Answer:
1). [tex]v = - 2960526m/s[/tex]
2). Toward us
3). [tex]v = - 493421m/s[/tex]
4). Toward us
5). [tex]v = 1480263m/s[/tex]
6). Away from us
7). [tex]v = 3207236m/s[/tex]
8). Away from us
Explanation:
Spectral lines will be shifted to the blue part of the spectrum if the source of the observed light is moving toward the observer, or to the red part of the spectrum when it is moving away from the observer (that is known as the Doppler effect).
The wavelength at rest is 121.6 nm ([tex]\lambda_{0} = 121.6nm[/tex])
[tex]Redshift: \lambda_{measured} > \lambda_{0} [/tex]
[tex]Blueshift: \lambda_{measured} < \lambda_{0} [/tex]
Then, for this particular case it is gotten:
Star 1: [tex]\lambda_{measured} = 120.4nm[/tex]
Star 2: [tex]\lambda_{measured} = 121.4nm[/tex]
Star 3: [tex]\lambda_{measured} = 122.2nm[/tex]
Star 4: [tex]\lambda_{measured} = 122.9nm[/tex]
Star 1:
[tex]Blueshift: 120.4nm < 121.6nm [/tex]
Toward us
Star 2:
[tex]Blueshift: 121.4nm < 121.6nm [/tex]
Toward us
Star 3:
[tex]Redshift: 122.2nm > 121.6nm [/tex]
Away from us
Star 4:
[tex]Redshift: 122.9nm > 121.6nm [/tex]
Away from us
Due to that shift the velocity of the star can be determine by means of Doppler velocity.
[tex]v = c\frac{\Delta \lambda}{\lambda_{0}}[/tex] (1)
Where [tex]\Delta \lambda[/tex] is the wavelength shift, [tex]\lambda_{0}[/tex] is the wavelength at rest, v is the velocity of the source and c is the speed of light.
[tex]v = c(\frac{\lambda_{measured}- \lambda_{0}}{\lambda_{0}})[/tex] (2)
Case for star 1 [tex]\lambda_{measured} = 120.4 nm[/tex]:
[tex]v = (3x10^{8}m/s)(\frac{120.4nm-121.6nm}{121.6nm})[/tex]
[tex]v = - 2960526m/s[/tex]
Notice that the negative velocity means that is approaching to the observer.
Case for star 2 [tex]\lambda_{measured} = 121.4 nm[/tex]:
[tex]v = (3x10^{8}m/s)(\frac{121.4nm-121.6nm}{121.6nm})[/tex]
[tex]v = - 493421m/s[/tex]
Case for star 3 [tex]\lambda_{measured} = 122.2 nm[/tex]:
[tex]v = (3x10^{8}m/s)(\frac{122.2nm-121.6nm}{121.6nm})[/tex]
[tex]v = 1480263m/s[/tex]
Case for star 4 [tex]\lambda_{measured} = 122.9 nm[/tex]:
[tex]v = (3x10^{8}m/s)(\frac{122.9nm-121.6nm}{121.6nm})[/tex]
[tex]v = 3207236m/s[/tex]
