Casos científicos

A brief study of the Pleiades open cluster

• Launch Aladin

• Open the server selector (File -> Load astronomical images --> Aladin image server

• Enter target 'pleiades', radius '30 arcmin' --> click "Submit"

• Select POSS I E image 1.7 x 1.7 degrees --> click "Submit"

• To make the image clearer, modify the pixel distribution: Click the "pixel" button

• Load the Hipparcos catalogue. In the "Server selector" window
  • Click "Surveys" and write "Hipparcos" in the Autor, free text window
  • Select I/239 and add /hip_main after I/239 in the Catalog window
  • Set radius to 100'
  • Click "Submit" in the Server Selector window. The catalogue points (41 sources) are overlaid on the pleiades J image in the main Aladin window.

• Launch TOPCAT

• In Aladin: Right click on the catalogue plane and select 'broadcast selected tables to TOPCAT'

• Switch to the TOPCAT window and select the Histogram plot from Graphics -> Histogram.
  • In the Histgram window change the x-axis coordinate field to parallaxes (plx).
  • Notice that the parallax for this cluster is around 8-9 mas, with some background stars and a few foreground ones.

• Add a new column to the catalogue
  • Select Views -> Column Info.
  • In the Table Columns window that opens, select Columns -> New Synthetic Column.
  • Correct the data for reddening using the relation (B-V)o = (B-V) - E(B-V) = (B-V) -0.04, for this cluster by inserting '(B-V)o into the 'Name' field. In the 'Expression' field choose the (B-V) column and add -0.04, i.e. type '$Number -0.04', where Number is the (B-V) column number. Input 'mag' into the 'Units' field and click 'OK'

• Check that the new column has been added by selecting 'Views -> Table Data', which will open a new window showing the table data

• In the main TOPCAT window select 'Graphics -> Plot', '(B-V)o' for the x-axis, 'Vmag' for the y axis and check the 'Flip' button for the y-axis. In the resulting plot the main sequence is clearly visible

• Match sources between Aladin and TOPCAT by selecting points in the top left corner of the TOPCAT plot by selecting 'Subsets -> Draw Subset Region'. Draw the region to be selected then go to 'Subsets -> Finish Drawing Region'. A 'New Subset' window appears. Type in the subset name ' ?TopLeft' and click 'Add Subset'. This subset appears in the plot as different coloured points. Broadcast this subset to Aladin by going back to the main TOPCAT window and changing the 'Row Subset' field to ' ?TopLeft'. Then select 'File -> Send table to Aladin. These stars appear in a third layer in Aladin. Note that they are mainly in the centre and most of them have parallaxes of 8 - 9 mas

• Repeat the above step and select points in the bottom right corner of the TOPCAT plot. Broadcast this subset to Aladin. The corresponding sources in the image are mainly at the edge of the field and from the parallaxes can be seen that they are mostly background sources.