Department of Physics University of Durham Level One

## 5. Measurement of the Proper Motion of Barnard's star: Part 1

Two archival photographic plates (taken in 1937 and 1960) of the sky area near Barnard's star have been scanned and are available on the PC (filenames b1937.fit and b1960.fit). These images cover a sky area of 15x15 arcminutes and the scale is 1.7 arcsecond per pixel.

 Archival 1937 image of Barnard's star region
 Archival 1960 image of Barnard's star region

These images have been calibrated onto the standard co-ordinate system, i.e. the translation between the x,y position on the image and RA, Dec has been determined. These images are in FITS format which is often used for astronomical data. The FITSview programme is used to display and inspect these images on the PC.

Start FITSview and load an image from the default folder. Test out the features of the programme. Note how the Zoom works, how the display levels of the image can be changed, how clicking the left mouse button on the image gives the indicated position in the panel and how the centroids of stars can be measured by clicking the right mouse button. One feature of FITSview is that the display is occasionally overwritten and an image must be Reloaded.

The position of Barnard's star on these two images can be measured as follows:

1. By studying the photographs on page 1254 of the article from Burnham's Handbook, identify Barnard's star.

2. Display the 1937 image, i.e. b1937.fit.

3. Identify Barnard's star on this image and record its RA and Dec.

4. Record the precise date of observation. This can be found from the Image info... item on the File menu of FITSview.

5. Repeat 2 to 4 for the 1960 image, i.e. b1960.fit.

6. Calculate the angular shift between the position of Barnard's star in the two images.

7. Derive the proper motion for Barnard's star in arcseconds per year for both the RA and Dec directions. (Your answer should be approximately -0.7 arcsecond per year in RA and 10.3 arcsecond per year in Dec.)

8. Estimate the uncertainty on your measured proper motion. Assume that the images have been perfectly calibrated, i.e. the only uncertainty is how well you can determine the centre of the star.