2,588 research outputs found
Ground-based photometry of the 21-day Neptune HD106315c
Space-based transit surveys such as K2 and TESS allow the detection of small
transiting planets with orbital periods beyond 10 days. Few of these warm
Neptunes are currently known around stars bright enough to allow for detailed
follow-up observations dedicated to their atmospheric characterization. The
21-day period and 3.95 planet HD106315c has been discovered based on
the observation of two of its transits by K2. We have observed HD106315 using
the 1.2m Euler telescope equipped with the EulerCam camera on two instances to
confirm the transit using broad band photometry and refine the planetary
period. Based on two observed transits of HD106315c, we detect its 1 mmag
transit and obtain a precise measurement of the planetary ephemerids, which are
critical for planning further follow-up observations. We have used the attained
precision together with the predicted yield from the TESS mission to evaluate
the potential for ground-based confirmation of Neptune-sized planets found by
TESS. We find that 1-meter-class telescopes on the ground equipped with precise
photometers could substantially contribute to the follow-up of 162 TESS
candidates orbiting stars with magnitudes of . Out of these, 74
planets orbit stars with and 12 planets orbit , which
makes these candidates high-priority objects for atmospheric characterization
with high-end instrumentation.Comment: Published in A&A letters, 4 pages, 3 figure
Sparse aperture masking at the VLT II. Detection limits for the eight debris disks stars Pic, AU Mic, 49 Cet, Tel, Fomalhaut, g Lup, HD181327 and HR8799
Context. The formation of planetary systems is a common, yet complex
mechanism. Numerous stars have been identified to possess a debris disk, a
proto-planetary disk or a planetary system. The understanding of such formation
process requires the study of debris disks. These targets are substantial and
particularly suitable for optical and infrared observations. Sparse Aperture
masking (SAM) is a high angular resolution technique strongly contributing to
probe the region from 30 to 200 mas around the stars. This area is usually
unreachable with classical imaging, and the technique also remains highly
competitive compared to vortex coronagraphy. Aims. We aim to study debris disks
with aperture masking to probe the close environment of the stars. Our goal is
either to find low mass companions, or to set detection limits. Methods. We
observed eight stars presenting debris disks ( Pictoris, AU
Microscopii, 49 Ceti, Telescopii, Fomalhaut, g Lupi, HD181327 and
HR8799) with SAM technique on the NaCo instrument at the VLT. Results. No close
companions were detected using closure phase information under 0.5 of
separation from the parent stars. We obtained magnitude detection limits that
we converted to Jupiter masses detection limits using theoretical isochrones
from evolutionary models. Conclusions. We derived upper mass limits on the
presence of companions in the area of few times the diffraction limit of the
telescope around each target star.Comment: 7 pages, All magnitude detection limits maps are only available in
electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr
(130.79.128.5
High resolution imaging of young M-type stars of the solar neighborhood: Probing the existence of companions down to the mass of Jupiter
Context. High contrast imaging is a powerful technique to search for gas
giant planets and brown dwarfs orbiting at separation larger than several AU.
Around solar-type stars, giant planets are expected to form by core accretion
or by gravitational instability, but since core accretion is increasingly
difficult as the primary star becomes lighter, gravitational instability would
be the a probable formation scenario for yet-to-be-found distant giant planets
around a low-mass star. A systematic survey for such planets around M dwarfs
would therefore provide a direct test of the efficiency of gravitational
instability. Aims. We search for gas giant planets orbiting around late-type
stars and brown dwarfs of the solar neighborhood. Methods. We obtained deep
high resolution images of 16 targets with the adaptive optic system of VLT-NACO
in the Lp band, using direct imaging and angular differential imaging. This is
currently the largest and deepest survey for Jupiter-mass planets around
Mdwarfs. We developed and used an integrated reduction and analysis pipeline to
reduce the images and derive our 2D detection limits for each target. The
typical contrast achieved is about 9 magnitudes at 0.5" and 11 magnitudes
beyond 1". For each target we also determine the probability of detecting a
planet of a given mass at a given separation in our images. Results. We derived
accurate detection probabilities for planetary companions, taking into account
orbital projection effects, with in average more than 50% probability to detect
a 3MJup companion at 10AU and a 1.5MJup companion at 20AU, bringing strong
constraints on the existence of Jupiter-mass planets around this sample of
young M-dwarfs.Comment: Accepted for publication in A&
ARCHI: pipeline for light curve extraction of CHEOPS background star
High precision time series photometry from space is being used for a number
of scientific cases. In this context, the recently launched CHEOPS (ESA)
mission promises to bring 20 ppm precision over an exposure time of 6 hours,
when targeting nearby bright stars, having in mind the detailed
characterization of exoplanetary systems through transit measurements. However,
the official CHEOPS (ESA) mission pipeline only provides photometry for the
main target (the central star in the field). In order to explore the potential
of CHEOPS photometry for all stars in the field, in this paper we present
archi, an additional open-source pipeline module{\dag}to analyse the background
stars present in the image. As archi uses the official Data Reduction Pipeline
data as input, it is not meant to be used as independent tool to process raw
CHEOPS data but, instead, to be used as an add-on to the official pipeline. We
test archi using CHEOPS simulated images, and show that photometry of
background stars in CHEOPS images is only slightly degraded (by a factor of 2
to 3) with respect to the main target. This opens a potential for the use of
CHEOPS to produce photometric time series of several close-by targets at once,
as well as to use different stars in the image to calibrate systematic errors.
We also show one clear scientific application where the study of the companion
light curve can be important for the understanding of the contamination on the
main target.Comment: 14 pages, 13 figures, accepted for publication in MNRAS, all code
available at https://github.com/Kamuish/arch
The thermal conductivity reduction in HgTe/CdTe superlattices
The techniques used previously to calculate the three-fold thermal
conductivity reduction due to phonon dispersion in GaAs/AlAs superlattices
(SLs) are applied to HgTe/CdTe SLs. The reduction factor is approximately the
same, indicating that this SL may be applicable both as a photodetector and a
thermoelectric cooler.Comment: 5 pages, 2 figures; to be published in Journal of Applied Physic
The Spitzer search for the transits of HARPS low-mass planets - II. Null results for 19 planets
Short-period super-Earths and Neptunes are now known to be very frequent
around solar-type stars. Improving our understanding of these mysterious
planets requires the detection of a significant sample of objects suitable for
detailed characterization. Searching for the transits of the low-mass planets
detected by Doppler surveys is a straightforward way to achieve this goal.
Indeed, Doppler surveys target the most nearby main-sequence stars, they
regularly detect close-in low-mass planets with significant transit
probability, and their radial velocity data constrain strongly the ephemeris of
possible transits. In this context, we initiated in 2010 an ambitious Spitzer
multi-Cycle transit search project that targeted 25 low-mass planets detected
by radial velocity, focusing mainly on the shortest-period planets detected by
the HARPS spectrograph. We report here null results for 19 targets of the
project. For 16 planets out of 19, a transiting configuration is strongly
disfavored or firmly rejected by our data for most planetary compositions. We
derive a posterior probability of 83% that none of the probed 19 planets
transits (for a prior probability of 22%), which still leaves a significant
probability of 17% that at least one of them does transit. Globally, our
Spitzer project revealed or confirmed transits for three of its 25 targeted
planets, and discarded or disfavored the transiting nature of 20 of them. Our
light curves demonstrate for Warm Spitzer excellent photometric precisions: for
14 targets out of 19, we were able to reach standard deviations that were
better than 50ppm per 30 min intervals. Combined with its Earth-trailing orbit,
which makes it capable of pointing any star in the sky and to monitor it
continuously for days, this work confirms Spitzer as an optimal instrument to
detect sub-mmag-deep transits on the bright nearby stars targeted by Doppler
surveys.Comment: Accepted for publication in Astronomy and Astrophysics. 23 pages, 21
figure
Strong HI Lyman- variations from the 11 Gyr-old host star Kepler-444: a planetary origin ?
Kepler-444 provides a unique opportunity to probe the atmospheric composition
and evolution of a compact system of exoplanets smaller than the Earth. Five
planets transit this bright K star at close orbital distances, but they are too
small for their putative lower atmosphere to be probed at optical/infrared
wavelengths. We used the Space Telescope Imaging Spectrograph instrument
onboard the Hubble Space Telescope to search for the signature of the planet's
upper atmospheres at six independent epochs in the Ly- line. We detect
significant flux variations during the transits of both Kepler-444e and f
(~20%), and also at a time when none of the known planets was transiting
(~40%). Variability in the transition region and corona of the host star might
be the source of these variations. Yet, their amplitude over short time scales
(~2-3 hours) is surprisingly strong for this old (11.2+-1.0Gyr) and apparently
quiet main-sequence star. Alternatively, we show that the in-transits
variations could be explained by absorption from neutral hydrogen exospheres
trailing the two outer planets (Kepler-444e and f). They would have to contain
substantial amounts of water to replenish such hydrogen exospheres, which would
reveal them as the first confirmed ocean-planets. The out-of-transit
variations, however, would require the presence of a yet-undetected Kepler-444g
at larger orbital distance, casting doubt on the planetary origin scenario.
Using HARPS-N observations in the sodium doublet, we derived the properties of
two Interstellar Medium clouds along the line-of-sight toward Kepler-444. This
allowed us to reconstruct the stellar Ly- line profile and to estimate
the XUV irradiation from the star, which would still allow for a moderate mass
loss from the outer planets after 11.2Gyr. Follow-up of the system at XUV
wavelengths will be required to assess this tantalizing possibility.Comment: Accepted for publication in A&A Name of the system added to the title
in most recent versio
Ultra-broadband wavelength-swept Tm-doped fiber laser using wavelength-combined gain stages
A wavelength-swept thulium-doped fiber laser system employing two parallel cavities with two different fiber gain stages is reported. The fiber gain stages were tailored to provide emission in complementary bands with external wavelength-dependent feedback cavities sharing a common rotating polygon mirror for wavelength scanning. The wavelength-swept laser outputs from the fiber gain elements were spectrally combined by means of a dichroic mirror and yielded over 500 mW of output with a scanning range from ~1740 nm to ~2070 nm for a scanning frequency of ~340 Hz
High-energy environment of super-Earth 55 Cnc e I: Far-UV chromospheric variability as a possible tracer of planet-induced coronal rain
The irradiation of close-in planets by their star influences their evolution
and might be responsible for a population of ultra-short period planets eroded
to their bare core. In orbit around a bright, nearby G-type star, the
super-Earth 55 Cnc e offers the possibility to address these issues through UV
transit observations. We used the Hubble Space Telescope to observe the transit
in the FUV over 3 epochs in Apr. 2016, Jan. 2017, and Feb. 2017. These
observations reveal significant short- and long-term variability in 55 Cnc
chromospheric emission lines. In the last 2 epochs, we detected a larger flux
in the C III, Si III, and Si IV lines after the planet passed the approaching
quadrature, followed by a flux decrease in the Si IV doublet. In the second
epoch these variations are contemporaneous with flux decreases in the Si II and
C II doublet. All epochs show flux decreases in the N V doublet as well, albeit
at different orbital phases. These flux decreases are consistent with
absorption from optically thin clouds of gas, are mostly localized at low and
redshifted radial velocities in the star rest frame, and occur preferentially
before and during the transit. These 3 points make it unlikely that the
variations are purely stellar, yet we show that the occulting material is also
unlikely to originate from the planet. We tentatively propose that the motion
of 55 Cnc e at the fringes of the stellar corona leads to the formation of a
cool coronal rain. The inhomogeneity and temporal evolution of the stellar
corona would be responsible for the differences between the visits. Additional
variations are detected in the C II doublet in the first epoch and in the O I
triplet in all epochs with a different behavior that points toward intrinsic
stellar variability. Further observations at FUV wavelengths are required to
disentangle between star-planet interactions and the activity of the starComment: 22 pages, 20 figures, accepted for publication in A&
Evidence for a spectroscopic direct detection of reflected light from 51 Peg b
The detection of reflected light from an exoplanet is a difficult technical
challenge at optical wavelengths. Even though this signal is expected to
replicate the stellar signal, not only is it several orders of magnitude
fainter, but it is also hidden among the stellar noise. We apply a variant of
the cross-correlation technique to HARPS observations of 51 Peg to detect the
reflected signal from planet 51 Peg b. Our method makes use of the
cross-correlation function of a binary mask with high-resolution spectra to
amplify the minute planetary signal that is present in the spectra by a factor
proportional to the number of spectral lines when performing the cross
correlation. The resulting cross-correlation functions are then normalized by a
stellar template to remove the stellar signal. Carefully selected sections of
the resulting normalized CCFs are stacked to increase the planetary signal
further. The recovered signal allows probing several of the planetary
properties, including its real mass and albedo. We detect evidence for the
reflected signal from planet 51 Peg b at a significance of 3\sigma_noise. The
detection of the signal permits us to infer a real mass of 0.46^+0.06_-0.01
M_Jup (assuming a stellar mass of 1.04\;M_Sun) for the planet and an orbital
inclination of 80^+10_-19 degrees. The analysis of the data also allows us to
infer a tentative value for the (radius-dependent) geometric albedo of the
planet. The results suggest that 51Peg b may be an inflated hot Jupiter with a
high albedo (e.g., an albedo of 0.5 yields a radius of 1.9 \pm 0.3 R_Jup for a
signal amplitude of 6.0\pm0.4 x 10^-5). We confirm that the method we perfected
can be used to retrieve an exoplanet's reflected signal, even with current
observing facilities. The advent of next generation of observing facilities
will yield new opportunities for this type of technique to probe deeper into
exoplanets.Comment: 9 pages, 6 figure
- …