Table 1 summarises some information about four stars in the constellation Cassiopeia - AQA - A-Level Physics - Question 2 - 2020 - Paper 4

Figure 1 illustrates the intensity of light received at Earth from the stars Caph and Schedar against wavelength.

• Caph has a peak intensity at approximately 450 nm, indicating a hotter temperature which aligns with its white color.
• Schedar peaks at a longer wavelength (around 600 nm), which corresponds to a slightly cooler orange color.

Using Wien's Law, we can calculate the temperature as: $T = \frac{b}{\lambda_{max}}$

Where 'b' is Wien's displacement constant (approximately 2898 µm·K).

• For Caph: $T_{Caph} = \frac{2898}{0.450} \approx 6440 K$
• For Schedar: $T_{Schedar} = \frac{2898}{0.600} \approx 4828 K$

Caph is hotter than Schedar, confirming that the blue wavelengths correspond to higher temperatures.

The dimmest star in the list is Tsih, due to its higher apparent magnitude.

To calculate the absolute magnitude, we use the formula: $M = m - 5 \cdot (\log_{10}(d) - 1)$ Where:

• $M$ is the absolute magnitude,
• $m$ is the apparent magnitude (2.2 for Schedar),
• $d$ is the distance in parsecs (converting 228 ly to parsecs gives approximately 69.8 pc): $M_{Schedar} = 2.2 - 5 \cdot (\log_{10}(69.8) - 1) \approx -1.0$