721 research outputs found
Midcourse navigation using statistical filter theory, a manual theodolite, and symbolic computer control
Midcourse navigation using statistical filter theory, manual theodolite, and symbolic computer control applied to manned spacecraf
On the detectability of habitable exomoons with Kepler-class photometry
In this paper we investigate the detectability of a habitable-zone exomoon
around various configurations of exoplanetary systems with the Kepler Mission
or photometry of approximately equal quality. We calculate both the predicted
transit timing signal amplitudes and the estimated uncertainty on such
measurements in order to calculate the confidence in detecting such bodies
across a broad spectrum of orbital arrangements. The effects of stellar
variability, instrument noise and photon noise are all accounted for in the
analysis. We validate our methodology by simulating synthetic lightcurves and
performing a Monte Carlo analysis for several cases of interest.
We find that habitable-zone exomoons down to 0.2 Earth masses may be detected
and ~25,000 stars could be surveyed for habitable-zone exomoons within Kepler's
field-of-view. A Galactic Plane survey with Kepler-class photometry could
potentially survey over one million stars for habitable-zone exomoons. In
conclusion, we propose that habitable exomoons will be detectable should they
exist in the local part of the galaxy.Comment: Accepted for publication in the Monthly Notices of the Royal
Astronomical Societ
Detection of a transit by the planetary companion of HD 80606
We report the detection of a transit egress by the ~ 3.9-Jupiter-mass planet
HD 80606b, an object in a highly-eccentric orbit (e ~ 0.93) about its parent
star of approximately solar type. The astrophysical reality of the signal of
variability in HD 80606 is confirmed by observation with two independent
telescope systems, and checks against several reference stars in the field.
Differential photometry with respect to the nearby comparison star HD 80607
provides a precise light curve. Modelling of the light curve with a full
eccentric-orbit model indicates a planet/star-radius ratio of 0.1057 +/-
0.0018, corresponding to a planet radius of 1.029 R_J for a solar-radius parent
star; and a precise orbital inclination of 89.285 +/- 0.023 degrees, giving a
total transit duration of 12.1 +/- 0.4 hours. The planet hence joins HD 17156b
in a class of highly eccentric transiting planets, in which HD 80606b has both
the longest period and most eccentric orbit. The recently reported discovery of
a secondary eclipse of HD 80606b by the Spitzer Space Observatory permits a
combined analysis with the mid-time of primary transit in which the orbital
parameters of the system can be tightly constrained. We derive a transit
ephemeris of T_tr = HJD (2454876.344 +/- 0.011) + (111.4277 +/- 0.0032) E.Comment: Accepted for publication in MNRAS Letter
Loose Ends for the Exomoon Candidate Host Kepler-1625b
The claim of an exomoon candidate in the Kepler-1625b system has generated
substantial discussion regarding possible alternative explanations for the
purported signal. In this work we examine in detail these possibilities. First,
the effect of more flexible trend models is explored and we show that
sufficiently flexible models are capable of attenuating the signal, although
this is an expected byproduct of invoking such models. We also explore trend
models using X and Y centroid positions and show that there is no data-driven
impetus to adopt such models over temporal ones. We quantify the probability
that the 500 ppm moon-like dip could be caused by a Neptune-sized transiting
planet to be < 0.75%. We show that neither autocorrelation, Gaussian processes
nor a Lomb-Scargle periodogram are able to recover a stellar rotation period,
demonstrating that K1625 is a quiet star with periodic behavior < 200 ppm.
Through injection and recovery tests, we find that the star does not exhibit a
tendency to introduce false-positive dip-like features above that of pure
Gaussian noise. Finally, we address a recent re-analysis by Kreidberg et al
(2019) and show that the difference in conclusions is not from differing
systematics models but rather the reduction itself. We show that their
reduction exhibits i) slightly higher intra-orbit and post-fit residual
scatter, ii) 900 ppm larger flux offset at the visit change, iii)
2 times larger Y-centroid variations, and iv) 3.5 times
stronger flux-centroid correlation coefficient than the original analysis.
These points could be explained by larger systematics in their reduction,
potentially impacting their conclusions.Comment: 21 pages, 4 tables, 11 figures. Accepted for publication in The
Astronomical Journal, January 202
Flicker as a tool for characterizing planets through Asterodensity Profiling
Variability in the time series brightness of a star on a timescale of 8
hours, known as 'flicker', has been previously demonstrated to serve as a proxy
for the surface gravity of a star by Bastien et al. (2013). Although surface
gravity is crucial for stellar classification, it is the mean stellar density
which is most useful when studying transiting exoplanets, due to its direct
impact on the transit light curve shape. Indeed, an accurate and independent
measure of the stellar density can be leveraged to infer subtle properties of a
transiting system, such as the companion's orbital eccentricity via
asterodensity profiling. We here calibrate flicker to the mean stellar density
of 439 Kepler targets with asteroseismology, allowing us to derive a new
empirical relation given by
. The calibration is valid for stars with
KK, and flicker estimates corresponding
to stars with . Our relation has a model error in the
stellar density of 31.7% and so has times lower precision than that
from asteroseismology but is applicable to a sample times greater.
Flicker therefore provides an empirical method to enable asterodensity
profiling on hundreds of planetary candidates from present and future missions.Comment: 6 pages, 3 figures, 1 table. Accepted to ApJ Letters. Code available
at https://www.cfa.harvard.edu/~dkipping/flicker.htm
Cerebellar Functional Parcellation Using Sparse Dictionary Learning Clustering
10.3389/fnins.2016.00188Frontiers in neuroscience10188GUSTO (Growing up towards Healthy Outcomes
Detection of transit timing variations in excess of one hour in the Kepler multi-planet candidate system KOI 806 with the GTC
We report the detection of transit timing variations (TTVs) well in excess of
one hour in the Kepler multi-planet candidate system KOI 806. This system
exhibits transits consistent with three separate planets -- a Super-Earth, a
Jupiter, and a Saturn -- lying very nearly in a 1:2:5 resonance, respectively.
We used the Kepler public data archive and observations with the Gran
Telescopio de Canarias to compile the necessary photometry. For the largest
candidate planet (KOI 806.02) in this system, we detected a large transit
timing variation of -103.56.9 minutes against previously published
ephemeris. We did not obtain a strong detection of a transit color signature
consistent with a planet-sized object; however, we did not detect a color
difference in transit depth, either. The large TTV is consistent with
theoretical predictions that exoplanets in resonance can produce large transit
timing variations, particularly if the orbits are eccentric. The presence of
large TTVs among the bodies in this systems indicates that KOI806 is very
likely to be a planetary system. This is supported by the lack of a strong
color dependence in the transit depth, which would suggest a blended eclipsing
binary.Comment: 9 pages, 4 figures, accepted into A&A Letter
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