Velraj ASTM 102 SPECTROSCOPY LAB S24
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Community College of Baltimore County *
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102
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Astronomy
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Apr 3, 2024
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Uploaded by ChancellorSnow1947
Spectroscopy Lab Submission Questions (25 pts.)
1.
How would astronomers use the continuous spectrum of a star to determine its surface temperature?
Astronomers use the continuous spectrum of a star to determine its surface temperature through a process called spectroscopy. By analyzing the intensity of light emitted by the star across different wavelengths, they can identify the peak wavelength of the emitted radiation, which corresponds to the star's temperature according to Wien's Law. Essentially, hotter stars
emit more of their light at shorter wavelengths, while cooler stars emit more at longer wavelengths. By comparing the observed spectrum with known temperature spectra, astronomers can accurately determine the surface temperature of the star (Myers, 2013).
2.
How would astronomers use an emission spectrum to identify the composition of a gas?
According to Halper (2023), astronomers use emission spectra to identify the composition of a gas by analyzing the specific wavelengths of light emitted by the gas. Each element or molecule emits light at characteristic wavelengths when excited. By comparing the observed emission lines in the spectrum to the known emission spectra of various elements and molecules, astronomers can identify which substances are present in the gas. This technique is known as spectroscopy and is crucial for understanding the chemical composition of astronomical objects such as stars, galaxies, and nebulae (Libretexts, 2023).
3.
Explain why the shape of the continuum (overall shape of the spectrum) is different for each spectral class.
The shape of the continuum in a stellar spectrum differs for each spectral class primarily due to variations in the temperature and surface characteristics of stars across different classes. The continuum represents the broad, continuous distribution of light emitted by a star across all wavelengths. The hotter stars, such as those in spectral classes O and B have spectra dominated by shorter wavelengths, with more energy emitted in the ultraviolet and blue parts
of the spectrum. This results in a continuum that peaks at shorter wavelengths and decreases toward longer wavelengths. Conversely, cooler stars, such as those in spectral class M, emit most of their light in the infrared and red parts of the spectrum, leading to a continuum that peaks at longer wavelengths and decreases toward shorter wavelengths. Additionally, factors such as the presence of absorption lines due to elements in the star's atmosphere and the effects of stellar activity and variability can also influence the shape of the continuum, contributing to the distinct spectral signatures observed across different stellar classes (Tielens, 1999).
4.
Describe the process used to determine the spectral class of a star using its absorption spectrum.
The process used to determine the spectral class of a star using its absorption spectrum involves analyzing the strengths and positions of absorption lines within the spectrum (Martins, 2017). Each spectral class is associated with specific absorption features indicative of the star's temperature, surface gravity, and chemical composition (Martins, 2017). First,
astronomers compare the observed absorption lines in the spectrum to reference spectra of known spectral classes. By identifying which absorption lines are present and their relative strengths, they can infer the temperature and surface characteristics of the star (Martins, 2017). For example, stars of spectral class O exhibit strong absorption lines of helium and hydrogen, indicating high temperatures and high surface gravity (Martins, 2017). In contrast, stars of spectral class M show absorption lines of molecules such as titanium oxide and vanadium oxide, suggesting lower temperatures and lower surface gravity (Martins, 2017).
5.
What are the spectral classes listed as OBAFGKM rather than ABCDE?
By matching the observed absorption features to those of known spectral classes, astronomers can accurately classify the star according to its spectral type, providing valuable insights into its physical properties and evolutionary stage (Giridhar, 2010). The spectral classes listed as OBAFGKM, rather than ABCDE, are assigned to stars based on their surface
temperatures, from hottest to coolest (Giridhar, 2010). The sequence stands for: O - Hottest stars B - Very hot stars A - Hot stars F - Moderately hot stars G - Stars like our Sun (such as the Sun) K - Moderately cool stars M - Coolest stars (Giridhar, 2010).
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References
Giridhar, S. (2010). Advances in spectral classification. ResearchGate
.
https://www.researchgate.net/publication/
45910814_Advances_in_Spectral_Classification
Libretexts. (2023, July 7). 6.3: Line Spectra and the Bohr model
. Chemistry LibreTexts.
https://chem.libretexts.org/Bookshelves/General_Chemistry/Map%3A_Chemistry_-
_The_Central_Science_(Brown_et_al.)/06%3A_Electronic_Structure_of_Atoms/
6.03%3A_Line_Spectra_and_the_Bohr_Model
Martins, F., & Palacios, A. (2017). Spectroscopic evolution of massive stars on the main sequence. Astronomy and Astrophysics
, 598
, A56. https://doi.org/10.1051/0004-6361/201629538
Spectra - Introduction
. (n.d.). https://imagine.gsfc.nasa.gov/science/toolbox/spectra1.html
Tielens, A. G. G. M. (1999). Stars, Spectroscopy of*. In Elsevier eBooks
(pp. 2684–2688). https://doi.org/10.1016/b978-0-12-374413-5.00354-7