B.4 Examples

1.	Given a source with a flux of 0.9mJy at 1350Å, convert this flux to erg s-1cm-2Å-1. From section 3, Table B.1, we see that the conversion constant β is 3×10–13 and the wavelength is 1350Å = 0.135μm. Thus:

 

2.	Given a V magnitude of 15.6, and knowledge that V–K=2.5 in the UKIRT system, estimate the flux in Jy at K. Since V–K=2.5 we know that K=13.1. From Table B.2, the zero-point flux in the UKIRT system for K is 657Jy. Thus the 2.2μm flux is:

 

3.	Given a surface brightness of 21.1 magnitudes arcsec-2 at J, convert this into Jy arcsec-2. Taking the zero-point for the J band from Table B.2, we determine that the surface brightness is:

 

4.	Given a flux at 0.9μm of 2.3×10–7Jy, estimate the I magnitude. 2.3×10–7Jy is less than 2.3×10–1Jy by three powers of a hundred, or 15 magnitudes. From Table B.3 we see that 0.25Jy is equivalent to an I-band magnitude of 9.89. Thus 2.3×10–7 is roughly 15 magnitudes fainter than this, or of order: