1407.7856
Dust formation in the presence of photons I: Evaporation rates for small dust grains
Kochanek
The temperature of newly forming dust is controlled by the radiation field. As dust forms around stars, stellar transients, quasars or SNe, the grains must grow through a regime where they are stochastically heated by individual photons. Since evaporation rates increase exponentially with temperature while cooling times decrease only as a power law, the evaporation rates for these small grains are dominated by the temperature spikes. Calculate effective evaporation temperatures for a broad range of input spectra that are encapsulated in a series of simple interpolation formulae for both graphic and silicate grains. These can be easily used to first determine if dust formation is possible and then to estimate the radius or time at which it commences for a broad range of radiation environments. With these additional physical effects, very small grains may form earlier than in standard models of AGB winds. Even for very high mass loss rates, the hottest stars that can form dust are G and F stars particularly in the case of silicate dusts. For hotter stars, the higher fluxes of UV photons prevent dust formation. Thus, episodic dust formation by OH/IR stars and LBVs is primarily driven by fluctuations in their apparent temperatures rather than changes in luminosity or mass loss rates.
1407.7860
Clustering-based redshift estimation: comparison to spectroscopic redshifts
Rahman, Ménard, Scranton, Schmidt, Morrison
Investigate the potential and accuracy of clustering-based redshift estimation using the method proposed by Menard+ (2013). This technique enables the inference of z distributions from measurements of the spatial clustering of arbitrary sources, using a set of reference objects for which redshifts are known. Apply it to a sample of spectroscopic galaxies from the SDSS and show that, after carefully controlling the sampling efficiency over the sky, can estimate z distributions with high accuracy. Probing the full color space of the SDSS galaxies, show recovery of the corresponding mean z with an accuracy ranging from dz=0.001 to 0.01. Indicate that this mapping can be used to infer the z PDF of a single galaxy. Show how the lack of information on the galaxy bias limits the accuracy of the inference and show comparisons between clustering redshifts and photometric redshifts for this dataset. This analysis demonstrates, using real data, that clustering-based redshift inference provides a powerful data-driven technique to explore the z distribution of arbitrary datasets, without any prior knowledge on the SED of the sources.
1407.7866
CLASH-VLT: insights on the mass substructures in the Frontier Fields Cluster MACS J0416.1-2403 through accurate strong lens modeling
Grillo, Suyu, Umetsu, Coe, Koekemoer, Zitrin, ... et al
Present a detailed mass reconstruction and a novel study on the substructure properties in the core of the CLASH and FF galaxy cluster MACS J0416. Show and employ the extensive spectroscopic data set, to confirm spectroscopically 10 SL systems and to select a sample of 175 plausible cluster members to a limiting stellar mass of log(M*/M_sun)~8.6. Reproduce the measured positions of 30 multiple images with a remarkable median offset of only 0.3" by means of a comprehensive SL model comprised of 2 cluster DM haloes, represented by cored elliptical pseudo-isothermal mass distributions, and the cluster member components. The latter have total M/L ratios increasing with F160W luminosities. The measurement of the total enclosed mass within the Einstein radius is accurate to ~5%, including systematic uncertainties. Emphasize that the use of multiple-image systems with spectroscopic redshifts and knowledge of cluster membership based on extensive spectroscopic information is key to constructing robust high-resolution mass maps. Also produce magnification maps over the central area that is covered with HST observations. Investigate the galaxy contribution, both in terms of total and stellar mass, to the total mass budget of the cluster. When compared with the outcomes of cosmo N-body sims, results point to a lack of massive sub haloes in the inner regions of simulated clusters with total masses similar to that of MACS J0416. Findings of the location and shape of the cluster DM halo density profiles and on the cluster substructures provide intriguing tests of the assumed collision less, cold nature of DM and of the role played by baryons in the process of structure formation.
Astrophysical conditions for planetary habitability
Guedel et al
With the discovery of hundreds of exoplanets and a potentially huge number of Earth-like planets waiting to be discovered, the conditions for their habitability have become a focal point in exoplanetary research. The classical picture of habitable zones primarily relies on the stellar flux and allowing liquid water to exist on the surface of an Earth-like planet with a suitable atmosphere. However, numerous further stellar and planetary properties constrain habitability. Apart from "geophysical" processes depending on the internal structure and composition of a planet, a complex array of astrophysical factors additionally determine habitability. Among these, variable stellar UV, EUV, and X-ray radiation, stellar and interplanetary magnetic fields, ionized winds, and energetic particles control the constitution of upper planetary atmospheres and their physical and chemical evolution. Short- and long-term stellar variability necessitates full time-dependent studies to understand planetary habitability at any point in time. Furthermore, dynamical effects in planetary systems and transport of water to Earth-like planets set fundamentally important constraints. Review these astrophysical conditions for habitability under the crucial aspects of the long-term evolution of stellar properties, the consequent extreme conditions in the early evolutionary phase of planetary systems, and the important interplay between properties of the host star and its planets.
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