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تسجيل مستخدم جديدSidelobe analysis for the Atacama Cosmology Telescope: a novel method for importing models in GRASP
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Telescopes for observing the Cosmic Microwave Background (CMB) usually have shields and baffle structures in order to reduce the pickup from the ground. These structures may introduce unwanted sidelobes. We present a method to measure and model baffling structures of large aperture telescope optics to predict the sidelobe pattern.
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In recent years there have been significant improvements in the sensitivity and the angular resolution of the instruments dedicated to the observation of the Cosmic Microwave Background (CMB). ACTPol is the first polarization receiver for the Atacama
Cosmology Telescope (ACT) and is observing the CMB sky with arcmin resolution over about 2000 sq. deg. Its upgrade, Advanced ACTPol (AdvACT), will observe the CMB in five frequency bands and over a larger area of the sky. We describe the optimization and implementation of the ACTPol and AdvACT surveys. The selection of the observed fields is driven mainly by the science goals, that is, small angular scale CMB measurements, B-mode measurements and cross-correlation studies. For the ACTPol survey we have observed patches of the southern galactic sky with low galactic foreground emissions which were also chosen to maximize the overlap with several galaxy surveys to allow unique cross-correlation studies. A wider field in the northern galactic cap ensured significant additional overlap with the BOSS spectroscopic survey. The exact shapes and footprints of the fields were optimized to achieve uniform coverage and to obtain cross-linked maps by observing the fields with different scan directions. We have maximized the efficiency of the survey by implementing a close to 24 hour observing strategy, switching between daytime and nighttime observing plans and minimizing the telescope idle time. We describe the challenges represented by the survey optimization for the significantly wider area observed by AdvACT, which will observe roughly half of the low-foreground sky. The survey strategies described here may prove useful for planning future ground-based CMB surveys, such as the Simons Observatory and CMB Stage IV surveys.
The six-meter Atacama Cosmology Telescope (ACT) in Chile was built to measure the cosmic microwave background (CMB) at arcminute angular scales. We are building a new polarization sensitive receiver for ACT (ACTPol). ACTPol will characterize the grav
itational lensing of the CMB and aims to constrain the sum of the neutrino masses with ~0.05 eV precision, the running of the spectral index of inflation-induced fluctuations, and the primordial helium abundance to better than 1%. Our observing fields will overlap with the SDSS BOSS survey at optical wavelengths, enabling a variety of cross-correlation science, including studies of the growth of cosmic structure from Sunyaev-Zeldovich observations of clusters of galaxies as well as independent constraints on the sum of the neutrino masses. We describe the science objectives and the initial receiver design.
Multichroic polarization sensitive detectors enable increased sensitivity and spectral coverage for observations of the Cosmic Microwave Background (CMB). An array optimized for dual frequency detectors can provide 1.7 times gain in sensitivity compa
red to a single frequency array. We present the design and measurements of horn coupled multichroic polarimeters encompassing the 90 and 150 GHz frequency bands and discuss our plans to field an array of these detectors as part of the ACTPol project.
We use Atacama Cosmology Telescope (ACT) observations at 98 GHz (2015--2019), 150 GHz (2013--2019) and 229 GHz (2017--2019) to perform a blind shift-and-stack search for Planet 9. The search explores distances from 300 AU to 2000 AU and velocities up
to 6.3 arcmin per year, depending on the distance. For a 5 Earth-mass Planet 9 the detection limit varies from 325 AU to 625 AU, depending on the sky location. For a 10 Earth-mass planet the corresponding range is 425 AU to 775 AU. The search covers the whole 18,000 square degrees of the ACT survey, though a slightly deeper search is performed for the parts of the sky consistent with Planet 9s expected orbital inclination. No significant detections are found, which is used to place limits on the mm-wave flux density of Planet 9 over much of its orbit. Overall we eliminate roughly 17% and 9% of the parameter space for a 5 and 10 Earth-mass Planet 9 respectively. We also provide a list of the 10 strongest candidates from the search for possible follow-up. More generally, we exclude (at 95% confidence) the presence of an unknown Solar system object within our survey area brighter than 4--12 mJy (depending on position) at 150 GHz with current distance $300 text{ AU} < r < 600 text{ AU}$ and heliocentric angular velocity $1.5/text{yr} < v cdot frac{500 text{ AU}}{r} < 2.3text{yr}$, corresponding to low-to-moderate eccentricities. These limits worsen gradually beyond 600 AU, reaching 5--15 mJy by 1500 AU.
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