Creative Commons License Copyright © Michael Richmond. This work is licensed under a Creative Commons License.

Using SIMBAD and Aladin

Today's lab exercise should be carried out in pairs, ideally, but it's okay to do it by yourself or in a group of three.

In order to gain credit for this exercise, you must create a PDF document which provides the answers to all the questions. Submit the PDF to the instructor via the "Assignments" tab in myCourses.


The goal of today's exercise is for you to become familiar with two tools which are heavily used by astronomers. Both are run by the Centre de Données astronomiques de Strasbourg (CDS for short), which provides them free of charge to scientists around the world.


SIMBAD -- basic info

SIMBAD has a wealth of information at its fingertips. If you are interested in acquiring the basic information about some celestial object, you can simply type its name into the "basic search" box:

Suppose we want to learn about the variable star V347 Aur. We type its name into the search box,

and then click on "SIMBAD search". The top of the resulting page has a bunch of basic information:

Further down on the page are references to additional measurements, and to papers which mention the object.

  1. How many papers have been published on V347 Aur between 2018 and 2024?

If you scroll down to the "External Archives" section of the page on V347 Aur, you will see a list of links to this star's entry in a number of catalogs. Click on the one labelled "V* V347 Aur", which points to a catalog of variable stars.

  1. What is the period of this star? (Hint: it is many days)


Querying catalogs with Vizier

But SIMBAD can do more than show you information about a single object. It holds thousands and thousands of catalogs, some with millions of objects, and will help you sift through this gigantic collection of information to find just the targets that you want. Let's look at how to exercise some of the catalog-search facilities within SIMBAD.

Goal: find a variable star which would be a good target for measurements in this class. In particular, it should

We will choose a catalog full of information about variable stars: the General Catalog of Variable Stars, or GCVS for short. The section of SIMBAD which holds catalogs is called "Vizier."

The top-level Vizier page asks for the name of a catalog(s) to search. We can use "GCVS" to get a list of all the relevant ones.

The top entry in the resulting list is the one we want:

For this single catalog, Vizier shows a long, long list of all the attributes, or "columns", of stars stored in the catalog. It goes on for several screens.

Now, if one just clicks on the "Submit" button at this point, Vizier will return a list of ALL the objects in the catalog. Try it.

  1. In the main catalog, called "B/gcvs/gcvs_cat", how many total items (or "rows") are there?
  2. However, by default, only a small number of all these items are returned immediately, to avoid overflowing the page. How many items are shown in the table which is returned?
  3. On the left-hand side of the window, under "Preferences," is a box labelled "max:". Changing the value and re-Submitting will yield a larger (or smaller) table. What is the name of star number 103 in this list?

But we aren't interested in ALL the stars; we want those which satisify the criteria listed above. For example, one criterion was be visible from Rochester. We can discard stars which are too far south to see at all, or too far north to see easily, by choosing this range of Declination values.



                 20 <  Dec  < 50

We can ask Vizier to show us all the stars which fall within this range of Declination values by placing constraints into the "DEJ2000" column, like so:

Submitting this query yields ... a lot of stars. But we're not done yet. We have other constraints that we need to take into account. We can keep adding constraints to narrow down the list of stars which satisfy all the conditions.

One of the conditions was that the star should be well-placed in the sky for observations in mid-March. Choose March 15, at 11 PM local time, as the desired time and date.

  1. Using Stellarium, what range of Right Ascension values contains stars which are "well-placed" at that time? Don't worry about the minutes or seconds -- just estimate the range of RA hours which is near the center of the sky at this time.
  2. Now add a constraint to the Vizier query in the "RAJ2000" column. You can type your range of RA values into the "RAJ2000" box with the following format, where "HH" is the smaller RA hour value, and "KK" is the larger RA value.
    
                          HH:00:00 .. KK:00:00
           
  3. How many stars satisfy both of these criteria?

Wait, though, there are still more constraints. Add the following to your query:

  1. How many stars in the GCVS satisfy all of these criteria?
  2. Pick any one of the stars to be your "target". Write down its name, RA, and Dec.


Making a finding chart with Aladin

The Aladin program is a great tool for making finding charts: maps of a small portion of the sky to help you to identify a particular star at night. Let's go through the process of making a chart for the star you chose as your "target" earlier.

Run the Aladin program on your computer. A big window should appear. In the menu items at upper left, choose "File -> Open Server Selector", and a smaller window should appear:

Choose the "SkyView" button at upper-left. Then fill in the boxes as follows:

Leave the other entries as-is, with their default values. Then click on "Submit". After a brief pause, the main Aladin window should show a picture of the sky centered on your target, something like this:

For some purposes, such as printing onto paper, it helps to reverse the color map, so that the stars appear as black on a white background.

  1. Use the menu item "Image -> Pixel contrast and map" to modify the image so that its colors are reversed. Save a screenshot of the window and insert it here into your report.
  2. Mark the location of your target on this screenshot.
  3. Use the "dist" item in the menu at the right-hand side of the screen (see picture below) to measure the width and height of your chart. What is the width, in arcminutes? What is the height, in arcminutes?

Now, making a chart, itself, can be very useful. But the real power of Aladin is that connects the image you've created with all the catalogs in SIMBAD and Vizier. In order to make these connections, use the menu at upper-left of the Aladin window. Select items "Collections -> Data Base -> SIMBAD Astronomical Database" as shown:

(It may be necessary to click on the "Load" button of a pop-up window)

When you have done so, the Aladin chart should show an overlay of colored icons. Each icon corresponds to an object in the SIMBAD database. Clicking on an icon should cause the bottom of the chart to display information about the object:

If you click on the name of this object in the lower-panel display,

your browser should create a new tab which shows the entry for that object in SIMBAD.

  1. Use "Collections -> Catalog -> Vizier -> II Photometric Data -> APASS" to load icons for all the stars in the APASS catalog, which is a very nice catalog of stellar magnitides.
  2. Select the icon over your star to look up the properties of your target in the APASS catalog. What are the B and V magnitudes of your target?
  3. Choose another star in the chart, one which is somewhat brighter than your target star. Mark this star on your screenshot as star "A".
  4. What is the RA and Dec of star "A"?
  5. What are the B and V magnitudes of star "A"?
  6. What is the distance (on the chart) between your target and star "A"? Express in arcminutes and also in arcseconds.


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Creative Commons License Copyright © Michael Richmond. This work is licensed under a Creative Commons License.