Helium is the second-most abundant element in the Universe after hydrogen and is one of the main constituents of gas-giant planets in our Solar System. Early theoretical models predicted helium to be ...among the most readily detectable species in the atmospheres of exoplanets, especially in extended and escaping atmospheres
. Searches for helium, however, have hitherto been unsuccessful
. Here we report observations of helium on an exoplanet, at a confidence level of 4.5 standard deviations. We measured the near-infrared transmission spectrum of the warm gas giant
WASP-107b and identified the narrow absorption feature of excited metastable helium at 10,833 angstroms. The amplitude of the feature, in transit depth, is 0.049 ± 0.011 per cent in a bandpass of 98 angstroms, which is more than five times greater than what could be caused by nominal stellar chromospheric activity. This large absorption signal suggests that WASP-107b has an extended atmosphere that is eroding at a total rate of 10
to 3 × 10
grams per second (0.1-4 per cent of its total mass per billion years), and may have a comet-like tail of gas shaped by radiation pressure.
Aims: This study investigates the antimicrobial activity and mode of action of two natural products, eugenol and thymol, a commonly utilized biostatic agent, triclocarban (TCC), and two surfactants, ...didecyldimethylammonium chloride (DDDMAC) and C10–C16 alkyldimethyl amine N‐oxides (ADMAO).
Methods and Results: Methods used included: determination of minimum inhibitory concentrations (MICs), lethal effect studies with suspension tests and the investigation of sub‐MIC concentrations on growth of E. coli, Staph. aureus and Ps. aeruginosa using a Bioscreen microbiological analyser. Leakage of intracellular constituents and the effects of potentiating agents were also investigated. Only DDDMAC was bactericidal against all of the organisms tested. Eugenol, thymol and ADMAO showed bacteriostatic and bactericidal activity, but not against Ps. aeruginosa. TCC was only bacteristatic against Staph. aureus, but like the other agents, it did affect the growth of the other organisms in the Bioscreen experiments. All of the antimicrobial agents tested were potentiated by the permeabilizers to some extent and leakage of potassium was seen with all of the agents except TCC.
Conclusions: DDDMAC was bactericidal against all organisms tested and all compounds had some bacteriostatic action. Low level static effects on bacterial growth were seen with sub‐MIC concentrations. Membrane damage may account for at least part of the mode of action of thymol, eugenol, DDDMAC and ADMAO.
Significance and Impact of the Study: The ingredients evaluated demonstrated a range of bactericidal and bacteriostatic properties against the Gram‐negative and ‐positive organisms evaluated and the membrane (leakage of intracellular components) was implicated in the mode of action for most (except TCC). Sub‐MIC levels of all ingredients did induce subtle effects on the organisms which impacted bacterial growth, even for those which had no true inhibitory effects.
ABSTRACT We present Hubble Space Telescope (HST) optical and near-ultraviolet transmission spectra of the transiting hot Jupiter HD189733b, taken with the repaired Space Telescope Imaging ...Spectrograph (STIS) instrument. The resulting spectra cover the range 2900-5700Å and reach per exposure signal-to-noise ratio levels greater than 11000 within a 500-Å bandwidth. We used time series spectra obtained during two transit events to determine the wavelength dependence of the planetary radius and measure the exoplanet's atmospheric transmission spectrum for the first time over this wavelength range. Our measurements, in conjunction with existing HST spectra, now provide a broad-band transmission spectrum covering the full optical regime. The STIS data also show unambiguous evidence of a large occulted stellar spot during one of our transit events, which we use to place constraints on the characteristics of the K dwarf's stellar spots, estimating spot temperatures around Teff 4250K. With contemporaneous ground-based photometric monitoring of the stellar variability, we also measure the correlation between the stellar activity level and transit-measured planet-to-star radius contrast, which is in good agreement with predictions. We find a planetary transmission spectrum in good agreement with that of Rayleigh scattering from a high-altitude atmospheric haze as previously found from HST Advanced Camera for Surveys. The high-altitude haze is now found to cover the entire optical regime and is well characterized by Rayleigh scattering. These findings suggest that haze may be a globally dominant atmospheric feature of the planet which would result in a high optical albedo at shorter optical wavelengths. PUBLICATION ABSTRACT
The nearby transiting planet HD 189733b was observed during three transits with the Advanced Camera for Surveys of the Hubble Space Telescope in spectroscopic mode. The resulting time-series of 675 ...spectra covers the 550–1050 nm range, with a resolution element of ∼8 nm, at extremely high accuracy (signal-to-noise ratio up to 10 000 in 50-nm intervals in each individual spectrum). Using these data, we disentangle the effects of limb darkening, measurement systematics and spots on the surface of the host star, to calculate the wavelength dependence of the effective transit radius to an accuracy of ∼50 km. This constitutes the ‘transmission spectrum’ of the planetary atmosphere. It indicates at each wavelength at what height the planetary atmosphere becomes opaque to the grazing stellar light during the transit. In this wavelength range, strong features due to sodium, potassium and water are predicted by atmosphere models for a planet like HD 189733b, but they can be hidden by broad absorption from clouds or hazes higher up in the atmosphere. We observed an almost featureless transmission spectrum between 550 and 1050 nm, with no indication of the expected sodium or potassium atomic absorption features. Comparison of our results with the transit radius observed in the near and mid-infrared (2–8 μm), and the slope of the spectrum, suggest the presence of a haze of submicrometre particles in the upper atmosphere of the planet.
Abstract
A major obstacle to detecting and characterizing long-period, low-mass exoplanets is the intrinsic radial-velocity (RV) variability of host stars. To better understand RV variability, we ...estimate disk-averaged RV variations of the Sun over its magnetic cycle, from the Fe
i
line observed by SDO/HMI, using a physical model for rotationally modulated magnetic activity that was previously validated against HARPS-N solar observations. We estimate the unsigned magnetic flux and show that a linear fit to it reduces the
rms
of RV variations by 62%, i.e., a factor of 2.6. We additionally apply the
FF
′ method, which predicts RV variations based on a star’s photometric variations. At cycle maximum, we find that additional processes must be at play beyond suppression of convective blueshift and velocity imbalances resulting from brightness inhomogeneities, in agreement with recent studies of RV variations. By modeling RV variations over the magnetic cycle using a linear fit to the unsigned magnetic flux, we recover injected planets at a period of ≈300 days with RV semi-amplitudes down to 0.3 m s
−1
. To reach 0.1 m s
−1
, we will need to identify and model additional phenomena that are not well traced by
∣
B
ˆ
obs
∣
or
FF
′. This study motivates ongoing and future efforts to develop observation and analysis techniques to measure the unsigned magnetic flux at high precision in slowly rotating, relatively inactive stars like the Sun. We conclude that the unsigned magnetic flux is an excellent proxy for rotationally modulated, activity-induced RV variations, and could become key to confirming and characterizing Earth analogs.
Abstract
The time-variable velocity fields of solar-type stars limit the precision of radial-velocity determinations of their planets’ masses, obstructing detection of Earth twins. Since 2015 July, ...we have been monitoring disc-integrated sunlight in daytime using a purpose-built solar telescope and fibre feed to the HARPS-N stellar radial-velocity spectrometer. We present and analyse the solar radial-velocity measurements and cross-correlation function (CCF) parameters obtained in the first 3 yr of observation, interpreting them in the context of spatially resolved solar observations. We describe a Bayesian mixture-model approach to automated data-quality monitoring. We provide dynamical and daily differential-extinction corrections to place the radial velocities in the heliocentric reference frame, and the CCF shape parameters in the sidereal frame. We achieve a photon-noise-limited radial-velocity precision better than 0.43 m s−1 per 5-min observation. The day-to-day precision is limited by zero-point calibration uncertainty with an RMS scatter of about 0.4 m s−1. We find significant signals from granulation and solar activity. Within a day, granulation noise dominates, with an amplitude of about 0.4 m s−1 and an autocorrelation half-life of 15 min. On longer time-scales, activity dominates. Sunspot groups broaden the CCF as they cross the solar disc. Facular regions temporarily reduce the intrinsic asymmetry of the CCF. The radial-velocity increase that accompanies an active-region passage has a typical amplitude of 5 m s−1 and is correlated with the line asymmetry, but leads it by 3 d. Spectral line-shape variability thus shows promise as a proxy for recovering the true radial velocity.
State-of-the-art radial-velocity (RV) exoplanet searches are currently limited by RV signals arising from stellar magnetic activity. We analyze solar observations acquired over a 3 yr period during ...the decline of Carrington Cycle 24 to test models of RV variation of Sun-like stars. A purpose-built solar telescope at the High Accuracy Radial-velocity Planet Searcher for the Northern hemisphere (HARPS-N) provides disk-integrated solar spectra, from which we extract RVs and log R HK ′ . The Solar Dynamics Observatory (SDO) provides disk-resolved images of magnetic activity. The Solar Radiation and Climate Experiment (SORCE) provides near-continuous solar photometry, analogous to a Kepler light curve. We verify that the SORCE photometry and HARPS-N log R HK ′ correlate strongly with the SDO-derived magnetic filling factor, while the HARPS-N RV variations do not. To explain this discrepancy, we test existing models of RV variations. We estimate the contributions of the suppression of convective blueshift and the rotational imbalance due to brightness inhomogeneities to the observed HARPS-N RVs. We investigate the time variation of these contributions over several rotation periods, and how these contributions depend on the area of active regions. We find that magnetic active regions smaller than 60 Mm2 do not significantly suppress convective blueshift. Our area-dependent model reduces the amplitude of activity-induced RV variations by a factor of two. The present study highlights the need to identify a proxy that correlates specifically with large, bright magnetic regions on the surfaces of exoplanet-hosting stars.
Social insect colonies are models for complex systems with sophisticated, efficient, and robust allocation of workers to necessary tasks. Despite this, it is commonly reported that many workers ...appear inactive. Could this be an artifact resulting from the simplified laboratory conditions in most studies? Here, we test whether the time allocated to different behavioral states differs between field and laboratory colonies of Temnothorax rugatulus ants. Our results show no difference in colony time budgets between laboratory and field observations for any of the observed behaviors, including ‘inactivity’. This suggests that, on the timescale of a few months, laboratory conditions do not impact task allocation at the colony level. We thus provide support for a previously untested assumption of laboratory studies on division of labor in ants. High levels of inactivity, common in social insects, thus appear to not be a laboratory artifact, but rather a naturally occurring trait.
We present Hubble Space Telescope (HST) optical and near-ultraviolet transmission spectra of the transiting hot Jupiter HD 189733b, taken with the repaired Space Telescope Imaging Spectrograph (STIS) ...instrument. The resulting spectra cover the range 2900-5700 Å and reach per exposure signal-to-noise ratio levels greater than 11 000 within a 500-Å bandwidth. We used time series spectra obtained during two transit events to determine the wavelength dependence of the planetary radius and measure the exoplanet's atmospheric transmission spectrum for the first time over this wavelength range. Our measurements, in conjunction with existing HST spectra, now provide a broad-band transmission spectrum covering the full optical regime. The STIS data also show unambiguous evidence of a large occulted stellar spot during one of our transit events, which we use to place constraints on the characteristics of the K dwarf's stellar spots, estimating spot temperatures around T
eff∼ 4250 K. With contemporaneous ground-based photometric monitoring of the stellar variability, we also measure the correlation between the stellar activity level and transit-measured planet-to-star radius contrast, which is in good agreement with predictions. We find a planetary transmission spectrum in good agreement with that of Rayleigh scattering from a high-altitude atmospheric haze as previously found from HST Advanced Camera for Surveys. The high-altitude haze is now found to cover the entire optical regime and is well characterized by Rayleigh scattering. These findings suggest that haze may be a globally dominant atmospheric feature of the planet which would result in a high optical albedo at shorter optical wavelengths.
Super-Earths belong to a class of planet not found in the Solar system, but which appear common in the Galaxy. Given that some super-Earths are rocky, while others retain substantial atmospheres, ...their study can provide clues as to the formation of both rocky and gaseous planets, and – in particular – they can help to constrain the role of photoevaporation in sculpting the exoplanet population. GJ 9827 is a system already known to host three super-Earths with orbital periods of 1.2, 3.6, and 6.2 d. Here, we use new HARPS-N radial velocity measurements, together with previously published radial velocities, to better constrain the properties of the GJ 9827 planets. Our analysis cannot place a strong constraint on the mass of GJ 9827 c, but does indicate that GJ 9827 b is rocky with a composition that is probably similar to that of the Earth, while GJ 9827 d almost certainly retains a volatile envelope. Therefore, GJ 9827 hosts planets on either side of the radius gap that appears to divide super-Earths into pre-dominantly rocky ones that have radii below ∼1.5Rꚛ, and ones that still retain a substantial atmosphere and/or volatile components, and have radii above ∼2Rꚛ. That the less heavily irradiated of the three planets still retains an atmosphere, may indicate that photoevaporation has played a key role in the evolution of the planets in this system.
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