362 research outputs found
Image Slicer Performances from a Demonstrator for the SNAP/JDEM Mission - Part I: Wavelength Accuracy
A well-adapted visible and infrared spectrograph has been developed for the
SNAP (SuperNova/Acceleration Probe) experiment proposed for JDEM. The
instrument should have a high sensitivity to see faint supernovae but also a
good redshift determination better than 0.003(1+z) and a precise
spectrophotometry (2%). An instrument based on an integral field method with
the powerful concept of imager slicing has been designed. A large prototyping
effort has been performed in France which validates the concept. In particular
a demonstrator reproducing the full optical configuration has been built and
tested to prove the optical performances both in the visible and in the near
infrared range. This paper is the first of two papers. The present paper focus
on the wavelength measurement while the second one will present the
spectrophotometric performances. We adress here the spectral accuracy expected
both in the visible and in the near infrared range in such configuration and we
demonstrate, in particular, that the image slicer enhances the instrumental
performances in the spectral measurement precision by removing the slit effect.
This work is supported in France by CNRS/INSU/IN2P3 and by the French spatial
agency (CNES) and in US by the University of California.Comment: Submitted to PAS
Photometric quality of Dome C for the winter 2008 from ASTEP South
ASTEP South is an Antarctic Search for Transiting Exo- Planets in the South
pole field, from the Concordia station, Dome C, Antarctica. The instrument
consists of a thermalized 10 cm refractor observing a fixed 3.88\degree x
3.88\degree field of view to perform photometry of several thousand stars at
visible wavelengths (700-900 nm). The first winter campaign in 2008 led to the
retrieval of nearly 1600 hours of data. We derive the fraction of photometric
nights by measuring the number of detectable stars in the field. The method is
sensitive to the presence of small cirrus clouds which are invisible to the
naked eye. The fraction of night-time for which at least 50% of the stars are
detected is 74% from June to September 2008. Most of the lost time (18.5% out
of 26%) is due to periods of bad weather conditions lasting for a few days
("white outs"). Extended periods of clear weather exist. For example, between
July 10 and August 10, 2008, the total fraction of time (day+night) for which
photometric observations were possible was 60%. This confirms the very high
quality of Dome C for nearly continuous photometric observations during the
Antarctic winter
The secondary eclipses of WASP-19b as seen by the ASTEP 400 telescope from Antarctica
The ASTEP (Antarctica Search for Transiting ExoPlanets) program was
originally aimed at probing the quality of the Dome C, Antarctica for the
discovery and characterization of exoplanets by photometry. In the first year
of operation of the 40 cm ASTEP 400 telescope (austral winter 2010), we
targeted the known transiting planet WASP-19b in order to try to detect its
secondary transits in the visible. This is made possible by the excellent
sub-millimagnitude precision of the binned data. The WASP-19 system was
observed during 24 nights in May 2010. The photometric variability level due to
starspots is about 1.8% (peak-to-peak), in line with the SuperWASP data from
2007 (1.4%) and larger than in 2008 (0.07%). We find a rotation period of
WASP-19 of 10.7 +/- 0.5 days, in agreement with the SuperWASP determination of
10.5 +/- 0.2 days. Theoretical models show that this can only be explained if
tidal dissipation in the star is weak, i.e. the tidal dissipation factor Q'star
> 3.10^7. Separately, we find evidence for a secondary eclipse of depth 390 +/-
190 ppm with a 2.0 sigma significance, a phase consistent with a circular orbit
and a 3% false positive probability. Given the wavelength range of the
observations (420 to 950 nm), the secondary transit depth translates into a day
side brightness temperature of 2690(-220/+150) K, in line with measurements in
the z' and K bands. The day side emission observed in the visible could be due
either to thermal emission of an extremely hot day side with very little
redistribution of heat to the night side, or to direct reflection of stellar
light with a maximum geometrical albedo Ag=0.27 +/- 0.13. We also report a
low-frequency oscillation well in phase at the planet orbital period, but with
a lower-limit amplitude that could not be attributed to the planet phase alone,
and possibly contaminated with residual lightcurve trends.Comment: Accepted for publication in Astronomy and Astrophysics, 13 pages, 13
figure
Transiting Exoplanet Studies and Community Targets for JWST's Early Release Science Program
The James Webb Space Telescope will revolutionize transiting exoplanet
atmospheric science due to its capability for continuous, long-duration
observations and its larger collecting area, spectral coverage, and spectral
resolution compared to existing space-based facilities. However, it is unclear
precisely how well JWST will perform and which of its myriad instruments and
observing modes will be best suited for transiting exoplanet studies. In this
article, we describe a prefatory JWST Early Release Science (ERS) program that
focuses on testing specific observing modes to quickly give the community the
data and experience it needs to plan more efficient and successful future
transiting exoplanet characterization programs. We propose a multi-pronged
approach wherein one aspect of the program focuses on observing transits of a
single target with all of the recommended observing modes to identify and
understand potential systematics, compare transmission spectra at overlapping
and neighboring wavelength regions, confirm throughputs, and determine overall
performances. In our search for transiting exoplanets that are well suited to
achieving these goals, we identify 12 objects (dubbed "community targets") that
meet our defined criteria. Currently, the most favorable target is WASP-62b
because of its large predicted signal size, relatively bright host star, and
location in JWST's continuous viewing zone. Since most of the community targets
do not have well-characterized atmospheres, we recommend initiating preparatory
observing programs to determine the presence of obscuring clouds/hazes within
their atmospheres. Measurable spectroscopic features are needed to establish
the optimal resolution and wavelength regions for exoplanet characterization.
Other initiatives from our proposed ERS program include testing the instrument
brightness limits and performing phase-curve observations.(Abridged)Comment: This is a white paper that originated from an open discussion at the
Enabling Transiting Exoplanet Science with JWST workshop held November 16 -
18, 2015 at STScI (http://www.stsci.edu/jwst/science/exoplanets). Accepted
for publication in PAS
Multicolour photometry for exoplanet candidate validation
Context. The TESS and PLATO missions are expected to find vast numbers of new
transiting planet candidates. However, only a fraction of these candidates will
be legitimate planets, and the candidate validation will require a significant
amount of follow-up resources. Radial velocity follow-up can be carried out
only for the most promising candidates around bright, slowly rotating, stars.
Thus, before devoting RV resources to candidates, they need to be vetted using
cheaper methods, and, in the cases for which an RV confirmation is not
feasible, the candidate's true nature needs to be determined based on these
alternative methods alone.
Aims. We study the applicability of multicolour transit photometry in the
validation of transiting planet candidates when the candidate signal arises
from a real astrophysical source. We seek to answer how securely can we
estimate the true uncontaminated star-planet radius ratio when the light curve
may contain contamination from unresolved light sources inside the photometry
aperture when combining multicolour transit observations with a physics-based
contamination model.
Methods. The study is based on simulations and ground-based transit
observations. The analyses are carried out with a contamination model
integrated into the PyTransit v2 transit modelling package, and the
observations are carried out with the MuSCAT2 multicolour imager installed in
the 1.5 m TCS in the Teide Observatory.
Results. We show that multicolour transit photometry can be used to estimate
the amount of flux contamination and the true radius ratio. Combining the true
radius ratio with an estimate for the stellar radius yields the true absolute
radius of the transiting object, which is a valuable quantity in statistical
candidate validation, and enough in itself to validate a candidate whose radius
falls below the theoretical lower limit for a brown dwarf.Comment: Accepted to A&
Obliquity measurement and atmospheric characterization of the WASP-74 planetary system
We present new transit observations of the hot Jupiter WASP-74 b
( 1860 K) using the high-resolution spectrograph HARPS-N
and the multi-colour simultaneous imager MuSCAT2. We refine the orbital
properties of the planet and its host star, and measure its obliquity for the
first time. The measured sky-projected angle between the stellar spin-axis and
the planet's orbital axis is compatible with an orbit well-aligned with the
equator of the host star (). We are not
able to detect any absorption feature of H, or any other atomic
spectral features, in its high-resolution transmission spectra due to low S/N
at the line cores. Despite previous claims regarding the presence of strong
optical absorbers such TiO and VO gases in the atmosphere of WASP-74 b, the new
ground-based photometry combined with a reanalysis of previously reported
observations from the literature shows a slope in the low-resolution
transmission spectrum steeper than expected from Rayleigh scattering alone.Comment: Accepted for publication in Astronomy & Astrophysics. 12 pages, 8
figures, 5 table
MOA-2010-BLG-477Lb: constraining the mass of a microlensing planet from microlensing parallax, orbital motion and detection of blended light
Microlensing detections of cool planets are important for the construction of
an unbiased sample to estimate the frequency of planets beyond the snow line,
which is where giant planets are thought to form according to the core
accretion theory of planet formation. In this paper, we report the discovery of
a giant planet detected from the analysis of the light curve of a
high-magnification microlensing event MOA-2010-BLG-477. The measured
planet-star mass ratio is and the projected
separation is in units of the Einstein radius. The angular
Einstein radius is unusually large mas. Combining
this measurement with constraints on the "microlens parallax" and the lens
flux, we can only limit the host mass to the range . In
this particular case, the strong degeneracy between microlensing parallax and
planet orbital motion prevents us from measuring more accurate host and planet
masses. However, we find that adding Bayesian priors from two effects (Galactic
model and Keplerian orbit) each independently favors the upper end of this mass
range, yielding star and planet masses of
and at a distance of kpc,
and with a semi-major axis of AU. Finally, we show that the
lens mass can be determined from future high-resolution near-IR adaptive optics
observations independently from two effects, photometric and astrometric.Comment: 3 Tables, 12 Figures, accepted in Ap
Kojima-1Lb is a mildly cold neptune around the brightest microlensing host star
We report the analysis of additional multiband photometry and spectroscopy and new adaptive optics (AO) imaging of the nearby planetary microlensing event TCPJ05074264+2447555 (Kojima-1), which was discovered toward the Galactic anticenter in 2017 (Nucita et al.). We confirm the planetary nature of the light-curve anomaly around the peak while finding no additional planetary feature in this event. We also confirm the presence of apparent blending flux and the absence of significant parallax signal reported in the literature. The AO image reveals no contaminating sources, making it most likely that the blending flux comes from the lens star. The measured multiband lens flux, combined with a constraint from the microlensing model, allows us to narrow down the previously unresolved mass and distance of the lens system. We find that the primary lens is a dwarf on the K/M boundary (0.581 ± 0.033Me) located at 505±47 pc, and the companion (Kojima-1Lb) is a Neptune-mass planet (20.0 ± 2.0M⊕) with a semimajor axis of-1.08+0.18 0.62 au. This orbit is a few times smaller than those of typical microlensing planets and is comparable to the snow-line location at young ages. We calculate that the a priori detection probability of Kojima-1Lb is only ∼35%, which may imply that Neptunes are common around the snow line, as recently suggested by the transit and radial velocity techniques. The host star is the brightest among the microlensing planetary systems (Ks = 13.7), offering a great opportunity to spectroscopically characterize this system, even with current facilities
MOA 2010-BLG-477Lb: Constraining the mass of a microlensing planet from microlensing parallax, orbital motion, and detection of blended light
Microlensing detections of cool planets are important for the construction of an unbiased sample to estimate the frequency of planets beyond the snow line, which is where giant planets are thought to form according to the core accretion theory of planet formation. In this paper, we report the discovery of a giant planet detected from the analysis of the light curve of a high-magnification microlensing event MOA 2010-BLG-477. The measured planet-star mass ratio is q = (2.181 ± 0.004) × 10-3 and the projected separation is s = 1.1228 ± 0.0006 in units of the Einstein radius. The angular Einstein radius is unusually large θE = 1.38 ± 0.11 mas. Combining this measurement with constraints on the microlens parallax and the lens flux, we can only limit the host mass to the range 0.13 \u3c M/M \u3c 1.0. In this particular case, the strong degeneracy between microlensing parallax and planet orbital motion prevents us from measuring more accurate host and planet masses. However, we find that adding Bayesian priors from two effects (Galactic model and Keplerian orbit) each independently favors the upper end of this mass range, yielding star and planet masses of M * = 0.67+0.33- 0.13 M and mp1.5+0.8- 0.3 M JUP at a distance of D = 2.3 ± 0.6kpc, and with a semi-major axis of a = 2 +3- 1AU. Finally, we show that the lens mass can be determined from future high-resolution near-IR adaptive optics observations independently from two effects, photometric and astrometric. © 2012. The American Astronomical Society. All rights reserved.
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