MNRAS 2015 454
Periodic impact cratering and extinction events over the last 260 million years
Rampino, Caldeira
The claims of periodicity in impact cratering and biological extinction events are controversial. A newly revised record of dated impact craters has been analyzed for periodicity, and compared with the record of extinctions over the past 260 Myr. A digital circular spectral analysis of 37 crater ages (ranging in age from 15 to 254 Myr ago) yielded evidence for a significant 25.8±0.6 Myr cycle. Using the same method, find a significant 27.0±0.7 Myr cycle in the dates of the eight recognized marine extinction events over the same period. The cycles detected in impacts and extinctions have a similar phase. The impact crater dataset shows 1 apparent peaks in the last 260 Myr, at least 5 of which correlated closely with significant extinction peaks. These results suggest that the hypothesis of periodic impacts and extinction events is still viable.
1510.06034
A new method to quantify the effects of baryons on the matter power spectrum
Schneider, Teyssier
Future large-scale galaxy surveys have the potential to become leading probes for cosmology provided the influence of baryons on the total mass distribution is understood well enough. As hydrodynamical simulations strongly depend on details in the feedback implementations, no unique and robust predictions for baryonic effects currently exist. In this paper, propose a baryonic correction model that modifies the density field of DM-only N-body sims to mimic the effects of baryons from any underlying adopted feedback recipe. The model assumes haloes to consist of 4 components: 1) hot gas in hydro equilibrium, 2) ejected gas from feedback processes, 3) central galaxy stars, and 4) adiabatically relaxed dark matter, which all modify the initial DM-only density profiles. This altered mass profiles allow definition of a displacement field for particles in N-body sims and to modify the total density field accordingly. The main advantage of the baryonic correction model is to connect the total matter density field to the observable distribution of gas and stars in haloes, making it possible to parametric baryonic effects on the matter power spectrum. Show that the most crucial quantities are the mass fraction of ejected gas and its corresponding ejection radius. The former controls how strongly baryons suppress the power spectrum, while the latter provides a measure of the scale where baryonic effects become important. A comparison with X-ray and Sunyaev-Zel'dovich cluster observations suggests that baryons suppress wave modes above k~0.5 h/Mpc with a maximum suppression of 10-25 percent around k~2 h/Mpc. More detailed observations of the gas in the outskirts of groups and clusters are required to decrease the large uncertainties of these numbers.
1510.06387
A disintegrating minor planet transiting a white dwarf
Vanderburg, Johnson, et al
WDs are the end state of most stars, including the Sun, after they exhaust their nuclear fuel. Between 1/4 and 1/2 of WDs have elements heavier than He in their atmospheres, even though these elements should rapidly settle into the stellar interiors unless they are occasionally replenished. The abundance ratios of heavy elements in WD atmospheres are similar to rocky bodies in the Solar system. This and the existence of warm dusty debris disks around about 4% of WDs suggest that rocky debris from WD progenitors' planetary systems occasionally pollute the stars' atmospheres. The total accreted mass can be comparable to that of large asteroids the solar system. However, the process of disrupting planetary material has not yet been observed. Here, report observations of a WD being transited by at least one and likely multiple disintegrating planetesimals with periods ranging from 4.5 hrs to 4.9 hours. The strongest transit signal occur every 4.5 hours and exhibit varying depths up to 40% and asymmetric profiles, indicative of a small object with a cometary tail of dust effluent material. The star hosts a dusty debris disk and the star's spectrum shows prominent lines from heavy elements like Mg, Al, Si, Ca, Fe, and Ni. This system provides evidence that heavy element pollution of WDs can originate from disrupted rocky bodies such as asteroids and minor planets.
No comments:
Post a Comment