We present the weak lensing analysis of the Wide-Field Imager Sunyaev–Zel'dovich Cluster of Galaxy (WISCy) sample, a set of 12 clusters of galaxies selected for their Sunyaev–Zel'dovich (SZ) effect. ...After developing new and improved methods for background selection and determination of geometric lensing scaling factors from absolute multiband photometry in cluster fields, we compare the weak lensing mass estimate with public X-ray and SZ data. We find consistency with hydrostatic X-ray masses with no significant bias, no mass dependent bias and less than 20 per cent intrinsic scatter and constrain
$f_{\rm{gas},500c}=0.128^{+0.029}_{-0.023}$
. We independently calibrate the South Pole Telescope significance–mass relation and find consistency with previous results. The comparison of weak lensing mass and Planck Compton parameters, whether extracted self-consistently with a mass–observable relation (MOR) or using X-ray prior information on cluster size, shows significant discrepancies. The deviations from the MOR strongly correlate with cluster mass and redshift. This could be explained either by a significantly shallower than expected slope of Compton decrement versus mass and a corresponding problem in the previous X-ray based mass calibration, or a size or redshift dependent bias in SZ signal extraction.
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 Teff 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 0.17b(+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.
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Context. GJ 1214b, the 6.55 Earth-mass transiting planet recently discovered by the MEarth team, has a mean density of ~35% of that of the Earth. It is thought that this planet is either a ...mini-Neptune, consisting of a rocky core with a thick, hydrogen-rich atmosphere, or a planet with a composition dominated by water. Aims. In the case of a hydrogen-rich atmosphere, molecular absorption and scattering processes may result in detectable radius variations as a function of wavelength. The aim of this paper is to measure these variations. Methods. We have obtained observations of the transit of GJ 1214b in the r- and I-band with the Isaac Newton Telescope (INT), in the g-, r-, i- and z-bands with the 2.2 m MPI/ESO telescope, in the Ks-band with the Nordic Optical Telescope (NOT), and in the Kc-band with the William Herschel Telescope (WHT). By comparing the transit depth between the the different bands, which is a measure for the planet-to-star size ratio, the atmosphere is investigated. Results. We do not detect clearly significant variations in the planet-to-star size ratio as function of wavelength. Although the ratio at the shortest measured wavelength, in g-band, is 2σ larger than in the other bands. The uncertainties in the Ks and Kc bands are large, due to systematic features in the light curves. Conclusions. The tentative increase in the planet-to-star size ratio at the shortest wavelength could be a sign of an increase in the effective planet-size due to Rayleigh scattering, which would require GJ 1214b to have a hydrogen-rich atmosphere. If true, then the atmosphere has to have both clouds, to suppress planet-size variations at red optical wavelengths, as well as a sub-solar metallicity, to suppress strong molecular features in the near- and mid-infrared. However, star spots, which are known to be present on the host-star’s surface, can (partly) cancel out the expected variations in planet-to-star size ratio, because the lower surface temperature of the spots causes the effective size of the star to vary with wavelength. A hypothetical spot-fraction of ~10%, corresponding to an average stellar dimming of ~5% in the i-band, would be able to raise the near- and mid-infrared points sufficiently with respect to the optical measurements to be inconsistent with a water-dominated atmosphere. Modulation of the spot fraction due to the stellar rotation would in such case cause the observed flux variations of GJ 1214.
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We report results of a study of Planck Sunyaev–Zel'dovich effect selected galaxy cluster candidates using the Panoramic Survey Telescope & Rapid Response System (Pan-STARRS) imaging data. We first ...examine 150 Planck-confirmed galaxy clusters with spectroscopic redshifts to test our algorithm for identifying optical counterparts and measuring their redshifts; our redshifts have a typical accuracy of σ
z/(1+z) ∼ 0.022 for this sample. Using 60 random sky locations, we estimate that our chance of contamination through a random superposition is ∼3 per cent. We then examine an additional 237 Planck galaxy cluster candidates that have no redshift in the source catalogue. Of these 237 unconfirmed cluster candidates we are able to confirm 60 galaxy clusters and measure their redshifts. A further 83 candidates are so heavily contaminated by stars due to their location near the Galactic plane that we do not attempt to identify counterparts. For the remaining 94 candidates, we find no optical counterpart but use the depth of the Pan-STARRS1 data to estimate a redshift lower limit
$z_{{\rm lim}(10^{15})}$
beyond which we would not have expected to detect enough galaxies for confirmation. Scaling from the already published Planck sample, we expect that ∼12 of these unconfirmed candidates may be real clusters.
Search for giant planets in M 67 Brucalassi, A.; Koppenhoefer, J.; Saglia, R. ...
Astronomy & astrophysics,
07/2017, Volume:
603
Journal Article
Peer reviewed
Open access
Context. We present the results of a seven-year-long radial velocity survey of a sample of 88 main-sequence and evolved stars to reveal signatures of Jupiter-mass planets in the solar-age and ...solar-metallicity open cluster M 67. Aims. We aim at studying the frequency of giant planets in this cluster with respect to the field stars. In addition, our sample is also ideal to perform a long-term study to compare the chemical composition of stars with and without giant planets in detail. Methods. We analyzed precise radial velocity (RV) measurements obtained with the HARPS spectrograph at the European Southern Observatory (La Silla), the SOPHIE spectrograph at the Observatoire de Haute-Provence (France), the HRS spectrograph at the Hobby Eberly Telescope (Texas), and the HARPS-N spectrograph at the Telescopio Nazionale Galileo (La Palma). Additional RV data come from the CORALIE spectrograph at the Euler Swiss Telescope (La Silla). We conducted Monte Carlo simulations to estimate the occurrence rate of giant planets in our radial velocity survey. We considered orbital periods between 1.0 day and 1000 days and planet masses between 0.2 MJ and 10.0 MJ. We used a measure of the observational detection efficiency to determine the frequency of planets for each star. Results. All the planets previously announced in this RV campaign with their properties are summarized here: 3 hot Jupiters around the main-sequence stars YBP1194, YBP1514, and YBP401, and 1 giant planet around the evolved star S364. Two additional planet candidates around the stars YBP778 and S978 are also analyzed in the present work. We discuss stars that exhibit large RV variability or trends individually. For 2 additional stars, long-term trends are compatible with new binary candidates or substellar objects, which increases the total number of binary candidates detected in our campaign to 14. Based on the Doppler-detected planets discovered in this survey, we find an occurrence of giant planets of ~18.0+12.0-8.0% in the selected period-mass range. This frequency is slightly higher but consistent within the errors with the estimate for the field stars, which leads to the general conclusion that open cluster and field statistics agree. However, we find that the rate of hot Jupiters in the cluster (~5.7+5.5-3.0%) is substantially higher than in the field.
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ABSTRACT We present the results of the decade-long M31 observation from the Wendelstein Calar Alto Pixellensing Project (WeCAPP). WeCAPP has monitored M31 from 1997 until 2008 in both R- and ...I-filters, and thus provides the longest baseline of all M31 microlensing surveys. The data are analyzed with difference imaging analysis, which is most suitable for studying variability in crowded stellar fields. We extracted light curves based on each pixel, and devised selection criteria that are optimized to identify microlensing events. This leads to 10 new events, and adds up to a total of 12 microlensing events from WeCAPP, for which we derive their timescales, flux excesses, and colors from their light curves. The colors of the lensed stars fall in the range (R − I) = 0.56 to 1.36, with a median of 1.0 mag, in agreement with our expectation that the sources are most likely bright, red stars at the post-main-sequence stage. The event FWHM timescales range from 0.5 to 14 days, with a median of 3 days, in good agreement with predictions based on the model of Riffeser et al.
Hot Jupiters seem to get rarer with decreasing stellar mass. The goal of the Pan-Planets transit survey was the detection of such planets and a statistical characterization of their frequency. Here, ...we announce the discovery and validation of two planets found in that survey, Wendelstein-1b and Wendelstein-2b, which are two short-period hot Jupiters that orbit late K host stars. We validated them both by the traditional method of radial velocity measurements with the HIgh Resolution Echelle Spectrometer and the Habitable-zone Planet Finder instruments and then by their Transit Color Signature (TraCS). We observed the targets in the wavelength range of 4000−24 000 Å and performed a simultaneous multiband transit fit and additionally determined their thermal emission via secondary eclipse observations. Wendelstein-1b is a hot Jupiter with a radius of 1.0314
−0.0061
+0.0061
R
J
and mass of 0.592
−0.129
+0.0165
M
J
, orbiting a K7V dwarf star at a period of 2.66 d, and has an estimated surface temperature of about 1727
−90
+78
K. Wendelstein-2b is a hot Jupiter with a radius of 1.1592
−0.0210
+0.0204
R
J
and a mass of 0.731
−0.311
+0.0541
M
J
, orbiting a K6V dwarf star at a period of 1.75 d, and has an estimated surface temperature of about 1852
−140
+120
K. With this, we demonstrate that multiband photometry is an effective way of validating transiting exoplanets, in particular for fainter targets since radial velocity follow-up becomes more and more costly for those targets.
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Context. Ground-based simultaneous multiband transit observations allow an accurate system parameter determination and may lead to the detection and characterization of additional bodies via the ...transit timing variations (TTVs) method. Aims. We aim to (i) characterize the heavily bloated WASP-4b hot Jupiter and its star by measuring system parameters and the dependence of the planetary radius as a function of four (Sloan g′, r′, i′, z′) wavelengths and (ii) search for TTVs. Methods. We recorded 987 images during three complete transits with the GROND instrument, mounted on the MPG/ESO-2.2 m telescope at La Silla Observatory. Assuming a quadratic law for the stellar limb-darkening, we derived the system parameters by simultaneous fitting a composite transit light curve over all bandpasses. To compute uncertainties of the fitted parameters, we employed the bootstrap Monte Carlo method. Results. The three central transit times are measured with precision down to 6 s. We find a planetary radius Rp = 1.413 ± 0.020 RJup, an orbital inclination \hbox{$i = 88\fdg 57 \pm 0.45^{\circ}$}i=88.°57±0.45◦ and calculate a new ephemeris, a period P = 1.33823144 ± 0.00000032 days and a reference transit epoch T0 = 2 454 697.798311 ± 0.000046 (BJD). Analysis of the new transit mid-times in combination with previous measurements shows no sign of a TTV signal greater than 20 s. We perform simplified numerical simulations to place upper-mass limits of a hypothetical perturber in the WASP-4b system.
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We report the discovery of WTS-2 b, an unusually close-in 1.02-d hot Jupiter (M
P
= 1.12M
J, R
P
= 1.30R
J) orbiting a K2V star, which has a possible gravitationally bound M-dwarf companion at 0.6 ...arcsec separation contributing ∼20 per cent of the total flux in the observed J-band light curve. The planet is only 1.5 times the separation from its host star at which it would be destroyed by Roche lobe overflow, and has a predicted remaining lifetime of just ∼40 Myr, assuming a tidal dissipation quality factor of
.
is a key factor in determining how frictional processes within a host star affect the orbital evolution of its companion giant planets, but it is currently poorly constrained by observations. We calculate that the orbital decay of WTS-2 b would correspond to a shift in its transit arrival time of T
shift ∼ 17 s after 15 yr assuming
. A shift less than this would place a direct observational constraint on the lower limit of
in this system. We also report a correction to the previously published expected T
shift for WASP-18 b, finding that T
shift = 356 s after 10 yr for
, which is much larger than the estimated 28 s quoted in WASP-18 b discovery paper. We attempted to constrain
via a study of the entire population of known transiting hot Jupiters, but our results were inconclusive, requiring a more detailed treatment of transit survey sensitivities at long periods. We conclude that the most informative and straightforward constraints on
will be obtained by direct observational measurements of the shift in transit arrival times in individual hot Jupiter systems. We show that this is achievable across the mass spectrum of exoplanet host stars within a decade, and will directly probe the effects of stellar interior structure on tidal dissipation.
Abstract
We report on the discovery of four ultra-short-period (P ≤ 0.18 d) eclipsing M-dwarf binaries in the Wide-Field Camera (WFCAM) Transit Survey. Their orbital periods are significantly shorter ...than that of any other known main-sequence binary system, and are all significantly below the sharp period cut-off at P ∼ 0.22 d as seen in binaries of earlier-type stars. The shortest-period binary consists of two M4-type stars in a P = 0.112 d orbit. The binaries are discovered as part of an extensive search for short-period eclipsing systems in over 260 000 stellar light curves, including over 10 000 M-dwarfs down to J = 18 mag, yielding 25 binaries with P ≤ 0.23 d. In a popular paradigm, the evolution of short-period binaries of cool main-sequence stars is driven by the loss of angular momentum through magnetized winds. In this scheme, the observed P ∼ 0.22 d period cut-off is explained as being due to time-scales that are too long for lower-mass binaries to decay into tighter orbits. Our discovery of low-mass binaries with significantly shorter orbits implies that either these time-scales have been overestimated for M-dwarfs, e.g. due to a higher effective magnetic activity, or the mechanism for forming these tight M-dwarf binaries is different from that of earlier-type main-sequence stars.
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