Pan-Planets: Searching for hot Jupiters around cool dwarfs

Abstract

The Pan-Planets survey observed an area of 42 sq deg. in the galactic disk for about 165 h. The main scientific goal of the project is the detection of transiting planets around M dwarfs. We establish an efficient procedure for determining the stellar parameters T eff and log g of all sources using a method based on SED fitting, utilizing a three-dimensional dust map and proper motion information. In this way we identify more than 60 000 M dwarfs, which is by far the largest sample of low-mass stars observed in a transit survey to date. We present several planet candidates around M dwarfs and hotter stars that are currently being followed up. Using Monte Carlo simulations we calculate the detection efficiency of the Pan-Planets survey for different stellar and planetary populations. We expect to find 3.0 +3.3 −1.6 hot Jupiters around F, G, and K dwarfs with periods lower than 10 days based on the planet occurrence rates derived in previous surveys. For M dwarfs, the percentage of stars with a hot Jupiter is under debate. Theoretical models expect a lower occurrence rate than for larger main sequence stars. However, radial velocity surveys find upper limits of about 1% due to their small sample, while the Kepler survey finds a occurrence rate that we estimate to be at least 0.17( +0.67 −0.04 )%, making it even higher than the determined fraction from OGLE-III for F, G and K stellar types, 0.14( +0.15 −0.076 )%. With the large sample size of Pan-Planets, we are able to determine an occurrence rate of 0.11( +0.37 −0.02 )% in case one of our candidates turns out to be a real detection. If, however, none of our candidates turn out to be true planets, we are able to put an upper limit of 0.34% with a 95% confidence on the hot Jupiter occurrence rate of M dwarfs. This limit is a significant improvement over previous estimates where the lowest limit published so far is 1.1% found in the WFCAM Transit Survey. Therefore we cannot yet confirm the theoretical prediction of a lower occurrence rate for cool stars.

K2 Discovers a Busy Bee: An Unusual Transiting Neptune Found in the Beehive Cluster

“…We utilize the spectral energy distribution (SED) fitting code from Obermeier et al (2016) as an additional layer of our stellar type characterization. In contrast to spectroscopy, this approach relies on broadband photometry.…”

“…The combined RV constraints from our multi-epoch HIRES observations are described further in Section 4.1. Note.References are: 1-EPIC Catalog, 2- Kraus & Hillenbrand (2007), 3-this work, 4-Pan-STARRS1 3π catalog (version PV3), 5-2MASS catalog, 6 -this work, using (Mann et al 2016a), 7-this work, using SED fitting from Obermeier et al (2016), 8-this work, using Newton et al (2015).…”

“…We supply the algorithm with all of our determined constraints, including stellar photometry from 2MASS and WISE, contrast curves from high-angular resolution imaging and the light curve from K2. Furthermore, we also extract the photometric light curve from Vanderburg & Johnson (2014), remove the periodic modulations, recover the signal with the Pan-Planets signal detection pipeline (Obermeier et al 2016) and then perform the same analysis. This way, we end up with an independent confirmation based on a different data reduction and signal detection routine.…”

An ALMA Survey of CO Isotopologue Emission from Protoplanetary Disks in Chamaeleon I

“…The initial disk mass, the evolution of the gas-to-dust ratio, the evolution of gas surface density distribution with time, and the gas dispersal timescale all influence how many and what types of planets can form in a stellar system (e.g., Pollack et al 1996;Boss 1997;Mordasini et al 2012;Alexander et al 2014). Statistical studies reveal possible correlations between stellar mass and planet occurrence rates, including a higher frequency of small planets in close orbits around M dwarfs than around FGK stars (Howard et al 2012;Mulders et al 2015a) and a higher occurrence rate of giant planets around solar-type stars than around M dwarfs , although this correlation may not apply to hot Jupiters (Obermeier et al 2016). While these relationships likely originate in correlations between stellar mass and disk properties, linking disk properties to the outcome of planet formation requires an unbiased census of initial disk masses and the evolution of disk mass and structure with time.…”

The CARMENES search for exoplanets around M dwarfs

“…Only 20 of them are more massive than 0.1 M Jupiter , suggesting that M dwarfs host fewer giant planets than solar-mass stars (Cumming et al 2008;Johnson et al 2010). While this may be a consequence of the hot Jupiters being more frequent around hotter stars because more building material is available (Mordasini et al 2012), the trend has not been confirmed so far in transit surveys (e.g., Johnson et al 2012;Obermeier et al 2016). Low-mass stars are also suspected to favor multi-planet systems, which results in an average of more than two planets per host star (Dressing & Charbonneau 2015).…”