 10.81 10.76 10.86 10.83 10.86 10.78 9.95 9.99

J-H

H-K

n

0.37

0.16

2

0.32

0.05

l

0.32

0.08

3

0.44

0.05

2

0.36

0.13

3

0.35

0.20

1

0.37

0.19

3

0.36

0.07

3

0.36

0.05

5

0.38

0.14

5

0.40

0.04

1

JHK PHOTOMETRY OF ASTEROIDS

459

T A B L E I--Continued

Asteroid

Type

124 124 124

Date (UT)

J

H

K

1986Mar 1986Mar 1986Mar

2.263 3.220 3.258

10.34 10.37 10.35

9.97 10.05 9.98

9.92 9.95 9.93

129 Antigone 129 129 129

M

1985Mar 1985Mar 1985 Mar 1985Mar

6.086 6.093 7.145 7.153

9.44 9.49 9.77 9.83

9.07 9.17 9.36 9.41

8.93 9.07 9.23 9.23

134 S o p h r o s y n e 134 134

C

1986Mar 1986Mar 1986Mar

1.162 2.175 3.182

11.14 11.14 11.09

10.89 10.82 10.77

10.87 10.74 10.75

135 H e r t h a

M

1985 Sep 24.237

8.57

8.22

8.06

163 Erigone 163 163

C

1985Mar 1985 Mar 1985Mar

6.236 6.246 8.299

11.04 11.01 11.06

10.73 10.72 10.62

10.56 10.58 10.53

176 Iduna 176

G

1985 N o v 27.226 1 9 8 5 N o v 28.189

11.11 11.07

10.78 10.72

10.68 10.57

183 Istria 183 183 183 183 183 183 183 183 183 183 183 183 183 183 183 183 183

S

1984 Dec 1984 Dec 1984 Dec 1984 Dec 1984Dec 1984Dec 1984 Dec 1984 Dec 1984 Dec 1984Dec 1984 Dec 1984 Dec 1984 Dec 1984 Dec 1984 Dec 1984 Dec 1984 Dec 1984 Dec

26.072 26.104 26.121 26.127 26.132 26.139 26.159 27.081 27.125 27.131 27.213 27.219 27.285 27.292 28.087 28.096 28.176 28.184

11.15 11.41 11.10 11.13 11.17 11.14 11.22 11.31 11.27 11.29 11.39 11.37 11.34 11.38 11.29 11.31 11.26 11.34

10.75 10.80 10.70 10.78 10.82 10.78 10.88 10.85 10.82 10.84 10.95 10.96 10.94 10.94 10.88 10.93 10.89 11.02

10.71 10.73 10.76 10.70 10.75 10.74 10.87 10.82 10,78 10.85 10.94 11.00 10.90 10.98 10.93 10.90 10.93 10.88

185 Eunike 185

C

1985 N o v 26.296 1985 N o v 28.261

10.53 10.52

10.19 10.17

10.01 9.97

192 N a u s i k a a 192 192 192 192 192 192 192

RS

1985 1985 1985 1985 1985 1985 1985 1985

7.07 8.62 8.63 8.63 8.70 8.71 8.78 8.74

6.62 8.18 8.18 8.15 8.22 8.22 8.28 8.23

6.57 8.10 8.12 8.08 8.14 8.14 8.22 8.15

Sep Nov Nov Nov Nov Nov Nov Nov

24.203 26.049 26.053 27.029 27.052 27.056 28.009 28.030

J-H

H-K

n

0.31

0.04

15

0.38

0.14

4

0.30

0.04

3

0.35

0.16

1

0.35

0.13

3

0.34

0.13

2

0.41

0.02

18

0.34

0.19

2

0.47

0.07

8

460

HAHN AND LAGERKVIST T A B L E I--Continued

Asteroid

Type

Date (UT)

J

H

K

10.79 10.77

10.41 10.44

10.29 10.33

201 Penelope 201

M

1985 N o v 26.274 1985 N o v 28.249

216 Kleopatra 216 216 216 216

M

1985 Sep 1985 Sep 1985Nov 1985 N o v 1985Nov

24.344 24.395 26.202 28.104 28.175

9.02 8.96 7.97 8.08 8.07

8.62 8.55 7.64 7.70 7.68

8.44 8.35 7.49 7.55 7.52

219 T h u s n e l d a 219 219

S

1985 Nov 26.212 1985 N o v 27.238 1985 N o v 28.203

10.47 10.48 10.58

10.06 10.04 10.14

10.02 9.98 10.03

230 A t h a m a n t i s 230

S

1985 Sep 23.220 1985 Sep 24.083

8.75 8.77

8.35 8.35

8.28 8.25

241 G e r m a n i a

CP

1985 Sep 23.100

10.53

10.16

10.01

258 T y c h e

S

1985 N o v 27.300

10.89

10.54

10.45

270 Anahita 270 270

S

1985 N o v 27.188 1985 N o v 27.196 1985 N o v 28.166

9.49 9.49 9.56

9.06 9.08 9.18

9.02 9.01 9.13

287 N e p h t h y s 287 287

S

1985 Mar 1985 Mar 1985 Mar

6.051 7.047 7.057

10.68 10.62 10.63

10.30 10.17 10.19

10.18 10.17 10.08

317 R o x a n e

E

1985 N o v 26.248

11.46

11.16

11.12

337 D e v o s a 337 337 337 337

EMP

1986Mar 1986Mar 1986Mar 1986Mar 1986Mar

1.229 2.229 2.279 3.271 3.313

10.72 10.87 10.71 10.80 10.76

10.39 10.46 10.33 10.41 10.39

10.28 10.31 10.24 10.31 10.23

345 Tercidina 345 345 345

C

1986Mar 1986Mar 1986Mar 1986Mar

1.176 2.188 3,196 3.232

10.58 10.66 10.69 10.65

10.26 10.32 10.32 10.30

10.18 10.19 10.24 10.20

346 H e r m e n t a r i a 346

S

1985 Sep 23.233 1985 Sep 23.302

8.91 8.93

8.39 8.39

8.27 8.27

349 D e m b o w s k a 349

R

1985 Mar 1985 Mar

6.375 6.381

10.08 10.11

9.66 9.68

9.58 9.58

354 Eleonora 354 354 354

S

1985 1985 1985 1985

24.379 26.116 27.178 28.075

9.85 9.09 9.21 9.13

9.19 8.51 8.55 8.49

9.01 8.38 8.42 8.37

Sep Nov Nov Nov

J-H

H-K

n

0.35

0.12

2

0.38

0.17

5

0.43

0.07

3

0.41

0.08

2

0.37

0.09

l

0.35

0.09

1

0.41

0.05

3

0.42

0,08

3

0.30

0,04

1

0.38

0.12

5

0,34

0.10

4

0.53

0.12

2

0.43

0.09

2

0.63

0.14

4

461

JHK PHOTOMETRY OF ASTEROIDS T A B L E I--Continued

Asteroid

Type

Date (UT)

J

H

K

369 Aeria

M

1985 N o v 28.308

11.49

11.15

11.24

386 Siegena 386

C

1985 Sep 23.205 1985 Sep 24.145

9.66 9.76

9.40 9.42

9.30 9.31

409 A s p a s i a 409

CEMP

1985 Sep 23.070 1985 Sep 24.093

10.26 10.42

9.91 10.02

9.77 9.86

416 Vaticana 416

S

1985 Sep 23.052 1985 Sep 24.019

10.38 10.38

9.92 9.88

9.84 9.78

1986 M a r

1.201

12.34

12.01

11.94

425 Cornelia

--

449 H a m b u r g a 449 449

C

1985 N o v 26.163 1985 N o v 27.142 1985 N o v 28.114

11.02 11.13 11.12

10.76 10.77 10.77

10.67 10.68 10.72

451 Patientia 451

CU

1985 N o v 26.309 1985 N o v 28.295

9.99 9.91

9.67 9.64

9.52 9.52

471 Papagena 471

S

1985 Sep 23.035 1985 Sep 24.006

10.03 10.13

9.60 9.67

9.55 9.59

511 Davida 511 511 511 511

C

1985 1985 1986 1986 1986

N o v 26.319 N o v 27.287 M a r 1.018 M a r 2.017 Mar 3.015

9.02 9.09 9.67 9.90 9.80

8.68 8.72 9.32 9.47 9.39

8.53 8.55 9.18 9.30 9.26

516 A m h e r s t i a 516 516 516 516 516

M

1985 1985 1985 1985 1985 1985

Mar Mar Mar Mar Mar Mar

6.127 6.132 7.167 7.177 8.274 8.281

9.71 9.68 9.56 9.66 9.69 9.75

9.38 9.42 9.22 9.35 9.31 9.35

9.28 9.42 9.15 9.25 9.24 9.23

532 Herculina 532 532 532

S

1985 1985 1985 1985

N o v 26.152 Nov27.130 N o v 28.092 N o v 28.272

8.68 8.82 8.73 8.75

8.33 8.40 8.32 8.36

8.25 8.34 8.24 8.29

582 Olympia 582

S

1985 N o v 27.327 1985 N o v 28.335

10.96 11.01

10.51 10.56

10.43 10.49

591 lrmgard 591

EMP

1985 M a r 1985 Mar

6.152 6.166

11.87 11.85

11.65 11.54

11.34 11.23

747 W i n c h e s t e r 747 747 747 747

PC

1984 1984 1984 1984 1984

26.180 26.186 27.150 27.162 27.231

9.67 9.66 9.77 9.79 9.64

9.31 9.28 9.31 9.33 9.19

9.13 9.14 9.15 9.17 9.02

Dec Dec Dec Dec Dec

J-H

H-K

n

0.34:

0.09:

1

0.30:

0.11

2

0.38:

0.15:

2

0.48

0.09

2

0.33:

0.07:

1

0.32

0.08

3

0.29

0.13

2

0.44

0.06

2

0.38

0.15

5

0.34

0.08

6

0.39

0.07

4

0.45

0.07

2

0.26

0.31

2

462

HAHN AND LAGERKVIST TABLE I--Continued

Asteroid

Type

747 747 747 747 747 747 747 747 747 747 747 747 747 747 747 747 747

Date (UT)

J

H

K

9.20 9.23 9.29

9.01 9.06

1984 Dec 1984 Dec 1984 Dec 1984 Dec 1984 Dec 1984 Dec 1984 Dec 1984 Dec 1984 Dec 1984 Dec 1984 Dec 1984 Dec 1984 Dec 1984 Dec 1984 Dec 1984 Dec 1984 Dec

27.233 27.311 27.314 27.319 27.324 28.116 28.120 28.124 28.201 28.205 28.243 28.246 28.270 28.281 28.286 28.289 28.292

9.65 9.64 9.63 9.72 9.66 9.64 9.71 9.63 9.47 9.60 9.56 9.55 9.60 9.64 9.65 9.63 9.63

9.23 9.25 9.27 9.24 9.13 9.19 9.16 9.20 9.22 9.26 9.26 9.25 9.25

9.07 9.08 9.10 9.09 9.07 8.93 8.94 9.03 9.02 9.09 9.13 9.13 9.10 9.10

1036 Ganymed 1036 1036 1036 1036 1036

S

1985 Nov 1985 Nov 1985 Nov 1985 Nov 1985 Nov 1985 Nov

26.127 26.259 27.104 27.249 28.006 28.280

9.41 9.45 9.54 9.52 9.57 9.48

9.10 9.15 9.18 9.16 9.20 9.14

9.06 9.14 9.12 9.12 9.16 9.11

1627 Ivar 1627 1627 1627 1627 1627 1627 1627 1627 1627 1627

S

1985 Sep 1985 Sep 1985 Sep 1985 Sep 1985 Sep 1985 Sep 1985 Sep 1985 Sep 1985 Sep 1985 Sep 1985 Sep

23.269 23.317 23.356 24.159 24.208 24.212 24.220 24.271 24.312 24.355 24.368

10.56 10.60 10.76 10.75 10.62 10.67 10.78 10.64 10.58 10.84 10.74

10.12 10.17 10.22 10.24

9.93 10.12 10.07 10.07 10.07 10.07

10.16 10.12 10.29

9.90 10.11 10.14

1866 Sisyphus 1866 1866 1866 1866 1866 1866 1866

S

1985 Nov 1985 Nov 1985 Nov 1985 Nov 1985 Nov 1985 Nov 1985 Nov 1985 Nov

26.090 26.192 27.043 27.093 27.169 28.021 28.055 28.153

9.71 9.65 9.74 9.73 9.63 9.69 9.60 9.55

9.37 9.30 9.33 9.29 9.22 9.29 9.20 9.16

9.25 9.21 9.22 9.19 9.13 9.22 9.10 9.15

J-H

H-K

n

0.38

0.15

22

0.34

0.04

0.46

0.14

0.39

0.09

Note. A colon (:) after the color indicates values of lower accuracy.

t u r e m a y b e f o u n d in T a b l e s III a n d V1. These colors have been transformed according to Table H whenever possible. F o r t h r e e a s t e r o i d s , 124 A l k e s t e , 183 I s -

t r i a , a n d 747 W i n c h e s t e r , l i g h t c u r v e s w e r e o b t a i n e d w h i c h a l l o w e d us to d e t e r m i n e the a m p l i t u d e s o f t h e r o t a t i o n a l v a r i a t i o n s in t h e J filter. W e f i n d f o r 124 A l k e s t e 0.2 m a g ,

JHK PHOTOMETRY OF ASTEROIDS O. 70

18

i

l

463

I

• 863

446 O. G5

24G

•

•

354

Type O. GO

mA O. 5 5

346

-R

8 512o • • 4 l B

O. 50

*R5

O. 45

0~°~a349

183 • O. 40 170 •

eS

aO@ • ~ 32

29

~700~0000258 20

O. 35

O. 30

O. ~5 I

- 0 . 10

~

i O. O0

I

,

k O. 10

,

H -

~ ,

L O. 20

,

I

i

I O. 30

i

K

FIG. 1. J H K colors m magnitudes for A-, R-, RS-, and S-type asteroids. The classification used in this figure, and in Figs. 2-6, is the classification by Tholen (1984).

for 183 Istria 0.15 mag, and for 747 Winchester 0.25 mag (cf. Table I). Since the magnitudes were not measured simultaneously an error is naturally introduced in the colors for those objects with fast spin and high lightcurve amplitude. For most of the objects we have several measurements of the colors and from the standard deviations we conclude that these effects are normally small.

DISCUSSIONS

Main-Belt Asteroids Of the 151 asteroids 135 have been classified by Tholen (1984, 1987 private communication); see Tables I, III, V, and VI. In order to better see the separations between the various types we have plotted J-H versus H-K in four separate diagrams for these asteroids with classifications.

T A B L E II TRANSFORMATIONS BETWEEN DIFFERENT PHOTOMETRIC SYSTEMS

Color

k

o-

l

o"

Corr.

n

J-H H-K

0.70 0.72

0.11 0.13

0.08 0.04

0.05 0.01

0.92 0.90

9 9

J-H H-K

0.45 0.38

0.19 0.15

0.17 0.10

0.10 0.02

0.63 0.67

10 10

J-H H-K

0.60 0.53

0.28 0.26

0.14 0.05

0.11 0.03

0.68 0.67

7 7

J-H H-K

0.43 0.78

0.15 0.17

0.19 0.04

0.06 0.01

0.71 0.84

10 10

J-H H-K

0.98 0.95

0.41 0.29

0.01 0.03

0.16 0.03

0.73 0.83

7 7

Reference Veeder et al. (1982, 1983a)

H a r t m a n n et al. (1982)

Chapman and Morrison (1976)

M c C h e y n e et al. (1985)

L e a k e e t al. (1978)

T A B L E III J H K DATA TAKEN FROM OTHER SOURCES Asteroid I Ceres 2 Pallas 4 Vesta 5 Astraea 5 5 6 Hebe 7 Iris 7 8 Flora 13 Egeria 15 E u n o m i a 15 16 P s y c h e 17 Thetis 19 F o r t u n a 20 Massalia 21 Lutetia 22 Kalliope 22 25 P h o c a e a 29 Amphitrite 31 E u p h r o s y n e 39 Laetitia 41 Daphne 41 44 N y s a 44 49 Pales 51 N e m a u s a 52 E u r o p a 52 57 M n e m o s y n e 63 A u s o n i a 64 Angelina 64 64 69 Hesperia 76 Freia 76 83 Beatrix 88 Thisbe 88 97 Klotho 115 T h y r a 116 Sirona 129 Antigone 129 135 Hertha 145 A d e o n a 148 Gallia 170 Maria 213 Lilaea

Type G B V S

S S S CG S M S G S M M S S C" S C E CG CU CF S S E

M P EMP CF M S S M M C GU S F

J-H

H-K

Source

Asteroid

0.31 0.21 0.26 0.36 0.34 0.34 0.34 0.38 0.41 0.49 0.33 0.43 0.39 0.34 0.36 0.34 0.35 0.36 0.36 0.38 0.40 0.38 0.38 0.43 0.38 0.34 0.32 0.33 0.43 0.36 0.34 0.40 0.38 0.46 0.30 0.36 0.34 0.36 0.39 0.38 0.40 0.38 0.37 0.34 0.35 0.35 0.39 0.37 0.37 0.34 0.36 0.38 0.28

0.05 0.04 -0.01 0.06 0.07 0.06 0.07 0.09 0.07 0.08 0.08 0.03 0.08 0.10 0.06 0.13 0.07 0.08 0.13 0.22 0.08 0.03 0.17 0.06 0.12 0.08 0.09 0.12 -0.05 0.13 0.11 0.17 0.07 0.07 0.09 0.13 0.11 0.13 0.18 0.17 0.13 0.11 0.17 0.08 0.08 0.09 0.17 0.14 0.16 0.06 -0.02 0.01 0.08

6 NT 6 NT 4 2 5 4 5 5 1 1 1 2 1 2 2 4 4 2 3 2 1 4 4 4 3 1 2 4 2 3 4 2 2 2 2 3 5 2 2 3 4 5 1 2 4 5 5 1 2 4 2 2 2

219 T h u s n e l d a 224 O c e a n a 246 Asporina 279 Thule 313 Chaldaea 334 Chicago 338 B u d r u s a 349 D e m b o w s k a 349 361 Bononia 379 H u e n n a 386 Siegena 409 A s p a s i a 434 Hungaria 446 Aeternitas 471 Papagena 496 Gryphia 497 Iva 511 Davida 511 512 Taurinensis 528 Rezia 584 Semiramis 617 Patroclus 617 624 H e k t o r 699 Hela 785 Z w e t a n a 863 Benkoela 884 Priamus 1025 Riema 1088 Mitaka 1162 Larissa 1162 1180 Rita 1208 Troilus 1269 Rollandia 1508 Kemi 1512 Oulo 1578 Kirkwood 1578 1593 Fagnes 1602 Indiana 1646 R o s s e l a n d 1656 Suomi 1658 R o e m e r a 1748 Mauderli 1748 1868 Thersites 1902 S h a p o s h n i k o v 2055 Dvorak 2060 Chiron 2078 N a n k i n g

Type S M" A D C C M R DP B C CEMP E A S S M C S S P D S M A D E S P P CFU D BCF P D -RU" -R"

RU" D -EMP -B --

J-H 0.44 0.36 0.63 0.43 0.33 0.35 0.37 0.41 0.40 0.35 0.39 0.36 0.37 0.34 0.69 0.41 0.40 0.38 0.40 0.41 0.48 0.35 0.46 0.35 0.37 0.45 0.36 0.40 0.68 0.36 0.30 0.42 0.42 0.42 0.40 0.37 0.41 0.30 0.43 0.43 0.41 0.45 0.44 0.34 0.40 0.38 0.48 0.44 0.44 0.44 0.31 0.32 0.35

H-K 0.09 0.11 0.11 0.17 0.08 0.16 0.15 0.10 0.09 0.10 0.08 0. l0 0.15 0.03 0.06 0.08 0.07 0.18 0.14 0.13 0.07 0.17 0.07 0.18 0.16 0.14 0.06 0.10 0.11 0.18 0.10 0.06 0.11 0.16 0.17 0.12 0.17 0.06 0.21 0.21 0.17 0.07 0.03 0.13 0.06 0.07 0.18 0.20 0.11 0.16 0.06 0.15 0.12

Source 2 2 2 2 2 2 2 4 2 3 2 4 1 2 2 4 2 2 5 1 2 2 2 2 3 2 2 2 2 3 2 2 2 3 2 3 3 2 2 2 3 2 2 2 2 2 2 3 2 2 2 3 2

N o t e . Sources: 1, L e a k e et al. (1978); 2, Veeder et al. (1982, 1983a, 1983b); 3, H a r t m a n n et al. (1982); 4, M c C h e y n e et al. (1985); 5, C h a p m a n and Morrison (1976); 6, J o h n s o n et al. (1975). NT, colors not t r a n s f o r m e d to our system. Classification from Bowell et al. (1979). 464

JHK PHOTOMETRY OF ASTEROIDS

ues o f J - H = 0.34 -+ 0.01 and H - K = 0.12 +_ 0.01. The J-H for l0 Hygiea seems to be a little too large for an asteroid of type C to fit in well (of. Table I). 10 Hygiea has also the highest albedo of this group of asteroids (Matson 1986). In Fig. 2 also the asteroids of types CF, CG, CP, FC, and PC are plotted. The asteroid 49 Pales has a large negative H - K (Veeder et al. 1983a) and is classified as CG by Tholen (1984). It has a period of 10.42 hr and a iightcurve amplitude of only 0.2 mag (Lagerkvist et al. 1987), so it is not very probable that a rapidly changing rotational phase is causing the large negative H-K. We note that this asteroid has been proposed to have a satellite (Tedesco 1979). For the M asteroids the spread in H-K is large, - 0 . 1 0 < H - K < 0.30, but very small in J-H = 0.36 -+ 0.01 (Fig. 3). This large spread is caused by the colors of the asteroids 55 Pandora and 369 Aeria, which may indicate either that these two asteroids are not belonging to the M type or that there is an exceptionally large color range in H - K for this type. Clearly, additional measurements for these objects are needed to decide this question. The P asteroids have

T A B L E IV MEAN J H K COLORS FOR THE MAJOR TAXONOMIC TYPES Type

J-H

o-

H-K

cr

n

C D E M P S

0.34 0.41 0.32 0.36 0.37 0.41

0.01 0.02 0.01 0.(X) 0.01 0.01

0.12 0.17 0.07 0.13 0.16 0.07

0.01 0.01 0.02 0.02 0.02 0.00

Ig 6 5 17 7 41

The S asteroids are all found in a very well-defined area of the color diagram (Fig. 1), which also shows asteroids of types A, R, and RS. The asteroid 354 Eleonora is rather well separated from the main group and seems to be more correlated with the A type defined by Veeder et al. (1983b). It has been found to be olivine rich in an IR spectroscopy study by Cruikshank et al. (1985), a feature detected for most asteroids of type A. 346 Hermentaria lies in the domain between the S- and A-type asteroids. Mean colors for all S-type asteroids are J-H = 0.41 +- 0.01 (mean error), and H - K = 0.07 + 0.00. The C asteroids (Fig. 2) have mean val-

O. 70

I

i

I

465

1

[

I

I

I

O. 65 Type

O. 60

O. 55

oC

O. 50

a

CG CF

O. 45

49

I0 t 511

0.40 241 o O. 35

48

O. 30

• 134

14513

52 Q 7 4 7 O 31 59 ~ ~9 o

• 41

449

•

00334

185 m 35

• 34

v

FC

o

CP

o

PC

O. 2 5

-0.

10

,

I

,

I O. O 0

,

I

,

I O. 10 H

, -

I

,

I O. 2 0

,

I

k

I O. 3 0

I<

FIG. 2. J H K colors in magnitudes for C-, CF-, CG-, CP-, FC-, and PC-type asteroids.

466

HAHN AND LAGERKVIST O. 70

I

I

I

I

I

I

r

I

O. 6! Type

O. 6( O. 55 0.50

•

E

•

1'1

•

F'

•

EI'IP

"I" I

1902

O. 45 785

0. 4.0

21 O. 35

1162 •

1180 V1512 76

• * m • mmm m m m • 22

411~34 97m ~ 516 : ,

16

617

¥87

• 369

65

O. 30

0 44

317

•

55

1025

591

O. 2 5

-0. I0

,

I

,

I

J

I

,

O. O0

F

,

O. I0 H

-

I

i

J

,

I

i

O. 20

I

i

O. 30

K

FIG. 3. JHK colors in magnitudes for E-, M-, P-, and EMP-type asteroids.

colors similar to those of the M types but do not have such a wide spread in H-K. In Fig. 3 are also plotted five asteroids of type E and these are grouped rather close in the same part of the diagram, with mean J-H = 0.32 -+ 0.01 and H - K = 0,07 + 0.02. The group of E M P is also found in this diagram. The data for the B-, D-, F-, G-, and VO. 70

I

I

type asteroids are plotted in Fig. 4. The three asteroids of type B, 2 Pallas, 379 Huenna, and 2060 Chiron, have a large spread in the J H K diagram, but their UBV colors are almost identical (Tedesco 1986). The colors for these asteroids begin to diverge at longer wavelengths as also seen in Zellner et al. (1985). Chiron has, however, ]

I

[

r

i

F

O. 6 5

Type O. 60

O. 5 5

•

B

O. 50

•

D

•

F

•

G

•

V

6;24 l

0.45

•

• 1748 279 •

0.40

• 979

O. 35

•

• 884

176

• 2060

•i

O. 30

• 1578

1269

A213 4

O. 2 5

•

I -0. I0

,

I

, 0.00

2

I

i

I

,

0. I0 H

-

I

i

I

O. 20

,

I

,

I

O. 30

K

FIG. 4. JHK colors in magnitudes for B-, D-, F-, G-, and V-type asteroids.

JHK

0. 70

PHOTOMETRY

I

I

OF

I

I

ASTEROIDS

I

I

467

I

I

0.65 Type O. 60

0.55

O. 50

•

arab.

•

DP

•

BCF

•

CEMP

"1I

1602 •

O. 45

1~03 • 1868 i 51

O. 40

1658 148

409

•

361 •

O. 3 5

2055 •

425

O. 30 • 1508

i1208 t

@528

•2078

@1646 41151

O. 25 I

- 0 . 10

J

I 0.00

J

t

J

I L 0. 10 H -

I

i

I 0. 20

t

I

~

I 0. 30

K

FIG. 5. J H K c o l o r s in m a g n i t u d e s f o r a s t e r o i d s w i t h no o r a m b i g u o u s c l a s s i f i c a t i o n s , plus f o r D P a n d BCF types.

TABLE

V

N E W OR CHANGES IN PREVIOUS CLASSIFICATIONS (THOLEN 1984) BASED UPON J H K PHOTOMETRY Asteroid

Type

IRAS

Comments

Pv

Old 83 B e a t r i x 148 G a l l i a

New

EMP

P

0.063

GU

S or M

0.14

337 D e v o s a

EMP

M or P

0.13

346 H e r m e n t a r i a

S

A?

0.13

354 E l e o n o r a

S

A

0.19

425 C o r n e l i a

--

C

0.046

528 R e n z i a

--

C

0.054

--

D

--

P

0.028

1868 T h e r s i t e s 1902 S h a p o s h n i k o v 51 N e m a u s a 361 B o n o n i a

EMP CU

--

0.086

DP

--

0.039

409 A s p a s i a 1208 T r o i l u s

CEMP CFU

---

0.057 0.036

1508 K e m i

BCF

--

--

1593 F a g n e s 1602 I n d i a n a 1646 R o s s e l a n d

-RU --

----

0.11

1656 S u o m i

R

--

0.11

1658 R o e m e r a 2055 D v o r a k 2078 N a n k i n g

RU ---

----

----

---

Albedo D e f i n i t e l y n o t an E - t y p e

Albedo

468

HAHN AND LAGERKVIST

quite large errors in the J H K colors (Hartmann et al. 1982). The D-type asteroids, which have m e a n J-H = 0.41 + 0.02 and H - K = 0.17 -+ 0.01, are found to be rather well c o n c e n t r a t e d in the J H K diagram, with the possible exception of 884 Priamus. For the asteroids of types F, G, R, and V we have only one or two objects per type, thus not allowing any calculation of the mean J H K colors for these types. We note that 2 Pallas and 4 Vesta are more blue in J-H than almost all the other asteroids in this study. The m e a n colors for the major taxonomic types are s u m m a r i z e d in Table IV together with their mean errors and the n u m b e r of each sample. 51 N e m a u s a (see Fig. 5) is a strange asteroid and it is not possible to classify it as either an S- or a C-type asteroid. It lies between the R-type 349 D e m b o w s k a and the group of three N E A (cf. Figs. 1 and 6). H a h n et al. (1986) reported spectral variations for 51 N e m a u s a , which also shows a c o m p l e x lightcurve (see, e.g., G a m m e l gaard and Kristensen 1986). Of the 137 mainbelt asteroids with J H K data 7 asteroids have no classification at all O. 70

I

I

and 6 asteroids have ambiguous classifications, meaning that they have types combined with an " U " for unclassifiable. Three additional asteroids (361 Bononia, 409 Aspasia, and 1508 Kemi) have intermediate types (Tholen 1984). These 16 asteroids are plotted in Fig. 5. In Table V we p r o p o s e new or changes in previous classifications based on J H K photometry, which of course m a y be different from classifications based on U B V photometry. Table V contains also all asteroids plotted in Fig. 5, together with their IRAS albedos pv (Matson 1986). N o further interpretation of these data has been made, because the IRAS albedos given here are still preliminary and m a y be subject to minor revisions (E. F. T e d e s c o , private communication). The main purpose was to show for which of the asteroids in this sample there also will be I R A S data available. Near-Earth Asteroids

The N E A data are plotted in Fig. 6 and a s u m m a r y of all available J H K p h o t o m e t r y from different sources is given in Table VI (transformed to our system, where possii

[

I

I

I

O. G 5 O.

Type

60

O. 55

•

IIEA

o

Comets

• 1943

O. 50

1862

O. 45

2 3 6 8 0|1~27 DA

4~ °1685

0.40

22811

1~66

"1915

~ ~ e2100 0 SB

BO

O. 3 5

I

0~

o AR

os H oR]OKK

OG2

6

I 1 1 9 7 9 vA

O. 30 3200 O. 25 I -0. I0

I O. O0

,

I

,

I O. I0 H

i -

I

,

I O. 20

,

I

,

I O. 30

L

K

FiG. 6. JHK colors m magnitudes for near-Earth asteroids and comets. G2, Gehrels 2; SG, SwiftGehrels; H, Howell; B, Bowell; SB, Slaughter-Burnham; KK, Kearns-Kwee, R1, Reinmuth 1; S, Shoemaker; N1, Neujmin 1; AR, Arend-Rigaux.

JHK PHOTOMETRY OF ASTEROIDS

469

TABLE VI JHK DATA FOR NEAR-EARTHASTEROIDS Asteroid

Type Old

433 Eros 1036 Ganymed 1627 Ivar 1685 Toro 1862 Apollo 1866 Sisyphus 1915 Quetzalcoatl 1943 Anteros 2100 Ra-Shalom 2201 Oljato 2368 Beltrovata 3200 Phaethon 1979 VA 1986 DA

S S S S Q S (10) SMU S (5) C -SQ B (7) CF M (10)

J-H

H-K

Source

0.44 0.34 0.46 0.41 0.44 0.39 0.39 0.54 0.36 0.39 0.45 0.26 0.33 0.46

0.07 0.04 0.14 0.06 0.07 0.09 0.04 0.06 0.17 0.02 0.13 0.01 0.18 0.14

l 2 2 3 4,9 2 3 5 4 6 NT 3 7,8 NT 9 10 NT

New

D? S A? D? D?

N o t e . Sources: 1, Chapman and Morrison (1976); 2, this paper; 3, Veeder et al. (1982); 4, Veeder et al. (1983a); 5, Veeder et al. (1981); 6, McFadden et al. (1984); 7, Green et al. (1985); 8, Veeder et al. (1984); 9, Hartmann et al. (1982);

10, Tedesco and Gradie (1987). NT, Colors not transformed to our system.

ble, s e e a b o v e ) . F r o m Fig. 6 it c a n b e s e e n t h a t t h e r e is a w i d e s p r e a d in t h e J H K colo r s f o r t h e s e o b j e c t s , p r o b a b l y reflecting a variety of surface materials. Almost half of t h e m fall i n t o t h e S - t y p e d o m a i n (cf. Fig. 1), w h i c h l o n g s e e m e d to b e t h e d o m i n a t i n g type among NEA. On the other hand, one finds 1862 A p o l l o in this r e g i o n , a n o b j e c t w h i c h is c l a s s i f i e d as Q b y T h o l e n (1984). The S classification by Tedesco and Grad i e (1987) o f 1866 S i s y p h u s is also c o n f i r m e d b y U B V p h o t o m e t r y d a t a : U-B = 0.45, B - V = 0.88 (G. H a h n , u n p u b l i s h e d r e s u l t s ) . 1943 A n t e r o s , c l a s s i f i e d as S b y V e e d e r e t a l . (1981), h a s a J - H w h i c h p l a c e s it n e a r t h e A - t y p e r e g i o n . T h e original J H K c o l o r s o f 1943 A n t e r o s a r e J - H = 0.66, H - K = 0.02 ( V e e d e r e t a l . 1981) a n d this a s t e r o i d is o n e o f t h e v e r y f e w c h a n g i n g its c o l o r s b y a larger amount through the transformation to o u r s y s t e m ( s e e a b o v e ) . T h e a s t e r o i d s 1627 I v a r , 2368 B e l t r o v a t a , a n d 1986 D A have almost identical JHK colors but are well s e p a r a t e d in a U B V d i a g r a m . T h e

U B V c o l o r s a r e f r o m H a h n e t a l . (1987), B o w e l l e t a l . (1979), a n d Z e l l n e r e t a l . (1985). 1986 D A w a s c l a s s i f i e d b y T e d e s c o a n d G r a d i e (1987) to b e a n M a s t e r o i d b e c a u s e o f t h e U B V c o l o r s a n d the a l b e d o . T h e U B V c o l o r s o f 1627 I v a r a n d 2368 Beltrovata are consistent with the S class. R e c e n t l y , W i s n i e w s k i (1987) f o u n d , o n t h e b a s i s o f f i v e - c o l o r p h o t o m e t r y , 1986 D A to be a m e m b e r o f t y p e E M P . J u d g i n g f r o m t h e J H K d i a g r a m t h e t y p e w h i c h s e e m s to b e m o s t g e n e t i c a l l y r e l a t e d to t h e s e t h r e e o b j e c t s is t h e D - t y p e . T h e r e is, h o w e v e r , a p o s s i b i l i t y t h a t t h e f a s t r o t a t i o n o f 1986 D A ( P = 3.58 hr, A = 0.3 m a g , W i s n i e w s k i 1987) c o u l d c a u s e s o m e s y s t e m a t i c e r r o r s in both the UBV and JHK colors. However, t h e a l b e d o s o f b o t h 1627 I v a r a n d 1986 D A a r e t o o high for t h e m to b e D - t y p e a s t e r oids. It is a l s o i n t e r e s t i n g to c o m p a r e t h e c o m e t a r y d o m a i n in the J H K d i a g r a m w i t h the N E A . In Fig. 6 w e h a v e p l o t t e d c o l o r s f o r

470

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eight active comets, taken from Hartmann et al. (1982), as well as the colors for the low-activity comets P/Neujmin 1 (Davies 1985) and P/Arend-Rigaux (Tokunaga and Harmer 1985, Brooke and Knacke 1986, Birkett et al. 1987, Veeder et al. 1987). Also these data have been transformed to our system, taking advantage of the fact that all cometary observations were made with the same equipment as used by McCheyne et al. (1985) or Veeder et al. (1982, 1983a). This comparison shows that at least two NEA, 2100 Ra-Shalom and 1979 VA, exhibit J HK colors similar to cometary dust and that also 1627 Ivar, 2368 Beltrovata, and 1986 DA are very close to the cometary domain in the J H K diagram. This vicinity could be interpreted as a possible cometary origin for these NEA. The extinct-cometary candidates, 2201 Oljato and 3200 Phaethon, cannot be classified uniquely on the basis of their JHK colors. The colors for 3200 Phaethon, taken as the mean from the two published values (Green et al. 1985, Veeder et al. 1984), resemble very closely those of 2 Pallas and 4 Vesta (see Fig. 4), but its aibedo (0.089) is much lower than that for these two asteroids. On the contrary, the albedo for 2201 Oljato found by IRAS turned out to be very high (0.33). None of these objects show any cometary correlation, based upon JHK photometry (cf. Fig. 6). However, some caution should be taken when comparing asteroid and comet colors since the comet colors depend to some extent on the size of the diaphragm used. One other uncertainty in interpreting J H K colors in terms of surface composition comes from the ambiguity of these colors when strong absorption features are not centered within the J H K broadbands (see, e.g., Clark 1982). Figure 6 shows that the NEA occupy a very large region in the J H K diagram, covering all taxonomic types. This large variety in the composition of the NEA suggests the conclusion that these objects originate from different regions in the main belt. A cometary origin for at least some NEA is

possible, mainly those found with red and dark surfaces (see also Hartmann et al. 1987). A definite determination of the chemical and mineralogical composition of the surface material of NEA will probably be possible only by an in situ analysis of a spacecraft lander or through a sample-return mission, which hopefully will become reality before the end of this century. ACKNOWLEDGMENTS We thank the night assistants at the ESO l-m telescope, Mr. R. Vega, Mr. N. A. Yagnan, and Mr. Baham o n d e s , for their experienced help. Especially we thank Dr. P. Bouchet, ESO, La Silla, for his kind help with the reductions. We also thank the referees Dr. D. J. Tholen and Dr. G. J. Veeder for their helpful criticism. REFERENCES BIRKETT, C. M., S. F. GREEN, J. C. ZARNECKI, AND K. S. RUSSEL 1987. Infrared and optical observations of low-activity comets, P/Arend-Rigaux (1984k) and P / N e u j m i n I (1984c). Mon. Not. R. Astron. Soc. 225, 285-296. BOUCHET, P. 1987. Reduction p r o g r a m m e s for infrared observations made at La Silla. Users Manual. ESO, La Silla. BOWELL, E., T. GEHRELS, AND B. ZELLNER 1979. Magnitudes, colours, types and adopted diameters of asteroids. In Asteroids (T. Gehrels, Ed.), pp. 1108-1129. Univ. of Arizona Press, Tucson. BROOKE, T. Y., AND R. F. KNACKE 1986. The nucleus of c o m e t P/Arend-Rigaux. Icarus 67, 80-87. CHAPMAN, C. R., AND D. MORRISON 1976. J , H , K photometry of 433 Eros and other asteroids. Icarus 28, 91-94. CLARK, R. N. 1982. Implications of using broadband p h o t o m e t r y for compositional remote sensing of icy objects. Icarus 49, 244-257. CRUIKSHANK, D. P., D. J. THOLEN, J. F. BELL, B. R. HAWKE, W. K. HARTMANN, AND A. D. STORRS 1985. The olivine-rich asteroids (abstract). Bull. Amer. Astron. Soc. 17, 730. DANKS, A. C. (Ed.) 1979. Users Manual, D.I., pp. 5 7. ESO, La Silla. DAVIES, J. K. 1985. Is 3200 Phaethon a dead comet? S t ' Tel. 70, 317-318. ELIAS, J. H., J. A. FROGEL, K. MATTHEWS, AND G. NEUGEBAUER 1982. Infrared standard stars. Astron. J. 87, 1029. ENGELS, O., W. A. SHERWOOD, W. WAMSTEKER, AND G. V. SCHVLTZ 1981. Infrared observations of southern bright stars. Astron. Astrophys. Suppl. Ser. 45, 5-9.

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