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).

IRC+10216 asks for respect for her privacy

In statements made to “The Life of the Stars”, the hottest “celebrities” program of the moment, the IRC+10216 circumstellar envelope has declared to be fed up with being persecuted by the paparazzi.

Distribution of matter around IRC+10216.

It’s been a few years since IRC+10216 rose to fame for going through a rather tumultuous moment in her life. However, in the latter stages, she confesses to being already very fed up with paparazzi’s persecution, who insist (in a way that becomes strenuous) to make known every detail of her daily existence. “I’m especially tired of such an ALMA, it doesn’t leave me alone,” she says angrily. 

Apparently, such “ALMA” has penetrated its intimacies to limits that exceed molecular sizes. Readers of heart magazines and social media users have made multiple comments about it, even with sometimes unwise tweets. “She is dangerously close,” said Luis Velilla (who is causally an astrophysicist and studies stars of this kind) after learning of her statements and her exhausting. Other tweets say “That happens to you for going star” or “as an audience, we don’t like to stay on the surface, we like to go beyond the envelope”.

ALMA, the “paparazzi” of the coldest stars

We have contacted ALMA, the paparazzi of the coldest stars, to find out her opinion. “I was working on cycle zero, which was a bit like my baptism of fire, and I gave to look closely at the celebrity I had closest. Others are dedicated to hot stars. I’m more into evolved, colder stars, who have a lot to tell but who hide their intimacy insistently. It was an impressive challenge for me. It’s not my fault she’s around and she’s a (role) model.”

The last assault on her intimacy perpetrated by ALMA and made public has been the one that has revealed  in detail how silicon is distributed in IRC+10216.

How did this happen?

In the spring of 2012 IRC+10216 was in her things when she realized she was being watched. She had been of interest to the pink press before. But this time it was different. ALMA’s ability to get “to the kitchen” was impressive. As if it were an impressive telephoto lens, ALMA draw with unprecedented precision the map of the distribution SiS, SiO and  SiC2  in the envelope of  this evolved star [1].

For us, who are very gossipy, this has been a real bomb, since knowing the inner parts of IRC+10216 in such detail is very revealing: in particular, the lines of high vibrational levels [2] of SiS come from a very warm region, an area very close to the star with which IRC+10216 maintains a special relationship. This is CW Leonis, who ended up making these statements:

“Yes, IRC+10216 and I have a very close relationship since I reached mature age. This is what happens to evolved stars: we eject the material to the outside in the form of layers. I will not deny it: something special has been born between us. My envelope and I are very close.”

This is not dirty laundry, this is molecules

Penetrating IRC+10216 to the limits with CW Leonis, as if it were the layer of an onion, we stumbled upon SiC2, but this molecule mysteriously disappears as we walk away to, oh surprise, reappear in a thin layer quite far from the star.  This may be due to the capabilities of ALMA [3].

As for SiO, it has a certain extensive and elongated structure. What could this be about? Explaining elongation is very speculative, but it gives rise to interesting ideas.

First, it could be the presence of a dust “belt” in the direction of elongation. This could cause more gas to form due to increased density in that area. Or, maybe, there is a companion star orbiting CW Leonis. This companion star could also create a preferred direction (the plane of the orbit) for material accumulation and increased density, favoring molecular formation. Although it could also be a molecular jet. For now, it’s all assumptions.

For ALMA this has just begun: “I am now finishing cycle two. If in cycle zero I was learning, now I’m taking a wagon: I’ve learned to use my tools and now there’s no one to stop me.”

IRC+10216 has stated that it will continue to grant exclusives as long as the privacy of its relationship with CW Leonis is respected (on the possible companion star she said not much, but it will undoubtedly be another of the hot topics of the “stellar summer”). The most chic community looks forward to news about this relationship that so many articles are generating in the pinker press (scientific, of course).

More information

Paper: “Si-bearing molecules toward IRC+10216: ALMA unveils the molecular envelope of CW Leo” (DOI: 10.1088/2041-8205/805/2/L13).


[1] Detailed maps of the SiS, SiO and SiC2 distribution have been carried out in IRC+10216. In particular, rotational transitions were observed and not only in the fundamental vibrational state, as the detected even SiS rotational transitions of high vibrational levels (v-7) and tentatively (v-10).

[2] Molecules have different energy levels: electronic, vibrational and rotational. Because the energy is quantized, we can know what kind of transition has taken place when a molecular species is excited or deexcited. Within a particular electronic state, the molecule can reach different types of vibrational states (those produced by the vibration of the atoms that make up the molecule) and, in turn, within the same vibrational state, the molecules rotate, producing a rotation spectrum that can be detected with radio telescopes in the domain of millimeter and submillimeter waves.

[3] There is some loss of flow (emission) in the outer thin layer because it has a very large size. This is because in ALMA (and any other interferometer) exists what is called an MRS (Maximum Recoverable Scale), the maximum recoverable scale. This means that any actual structure that is larger than a given formula is filtered and we lose much of its emission.


Image 1: This image shows the central section of a series of images that, as in a scan, allow us to distinguish the distribution of matter around the star IRC+10216. The data for composing this image has been obtained by the IRAM 30m telescope and was developed for the article Molecular shells in IRC+10216: tracing the mass loss history“.

Image 2: ALMA, the “paparazzi” of the coldest stars. Credit:  ESO/B. Tafreshi  (

Originally published in Spanish on the Naukas website:  IRC+10216 pide respeto a su privacidad (2015/07/16).

Twenty years is nothing (for silicon carbide)

Gardel’s tango “Volver” sounds, the one that I like so much and to which I have resorted on occasion for its temporal implications, and I arrive at that part in which he sings that “twenty years is nothing”.  And hearing it I can’t help but remember the SiCSi molecule and silicon carbide (SiC, not to be confused with  sic). All because, in the 1990s, scientists were already talking about SiCSi as a missing link in the formation of silicon carbide and that there should be a lot in the most intimate and hidden regions of carbon-rich dying star envelopes. But it took twenty years to be able to confirm this by astronomical observations.

Circumstellar enveloppe IRC+10216

The SiCSi molecule is formed by two silicon atoms and one carbon atom. The fact that it has been called a ‘missing link’ is simple, although we have to explain it step by step.

For starters, we go back to our fetish envelope, which is providing a huge amount of information to astrochemists. We’re talking about the envelope of the star CW Leonis, also known as IRC+10216. Let us remember that it is an evolved star, a star that has begun the final phase of its life, ejecting into the environment the matter that composes it in the form of layers. At the end of its life it will form a planetary nebula and, at its center, there will be a white dwarf star. But there´s still a long way to go to reach that point.

About 400 light years from us, this star is one of the brightest infrared sources in the sky and, thanks to its proximity, we can study its envelope in great detail (and more since we have tools and data with Herschel and ALMA). IRC+10216 has been found to be exceptionally rich in molecular species (in fact, half of the known interstellar and circumstellar species have been observed in this carbon-rich envelope). But astrochemistry has an interdisciplinary way of working: observations are not enough; you have to corroborate the information in a laboratory.

The laboratory

Before interpreting astronomical observations, astrochemistry looks for answers in laboratories. This is where they work to characterize molecular species and chemical processes, emulating the conditions that occur in very specific environments (such as the envelopes of evolved stars or the interstellar medium).

Experts had been trying to “catch” the SiCSi molecule for many years, but it took a long time. After numerous attempts, McCarthy et al. (2015, Harvard University) managed to synthesize and characterize it in the laboratory, allowing the community to confirm that what was seen in the astronomical  observations  was, indeed, the molecule SiCSi. It was finally possible to put a name to those lines obtained by the team of astronomers of Astromol/Nanocosmos: in total,  112 lines of this molecule in the spectrum of IRC + 10216 using data from the  IRAM 30m radio telescope  [1].

By obtaining such an accurate spectroscopic characterization, it was possible to validate the hypothesis that this molecule is abundant in this type of environment, where it is very likely to play a fundamental role in the early stages of formation of silicon carbide (SiC) powder grains. However, many unknowns remain about that role.

How are dust grains formed?

We know that dust grains, an ubiquitous component in the interstellar medium of galaxies, are synthesized mainly in two types of sources: in the internal winds of AGB stars (Asymptotic Giant Branch) [2] and in the ejection of massive stars when they explode as supernovae.

In supernovae different types of dust can form depending on the degree of enrichment in heavy elements, although the effectiveness of dust formation in supernovae is still a matter of debate (in fact, recent studies with the Herschel Space Telescope suggest that the masses of dust formed are much greater than previously thought).

The formation of dust grains can be simplified by explaining it as a two-stage process: first the “seeds”, called nucleation seeds, are formed from gas-phase species composed of chemical elements of a high refractory character. When we talk about refractory character we refer to those chemical elements that, below a certain temperature (the higher the temperature the greater the refractory character), tend to disappear from the gas phase and participate in the formation of solid condensates.

The second stage involves the growth of the grain: on the nuclei formed, compounds of a certain refractory character are condensed (in theory, less refractory than the elements that have formed the nucleus). That is, after forming a small nucleus, atoms and molecules are glued to it.

There are still many mysteries in this sequence of events, starting with the fundamental step of the formation of the seeds of nucleation, in which simple species in the gas phase are added to form nanoparticles. In fact, that’s one of the goals of Nanocosmos – to recreate this process in a lab to learn more about how those dust grains are born.

Silicon carbide (SiC): grain versus molecule

Silicon carbide (SiC) grains are abundant in space. In fact, their presence in micrometeorites is proof of the importance of the chemistry of these compounds (SiC, Si2C and SiC2) in the environment of red giant stars [3].

That’s because micrometeorites are a repository of primordial matter, since we assume that these remains formed in the same molecular cloud from which the entire Solar System emerged. If that is the case, the primordial molecular cloud could, in turn, be made up of material ejected by a red giant star [3] into the interstellar medium. This would close, for now, the cycle of silicon carbide: from a dying star to the interstellar medium, where a cloud would form from which, in turn, stars would be born that would eventually die, either as supernovae or as red giant stars, and so on. But knowing the process does not explain how silicon carbide was born.

On the one hand, it would be logical to think that the molecular precursors from which these grains of silicon carbide are born were the gas-phase molecules of silicon carbide themselves, but that does not seem to be the case.

In fact, the gas-phase silicon carbide (SiC) molecule has been detected in the outer regions of the IRC +10216 envelope (and not in the inner ones). Therefore, if it is not in the internal ones, it does not participate in the formation of the grains. In contrast, in the inner layers, where the dust is formed, the most abundant molecules containing Si−C bonds are SiC2  and the newly discovered SiCSi.

Both molecules should play a key role in the formation of grains of silicon carbide (SiC) dust. Add to this the fact that the abundance of SiCSi decreases as we move away from the star, and the data suggest that these molecules could be progressively incorporated into silicon carbide grains as they move into a colder environment.

Further deepening in this process of birth and formation of silicon carbide grains will require high-resolution interferometric observations. We still don’t know how that nucleation seed is born, whether it’s silicon carbide or any other grain of dust. Again, laboratories and frontier projects such as Nanocosmos will help us to obtain more data to draw more clearly the path of the formation of the dust grains that populate the interstellar medium and that are so important in the process of star and planet formation. Perhaps, recalling Gardel again, we should not wait another twenty years to uncover this mystery.


[1] Nine of these lines have also been detected with the  Submillimeter Array (SMA).

[2] AGB stars are stars with masses less than 8 solar masses that are in their last evolutionary stages. Since the early twentieth century it has been known that, in the photospheres of AGB stars, there are molecules such as TiO, VO, ZrO, CN, C2 and C3, among others.

[3] The presence of silicon carbide in carbon-rich AGB stars was first confirmed in the 1970s.

Article based on astromol’s press release (in Spanish): “How silicon carbide is formed“.


– Paper: “Discovery of SiCSi in IRC +10216: A missing link between Gas and Dust Carriers of Si−C Bonds”


Image 1: Large-scale structure of the circumstellar envelope IRC+10216, seen through the brightness of the J=2-1 carbon monoxide (CO) line. The observations have been made with the IRAM 30m radio telescope (Granada) and are described in the article (Cernicharo et al 2015, A&A, 575, A91). The region in which the SiCSi molecule has been found and where the formation of the dust grains takes place corresponds to the innerst region.

Originally published in Spanish on the Naukas website:  Veinte años no son nada para el carburo de silicio (2015/06/16).