arXiv subjects

Pedro Lacerda

Publications and source records attributed to Pedro Lacerda.

43 records · Page 3Linked to original sources

arXiv2008

Color-Inclination Relation of the Classical Kuiper Belt Objects

We re-examine the correlation between the colors and the inclinations of the Classical Kuiper Belt Objects (CKBOs) with an enlarged sample of optical measurements. The correlation is strong (rho=-0.7) and highly significant (>8 sigma) in the range 0-34 deg. Nonetheless, the optical colors are independent of inclination below ~12 deg, showing no evidence for a break at the reported boundary between the so-called dynamically "hot" and "cold" populations near ~5 deg. The commonly accepted parity between the dynamically cold CKBOs and the red CKBOs is observationally unsubstantiated, since the group of red CKBOs extends to higher inclinations. Our data suggest, however, the existence of a different color break. We find that the functional form of the color-inclination relation is most satisfactorily described by a non-linear and stepwise behavior with a color break at ~12 deg. Objects with inclinations >12 deg show bluish colors which are either weakly correlated with inclination or are simply homogeneously blue, whereas objects with inclinations <12 deg are homogeneously red.

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arXiv2008

High Precision Photometry of Extreme KBO 2003 EL61

We present high precision, time-resolved visible and near infrared photometry of the large (diameter ~ 2500 km) Kuiper belt object (136108) 2003 EL61. The new data confirm rapid rotation at period P = 3.9155+/-0.0001 hr with a peak-to-peak photometric range (Delta m_R) = 0.29+/-0.02 mag and further show subtle but reproducible color variations with rotation. Rotational deformation of 2003 EL61 alone would give rise to a symmetric lightcurve free of color variations. The observed photometric deviations from the best-fit equilibrium model show the existence of a large surface region with an albedo and color different from the mean surface of 2003 EL61. We explore constraints on the nature of this anomalous region set by the existing data.

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arXiv2007

Detection of Contact Binaries Using Sparse High Phase Angle Lightcurves

We show that candidate contact binary asteroids can be efficiently identified from sparsely sampled photometry taken at phase angles >60deg. At high phase angle, close/contact binary systems produce distinctive lightcurves that spend most of the time at maximum or minimum (typically >1mag apart) brightness with relatively fast transitions between the two. This means that a few (~5) sparse observations will suffice to measure the large range of variation and identify candidate contact binary systems. This finding can be used in the context of all-sky surveys to constrain the fraction of contact binary near-Earth objects. High phase angle lightcurve data can also reveal the absolute sense of the spin.

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arXiv2007

Fraction of Contact Binary Trojan Asteroids

We present the results of an optical lightcurve survey of 114 Jovian Trojan asteroids conducted to determine the fraction of contact binaries. Sparse-sampling was used to assess the photometric range of the asteroids and those showing the largest ranges were targeted for detailed follow-up observations. This survey led to the discovery of two Trojan asteroids, (17365) and (29314) displaying large lightcurve ranges (~1 magnitude) and long rotation periods (< 2 rotations per day consistent with a contact binary nature. The optical lightcurves of both asteroids are well matched by Roche binary equilibrium models. Using these binary models, we find low densities of ~600 kg/m^3 and 800 kg/m^3, suggestive of porous interiors. The fraction of contact binaries is estimated to be between 6% and 10%, comparable to the fraction in the Kuiper Belt. The total binary fraction in the Trojan clouds (including both wide and close pairs) must be higher.

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arXiv2006

Densities of Solar System Objects from their Rotational Lightcurves

We present models of the shapes of four Kuiper belt objects (KBOs) and Jovian Trojan (624) Hektor as ellipsoidal figures of equilibrium and Roche binaries. Our simulations select those figures of equilibrium whose lightcurves best match the measured rotational data. The best fit shapes, combined with the knowledge of the spin period of the objects provide estimates of the bulk densities of these objects. We find that the lightcurves of KBOs (20000) Varuna and 2003 EL61 are well matched by Jacobi triaxial ellipsoid models with bulk densities 992 (-15,+86) kg/m^3 and 2551 (-10,+115) kg/m^3, respectively. The lightcurves of (624) Hektor and KBO 2001 QG298 are well-described by Roche contact binary models with densities 2480 (-80,+292) kg/m^3 and 590 (-47,+143) kg/m^3, respectively. The nature of 2000 GN171 remains unclear: Roche binary and Jacobi ellipsoid fits to this KBO are equivalent, but predict different densities, ~2000 kg/m^3 and ~650 kg/m^3, respectively. Our density estimates suggest a trend of increasing density with size.

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arXiv2006

Analysis of the rotational properties of Kuiper belt objects

We use optical data on 10 Kuiper Belt objects (KBOs) to investigate their rotational properties. Of the 10, three (30%) exhibit light variations with amplitude delta_m >= 0.15 mag, and 1 out of 10 (10%) has delta_m >= 0.40 mag, which is in good agreement with previous surveys. These data, in combination with the existing database, are used to discuss the rotational periods, shapes, and densities of Kuiper Belt objects. We find that, in the sampled size range, Kuiper Belt objects have a higher fraction of low amplitude lightcurves and rotate slower than main belt asteroids. The data also show that the rotational properties and the shapes of KBOs depend on size. If we split the database of KBO rotational properties into two size ranges with diameter larger and smaller than 400 km, we find that: (1) the mean lightcurve amplitudes of the two groups are different with 98.5% confidence, (2) the corresponding power-law shape distributions seem to be different, although the existing data are too sparse to render this difference significant, and (3) the two groups occupy different regions on a spin period vs. lightcurve amplitude diagram. These differences are interpreted in the context of KBO collisional evolution.

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arXiv2004

On the detectability of lightcurves of Kuiper Belt objects

We present a statistical study of the detectability of lightcurves of Kuiper Belt objects (KBOs). Some Kuiper Belt objects display lightcurves that appear "flat", i.e., there are no significant brightness variations within the photometric uncertainties. Under the assumption that KBO lightcurves are mainly due to shape, the lack of brightness variations may be due to (1) the objects have very nearly spherical shapes, or (2) their rotation axes coincide with the line of sight. We investigate the relative importance of these two effects and relate it to the observed fraction of "flat" lightcurves. This study suggests that the fraction of KBOs with detectable brightness variations may provide clues about the shape distribution of these objects. Although the current database of rotational properties of KBOs is still insufficient to draw any statistically meaningful conclusions, we expect that, with a larger dataset, this method will provide a useful test for candidate KBO shape distributions.

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