311 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
Evidence Against an Edge-On Disk Around the Extrasolar Planet 2MASS 1207 b and a New Thick Cloud Explanation for its Under-Luminosity
(Abridged) Since the discovery of the first directly-imaged, planetary-mass
object, 2MASS 1207 b, several works have sought to explain a disparity between
its observed temperature and luminosity. Given its known age, distance, and
spectral type, 2MASS 1207 b is under-luminous by a factor of ~10 (~2.5 mags)
when compared to standard models of brown-dwarf/giant-planet evolution. In this
paper, we study three possible sources of 2MASS 1207 b's under-luminosity.
First, we investigate Mohanty et al. (2007)'s hypothesis that a near edge-on
disk might be responsible for 2MASS 1207 b's under-luminosity. We conclude that
the hypothesis is unlikely due to the lack of variability seen in multi-epoch
photometry and unnecessary due to the increasing sample of under-luminous
brown-dwarfs/giant-exoplanets that cannot be explained by an edge-on disk.
Next, we test the analogous possibility that a spherical shell of dust, could
explain 2MASS 1207 b's under-luminosity. Models containing enough dust to
create ~2.5 mags of extinction, placed at reasonable radii, are ruled out by
our new Gemini/T-ReCS 8.7 micron photometric upper-limit for 2MASS 1207 b.
Finally, we investigate the possibility that 2MASS 1207 b is intrinsically
cooler than the commonly used AMES-DUSTY fits to its spectrum, and thus it is
not, in fact, under-luminous. New, thick cloud model grids by Madhusudhan et
al. (2011) fit 2MASS 1207 b's 1-10 micron SED well, but they do not quite fit
its near-infrared spectrum. However, we suggest that with some "tuning", they
might be capable of simultaneously reproducing 2MASS 1207 b's spectral shape
and luminosity. In this case, the whole class of young, under-luminous
brown-dwarfs/giant-exoplanets might be explained by atmospheres that are able
to suspend thick, dusty clouds in their photospheres at lower temperatures than
field brown-dwarfs.Comment: 35 pages, 9 figures, accepted to Ap
Simultaneous Water Vapor and Dry Air Optical Path Length Measurements and Compensation with the Large Binocular Telescope Interferometer
The Large Binocular Telescope Interferometer uses a near-infrared camera to
measure the optical path length variations between the two AO-corrected
apertures and provide high-angular resolution observations for all its science
channels (1.5-13 m). There is however a wavelength dependent component to
the atmospheric turbulence, which can introduce optical path length errors when
observing at a wavelength different from that of the fringe sensing camera.
Water vapor in particular is highly dispersive and its effect must be taken
into account for high-precision infrared interferometric observations as
described previously for VLTI/MIDI or the Keck Interferometer Nuller. In this
paper, we describe the new sensing approach that has been developed at the LBT
to measure and monitor the optical path length fluctuations due to dry air and
water vapor separately. After reviewing the current performance of the system
for dry air seeing compensation, we present simultaneous H-, K-, and N-band
observations that illustrate the feasibility of our feedforward approach to
stabilize the path length fluctuations seen by the LBTI nuller.Comment: SPIE conference proceeding
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
New Spatially Resolved Observations of the T Cha Transition Disk and Constraints on the Previously Claimed Substellar Companion
We present multi-epoch non-redundant masking observations of the T Cha
transition disk, taken at the VLT and Magellan in H, Ks, and L' bands. T Cha is
one of a small number of transition disks that host companion candidates
discovered by high-resolution imaging techniques, with a putative companion at
a position angle of 78 degrees, separation of 62 mas, and contrast at L' of 5.1
mag. We find comparable binary parameters in our re-reduction of the initial
detection images, and similar parameters in the 2011 L', 2013 NaCo L', and 2013
NaCo Ks data sets. We find a close-in companion signal in the 2012 NaCo L'
dataset that cannot be explained by orbital motion, and a non-detection in the
2013 MagAO/Clio2 L' data. However, Monte-carlo simulations show that the best
fits to the 2012 NaCo and 2013 MagAO/Clio2 followup data may be consistent with
noise. There is also a significant probability of false non-detections in both
of these data sets. We discuss physical scenarios that could cause the best
fits, and argue that previous companion and scattering explanations are
inconsistent with the results of the much larger dataset presented here.Comment: 25 pages, 22 figures, accepted for publication in Ap
LBT observations of the HR 8799 planetary system: First detection of HR8799e in H band
We have performed H and Ks band observations of the planetary system around
HR 8799 using the new AO system at the Large Binocular Telescope and the PISCES
Camera. The excellent instrument performance (Strehl ratios up to 80% in H
band) enabled detection the inner planet HR8799e in the H band for the first
time. The H and Ks magnitudes of HR8799e are similar to those of planets c and
d, with planet e slightly brighter. Therefore, HR8799e is likely slightly more
massive than c and d. We also explored possible orbital configurations and
their orbital stability. We confirm that the orbits of planets b, c and e are
consistent with being circular and coplanar; planet d should have either an
orbital eccentricity of about 0.1 or be non-coplanar with respect to b and c.
Planet e can not be in circular and coplanar orbit in a 4:2:1 mean motion
resonances with c and d, while coplanar and circular orbits are allowed for a
5:2 resonance. The analysis of dynamical stability shows that the system is
highly unstable or chaotic when planetary masses of about 5 MJup for b and 7
MJup for the other planets are adopted. Significant regions of dynamical
stability for timescales of tens of Myr are found when adopting planetary
masses of about 3.5, 5, 5, and 5 Mjup for HR 8799 b, c, d, and e respectively.
These masses are below the current estimates based on the stellar age (30 Myr)
and theoretical models of substellar objects.Comment: 13 pages, 10 figures, A&A, accepte
Exoplanet science with the LBTI: instrument status and plans
The Large Binocular Telescope Interferometer (LBTI) is a strategic instrument
of the LBT designed for high-sensitivity, high-contrast, and high-resolution
infrared (1.5-13 m) imaging of nearby planetary systems. To carry out a
wide range of high-spatial resolution observations, it can combine the two
AO-corrected 8.4-m apertures of the LBT in various ways including direct
(non-interferometric) imaging, coronagraphy (APP and AGPM), Fizeau imaging,
non-redundant aperture masking, and nulling interferometry. It also has
broadband, narrowband, and spectrally dispersed capabilities. In this paper, we
review the performance of these modes in terms of exoplanet science
capabilities and describe recent instrumental milestones such as first-light
Fizeau images (with the angular resolution of an equivalent 22.8-m telescope)
and deep interferometric nulling observations.Comment: 12 pages, 6 figures, Proc. SPI
Co-phasing the Large Binocular Telescope: status and performance of LBTI/PHASECam
The Large Binocular Telescope Interferometer is a NASA-funded nulling and
imaging instrument designed to coherently combine the two 8.4-m primary mirrors
of the LBT for high-sensitivity, high-contrast, and high-resolution infrared
imaging (1.5-13 um). PHASECam is LBTI's near-infrared camera used to measure
tip-tilt and phase variations between the two AO-corrected apertures and
provide high-angular resolution observations. We report on the status of the
system and describe its on-sky performance measured during the first semester
of 2014. With a spatial resolution equivalent to that of a 22.8-meter telescope
and the light-gathering power of single 11.8-meter mirror, the co-phased LBT
can be considered to be a forerunner of the next-generation extremely large
telescopes (ELT).Comment: 8 pages, 5 figures, SPIE Conference proceeding
Unusual Isotopic Abundances in a Fully-Convective Stellar Binary
Low-mass M dwarfs represent the most common outcome of star formation, but
their complex emergent spectra hinder detailed studies of their composition and
initial formation. The measurement of isotopic ratios is a key tool that has
been used to unlock the formation of our Solar System, the Sun, and the nuclear
processes within more massive stars. We observed GJ 745AB, two M dwarfs
orbiting in a wide binary, with the IRTF/iSHELL spectrograph. Our spectroscopy
of CO in these stars at the 4.7 micron fundamental and 2.3 micron
first-overtone rovibrational bandheads reveals 12C16O, 13C16O, and 12C18O in
their photospheres. Since the stars are fully convective, the atomic
constituents of these isotopologues should be uniformly mixed throughout the
stars' interiors. We find that in these M dwarfs, both 12C/13C and 16O/18O
greatly exceed the Solar values. These measurements cannot be explained solely
by models of Galactic chemical evolution, but require that the stars formed
from an ISM significantly enriched by material ejected from an exploding
core-collape supernova. These isotopic measurements complement the elemental
abundances provided by large-scale spectroscopic surveys, and open a new window
onto studies of Galactic evolution, stellar populations, and individual
systems.Comment: 11 pages, 4 data files, 3 figures, 2 tables. ApJ in pres
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