Three new doctors

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).

 

Calibrating the Submillimetre Sky

For astronomers, one of the most important things in order to be able to confirm and compare the huge amount of data received during the observations is to have accurate calibration references. In astronomy, millimetre and submillimetre wavelengths are important to study relatively cold objects in the Universe, such as the interstellar medium, star forming regions, circumstellar matter, planetary atmospheres and highly red-shifted objects.  Reference calibration standards are, however, very scarce specially at submillimetre wavelengths (Bands 7, 8, 9 and 10 of the Atacama Large Millimetre Array, ALMA, in Northern Chile).

Fortunately, some years ago a team of astronomers suggested the use of the planets of our Solar System as possible calibration references at submillimetre wavelengths. First works developed on that subject revealed the submillimetre lines of Phosphine (PH3) in the atmospheres of Jupiter and Saturn, although the overall shape of these extremely wide features could not be measured due to technical limitations.

Now, for the first time, a team has measured the emission of the giant planets Jupiter and Saturn across the 0.3 to 1.3 mm wavelength range using a Fourier Transform Spectrometer mounted on the 10.4-meter dish of the CSO, Caltech Submillimetre Observatory (now retired) at Mauna Kea, Hawaii, 4100 meters above sea level. The calibrated data allowed the team to verify the predictions of standard radiative transfer models for both planets in this spectral region, and to confirm the absolute radiometry in the case of Jupiter.

This careful calibration included the evaluation of the antenna performance over such a wide wavelength range and the removal of the Earth’s atmosphere effects, allowing the detection of broad absorption features on those planets’ atmospheres.

As mentioned by Juan Ramón Pardo (lead author of the study, ICMM-CSIC, Spain), “Besides their physical interest, the results are also important as both planets are calibration references in the current era of operating ground-based and space-borne submillimetre instruments”.

Jupiter and Saturn are gaseous giants much larger but less dense than the inner rocky planets of our Solar System. Their atmospheres are extremely thick. Very wide collision-broadened lines of Ammonia (NH3) and Phosphine (PH3) dominate the overall shape of their submillimetre spectrum. Most of the several thousand exoplanets discovered to date are gaseous giants thought to be similar to Jupiter and Saturn. Therefore, the now measured submillimetre spectrum of our giant neighbours could also help as a reference in future spectroscopic studies of other planetary systems.

More information:

This research was presented in a paper entitled “Ground-based measurements of the 1.3 to 0.3 mm spectrum of Jupiter and Saturn, and their detailed calibration” by Juan R. Pardo et al., to appear in the journal Icarus on July 1st 2017, but already available on-line: http://www.sciencedirect.com/science/article/pii/S0019103516303827

 The team is composed of Juan R. Pardo (Molecular Astrophysics Group, ICMM, CSIC, Spain); Eugene Serabyn (NASA-Jet Propulsion Laboratory, California Institute of Technology, USA); Martina C. Wiedner (LERMA, Paris Observatory, PSL Research University, CNRS, Sorbonne Universités, UPMC, France); Raphäel Moreno (LESIA, Paris-Meudon Observatory, France); Glenn Orton (NASA-Jet Propulsion Laboratory, California Institute of Technology, USA).

Source of Jupiter Raw Image: technotifier.com