Presentation on theme: "General Astronomy Spectral Classes. Spectroscopy Although astronomy has been practiced for thousands of years, it consisted mostly of observing and cataloguing."— Presentation transcript:
General Astronomy Spectral Classes
Spectroscopy Although astronomy has been practiced for thousands of years, it consisted mostly of observing and cataloguing the motions of stars. The use of spectroscopy to determine the properties of stars (c.a. 1814) allowed astronomers to investigate the the stars scientifically. The solar spectrum
Spectroscopy In 1814, Joseph Fraunhofer catalogued 475 sharp, dark lines in the solar spectrum. Discovered but misinterpreted in 1804 by William Wollaston Spectrum was obtained by passing sunlight through a prism
Spectral lines The wavelength of one particular line in the solar spectrum (at 589 nm) was found to be identical to the wavelength emitted by sodium (for example when salt is sprinkled on a flame). Sodium D-line
What elements are present in the Sun? Example: the solar spectrum
Balmer lines Example: the solar spectrum What elements are present in the Sun? α
NaD Example: the solar spectrum What elements are present in the Sun?
Ca H+K Example: the solar spectrum What elements are present in the Sun?
So: the Sun is mostly calcium, iron and sodium?? No! Not quite that simple…
Spectral Classification In 1885, E. C. Pickering, Director of the Harvard College Observatory, began the first extensive attempt to classify the stars spectroscopically. He hired many women as "computers" to handle the complex data reduction. He paid them 50 cents to the dollar, but he paid them. Many of these women became recognized members of the astronomical community This effort culminated in the Henry Draper Catalog of 1924 which lists the spectral classifications of over 250,000 stars
The Harvard Computors
The Harvard Computors One of the more notable ‘computors’ (not shown here since she died in 1911) was Wilhelmina Fleming. Fleming was placed in charge of dozens of women hired to do mathematical classifications and edited the observatory's publications. Fleming moved from Scotland to Boston with her husband, Once there, she and her child were deserted. She found work as a maid in the home of Professor Edward Pickering. Pickering became frustrated with his male assistants at the Harvard College Observatory and, legend has it, famously declared his maid could do a better job. Turns out she could. In 1881, Pickering hired Fleming to do clerical work at the observatory. While there, she devised and helped implement a system of assigning stars a letter according to how much hydrogen could be observed in their spectra. Later, Annie Jump Cannon would improve upon this work to develop a simpler classification system based on temperature. In nine years, she catalogued more than 10,000 stars. During her work, she discovered 59 gaseous nebulae, over 310 variable stars, and 10 novae and 222 variable stars.
"Computing" in 1912
Annie Jump Cannon Born: Dover, Delaware, December 11, 1863 Died: Cambridge, Massachusetts, April 13, 1941 She became the world's expert in classifying stars. She assigned over a quarter million stars to their place in the great spectral catalog: the Henry Draper Catalog. She discovered 5 novas and more than 300 variable stars Her Harvard classification is still used today. She became curator of the Observatory in She received a permanent position there in She was the first woman to receive a doctor of astronomy degree from Groningen University (1921). She received an honorary degree from Oxford in She won several prizes. In her honor the American Association of University Women presents the Annie J. Cannon Award each year to a woman beginning her astronomical career. In 1923 she was voted one of the twelve greatest living American women. In 1931 she received the Draper Award from the National Academy of Sciences.
Spectral Classes Subdivisions are indicated by a number 0-9 Such that A0 is close to B9 and A9 is close to F0 There are additional classes: W, P, N, R, S, L, T representing rare (or new) types
Mnemonics It is somewhat traditional to learn the mnemonics for the spectral classes Oh Be A Fine Girl, Kiss Me Oh Brother, Another F Grade Kills Me Our Bill, Arkansas’ Finest Governor, Kissed Many Only Bungling Astronomers Forget Generally Known Mnemonics Oh Brutal And Fearless Gorilla, Kill My Roommate And my personal favorite, Only Boys Accepting Feminism Get Kissed Meaningfully Oh Brother, Astronomers Frequently Give Killer Midterms
Extending the Mnemonic Obese Balding Astronomer Found Guilty Killing Many Reluctant Nonscience Students Oh Be A Fine Girl, Kiss Me Right Now (Smack) Oh Brutal And Fearless Gorilla, Kill My Roommate Next Saturday Adding more is up to your imagination! But what about: OBAFGKMRNS or WOBAFGKMLT ??
Naos Alnilam Sirius Canopus Capella Arcturus Betelgeuse Mira
Compare the Star to the Standard
Luminosity Classes Class Description Relative Brightness Examples Ia Most Luminous Supergiants x Lsun Rigel (B8) Ib Luminous Supergiants x Lsun Betelgeuse(M3); Antares(M1) II Bright Giants 1000 x Lsun Adara(B2);Sargas(F1) III Normal Giants 100 x Lsun Arcturus(K2);Aldebaran(K5) IV Subgiants 10 x Lsun Acrux(B0.5) V Dwarfs 1 x Lsun Vega(A0);Alpha Cent.(G2) The Sun is classified as a G2 V star
Luminosity Classes The luminosity class is related to the width of the spectral line