U Cephei is an eclipsing binary system consisting of two stars that orbit their common centre of mass - AQA - A-Level Physics - Question 2 - 2022 - Paper 4
Question 2
U Cephei is an eclipsing binary system consisting of two stars that orbit their common centre of mass.
The primary star is class B; the secondary star is class G.
F... show full transcript
Worked Solution & Example Answer:U Cephei is an eclipsing binary system consisting of two stars that orbit their common centre of mass - AQA - A-Level Physics - Question 2 - 2022 - Paper 4
Step 1
Explain the shape of the graph in Figure 1.
96%
114 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
The minima in the graph are caused by one star passing in front of the other.
The deeper minima indicate that the cooler star passing in front reduces the apparent brightness more significantly than the hotter star.
Step 2
State why the average of the values in Table 1 is different from the laboratory value.
99%
104 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
The average is different from the laboratory value because the observed values indicate a Doppler effect, likely due to the orbital motion of the star, causing a shift in the absorption wavelength.
Step 3
Show that the orbital speed of the primary star is about 250 km s⁻¹.
96%
101 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
To find the orbital speed, we can use the formula:
v=td
Assuming the period is about 2.5 days, we convert it to seconds:
T=2.5×24×60×60=216000 seconds
Using the change in wavelength from Table 1:
\Delta \lambda_{observed} = 0.362 \times 10^{-9} m$$
Now, we apply:
$$v = \frac{\Delta \lambda}{\lambda} \times c \
v = \frac{0.362 \times 10^{-9}}{486.136 \times 10^{-9}} \times 3 \times 10^8 m/s$$
Calculating gives an approximate speed of 255 km/s, which rounds to about 250 km/s.
Step 4
Calculate the orbital radius of the primary star.
98%
120 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
Using the formula for orbital radius:
r=2πvT
Substituting the values:
r=2π250×103×216000
Calculating gives an orbital radius of approximately (roundvalue)m.
Step 5
Which absorption lines would be most prominent in the spectrum of the primary star? Tick (✓) one box.
97%
117 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
The most prominent absorption lines in the spectrum of the primary star would be from hydrogen and helium.
Step 6
Discuss how astronomers could confirm that the system consists of a white dwarf and a neutron star.
97%
121 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
Astronomers could confirm this by observing the spectral signatures that indicate the presence of a white dwarf's H and He absorption lines, coupled with potential neutron star signatures such as X-ray emissions or varying brightness levels that indicate a pulsar behavior. Spectroscopic analysis would play a key role in distinguishing these objects.
