The IRAM 30m Summerschool 2019 will take place, from the 6th to the 13th of September, in Pradollano (near Granada, Spain). This year, one of the scientific talks will be given by one of our members, Guillermo Quintana-Lacaci, and it will be focused on Evolved Stars.
The 9th IRAM 30m summerschool will combine lectures on millimeter astronomy with observations using the 30m telescope.
Lectures will be given by experienced scientists and 30m observers, covering a range of topics, from comets and planetary atmospheres in the solar system to the study of the chemistry of interstellar clouds, low and high mass star formation, in the Milky Way, in nearby galaxies, and in ultra-luminous objects at high-redshifts.
These lectures will be complemented by shorter lectures on instrumentation, observing techniques, and data processing.
The contest ‘We are scientists, get us out of here!’ in its Spanish version has a winner: Miriam Garcia Santa-Maria, an astrophysicist member of our group and PhD student in the IFF (Instituto de Física Fundamental). She was the most voted scientist by the students of the 17 participating schools in the Zona CSIC, all of them in the villages of the Ciudad Ciencia net.
After two weeks answering questions through a chat, students have been able to know more about six scientists and their jobs, their lives and their expertise. 1972 young students, between 10 an d 18 years old, have participated, sending 1366 questions and having 95 text chats online. The ‘Zona CSIC’ received more participants than other zones of the contest.
Getting data from a telescope can be very exciting. Basically, because getting them and interpreting them is a whole process that can take several years… Since the observation program is designed, the time is requested, it is granted (or not), the observations are carried out, the data is obtained and, finally, the information is analyzed and extracted… the whole process is a marathon full of uncertainty and challenges.
Image 1: Red-green-blue image showing three different velocities of the gas associated with the heart of the Orion cloud.
Of course, it can be data from a ground-based telescope or a space telescope.
Or, as in our case, it can be both.
SOFIA: Ground or space telescope? Well, both!
We’re talking about a telescope installed in a modified NASA Jumbo 747 aircraft. It is called SOFIA (Stratospheric Observatory for Infrared Astronomy) and, at each observation, it takes flight to the stratosphere, about 13 km above sea level (a couple of km above commercial flights) and goes back down, perching at its Californian airport and returning home to rest.
Each observational flight lasts about 10 hours, and the data obtained are very important, among other things because, right now, there is no instrument outside the Earth (that is, above the atmosphere and its nefarious turbulence) that observes in the far infrared, a range of the electromagnetic spectrum critical to understand how stars form and interact with the interstellar medium.
With a mirror of 2.5 meters in diameter, SOFIA is the name of the whole set. And Javier R. Goicoechea says (I will introduce him in a moment) that it is impressive to see how the whole plane can tremble from the turbulence while the intelligent hydraulic structure that supports the telescope and its instruments compensates for those alterations and remains perfectly still (I would love to change myself for the instrument, I want one of those compensators for my air trips).
Image 2: SOFIA (The Stratospheric Observatory for Infrared Astronomy)
SOFIA is 80% NASA (which has built and operates the observatory) and 20% DLR (the German space agency).
For starters, getting a plane to fly with an impressive door open (yes, you read that right, open), is already quite a feat. That it does so, in addition, with a team formed by telescope and instrument of about 20 tons of weight, also has its complications.
But let’s get to deeper.
It turns out that Javier R. Goicoechea, senior scientist at the Institute of Fundamental Physics (IFF) of the CSIC, participates in an international team that studies the destructive effects of ultraviolet radiation and the strong winds emitted by young massive stars in the interstellar clouds where they are born. Last year the team obtained 10 observation flights in order to map the Orion cloud in the emission of ionized carbon, the brightest emission from interstellar gas. As he states, “SOFIA is like a space telescope, in the sense that it allows us to observe in the infrared above 99% of atmospheric water vapor, but after a night of observations, astronomers and telescope land on the ground to regain strength.”
Image 3: Javier R. Goicoechea (IFF-CSIC) in full flight and data collection. In the background is Jürgen Stutzki (University of Cologne, Germany), co-Principal Investigator of the GREAT instrument.
The results have been really amazing.
WHAT A PROGENY!Daughters eating parents.
As we have told in other articles, dense clouds of gas and dust are the birthplace of the most massive stars in the galaxy. The mass is concentrated, condensed, the reactions begin in the nucleus and… A star is born!
The more mass the star has, the more violent it is and the less time it will live. The fact is that we know that, in this area of Orion, there are very massive stars -the Trapezium cluster- that are “sweeping” the surrounding material, undoing the cloud that saw them born with their powerful stellar winds and their intense ultraviolet radiation. A kind of “parentophagy” (I know this word does not exist…).
The data obtained with SOFIA have revealed that this happens much earlier than previously thought. In just a few hundred thousand years the winds coming from the most massive star of the Trapezium have pierced the natal cloud, creating a huge bubble, whose expansion and movements have been revealed thanks to the 3D observations obtained (have I not said that an amazing 3D film has been made with the data?). A single star giving shape to one of the most observed and known regions of the sky.
What a blow.
Measuring speeds for the first time
The results obtained have given, for the first time (yes, we always say that because it is very cool in astronomy to say “as never before”, “for the first time”, “with an unprecedented resolution”, and again and again)… For the very first time a 3D map of the gas velocities in the studied area has been made. Thanks to the spectroscopy of very high spectral resolution, maps of the speed of the expanding gas bubble have been obtained, resulting in this amazing video:
A stellar wind created by a newborn star in the Orion Nebula is blowing a bubble — preventing more stars from forming nearby. Until now, scientists thought that other processes, like supernovae, were responsible for regulating forming stars. More: https://t.co/XsPFezRmsm#AAS233pic.twitter.com/jrVM8Uw2DS
In short. Everything is going faster than predicted, in every way. The young massive stars determine, much earlier than previously thought, the shape and evolution of the interstellar environment that saw them born, ravaging and cleaning, with their strong stellar winds, the entire region that surrounds them. That means they sweep away the interstellar material needed for the formation of new stars.
For Javier R. Goicoechea, “It is incredible that after more than 400 years observing the great Orion Nebula, we have now been able to understand that the winds coming from the most massive stars blow the surrounding cloud and give it that morphology so recognizable“.
Images
Image 1: Red-green-blue image showing three different velocities of the gas associated with the heart of the Orion cloud. The wind from the most massive stars has created a bubble (in black) and prevents the formation of new stars in its environment. At the same time, the wind sweeps the gas from the edges (in color), creating a shell of thin gas around the bubble and where perhaps a new generation of stars can form. Credits: NASA/SOFIA/Pabst et al.
Image 2: SOFIA (The Stratospheric Observatory for Infrared Astronomy) flying over the California sky. The telescope can be seen inside the open cavity at the rear of the aircraft. Credit: NASA/Jim Ross
Image 3: Javier R. Goicoechea (IFF-CSIC) in full flight and data collection. In the background is Jürgen Stutzki (University of Cologne, Germany), co-Principal Investigator of the GREAT instrument.
The discovery of the new NS+ cation, present in numerous astrophysical environments, confirmed with laboratory spectroscopy
NS+. Credits: KIDA, Kinetic Database for Astrochemistry.
A team of researchers, led by José Cernicharo (IFF-CSIC) has announced the detection in space of a new molecular species, identified from astrophysical data obtained with observations carried out with the IRAM 30m telescope.
Although nitrogen sulfide (NS) was first detected in space in 1975, the presence of its NS+ cation had not been discovered until now. A cation is an atom or molecule with a positive electric charge because it has lost electrons from its original endowment. In the case of NS+, the chemical models applied in this work indicate that it is formed by the reactions of the neutral atom N with the cation SH+ and that of the neutral atom S with the cation NH+.
The interesting thing about this work is not only the first detection of NS+ [1], but the discovery of its ubiquity and its presence in most astrophysical environments: it has been detected in cold and faint molecular clouds where there is still no activity of star formation, in somewhat denser clouds where matter begins to collapse and prestellar nuclei begin to be seen, and in clouds that are authentic stellar nurseries, where violent processes due to ultraviolet radiation from young stars and to jets of material ejected by the protostars [2] are already taking place.
A detective work confirmed in the laboratory
The gaseous phase chemistry of cold and dark clouds is mainly based on the reactions between ions (electrically charged molecules) and neutral molecules. However, ions (positively charged cations, or negatively charged anions) represent only a small percentage (about 15%) of the molecular species detected.
But if NS+ is present in so many astrophysical environments, why wasn’t it identified before?
Since astrochemistry has increasingly precise tools, we often talk about spectra with “forests of lines”, a deep collection of overlapping data that is difficult to discriminate. Where does one molecule end and another begin? If they have never been characterized before, if they have not been studied and checked against laboratory data or if their possible presence has not been theorized, it is very likely that they will remain anonymous, sometimes before our eyes.
In the words of José Cernicharo (Institute of Fundamental Physics, CSIC),“The detection of NS+ was a real work of “molecular detectives”. When we realized that in that observational data there was a pattern that was repeated, we started a search in which, first, we discarded various candidates.”
An in-depth understanding of how molecular spectroscopy works and interstellar chemistry were the tools that led the team to determine that the NS+ cation is the species most likely responsible for producing the lines found.
On the other hand, in astrochemistry there is a lot of laboratory effort whose purpose is to validate the results of the theoretical models and the data observed with the telescopes (in this case the IRAM 30m antenna, in Pico Veleta, Granada). To confirm that it was possible for NS+ to be in so many different environments, the “Laboratory of Atoms, Molecules and Lasers Physics” (CNRS and University of Lille, France) carried out several experiments to reproduce NS+.
The information obtained, applying spectroscopy techniques, corroborated full coincidences with both observational data and theoretical models: they had found a new molecular species in space.
Notas
[1] The NS+ cation has been completely characterized through three rotational transitions, one of them with hyperfine structure, distinctive of a molecule with an atom with spin 1.
[2] Although present in a wide variety of environments, it is apparently not in others such as, for example, the hots cores of Orion-KL or the evolved star IRC+10216.
More information:
This work has been presented in the paper Discovery of the ubiquitous cation NS+ in space confirmed by laboratory spectroscopy and its authors are J. Cernicharo (Molecular Astrophysics Group (ICMM-CSIC)/Molecular Astrophysics Group, Department of atomic, molecular and surface processes (IFF-CSIC), Spain); B. Lefloch (University Grenoble Alpes, France); M. Agundez (Molecular Astrophysics Group (ICMM-CSIC)/Molecular Astrophysics Group, Department of atomic, molecular and surface processes (IFF-CSIC), Spain); S. Bailleux (Laboratory of Atoms, Molecules and Lasers Physics, CNRS, University of Lille, France); L. Margulès (Laboratory of Atoms, Molecules and Lasers Physics, CNRS, University of Lille, France); E. Roueff (LERMA, Paris Observatory, PSL Research University, CNRS, University of The Sorbona, France); R. Bachiller (National Astronomical Observatory (OAN, IGN), Spain); N. Marcelino (Molecular Astrophysics Group (ICMM-CSIC)/Molecular Astrophysics Group, Department of atomic, molecular and surface processes (IFF-CSIC), Spain); B. Tercero (Molecular Astrophysics Group (ICMM-CSIC)/ National Astronomical Observatory (OAN, IGN), Spain); C. Vastel (IRAP, University of Toulouse, CNRS, UPS, CNES, France); E. Caux (IRAP, University of Toulouse, CNRS, UPS, CNES, France).
Artist’s impression of James Webb Space Telescope in space. Credit: STScI-JWST
After the Peer Review Panels and final review by the Space Telescope Science Institute (STScI) Director, the James Webb Space Telescope Proposal, led by Olivier Berne (IRAP-CNRS, France), “Radiative Feedback from Massive Stars as Traced by Multiband Imaging and Spectroscopic Mosaics” has been approved for the Cycle 1 Director’s Discretionary Early Release Science (DD ERS) Program with 27.8 hours of observation time.
Two members of the team are from our group: Javier R. Goicoechea and Emeric Bron.
A total of 106 proposals requesting 3683.4 hours of observations were submitted in response to the DD ERS Call and 13 Proposals for 460 Hours have been approved by the Director.
The proposal makes a strong case for the role and significance of interstellar photodissociation regions (PDR) observations with JWST, with a plethora of anticipated science-enabling products and templates for the community ahead of Cycle 2, while also anticipating a series of papers on the ERS data.
The JWST launch window is set for March to June 2019.
Congratulations on the success of the proposal and best wishes for your future participation in and contributions to the scientific program of JWST.
… and the loss of mass of the yellow hypergiant star IRC+10420
Why is there a seemingly empty area of the Hertzprung-Russell diagram? And why is it called a “yellow void”? And, while we are ai it… what is the Hertzprung-Russell or H-R diagram?
First of all, welcome to a report that is going to be totally yellow (but not yellow press, we leave that to IRC+10216).
I’m going to take it for a fact that you have no idea about astronomy. (If you already know what the H-R diagram is, you can go to the next heading: ‘The “yellow empty” area’).
The Hertzsprung-Russell diagram (yes, I know you can search for it on Wikipedia, but I’m going to explain it to you anyway) is a way to visually illustrate a set of star-related data, so that we can understand its distribution according to certain parameters. There are many types of diagrams, but the one that Hertzprung and Russell invented independently makes us see the distribution of the stars according to their brightness and temperature. It’s like taking all the stars in the Milky Way – imagine a bunch of colored marbles – and put them in a box distributed according to those parameters. We would see them classified into a single image, giving us an idea of how many of them are in each class.
Well, there’s supposed to be something yellow in one part of that box… And there isn’t.
The “yellow empty” area
In the H-R diagram there are two regions that have very few stars: the ‘Hertzsprung Gap’ and the Yellow Void. In the first, it is believed that the problem is that stars have not yet been observed at that stage because it is a rapid stage in the life of a solar-type star; in the case of yellow void, it is believed that there should be yellow hypergiants, but there is none.
Yellow hypergiant stars are a type of evolved massive star that have extreme initial masses and very high luminosities [1]. In fact, they are supposed to end up exploding as supernovae after going through several phases in which they lose a lot of mass.
The thing is these stars are very unstable. When, by the evolution of their characteristics (specifically, by the changes in their effective temperature), they are about to enter the ‘yellow void’ area of the diagram, they “bounce” and go back to an area where they appear as red… But how on Earth! What’s wrong with yellow hypergiants? Why don’t they step into that empty area (there is so many space!)?
Image 2: The yellow void. Illustration of the hypergiant star HR 8752 through the yellow void. The diagram shows the surface temperature of the star observed in the last 100 years. It increased from ~5000 to ~8000 degrees between 1985 and 2005, while the radius decreased from 750 to 400 times the radius of the Sun. Credit: A. Lobel ROB.
IRC+10420
There are two types of yellow hypergiant stars. The first are stars that are starting to age after finishing their main sequence, moving to the red supergiant phase (i.e., they do not yet have an envelope created by matter that they release into the environment when they start “dying”).
But our yellow hypergiants are of the second type, evolved stars with envelopes and large mass loss that go from the yellow supergiant phase to the WR (Wolf-Rayet) star phase. Afterwards, they will move to the blue luminous variable star stage, then to hydrogen-poor WR star and eventually explode like supernovae (to see it very clearly, go to “Stellar Evolution” of @molasaber).
IRC+10420 is a prototypical yellow hypergiant (located in the Aquila Constellation) that has already passed the red supergiant phase (in which they can lose up to half of their initial mass) and has evolved to higher temperatures in the H-R diagram [2].
The yellow void stage results in a series of episodes of mass ejection that occurs in the form of bursts. As a result, the star is surrounded by dust, so perhaps what is happening is that we cannot measure one of the parameters of the H-R diagram correctly because the effective temperature of the star, that is, the temperature of its detectable surface… can’t be detected!
Our yellow hypergiant is hidden behind the dust, so we see her as a reddish star. But the actual effective temperature continues to rise and a pseudo-photosphere that keeps them at the low temperature limits of the yellow void in the HR diagram is formed around the yellow hypergiant stars. As the ejected material is diluted in the outer area, we induce that at the end they will appear just beyond the high temperature limit of the yellow void. That’s why they look like bouncing off the diagram!
Therefore, the evolution of yellow hypergiants remains hidden until they become what has been called slash stars [3] (renamed by myself as oldyoung stars) and eventually enter the Wolf-Rayet phase.
The rich chemistry of this yellow hypergiant star
There is something important to keep in mind: these stars are aging, they are losing mass at an extremely high rate, they are ejecting matter to the medium at an incredible speed… [4] And all that matter is the one that feeds back the interstellar medium. Here we get to the heart of the matter: what we are interested in is knowing more about the chemical properties of circumstellar matter ejected by the most massive evolved stars. And studying their behavior helps us better understand the processes that occur before supernova explosions and determine when different species of molecules are formed.
Using the IRAM30m telescope, a team of astronomers, leaded by Quintana-Lacaci (CSIC), did an IRC+10420 probe confirming that the chemistry of this object is especially rich: they detected 22 molecular species in the circumstellar envelope of this object [5].
Although it is predicted that the mass ejections are huge in these objects, only three yellow hypergiants, IRC+10420, AFGL 2343 and IRAS 17163-3907, have shown molecular emission.
The expulsion of this material may also be explained in a similar way to that of ejections that take place in low-mass AGB stars, the small counterpart of massive stars, which also age by ejecting matter but do not end up bursting as supernovae. In this case, mass ejection is driven by radiation pressure in dust grains.
But this is not all: the ejections prior to the yellow hypergiant phase… are no longer part of the envelope around them. For Quintana-Lacaci “All the molecular material we observe had to be expelled only during the yellow hypergiant phase. Any gas expelled during the previous phase of red giant star would have been rapidly diluted in the interstellar medium and would have been photodissociatedby the ultraviolet radiation of the interstellar medium”.
Which means that there may be no stars in the “yellow void” of the diagram because they hide behind the dust they have recently ejected, while the dust they ejected in previous episodes has already become part of that interstellar medium composed of dust grains (1%) and gas (the remaining 99%).
Behold, we have a possible answer to that yellow void. Along the way, we seem to have learned things about huge stars who like to play hide-and-seek, hiding behind layers of dust and leaving an “empty space” in our knowledge. A void we strive to fill.
Notes:
[1] This one in particular has a brightness of L ~ 5 × 105L⊙ and an estimated initial mass of Minit ~ 50M⊙.
[2] In particular, the spectral type of IRC+10420 has changed from F8Ia (with an effective temperature of 6300K) to A5Ia (8300K) in just 20 years.
[3] Slash stars are massive, hot stars that have typical characteristics of both old stars (in this case Wolf-Rayet) and young stars (type O). Slash comes from the “/” symbol that is used to separate young star characteristics from old star characteristics (as happens, for example, in Ofpe/WN9 stars). I mean, they’re oldyoung stars.
[4] In particular, for the IRC+10420 yellow hypergiant, they detected a separate circumstellar envelope with an extension of 5×1017cm expanding at speeds of ~37 km/s. There are two episodes of strong mass ejection responsible of the formation of this circumstellar envelope, which occurred within 1,200 years and reached a mass loss rate of 3 ×10−4M⊙ yr−1.
[5] The team has conducted a survey of IRC+10420 at wavelengths of 1 and 3 mm, identifying 106 molecular emission lines from 22 molecular species: CO, 13CO, CN, H13CN, HCN, SiO, 29SiO, SO, SiS, HCO+,CN, HNC, HN13C and CS.
Image 2: The yellow void. Illustration of the hypergiant star HR 8752 through the yellow void. The diagram shows the surface temperature of the star observed in the last 100 years. It increased from ~5000 to ~8000 degrees between 1985 and 2005, while the radius decreased from 750 to 400 times the radius of the Sun. Credit: A. Lobel ROB.
Yes, may be this reminds you the lyrics of “Ultraviolet”, a song from U2 that fits perfectly with our topic. Let’s sing some astrochemistry.
Image 1: Orion Nebula.
The world of science often says that space is hostile, that it is very difficult to find complex molecules (even if there are). The fact is that one of the culprits of breaking bonds between atoms and leaving everything broken is ultraviolet radiation from stars, and in this case, the distant ultraviolet. But also, like Ying and yang, it may be responsible for liven up certain organic molecules.
Astrochemistry looks for those molecules and study their endurance and how they react. In this particular work, scientists have studied the molecular gas in space that is being strongly irradiated by ultraviolet rays. The team, led by Sara Cuadrado (ICMM-CSIC), has performed (the words in bold are explained below) a complete spectral survey of lines in the millimeter range using the IRAM30m telescope. This spectral survey (a kind of thorough review of that entire range of the electromagnetic spectrum) has been carried out at the edge of the photodissociation region of the Orion Bar, which is being irradiated by a very intense field of distant ultraviolet radiation.
But let us take it one step at a time.
Maybe you already know the Orion Barfrom other previous reports: it is located within the well-known Orion Nebula, about 1,300 light years from Earth, and is the closest massive stars formation region.
The energetic farultraviolet reaches this area of the Orion Bar. This ultraviolet range of light comes from young and massive stars that are forming nearby (the stars known by the name of the Trapezium) and emit much of their energy in this range of the electromagnetic spectrum. The far ultraviolet is responsible, in this case, for the photodissociation of the molecules.
The photodissociation region is the one in which ultraviolet light is dissociating, that is, separating the atoms of the molecules (although, at the same time, new bonds between atoms may be forming, creating new molecules). The photodissociation region of the Orion Bar is very special because, being “close”, we can study it in detail.
The millimeter range is the range of the electromagnetic spectrum that allows us to study cold areas of the cosmos. For an astronomer a “cold” environment is one in which the temperature does not allow us to observe it because it emits poorly and it is very difficult to detect objects. Infrared and millimeter help us “see” those cold objects.
Finally, the lines we are talking about are like fingerprints of chemical species. We detect them in space and they are reflected in lines like the ones I show you:
Image 2: Orion Bar Spectrum.
Well, despite the fact that the Orion Bar is a hostile environment where it was only expected to find very simple molecules, the observations show spectra with many lines (the team has detected more than 850!), of which about 250 correspond to complex organic molecules and related precursors [1]: methanol, formaldehyde, formic acid (the ants one), acetaldehyde, etc.
What does this mean?
La zona de la Barra de Orión sufre el castigo constante de la radiación ultravioleta emitida por estrellas masivas jóvenes del entorno. Por eso se pensaba que no podía haber complejidad química. Pero la hay. Y, aunque se desconocen los procesos por los cuales se forman estas especies descubiertas en el borde de la Barra, se han planteado varios escenarios que explicarían cómo se forman las moléculas orgánicas complejas halladas:
The Orion Bar area suffers the constant punishment of ultraviolet radiation emitted by young massive stars in the environment. That’s why it was thought that there could be no chemical complexity. But there is. And, although the processes by which these species discovered at the edge of the Bar are formed are unknown, several scenarios have been proposed that would explain the formation of the complex organic molecules found:
The first scenario would take into account new chemical reactions that only occur in the hottest gas and that have not yet been included in current theoretical chemistry models that try to reproduce the processes that occur in the interstellar medium.
In the second, complex organic molecules would be produced on the hot surfaces of the nearly bare grains (without ice sheets [2]).
And, in the third scenario, the dynamics of the photodissociation regions (something like currents of motion within the cloud) would cause complex organic molecules or their precursors, which have formed in the icy mantles of dust grains inside the molecular cloud, to sublimate and reach the edge of the Bar.
In short: the presence of complex organic molecules in the interstellar medium is more ubiquitous than initially expected. It includes environments as adverse as gas in the process of colliding at high speeds and, now, gas strongly illuminated by distant ultraviolet radiation. The formation of complex organic molecules reflects the complicated interaction between the chemical processes that occur in the gas phase and on the surface of the dust grains, leaving us with the question of what do all these molecules do in the Bar?
For Sara Cuadrado, “The formation routes of these species are not entirely clear and may not even be the same in different environments. More theoretical studies and laboratory experiments are needed to investigate the different chemical processes that take place on the surface of grains. The next step is, thanks to the new and increasingly powerful telescopes, to study regions similar to the Orion Bar to learn more about the different mechanisms taking place in these chemically surprising regions.”
Going back to the title of this report, you will understand that we sing the chorus of the “Ultraviolet” song from U2, “Baby, baby, baby, light (photodissociate, photoionize and photodesorb) my way”.
Notes:
[1] H2CO, CH3OH, HCO, H2CCO, CH3CHO, H2CS, HCOOH, CH3CN, CH2NH, HNCO, H213 CO, and HC3N (in decreasing order of abundance). The inferred column densities are in the range 1011— 1013 cm-2. The work also provides the upper limit of abundance for some organic molecules that have not been detected in spectral scanning, but are present in other star formation regions: HDCO, CH3O, CH3NC, CH3CCH, CH3OCH3, HCOOCH3, CH3CH2OH, CH3CH2CN, and CH2CHCN.
[2] The desorption of complex organic molecules from the icy mantles that coat the dust grains by the action of UV radiation is one of the main mechanisms of formation of these species in the interstellar medium, a mechanism known as photodesorption. But this process does not occur on the illuminated and warmer edge of the Orion Bar, as the dust grains are no longer coated by ice.
More information:
This work has been published in the paper “Complex organic molecules in strongly UV-irradiated gas”, by S. Cuadrado (Molecular Astrophysics Group, Institute of Materials Science of Madrid –CSIC, Spain); J. R. Goicoechea (Molecular Astrophysics Group, ICMM-CSIC, Spain); J. Cernicharo (Molecular Astrophysics Group, ICMM-CSIC, Spain); A. Fuente (Observatorio Astronómico Nacional – IGN, Spain); J. Pety (Institute of Millimeter Radio Astronomy (IRAM); LERMA, Paris Observatory, CNRS/PSL Research University, France); and B. Third (Molecular Astrophysics Group, ICMM-CSIC, Spain).
IMAGES
Image 1: Orion Nebula: The Orion Nebula, an immense stellar nursery about 1,500 light-years away. This stunning false-color view has been based on infrared data obtained with the Spitzer Space Telescope. Credits: NASA/JPL-Caltech
Image 2: Orion Bar spectrum: Part of the spectral survey in the Orion Bar photodissociation region obtained with the IRAM-30m radio telescope. Credit: Sara Cuadrado.
The Molecular Astrophysics Group has three new doctors, who defended their thesis in the last months. Luis Velilla, Alicia López and Sara Cuadrado: here we present a resume of their work. Congratulations!
Luis Velilla:
“Molecular complexity in envelopes of evolved stars: detailed study of the molecular emission of the objects IKTau, OH231.8+4.2, and IRC+10216”
Circumstellar envelopes of evolved stars are the main contributors to the enrichment of the interstellar medium, and are excellent laboratories to study the molecular complexity and the chemical evolution of the Universe. In this thesis, we present our study of the molecular emission in the millimeter wavelength range with the IRAM-30m telescope, Herschel-HIFI, and ALMA, of three circumstellar envelopes around the evolved stars IKTau, OH231.8+4.2, and IRC+10º216.
The main results obtained show that the chemistry of oxygen-rich objects is not as poor as it was previously thought. In particular, the chemistry of OH231.8+4.2 has been probably altered by high-speed shocks caused by the interaction between the slow AGB wind and fast (few 100 km· s−1) highly collimated bipolar winds. We also present the first sub-arcsecond resolution observations obtained with ALMA, for species such as SiO, SiS, or SiC2 towards IRC+10º216. This work will serve as a reference for future studies of the molecular emission in circumstellar envelopes of evolved stars, particularly for the oxygen rich envelopes.
Thesis defense: 09/06/2017
Thesis directors: Carmen Sánchez Contreras, José Cernicharo.
Alicia López:
“Organic molecules chemistry in massive stars formation regions”
“Radioastronomy needs information from the laboratory for the spectral characterization and identification of abundant molecules in the Orion-KL molecular cloud. The temperature of this high-mass star forming region causes many of the low-lying vibrational states of these molecules to be excited so that, in addition to lines from rare isotopologues, we have to identify lines arising from vibrationally excited states, thanks to the availability of laboratory measurements in the millimeter and submillimeter domains. This work has permitted to characterize the spectrum of this prototypical hot core and will be of great importance to detect and identify molecular lines using ALMA in other high-mass star forming regions.”
Thesis defense: 14/09/2017
Thesis directors: José Cernicharo, Belén Tercero.
Sara Cuadrado:
“Molecular content in the Orion Bar photodissociation region”
“In this PhD thesis, a detailed study of the molecular emission of the Orion Bar photodissociation region (PDR) has been presented. The Orion Bar is the prototypical warm PDR with a far-UV (FUV) radiation field of a few 104 times the mean interstellar field. Owing to its proximity (~414 pc) and nearly edge-on orientation, the Orion Bar offers the opportunity to determine the chemical content, spatial stratification of different species, and chemical formation-destruction routes in strongly FUV-illuminated gas.
We carried out a millimetre line survey of the irradiated edge of the Orion Bar PDR using the IRAM-30m telescope, and complemented it with ~7′′ resolution maps at 0.8 mm, in order to study the chemistry prevailing in molecular gas that is directly exposed to strong FUV fields. Despite being a very harsh environment, our observations show a relatively rich molecular line spectra, with hundreds of lines arising from hydrocarbons and complex organic molecules (Cuadrado et al. 2015, 2017). We have also reported the first interstellar detection of the less stable conformer of formic acid, cis-HCOOH (Cuadrado et al. 2016). In addition, we have used ALMA to observe a small field-of-view with a high angular resolution (~1′′) where the transition from atomic to molecular gas takes place, in the context of investigating the structure and dynamics of FUV-irradiated molecular gas. The images (in the rotationally excited emission of CO, HCO+, SH+, HOC+, SO+, and SO) reveal a pattern of high-density substructures, photo-ablative gas flows and instabilities at the edge of the molecular cloud (Goicoechea et al. 2016, 2017).
Thesis defense: 15/09/2017
Thesis directors: Javier R. Goicoechea, José Cernicharo.
Acknowledgements: AYA2009-07304, AYA2012-32032, CSD2009-00038, and ERC-610256 (Nanocosmos).
Summer has passed and, both CW Leonis and his companion envelope, IRC+10216, have come out of their media silence to make a statement to the hottest program of the moment (well, of the decade, just in case this takes longer). After her first statements, torn out in 2015, and a new complaint about the treatment given to her by the media in 2016, CW Leonis first told to the journalists of “The Life of the Stars” that, since ALMA (the daring paparazza who pursues her and her wrapping) does not give in to her efforts, she will be the one who tells the latest events herself. And, apparently, the thing is burning.
As in the most famous soaps, as in the most classic Variete programs, as in the most vitoreed gossip television programs (??), the life of this star and its envelope continues to hoard astronomical covers. It is the price to pay for a star that is close to us (who are very curious): that you become a model (to follow) of evolved (carbon)rich star.
And this is precisely the protagonist on this occasion: carbon.
In many astronomical environments it is common to find molecules formed by linear carbon chains (atoms go more or less “in a row”, but making a kind of zigzag, depending on the case). As always in astrochemistry, we are surprised to find long chains, as the conditions are so hostile that we assume that the bonds between atoms will be photodissociated as soon as an ultraviolet beam arrives. But the thing is, there they are.
Possible formation mechanisms involve upward and downward pathways, i.e., molecules can be formed by destroying larger molecules (carbon species such as C60 or polycyclic aromatic hydrocarbons –PAHs-) or step by step, from smaller molecules.
Our protagonist, IRC+10216 (the envelope formed when the star CW Leonis begun to age and expand), has again been spied on by the set of ALMA antennas that, with the help of gossipy researchers, has combined these stolen photos with a computer simulation to discover how linear carbon chains are formed.
Thus, as Marcelino Agundez (ICMM-CSIC), leader of the gossipy researchers, mentions, “We have been able to witness the polymerization of acetylene and hydrogen cyanide induced by ultraviolet photons, that is, how the carbonated chains grow ‘step by step, we stick little by little…’ -sorry, it’s a famous Spanish song-, it is, very slowly. In addition, in this place, the carbonated chains are formed by a very concrete upward route. Oh, haven’t we said where yet? Because the most curious thing about this case is where we found these long chains. They really had that under wraps!
A hollow sphericalshell
“I am really tired,” declares the envelope somewhat irritated. “I see on the covers of those gossip magazines that you have managed to capture several hydrocarbon radicals and other species [1]. And you have found them in an area of myself that you have called “hollow spherical shell”! This is the end… you don’t even let me have an inhomogeneity! Well, if you want a perfect envelope, do it with Photoshop! Stop it!
It turns out that all the species that ALMA has unveiled in this photo shoot are distributed in a hollow spherical shell [2]. It is as if, in the envelope itself, there was a bubble, someway isolated from the rest of the environment, that facilitates the growth of these molecules by protecting them from the conditions that occur outside it. This finding implies that the carbon chain formation mechanism in IRC+10216 is only activated in a very specific region of the external envelope [3].
In addition, it has been seen that the spherical shell itself has several thin layers (such is the capacity of ALMA’s “super-lens”) of an angular resolution of 1-2”, which are not strictly concentric. And here, dear readers, is where the third character reappears… the possible companion star!
CW Leonis, IRC+216… and the mysterious companion star
Why is the fact that the layers of the bubble are not concentric suspicious? The process of mass loss of CW Leonis (which is not the consequence of a diet, poor star, but of a process of aging towards white dwarf… although that will be another story) is discontinuous and not isotropic.
What does this mean? There is something, some kind of process related to a possible gravitational attraction, which is making the envelope not uniform, to have “deformations” that take place periodically and affect the distribution of its matter.
And what could be producing that effect? We’re pretty sure it’s a companion star. All we have to do is see it (here ALMA looks at us dismissingly, “I let this job to the HST or the JWST, this is not my busines. I’ve done enough already, before me you didn’t see the details so accurately.”
So we may face a very special threesome. CW Leonis does not want to comment on this. She merely talked about carbon chains by saying: “We know that, due to our proximity and luminosity, we are an ideal “laboratory” for studying the formation of carbon chains; we are aware that, for years, we have been persecuted by the paparazzi (there they have been IRAM30m, BIMA, IRAM Plateau de Bure, VLAand SMA). That won’t be necessary anymore. For a small price we will gladly tell you.”
This astounded us. Without a doubt, given the results of so much pressure exerted on our star, we only have to hope that some paparazzi will get in the future a deeper look to tell us more about the mechanisms that hide behind the formation of carbon chains. Or, what the hell: about the trio, which is what we’re really interested in. What will be the name of the mysterious companion star (if any)?
Notes:
[1] The λ 3 mm emission of rotational lines of hydrocarbon radicals C2H, C4H and C6H and species containing CN, such as CN, C3N, HC3N and HC5N with an angular resolution of ~ 1’’’ have been mapped. Hydrocarbon radicals C2H, C4H and C6H show very similar radial distributions, while species containing CN show a more diverse radial stratification, with HC3N presence in shorter radius and the CN radical extending outwards to larger radius.
[2] The spatial distribution of these species is a hollow spherical shell, with a width of 5-10”, located within a radius of 10-20” from the star, and no appreciable compact emission sample near the star.
[3] The observed morphology can be explained by a chemical model in which the growth of polyines is mainly caused by chemical reactions of radicals C2H and C4H with unsaturated hydrocarbons, while cyanopolyines are mainly formed from polyines by reactions with CN and C3N radicals.
In red and green, dust detected by Herschel; in blue, the visible scattered light seen by the Very Large Telescope. The center light has been removed, so we don’t actually see the CW Leonis star, but rather her envelope. Credit: ESA/PACS/MESS & ESO/VLT
The journal Nature recently published an article titled “Multi-molecular views of a stellar nursery” outlining the Orion-B mapping program that is being carried out with the IRAM30m telescope. Two members of our group, Emeric Bron and Javier R. Goicoechea, are involved in this research (led by Jérôme Pety, IRAM) whose goal is to simultaneously image emissions from many different molecules across a very wide area of the star-forming cloud Orion-B, in the iconic Orion constellation.
