Exoplanets and Stellar Physics

Abstract:

In the past fifteen years, file sharing of digital cultural works between individuals has been at the center of a number of debates on the future of culture itself. To some, sharing constitutes piracy, to be fought against and eradicated. Others see it as unavoidable, and table proposals to compensate for its harmful effects. Meanwhile, little progress has been made towards addressing the real challenges facing culture in a digital world. Sharing starts from a radically different viewpoint, namely that the non-market sharing of digital works is both legitimate and useful. It supports this premise with empirical research, demonstrating that non-market sharing leads to more diversity in the attention given to various works. Taking stock of what we have learnt about the cultural economy in recent years, Sharing sets out the conditions necessary for valuable cultural functions to remain sustainable in this context.

Abstract:

As radial velocity (RV) spectrographs reach unprecedented precision and stability below 1 m s, the challenge of granulation in the context of exoplanet detection has intensified. Despite promising advancements in post-processing tools, granulation remains a significant concern for the EPRV (extremely precise radial velocity) community. We present a pilot study to detect and characterize granulation using the High-Accuracy Radial-velocity Planet Searcher for the Northern hemisphere (HARPS-N) spectrograph. We observed HD 166620, a K2 star in the Maunder Minimum phase, intensely for two successive nights, expecting granulation to be the dominant nightly noise source in the absence of strong magnetic activity. After correcting for a newly identified instrumental signature, originating from CCD illumination variations under optimal seeing conditions, we detected the granulation signal using structure-function (SF) analysis and a single-component Gaussian process (GP) model. The granulation signal has a characteristic time-scale of min, within 1, and a standard deviation of cm s, within 3 of the predicted value. By examining spectra and RVs as a function of line formation temperature, we investigated the sensitivity of granulation-induced RV variations across different photospheric layers. We extracted RVs from various photospheric depths using both the line-by-line and cross-correlation function methods to mitigate any extraction method biases. Our findings indicate that granulation variability is detectable in both temperature bins, with the cooler bins, corresponding to the shallower layers of the photosphere, aligning more closely with predicted values.