| 1. |
- Ye, Quanzhi, et al.
(författare)
-
Debris of Asteroid Disruptions Close to the Sun
- 2019
-
Ingår i: Astrophysical Journal. - : Institute of Physics (IOP). - 0004-637X .- 1538-4357. ; 873:2
-
Tidskriftsartikel (refereegranskat)abstract
- The under-abundance of asteroids on orbits with small perihelion distances suggests that thermally driven disruption may be an important process in the removal of rocky bodies in the solar system. Here we report our study of how the debris streams arise from possible thermally driven disruptions in the near-Sun region. We calculate that a small body with a diameter 0.5 km can produce a sufficient amount of material to allow the detection of the debris at the Earth as meteor showers, and that bodies at such sizes thermally disrupt every ~2 kyr. We also find that objects from the inner parts of the asteroid belt are more likely to become Sun-approachers than those from the outer parts. We simulate the formation and evolution of the debris streams produced from a set of synthetic disrupting asteroids drawn from Granvik et al.'s near-Earth object population model, and find that they evolve 10–70 times faster than streams produced at ordinary solar distances. We compare the simulation results to a catalog of known meteor showers on Sun-approaching orbits. We show that there is a clear overabundance of Sun-approaching meteor showers, which is best explained by a combining effect of comet contamination and an extended disintegration phase that lasts up to a few thousand years. We suggest that a few asteroid-like Sun-approaching objects that brighten significantly at their perihelion passages could, in fact, be disrupting asteroids. An extended period of thermal disruption may also explain the widespread detection of transiting debris in exoplanetary systems.
|
|
| 2. |
- Gustafsson, Magnus, et al.
(författare)
-
Infrared Absorption Spectra of Collisionally Interacting He and H Atoms
- 2001
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 546:2, s. 1168-1170
-
Tidskriftsartikel (refereegranskat)abstract
- On the basis of recent state-of-the-art ab initio calculations of the interatomic potential and dipole surface of interacting helium (He) and hydrogen (H) atoms, we calculate the collision-induced absorption spectra in the infrared of the He-H pair, using a rigorous quantum mechanical formalism. Furthermore, we present a simple analytical model which is capable of reproducing these calculated spectra with precision, for frequencies from 50 to roughly 10,000 cm-1 and temperatures from 1500 to 10,000 K. For a given temperature and frequency, the ratio of the absorption coefficient and the product of the H and He densities may be evaluated in seconds, even on small computers (e.g., PCs), provided this ratio exceeds a certain (very small) lower numerical limit.
|
|
| 3. |
- Montanes-Rodriguez, Pilar, et al.
(författare)
-
Vegetation signature in the observed globally integrated spectrum of earth considering simultaneous cloud data : Applications for extrasolar planets
- 2006
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 651:1 I, s. 544-552
-
Tidskriftsartikel (refereegranskat)abstract
- A series of missions will be launched over the next few decades that will be designed to detect and characterize extrasolar planets around nearby stars. These missions will search for habitable environments and signs of life (biosignatures) in planetary spectra. The vegetation's "red edge," an enhancement in the Earth's spectrum near 700 nm when sunlight is reflected from greenery, is often suggested as a tool in the search for life in terrestrial-like extrasolar planets. Here, through ground-based observations of the Earth's spectrum, satellite observations of clouds, and an advanced atmospheric radiative-transfer code, we determine the temporal evolution of the vegetation signature of Earth. We find a strong correlation between the evolution of the spectral intensity of the red edge and changes in the cloud-free vegetated area over the course of observations. This relative increase for our single day corresponds to an apparent reflectance change of about 0.0050 ± 0.0005 with respect to the mean albedo of 0.25 at 680 nm (2.0% ± 0.2%). The excellent agreement between models and observations motivated us to probe more deeply into the red-edge detectability using real cloud observations at longer timescales. Overall, we find the evolution of the red-edge signal in the globally averaged spectra to be weak, and only attributable to vegetation changes when the real land and cloud distributions for the day are known. However, it becomes prominent under certain Sun-Earth-Moon orbital geometries that are applicable to the search for life in extrasolar planets. Our results indicate that vegetation detection in Earth-like planets will require a considerable level of instrumental precision and will be a difficult task, but not as difficult as the normally weak earthshine signal might seem to suggest.
|
|
