1,713 research outputs found
A transiting planet among 23 new near-threshold candidates from the OGLE survey - OGLE-TR-182
By re-processing the data of the second season of the OGLE survey for
planetary transits and adding new mesurements on the same fields gathered in
subsequent years with the OGLE telescope, we have identified 23 new transit
candidates, recorded as OGLE-TR-178 to OGLE-TR-200. We studied the nature of
these objects with the FLAMES/UVES multi-fiber spectrograph on the VLT. One of
the candidates, OGLE-TR-182, was confirmed as a transiting gas giant planet on
a 4-day orbit. We characterised it with further observations using the FORS1
camera and UVES spectrograph on the VLT. OGLE-TR-182b is a typical ``hot
Jupiter'' with an orbital period of 3.98 days, a mass of 1.01 +- 0.15 MJup and
a radius of 1.13 (+0.24-0.08) RJup. Confirming this transiting planet required
a large investment in telescope time with the best instruments available, and
we comment on the difficulty of the confirmation process for transiting planets
in the OGLE survey. We delienate the zone were confirmation is difficult or
impossible, and discuss the implications for the Corot space mission in its
quest for transiting telluric planets.Comment: 7 pages, submitted to Astronomy and Astrophysic
A Gaussian process framework for modelling instrumental systematics: application to transmission spectroscopy
Transmission spectroscopy, which consists of measuring the
wavelength-dependent absorption of starlight by a planet's atmosphere during a
transit, is a powerful probe of atmospheric composition. However, the expected
signal is typically orders of magnitude smaller than instrumental systematics,
and the results are crucially dependent on the treatment of the latter. In this
paper, we propose a new method to infer transit parameters in the presence of
systematic noise using Gaussian processes, a technique widely used in the
machine learning community for Bayesian regression and classification problems.
Our method makes use of auxiliary information about the state of the
instrument, but does so in a non-parametric manner, without imposing a specific
dependence of the systematics on the instrumental parameters, and naturally
allows for the correlated nature of the noise. We give an example application
of the method to archival NICMOS transmission spectroscopy of the hot Jupiter
HD 189733, which goes some way towards reconciling the controversy surrounding
this dataset in the literature. Finally, we provide an appendix giving a
general introduction to Gaussian processes for regression, in order to
encourage their application to a wider range of problems.Comment: 6 figures, 1 table, accepted for publication in MNRA
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
Interpreting the yield of transit surveys: Are there groups in the known transiting planets population?
Each transiting planet discovered is characterized by 7 measurable
quantities, that may or may not be linked together (planet mass, radius,
orbital period, and star mass, radius, effective temperature, and metallicity).
Correlations between planet mass and period, surface gravity and period, planet
radius and star temperature have been previously observed among the known
transiting giant planets. Two classes of planets have been previously
identified based on their Safronov number. We use the CoRoTlux code to compare
simulated events to the sample of discovered planets and test the statistical
significance of these correlations. We first generate a stellar field with
planetary companions based on radial velocity discoveries and a planetary
evolution model, then apply a detection criterion that includes both
statistical and red noise sources. We compare the yield of our simulated survey
with the ensemble of 31 well-characterized giant transiting planets, using a
multivariate logistic analysis to assess whether the simulated distribution
matches the known transiting planets. Our multivariate analysis shows that our
simulated sample and observations are consistent to 76%. The mass vs. period
correlation for giant planets first observed with radial velocity holds with
transiting planets. Our model naturally explains the correlation between planet
surface gravity and period and the one between planet radius and stellar
effective temperature. Finally, we are also able to reproduce the previously
observed apparent bimodal distribution of Safronov numbers in 10% of our
simulated cases, although our model predicts a continuous distribution. This
shows that the evidence for the existence of two groups of planets with
different intrinsic properties is not statistically significant.Comment: 17 page
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
The White Dwarf Cooling Age of M67
A deep imaging survey covering the entire 23\arcmin diameter of the old
open cluster M67 to has been carried out using the mosaic imager
(UHCam) on the Canada-France-Hawaii Telescope. The cluster color-magnitude
diagram (CMD) can be traced from stars on its giant branch at down
through main sequence stars at least as faint as . Stars this low
in luminosity have masses below . A modest white dwarf (WD)
cooling sequence is also observed commencing slightly fainter than
and, after correction for background galaxy and stellar field contamination,
terminating near . The observed WDs follow quite closely a
theoretical cooling sequence for pure carbon core WDs with
hydrogen-rich atmospheres (DA WDs). The cooling time to an of 14.6 for
such WDs is 4.3 Gyr which we take as the WD cooling age of the cluster. A fit
of a set of isochrones to the cluster CMD indicates a turnoff age of 4.0 Gyr.
The excellent agreement between these results suggests that ages derived from
white dwarf cooling should be considered as reliable as those from other dating
techniques. The WDs currently contribute about 9% of the total cluster mass but
the number seen appears to be somewhat low when compared with the number of
giants observed in the cluster.Comment: 15 pages plus 3 diagrams, minor corrections, Accepted for publication
in the Astrophysical Journal Letters, to be published September 10, 199
The spin-orbit angle of the transiting hot jupiter CoRoT-1b
We measure the angle between the planetary orbit and the stellar rotation
axis in the transiting planetary system CoRoT-1, with new HIRES/Keck and
FORS/VLT high-accuracy photometry. The data indicate a highly tilted system,
with a projected spin-orbit angle lambda = 77 +- 11 degrees. Systematic
uncertainties in the radial velocity data could cause the actual errors to be
larger by an unknown amount, and this result needs to be confirmed with further
high-accuracy spectroscopic transit measurements.
Spin-orbit alignment has now been measured in a dozen extra-solar planetary
systems, and several show strong misalignment. The first three misaligned
planets were all much more massive than Jupiter and followed eccentric orbits.
CoRoT-1, however, is a jovian-mass close-in planet on a circular orbit. If its
strong misalignment is confirmed, it would break this pattern. The high
occurence of misaligned systems for several types of planets and orbits favours
planet-planet scattering as a mechanism to bring gas giants on very close
orbits.Comment: to appear in in MNRAS letters [5 pages
Accurate Spitzer infrared radius measurement for the hot Neptune GJ 436b
We present Spitzer Space Telescope infrared photometry of a primary transit
of the hot Neptune GJ 436b. The observations were obtained using the 8 microns
band of the InfraRed Array Camera (IRAC). The high accuracy of the transit data
and the weak limb-darkening in the 8 microns IRAC band allow us to derive
(assuming M = 0.44 +- 0.04 Msun for the primary) a precise value for the
planetary radius (4.19 +0.21-0.16 Rearth), the stellar radius (0.463
+0.022-0.017 Rsun), the orbital inclination (85.90 +0.19-0.18 degrees) and
transit timing (2454280.78186 +0.00015-0.00008 HJD). Assuming current planet
models, an internal structure similar to that of Neptune with a small H/He
envelope is necessary to account for the measured radius of GJ 436b.Comment: Accepted for publication in A&A on 21/07/2007; 5 pages, 3 figure
Hubble Space Telescope times-series photometry of the planetary transit of HD189733: no moon, no rings, starspots
We monitored three transits of the giant gas planet around the nearby K dwarf
HD 189733 with the ACS camera on the Hubble Space Telescope. The resulting
very-high accuracy lightcurve (signal-to-noise ratio near 15000 on individual
measurements, 35000 on 10-minute averages) allows a direct geometric
measurement of the orbital inclination, radius ratio and scale of the system: i
= 85.68 +- 0.04, Rpl/R*=0.1572 +- 0.0004, a/R*=8.92 +- 0.09. We derive improved
values for the stellar and planetary radius, R*=0.755+- 0.011 Rsol, Rpl=1.154
+- 0.017 RJ, and the transit ephemerides, Ttr=2453931.12048 +- 0.00002 + n
2.218581 +- 0.000002$. The HST data also reveal clear evidence of the planet
occulting spots on the surface of the star. At least one large spot complex
(>80000 km) is required to explain the observed flux residuals and their colour
evolution. This feature is compatible in amplitude and phase with the
variability observed simultaneously from the ground. No evidence for satellites
or rings around HD 189733b is seen in the HST lightcurve. This allows us to
exlude with a high probability the presence of Earth-sized moons and
Saturn-type debris rings around this planet. The timing of the three transits
sampled is stable to the level of a few seconds, excluding a massive second
planet in outer 2:1 resonance.Comment: revised version. Significant updates and new figures; to appear in
Astronomy and Astrophysic
- …