Radioastronomy

is also supported by the fact that Class 0 protostars are short-lived (10⁴ −10⁵ yrs). The reasons for the high deuteration levels towards the cold envelope are the same as for the pre-stellar cores. Here, the grain species originating from the past remain accreted on the grain surfaces.

From the above considerations it is evident that deuterium fractionation is strongly cor-related with the physical conditions of the source: low temperatures favour the production ofH₂D⁺and high densities lead to efficient freeze-out of CO (and other species). Therefore, the deuteration level of a molecule can reveal information about the evolutionary stage of an observed source. In addition to single deuteration, one can also study the D/D2 abun-dance ratio of molecules; this helps us understand better the formation and destruction routes of deuterated species and put additional constraints on chemical models. Since the deuteration level in the gas phase is expected to increase with time via successive reactions with H₂D⁺ and eventually reach a stationary value, the determination of both single and double deuteration can be used as a chemical clock and constrain the age of the core.

In this thesis we study the single and double deuteration ofc-C₃H₂ towards starless/pre-stellar cores and Class 0 protostars. This molecule provides two main advantages: it is quite abundant in space and also has the possibility of double deuteration. The most prominent evolutionary tracer so far has been N₂H⁺. This species has proven to be more resistant to depletion than carbon-bearing species, and thus being able to trace the denser, central parts of the core, while c-C₃H₂ is believed to trace the outer layers of the core, which are less dense and more exposed to UV radiation. The study of the c-C₃H₂ deuteration can reveal possible differences between the deuteration of carbon- and nitrogen-bearing species.

In addition, sincec-C₃H₂ is strongly affected by depletion, comparing its deuteration level towards pre-stellar cores and young protostars can unveil possible deuteration processes on dust grains happening in the pre-stellar core phase, right before the ignition of a protostar.

More information on the deuteration of c-C₃H₂ in star forming regions can be found in Chapter 2.

of 2850 m, operating between 70 and 370 GHz. With a diameter of 30 m and a surface accuracy of 55 µm, the IRAM 30m telescope is one of the most powerful and sensitive observational facilities, suitable for observing cold matter that radiates predominantly in the millimeter range.

Radiation

A

B

C A

A - primary mirror B - secondary mirror C - receiver

Figure 1.6: Main components of the IRAM 30m telescope, labeled as A, B and C.

A typical single dish radio telescope consists mainly of an antenna and a receiver, as shown in Fig. 1.6. The signal from the sky is collected by a parabolic antenna, also known as the primary reflector, and is subsequently focused on a secondary mirror, or sub-reflector, which finally passes the signal to the detectors/receivers. The detector’s signal is then processed and analyzed by a spectrometer/backend. The IRAM 30m telescope in particular is built in a so-called Nasmyth configuration with a hyperbolic secondary reflector and an additional flat mirror that focuses the radiation on the receiver. Due to diffraction taking place at the primary antenna, the beam pattern of the telescope consists of a main beam that contains most of the incoming signal intensity, and the side lobes, which are axisymmetric to the beam pattern surrounding the main lobe. The more intensity is concentrated in the main beam, the less power is lost through the side lobes.

The half power beam width (HPBW) of the main lobe gives the angular resolution of the telescope, which at a given wavelength λ and a telescope diameter D is described as HPBW ∼ λ/D. For example, at a frequency of 345 GHz, the beam size of the IRAM 30 telescope is ∼ 7⁰⁰, while a frequency of 115 GHz corresponds to a ∼ 21⁰⁰ beam. The intensity scale of a radioastronomical observation is often given in K, and is expressed as antenna temperature TA: this quantity is not a physical temperature but is a measure of the incident energy flux collected by the primary antenna at the direction of the observing

source. The system temperatureT_syson the other hand, is a measure of the noise generated by the electronics and the sky. Following the data collection, astronomers calibrate the recorded spectra, which involves converting the intensity scale into antenna temperature, and correcting for any atmospheric and instrumental losses.

The observational data for this thesis were recorded by using as a frontend the Eight MIxer Receiver (EMIR) that operates in the 3, 2, 1.3 and 0.9 mm range. Depending on their center frequency in GHz these bands are characterized as E090, E150, E230, and E330.

Every band has two orthogonal linear polarization channels that are tuned to the same frequency. In addition, each EMIR band is equipped with dual sideband mixers (2SB), that generate an output signal of two sidebands, described as Lower Sideband (LSB) and Upper Sideband (USB). The available frequency bandwidth per sideband and polarization is 8 GHz, leading to a maximum frequency coverage of 32 GHz. In this work we have used the E090 band that corresponds to the 3 mm atmospheric window and can cover the frequency range from 73 to 117 GHz. The receiver was connected to a Fourier Transform Spectrometer (FTS) backend that achieved a frequency resolution of 50 kHz. Based on the above configuration we report in Chapter 2 observations of the main isotopologuec-C₃H₂, the singly and doubly deuterated species c-C₃HD and c-C₃D₂ as well as the isotopologue c-H¹³CC₂H, where one ¹³C is off the principal axis of the molecule. In Chapter 5 we aim for the phosphorus-bearing molecules HCP, CP, PN, and PO in the 3 mm range as well.