I need a tutor to check my answers. I am not sure if I answered parts 2 and 3 correctly – Thank you..
I need a tutor to check my answers. I am not sure if I answered parts 2 and 3 correctly – Thank you. Lab 7 – Stellar Spectra
Directions: Given a set of stellar spectra, identify the spectral types for each star.
Part 1: Definitions
Define the following:
Spectra – The spectrum of a chemical element is obtained when we decompose the light it emits into its component colors, making it pass through a scattering element. The spectra of stars are like your fingerprints. By comparing them with known spectra, we can determine their composition.
The spectrum of stars has a thermal origin. Most of them are made up of a bright background, the continuum, whose radiation intensity varies with wavelength according to a law, which can initially be approximated by a black body of the same effective temperature as the star would follow. Absorption lines (dark) and, exceptionally, emission lines (bright) are superimposed on the continuum, emitted by the elements and chemical compounds that constitute the emitting matter, that is, the stellar atmosphere.
When two stars have similar spectra, they also have common physical properties. This facilitates the development of a classification system based on the appearance of the spectra.
The stars are grouped under a letter that symbolizes their spectral type. From the hottest to the coldest, the letters’ sequence is: O – B – A – F – G – K – M. Also, each of these groups is subdivided into ten others, numbered from 0 to 9.
Absorption Line – It is a dark line on a continuous spectrum. It is produced by cold gases that surround hot gases. For example, if the gas is between the detector and the light source -which will generally be a continuous spectrum source- the detector can observe the spectrum of both the gas and the light source. The source will decrease in the intensity of the light observed in the incident photon’s frequency; most of the re-emitted photons will go out in different directions than the original photons had. In this case, an absorption line will be observed.
Fraunhofer Lines – They are a set of dark bands in the solar spectrum. Named after the German physicist Joseph von Fraunhofer who was the first to study them. There are about 570 lines. The prominent bands were assigned the letters from A to K and the thinner ones with other letters.
Emission Lines – They are bright-lines in a specific location of the spectrum radiating material, which corresponds to light emission at a specific frequency. The intensity of the emission lines depends on the number of atoms in each state. For example: If the detector can observe the gas but cannot see the light source, only the re-emitted photons will be observed, resulting in emission lines.
Wein’s Law – It quantitatively expresses the empirical fact that the peak or maximum of emission in the spectrum of a black body shifts towards shorter wavelengths (higher frequencies) as the temperature increases.
When the temperature of a blackbody radiator increases, the overall radiated energy increases. The peak of the radiation curve moves towards shorter wavelengths. When the maximum is evaluated from the Planck radiation formula, the product of the maximum wavelength and the temperature is found to be constant.
This relationship is called Wien’s displacement law. It is useful for determining the temperature of hot radiating objects such as stars, and indeed for determining the temperature of any radiating object, the temperature of which is much higher than that of its environment.
Part 2: Characterizations
Research the following. Find what absorption lines you need to look for in each spectral type-as well as the average temperature for the stars in that spectral type. Write down the absorption lines in nanometers!
Absorption Lines Average Temperature Absorption Lines in Nanometers
O – Purple 28,000 – 50,000 435 – 380 nm
B – Blue 10,000 – 28,000 500 – 435 nm
A – Light Blue 7,500 – 10,000 520 – 500 nm
F – White (no green) 6,000 – 7,500 565 – 520 nm
G – Yellow 5,000 – 6,000 590 – 565 nm
K – Orange 3,500 – 5,000 625 – 590 nm
M – Red 2,500 – 3,500 740 – 625 nm
Part 3: Identify the Spectral Types
Using what you researched from part II, find the spectral type for each star using the star’s absorption spectra below. (HINT: you can use peak temperature AND absorption lines to ID a stellar spectra!)
Image transcription text
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I need a tutor to check my answers. I am not sure if I answered parts 2 and 3 correctly – Thank you.
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