6,716 research outputs found
Dynamics of the TrES-2 system
The TrES-2 system harbors one planet which was discovered with the transit
technique. In this work we investigate the dynamical behavior of possible
additional, lower-mass planets. We identify the regions where such planets can
move on stable orbits and show how they depend on the initial eccentricity and
inclination. We find, that there are stable regions inside and outside the
orbit of TrES-2b where additional, smaller planets can move. We also show that
those planets can have a large orbital inclination which makes a detection with
the transit technique very difficult.Comment: accepted for publication in AN 330 (2009
An analysis of the transit times of CoRoT-1b
I report the results from a study of the transit times for CoRoT-1b, which
was one of the first planets discovered by CoRoT. Analysis of the pipeline
reduced CoRoT light curve yields a new determination of the physical and
orbital parameters of planet and star, along with 35 individual transit times
at a typical precision of 36 s. I estimate a planet-to-star radii ratio of
0.1433 +/- 0.0010, a ratio of the planet's orbital semimajor axis to the host
star radius of 4.751 +/- 0.045, and an orbital inclination for the planet of
83.88 +/- 0.29 deg. The observed transit times are consistent with CoRoT-1b
having a constant period and there is no evidence of an additional planet in
the system. I use the observed constancy of the transit times to set limits on
the mass of a hypothetical additional planet in a nearby, stable orbit. I
ascertain that the most stringent limits (4 M_earth at 3 sigma confidence) can
be placed on planets residing in a 1:2 mean motion resonance with the
transiting planet. In contrast, the data yield less stringent limits on planets
near a 1:3 mean motion resonance (5 M_jup at 3 sigma confidence) than in the
surrounding parameter space. In addition, I use a simulation to investigate
what sensitivity to additional planets could be obtained from the analysis of
data measured for a similar system during a CoRoT long run (100 sequential
transit times). I find that for such a scenario, planets with masses greater
than twice that of Mars (0.2 M_earth) in the 1:2 mean motion resonance would
cause high-significance transit time deviations. Therefore, such planets could
be detected or ruled out using CoRoT long run data. I conclude that CoRoT data
will indeed be very useful for searching for planets with the transit timing
method.Comment: accepted for publication in A&A; v2 replaces with accepted versio
Observational evidence for a metal rich atmosphere on the super-Earth GJ1214b
We report observations of two consecutive transits of the warm super-Earth
exoplanet GJ1214b at 3.6 and 4.5 microns with the Infrared Array Camera
instrument on-board the Spitzer Space Telescope. The two transit light curves
allow for the determination of the transit parameters for this system. We find
these paremeters to be consistent with the previously determined values and no
evidence for transit timing variations. The main investigation consists of
measuring the transit depths in each bandpass to constrain the planet's
transmission spectrum. Fixing the system scale and impact parameters, we
measure R_p/R_star=0.1176 (+0.0008/-0.0009) and 0.1163 (+0.0010/-0.0008) at 3.6
and 4.5 microns, respectively. Combining these data with the previously
reported MEarth Observatory measurements in the red optical yields constraints
on the GJ1214b's transmission spectrum and allows us to rule-out a cloud-free,
solar composition (i.e., hydrogen-dominated) atmosphere at 4.5 sigma
confidence. This independently confirms a recent finding that was based on a
measurement of the planet's transmission spectrum using the VLT. The Spitzer,
MEarth, and VLT observations together yield a remarkably flat transmission
spectrum over the large wavelength domain spanned by the data. Consequently,
cloud-free atmospheric models require more than 30% metals (assumed to be in
the form of H2O by volume to be consistent with all the observations.Comment: Accepted for publication in ApJL. 13 pages, 3 figures, 1 tabl
Broadband Transmission Spectroscopy of the super-Earth GJ 1214b suggests a Low Mean Molecular Weight Atmosphere
We used WIRCam on CFHT to observe four transits of the super-Earth GJ 1214b
in the near-infrared. For each transit we observed in two bands
nearly-simultaneously by rapidly switching the WIRCam filter wheel back and
forth for the duration of the observations. By combining all our J-band (~1.25
microns) observations we find a transit depth in this band of 1.338\pm0.013% -
a value consistent with the optical transit depth reported by Charbonneau and
collaborators. However, our best-fit combined Ks-band (~2.15 microns) transit
depth is deeper: 1.438\pm0.019%. Formally our Ks-band transits are deeper than
the J-band transits observed simultaneously by a factor of 1.072\pm0.018 - a
4-sigma discrepancy. The most straightforward explanation for our deeper
Ks-band depth is a spectral absorption feature from the limb of the atmosphere
of the planet; for the spectral absorption feature to be this prominent the
atmosphere of GJ 1214b must have a large scale height and a low mean molecular
weight. That is, it would have to be hydrogen/helium dominated and this planet
would be better described as a mini-Neptune. However, recently published
observations from 0.78 - 1.0 microns, by Bean and collaborators, show a lack of
spectral features and transit depths consistent with those obtained by
Charbonneau and collaborators. The most likely atmospheric composition for GJ
1214b that arises from combining all these observations is less clear; if the
atmosphere of GJ 1214b is hydrogen/helium dominated then it must have either a
haze layer that is obscuring transit depth differences at shorter wavelengths,
or significantly different spectral features than current models predict. Our
observations disfavour a water-world composition, but such a composition will
remain a possibility until observations reconfirm our deeper Ks-band transit
depth or detect features at other wavelengths. [Abridged]Comment: ApJ accepted. 12 pages, 6 figures, in EmulateApJ forma
The Atmospheric Chemistry of GJ 1214b: Photochemistry and Clouds
Recent observations of the transiting super-Earth GJ 1214b reveal that its
atmosphere may be hydrogen-rich or water-rich in nature, with clouds or hazes
potentially affecting its transmission spectrum in the optical and
very-near-IR. Here we further examine the possibility that GJ 1214b does indeed
possess a hydrogen-dominated atmosphere, which is the hypothesis that is
favored by models of the bulk composition of the planet. We study the effects
of non-equilibrium chemistry (photochemistry, thermal chemistry, and mixing) on
the planet's transmission spectrum. We furthermore examine the possibility that
clouds could play a significant role in attenuating GJ 1214b's transmission
spectrum at short wavelengths. We find that non-equilibrium chemistry can have
a large effect on the overall chemical composition of GJ 1214b's atmosphere,
however these changes mostly take place above the height in the atmosphere that
is probed by transmission spectroscopy. The effects of non-equilibrium
chemistry on GJ 1214b's transmission spectrum are therefore minimal, with the
largest effects taking place if the planet's atmosphere has super-solar
metallicity and a low rate of vertical mixing. Interestingly, we find that the
best fit to the observations of GJ 1214b's atmosphere in transmission occur if
the planet's atmosphere is deficient in CH4, and possesses a cloud layer at a
pressure of ~200 mbar. This is consistent with a picture of efficient methane
photolysis, accompanied by formation of organic haze that obscures the lower
atmosphere of GJ 1214b at optical wavelengths. However, for methane to be
absent from GJ 1214b's transmission spectrum, UV photolysis of this molecule
must be efficient at pressures of greater than ~1 mbar, whereas we find that
methane only photolyzes to pressures less than 0.1 mbar, even under the most
optimistic assumptions. (Abridged)Comment: Accepted to ApJ; 32 pages, 8 figures, 1 tabl
Fast Inversion Method for Determination of Planetary Parameters from Transit Timing Variations
The Transit Timing Variation (TTV) method relies on monitoring changes in
timing of transits of known exoplanets. Non-transiting planets in the system
can be inferred from TTVs by their gravitational interaction with the
transiting planet. The TTV method is sensitive to low-mass planets that cannot
be detected by other means. Here we describe a fast algorithm that can be used
to determine the mass and orbit of the non-transiting planets from the TTV
data. We apply our code, ttvim.f, to a wide variety of planetary systems to
test the uniqueness of the TTV inversion problem and its dependence on the
precision of TTV observations. We find that planetary parameters, including the
mass and mutual orbital inclination of planets, can be determined from the TTV
datasets that should become available in near future. Unlike the radial
velocity technique, the TTV method can therefore be used to characterize the
inclination distribution of multi-planet systems
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
Constraining High Speed Winds in Exoplanet Atmospheres Through Observations of Anomalous Doppler Shifts During Transit
Three-dimensional (3-D) dynamical models of hot Jupiter atmospheres predict
very strong wind speeds. For tidally locked hot Jupiters, winds at high
altitude in the planet's atmosphere advect heat from the day side to the cooler
night side of the planet. Net wind speeds on the order of 1-10 km/s directed
towards the night side of the planet are predicted at mbar pressures, which is
the approximate pressure level probed by transmission spectroscopy. These winds
should result in an observed blue shift of spectral lines in transmission on
the order of the wind speed. Indeed, Snellen et al. (2010) recently observed a
2 +/- 1 km/s blue shift of CO transmission features for HD 209458b, which has
been interpreted as a detection of the day-to-night winds that have been
predicted by 3-D atmospheric dynamics modeling. Here we present the results of
a coupled 3-D atmospheric dynamics and transmission spectrum model, which
predicts the Doppler-shifted spectrum of a hot Jupiter during transit resulting
from winds in the planet's atmosphere. We explore four different models for the
hot Jupiter atmosphere using different prescriptions for atmospheric drag via
interaction with planetary magnetic fields. We find that models with no
magnetic drag produce net Doppler blue shifts in the transmission spectrum of
~2 km/s and that lower Doppler shifts of ~1 km/s are found for the higher drag
cases, results consistent with -- but not yet strongly constrained by -- the
Snellen et al. (2010) measurement. We additionally explore the possibility of
recovering the average terminator wind speed as a function of altitude by
measuring Doppler shifts of individual spectral lines and spatially resolving
wind speeds across the leading and trailing terminators during ingress and
egress.Comment: Submitted to ApJ, 28 pages including 9 figures in manuscript forma
On the Emergent Spectra of Hot Protoplanet Collision Afterglows
We explore the appearance of terrestrial planets in formation by studying the
emergent spectra of hot molten protoplanets during their collisional formation.
While such collisions are rare, the surfaces of these bodies may remain hot at
temperatures of 1000-3000 K for up to millions of years during the epoch of
their formation. These object are luminous enough in the thermal infrared to be
observable with current and next generation optical/IR telescopes, provided
that the atmosphere of the forming planet permits astronomers to observe
brightness temperatures approaching that of the molten surface. Detectability
of a collisional afterglow depends on properties of the planet's atmosphere --
primarily on the mass of the atmosphere. A planet with a thin atmosphere is
more readily detected, because there is little atmosphere to obscure the hot
surface. Paradoxically, a more massive atmosphere prevents one from easily
seeing the hot surface, but also keeps the planet hot for a longer time. In
terms of planetary mass, more massive planets are also easier to detect than
smaller ones because of their larger emitting surface areas. We present
preliminary calculations assuming a range of protoplanet masses (1-10
M_\earth), surface pressures (1-1000 bar), and atmospheric compositions, for
molten planets with surface temperatures ranging from 1000 to 1800 K, in order
to explore the diversity of emergent spectra that are detectable. While current
8- to 10-m class ground-based telescopes may detect hot protoplanets at wide
orbital separations beyond 30 AU (if they exist), we will likely have to wait
for next-generation extremely large telescopes or improved diffraction
suppression techniques to find terrestrial planets in formation within several
AU of their host stars.Comment: 28 pages, 6 figures, ApJ manuscript format, accepted into the Ap
- …