A FPGA-based fast converging digital adaptive filter for real time RFI mitigation on ground based radio telescopes

Radio Frequency Interference (RFI) is a growing concern in the radio astronomy community. Single-dish telescopes are particularly susceptible to RFI. Several methods have been developed to cope with RF-polluted environments, based on flagging, excision, and real-time blanking, among others. All these methods produce some degree of data loss or require assumptions to be made on the astronomical signal. We report the development of a real-time, digital adaptive filter implemented on a Field Programmable Gate Array (FPGA) capable of processing 4096 spectral channels in a 1 GHz of instantaneous bandwidth. The filter is able to cancel a broad range of interference signals and quickly adapt to changes on the RFI source, minimizing the data loss without any assumption on the astronomical or interfering signal properties. The speed of convergence (for a decrease to a 1%) was measured to be 208.1 mu s for a broadband noise-like RFI signal and 125.5 mu s for a multiple-carrier RFI signal recorded at the FAST radio telescope.Chilean National Commission for Scientific and Technological Research (CONICYT) CATA-Basal PFB06 ALMA 31150012 FONDECYT 11140428 Chinese Academy of Science South America Center for Astronomy (CASSACA) Chinese Academy of Sciences 114A11-KYSB2016000

ALMA band 1 optics (35-50 GHz): tolerance analysis, effect of cryostat infrared filters and cold beam measurements

The Atacama Large Millimeter/Sub-millimeter Array (ALMA) is currently the largest (sub-)mm wave telescope in the world and will be used for astronomical observations in all atmospheric windows from 35 to 950 GHz when completed. The ALMA band 1 (35-50 GHz) receiver will be used for the longest wavelength observations with ALMA. Because of the longer wavelength, the size of optics and waveguide components will be larger than for other ALMA bands. In addition, all components will be placed inside the ALMA cryostat in each antenna, which will impose severe mechanical constraints on the size and position of receiver optics components. Due to these constraints, the designs of the corrugated feed horn and lens optics are highly optimized to comply with the stringent ALMA optical requirements. In this paper, we perform several tolerance analyses to check the impact of fabrication errors in such an optimized design. Secondly, we analyze the effects of operating this optics inside the ALMA cryostat, in particular the effects of having the cryostat IR filters placed next to the band 1 feed horn aperture, with the consequent near-field effects. Finally, we report on beam measurements performed on the first three ALMA band 1 receivers inside test cryostats, which satisfy ALMA specifications. In these measurements, we can clearly observe the effects of fabrication tolerances and IR filter effects on prototype receiver performance

Figlia di un dio minore: storia di Giovanna Faè

Context. The bulk of the molecular gas in the central molecular zone (CMZ) of the Galactic center region shows warm kinetic temperatures, ranging from > 20 K in the coldest and densest regions (n similar to 10(4-5) cm(-3)) up to more than 100 K for densities of about n similar to 10(3) cm(-3). Recently, a more diffuse, hotter (n similar to 100 cm(-3), T similar to 250 K) gas component was discovered through absorption observations of H-3(+). This component may be widespread in the Galactic center, and low density gas detectable in absorption may be present even outside the CMZ along sightlines crossing the extended bulge of the Galaxy. Aims. We aim to observe and characterize diffuse and low density gas using observations of 3-mm molecular transitions seen in absorption. Methods. Using the Atacama Large (sub) Millimeter Array (ALMA) we observed the absorption against the quasar J1744-312, which is located toward the Galactic bulge region at (l; b) = (-2 degrees.13, -1 degrees.0), but outside the main molecular complexes. Results. ALMA observations in absorption against the J1744-312 quasar reveal a rich and complex chemistry in low density molecular and presumably diffuse clouds. We detected three velocity components at similar to 0, 153, and 192 km s(-1). The component at similar to 0 km s(-1) could represent gas in the Galactic disk while the velocity components at 153, and 192 km s(-1) likely originate from the Galactic bulge. We detected 12 molecules in the survey, but only 7 in the Galactic bulge gas.Deutsche Forschungsgemeinschaft (DFG) 956 CONICYT CATA-Basal project PFB-0

Revealing the CO X-factor in Dark Molecular Gas through Sensitive ALMA Absorption Observations

Carbon-bearing molecules, particularly CO, have been widely used as tracers of molecular gas in the interstellar medium (ISM). In this work, we aim to study the properties of molecules in diffuse, cold environments, where CO tends to be underabundant and/or subthermally excited. We performed one of the most sensitive (down to trms 0.002CO and t + rms 0.0008HCO) submillimeter molecular absorption line observations toward 13 continuum sources with the ALMA. CO absorption was detected in diffuse ISM down to Av < 0.32 mag and HCO+ was detected down to Av < 0.2 mag, where atomic gas and dark molecular gas start to dominate. Multiple transitions measured in absorption toward 3C454.3 allow for a direct determination of excitation temperatures Tex of 4.1 and 2.7 K, for CO and for HCO+, respectively, which are close to the cosmic microwave background and explain their being undercounted in emission surveys. A stronger linear correlation was found between NHCO+ and NH2 (Pearson correlation coefficient P 0.93) than that of NCO and NH2 (P 0.33), suggesting HCO+ is a better tracer of H2 than CO in diffuse gas. The derived CO-to-H2.conversion factor (the CO X-factor) of (14 +/- 3).x.1020 cm-2 (K km s-1)-1 is approximately six times larger than the average value found in the Milky Way.National Natural Science Foundation of China 11988101 11725313 11803051 U1631237 National Key R&D Program of China 2017YFA0402600 CAS Strategic Priority Research Program XDB23000000 CAS International Partnership Program 114A11KYSB20160008 CAS "Light of West China" Program Chinese Academy of Sciences Australian Research Council DE170101086 Comision Nacional de Investigacion Cientifica y Tecnologica (CONICYT) Basal AFB-17000