The Optical System and the Astronomical Potential of A-MKID, a New Camera Using Microwave Kinetic Inductance Detector Technology

Abstract

In the framework of sub-millimeter astronomy, the need to create more efficient cameras with more pixels, with larger FoV and with higher mapping speed is highly desirable. In order to satisfy this necessity a new camera based on Microwave Kinetic Inductance Detectors (MKID) technology has been developed for the APEX Telescope (located in one of the best sites on Earth for sub-millimeter observations). In order to increase even more the observing efficiency, the camera works at two frequencies simultaneously (LFA: 345 GHz and HFA: 850 GHz). Also, the high angular resolution of the HFA (∼ 8′′), provides more accurate size estimates and position of the sources.<br /> With this aim, a novel optical design with a complete diffraction limited field of view of >15 x 15 arcmin², in the two working frequencies, has been developed for the new camera. The system has been designed to optimize the MKIDs’ response, as well as to minimize the number of optical elements used in order to optimize its compactness.<br /> The first commissioning of the new camera, called A-MKID, was accomplished during December 2013. Some problems regarding cryogenics and read-out electronics were detected. Beam characterization studies revealed misalignments produced during the optics installation. This fact caused some aberration in several parts of the array.<br /> Furthermore, observations of an astronomical Galactic target, the nebula NGC3603, have been performed with the new camera, obtaining a map with a sensitivity per beam a factor ∼ 3 worse than that of the Large APEX Bolometer Camera (LABOCA). This low sensitivity was mainly due to read-out electronics issues and the misalignments produced. Nevertheless, no strange artifacts were detected in these observations and no fundamental obstacles were encountered.<br /> In order to demonstrate the high scientific potential of continuum observations at these wavelengths, a study of the dust component of the well known nebula M17 SW has been carried out. Although no data of the new camera could be included in this study (they will be included in further publications), interesting results have been achieved with the available data of this source in the sub-millimeter and infrared wavelength regime. At the same time, the study also reveals that observations of this kind of structures in the sub-millimeter range could be done in a more efficient way with a the larger A-MKID camera. In addition, the new camera will provide data at 850 GHz which is not currently available for this and other important sources.<br /> Spectral Energy Distributions (SEDs) were calculated along a strip of measurements using a specific aperture size. This allowed to cover the complete region in order to characterize the different gas phases from the H_II region to the molecular cloud, including the photon-dominated region (PDR) located in between.<br /> The SEDs were well modelled using a combined function of two gray-body laws, each of them representing a cold and a hot component.<br /> Temperatures between 50 and 120 K and column densities (N_H2) around 10²² cm^-2 were obtained for the cold component, while for the hot component a temperature range between 250 and 310 K, and column densities (N_H2) of roughly 1019 cm^-2 were estimated. Moreover, additional important parameters such as mass, optical depth and visual extinction were also derived from our SED fits.<br /> Our results are in agreement with the common PDR structure reported by Hollenbach & Tielens (1997), but they could also be interpreted in terms of a clumpy PDR model.