Copyright © Michael Richmond.
This work is licensed under a Creative Commons License.
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 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.
14
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.
346 days
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
- be bright enough for us to measure precisely
- be visible from Rochester
- be visible at night around mid-March
- have a relatively short period (so we don't need to observe for many nights)
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.
58,200 rows
50 are shown by default
number 103 in the list is "CD And"
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.
The LST is 9:26:09, so stars with RA = 9:26 are on the meridian. Stars within 1 to 3 hours of RA value in both directions are "well-placed", so this is a reasonable range 7:00:00 < RA < 12:00:00 But other ranges in this neighborhood are fine, too.
HH:00:00 .. KK:00:00
So, in my case, I'd use 07:00:00 .. 12:00:00
In my case, the GCVS contains 969 stars with (20 < Dec < 50) and (7 < RA < 12)
Wait, though, there are still more constraints. Add the following to your query:
In practice, this means that the star should have a magnitude brighter than about 12. So, place into the "magMax" column the following condition:
Place a constraint into the "Period" column that asks for stars with periods less than 0.8 days.
in my case, 90 stars
name: MO Leo
RA: 10 08 43.71
Dec: +26 03 56.6
mag: 11.550
Period: 0.6396930000
Note: from this point forward, the answers shown are appropriate for my choice of target: MO Leo. Other targets are perfectly fine, too.
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.
see cross-hairs in the image above
Width = 36 arcminutes, Height = 33 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.
Okay, I did.
B = 12.538 V = 11.691
RA = 10 08 52.56, Dec = +26 13 23.9
B = 11.734 V = 11.200
Dist = 9.70 arcminutes = 582 arcseconds
Copyright © Michael Richmond.
This work is licensed under a Creative Commons License.
