6,170 research outputs found
Lack of Transit Timing Variations of OGLE-TR-111b: A re-analysis with six new epochs
We present six new transits of the exoplanet OGLE-TR-111b observed with the
Magellan Telescopes in Chile between April 2008 and March 2009. We combine
these new transits with five previously published transit epochs for this
planet between 2005 and 2006 to extend the analysis of transit timing
variations reported for this system. We derive a new planetary radius value of
1.019 +/- 0.026 R_J, which is intermediate to the previously reported radii of
1.067 +/- 0.054 R_J (Winn et al. 2007) and 0.922 +/- 0.057 R_J (Diaz et al.
2008). We also examine the transit timing variation and duration change claims
of Diaz et al. (2008). Our analysis of all eleven transit epochs does not
reveal any points with deviations larger than 2 sigma, and most points are well
within 1 sigma. Although the transit duration nominally decreases over the four
year span of the data, systematic errors in the photometry can account for this
result. Therefore, there is no compelling evidence for either a timing or a
duration variation in this system. Numerical integrations place an upper limit
of about 1 M_E on the mass of a potential second planet in a 2:1 mean-motion
resonance with OGLE-TR-111b.Comment: 28 pages, 7 tables, 6 figures. Accepted by Ap
Discovery and Characterization of Transiting SuperEarths Using an All-Sky Transit Survey and Follow-up by the James Webb Space Telescope
Doppler and transit surveys are finding extrasolar planets of ever smaller
mass and radius, and are now sampling the domain of superEarths (1-3 Earth
radii). Recent results from the Doppler surveys suggest that discovery of a
transiting superEarth in the habitable zone of a lower main sequence star may
be possible. We evaluate the prospects for an all-sky transit survey targeted
to the brightest stars, that would find the most favorable cases for
photometric and spectroscopic characterization using the James Webb Space
Telescope (JWST). We use the proposed Transiting Exoplanet Survey Satellite
(TESS) as representative of an all-sky survey. We couple the simulated TESS
yield to a sensitivity model for the MIRI and NIRSpec instruments on JWST. We
focus on the TESS planets with radii between Earth and Neptune. Our simulations
consider secondary eclipse filter photometry using JWST/MIRI, comparing the 11-
and 15-micron bands to measure CO2 absorption in superEarths, as well as
JWST/NIRSpec spectroscopy of water absorption from 1.7-3.0 microns, and CO2
absorption at 4.3-microns. We project that TESS will discover about eight
nearby habitable transiting superEarths. The principal sources of uncertainty
in the prospects for JWST characterization of habitable superEarths are
superEarth frequency and the nature of superEarth atmospheres. Based on our
estimates of these uncertainties, we project that JWST will be able to measure
the temperature, and identify molecular absorptions (water, CO2) in one to four
nearby habitable TESS superEarths.Comment: accepted for PASP; added discussion and figure for habitable planets;
abridged Abstrac
The Zeeman effect in the G band
We investigate the possibility of measuring magnetic field strength in G-band
bright points through the analysis of Zeeman polarization in molecular CH
lines. To this end we solve the equations of polarized radiative transfer in
the G band through a standard plane-parallel model of the solar atmosphere with
an imposed magnetic field, and through a more realistic snapshot from a
simulation of solar magneto-convection. This region of the spectrum is crowded
with many atomic and molecular lines. Nevertheless, we find several instances
of isolated groups of CH lines that are predicted to produce a measurable
Stokes V signal in the presence of magnetic fields. In part this is possible
because the effective Land\'{e} factors of lines in the stronger main branch of
the CH A--X transition tend to zero rather quickly for
increasing total angular momentum , resulting in a Stokes spectrum of
the G band that is less crowded than the corresponding Stokes spectrum. We
indicate that, by contrast, the effective Land\'{e} factors of the and
satellite sub-branches of this transition tend to for increasing .
However, these lines are in general considerably weaker, and do not contribute
significantly to the polarization signal. In one wavelength location near 430.4
nm the overlap of several magnetically sensitive and non-sensitive CH lines is
predicted to result in a single-lobed Stokes profile, raising the
possibility of high spatial-resolution narrow-band polarimetric imaging. In the
magneto-convection snapshot we find circular polarization signals of the order
of 1% prompting us to conclude that measuring magnetic field strength in
small-scale elements through the Zeeman effect in CH lines is a realistic
prospect.Comment: 22 pages, 6 figures. To be published in the Astrophysical Journa
Transit Detection in the MEarth Survey of Nearby M Dwarfs: Bridging the Clean-First, Search-Later Divide
In the effort to characterize the masses, radii, and atmospheres of
potentially habitable exoplanets, there is an urgent need to find examples of
such planets transiting nearby M dwarfs. The MEarth Project is an ongoing
effort to do so, as a ground-based photometric survey designed to detect
exoplanets as small as 2 Earth radii transiting mid-to-late M dwarfs within 33
pc of the Sun. Unfortunately, identifying transits of such planets in
photometric monitoring is complicated both by the intrinsic stellar variability
that is common among these stars and by the nocturnal cadence, atmospheric
variations, and instrumental systematics that often plague Earth-bound
observatories. Here we summarize the properties of MEarth data gathered so far,
and we present a new framework to detect shallow exoplanet transits in wiggly
and irregularly-spaced light curves. In contrast to previous methods that clean
trends from light curves before searching for transits, this framework assesses
the significance of individual transits simultaneously while modeling
variability, systematics, and the photometric quality of individual nights. Our
Method for Including Starspots and Systematics in the Marginalized Probability
of a Lone Eclipse (MISS MarPLE) uses a computationally efficient semi-Bayesian
approach to explore the vast probability space spanned by the many parameters
of this model, naturally incorporating the uncertainties in these parameters
into its evaluation of candidate events. We show how to combine individual
transits processed by MISS MarPLE into periodic transiting planet candidates
and compare our results to the popular Box-fitting Least Squares (BLS) method
with simulations. By applying MISS MarPLE to observations from the MEarth
Project, we demonstrate the utility of this framework for robustly assessing
the false alarm probability of transit signals in real data. [slightly
abridged]Comment: accepted to the Astronomical Journal, 21 pages, 12 figure
The Transit Light Curve Project. XII. Six Transits of the Exoplanet XO-2b
We present photometry of six transits of the exoplanet XO-2b. By combining
the light-curve analysis with theoretical isochrones to determine the stellar
properties, we find the planetary radius to be 0.996 +0.031/-0.018 rjup and the
planetary mass to be 0.565 +/- 0.054 mjup. These results are consistent with
those reported previously, and are also consistent with theoretical models for
gas giant planets. The mid-transit times are accurate to within 1 min and are
consistent with a constant period. However, the period we derive differs by 2.5
sigma from the previously published period. More data are needed to tell
whether the period is actually variable (as it would be in the presence of an
additional body) or if the timing errors have been underestimated.Comment: Accepted for publication in AJ. 20 pages, 3 tables, 4 figure
The Transit Light Curve Project. IV. Five Transits of the Exoplanet OGLE-TR-10b
We present I and B photometry of five distinct transits of the exoplanet
OGLE-TR-10b. By modeling the light curves, we find the planetary radius to be
R_P = 1.06 +/- 0.08 R_Jup and the stellar radius to be R_S = 1.10 +/- 0.07
R_sun. The uncertainties are dominated by statistical errors in the photometry.
Our estimate of the planetary radius is smaller than previous estimates that
were based on lower-precision photometry, and hence the planet is not as
anomalously large as was previously thought. We provide updated determinations
of all the system parameters, including the transit ephemerides.Comment: Accepted in the Astrophysical Journal, 23 October 2006. Includes
observations of additional transits to confirm earlier results. [15 pg, 6
figs
High Cadence Near Infrared Timing Observations of Extrasolar Planets: I. GJ 436b and XO-1b
Currently the only technique sensitive to Earth mass planets around nearby
stars (that are too close for microlensing) is the monitoring of the transit
time variations of the transiting extrasolar planets. We search for additional
planets in the systems of the hot Neptune GJ 436b, and the hot-Jupiter XO-1b,
using high cadence observations in the J and Ks bands. New high-precision
transit timing measurements are reported: GJ 436b Tc = 2454238.47898 \pm
0.00046 HJD; XO-1b Tc(A) = 2454218.83331 \pm 0.00114 HJD, Tc(B) = 2454222.77539
\pm 0.00036 HJD, Tc(C) = 2454222.77597 \pm 0.00039 HJD, Tc(D) = 2454226.71769
\pm 0.00034 HJD, and they were used to derive new ephemeris. We also determined
depths for these transits. No statistically significant timing deviations were
detected. We demonstrate that the high cadence ground based near-infrared
observations are successful in constraining the mean transit time to ~30 sec.,
and are a viable alternative to space missions.Comment: 7 pages, 4 figures. To appear in A&
MOST Spacebased Photometry of the Transiting Exoplanet System HD 189733: Precise Timing Measurements for Transits Across an Active Star
We have measured transit times for HD 189733b passing in front of its bright
(V = 7.67) chromospherically active and spotted parent star. Nearly continuous
broadband optical photometry of this system was obtained with the MOST
(Microvariability & Oscillations of STars) space telescope during 21 days in
August 2006, monitoring 10 consecutive transits. We have used these data to
search for deviations from a constant orbital period which can indicate the
presence of additional planets in the system that are as yet undetected by
Doppler searches. There are no transit timing variations above the level of
s, ruling out super-Earths (of masses 1 - 4 M_{\earth}) in the 1:2
and 2:3 inner resonances and planets of 20 M_{\earth} in the 2:1 outer
resonance of the known planet. We also discuss complications in measuring
transit times for a planet that transits an active star with large star spots,
and how the transits can help constrain and test spot models. This has
implications for the large number of such systems expected to be discovered by
the CoRoT and Kepler missions.Comment: 26 pages, 7 figures, accepted to Ap
- âŠ