Sunspot Evolution

Santos

Udry

et al. 2011

A&A

123

116

Context. The detection of small mass planets with the radial-velocity technique is now confronted with the interference of stellar noise. HARPS can now reach a precision below the meter-per-second, which corresponds to the amplitudes of different stellar perturbations, such as oscillation, granulation, and activity. Aims. Solar spot groups induced by activity produce a radial-velocity noise of a few meter-per-second. The aim of this paper is to simulate this activity and calculate detection limits according to different observational strategies. Methods. Based on Sun observations, we reproduce the evolution of spot groups on the surface of a rotating star. We then calculate the radial-velocity effect induced by these spot groups as a function of time. Taking into account oscillation, granulation, activity, and a HARPS instrumental error of 80 cm s −1 , we simulate the effect of different observational strategies in order to efficiently reduce all sources of noise. Results. Applying three measurements per night of 10 min every three days, 10 nights a month seems the best tested strategy. Depending on the level of activity considered, from log R HK = −5 to −4.75, this strategy would allow us to find planets of 2.5 to 3.5 M ⊕ in the habitable zone of a K1V dwarf. Using Bern's model of planetary formation, we estimate that for the same range of activity level, 15 to 35% of the planets between 1 and 5 M ⊕ and with a period between 100 and 200 days should be found with HARPS. A comparison between the performance of HARPS and ESPRESSO is also emphasized by our simulations. Using the same optimized strategy, ESPRESSO could find 1.3 M ⊕ planets in the habitable zone of K dwarfs. In addition, 80% of planets with mass between 1 and 5 M ⊕ and with a period between 100 and 200 days could be detected.

Section: Activity Of the Sunmentioning

confidence: 99%

Section: Activity Of the Sunmentioning

confidence: 99%

See 1 more Smart Citation

Planetary detection limits taking into account stellar noise

Santos

Udry

et al. 2011

A&A

123

116

“…Depending on the coverage and evolution of active regions, the amplitude of the activity signal can strongly vary from one rotational period to the next because these regions only live for a short amount of time. On the Sun, the lifetime of active regions is about a few rotational periods (e.g Howard & Murdin 2000)…”

mentioning

confidence: 99%

The Kepler-10 Planetary System Revisited by Harps-N: A Hot Rocky World and a Solid Neptune-Mass Planet

Bonomo

Haywood

et al. 2014

ApJ

184

147

Kepler-10b was the first rocky planet detected by the Kepler satellite and confirmed with radial velocity follow-up observations from Keck-HIRES. The mass of the planet was measured with a precision of around 30%, which was insufficient to constrain models of its internal structure and composition in detail. In addition to Kepler-10b, a second planet transiting the same star with a period of 45 days was statistically validated, but the radial velocities were only good enough to set an upper limit of 20 M ⊕ for the mass of Kepler-10c. To improve the precision on the mass for planet b, the HARPS-N Collaboration decided to observe Kepler-10 intensively with the HARPS-N spectrograph on the Telescopio Nazionale Galileo on La Palma. In total, 148 high-quality radial-velocity measurements were obtained over two observing seasons. These new data allow us to improve the precision of the mass determination for Kepler-10b to 15%. With a mass of 3.33 ± 0.49 M ⊕ and an updated radius of 1.47 +0.03 −0.02 R ⊕ , Kepler-10b has a density of 5.8 ± 0.8 g cm −3 , very close to the value predicted by models with the same internal structure and composition as the Earth. We were also able to determine a mass for the 45-day period planet Kepler-10c, with an even better precision of 11%. With a mass of 17.2 ± 1.9 M ⊕ and radius of 2.35 +0.09 −0.04 R ⊕ , Kepler-10c has a density of 7.1 ± 1.0 g cm −3 . Kepler-10c appears to be the first strong evidence of a class of more massive solid planets with longer orbital periods.

“…We followed Dumusque et al (2011c) to simulate the appearance and evolution of spot groups and started with an empirical law from solar observations that describes their lifetime distribution (Howard 2000):…”

Section: Appearance and Evolution Of Active Region Groupsmentioning

confidence: 99%

Radial velocity fitting challenge

2016

A&A

Context. Radial-velocity (RV) signals arising from stellar photospheric phenomena are the main limitation for precise RV measurements Those signals induce RV variations an order of magnitude larger than the signal created by the orbit of Earth-twins, thus preventing their detection. Aims. Different methods have been developed to mitigate the impact of stellar RV signals. The goal of this paper is to compare the efficiency of these different methods to recover extremely low-mass planets despite stellar RV signals. However, because observed RV variations at the meter-per-second precision level or below is a combination of signals induced by unresolved orbiting planets, by the star, and by the instrument, performing such a comparison using real data is extremely challenging. Methods. To circumvent this problem, we generated simulated RV measurements including realistic stellar and planetary signals. Different teams analyzed blindly those simulated RV measurements, using their own method to recover planetary signals despite stellar RV signals. By comparing the results obtained by the different teams with the planetary and stellar parameters used to generate the simulated RVs, it is therefore possible to compare the efficiency of these different methods. Results. The most efficient methods to recover planetary signals take into account the different activity indicators, use red-noise models to account for stellar RV signals and a Bayesian framework to provide model comparison in a robust statistical approach. Using the most efficient methodology, planets can be found down to K/N = K pl /RV rms × √ N obs = 5 with a threshold of K/N = 7.5 at the level of 80-90% recovery rate found for a number of methods. These recovery rates drop dramatically for K/N smaller than this threshold. In addition, for the best teams, no false positives with K/N > 7.5 were detected, while a non-negligible fraction of them appear for smaller K/N. A limit of K/N = 7.5 seems therefore a safe threshold to attest the veracity of planetary signals for RV measurements with similar properties to those of the different RV fitting challenge systems.