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In their study Bottke et al. (2007) suggest that a member of the Baptistina asteroid family was the probable source of the K/T impactor which ended the reign of the Di-nosaurs 65 Myr ago. Knowledge of the physical and material properties pertaining to the Baptistina asteroid family are, however, not well constrained. In an effort to begin addressin...
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... rotational period of PR = 16.23 ± 0.02 hours was determined for 298 Baptistina from the analysis, and the resulting phased light curve is presented in Figure 2. The light curve exhibits a peak to peak amplitude of ≃ 0.15 mag- nitude and displays complex characteristics that are likely indicative of irregular surface features. ...
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Context. Recent studies have uncovered evidence that the statistical
properties of asteroids' physical parameters are a fundamental source of
information on the physics of their collisions and evolution. The
analysis of the spin rates and spin vector distributions helps us to
understand the role of various known and new effects. The alignment of
spin vectors and the correlation of spin rates are for the first time
observed for ten members of the Koronis family. These unexpected
non-random orientations of the spin axes and correlations of the spin
rates, now known as Slivan states are interpreted in terms of a YORP
effect and spin-orbit resonances. Aims: To study
non-gravitational-effects, there appears to be a need for new
observational campaigns devoted to determining the physical parameters
of the asteroid families. Methods: We analysed the photometric
observations of the asteroids, which are the most efficient method of
studying asteroid physical parameters. Results: We report the
results of a ten-year long observational survey of the light variations
of objects in the Flora region. We present 544 individual lightcurves of
55 objects obtained at various observing geometries. These lightcurves
yield new or refined synodic periods for 32 asteroids and confirm period
determinations for 23 objects in our sample. To improve the statistics
of the Flora family objects, we add to our dataset 91 objects with
reliably determined periods. The distribution of rotation rates for the
Flora family is non-Maxwellian at a confidence level of 94% and
different from those of the Koronis and the Hungaria families. It seems
to be consistent with the long-term influence of the YORP effect,
although it is also indicative of a younger age for the Flora family
compared to both the Koronis and the Hungaria families.
Conclusions: Our new data is a foundation for the spin vector and shape
determinations that will be the objectives of the second paper of the
series. We search for spin vector and spin periods correlations in order
to determine whether Slivan states exist in the Flora family.
Photometric data is available in electronic form at the CDS via
anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/546/A72
Abstract— Bottke et al. (2007) suggested that the breakup of the Baptistina asteroid family (BAF) 160+30/-20 Myr ago produced an “asteroid shower” that increased by a factor of 2–3 the impact flux of kilometer-sized and larger asteroids striking the Earth over the last ˜120 Myr. This result led them to propose that the impactor that produced the Cretaceous/Tertiary (K/T) mass extinction event 65 Myr ago also may have come from the BAF. This putative link was based both on collisional/dynamical modeling work and on physical evidence. For the latter, the available broadband color and spectroscopic data on BAF members indicate many are likely to be dark, low albedo asteroids. This is consistent with the carbonaceous chondrite-like nature of a 65 Myr old fossil meteorite (Kyte 1998) and with chromium from K/T boundary sediments with an isotopic signature similar to that from CM2 carbonaceous chondrites. To test elements of this scenario, we obtained near-IR and thermal IR spectroscopic data of asteroid 298 Baptistina using the NASA IRTF in order to determine surface mineralogy and estimate its albedo. We found that the asteroid has moderately strong absorption features due to the presence of olivine and pyroxene, and a moderately high albedo (˜20%). These combined properties strongly suggest that the asteroid is more like an S-type rather than Xc-type (Mothé-Diniz et al. 2005). This weakens the case for 298 Baptistina being a CM2 carbonaceous chondrite and its link to the K/T impactor. We also observed several bright (V Mag. ≤16.8) BAF members to determine their composition.
Here we present visible and mid-infrared observations of the asteroid (298) Baptistina, obtained with the Gemini South telescope, the 2.2-m European Southern Observatory (ESO) telescope in La Silla and the 1.5-m telescope at the Observatório do Pico dos Dias (OPD). From photometry at the R band and observations with a solar phase angle separation of 11° we have determined HR= 10.92+0.13−0.11 and GR= 0.25+0.13−0.11. From VRI photometry we determined V−R= 0.38 ± 0.03 and R−I= 0.39 ± 0.02. Finally, from thermal photometry in the N band, and using the derived values of H and G, we obtained pV= 0.347+0.1090.076–, η= 0.969+0.221−0.210 and D= 12.4 km, for the geometric albedo, beaming parameter and diameter, respectively. If one assumes that Baptistina is indeed a member of the family it names, these results rule out the recently suggested link between the dynamical family associated with this asteroid and the cretaceous/tertiary (K/T) event since (1) this albedo is incompatible with the mineralogy of the impactor and (2) the age of the family derived through Yarkovisky spreading would be too young to be related to that event.
A VI Wesenheit diagram featuring SX Phoenicis, delta Scuti, RR Lyrae, type II and classical Cepheid variables is calibrated by means of geometric-based distances inferred from HST, Hipparcos, and VLBA observations (n=30). The distance to a target population follows from the offset between the observed Wesenheit magnitudes and the calibrated template. The method is evaluated by ascertaining the distance moduli for the LMC (mu_0=18.43+-0.03 se) and the globular clusters omega Cen, M54, M13, M3, and M15. The results agree with estimates cited in the literature, although a nearer distance to M13 is favoured (pending confirmation of the data's photometric zero-point) and observations of variables near the core of M15 suffer from photometric contamination. The calibrated LMC data is subsequently added to the Wesenheit template since that galaxy exhibits precise OGLE photometry for innumerable variables of differing classes, that includes recent observations for delta Scuti variables indicating the stars follow a steeper VI Wesenheit function than classical Cepheids pulsating in the fundamental mode. VI photometry for the calibrators is tabulated to facilitate further research, and includes new observations acquired via the AAVSO's robotic telescope network (e.g., VY Pyx: =7.25 and - =0.67). The approach outlined here supersedes the lead author's prior first-order effort to unify variables of the instability strip in order to establish reliable distances. Comment: Accepted for Publication (JAAVSO)
