Doppler Monitoring of five K2 Transiting Planetary Systems

Doppler Monitoring of five K2 Transiting Planetary Systems

Authors:

Dai et al

Abstract:

In an effort to measure the masses of planets discovered by the NASA {\it K2} mission, we have conducted precise Doppler observations of five stars with transiting planets. We present the results of a joint analysis of these new data and previously published Doppler data. The first star, an M dwarf known as K2-3 or EPIC~201367065, has three transiting planets ("b", with radius 2.1 R⊕; "c", 1.7 R⊕; and "d", 1.5 R⊕). Our analysis leads to the mass constraints: Mb=8.1+2.0−1.9 M⊕ and Mc less than 4.2 M⊕~(95\%~conf.). The mass of planet d is poorly constrained because its orbital period is close to the stellar rotation period, making it difficult to disentangle the planetary signal from spurious Doppler shifts due to stellar activity. The second star, a G dwarf known as K2-19 or EPIC~201505350, has two planets ("b", 7.7 R⊕; and "c", 4.9 R⊕) in a 3:2 mean-motion resonance, as well as a shorter-period planet ("d", 1.1 R⊕). We find Mb= 28.5+5.4−5.0 M⊕, Mc= 25.6+7.1−7.1 M⊕ and Md less than 14.0 M⊕~(95\%~conf.). The third star, a G dwarf known as K2-24 or EPIC~203771098, hosts two transiting planets ("b", 5.7 R⊕; and "c", 7.8 R⊕) with orbital periods in a nearly 2:1 ratio. We find Mb= 19.8+4.5−4.4 M⊕ and Mc = 26.0+5.8−6.1 M⊕.

Determining the Masses of K2-19b and K2-19c

Mass determination of K2-19b and K2-19c from radial velocities and transit timing variations

Authors:

Nespral et al

Abstract:

We present FIES@NOT and HARPS-N@TNG radial velocity follow-up observations of K2-19, a compact planetary system hosting three planets, of which the two larger ones, namely K2-19b and K2-19c, are close to the 3:2 mean motion resonance. The masses of these larger planets have previously been derived from transit timing only. An analysis considering only the radial velocity measurements is able to detect only K2-19b, the largest and more massive planet in the system, with a mass of 71.7±6.3 M⊕. We also used the TRADES code to simultaneously model both our RV measurements and the existing transit-timing measurements. We derived a mass of K2-19b of 59.5+7.2−11.4 M⊕ and of K2-19c of 9.7+3.9−2.0 M⊕. A prior K2-19b mass estimated by Barros 2015, based exclusively on transit timing measurements, is only consistent with our combined TTV and RV analysis, but not with our analysis based purely on RV measurements. K2-19b supports the suspicion that planet masses and densities involving TTV data are systematically lower than those based purely on RV measurements.

A Different Interpretation of K2-19: An Inflated hot Neptune and Regular Neptune Class

Photo-dynamical mass determination of the multi-planetary system K2-19

Authors:

Barros et al

Abstract:

K2-19 is the second multi-planetary system discovered with K2 observations. The system is composed of two Neptune size planets close to the 3:2 mean-motion resonance. To better characterise the system we obtained two additional transit observations of K2-19b and five additional radial velocity observations. These were combined with K2 data and fitted simultaneously with the system dynamics (photo-dynamical model) which increases the precision of the transit time measurements. The higher transit time precision allows us to detect the chopping signal of the dynamic interaction of the planets that in turn permits to uniquely characterise the system. Although the reflex motion of the star was not detected, dynamic modelling of the system allowed us to derive planetary masses of Mb=44±12M⊕ and Mc=15.9±7.0M⊕ for the inner and the outer planets respectively, leading to densities close to Uranus. We also show that our method allows the derivation of mass ratios using only the 80 days of observations during the first campaign of K2.