OT tutorial SISS
The objective of this tutorial is that you understand the key observation parameters which you would need to define to propose for ALMA observations (spatial resolution, sensitivity, spectral setup), and play extensively with the parameters and options in the OT so that you feel comfortable enough to craft your own proposal for the next Call for Proposals. This worksheet is intended as a step-by-step guide on how to prepare a mock proposal for the last ALMA Call for Proposals, by using the ALMA proposal preparation and submission tool ('Observing Tool' or OT). As in a real proposal preparation, you will probably need to go back and forth between the different steps while you are setting up your project, refining the different observation parameters. Please feel free to skip any of the proposed steps which you consider not useful or irrelevant for your own training. Sentences in brackets describe things which you would do in the case of a real proposal, and which are not relevant for this tutorial.
Before starting the proposal, you should have handy the sources' characteristics (or at least estimates) which will be necessary to define the proposal. These include (but are not limited to):
- The coordinates of the source(s), their velocity towards the observer (in km/s or redshift)
- The size of the source(s) (in arcseconds "), if they are not point-sources
- Whether the sources' emits continuum emission in the mm-range, and, if it is possible, an estimation of their continuum emission based on your own models or previous observations (in Jy at a given frequency, or in brightness temperature).
- What molecular species which can observed by ALMA are present (or expected) in the sources. You can use the Splatalogue to determine which lines of interest are encompassed within the ALMA bands. Be careful to include the sources' redshift/velocity when you do your line search.
If you already have a preferred source (or a set of sources) in mind, please use those for this tutorial. Otherwise, consider that you are interested in mapping the mm-wave emission from G0.253+0.016, a galactic molecular cloud. This source has already been observed by at submm-wavelengths with the JCMT (Di Francesco et al., 2008), the MALT90 survey (Foster et al., 2011) and Herschel (Molinari et al., 2011). You can look up for the source information in the Longmore et al. 2012 paper. You can also go ahead and just make up something that seems sensible to you.
Now that you know a little more about your source(s), you should decide what are the scientific goals which you want to achieve, and which are the measurements which allow you to meet your scientific goals. For example, measure the continuum distribution with a spatial resolution of 1.5". Or obtain a 10 sigma detection of HCN in a given region of the source. Or both. The measurements must be achievable within the capabilities offered by ALMA. We will here assume that you are proposing for a Cycle 2 project, for which capabilities are listed here.
You should in particular estimate:
- The spatial resolution do you want to reach
- The signal to noise do you want to achieve (on the different line detections, on the continuum detection)
- The frequency range(s) which you want to observe.
- For continuum observations, the choice of frequency is usually driven by the optimal compromise between signal to noise and spatial resolution. You can play with the continuum reference frequency in the OT to determine which is the best option depending on your goal.
- For line observations, this choice is driven by the sky frequencies of the lines would be the most suited for your scientific goal (based on your own models, previous publications, line parameters from Splatalogue)
- The maximal spatial scale which you want to be able to retrieve
It is very likely that will go back and forth and modify your original goals while preparing the proposal, to satisfy constraints on ALMA observational setups, or optimize the signal to noise.
Starting your proposal in the OT
Now you can open the OT to prepare your proposal
- type ./ALMA-OT.sh in your shell in the directory where you have installed the OT. Or if you use the web-based OT, just click on the 'Webstart' button on this page: https://almascience.nrao.edu/proposing/observing-tool - select 'Create a new proposal' in the pop-up window. You will see a tree structure on the left panel of the OT display, which describes the structure of the proposal. - click on 'Proposal' in the tree strcuture - [on the main panel, write some high-level information on the proposal (Title, Abstract, Keywords). ] - [add yourself as a PI and collaborators as co-Is. You can only add people who are registered in the ALMA userbase. You can register at almascience.org ('Register' link at the top-right corner)] - [attach a pdf of your scientific justification]
D) Define the science goals
An ALMA proposal is composed on one or several scientific goals (SG). A scientific goal groups observations which can be obtained in 'one go'. In pratice this means that a SG can include only sources which are nearby in the sky (XX), with a single receiver and correlator setup (central rest frequencies, resolution and width of spectral windows). However, a single science goal can be defined for different arrays or configurations (for example, ACA and 12-m array, or extended 12-m and compact 12-m configurations). It is also possible to include sources with different velocities in a single SG, as long as the spectral setup can be observed within a single ALMA band. The set of rules which define what can and what cannot be gathered in a single SB can be found here XX. From a scientific goal is produced a scheduling block, which is the set of instructions given to the telescope to perform an observation.
- Create one (or several) scientific goals by clicking on the 'target' button on the task bar of the OT ('New phase 1 science goal') - Each SG is divided in 6 sections (General, Field, Spectral, Calibration, control, justification) - In the general section of each SG, give a distinctive name to the science goal - the next sections describe how you can completely set up a SG
E) Spectral Setup Panel
- In the tree structure on the left panel in the display, click on the 'Spectral Setup' section of a SG - you need to define if this is a line project (spectral line or spectral scan) or a continuum project - if it is a pure continuum project, you will probably want to maximize the observed bandwidth. Define the receiver band, and you'll be given a default suggested frequency and a correlator setup (4 2-GHz wide spectral windows). You can change the average sky frequency with the receiver band if preferred. The spectral setup is graphically represented over the sky spectrum in the 'Spectral' tab on the top of the panel. - In the case of a line project XXXXXXX
E) Control and Performance Parameters
F) Field Setup Panel
- In the tree structure on the left panel in the display, click on the 'Field Setup' section of a SG - A panel opens where you define the name, coordinates and velocity (in km/s or z) of one source, as well as some expected properties - If you want to add additional sources to the SG, click on 'Add Source' - You may need several pointings for one source if your source size extends beyond half of the primary beam of the telescope, or if it composed of several regions of interest which are more than half of the primary beam away from each other. Estimate if you need one or several pointings - Under target type, you can define if you want the observations to be perfomed as individual pointings. In that case, you will need to define the coordinates of each pointing in the 'Field Center Coordinates' section of the panel (in RA/Dec or offsets from the coordinates defined above). - Under target type, you can define if you want to setup a regular pattern of pointing so as to ideally cover a given area around the source center (Rectangular field). In that case, you will need to define the size of the area. - The OT will suggest a number of pointing with the 12-m array, and - if necessary- a number of pointings with the 7m array. - In the 'Spatial' tab (top of the panel), you can obtain a graphic view of the chosen pointing pattern. You will need to upload a fits file of the source or make an image query.
G) Wrap it up
If you used the G0.253+0.016 example, compare your setup with the ALMA observation of that source which were performed in Cycle 0: http://fr.arxiv.org/abs/1403.4734 (Higuchi et al., 2014)
G0.253+0.016 resolution 1.7" G0.253+0.016 resolution 1.7"
G0.253+0.016 (hereafter G0.25) is very massive (∼2×105 M⊙ , radius of 2.8 pc; Longmore et al. 2012) and dense (∼3×104 cm−3 ; Kauﬀmann et al. 2013), with low duow dust temperature of 23 K (Rodrıguez & Zapata 2013) and no obvious signs of cluster formation
http://fr.arxiv.org/abs/1403.4734 higuchi G0.253+0.016 2011.0.00217.S http://fr.arxiv.org/abs/1307.2590 peretto SDC335 2011.0.00474.S_2012-02-09 http://fr.arxiv.org/abs/1307.3680 indebetouw 2011.0.00471.S Doradus