ALMA Programme News

EU-ALMA Gears up for Band 2 Production

ALMA Band 2 (67 - 90 GHz) is the last of the original ALMA band definition yet be approved for construction.  It will deliver new science by probing nearby molecular tracers of high density star formation, searching for amino acids like glycene in protoplanetary discs, measuring the carbon monoxide contents in galaxies out to higher redshifts, more sensitive measurements of the SZ effect from galaxy clusters, more efficient spectral scans for redshift surveys, and much more.  Following a successful preliminary design review of the Band 2 prototype cartridge in November 2017, the European ALMA region — in partnership with institutions spanning all of ALMA’s regions — is now taking the initial steps in preparation for the production of this band.  Two projects, led by ESO, are now underway: optimization of the active components for the Band 2 receiver cartridges, and optimization of optical components for those cartridges.  The final cartridge design will likely extend beyond the original upper frequency specification for ALMA Band 2, and will anticipate the expansion of ALMA’s wideband capabilities to cover bandwidths exceeding 8 GHz in each of the sidebands.

Improvement of the ATM Atmospheric Model

ATM (Atmospheric Transmission at Mircowaves) is a library of routines for modelling transmission of cm/mm/sub-mm wavelength radiation through the Earth's atmosphere. ATM will be used in certain calibration procedures of ALMA. It is designed to simulate both the absorption/emission of radiation and the dispersion (i.e., the frequency dependent refractive index of the atmosphere). The ATM atmospheric model, included as part of the TelCal package inside the ALMA software was developed under an ESO contract by Juan R. Pardo of the Spanish National Research Council (CSIC) from 2005 to 2011. After period of absence Pardo rejoined CSIC and restarted his collaboration with the project. Besides bug-fixing and some improvements requested by the ALMA software team, the following issues are currently being addressed:

1. Minor components vertical distributions and line shapes,
2. Dry and wet atmospheric collision induced absorption,
3. Zeeman effect on isotopic substitutions of atmospheric O2.
4. Accessing ALMA Calibration data within the ASDM to build ALMA real-measured atmospheric spectra,
5. Studying the fractal nature of the atmospheric screen above ALMA
6. Cross-checking the WVR and O2 sounder data with the calibration data in astronomical bands.

Some of these issues aim only at making the atmospheric model for ALMA as reliable as possible. Other issues may have their own scientific interest and could lead to publications in journals specialized in radiative transfer, atmospheric and geophysical research.

Contributions from the ARC Nodes

KAFE: the Key-analysis Automated FITS-images Explorer
Jan Brand (Italian Node)

Sandra Burkutean at the Italian ARC-node developed KAFE — the Key-analysis Automated FITS-images Explorer. KAFE is a web-based FITS image postprocessing analysis tool designed to be applicable in the radio to sub-mm wavelength domain. KAFE was developed to complement selected FITS files with metadata based on a uniform image analysis approach as well as to provide advanced image diagnostic plots. It is ideally suited for data mining purposes and multiwavelength/multi-instrument data samples that require uniform data diagnostic criteria.

This work has recently been published in the Journal of Astronomical Telescopes, Instruments, and Systems (doi.org/10.1117/1.JATIS.4.2.028001), where Burkutean and collaborators present the code structure and interface, the keyword definitions, the products generated for selected users’ science cases, and application examples.

Band-to-band phase calibration: enabling long-baseline ALMA observations at high frequencies
Luke Maud (Allegro)

High frequency observations in the sub-mm regime (<0.85mu, >350GHz) pose a number of challenges for astronomers - even when considering the excellent conditions at the ALMA Array Operations Site (AOS) on the Chajnantor plateau and the outstanding instrumental accuracies and tolerances. The challenges arise in calibrating the data with standard ‘in-band’ phase referencing techniques; firstly because the quasars used as point-source calibrators become weaker with increasing
observing frequency, and secondly because the atmospheric fluctuations we wish to calibrate out are seen to be more rapid and of increasing amplitude as we move to higher frequencies and longer baselines. Critically, increased phase instabilities lead to poor calibration and ultimately image artefacts and defects. Unfortunately, because the high frequency observations need low precipitable-water-vapour (PWV) conditions for transmission, the water-vapour-radiometers (WVRs) do not help phase corrections much because there is little water-vapour to correct for.

At ALMA we are testing the technique of Band-to-Band (B2B) phase transfer. In the simplest sense, this is where we observe phase calibrators at a lower frequency compared to the chosen science target frequency. This means that the phase calibrators are much stronger, allowing us to use the short cycle times needed to track and correct for the rapid atmospheric variations. The B2B technique, although theoretically allowing us to observe at high frequencies using the long baselines, comes with a number of technical challenges. These include now ensuring that ALMA is stable in amplitude and phase, over hour long observations at two observing frequencies that are frequently reset, and also ensuring we can accurately transfer the phase solutions between any low frequency to any higher one. We have conducted a number of intensive tests towards the end of Cycle 4 and into Cycle 5, to directly compare standard ‘in-band’ phase referencing to B2B phase referencing, with promising results. Although for a limited number of frequency ranges, our tests have validated that we can calibrated data at Band 7 and 8 using calibrators at bands 3 and 4 respectively. In the figure we show the B2B image for the B4-B8 pair on the left and the normal `in-band’ phase referenced image at B8 to the right. These were observed in appropriate stability conditions for Band 8 (385-500GHz) when using a 40 sec cycle time, and therefore we can make a fair comparison of calibration. In terms of image coherence and structure the B2B image well matches the `in-band’ image, indicating that B2B phase calibration is successful. Note the B2B image has a lower signal-to-noise due to extra data flagging required caused by hardware fluctuations in the experimental B2B tests. We are now pushing the testing in Cycle with bug fixes to alleviate hardware problems. We will also cover more of the ALMA frequency bands and include new tests in Bands 9 and 10. B2B is proving to be a promising technique in enabling ALMA long baselines observations at the highest frequencies.

We are now pushing the testing in Cycle 6 with bug fixes to alleviate software problems and after problematic hardware was replaced or repaired. We will also cover more of the ALMA frequency bands and include new tests in Bands 9 and 10. B2B is proving to be a promising technique in enabling ALMA long baselines observations at the highest frequencies.

Report on the Proposal Tools Workshop
Andy Biggs (ESO ARC)

The ALMA Observing Tool (OT) has been used to submit proposals and prepare observing materials since Cycle 0 with great success. Cycle 6 saw the most submissions received to date during the Call for Proposals (>1800) and yet no major problems were encountered by the OT and its associated submission service. Despite this, the underlying technology which powers the OT is becoming increasingly outdated and the code harder to maintain. As such, a two-year ALMA Upgrade Study was recently launched with a view to examining options for a future version of the tool.

As part of the study, it was decided to host a workshop at ESO Garching that would bring together groups working on proposal submission systems at observatories around the world. As well as giving a valuable opportunity for developers to share knowledge and experience, it would also allow all participants to gain an overview of developments happening within the community. As it turned out, the timing of the workshop was excellent as a number of observatories are actively looking at significant upgrades to their proposal submission systems.

The observatories represented at the meeting were (in alphabetical order) ALMA, ASTRON, CTA, ESO, Gemini, GMRT, IRAM, NAOJ, NOAO, NRAO and SKA. Also in attendance were experts in federated login and "triple A" (Authentication, Authorisation and Accounting). The emphasis of the meeting was on discussion, with the agenda kept as flexible as possible in order to allow those topics to be discussed that most interested the attendees. Demonstrations of new tools were also given by ESO, Gemini and the GMRT, in addition to a first look at a prototype of potential new OT functionality.

One specific outcome of the workshop was the decision to form a working group to look into the possibility of using federated logins for proposal submission tools. Beyond this though, it is hoped that this workshop will act as a catalyst for continuing collaboration between observatories in the area of proposal submission. The presentations given by the participating observatories will be published on Zenodo.

Report on the 16th Synthesis Workshop
Fabrizia Guglielmetti (ESO ARC)

The 16th Synthesis Imaging Workshop (http://www.cvent.com/events/16th-synthesis-imaging-workshop/agenda-b36e4bc16b574d5d94229f9d885d0eff.aspx) was held during May 16th-23rd at New Mexico Tech (Socorro, NM). 

A sound introduction to Radio Interferometry given by Rick Perley (NRAO),  Lisa Young (NRAO) and Bryan Butler (NRAO) was followed by the hardware description, i.e. antennas, receivers, cross-correlators and array design. Polarization, Very long Baseline Interferometry and Low Frequency interferometry were also discussed both from the hardware and science perspectives.

The major part of the workshop concentrated on data analysis, giving details on calibration, imaging deconvolution, spectral line data analysis, wideband and wideimaging deconvolution, mosaicking, error-recognition. Several data analysis lectures were presented, including those by Crystal Brogan (NRAO), Urvashi Rao Venkata (NRAO) and Ylva Pihlstrom (UNM). These data analyis talks were followed by tutorials, in which self-calibration was widely applied.  

At the end of each day, all lectures were followed by discussions lasting from one to three hours. Very interesting scientific talks were provided, including "High z Universe, Magnified" (from Dan Marrone) and "II Zw 40: A Test Case for Studying Baryon Cycling in the Nearby Universe" (from Amanda Kepley). 

Upcoming ALMA or ALMA-related Meetings

• Announcement for the 10th IRAM Millimeter Interferometry School
  1 – 5 October, 2018, IRAM, Grenoble, France
  The 10th IRAM millimeter interferometry school will be held October  1st - 5th 2018 at the IRAM headquarters (Grenoble, France). It is  intended for students, post-docs and scientists who want to acquire a  good knowledge of interferometry and data reduction techniques at  millimeter wavelengths, with a special emphasis on the NOEMA  interferometer and its new capabilities.

• From First Stars to Life: Science with the OST
  4 - 7 September, 2018, Univ. of Oxford, UK
  The infrared is the key wavelength regime for understanding the formation and early evolution of galaxies, stars and planetary systems. These wavelengths probe the obscured Universe from Cosmic Dawn to proto-planetary disks tracing both the dust and the dominant atomic, ionic and molecular cooling lines. When studied together, dust continuum and lines allow us to trace the chemical enrichment of the gas in the Universe and the physical processes which determine the evolution from the primordial gas to habitable exoplanets. In particular, the infrared is host to a series of molecular bio-markers that can be used to characterize the atmospheres of exoplanets. Only in the IR can we follow the water trail in the Universe, from distant galaxies down to the solar system.

• The Interstellar Medium of Galaxies: Status and Future Perspectives
  5-9 November, Leiden, the Netherlands
  The 100th birthday of Henk van de Hulst presents an opportune moment to take stock of our understanding of the structure, composition, origin and evolution of the interstellar medium of galaxies over cosmic times and chart the future of research in this area. The interstellar medium plays a central role in the evolution of galaxies as the repository of stellar ashes and the birth sites of new stars. Over the last two decades, the Spitzer Space Telescope and the Herschel Space Observatory have opened up the infrared sky to surveys of the ISM. With ALMA on line, JWST on the horizon, and SKA turning into reality, the ISM of galaxies can be probed out to high redshifts. This can be expected to provide much new insight in the evolution of the ISM over the history of the Universe.

• TORUS 2018: The many face of AGN obscuration
  10-14 December 2018, Puerto Varas, Chile
  Continuing the long tradition of international TORUS workshops, we announce TORUS2018 in Puerto Varas, Chile, to investigate the many faces of AGN obscuration. Considering the new theoretical and observational work carried out across the electromagnetic spectrum, the scientific goal of the workshop is to critically assess and challenge our current "common knowledge" and "widely accepted" torus picture. What do we really know for sure? What do we only think we know? And what is it that we do not know?