357 research outputs found
The Hunt for Exomoons with Kepler (HEK): II. Analysis of Seven Viable Satellite-Hosting Planet Candidates
From the list of 2321 transiting planet candidates announced by the Kepler
Mission, we select seven targets with favorable properties for the capacity to
dynamically maintain an exomoon and present a detectable signal. These seven
candidates were identified through our automatic target selection (TSA)
algorithm and target selection prioritization (TSP) filtering, whereby we
excluded systems exhibiting significant time-correlated noise and focussed on
those with a single transiting planet candidate of radius less than 6 Earth
radii. We find no compelling evidence for an exomoon around any of the seven
KOIs but constrain the satellite-to-planet mass ratios for each. For four of
the seven KOIs, we estimate a 95% upper quantile of M_S/M_P<0.04, which given
the radii of the candidates, likely probes down to sub-Earth masses. We also
derive precise transit times and durations for each candidate and find no
evidence for dynamical variations in any of the KOIs. With just a few systems
analyzed thus far in the in-going HEK project, projections on eta-moon would be
premature, but a high frequency of large moons around
Super-Earths/Mini-Neptunes would appear to be incommensurable with our results
so far.Comment: 32 pages, 11 figures, 23 tables, Accepted to Ap
The Hunt for Exomoons with Kepler (HEK): III. The First Search for an Exomoon around a Habitable-Zone Planet
Kepler-22b is the first transiting planet to have been detected in the
habitable-zone of its host star. At 2.4 Earth radii, Kepler-22b is too large to
be considered an Earth-analog, but should the planet host a moon large enough
to maintain an atmosphere, then the Kepler-22 system may yet possess a telluric
world. Aside from being within the habitable-zone, the target is attractive due
to the availability of previously measured precise radial velocities and low
intrinsic photometric noise, which has also enabled asteroseismology studies of
the star. For these reasons, Kepler-22b was selected as a target-of-opportunity
by the 'Hunt for Exomoons with Kepler' (HEK) project. In this work, we conduct
a photodynamical search for an exomoon around Kepler-22b leveraging the
transits, radial velocities and asteroseismology plus several new tools
developed by the HEK project to improve exomoon searches. We find no evidence
for an exomoon around the planet and exclude moons of mass >0.5 Earth masses to
95% confidence. By signal injection and blind retrieval, we demonstrate that an
Earth-like moon is easily detected for this planet even when the
time-correlated noise of the data set is taken into account. We provide updated
parameters for the planet Kepler-22b including a revised mass of <53 Earth
masses to 95% confidence and an eccentricity of 0.13(-0.13)(+0.36) by
exploiting Single-body Asterodensity Profiling (SAP). Finally, we show that
Kepler-22b has a >95% probability of being within the empirical habitable-zone
but a <5% probability of being within the conservative habitable-zone.Comment: 19 pages, 11 figures, 7 tables. Accepted in ApJ. Planet-moon transit
animations available at https://www.cfa.harvard.edu/~dkipping/kepler22.htm
The Hunt for Exomoons with Kepler (HEK): V. A Survey of 41 Planetary Candidates for Exomoons
We present a survey of 41 Kepler Objects of Interest (KOIs) for exomoons
using Bayesian photodynamics, more than tripling the number of KOIs surveyed
with this technique. We find no compelling evidence for exomoons although
thirteen KOIs yield spurious detections driven by instrumental artifacts,
stellar activity and/or perturbations from unseen bodies. Regarding the latter,
we find seven KOIs exhibiting >5 sigma evidence of transit timing variations,
including the 'mega-Earth' Kepler-10c, likely indicating an additional planet
in that system. We exploit the moderately large sample of 57 unique KOIs
surveyed to date to infer several useful statistics. For example, although
there is a diverse range in sensitivities, we find that we are sensitive to
Pluto-Charon mass-ratio systems for ~40% of KOIs studied and Earth-Moon
mass-ratios for 1 in 8 cases. In terms of absolute mass, our limits probe down
to 1.7 Ganymede masses, with a sensitivity to Earth-mass moons for 1 in 3 cases
studied and to the smallest moons capable of sustaining an Earth-like
atmosphere (0.3 Earth masses) for 1 in 4. Despite the lack of positive
detections to date, we caution against drawing conclusions yet, since our most
interesting objects remain under analysis. Finally, we point out that had we
searched for the photometric transit signals of exomoons alone, rather than
using photodynamics, we estimate that 1 in 4 KOIs would have erroneously been
concluded to harbor exomoons due to residual time correlated noise in the
Kepler data, posing a serious problem for alternative methods.Comment: 18 pages, 9 figures, 4 tables. Accepted in Ap
The first CCD photometric study of the open cluster NGC 2126
We present the first CCD photometric observations of the northern open
cluster NGC 2126. Data were taken on eight nights in February and December 2002
with a total time span of ~57 hours. Almost 1000 individual V-band frames were
examined to find short-period variable stars. We discovered six new variable
stars, of which one is a promising candidate for an eclipsing binary with a
pulsating component. Two stars were classified as delta Scuti stars and one as
Algol-type eclipsing binary. Two stars are slow variables with ambiguous
classification. From absolute VRI photometry we have estimated the main
characteristics of the cluster: m-M=11.0+/-0.5, E(V-I)=0.4+/-0.1,
E(V-R)=0.08+/-0.06 (E(B-V)=0.2+/-0.15) and d=1.3+/-0.6 kpc. Cluster membership
is suggested for three variable stars from their positions on the
colour-magnitude diagram.Comment: 7 pages, 10 figures, accepted for publication in A&
The nearby eclipsing stellar system delta Velorum - I. Origin of the infrared excess from VISIR and NACO imaging
- Context: The triple stellar system delta Vel system presents a significant
infrared excess, whose origin is still being debated. A large infrared bow
shock has been discovered using Spitzer/MIPS observations. Although it appears
as a significant contributor to the measured IR excess, the possibility exists
that a circumstellar IR excess is present around the stars of the system. -
Aims: The objective of the present VISIR and NACO observations is to identify
whether one of the stars of the delta Vel system presents a circumstellar
photometric excess in the thermal IR domain and to quantify it. - Methods: We
observed delta Vel using the imaging modes of the ESO/VLT instruments VISIR (in
BURST mode) and NACO to resolve the A-B system (0.6" separation) and obtain the
photometry of each star. We also obtained one NACO photometry epoch precisely
at the primary (annular) eclipse of delta Vel Aa by Ab. - Results: Our
photometric measurements with NACO (2.17 mic), complemented by the existing
visible photometry allowed us to reconstruct the spectral energy distribution
of the three stars. We then compared the VISIR photometry (8.6-12.8 mic) to the
expected photospheric emission from the three stars at the corresponding
wavelengths. - Conclusions: We can exclude the presence of a circumstellar
thermal infrared excess around delta Vel A or B down to a few percent level.
This supports the conclusions of Gaspar et al. (2008) that the IR excess of
delta Vel has an interstellar origin, although a cold circumstellar disk could
still be present. In addition, we derive the spectral types of the three stars
Aa, Ab, and B (respectively A2IV, A4V and F8V), and we estimate the age of the
system around 400-500 Myr.Comment: 8 pages, 9 figures, A&A, in pres
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