Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.stsci.edu/hst/training/events/VO/handsOn1.pdf Дата изменения: Thu Mar 30 00:15:53 2006 Дата индексирования: Sun Dec 23 00:02:46 2007 Кодировка: Поисковые слова: http astrokuban.info astrokuban

NVO DEMONSTRATION
PART I: ACQUIRE DATA 1. Go to the NVO website at http://us-vo.org/index.cfm

2. Open the Data Scope window, approximately half way down the page, by entering M51.


NOTE: It should take approximately 5 minutes for Data Scope to check all possible sources of information (n=435).

The green bar at the top of the Data Scope page should make note of 362 sources found out of a possible 435. The progress for data sources containing information on M51 can be seen at the bottom of the page. NOTE: You can select and retrieve the needed data prior to Data Scope completing its search of all 435 sources. As well, if another individual at STScI has selected the data set in the past week, the search will be cached, reducing the retrieval time.


3. Click on SDSSDR3-I(0/8) [ I band SDSS image], and click "ok" in the confirmation box. A preview of the image can be viewed by clicking on the "?" for each entry. From this, you will see that image 2 is the best.

4. Click in the box next to image 2 to select the image, and then click on "Return to summary page".


5. Click on "Save locally as TAR file", and choose a directory to save the file in. 6. It will then be necessary to go to the directory where you saved the file to untar and unzip it. Untarring and unzipping the file will vary from one operating system to the next. In UNIX/LINUX it will be necessary to untar "datascope-4267.tar" (number will vary), change directories to "SDSSDR3-I", and then unzip the .fits file. In Windows, it will be necessary to use WinZip by double-clicking the file, "datascope_4267.tar", select the listed file "SDSSDR3-I.1.2.fits", answer "yes" in the caution window. This will open a new window allowing you to save the .fits file by using the "extract" button. Use My Documents to locate the file, and then rename it if you like (e.g., SDSSDR3_M51_feb15) (5.82 MB). PART II: PHOTOMETRY & DATA CROSS-MATCH 1. Go back to the NVO home page, http://us-vo.org/index.cfm, and select the link "Perform Source Extraction and Object Identification", approximately 2/3 of the way down the page. This will take you to the WESIX main page.


2. Under "Step 1: Specify the file...", click on the Browse button, locate the .fits file in your directory structure, and select it. NOTE: Do Not hit the first "here" near the top of the WESIX main page. This will take 20+ minutes to download and will not provide a useable image.

3. Under "Step 2: Select the catalog...", click on "TWOMASS". 4. Under "Step 3: Choose whether you want...", click in the box. 5. Under "Step 4: Submit your file...", click submit.


6. Under "Step 5: Select the output...", select "NUMBER".

NOTE: T For MAC seams as t However,

o make multiple selections, use ctrl-left click simultaneously to make n selections. users, use the "apple" button-left click to make your selections. For some reason, it hough WESIX will select all variables regardless of the ones that you specify. it is necessary to choose at least one for the software to run correctly.

7. Under "Step 6: Choose the columns...", select "objID", "j_m", and "h_m". NOTE: j_m looks more like i_m on screen.


8. Under "Step 7: SExtractor params", change the "Detection Threshold" and "Analysis Threshold" both, from 1.5 to 10.

9. Under "Step 8" Click "Go do it!". NOTE: A common error message encountered at this point suggests that output might be too large. It will sometimes help to use a higher S/N in the previous step.


10. Click on the link, "Here is the matched file" to view the cross-matched catalog. You can also view the SExtractor catalog at, "Here is the source catalog file", and the 2MASS catalog at, "Here are the sources from OpenSkyQuery.net in the region of your image.".

11. To view the cross-matched image data, you can either click "here" in the sentence, "To begin visualizing your data, click here...", or you could simply click the link to "Aladin" in the WESIX toolbar at the top of the page.


NOTE: Please be patient as it make take a few minutes for Aladin to display all cross-matched layers. 12. If you click on the "hist" button in the vertical toolbar just to the right of the display, you can move the center triangle to adjust the contrast of the image display. 13. You can use the "zoom" button to zoom in and to adjust the position of the object in the display. 14. Click on the colored labels, just above the zoom screen (bottom right), to turn various crossmatch image layers on and off.

PART III: PLOTTING & CLASSIFICATION 1. To view a plot of the cross-matched data, begin by going back to the previous screen (from Part II, Step 11).


2. You can either click "here" in the sentence, "To plot your data, click here...", or you could simply click the link to "Plotter" in the WESIX toolbar at the top of the page.

3. From the top two pull-down menus located to the right of the plot grid (both of which are initially set to RA), select "twomass_j_m" for the y-axis variable, and "twomass_h_m" for the x-axis variable, and then click on the "plot" button.


4. Try clicking on the "histogram" button.

5. Create a new column to plot by clicking on the "Functions" pull-down menu in the toolbar just above the plot grid, and select "Create New Columns".


6. By clicking on the individual cells in the "Column Id" column and clicking the buttons in the "Operator Calculator" menu, enter the following expression in the "Enter expression:" window: $11 - $7. 7. Enter a name for the new column, "Aper-Iso", and click "Add", and then "Close". 8. As before, use the pull-down menus to the right of the plot grid to plot "Aper-Iso" versus "mydata_mag_aper". 9. Confirm that the "mode" in the bottom right of the plot screen is set to "Select", and clickand-drag to select points on the plot.


10. Using the "Data in Table Format" icon near the bottom right corner of the screen, you can view the table of selected points.