Никола 2018, 4 септември — Задача 12. Clusters.

4 септември 2018г.

Условие

Using the moving cluster method, the Hyades cluster is known to be 45 pc away. This open cluster is important as a standard candle, because we can use it to determine the distances of other clusters. However, the interstellar medium absorbs light making a star appear fainter and redder, which is called the interstellar extinction $A_V$ and reddening $E_{(B-V)}$, both measured in stellar magnitudes. The true distance modulus can be computed using the relation

The empirical relation between $A_V$ and $E_{(B-V)}$ is

In Tables I and II, you are provided with photometric data of the stars of the two open clusters, Hyades and NGC 2682.

8.1. Make the colour-magnitude diagrams of the Hyades cluster and NGC 2682 using the provided scaled marked graph paper (A). In the diagrams, draw the main sequence line of each cluster.

8.2. Plot the colour-colour diagrams of the Hyades cluster and NGC 2682 using the provided scaled marked graph paper (B).

8.3. Assuming that the interstellar reddening of Hyades cluster is negligible, derive the interstellar reddening, $E_{(B-V)}$ of NGC 2682.

8.4. Determine the distance to NGC 2682.

8.5. Find the absolute magnitude and colour index (B-V) of the main sequence turn-off star in each cluster, approximately.

8.6. Which cluster is older? (Write in English «Hyades» or «NGC 2682».)

Table 1. Hyades data

Table 2. NGC 2682 data

Решение

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Оригинал в Архива: 4092018.pdf