We are all stardust—carbon star LX Cygni provides insights on the chemical evolution of the universe

November 17, 2015 by Tomasz Nowakowski, Phys.org report
An image of LX Cyg and its surroundings, obtained with the 80cm telescope at the University of Vienna Observatory. Credit: Stefan Uttenthaler et al./University of Vienna.

(Phys.org)—A carbon star is a giant red star nearing the end of its life, with an atmosphere containing more carbon than oxygen. LX Cygni could be an interesting example of an object that is currently in the process of transitioning into a carbon star. An international team of astronomers, led by Stefan Uttenthaler of the University of Vienna, has recently published a paper on Arxiv describing LX Cygni as a new carbon star being born, that could help us collect substantial information regarding the chemical evolution of the universe.

"These are important to understand the of the universe, because most of the carbon in the universe is thought to come from just like LX Cygni," Uttenthaler told Phys.org.

Carbon, the fourth most abundant element in the universe, is the key component for all known life on Earth. It is assumed that if life exists somewhere else in the universe, it will also be carbon based.

"Carbon is a very important element because it is key to all forms of life as we know it. Most of the carbon in our bodies comes from an earlier generation of stars such as LX Cygni. We are literally stardust!" Uttenthaler added.

Uttenthaler and his colleagues noted that carbon stars are a special class of stars that have a that is distinct from that of other stars throughout the universe. In most stars, including our sun, oxygen is more abundant than carbon, as measured by the carbon/oxygen ratio. They underline the importance of the observations of LX Cygni as it is a rare case of a star enabling observations of in real time. The study of its general properties and evolution may lead to unique insights into the transition from oxygen rich to carbon-rich stars.

"These observations tell us quite something about stellar evolution because, if our interpretation of the observations is correct, it tells us something about how the short but decisive evolution from oxygen- to carbon-rich phase happens. Many stars in the are thought to go through this evolution and it is predicted by theory, yet few observations have really caught a star in the act of this evolution. We now have a glimpse at this phase, we can see stellar evolution in real-time," Uttenthaler said.

The researchers obtained optical high- and low-resolution spectra as well as mid-resolution infrared spectra to investigate LX Cygni's spectral features. These observations indicated a dramatic increase of the star's pulsation period in recent decades so the scientists concluded that LX Cygni appears to undergo an important transition in its evolution. They believe that is related to a process that brought up carbon from the interior of the star and a genuine abundance change happened.

Uttenthaler revealed that it must have happened quickly when compared to other processes in a star's lifetime.

"The whole process seems to have taken only some 30 years," he said.

Unfortunately, he admitted that it is not possible to determine precisely how fast it was because the star has received little observational attention in the past.

What is interesting is that LX Cygni's transition process may be already completed. The observations conducted in 2008, using NASA's Spitzer telescope, suggest that LX Cygni was a carbon star at that time. To resolve all the uncertainties, Uttenthaler's research team recommends that the community continues observing this star, most importantly to conduct observations in the mid-infrared and in the radio regime to study the dust and molecular composition of the circumstellar envelope of LX Cygni.

"From this, we would learn what the chemical composition and the mass-loss rate of the star was in the past, how the dust and molecular inventory of the star evolved over the past few thousand years. This would be extremely interesting to know!" Uttenthaler said.

Explore further: Fingerprinting the formation of giant planets

More information: LX Cygni: A carbon star is born, arXiv:1511.02159 [astro-ph.SR] arxiv.org/abs/1511.02159v2

The Mira variable LX Cyg showed a dramatic increase of its pulsation period in the recent decades and appears to undergo an important transition in its evolution. Aims: We aim at investigating the spectral type evolution of this star over the recent decades as well as during one pulsation cycle in more detail and discuss it in connection with the period evolution. Methods: We present optical, near- and mid-IR low-resolution as well as optical high-resolution spectra to determine the current spectral type. The optical spectrum of LX Cyg has been followed for more than one pulsation cycle. Recent spectra are compared to archival spectra to trace the spectral type evolution and a Spitzer mid-IR spectrum is analysed for the presence of molecular and dust features. Furthermore, the current period is derived from AAVSO data. Results: It is found that the spectral type of LX Cyg changed from S to C sometime between 1975 and 2008. Currently, the spectral type C is stable during a pulsation cycle. It is shown that spectral features typical of C-type stars are present in its spectrum from ~0.5 to 14 μm. An emission feature at 10.7 μm is attributed to SiC grains. The period of LX Cyg has increased from ~460 d to ~580 d within only 20 years, and is stable now. Conclusions: We conclude that the change in spectral type and the increase in pulsation period happened simultaneously and are causally connected. Both a recent thermal pulse (TP) and a simple surface temperature decrease appear unlikely to explain the observations. We therefore suggest that the underlying mechanism is related to a recent third dredge-up mixing event that brought up carbon from the interior of the star, i.e. that a genuine abundance change happened. We propose that LX Cyg is a rare transition type object that is uniquely suited to study the transformation from O- to C-rich stars in detail.

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2.5 / 5 (8) Nov 17, 2015
Should first indicate, mass, radius, and temperature before performing any the conclusion.
From the general rules of life star (WD) this star will live a long time. First, she is a dwarf and the young star, the other red stars are less likely to explode (cyclones are on the poles shallower and slower). If there is a slowing down of rotation, there must be a lowering of temperature. Lower temperatures (especially in younger star) means more complex elements.
Above all the data first.
4.3 / 5 (6) Nov 17, 2015
It's a giant, not a dwarf.
3.2 / 5 (9) Nov 17, 2015
Yeah, it's not a dwarf, but I'm not sure if wduckss really has a clue what that article was talking about anyway. It's not a young star either, and I have no idea what he meant by all that lower temperature and complex elements stuff. I'm kinda torn between wondering about the intent of his comment and translation problems in it.

I'll at least agree with him about his final comment, as I interpret it: Data is the king.
3 / 5 (6) Nov 18, 2015
In each article should specify more data, less speculation.
Red stars = lower temperatures (up to 5000 ° K). Height temperature is directly related to the presence higher elements. Lower temperatures = more higher elements (temperature decomposes more elements in the lower, naturally, without radiation, without fission).
The difference between the S and C stars (giant) is the speed of rotation around the axis (which pulls the the other data, larger the radius, a lower surface gravity ...) See: http: //www.svemir-ipaksevrti.com/Universe-and-rotation .html # causal relation The relation between a star and its temperature, gravity, radius and color
3.7 / 5 (6) Nov 18, 2015
The difference between the S and C stars (giant) is the speed of rotation around the axis (which pulls the the other data, larger the radius, a lower surface gravity
- Oh boy, this guy's ducks are definitely not in a row.

And the website he links to is pure hogwash.
3.4 / 5 (5) Nov 18, 2015
The difference between the S and C stars (giant) is the speed of rotation around the axis (which pulls the the other data, larger the radius, a lower surface gravity
- Oh boy, this guy's ducks are definitely not in a row.

And the website he links to is pure hogwash.

You must know your own language. W.Duckss derives from German language, meaning are not even similar.
The rules say it is allowed to attack, to comment (with the arguments) not on user name.

Betelgeuse T 3.140-3.641 Rotation 5 km / sec mass from 7.7 to 20 Radius 950-1200 surface gravity 0,5

Polaris: T 6.015 rotation 119 d masses 4,5 radius 46 ± 3 surface gravity 2.2
4.5 / 5 (8) Nov 18, 2015
@wdducks: "In each article should specify more data, less speculation."

Let us see you heed that yourself. Stop claiming inanities, find a book in star evolution and start to quote from that.

E.g. you are citing surface temperatures, but the core heat of stars are not enough to 'decompose' elements but the nuclei are produced by fusion (irrespective of rotation) and lasts *which is what the article describes*. "Once the hydrogen in the core of a star is nearly exhausted, almost all naturally occurring elements heavier than helium are created by stellar nucleosynthesis during the star's lifetime." "Almost everything about a star is determined by its initial mass". [ https://en.wikipe...iki/Star ]
3 / 5 (4) Nov 18, 2015
W.Duckss derives from German language...
- Tja, wenn es wie eine Ente aussieht, und wie eine Ente schnattert, was soll man denken?
3 / 5 (4) Nov 18, 2015

Quote can anyone who knows how to read.
The attached are the data and short analysis.

You enclose any fission, without traces of radiation, combustion, regardless of the mass, a static universe, although everything rotates, ... all without proof and possibilities of proving (only copying).

Analysis is only statistics that do not lie. Mass of small, medium and giants, red stars have a low temperature, slow rotation, a low surface gravity and larger radius. At the other end of the inverted data for white (blue) stars.
3.3 / 5 (7) Nov 18, 2015
wducks, you are VERY confused about the evolution of stars. Stars go through a series of changes as they grow older. Young stars burn hydrogen. Next comes helium. They don't start to produce large amounts of carbon until they are very old, and are nearing the end of their lives as stars. This happens the same for large, hot stars, as well as small, cooler stars. As far as we know, all stars produce carbon near the end of their lives.

Perhaps you are confused by the existence of second and third generation stars? Stars that are formed from the remains of a previous supernova will have heavy elements in them, but this is not due to anything happening inside the star itself, and it has little, if any effect on the life cycle of that star.

The so-called carbon stars they are talking about in the article above are simply old stars, which are getting near the end of a star's life cycle. They can be large or small stars.
2 / 5 (4) Nov 18, 2015
Yar, the space pyrates tells me of the cold white dwarf, yar, a diamond size o'earth! Untold riches to any grubby paw or claw that lays clam to it! Guarded by the space whale, t'is. Keep yer warp sails hot and your watchmen scared, or perish they say.
3 / 5 (4) Nov 19, 2015

Earth is not (even) nor a star and has more carbon from the star about which you speak.

Small stars are (the same as mid and Giants star) "cold", warm and hot, there is no difference.
If a star explodes (any size) and created by the most of the material the black hole, where material for the formation of the next star?
The processes do not take place in such a way.

Why did not you (with it) confused?

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