ACTA ASTRONOMICA Vol. 42 (1992) pp. 67±72

Asteroid 126 Velleda: and -Phase Curve

by A. N. Dovgopol

The Main Astronomical Observatory of Ukrainian Academy of Sciences, Goloseevo, Kiev, 252127, Ukraine

Yu. N. K r u g l y and V. G. Shevchenko

The Astronomical Observatory of Kharkov University, Sumskaya str. 35, Kharkov, 310022, Ukraine

Received January 2, 1992

ABSTRACT

Photoelectric observations of the 126 Velleda were carried out during 1990 opposi-

h

= 

tion. The rotation period P 5. 364 0 003 and lightcurve amplitude 0.22 mag were determined.

 

 H =

The magnitude-phase relation has been obtained in the range 0. 14  23. 8 ( 9 28mag,

= G 0 29). The comparative analysis of the opposition effects of Velleda and other S-type was made. Key words:

1. Introduction

Asteroid 126 Velleda is an insuf®ciently studied object in the main belt. The

B = B V = color indices U 0 49 mag and 0 87 mag corresponding to S- type asteroids are given in TRIAD (Bowell et al. 1979). According to IRAS-data (Matson 1986) the diameter and albedo of 126 Velleda are 46.5 km and 0.15 respectively. We have not found any more data on this asteroid in the literature. The main feature of the 1990 opposition was that the minimum value of the solar phase angle as small as 0. 1 was approached. This rare phenomenon among asteroids is very important for understanding the nature of opposition effect (OE) of atmosphereless bodies. So, it was important for us to determine phase relation at small phase angle. 68 A. A.

2. Observations

In1990thephotoelectricobservationsof126Velledawerecarried out during the eight nights at the Astronomical Observatory of Kharkov University and the night of October 9 at the High Altitude Observation Station of the Main Astronomical Observatory of Ukrainian Academy of Sciences (Mount Maidanak, Central Asia).

Measurements were obtained in band close to the standard V . The reductions of data were performed with the standard procedure (Velichko 1991, Bugaenko et al. 1985, and Bugaenko and Guralchuk 1985).

Table 1 contains aspect data at the mean time of observation and the magnitude

( ) M V 1 reduced to maximum 1 (seeFig. 1). Thedesignationsofthe comparison stars are given in the last column of Table 1. Table1

Aspect and photometric data of asteroid 126 Velleda

 V ( ) Date 1950 1950 1950 1950 r 1 Comp.

U.T. a.u. a.u. stars

0    Sep. 25.04 1h 41.m 65 9  50.4 27.13 -0.66 2.203 1.257 11.6 9.m 87 1 Oct. 9.86 1 29.25 9 04.9 24.00 -0.25 2.211 1.218 3.7 9.61 2,3 11.01 1 28.16 9 00.6 23.73 -0.22 2.212 1.217 3.1 9.59 4 14.86 1 24.45 8 45.9 22.78 -0.11 2.214 1.217 0.9 9.39 5 16.82 1 22.57 8 38.4 22.31 -0.05 2.215 1.219 0.1 9.23 6 17.79 1 21.64 8 34.7 22.07 -0.02 2.216 1.220 0.7 9.34 7 19.88 1 19.63 8 26.6 21.56 0.04 2.217 1.223 1.8 9.57 8 23.78 1 15.99 8 11.9 20.63 0.15 2.220 1.232 4.0 9.65 9 Dec. 18.70 1 03.94 8 09.3 17.86 1.24 2.265 1.705 23.8 10.21 10

Table2

Comparison and standard stars Comp. 1950 1950 V Standard

star stars 0 1 1h 40.m 7 9  50 11.m 07 1545, 1581 2 129.0 9 10 11.98 1544,1545

3 128.9 918 11.06  4 128.4 9 01 11.93 1545,1581

5 124.7 845 11.43 

6 122.8 841 10.04 

7 122.1 8.33 11.57 

8 120.1 8.37 11.20 

9 115.6 809 12.32  10 103.6 808 11.11 1313

The equatorial coordinates and measured magnitudes of the comparison stars and the numbers of standard stars used (Blanco et al. 1968) are listed in Table 2. Vol. 42 69

Fig. 1. Lightcurves of 126 Velleda obtained during 1990 opposition. 3. Lightcurves and rotation period

Fig. 1 shows the lightcurves of 126 Velleda obtained in the 1990 opposition. The mean amplitude of light variations is 0.22 mag. The complex, yet symmetrical 70 A. A. shape of Velleda's lightcurve raises the problem of ambiguity of rotation period. One can suppose two possible rotation periods of approximately 2.7 and 5.4 .

h

=  Analysis of all available lightcurves shows that the "long" period P 5. 364

0003 is the most probable. In that case Velleda's lightcurve contains two deep minima and two double maxima. The nearest maxima are divided by a small depression with amplitude about 0.04 mag. The similar depression is situated at one of the rising branch of the lightcurve. The levels of deep minima differ by 0.02 mag from each other. The surprising symmetry of Velleda's lightcurve is apparently connected with shape irregularities of a photometrically homogeneous asteroid (Akimov et al. 1983).

4. Magnitude-phase relation

The phase curve of asteroid 126 Velleda is shown in Fig. 2. As one can see, 

the range of phase angles is from 0. 14 to 23. 8. Values of reduced magnitudes

( )

V 1 from Table 1 are used for plotting the phase curve. The parameters

=  G = 

H 9 28 0 02 mag and 0 29 0 03 are obtained according to Bowell et

G al. (1989) and they are typical for the S-type asteroids. Note that the H function gives rather poor approximation of real magnitude-phase changes at small phase angles.

Fig. 2. Phase curve for 126 Velleda in 1990. Vol. 42 71

It is interesting to compare the measured value of Velleda's OE with the data

of S-type asteroids. We have chosen asteroids with phase curves measured up to

  small phase angles ( 2 ). They are: 6 Hebe, 20 Massalia, 29 Amphitrita and 133 Cyrena. We consider OE as an increase of brightness with respect to the linear part of the phase curve (Scaltriti and Zappala 1980). Fig. 3 shows OE of the ®ve S-type asteroids obtained by subtracting the linear part from each phase curve. As one can see, there are differences between OEs of the asteroids of same type. Only 126 Velleda and 133 Cyrene have shown the similar OEs. Apparently, these two asteroids have the same nature of OE.

Fig. 3. Reduced phase curves of ®ve S-type asteroids. The dashed line is parabola ®tted by least squares to the opposition part of Velleda's phase curve.

Acknowledgements. We wish to express our special thanks to Dr. V.A. Shor from ITA for the calculations of Velleda's near opposition ephemerides, and to F.P. Velichko, R. Mohamed, and M.V.Tyomny from the Astronomical Observatory of Kharkov University for the help in our observation.

REFERENCES

Akimov, L.A., Lupishko, D.F., and Belskaya, I.N. 1983, Soviet Astron. J., 66, 999. Blanco, W.M., Demers, S., Douglass, G.G., and Fitzgerald, M.P. 1968, Publications of the United States Naval Observatory (Washington), Vol. 21. Bowell, E., Gehrels, T., and Zellner, B. 1979, in Asteroids, ed. T. Gehrels (Tucson: Univ. of Arizona Press), 1108. Bowell, E., Hapke, B., Domingue, D., Lumme, K., Peltoniemi, J., and Harris, A.W. 1989, in Asteroids II, eds. R.P. Binzel, T. Gehrels, M.S. Matthews (Tucson: Univ. of Arizona Press), 524. 72 A. A.

Bugaenko, L.A., Mel'nikov, M.A., Ragozina, L.E., and Samoilov, V.S. 1985, in Photometric and polarimatric investigation of celestial bodies, ed. A.V. Morozhenko (Kiev: Naukova dumka), 164. Bugaenko, O.I., and Guralchuk, A.L. 1985, in Photometric and polarimatric investigation of celestial bodies, ed. A.V. Morozhenko (Kiev: Naukova dumka), 160. Gehrels, T. 1956, Astrophys. J., 123, 331. Gehrels, T., and Taylor, R.C. 1977, Astron. J., 82, 229. Harris, A.W., Carlsson, M., Young, J.W., and Lagerkvist, C.-I. 1984, Icarus, 58, 377. Lupishko, D.F., Tupieva, F.A., Velichko, F.P., Kiselev, N.N., and Chernova, G.P.1981, Astron. Vestnik, 15, 25. Matson, D.L., ed. 1986, IRAS Asteroid and Survey: Preprint Version No.1,, JPL Document No. D-3698. Scaltriti, F., and Zappala, V. 1980, Astron. Astrophys., 83, 249. Velichko, F.P. 1991, Ph. D. Thesis, Kharkov University (in Ukraine).