ALMA time domain capabilities: current status, outlook

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Peter Williams

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Oct 17, 2016, 2:25:30 PM10/17/16
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Dear colleagues,

This email presents a somewhat lengthy overview of my current understanding of the "lay of the land" regarding ALMA's time-domain (TD) capabilities. This understanding could certainly contain gaps and/or errors! Please chime in if you have any comments or corrections.

What's currently possible. It has been emphasized to me that ALMA has already performed various kinds of TD observations. For instance, there was recently a long stare at the Galactic Center, performed simultaneously with space-based telescopes. So it is possible to make "TD-style" observations happen — but my understanding is that such observations have usually (always?) been proposed through the DDT process, which seems to have quite a high bar in ALMA.

In other words, it's not that TD observations are literally impossible with ALMA — it's that they're not explicitly supported in the Calls for Proposals (CFPs) and/or the ALMA Observing Tool. It certainly sounds as if there are technical improvements that would make certain kinds of TD observations easier, but the limiting factor seems to be more about getting TD features to be officially recognized capabilities, rather than actual development of observatory infrastructure.

The Cycle 5 Call for Proposals. To my mind, improvement in ALMA's TD support is therefore largely about the process that develops and publishes the CFPs. My understanding is that the process of preparing the formal CFP for Cycle 5 (CFP 5) is underway, and that the set of capabilities to be offered for Cycle 5 is essentially fixed at this point.

A piece of good news: while ALMA's TD capabilities for Cycle 5 are probably going to remain largely unchanged, I'm told that the promised TOO turnaround time might decrease substantially from its current value of 15 days. No promises have been made, but that 15-day value comes from Cycle 0 when there were whole weeks dedicated to engineering time, which hasn't been the case for a while.

Other than that improvement, the expectation is that TD capabilities will remain about the same as in Cycle 4.

Influencing future capabilities/CFPs. So, how do we influence what capabilities are developed and the contents of future CFPs? The closest thing to a formal channel is the international ALMA Science Advisory Committee (ASAC), which is charged with providing scientific advice to the ALMA board:

They do fun things like write reports to the Board: here's the most recent one:
If you read the official charges given to the committee, ATSIG's interests are emphatically on-topic for the ASAC.

Based on my conversations, there's no more formal way to try to get TD science onto the ASAC's radar than to send them reports that persuade them that it's a priority of the ever-nebulous "community". ASAC then makes recommendations to the Board ... which may or may not actually do anything about those recommendations. As far as I can tell, the Board can do whatever it wants, and trying to influence it is a matter of high-level politics.

Timeline. As I understand it the annual timeline for the CFPs is:

April — planning for capabilities of new cycle
October — beginning preparation of cycle's CFP
March — release of CFP

And the ASAC meets twice a year, in October and April. In fact, the October ASAC meeting is happening today and tomorrow!

Therefore, to influence the capabilities offered in Cycle 6, we need to have made our case by April 2017. It was suggested to me that to maximize the impact of any documents we submit to the ASAC, it would be best to have something submitted by around mid-January.

Prior art: planetary science letter. Finally, I wanted to mention that members of the planetary science community have already begun following exactly the strategy implied above — it turns out that ALMA Solar System observations end up have many similar time-domain requirements as extragalactic-transient type studies. Here is a link to a "white letter" prepared by a team of interested parties:
And a list of signatories:
And a Google Form to add your own name to the list:
I am told that this letter has not yet been officially submitted to the ASAC.

As far as I can see, "the more the merrier" when it comes to pushing TD science to the ASAC, so I don't think these efforts are at all mutually exclusive. My hope is that ATSIG will provide a nice big umbrella that can fit planetary scientists, transients types, and anyone else whose science calls for enhanced time-domain capabilities at ALMA.

Cheers,

Peter

Steven Willner

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Oct 17, 2016, 4:27:40 PM10/17/16
to Peter Williams, ATSIG List
On 10/17/16 2:25 PM, Peter Williams wrote:
> For instance, there was recently a long stare at the Galactic Center,
> performed simultaneously with space-based telescopes.

In particular, we received two 6-hour tracks, the second one
interrupted. Exact times are at
https://www.cfa.harvard.edu/irac/gc/

We received the time via the DDT process. We would have preferred
longer tracks, but we wouldn't have needed the full suite of antennas.
(I haven't worked out how many we would have needed, but given the
source flux density, I'm guessing five or ten would have been enough.)
There is at present no subarray capability so far as I can tell, so we
got the whole array.

My personal interest is that we'd like two more tracks on Sgr A* in 2017
and possibly more in future years.
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