Kelas V Bintang deret utama
nomor 56) Spectral Type Magnitude Apparent
Luminosity (solar
units) Temperature Color
Sirius A A1 V -1.44 26.1 Arcturus K2 III -0.05 190 Alpha Centauri A G2 V -0.01 1.77 Alpha Centauri B K0 V +1.35 0.55 Vega A0 V +0.03 61.9 Capella G8 III +0.08 180 Rigel B8 I +0.18 7.0 x 105 Betelgeuse M2 I +0.45 4.1 x 104 Altair A7 IV +0.76 11.8 Pollux K0 III +1.16 46.6 Barnard’s Star M4 V +9.54 3.6 x 10-3
60. Soal pengolahan data : Pendahuluan
Salah satu instrumen astronomi yang penting adalah spektroskop yang memecah cahaya bintang dari bintang ke dalam bentuk spektrum. Spektrum yang dihasilkan dapat digunakan untuk menurunkan berbagai muatan astrofisis yang ada.
Data
Data awal ditampilkan dalam Tabel 1 dan paralaks p serta magnitudo semu m dari 18 bintang ditampilkan pada Gambar 2.
Pertanyaan :
a. Fotokopi-lah Gambar 2 dan bandingkan spektrum 18 bintang yang tak dikenal tersebut dengan kumpulan spektrum pada Gambar 1 ! Perkirakanlah temperatur permukaan dari bintang-bintang yang tak dikenal tersebut !
b. Hitung magnitudo absolut M dari bintang-bintang tersebut dan hitung pula luminositas L jika diketahui magnitudo absolut Matahari M = +4,84 dan luminositas Matahari L sebesar 4 x 1033 erg/detik !
c. Hitung radius R bintang–bintang tak dikenal jika diketahui radius Matahari R = 7 x 1010 cm dan temperatur efektif Matahari T = 5800 K !
d. Mengapa spektrum-spektrum pada Gambar 1 berbeda satu sama lain padahal spektrum-spektrum bintang tersebut menunjukkan komposisi yang dapat dikatakan identik ?
e. Jelaskan efek bintang-bintang tak dikenal tersebut terhadap Bumi dan iklimnya apabila bintang-bintang itu menggantikan posisi matahari di pusat Tata Surya !
(Untuk latihan lanjutan bisa menggunakan software Contemporary Laboratory Experiences in Astronomy (CLEA) Exercise – Stellar Spectra untuk lebih mendalami keterampilan mengklasifikasikan spektrum bintang)
II. Pilihan Ganda
1. Compare Planck curves for stars of spectral types O, G, and M.
a. The Planck curves for O stars are higher at all wavelengths and peak farther to the blue than do Planck curves for G stars; the relation of Planck curves for G stars and M stars is similar to that of O and G stars.
b. The Planck curves for O stars are lower at all wavelengths and peak farther to the red than do Planck curves for G stars; the relation of Planck curves for G stars and M stars is similar to that of O and G stars.
c. The Planck curves for O stars are higher at all wavelengths and peak farther to the blue than do Planck curves for G stars; the Planck curves for G stars are lower at all wavelengths and peak farther to the red than do Planck curves for M stars.
d. The Planck curves for O stars are lower at all wavelengths and peak farther to the red than do Planck curves for G stars; the Planck curves for G stars are higher at all wavelengths and peak farther to the blue than do Planck curves for M stars.
e. None of these.
2. Adanya pergeseran merah mengindikasikan bahwa galaksi: a. Bergerak mendekati Bumi
b. Bergerak sangat cepat c. Bergerak melambat d. Bergerak menjauhi Bumi e. Bergerak ke segala arah
3. Bintang-bintang yang termasuk mempunyai temperatur permukaan tinggi (>10000 K) adalah …
a) bintang kelas spektrum O5 dan G2 b) bintang kelas spektrum K2 dan M8 c) bintang kelas spektrum O3 dan B5 d) bintang kelas spektrum O5 dan A5 e) semua kelas spektrum
4. Warna bintang menunjukkan ... a) diameter bintang
b) komposisi kimiawi bintang c) temperatur permukaan bintang d) jarak bintang
e) umur bintang
5. Astronomers know that iron atoms are present in the Sun because _____ .
a. astronomers have analyzed samples retrieved from the Sun in laboratories on the Earth
b. much of the Earth is iron so that, by inference, the Sun must also contain large amounts of iron
c. the Sun is more massive than the Earth and so must contain more massive elements like iron
d. dark lines whose wavelength match those of iron are observed in the Solar spectrum
e. the Sun has a faint reddish color suggestive of rust
6. If an observing is looking towards a blackbody source through a cloud of gas, what kind of spectrum will be observed ?
b. emission c. absorption
d. none of the above e. all of the above
7. If an observing is looks at the light emitted from a cloud of gas, what kind of spectrum will be observed ?
a. Continuous b. emission c. absorption
d. none of the above e. all of the above
8. Star A has a surface temperature of 3000K, while Star B has a surface temperature of 12,000K. Therefore the wavelength of the peak of the spectrum of Star A is:
a) Half the wavelength of the peak of the spectrum of Star B. b) Twice the wavelength of the peak of the spectrum of Star B. c) Four times the wavelength of the peak of the spectrum of Star B. d) One quarter the wavelength of the peak of the spectrum of Star B. e) Sixteen times the wavelength of the peak of the spectrum of Star B. 9. A Doppler shift is:
a) A change in the wavelength of the peak of the spectrum of an object, as the temperature of the object changes
b) A change in the wavelength of the light from an object, due to the relative motion of the object and the observer
c) A change in the energy of an electron, when it jumps to a higher energy level in an atom
d) The bending of a ray of light as it goes from one medium to another
e) The emission of a photon of light by an atom, when an electron in the atom jumps to a lower energy level
10. The Sun has a yellowish appearance, Betelgeuse has a reddish glow, and Vega has a blueish white glow. Therefore, the temperature order, from coldest to hottest, is:
a) Vega, the Sun, Betelgeuse b) Betelgeuse, Vega, the Sun c) The Sun, Vega, Betelgeuse d) Betelgeuse, the Sun, Vega e) Vega, Betelgeuse, the Sun.
11. The H-alpha line of hydrogen is observed in Star A at a wavelength of 6000 Angstroms. In the laboratory, the wavelength of the H-alpha line is 6563 Angstroms. This means that:
a) Star A is a blue star
b) Star A is moving towards us c) Star A is moving away from us d) Star A is very hot
e) Star A is very cold
12. Assume an atom has only three lines in its emission spectrum – one red, one green, and one blue. If you shine yellow light through a low-density cloud of
these atoms, what would you expect to happen to the emission spectrum seen from these atoms?
A) The red line would be less intense
B) The green and blue lines would be less intense C) The red line would be more intense
D) The green and blue lines would be more intense E) No change
13. If the rest wavelength of a certain line is 600 nm, but we observe it at 594 nm, then:
A) The source is approaching us at 60% of the speed of light. B) The source is receding from us at 60% of the speed of light. C) The source is receding from us at 1% of the speed of light. D) The source is approaching us at 1% of the speed of light. E) The source is getting 1% hotter as we watch.
14. A new star is discovered; it is bright and hot, and emits mostly ultraviolet light. If we observe it with blue and yellow filters (separately), what would we find? A) More blue intensity than yellow
B) More yellow intensity than blue C) Equal yellow and blue intensity
D) Blue and yellow intensities are both zero E) Not enough information given
15. Which of these stars would be the hottest?
A) A0 B) B0 C) G2 D) K9 E) Ml0 16. Proper motion …
a. The apparent shift in position of a foreground object relative to background objects due to a change of position of the observer
b. As viewed from the Earth, the apparent motion of a planet near opposition when it moves westward relative to the background stars
c. The conical motion of the Earth’s axis of rotation about the perpendicular to Earth’s orbital plane over the course of approximately 26,000 years
d. The rate in seconds of arc per year at which a star moves across the plane of the sky
17. The fact that strengths of absorption lines due to neutral, singly-ionized and doubly-ionized atoms vary from star to star is a consequence of …
a. different temperatures in the photospheres of stars
b. different chemical compositions in the photospheres of stars c. different luminosities for stars
d. all of the above
18. From the shape, width, and strength of absorption lines in spectra, astronomers can infer …
a. random thermal motions, existence of streams of gas, and rotation of the star b. the chemical composition of a star's photosphere
c. the variation in temperature and density down through the star's photosphere d. all of the above
19. If Star A is hotter than Star B, and Star A is emitting most of its light at a wavelength corresponding to yellow light, which of the following statements is true?
a. Star B will emit most of its light at a wavelength longer than yellow b. Star B will emit most of its light at a wavelength shorter than yellow c. Star B will emit most of its light at the same wavelength as Star A d. more information is required to answer this question
20. Spectral lines unique to each type of atom are caused by … a. each atom having a unique set of protons.
b. the unique sets of electron orbits.
c. the neutron-electron interaction being unique for each atom. d. each type of photon emitted by the atom being unique.
e. none of the above; spectral lines are not unique to each type of atom.
21. Consider a cloud of (cool) gas between a star and an observer to be moving away from a source of continuous radiation (and towards the observer). Suppose the atoms in the gas have two energy levels separated by an energy corresponding to 5000 Angstroms. The observer will see a spectrum with absorption at a wavelength …
a. less than 5000 Angstroms. b. equal to 5000 Angstroms. c. greater than 5000 Angstroms. d. no absorption will take place.
22. A star has an absorption spectrum showing many lines corresponding to silicon. Before it reaches an observer, the light from this star passes through a cool gas cloud containing a large amount of silicon. What will the observer detect?
a. an absorption spectrum with many silicon lines
b. an absorption and emission spectrum with lines corresponding to silicon c. an emission spectrum of many silicon lines
d. a continuous spectrum
23. If an electron moves from a lower energy level to the next higher energy level, then …
a. the atom has become excited. b. the atom has become ionized. c. the atom's light will be blue shifted. d. the atom's light will be red shifted.
24. When you see a spectrum with absorption lines in it, you can infer that: … A. the light passed through ionized atoms
B. electrons moved up in energy levels to absorb the light C. electrons moved down in energy levels to absorb the light D. all the atoms were in excited states
25. Spectra from neutral atoms compared with spectra from ionized atoms of the same element …
a) are the same
b) are slightly redshifted c) are slightly blueshifted
d) have different sets of spectral lines
e) have the same sets of spectral lines but different widths for those lines
26. Studying the spectrum of a star can tell us a lot. All of the following statements are true except one. Which one?
a) the peak of the star’s thermal emission tells us its temperature: hotter stars peak at shorter (bluer) wavelengths
b) the total amount of light in the spectrum tells us the star’s radius
c) we can identify chemical elements present in the star by recognizing patterns of spectral lines that correspond to particular chemicals
d) we can look at Doppler shifts of spectral lines to determine the star’s speed toward or away from us
e) we can determine the temperature of the star’s photosphere
27. We view a hot thermal source through a cloud of gas having a variety of chemical elements. Which of the following would we predict we would see?
A. An absorption spectrum with lines characteristic of the elements in the cloud B. An emission spectrum with lines characteristic of the elements in the cloud C. A continuous spectrum with no lines
D. Only hydrogen lines because hydrogen is the most common element in the Universe
E. Not enough information is given
28. A star having a surface temperature of around 4000 Kelvin has a spectrum that has more absorption lines than, say, a star having a surface temperature of 10,000 Kelvin because …
A. the hotter star has consumed most of its elements
B. the atoms in the cooler stars have more electrons capable of changing energy states
C. the atoms in the cooler stars have less electrons capable of changing energy states
D. hydrogen lines are more prevalent in cooler stars E. More than one of the above answers are correct
29. Why don't we rely solely on the thermal properties (continuous spectrum) of a star to determine the temperatures of stars ?
A. Stars can change their temperatures from week to week and thus we would have to keep observing the same stars
B. The thermal radiation of a star depends upon the distance to the star, and we can't calculate distances to stars farther than about 100 parsecs
C. Thermal radiation is independent of the distance to a star, but not its temperature
D. The Earth's atmosphere gets in the way for very hot and very cool stars E. None of the above is correct
30. Why do stars appear to be different in color?
A. Because they have different absolute magnitudes B. Because they have different chemical compositions C. Because they have different temperatures
D. Because they are all at different distances
E. Stars aren't really different colors; it's just that our atmosphere blocks some kinds of electromagnetic radiation.
31. What changes would you expect to see in the resulting spectrum of emitted light from a piece of metal when it is heated slowly in an intense flame from 500K to 1,500K?
A. Intensity of radiation would increase greatly and its color would change from red through white to blue.
B. Intensity of radiation would increase greatly and its color would change from blue through white to red.
C. Intensity of radiation would increase greatly and its color would remain red. D. Intensity of radiation would change only slightly and its color would change
from blue through white to red.
32. A small particle of interplanetary material is heated by friction from a temperature of 400 K to 4000 K as it falls into the atmosphere of the Earth and produces a meteor or a shooting star in our sky. If this object behaves like a perfect blackbody over this short time, how will its emitted radiation change as it is heated?
A) Its intensity will rise by a factor of 100 while the peak wavelength of emitted light will become shorter by a factor of 100, moving from the infrared to the ultraviolet.
B) Its total intensity will rise by a factor of 10,000 while its peak wavelength will become longer by a factor of 10, moving from the visible to the infrared or heat radiation.
C) Its total emitted intensity will rise by a factor of 10,000 while its peak wavelength will become shorter by a factor of 10, from infrared to red visible light.
D) Its total intensity will rise by a factor of 10, while its peak wavelength will become shorter by a factor of 10, moving from the infrared to red visible light. 33. The dark absorption lines in the solar spectrum are caused …
A) by a cooler layer of gas overlying the hot solar interior, which contains many elements including H, He, Mg, Ca, Fe, etc.
B) by a cooler layer overlying the hot solar interior, consisting solely of hydrogen gas, which produces all the absorption lines.
C) solely by absorption by atoms and molecules in the Earth's cool atmosphere. D) by a hotter layer of gas that overlies the cooler solar interior, and which
produces the absorption lines.
34. Suppose that a certain spectral line has a wavelength of 600 nm and that when it is observed in a distant galaxy it is observed to have a wavelength of 612 nm. How can this be ?
A) The line is from a previously unknown element. B) The galaxy is moving toward Earth.
C) The galaxy is moving away from Earth.
D) The wavelength of the line may have been changed by material between the galaxy and Earth.
E) The situation described in this question cannot happen because the wavelengths of a particular element are fixed and cannot be changed.
35. Which of the following CANNOT be detected by using the Doppler effect? A) the rotation of the Sun.
B) the rotation of planets.
C) the motion of binary star systems.
D) the radial motion of a star moving toward the Earth.
E) None of the above, from A to D, could be detected by using the Doppler effect 36. The spectrum of a star shows an equivalent set of dark absorption lines to those of
the Sun, but with one exception. Every line appears at a slightly longer wavelength, shifted toward the red end of the spectrum. What conclusion can be drawn from this observation?
A) A cloud of cold gas and dust surrounds the star and is absorbing light from it. B) The star is moving rapidly toward the Earth.
C) The temperature of the star's surface is higher than that of the Sun. D) The star is moving rapidly away from Earth.
37. The proper motions of stars are …
A) easy to measure for most stars, on photographs taken six months apart.
B) noticeable to the unaided eye as a gradual shift of the constellations westward over the course of a month or two.
C) easy to observe with the unaided eye over the course of an hour or two.
D) difficult to measure even on photographs taken several years apart, for any but the nearest stars.
38. Why is there a limited range of stellar surface temperatures around 10,000 K at which neutral hydrogen gas will absorb visible light in the Balmer series?
A) Because there must be electrons at the n = 3 energy level in order for Balmer absorption to occur. If the gas is too cold, electrons are only in the n = 1 and 2 levels, while if the gas is too hot, the gas is ionized and no electrons are left in the hydrogen atoms.
B) Because electrons in hydrogen have to be at the n = 2 energy level in order to produce absorption in this series. If the gas is too cold, most atoms are in the n = 1 state and if it is too hot, most atoms are ionized.
C) Because electrons must be in the ground state n = 1 in order to undergo Balmer absorption. If the gas is too cold, electrons cannot be excited from this level, while, if it is too hot, there are no electrons left in the n = 1 level.
D) Because there must be sufficient continuum radiation from the stellar surface in the visible region to be absorbed by the hydrogen gas.
39. If you observe the brightness of a star only in the visible part of the electromagnetic spectrum (i.e., you have one data point on the star's energy spectrum), you are …
A) able to determine accurately the surface temperature of the star. B) observing the brightest emission given by the star.
C) observing the coolest part of the star's surface.
D) missing a lot of information about the star since the star emits in all wavelengths.
E) able to determine the star's radial velocity.
40. If we see a blue shift for a star in our galaxy, the star… A. must be hotter-than-normal.
B. must be moving away from us faster than is normal. C. must be moving toward us.
D. must be giving off more blue light than a normal star. E. both (a) and (d) above; they mean the same thing. 41. Manakah peryataan di bawah ini yang paling benar ?
a. Bila gas bertekanan rendah dipijarkan, maka hanya akan menghasilkan spektrum emisi.
b. Bila garis hidrogen dalam spektrum suatu bintang terlihat lemah, berarti suhu bintang tersebut termasuk tinggi atau rendah.
c. Garis spektrum molekul TiO mulai tampak pada spektrum bintang dengan kelas spektrum B.
d. Bintang dengan klasifikasi B5 III berarti bintang tersebut adalah bintang maharaksasa dengan temperatur sekitar 20.000 K.
e. Garis spektrum molekul CH (G-Band) tampak sangat kuat pada spektrum