Prof Suzanne Aigrain

Abstract:

© 2020 Oxford University Press. All rights reserved. Stellar activity is the major roadblock on the path to finding true Earth-analogue planets with the Doppler technique. Thus, identifying new indicators that better trace magnetic activity (i.e. faculae and spots) is crucial to aid in disentangling these signals from that of a planet's Doppler wobble. In this work, we investigate activity related features as seen in disc-integrated spectra from the HARPS-N solar telescope. We divide high-activity spectral echelle orders by low-activity master templates (as defined using both logR _ HK and images from the Solar Dynamics Observatory, SDO), creating 'relative spectra'.With resolved images of the surface of the Sun (via SDO), the faculae and spot filling factors can be calculated, giving a measure of activity independent of, and in addition to, logR ' HK.We find pseudo-emission (and pseudoabsorption) features in the relative spectra that are similar to those reported in our previous work on α Cen B. In α Cen B, the features are shown to correlate better to changes in faculae filling factor than spot filling factor. In this work, we more confidently identify changes in faculae coverage of the visible hemisphere of the Sun as the source of features produced in the relative spectra. Finally, we produce trailed spectra to observe the radial velocity component of the features, which show that the features move in a redward direction as one would expect when tracking active regions rotating on the surface of a star.

Abstract:

We present Mon-735, a detached double-lined eclipsing binary (EB) member of the ∼3 Myr old NGC 2264 star-forming region, detected by Spitzer. We simultaneously model the Spitzer light curves, follow-up Keck/HIRES radial velocities, and the system’s spectral energy distribution to determine self-consistent masses, radii, and effective temperatures for both stars. We find that Mon-735 comprises two pre-main-sequence M dwarfs with component masses of M = 0.2918 ± 0.0099 and 0.2661 ± 0.0095 M⊙, radii of R = 0.762 ± 0.022 and 0.748 ± 0.023 R⊙, and effective temperatures of Teff = 3260 ± 73 and 3213 ± 73 K. The two stars travel on circular orbits around their common centre of mass in P = 1.9751388 ± 0.0000050 d. We compare our results for Mon-735, along with another EB in NGC 2264 (CoRoT 223992193), to the predictions of five stellar evolution models. These suggest that the lower mass EB system Mon-735 is older than CoRoT 223992193 in the mass–radius diagram (MRD) and, to a lesser extent, in the Hertzsprung–Russell diagram (HRD). The MRD ages of Mon-735 and CoRoT 223992193 are ∼7–9 and 4–6 Myr, respectively, with the two components in each EB system possessing consistent ages.