The Atacama Large Millimeter/submillimeter Array (ALMA) radio telescope has commenced science observations of the Sun starting in late 2016 Since the Sun is much larger than the field of view of individual ALMA dishes, the ALMA interferometer is unable to measure the background level of solar emission when observing the solar disk The absolute temperature scale is a critical measurement for much of ALMA solar science, including the understanding of energy transfer through the solar atmosphere, the properties of prominences, and the study of shock heating in the chromosphere In order to provide an absolute temperature scale, ALMA solar observing will take advantage of the remarkable fast-scanning capabilities of the ALMA 12 m dishes to make single-dish maps of the full Sun This article reports on the results of an extensive commissioning effort to optimize the mapping procedure, and it describes the nature of the resulting data Amplitude calibration is discussed in detail: a path that uses the two loads in the ALMA calibration system as well as sky measurements is described and applied to commissioning data Inspection of a large number of single-dish datasets shows significant variation in the resulting temperatures, and based on the temperature distributions, we derive quiet-Sun values at disk center of 7300 K at $\lambda = 3~\mbox{mm}$
 and 5900 K at $\lambda = 13~\mbox{mm}$
  These values have statistical uncertainties of about 100 K, but systematic uncertainties in the temperature scale that may be significantly larger Example images are presented from two periods with very different levels of solar activity At a resolution of about $25''$
 , the 13 mm wavelength images show temperatures on the disk that vary over about a 2000 K range Active regions and plages are among the hotter features, while a large sunspot umbra shows up as a depression, and filament channels are relatively cool Prominences above the solar limb are a common feature of the single-dish images

/pdf/observing-the-sun-with-the-atacama-large-millimeter-2o9psef1sn.pdf

Observing the Sun with the Atacama Large Millimeter/submillimeter Array (ALMA): Fast-Scan Single-Dish Mapping

Extremely large telescopes will be constructed in the near future, and new radiotelescopes will operate at considerably higher radio frequencies; both features create significantly increased pointing accuracy requirements that have to be addressed by control system engineers. This paper presents control and pointing problems encountered during design, testing, and the operation of antennas, radiotelescopes, and optical telescopes. This collection of challenges informs of their current status, helps to evaluate their importance, and is a basis for discussion on the ways of improvement of antenna pointing accuracy

Control and Pointing Challenges of Large Antennas and Telescopes

Observations of the Sun at millimeter and submillimeter wavelengths offer a unique probe into the structure, dynamics, and heating of the chromosphere; the structure of sunspots; the formation and eruption of prominences and filaments; and energetic phenomena such as jets and flares High-resolution observations of the Sun at millimeter and submillimeter wavelengths are challenging due to the intense, extended, low-contrast, and dynamic nature of emission from the quiet Sun, and the extremely intense and variable nature of emissions associated with energetic phenomena The Atacama Large Millimeter/submillimeter Array (ALMA) was designed with solar observations in mind The requirements for solar observations are significantly different from observations of sidereal sources and special measures are necessary to successfully carry out this type of observations We describe the commissioning efforts that enable the use of two frequency bands, the 3-mm band (Band 3) and the 125-mm band (Band 6), for continuum interferometric-imaging observations of the Sun with ALMA Examples of high-resolution synthesized images obtained using the newly commissioned modes during the solar-commissioning campaign held in December 2015 are presented Although only 30 of the eventual 66 ALMA antennas were used for the campaign, the solar images synthesized from the ALMA commissioning data reveal new features of the solar atmosphere that demonstrate the potential power of ALMA solar observations The ongoing expansion of ALMA and solar-commissioning efforts will continue to enable new and unique solar observing capabilities

/pdf/observing-the-sun-with-the-atacama-large-millimeter-42qp38plxx.pdf

Observing the Sun with the Atacama Large Millimeter/submillimeter Array (ALMA): High-Resolution Interferometric Imaging

The sub-mm sky is a unique window for probing the architecture of the Universe and structures within it. From the discovery of dusty sub-mm galaxies, to the ringed nature of protostellar disks, our understanding of the formation, destruction, and evolution of objects in the Universe requires a comprehensive view of the sub-mm sky. The current generation single-dish sub-mm facilities have shown of the potential for discovery, while interferometers have presented a high resolution view into the finer details. However, our understanding of large-scale structure and our full use of these interferometers is now hampered by the limited sensitivity of our sub-mm view of the universe at larger scales. Thus, now is the time to start planning the next generation of sub-mm single dish facilities, to build on these revolutions in our understanding of the sub-mm sky. Here we present the case for the Atacama Large Aperture Submillimeter Telescope (AtLAST), a concept for a 50m class single dish telescope. We envision AtLAST as a facility operating as an international partnership with a suite of instruments to deliver the transformative science described in many Astro2020 science white papers. A 50m telescope with a high throughput and 1$^\circ$ FoV with a full complement of advanced instrumentation, including highly multiplexed high-resolution spectrometers, continuum cameras and Integral Field Units, AtLAST will have mapping speeds thousands of times greater than any current or planned facility. It will reach confusion limits below $L_*$ in the distant universe and resolve low-mass protostellar cores at the distance of the Galactic Center, providing synergies with upcoming facilities across the spectrum. Located on the Atacama plateau, to observe frequencies un-obtainable by other observatories, AtLAST will enable a fundamentally new understanding of the sub-mm universe at unprecedented depths.

/pdf/the-atacama-large-aperture-submillimeter-telescope-atlast-394dyukbe2.pdf

The Atacama Large Aperture Submillimeter Telescope (AtLAST)

Radio Astronomy and Radio Telescopes.- Radio Telescope Constructions in View of Thermal Aspects.- Telescope Enclosures.- The Variable Thermal Environment.- Calculation of Solar Illumination.- Temperature Measurements and FEM Thermal Deformation Calculations.- Heat Transfer.- Radiative Coupling towards Sky and Ground (External View Factor).- Measured Thermal Behaviour of Radio Telescopes.- Measured Thermal Behaviour of Enclosures.- Thermal Model Calculations.- Beam Formation and Beam Degradation.- Thermal Tolerances.- Optical Telescopes and Enclosures.- A Summary and Further Studies.

Thermal Design and Thermal Behaviour of Radio Telescopes and their Enclosures

In this contribution I briefly describe the ALMA project and its current status and timeline. ALMA has been designed and is being built to allow to achieve transformational science in the coming decades. The combination of ALMA, the fully mature VLT/VLTI and later the E-ELT will be a unique asset offered by ESO to the european astronomical community.

The Atacama Large Millimeter/Submillimeter Array

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The Atacama Large Millimeter/Submillimeter Array