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تسجيل مستخدم جديدPhoton mean free paths, scattering, and ever-increasing telescope resolution
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We revisit an old question: what are the effects of observing stratified atmospheres on scales below a photon mean free path? The mean free path of photons emerging from the solar photosphere and chromosphere is near 100 km. Using current 1m-class telescopes, the mean free path is on the order of the angular resolution. But the Daniel K. Inoue Solar Telescope will have a diffraction limit of 0.020 near the atmospheric cutoff at 310nm, corresponding to 14 km at the solar surface. Even a small amount of scattering in the source function leads to physical smearing due to this solar fog, with effects similar to a degradation of the telescope PSF. We discuss a unified picture that depends simply on the nature and amount of scattering in the source function. Scalings are derived from which the scattering in the solar atmosphere can be transcribed into an effective Strehl ratio, a quantity useful to observers. Observations in both permitted (e.g., Fe I 630.2 nm) and forbidden (Fe I 525.0 nm) lines will shed light on both instrumental performance as well as on small scale structures in the solar atmosphere.
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Electron cyclotron resonant scattering features (CRSFs) are observed as absorption-like lines in the spectra of X-ray pulsars. A significant fraction of the computing time for Monte Carlo simulations of these quantum mechanical features is spent on t
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The recent measurement of an ionising mean free path $lambda_{text{mfp}}<1$ pMpc at $z=6$ challenges our understanding of the small-scale structure of the intergalactic medium (IGM) at the end of reionisation. We introduce a new method to constrain m
fp at $z=6$ by using lower limits on the individual free paths of ionisation around quasars. Lyman-limit absorbers with a density sufficient to halt ionising photons produce strong absorption in the 6 lowest-energy Lyman transitions, in the absence of which a robust lower limit can be placed on the individual free path. Applying this method to a set of $26$ quasars at $5.5<z<6.5$, we find that $80%$ of bright quasars ($M_{1450}<-26.5$) require individual free paths larger than $2$ pMpc. We model the relation between opacity $kappa$ and photo-ionisation rate $Gamma$ via the parameter $xi$ such that $kappaproptoGamma^{-xi}$, and pose joint limits on mfp and $xi$. For the nominal value of $xi=2/3$, we constrain $lambda_{text{mfp}}>0.31 (0.18)$ pMpc at $2sigma (3sigma)$: a much tighter lower bound than obtained through traditional stacking methods. Our constraints get significantly stronger for lower values of $xi$. New constraints on mfp and $xi$ are crucial to our understanding of the reionisation-era IGM.
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