Ermanno F. Borra

Extremely peculiar emission lines have been found in the spectra of some active galactic nuclei and quasars. Their origin is totally unknown. We investigate the hypothesis that they are generated from ultra-rapid quasi-periodic oscillations that may occur in jets or black holes, as predicted in a published theoretical paper. We conclude that, although not totally certain, this hypothesis is just as valid as the other highly peculiar hypotheses that have been previously made (e.g. blueshifts due to bulk motions close to the speed of light). We consider ways to further validate our hypothesis.

Here are presented the experimental results obtained with a ferrofluidic deformable mirror controlled by electro-magnet actuators. Using a step input through a single actuator we obtain a steady-state settling time of 100ms; however, different combinations of overdrive inputs can be used to decrease it to 25ms. Also, a new technique which consists in laying down an elastomer membrane, coated with an aluminum film, on the ferrofluid is discussed. By adding the membrane on the ferrofluid, it further decreases the time response by a factor of 2. Furthermore, the thin aluminum layer improves the reflectivity of the mirror. Finally, using the membrane and the overdrive techniques combined, the time response is improved by a factor of 20. Numerical simulations show that ferrofluidic mirrors using membranes and improved electronics should reach settling times of the order of a millisecond. Presumably even lower settling times could be possible.

We consider an alternative to the cross-correlation function (CCF), that uses the autocorrelation function (ACF), to measure in spectra the reflected light of the stars by their planetary companion. The objective of this work is to assess and analyse the efficiency of the ACF in detecting planetary signals by a detection of reflected light. To do so, we first compare the ACF and the CCF using artificial spectra containing a planetary signal. We then use the ACF to analyse spectra of the 51 Peg + 51 Peg b system and compare our results with those obtained by Martins et al. (2015) who previously analysed the same system using the CCF. The functionalities of the ACF and the way it is implemented are similar to that of the CCF. One of the main advantages of the ACF is the fact that, unlike the CCF, no weighted binary mask is required. This makes the ACF easier to use. The results related to simulated spectra showed that the ACF allowed us to decrease the boundary condition threshold for the use of spectra compared to the CCF so that more data could be used to recover the planetary signal. For the 51 Peg b planet, we achieved a detection significance of 5.52 σ_noise with the ACF compared to 3.70 σ_noise with the CCF (Martins et al. 2015). We conclude that the ACF has the potential to become a prominent technique in detecting exoplanets considering its efficiency, ease of use and rapid execution time.

We demonstrate that extremely rapid and weak periodic and non-periodic signals can easily be detected by using the autocorrelation of intensity as a function of time. We use standard radio-astronomical observations that have artificial periodic and non-periodic signals generated by the electronics of terrestrial origin. The autocorrelation detects weak signals that have small amplitudes because it averages over long integration times. Another advantage is that it allows a direct visualization of the shape of the signals, while it is difficult to see the shape with a Fourier transform. Although Fourier transforms can also detect periodic signals, a novelty of this work is that we demonstrate another major advantage of the autocorrelation, that it can detect non-periodic signals while the Fourier transform cannot. Another major novelty of our work is that we use electric fields taken in a standard format with standard instrumentation at a radio observatory and therefore no specialized instrumentation is needed. Because the electric fields are sampled every 15.625 nanoseconds, they therefore allow detection of very rapid time variations. Notwithstanding the long integration times, the autocorrelation detects very rapid intensity variations as a function of time. The autocorrelation could also detect messages from Extraterrestrial Intelligence as non-periodic signals.

The experimental results obtained with a ferrofluidic deformable mirror controlled by electro-magnet actuators are presented here. Using a step input through a single actuator, we obtained a steady-state settling time of 100 ms; however, different combinations of overdrive inputs can be used to decrease it to 25 ms. A new technique which consists of laying down an elastomer membrane, coated with an aluminum film, on the ferrofluid is also discussed. By adding the membrane on the ferrofluid, it further decreases the time response by a factor of 2. Furthermore, the thin aluminum layer improves the reflectivity of the mirror. Finally, using the membrane and the overdrive techniques combined, the time response is improved by a factor of 20. Numerical simulations show that ferrofluidic mirrors using membranes and improved electronics should reach settling times of the order of a millisecond. Presumably, even lower settling times could be possible.

The autocorrelation function (ACF) is a simple and useful tool that allows us to measure the average linewidth of spectra with great precision. Unlike the cross-correlation function, the ACF can be used without having to rely on weighted binary masks. It makes the ACF much easier to use. We analyse seven Cepheids and present a new method to obtain very precise turbulent velocity curves for six of them using the ACF. We compare our full width at half-maximum (FWHM) curves as a function of the pulsational phase to those of Nardetto et al., who used the Fe i 6056.005 Å line only. We note a significant improvement in the shape of the FWHM curves for all Cepheids on using the ACF. From the FWHM curves, we measure microturbulence curves for six Cepheids using a Gaussian approximation. Finally, we artificially degrade the resolution of the spectra and add noise to further assess and highlight the advantages of the ACF. The FWHM curves obtained with the ACF remain virtually unchanged up to degradation by a factor of 10. Degradation by a factor of 20 slightly affected the results but an average linewidth variation remains easily detectable.

The autocorrelation function (ACF) is a simple and useful tool that allows to measure the average linewidth of spectra with great precision. Unlike the cross-correlation function (CCF), the ACF can be used without having to rely on weighted binary masks. It makes the ACF much easier to use. We analyze 7 Cepheids and present a new method to obtain very precise turbulent velocity curves for 6 of them by using the ACF. We compare our Full Widths at Half-Maximum (FWHM) curves as a function of the pulsational phase to those of Nardetto et al. (2006) who used the Fe I 6056.005 {\AA} line only. We note a significant improvement in the shape of the FWHM curves for all Cepheids by using the ACF. From the FWHM curves, we measure microturbulence curves for 6 Cepheids by using a Gaussian approximation. Finally, we artificially degrade the resolution of the spectra and add noise to further assess and highlight the advantages of the ACF. The FWHM curves obtained with the ACF remain virtually unchanged up to a degradation by a factor of 10. A degradation by a factor of 20 slightly affected the results but an average linewidth variation remains easily detectable.