Lightcurves and Synodic Periods for Asteroids 1998 ST49, (13154) and (27529)

The first photometric observations of the near-Earth asteroid 1998 ST₄₉ and the main belt asteroids (13154) and (27529) are reported. The synodic rotation periods and amplitudes of the lightcurves are:

? 2.3017 h, 0.11 mag for 1998 ST₄₉;

? 2.98502 h, 0.18 mag for (13154);

? 4.1290 h, 0.51 mag for (27529).

The periods for the first two asteroids are unambiguous, while the period of 4.1570 h is not ruled out for the third asteroid. Despite fast rotations, none of the presented asteroids exhibited any sign of binarity. Lightcurves were obtained at Modra Observatory.     

Worldwide photometry and lightcurve observations of 16 Psyche during the 1975–1976 apparition

We present 26 lightcurves of 16 Psyche from 1975 and 1976. The synodic period during this apparition was 4^h.1958. Combining photometric data from this opposition with those from previous apparitions allowed us to derive a mean phase coefficient in V of 0.026 ± 0.002 mag/deg and to establish that Psyche's absolute V₀ magnitude and rotational amplitude vary with aspect; at 90° aspect, V₀(1, 0) = 6.27 ± 0.05 and the lightcurve amplitude is 0.30 mag, while at 0° or 180° aspect, V₀(1, 0) = 6.02 ± 0.02 and the amplitude is ?0.03 mag. This behavior is accounted for if, to first order, Psyche's shape is that of a triaxial ellipsoid with axial ratios near 5:4:3. Colors at zero phase are U-B = 0.26 ± 0.01 and B-V = 0.71 ± 0.01. Color phase coefficients are <0.001 mag/deg in U-B and 0.0010 ± 0.0004 mag/deg in B-V.     

JOINT LIGHTCURVE OBSERVATIONS OF 10 NEAR-EARTH ASTEROIDS FROM MODRA AND ONDŘEJOV

The effort in photometry of near-Earth asteroids (NEAs) at Modra Observatory has been enhanced following a recent collaboration with Ondřejov Observatory. We present a part of our collaborative work on measuring rotation lightcurve data for 10 NEAs. We derived following synodic periods P and amplitudes of their composite lightcurves: (3553), 3.1944 h, 0.08 mag; (22753), 10.24 h, 0.11 mag; (31669), 5.807 h, 0.07–0.27 mag; (40267), 4.9568 h, 1.01–1.11 mag; (66146), 2.3774 h, 0.12–0.15 mag; (88188), 2.6906 h, 0.06 mag; (103067), 9.489 h, 0.49 mag; 2001 CB₂₁, 3.302 h, 0.19 mag; 2004 LJ₁, 2.7247 h, 0.17–0.59 mag; 2004 XO₁₄, 8.417 h, 0.19–0.25 mag. While the derived periods are unique (the reliability code U=3) for most of the objects, those of (3553), (22753) and 2001 CB₂₁ are somewhat less reliable (U=2). We checked all the U=3 data for deviations from strict periodicity, but found no significant attenuation that would indicate the presence of a satellite. Absolute magnitudes in Cousins R band (H _R ) were derived for (3553), 16.05; (40267), 15.59; (88188), 16.04; 2004 XO₁₄, 15.84; errors of the first three H _R estimates are 0.20 mag, but that of 2004 XO₁₄ is <0.10 mag.     

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.     

CCD Photometry of Asteroids 168, 206 and 506

A quantity of C-type asteroids with intermediate size has been selected as the targets of our observational program in Yunnan Observatory, China since 2000. In this paper, we report the results of the photometric observation for three of them, 168 Sibylla, 206 Hersilia and 506 Marion during 2002–2003. The synodic period of 9.100±0.009 h of 206 is different from the value given by Harris (2003). The synodic periods of 168 and 506 we estimated are 24.41±0.01 h, and 13.51±0.01 h, respectively, which are slightly different from the values given by Harris (2003). Their composed lightcurves using new periods are presented.     

The Rotational Periods of Three C-Type Asteroids 431, 521 and 524

The determination for asteroids’ spin parameters is very important for the physical study of asteroids and their evolution. Sometimes, the low amplitude of light curves and kinds of systematic errors in photometric data prevent the determination of the asteroids’ spin period. To solve such a problem, we introduced the de-correlation methods developed in searching for exoplanetary transit signal into the asteroid’s data reduction in this paper. By applying the principle of Collier Cameron (MNRAS 373:799–810, 2006) and Tamuz et al. (MNRAS 356:1466–1470, 2005)’s, we simulated the systematic effects in photometric data of asteroid, and removed those simulated errors from photometric data. Therefore the S/N of intrinsic signals of three selected asteroids are enhanced significantly. As results, we derived the new spin periods of 18.821 ± 0.011 h, 28.202 ± +0.071 h for (431) and (521) respectively, and refined the spin period of (524) as 14.172 ± 0.016 h.     

Lightcurves and phase relation of asteroid 324 Bamberga

A worldwide photometric investigation of the asteroid 324 Bamberga was conducted during the period September–November 1978. The full-cycle lightcurve shows two maxima and two minima with a maximum amplitude of 0.075 mag; the rotation period was found to be P_syn = 29.^h42 ± 0.^h01. A linear least-squares solution of the phase relation gives β_y = (0.334 ± 0.001) mag/degree and V₀ (1, 0) = (7.17 ± 0.01) mag. The color indices measured are B-V = 0.69, U-B=0.36, in agreement with the C taxonomic type given for 324 Bamberga. The very long period indicates 324 Bamberga is an unusual object among asteroids with diameters greater than 200 km.     

Photoelectric lightcurves and rotation periods of the asteroids 46 Hestia and 115 Thyra

Results of photoelectric observations of the asteriods 46 Hestia and 115 Thyra, performed in a cooperative program between the Torino and Table Mountain Observatories, are presented. The rotation periods and the maximum amplitudes are: P_syn = 21^h.0.4 ± 0^h.01, Amplitude = 0.12 mag and P_syn = 7^h.241 ± 0.^h.001, Amplitude = 0.20 mag, for Hestia and Thyra, respectively. The multiple-scattering factors, Q, inferred from the phase relation data are 0.054 ± 0.003 and 0.058 ± 0.002 for Hestia and Thyra, respectively. The low value obtained for Thyra disagrees with the mean one given by Bowell and Lumme (1979, in Asteroids (T. Gehrels, Ed.), pp. 132–169. University of Arizona Press, Tucson) for S-type asteroids.     

Flattening,pole, and albedo features of 4 vesta from photometric data

A number of large asteroids show irregular lightcurves of relatively small amplitude and/or ambiguous rotational periods. These observations and the fact that their strong gravitational binding probably results in quasi-equilibrium shapes lead to model these bodies as axisymmetric, biaxial ellipsoids covered by albedo markings. We developed a general numerical algorithm for obtaining simulated lightcurves of “spotted” asteroids and varied the most critical geometrical and physical parameters (albedo contrast, size, and position of the spots; polar coordinates, and shape of the asteroid). We then analyzed the case of 4 Vesta by assuming an axisymmetric ellipsoidal shape with a large brighter region on one hemisphere, in agreement with the results of photometric and polarimetric observations. Fitting the numerical simulations to the available data, we obtained the flattening of the ellipsoid (0.79 ± 0.03), the albedo contrast and geometry of the brighter region, and the orientation of the polar axis. If the derived flattenning corresponds to the equilibrium shape of a nearly homogeneous body, a density of 2.4 ± 0.3 g cm⁻³ can be inferred. These results show satisfactory agreement with values by different techniques. We plan to apply the same method both to other large asteroids and to smaller, irregularly shaped ones; in the latter case, this will allow us to test the uncertainties in current pole determination methods.     

Asteroid 532 Herculina: Lightcurves,pole orientation and a model

Photoelectric lightcurves of 532 Herculina in 1984 show two maxima and two minima with a synodic rotation period of 0.39185 ± 0.00002 day (1σ). During some other oppositions the Herculina lightcurve has only one maximum and one minimum over that same rotation period. The absolute magnitude in V is 6.13 ± 0.02 mag, the phase coefficient in V is 0.037 ± 0.002, and the mean colors are B−V = +0.86 ± 0.04 and U−B = +0.43 ± 0.02. We applied photometric astrometry and the results indicate a sideral period of 0.3918711 ± 0.0000001 day with retrograde rotation for a north pole at 276° long and +1° lat. The uncertainty of the pole is ±1°. A model of Herculina is presented that generates lightcurves consistent with both the observed amplitudes and the timings of extrema over precisely 28,630 sideral rotations during 30 years. The model is a sphere with two dark regions that are each about 0.13 times the brightness of the surrounding surface. The regions are at 0° asterocentric longitude, +15° lat, with a radius of 30°, and 170° long, −38° lat, with a radius of 26°. With the photometric astrometry pole and the model with two dark regions, predicted lightcurves are shown for the next four oppositions.     

Using sparse photometric data sets for asteroid lightcurve studies

With the advent of wide-field imagers, it has become possible to conduct a photometric lightcurve survey of many asteroids simultaneously, either for that single purpose (e.g., Dermawan, B., Nakamura, T., Yoshida, F. [2011]. Publ. Astron. Soc. Japan 63, S555–S576; Masiero, J., Jedicke, R., ?urech, J., Gwyn, S., Denneau, L., Larsen, J. [2009]. Icarus 204, 145–171), or as a part of a multipurpose survey (e.g., Pan-STARRS, LSST). Such surveys promise to yield photometric data for many thousands of asteroids, but these data sets will be “sparse” compared to most of those taken in a “targeted” mode directed to one asteroid at a time.We consider the potential limitations of sparse data sets using different sampling rates with respect to specific research questions that might be addressed with lightcurve data. For our study we created synthetic sparse data sets similar to those from wide-field surveys by generating more than 380,000 individual lightcurves that were combined into more than 47,000 composite lightcurves. The variables in generating the data included the number of observations per night, number of nights, noise, and the intervals between observations and nights, in addition to periods ranging from 0.1 to 400 h and amplitudes ranging from 0.1 to 2.0 mag.A Fourier analysis pipeline was used to find the period for each composite lightcurve and then review the derived period and period spectrum to gauge how well an automated analysis of sparse data sets would perform in finding the true period. For this part of the analysis, a normally distributed noise level of 0.03 mag was added to the data, regardless of amplitude, thus simulating a relatively high SNR for the observations. For the second part of the analysis, a smaller set of composite curves was generated with fixed core parameters of eight observations per night, 8 nights within a 14-day span, periods ranging from 2 to 6 h, and an amplitude of either 0.3 mag or 0.4 mag. Individual data sets using these fixed parameters added normally-distributed noise of 0.05, 0.1, or 0.2 mag. The analysis examined the success rates for finding the true period as the noise increased towards levels simulating data for objects close to sky background levels.After applying a filter to remove highly-ambiguous solution sets, the best chance for success was found to be when the true period was in the range of P ≈ 2–5 h and amplitudes were A ? 0.5 mag. The solution sets for lightcurves with low amplitude, long periods, and/or those that were sampled too sparsely in comparison to the period were often too ambiguous to be considered reliable for statistical rotation studies. Analysis of slow rotators (P > 24 h) found that somewhat reasonable solutions of P < 6 h could be found for about 15–20% of those objects, even at higher amplitudes, indicating that the Fourier analysis had locked onto the noise in the data.Efforts to produce an automated pipeline to help determine an unambiguous (or nearly so) solution based on the period spectrum from the Fourier analysis were made. These proved unsuccessful because of the number of parameters that must be considered and the difficulties in assigning an objective weight to each one in finding a final result. Despite this initial failure, further attempts will be made to quantify the U rating system.Comparison of the synthetic data analysis results to those from two actual surveys shows a reasonable agreement between the two. A review of the pros and cons of sparse versus dense data sets shows that each has a significant role in future studies and that it will be critical to establish open lines of communications and data exchange between the deep wide-field sparse data surveys and dense data programs.     

Photometry of Aten asteroids—More than a handful of binaries

Photometric observations were conducted on eight Aten near-Earth asteroids, with the goal of building physical models for the objects (85989) 1999 JD₆, (86450) 2000 CK₃₃, (86667) 2000 FO₁₀, (137170) 1999 HF₁, 1999 MN, 2000 PJ₅, 2002 JC and 2003 NZ₆. The results show rotation periods from 2.3 to almost 26 h. Some objects exhibit amplitudes higher than one magnitude on their lightcurves (1999 JD₆, 2000 CK₃₃ and 2003 NZ₆). Phase curve values (β, H^′, see below) were derived for four Atens and H-G values were found for two. Five Atens were classified by using their B-V and V-R color indices. This taxonomy was compared with the phase coefficient-albedo correlation defined by Belskaya and Shevchenko [Belskaya, I.N., Shevchenko, V.G., 2000. Icarus 147, 94-105]. Color variations during rotation and phase angle change were searched for. Our study demonstrates the high variety among Atens. Five out of the eight Atens are binaries or possible binaries, a significantly higher fraction than the expected 15% [Bottke, W.F., Melosh, H.J., 1996. Nature 281, 51-53]. The lightcurve of 2000 PJ₅ exhibits a binary character with a probable highly eccentric orbital rotation of the secondary component. The different periods of the known binary 1999 HF₁'s are easily detected. Other Atens have lightcurve with features such as high amplitude, V-shaped minima and U-shaped maxima that can be interpreted as a binary asteroid with a synchronous rotation (2003 NZ₆, 2000 CK₃₃ and perhaps also 1999 JD₆). The very red colors of 2000 CK₃₃ suggest a unique surface composition for this near-Earth object.     

Pole coordinates of the asteroids 9 metis, 22 kalliope,and 44 Nysa

By means of new photoelectric observations made in 1974 an attempt to determine the poles of asteroids 9 and 44 was made. Following a method based upon the magnitude-aspect and amplitude-aspect relations, the coordinates of the poles for 9 and 44 were found to be, respectively, λ₀ = 191° ± 5°, β₀ = 56° ± 6° and λ₀ = 100° ± 10°, β₀ = 50° ± 10°. The previously published pole for asteroid 22, λ₀ = 215° ± 10°, β₀ = 45° ± 15°, was confirmed. From its phase relation we determined the phase coefficient of 44 Nysa, a very high albedo object (p_v = 0.377). The very low phase coefficient obtained (β_v = 0.018 mag/deg) agrees very well with an inverse relation between geometrical albedo and phase coefficient. The results are summarized in a table.     

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.     

The rotation,color, phase coefficient,and diameter of 1915 quetzalcoatl

Photoelectric observations of 1915 Quetzalcoatl on March 2, 1981 show that this asteroid has a rotational period of 4.9 ± 0.3 hr and a lightcurve amplitude of 0.26 magnitudes. B-V and U-B colors are found to be 0.83 ± 0.04 and 0.43 ± 0.03, respectively, consistent with Quetzalcoatl being an S-type asteroid. Additional observations from March 31, 1981 give a linear phase coefficient of 0.033 mag deg^?1 and a mean B(1,0) magnitude of 20.10. The resulting estimated mean diameter for Quetzalcoatl is only 0.37 km, making it one of the smallest asteroids for which physical observations have yet been made.     

Photoelectric photometry of asteroids 45, 120, 776, 804, 814, and 1982DV

Photoelectric lightcurves of six asteroids, observed at the ESO 50-cm photometric telescope, are presented. 45 Eugenia, observed for pole determination program, showed a small amplitude of light variation, i.e., about 0.09÷0.10 mag. For 120 Lachesis, no period of rotation was deduced from three observing nights; it is probably longer than 20 hr. 776 Berbericia was observed again to eliminate the ambiguity between 23^h and 15^h.3 periods, as pointed out by Schober (1979). The longer period is ruled out, but we suggest a very plausible shorter period of 7^h.762, implying, at least at this opposition, one maximum and one minimum per cycle. A similar ambiguity is present for 804 Hispania also. The period could be either 14.^h.84 or 7^h.42. These two objects are typical of a class of asteroids whose periods are uncertain by a factor two. A short discussion on this problem is given. For 814 Tauris a long period of 35.8 hr is found, confirming the tendency of dark asteroids of intermediate size to rotate more slowly than larger ones. Finally a single-night lightcurve of the fast-moving object 1982DV is presented. Our observations agree very well with Harris' results (1982, private communication).     

Modeling of lightcurves of binary asteroids

We present a numerical method for inverting long-period components of lightcurves of asynchronous binary asteroids. Data of five near-Earth binary asteroids, (175706) 1996 FG₃, (65803) Didymos, (66391) 1999 KW₄, (185851) 2000 DP₁₀₇ and (66063) 1998 RO₁, for two of them from more than one apparition, were inverted. Their mutual orbits' poles and Keplerian elements, size ratios, and ellipsoidal shape axial ratios were estimated via this inversion. The pole solutions and size ratios for 1999 KW₄ and 2000 DP₁₀₇ are in a good agreement with independent estimates from radar measurements. We show that uncertainties of estimates of bulk densities of binary systems can be large, especially when observed on short arcs.     

Serendipitous Asteroid Lightcurve Survey Using SuperWASP

The SuperWASP project is an ultra-wide angle search for extra solar planetary transits. However, it can also serendipitously detect solar system objects, such as asteroids and comets. Each SuperWASP instrument consists of up to eight cameras, combined with high-quality peltier-cooled CCDs, which photometrically survey large numbers of stars in the magnitude range 7–15. Each camera covers a 7.8 × 7.8 degree field of view. Located on La Palma, the SuperWASP-I instrument has been observing the Northern Hemisphere with five cameras since its inauguration in April 2004.The ultra-wide angle field of view gives SuperWASP the possibility of discovering new fast moving (near to Earth) asteroids that could have been missed by other instruments. However, it provides an excellent opportunity to produce a magnitude-limited lightcurve survey of known main belt asteroids. As slow moving asteroids stay within a single SuperWASP field for several weeks, and may be seen in many fields, a survey of all objects brighter than magnitude 15 is possible. This will provide a significant increase in the total number of lightcurves available for statistical studies without the inherent bias against longer periods present in the current data sets.We present the methodology used in the automated collection of asteroid data from SuperWASP and some of the first examples of lightcurves from numbered asteroids.     

Turning Asteroids into Comets with ELTs

It is clear that ELTs will be able to detect extremely weak outgassing from Solar system bodies via a number of different methods. Occultations will allow probing for outgassing around 20 km main-belt asteroids. Imaging can reveal dust emission rates of only milligrams/second in the inner solar system, while sublimation rates of gasses should be measurable down to gram/second levels. Suitable targets will be identified via the coming all-sky surveys, through both the classical dynamical Tisserand Invariant and long-baseline lightcurves. It is possible that using these methods, ELTs may allow the discovery of much more activity throughout the Solar system than is presently known.     

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.