Photoelectric lightcurves of Asteroid 433 Eros

ZeAlOUS 28, 39-42 (1976)

Photoelectric Lightcurves of Asteroid 433 Eros CORNELIA CRISTESCU Astronomical Observatory, Bucharest, Romania R e c e i v e d O c t o b e r 30, 1975 D u r i n g J a n u a r y a n d F e b r u a r y , 1975, four l i g h t c u r v e s o f A s t e r o i d 433 E r o s were o b t a i n e d a t t h e B u c h a r e s t O b s e r v a t o r y w i t h a 50-cm reflector, in integ r a t e d light. A sizeable v a r i a t i o n o f t h e a m p l i t u d e (from 1.3 to 0.9 m a g n i t u d e s ) was o b s e r v e d .

Photometric lightcurves of asteroid 433 Eros were obtained at the Bucharest Observatory during 4 nights in J a n u a r y and February, 1975, with a 50 cm reflector. Due to the town illumination, the asteroid was too faint to be observed with UBV filters; therefore, all the lightcurves are in integrated light. The photomultiplier used is of the type EM19502-B. Table I contains information on the observing nights, and the corresponding lightcurves are given in Figs. l-4. The distances from the asteroid to the Sun (r) and to the E a r t h (p) were taken from the Ephemeris of Minor Planets for 1974 (published in Leningrad). The observations were made in the usual way, i.e. at most two asteroid readings were referred to one comparison star reading, and the reductions included corrections for extinction, distance and ephemeris time. A nomogram for computing the air masses at Bucharest Observatory (Dinescu, 1967) was used for extinction corrections. The comparison

stars (Table II) have been chosen as close as possible to the asteroid in regard to not only the position but also the magnitude and the color. The nights of J a n u a r y 6 and 25 were very favorable, with very good seeing, while the night of February 11 was the poorest. Open circles in the figures correspond to doubtful readings. In Table I I I are given the times of observed maxima (M primary, M 2 secondary maxima) and minima (m 1 primary, m 2 secondary minima). Adopting a period of 0.d2196 (Dunlap, personal communication) and superposing the four lightcurves, Fig. 5 was obtained. The best fits are along the descending branches, and especially t h a t following the primary maximum. From the first to the last observations, decreasing amplitude and displacement of the minima towards smaller rotational phase angles is present, along with a slight decrease of the interval between the secondary minimum (m2) and the principal minimum (m~) from 0.54 rotational phase angle to 0.49.

TABLE I DATA :FOR THE LIGHTCU~VES OF EROS

Obs. d a t e 1975UT 6.827 11.001 25.048 11.830

January January January February

Distance Distance from the from the Sun r Earth p (AU) (AU) 1.141 1.138 1.133 1.142

0.171 0.162 0.152 0.177

Copyright~t~) 1976 by Academic Press, Inc. All rights o f reproduction in any form reserved. Printed in Great Britain

R.A. Dec. (1950.0)

Lighttime 0~00099 0.00094 0.00088 0.00102

7n57~. 7 7 53.7 7 40.7 7 37.2 39

+43°36 ' +39 43 +23 21 +03 28

Ecliptic long.

lat.

112°38 ' 112 43 113 00 115 34

+22°27 ' +18 29 +01 54 --17 49

Phase angle

20~.1 16.1 9.8 27.1

40

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TABLE COMPAR

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41

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FIG. 5. T h e c o m p a r i s o n of t h e four light curves. T h e decrease of t h e a m p l i t u d e is a c c o m p a n i e d b y a d i s p l a c e m e n t o f tile m i n i m a .

42

CORNELIA

CRISTESCU

TABLE III TIMES OF OBSERVED MAXIMA AND MINIMA

Date 6

Jan.

10-1l Jan. 24-25 J a n . 11 Feb.

~i 1

zll 2

m 1

m2

6.82731 11.00097 25.04825 11.83005

-10.89056

6.87870 10.83153 25.10311 11.88282

6.77662 10.94750 24.99478 11.77171

11.93699

ACKNOWLEDGMENT

REFERENCE

The a u t h o r expresses t h a n k s to D u m i t r e s e u A l e x a n d r u who h e l p e d h e r d u r i n g tile o b s e r v a tions.

DINESCU, I~. (1967). N o m o g r a m a p e n t r u calculul m a s e i de aer. S t u d i i si Cercetari de Astronomie 1 2 , 179-183.