EA-ARC ALMA ARCHIVE DATA USER GUIDEBOOK

Transcription

1 EA-ARC ALMA ARCHIVE DATA USER GUIDEBOOK Prepared by James O. Chibueze NAOJ Chile Observatory

2 Purpose of this handbook: This handbook is aimed at providing fundamental information on how and where to access ALMA archive processed and raw data for scientific research purposes. Who is this handbook designed for? All astronomy researchers or students with interest in ALMA, but having little or no time to read lengthy archive documentation. (One outstanding features of this document is that it is designed to help you locate the answers to your ALMA archive questions within a few seconds, with good illustrations) Beginners (novice) with little or no experience in archive science or ALMA data reduction with CASA (Common Astronomy Software Applications) used for ALMA data reduction (calibration and imaging). Refer to parts I, II and IV. Experts (astronomer with data reduction experience), who may want to engage in ALMA archive science or compare ALMA results with their own data (obtained with other telescopes) for better scientific discussions. Refer to parts I, III and IV. This handbook is composed of four (4) parts, as follows; Part I: Nature of ALMA data and where to access them** Part II: Japanese Virtual Observatory (JVO) science-ready ALMA images Part III: Re-processing ALMA data (especially for experts) Part IV: Acknowledgement ** NB: The size of ALMA archive data includes all the raw data can be large, those who are particularly interest in the.fits images only, may prefer to search the JVO.

3 Part I ALMA Data Archive Access ALMA is currently the world's best millimeter and sub-millimeter array, established through the collaboration between the European Southern Observatory (ESO), National Radio Astronomy Observatory (NRAO) and the National Astronomical Observatory of Japan (NAOJ). More details of the ALMA can be found on the URL below; ALMA archive data is made of the following; Raw data (in form of ALMA science data model [ASDM], and measurement set [MS]), which can be re-processed with CASA. Processed image files (in.fits format), science-ready. CASA data reduction script used for producing the processed image files. Note that the script and the resulting FITS are not optimized to the best quality image possible, but adopts standard procedures. For example, point-like sources are not self-calibrated. Proprietary period = 12 months after data delivery to PI Science verification (SV) data are available to all after release. Prior to the expiration of the proprietary, only the PI can access the data. Directors Discretion Time (DDT) data (proprietary period = 6 months) ALMA archive data download steps: 1. Click on 2. Search using the archive query (source name, coordinates..) or delivery list (data sets with future release data can only be accessed

4 by the PI due to proprietary protection). 3. Request the desired data-set 4. Download the data 5. Expand the downloaded file and use the science-ready image included in.fits format The steps are illustrated below: Step1 Step 2

5 Step 3

6 Part II Japanese Virtual Observatory (JVO) science-ready ALMA images JVO portal ( hosts a wide variety of astronomy archive data including ALMA data in a scienceready image formats. You can also download, e.g., calibrated image files taken by Subaru telescope. By clicking the JVO Portal on the top page, you will be navigated to a menu page to select data of interest, as can be seen below.

7 JVO currently hosts the.fits images of all the ALMA SV data and other already released PI data (see below). Newly released PI data will also be published accordingly. By selecting any of the object names, you will find the dataset (differentiated with IDs, and some description) of the selected object. Clicking on any of the IDs leads you to the page where you can download the fits data, as shown below. **Note** It is important to note that only the following files are extracted from the ALMA archive, modified and published in JVO - FITS file(s) for each project - README file for each project 1. The FITS file(s) accessible ALMA Archive data (as well as in JVO) may not be thoroughly optimized or legitimate for the specific research interest. It is designed to serve as a initial image with a certain level of quality. Depending on each researcher's need, it is strongly recommended to retrieve original tar file from ALMA Archive. The tar file contains the parameter scripts to generate original ALMA FITS file, and researchers can easily modify those parameters in order to refine the output FITS data image to suit their interest. These can be done with the supportive provisions of the Astronomy Data Center.

8 2. Astronomy Data Center (ADC) The ALMA Archive user are encouraged to utilize NAOJ Astronomy Data Center facility, where relevant ALMA data analysis software available for service. Instructions concerning ADC account registration and how to use the available software can be found in the URL below; In English page : No article on ADC! In Japanese page Also, please include acknowledgement when applicable Web QL (bottom right)

9 The ALMA Web QL is a web-based quick-look tool which allows you to take a closer look at the desired image file. It has the following functions: Zoom in and out function Log scale plot function Resolution adjustment function Frequency range definition for the spectra only Vissage Vissage, developed by Wataru Kawasaki of the NAOJ Chile Observatory, stands for VISualisation Software for Astronomical Gigantic data cubes. It is brand-new FITS browser for viewing FITS data on your LOCAL ENVIRONMENT. Its main aims include: to view FITS data cubes in a variety of expressions (cuts) to search for other data via JVO based on the data displayed

10 to view multiple images in a free layout To download and use of Vissage on your personal computer, refer to

11 Part III Re-processing ALMA data (especially for experts) For researchers who already have good knowledge of interferometric data calibration and imaging procedures, this part provides some ideas on how to get the best out of the ALMA archive. If you do not already know how to obtain ALMA archive data of interest, please refer to part I above. Install CASA, if you have not already done so. CASA can be obtained here; Knowledge of python (script code) is advantageous, but not compulsory. CASA guide for ALMA data calibration and imaging is provided here; As noted earlier in this document, the fits images included in the archive data is unoptimized, standard image. Modifying the calibration and imaging scripts, improving the data by flagging bad visibilities, you can obtain a better results (images). For a reference to CASA tasks, see You can also contact the East Asian ALMA Regional Center (EA-ARC) at NAOJ for help. This can be done through the help-desk You need an ALMA Science portal account to be able to contact the ARC through the help-desk. If you do not have an account yet, you can create one by registering here The functionalities of CASA varies slightly from version to

12 version. It is important to first confirm the version of CASA you need for the dataset you want to process. Cycle 0 data were largely reduced with CASA v3.4, while the latest version is released May 30, 2013 for cycle 1. When you startup CASA, the initial startup messages include the CASA version information. On the ADC workstations, the latest CASA version is usually the default, but CASA v3.4 can be accessed in the machines and directories as indicated below. This can be done by defining the PATHs below and commenting out with '#' the version that is not needed. For C shell (.chsrc) #set path = (/data/local/casa/casapy b/ $path) #set path = (/data/local/casa/casapy b/ $path) set path = (/data/local/casa/release/ $path) For Bash (.bashrc) #export PATH=$PATH:/data/local/casa/casapy b/ #export PATH=$PATH:/data/local/casa/casapy b/ export PATH=$PATH:/data/local/casa/release/

13 Part IV Acknowledgement There is no doubt that ALMA archive science can produce impressive results beyond the original PI-proposed scientific goals. Have you obtained a new result? If so, publishing it must be the next thing on your mind. We encourage you to do just that. But there is one important thing to include in your manuscript, and that is ALMA acknowledgement as described below. Publications making use of ALMA data must include the following statement in the acknowledgement: This paper makes use of the following ALMA data: ADS/JAO.ALMA# S. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada) and NSC and ASIAA (Taiwan), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. Please substitute the place-holder project code S with the code(s) of the data used. For images obtained from the JVO, please also include the following sentence on the title page as a footnote to the title or in the acknowledgment of the paper. [Part of] the data are retrieved from the JVO portal ( operated by the NAOJ. Astronomy Data Center can be acknowledged as follows, when applicable: "Data analysis were [in part] carried out on common use data analysis computer system at the Astronomy Data Center, ADC, of the National Astronomical Observatory of Japan." While this may not apply to researcher affiliated to Japanese institutes, publications from North American authors must include the standard NRAO acknowledgement: The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.