Stellar Spectral
Classification
Literature
⚫ The bible: „Stellar Spectral Classification“,
R.O. Gray, C. J. Corbally, 2009, Princeton Series
in Astrophysics
⚫ Older, but a good overview: „The
Classification of Stars“, C. Jaschek & M.
Jaschek, 1987, Cambridge University Press
„Pickerings Harem“ (Harvard, 1870 to 1920): O-B-A-F-G-K-M
Basic Classification
⚫ Parameters to estimate:
1. Spectral type (temperature)
2. Luminosity class (log g, age)
3. v sin i (rotation)
4. [metallicity]
⚫ How?
1. Line strengths
2. Line ratios
3. Equivalent widths
⚫ Why?
1. Very efficient
2. Well tested
Used Notation I
⚫ O-B-A-F-G-K-M-(-R-N), Yerkes = MKK Classification
⚫ „Official subclasses“
⚫ O: 4, 5, 6, 7, 8, 9, 9.5
⚫ B: 0, 0.5, 1, 2, 3, 5, 7, 8, 9.5
⚫ A: 0, 2, 3, 5, 7
⚫ F: 0, 2, 3, 5, 7, 8, 9
⚫ G: 0, 2, 5, 8
⚫ K: 0, 2, 3, 4, 5
⚫ M: 0, 1, 2, 3, 4, 7, 8
⚫ For these subclasses you will find also “official”
standard stars
Used Notation II
⚫ These subclasses were extended during time,
see for example Gray (1989, AJ 89, 1049)
⚫ Additional suffices: n, nn, e, weak, st…
⚫ Especially for B/A/F stars: i.e. hA0kA5mA3 V
this means that the hydrogen lines (h) have the
characteristics as in a A0 star, CaH&K (k) A5
and the metallic lines (m) A3
Freedman & Kaufmann, 2002, Universe, Sixth Edition, Freeman Company
⚫ Resolution: R = l/Dl
1. Photometry: U (3600Å, 700Å, 5), B (4350, 1000,
4), V (5550, 900, 6), u (3500, 340, 10), v (4100, 200,
21), b (4700, 160, 29), y (5500, 240, 23)
2. Classification spectroscopy:
⚫ „Very low“: 2000 – 400Å/mm = 30 – 6Å/pixel
(140 – 700)
⚫ „Low“: 400 – 120Å/mm = 6 – 1.8Å/pixel (700 -
2330)
⚫ „Classification“: 120 – 80Å/mm = 1.8 – 1.2Å/pixel
(2330 - 3500)
⚫ „Intermediate“: 80 – 20Å/mm = 1.2 – 0.3Å/pixel
(3500 - 14000)
To calculate Å/mm:
Typical pixel size of a CCDs
15 mm = 0.015 mm
1 Å/mm = 0.015 Å/pixel
Here, a wavelength of 4200Å was used
Broadening of Lines I
⚫ Intrumental profile determined by the
resolution:
⚫ Rotational broadening:
355.2
mit
)(
5.0exp)(
2
FWHM
IP =













 D−
−=D 

ll
l
c
iv
xxcxcRP
L
L
sin
1with)(
2
21
ll
l
l
l
=D






D
D
−=+=D
Broadening of Lines II
Broadening of Lines III
Classification spectroscopy I
Classification spectroscopy II
Classification spectroscopy III
MKCLASS
⚫ Gray et al., 2016, AJ, 151, 13: „LAMOST
Observations in the Kepler Field: Spectral
Classification with the MKCLASS Code”
⚫ http://www.appstate.edu/~grayro/mkclass/
⚫ Command line tool for Linux and Windows
⚫ Libraries included
⚫ Normalization not needed
⚫ Huemmerich et al., 2020, A&A, 640, A40: “A
plethora of new, magnetic chemically peculiar
stars from LAMOST DR4”
Our stars
Our stars