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!
“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.
“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.
“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).