Các câu hỏi thảo luận tại lớp học Thiên Văn, ĐHSP Hà Nội

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Các câu hỏi thảo luận tại lớp học Thiên Văn, ĐHSP Hà Nội

Bài viết chưa xemgửi bởi antrang » Chủ nhật Tháng 9 02, 2007 7:39 pm

Các câu hỏi thảo luận tại lớp học. Đây là các câu hỏi tương đối cụ thể và sâu, các bạn nào quan tâm đến astronomy thì cùng thảo luận.
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Re: Các câu hỏi thảo luận tại lớp học Thiên Văn, ĐHSP Hà Nội

Bài viết chưa xemgửi bởi antrang » Chủ nhật Tháng 9 02, 2007 7:43 pm

Câu 1:
Some questions to think about before the next lecture, and for discussion.

1. If m = 6 stars are 100 times fainter than m = 1 stars, and if the magnitude scale is logarithmic, then prove that *. Also show that*, where R = 100.4 = 2.512.

2. In the two-colour diagram, why do stars and black bodies occupy different loci, (that is, different places in the diagram)?

3. The angular diameter of the Sun is about 0.5 degrees, and the solar constant (flux of sunlight at the Earth) is 1.4 kW/m2. Calculate the effective temperature of the Sun. (The Stefan-Boltzmann constant is ? = 5.67 * 10–8 Wm–2K–4.)


Câu 2:


1. The ‘merit’, M, of a spectrograph (a measure of overall performance) is sometimes defined as resolving power R times the throughput T (throughput is the fraction of photons received at the telescope which are recorded by the detector). Thus
M = R x T. In practice high R always results in low T, high T results in low R.
(a) Explain why high R leads to low T and vice versa.
(b) What types of observations require high R?
(c) What types of observations require high T?

2. Spectrographs attached to very large telescopes often have low throughput, T, so they are quite inefficient (waste photons). Why?

3. What’s the advantage of having a telescope plus spectrograph in space, as with the Hubble Space Telescope?

Câu 3:

Some questions to think about before the next lecture, and for discussion.

1. The acceleration due to gravity in a stellar atmosphere, g = GM(r)/r2, is usually taken as a constant throughout the photosphere. How can this be justified theoretically?

2. Most stellar atmosphere models assume that no radiation is incident on top of the photosphere. For which stars might this not be valid?

3. Why do high luminosity stars have low pressures in their photospheres?

Câu 4
1. How can the relation between temperature and optical depth, T(?), be measured for the Sun? And how can we find this relationship for other stars?

2. What’s the difference between continuous opacity and line opacity?

3. Are most stars in thermodynamic equilibrium (TE), local thermodynamic equilibrium (LTE), or non-thermodynamic equilibrium (non-LTE)?
(Note: TE is the conditions inside a black body).

4. (a) Is this room in TE, LTE or non-LTE?
(b) If you go to a place in TE (that is, inside a black body) what would you see?


Câu 5
Some questions to think about before the next lecture, and for discussion.

1. Why can’t we see deep inside the Sun?

2. The Sun’s photosphere has many free electrons. But the most abundant elements in the Sun (H, He, C, N, O) are largely neutral in the photosphere. So where do the free electrons come from?

3. When we observe the spectrum of a star, do we measure flux F? or intensity I?? What do we measure when we observe the Sun?

Câu 6
1. A stellar spectrum shows that all the absorption lines are very broad (wide). What is the most likely cause? If only the strongest lines have extended wings, what would be the cause of that probably be?

2. What’s the difference between microturbulence and macroturbulence?

3. Protons and electrons are both charged and can broaden Balmer lines in early-type stars by Stark pressure broadening. But protons broaden lines in a different way than the electrons. Why is this?

Câu 7
1. Weak lines are the more sensitive to element abundances than intermediate or strong ones. Would you say, therefore, that weak lines are the best for element abundance measurements in stars?

2. Why are the Balmer hydrogen lines stronger as one goes from spectral type G0 to F0 and then to A0? But when one goes from A0 to B0 and then to O5 they get rapidly weaker again. Explain these facts.

3. Why is the Balmer jump stronger in F supergiants than in F dwarfs (of the same temperature)?

4. The elements in nature have very different abundances. Some like lithium, beryllium and boron have abundances tens of billions of times (10–10 to 10–11 x) less than H. Do you have any ideas about how could such big differences in abundance be explained?
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Ngày tham gia: Thứ 6 Tháng 3 11, 2005 6:27 am
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