Stellar activity as noise in exoplanet detection – II. Application to M dwarfs

Abstract

The ubiquity of M dwarf stars combined with their low masses and luminosities make them prime targets in the search for nearby, habitable exoplanets. We investigate the effects of starspot-induced radial velocity (RV) jitter on detection and characterization of planets orbiting M dwarfs. We create surface spot configurations with both random spot coverage and active regions. Synthetic stellar spectra are calculated from a given spot map, and RV measurements are obtained using cross-correlation technique. We add the RV signal of an orbiting planet to these jitter measurements, and reduce the data to "measure" the planetary parameters. We investigate the detectability of planets around M dwarfs of different activity levels, and the recovery of input planetary parameters. When studying the recovery of the planetary period we note that while our original orbital radius places the planet inside the HZ of its star, even at a filling factor of 2% a few of our measurements fall outside the "conservative Habitable Zone". Higher spot filling factors result in more and higher deviations. Our investigations suggest that caution should be used when characterizing planets discovered with the RV method around stars that are (or are potentially) active.in the habitable zone should be just 5 pc away, although Mann et al. (2013) contests that this estimate might be too high based on their revised values of R * , L * , M * for a sample of Kepler stars, which resulted in some of the formerly HZ planets no longer orbiting within the HZ.The HZ is most loosely defined as the area around a star in which liquid water could exist on the planet's surface. According to the model developed by Kopparapu et al. (2013), the inner and outer HZ limits for our Solar System are 0.99 AU and 1.70 AU, respectively. Kopparapu et al. (2013) point out that their model does not include the radiative effects of clouds, so the boundaries could extend farther. M dwarfs are much less massive and less luminous than solar-type stars, which means the HZ is significantly closer to the star (for example, for an M dwarf of mass M ≈ 0.5M⊙, and R ≈ 0.5R⊙, the HZ is between ∼0.1 and ∼0.2 AU). This makes small planets orbiting in the HZ around M dwarfs easier to detect than their counterparts orbiting more massive stars for a few reasons: (1) Transits are more likely to be detected due to the the HZ being significantly closer to the

A Transient Transit Signature Associated with the Young Star RIK-210

“…(Pecaut & Mamajek 2013). This corresponds to a temperature difference of ∼100-200K, which is consistent with spot temperature contrasts published for M-dwarfs of similar temperatures (Andersen & Korhonen 2015). The temperature ratio between the coolest and warmest hemispheres can also be estimated from the peak-to-trough amplitude of the K2 light curve and the Stefan-Boltzmann law: ( ) consistent with the temperature difference estimated from the -¢ V i variability amplitude.…”

Modelling the RV jitter of early-M dwarfs using tomographic imaging

“…This tendency needs to be examined in a larger sample with new spectropolarimetric surveys of moderately active M dwarfs. Besides, given that surface spot distributions are significantly impacting our ability at detecting Earth-like planets (see, e.g., simulations done by Andersen & Korhonen 2015), it will be worthwhile to extent this study to later-type M dwarfs to improve our knowledge of their spot patterns. For example, the Doppler Imaging is a powerful tool to investigate whether spot patterns change and, e.g., evolve towards more even distributions of smaller features, when going from partially to fully convective stars.…”

Magnetic Inflation and Stellar Mass. I. Revised Parameters for the Component Stars of the Kepler Low-mass Eclipsing Binary T-Cyg1-12664

“…Starspots on a rotating photosphere can introduce radial velocity variations (e.g., Andersen & Korhonen 2015). Gagné et al (2016) investigated the effect of starspots on radial velocity measurements and found that an active star shows a long-term radial velocity variation of 25-50 m s −1 in the near-infrared.…”