206 research outputs found
Discovering planets with PLATO: Comparison of algorithms for stellar activity filtering
Context. To date, stellar activity is one of the main limitations in
detecting small exoplanets via transit photometry. Since this activity is
enhanced in young stars, traditional filtering algorithms may severely
under-perform in detecting such exoplanets.
Aims.This paper aims to compare the relative performances of four algorithms
developed by independent research groups specifically for the filtering of
activity in the light curves (LCs) of young active stars, prior to the search
for planetary transit signals: Notch and LOCoR(N&L), Young Stars
Detrending(YSD), K2 Systematics Correction(K2SC) and VARLET. We include in the
comparison also the two best-performing algorithms implemented in Wotan, namely
the Tukey's biweight and the Huber Spline.
Methods. We performed a series of injection-retrieval tests of planetary
transits of different types, from Jupiter down to Earth-sized planets, moving
both on circular and eccentric orbits. The tests were carried out over 100
simulated LCs of both quiet and active solar-like stars that will be observed
by the ESA space telescope PLATO.
Results. We found that N&L is the best choice in many cases, since it misses
the lowest number of transits. However, it under-performs if the planetary
orbital period closely matches the stellar rotation period, especially in the
case of small planets for which the biweight and VARLET algorithms work better.
For LCs with a large number of data, the combined results of YSD and Huber
Spline yield the highest recovery percentage. Filtering algorithms allow us to
get a very precise estimate of the orbital period and the mid-transit time of
the detected planets, while the planet-to-star radius is under-estimated most
of the time, especially in the case of grazing transits or eccentric orbits. A
refined filtering taking into account the presence of the planet is compulsory
for a proper planetary characterization.Comment: 25 pages, accepted for publication by A&
Sub-stellar companions of intermediate-mass stars with CoRoT: CoRoTâ34b, CoRoTâ35b, and CoRoTâ36b
Theories of planet formation give contradicting results of how frequent close-in giant planets of intermediate mass stars (IMSs; 1.3â€Mââ€3.2Mââ ) are. Some theories predict a high rate of IMSs with close-in gas giants, while others predict a very low rate. Thus, determining the frequency of close-in giant planets of IMSs is an important test for theories of planet formation. We use the CoRoT survey to determine the absolute frequency of IMSs that harbour at least one close-in giant planet and compare it to that of solar-like stars. The CoRoT transit survey is ideal for this purpose, because of its completeness for gas-giant planets with orbital periods of less than 10 d and its large sample of main-sequence IMSs. We present a high precision radial velocity follow-up programme and conclude on 17 promising transit candidates of IMSs, observed with CoRoT. We report the detection of CoRoTâ34b, a brown dwarf close to the hydrogen burning limit, orbiting a 1.1âGyr A-type main-sequence star. We also confirm two inflated giant planets, CoRoTâ35b, part of a possible planetary system around a metal-poor star, and CoRoTâ36b on a misaligned orbit. We find that 0.12±0.10 per cent of IMSs between 1.3â€Mââ€1.6Mâ observed by CoRoT do harbour at least one close-in giant planet. This is significantly lower than the frequency (â 0.70±0.16 per centâ ) for solar-mass stars, as well as the frequency of IMSs harbouring long-period planets (â âŒ8 per centâ )
Revisiting the transits of CoRoT-7b at a lower activity level
CoRoT-7b, the first super-Earth with measured radius discovered, has opened
the new field of rocky exoplanets characterisation. To better understand this
interesting system, new observations were taken with the CoRoT satellite.
During this run 90 new transits were obtained in the imagette mode. These were
analysed together with the previous 151 transits obtained in the discovery run
and HARPS radial velocity observations to derive accurate system parameters. A
difference is found in the posterior probability distribution of the transit
parameters between the previous CoRoT run (LRa01) and the new run (LRa06). We
propose this is due to an extra noise component in the previous CoRoT run
suspected to be transit spot occultation events. These lead to the mean transit
shape becoming V-shaped. We show that the extra noise component is dominant at
low stellar flux levels and reject these transits in the final analysis. We
obtained a planetary radius, , in agreement
with previous estimates. Combining the planetary radius with the new mass
estimates results in a planetary density of
which is consistent with a rocky composition. The CoRoT-7 system remains an
excellent test bed for the effects of activity in the derivation of planetary
parameters in the shallow transit regime.Comment: 13 pages, 13 figures, accepted to A&
K2-137 b: an Earth-sized planet in a 4.3-hour orbit around an M-dwarf
We report the discovery from K2 of a transiting terrestrial planet in an
ultra-short-period orbit around an M3-dwarf. K2-137 b completes an orbit in
only 4.3 hours, the second-shortest orbital period of any known planet, just 4
minutes longer than that of KOI 1843.03, which also orbits an M-dwarf. Using a
combination of archival images, AO imaging, RV measurements, and light curve
modelling, we show that no plausible eclipsing binary scenario can explain the
K2 light curve, and thus confirm the planetary nature of the system. The
planet, whose radius we determine to be 0.89 +/- 0.09 Earth radii, and which
must have a iron mass fraction greater than 0.45, orbits a star of mass 0.463
+/- 0.052 Msol and radius 0.442 +/- 0.044 Rsol.Comment: 12 pages, 9 figures, accepted for publication in MNRA
Ease of use and comfort of a novel sensor insertion device for continuous glucose monitoring.
Background: In continuous glucose monitoring (CGM) the accurate positioning of the sensor in the subcutaneous tissue is a prerequisite for adequate sensor performance. In this study a novel insertion device was investigated with regard to success and reliability of sensor insertion, ease-of-use of the device and discomfort associated with the insertion procedure.
Methods: 50 people with diabetes inserted themselves two sensors, one at the abdomen and a second at the hip/buttock. To determine the insertion length, a sensor with a special scaling was used. The study was approved by the Institutional Review Board and subjects had signed written informed consent.
Results: The sensors were inserted successfully with an insertion length â„8âmm leading to a success rate of sensor insertion of 100%. Pain upon sensor insertion was reported to be low (77.5%) or moderate (18.3%). In comparison to any of the compared measures in diabetes treatment, the discomfort associated with insertion was reported to be equal or less than finger pricking (79.6%), insulin injection (77.6%) and applying other CGM systems (83.3%). Regarding the handling of the insertion device, 80% of the subjects assessed it very easy to use, and 98% rated the operating steps easy to understand.
Conclusion: The novel CGM sensor insertion device can provide people with diabetes a reliable and easy to perform procedure for safe and successful sensor insertion with a minimum of discomfort, also when compared to other CGM devices and in comparison to other measures in diabetes treatment like insulin administration or finger pricking
The transiting multi-planet system HD3167: a 5.7 MEarth Super-Earth and a 8.3 MEarth mini-Neptune
HD3167 is a bright (V=8.9 mag) K0V star observed by the NASA's K2 space
mission during its Campaign 8. It has been recently found to host two small
transiting planets, namely, HD3167b, an ultra short period (0.96 d)
super-Earth, and HD3167c, a mini-Neptune on a relatively long-period orbit
(29.85 d). Here we present an intensive radial velocity follow-up of HD3167
performed with the FIES@NOT, [email protected], and HARPS-N@TNG spectrographs. We
revise the system parameters and determine radii, masses, and densities of the
two transiting planets by combining the K2 photometry with our spectroscopic
data. With a mass of 5.69+/-0.44 MEarth, radius of 1.574+/-0.054 REarth, and
mean density of 8.00(+1.0)(-0.98) g/cm^3, HD3167b joins the small group of
ultra-short period planets known to have a rocky terrestrial composition.
HD3167c has a mass of 8.33 (+1.79)(-1.85) MEarth and a radius of
2.740(+0.106)(-0.100) REarth, yielding a mean density of 2.21(+0.56)(-0.53)
g/cm^3, indicative of a planet with a composition comprising a solid core
surrounded by a thick atmospheric envelope. The rather large pressure scale
height (about 350 km) and the brightness of the host star make HD3167c an ideal
target for atmospheric characterization via transmission spectroscopy across a
broad range of wavelengths. We found evidence of additional signals in the
radial velocity measurements but the currently available data set does not
allow us to draw any firm conclusion on the origin of the observed variation.Comment: 18 pages, 11 figures, 5 table
EPIC 219388192 b - an inhabitant of the brown dwarf desert in the Ruprecht 147 open cluster
We report the discovery of EPIC 219388192 b, a transiting brown dwarf in a
5.3-day orbit around a member star of Ruprecht-147, the oldest nearby open
cluster association, which was photometrically monitored by K2 during its
Campaign 7. We combine the K2 time-series data with ground-based adaptive
optics imaging and high resolution spectroscopy to rule out false positive
scenarios and determine the main parameters of the system. EPIC 219388192 b has
a radius of =~ and mass of
=~, yielding a mean density of
~. The host star is nearly a Solar twin with
mass =~, radius
=~, effective temperature
=~K and iron abundance [Fe/H]=~dex.
Its age, spectroscopic distance, and reddening are consistent with those of
Ruprecht-147, corroborating its cluster membership. EPIC 219388192 b is the
first brown dwarf with precise determinations of mass, radius and age, and
serves as benchmark for evolutionary models in the sub-stellar regime.Comment: 13 pages, 11 figures, 4 tables, submitted to AAS Journal
Three Small Planets Transiting a Hyades Star
We present the discovery of three small planets transiting K2-136 (LP 358
348, EPIC 247589423), a late K dwarf in the Hyades. The planets have orbital
periods of , , and
days, and radii of , , and , respectively. With an age of
600-800 Myr, these planets are some of the smallest and youngest transiting
planets known. Due to the relatively bright (J=9.1) host star, the planets are
compelling targets for future characterization via radial velocity mass
measurements and transmission spectroscopy. As the first known star with
multiple transiting planets in a cluster, the system should be helpful for
testing theories of planet formation and migration.Comment: Accepted to The Astronomical Journa
Exoplanets around Low-mass Stars Unveiled by K2
We present the detection and follow-up observations of planetary candidates
around low-mass stars observed by the K2 mission. Based on light-curve
analysis, adaptive-optics imaging, and optical spectroscopy at low and high
resolution (including radial velocity measurements), we validate 16 planets
around 12 low-mass stars observed during K2 campaigns 5-10. Among the 16
planets, 12 are newly validated, with orbital periods ranging from 0.96-33
days. For one of the planets (K2-151b) we present ground-based transit
photometry, allowing us to refine the ephemerides. Combining our K2 M-dwarf
planets together with the validated or confirmed planets found previously, we
investigate the dependence of planet radius on stellar insolation and
metallicity [Fe/H]. We confirm that for periods days, planets
with a radius are less common than planets with a
radius between 1-2. We also see a hint of the "radius valley"
between 1.5 and 2 that has been seen for close-in planets around
FGK stars. These features in the radius/period distribution could be attributed
to photoevaporation of planetary envelopes by high-energy photons from the host
star, as they have for FGK stars. For the M dwarfs, though, the features are
not as well defined, and we cannot rule out other explanations such as
atmospheric loss from internal planetary heat sources, or truncation of the
protoplanetary disk. There also appears to be a relation between planet size
and metallicity: those few planets larger than about 3 are found
around the most metal-rich M dwarfs.Comment: 29 pages, 21 figures, 6 tables, Accepted in Astronomical Journa
K2-60b and K2-107b. A Sub-Jovian and a Jovian Planet from the K2 Mission
We report the characterization and independent detection of K2-60b, as well as the detection and characterization of K2-107b, two transiting hot gaseous planets from the K2 space mission. We confirm the planetary nature of the two systems and determine their fundamental parameters combining the K2 time-series data with FIES @ NOT and HARPS-N @ TNG spectroscopic observations. K2-60b has a radius of 0.683 +/- 0.037 R-Jup and a mass of 0.426 +/- 0.037 M-Jup and orbits a G4 V star with an orbital period of 3.00267 +/- 0.00006 days. K2-107b has a radius of 1.44 +/- 0.15 R-Jup and a mass of 0.84 +/- 0.08 M-Jup and orbits an F9 IV star every 3.31392 +/- 0.00002 days. K2-60b is among the few planets at the edge of the so-called desert of short-period sub-Jovian planets. K2107b is a highly inflated Jovian planet orbiting an evolved star about to leave the main sequence
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