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Francesco Borsa

Publications and source records attributed to Francesco Borsa.

24 records · Page 2Linked to original sources
arXiv2018

Mapping the Periphery and Variability of the Magellanic Clouds

We propose a combination of a modified Wide-Fast-Deep survey, a mini-survey of the South Celestial Pole, and a Deep Drilling-style survey to produce a 3-D map of the Magellanic System and to provide a detailed census of the transient and variable populations in the Clouds. We support modifying the Wide-Fast-Deep survey to cover the declination range $-72.25°<{\rm Dec}<12.4°$ and the Galactic latitude range $|b|>15°$, as proposed in a separate white paper. We additionally propose a mini-survey covering the 950$°^2$ with ${\rm Dec} < -72.25$ in $ugriz$ to the standard LSST single-exposure depth and with 40 visits per filter per field. Finally, we propose a mini-survey covering $\sim100 °^2$ of the main bodies of the Clouds with twelve total pointings, 2000 total visits per field, and shorter exposure time.

astro-ph.IM↗
arXiv2018

Mass, radius, and composition of the transiting planet 55 Cnc e : using interferometry and correlations --- A quick update

In a recent paper (Crida et al. 2018, accepted on April 19), we presented a method to derive the mass and radius of a transiting exoplanet and their intrinsic correlation, that we applied to 55 Cnc e. We wrote: "More precise observations of the transit would be very useful in this particular case and would allow to increase significantly the gain on the planetary density precision." Three months later, Bourrier et al. (2018) published new observations of the system. Additionally, Gaia's DR2 was released on April 25, 2018. The purpose of this research note is solely to implement these precise new data in our pipeline to provide an up-to-date result of our model. We find $R_p = 1.947\pm 0.038\,R_\oplus$ and $M_p = 8.59\pm 0.43\,M_\oplus$. We also double the precision on the planetary density ($ρ_p = 1.164\pm 0.062\,ρ_\oplus$), which allows us to refine the estimates for all interior parameters of interest. In particular, we now find that the radius of the gaseous envelope is $0.03\pm 0.02\,R_p$.

astro-ph.EP↗
arXiv2018

Stellar contributions to the line profiles of high-resolution transmission spectra of exoplanets

In-depth studies of exoplanetary atmospheres are starting to become reality. In order to unveil their properties in detail, we need spectra with a higher S/N and also more sophisticated analysis methods. With high-resolution spectrographs, we can not only detect the sodium feature in the atmosphere of exoplanets, but also characterize it by studying its line profile. After finding a clearly w-shaped sodium line profile in the transmission spectrum of HD189733b, we investigated possible sources of contamination given by the star and tried to correct for these spurious deformations. By analyzing the single transmission spectra of HD189733b in the wavelength space, we show that the main sodium signal that causes the absorption in the transmission spectrum is centered on the stellar rest frame. We concentrate on two main stellar effects that contaminate the transmission spectrum: center-to-limb variations and stellar rotation. We show the effects on the line profile: while we correct for the CLV using simulated theoretical stellar spectra, we provide a new method, based directly on observational data, to correct for the RM contribution to the line profile of the retrieved transmission spectrum. We apply the corrections to the spectra of HD189733b. Our analysis shows line profiles of the Na D lines in the transmission spectrum that are narrower than reported previously. The correction of the D2 line, which is deeper than the D1, is probably still incomplete since the planetary radius is larger at this wavelength. A careful detrending from spurious stellar effects followed by an inspection in the velocity space is mandatory when studying the line profile of atmospheric features in the high-resolution transmission spectrum of exoplanets. Data with higher S/N coupled with improved atmospheric models will allow us to adapt the magnitude of the corrections of stellar effects in an iterative way.

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arXiv2016

SIOUX project: a simultaneous multiband camera for exoplanet atmospheres studies

The exoplanet revolution is well underway. The last decade has seen order-of-magnitude increases in the number of known planets beyond the Solar system. Detailed characterization of exoplanetary atmospheres provide the best means for distinguishing the makeup of their outer layers, and the only hope for understanding the interplay between initial composition chemistry, temperature-pressure atmospheric profiles, dynamics and circulation. While pioneering work on the observational side has produced the first important detections of atmospheric molecules for the class of transiting exoplanets, important limitations are still present due to the lack of sys- tematic, repeated measurements with optimized instrumentation at both visible (VIS) and near-infrared (NIR) wavelengths. It is thus of fundamental importance to explore quantitatively possible avenues for improvements. In this paper we report initial results of a feasibility study for the prototype of a versatile multi-band imaging system for very high-precision differential photometry that exploits the choice of specifically selected narrow-band filters and novel ideas for the execution of simultaneous VIS and NIR measurements. Starting from the fundamental system requirements driven by the science case at hand, we describe a set of three opto-mechanical solutions for the instrument prototype: 1) a radial distribution of the optical flux using dichroic filters for the wavelength separation and narrow-band filters or liquid crystal filters for the observations; 2) a tree distribution of the optical flux (implying 2 separate foci), with the same technique used for the beam separation and filtering; 3) an exotic solution consisting of the study of a complete optical system (i.e. a brand new telescope) that exploits the chromatic errors of a reflecting surface for directing the different wavelengths at different foci.

astro-ph.IM↗
arXiv2016

Chromatic line-profile tomography to reveal exoplanetary atmospheres: application to HD 189733b

Transmission spectroscopy can be used to constrain the properties of exoplanetary atmospheres. During a transit, the light blocked from the atmosphere of the planet leaves an imprint in the light coming from the star. This has been shown for many exoplanets with different techniques, with both photometry and spectroscopy. We aim at testing chromatic line-profile tomography as a new tool to investigate exoplanetary atmospheres. The signal imprinted on the cross-correlation function (CCF) by a planet transiting its star is dependent on the planet-to-star radius ratio. We want to verify if the precision reachable on the CCF obtained from a subset of the spectral orders of the HARPS spectrograph is enough to discriminate the radius of a planet at different wavelengths. Methods. We analyze HARPS archival data of three transits of HD 189733b. We divide the HARPS spectral range in 7 broadbands, calculating for each band the ratio between the area of the out-of-transit CCF and the area of the signal imprinted by the planet on it during the full part of the transit. We take into account the effect of the limb darkening using the theoretical coefficients of a linear law. Averaging the results of three different transits allows us to obtain a good quality broadband transmission spectrum of HD 189733b, with a precision greater than that of the chromatic RM effect. Results. We proved chromatic line-profile tomography to be an interesting way to reveal broadband transmission spectra of exoplanets: our analysis of the atmosphere of HD 189733b is in agreement with other ground- and space-based observations. The independent analysis of different transits puts in evidence the probability that stellar activity plays a role in the extracted transmission spectrum. Care has thus to be taken when claiming for Rayleigh scattering in the atmosphere of exoplanets orbiting active stars using only one transit.

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