Questions

1. Look up this object using the SIMBAD reference database. There is a link on our web site, or go directly to http://simbad.u-strasbg.fr/Simbad Under Queries on the site use by identifier and enter exactly the name of the quasar as it appeared in the article HE0450-2958. Click Submit and it will return coordinates and other names the same object may be known by.
   1. What are the coordinates in Right Ascension (hours, minutes and seconds of time) and Declination (degrees, minutes and seconds of arc) for epoch 2000.0 (in the FK5 reference system)?
   2. What is the "V" apparent magnitude? (It's the only one given here.)
   3. What is the measured redshift $z$?
   4. When it was cataloged by IRAS (Infrared Astronomy Satellite), what was its name?
2. Use this $z$ to compute the distance $d$ using the Hubble Law. Use the apparent V magnitude and the distance to find the absolute magnitude $M$ of the quasar.
3. Your answer will probably differ from that given in the article (-25.8). In the caption to Fig. 1, the article discusses the absolute magnitude and mentions ``dust'' among the corrections that have to be applied. What do you think this means, and why is this important?
4. The data from HST that were used for this work will not be public until October, but earlier data are in the Hubble MAST Archive. There is a link to the archive on our web site and you may explore (and retrieve) data yourself, but for this object we have downloaded an image for you. It is in the file /home/data/bright_quasar/u2wk0901b.c0.fits. This is a 10 MB Flexible Image Transport System (FITS) file, the standard image storage format for astronomy. Use the systems in Room 207 and the program ds9 to view this file. The command line will be
   ds9 /home/data/bright_quasar/u2wk0901b.c0.fits
   You could also do this at home on a Windows computer if you install ds9. It is free software and a link to it is on our website, as is a link to this image file. A high speed internet connection to download the software and the image is advised if you were to try this. Separate instructions for use of ds9 will be provided.

   When you first see this image on the display it will show only two bright spots, the quasar+blob and the star. Check the orientation and compare this to Fig. 1. Put the cursor over the quasar, and over the star. Inspect the ``Value'', which is the digital signal from each one.

   1. Which one is brighter?
   2. What is the difference in their magnitudes?

5. Notice that the image is not oriented NSEW. Move the cursor so that the RA ($\alpha$) remains the same but only the Dec ($\delta$) changes. Note $(x,y)$ and $\delta$ intially, and after you move the cursor. Calculate how far in pixels you moved the cursor ( $\sqrt{x^2+y^2}$) and how far in seconds of arc. What is the image scale in seconds of arc per pixel?

6. What is the size in seconds of arc of the image of the star? Measure the full width at half maximum using the ``Analysis$\rightarrow$Horizontal Cut Graph'' tool. You should zoom in first to see this in great detail.

7. Change the gray scale on the display. You can do this in several ways, so you will have to explore to find what works best for you. For example, if you hold the right mouse button down the display will change as you move the mouse. You may also use the buttons under ``Scale'' on the lower menu bar, or the interactive option under ``Scale$\rightarrow$Scale Parameters ...'' on the upper bar.

   Adjust the display so that you can see the companion galaxy.

   1. What is the angular separation of the companion and the quasar?
   2. How far apart are they in parsecs?
   3. What is the diameter of the companion in parsecs?

8. Notice that the galaxy has several bright spots in it. These are probably clusters of young hot stars in regions of active star formation. Place the cursor on one of those knots (it may help to zoom in) and measure the value for the signal. Subtract the value for the signal from the fuzzy background. How many times brighter is the quasar than one of these knots?

9. Use Oslo and the Hubble Telescope model to find the Airy disk for a perfect on-axis image with Hubble. What is the FWHM of the theoretical Hubble Airy disk in seconds of arc? Compare that with what you measured on this image.