On the shape of meteor light curves, and a fully analytic solution to the equations of meteoroid ablation

The shape and characteristics (beginning and end heights, and height of maximum brightness) of meteor light curves are investigated under the constraint that the surface area S that a meteoroid presents to the oncoming air flow varies as a power law in the meteoroid mass m such that   S ∼ m ^α  . We investigate the meteoroid ablation for a range of values of α, and find that the  α= 1  condition allows for a fully analytic solution to the coupled differential equations of meteoroid ablation when the density profile is that of an isothermal atmosphere. The possible geometrical properties of Geminid meteoroids are discussed in terms of the  α= 1  ablation model and it is shown that they are consistent with being derived from an asteroidal, rather than cometary, parent body.     

Searching for Light Curve Evidence of Meteoroid Structure and Fragmentation

We used light curve analysis to search for evidence of the dustball meteoroid model. Leonid, Taurid, Alpha Monocerotid and sporadic meteors from November 2003 were observed and analyzed using uniform methodology. Meteors from these four sources were examined for evidence of fragmentation by examining light curve shape and searching for light curve irregularities. Differences in meteoroid structure should be reflected by differences in meteor light curves. The resulting meteor light curve F-parameter values showed no statistically significant differences between the meteors from the various cometary showers or the sporadic meteors. The F-parameter values also suggest that the meteoroids from these sources do not follow a single body ablation model, which suggests that all four sources produce meteoroids with a dustball structure.     

Sputtering and high altitude meteors

Conventional ablation theory assumes that a meteoroid undergoes intensive heating during atmospheric flight and surface atoms are liberated through thermal processes. Our research has indicated that physical sputtering could play a significant role in meteoroid mass loss. Using a 4th order Runge-Kutta numerical integration technique, we tabulated the mass loss due to the two ablation mechanisms and computed the fraction of total mass lost due to sputtering. We modeled cometary structure meteoroids with masses ranging from 10⁻¹³ to 10⁻³ kg and velocities ranging from 11.2 to 71 km s⁻¹. Our results indicate that a significant fraction of the mass loss for small, fast meteors is due to sputtering, particularly in the early portion of the light curve. In the past 6 years evidence has emerged for meteor luminosity at heights greater than can be explained by conventional ablation theory. We have applied our sputtering model and find excellent agreement with these observations, and therefore suggest that sputtered material accounts for the new type of radiation found at great heights.     

Spot activity in the RS CVn binary UX arietis

Photoelectric observations of the RS CVn type non-eclipsing binary UX Arietis obtained at Nizamiah Observatory during the observing seasons of 1975–76, 1981–82 and 1982–83 are presented. The light curve of UX Ari showed a distortion wave with an amplitude inV varying from 0.02 mag during 1975–76 to 0.15 mag during 1982–83. An analysis of the available data shows that the light maximum is almost constant. It is also evident that the light-curve minimum decreases as the wave amplitude increases. The constant light at maximum,V = 6.51 ± 0.03 indicates the unspotted photospheric brightness. It is also suggested that the variation in meanV brightness is mainly due to spot activity and not due to intrinsic variation.     

Constraining the luminous efficiency of meteors

We propose a new approach for studying the radiation of a fireball, one of the main processes which occur when the meteor body enters the planetary atmosphere. The only quantities which directly follow from the available observations are the fireball brightness, its height above sea level, the length along the trajectory, and as a consequence its velocity as a function of time. Other important parameters like meteoroid’s mass, its shape, bulk and grain density, temperature remain unknown. The present study takes recent results in fireball aerodynamics and considers them together with the classical postulate that a fraction of the meteoroid kinetic energy is transformed into radiation during its flight. This gives us a new analytical dependence, which in particular shows that the fireball luminosity in general is proportional to the body pre-entry mass value, its initial velocity to the power of 3, and the sine of the slope between horizon and trajectory. Research helps in finding an answer to the general important question: Which fraction of the fireball kinetic energy is transformed into light during meteoroid drag and ablation in the atmosphere?     

Radiative cooling flows of self-gravitating filamentary clouds

We study the dynamics of a self-gravitating cooling filamentary cloud using a simplified model. We concentrate on the radial distribution and restrict ourselves to quasi-hydrostatic, cylindrically symmetric cooling flows. For a power-law dependence of cooling function on the temperature, self-similar solutions which describe quasi-hydrostatic cooling flows are derived. We consider obtically thin filaments with a constant mass per unit length and the solutions are parameterized by their line masses. There is no polytropic relation between the density and the pressure. The filament experiences radiative condensation, irrespective of the γ,the gas specific heat ratio. So, the filament becomes denser due to the quasi-hydrostatic flows and the density at the center (ρ_c) increases in proportion to (t ₀-t)^-1, where t denotes the time. The term,t ₀, denotes an epoch at which the central density increases infinitely. We also found that the radius of the filament (r _c) decreases in proportion to (t ₀-t)^1/2. This revised version was published online in July 2006 with corrections to the Cover Date.     

Image‐intensified video results from the 1998 Leonid shower: I. Atmospheric trajectories and physical structure

Abstract— Two‐station electro‐optical observations of the 1998 Leonid shower are presented. Precise heights and light curves were obtained for 79 Leonid meteors that ranged in brightness (at maximum luminosity) from +0.3 to +6.1 astronomical magnitude. The mean photometric mass of the data sample was 1.4 × 10^?6 kg. The dependence of astronomical magnitude at peak luminosity on photometric mass and zenith angle was consistent with earlier studies of faint sporadic meteors. For example, a Leonid meteoroid with a photometric mass of ～1.0 × 10‐⁷ kg corresponds to a peak meteor luminosity of about +4.5 astronomical magnitudes. The mean beginning height of the Leonid meteors in this sample was 112.6 km and the mean ending height was 95.3 km. The highest beginning height observed was 144.3 km. There is relatively little dependence of either the first or last heights on mass, which is indicative of meteoroids that have clustered into constituent grains prior to the onset of intensive grain ablation. The height distribution, combined with numerical modelling of the ablation of the meteoroids, suggests that silicate‐like materials are not the principal component of Leonid meteoroids and hints at the presence of a more volatile component. Light curves of many Leonid meteors were examined for evidence of the physical structure of the associated meteoroids: similar to the 1997 Leonid meteors, the narrow, nearly symmetric curves imply that the meteoroids are not solid objects. The light curves are consistent with a dustball structure.     

Meteoroid rotation and fireball flickering: a case study of the Innisfree fireball

Some 5 per cent of bright meteors show rapid, quasi-periodic brightness variations. It is argued that this effect, observationally known as flickering, is a manifestation of the rotational modulation of surface mass loss through ablation of a non-spherical meteoroid. We develop a set of time-dependent, single-body ablation equations that include the effect of cross-section area modulation. We present a discussion of the effects that the rotation of a non-spherical meteoroid has on the resultant meteor light curve, and we look in depth at the data related to the fireball associated with the fall of the Innisfree meteorite. We find that the parent object to the Innisfree meteorite was spinning at a rotation frequency of 2.5 Hz when it encountered the Earth's upper atmosphere. We also find that the Innisfree parent body had an initial mass of about 20 kg and that the ratio of its semiminor and semimajor axes was about 0.5.     

Fragmentation model analysis of the observed atmospheric trajectory of the Tagish Lake fireball

Abstract— A recently published meteoroid fragmentation model (FM) was applied to observational data on the Tagish Lake meteoric fireball. An initial mass of 56,000 kg, derived from seismic and infrasound data by Brown et al. (2002), proved to be consistent with a very low value of intrinsic ablation coefficient of 0.0009 s² km^?2. The average residual of the best fit to the observed light curve was ±0.10 stellar magnitude. The apparent ablation coefficient varied from 0.0009 to 1.52 s² km^?2 with an average value of 0.054 s² km^?2 (determined by the gross fragmentation [GF] model). The FM found 33 individual fragmentation events during the penetration of the 56,000 kg initial mass of the Tagish Lake meteoroid through the atmosphere, with five of the events fragmenting more than 10% of the instantaneous mass of the main body. The largest event fragmented 88% of the mass of the main body at a height of 34.4 km. The velocity of the main body mass of 2660 kg at a height of 29.2 km (the last observed light) was 13.1 km/s. Strong fragmentation at heights lower than 29.2 km is very probable. The extreme fragmentation process of the Tagish Lake meteoroid puts its classification well outside the IIIB type in the direction of less cohesive bodies. The light curve could not be explained at all by making use of only the apparent ablation coefficient and apparent luminous efficiency.     

Aq Psc – Analysis of New Light Curves

New BV light curves of the A-type W UMa star AQ Psc (P = 0.476d) have been observed and are described. A few times of minimum light are obtained and the ephemeris is improved. The light curves are analyzed for the binary parameters with a light curve synthesis method. Combining the results with Lu and Rucinski’s spectroscopic mass ratio we determined the masses and radii of the components: M ₁ = 1.69M _⊙, M ₂ = 0.38M _⊙, R ₁ = 1.77R _⊙, and R ₂ = 0.89R _⊙.     

Bimodal brightness oscillations in models of young binary systems

We consider a model for the cyclic activity of young binary stars that accrete matter from the remnants of a protostellar cloud. If the orbit of such a binary system is inclined at a small angle to the line of sight, then the streams of matter and the density waves excited in the circumbinary disk can screen the primary component of the binary from the observer. To study these phenomena by the SPH (smoothed particle hydrodynamics) method, we have computed grids of hydrodynamic models for binary systems based on which we have constructed the light curves as a function of the orbital phase. The main emphasis is on investigating the properties of the brightness oscillations. Therefore, the model parameters were varied within the following ranges: the component mass ratio q = M ₂: M ₁ = 0.2–0.5 and the eccentricity = 0–0.7. The parameter that defined the binary viscosity was also varied. We adopted optical grain characteristics typical of circumstellar dust. Our computations have shown that bimodal oscillations are excited in binaries with eccentric orbits, provided that the binary components do not differ too much in mass. In this case, the ratios of the periods and amplitudes of the bimodal oscillations and their shape depend strongly on the inclination of the binary plane and its orientation relative to the observer. Our analysis shows that the computed light curves can be used in interpreting the cyclic activity of UX Ori stars.     

Photometric Observations and Light Curve Studies of the Semi-Detached Eclipsing Binary R CMa

We present observations and light curve analysis of the eclipsing binary R CMa in the narrow band filters v and b. Observations were made during 1993 at Biruni Observatory and the light curves have been analyzed using the Wilson-Devinney light curve interpretation program. Assuming a semi-detached configuration for R CMa, the parameters i, Ω₁, L ₁, T ₂ and A ₂ were adjusted for the best fit between the synthesized light curves and observations. Both light curves were fitted well with a lower value of bolometric albedo than what would be expected for a normal cool star with a convective envelope. The masses of the primary and secondary components and the absolute dimensions of the stars have been calculated using the derived relative dimensions from Wilson-Devinney codes and the spectroscopic observations.     

Investigation of X-Ray Flares with Long Rising Phases

We have used Yohkoh and GOES X-ray observations to investigate flares with a long rising phase. We have found that a characteristic feature of such flares is a long time interval, Δ t ≥ 20 min, between the temperature maximum and the maximum of the emission measure. We have carried out detailed analysis for 10 limb flares of this type. Time variation of the heating function, E_H(t), has been determined for their loop-top X-ray kernels. The time variation of E_H(t), together with the temperature–density diagnostic diagrams, have been used to explain the large value of the time interval, Δ t. The main point is that for these flares the heating function E_H(t) decreases so slowly after the temperature maximum, that for the long time, Δ t, the energy flux reaching flare foot points is sufficient to maintain significant chromospheric evaporation. Investigation of the flare evolution in the temperature–density diagnostic diagrams allowed us to work out a new method of determination of the density for flare kernels. This method can be applied to all the kernels for which their altitudes can be estimated. The advantage of this method is that for the density determination it is not necessary to assume what is the extension of the emitting plasma along the line of sight.     

Latitudinal and Solar-Cycle Variations of the White-Light Corona from SOHO/LASCO Observations

SOHO/LASCO data were used to obtain the latitudinal and radial distributions of the brightness of the K- and F-corona in the period of 1996 – 2007, and their solar-cycle variations were studied. Then an inversion method was employed to obtain the radial distributions of the electron density N _e(R,θ) for various latitude values on the coronal images. Our values of N _e(R,θ) are in good agreement with the findings of other authors. We found that in an edge-on streamer belt the electron density, like the K-corona brightness, varies with distance more slowly in the near-equatorial rays than in near-polar regions. We have developed a method for assessing the maximum values of the electron density at the center of the face-on streamer belt in its bright rays and depressions between them. Not all bright rays observed in the face-on streamer belt are found to be associated with an increased electron density in them. Mechanisms for forming such rays have been suggested.     

OPTICAL PREDICTIONS FOR HIGH GEOCENTRIC VELOCITY METEORS

In this study we numerically modelled the atmospheric ablation and luminosity of cometary structure meteoroids with geocentric velocities from 71 to 200 km/s. We considered meteoroid masses ranging from 10⁻¹³ to 10⁻⁶ kg. Expected heights of ablation and maximum luminosity absolute magnitudes are determined. Height and trail length values are used to calculate the angle traversed in a single video frame. It is found that for pre-atmospheric meteoroid masses of greater than 10⁻⁸ kg, high geocentric velocity meteors should be detectable with current electro-optical technology if properly optimised.     

Brightness oscillations in models of young binary systems with low-mass secondary components

We consider a model for the cyclic brightness variations of a young star with a low-mass companion that accretes matter from the remnants of a protostellar cloud. At small inclinations of the binary orbit to the line of sight, the streams of matter and the density waves excited in the circumbinary disk can screen the primary component of the binary from the observer. To study these phenomena, we have computed grids of hydrodynamic models for binary systems by the SPH method based on which we have calculated the phase light curves for the different orientations of the orbit. The model parameters were varied within the following ranges: the component mass ratio q = 0.01–0.1 and the eccentricity e = 0–0.5. We adopted optical grain characteristics typical of circumstellar dust. Our computations have shown that the brightness oscillations with orbital phase can have a complex structure. The amplitudes and shapes of the light curves depend strongly on the inclination of the binary orbit and its orientation relative to the observer and on the accretion rate. The results of our computations are used to analyze the cyclic activity of UX Ori stars.     

Photometric and Hα Observations of the Cataclysmic Star UX UMa

UBVRI photometry and spectroscopic observations around the H_α line of the cataclysmic star UX UMa are presented. The analysis of the 9-year photometry shows that the out-of-eclipse brightness of the system and the depth of the eclipse changes in different time scales while the width of the eclipse remains constant. The observed features of the light curves as well as the features of the two-peaked H_α profiles were attributed to an inhomogeneity of the accretion disk. “Spiral arm” model for a fitting of the light curves of UX UMa is proposed. It reproduces well the observational data. The obtained azimuthal extent of the spiral arms is of ∼90° and their light contribution is about 17–30of the total V flux of the disk. The obtained two dense structures at the outer disk covering partially the inner hot disk and the white dwarf at orbital phases ∼0.7 and ∼0.2 is in agreement with the predictions of the theoretical computations.     

Radial Velocity and Light Curve Analysis of the Eclipsing Binary Nn Vir

The eclipsing binary NN Vir is a short period system showing an EW-type light curve. Photometric observations of NN Vir were done by Gomez–Ferrellad and Garcia–Melendo (1997) at Esteve Duran Observatory. The first spectroscopic observations of this system were obtained by Rucinski and Lu (1999). The radial velocity and light curves analysis was made with the latest version of the Wilson program (1998), and the geometric and physical elements of the system are derived. From the simultaneous solutions of the system, we determined the masses and radii of the components: 1.89 M _⊙ and 1.65 R _⊙ for the primary component; 0.93 M _⊙ and 1.23 R _⊙ for the secondary component. We estimated effective temperatures of 7030 K for the primary and 6977 K for the secondary component.     

A rotational light curve for the Kuiper belt object 1997 CV29

We present R- and V-band rotational light curves for classical Kuiper belt object 1997 CV₂₉. The imaging data was obtained from the Canada-France-Hawaii Telescope (CFHT) archive located at the Canadian Astronomical Data Center (CADC). The data consist of one nights observations of a series of 42, 8 minute exposures in R band followed by 33, 8 minute exposures in V band acquired on the following night. Using relative photometry we determined a highly significant variation in the brightness of 1997 CV₂₉. Using phase-dispersion-minimization we find 8.0, 11.2, and 15.8 hrs to be the most likely, periods of rotation and we argue that the ∼16 hr period is the most likely based on our limited observing window. The phased light curve has a peak-to-peak range of Δm?0.4±0.1 mag suggesting an axial ratio of a/b?1.45.     

Infrared photometry for three RV Tau variable stars

We have analyzed our long-term (1995–2008) JHKLM photometry for three variable RV Tau supergiants. It follows from this analysis that: the amplitude of the JHK brightness variations is approximately the same, 0 ^m . 9–1 ^m , for the three stars; a negative linear trend is noticeable in the variations of the mean J brightness for AC Her; and the mean J brightness of R Sct and V Vul remained constant. The observed J brightness fluctuations in the supergiants are shown to be consistent either only with the temperature pulsations (AC Her and V Vul) or with the temperature and radial pulsations (R Sct). We have detected long-term pulsations in the J brightness and J-H color variations of the supergiants with the following characteristic time scales: ∼1500 days (AC Her), ∼3500 days (R Sct), and ∼800 and ∼1500 days (V Vul). Our search for a periodic component in the infrared brightness variations of the three stars has revealed periods that differ from those obtained from optical observations. We show that relatively hot dust shells (T _d ∼ 700–800 K) exist around the supergiants under study; the densest and most massive shell was observed for V Vul. The ranges of optical-depth variations for the dust shells were τ(1.25 μm) ≈ 0.04–0.10 (AC Her), ≈0.02–0.12 (R Sct), and ≈0.18–0.32 (V Vul). The spectral types in the infrared varied over narrower ranges than those that followed from optical observations of these stars.