619 research outputs found
Lupus-TR-3b: A Low-Mass Transiting Hot Jupiter in the Galactic Plane?
We present a strong case for a transiting Hot Jupiter planet identified
during a single-field transit survey towards the Lupus Galactic plane. The
object, Lupus-TR-3b, transits a V=17.4 K1V host star every 3.91405d.
Spectroscopy and stellar colors indicate a host star with effective temperature
5000 +/- 150K, with a stellar mass and radius of 0.87 +/- 0.04M_sun and 0.82
+/- 0.05R_sun, respectively. Limb-darkened transit fitting yields a companion
radius of 0.89 +/- 0.07R_J and an orbital inclination of 88.3 +1.3/-0.8 deg.
Magellan 6.5m MIKE radial velocity measurements reveal a 2.4 sigma K=114 +/-
25m/s sinusoidal variation in phase with the transit ephemeris. The resulting
mass is 0.81 +/- 0.18M_J and density 1.4 +/- 0.4g/cm^3. Y-band PANIC image
deconvolution reveal a V>=21 red neighbor 0.4'' away which, although highly
unlikely, we cannot conclusively rule out as a blended binary with current
data. However, blend simulations show that only the most unusual binary system
can reproduce our observations. This object is very likely a planet, detected
from a highly efficient observational strategy. Lupus-TR-3b constitutes the
faintest ground-based detection to date, and one of the lowest mass Hot
Jupiters known.Comment: 4 pages, 4 figures, accepted for publication in ApJ
The `666' collaboration on OGLE transits: I. Accurate radius of the planets OGLE-TR-10b and OGLE-TR-56b with VLT deconvolution photometry
Transiting planets are essential to study the structure and evolution of
extra-solar planets. For that purpose, it is important to measure precisely the
radius of these planets. Here we report new high-accuracy photometry of the
transits of OGLE-TR-10 and OGLE-TR-56 with VLT/FORS1. One transit of each
object was covered in Bessel V and R filters, and treated with the
deconvolution-based photometry algorithm DECPHOT, to ensure accurate
millimagnitude light curves. Together with earlier spectroscopic measurements,
the data imply a radius of 1.22 +0.12-0.07 R_J for OGLE-TR-10b and 1.30 +- 0.05
R_J for OGLE-TR-56b. A re-analysis of the original OGLE photometry resolves an
earlier discrepancy about the radius of OGLE-TR-10. The transit of OGLE-TR-56
is almost grazing, so that small systematics in the photometry can cause large
changes in the derived radius. Our study confirms both planets as inflated hot
Jupiters, with large radii comparable to that of HD 209458 and at least two
other recently discovered transiting gas giants.Comment: Fundamental updates compared to previous version; accepted for
publication in Astronomy & Astrophysic
High angular resolution imaging and infrared spectroscopy of CoRoT candidates
Studies of transiting extrasolar planets are of key importance for
understanding the nature of planets outside our solar system because their
masses, diameters, and bulk densities can be measured. An important part of
transit-search programmes is the removal of false-positives. The critical
question is how many of the candidates that passed all previous tests are false
positives. For our study we selected 25 CoRoT candidates that have already been
screened against false-positives using detailed analysis of the light curves
and seeing-limited imaging, which has transits that are between 0.7 and 0.05%
deep. We observed 20 candidates with the adaptive optics imager NaCo and 18
with the high-resolution infrared spectrograph CRIRES. We found previously
unknown stars within 2 arcsec of the targets in seven of the candidates. All of
these are too faint and too close to the targets to have been previously
detected with seeing-limited telescopes in the optical. Our study thus leads to
the surprising results that if we remove all candidates excluded by the
sophisticated analysis of the light-curve, as well as carrying out deep imaging
with seeing-limited telescopes, still 28-35% of the remaining candidates are
found to possess companions that are bright enough to be false-positives. Given
that the companion-candidates cluster around the targets and that the J-K
colours are consistent with physical companions, we conclude that the
companion-candidates are more likely to be physical companions rather than
unrelated field stars.Comment: 12 pages, 12 figures, A&A in pres
The Transit Light Curve Project. VII. The Not-So-Bloated Exoplanet HAT-P-1b
We present photometry of the G0 star HAT-P-1 during six transits of its
close-in giant planet, and we refine the estimates of the system parameters.
Relative to Jupiter's properties, HAT-P-1b is 1.20 +/- 0.05 times larger and
its surface gravity is 2.7 +/- 0.2 times weaker. Although it remains the case
that HAT-P-1b is among the least dense of the known sample of transiting
exoplanets, its properties are in accord with previously published models of
strongly irradiated, coreless, solar-composition giant planets. The times of
the transits have a typical accuracy of 1 min and do not depart significantly
from a constant period.Comment: To appear in AJ [19pg, 3 figures]. New co-author added. Minor
revisions to match published versio
The nature of p-modes and granulation in HD 49933 observed by CoRoT
Context: Recent observations of HD49933 by the space-photometric mission
CoRoT provide photometric evidence of solar type oscillations in a star other
than our Sun. The first published reduction, analysis, and interpretation of
the CoRoT data yielded a spectrum of p-modes with l = 0, 1, and 2. Aims: We
present our own analysis of the CoRoT data in an attempt to compare the
detected pulsation modes with eigenfrequencies of models that are consistent
with the observed luminosity and surface temperature. Methods: We used the
Gruberbauer et al. frequency set derived based on a more conservative Bayesian
analysis with ignorance priors and fit models from a dense grid of model
spectra. We also introduce a Bayesian approach to searching and quantifying the
best model fits to the observed oscillation spectra. Results: We identify 26
frequencies as radial and dipolar modes. Our best fitting model has solar
composition and coincides within the error box with the spectroscopically
determined position of HD49933 in the H-R diagram. We also show that
lower-than-solar Z models have a lower probability of matching the observations
than the solar metallicity models. To quantify the effect of the deficiencies
in modeling the stellar surface layers in our analysis, we compare adiabatic
and nonadiabatic model fits and find that the latter reproduces the observed
frequencies better.Comment: accepted to be published in A&A, 9 pages, 5 figure
Multi-object spectroscopy of stars in the CoRoT fields II: The stellar population of the CoRoT fields IRa01, LRa01, LRa02, and LRa06
With now more than 20 exoplanets discovered by CoRoT, it has often been
considered strange that so many of them are orbiting F-stars, and so few of
them K or M-stars. Although transit search programs are mostly sensitive to
short-period planets, they are ideal for verifying these results. To determine
the frequency of planets as a function of stellar mass, we also have to
characterize the sample of stars that was observed. We study the stellar
content of the CoRoT-fields IRa01, LRa01 (=LRa06), and LRa02 by determining the
spectral types of 11466 stars. We used spectra obtained with the multi-object
spectrograph AAOmega and derived the spectral types by using template spectra
with well-known parameters. We find that 34.8+/-0.7% of the stars observed by
CoRoT in these fields are F-dwarfs, 15.1+/-0.5% G-dwarfs, and 5.0+/-0.3%
K-dwarfs. We conclude that the apparent lack of exoplanets of K- and M-stars is
explained by the relatively small number of these stars in the observed sample.
We also show that the apparently large number of planets orbiting F-stars is
similarly explained by the large number of such stars in these fields. Our
study also shows that the difference between the sample of stars that CoRoT
observes and a sample of randomly selected stars is relatively small, and that
the yield of CoRoT specifically is the detection one hot Jupiter amongst
2100+/-700 stars. We conclude that transit search programs can be used to study
the relation between the frequency of planets and the mass of the host stars,
and that the results obtained so far generally agree with those of radial
velocity programs.Comment: 231 pages with 6 figures, A&A accepte
OGLE-TR-211 - a new transiting inflated hot Jupiter from the OGLE survey and ESO LP666 spectroscopic follow-up program
We present results of the photometric campaign for planetary and
low-luminosity object transits conducted by the OGLE survey in 2005 season
(Campaign #5). About twenty most promising candidates discovered in these data
were subsequently verified spectroscopically with the VLT/FLAMES spectrograph.
One of the candidates, OGLE-TR-211, reveals clear changes of radial velocity
with small amplitude of 82 m/sec, varying in phase with photometric transit
ephemeris. Thus, we confirm the planetary nature of the OGLE-TR-211 system.
Follow-up precise photometry of OGLE-TR-211 with VLT/FORS together with radial
velocity spectroscopy supplemented with high resolution, high S/N VLT/UVES
spectra allowed us to derive parameters of the planet and host star.
OGLE-TR-211b is a hot Jupiter orbiting a F7-8 spectral type dwarf star with the
period of 3.68 days. The mass of the planet is equal to 1.03+/-0.20 M_Jup while
its radius 1.36+0.18-0.09 R_Jup. The radius is about 20% larger than the
typical radius of hot Jupiters of similar mass. OGLE-TR-211b is, then, another
example of inflated hot Jupiters - a small group of seven exoplanets with large
radii and unusually small densities - objects being a challenge to the current
models of exoplanets.Comment: 6 pages. Submitted to Astronomy and Astrophysic
Transit spectrophotometry of the exoplanet HD189733b. II. New Spitzer observations at 3.6 microns
We present a new primary transit observation of the hot-jupiter HD189733b,
obtained at 3.6 microns with the Infrared Array Camera (IRAC) onboard the
Spitzer Space Telescope. Previous measurements at 3.6 microns suffered from
strong systematics and conclusions could hardly be obtained with confidence on
the water detection by comparison of the 3.6 and 5.8 microns observations. We
use a high S/N Spitzer photometric transit light curve to improve the precision
of the near infrared radius of the planet at 3.6 microns. The observation has
been performed using high-cadence time series integrated in the subarray mode.
We are able to derive accurate system parameters, including planet-to-star
radius ratio, impact parameter, scale of the system, and central time of the
transit from the fits of the transit light curve. We compare the results with
transmission spectroscopic models and with results from previous observations
at the same wavelength. We obtained the following system parameters:
R_p/R_\star=0.15566+0.00011-0.00024, b=0.661+0.0053-0.0050, and
a/R_\star=8.925+0.0490-0.0523 at 3.6 microns. These measurements are three
times more accurate than previous studies at this wavelength because they
benefit from greater observational efficiency and less statistic and systematic
errors. Nonetheless, we find that the radius ratio has to be corrected for
stellar activity and present a method to do so using ground-based long-duration
photometric follow-up in the V-band. The resulting planet-to-star radius ratio
corrected for the stellar variability is in agreement with the previous
measurement obtained in the same bandpass (Desert et al. 2009). We also discuss
that water vapour could not be evidenced by comparison of the planetary radius
measured at 3.6 and 5.8 microns, because the radius measured at 3.6 microns is
affected by absorption by other species, possibly Rayleigh scattering by haze.Comment: 19 pages, 13 figures, accepted for publication in Astronomy &
Astrophysic
The K2-ESPRINT Project. I. Discovery of the Disintegrating Rocky Planet K2-22b with a Cometary Head and Leading Tail
We present the discovery of a transiting exoplanet candidate in the K2
Field-1 with an orbital period of 9.1457 hr: K2-22b. The highly variable
transit depths, ranging from 0\% to 1.3\%, are suggestive of a planet
that is disintegrating via the emission of dusty effluents. We characterize the
host star as an M-dwarf with K. We have obtained
ground-based transit measurements with several 1-m class telescopes and with
the GTC. These observations (1) improve the transit ephemeris; (2) confirm the
variable nature of the transit depths; (3) indicate variations in the transit
shapes; and (4) demonstrate clearly that at least on one occasion the transit
depths were significantly wavelength dependent. The latter three effects tend
to indicate extinction of starlight by dust rather than by any combination of
solid bodies. The K2 observations yield a folded light curve with lower time
resolution but with substantially better statistical precision compared with
the ground-based observations. We detect a significant "bump" just after the
transit egress, and a less significant bump just prior to transit ingress. We
interpret these bumps in the context of a planet that is not only likely
streaming a dust tail behind it, but also has a more prominent leading dust
trail that precedes it. This effect is modeled in terms of dust grains that can
escape to beyond the planet's Hill sphere and effectively undergo `Roche lobe
overflow,' even though the planet's surface is likely underfilling its Roche
lobe by a factor of 2.Comment: 22 pages, 16 figures. Final version accepted to Ap
Global analysis of the TRAPPIST Ultra-Cool Dwarf Transit Survey
ABSTRACT
We conducted a global analysis of the TRAPPIST Ultra-Cool Dwarf Transit Survey – a prototype of the SPECULOOS transit search conducted with the TRAPPIST-South robotic telescope in Chile from 2011 to 2017 – to estimate the occurrence rate of close-in planets such as TRAPPIST-1b orbiting ultra-cool dwarfs. For this purpose, the photometric data of 40 nearby ultra-cool dwarfs were reanalysed in a self-consistent and fully automated manner starting from the raw images. The pipeline developed specifically for this task generates differential light curves, removes non-planetary photometric features and stellar variability, and searches for transits. It identifies the transits of TRAPPIST-1b and TRAPPIST-1c without any human intervention. To test the pipeline and the potential output of similar surveys, we injected planetary transits into the light curves on a star-by-star basis and tested whether the pipeline is able to detect them. The achieved photometric precision enables us to identify Earth-sized planets orbiting ultra-cool dwarfs as validated by the injection tests. Our planet-injection simulation further suggests a lower limit of 10 per cent on the occurrence rate of planets similar to TRAPPIST-1b with a radius between 1 and 1.3 R⊕ and the orbital period between 1.4 and 1.8 d.</jats:p
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