We present interferometric continuum and molecular line emission maps obtained with the Atacama Large Millimeter/submillimeter Array (ALMA) of OH231.8+4.2, a well studied bipolar nebula around an asymptotic giant branch (AGB) star that is key to understand the remarkable changes in nebular morphology and kinematics during the short transition from the AGB to the Planetary Nebula (PN) phase. The excellent angular resolution of our maps (∼20 mas ∼30 AU) allows us to scrutinize the central nebular regions of OH231.8+4.2, which hold the clues to understanding how this iconic object assembled its complex nebular architecture. We report, for the first time in this object and others of its kind (i.e. pre-PNe with massive bipolar outflows), the discovery of a rotating circumbinary disk of radius ∼30 AU traced by NaCl, KCl, and H2O emission lines. The disk lies at the base of a young bipolar wind with signs of rotation as well. A compact spatially resolved dust disk is found perpendicular to the bipolar outflow. We also identify a point-like continuum source, which likely represents the central Mira star enshrouded by a ∼3 R* shell or disk of hot (∼1400 K) freshly formed dust. The point source is slightly off-centre from the disk centroid, enabling us for the first time to place constraints to the orbital separation of the central binary system.

The synthesis of dust grains mostly takes place in the circumstellar envelopes (CSEs) of asymptotic giant branch (AGB) stars. What are the precursor seeds of condensation nuclei and how do these particles evolve toward the micrometer sized grains that populate the interstellar medium? These are key questions of the NANOCOSMOS project. In this study, we carried out an observational study to constrain what the main gas-phase precursors of dust in C-rich AGB stars are.

AGB stars are important contributors of processed matter to the ISM. However, the physical and chemical mechanisms involved in its ejection are still poorly known. This process is expected to have remarkable effects in the innermost envelope, where the dust grains are formed, the gas is accelerated, the chemistry is active, and the radiative excitation becomes important. A good tracer of this region in C-rich stars is SiS, an abundant refractory molecule that can display maser lines, very sensitive to changes in the physical conditions. We present high angular resolution interferometer observations (HPBW ≳0.″.25) of the v = 0 J = 14 – 13 and 15 – 14 SiS maser lines towards the archetypal AGB star IRC+10216, carried out with CARMA and ALMA to explore the inner 1” region around the central star. We also present an ambitious monitoring of these lines along one single pulsation period carried out with the IRAM 30 m telescope.

Silicon carbide together with amorphous carbon are the main components of dust grains in the atmospheres of C-rich AGB stars. Small gaseous Si-C bearing molecules (such as SiC, SiCSi, and SiC2) are efficiently formed close to the stellar photosphere. They likely condense onto dust seeds owing to their highly refractory nature at the lower temperatures (i.e., below about 2500 K) in the dust growth zone which extends a few stellar radii from the photosphere. Beyond this region, the abundances of Si-C bearing molecules are expected to decrease until they are eventually reformed in the outer shells of the circumstellar envelope, owing to the interaction between the gas and the interstellar UV radiation field. Our goal is to understand the time-dependent chemical evolution of Si-C bond carriers probed by molecular spectral line emission in the circumstellar envelope of IRC+10216 at millimeter wavelengths.

Silicon carbide dust grains are ubiquitous in circumstellar envelopes around C-rich AGB stars. However, the main gas-phase precursors leading to the formation of SiC dust have not yet been identified. To date, only three molecules containing an Si–C bond have been identified to have significant abundances in C-rich AGB stars: SiC2, SiC, and Si2C. The ring molecule SiC2 has been observed in a handful of evolved stars, while SiC and Si2C have only been detected in the C-star envelope IRC +10216. We aim to study how widespread and abundant SiC2, SiC, and Si2C are in envelopes around C-rich AGB stars and whether or not these species play an active role as gas-phase precursors of silicon carbide dust in the ejecta of carbon stars.

Far-UV photons (FUV, E < 13.6 eV) from hot massive stars regulate, or at least influence, the heating, ionization, and chemistry of most of the neutral interstellar medium (H i and H2 clouds). Investigating the interaction between FUV radiation and interstellar matter (molecules, atoms and grains) thus plays an important role in astrochemistry.

The Orion Bar, an interface region between the Orion A molecular cloud and the H ii  region around the Trapezium cluster, is a textbook example of a strongly illuminated dense PDR (photodissociation region). The Bar is illuminated by a FUV field of a few 104 times the mean interstellar radiation field. Because of its proximity and nearly edge-on orientation, it provides a very good template to investigate the chemical content, structure, and dynamics of a strongly irradiated molecular cloud edge. We have used ALMA to mosaic a small field of the Bar where the critical transition from atomic to molecular gas takes place. These observations provide an unprecedented sharp view of this transition layer (≲ 1″ resolution or ≲ 414 AU). The resulting images (so far in the rotational emission of CO, HCO+, H13CO+, SO+, SO, and reactive ions SH+ and HOC+) show the small-scale structure in gas density and temperature, and the steep abundance gradients. The images reveal a pattern of high-density substructures, photo-ablative gas flows and instabilities at the edge of the molecular cloud. These first ALMA images thus show a more complex morphology than the classical clump/interclump static model of a PDR.

In order to quantify the chemical content in strongly FUV-irradiated gas, we have also used the IRAM-30 m telescope to carry out a complete line-survey of the illuminated edge of the Bar in the millimeter domain. Our observations reveal the presence of complex organic molecules (and precursors) that were not expected in such a harsh environment. In particular, we have reported the first detection of the unstable cis conformer of formic acid (HCOOH) in the ISM. The energy barrier to internal rotation (the conversion from trans to cis) is approximately 4827 cm−1 (≈7000 K). Hence, this detection is surprising. The low inferred trans-to-cis abundance ratio of 2.8±1.0 supports a photoswitching mechanism: a given conformer absorbs a FUV stellar photon that radiatively excites the molecule to electronic states above the interconversion barrier. Subsequent fluorescent decay leaves the molecule in a different conformer form. This mechanism, which we have specifically studied with ab initio quantum calculations, was not considered so far in astrochemistry although it can affect the structure of a variety of molecules in PDRs.

The interpretation of molecular line surveys at millimetre and submillimetre wavelengths towards astrophysical objects requires a good knowledge of the spectroscopy of the molecules present in the gas phase, and of the basic collisional processes between them and molecular and atomic Hydrogen, Helium, and electrons. From the chemical point of view, the modeling of these data requires a large amount of laboratory information concerning the reactivity of these species in the gas phase and in the ice mantles of dust grains. In this contribution I will focus on the problems to interpret line surveys and I will discuss how we will have to proceed in the new era opened by ALMA where sensitivity and angular resolution will surpass by nearly a factor 10 those of existing facilities, and where the spectral confusion limit could be reached towards many sources.

The study of molecules in space, known as astrochemistry or molecular astrophysics, is a rapidly growing field. Molecules exist in a wide range of environments in both gaseous and solid form, from our own solar system to the distant early universe. To astronomers, molecules are indispensable and unique probes of the physical conditions and dynamics of regions in which they are detected, especially the interstellar medium. In particular, the many stages of both low-mass and high-mass star formation are better understood today thanks to the analysis of molecular observations. Molecules can also yield a global picture of the past and present of sources. Moreover, molecules affect their environment by contributing to the heating and cooling processes that occur.

The observation of evolved stars in selected evolutionary stages allow us to track the evolution of the physical properties and chemical composition of the matter that is being returned to the interstellar medium during these last stages of the life of stars. While the dust component can be characterized through the observation of the spectral energy distribution in the infrared part of the spectrum, spectral line surveys carried out in a wide spectral band provide the best probe of the physical properties and chemical composition of the gas phase. In this lecture we review the different line surveys carried out toward these objects and their impact in our understanding of the chemical complexity evolution in the circumstellar envelopes around evolved stars.

New images of the interstellar medium provided by Herschel and Planck bring spectacular evidence of the intricate and filamentary structure of the interstellar medium, betraying its turbulent nature. Although turbulence is a subject of interest in astronomy, little is know about the origin of turbulence in the interstellar medium. We suggest that part of the turbulence in the Orion molecular cloud be due to the decay of the Kelvin-Helmholtz instability.

Ethylene (C2H4) is a symmetric molecule that is best detected using mid-infrared transitions. We report on observations of the 10.5 μm ν7 band using the cryogenic grating spectrograph TEXES. These confirm the previous ethylene detection in the IRC+10216 circumstellar shell. We detect 18 ethylene lines. The lines are both narrow and weak with depths of no more than ~2%. The ethylene lines suggest an excitation temperature of ~80 K.

A mid-infrared high-resolution spectral survey of the source IRC+10216 (CW Leo) has been carried out between 11 and 14 $\mu$m. A large number of lines of C$_2$H$_2$ and HCN and their most abundant isotopologues, have been identified. Lines involving high-energy ro-vibrational levels allow an accurate derivation of the physical and chemical conditions in the innermost envelope. We have developed a radiative transfer model capable of fitting the observed lines satisfactorily. The fit of more than 200 ro-vibrational lines allowed us to get the kinetic, vibrational and rotational temperatures and the abundances of the C$_2$H$_2$ and HCN between 1 and 300 R$_*$.

CASPER (Concordia Atmospheric SPectroscopy of Emitted Radiation)is a spectrometer proposed for installation at Dome C, devoted tomeasurements of atmospheric emission in the spectral regionbetween 180 μm and 3 mm (3–55 cm-1). Thisinstrument will be able to perform continuous spectral sampling atdifferent altitudes at angular scales of ~1°. From therecorded data it is possible to extract atmospheric transmittancewithin 1% in the whole wide operating band, together with watervapour content and O2 and O3 concentrations. CASPER willallow us to characterize the site for future FIR/mm telescopes.Atmospheric data recorded by CASPER will allow for correction ofastrophysical and cosmological observations without the need fortelescope-specific procedures and further loss of observation timewith more precision in the observations themselves. Calibration ofground-based telescopes on known sky sources is strongly affectedby atmospheric absorption. CASPER has this as its primary goal.The spectrometer is based on a Martin-Puplett interferometer. Twodata sampling solutions will be performed: phase modulation &fast scan strategy. Sky radiation is collected towards theinterferometer by an optical setup that allows the field of view,to explore the full 0° ÷ 90° range of elevation angles. Witha low spurious polarization instrument, monitoring of polarizedatmospheric contribution will be possible.

The recent results of the ISO satellite in the field of molecular spectrocopy of AGB stars are reviewed. For the fist time, the two spectrometers onboard ISO have provided the opportunity to observe the pure rotational lines of several molecules in the far infrared and the ro-vibrational bands of the most abundant molecular species in the near and mid-infrared. These data allow to carry out a systematic study of the circumstellar envelopes of AGB stars and Planetary Nebulae. I analyze in this paper the role of resonant scatterring in the pumping of the ro-vibrational molecular levels in CSEs.

We present high angular resolution observations of the molecular outflow associated with the optical jet and HH objects of the HH111 system. Interferometric observations in the CO J =2–1 and J =1–0 lines of the high velocity bullets associated with HH111 are presented for the first time. The molecular gas in these high velocity clumps has a moderate kinetic temperature and a mass of a few 10–4 M⊙ per bullet. We favor the view that HH jets and CO bullets, which represent different manifestations of the same physical phenomena, are driving the low-velocity molecular outflow.

VLBI observations show that the SiO maser emitting regions in oxygen-rich stars are very clumpy and that these clumps extend over a few stellar radii (Mclntosh et al. 1987; Colomer et al. 1992). These observations indicate that the ideal instrument for the study of the SiO masers is an interferometer with baselines covering between a few and several hundreds/thousands km. Such an instrument is so far unavailable.

A classical way to get high angular resolution and a full beam synthesis with a single telescope of moderate size is through lunar occultations. This observing technique provides the angular resolution of a single linear antenna several kilometers long. However, at millimeter wavelengths the Fresnel fringes produced by the Moon limb as the source under study is occulted have never been observed. We present here the observation with the 30-m IRAM radio telescope of the v=1 J=2-1 line of SiO during an occultation (and reappearance) of R Leo by the Moon.

Using the IRAM interferometer, we have mapped with a 2″.4 = 3″.4 resolution the J = 1 → 0 HCN line emission in the proto–planetary nebula CRL 618. Our maps resolve the 200 kms−1 molecular outflow (Cernicharo et al. 1989), as well as the slowly expanding circumstellar envelope (Bujarrabal et al. 1988), allowing a very precise positioning (≤ 0″.1) of these components with respect to the central HII region. 70% of the HCN envelope emission comes from a very compact, spherically symmetric core of size ≃ 3″.2. The core surrounds the high velocity gas which appears localized in a number of small ‘clumps’ (≤ 0″.5) – see figure. The large range of velocities observed in the ‘clumps’ suggests that we are not observing a decelerating molecular flow, but the impacts of a bipolar outflow on the slowly moving core, close to the HII region. The collision of a neutral gas outflow with high density regions (the ‘clumps’) results in the generation of dissociative shock-waves pushing and tearing the inner surface of the envelope. CRL 618 appears to have reached the stage where the stellar winds begin to disrupt and to scrape through the massive envelope, shortly before it evolves towards a Planetary Nebula.

Astronomical searches for H2CCC and H2CCCC, based on frequencies from our laboratory identifications, have resulted in detections toward TMC-1 and IRC+10216. These new interstellar species are possibly the first of a new family of highly polar carbon chains; they are only the second and third carbenes (carbon molecules with two nonbonded electrons) known in space.

Two molecular clouds associated with well known reflection nebulosities have been studied in order to stablish the effects of the UV radiation on the surrounding gas and dust. Observations of the J=2 →1 and J=1 →0 transitions of CO and 13CO have been carried out with the telescopes POM 1 and POM 2 towards the clouds associated with LKHα 198 and HD200775. The IRAS maps at 12, 25, 60 and 100 μm towards these globules have been also examined.