Visible and near-infrared lightcurves of eight asteroids

B lightcurves are presented for seven asteroids (4, 20, 29, 31, 39, 115, and 349) together with visual and infrared color curves (BV, BK, VJ, and JK). A V broadband lightcurve for 40 Harmonia is also included. Color variations are observed for three asteroids (4, 31, and 115). The variation in the colors of 4 Vesta is discussed in terms of differences in surface composition. Pole positions and shapes are estimated for 20 Massalia, 29 Amphitrite, 31 Euphrosyne, and 39 Laetitia. Various UBVRIJHK colors are listed for these asteroids as well as for 5, 19, 44, 52, 83, 145, 386, and 471.     

Determination of physical properties of the Asteroid (41) Daphne from interferometric observations in the thermal infrared

We describe interferometric observations of the Asteroid (41) Daphne in the thermal infrared obtained with the Mid-Infrared Interferometric Instrument (MIDI) and the Auxiliary Telescopes (ATs) of the European Southern Observatory (ESO) Very Large Telescope Interferometer (VLTI). We derived the size and the surface thermal properties of (41) Daphne by means of a thermophysical model (TPM), which is used for the interpretation of interferometric data for the first time. From our TPM analysis, we derived a volume equivalent diameter for (41) Daphne of 189 km, using a non-convex 3-D shape model derived from optical lightcurves and adaptive optics images (B. Carry, private communication). On the other hand, when using the convex shape of Kaasalainen et al. (Kaasalainen, M., Mottola, S., Fulchignoni, M. [2002]. Icarus 159, 369-395) in our TPM analysis, the resulting volume equivalent diameter of (41) Daphne is between 194 and 209 km, depending on the surface roughness. The shape of the asteroid is used as an a priori information in our TPM analysis. No attempt is made to adjust the shape to the data. Only the size of the asteroid and its thermal parameters such as, albedo, thermal inertia and roughness are adjusted to the data. We estimated our model systematic uncertainty to be of 4% and of 7% on the determination of the asteroid volume equivalent diameter depending on whether the non-convex or the convex shape is used, respectively. In terms of thermal properties, we derived a value of the surface thermal inertia smaller than 50 J m⁻² s^−0.5 K⁻¹ and preferably in the range between 0 and ∼30 J m⁻² s^−0.5 K⁻¹. Our TPM analysis also shows that Daphne has a moderate macroscopic surface roughness.     

The lightcurve and rotation period of asteroid 139 Juewa

Results of broad-band photoelectric photometry of 139 Juewa during 5 consecutive nights in March 1974 are presented. The synodic period found is 20.9 hr. A linear phase coefficient, β = 0.080 ± 0.004, is determined between phase angles of 0.9° to 1.5°. This value is similar to that for the lunar highlands and for three other asteroids (4 Vesta, 20 Massalia, 110 Lydia) at similar phase angles, indicating that these surfaces have comparable porosities. The composite lightcurve presented covers 80% of the rotational period; short timescale features in the lightcurve are seen which correspond to topography a few kilometers in size.     

The lightcurve and phase function of the asteroid 304 Olga

Photoelectric lightcurves of 304 Olga were obtained at Table Mountain Observatory in 1978 near opposition. From these observations, and several observations made from Lowell Observatory a month later, we obtain a rotation period of 18.36 ± 0.02 hr and lightcurve amplitude of 0^m·20. The range of solar phase angle covered by the observations is from 2°·0 to 22°. The resulting phase function is well fit by the Bowell and Lumme model (1979, in Asteroids, T. Gehrels, Ed., pp. 132–169, Univ. of Arizona Press, Tucson), with Q = 0.02. This low value of Q is suggestive of a low-albedo object.     

Photoelectric photometry of asteroids 9 Metis, 18 Melpomene, 60 Echo, 116 Sirona, 230 Athamantis, 694 Ekard,and 1984 KD

Photoelectric observations of seven asteroids were made from Gila Observatory between October 14, 1983, and June 21, 1984. The following synodic rotational periods and amplitudes are reported: 9 Metis, P = 5.04 hr, ΔM = 0.05; 18 Melpomene, P = 11.570 hr, ΔM = 0.22; 60 Echo, P = 25.208 hr, ΔM = 0.22; 116 Sirona, P = 12.028 hr, ΔM = 0.42; 230 Athamantis, P = 23.99 hr, ΔM > 0.20; 694 Ekard, P = 5.925 hr, ΔM = 0.50; 1984 KD, P = 1.97 hr, ΔM = 0.26. The rotational periods reported for asteroid 60 Echo, 116 Sirona, 694 Ekard, and 1984 KD represent completely new results. The synodic rotational period reported for asteroid 1984 KD is tentative and is based largely upon the observations of a single night. The reported synodic periods of the remaining six asteroids are based upon a minimum of 3 nights of photometric observations.     

Photoelectric lightcurves of the asteroid 1862 Apollo

Photoelectric lightcurves of the asteroid 1862 Apollo were obtained in November–December 1980 and in April–May 1982. The period of rotation is unambiguously determined to be 3.0655 ± 0.0008 hr. The 1980 observations span a range of solar phase angle from 30° to 90°, and the 1982 observations, 0.°2 to 90°. The Lumme-Bowell-Harris phase relation can be fit to the absolute magnitudes at maximum light with an RMS scatter of 0.06 magnitude over the entire range of phase angle. The constants of the solution are absolute V magnitude at zero phase angle and at maximum light, 16.23 ± 0.02; slope parameter, 0.23 ± 0.01. These constant corresponds to values in the linear phase coefficient system of V(1, 0) = 16.50 ± 0.02 and a phase coefficient of β_v = 0.0305 ± 0.0012 mag/degree in the phase range 10°–20°. The slope of the phase curve is typical for a moderate albedo asteroid. The absolute magnitudes observed in 1980 and 1982 fall along a common phase curve. That is, Apollo was not intrinsically brighter at one apparition than the other. This is not surprising, since the two apparitions were almost exactly opposite one another in the sky. A pole position was calculated from the observed deviation of the lightcurve from constant periodicity (synodic-sidereal difference) during both apparitions. The computed 1950 ecliptic coordinates of the pole are: longitude = 56°, latitude = −26°. This is the “north” pole with respect to right-handed (counter-clockwise) rotation. The formal uncertainty of the solution for the pole position is less than 10°, but realistically may be several times that, or even completely wrong. The sidereal period of rotation asscociated with this pole solution is 3.065436 ± 0.000012 hr.     

Lightcurves and the axis of rotation of 433 Eros

Ten lightcurves and UBV photometry of 433 Eros were obtained between August 1972 and May 1975. The absolute magnitude of the lightcurve maximum is 10.75 and the phase coefficient is 0.025 mag/deg. There may be a small difference in B-V color between the northern and southern hemispheres. The pole of the axis of rotation is directed toward λ₀ = 16°, β₀ = 12°, ecliptic longitude and latitude, respectively, and the rotation is direct with a sidereal period of 0.^d219599 or 5^h16^m13^s4 ± 0.^s2. The dimensions derived from the polarimetric albedo and the lightcurve amplitudes are 12km × 12km × 31km for a smooth cylinder with hemispherical ends.     

Opposition polarimetry and photometry of S- and E-type asteroids

The first results of the observational program devoted to simultaneous investigation of asteroid polarimetric and photometric opposition phenomena are presented. UBVRI polarimetric and V-band photometric observations of the S-type Asteroid 20 Massalia and the E-type Asteroids 214 Aschera and 620 Drakonia were carried out in 1996-1999 down to phase angles of 0.08°, 0.7°, and 1.2°, correspondingly. The S-type Asteroid 20 Massalia is characterized by the pronounced brightness opposition surge with an amplitude larger than that observed for the E-type asteroids. A sharp peak of negative polarization at small phase angles was not observed for this asteroid. The value of polarization degree at phase angle α<1° is less than 0.5% for both S and E types. The negative polarization branches of S and especially E-asteroids have an asymmetrical shape. The phase angle at which the polarization minimum occurs is close to the angle at which non-linear increase begins in the asteroid magnitude phase curves. A relation of the observed effects to the mechanism of coherent backscattering is discussed.     

Figure of the double Asteroid 90 Antiope from adaptive optics and lightcurve observations

A long-term adaptive optics (AO) campaign of observing the double Asteroid (90) Antiope has been carried out in 2003-2005 using 8-10-m class telescopes, allowing prediction of the circumstances of mutual events occurring during the July 2005 opposition [Marchis, F., Descamps, P., Hestroffer, D., Berthier, J., de Pater, I., 2004. Bull. Am. Astron. Soc. 36, 1180]. This is the first opportunity to use complementary lightcurve and AO observations to extensively study the (90) Antiope system, an interesting visualized binary doublet system located in the main belt. The orbital parameters derived from the AO observations have served as input quantities for the derivation of a whole set of other physical parameters (namely shapes, surface scattering, bulk density, and internal properties) from analysis of collected lightcurves. To completely model the observed lightcurves, we employed Roche figures to construct an overall shape solution. The combination of these complementary observations has enabled us to derive a reliable physical and orbital solution for the system. Our model is consistent with a system of slightly non-spherical components, having a size ratio of 0.95 (with Ravg=42.9±0.5 km, separation=171±1 km), and exhibiting equilibrium figures for homogeneous rotating bodies. A comparison with grazing occultation event lightcurves suggests that the real shapes of the components do not depart from Roche equilibrium figures by more than 10%. The J2000 ecliptic coordinates of the pole of the system are λn=200°±2° and αn=38°±2°. The orbital period was refined to P=16.5051±0.0001 h, and the density is found to be slightly lower than previous determinations, with a value of 1.25±0.05 g/cm³, leading to a significant macro-porosity of 30%. Possible scenarios for the origin of the system are also discussed.     

A radar survey of M- and X-class asteroids

We observed ten M- and X-class main-belt asteroids with the Arecibo Observatory's S-band (12.6 cm) radar. The X-class asteroids were targeted based on their albedos or other properties which suggested they might be M-class. This work brings the total number of main-belt M-class asteroids observed with radar to 14. We find that three of these asteroids have rotation rates significantly different from what was previously reported. Based on their high radar albedo, we find that only four of the fourteen—16 Psyche, 216 Kleopatra, 758 Mancunia, and 785 Zwetana—are almost certainly metallic. 129 Antigone has a moderately high radar albedo and we suggest it may be a CH/CB/Bencubbinite parent body. Three other asteroids, 97 Klotho, 224 Oceana, and 796 Sarita have radar albedos significantly higher than the average main belt asteroid and we cannot rule out a significant metal content for them. Five of our target asteroids, 16 Psyche, 129 Antigone, 135 Hertha, 758 Mancunia, and 785 Zwetana, show variations in their radar albedo with rotation. We can rule out shape and composition in most cases, leaving variations in thickness, porosity, or surface roughness of the regolith to be the most likely causes. With the exception of 129 Antigone, we find no hydrated M-class asteroids (W-class; Rivkin, A.S., Howell, E.S., Lebofsky, L.A., Clark, B.E., Britt, D.T., 2000. Icarus 145, 351-368) to have high radar albedos.     

Photoelectric photometry of 14 asteroids

Results of observations of 14 asteroids are reported; all of them, except 181 Eucharis, have been previously observed at least once. V photoelectric lightcurves were obtained from September 1982 to June 1983 at the Astronomical Observatory of Torino and at the Astrophysical Observatory of Catania. Part of this program aims to obtain complete lightcurves and, when possible, phasecurve information and to determine amplitudes and V magnitudes at different longitudes for a selected group of asteriods, in order to enlarge the set of known rotational axis directions.     

Observations of Saturn's inner satellites and the orbit of Janus in 1980

Systematic observations of faint satellites were conducted at Pic-du-Midi with a focal coronograph from 1980 March 20 to 24, during which 150 exposures covering 17 hr were obtained; in addition, the 1966 discovery plates of satellites S10 Janus were reexamined together with other 1966 observations. Janus had its greatest eastern elongation on 1966 December 15.720 (±0.003) + light time, at a distance of 2.53R_eq. It is recognized that some of the observations thought to be 1966 S2 were in fact reobservations of Janus a few days after its discovery. Among the 1980 observations, differences in magnitudes indicate that is satellite 1980 S1 which corresponds to Janus; its greatest eastern elongation was observed on March 23.876 (±0.002) + light time. Subjected to corrections for librations, the mean period over the past 14 years has most probably one of three values: P₁ = 0.69458 day, P₂ = 06.9448 day or P₃ = 0.69438 day. The fainter satellite, S11, which is also 1980 S3, gravitates in an orbit similar to that of Janus and was leading it by +190° in March 1980; this difference of longitude was +224° in December 1966. An object of magnitude 15–16 was seen not detached from the ring; it could be a condensation in the external part of the rings or an additional faint inner satellite.     

Strong turbulence and atmospheric waves in stellar occultations

Many of the problems of stellar occultation observations stem from the difficulty of determining the effects of realistic atmospheric structure on the lightcurves. General techniques for producing model lightcurves for a variety of realistic atmospheric irregularities, including turbulence and inertia-gravity waves, are presented and applied. Using numerical simulations which model the propagation of a wave through a phase-changing screen, the limit of strong scintillations for one-dimensional, Kolmogorov-like turbulence, both for a point source and for extended sources, is investigated in some detail, and significant departures from the behavior in the weak scintillation regime are found. The results are compared with published analytical results and recent occultation data. The effects of large-scale atmospheric waves with realistic horizontal structure are examined, and the reliability of the numerical inversion method of retrieving the true atmospheric vertical structure under circumstances of strong ray crossing and horizontal inhomogeneities is assessed. The simulations confirm that large-scale layered features of the atmosphere are accurately recovered; horizontally inhomogeneous structures (including turbulence) with coherence scale $\text{L ? (2πRH)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ (where R = planetary radius and H = scale height) have little effect on the derived temperature profiles. It is concluded that analysis of occultations may eventually allow us to determine both the quasiglobal atmospheric structure and the statistical characteristics of small-scale refractivity variations.     

Photoelectric photometry of 17 asteroids

Seventeen asteroids were observed photoelectrically in the V band at the Torino Observatory in 1983–1984 as part of the coordinated campaign for pole determinations. The obtained lightcurves allowed us to deduce new pole coordinates of four objects, while for the other three a check of previous results was possible. Additionally, the ambiguity for the rotation period of 776 Berbericia was solved in favor of a shorter value, and the importance of this problem was evidenced once more after analyzing the lightcurves of 69 Hesperia and 349 Dembowska. A new possible value of the period of 121 Hermione was also suggested.     

Dust Grains in the Comae and Tails of Sungrazing Comets: Modeling of Their Mineralogical and Morphological Properties

Observations of sungrazing comets, all of which belong to the Kreutz family, provide the opportunity of studying the properties of dust in the comae and tails of the comets. On the basis of available information on cometary and interplanetary dust as well as observations of dust in the tails of sungrazers, we model dust in sungrazing comets as fluffy silicate aggregates of submicrometer sizes. To better interpret observational data, we numerically calculate the solar radiation pressure, the equilibrium temperature, and the sublimation and crystallization rates of silicate grains near the Sun. Our results show that the dust tails contain aggregates of submicrometer crystal grains, but not amorphous grains, since amorphous silicates mostly crystallize after release from the comets. The peak in the lightcurves of the dust comae observed either at 11.2 or 12.3 solar radii (R_⊙) seems to result from sublimation of fluffy aggregates consisting of crystalline or amorphous olivines, respectively. We attribute an additional enhancement in the lightcurves inside 7 R_⊙ to increasing out-flow of crystalline and amorphous pyroxenes composed fluffy aggregates. According to our model, the observed lightcurves indicate a high abundance of olivine and a low abundance of pyroxene in the comets, which may bear implications about the dynamical and thermal history of the sungrazers and their progenitor.     

Photometric lightcurves and pole determination of 433 Eros

Fourteen photometric lightcurves of 433 Eros were made at the Astronomical Observatory of Torino during the 1974–75 close passage. The absolute magnitude of the primary maximum (10^m78), the phase coefficient (0.023 mag/degree), the synodic and sidereal period of rotation (0^d.21956 and 0^d.21959, respectively) and the ecliptic coordinates of the pole (λ = 17°, β = 10°) were deduced.     

Five-color photoelectric photometry of asteroid 433 Eros

Five-color photoelectric lightcurves of asteroid 433 Eros were obtained on 9 nights during the 1974/75 apparition. Although color differences due to changing solar phase angle were detected, color differences during a single rotation of Eros are less than 1%. Amplitudes of up to 1^m.44 were measured, and there are indications that three reversals in the relative depths of the two minima occured between late December 1974 and late January 1975. The absolute visual magnitude at primary maximum, corrected to zero phase and to one AU from Earth and Sun, is about V₀(1,0) = 10^m.8.     

The pole of (51) Nemausa

The complex lightcurves make (51) Nemausa a good case for the study of general methods for pole determination. From six lightcurves the pole is determined to 20^h24^m; +53° (1950); the rotation is retrograde with period 7^h.782936 ± 0^h.000005. Presence of nongeometric scattering is proved by a significant 0.008 mag amplitude. Formulae and photometric elements are given for predictions of the shapes of lightcurves in future oppositions. The precision of the Fourier coefficients may be reduced below the present ±0.003 mag level by avoiding the systematic errors in the observations due to phase factor variations and discontinuities when changing comparison stars.     

Photometric observations and modelling of the asteroid 85 Io in conjunction with data from an occultation event during the 1995–96 apparition

The asteroid 85 Io has been observed using CCD and photoelectric photometry on 18 nights during its 1995–96 and 1997 apparitions. We present the observed lightcurves, determined colour indices and modelling of the asteroid spin vector and shape. The colour indices (U-B = 0.35±0.02, B-V = 0.66±0.02, V-R = 0.34±0.02, R-I = 0.36±0.02) are as expected for a C-type asteroid. The allowed spin vector solutions have the pole co-ordinates λ₀ = 285±4°, β₀ = −52±9° or λ₀ = 108±10°, β₀ = −46±10° and λ₀ = 290±10°, β₀ = −16±10° with a retrograde sense of rotation and a sidereal period P_sid = 0^d.286463±0^d.000001. During the 1995–96 apparition the International Occultation Time Association (IOTA) observed an occultation event by 85 Io. The observations and modelling presented here were analysed together with the occultation data to develop improved constraints on the size of the asteroid. The derived value of 164 km is about 5% larger than the IRAS diameter. © 1999 Elsevier Science Ltd. All rights reserved.