Photoelectric photometry of 21 asteroids

ICARUS 56, 325--344 (1983)

Photoelectric Photometry of 21 Asteroids V. ZAPPAL,A,, F. SCALTRITI, AND M. DI MARTINO Astronomical Observatory of Torino, 10025 Pino Torinese, Turin, Italy Received F e b r u a r y 21, 1983; revised June 13, 1983 Photoelectric lightcurves of 21 asteroids are presented. T h e observations were carried out from 1978 to 1982 at the Astronomical O b s e r v a t o r y of Torino (at the Astrophysical O b s e r v a t o r y of Catania for 137 Meliboea). For l0 objects a reliable rotation period has been obtained, while for two others a rough estimate is given. In several c a s e s the analysis of the o b s e r v e d amplitudes v e r s u s the ecliptic longitudes indicates the m o s t favorable future oppositions for period and/or pole determination. For s o m e asteroids transformations to U B V Standard S y s t e m were performed.

ing night. In this case we adjusted our vertical scale by sliding the lightcurves to obtain the best fit, The ordinates are magnitudes (the zero of the scale being at maximum) and the abscissae are UT hours, not corrected for light time, and refer to the observing night whose date is reported in the figure. Sometimes at the end of the curves groups of points are repeated for reasons of completeness. When no reliable value of the period was found, the ordinates represent magnitude differences in the instrumental system. In Table II we summarize our results for the observed asteroids, and for each object the taxonomic type and the diameter are reported at the beginning.

INTRODUCTION

This paper presents photoelectric lightcurves of 21 asteroids. Eight of them are Stype, 9 are C-type, 1 is M-type, and 3 are not of well-defined classification, i.e., CEU, CU, and CMEU. The range of sizes is 20 to 208 km. Types and diameters are taken from Bowell et al. (1979). Among these objects, 10 previously unknown rotation periods were determined accurately, while for two others only a tentative value was obtained. The observations cover the period from 1978 to 1982, and were performed with three telescopes: the 45 and 105-cm reflectors of Torino Observatory, and the 91-cm reflector of Catania Observatory. The last one was used only for 137 Meliboea. The observing and reduction procedure was the standard one, based on consecutive measurements of selected comparison star, sky reading, and asteroid. In some cases transformation to the UBV System was performed by means of groups of standard stars taken mainly from Blanco et al. (1968). All the aspect and magnitude data are listed in Table I; the last two columns give the identification of the adopted comparison stars and the telescope's size. We present also a set of 29 figures. When possible a composite lightcurve is shown, adopting different symbols for each observ-

ANALYSIS OF THE LIGHTCURVES

8 Flora Flora is classified as a S-type object, with a diameter of 160 km. It is considered the largest remnant of one of the Hirayama families, and therefore the knowledge of its rotational properties is of the highest importance. However, even though observations of this bright object were performed during five oppositions, no reliable value of its rotational period was deduced. It was observed photoelectrically for the first time by Ahmad (1954), during the 1953 apparition, at a longitude of about 157°. The amplitude of the light variation was very small (about 0.02 mag), suggesting a pole-on view 325 0019-1035/83 $3.00 Copyright © 1983by AcademicPress, Inc. All rights of reproduction in any form reserved.

326

ZAPPALA, SCALTRITI, AND DI MARTINO TABLE

I

ASPECT DATA, MAGNITUDE INFORMATION, COMPARISON STARS, AND TELESCOPES USED FOR THE ASTEROIDS

8 Flora, 11 Parthenope, 60 Echo, 63 Ausonia, 75 Eurydike, 77 Frigga, AND 78 Diana Date (0h UT)

RA (1950)

Decl (1950)

Long (1950)

Lat (1950)

r (AU)

A (AU)

Phase

09h28~3 0922.0

+19°04 ' +19 55

138736 136.69

+ 3?94 + 4.27

2.190 2.201

1.221 1.220

6?2 3.1

11h12% 10 5 3 . 6

+10023 ' +12034 '

165704 159.89

+ 4?87 + 5.08

2.664 2.651

1.675 1.758

2?4 12.0

05h02~3

+17007 '

76715

-

5?64

2.006

1.050

9?8

01h04~6

+14034 '

20?48

+ 7710

2.485

1.512

6?0

02h03~4 0202.5

+17022 ' +17 21

34.°72 34.50

+ 4?54 + 4.60

2.024 2.026

1.046 1.046

03~)8~6 0307.7

+20°37 ' +20 35

50?40 50.19

+ 2?87 + 2.89

2.327 2.326

01h55~3

+25013 '

35.70

+12755

2.511

V0(l,a)

Comp. star

Telescope

8Flora 1979 01 26 02 01

1 2

45 45

11 Parthenope 1980 03 10 04 03

BD +11°2336 BD +13°2327

105 45

60 Echo 1979 11 20

BD +16°691

45

63Aasonia 1981 10 28 1980 10 13 10 14 77

7~75

3

105

7?8 7.2

4 4

45 45

1.352 1.349

671 5.6

5 5

45 45

1.532

5?0

6

45

Eurydike

75

Frigga 1980 10 30 10 31

78Diana 1980 10 27 123456-

RA(1950) RA(1950) RA(1950) RA(1950) RA(1950) RA(1950)

= 09h28~1; =0921.5; = 01 04.3; = 02 03.0; = 03 08.4; = 01 55.1;

Decl(1950) Decl(1950) Decl(1950) Decl(1950) Decl(1950) Decl(1950)

= = = = = =

+ 19017 , +20o00 ' + 14°35 ' +17°16 ' +20°50 ' +25016 ' TABLE

ASPECT DATA,

MAGNITUDE INFORMATION, COMPARISON STARS, AND TELESCOPES USED FOR THE ASTEROIDS 83

Date (0hUT) 83

l--Continued

RA (1950)

Beatrix, 109 Felicitas, 137 Meliboea, AND 144 Vibilia

Decl (1950)

Long (1950)

Lat (1950)

r (AU)

A (AU)

Phase

08h10~5 0809.4 0808.3 0807.1

+28°46 ' +28 49 +28 52 +28 55

118755 118.29 118.04 117.78

+ + + +

8?50 8.50 8.49 8.48

2.358 2.357 2.356 2.355

1.381 1.381 1.382 1.382

06h06~3 0600.9

+39003 ' +39 10

91727 90.18

+15761 +15.71

1.947 1.955

23h39~.5 23 38.8 23 38.2

+ 8050 ' + 8 41 + 8 31

358?84 358.62 358.41

+10715 +10.07 + 9.98

1980 12 18 1981 01 09 01 10 01 16

06h34% 06 11.1 0610.1 0604.9

+25031 ' +26 24 +26 26 +26 34

97781 92.48 92.27 91.10

+ + + +

7891011-

= = = = =

V0(1,a)

Comp. star

Telescope

3?8 4.1 4.4 4.7

7 8 9 10

105 105 105 105

0.989 0.991

9?4 8.1

BD +38°1393 BD +39°1495

45 45

2.547 2.549 2.551

1.560 1.559 1.559

5?5 5.2 4.9

BD +8°5101 BD +8°5101 BD +7°5074

91 91 91

2.446 2.502 2.505 2.520

1.476 1.542 1.548 1.591

4?9 6.2 6.7 9.3

BD +25°1344 BD +26°1142 BD +26°1142 11

45 45 45

Bea~ix 1982 01 01 01 01

23 24 25 26

109Fel~itas 1980 12 13 12 18

137Meliboea 1980 09 12 09 13 09 14

144Vibilia

RA(1950) RA(1950) RA(1950) RA(1950) RA(1950)

08h11~0; 08 09.2; 08 07.5; 08 07.2; 06 04.9;

Decl(1950) Decl(1950) Decl(1950) Decl(1950) Decl(1950)

= = = = =

2731 2.98 3.00 3.13

+28°47 , +28°52 ' +28°55 ' +28°57 ' +26°32 ,

8.m21 8.32 8.34 8.47

PHOTOELECTRIC PHOTOMETRY OF 21 ASTEROIDS TABLE ASPECT

327

I--Continued

DATA, M A G N I T U D E INFORMATION, COMPARISON STARS, AND TELESCOPES USED FOR THE ASTEROIDS 196 Philomela, 211 lsolda, 372 Palma, 556 Phyllis, AND 593 Titania

Date (0hUT)

RA (1950)

Decl (1950)

Long (1950)

Lat (1950)

r (AU)

A (AU)

Phase

V0(l,~)

Comp. star

Telescope

05h09~4 05 0 7 . 6 05 0 5 . 8

+23025 , +23 27 +23 29

78?40 78.00 77.59

+ 0?49 + 0.55 + 0.61

3.167 3.167 3.167

2.193 2.189 2.186

3?4 2.7 2.0

6~87

12 13 14

105 105 105

196Philomela 1981 11 30 12 02 12 04

6.86

2111solda 1980 12 10

05h42~2

÷23°29 '

85?92

+ 0710

2.586

1.608

371

BD +23°1027

45

372 Palma 1979 01 16 01 17

06h38% 0637.4

+50o34 , +50 22

96?89 96.69

+27?36 +27.14

2.347 2.348

1.457 1.460

1279 13.1

15 15

45 45

556 PhyH~ 1981 11 16

02h33~4

+23010 '

43?30

+ 7769

2.309

1.334

5?3

16

105

07h07~7 07 0 5 . 4

+37058 ' +38 20

103777 103.26

+15733 + 15.63

2.122 2.122

1.158 1.160

771 7.4

17 18

45 45

593Titania 1981 01 06 01 08 12-RA(1950) 13-RA(1950) 14-RA(1950) 15-RA(1950) 16-RA(1950) 17-RA(1950) 18- RA(1950)

= 05h09~7; = 05 08.2; = 05 05.9; = 06 38.8; = 0 2 33.1; = 0706.9; =0704.3;

Decl(1950) Decl(1950) Decl(1950) Decl(1950) Decl(1950 ) Decl(1950) Decl(1950)

= = = = = = =

+23o28 , +23029 ' +23o55 ' +50029 , +23010 ' +37056 ' +38017 ' TABLE

I--Continued

ASPECT DATA, MAGNITUDE INFORMATION, COMPARISON STARS, AND TELESCOPES USED FOR THE ASTEROIDS 622 Date (0hUT)

Esther, 674 Rachele, 712 Boliviana, 739 Mandeville, AND 747 Winchester

RA (1950)

Decl (1950)

Long (1950)

Lat (1950)

r (AU)

A (AU)

Phase

1981 11 17 11 18 11 19

02h51~1 02 5 0 . 4 02 4 9 . 7

--02°37 ' --02 37 --02 37

39?50 39.32 39.14

674 Rachele 1978 10 05 I0 08

02h11~3 02 0 9 . 0

+00021 ' +0016

712 Boliviana 1980 10 13 10 14 10 27

01h27~0 Ol 26.3 Ol 16.9

V0(l ,a)

Comp. star

Telescope

--18717 --18.12 --18.06

1.829 1.830 1.830

0.879 0.882 0.885

1273 12.6 13.0

19 19 19

105 105 105

30?74 30.16

-12712 -12.01

2.691 2.685

1.742 1.725

8?4 7.3

20 20

45 45

+20o52 ' +20 41 +17 56

27?89 27.66 24.52

+10789 +10.78 + 9.09

2.125 2.124 2.113

1.143 1.140 1.132

6?4 6.1 5.9

21 21 22

45 45 45

10h56~6 10 5 6 . 0 10 5 5 . 6

+15°08 ' + 15 36 +15 51

159757 159.26 159.07

+ 7?73 + 8.11 + 8.30

2.381 2.380 2.379

1.461 1.449 1.443

1078 10.0 9.6

BD + 15°2274 BD + 15°2274 BD +16°2190

45 45 45

08h23~5 08 2 2 . 6 08 18.0 08 14.0 08 10.4

+18°13 ' + 18 23 + 19 25 +20 20 +21 23

123782 123.59 122.28 121.16 120.12

+ +

2.555 2.559 2.581 2.603 2.632

1.581 1.587 1.630 1.683 1.766

4?3 4.7 7.4 9.9 12.8

622Esther

739Mandeville 1981 02 03 02 05 02 06

9m44 9.42 9.40

747Winchester 1980 02 02 02 02 02

05 06 12 18 26

19- RA(1950) 20- RA(1950) 21- RA(1950) 22-RA(1950)

= = = =

02h50~.6; 02 10.3; 01 26.6; 01 16.7;

Decl(1950) Decl(1950) Decl(1950) Decl(1950)

= = = =

1712 0.99 0.25 0.45 1.28

-02034 , +00024 ' +20050 ' +17°46 '

BD BD BD BD BD

+ 18°1936 +18°1935 +19°1985 +20°2038 +21°1786

105 105 45 105 105

328

ZAPPALA,

SCALTRITI,

AND DI MARTINO

T A B L E II PERIODS, AMPLITUDES, AND REMARKS CONCERNING THE ASTEROIDS PRESENTED IN THE PAPER

Asteroid

8 11 60 63

Flora Parthenope Echo Ausonia

Period (hr) ---9.297

Amplitude (mag) <0.02 >0.07 >0.03 0.81

Remarks

a/b ~ 2.4; b/c ---- 1.0; possible longitude of the pole 130°

(310o) 75 Eurydike 77 Frigga

8.92 9.00

0.14 0.07

78 83 109 137 144 196 211 372

Diana Beatrix Felicitas Meliboea Vibilia Philomela Isolda Palma

-10.16 26.3 >16 13.810 8.32 -8.67 or 12.83

>0.01 0.18 ~0.06 >0.04 0.13 0.07 >0.07 0.12

556 593 622 674 712 739 747

Phyllis Titania Esther Rachele Bolioiana Mandeville Winchester

4.28 9.39 47.5 -11.87 15.9 9.40

0.24 0.24 0.6-0.7 >0.04 0.11 0.14 0.13

Three e x t r e m a C o m p l e x lightcurve; possible equatorial view at h = 120° + 160 ° (300 ° + 340 °) Possible equatorial view at h = 140° (320 °) Irregular and a s y m m e t r i c lightcurve

Possible equatorial view at h = 0 ° + 20°(180 ° + 200 °) Lightcurve resembling that of an eclipsing binary The shorter period implies that the s e c o n d a r y m i n i m u m is not present or that it is m a s k e d by a broad irregular maximum

Long period Also the double period (23.h75) is possible

or a quasi-spherical shape. Van HoutenGroeneveld and Van Houten (1958) repeated the observations during 1955-1956 at a longitude of about 118°. The light variation in this case also had a small amplitude (about 0.04 mag); however, these authors could suggest a very tentative period of about 13.6 hr. This value seemed confirmed by Veverka (1971), based on observations performed during 1969. The amplitude was again very small (about 0.04 mag), while the longitude was nearly 95°. The observations of the present paper refer to the 1979 opposition, when the longitude was 137° and the amplitude less than 0.02 mag. The lightcurves obtained, shown in Figs. 1 and 2, seem to be against the suggested period, but cannot give additional information for its determination. More important were the 1980 observations carried out by Harris (1981, private communication), who re-

ported an amplitude of about 0.1 mag at a longitude of about 240° . However, he also failed to obtain a reliable period, suggesting a possible value of the order of 8-9 hr, not in disagreement with our lightcurves. The relatively large amplitude obtained in the 1980 opposition confirms that all the previous observations were performed very close to a pole-on view and that the shape of Flora is not as spherical as we formerly believed. Av, -0,~2

Jan 25-26,1979

°"

o o~

• 0 oe

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qt e"e

•

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3.14

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22 h I

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UT(n.c) I

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FIG. 1. Lightcurve o f 8 Flora obtained on January 25-26, 1979.

PHOTOELECTRIC PHOTOMETRY OF 21 ASTEROIDS AV n --~.26

Jan 31-Feb 1,1979

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FIG. 2. Lightcurve of 8Flora obtained on January 31-February 1, 1979.

Figure 3 shows the amplitude-longitude plot and a tentative trend for this asteroid. It appears that the amplitude should be the largest, and therefore the best conditions for identifying the rotational period should be optimized at longitudes 40-60 ° or 220240°. The next favorable oppositions will be those of May 1983 (longitude -220 °) and October 1984 (longitude -20°). Due to the high physical interest of this object, we strongly suggest performing a coordinated campaign during these apparitions. Figure 3 gives a rough indication for a pole longitude close to 120-160 ° or 300340°.

11 Parthenope This asteroid (S-type, D = 155 km) shows problems similar to those of 8 Flora. After three oppositions no reliable period can be suggested, Van Houten-Groeneveld and Van Houten (1958) observed it in 1956 for the first time. They suggested a period of about 10.7 hr, doubling their longest run, in which maxima seemed to be present at the beginning and at the end. However, the real presence of these extrema is highly doubtful. In 1960, Wood and Kuiper (1963)

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observed Parthenope again, but could not give further information on its rotational properties. They only stated that their lightcurves were not against the suggested period. In this paper we present two lightcurves performed during the 1980 opposition. The longest of them (April 2-3) seems to disagree with the suggested rotation because the decrease, lasting about 4 hr, suggests a period at least of the order of 16 hr. However, this last conclusion can be valid only if the complete lightcurve is really symmetric, and we do not know if this is true in the case of Parthenope. Our observations are shown in Fig. 4, while in Fig. 5 amplitudes are plotted against longitudes, in the same way as for Flora. The only favorable opposition, with an expected amplitude of about 0.1 mag, will be that of December 1986. Also in this case a coordinated campaign will be very useful. For 11 Parthenope we could suggest a pole longitude of about 20 or 200°.

60 Echo Our single-night lightcurve, performed on November 1979 and shown in Fig. 6, cannot help in determining the period of this small (D = 52 km) S-type object, which is already supposed to be very long. A slow rotation was pointed out by Gehrels and • wings (1962), who suggested a tentative value of about 30 hr, and by Schober (1979, private communication), who hazarded a period of about 52 hr. Harris and Young's data (1983), even if affected by a suspected variability of the comparison star, seem to confirm this latter value. However, further

330

ZAPPALA, SCALTRITI, AND DI MARTINO -0.~3

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0.57

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FIG. 4. Lightcurves o f 11 Parthenope observed on March 9 and April 2-3, 1980.

observations are needed. The amplitude of our lightcurve is about 0.03 mag. 63 Ausonia

63 Ausonia is classified as a S-type object with a diameter of about 94 km. In 1976 a considerable number of lightcurves was obtained by Scaltriti and Zappal~ (1977). They found a rotational period of 9.h297 -+ 0.h001 and a maximum amplitude of 0.47 mag; moreover a V0 (I,0) magnitude of 7.49 mag and a phase coefficient of 0.035 were deduced. In 1980 Lagerkvist (1981) reobserved this asteroid on two nights, confirming the period, but obtaining a much higher amplitude of about 0.95 mag, quite uncommon for a main-belt object.

The high amplitude and the regular trend of the complete lightcurve of 63 Ausonia led us to list this asteroid as a candidate for pole determination (Zappalh, 1981; Zappal~ and Scaltriti, 1982) and therefore observations at different longitudes have been planned. In the present paper we report those obtained in 1981, on October 27-28 (Fig. 7). The amplitude was 0.81 mag. Some preliminary considerations can be made: (a) The V0 magnitudes obtained in the three oppositions, when the aspect was surely quite different, as confirmed by the amplitudes, satisfy the same magnitude-phase relation, implying that Ausonia should have a cigarlike shape; i.e., the b/c ratio between the shortest axes is very close to 1. (b) The AV I •

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h 119

,

211

,

213

UT (n.c.) ,

FIG. 6. L i g h t c u r v e o f 60 Echo obtained on N o v e m ber 19-20, 1979.

PHOTOELECTRIC PHOTOMETRY OF 21 ASTEROIDS _

331

AV I al'~qt ~

Oct

27-28,1981

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maximum possible amplitude should be about 0.95-1.00 mag, implying an a/b ratio of about 2.4. (c) The pole longitude should be about 130 or 310°, but other observations, mainly from 60 to 140° or 240320°, are needed to determine a reliable value of the rotational axis direction. The most favorable oppositions for this purpose will be on 1984 and 1989.

very fast rotation, mainly when the size is larger than about 100 km (Zappal~t et al., 1982). Some of them can be interpreted as triaxial equilibrium ellipsoids (Farinella et al., 1981a). Indeed Harris (1982, private communication) suggested a very short rotational period, i.e., 5.356 hr, in good agreement with the typical rotation of this group. This value, obtained assuming as usual two maxima and minima per cycle, could be confirmed by a previous photographic observation by Lagerkvist and SjOlander (1979). However, our data contrast with the former conclusion. The longest run (Octo-

75 Eurydike This object is classified as a CMEU type, having a diameter of 99 km. Several asteroids belonging to this peculiar group show

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FIG. 8. C o m p o s i t e lightcurve o f 75 Eu~/dike (with Psy, = 8.~92). &, O c t o b e r 12-13; Q, O c t o b e r 1314, 1980.

332

ZAPPALA, SCALTRITI, AND DI MARTINO

ber 12-13, triangles in Fig. 8) clearly shows an ad hoc example for the problem evithat three extrema are present in the full denced before for 75 Eurydike. If we accept cycle, and therefore the period of rotation two maxima and two minima per cycle, the results 8~.92 --+ 0.h01, with a total amplitude corresponding period results 6.75 hr. Howof about 0.14 mag. The only possibility for ever, assuming a more complex lightcurve, o , r measurements to be in agreement with we could easily obtain 9.h00 --- 0.h01, in very Harris' determination is that at about 4-5 h good agreement with Lagerkvist and RickUT on October 13 an unseen faint star man's result. The fact that the lightcurves crossed our diaphragm. However, the dura- of some asteroids can have different shapes tion of the transit, taking into account the at different aspects is well evidenced. This asteroid motion and the diaphragm size, probably implies some macroscopic topocould not be longer than 20 min. while the graphic feature on one hemisphere of the observed increase in magnitude persisted asteroid (the observations being very probfor about 50 min. Therefore we are quite ably obtained after and before the equatosure that the extremum at 4-5 h UT was rial view). The composite lightcurve, different from that at 22-23 h UT. The adopting the 9.h00 period, is given in Fig. 9. composite lightcurve is shown in Fig. 8. Figure 10 represents a comparison between If our period is correct, as we believe, 75 1980 and 1982 observations. Assuming arbiEurydike is a further example of an object trarily that the deepest minimum was the with an unusual lightcurve. It gives evi- same in both oppositions, we see that at the dence that some adopted periods, based on epoch of the 1982 secondary minimum we single-night curves with the assumption of should probably expect a third maximum or two maxima and two minima per cycle, a very flat minimum in 1980. Moreover the might be wrong. This possibility should be maximum epochs are considerably shifted. taken into account, because it is relevant Analyzing the amplitude-longitude plot, for statistical studies. equatorial view should occur at 120-160 ° or 300-340 °. Therefore favorable opposi77 Frigga tions will be those of 1984, 1986, and 1988. This is an M-type object, with a diameter of 77 km. Lagerkvist and Rickman (1982) 78 Diana obtained lightcurves during the 1982 oppoThe only available lightcurve for this Csition. The deduced period was (9.01 -+ type asteroid (D = 144 km) was obtained by 0.01) hours and the maximum amplitude re- Dunlap in 1969 (Taylor et al., 1976). Acsulted 0.19 mag. 77 Frigga showed a typical cording to the authors, a period of about 8 double-wave lightcurve. Our observations hr was highly possible. The amplitude rewere performed two years before and give sulted 0.13 mag. In 1980 this object was

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FIG. 9. Composite lightcurve of 77 Frigga (assuming Psyn = 9.h00). &, October 29; O, October 30-31, 1980.

PHOTOELECTRIC PHOTOMETRY OF 21 ASTEROIDS

333

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FIG. 10. Comparison of synthetic lightcurves of 77 Frigga between the 1980 and 1982 apparition.

reobserved by us and by Harris (1981, private communication). Our single-night lightcurve cannot say anything more on the period, but Harris could obtain unambiguously a value of 7.22 hr, with a very low amplitude of 0.03 mag. Our run is shown in Fig. 1I. The amplitude-longitude trend indicates that the maximum possible amplitude should occur for longitudes very close to 140° (320°). Therefore the most favorable oppositions for pole and shape determination are foreseen for 1987 (276°) and 1990 (118°).

during the 1978 apparition (Haupt, 1980). Only a broad maximum and a secondary peak were covered during this run and therefore no reliable period could be deduced. The present paper reports four nights of observation, which seem to infer only one possible period, namely 10h.16 --+ 0h.05, with an amplitude of 0.18 mag. The composite curve is presented in Fig. 12. It appears very irregular and asymmetricl Further observations of 83 Beatrix are recommended. 109 Felicitas

83 Beatrix

Classified as a C type, having a diameter of 118 km, Beatrix was observed one night

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FIG. 11. Lightcurve of 78 Diana obtained on October 26, 1980.

This small (D = 76 kin) C-type object was never photometrically observed before 1980. During this opposition we obtained two lightcurves, showing two maxima apparently of different shape. Taking into account the duration of the increase and decrease of the light variation, we could suggest a period longer than about 25 hr, but 26.h3 or 33h.8 might be plausible values. The first one is partially confirmed by Harris (1981, private communication), who reports a period of about 26 hr. From our lightcurves, presented in Figs. 13 and 14, the amplitude should be at least 0.06 mag.

334

ZAPPALA, SCALTRITI, AND DI MARTINO

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higher than 0.04 mag. The three lightcurves are shown in Fig. 15.

137 Meliboea Meliboea is a quite large C object (D = 153 km) for which no previous lightcurves were obtained. We observed it on three consecutive nights, but no period could be deduced. We can only state that it should be longer than 16 hr and the amplitude

144 Vibilia Vibilia is classified as a C type with a diameter of 132 kin. No previous results were found in the literature for its rotational properties. From our four observing nights,

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PHOTOELECTRIC PHOTOMETRY OF 21 ASTEROIDS

335

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during the 1980-1981 apparition, we deduce Psy, = 13.h810 ± 0-h003- The total amplitude is about 0.13 mag. The composite curve is shown in Fig. 16. 196 Philomela

This quite large asteroid (D = 162 km) is classified as a S type. During 1964, Yang et al. (1965) reported a period of 8.333 hr and an amplitude of about 0.33 mag. Our 1981 lightcurves, performed in three AVI

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nights, give a period of 8.h32 ± 0h.02, in good agreement with Yang's result. The composite lightcurve is presented in Fig. 17. Considering the amplitude obtained in both oppositions and the corresponding longitudes, a dramatic change in amplitude during a very small longitude interval (about 40°) is suggested. Since the phase angles were very small for both sets of observations, and therefore no amplitudephase effect is expected, the variation of amplitude should be completely due to the change in aspect. Consequently, a much higher amplitude (-0.4 mag) could be expected at longitudes between 180 and 200°. For an opposition close to the equatorial view we must wait until 1989.

1 I

FIG. 15. Lightcurves of 137 Meliboea obtained on September 11-12, September 12-13, and September 13-14, 1980.

211 Isolda is a quite large C asteroid (D = 168 km). Our single night lightcurve, performed on December 9-10, 1980 (Fig. 18), presents initially a fast increase in luminosity, followed by a very long fiat trend. Harris (1981, private communication) reported a period of 18.75 hr with an amplitude of about 0.10 mag. Therefore, our run should cover an interval slightly smaller than half the rotation period. This means

336

ZAPPALA, SCALTRITI, AND DI MARTINO

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that the complete cycle of 211 Isolda could look like that of 46 Hestia (Scaltriti et al., 1981a), resembling the lightcurve of an eclipsing binary system. Laboratory simulations are planned in order to separate the effects of a rough and irregular surface from

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those due to a real duplicity (Barucci et al., 1983). 372 Palma

372 Palma has been classified as a CEU type, with a diameter of 196 km. Informa-

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tion about the rotational properties is given only by Harwood (1921), who reported a period of about 0. ! day, assuming one extremum per cycle. Doubling it, we obtain a period of about 5 hr, as listed by Tedesco (1979). This tentative value must be now ruled out, according to the two consecutive lightcurves obtained by us in 1979. Two possible rotation periods result from their analysis: 8h.67 --+ 0h.04 or 12.h83 --+ 0h06. Adopting the shorter one, no secondary minimum appears; however, this could be masked in the very irregular broad maximum. If we remember the cases of 37 Fides (Zappal~ et al., 1983), 16 Psyche (Tedesco et al., 1983), 14 Irene (Scaltriti et al., 1981b), etc., this possibility cannot be disregarded. The composite curve is shown in Fig. 19. Obviously also a double period could be accepted. On the other hand, Psy, = 12h.83can be adopted and the consequent composite curve is shown in Fig. 20. In this case the secondary minimum, even if not covered by the observations, should occur at about 4 - 5 h UT. Both periods seem plausible to us, and therefore further observations are needed, mainly taking into account that Palma is one of the very few large asteroids without a reliable determination of its rotational properties. In both cases the total amplitude is about 0.12 mag.

556 Phyllis N o determination of the diameter has

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PHOTOELECTRIC PHOTOMETRY OF 21 ASTEROIDS

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been obtained for this object. Assuming for it an S type, as suggested by its orbital axis and adopting the absolute magnitude listed by Bowell et al. (1979) and the mean albedo for its taxonomic class (Zellner, 1979), we

could estimate a value of about 40 km. Only one observing night was performed in November 1981, but it was sufficient for period determination, assuming, however, two maxima and minima per cycle. The rotation

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FIG. 23. Representation of the full-cycle lightcurve of 622 Esther with the two possible periods P,y. = 47.h5 and Psyn = 15h.8, obtainable with our observations. The continuous and dashed lines refer to our runs; the dotted ones represent the possible trends.

340

ZAPPALA, SCALTRITI, AND DI MARTINO period results 4.h28 --+ 0h.02, with an amplitude of about 0.24 mag. Figure 21 shows the single-night curve.

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593 Titania

It is classified as a CU type, with D = 82 km. No previous information on its rotational properties was available in the literature. We observed it on two nights during the 1981 apparition. The lightcurve is regular with two well-defined maxima and minima, slightly different from each other. The period is 9h39 --+ 0.h03, the total amplitude about 0.24 mag. The composite curve is shown in Fig. 22.

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for small asteroids are not uncommon, as evidenced by Farinella et al. (1981b) and strengthened by some new results (Schober et al., 1982; Dermott et al., 1983). Figures 24 and 25 present the observed lightcurves.

ing into account their magnitude level, corrected for heliocentric and geocentric distances (the comparison star was always the same), we could state that the same minimum was seen in the first and third night, the second one being much deeper. Figure 23 presents the observational situation where the continuous lines refer to the observed intervals: only two periods are possible. The first one might be 15.8 hr, shown by the dashed line, but it seems very unlikely because of the " j u m p " needed at about 10h UT on November 17. Therefore we prefer to adopt a longer period, shown by the dotted line; it results in 4795. Very roughly we could also estimate a total amplitude of 0.6-0.7 mag. Very long periods

674 Rachele

674 Rachele is a S-type asteroid, having a diameter of 96 km. Harris and Young (1980) were not able to determine the period, but they stated that it should be longer than 30 hr. Our lightcurves, performed in 1978 and shown in Fig. 26, can only confirm this slow rotation, without any further contribution for solving the problem. Future observations are needed.

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342

ZAPPALA, SCALTRITI, AND DI MARTINO

712 Boliviana

This medium-size object (D = 128 km) is classified as a C type. We observed it on three nights during 1980. Its lightcurve resembles that of the asteroid 49 Pales (Scaltriti et al., 1979), for which a binary model was proposed by Van Flandern et al. (1979). We cannot be sure that the minimum, at about 2h UT in the composite lightcurve shown in Fig. 27, is a real feature; however, assuming this possibility, the period is 11.h87 _ ~01 and the amplitude is 0.11 mag. Obviously a double period of 23.~75 has also a good reliability.

e

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q/

2 739 Mandeville

For this medium-size object a diameter of 116 km and a C type is adopted. During 1981 three nights' data were taken. Taking into account the duration of the increase and decrease of the light variations, two periods seem plausible: 11.~9 or 15.h9. The first one, however, leads to a quite irregular shape of the complete cycle, producing minima not equally spaced. Moreover, Harris (1981, private communication) suggested a period of about 16h. For these reasons we prefer to adopt P~y, = 15~.9 +- 0.~1; the composite curve is shown in Fig. 28. The total amplitude is 0.14 mag.

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747 Winchester

This is a large asteroid (D = 208 km), belonging to the C taxonomic type. Also for this object no precise rotation period was found until now. Harris and Young (1980) proposed a value of 8h with a high degree of uncertainty. Adopting this period they noted, however, almost no magnitude correction for decreasing phase angle between their two nights. By means of our five nights we are able to determine a precise period of 9.M0 - 0~.01. This value also satisfies very well the Harris and Young data, producing a broader maximum, in good agreement with our result. Moreover our period implies a magnitude correction of about 0.02-0.03

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PHOTOMETRY

343

OF 21 ASTEROIDS

.

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FIG. 29. Composite lightcurve of 747 Winchester (with P,,, = 9?40). V, February 11; 0, February 17-18; A, February 25, 1980.

mag in their curves, which is reasonable for very small phase angles. The total amplitude is 0.13 mag. ACKNOWLEDGMENTS The authors thank A. W. Harris for many results in advance of publication and the Astrophysical Observatory of Catania for the observing time. This work was partially supported by the National Research Council of Italy (CNR).

REFERENCES AHMAD, I. I. (1954). Photometric studies of asteroids. IV. The lightcurves of Ceres, Hebe, Flora, and Kalliope. Astrophys. J. 120, 551-559. BARUCCI, M. A., R. CASACCHIA,M. FULCHIGNONI, R. BURCHI, A. DI PAOLOANTONIO,C. GIULIANI, L. MILANO, V. ZAPPAL& AND F. SCALTRITI (1983). Laboratory simulation of lightcurves for asteroidlike models. Moon Planets 27, 387-395. BLANCO, V. M., S. DEMERS, G. G. DOUGLASS,AND M. P. FITZGERALD(1968). Photoelectric Catalogue. Publ. U.S. Naval Obs., Second Series, 21. BOWELL, E., T. GEHRELS, AND B. ZELLNER (1979). Magnitudes, colors, types and adopted diameters of the asteroids. In Asteroids (T. Gehrels, Ed.), pp. 1108-l 129. Univ. of Arizona Press, Tucson. DERMOT~,S. F., A. W. HARRIS, AND C. D. MURRAY (1983). Asteroid rotation rates. Icarus, submitted for publication.

I

5

1

7

n , February 4; 0, February 5;

FARINELLA, P., P. PAOLICCHI, E. F. TEDESCO, AND V. ZAPPALA(198la). Triaxial equilibrium ellipsoids among the asteroids? Icarus 46, 114-123. FARINELLA, P., P. PAOLICCHI, AND V. ZAPPAL~ (198lb). Analysis of the spin rate distribution of asteroids. Astron. Asrrophys. 184, 159-165. GEHRELS, T., AND D. OWINGS (1962). Photometric studies of asteroids. IX. Additional lightcurves. Astrophys.

J. 135, 906-924.

HARRIS, A. W., AND J. W. YOUNG (1980). Asteroid rotation III. 1978 observations. Icarus 43, 20-32. HARRIS, A. W., AND J. W. YOUNG (1983). Asteroid rotation IV. 1979 observations. Icarus 54, 59-109. HARWOOD,M. (1921). Eros and Palma. HarvardBull. 766.

HAUPT, H. (1980). Photoelektrische Beobachtungen der Kleinen Planeten (83) Beatrix, (139) Juewa, (349) Dembowska und (389) Industria. Mitt. Universit&stern.

Graz 69.

LAGERKVIST,C.-I. (1981). Physical studies of asteroids II. Photoelectric observations of the asteroids 63, 93, 135 and 409. Astron. Astrophys. Suppl. 44, 345-347.

LAGERKVIST,C-i., AND N.-G. SJ~LANDER (1979). Photographic photometry of asteroids with Schmidt telescopes. II. Observations of 11 asteroids during 1977 and 1978. Acta Astron. 29 No. 3, 455-461. LAGERKVIST,C.-I., AND H. RICKMAN(1982). Physical studies of asteroids IX. The lightcurve of the M asteroid 77 Frigga. Moon Planets 27, 107-I 10. SCALTRITI,F., AND V. ZAPPALA(1977). A photometric study of the minor planet (63) Ausonia. Icarus 31,498-502.

344

ZAPPALA, SCALTRITI, AND DI MARTINO

SCALTRIT1, F., V. ZAPPALA., AND H. J. SCPIOBER (1979). Photoelectric photometry and rotation periods of three large and dark asteroids 49 Pales, 88 Thisbe and 92 Undina. Astron. Astrophys. Suppl. 36, 1-8. SCALTRITI, F., V. ZAPPAL.A,, AND A. W. HARRIS (1981a). Photoelectric lightcurves and rotation periods of the asteroids 46 Hestia and 115 Thyra. Icarus 46, 275-280. SCALTRITI, F., V. ZAPPAL)~, H. J. SCHOBER, A. HANSLMEIER, A. SUDY, J. PIIRONEN, C. BLANCO, AND S. CATALANO (1981b). 14 Irene: A puzzling asteroid. Astron. Astrophys. 100, 326-329. SCHOBER, H. J., J. SURDEJ, A. W. HARRIS, AND J. W. YOUNG (1982). The six-day rotation period of 1689 Floris-Jan: A new record among slowly rotating asteroids. Astron. Astrophys. 115, 257-262. TAYLOR, R. C., T. GEHRELS, AND R. C. CAPEN (1976). Minor planets and related objects. XXI. Photometry of eight asteroids. Astron. J. 81, 778-786. TEDESCO, E. F. (1979). Lightcurve parameters of asteroids. In Asteroids (T. Gehrels, Ed.), pp. 10981107. Univ. of Arizona Press, Tucson. TEDESCO, E. F., R. C. TAYLOR, P. V. BIRCH, J. DRUMMOND, I. NICKOLOFF, F. SCALTRITI, AND V. ZAPPAL~ (1983). Worldwide photometry and lightcurve observations of 16 Psyche during the 19751976 apparition. Icarus, 54, 30-37. VAN FLANDERN, T. C., E. F. TEDESCO, AND R. P. BINZEL (1979). Satellites of asteroids. In Asteroids (T. Gehrels, Ed.), pp. 443-465. Univ. of Arizona Press, Tucson.

VAN HOUTEN-GROENEVELD, I., AND C. VAN HOUTEN (1958). Photometric studies of asteroids. VII. Astrophys. J. 127, 253-273. VEVERKA, J. (1971). Photopolarimetric observations of the minor planet Flora. Icarus 15, 454-460. WooD, H. J., AND G. P. KUIPER (1963). Photometric studies of asteroids. X. Astrophys. J. 137, 12791285. YANG, X. Y., Y. Y. ZHANG, AND X. Q. Ll (1965). Photometric observations of variable asteroids. III. Acta Astron. Siniea 13, 66. ZAPPALA, V. (1981). A semi-analytic method for pole determination of asteroids. Moon Planets 24, 319325. ZAPPAL,~, V., AND F. SCALTRITI (1982). A coordinate program for pole determination of asteroids. In Sun and Planetary System (W. Fricke and G. Teleki, Eds.), pp. 303-304. Reidel, Dordrecht. ZAPPALA, V., H. DEBEHOGNE, C.-I., LAGERKVIST, AND H. RICKMAN (1982). Physical studies of asteroids VII: The unusual rotation of M and CMEU asteroids. Astron. Astrophys. Suppl. 50, 23-26. ZAPPALA, V., M. DI MARTINO, F. SCALTRITI, R. BURCHI, L. MILANO, J. W. YOUNG, G. WHALGREN, AND K. PAVLOVSKI (1983). Remarkable modification of lightcurves for shadowing effects on irregular surfaces: The case of the asteroid 37 Fides. Astron. Astrophys. 123, 326-330. ZELLNER, B. (1979). Asteroid taxonomy and the distribution of the compositional types. In Asteroids (T. Gehrels, Ed.), pp. 783-806. Univ. of Arizona Press, Tucson.