اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدA fast, wide-field and distortion-free telescope with curved detectors for surveys at ultra-low surface brightness
56
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
We present the design of an all-reflective, bi-folded Schmidt telescope aimed at surveys of extended astronomical objects with extremely-low surface brightness. The design leads to a high image quality without any diffracting spider, along with a large aperture and field of view, with a small central obstruction which barely alters the PSF. As an example, we present the design of a high-quality, 36 cm diameter, fast ( f /2.5) telescope working in the visible with a large field of view (1.6{deg}x 2.6{deg}). The telescope can operate with a curved detector (or with a flat detector with a field flattener) and a set of filters. The entrance mirror is anamorphic and replaces the classical Schmidt entrance corrector plate. We show that this anamorphic primary mirror can be manufactured through stress polishing, avoiding high spatial frequency errors, and tested with a simple interferometer scheme. This prototype is intended to serve as a fast-track scientific and technological pathfinder for the future space-based MESSIER mission.
قيم البحث
اقرأ أيضاً
In the present paper we consider quantitative estimation of the tolerances widening in optical systems with curved detectors. The gain in image quality allows to loosen the margins for manufacturing and assembling errors. On another hand, the require
ments for the detector shape and positioning become more tight. We demonstrate both of the effects on example of two optical designs. The first one is a rotationally-symmetrical lens with focal length of 25 mm, f-ratio of 3.5 and field of view equal to 72$^circ$, working in the visible domain. The second design is a three-mirror anastigmat telescope with focal length of 250 mm, f-ratio of 2.0 and field of view equal to $4^circ times 4^circ$. In both of the cases use of curved detectors allow to increase the image quality and substantially decrease the requirements for manufacturing precision
While Euclid is an ESA mission specifically designed to investigate the nature of Dark Energy and Dark Matter, the planned unprecedented combination of survey area ($sim15,000$ deg$^2$), spatial resolution, low sky-background, and depth also make Euc
lid an excellent space observatory for the study of the low surface brightness Universe. Scientific exploitation of the extended low surface brightness structures requires dedicated calibration procedures yet to be tested. We investigate the capabilities of Euclid to detect extended low surface brightness structure by identifying and quantifying sky background sources and stray-light contamination. We test the feasibility of generating sky flat-fields to reduce large-scale residual gradients in order to reveal the extended emission of galaxies observed in the Euclid Survey. We simulate a realistic set of Euclid/VIS observations, taking into account both instrumental and astronomical sources of contamination, including cosmic rays, stray-light, zodiacal light, ISM, and the CIB, while simulating the effects of the presence of background sources in the FOV. We demonstrate that a combination of calibration lamps, sky flats and self-calibration would enable recovery of emission at a limiting surface brightness magnitude of $mu=29.5^{+0.08}_{-0.27} $ mag arcsec$^{-2}$ ($3sigma$, $10times10$ arcsec$^2$) in the Wide Survey, reaching regions 2 magnitudes deeper in the Deep Surveys. Euclid/VIS has the potential to be an excellent low surface brightness observatory. Covering the gap between pixel-to-pixel calibration lamp flats and self-calibration observations for large scales, the application of sky flat-fielding will enhance the sensitivity of the VIS detector at scales of larger than 1 degree, up to the size of the FOV, enabling Euclid to detect extended surface brightness structures below $mu=31$ mag arcsec$^{-2}$ and beyond.
This paper presents an ultra-low noise L-band radio astronomical cryogenic receiver for FAST telescope. The development of key low noise microwave parts of Coupling-LNA and conical quad-ridge OMT and reasonable system integration achieve outstanding
performance of receiver.It covers the frequency range of 1.2 GHz to 1.8 GHz. Novel cryogenic Coupling-LNAs with low noise, large return loss, high dynamic range and the function of coupling calibration signals are developed for the proposed receiver.Amplification and coupling function circuits are integrated as a single Coupling-LNA with full noise temperature of 4 K at the physical temperature of 15 K. And its return loss is more than 18 dB, and output 1 dB compression power is +5 dBm. A cryogenic dewar is fabricated to provide 55 K and 15 K cryogenic environment for OMT and Coupling-LNAs, respectively. The receivers system noise temperature is below 9 K referred to feed aperture plane. Benefiting from optimal design and precise mechanical treatment, good scattering performance of OMT and equalized radiation patterns of horn are achieved with an antenna efficiency above 75%.
The presence of substructures in dark matter haloes is an unavoidable consequence of the cold dark matter paradigm. Indirect signals from these objects have been extensively searched for with cosmic rays and gamma-rays. At first sight, Cherenkov tele
scopes seem not very well suited for such searches, due to their small fields of view and the random nature of the possible dark matter substructure positions in the sky. However, with long enough exposure and an adequate observation strategy, the very good sensitivity of this experimental technique allows us to constrain particle dark matter models. We confront here the sensitivity map of the HESS experiment built out of their Galactic scan survey to the state-of-the-art cosmological N-body simulation Via Lactea II. We obtain competitive constraints on the annihilation cross section, at the level of 10^-24 -10^-23 cm^3s^-1. The results are extrapolated to the future Cherenkov Telescope Array, in the cases of a Galactic plane survey and of an even wider extragalactic survey. In the latter case, it is shown that the sensitivity of the Cherenkov Telescope Array will be sufficient to reach the most natural particle dark matter models.
The low surface brightness Universe holds clues to the first formation of galaxies. Specifically, the shape and morphology of local stellar haloes have encoded in them the early formation history of their parent galaxies. Early progenitor galaxies we
re absorbed by the dark halo and scattered their stars in a diffuse halo around the main galaxy. If the accretion event was relatively recent, it may show as a coherent stream of stars within the halo. in addition, the low-mass, low-surface brightness satellite galaxies, perhaps the ultradiffuse galaxies recently reported would help solve the Missing Dwarf Problem, the apparent over-prediction of $Lambda$CDM models of the number of satellite galaxies around a Milky Way Halo. However low surface brightness is not what most telescopes are optimized for, most are best for resolving point sources and not sensitivity for large-scale low-light. To be sensitive to the low surface brightness Universe, a telescope needs a simple, unobstructed light path (disfavoring mirrors), fast optics (low f/D), and relatively coarse sampling (big pixels). Exceptions are the superb Dragonfly and Huntsman telescopes which are purposely designed to be sensitive to low surface brighnesses. Similarly designed, if not with low surface brightness in mind is the successfully launched TESS satellite. We show in this Research Note that the envisaged total exposure times and optical setup are near-ideal for low surface brightness work in the local Universe. With combined TESS imaging, one can model the stellar halo surrounding a galaxy. Technical challenges include the image quality, zodiacal and Galactic cirrus background light, PSF characterization and subtraction. Once accounted for with a processing pipeline, one can model the stellar halo for all nearby galaxies and to search for substructure in these haloes.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
