692 research outputs found
Planetary Transits Toward the Galactic Bulge
The primary difficulty with using transits to discover extrasolar planets is
the low probability a planet has of transiting its parent star. One way of
overcoming this difficulty is to search for transits in dense stellar fields,
such as the Galactic bulge. Here I estimate the number of planets that might be
detected from a monitoring campaign toward the bulge. A campaign lasting 10
nights on a 10 meter telescope (assuming 8 hours of observations per night and
a 5'x5' field of view) would detect about 100 planets with radius \rp=1.5
\rjup, or about 30 planets with \rp=1.0 \rjup, if the frequency and
distribution of planets in the bulge is similar to that in the solar
neighborhood. Most of these planets will be discovered around stars just below
the turn-off, i.e. slightly evolved G-dwarfs. Campaigns involving 1- or 4-m
class telescopes are unlikely to discover any planets, unless there exists a
substantial population of companions with \rp > 1.5 \rjup.Comment: 4 pages, 4 figures. Submitted to ApJ Letter
A rigorous comparison of different planet detection algorithms
The idea of finding extrasolar planets (ESPs) through observations of drops
in stellar brightness due to transiting objects has been around for decades. It
has only been in the last ten years, however, that any serious attempts to find
ESPs became practical. The discovery of a transiting planet around the star HD
209458 (Charbonneau et al. 2000) has led to a veritable explosion of research,
because the photometric method is the only way to search a large number of
stars for ESPs simultaneously with current technology. To this point, however,
there has been limited research into the various techniques used to extract the
subtle transit signals from noise, mainly brief summaries in various papers
focused on publishing transit-like signatures in observations. The scheduled
launches over the next few years of satellites whose primary or secondary
science missions will be ESP discovery motivates a review and a comparative
study of the various algorithms used to perform the transit identification, to
determine rigorously and fairly which one is the most sensitive under which
circumstances, to maximize the results of past, current, and future
observational campaigns.Comment: Accepted for publications by Astronomy and Astrophysic
Constraining the False Positive Rate for Kepler Planet Candidates with Multi-Color Photometry from the GTC
Using the OSIRIS instrument installed on the 10.4-m Gran Telescopio Canarias
(GTC) we acquired multi-color transit photometry of four small (Rp < 5 R_Earth)
short-period (P < 6 days) planet candidates recently identified by the Kepler
space mission. These observations are part of a program to constrain the false
positive rate for small, short-period Kepler planet candidates. Since planetary
transits should be largely achromatic when observed at different wavelengths
(excluding the small color changes due to stellar limb darkening), we use the
observed transit color to identify candidates as either false positives (e.g.,
a blend with a stellar eclipsing binary either in the background/foreground or
bound to the target star) or validated planets. Our results include the
identification of KOI 225.01 and KOI 1187.01 as false positives and the
tentative validation of KOI 420.01 and KOI 526.01 as planets. The probability
of identifying two false positives out of a sample of four targets is less than
1%, assuming an overall false positive rate for Kepler planet candidates of 10%
(as estimated by Morton & Johnson 2011). Therefore, these results suggest a
higher false positive rate for the small, short-period Kepler planet candidates
than has been theoretically predicted by other studies which consider the
Kepler planet candidate sample as a whole. Furthermore, our results are
consistent with a recent Doppler study of short-period giant Kepler planet
candidates (Santerne et al. 2012). We also investigate how the false positive
rate for our sample varies with different planetary and stellar properties. Our
results suggest that the false positive rate varies significantly with orbital
period and is largest at the shortest orbital periods (P < 3 days), where there
is a corresponding rise in the number of detached eclipsing binary stars...
(truncated)Comment: 13 pages, 12 figures, 3 tables; revised for MNRA
Tests of a multichannel photometer based on silicon diode detectors
A breadboard photometer was constructed that demonstrates a precision of 2 times 10 to the 4th power in the laboratory and scintillation-limited performance when used with an 0.5 m aperture telescope. Because the detectors and preamps are not cooled, only stars with m sub v approx. less than 4 are bright enough to allow the photometer to attain a precision of 1 times 10 to the 3rd power for three minute observations with an 0.5 m aperature telescope. Cooling the telescope should allow much fainter stars to be observed. Increasing the aperture of the telescope will allow higher precision and the observation of fainter stars
Can planetary instability explain the Kepler dichotomy?
The planet candidates discovered by the Kepler mission provide a rich sample
to constrain the architectures and relative inclinations of planetary systems
within approximately 0.5 AU of their host stars. We use the triple-transit
systems from the Kepler 16-months data as templates for physical triple-planet
systems and perform synthetic transit observations. We find that all the Kepler
triple-transit and double-transit systems can be produced from the
triple-planet templates, given a low mutual inclination of around five degrees.
Our analysis shows that the Kepler data contains a population of planets larger
than four Earth radii in single-transit systems that can not arise from the
triple-planet templates. We explore the hypothesis that high-mass counterparts
of the triple-transit systems underwent dynamical instability to produce a
population of massive double-planet systems of moderately high mutual
inclination. We perform N-body simulations of mass-boosted triple-planet
systems and observe how the systems heat up and lose planets, most frequently
by planet-planet collisions, yielding transits in agreement with the large
planets in the Kepler single-transit systems. The resulting population of
massive double-planet systems can nevertheless not explain the additional
excess of low-mass planets among the observed single-transit systems and the
lack of gas-giant planets in double-transit and triple-transit systems.
Planetary instability of systems of triple gas-giant planets can be behind part
of the dichotomy between systems hosting one or more small planets and those
hosting a single giant planet. The main part of the dichotomy, however, is more
likely to have arisen already during planet formation when the formation,
migration or scattering of a massive planet, triggered above a threshold
metallicity, suppressed the formation of other planets in sub-AU orbits.Comment: Accepted for publication in Ap
Detection of a transit of the super-Earth 55 Cnc e with Warm Spitzer
We report on the detection of a transit of the super-Earth 55 Cnc e with warm
Spitzer in IRAC's 4.5-micron band. Our MCMC analysis includes an extensive
modeling of the systematic effects affecting warm Spitzer photometry, and
yields a transit depth of 410 +- 63 ppm, which translates to a planetary radius
of 2.08 +- 0.16 R_Earth as measured in IRAC 4.5-micron channel. A planetary
mass of 7.81 +- 0.58 M_Earth is derived from an extensive set of
radial-velocity data, yielding a mean planetary density of 4.8 +- 1.3 g cm-3.
Thanks to the brightness of its host star (V = 6, K = 4), 55 Cnc e is a unique
target for the thorough characterization of a super-Earth orbiting around a
solar-type star.Comment: Accepted for publication in A&A on 31 July 2011. 9 pages, 7 figures
and 3 tables. Minor changes. The revised version includes a baseline models
comparison and a new figure presenting the spatially- and time-dependent
terms of the model function used in Eq.
Characterizing Transiting Extrasolar Planets with Narrow-Band Photometry and GTC/OSIRIS
We report the first extrasolar planet observations from the 10.4-m Gran
Telescopio Canarias (GTC), currently the world's largest, fully steerable,
single-aperture optical telescope. We used the OSIRIS tunable filter imager on
the GTC to acquire high-precision, narrow-band photometry of the transits of
the giant exoplanets, TrES-2b and TrES-3b. We obtained near-simultaneous
observations in two near-infrared (NIR) wavebands (790.2 and 794.4 +/- 2.0 nm)
specifically chosen to avoid water vapor absorption and skyglow so as to
minimize the atmospheric effects that often limit the precision of ground-based
photometry. Our results demonstrate a very-high photometric precision with
minimal atmospheric contamination despite relatively poor atmospheric
conditions and some technical problems with the telescope. We find the
photometric precision for the TrES-2 observations to be 0.343 and 0.412 mmag
for the 790.2 and 794.4 nm light curves, and the precision of the TrES-3
observations was found to be 0.470 and 0.424 mmag for the 790.2 and 794.4 nm
light curves. We also discuss how future follow-up observations of transiting
planets with this novel technique can contribute to the characterization of
Neptune- and super-Earth-size planets to be discovered by space-based missions
like CoRoT and Kepler, as well as measure atmospheric properties of giant
planets, such as the strength of atmospheric absorption features.Comment: 9 pages, including 3 figures and 2 tables; accepted for publication
in MNRA
Benefits of Ground-Based Photometric Follow-Up for Transiting Extrasolar Planets Discovered with Kepler and CoRoT
Currently, over forty transiting planets have been discovered by ground-based
photometric surveys, and space-based missions like Kepler and CoRoT are
expected to detect hundreds more. Follow-up photometric observations from the
ground will play an important role in constraining both orbital and physical
parameters for newly discovered planets, especially those with small radii (R_p
less than approximately 4 Earth radii) and/or intermediate to long orbital
periods (P greater than approximately 30 days). Here, we simulate transit light
curves from Kepler-like photometry and ground-based observations in the
near-infrared (NIR) to determine how jointly modeling space-based and
ground-based light curves can improve measurements of the transit duration and
planet-star radius ratio. We find that adding observations of at least one
ground-based transit to space-based observations can significantly improve the
accuracy for measuring the transit duration and planet-star radius ratio of
small planets (R_p less than approximately 4 Earth radii) in long-period (~1
year) orbits, largely thanks to the reduced effect of limb darkening in the
NIR. We also demonstrate that multiple ground-based observations are needed to
gain a substantial improvement in the measurement accuracy for small planets
with short orbital periods (~3 days). Finally, we consider the role that higher
ground-based precisions will play in constraining parameter measurements for
typical Kepler targets. Our results can help inform the priorities of transit
follow-up programs (including both primary and secondary transit of planets
discovered with Kepler and CoRoT), leading to improved constraints for transit
durations, planet sizes, and orbital eccentricities.Comment: 29 pages, including 4 tables and 5 figures; accepted for publication
in Ap
Transit Timing Observations from Kepler: VI. Potentially interesting candidate systems from Fourier-based statistical tests
We analyze the deviations of transit times from a linear ephemeris for the
Kepler Objects of Interest (KOI) through Quarter six (Q6) of science data. We
conduct two statistical tests for all KOIs and a related statistical test for
all pairs of KOIs in multi-transiting systems. These tests identify several
systems which show potentially interesting transit timing variations (TTVs).
Strong TTV systems have been valuable for the confirmation of planets and their
mass measurements. Many of the systems identified in this study should prove
fruitful for detailed TTV studies.Comment: 32 pages, 6 of text and one long table, Accepted to Ap
Using color photometry to separate transiting exoplanets from false positives
The radial velocity technique is currently used to classify transiting
objects. While capable of identifying grazing binary eclipses, this technique
cannot reliably identify blends, a chance overlap of a faint background
eclipsing binary with an ordinary foreground star. Blends generally have no
observable radial velocity shifts, as the foreground star is brighter by
several magnitudes and therefore dominates the spectrum, but their combined
light can produce events that closely resemble those produced by transiting
exoplanets.
The radial velocity technique takes advantage of the mass difference between
planets and stars to classify exoplanet candidates. However, the existence of
blends renders this difference an unreliable discriminator. Another difference
must therefore be utilized for this classification -- the physical size of the
transiting body. Due to the dependence of limb darkening on color, planets and
stars produce subtly different transit shapes. These differences can be
relatively weak, little more than 1/10th the transit depth. However, the
presence of even small color differences between the individual components of
the blend increases this difference. This paper will show that this color
difference is capable of discriminating between exoplanets and blends reliably,
theoretically capable of classifying even terrestrial-class transits, unlike
the radial velocity technique.Comment: 8 pages, 4 figures, accepted by A&
- …