Astronomer’s Pocket Field Guide
For other titles published in this series, go to www.springer.com/series/7814
Jack Martin
A Spectroscopic Atlas of Bright Stars A Pocket Field Guide
Jack Martin Forest Gate London United Kingdom E7 6DH
[email protected] ISBN 978-1-4419-0704-2 e-ISBN 978-1-4419-0705-9 DOI 10.1007/978-1-4419-0705-9 Springer Dordrecht Heidelberg London New York Library of Congress Control Number: 2009929021 © Springer Science+Business Media, LLC 2010 All rights reserved. This work may not be translated or copied in whole or in part without the written permission of the publisher (Springer Science+Business Media, LLC, 233 Spring Street, New York, NY 10013, USA), except for brief excerpts in connection with reviews or scholarly analysis. Use in connection with any form of information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed is forbidden. The use in this publication of trade names, trademarks, service marks, and similar terms, even if they are not identified as such, is not to be taken as an expression of opinion as to whether or not they are subject to proprietary rights. Printed on acid-free paper Springer is part of Springer Science+Business Media (www.springer.com)
To my parents, Louis and Polly, who fired my interest in astronomy by buying me my first telescope when I was 13.
Acknowledgements
I would like to thank Dr. Mike Dworetsky and Stephen Boyle, University of London Observatory, Dr. Robert Lombourne Open University, Professor Emeritus Jim Kaler University of Illinois, Dr. John Fisher, Valerie Desnoux, Christian Buil, Martin Peston, Charles Munton and Ed Palmer for their advice and encouragement in producing this book. And finally thanks to Jim Badura, producer of the Rainbow Optics Star Spectroscope, who said in the owner’s manual, “This seems to be a golden opportunity for amateur spectroscopists to create their own atlas of stellar spectra.” Well, Jim, here it is.
Contents
Dedication...........................................................................................
v
Acknowledgements...........................................................................
vii
Part I 1. Introduction...............................................................................
3
2. The Greek Alphabet..................................................................
11
3. The Periodic Table of Elements..............................................
13
4. The Spectral Sequence............................................................
15
Part II 5. The Star Atlas.............................................................................
25
6. Star Atlas Index......................................................................... 171 7. Stars By Right Ascension......................................................... 177 8. Other Examples of Stellar Spectra ....................................... 181 Glossary of Terms .............................................................................. 189 Further Reading.................................................................................. 199 Index..................................................................................................... 201
Part I
Introduction
3
Chapter 1
Introduction Astronomical Spectroscopy Spectroscopy has given us more information about stars than any other branch of Astronomy. Traditionally the domain of professional astronomers, it was an area of astronomy that very few amateurs would get involved in. Complicated texts and mathematics soon puts people off, and they lose interest in a subject that was always thought to be academically and technically difficult. This book demonstrates that this is not the case on a basic understanding level. Useful results can be obtained with relatively modest equipment. One of the purposes of this book is to kick-start an interest in astronomical spectroscopy. There is a need, to make accessible basic information from a theoretical and practical viewpoint for beginners and amateurs that is not available at this level in other books. It is a basic reference book, set out in a practical user-friendly way, that anyone should be able to use without assuming any prior knowledge of the subject. It gives facts and information about a star that may prove difficult for the reader to find elsewhere and certainly not in one book, as is the case with this publication. The spectra of stars contain their own unique signatures. This is a useful guide for those who wish to gain a basic insight into the makeup of stars. This atlas has been created from spectra taken on black and white films by an amateur astronomer for amateur astronomers and educational establishments. Their use as educational aids should not be underestimated. They are especially useful for GCSE astronomy, A level and undergraduate courses. They can also be used by the amateur for classification and identification purposes. This atlas is about bright stars that you can see with the naked eye, and relate to, as seen by a naked eye observer (in this case, from light polluted London, England, latitude 51°32′ N, longitude 0°5′ W ).
J. Martin, A Spectroscopic Atlas of Bright Stars, Astronomer’s Pocket Field Guide, DOI 10.1007/978-1-4419-0705-9_1, © Springer Science + Business Media, LLC 2010
4
Chapter 1
What’s in This Book? What you will find in this book is a Greek alphabet, a periodic table of elements; the spectral sequence explained; the star atlas containing 72 labeled spectrograms of bright stars listed in order of the spectral sequence (O B A F G K M), hottest to coolest, showing the elements present, information about their positions and spectroscopic properties (Henry Draper number, right ascension coordinate, declination coordinate, magnitude, distance, spectral type, luminosity class, B–V color index, temperature, and radial velocity); a table of spectral lines and wavelengths identified; a drawing of the constellation highlighting the star in question; a star atlas index; a table of stars by right ascension; other examples of stellar spectra; a glossary; and a further reading section.
Equipment Splitting starlight and imaging the resulting spectrum is not as difficult as one might think. The author’s setup (see Fig. 1.1) consists of a 0.30 m F5.3 Newtonian reflector, Rainbows Optics transmission grating, grating mount, low profile helical focuser, tele-extender (variable focus eyepiece projection tube), T-ring, 35 mm SLR camera body, and a suitable detector, in this case 35 mm black and white film. There is no slit in the spectroscope, so it only works on pinpoint star-like objects and not on extended objects such as planets. The grating mount is simply a piece of internally threaded aluminum tube that the grating screws into. This, in turn, is housed inside the tele-extender and is locked securely in position by a thumbscrew (see Fig. 1.2). The tele-extender is especially well suited to this type of photography, because it allows the camera/draw tube assembly to be rotated while the grating is in the locked position. The tele-extender is the variable focus type, so when the draw tube is pulled back to enlarge the image, it will go out of focus. The only way to focus the enlarged image is to move the focusing rack mounting plate further forward. But, because of the way a Newtonian reflector is designed, there are limits as to how far forward the focusing rack mounting plate can be moved.
Introduction
Fig. 1.1 0.30 m F5.3 Newtonian reflector (Photo by author.)
5
6
Chapter 1
Fig. 1.2 Olympus OM-1N camera bodies and slitless spectroscope assembly (Photo by author.)
It is important to bear in mind that the more the image is enlarged the fainter it becomes. In general, a small but brighter image is better than a large but fainter one. So for this setup, the draw tube focus is always set at the minimum travel image magnification. The camera body, an Olympus OM-1N, is particularly well suited for astrophotography, because it is a lightweight mechanical camera that does not use a battery, except for the light meter (which is not used for astrophotography), so the shutter can remain open for as long as necessary. Also, the focusing screen is interchangeable. Olympus made a 1–8 focusing screen especially for astrophotography.
Types of Black and White Film Color films are not recommended, because the tricolor emulsion has the effect of masking the spectral lines, and the blue end response is poor. When using a digital camera, you will note that the blue end response was also poor compared with black and white films. As a result, very few spectral lines were visible in either case.
Introduction
7
Fig. 1.3 Spectral sensitivities of different black and white films (Courtesy of Michael Covington, Astrophotography for the Amateur, reprinted with the permission of Cambridge University Press, 2001.)
Where black and white photography is concerned, there are four different film emulsions (see Fig. 1.3): 1. Blue-sensitive to blue, violet, and ultraviolet light 2. Orthochromatic-sensitive to blue and green light 3. Panchromatic-sensitive to blue, green and red light, i.e. the entire range of the visible spectrum approximately 400–700 nm 4. Extended red panchromatic-sensitive to red and thermal infrared radiation Panchromatic films such as Kodak TMAX 100–400–3200, Ilford Pan F 50, FP4 125, HP5 400, Delta 400–3200, Fuji Neopan 400–1600, and Paterson Acupan 200–800 were tested. Ilford emulsions are best suited for stellar spectra photography. The six factors that affect the result are: 1. Film speed ASA 2. Spectral sensitivity of the film
8
Chapter 1
3. Color of the star 4. Magnitude 5. Phase of the Moon. 6. Aperture of the telescope primary mirror/lens. The general rule of thumb is to use slow films for bright stars and fast films for fainter stars. The spectral sensitivity of different panchromatic films can vary. In the spectrograms of Mizar A + B (see Fig. 1.4), taken on Fuji Neopan 1600 and Ilford Delta 3200 films, the latter has an extended red sensitivity and shows the Ha line 656.3 nm. Film manufacturers’ technical data usually contains a spectral sensitivity curve (see Fig. 1.5), which shows sensitivity against wavelength (nm). The cooler stars do not photograph as well as the hotter stars, because the panchromatic film is less sensitive to the star’s color, an all important factor, which is ultimately determined by the star’s temperature. Photographing stellar spectra is best done in the absence of moonlight, so sunrise and sunset tables are needed and should be used to determine when astronomical twilight begins and ends, before starting an observing session.
Fig. 1.4 The spectra of Mizar A and B taken on Fuji Neopan 1600 and Ilford Delta 3200 black and white films (Spectrograms by author.)
Introduction
9
Fig. 1.5 Spectral sensitivity of Ilford Delta 3200 black and white film (Reprinted with the permission of llford/Harman films.)
Method of Photography The star’s spectrum is recorded using the motion of Earth (diurnal motion), by allowing the star and its first-order spectrum to drift across the field of view, parallel to the long edge of the camera viewfinder, until the spectrum is widened sufficiently enough to show the detail of the spectral lines. Since all stars from London appear to revolve around Polaris, the pole star, the drift time can vary from 15 s to 2 min to produce a satisfactory spectrogram.
Developing and Printing of Film All developing and printing is done by this author in a darkroom. Black and white photographic paper size 12.7 × 17.8 cm is used. The process is the same for all black and white films. The only variant is the development time. The width of the spectral image on the negative varies, depending on the spectral sensitivity of the film. The image is then enlarged to the same magnification as the spectral lines of a guide print of a star of the same spectral type, as seen when superimposed on the negative image.
10
Chapter 1
Digitizing Black and White Prints The print is scanned at the lowest resolution and saved as a bitmap image. The image is loaded into Christian Buil’s IRIS program and saved as a FITS (Flexible Image Transport System) image. The FITS image is then loaded into Valerie Desnoux’s Visual Specs program, which converts the image to the spectral profile of the star, showing a wavelength scale in angstrom units on the x-axis and an arbitrary brightness scale on the y-axis, these were not calibrated as photometric uni. The more modern nanometer unit is used in the table of spectral lines and wavelengths identified, which are rest wavelengths (see glossary for definition) as opposed to measured ones. The FITS image and the spectral profile is exported to a Microsoft Word document. The profile is then stacked on top of the spectrogram to give the final result, the spectrum of the star and its profile (see Fig. 1.6).
Fig. 1.6 The spectrum and profile of a CMa Sirius (Spectrogram by author.)
11
The Greek Alphabet
Chapter 2
The Greek Alphabet Alpha Beta Gamma Delta Epsilon Zeta Eta Theta Iota Kappa Lambda Mu Nu Xi Omicron Pi Rho Sigma Tau Upsilon Phi Chi Psi Omega
a b g d e z h q i k l m n x o p r s t u f c y w
J. Martin, A Spectroscopic Atlas of Bright Stars, Astronomer’s Pocket Field Guide, DOI 10.1007/978-1-4419-0705-9_2, © Springer Science + Business Media, LLC 2010
13
The Periodic Table of Elements
Chapter 3
The Periodic Table of Elements
Atomic number
Element
Symbol
Atomic number
Element
Symbol
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28
Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Sodium Magnesium Aluminum Silicon Phosphorus Sulfur Chlorine Argon Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel
H He Li Be B C N O F Ne Na Mg Al Si P S Cl Ar K Ca Sc Ti Va Cr Mn Fe Co Ni
53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80
Iodine Xenon Cesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutecium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury
I Xe Cs Ba La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf Ta W Re Os Ir Pt Au Hg
(continued)
J. Martin, A Spectroscopic Atlas of Bright Stars, Astronomer’s Pocket Field Guide, DOI 10.1007/978-1-4419-0705-9_3, © Springer Science + Business Media, LLC 2010
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Chapter 3
(continued) Atomic number
Element
Symbol
29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52
Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium
Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te
Atomic number
Element
Symbol
81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103
Thallium Lead Bismuth Polonium Astatine Radon Francium Radium Actinium Thorium Protoactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium
Tl Pb Bi Po At Rn Fr Ra Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr
15
The Spectral Sequence
Chapter 4
The Spectral Sequence The Spectral sequence is a surface temperature sequence pioneered by Father Angelo Secchi in 1866 and developed at Harvard in the 1890’s by EC pickering, Williamina Fleming Antonia Maury and Annie Cannon resulting in the famous seven letter sequence OBAFGKM. The Harvard-Drape system was further improved at the Yerkes Observatory in 1943 by William Morgan, Phillip Keenan and Edith Kellman, known as the MKK system in which the spectral characteristics are related to the luminosity of the star concerned.
Spectral Class Characteristics Spectral class O
B
A
F
G
Principal characteristics
Temperature (K)
Hot blue stars relatively few lines Hydrogen Balmer HI lines weak ionized Helium HeII lines dominate Blue white stars Hydrogen Balmer HI lines stronger neutral Helium HeI lines dominate White stars ionized Calcium CaII lines strengthening Hydrogen Balmer HI lines dominate Whitish stars neutral metals Iron FeI and Chromium CrI lines and ionized Calcium CaII lines strengthening Yellow stars many neutral metals Iron FeI Manganese MnI lines ionized Calcium CaII lines dominate
28,000–50,000
9,900–28,000
7,400–9,900
6,000–7,400
4,900–6,000
(continued)
J. Martin, A Spectroscopic Atlas of Bright Stars, Astronomer’s Pocket Field Gride, DOI 10.1007/978-1-4417-1346-9_4, © Springer Science + Business Media, LLC 2010
16
Chapter 4
(continued) Spectral class K
M
Principal characteristics
Temperature (K)
Orange red stars molecular bands appear neutral metal Iron FeI lines and Titanium Oxide TiO2 bands dominate Cool red stars neutral metal Magnesium MgI lines strong Titanium Oxide TiO2 bands dominate
3,600–4,900
2,000–3,600
Readers please note C-R, C-N, S, L, T, Y type stars are mentioned in the glossary see /Spectral type/ p 196.
Fig. 4.1 Spectral absorption features (Reprinted by permission of HarperCollins Publishers Limited. Collins Dictionary of Astronomy © 1994 Collins (edited by Valerie Illingworth).
Fig. 4.2 Elements in the Sun (Courtesy of James B. Kaler, The Cambridge Encyclopedia of Stars, reprinted with the permission of Cambridge University Press, 2006.)
The Spectral Sequence
17
18
Chapter 4
d Ori Mintaka Spectral type 09.5 Luminosity Class II Temperature 30,000 K Magnitude 2.23. Contains singly ionized Helium (HeII) lines. Hydrogen Balmer (H) lines appear only weakly.
g Ori Bellatrix Spectral type B2 Luminosity Class III Temperature 21,500 K Magnitude 1.64. Neutral Helium (HeI) lines dominate. Hydrogen Balmer (H) lines become stronger.
The Spectral Sequence
19
a Lyr Vega Spectral type A0 Luminosity Class V Temperature 9,500 K Magnitude 0.03. Hydrogen Balmer (H) lines dominate and merge into a continuum.
a CMi Procyon Spectral type F5 Luminosity Class IV–V Temperature 6,530 K Magnitude 0.38. The H and K lines of ionized Calcium (CaII) and other metal lines strengthen.
20
Chapter 4
a Aur Capella Spectral type G8 Luminosity Class III Temperature 5,300 K Magnitude 0.08. The H and K lines of ionized Calcium (CaII) are strong. Neutral metal lines Iron (FeI) Magnesium (MgI) and Calcium (CaI) are strengthening.
b Gem Pollux Spectral type K0 Luminosity Class III Temperature 4,770 K Magnitude 1.14. The Hydrogen lines are almost gone. The H and K lines of ionized Calcium (CaII) are strong other neutral metal lines Magnesium (MgI) and Iron (FeI) are very prominent.
The Spectral Sequence
21
a Ori Betelgeuse Spectral type M2 Luminosity Class I Temperature 3,600 K Magnitude 0.50. The neutral metal lines Magnesium (MgI) are strong. Molecular bands are prominent with broad Titanium Oxide (TiO) bands dominating.
Part II
The Star Atlas
Chapter 5
The Star Atlas
J. Martin, A Spectroscopic Atlas of Bright Stars, Astronomer’s Pocket Field Guide, DOI 10.1007/978-1-4419-0705-9_5, © Springer Science + Business Media, LLC 2010
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26
Chapter 5
27
h
2.77
III
B-V
K
The Star Atlas
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Chapter 5
29
h
m
B-V
K
-1
The Star Atlas
30
Chapter 5
31
h
m
915
II
B-V
K
−1
The Star Atlas
32
Chapter 5
33
h
m
447.1
B-V
K
-1
The Star Atlas
34
Chapter 5
35
h
B-V
K
-1
The Star Atlas
36
Chapter 5
37
5394
56
656.3
B-V
K
−1
The Star Atlas
38
Chapter 5
39
44743
h
m
2
B-V
K
33.7
The Star Atlas
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Chapter 5
41
h
m
s
x
B-V
K
The Star Atlas
42
Chapter 5
43
h
m
ly
K
The Star Atlas
44
Chapter 5
45
h
m
393.4
B-V
χ
K
The Star Atlas
46
Chapter 5
47
h
m
333
IV
B-V
K
The Star Atlas
48
Chapter 5
49
h
3.66
B-V
K
The Star Atlas
50
Chapter 5
51
h
m
B3
V
B-V
K
The Star Atlas
52
Chapter 5
53
h
m
.5
434
B3
III
B-V
K
The Star Atlas
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Chapter 5
55
h
m
ly
B6
III
B-V
K
The Star Atlas
56
Chapter 5
57
B7
III
B-V
K
The Star Atlas
a Leo Regulus
58 Chapter 5
59
h
m
77
B7
V
B-V
K
h
The Star Atlas
60
Chapter 5
61
h
V
o
B-V
K
The Star Atlas
41 Ari 41 Arietis
62 Chapter 5
63
h
m
s
3.63
a
K
The Star Atlas
64
Chapter 5
65
h
Ve
B-V
K
The Star Atlas
66
Chapter 5
67
14
m
775
B-V
K
−1
The Star Atlas
68
Chapter 5
m
B-V
K
The Star Atlas
69
70
Chapter 5
71
K DEC
B9
V
α
B-V
9500
The Star Atlas
72
Chapter 5
73
h
m
III
B-V
K
The Star Atlas
74
Chapter 5
75
m
ly
B-V
K
The Star Atlas
76
Chapter 5
77
h
m
75
V
K
The Star Atlas
78
Chapter 5
79
m
B-V
K
3.3
The Star Atlas
80
Chapter 5
81
h
θ
IV
B-V
K
The Star Atlas
82
Chapter 5
83
h
m
B-V
K
e
The Star Atlas
84
Chapter 5
85
h
m
B3
V
B-V
K
The Star Atlas
86
Chapter 5
87
36m
656.31
K
The Star Atlas
88
Chapter 5
89
m
B-V
K
The Star Atlas
90
Chapter 5
91
37
z
K
The Star Atlas
92
Chapter 5
h
m
656.3
ly V
B-V K –7.6
The Star Atlas
93
94
a Gem Castor
Chapter 5
95
h
656.3
ly
B-V
K
x
The Star Atlas
96
Chapter 5
97
h
Vnn
B-V
K
The Star Atlas
98
Chapter 5
99
h
m
V
B-V
K
The Star Atlas
100
Chapter 5
m
m
RA
DEC 2.27 3.95
A2 A1
V m
K -5.6
The Star Atlas
101
a Cyg Deneb
102
Chapter 5
103
h
m
B-V
K
-4.5
The Star Atlas
104
Chapter 5
105
m
3.34
V
B-V
K
7.6
The Star Atlas
106
Chapter 5
107
h
B-V
K
The Star Atlas
108
Chapter 5
109
h
m
V
B-V
K
The Star Atlas
110
Chapter 5
111
m
656.3
B-V
K
The Star Atlas
112
Chapter 5
113
36 m h
ly
V
B-V
K
The Star Atlas
114
Chapter 5
115
h
V
B-V
K
The Star Atlas
116
Chapter 5
117
h
m
ly
B-V
K
6.7
The Star Atlas
118
Chapter 5
119
m
ly
V
B-V
K
The Star Atlas
120
Chapter 5
121
h
m
B-V
K
The Star Atlas
122
Chapter 5
123
13h
m
V
B-V
K
–1
The Star Atlas
H11
H10
H9
H8
CaII
H
H
H H
Cep Alderamin
124 Chapter 5
125
h
B-V
K
The Star Atlas
126
Chapter 5
127
h
m
0304;
K
The Star Atlas
128
Chapter 5
m
3.44
Mag
B-V K -1
-15.6
The Star Atlas
129
130
Chapter 5
131
36673
h
m
h
B-V
K
−1
The Star Atlas
132
Chapter 5
133
m
50
K
The Star Atlas
134
Chapter 5
135
h
m
F5
B-V
K
−3.2
The Star Atlas
136
Chapter 5
137
h
m
431.4
F5
z
B-V
K
-1
The Star Atlas
138
Chapter 5
00112
h
m
431.4
3.41
65
F6
B-V K −1
The Star Atlas
139
H9
H8
CaII
CaII/Hε
FeI
G
Hγ
γ Cyg
Hβ
Sadr
140 Chapter 5
RA 2000
DEC 2000
Wavelength/nm 486.1 434.0 431.4 417.1 397.0 396.8 393.4 388.9 383.5
Spectral lines identified
Spectral line Hβ Hγ G FeI Hε CaII CaII H8 H9
ζ
Properties
ε
α
1500
δ
θ
Iab
γ Cyg Sadr
F8
Mag Distancely Spectral Luminosity Type Class
194093 20h 22m 13.6s +40° 15´ 24˝ 2.20
HD
η
χ
ϕ
Cygnus
β
B-V Temperature Radial Color K Velocity –1 Index km s 0.66 6500 –7.5
The Star Atlas
141
142
Chapter 5
4614
m
431.4
3.44
ty p
B-V K −1
The Star Atlas
143
144
Chapter 5
43
m
396.8 393.4
431.4
438.3
B-V K -1
The Star Atlas
145
146
Chapter 5
h
m
383.5
431.4
518.4 517.3 516.7 486.1
B-V K -1
The Star Atlas
147
148
Chapter 5
149
h
m
393.4
c
B-V
K
The Star Atlas
150
Chapter 5
h
m
396.8 393.4
438.3
3.48
117
G8
K -1
The Star Atlas
151
152
Chapter 5
h
396.8 393.4
438.3 431.4
518.4 517.3 516.7
1.14
34
#$% K
x
−1
The Star Atlas
153
154
Chapter 5
197989
m
438.3 431.4 396.8 393.4
B-V K
ϕ
−1
The Star Atlas
155
156
Chapter 5
#
438.3 431.4 396.8 393.4
1.18
B-V K -1
-3.8
The Star Atlas
157
158
Chapter 5
95689
11h
m
438.3 431.4 396.8 393.4
1.49
B-V K -1
-8.9
The Star Atlas
159
160
Chapter 5
h
396.8 393.4
431.4
66
1.15
B-V K
b
-1
The Star Atlas
161
162
Chapter 5
h
m
438.3
518.4 517.3 516.7
K5
68
1.54
$%& K -1
54.3
The Star Atlas
163
164
Chapter 5
165
m
B-V
K
The Star Atlas
166
Chapter 5
m
518.4 517.3 516.7
1.67
B-V K 7.9
-1
The Star Atlas
167
168
Chapter 5
h
m
518.4 517.3 516.7 499.5
1.77
K −1
The Star Atlas
169
Star Atlas Index
Chapter 6
Star Atlas Index
J. Martin, A Spectroscopic Atlas of Bright Stars, Astronomer’s Pocket Field Gude, DOI 10.1007/978-1-4417-1346-9_6, © Springer Science + Business Media, LLC 2010
171
Nair al Saif Alnitak Mintaka Saiph Alnilam Cih Mirzam
i Ori z Ori d Ori k Ori e Ori g Cas b CMa z Per a Vir g Ori g Peg z Cas h UMa e Cas z Dra b Tau a Leo b Per 41 Ari b CMi
O9 O9.5 O9.5 B0 B0 B0 B1 B1 B1 B2 B2 B2 B3 B3 B6 B7 B7 B8 B8 B8 Alkaid Segin Nodus 1 El Nath Regulus Algol 41 Arietis Gomeisa
Spica Bellatrix Algenib
Proper name
Bayer name
Spectral type
Orion Orion Orion Orion Orion Cassiopeia Canis Major Perseus Virgo Orion Pegasus Cassiopeia Ursa Major Cassiopeia Draco Taurus Leo Perseus Aries Canis Minor
Constellation
Ori Ori Ori Ori Ori Cas CMa Per Vir Ori Peg Cas UMa Cas Dra Tau Leo Per Ari CMi
Abbreviation
Orionis Orionis Orionis Orionis Orionis Cassiopeiae Canis Majoris Persei Virginis Orionis Pegasi Cassiopeiae Ursae Majoris Cassiopeiae Draconis Tauri Leonis Persei Arietis Canis Minoris
Latin genitive
172 Chapter 6
b Ori a And a Peg g 1 + 2 Ari d Cyg q Aur a CrB
h Leo z Aql g UMa a Lyr e UMa g Gem a CMa a Gem g Tri b UMa z UMa
B8 B8 B9 B9/A0 B9.5 A0 A0
A0 A0 A0 A0 A0 A0 A1 A1 A1 A1 A2/A1
Merak Mizar A + B
Al Jabhah Deneb el Okab Phecda Vega Alioth Alhena Sirius Castor
Alphecca
Rigel Alpheratz Markab Mesarthim
Leo Aquila Ursa Major Lyra Ursa Major Gemini Canis Major Gemini Triangulum Ursa Major Ursa Major
Orion Andromeda Pegasus Aries Cygnus Auriga Corona Borealis Leo Aql UMa Lyr UMa Gem CMa Gem Tri UMa UMa
Ori And Peg Ari Cyg Aur CrB
(continued)
Orionis Andromedae Pegasi Arietis Cygni Aurigae Coronae Borealis Leonis Aquilae Ursae Majoris Lyrae Ursae Majoris Geminorum Canis Majoris Geminorum Trianguli Ursae Majoris Ursae Majoris
Star Atlas Index
173
Proper name
Deneb Chort Menkalinan Megrez Pherkad Denebola Zosma Ruchbah Sheratan Deltotron Alcor Alderamin Altair Aldhafera Arneb Caph Procyon Mirfak
Bayer name
a Cyg q Leo b Aur d UMa g UMi b Leo d Leo d Cas b Ari b Tri 80 UMa a Cep a Aql z Leo a Lep b Cas a CMi a Per
Spectral type
A2 A2 A2 A3 A3 A3 A4 A5 A5 A5 A5 A7 A7 F0 F0 F2 F5 F5
(continued)
Cygnus Leo Auriga Ursa Major Ursa Minor Leo Leo Cassiopeia Aries Triangulum Ursa Major Cephus Aquila Leo Lepus Cassiopeia Gemini Perseus
Constellation Cyg Leo Aur UMa UMi Leo Leo Cas Ari Tri UMa Cep Aqu Leo Lep Cas Gem Per
Abbreviation Cygni Leonis Aurigae Ursae Majoris Ursae Minoris Leonis Leonis Cassiopeiae Arietis Trianguli Ursae Majoris Cephei Aquilae Leonis Leporis Cassiopeiae Geminorum Persei
Latin genitive
174 Chapter 6
F6 F8 G0 G2 G8 G8 G8 K0 K0 K0 K0 K2 K5 M0 M2 M2
a Tri g Cyg h Cas h Peg a Aur z Cyg m Peg b Gem e Cyg a Cas a UMa a Ari a Tau b And b Peg a Ori
Sad al Bari Pollux Gienah Shedar Dubhe Hamal Aldebaran Mirach Sheat Betelgeuse
Mothallah Sadr Achird Martar Capella
Triangulum Cygnus Cassiopeia Pegasus Auriga Cygnus Pegasus Gemini Cygnus Cassiopeia Ursa Major Aries Taurus Andromeda Pegasus Orion
Tri Cyg Cas Peg Aur Cyg Peg Gem Cyg Cas UMa Ari Tau And Peg Ori
Trianguli Cygni Cassiopeiae Pegasi Aurigae Cygni Pegasi Geminorum Cygni Cassiopeiae Ursae Majoris Arietis Tauri Andromedae Pegasi Orionis
Star Atlas Index
175
177
Stars by Right Ascension
Chapter 7
Stars by Right Ascension Bayer name
Proper name
RA 2000
DEC 2000
a And b Cas g Peg z Cas a Cas h Cas g Cas b And d Cas a Tri g1 Ari g2 Ari e Cas b Ari a Ari b Tri g Tri 41 Ari b Per a Per z Per a Tau b Ori a Aur g Ori b Tau d Ori a Lep i Ori
Alpheratz Caph Algenib
00 h 08 min 23.2s 00 h 09 min 10.6s 00 h 13 min 14.1s 00 h 36 min 58.2s 00 h 40 min 30.4s 00 h 49 min 06.0s 00 h 56 min 42.4s 01 h 09 min 43.9s 01 h 25 min 48.9s 01 h 53 min 04.8s 01 h 53 min 31.7s 01 h 53 min 31.8s 01 h 54 min 23.6s 01 h 54 min 38.3s 02 h 07 min 10.3s 02 h 09 min 32.5s 02 h 17 min 18.8s 02 h 49 min 59.0s 03 h 08 min 10.1s 03 h 24 min 19.3s 03 h 54 min 07.9s 04 h 35 min 55.2s 05 h 14 min 32.2s 05 h 16 min 41.3s 05 h 25 min 07.8s 05 h 26 min 17.5s 05 h 32 min 00.3s 05 h 32 min 43.7s 05 h 35 min 25.9s
+29°05¢26 +59°08¢59” +15°11¢01” +53°53¢49” +56°32¢15” +57°48¢58” +60°43¢00” +35°37¢14” +60°14¢07” +29°34¢44” +19°17¢45” +19°17¢37” +63°40¢13” +20°48¢29” +23°27¢45” +34°59¢14” +33°50¢50” +27°15¢38” +40°57¢21” +49°51¢41” +31°53¢01” +16°30¢33” −08°12¢06” +45°59¢53” +06°20¢59” +28°36¢27” −00°17¢57” −17°49¢20” −05°54¢36”
Shedar Archird Cih Mirach Ruchbah Mothallah Mesarthim Mesarthim Segin Sheratan Hamal Deltotron 41 Arietis Algol Mirfak Aldebaran Rigel Capella Bellatrix El Nath Mintaka Arneb Nair al Saif
(continued)
J. Martin, A Spectroscopic Atlas of Bright Stars, Astronomer’s Pocket Field Guide, DOI 10.1007/978-1-4419-0705-9_7, © Springer Science + Business Media, LLC 2010
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Chapter 7
(continued)
Bayer name
Proper name
RA 2000
DEC 2000
e Ori z Ori k Ori a Ori b Aur q Aur b CMa g Gem a CMa b CMi a Gem a CMi b Gem h Leo a Leo z Leo b UMa a UMa d Leo q Leo b Leo g UMa d UMa e UMa z A UMa z B UMa a Vir 80 UMa h UMa a Boo g UMi a CrB z Dra a Lyr z Aql d Cyg
Alnilam Alnitak Saiph Betelgeuse Menkalinan
05 h 36 min 12.7s 05 h 40 min 45.5s 05 h 47 min 45.3s 05 h 55 min 10.3s 05 h 59 min 31.7s 05 h 59 min 43.2s 06 h 22 min 41.9s 06 h 37 min 42.7s 06 h 45 min 08.9s 07 h 27 min 09.0’s 07 h 34 min 35.9s 07 h 39 min 18.1s 07 h 45 min 18.9s 10 h 07 min 19.9s 10 h 08 min 22.2s 10 h 16 min 41.4s 11 h 01 min 50.4s 11 h 03 min 43.6s 11 h 14 min 06.4s 11 h 14 min 14.3s 11 h 49 min 03.5s 11 h 53 min 49.8s 12 h 15 min 25.5s 12 h 54 min 01.7s 13 h 23 min 55.5s 13 h 23 min 56.3s 13 h 25 min 11.5s 13 h 25 min 13.4s 13 h 47 min 32.3s 14 h 15 min 39.6s 15 h 20 min 43.6s 15 h 34 min 41.2s 17 h 08 min 47.1s 18 h 36 min 56.2s 19 h 05 min 24.5s 19 h 44 min 58.4s
−01°12¢07” −01°56¢34” −09°40¢11” +07°24¢25” +44°56¢51” +37°12¢45” −17°57¢22” +16°23¢57” −16°42¢58” +08°17¢21” +31°53¢18” +05°13¢30” +28°01¢34” +16°45¢45” +11°58¢02” +23°25¢02” +56°22¢56” +61°45¢03” +20°31¢25” +15°25¢46” +14°34¢19” +53°41¢41” +57°01¢57” +55°57¢35” +54°55¢31” +54°55¢18” −11°09¢41” +54°59¢17” +49°18¢48” +19°10¢57” +71°50¢02” +26°42¢53” +65°42¢53” +38°47¢01” +13°51¢48” +45°07¢51”
Mirzam Alhena Sirius Gomeisa Castor Procyon Pollux Al Jabhah Regulus Aldhafera Merak Dubhe Zosma Chort Denebola Phecda Megrez Alioth Mizar A Mizar B Spica Alcor Alkaid Arcturus Pherkad Alphecca Nodus 1 Vega Deneb el Okab
(continued)
179
Stars by Right Ascension
(continued)
Bayer name
Proper name
RA 2000
DEC 2000
a Aql g Cyg a Cyg e Cyg z Cyg a Cep h Peg m Peg b Peg a Peg
Altair Sadr Deneb Gienah
19 h 50 min 46.9s 20 h 22 min 13.6s 20 h 41 min 25.8s 20 h 46 min 12.6s 21 h 12 min 56.1s 21 h 18 min 34.7s 22 h 43 min 00.1s 22 h 50 min 00.1s 23 h 03 min 46.4s 23 h 04 min 45.6s
+08°52¢06” +40°15¢24” +45°16¢49” +33°58¢13” +30°13¢37” +62°35¢08” +30°13¢17” +24°36¢06” +28°04¢58” +15°12¢19”
Alderamin Martar Sad al Bari Scheat Markab
181
Other Examples of Stellar Spectra
Chapter 8
Other Examples of StellaR Spectra a Boo Arcturus
CaII
CaII
G
Hβ
CaI
Properties HD
RA
h
m
DEC
s
124897 14 15 39.6
Mag
Distance Spectral Luminosity B-V Temperature ly Type Class Colour K Index +19° 10´ 57˝ – 0.04 37 K2 III 1.15 4290
Radial Velocity –1 km s –5.2
Fig. 8.1 Spectrum and properties of Arcturus. Spectrogram by Author.
Fig. 8.2 Aries. 41 Arietis Hamal Sheratan Mesarthim. Spectrograms by author.
J. Martin, A Spectroscopic Atlas of Bright Stars, Astromer’s Pocket Field Guide, DOI 10.1007/978-1-4419-0705-9_8, © Springer Science + Business Media, LLC 2010
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Chapter 8
Fig. 8.3 Spectra of stars from B6 to A4 showing the appearance and increase in strength of the K line at 3934Å as the temperature decreases. Spectrograms by author.
Fig. 8.4 Double stars Mizar A+B and Mesarthim. The spectrum of each star is blended into the spectrogram. Both components of each double star system are visible. Spectrograms by author.
Other Examples of Stellar Spectra
Fig. 8.5 Pleiades 1. Spectrogram by author.
183
184
Fig. 8.6 Pleiades 2. Spectrogram by author.
Chapter 8
Other Examples of Stellar Spectra
185
Fig. 8.7 The Summer Triangle Vega Deneb Altair. Spectrograms by author.
Fig. 8.8 The Winter Triangle. Betelgeuse Procyon Sirius. Spectrograms by author.
186
Chapter 8
Fig. 8.9 Triangulum. Mothallah Deltotron Gamma Trianguli. Spectrograms by author.
Other Examples of Stellar Spectra
Fig. 8.10 The Square of Pegasus. Algenib Alpheratz Markab Scheat. Spectrograms by author.
187
188
Chapter 8
Core temperature 15,000,000 K Photosphere 5780 K Chromosphere 6,000-20,000 K Corona 2,000,000 K Spectral type G2 Luminosity class V Luminosity 3.85 x 1026 Js−1 Mean distance 1.495 x 1011 m Rotation period 26.8 days FeI/FeII MgI
MgI
MgI
516.7
517.3
518.4
Magnesium Triplet
NaI
NiI NaI
Sodium Doublet 589.0
589.6 Hα
Hydrogen Alpha Lhires 3 Spectrograph 2400g/mm grating 25mm Zeiss eyepiece Canon EOS 400D
656.3
Fig. 8.11 Some prominent Spectral lines in the Sun.
Glossary of Terms
189
Glossary of Terms Absorption line: A dark line formed at a particular wavelength when an electron jumps from a lower to a higher energy level in an atom while absorbing light from a bright, continuous background source. Angstrom Å: A unit of length equal to 10−10 m, or 10−8 cm, or 0.1nm. Atomic spectra: Transitions between atomic energy levels within atoms that lead to the absorption or emission of radiation in a series of sharply defined lines, corresponding to fixed wavelengths representing radiation quanta of definite energies. There are six named series of lines for hydrogen: Lyman far ultraviolet Balmer series seen at visible wavelengths Paschen infrared Brackett far infrared Pfund far infrared Humphreys far infrared Be-type stars: B-type stars with bright emission lines of hydrogen, which are superimposed on the normal dark absorption lines, e.g., Gamma Cassiopeiae. Blackbody radiation: The emission of radiation from incandescent material independent of the chemical composition and physical nature of the material. A black body is both a perfect absorber and emitter of radiation. Any radiation is absorbed without loss due to reflection or transmission. Blaze angle: In a grating the faces of the grooves are cut at a constant angle to the plane of the original surface of the grating material. The angle of inclination of the grooves is known as the blaze angle. Blazing concentrates the diffracted spectrum in a specific order and wavelength range. B–V color index: The color or measure of a star’s color. B–V may need to be corrected for interstellar reddening before an accurate temperature value can be estimated. Estimation is done by observing the star’s magnitude through two different filters from the UBVRI Johnson–Cousins filters system, where U is sensitive to ultraviolet light, B is sensitive to blue light, V is
190
Glossary of Terms
sensitive to green-yellow light, R is sensitive to red light, and I is sensitive to infrared light. The difference in magnitude found is the B–V color index. The more negative the color index, the bluer (the hotter) the object is, e.g., Rigel is −0.03. (Its B magnitude is 0.09 and its V magnitude is 0.12; so B–V = −0.03.) The more positive the color index, the redder (the cooler) the object is, e.g., the Sun +0.66. Chromosphere: A region of the sun’s atmosphere lying above the photosphere with a temperature of 6,000–20,000K. Color magnitude diagram: A graph showing significant correlations between a star’s color and its luminosity. Color is related to effective temperature and spectral class. See HR diagram. Continuous spectrum: Incandescent solids emit a spectrum consisting of all wavelengths in a given range (a continuous spectrum), without any absorption or emission lines. Continuum: Part of the spectrum that has neither absorption or emission lines with only a smooth wavelength distribution. Corona: The outermost region of the sun’s atmosphere with a temperature of around 2,000,000K. Declination (DEC d): A coordinate used with right ascension in the equatorial coordinate system analogous to latitude, expressed in degrees (°), minutes (¢) and seconds (″) of arc. Objects north of the celestial equator have + declinations, and those south have − declinations. Objects on the celestial equator have a declination of 0°, and the poles ±90°. Diffraction: This occurs when a wavefront passes through narrow slits and at sharp edges. It is due to the wave nature of light. Diffraction grating: Invented by American astronomer David Rittenhouse in 1785. The conventional grating consists of a series of closely spaced parallel lines scored onto the surface of a metal or glass. Spectra are produced by diffraction of the wavefront at the grating surface. The dispersion of spectral lines through a grating is linear, whereas through a prism it is nonlinear.
Glossary of Terms
191
Dispersion: The ability of a grating or prism to separate the visible wavelengths of radiant energy into a spectrum measured in Å/mm or nm/mm. Doppler broadening: The broadening of absorption or emission lines by the thermal motion of atoms. Doppler effect: A change of frequency of electromagnetic radiation due to relative motion between the observer and the source along the observer’s line of sight. Doppler shift: The change in wavelength observed when a body emitting light is moving away from (red shifted) or toward (blue shifted) along the observer’s line of sight. Echelette/Echelle gratings: A very accurately ruled reflection grating with about 1,000 lines cm−1 and a broad groove such that about 75% of the reflected light is concentrated in one order. An echelle grating is a coarse form of echelette grating with fewer fine lines that are more widely spaced. This arrangement gives a higher resolution over a narrower waveband such that 50 lines cm−1 can give a resolving power comparable to 10,000 lines cm−1. Electromagnetic radiation: Radiation that carries energy through space in a vacuum at the speed of light. Electromagnetic spectrum: Considered to consist of the region of radiant energy ranging from wavelengths of 1 × 10−10 cm to 10m, that is gamma rays–xrays–ultraviolet–visible–infrared and radio waves. Electron: The Greek word for amber, also called a negatron, a negatively charged elementary particle theorized by G. Johnstone Stoney in 1874 and discovered by J.J. Thomson in 1897: Mass = 9.109,534 × 10−31 kg Charge = 1.602,189 × 10−19 C Spin quantum number = 1/2 Electron volt: The eV is a unit of energy equal to the energy gained by an electron when it accelerates through a potential difference of 1 V in a vacuum equal to 1.602 × 10−19 joules.
192
Glossary of Terms
Emission line: A bright line formed at a particular wavelength when an electron jumps from a higher to a lower energy level in an atom by emitting a photon of a specific wavelength. See Be-type stars. Energy level: A quantity of energy associated with a bound electron orbiting around an atomic nucleus. An increase in energy will shift the electron to a higher energy level within an atom. Excitation: An atomic process where an atom or ion is raised to a higher energy state by an electron jumping from a lower to a higher energy level. Flash Spectrum: An emission line spectrum of the solar chromosphere seen just before and after totality of an eclipse of the sun. Forbidden lines: Lines not found in spectra under normal terrestial conditions, but are observed in certain astronomical spectra such as emission nebulae, because under normal laboratory conditions such atoms would be deexicited by collisions with other atoms before they had time to radiate. Fraunhofer lines: Dark absorption lines in the solar spectrum first observed by William Wollaston in 1802. First studied in detail by Joseph Von Fraunhofer in 1814, he catalogued over 500 lines and labelled the more prominent ones with letters. Frequency (v): Refers to any periodic phenomenon, particularly to the number of cycles per unit time, measured in Hertz and varies inversely with wavelength. Ground state: The lowest possible energy level for a given atom or molecule. HD: Named after Henry Draper, HD is a catalog of spectral types and positions of 225,300 stars numbered in right ascension for 1900 epoch. Compiled by Annie Jump Cannon and co-workers at Harvard College Observatory between 1918 and 1924, each star is assigned with its own HD number. Stars in the range 225,301–359,082 are from the Henry Draper Extension catalog denoted HDE published from 1925 through 1936 and 1949.
Glossary of Terms
193
HR diagram: Hertzsprung–Russell diagram in which a star’s absolute magnitude is plotted against its spectral type. Intensity: The amount of radiation received from an object. Optical astronomers prefer the term brightness. Ion: Molecules and atoms that have acquired a positive or negative charge through losing or gaining one or more electrons. Ionization: A process in which a neutral atom or molecule is given charge by removal of an electron from an atom, ion or molecule by collisians with other atoms or electrons. Because of the high temperatures in stars, much of the matter present is in an ionised state. Kelvin: A unit of thermodynamic temperature, or the fraction 1/273.16 of the thermodynamic temperature of the triple point of water, denoted by the symbol K. 0 K = −273.16°C absolute zero. Light: A specific part of the electromagnetic spectrum covering the visible region normally associated with human vision from violet 380.0 nm to red 780.0 nm. Light year: The distance light travels in a vacuum in 1 year. Numerically equal to: 63,241 au 0.306 pc 9,460,730,472,580.8 km Luminosity: The total energy radiated per second by a star expressed in joules per second, which is determined by its surface area and surface temperature. Luminosity class: Indicates whether a star is a dwarf, giant, or a supergiant as follows: Ia Bright supergiants Ib Supergiants II Bright giants III Giants IV Sub giants V Main sequence dwarfs
194
Glossary of Terms
For the spectrum descriptors, the suffix is placed after the Luminosity class descriptor, i.e., Iae. Suffixes for emission lines: e Emission line star em Emission by metal lines ep Peculiar emission eq P Cygni emission er Reversed emission f Helium and Nitrogen emission Other suffixes: k Interstellar lines m Strong metallic absorption n Nebulous diffuse lines nn Very diffuse lines p = pec Chemically peculiar spectrum no Luminosity class assigned s Sharp lines si Silicon star v Variation in the spectrum not caused by velocity effects wk Weak lines Magnitude: A logarithmic measure of the brightness of an object. Apparent magnitude (m) is a measure of its relative brightness as if seen by an observer on Earth. For example, the apparent magnitude of the sun is –26.74. Absolute magnitude (M) is the apparent magnitude it would have if it were at a standard luminosity distance of 10 parsecs from the observer, allowing the true brightness to be compared without regard to distance. The absolute magnitudes of most stars are between –5 and +15. Main sequence: A diagonal region in the Hertzsprung–Russell diagram that contains about 90% of all stars. Stars on the main sequence are those converting hydrogen into helium in their cores. Main sequence star: One of the classes of stars that increase in size, temperature, and brightness in a regular progression, e.g., the Sun. Its Luminosity class suffix is V in the MK spectral classification (see below).
Glossary of Terms
195
Metallicity: The proportion of matter in an object made up of chemical elements other than hydrogen or helium. Astronomers label all heavier elements “metal.” For example, a star rich in carbon would be called “metal rich” even though carbon is not a metal. MK system: The Morgan–Keenan system for classifying stellar spectra. Introduced in 1943. Monochromatic light: Light of one wavelength, e.g., a green laser beam has a wavel length of 532 nm. Nanometer (nm): A unit of length. 1 nm = 10−9 m = 10 Å. Nuclear fusion: A process by which stars generate energy. The nucleus of an atom fuses with the nuclei of other atoms, producing heavier atoms and releasing large amounts of energy. In the Sun, hydrogen is converted into helium. Objective prism: A small-angle prism placed in front of a telescope objective to disperse each star image into its spectrum. Photon: Electromagnetic energy is produced in discrete small quantities called photons. Photons produced at a particular frequency all have the same energy. The amount of energy present depends on the frequency of the radiation. Photosphere: The bright visible region of a star’s atmosphere where spectral lines are produced. Prism: A transparent piece of glass with flat polished surfaces that ref ract light. The dispersion is nonlinear, blue light is bent more than red light. There are four types of dispersive prism: triangular, Abbe, Porro, and Porro–Abbe. Radial velocity: The velocity of a star along the line of sight of an observer calculated from the Doppler shift in the spectral lines. If the star is receding, there will be a red shift in its spectral lines, and the radial velocity will be positive. An approaching star will produce a blue shift, and the radial velocity will be negative, measured in KMS–1.
196
Glossary of Terms
Rest wavelengths: Those wavelengths measured from a source at rest in the laboratory (as opposed to Doppler shifted wavelengths from a moving source). Right ascension (RA a): A coordinate used with declination in the equatorial coordinate system comparable to longitude, expressed in hours (h), minutes (min) and seconds (s), from 0 to 24 h. Measured eastward from the vernal equinox, uniquely identifying the position of a star in the sky. The effect of precession means it must be specified with reference to a particular epoch, currently J2000 January 1, 2000, at 12.00 UT1. The prefix J indicates a Julian epoch. Spectral line: A radiative Feature observed in absorption (dark) or emission (bright) at specific frequencies or wave lengths, produced by atoms or ions as they absorb or emit light. Spectral type: The different groups into which stars may be classified according to the characteristics of their spectra. The surface temperature of a star may often be inferred from its spectral type, as follows: W 30,000–70,000 K O 28,000–50,000 K B 9,900–28,000 K A 7,400–9,900 K F 6,000–7,400 K G 4,900–6,000 K K 3,600–4,900 K M 2,000–3,600 K C-R 2,800–5,100 K (Carbon star equivalent of late G/early K) C-N 2,600–3,100 K (Carbon star equivalent of late K/early M) S
