Spectral classification

The evidence on which this theory of stellar evolution is based comes not only from known nuclear reactions and the relativistic equivalence of mass and energy, but also from the spectroscopic analysis of the light reaching us from the stars. This leads to the spectral classification of stars, which is the cornerstone of modem experimental astrophysics. The spectroscopic analysis of starlight reveals much information about the... 

Spectral classification and absorption maxima (nm) of cast bilayer films... 

Before considering the chemistry of asteroids, we will briefly review their physical properties, spectral classifications, and distributions in space. This information will provide some context for the chemical data to follow. 

The data cube combines spectral and spatial information and therefore includes the requisite statistics for spectral classifications. However, new chemometric strategies have to be applied to interpret chemical imaging results. 

We have been making survey observations of faint cool carbon stars using the Kiso 105-cm Schmidt telescope. Kodak IN and 103aF plates are respectively taken behind the 4-degree objective prism (700 Amm-1 at Ha) for the detection and for the spectral classification. F-band plates are utilized to obtain the position and... 

The space distribution in the Cassiopeia region is estimated on the basis of the spectral classification and the absolute magnitudes determined by Mikami (1975). It is shown that the carbon stars are distributed over the galactic plane without strong concentration onto the (Perseus) arm. The number ratio of C4 - C5, C6 -C7, and C8 - C9 stars is nearly 1 0.4 < 0.1. 

The results are summarized in Figure 1. The different symbols denote the spectral classification of the individual stars, whereas four groups are distinguished WNE-A, WNE-B, WNL and WC stars. The size of the symbols indicates the mass-loss rates. The uncertainties of the results are estimated to be 0.1 dex in T, 0.4 dex in M and 0.5 dex in L. For the 11 stars in common with the sample of Abbott et al. (1986) we find our mass-loss rates to be compatible with their radio flux if the correct ionization equilibrium in the radio emitting region is applied (Schmutz and Hamann, 1986). The model calculations show that for all but the WN2 and WN3 stars helium recombines to He before the ions enter the radio-emitting region. 

Fig. 17.5. Sample search for Fe X transitions near 10 nm, in a range of 0.4 nm, wavelength ordered, with energy level data and spectral classifications...

S.A. Clough, M.W. Shephard, E.J. Mlawer, J.S. Delamere, M.J. lacono, K. Cady-Pereira, S. Boukabara, P.D. Brown, Atmospheric radiative transfer modeling A summary of the AER codes. Journal of Quantitative Spectroscopy and Radiative Transfer 91(2) 233-244 (2005). A.N. Dills, Temporal and spectral classification of battlespace detonations, Ph.D. dissertation. Air Force Institute of Technology, AFlT/DS/ENP/04-2 (2005). 

It is useful to remember the spectral classification, of which the six regular types are B(25000K), A(12000K), F(8000K), G(6000K), K(5000K) and M(3700 K) where the T in parentheses are representative values for BO, AO,. 

Far more complete descriptions of the classification and statistics of white dwarfs will be found in the McCook et al. catalogue [169] and its online supplements. These introduce a system of half-integer subclasses linked to the inverse effective temperature (10 x 5040/Teff)- Whether a spectral classification should depend on an analysis remains contentious - but it is clearly necessary to distinguish the huge spectral range exhibited within each white dwarf class (DQ, for example). As sky surveys go deeper, there is no shortage of new white dwarfs to discover, with 9316 confirmed in SDSS Data Release 4 [170,171],... 

Summary. Beginning with a historical account of the spectral classification, its refinement through additional criteria is presented. The line strengths and ratios used in two dimensional classifications of each spectral class are described. A parallel classification scheme for metal-poor stars and the standards used for classification are presented. The extension of spectral classification beyond M to L and T and spectroscopic classification criteria relevant to these classes are described. Contemporary methods of classifications based upon different automated approaches are introduced. 

Keywords Spectral classification, luminosity classes, metal-poor stars, M-L-T spectral classes... 

The above mentioned system also known as Yerkes Spectral Classification. Within the system, six luminosity classes are defined on the basis of standard stars over the observed luminosity range. 

The massive surveys both ground based as well as from space missions provide large number of stellar spectra covering distant components of Galaxy. To understand the complex evolutionary history of our Galaxy, rapid and accurate methods of stellar classification are necessary. A short review of the automated procedures are presented here. The most commonly used automated spectral classification methods are based on (a) Minimum Distance Method (MDM) (b) Gaussian Probability Method (GPM) (c) Principal Component Analysis (PCA) and (d) Artificial Neural Network (ANN). We chose to describe only two of them to introduce the automated approach of classification. 

It is very important to envisage an approach that would give quick, reliable spectral classifications (or stellar parameters) for stars falling in all regions of HR diagram. The pipeline procedures are being developed for the future ambitious missions such as GAIA and PAN-STARS. 

This technique also has important applications in medicine. For example, it can be used for the spectral classification of a normal human liver cell versus a cancerous liver cell as shown in Figure 4.14. Both the normal human liver cell (E) and the cancerous liver cell (F) contain three dominant types of spectra, each of which is displayed as a distinct colour. However, when the two cells are compared quantitatively, as shown in the histogram area measurements, the abnormalities in the cancerous cell can be quantified objectively. Another example of the use of fluorescence microscopy in medicine is illustrated in Figure 4.15. Using confocal fluorescence imaging, the uptake and distribution of drug (in this case an anthracycline) can be profiled in tumour cells. 

Figure 17.2 shows the relative abundance of the elements of the universe and of the earth. The abundances are approximate, as a consequence of die difficulties in their assessment and limitations of experimental techniques. The abundances in the universe (based on spectral measurements on stars and interstellar matter) are used as a refinement of data obtained for the solar system. Stellar light is divided in spectral classes depending on the surface temperature of the star, see Fig. 17.1. The various classes (Harvard Spectral Classification) show lines of the elements as listed below in approximately decreasing intensity ...

Disks are generally associated with the Class 11 spectral energy distributions (SED) from the pre-main-sequence (PMS) infrared spectral classification of Young Stellar Objects (YSO) (Lada 1987). This initial classification was based on whether the emitted energy from YSOs was rising in the mid-IR or with negligible IR excess. 

A point in the star-forming part of the Orion nebula that emits infrared radiation (but no visible radiation, probably because it is scattered by the dense dust of the nebula). It is thought to be a young near main-sequence star of type B spectral classification, and one of the youngest stars so far observed. 

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