Abstract
We present the distance-calibrated spectral energy distribution (SED) of the d/sdL7 SDSS J14162408+1348263A (J1416A) and an updated SED for SDSS J14162408+1348263B (J1416B). We also present ...the first retrieval analysis of J1416A using the Brewster retrieval code base and the second retrieval of J1416B. We find that the primary is best fit by a nongray cloud opacity with a power-law wavelength dependence but is indistinguishable between the type of cloud parameterization. J1416B is best fit by a cloud-free model, consistent with the results from Line et al. Most fundamental parameters derived via SEDs and retrievals are consistent within 1
σ
for both J1416A and J1416B. The exceptions include the radius of J1416A, where the retrieved radius is smaller than the evolutionary model-based radius from the SED for the deck cloud model, and the bolometric luminosity, which is consistent within 2.5
σ
for both cloud models. The pair’s metallicity and carbon-to-oxygen ratio point toward formation and evolution as a system. By comparing the retrieved alkali abundances while using two opacity models, we are able to evaluate how the opacities behave for the L and T dwarf. Lastly, we find that relatively small changes in composition can drive major observable differences for lower-temperature objects.
ABSTRACT
We present the most detailed data-driven exploration of cloud opacity in a substellar object to-date. We have tested over 60 combinations of cloud composition and structure, particle-size ...distribution, scattering model, and gas phase composition assumptions against archival 1–15 μm spectroscopy for the unusually red L4.5 dwarf 2MASSW J2224438-015852 using the Brewster retrieval framework. We find that, within our framework, a model that includes enstatite and quartz cloud layers at shallow pressures, combined with a deep iron cloud deck fits the data best. This model assumes a Hansen distribution for particle sizes for each cloud, and Mie scattering. We retrieved particle effective radii of $\log _{10} a {\rm (\mu m)} = -1.41^{+0.18}_{-0.17}$ for enstatite, $-0.44^{+0.04}_{-0.20}$ for quartz, and $-0.77^{+0.05}_{-0.06}$ for iron. Our inferred cloud column densities suggest ${\rm (Mg/Si)} = 0.69^{+0.06}_{-0.08}$ if there are no other sinks for magnesium or silicon. Models that include forsterite alongside, or in place of, these cloud species are strongly rejected in favour of the above combination. We estimate a radius of 0.75 ± 0.02 RJup, which is considerably smaller than predicted by evolutionary models for a field age object with the luminosity of 2M2224-0158. Models which assume vertically constant gas fractions are consistently preferred over models that assume thermochemical equilibrium. From our retrieved gas fractions, we infer ${\rm M/H} = +0.38^{+0.07}_{-0.06}$ and ${\rm C/O} = 0.83^{+0.06}_{-0.07}$. Both these values are towards the upper end of the stellar distribution in the Solar neighbourhood, and are mutually consistent in this context. A composition towards the extremes of the local distribution is consistent with this target being an outlier in the ultracool dwarf population.
Abstract
We present the first retrieval analysis of a substellar subdwarf, SDSS J125637.13−022452.4 (SDSS J1256−0224), using the
Brewster
retrieval code base. We find SDSS J1256−0224 is best fit by a ...cloud-free model with an ion (neutral H, H
−
, and electron) abundance corresponding to
Fe
/
H
ion
=
−
1.5
. However, this model is indistinguishable from a cloud-free model with
Fe
/
H
ion
=
−
2.0
and a cloud-free model with
Fe
/
H
ion
=
−
1.5
assuming a subsolar carbon-to-oxygen ratio. We are able to constrain abundances for H
2
O, FeH, and CrH, with an inability to constrain any carbon-bearing species likely due to the low metallicity of SDSS J1256−0224. We also present an updated spectral energy distribution (SED) and semiempirical fundamental parameters. Our retrieval- and SED-based fundamental parameters agree with the Baraffe low-metallicity evolutionary models. From examining our “rejected” models (those with ΔBIC > 45), we find that we are able to retrieve gas abundances consistent with those of our best fitting model. We find the cloud in these poorer fitting “cloudy” models is either pushed to the bottom of the atmosphere or made optically thin.
We present final Spitzer trigonometric parallaxes for 361 L, T, and Y dwarfs. We combine these with prior studies to build a list of 525 known L, T, and Y dwarfs within 20 pc of the Sun, 38 of which ...are presented here for the first time. Using published photometry and spectroscopy as well as our own follow-up, we present an array of color–magnitude and color–color diagrams to further characterize census members, and we provide polynomial fits to the bulk trends. Using these characterizations, we assign each object a T(eff) value and judge sample completeness over bins of T(eff) and spectral type. Except for types ≥T8 and T(eff) < 600 K, our census is statistically complete to the 20 pc limit. We compare our measured space densities to simulated density distributions and find that the best fit is a power law (dN/dM ∝ M^(-α) with α = 0.6 ± 0.1. We find that the evolutionary models of Saumon & Marley correctly predict the observed magnitude of the space density spike seen at 1200 K < T(eff) < 1350 K, believed to be caused by an increase in the cooling timescale across the L/T transition. Defining the low-mass terminus using this sample requires a more statistically robust and complete sample of dwarfs ≥Y0.5 and with T(eff) < 400 K. We conclude that such frigid objects must exist in substantial numbers, despite the fact that few have so far been identified, and we discuss possible reasons why they have largely eluded detection.
Abstract
We present the distance-calibrated spectral energy distribution (SED) of TRAPPIST-1 using a new medium-resolution (
R
∼ 6000) near-infrared (NIR) Folded-port InfraRed Echellette (FIRE) ...spectrum and its
Gaia
parallax. We report an updated bolometric luminosity (
L
bol
) of −3.216 ± 0.016, along with semiempirical fundamental parameters: effective temperature
T
eff
= 2628 ± 42 K, mass = 90 ± 8
M
Jup
, radius = 1.16 ± 0.03
R
Jup
, and log
g
= 5.21 ± 0.06 dex. Its kinematics point toward an older age, while spectral indices indicate youth; therefore, we compare the overall SED and NIR bands of TRAPPIST-1 to field-age, low-gravity, and low-metallicity dwarfs of similar
T
eff
and
L
bol
. We find field dwarfs of similar
T
eff
and
L
bol
best fit the overall and band-by-band features of TRAPPIST-1. Additionally, we present new Allers & Liu spectral indices for the SpeX SXD and FIRE spectra of TRAPPIST-1, both classifying it as intermediate gravity. Examining
T
eff
,
L
bol
, and absolute
JHKW
1
W
2 magnitudes versus optical spectral type places TRAPPIST-1 in an ambiguous location containing both field and intermediate-gravity sources. Kinematics place TRAPPIST-1 within a subpopulation of intermediate-gravity sources lacking bona fide membership in a moving group with higher tangential and
UVW
velocities. We conclude that TRAPPIST-1 is a field-age source with subtle spectral features reminiscent of a low surface gravity object. To resolve the cause of TRAPPIST-1's intermediate-gravity indicators we speculate on two avenues that might be correlated to inflate the radius: (1) magnetic activity or (2) tidal interactions from planets. We find the M8 dwarf LHS 132 is an excellent match to TRAPPIST-1's spectral peculiarities along with the M9
β
dwarf 2MASS J10220489+0200477, the L1
β
2MASS J10224821+5825453, and the L0
β
2MASS J23224684−3133231, which have distinct kinematics, making all four intriguing targets for future exoplanet studies.
Abstract We present an atmospheric retrieval analysis on a set of young, cloudy, red L dwarfs—CWISER J124332.12+600126.2 (BD+60 1417B) and WISEP J004701.06+680352.1 (W0047)—using the Brewster ...retrieval framework. We also present the first elemental abundance measurements of the young K-dwarf (K0) host star, BD+60 1417, using high-resolution ( R = 50,000) spectra taken with the Potsdam Echelle Polarimetric and Spectroscopic Instrument on the Large Binocular Telescope. In the complex cloudy L-dwarf regime the emergence of condensate cloud species complicates retrieval analysis when only near-infrared data are available. We find that for both L dwarfs in this work, despite testing three different thermal profile parameterizations we are unable to constrain reliable abundance measurements and thus the carbon-to-oxygen ratio. While we cannot conclude what the abundances are, we can conclude that the data strongly favor a cloud model over a cloudless model. We note that the difficulty in retrieval constraints persists regardless of the signal-to-noise ratio of the data examined (S/N ∼ 10 for CWISER BD+60 1417B and 40 for WISEP W0047). The results presented in this work provide valuable lessons about retrieving young, low-surface-gravity cloudy L dwarfs. This work provides continued evidence of missing information in models and the crucial need for JWST to guide and inform retrieval analysis in this regime.
Abstract
Comparisons of atmospheric retrievals can reveal powerful insights on the strengths and limitations of our data and modeling tools. In this paper, we examine a sample of five L dwarfs of ...similar effective temperature (
T
eff
) or spectral type to compare their pressure–temperature (P-T) profiles. Additionally, we explore the impact of an object’s metallicity and the signal-to-noise ratio (S/N) of the observations on the parameters we can retrieve. We present the first atmospheric retrievals: 2MASS J15261405+2043414, 2MASS J05395200−0059019, 2MASS J15394189−0520428, and GD 165B increasing the small but growing number of L dwarfs retrieved. When compared to the atmospheric retrievals of SDSS J141624.08+134826.7, a low-metallicity d/sdL7 primary in a wide L+T binary, we find that similar
T
eff
sources have similar P-T profiles with metallicity differences impacting the relative offset between their P-T profiles in the photosphere. We also find that for near-infrared spectra, when the S/N is ≳80 we are in a regime where model uncertainties dominate over data measurement uncertainties. As such, S/N does not play a role in the retrieval’s ability to distinguish between a cloud-free and cloudless model, but may impact the confidence of the retrieved parameters. Lastly, we also discuss how to break cloud model degeneracies and the impact of extraneous gases in a retrieval model.
Abstract
As next-generation imaging instruments and interferometers search for planets closer to their stars, they must contend with increasing orbital motion and longer integration times. These ...compounding effects make it difficult to detect faint planets but also present an opportunity. Increased orbital motion makes it possible to move the search for planets into the orbital domain, where direct images can be freely combined with the radial velocity and proper motion anomaly, even without a confirmed detection in any single epoch. In this paper, we present a fast and differentiable multimethod orbit-modeling and planet detection code called Octofitter. This code is designed to be highly modular and allows users to easily adjust priors, change parameterizations, and specify arbitrary function relations between the parameters of one or more planets. Octofitter further supplies tools for examining model outputs including prior and posterior predictive checks and simulation-based calibration. We demonstrate the capabilities of Octofitter on real and simulated data from different instruments and methods, including HD 91312, simulated JWST/NIRISS aperture masking interferometry observations, radial velocity curves, and grids of images from the Gemini Planet Imager. We show that Octofitter can reliably recover faint planets in long sequences of images with arbitrary orbital motion. This publicly available tool will enable the broad application of multiepoch and multimethod exoplanet detection, which could improve how future targeted ground- and space-based surveys are performed. Finally, its rapid convergence makes it a useful addition to the existing ecosystem of tools for modeling the orbits of directly imaged planets.
Abstract
We present the distance-calibrated spectral energy distribution (SED) of the sdL3.5 subdwarf SDSS J125637.13−022452.4 (J1256−0224) using its
Gaia
DR2 parallax. We report the bolometric ...luminosity and semi-empirical fundamental parameters, as well as updated UVW velocities. The SED of J1256−0224 is compared to field-age and low-gravity dwarfs of the same effective temperature (
T
eff
) and bolometric luminosity. In the former comparison, we find that the SED of J1256−0224 is brighter than the field source in the optical, but dims in comparison beyond the
J
band, where it becomes fainter than the field from the H through W2 bands. Compared to the young source, it is fainter at all wavelengths. We conclude that J1256−0224 is depleted of condensates compared to both objects. A near-infrared band-by-band analysis of the spectral features of J1256−0224 is done and is compared to the equivalent
T
eff
sample. From this analysis, we find a peculiar behavior of the
J
-band K
i
doublets whereby the 1.17
μ
m doublet is stronger than the field or young source, as expected, while the 1.25
μ
m doublet shows indications of low gravity. In examining a sample of four other subdwarfs with comparable data, we confirm this trend across different subtypes indicating that the 1.25
μ
m doublet is a poor indicator of gravity for low-metallicity objects. In the
K
-band analysis of J1256−0224, we detect the 2.29
μ
m CO line of J1256−0224, previously unseen in the low-resolution SpeX data. We also present fundamental parameters using
Gaia
parallaxes for nine additional subdwarfs with spectral types M7–L7 for comparison. The 10 subdwarfs are placed in a temperature sequence, and we find a poor linear correlation with spectral type. We present polynomial relations for absolute magnitude in JHKW1W2, effective temperature, and bolometric luminosity versus spectral type for subdwarfs.
Abstract
Thermal phase variations of short-period planets indicate that they are not spherical cows: day-to-night temperature contrasts range from hundreds to thousands of degrees, rivaling their ...vertical temperature contrasts. Nonetheless, the emergent spectra of short-period planets have typically been fit using one-dimensional (1D) spectral retrieval codes that only account for vertical temperature gradients. The popularity of 1D spectral retrieval codes is easy to understand: they are robust and have a rich legacy in solar system atmospheric studies. Exoplanet researchers have recently introduced multidimensional retrieval schemes to interpret the spectra of short-period planets, but these codes are necessarily more complex and computationally expensive than their 1D counterparts. In this paper we present an alternative: phase-dependent spectral observations are inverted to produce longitudinally resolved spectra that can then be fit using standard 1D spectral retrieval codes. We test this scheme on the iconic phase-resolved spectra of WASP-43b and on simulated observations for the James Webb Space Telescope (JWST) using the open-source
Pyrat Bay
1D spectral retrieval framework. Notably, we take the model complexity of the simulations one step further from previous studies by allowing for longitudinal variations in composition in addition to temperature. We show that performing 1D spectral retrieval on longitudinally resolved spectra is more accurate than applying 1D spectral retrieval codes to disk-integrated emission spectra, even though this is identical in terms of computational load. We find that for the extant Hubble and Spitzer observations of WASP-43b, the difference between the two approaches is negligible, but JWST phase measurements should be treated with longitudinally
re
solved
spect
ral retrieval (ReSpect).
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