IRC+10216 returns: “Leave me alone!”

Following the angry statements made last summer in a well-known star celebrity program asking for respect for their intimacy, the IRC+10216 circumstellar envelope and her partner, CW Leonis, offer new exclusive statements.

Large-scale structure of the IRC+10216 circumstellar envelope

“I love CW Leonis, not because she’s rich -in carbon-.  We are in a moment of maturity and we want to enjoy the years that remain,” confesses the IRC+10216 envelope, very close to its starmate.

From her side, the evolved star states: “I know that we are special, but that is no reason for ALMA to continue to be a pin in the neck. What does it matter if we have a peculiar distribution of CH3CN?”

For those who are not aware this hot topic (quite literally), we should remember that IRC+10216 and CW Leonis maintain a very close relationship. Last July they were caught in fraganti by the powerful paparazzi (or, rather, paparazza) of the stars, ALMA [1].

In those “stolen” photos, ALMA allowed a group of researchers (very snoopers) to determine the distribution of SiS, SiO and SiC2 in IRC+10216.

She didn’t stop there, and she now reveals that, at the time, she also discovered something unexpected: the peculiar distribution of CH3CN (known as acetonitrile).


What we thought we knew

Until now, the chemical structure of carbon-rich evolved star envelopes was thought to be well known. It was described mainly by the action given in two scenarios: one, located in the warm and dense surroundings of the star, in which we find a chemical balance that allows the formation of stable molecules, and another, located in the outer layers of the envelope, in which, due to the penetration of ultraviolet photons, radicals and more exotic species are formed. 

However, these last few years have been disconcerting, as aspects that do not fit in these scenarios have been discovered [2].

The latest “photos” made public by ALMA indicate that CH3CN is not formed far, but in the inner regions of the envelope with much greater abundances than predicted by chemical balance [3].

Most of the emission is distributed as a hollow shell located just 2 arcseconds from the star (which, over astronomical distances, and for the case at hand, is very little). What catches the eye is that this spatial distribution is much more different from those found to date in this source for other molecules.

In fact, the standard chemical models of IRC + 10216 predict that most CH3CN molecules should be present at a distance of 15 arcseconds from the star.

Is it possible that phenomena related to dust grain condensation or the action of interstellar ultraviolet photons (capable of passing through our lumpy envelope) are reaching chemical equilibrium zones? Or maybe it is related to the non-uniform structure of IRC+10216, as it has gaps, arches and areas where matter accumulates that could explain this mystery.

IRC+10216 and CW Leonis say they don’t know anything about acetonitrile. “Let it get distributed as it pleases, of course. And if I catch ALMA again sticking her nose in our private lives, we’re going to get into hot water. We have left the matter in the hands of our lawyers.”

For Marcelino Agúndez, one of the “snoopers” researchers who has worked on this topic, from the Molecular Astrophysics Group of the Institute of Materials Science of Madrid (CSIC), “IRC+10216 does not know where she is getting into. Why CH3CN and no other molecular species? She will have to give a lot of explanations. And not because we’re interested in her private life, that’s not what it’s about. They’re hiding something and sooner or later everything will come to light.”

We said it last summer: maybe there’s a companion star orbiting CW Leonis. As this ends up being true, the scenes in “Save Me from Star” will give enough material to create a Youtube channel.


[1] The use of millimeter and submillimeter interferometers such as ALMA, able to investigate the distribution of different molecules in the inner regions of the circumstellar envelopes, is a very promising tool to reveal the role of the processes outside the thermodynamic balance that take place in these inner regions. These results come from data obtained in ALMA Cycle 0, with observations in band 6 of rotational transition J = 14-13 of CH3CN in IRC+10216.

[2] The most prominent examples are the detection of hot water vapour in IRC+10216 and other carbon-rich envelopes, as well as the observation of HCN in oxygen-rich envelopes, NH3 in carbon and oxygen-rich envelopes, and PH3 in IRC + 10216.

[3] Maximum s abundance of ~ 0.02 molecules per cm-3 to 2 arcseconds of the star are reached.

More information

Paper: “The peculiar distribution of CH3CN in IRC+10216 seen by ALMA” (DOI: 10.1088/0004-637X/814/2/143), Astrophysical Journal (ApJ)


Image 1: Large-scale structure of the IRC+10216 circumstellar envelope, seen through the brightness of the carbon monoxide (CO) J=2-1 line. Observations have been made with the radio telescope IRAM 30m (Granada) and are described in this article (Cernicharo et al 2015, A&A, 575, A91).

Image 2: Spacefill model of acetonitrile. Credits: Benjah-bmm27, wikipedia.


IRC+10216 time-lapse:

“The animation to the left cycles back and forth over about 3 years of time-lapse images. The motion of the clumps and plumes of dust, which are glowing hot here in the inner regions near the star, can be seen as a sort of “breathing” in the movie. As the dust flows out from the star, it eventually disperses into the galaxy, finding its way into big clouds which may, in due time, collapse again to form a new generation of stars (see the young star images). What is crucial, however, is that this new generation of stars will be formed from material with a different chemical composition, because the outflows from stars like IRC +10216 contain elements heavier than hydrogen and helium, elements like carbon, nitrogen, iron, silicon. Indeed if it weren’t for these dying stars enriching the chemistry of the matter in the galaxy, there would be no rocky planets, no metals, and no life. Most of the matter which forms every human body, if you go back a few billion years, must have been part of the shroud of a dying star just like this one”.

Credits: Peter Tuthill, Australian Research Council, US National Science Foundation Stellar Astronomy and Astrophysics Program.

Originally published in Spanish on the Naukas website: Vuelve IRC+10216: “¡Que me dejéis en paz!” (2016/02/15).