Dispersed Matter Planet Project discoveries of ablating planets orbiting nearby bright stars

Abstract

Some highly irradiated close-in exoplanets orbit stars showing anomalously low stellar chromospheric emission. We attribute this to absorption by circumstellar gas replenished by mass loss from ablating planets. Here we report statistics validating this hypothesis. Among ~3000 nearby, bright, main sequence stars ~40 show depressed 51chromospheric emission indicative of undiscovered mass-losing planets. The Dispersed Matter Planet Project uses high precision, high cadence radial velocity measurements to detect these planets. We summarise results for two planetary systems (DMPP-1 and DMPP-3) and fully present observations revealing a Mp sin i = 0.469 MJ planet in a 5.207 d orbit around the γ-Doradus pulsator HD 11231 (DMPP-2). We have detected short period planets wherever we have made more than 60 RV measurements, demonstrating that we have originated a very efficient method for detecting nearby compact planetary systems. Our shrouded, ablating planetary systems may be a shortlived phase related to the Neptunian desert: i.e. the dearth of intermediate-mass planets at short orbital periods. The circumstellar gas facilitates compositional analysis; allowing empirical exogeology in the cases of sublimating rocky planets. Dispersed Matter Planet Project discoveries will be important for establishing the empirical mass-radius-composition relationship(s) for low mass planets.Massive planets in short period orbits were the first exoplanets to be discovered, but their low-mass analogues remained elusive for almost two decades. Recently, however, Kepler results have established there is a significant population of low-mass, ultra-short period (USP) planets: 0.51 ± 0.07% of G dwarfs host low-mass USP planets with Porb < 1 d 1 . Most of these planets are smaller than 2 R⊕. Kepler has a narrow field of view, so the planets it discovers are generally distant and difficult to study in detail. Radial velocity (RV) mass determinations of the overwhelming majority of Kepler's small planet discoveries are consequently more-or-less precluded. Nearby analogues of these Kepler USPs must exist, but an enormous effort would be required to find them through targeted RV observations of bright nearby stars with only a 0.5% chance of success for each target. DMPP selects target stars likely to host planets with short orbital periods using archival stellar spectral information. This paper (i) explains the motivation and underlying hypothesis for the DMPP selection criteria, which were developed using inferences from observations of transiting hot Jupiters; (ii) uses the statistics of our first three DMPP planetary system discoveries to test the underlying hypothesis (iii) presents the discovery of DMPP-2 and our RV survey methodology. Companion papers present the discoveries of DMPP-1 and DMPP-3 (this issue of NA); the characteristics of these two systems are briefly summarised to place the hypothesis testing in context.The discovery of an extensive H I exosphere surrounding the hot Jupiter HD 209458 b 2 , and subsequent evidence suggests th...

Atmospheric regimes and trends on exoplanets and brown dwarfs

“…Moreover, the circumstellar gas replenished by mass loss from ablating low-mass planets could absorb stellar chromospheric emission. The Dispersed Matter Planet Project (e.g., Barnes et al 2020;Haswell et al 2020;Staab et al 2020) has recently detected low stellar chromospheric emission around about 40 out of 3000 nearby bright stars, indicating possible existence of highly irradiated, mass-losing exoplanets in these systems. Also, the observed high variability in the transit depths of so-called "super-comets" such as Kepler 1520 b (Rappaport et al 2012;Perez-Becker & Chiang 2013) and K2-22 b (Sanchis-Ojeda et al 2015) suggests that they might experience significant evaporation (e.g., Budaj et al 2020).…”

Discovery and characterization of the exoplanets WASP-148b and c

“…This might be explained by absorption in circumstellar gas that is ablated from the hot planets. This gas will absorb in cores of the Ca II H+K lines (Haswell et al 2012(Haswell et al , 2019Fossati et al 2013;Staab et al 2017). This circumstellar absorption phenomenon may operate in the WASP-148 system, but it has not decreased the log R HK value below the basal limit.…”

LRG-BEASTS: sodium absorption and Rayleigh scattering in the atmosphere of WASP-94A b using NTT/EFOSC2

“…This excess absorption is similar to that seen in WASP-12 b and a number of other hot Jupiters (Fossati et al 2013), where it is interpreted as absorption by circumstellar material escaping the hot Jupiter atmosphere and absorbing the stellar emission of CaII in the H&K lines. This interpretation is supported by the statistical analysis of a larger sample of stars by Haswell et al (2020). It is also supported by the fact that a log 𝑅 HK value this low (and in combination with the colour of the star 𝐵 − 𝑉 = 0.69) would suggest a rotation period of 40 days and a high age of 8 Gyr (Mamajek & Hillenbrand 2008).…”