Cooking with Sloan: CASCA 2007
| Pat Hall (York), Jordan Raddick, Ani Thakar (JHU) | |
| Alex Szalay, Maria Nieto-Santisteban, Nolan Li, | |
| Wil O’Mullane, Adrian Pope, Tamas Budavari, George Fekete, | |
| Sam Carliles | |
| JHU | |
| Brian Yanny, Svetlana Lebedeva | |
| FermiLab | |
| Jim Gray | |
| Microsoft Research |
SDSS-I is now SDSS-II, with 3 subsurveys:
| Legacy | |||
| Continuation of SDSS-I (completion of 8500 sq.deg.) | |||
| Completeness is same as for SDSS-I | |||
| Flux limits are the same | |||
| Target all galaxies with r_petro < 17.77, plus LRGs, quasars, … | |||
| SEGUE | |||
| Sparse-sampled 3-d map of the Galaxy | |||
| Spectra of 240,000 stars in the disk and spheroid | |||
| Age, composition and phase space distribution | |||
| CAS component cataloged in SegueDRx DB | |||
| Supernova Survey | |||
| Repeated scans of SDSS Southern Stripe over 3 months/yr | |||
| Data not available in CAS yet, will be on DAS soon | |||
| Data Archive Server (DAS) | ||
| FITS files (raw data) | ||
| Images, spectra, corrected frames, atlas images, binned images, masks | ||
| Online form-based access | ||
| Rsync and wget file retrieval | ||
| BestDRx (DR5 now, DR6 later this summer) | ||
| Latest, greatest calibration of the data | ||
| Photometric and spectroscopic objects | ||
| The default and most accessed (by far) dataset | ||
| TargDRx | ||
| The calibration from which spectroscopic targets were chosen | ||
| RUNS | ||
| All the runs (processings) other than Best, Target | ||
| SegueDRx | ||
| New with DR6 (SDSS-II) | ||
| http://www.sdss.org | ||
| Click on `Data Products’ – has someone already done your work for you? | ||
| If not, click on ‘Data Access’ for links to both CAS and DAS: http://www.sdss.org/dr5/access/ | ||
| Or CAS SkyServer: http://cas.sdss.org/astro/ | ||
| Search Tools | ||
| Advanced Tools, including visual tools & CasJobs | ||
| Help and Tutorials | ||
| SkyServer | ||
| Web browser is all you need | ||
| Meant to support several levels of users: http://cas.sdss.org/astro/ | http://skyserver.sdss.org/ | ||
| Visual tools to browse image and catalog data | ||
| Command-line application programming interfaces: emacs, sqlcl …also see http://cas.sdss.org/astro/en/help/docs/api.asp | ||
| Strict limits on execution time and output size … always test-drive your query (‘quick’ or ‘top 100’)! | ||
| Major sections linked from main page | |
| http://cas.sdss.org/astro/ | |
Cooking with Sloan website tutorials
| http://cas.sdss.org/astro/en/help/cooking/ | |
| How do I get an image, spectrum, and other info for my favorite object in the SDSS area? http://cas.sdss.org/astro/en/help/cooking/general/getimage.asp | |
| Are the SDSS data for a given object reliable? | |
| Consult the object’s flags to find out. http://cas.sdss.org/astro/en/help/cooking/general/flags.asp |
Searching for data meeting certain criteria
| Search for data that meets certain criteria | ||
| Return matching data, and only matching data | ||
| Example: search for galaxies with spectra in Abell 168 |
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| RA = 18.84, Dec = 0.26, radius = 3 arcmin |
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| Limit to galaxies g < 18 | ||
| Return RA, Dec, magnitudes, redshift |
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Query with Imaging Constraints
| http://cas.sdss.org/astro/en/tools/search/IQS.asp | |
| Tools -> Imaging Query |
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| Constraints by position or imaging |
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| Get data as HTML or CSV |
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| For actual images, save as CSV & upload to DAS retrieval form |
| SQL – computer language for searching databases | ||
| Advantages | ||
| You get longer queries and more results returned | ||
| You can write more complex queries | ||
| You can use command-line tools | ||
| Data are stored in a database | |
| Similar data types are stored in tables: photoObj (photometry), specObj (spectroscopy), etc. | |
| A request to a database to return data is called a query | |
| Queries usually request data that meets certain constraints |
| Languages have grammar and vocabulary | ||
| Dutch grammar | ||
| In sub-clause, verb goes at the end | ||
| English: | ||
| I think that astronomy is fun. | ||
| Dutch: | ||
| Ik denk dat het sterrenkunde leuk is. | ||
| Select – choose which columns of data you want to see | |
| From – choose the table(s) from which you want to retrieve data | |
| Where – set constraints on the search |
| Go to Help -> Schema Browser | |
| http://cas.sdss.org/astro/en/help/browser/browser.asp | |
| Go to Help -> Sample SQL Queries | |
| Go to Search Tools -> SQL Search | |
| Copy, paste, modify |
| http://cas.sdss.org/dr5/en/tools/chart/list.asp | |
| Go to Advanced Tools -> Image List |
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| ‘Use query to fill form’ |
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| Query must have: select x, ra, dec |
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| from … | |
| [where …] |
| Go to Search Tools -> CasJobs | |
| Best method for long or complex queries |
| Register and log in |
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| Quick mode: 1 minute |
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| Submit: 24 hours |
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| Results stored in MyDB |
| MyDB database to save results of your queries | ||
| Define your own functions, procedures too | ||
| Share your tables with collaborators (groups) | ||
| History of | ||
| Output data as FITS/CSV/VOTable | ||
| Plot data in browser | ||
| Table Import (upload) for your own data | ||
| Groups to share your results with collaborators | ||
| Command-line access Java tool also downloadable | ||
| Shares SQL Intro, Schema Browser with SkyServer | ||
| Has its own FAQ page | ||
| Lists differences between CasJobs and SkyServer due to distributed query execution | ||
| Advanced CasJobs Queries page | ||
| Neighbor searches with fixed and variable search radii | ||
| Cursors | ||
| Compound queries | ||
| Do not submit a query unless you have some idea how long it will take! | ||
| It could tie up the server for hours (even days)! | ||
| Use “select count(*)” or “select top 10” instead | ||
| Or try “quick” first, to see if it can be done quickly | ||
| Do use predefined views for commonly-used objects and parameters | ||
| PhotoObj, PhotoPrimary for photometry | ||
| PhotoTag if you only need popular fields | ||
| SpecObj for spectra | ||
| Schema Browser |
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| FAQ | |
| Glossary – of SDSS terms |
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| Algorithms | |
| Helpdesk | |
| (use contact link, | |
| not direct e-mail) |
| Extensive education content in SkyServer | ||
| Use Projects link on the menu at the top | ||
| K-12 and college level student exercises and teacher resources | ||
| Go to public site – http://cas.sdss.org | ||
| Go to Projects | ||
| Great as labs for intro classes | ||
| When you want to browse images, or when you know a position… | ||
| ToolsŽVisual ToolsŽ | ||
| Find images and data: Navigate | ||
| Browse objects one at a time: Explore | ||
| Find objects on a frame, compare your own observations: Finding Chart | ||
| View multiple objects or thumbnail search results: Image List | ||
| When you don’t know specific objects… | ||
| ToolsŽSearchŽ | ||
| Find objects in a patch of sky: Radial or Rectangular | ||
| Simple search for imaging data: Imaging Query Form | ||
| Simple search for spectral data: Spectro Query form | ||
| More sophisticated searches: SQL | ||
| Long, complex queries: CasJobs | ||
What does SDSS know about my objects?
| When you have a list of objects, and you want to see what SDSS knows about them… | ||
| ToolsŽObject CrossidŽ | ||
| Imaging crossid: Upload | ||
| Spectro crossid: SpecList | ||
| When in doubt, consult website or publications: | |
| http://www.sdss.org/publications/#technical | |
| http://www.sdss.org/publications/#data%20release … especially EDR paper (Stoughton et al) | |
| The SDSS can function as a data pipeline, but not as a science pipeline. You will have to decide what magnitudes are best for your science, what flag values to use to accept or reject objects, etc. | |
| Try the queries on the next few pages, or at http://cas.sdss.org/astro/en/help/cooking/ | |