Interaction of meteoric bodies with the terrestrial atmosphere

Meteorite interaction with earth atmosphere and gravitational fiel

Accessibility of the resources of near Earth space using multi-impulse transfers

Most future concepts for exploration and exploitation of space require a large initial mass in low Earth orbit. Delivering this mass requires overcoming Earth's natural gravity well, which imposes a distinct obstacle to space-faring. An alternative for future space progress is to search for resources in-situ among the near Earth asteroid population. This paper examines the scenario of future utilization of asteroid resources. The near Earth asteroid resources that could be transferred to a bound Earth orbit are determined by integrating the probability of finding asteroids inside the Keplerian orbital element space of the set of transfers with an specific energy smaller than a given threshold. Transfers are defined by a series of impulsive maneuvers and computed using the patched-conic approximation. The results show that even moderately low energy transfers enable access to a large mass of resources

Impact hazard protection efficiency by a small kinetic impactor

In this paper the ability of a small kinetic impactor spacecraft to mitigate an Earth-threatening asteroid is assessed by means of a novel measure of efficiency. This measure estimates the probability of a space system to deflect a single randomly-generated Earth-impacting object to a safe distance from the Earth. This represents a measure of efficiency that is not biased by the orbital parameters of a test-case object. A vast number of virtual Earth-impacting scenarios are investigated by homogenously distributing in orbital space a grid of 17,518 Earth impacting trajectories. The relative frequency of each trajectory is estimated by means Opik’s theory and Bottke’s near Earth objects model. A design of the entire mitigation mission is performed and the largest deflected asteroid computed for each impacting trajectory. The minimum detectable asteroid can also be estimated by an asteroid survey model. The results show that current technology would likely suffice against discovered airburst and local damage threats, whereas larger space systems would be necessary to reliably tackle impact hazard from larger threats. For example, it is shown that only 1,000 kg kinetic impactor would suffice to mitigate the impact threat of 27.1% of objects posing similar threat than that posed by Apophis

A Hubble Space Telescope ACS Search for Brown Dwarf Binaries in the Pleiades Open Cluster

We present the results of a high-resolution imaging survey for brown dwarf binaries in the Pleiades open cluster. The observations were carried out with the Advance Camera for Surveys onboard the Hubble Space Telescope. Our sample consists of 15 bona-fide brown dwarfs. We confirm 2 binaries and detect their orbital motion, but we did not resolve any new binary candidates in the separation range between 5.4AU and 1700AU and masses in the range 0.035--0.065~Msun. Together with the results of our previous study (Martin et al., 2003), we can derive a visual binary frequency of 13.3$^{+13.7}_{-4.3}$\% for separations greater than 7~AU masses between 0.055--0.065~M_{\sun} and mass ratios between 0.45--0.9$<q<$1.0. The other observed properties of Pleiades brown dwarf binaries (distributions of separation and mass ratio) appear to be similar to their older counterparts in the field.Comment: 29 pages, 7 figures, 6 tables, accepted for publication in Ap

A search for L dwarf binary systems

We present analysis of HST Planetary Camera images of twenty L dwarfs identified in the course of the Two Micron All-Sky Survey. Four of the targets have faint, red companions at separations between 0.07 and 0.29 arcseconds (1.6 to 7.6 AU). In three cases, the bolometric magnitudes of the components differ by less than 0.3 magnitudes. Since the cooling rate for brown dwarfs is a strong function of mass, similarity in luminosities implies comparable masses. The faint component in the 2M0850 system, however, is over 1.3 magnitudes fainter than the primary in the I-band, and ~0.8 magnitudes fainter in M(bol). Indeed, 2M0850B is ~0.8 magnitudes fainter in I than the lowest luminosity L dwarf currently known, while the absolute magnitude we deduce at J is almost identical with M_J for Gl 229B. Theoretical models indicate a mass ratio of \~0.75. The mean separation of the L dwarf binaries in the current sample is smaller by a factor of two than amongst M dwarfs. We discuss the implications of these results for the temperature scale in the L/T transition region and for the binary frequency amongst L dwarfs.Comment: 38 pages, 11 figures; accepted for A

Candidate Disk Wide Binaries in the Sloan Digital Sky Survey

Using SDSS Data Release 6, we construct two independent samples of candidate stellar wide binaries selected as i) pairs of unresolved sources with angular separation in the range 3'' - 16'', ii) common proper motion pairs with 5'' - 30'' angular separation, and make them publicly available. These samples are dominated by disk stars, and we use them to constrain the shape of the main-sequence photometric parallax relation M_r(r-i) and to study the properties of wide binary systems. We estimate M_r(r-i) by searching for a relation that minimizes the difference between distance moduli of primary and secondary components of wide binary candidates. We model M_r(r-i) by a fourth degree polynomial and determine the coefficients using Markov Chain Monte Carlo fitting, independently for each sample. Aided by the derived photometric parallax relation, we construct a series of high-quality catalogs of candidate main-sequence binary stars. Using these catalogs, we study the distribution of semi-major axes of wide binaries, a, in the 2,000 < a < 47,000 AU range. We find the observations to be well described by the Opik distribution, f(a)~1/a, for a<a_{break}, where a_{break} increases roughly linearly with the height Z above the Galactic plane (a_{break}~12,300 Z[kpc]^0.7 AU). The number of wide binary systems with 100 AU < a < a_{break}, as a fraction of the total number of stars, decreases from 0.9% at Z=0.5 kpc to 0.5% at Z=3 kpc. The probability for a star to be in a wide binary system is independent of its color. Given this color, the companions of red components seem to be drawn randomly from the stellar luminosity function, while blue components have a larger blue-to-red companion ratio than expected from luminosity function.Comment: emulateApJ, 47 pages, 28 figures, accepted to Ap

Can Planets survive Stellar Evolution?

We study the survival of gas planets around stars with masses in the range 1-5 Msun, as these stars evolve off the Main Sequence. We show that planets with masses smaller than one Jupiter mass do not survive the Planetary Nebula phase if located initially at orbital distances smaller than (3-5) AU. Planets more massive than two Jupiter masses around low mass (1 Msun on the Main Sequence) stars survive the Planetary Nebula stage down to orbital distances of 3 AU. As the star evolves through the Planetary Nebula phase, an evaporation outflow will be established at the planet's surface. Evaporating planets may be detected using spectroscopic observations. Planets around white dwarfs with masses M_WD > 0.7 Msun are generally expected to be found at orbital radii r > 15 AU. If planets are found at smaller orbital radii around massive white dwarfs, they had to form as the result of the merger of two white dwarfs.Comment: 30 pages, 7 figures, 2 tables, accepted for publication in Ap

A Pan-STARRS 1 study of the relationship between wide binarity and planet occurrence in the Kepler field

The NASA Kepler mission has revolutionized time-domain astronomy and has massively expanded the number of known extrasolar planets. However, the effect of wide multiplicity on exoplanet occurrence has not been tested with this data set. We present a sample of 401 wide multiple systems containing at least one Kepler target star. Our method uses Pan- STARRS 1 and archival data to produce an accurate proper motion catalogue of the Kepler field. Combined with Pan-STARRS 1 SED fits and archival proper motions for bright stars, we use a newly developed probabilistic algorithm to identify likely wide binary pairs which are not chance associations. As byproducts of this we present stellar SED templates in the Pan-STARRS 1 photometric system and conversions from this system to Kepler magnitudes. We find that Kepler target stars in our binary sample with separations above 6 arcsec are no more or less likely to be identified as confirmed or candidate planet hosts than a weighted comparison sample of Kepler targets of similar brightness and spectral type. Therefore we find no evidence that binaries with projected separations greater than 3000 au affect the occurrence rate of planets with P <300 d around FGK stars.Peer reviewe

The Virgo cluster distance from 21 cm-line widths

The distance of the Virgo cluster is derived in the B band from the 21 cm-line width-absolute magnitude relation. The latter is calibrated using 18 spirals with Cepheid distances mainly from HST. The calibration is applied to a complete sample of non-peculiar spirals with i>45 deg and lying within the optical (n=49) or X-ray (n=35) contour of the cluster, resulting in a mean cluster distance of (m-M)_0=31.58+/-0.24 mag (external error) or 20.7+/-2.4 Mpc. The mean distance of subcluster A is 0.46+/-0.18 mag smaller than that of subcluster B, but the individual distances of the members of the two substructures show considerable overlap. The distance modulus is corrected by -0.07 mag for the fact that cluster members have lower H I-surface fluxes and are redder in (B-I) at a given line width than the (field) calibrators. Different sources of the B magnitudes and line widths have little effect on the resulting distance. Different precepts for the internal-absorption correction change the result by no more than +/-0.17 mag. The individual distances of the cluster members do not show any dependence on recession velocity, inclination, Hubble type or line width. The dependence on apparent magnitude reflects the considerable depth effect of the cluster. The adopted distance is in good agreement with independent distance determinations of the cluster. Combining the cluster distance with the corrected cluster velocity of 1142+/-61 km/s gives H_0=55+/-7 km/s/Mpc (external error). If the Virgo cluster distance is inserted into the tight Hubble diagram of clusters out to 11000 km/s using relative distances to the Virgo cluster one obtains a global value of H_0=57+/-7 km/s/Mpc.Comment: 37 pages, LaTeX using AAS aaspp4 style, 14 eps figures, 7 Tables; to be published in the Astrophysical Journal (Main Journal

Semiempirical calculation of van der Waals coefficients for alkali-metal and alkaline-earth-metal atoms

The van der Waals coefficients, C-6, C-8, and C-10 for the alkali-metal (Li, Na, K, and Rb) and alkaline-earth-metal (Be, Mg, Ca, and Sr) atoms are estimated by a combination of ab initio and semiempirical methods. Polarizabilities and atom-wall coefficients are given as a diagnostic check, and the lowest order nonadiabatic dispersion coefficient, D-8 and the three-body coefficient, C-9 are also presented. The dispersion coefficients are in agreement with the available relativistic many-body perturbation theory calculations. The contribution from the core was included by using constrained sum rules involving the core polarizability and Hartree-Fock expectation values to estimate the f-value distribution