BRIEF How to Read the WDS Catalog Boyce Astro: http://www.boyce-astro.org 1
Overview: This lesson will show you how to access the WDS, how it is segmented, its format, and how to read the catalog so that you can better understand from the WDS Summary pages what the known history of a particular Double Star is. The WDS Catalog is meant as an overview. After completing this lesson, you will understand how read this overview and select candidate stars for your analysis. Once you have selected your Double Star systems, subsequent lessons will review the process for obtaining and understanding the complete history of that particular system. The first part of the lesson will outline how to read the catalog. Then, case studies will follow. Boyce Astro: http://www.boyce-astro.org 2
1. Open your preferred web browser. 2. Go to the following URL: http://www.usno.navy.mil/usno/astrometry/optical-ir-prod/wds/wds 3. You will see a page that looks similar to this: Boyce Astro: http://www.boyce-astro.org 3
4) The catalog is broken down into sections of the sky based on Right Ascension. An understanding of Celestial Coordinates can be found under the Celestial Coordinates lesson. An additional lesson outlines how to determine when various RA Hours are visible in the night sky for a given time of year. 5) Once you have an idea of the appropriate section of sky to review for your Double Star selection, click on that hour range. For this session we will use the 12-18 hour section 6) When you click on the 12-18, you will see data that appears like the following: Boyce Astro: http://www.boyce-astro.org 4
7) Here is how to read this data file: WDS Identifier: These numbers are based off of the Precise Coordinates (located on the far right of the image). Note the correlation for the first Double Star system 12000+5728. The Identifier is a series of 5 digits, followed by a + or sign and then 4 digits. The first 5 digits are related to the Right Ascension (RA Hour), the + or is tied to the Declination of the Double Star, and the last 4 digits are related to the degrees of Declination Boyce Astro: http://www.boyce-astro.org 5
8) Here is how to read this data file: Discovr: Each measurer of a Double Star is provided with a code. The individual whom first recorded the positons of the Double Star are listed as the Discovr. These codes are typically, but not always, 3 letters followed by 3 numbers. Boyce Astro: http://www.boyce-astro.org 6
8) Here is how to read this data file: Comp: Comp stands for Components. In each Double Star system there are the main, or Primary, star (A) and secondary stars indicated by other letters of the alphabet. The Primary star is determined as the brightest (lowest Magnitude number) of the Double Star system. The rest of the stars are indicated in descending order of brightness by B, C, D, E, and so on. NOTE: If an there isn t a designation in this column, then the Primary is the A and the Secondary is the B. Example: In a 3-star system, you would have an A, B, and a C star. When you look at WDS 12000+4731 below, you will see that there are two listings. The first line is data related to the A and B stars. The second line is the A and C stars. Notice how there isn t a third line for a B and C combination? You could be the first to measure a BC combination for that Double Star. IMPORTANT: Not every Double Star will have all measurements connecting all components of a Double Star system. Boyce Astro: http://www.boyce-astro.org 7
8) Here is how to read this data file: EPOCH: Epoch stands for date or time. This column provides the year of the First and Last measurement of a particular Double Star system. Example: In the Double Star 12000+5728, the year of first measurement was 1966 and the latest measurement was 2000. For Double Star 12000+1720, the First was 1992 and the Last was 1992. In such a case, you will often find that there has been only one measurement. Boyce Astro: http://www.boyce-astro.org 8
8) Here is how to read this data file: #: This is the total number of measurements taken of a particular Double Star. Example: For Double Star 12000+1720 there has been only 1 measurement. For Double Star 12000+0104, there have been 3 measurements between the years 1996 and 2000. Boyce Astro: http://www.boyce-astro.org 9
8) Here is how to read this data file: Theta: The angle of measurement from the A star to the next component of the Double Star system (B, C, etc.) As with Epoch, Theta is given for the First and Last (latest) measurement. This measurement is taken where North is at the bottom and rotates counter-clockwise. Example: WDS 12000+5728 had the first angle measured at 358 in 1966, and 0 degrees in 2000. Boyce Astro: http://www.boyce-astro.org 10
8) Here is how to read this data file: Rho: This is the distance between the stars measured in arcseconds. These can be as low as 0.1 to separations as high as 300+ between stars. Example: In WDS 12000+5728, the first separation was measured at 8.0 arcseconds, and the latest in 2000 was 7.5 arc-seconds. Boyce Astro: http://www.boyce-astro.org 11
8) Here is how to read this data file: Magnitudes: These are the apparent brightness of the stars for that particular Double Star. The lower the number, the brighter the star. IMPORTANT: These numbers are not always provided and even when they are, they may contain errors. Use these as general reference in your research. Example: WDS 12000+5728, the Primary star is magnitude 13.8 and the Secondary is 18.0. The Primary and Secondary star of WDS 12000+1720 are very close in brightness. In instances such as this, it may be difficult to determine which star is the Primary (A) and which is the Secondary, but don t let that dissuade you from choosing stars of similar magnitude. There are many interesting Doubles that have very similar brightnesses. Boyce Astro: http://www.boyce-astro.org 12
8) Here is how to read this data file: Spectral Type: This indicates the temperature of a Star. This column is not always reported in the WDS. Usage of this line is for more advanced papers and not typically used in introductory level Stellar papers. Boyce Astro: http://www.boyce-astro.org 13
8) Here is how to read this data file: Prop Mot: This outlines the Proper Motion of a star through the sky. These are listed in milliarcseconds and are not always specified in the WDS. This column is not typically used in introductory writing and is reserved for more advanced papers when the process, Double Stars, and proper motions are better understood. Boyce Astro: http://www.boyce-astro.org 14
8) Here is how to read this data file: DM Desig: Not used in most Double Star papers Boyce Astro: http://www.boyce-astro.org 15
8) Here is how to read this data file: Note: An N in this column indicates whether the files on the particular Double Star contain any notes from previous observations. When the presence of notes are indicated, they will be included in the historical data file received from the USNO when you begin your research. Notes will be reviewed in another lesson. Boyce Astro: http://www.boyce-astro.org 16
8) Here is how to read this data file: Precise Coordinate: These are the precise RA and Dec coordinates for the Primary star in the Double Star system. These coordinates will be used when scheduling your star for imaging and when requesting data from the USNO. Now, that you have achieved a basic understanding of the data fields in the WDS catalog, the next slides will randomly select some Double Star systems and walk you through a cursory analysis based on the data contained therein. The purpose of this section is to develop your skills in reading data, and understanding the rough story that is being told. Boyce Astro: http://www.boyce-astro.org 17
9) Case Studies WDS 12033+2902: Discovered by LDS1275 Has three reported components: A, B, C. Note how there are two lines: AB and AC. Also, note how there aren t any listings for AC? You could be the first. The first measurement of AB was in 1963 with the last in 2000. The AC was 1955 and 2013 respectively. Remember the numbering of the components? A is brightest, B is next, C is next and so on? Here the AC system was first observed with the B component not being measured until 1963. A total of 2 measurements are contained for the AB system and 9 for the AC system. Theta, the angular measurement from North for AB was 14 degrees at first measurement and 4 degrees at the last. The AC was 299 and 299 degrees in both. Here we see that there has been some reported movement in AB, but not in AC. I wonder what the movement between BC was? Rho, the separation between the stars was first reported at 3 arcseconds for the AB and last reported at 2.9 arcseconds. The AC was first measured at 34.7 and last at 34.5. The magnitudes of all these stars are very close. Each of these star systems have Notes. These will be included in your historical data file request. Boyce Astro: http://www.boyce-astro.org 18
9) Case Studies WDS 12046-6820: The Declination of this star is around -68 degrees. This indicates that observation from the Northern Hemisphere is very difficult as this system lies far to the south. There are 3 different measurements here by two different Discoverers: HDS1698 & SHT 44. Note how the first has two systems located and they contain uppercase and lowercase numbers? This indicates that the secondary stars, the lower case numbers, lie very close to the Primary. In this case, the Rho is reported at 0.7 arcseconds. Both of these component pairs contain very few measurements: 3, 1, and 1 respectively All measurements have been fairly recent, yet nothing new recorded since the year 2000. Double Star 12046-6820 SHT 44 AB has very different stellar magnitudes. The A star is reported at 5.67 while the B is very faint at 13.82. This would make CCD imaging of this star pair difficult. Not impossible, but difficult. Only the AB and AC pairs contain notes. The angular measurements are relatively unchanged. This is to be expected from a system with very few measurements. Boyce Astro: http://www.boyce-astro.org 19
9) Case Studies WDS 12056+6848: The Declination of this star is around +68 degrees. This indicates that observation from the Southern Hemisphere is very difficult as this system lies far to the North. There are 6 reported components to this system: A, B, C, D, E, F, and two close components to E (Ea, Eb) The years of first observation begin in 1831 with the close Ea, Eb stars discovered in 1953. The number of measurements between stellar pairs vary from 1 total to as high as 28 total. Most stars show very little angular movement with the AE pair showing the greatest movement from 179 to 182. The AC and AE pairs show the greatest amount of movement in Rho (separation in arcseconds). All systems contain some notes in their historical files. Boyce Astro: http://www.boyce-astro.org 20
9) Case Studies WDS 12532-6044: Since there aren t any designated Components, this is a simple AB system/ The first observation was in 1929 with the last reported observation in 1938. It has been 78 years since the last reported measurement. Do you want to be next? There are only 2 recorded measurements. There was 1 degree in angular movement and very little change in distance. There are no notes on the particular system in the historical file Boyce Astro: http://www.boyce-astro.org 21
9) Case Studies WDS 18024-2302: Take some time with this system. See if you can answer the following questions: How many total components are there? How many discoverers are there? Which pair contains the greatest number of measurements? Which pair showed the greatest change in Theta (angular movement)? Rho (distance separation)? How many pairs contain notes in the historical files? Boyce Astro: http://www.boyce-astro.org 22
9) Case Studies WDS 18031-5139: What is the story here? Look at the Epochs of measurement? All in 2004. Notice the number of observations? All with 1. How many components? Want to be the next to observe this one? Where do you stand a better chance of viewing this system: Northern or Southern Hemisphere? Boyce Astro: http://www.boyce-astro.org 23
9) Case Studies WDS 18055+0230: How many observations has this system had? Who is the discoverer? How much has Theta changed? How much as Rho changed? What was the year of first measurement? Can you figure out what star system this is? With 1698 observations, I am willing to bet that it is a famous one. Boyce Astro: http://www.boyce-astro.org 24
Questions? Boyce Astro: http://www.boyce-astro.org 25