The Notion of Astronomical Spectroscopy - Research Paper Example

Astronomical Spectroscopy Spectroscopy is the study of light emissions and absorptions. It’s a tool that an astronomer uses for studying the universe. This essay begins by deliberating the basics, including the diverse types of optical spectrographs, with addition to the ultraviolet and the near-infrared. Importance is given to the essentials in what manner spectrographs are used, together with the barriers involved in designing an observational experiment. It further elaborates observation and reduction methods, observing that some of the typical practices of flat-fielding often actually degrade the quality of the data rather than advance it. Even though the attention is on fact foundations, spatially fixed spectroscopy of prolonged sources is also concisely discussed. Argument of variance extinction, the effect of crowding, multi-object techniques, optimal abstractions, flat-fielding deliberations, and decisive centrifugal velocities and velocity dispersions provide the spectroscopies with the fundamentals needed to obtain the superlative data. Finally the essay conglomerates the preceding material by providing some examples of real life observing experiences with several typical instruments. Introduction Spectroscopy is the study of light emissions and absorptions.It’s is a technique of spectroscopy used in space science. It can as well be defined as the object of learning is the band of electromagnetic radiation, this includes visible light, which emits from stars and other astronomic objects. Spectroscopy sometimes is used to develop many properties of faraway stars and galaxies, e.g. their chemical structure and motion, via the Doppler shift.it’s one of the fundamental tools at an astronomer’s disposal, allowing one to determine the chemical structures, physical chattels, and radial velocities of astronomical sources. Spectroscopy is the means used to measure the dark matter content of galaxies, the masses of two stars in orbit about each other, the mass of a cluster of galaxies, the rate of expansion of the Universe, or ascertain an exoplanet nearby other stars, all using the Doppler shift. It makes it possible for the astronomer to determine the physical conditions in distant stars and nebulae, including the chemical elements and temperatures, by quantitative analysis of the strengths of spectral features, thus constraining models of chemical enrichment in galaxies and the evolution of the space, the same way a famous astronomer defines it, “You may not perform astrophysics just by captivating images through little colored fragments of glass,” supplementing the effect of astronomic spectroscopy with that of broad-band imaging. Astronomical spectroscopy has established an amusing treatment in the literature. The volume on Astronomical Techniques in the original Stars and Stellar Systems series contains a number of seminal treatments of spectroscopy. In particular, the introduction to spectrographs by Bowen (1962) remains useful even 50 years later, as the fundamental physics remains the same even though photographic plates have given way to CCDs as detectors. The volume on diffraction gratings by Loewen & Popov (1997) is also a valuable resource. Grey (1976) and Schroeder (1974) provide very accessible descriptions of astronomical spectrographs, while the “how to” guide by Wagner (1992) has also proven to be very useful. Similarly the monograph by Walker (1987) delves into the field of astronomical spectroscopy in a more comprehensive manner than is possible in a single chapter, and is recommended. The hardware Feature of Astronomical Spectroscopy When the first author was an undergraduate, his astronomical techniques professor, one Maarten Schmidt, drew a schematic diagram of a spectrograph on the blackboard, and said that all astronomical spectrographs contained these essential elements: a slit on to which the light from the telescope would be focused; the collimator, which would control the deviating light rays and turn it into parallel light; a disperser (usually a reflection grating); and a camera that would then focus the spectrum onto the detector. In the subsequent 35 years of doing astronomical spectroscopy for a living, the first author has yet to encounter a spectrograph that didn’t meet this description, at least in functionality. In a multi-object fiber spectrometer, such as Hectospec on the MMT (Fabricant et al. 2005), the slit is replaced with a successions of threads. In the occasion such as of an echelle, like Mage on the Clay 6.5-m telescope (Marshall et al. 2009), prisms are interleaved in the shaft of light after the diffraction grating to provide dispersion. For instance, an objective-prism spectroscopy, the star itself acts as a slit “and the Universe for a collimator” (Newall 1910; see also Bidelman 1966). However, this experimental picture offers the reference for such variations, and a version. A broad spectrum of emissions from a non-specific light source e.g. light globe. Figure 1: Spectroscope (Thackeray 1961) Figure 2: Creating a spectrum(Thackeray 1961) Kirchhoff’s Laws (Origins of different Spectra) 1st law: A luminous solid or liquid, or adequately compact gas, produces light of all wavelengths and produces a continuous spectrum of radiation. Figure 3 (Kitchen, C 1995) 2nd law: A low-density hot gas emits light whose spectrum consists of a series of bright emission lines which are characteristic of the chemical composition of the gas. Figure 4 (Kitchen, C 1995) 3rd law: The unruffled tinny gas enthralls definite wavelengths on or after a continuous spectrum, leaving dark absorption lines in their place superimposed on the continuous spectrum. Figure 5 (Kitchen, C 1995) The Sun – A Nuclear Reactor Energy is coming from the star’s core through fusion. Gravity is pulling the star towards its centre. When the star is born, the energy pressure outwards equals the gravity. Figure 6 (Fievez, Charles 1995) Atomic Emission Lines An emission line is formed when an electron makes a transition from a particular discrete energy equal of an atom, to a lesser energy state, producing a photon of a particular energy and wavelength. A band of many such photons displays an emission spike at the wavelength associated with these photons. When the electrons in the element are enthusiastic, they hurdle to upper energy levels. While the electrons fall back down, and vacates the excited state, energy is emitted again, the wavelength which denotes to the distinct lines of the emission spectrum. Electron Excitation: The Hydrogen Atom The Bohr model of the hydrogen atom, such that the negatively charged electrons restricted to atomic shells encircle a small positively charged atomic nucleus, where an electron hurdles amid orbits must be accompanied by an emitted or absorbed amount of electromagnetic energy. For every possible transition back to ‘ground state’, there exists a line in the emission spectrum corresponding to a specific frequency of emitted energy. These frequencies don’t have to fall in the visible region of the spectrum. Figure 7 (Fievez, Charles 1995) Helium May expect narrow, distinct spectral lines, physical mechanisms can broaden spectral lines. And the Doppler Effect which includes: Thermal motion, Rotation and Gas Turbulence Collision Broadening Magnetism Figure 8 (Fievez, Charles 1995) Emissions’ from an element gas Emissions from a single element in the gas discharge tube. Figure 9 (Hearn Shaw, J. B 1986) The Atomic Absorption Line. An absorption line is formed when an electron makes a transition from a lower to a higher distinct energy nature, with photons absorptions’ in the process. These immersed photons usually come from related continuum radiation and a spectrum will show a drop in the continuum radiation at the wavelength associated with the absorption. Reflection gratings Light dazzling from grooves A and B will obstruct constructively if the difference in path length is an integer number of wavelengths. The path difference is dsin + dsin (Such that d is the distance amid facets on the grating), Therefore; dsin + dsin = n  the grating equation n is the “spectral order” and quantifies how many wavelengths of path difference are introduced between successive facets or grooves on the grating) Figure 10 (Hearn Shaw, J. B 1986) The Grating Equation d (sin  + sin) = n A groove spacing d is a piece of the grating The angle of incidence, , is the same for all wavelengths The angle of diffraction, , must then be a function of wavelength Sin b = nl/d – sin a Reflection Grating Efficiency Gratings can be designed to concentrate most of the incident intensity into a particular order, by a process called “blazing”. This is a process where the grooves of a grating are cut so that the reflecting surfaces are at a certain angle, the blaze angle. About 90% of the incident light is diffracted preferentially into the first order. Disadvantage: One major limitation is that a grating diffracts light into many orders; one order contains only a fraction of the light Mathematica with ROOT Mathematica with ROOT imports data into Mathematica by linking to the concern libraries with MATHLINK It capable of dealing with all of the commonly used data generated by the large Physics and Astronomy community that has adopted the concern technologies. In plots below, in plots below, I checked gain balancing layers of 2 calorimeters on either side of the ATLAS collision point 280 m apart. Use of Mathematica works because like Paired Histogram it turns up when you need them. Working with Mathematica because things like “Paired Histogram” turn up when you need them. In plots below I am checking gain balancing in layers of 2 calorimeters on either side of the ATLAS collision point, 280 m apart. Matrix and vector operations often useful in data reconstruction. Makes for readable code (last line) Conclusion Astronomical spectroscopy is a stool that must sit on three legs for it to be a useful: simply taking data with sufficient counts and resolution is not enough. One has to carefully think through the calibration requirements of the data as needed by one’s program, and one must perform the reductions in such a way that honors the data. Quantitative quick-look at the telescope is essential for the process. Many authors knowledge of spectroscopy is what it is due to contact with many individuals over the years, and in particular the authors want to acknowledge the influence of some few authors with constructive comments were made on parts or the whole of a draft of this chapter. Works Cited Thackeray, A. Astronomical spectroscopy. New York: Macmillan, 1961. Print Kitchen, C. Optical astronomical spectroscopy. Bristol: Institute of Physics Pub., 1995. Print. Fievez, Charles. Workshop on Laboratory and Astronomical High Resolution Spectra: held in Brussels, Belgium 29 August-2 September 1994 in honor of the 150th birthday of Charles Vievez [i.e. Fievez] (1844-1890), the pioneer of astronomical spectroscopy in Belgium. San Francisco: Astronomical Society of the Pacific, 1995. Print. Hearn Shaw, J. B. The analysis of starlight: one hundred and fifty years of astronomical spectroscopy. Cambridge shire: Cambridge University Press, 1986. Print. Read More