10 research outputs found
High Spatial Resolution Thermal-Infrared Spectroscopy with ALES: Resolved Spectra of the Benchmark Brown Dwarf Binary HD 130948BC
We present 2.9-4.1 micron integral field spectroscopy of the L4+L4 brown
dwarf binary HD 130948BC, obtained with the Arizona Lenslets for Exoplanet
Spectroscopy (ALES) mode of the Large Binocular Telescope Interferometer
(LBTI). The HD 130948 system is a hierarchical triple system, in which the G2V
primary is joined by two co-orbiting brown dwarfs. By combining the age of the
system with the dynamical masses and luminosities of the substellar companions,
we can test evolutionary models of cool brown dwarfs and extra-solar giant
planets. Previous near-infrared studies suggest a disagreement between HD
130948BC luminosities and those derived from evolutionary models. We obtained
spatially-resolved, low-resolution (R~20) L-band spectra of HD 130948B and C to
extend the wavelength coverage into the thermal infrared. Jointly using JHK
photometry and ALES L-band spectra for HD 130948BC, we derive atmospheric
parameters that are consistent with parameters derived from evolutionary
models. We leverage the consistency of these atmospheric quantities to favor a
younger age (0.50 \pm 0.07 Gyr) of the system compared to the older age (0.79
\pm 0.22 Gyr) determined with gyrochronology in order to address the luminosity
discrepancy.Comment: 17 pages, 9 figures, Accepted to Ap
High Contrast Thermal Infrared Spectroscopy with ALES: The 3-4m Spectrum of Andromedae b
We present the first band (2.8 to 4.1~m) spectroscopy of
~Andromedae~b, a companion orbiting at
projected separation from its B9-type stellar host. We
combine our Large Binocular Telescope ALES integral field spectrograph data
with measurements from other instruments to analyze the atmosphere and physical
characteristics of ~And~b. We report a discrepancy of
() in the flux of ~And~b when comparing to
previously published values. We add an additional constraint using
an unpublished imaging dataset collected in 2013 using LBTI/LMIRCam, the
instrument in which the ALES module has been built. The LMIRCam measurement is
consistent with the ALES measurement, both suggesting a fainter -band
scaling than previous studies. The data, assuming the flux scaling measured by
ALES and LMIRCam imaging, are well fit by an L3-type brown dwarf. Atmospheric
model fits to measurements spanning 0.9-4.8~m reveal some tension with the
predictions of evolutionary models, but the proper choice of cloud parameters
can provide some relief. In particular, models with clouds extending to
very-low pressures composed of grains m appear to be necessary. If
the brighter photometry is accurate, there is a hint that
sub-solar metallicity may be required.Comment: Accepted for publication in A
L-band Integral Field Spectroscopy of the HR 8799 Planetary System
Understanding the physical processes sculpting the appearance of young
gas-giant planets is complicated by degeneracies confounding effective
temperature, surface gravity, cloudiness, and chemistry. To enable more
detailed studies, spectroscopic observations covering a wide range of
wavelengths is required. Here we present the first L-band spectroscopic
observations of HR 8799 d and e and the first low-resolution wide bandwidth
L-band spectroscopic measurements of HR 8799 c. These measurements were
facilitated by an upgraded LMIRCam/ALES instrument at the LBT, together with a
new apodizing phase plate coronagraph. Our data are generally consistent with
previous photometric observations covering similar wavelengths, yet there
exists some tension with narrowband photometry for HR 8799 c. With the addition
of our spectra, each of the three innermost observed planets in the HR 8799
system have had their spectral energy distributions measured with integral
field spectroscopy covering to . We combine these
spectra with measurements from the literature and fit synthetic model
atmospheres. We demonstrate that the bolometric luminosity of the planets is
not sensitive to the choice of model atmosphere used to interpolate between
measurements and extrapolate beyond them. Combining luminosity with age and
mass constraints, we show that the predictions of evolutionary models are
narrowly peaked for effective temperature, surface gravity, and planetary
radius. By holding these parameters at their predicted values, we show that
more flexible cloud models can provide good fits to the data while being
consistent with the expectations of evolutionary models.Comment: 19 pages, 11 figures, accepted for publication in The Astronomical
Journal; added reference, updated figure 6 and table
Direct images and spectroscopy of a giant protoplanet driving spiral arms in MWC 758
Understanding the driving forces behind spiral arms in protoplanetary disks
remains a challenge due to the faintness of young giant planets. MWC 758 hosts
such a protoplanetary disk with a two-armed spiral pattern that is suggested to
be driven by an external giant planet. We present new thermal infrared
observations that are uniquely sensitive to redder (i.e., colder or more
attenuated) planets than past observations at shorter wavelengths. We detect a
giant protoplanet, MWC 758c, at a projected separation of ~100 au from the
star. The spectrum of MWC 758c is distinct from the rest of the disk and
consistent with emission from a planetary atmosphere with Teff = 500 +/- 100 K
for a low level of extinction (AV<30), or a hotter object with a higher level
of extinction. Both scenarios are commensurate with the predicted properties of
the companion responsible for driving the spiral arms. MWC 758c provides
evidence that spiral arms in protoplanetary disks can be caused by cold giant
planets or by those whose optical emission is highly attenuated. MWC 758c
stands out both as one of the youngest giant planets known, and also as one of
the coldest and/or most attenuated. Furthermore, MWC 758c is among the first
planets to be observed within a system hosting a protoplanetary disk.Comment: Published in Nature Astronom
The JWST Early Release Science Program for Direct Observations of Exoplanetary Systems. IV. NIRISS Aperture Masking Interferometry Performance and Lessons Learned
We present a performance analysis for the aperture masking interferometry (AMI) mode on board the James Webb Space Telescope Near Infrared Imager and Slitless Spectrograph (JWST/NIRISS). Thanks to self-calibrating observables, AMI accesses inner working angles down to and even within the classical diffraction limit. The scientific potential of this mode has recently been demonstrated by the Early Release Science (ERS) 1386 program with a deep search for close-in companions in the HIP 65426 exoplanetary system. As part of ERS 1386, we use the same data set to explore the random, static, and calibration errors of NIRISS AMI observables. We compare the observed noise properties and achievable contrast to theoretical predictions. We explore possible sources of calibration errors and show that differences in charge migration between the observations of HIP 65426 and point-spread function calibration stars can account for the achieved contrast curves. Lastly, we use self-calibration tests to demonstrate that with adequate calibration NIRISS F380M AMI can reach contrast levels of ∼9–10 mag at ≳λ/D. These tests lead us to observation planning recommendations and strongly motivate future studies aimed at producing sophisticated calibration strategies taking these systematic effects into account. This will unlock the unprecedented capabilities of JWST/NIRISS AMI, with sensitivity to significantly colder, lower-mass exoplanets than lower-contrast ground-based AMI setups, at orbital separations inaccessible to JWST coronagraphy
Recommended from our members
The JWST Early-release Science Program for Direct Observations of Exoplanetary Systems II: A 1 to 20 μ m Spectrum of the Planetary-mass Companion VHS 1256–1257 b
We present the highest fidelity spectrum to date of a planetary-mass object. VHS 1256 b is a <20 M Jup widely separated (∼8″, a = 150 au), young, planetary-mass companion that shares photometric colors and spectroscopic features with the directly imaged exoplanets HR 8799c, d, and e. As an L-to-T transition object, VHS 1256 b exists along the region of the color–magnitude diagram where substellar atmospheres transition from cloudy to clear. We observed VHS 1256 b with JWST's NIRSpec IFU and MIRI MRS modes for coverage from 1 to 20 μm at resolutions of ∼1000–3700. Water, methane, carbon monoxide, carbon dioxide, sodium, and potassium are observed in several portions of the JWST spectrum based on comparisons from template brown dwarf spectra, molecular opacities, and atmospheric models. The spectral shape of VHS 1256 b is influenced by disequilibrium chemistry and clouds. We directly detect silicate clouds, the first such detection reported for a planetary-mass companion
The JWST Early Release Science Program for Direct Observations of Exoplanetary Systems I: High Contrast Imaging of the Exoplanet HIP 65426 b from 2−16 µm
We present JWST Early Release Science (ERS) coronagraphic observations of the
super-Jupiter exoplanet, HIP 65426 b, with the Near-Infrared Camera (NIRCam)
from 2-5 m, and with the Mid-Infrared Instrument (MIRI) from 11-16 m.
At a separation of 0.82" (86 au), HIP 65426 b is clearly
detected in all seven of our observational filters, representing the first
images of an exoplanet to be obtained by JWST, and the first ever direct
detection of an exoplanet beyond 5 m. These observations demonstrate that
JWST is exceeding its nominal predicted performance by up to a factor of 10,
depending on separation and subtraction method, with measured 5
contrast limits of 1 and 2 at 1" for
NIRCam at 4.4 m and MIRI at 11.3 m, respectively. These contrast
limits provide sensitivity to sub-Jupiter companions with masses as low as
0.3 beyond separations of 100 au. Together with existing
ground-based near-infrared data, the JWST photometry are well fit by a BT-SETTL
atmospheric model from 1-16 m, and span 97% of HIP 65426 b's
luminous range. Independent of the choice of model atmosphere we measure an
empirical bolometric luminosity that is tightly constrained between
=-4.31 to 4.14, which
in turn provides a robust mass constraint of 7.11.2 . In
totality, these observations confirm that JWST presents a powerful and exciting
opportunity to characterise the population of exoplanets amenable to
high-contrast imaging in greater detail.Comment: 35 pages, 16 figures, 4 tables, 1 wonderful telescope; Submitted to
AAS Journal
Recommended from our members
The JWST Early Release Science Program for Direct Observations of Exoplanetary Systems. V. Do Self-consistent Atmospheric Models Represent JWST Spectra? A Showcase with VHS 1256–1257 b
Abstract
The unprecedented medium-resolution (R
λ
∼ 1500–3500) near- and mid-infrared (1–18 μm) spectrum provided by JWST for the young (140 ± 20 Myr) low-mass (12–20 M
Jup) L–T transition (L7) companion VHS 1256 b gives access to a catalog of molecular absorptions. In this study, we present a comprehensive analysis of this data set utilizing a forward-modeling approach applying our Bayesian framework, ForMoSA. We explore five distinct atmospheric models to assess their performance in estimating key atmospheric parameters: T
eff, log(g), [M/H], C/O, γ, f
sed, and R. Our findings reveal that each parameter’s estimate is significantly influenced by factors such as the wavelength range considered and the model chosen for the fit. This is attributed to systematic errors in the models and their challenges in accurately replicating the complex atmospheric structure of VHS 1256 b, notably the complexity of its clouds and dust distribution. To propagate the impact of these systematic uncertainties on our atmospheric property estimates, we introduce innovative fitting methodologies based on independent fits performed on different spectral windows. We finally derived a T
eff consistent with the spectral type of the target, considering its young age, which is confirmed by our estimate of log(g). Despite the exceptional data quality, attaining robust estimates for chemical abundances [M/H] and C/O, often employed as indicators of formation history, remains challenging. Nevertheless, the pioneering case of JWST’s data for VHS 1256 b has paved the way for future acquisitions of substellar spectra that will be systematically analyzed to directly compare the properties of these objects and correct the systematics in the models.</jats:p