Tag Archives: astronomic spectroscopy

Annie Jump Cannon: the legend behind stellar classification

It is striking that today, we can not only discover but even classify stars that are light-years from Earth — sometimes, even billions of light-years away. Stellar classification often uses the famous Hertzsprung–Russell diagram, which summarises the basics of stellar evolution. The luminosity and the temperature of stars can teach us a lot about their life journey, as they burn their fuel and change chemical composition.

We know that some stars are made up mostly of ionised helium or neutral helium, some are hotter than others, and we fit the Sun as a not so impressive star compared to the giants. Part of that development came from Annie Jump Cannon’s contribution during her long career as an astronomer. 

The Hertzsprung diagram where the evolution of sun-like stars is traced. Credits: ESO.

On the shoulders of giantesses

Cannon was born in 1863 in Dover, Delaware, US. When she was 17 years old, thanks to her father’s support, she managed to travel 369 miles all the way from her hometown to attend classes at Wellesley College. It’s no big deal for teens today, but back then, this was an imaginable adventure for a young lady. The institution offered education exclusively for women, an ideal environment to spark in Cannon an ambition to become a scientist. In 1884, she graduated and later in 1896 started her career at the Harvard Observatory.

In Wellesley, she had Sarah Whiting as her astronomy professor, who sparked Cannon’s interest in spectroscopy:

“… of all branches of physics and astronomy, she was most keen on the spectroscopic development. Even at her Observatory receptions, she always had the spectra of various elements on exhibition. So great was her interest in the subject that she infused into the mind of her pupil who is writing these lines, a desire to continue the investigation of spectra.”

Whiting’s obituary in 1927, Annie Cannon.

Cannon had an explorer spirit and travelled across Europe, publishing a photography book in 1893 called “In the footsteps of Columbus”. It is believed that during her years at Wellesley, after the trip, she got infected with scarlet fever. The disease infected her ears and she suffered severe hearing loss, but that didn’t put an end to her social or scientific activities. Annie Jump Cannon was known for not missing meetings and participating in all American Astronomical Society meetings during her career.

OBAFGKM

At Radcliffe College, she began working more with spectroscopy. Her first work with southern stars spectra was later published in 1901 in the Annals of the Harvard College Observatory. The director of the observatory, Edward C. Pickering chose Cannon as the responsible for observing stars which would later become the Henry Draper Catalogue, named after the first person to measure the spectra of a star. 

Annie Jump Cannon at her desk at the Harvard College Observatory. Image via Wiki Commons.

The job didn’t pay much. In fact, Harvard employed a number of women as “women computers” that processed astronomic data. The women computer at Harvard earned less than secretaries, and this enabled researchers to hire more women computers, as men would have need to be paid more.

Her salary was only 25 cents an hour, a small income for a difficult job to look at the tiny details from the spectrographs, often only possible with magnifying glasses. She was known for being focused (possibly also influenced by her deafness), but she was also known for doing the job fast. Simply put,

During her career, she managed to classify the spectra of 225,000 stars. At the time, Williamina Fleming, a Scottish astronomer, was the Harvard lady in charge of the women computers. She had previously observed 10,000 stars from Draper Catalogue and classified them from letters A to N. But Annie Jump Cannon saw the link between the stars’ temperature and rearranged Fleming’s classification to the OBAFGKM system. The OBAFGKM system divides the stars from the hottest to the coldest, and astronomers created a popular mnemonic for it: “Oh Be A Fine Guy/Girl Kiss Me”.

Legacy

“A bibliography of Miss Cannon’s scientific work would be exceedingly long, but it would be far easier to compile one than to presume to say how great has been the influence of her researches in astronomy. For there is scarcely a living astronomer who can remember the time when Miss Cannon was not an authoritative figure. It is nearly impossible for us to imagine the astronomical world without her. Of late years she has been not only a vital, living person; she has been an institution. Already in our school days she was a legend. The scientific world has lost something besides a great scientist.”

Cecilia Payne-Gaposchkin in Annie Jump Cannon’s obituary.
Annie Jump Cannon at Harvard University. Smithsonian Institution @ Flickr Commons.

Annie Jump Cannon was awarded many prizes, she became honorary doctorate of Oxford University, the first woman to receive the Henry Draper Medal in 1931, and the first woman to become an officer of the American Astronomical Society. 

Her work in stellar classification was followed by Cecilia Payne-Gaposchkin, another dame of stellar spectroscopy. Payne improved the system with quantum mechanics and described what stars are made of

Very few scientists have such a competent and exemplary career as Cannon. Payne continued the work left from Cannon, her advisor, Henry Norris Russell, then improved it with minimum citation. From that, we got today’s basic understanding of stellar classification. Her beautiful legacy has been rescued recently by other female astronomers who know the importance of her life’s work.

First remote reconnaissance of another solar systems reveals unlike “any other known object in our Universe”

Researchers have for the first time conducted a remote reconnaissance of a distant planetary system with a new telescope imaging system.

Peeking at other planets

reconnaissance

Project 1640 is a dedicated high contrast imaging program at Palomar Observatory with the goal of obtaining images and spectra of brown dwarfs and planetary mass companions to nearby stars. The solar system they analyzed is 128 light years away, and has four red exoplanets; a detailed description of the planets was published in the Astrophysical Journal, showing what an unbelievable diversity of planets our galaxy hosts.

“An image is worth a thousand words, but a spectrum is worth a million,” said lead author Ben R. Oppenheimer, associate curator and chair of the Astrophysics Department at the American Museum of Natural History.

Spectroscopic measurements

spectroscopy1Oppenheimer is the main investigator working on the project. He explained that the planets orbiting the star in case, but until now, the star’s bright light overwhelmed previous attempts to study the planets with spectroscopy. Simplistically put, spectroscopy studies how white light is split into its constituent wavelenghts, much like when it passes through a prism; it’s very useful in such studies, because every chemical element has its unique spectroscopic signature, and if the conditions allow it to be applied properly, the technique can reveal the chemical composition of a planet’s atmosphere.

“In the 19th century it was thought impossible to know the composition of stars, but the invention of astronomical spectroscopy has revealed detailed information about nearby stars and distant galaxies,” said Charles Beichman, executive director of the NASA Exoplanet Science Institute at the California Institute of Technology. “Now, with Project 1640, we are beginning to turn this tool to the investigation of neighboring exoplanets to learn about the composition, temperature, and other characteristics of their atmospheres.”

With this new system, the conditions were just right, allowing a fantastic observation of the planets orbiting HR 8799.

“It’s fantastic to nab the spectra of four planets in a single observation,” said co-author Gautam Vasisht, an astronomer at the Jet Propulsion Laboratory.

Unexpected results

spectroscopy 2

The results were very strange – unlike anything astronomers were prepared for.

“These warm, red planets are unlike any other known object in our universe. All four planets have different spectra, and all four are peculiar. The theorists have a lot of work to do now.”

The first anomaly that strikes the eye is the apparent chemical imbalance. From what we know of basic chemistry, ammonia and methane should naturally coexist in varying quantities unless they are in extremely cold or hot environments. However, at temperatures just over 700 degrees Celsius (1340 degrees Fahrenheit), which are “lukewarm” by astronomic standards, all the planets either have methane or ammonia, with little or no signs of their chemical partners.

The planets are also surprisingly red – emitting longer wavelengths of light, than celestial objects with similar temperatures. The most likely explanation for this phenomena is a patchy cloud covering all the planets.

“The spectra of these four worlds clearly show that they are far too toxic and hot to sustain life as we know it,” said co-author Ian Parry, a senior lecturer at the Institute of Astronomy, Cambridge University. “But the really exciting thing is that one day, the techniques we’ve developed will give us our first secure evidence of the existence of life on a planet outside our solar system.”

A bright future

Aside from the unquestionable value of this particular study, the system has proven its worth and now, researchers will definitely want to take a glance at other solar systems, perhaps some which are more likely to harbor life.

“Astronomers are now able to monitor cloudy skies on extrasolar planets, and for the first time, they have made such observations for four planets at once,” said Maria Womack, program director for the Division of Astronomical Sciences at the National Science Foundation. “This new ability enables astronomers to now make comparisons as they track the atmospheres, and maybe even weather patterns, on the planets.”

The fact that all these planets were different also shows that the technique works in a number of environments, bringing even more hope to the table.

“The variation in the spectra of the four planets is really intriguing,” said Didier Saumon, an astronomer at Los Alamos National Laboratory who was not involved in this study. “Perhaps this shouldn’t be too surprising, given that the four gaseous planets of the solar system are all different. The hundreds of known exoplanets have forced us to broaden our thinking, and this new data keeps pushing that envelope.”