Download PHYS 2410 General Astronomy Homework 5

PHYS 2410 General Astronomy Homework 5
Due 10/28 before the classes
!!請將答案用筆寫在一張A4 紙上交給助教!!
Calculation (12%)
1. Derive the Distance Modulus= mV –MV= -5 + 5 log10(d [pc]) from the definitions of the
apparent and absolute visual magnitude.
Ans: see http://en.wikipedia.org/wiki/Distance_modulus
Multiple Choice (單選題, 88%)
1.
High temperatures are required to get H nuclei to fuse because they ____________ one another
because of their _________________electric charges.
a.
attract, negative
b.
attract, positive
c.
repel, negative
*
d.
repel, positive
2.
Sunspots are known to be magnetic phenomena because
*
3.
*
4.
a.
Doppler shifts in spectral lines are observed.
b.
the Zeeman Effect is observed in sunspots.
c.
collisional broadening is observed in spectral lines.
d.
infrared observations indicate that the sunspots are cooler than their surroundings.
e.
observations during eclipses reveal a very extensive photosphere.
Sunspots are dark because
a.
regions of the photosphere are obscured by material in the chromosphere.
b.
shock waves move through the photosphere.
c.
the sun rotates differentially.
d.
the strong magnetic field inhibits the currents of hot gas rising from below.
e.
they radiate their energy into space faster than the rest of the photosphere.
The sunspot cycle affects
I. the latitude at which sunspots are visible at a given time.
II. the number of sunspots that are visible at a given time.
III. the rotation rate of the sun's equator at a given time.
IV. the magnetic polarity of the sunspots at a given time.
a.
I & II
b.
I & IV
c.
II & III
d.
I, II & III
*
e.
I, II, & IV
5.
The most recent sunspot maximum occurred in 2001. When is the next sunspot maximum
expected if the solar cycle continues?
*
6.
a.
1990
b.
2006
c.
2012
d.
2023
e.
The last cycle started a Maunder minimum, and the next maximum can not be predicted.
A ___________ is believed to occur when energy, stored in a twist in the solar magnetic field
above a sunspot, is suddenly released.
*
a.
solar flare
b.
supergranule
c.
spicule
d.
coronal hole
e.
none of the above
Use the following chart to answer the next two questions:
Star
mv
65 Tau
4.2
HR 4621
2.6
1.8
58 Ori
-6.0
-1.5
d (pc)
a.
65 Tau
b.
HR 4621
(sec of arc)
Type
0.025
A7 IV
B2 IV
20
A7 V
0.005
2.5
Which star in the table above is the closest to Earth?
it is not given explicitly.
Spectral
-0.3
 Pic
HR 2491
7.
Mv
Parallax
M2 I
A1 V
Note that the distance may be calculated if
c.
 Pic
d.
58 Ori
*
e.
HR 2491
8.
Which star in the table above would appear the faintest in the night sky?
*
a.
65 Tau
b.
HR 4621
c.
 Pic
d.
58 Ori
e.
HR 2491
9.
*
Which star in the table above has the greatest luminosity?
a.
65 Tau
b.
HR 4621
c.
 Pic
d.
58 Ori
e.
HR 2491
10. Which star in the table above has the greatest surface temperature?
*
a.
65 Tau
b.
HR 4621
c.
 Pic
d.
58 Ori
e.
HR 2491
11. Which star in the table above has the greatest diameter?
*
a.
65 Tau
b.
HR 4621
c.
 Pic
d.
58 Ori
e.
HR 2491
12. Parallax would be easier to measure if
*
a.
Earth's orbit was larger.
b.
the stars were farther away.
c.
Earth moved slower along its orbit.
d.
all of these
e.
none of these
13. A star's absolute magnitude depends only on the star's
*
a.
distance and diameter.
b.
temperature and distance.
c.
distance.
d.
temperature and diameter.
e.
apparent magnitude.
14. We know that giant stars are larger in diameter than the sun because
*
a.
they are more luminous but have about the same temperature.
b.
they are less luminous but have about the same temperature.
c.
they are hotter but have about the same luminosity.
d.
they are cooler but have about the same luminosity.
e.
they have a larger absolute magnitude than the sun.
15. Sheat is an M2 II star.
I.
Based on this information, which of the following are true?
Sheat has a surface temperature less than the sun.
II. Sheat has a diameter that is greater than that of the sun.
III. Sheat is more luminous than the sun.
IV. Sheat is located near the upper left hand corner in the HR diagram.
*
a.
I & II
b.
II & IV
c.
II, III, & IV
d.
I, II, & III
e.
I, II, III, & IV
Use the following HR diagram to answer the next three questions:
10
+6
Alnilam
10
10
+4
Antares
Arcturus
+2
Luminosity
1
HR 5337
10 -2
Sirius B
10 -4
O
B
A
F
G
K
M
Spectral Type
16. Which star in the diagram above is most like the sun?
*
a.
Alnilam
b.
Antares
c.
Arcturus
d.
HR 5337
e.
Sirius B
17. Which star in the diagram above has the greatest surface temperature?
*
a.
Alnilam
b.
Antares
c.
Arcturus
d.
HR 5337
e.
Sirius B
18. Which of the stars in the diagram above has the brightest absolute visual magnitude?
*
a.
Alnilam
b.
Antares
c.
Arcturus
d.
HR 5337
e.
Sirius B
19. A pair of stars orbit around one another in an elliptical orbit with a semimajor axis, "a", of 1 AU
with an orbital period, "P" of 1 year.
*
a.
m1+m2=a³/P²=1 solar mass
What is the mass of the pair of stars?
b.
m1+m2=a³/P²=2 solar mass
c.
m1+m2=a³/P²=4 solar mass
d.
m1+m2=a³/P²=8 solar mass
e.
m1+m2=a³/P²=16 solar mass
20. Binary (double) stars can be detected by
*
a.
being seen as two separate stars with a telescope.
b.
one star traveling a wiggly proper motion path across the sky.
c.
one star dimming abruptly as another passes in front of it.
d.
pairs of absorption lines seen in the spectrum of what appears to be one star.
e.
all of the above
21. In the H-R diagram, 90 percent of all stars are
*
a.
in the giant region.
b.
in the supergiant region.
c.
among the B stars.
d.
among the G stars.
e.
on the main sequence.
22. We can determine the surface temperature of a star from
*
a.
studying its continuous spectrum.
b.
studying its line absorption spectrum.
c.
me
a
s
u
r
i
ngt
h
es
t
a
r
’
sl
umi
n
os
i
t
y
.
d.
Both a and c
e.
All of a, b, and c