<title>Luminous efficiencies of bolides</title>

Abstract

Observational data on luminosity of bolides observed from ground-based stations as well as from satellite systems can be converted into masses or sizes of bodies assuming we know the luminous efficiency of the atmospheric interaction process. Problems of luminous efficiency were very much simplified until recently. Traditional approach assigned just a single value for each velocity and the calibration was derived only from early experiments with artificial meteors produced by masses of the order of grams. A recent analysis of the Lost City fireball enabled a precise and reliable determination of masses from the motion of the body and revealed that the differential luminous efficiencies for bodies in a mass ranges of hundred kilograms are out 10 times larger than the traditionally used values. This paper presents results on luminous efficiencies from detailed analysis of 29 Prairie Network (PN) bolides brighter than magnitude minus 10. This analysis is based on independent solutions for motion of the body, combines them with the experimental results for gram masses and applies them to satellite observed bolides. Masses resulting from such dynamic solutions are compared to radiated energies and the luminous efficiencies are computed by two different approaches: (1) total radiated energy is compared to the initial kinetic energy of the body resulting in total luminous efficiency (The only concept used on space observed bolides so far); (2) time change of kinetic energy of ablated mass is compared to power of radiation for each time-mark on the photographic record resulting in differential luminous efficiency (the traditional quantity used in meteor physics). Within a factor of two, the total luminous efficiency is identical to the differential one for majority of the 29 PN bolides. Some values of the total luminous efficiency are smaller than the differential ones due to velocity dependence and due to a significant part of kinetic energy going into changing the momentum of the body. Some values of the total luminous efficiency are greater than the differential ones due to sudden release of radiation energy at discrete points (bolides with large flares of many stellar magnitudes over the smooth light curve). Values of the differential luminous efficiencies for 29 PN bolides were derived altogether at 1324 different points of their trajectories. Correlations of these values with height, velocity, deceleration, and brightness were used to get correction factors for the actual bulk density and shape of the body (comparing these correlations with data on the Lost City bolide). These corrections were applied to the values of the total luminous efficiencies. The resulting total luminous efficiencies mostly depend on total radiated energy and, to a lesser extent, also on velocity. No reliable correlations with other parameters were found. Each bolide from these 29 behaves as an independent individual from the point of view of radiation efficiency in analogical way to ablation efficiency (Figure 8). There is no statistical correlation between ablation and radiation efficiency, but we can find groups of similar behavior: the most frequent are poor 'ablators' an good radiators (13 cases); the second in importance are good 'ablators' and poor radiators (9 cases). It is highly probable that this individualistic behavior is also valid for the much brighter bolides observed by DOD satellites. The average total luminous efficiency for the 29 PN bolides resulted as (tau) t equals 1.36% of total kinetic energy amounting to an average of 5 multiplied by 107 J of total radiated energy, which corresponds to the average initial mass of 15 kg for this sample of 29 PN bolides. These values were compared with experimental data on gram size meteoroids. Total luminous efficiencies and their expected errors for radiated energies in the range 109 to 1013 were predicted (Table 5). Resulting total luminous efficiencies were applied to data published on 21 very bright bolides observed by sensors on DOD satellites and their masses were determined (Table 6).