68 research outputs found
Hunting for planets in the HL Tau disk
Recent ALMA images of HL Tau show gaps in the dusty disk that may be caused
by planetary bodies. Given the young age of this system, if confirmed, this
finding would imply very short timescales for planet formation, probably in a
gravitationally unstable disk. To test this scenario, we searched for young
planets by means of direct imaging in the L'-band using the Large Binocular
Telescope Interferometer mid-infrared camera. At the location of two prominent
dips in the dust distribution at ~70AU (~0.5") from the central star we reach a
contrast level of ~7.5mag. We did not detect any point source at the location
of the rings. Using evolutionary models we derive upper limits of ~10-15MJup at
<=0.5-1Ma for the possible planets. With these sensitivity limits we should
have been able to detect companions sufficiently massive to open full gaps in
the disk. The structures detected at mm-wavelengths could be gaps in the
distributions of large grains on the disk midplane, caused by planets not
massive enough to fully open gaps. Future ALMA observations of the molecular
gas density profile and kinematics as well as higher contrast infrared
observations may be able to provide a definitive answer.Comment: Accepted for publication on ApJ Letter
Characterization of the Benchmark Binary NLTT 33370
We report the confirmation of the binary nature of the nearby, very low-mass
system NLTT 33370 with adaptive optics imaging and present resolved
near-infrared photometry and integrated light optical and near-infrared
spectroscopy to characterize the system. VLT-NaCo and LBTI-LMIRCam images show
significant orbital motion between 2013 February and 2013 April. Optical
spectra reveal weak, gravity sensitive alkali lines and strong lithium 6708
Angstrom absorption that indicate the system is younger than field age.
VLT-SINFONI near-IR spectra also show weak, gravity sensitive features and
spectral morphology that is consistent with other young, very low-mass dwarfs.
We combine the constraints from all age diagnostics to estimate a system age of
~30-200 Myr. The 1.2-4.7 micron spectral energy distribution of the components
point toward T_eff=3200 +/- 500 K and T_eff=3100 +/- 500 K for NLTT 33370 A and
B, respectively. The observed spectra, derived temperatures, and estimated age
combine to constrain the component spectral types to the range M6-M8.
Evolutionary models predict masses of 113 +/- 8 M_Jup and 106 +/- 7 M_Jup from
the estimated luminosities of the components. KPNO-Phoenix spectra allow us to
estimate the systemic radial velocity of the binary. The Galactic kinematics of
NLTT 33370AB are broadly consistent with other young stars in the Solar
neighborhood. However, definitive membership in a young, kinematic group cannot
be assigned at this time and further follow-up observations are necessary to
fully constrain the system's kinematics. The proximity, age, and late-spectral
type of this binary make it very novel and an ideal target for rapid, complete
orbit determination. The system is one of only a few model calibration
benchmarks at young ages and very low-masses.Comment: 25 pages, 3 tables, 13 figures, accepted for publication in The
Astrophysical Journa
Directly Imaged L-T Transition Exoplanets in the Mid-Infrared
Gas-giant planets emit a large fraction of their light in the mid-infrared
(3m), where photometry and spectroscopy are critical to our
understanding of the bulk properties of extrasolar planets. Of particular
importance are the L and M-band atmospheric windows (3-5m), which are the
longest wavelengths currently accessible to ground-based, high-contrast
imagers. We present binocular LBT AO images of the HR 8799 planetary system in
six narrow-band filters from 3-4m, and a Magellan AO image of the 2M1207
planetary system in a broader 3.3m band. These systems encompass the five
known exoplanets with luminosities consistent with LT transition
brown dwarfs. Our results show that the exoplanets are brighter and have
shallower spectral slopes than equivalent temperature brown dwarfs in a
wavelength range that contains the methane fundamental absorption feature
(spanned by the narrowband filters and encompassed by the broader 3.3m
filter). For 2M1207 b, we find that thick clouds and non-equilibrium chemistry
caused by vertical mixing can explain the object's appearance. For the HR 8799
planets, we present new models that suggest the atmospheres must have patchy
clouds, along with non-equilibrium chemistry. Together, the presence of a
heterogeneous surface and vertical mixing presents a picture of dynamic
planetary atmospheres in which both horizontal and vertical motions influence
the chemical and condensate profiles.Comment: Accepted to Ap
The LEECH Exoplanet Imaging Survey: Limits on Planet Occurrence Rates Under Conservative Assumptions
We present the results of the largest (m) direct
imaging survey for exoplanets to date, the Large Binocular Telescope
Interferometer (LBTI) Exozodi Exoplanet Common Hunt (LEECH). We observed 98
stars with spectral types from B to M. Cool planets emit a larger share of
their flux in compared to shorter wavelengths, affording LEECH an
advantage in detecting low-mass, old, and cold-start giant planets. We
emphasize proximity over youth in our target selection, probing physical
separations smaller than other direct imaging surveys. For FGK stars, LEECH
outperforms many previous studies, placing tighter constraints on the hot-start
planet occurrence frequency interior to au. For less luminous,
cold-start planets, LEECH provides the best constraints on giant-planet
frequency interior to au around FGK stars. Direct imaging survey
results depend sensitively on both the choice of evolutionary model (e.g., hot-
or cold-start) and assumptions (explicit or implicit) about the shape of the
underlying planet distribution, in particular its radial extent. Artificially
low limits on the planet occurrence frequency can be derived when the shape of
the planet distribution is assumed to extend to very large separations, well
beyond typical protoplanetary dust-disk radii ( au), and when
hot-start models are used exclusively. We place a conservative upper limit on
the planet occurrence frequency using cold-start models and planetary
population distributions that do not extend beyond typical protoplanetary
dust-disk radii. We find that of FGK systems can host a 7 to 10
planet from 5 to 50 au. This limit leaves open the
possibility that planets in this range are common.Comment: 31 pages, 13 figures, accepted to A
Characterization of the gaseous companion {\kappa} Andromedae b: New Keck and LBTI high-contrast observations
We previously reported the direct detection of a low mass companion at a
projected separation of 55+-2 AU around the B9 type star {\kappa} Andromedae.
The properties of the system (mass ratio, separation) make it a benchmark for
the understanding of the formation and evolution of gas giant planets and brown
dwarfs on wide-orbits. We present new angular differential imaging (ADI) images
of the Kappa Andromedae system at 2.146 (Ks), 3.776 (L'), 4.052 (NB 4.05) and
4.78 {\mu}m (M') obtained with Keck/NIRC2 and LBTI/LMIRCam, as well as more
accurate near-infrared photometry of the star with the MIMIR instrument. We
derive a more accurate J = 15.86 +- 0.21, H = 14.95 +- 0.13, Ks = 14.32 +- 0.09
mag for {\kappa} And b. We redetect the companion in all our high contrast
observations. We confirm previous contrasts obtained at Ks and L' band. We
derive NB 4.05 = 13.0 +- 0.2 and M' = 13.3 +- 0.3 mag and estimate
Log10(L/Lsun) = -3.76 +- 0.06. We build the 1-5 microns spectral energy
distribution of the companion and compare it to seven PHOENIX-based atmospheric
models in order to derive Teff = 1900+100-200 K. Models do not set constrains
on the surface gravity. ``Hot-start" evolutionary models predict masses of
14+25-2 MJup based on the luminosity and temperature estimates, and considering
a conservative age range for the system (30+120-10 Myr). ``warm-start"
evolutionary tracks constrain the mass to M >= 11 MJup. Therefore, the mass of
{\kappa} Andromedae b mostly falls in the brown-dwarf regime, due to remaining
uncertainties in age and mass-luminosity models. According to the formation
models, disk instability in a primordial disk could account for the position
and a wide range of plausible masses of {\kappa} And b.Comment: 20 pages, 16 figures, accepted for publication in Astronomy and
Astrophysics on August 6, 201
Exoplanet Characterization and the Search for Life
Over 300 extrasolar planets (exoplanets) have been detected orbiting nearby
stars. We now hope to conduct a census of all planets around nearby stars and
to characterize their atmospheres and surfaces with spectroscopy. Rocky planets
within their star's habitable zones have the highest priority, as these have
the potential to harbor life. Our science goal is to find and characterize all
nearby exoplanets; this requires that we measure the mass, orbit, and
spectroscopic signature of each one at visible and infrared wavelengths. The
techniques for doing this are at hand today. Within the decade we could answer
long-standing questions about the evolution and nature of other planetary
systems, and we could search for clues as to whether life exists elsewhere in
our galactic neighborhood.Comment: 7 pages, 2 figures, submitted to Astro2010 Decadal Revie
Characterizing the atmosphere of Proxima b with a space-based mid-infrared nulling interferometer
Proxima b is our nearest potentially rocky exoplanet and represents a formidable opportunity for exoplanet science and possibly astrobiology. With an angular separation of only 35 mas (or 0.05 AU) from its host star, Proxima b is however hardly observable with current imaging telescopes and future space-based coronagraphs. One way to separate the photons of the planet from those of its host star is to use an interferometer that can easily resolve such spatial scales. In addition, its proximity to Earth and its favorable contrast ratio compared with its host M dwarf (approximately 10-5 at 10 microns) makes it an ideal target for a space-based nulling interferometer with relatively small apertures. In this paper, we present the motivation for observing this planet in the mid-infrared (5-20 microns) and the corresponding technological challenges. Then, we describe the concept of a space-based infrared interferometer with relatively small (<1m in diameter) apertures that can measure key details of Proxima b, such as its size, temperature, climate structure, as well as the presence of important atmospheric molecules such as H2O, CO2, O3, and CH4. Finally, we illustrate the concept by showing realistic observations using synthetic spectra of Proxima b computed with coupled climate chemistry models.DD and OA thank the Belgian national funds for scientific research (FNRS). This work was partly funded by the European Research Council under the European Union’s Seventh Framework Program (ERC Grant Agreement n. 337569) and by the French Community of Belgium through an ARC grant for Concerted Research Action
Technology for a Mid-IR Flagship Mission to Characterize Earth-like Exoplanets
The exploration of Earth-like exoplanets will be enabled at mid-infrared wavelengths
through technology and engineering advances in nulling interferometry and precision formation
flying. Nulling interferometry provides the dynamic range needed for the detection of
biomarkers. Formation flying provides the angular resolution required in the mid-infrared to
separately distinguish the spectra of planets in multi-planet systems. The flight performance
requirements for nulling have been met and must now be validated in a flight-like environment.
Formation-flying algorithms have been demonstrated in the lab and must now be validated in
space. Our proposed technology program is described
The HOSTS Survey for Exozodiacal Dust: Observational Results from the Complete Survey
The Large Binocular Telescope Interferometer (LBTI) enables nulling
interferometric observations across the N band (8 to 13 um) to suppress a
star's bright light and probe for faint circumstellar emission. We present and
statistically analyze the results from the LBTI/HOSTS (Hunt for Observable
Signatures of Terrestrial Systems) survey for exozodiacal dust. By comparing
our measurements to model predictions based on the Solar zodiacal dust in the N
band, we estimate a 1 sigma median sensitivity of 23 zodis for early type stars
and 48 zodis for Sun-like stars, where 1 zodi is the surface density of
habitable zone (HZ) dust in the Solar system. Of the 38 stars observed, 10 show
significant excess. A clear correlation of our detections with the presence of
cold dust in the systems was found, but none with the stellar spectral type or
age. The majority of Sun-like stars have relatively low HZ dust levels
(best-fit median: 3 zodis, 1 sigma upper limit: 9 zodis, 95% confidence: 27
zodis based on our N band measurements), while ~20% are significantly more
dusty. The Solar system's HZ dust content is consistent with being typical. Our
median HZ dust level would not be a major limitation to the direct imaging
search for Earth-like exoplanets, but more precise constraints are still
required, in particular to evaluate the impact of exozodiacal dust for the
spectroscopic characterization of imaged exo-Earth candidates
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