Considerations for atmospheric retrieval of high-precision brown dwarf spectra

ABSTRACT Isolated brown dwarfs provide remarkable laboratories for understanding atmospheric physics in the low-irradiation regime, and can be observed more precisely than exoplanets. As such, they provide a glimpse into the future of high-signal-to-noise ratio (SNR) observations of exoplanets. In this work, we investigate several new considerations that are important for atmospheric retrievals of high-quality thermal emission spectra of sub-stellar objects. We pursue this using an adaptation of the h y dra atmospheric retrieval code. We propose a parametric pressure–temperature (P–T) profile for brown dwarfs consisting of multiple atmospheric layers, parametrized by the temperature change across each layer. This model allows the steep temperature gradient of brown dwarf atmospheres to be accurately retrieved while avoiding commonly encountered numerical artefacts. The P–T model is especially flexible in the photosphere, which can reach a few tens of bar for T-dwarfs. We demonstrate an approach to include model uncertainties in the retrieval, focusing on uncertainties introduced by finite spectral and vertical resolution in the atmospheric model used for retrieval (∼8 per cent in the present case). We validate our retrieval framework by applying it to a simulated data set and then apply it to the HST/WFC3 (Hubble Space Telescope’s Wide-Field Camera 3) spectrum of the T-dwarf 2MASS J2339+1352. We retrieve sub-solar abundances of H2O and CH4 in the object at ∼0.1 dex precision. Additionally, we constrain the temperature structure to within ∼100 K in the photosphere. Our results demonstrate the promise of high-SNR spectra to provide high-precision abundance estimates of sub-stellar objects.

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A Search for Brown Dwarfs in the Alpha Persei Cluster

Symposium - International Astronomical Union ◽

10.1017/s0074180900210528 ◽

2003 ◽

Vol 211 ◽

pp. 179-180

Author(s):

Nicolas Lodieu ◽

Mark McCaughrean ◽

Jérôme Bouvier ◽

David Barrado y Navascués ◽

John R. Stauffer

Keyword(s):

Near Infrared ◽

Open Cluster ◽

Brown Dwarfs ◽

Wide Field ◽

Brown Dwarf ◽

Young Open Cluster ◽

Low Mass ◽

Alpha Persei ◽

Calar Alto ◽

Infrared Survey

We present preliminary results from a deep near-infrared survey of a ~ 1 square degree area in the young open cluster Alpha Persei using the wide-field Omega-Prime camera on the Calar Alto 3.5m telescope, yielding a list of new low-mass cluster members, including brown dwarf candidates.

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SK 1: A possible case of triggered star formation in perseus

Proceedings of the International Astronomical Union ◽

10.1017/s1743921307001500 ◽

2006 ◽

Vol 2 (S237) ◽

pp. 217-221

Author(s):

Miriam Rengel ◽

Klaus Hodapp ◽

Jochen Eislöffel

Keyword(s):

Star Formation ◽

Molecular Clouds ◽

Thermal Emission ◽

Young Stellar Objects ◽

Wide Field ◽

Dust Shell ◽

Stellar Objects ◽

Star Forming ◽

Star Forming Regions ◽

Suitable Target

AbstractAccording to a triggered star formation scenario (e.g. Martin-Pintado & Cernicharo 1987) outflows powered by young stellar objects shape the molecular clouds, can dig cavities, and trigger new star formation. NGC 1333 is an active site of low- and intermediate star formation in Perseus and is a suggested site of self-regulated star formation (Norman & Silk 1980). Therefore it is a suitable target for a study of triggered star formation (e.g. Sandell & Knee 2001, SK1). On the other hand, continuum sub-mm observations of star forming regions can detect dust thermal emission of embedded sources (which drive outflows), and further detailed structures.Within the framework of our wide-field mapping of star formation regions in the Perseus and Orion molecular clouds using SCUBA at 850 and 450 μm, we mapped NCG 1333 with an area of around 14′× 21′. The maps show more structure than the previous maps of the region observed in sub-mm. We have unveiled the known embedded SK 1 source (in the dust shell of the SSV 13 ridge) and detailed structure of the region, among some other young protostars.In agreement with the SK 1 observations, our map of the region shows lumpy filaments and shells/cavities that seem to be created by outflows. The measured mass of SK 1 (~0.07 M) is much less than its virial mass (~0.2-1 M). Our observations support the idea of SK 1 as an event triggered by outflow-driven shells in NGC 1333 (induced by an increase in gas pressure and density due to radiation pressure from the stellar winds that have presumably created the dust shell). This kind of evidences provides a more thorough understanding of the star formation regulation processes.

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CHAOS: The Cornell High-Order Adaptive Optics Survey for Brown Dwarfs

Symposium - International Astronomical Union ◽

10.1017/s0074180900210723 ◽

2003 ◽

Vol 211 ◽

pp. 271-274 ◽

Cited By ~ 1

Author(s):

Joseph Carson ◽

Stephen Eikenberry ◽

Bernhard Brandl ◽

J. C. Wilson ◽

T. L. Hayward

Keyword(s):

Monte Carlo ◽

Adaptive Optics ◽

Brown Dwarfs ◽

High Order ◽

Brown Dwarf ◽

Data Set ◽

Early Results ◽

Target Sample ◽

Adaptive Optics System

The Cornell High-order Adaptive Optics Survey for brown dwarfs (CHAOS), currently about 90% complete, uses the Palomar Hale Telescope's adaptive optics system to survey 80 bright stars out to 13 parsecs. Using the telescope's AO Science camera, brown dwarf companions 4–200 AU can be identified using coronagraphic imaging and spectroscopic modes. We will be using monte carlo simulations to create population models consistent with the CHAOS data set.Currently, we have observed 70 systems out of a target sample of 80. Five candidate companions await follow-up observations. As of now, no systems in the target sample have shown strong evidence of having brown dwarf companions. These early results support previous speculations of a “brown dwarf desert” at orbital separations out to 200 AU.While the target sources revealed no evidence of brown dwarf companions, accompanying observations of calibration stars provided evidence of an early methane dwarf candidate around the binary system HD150451AB. Forty seven parsecs from earth, the candidate indicated a projected orbital separation of 280 AU.

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Brown dwarf census with the Dark Energy Survey year 3 data and the thin disc scale height of early L types

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz2398 ◽

2019 ◽

Vol 489 (4) ◽

pp. 5301-5325 ◽

Cited By ~ 3

Author(s):

A Carnero Rosell ◽

B Santiago ◽

M dal Ponte ◽

B Burningham ◽

L N da Costa ◽

...

Keyword(s):

Dark Energy ◽

Structural Parameters ◽

Brown Dwarfs ◽

Scale Height ◽

Wide Field ◽

Brown Dwarf ◽

Thin Disc ◽

Dark Energy Survey ◽

Significant Difference ◽

Energy Survey

ABSTRACT In this paper we present a catalogue of 11 745 brown dwarfs with spectral types ranging from L0 to T9, photometrically classified using data from the Dark Energy Survey (DES) year 3 release matched to the Vista Hemisphere Survey (VHS) DR3 and Wide-field Infrared Survey Explorer (WISE) data, covering ≈2400 deg2 up to iAB = 22. The classification method follows the same phototype method previously applied to SDSS-UKIDSS-WISE data. The most significant difference comes from the use of DES data instead of SDSS, which allow us to classify almost an order of magnitude more brown dwarfs than any previous search and reaching distances beyond 400 pc for the earliest types. Next, we also present and validate the GalmodBD simulation, which produces brown dwarf number counts as a function of structural parameters with realistic photometric properties of a given survey. We use this simulation to estimate the completeness and purity of our photometric LT catalogue down to iAB = 22, as well as to compare to the observed number of LT types. We put constraints on the thin disc scale height for the early L (L0–L3) population to be around 450 pc, in agreement with previous findings. For completeness, we also publish in a separate table a catalogue of 20 863 M dwarfs that passed our colour cut with spectral types greater than M6. Both the LT and the late M catalogues are found at DES release page https://des.ncsa.illinois.edu/releases/other/y3-mlt.

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TOI-519 b: A short-period substellar object around an M dwarf validated using multicolour photometry and phase curve analysis

Astronomy and Astrophysics ◽

10.1051/0004-6361/202038934 ◽

2020 ◽

Vol 645 ◽

pp. A16

Author(s):

H. Parviainen ◽

E. Palle ◽

M. R. Zapatero-Osorio ◽

G. Nowak ◽

A. Fukui ◽

...

Keyword(s):

Effective Temperature ◽

Planet Formation ◽

Thermal Emission ◽

Brown Dwarfs ◽

Curve Analysis ◽

Phase Curve ◽

Brown Dwarf ◽

M Dwarfs ◽

Short Period ◽

M Dwarf

Context. We report the discovery of TOI-519 b (TIC 218795833), a transiting substellar object (R = 1.07 RJup) orbiting a faint M dwarf (V = 17.35) on a 1.26 d orbit. Brown dwarfs and massive planets orbiting M dwarfs on short-period orbits are rare, but more have already been discovered than expected from planet formation models. TOI-519 is a valuable addition to this group of unlikely systems, and it adds towards our understanding of the boundaries of planet formation. Aims. We set out to determine the nature of the Transiting Exoplanet Survey Satellite (TESS) object of interest TOI-519 b. Methods. Our analysis uses a SPOC-pipeline TESS light curve from Sector 7, multicolour transit photometry observed with MuSCAT2 and MuSCAT, and transit photometry observed with the LCOGT telescopes. We estimated the radius of the transiting object using multicolour transit modelling, and we set upper limits for its mass, effective temperature, and Bond albedo using a phase curve model that includes Doppler boosting, ellipsoidal variations, thermal emission, and reflected light components. Results. TOI-519 b is a substellar object with a radius posterior median of 1.07 RJup and 5th and 95th percentiles of 0.66 and 1.20 RJup, respectively, where most of the uncertainty comes from the uncertainty in the stellar radius. The phase curve analysis sets an upper effective temperature limit of 1800 K, an upper Bond albedo limit of 0.49, and a companion mass upper limit of 14 MJup. The companion radius estimate combined with the Teff and mass limits suggests that the companion is more likely a planet than a brown dwarf, but a brown-dwarf scenario is a priori more likely given the lack of known massive planets in ≈ 1 day orbits around M dwarfs with Teff < 3800 K, and given the existence of some (but few) brown dwarfs.

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Extending Gaia DR2 with HST narrow-field astrometry – II. Refining the method on WISE J163940.83−684738.6★

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa540 ◽

2020 ◽

Vol 494 (2) ◽

pp. 2068-2075

Author(s):

L R Bedin ◽

C Fontanive

Keyword(s):

High Precision ◽

Reference System ◽

Hubble Space Telescope ◽

High Accuracy ◽

Test Case ◽

Wide Field ◽

Brown Dwarf ◽

Space Telescope ◽

Infra Red ◽

Gaia Dr2

ABSTRACT In the second paper of this series, we perfected our method of linking high-precision Hubble Space Telescope astrometry to the high-accuracy Gaia DR2 absolute reference system to overcome the limitations of relative astrometry with narrow-field cameras. Our test case here is the Y brown dwarf WISE J163940.83−684738.6, observed at different epochs spread over a 6-yr time baseline with the Infra-Red channel of the Wide Field Camera 3. We derived significantly improved astrometric parameters compared to previous determinations, finding (μαcos δ, μδ, ϖ) = (577.21 ± 0.24 mas yr−1, −3108.39 ± 0.27 mas yr−1, 210.4 ± 1.8 mas). In particular, our derived absolute parallax (ϖ ) corresponds to a distance of 4.75 ± 0.05 pc for the faint ultracool dwarf.

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Outflow activity in brown dwarfs

Proceedings of the International Astronomical Union ◽

10.1017/s1743921307009714 ◽

2007 ◽

Vol 3 (S243) ◽

pp. 357-364

Author(s):

Emma T. Whelan ◽

Thomas P. Ray ◽

Francesca Bacciotti ◽

Sofia Randich ◽

Ray Jayawardhana ◽

...

Keyword(s):

Spatial Information ◽

Ambient Medium ◽

Brown Dwarfs ◽

Emission Lines ◽

Young Stellar Objects ◽

Brown Dwarf ◽

Stellar Objects ◽

Novel Technique ◽

Driving Source ◽

Future Plans

AbstractWhile numerous studies have been aimed at understanding the properties of young brown dwarfs relatively little exploration of their potential as drivers of outflows has occurred. Forbidden emission lines are important probes of outflows from young stellar objects, as they trace the shocks which form as an outflow interacts with the ambient medium of its driving source. While forbidden emission was identified in the spectra of young brown dwarfs, indicating the presence of outflows, these lines were weak and confined to the brown dwarf continuum position. Hence their origin in an outflow could not be confirmed. Our approach to this problem, is to analyse the forbidden line regions of brown dwarfs using spectro-astrometry. Spectro-astrometry is a novel technique which allows the user to recover spatial information from a spectrum beyond the limitations of the seeing of the observation. Using this technique we have found two brown dwarf outflows to date. In this chapter we outline this technique, describe our results for the brown dwarfs ρ-Oph 102 and 2MASS1207-3932 and discuss our future plans.

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HST/WFC3 Complete Phase-resolved Spectroscopy of White-dwarf-brown-dwarf Binaries WD 0137 and EPIC 2122

The Astronomical Journal ◽

10.3847/1538-3881/ac3095 ◽

2021 ◽

Vol 163 (1) ◽

pp. 17

Author(s):

Yifan Zhou ◽

Dániel Apai ◽

Xianyu Tan ◽

Joshua D. Lothringer ◽

Ben W. P. Lew ◽

...

Keyword(s):

Heat Transfer ◽

White Dwarf ◽

Hubble Space Telescope ◽

Hot Spot ◽

Brown Dwarfs ◽

Wide Field ◽

Brown Dwarf ◽

Object A ◽

M Phase ◽

Night Flux

Abstract Brown dwarfs in close-in orbits around white dwarfs offer an excellent opportunity to investigate properties of fast-rotating, tidally locked, and highly irradiated atmospheres. We present Hubble Space Telescope Wide Field Camera 3 G141 phase-resolved observations of two brown-dwarf-white-dwarf binaries: WD 0137-349 and EPIC 212235321. Their 1.1–1.7 μm phase curves demonstrate rotational modulations with semi-amplitudes of 5.27% ± 0.02% and 29.1% ± 0.1%; both can be fit well by multi-order Fourier series models. The high-order Fourier components have the same phase as the first-order and are likely caused by hot spots located at the substellar points, suggesting inefficient day/night heat transfer. Both brown dwarfs’ phase-resolved spectra can be accurately represented by linear combinations of their respective day- and nightside spectra. Fitting the irradiated brown dwarf model grids to the dayside spectra require a filling factor of ∼50%, further supporting a hot spot dominating the dayside emission. The nightside spectrum of WD 0137-349B is fit reasonably well by non-irradiated substellar models, and the one of EPIC 21223521B can be approximated by a Planck function. We find strong spectral variations in the brown dwarfs’ day/night flux and brightness temperature contrasts, highlighting the limitations of band-integrated measurements in probing heat transfer in irradiated objects. On the color–magnitude diagram, WD 0137-349B evolves along a cloudless model track connecting the early-L and mid-T spectral types, suggesting that clouds and disequilibrium chemistry have a negligible effect on this object. A full interpretation of these high-quality phase-resolved spectra calls for new models that couple atmospheric circulation and radiative transfer under high-irradiation conditions.

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The Brown Dwarf Deficit in Taurus: Evidence for a Non-Universal IMF

Symposium - International Astronomical Union ◽

10.1017/s0074180900210322 ◽

2003 ◽

Vol 211 ◽

pp. 81-82 ◽

Cited By ~ 2

Author(s):

César Briceño ◽

Kevin L. Luhman ◽

Lee Hartmann ◽

John R. Stauffer ◽

J. Davy Kirkpatrick

Keyword(s):

Brown Dwarfs ◽

Mass Function ◽

Initial Mass Function ◽

Wide Field ◽

Low Density ◽

Brown Dwarf ◽

New Members ◽

Star Forming ◽

Field Imaging ◽

Wide Field Imaging

We present the results of a deep, optical/IR wide field imaging survey of selected fields in the nearby (d~ 140 pc) Taurus star-forming region. We report the discovery of 9 new members with spectral types M5.75–M9.5. We derive an Initial Mass Function encompassing 54% of the known members in Taurus. Comparison with dense regions like the Trapezium Cluster in Orion shows that Taurus has produced x2 less brown dwarfs. We suggest that the lower frequency of brown dwarfs in Taurus may result from the low-density star-forming environment, leading to larger minimum Jeans masses.

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