ALMA - Introducing the status and capabilities of ALMA
Wouter Vlemmings (Nordic ALMA Regional Center/Chalmers University of Technology, Onsala Space Observatory, Sweden)
ALMA, the Atacama Large Millimeter/submillimeter Array, is soon entering its fifth year of operations. This transformational facility, located at 5 km altitude in the Atacama desert in Chile, has already produced groundbreaking results across many astonomical research areas. Soon Solar observations will also be possible. In this talk, I will present a basic overview of the ALMA project, the user interaction through the regional centers, and the ALMA capabilities that are offered and expected in the future.
Solar Observations in Cycle 4 of ALMA
Masumi Shimojo (National Astronomical Observatory of Japan ) & ALMA Solar Development Team
The Sun is one of scientific targets of the Atacama Large Millimeter/sub-millimeter Array (ALMA). However, solar observations had not been offered until Cycle 3, because of a lot of difficulties for observing the Sun with the radio interferometer for night astronomy. We have been developing observing schemes for the Sun since 2010, and the joint ALMA observatory started to offer solar observations from Cycle 4 at last. Since the special treatments are needed for solar observations, there are some limitations for observing the Sun in comparison with the observations of other celestial targets. We held the commissioning campaign in December 2015 for verifying the observing modes, and the images synthesized from the commissioning data show us new sights of solar physics. The data obtained with the ALMA will bring about great scientific achievements.
The Cold Heart of the Solar Chromosphere
Tom Ayres (Center for Astrophysics & Space Astronomy, University of Colorado at Boulder, USA)
There is no doubt that the solar chromosphere is a complicated place. It is pervaded by strong tangled interacting magnetic fields, threaded by thin plasma jets arcing into the corona, and constantly bombarded by shock waves from below. Less appreciated, the ostensibly hot chromosphere harbors pockets of surprisingly cool gas, source of the curious off-limb emissions of strong CO lines in the thermal IR. An early notion linked the cold gas to a “molecular cooling catastrophe” confined to quiescent areas of the low chromosphere, surrounding the more disturbed small-scale magnetic flux concentrations. Modern 3D time-dependent models have suggested, alternatively, that transient cool plumes could be a natural consequence of adiabatically expanding convective bubbles overshooting into the low chromosphere. Up to this point there has been no way to dynamically map the cold patches on the solar disk, and test the alternative ideas. This is about to change, however, thanks to ALMA: the sub-mm continuum becomes optically thick in the right altitude range, is a reliable thermometer, and the imaging resolution and cadence are terrific.
Stellar observations with ALMA
Sofia Ramstedt (Uppsala University, Sweden)
The Atacama Large Millimeter/submillimeter Array (ALMA) has, in its few years of operation at limited capabilities, already revolutionized our view on cool stars. For young and evolved stars, the early observations have mainly focused on circumstellar molecular gas and dust. With the capabilities improving, for example with long baselines offering extreme resolution capable of resolving the surfaces of nearby giant stars, and with polarization measurements, both in continuum and lines being offered in the latest cycle, the first attempts at exploring magnetic activity have recently been published. In this talk I will review stellar observations with ALMA by selecting some highlights, and with focus on observational techniques interesting also for solar observations when available.
Mapping the 'Radio Surface' of an Evolved Star with ALMA
Eamon OGorman (Dublin Institute for Advanced Studies, Ireland), Pierre Kervella (Observatoire de Paris; Universidad de Chile), Leen Decin (Leuven), Anita Richards (Manchester), Iain McDonald (Manchester), Andrea Chiavassa (Observatoire de la Côte d'Azur), Xavier Haubois (ESO), Guy Perrin (Observatoire de la Côte d'Azur), Graham Harper (Colorado), Miguel Montarges (IRAM), Keiichi Ohnaka (UCN Chile), Jan Martin Winters (IRAM), Arancha Castro-Carrizo (IRAM)
ALMA has the potential to spatially resolve a limited sample of stars at multiple frequencies. Such observations would allow the temperature structure to be probed at varies depths in the star's extended atmosphere. An even smaller sample of stars can not only be spatially resolved with ALMA, but can be mapped with good detail (i.e., a few beams across the 'radio surface'). Here we present our initial ALMA long baseline Band 7 mapping of the radio surface of one such star, Betelgeuse, a red supergiant with one of the largest angular diameters at ALMA frequencies.
Prospects for ALMA studies of the solar-stellar connection
Jeffrey L. Linsky (JILA/University of Colorado and NIST, Boulder, USA)
ALMA provides a splendid opportunity to observe a wide range of star types at millimeter wavelengths to investigate the solar-stellar connection. I will compare the sensitivities and wavelength coverages of ALMA and the JVLA to highlight the discovery space that ALMA has for stellar astronomy. At millimeter wavelengths, ALMA will be able to detect thermal and gyroresonance emission from nearby stellar chromospheres and transition regions. Comparison of millimeter fluxes from ALMA with centimeter fluxes from JVLA may be able to separate thermal from gyrosynchrotron emission from stellar coronae and thereby measure magnetic field strengths in stellar coronae. Measurements of stellar wind mass-loss rates are feasible with ALMA for giants but will be difficult for main sequence stars. The study of stellar flares should be an active area of research with ALMA.