Mapping the Pressure-dependent Day–Night Temperature Contrast of a Strongly Irradiated Atmosphere with HST Spectroscopic Phase Curve

Abstract Many brown dwarfs are on ultrashort-period and tidally locked orbits around white dwarf hosts. Because of these small orbital separations, the brown dwarfs are irradiated at levels similar to hot Jupiters. Yet, they are easier to observe than hot Jupiters because white dwarfs are fainter than main-sequence stars at near-infrared wavelengths. Irradiated brown dwarfs are, therefore, ideal hot Jupiter analogs for studying the atmospheric response under strong irradiation and fast rotation. We present the 1.1–1.67 μm spectroscopic phase curve of the irradiated brown dwarf (SDSS1411-B) in the SDSS J141126.20 + 200911.1 brown dwarf–white dwarf binary with the near-infrared G141 grism of the Hubble Space Telescope Wide Field Camera 3. SDSS1411-B is a 50M Jup brown dwarf with an irradiation temperature of 1300 K and has an orbital period of 2.02864 hr. Our best-fit model suggests a phase-curve amplitude of 1.4% and places an upper limit of 11° for the phase offset from the secondary eclipse. After fitting the white dwarf spectrum, we extract the phase-resolved brown dwarf emission spectra. We report a highly wavelength-dependent day–night spectral variation, with a water-band flux variation of about 360% ± 70% and a comparatively small J-band flux variation of 37% ± 2%. By combining the atmospheric modeling results and the day–night brightness temperature variations, we derive a pressure-dependent temperature contrast. We discuss the difference in the spectral features of SDSS1411-B and hot Jupiter WASP-43b, as well as the lower-than-predicted day–night temperature contrast of J4111-BD. Our study provides the high-precision observational constraints on the atmospheric structures of an irradiated brown dwarf at different orbital phases.

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NLTT5306B: an inflated, weakly irradiated brown dwarf

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3184 ◽

2020 ◽

Vol 499 (4) ◽

pp. 5318-5324

Author(s):

S L Casewell ◽

J Debes ◽

I P Braker ◽

M C Cushing ◽

G Mace ◽

...

Keyword(s):

Effective Temperature ◽

White Dwarf ◽

Near Infrared ◽

Brown Dwarfs ◽

Magnetic Interactions ◽

Brown Dwarf ◽

Primary Star ◽

Brightness Temperatures ◽

Night Side ◽

Low Mass

ABSTRACT We present Spitzer observations at 3.6 and 4.5 µm and a near-infrared IRTF SpeX spectrum of the irradiated brown dwarf NLTT5306B. We determine that the brown dwarf has a spectral type of L5 and is likely inflated, despite the low effective temperature of the white dwarf primary star. We calculate brightness temperatures in the Spitzer wavebands for both the model radius, and Roche Lobe radius of the brown dwarf, and conclude that there is very little day–night side temperature difference. We discuss various mechanisms by which NLTT5306B may be inflated, and determine that while low-mass brown dwarfs (M < 35 MJup) are easily inflated by irradiation from their host star, very few higher mass brown dwarfs are inflated. The higher mass brown dwarfs that are inflated may be inflated by magnetic interactions or may have thicker clouds.

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Simplified 3D GCM modelling of the irradiated brown dwarf WD 0137−349B

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1882 ◽

2020 ◽

Vol 496 (4) ◽

pp. 4674-4687 ◽

Cited By ~ 3

Author(s):

Graham K H Lee ◽

Sarah L Casewell ◽

Katy L Chubb ◽

Mark Hammond ◽

Xianyu Tan ◽

...

Keyword(s):

Radiative Transfer ◽

White Dwarf ◽

Near Infrared ◽

Circulation Model ◽

Dual Band ◽

Phase Curve ◽

Radiative Transfer Model ◽

Transfer Model ◽

Brown Dwarf ◽

Short Period

ABSTRACT White dwarf–brown dwarf short-period binaries (Porb ≲ 2 h) are some of the most extreme irradiated atmospheric environments known. These systems offer an opportunity to explore theoretical and modelling efforts of irradiated atmospheres different to typical hot Jupiter systems. We aim to investigate the three-dimensional (3D) atmospheric structural and dynamical properties of the brown dwarf WD 0137−349B. We use the 3D global circulation model (GCM) Exo-Flexible Modelling System (FMS) with a dual-band grey radiative transfer scheme to model the atmosphere of WD 0137−349B. The results of the GCM model are post-processed using the 3D Monte Carlo radiative transfer model cmcrt. Our results suggest inefficient day–night energy transport and a large day–night temperature contrast for WD 0137−349B. Multiple flow patterns are present, shifting energy asymmetrically eastward or westward depending on their zonal direction and latitude. Regions of overturning are produced on the western terminator. We are able to reproduce the start of the system near-infrared (IR) emission excess at ≳1.95 μm as observed by the Gemini Near-Infrared Spectrograph (GNIRS) instrument. Our model overpredicts the IR phase curve fluxes by factors of ≈1–3, but generally fits the shape of the phase curves well. Chemical kinetic modelling using vulcan suggests a highly ionized region at high altitudes can form on the dayside of the brown dwarf. We present a first attempt at simulating the atmosphere of a short-period white dwarf–brown dwarf binary in a 3D setting. Further studies into the radiative and photochemical heating from the ultraviolet irradiation are required to more accurately capture the energy balance inside the brown dwarf atmosphere. Cloud formation may also play an important role in shaping the emission spectra of the brown dwarf.

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Bayesian Spectroscopic Characterization of Directly Imaged Planets and Brown Dwarfs and Implications for Ultracool Model Atmospheres

10.5194/epsc2021-818 ◽

2021 ◽

Author(s):

Zhoujian Zhang ◽

Michael Liu ◽

Mark Marley ◽

Michael Line ◽

William Best

Keyword(s):

Physical Properties ◽

Near Infrared ◽

Brown Dwarfs ◽

Spectroscopic Characterization ◽

Cool Temperature ◽

Brown Dwarf ◽

Modeling Framework ◽

High Quality ◽

Model Predictions

Spectroscopic characterization of imaged exoplanets and brown dwarfs is essential for understanding their atmospheres, formation, and evolution, but such work is challenged by the unavoidably simplified model atmospheres needed to interpret spectra. While most previous work has focused on single or at most a few objects, comparing a large collection of spectra to models can uncover trends in data-model inconsistencies needed to improve model predictions, thereby leading to robust properties from exoplanet and brown dwarf spectra. Therefore, we are conducting a systematic analysis of a valuable but underutilized resource: the numerous high-quality spectra of (directly imaged and free-floating) exoplanets and brown dwarfs already accumulated by the community.&#160; Focusing on the cool-temperature end, we have constructed a Bayesian modeling framework using the new Sonora-Bobcat model atmospheres and have applied it to study near-infrared low-resolution spectra of >50 late-T imaged planets and brown dwarfs (&#8776;600-1200K, &#8776;10-70 MJup) and infer their physical properties (effective temperature, surface gravity, metallicity, radii, mass). By virtue of having such a large sample of high-quality spectra, our analysis identifies the systematic offsets between observed and model spectra as a function of wavelength and physical properties to pinpoint specific shortcomings in model predictions. We have also found that the spectroscopically inferred metallicities, ages, and masses of our sample all considerably deviate from expectations, suggesting the physical and chemical assumptions made within these models need to be improved to fully interpret data. Our work has established a systematic validation of cloudless model atmospheres to date and we discuss extending such analysis to wider temperature and wavelength (e.g., JWST) ranges, as well as finding new planetary-mass and brown dwarf benchmarks, in order to validate ultracool model atmospheres over larger parameter space.

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Secondary eclipse of the hot Jupiter WASP-121b at 2 μm

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834325 ◽

2019 ◽

Vol 625 ◽

pp. A80 ◽

Cited By ~ 8

Author(s):

Géza Kovács ◽

Tamás Kovács

Keyword(s):

Near Infrared ◽

Infrared Emission ◽

Current Data ◽

Emission Analysis ◽

Hot Jupiters ◽

Occultation Data ◽

The One ◽

Near Infrared Emission ◽

Absorption Features ◽

Hot Jupiter

Ground-based observations of the secondary eclipse in the 2MASS K band are presented for the hot Jupiter WASP-121b. These are the first occultation observations of an extrasolar planet that were carried out with an instrument attached to a 1 m class telescope (the SMARTS 1.3 m). We find a highly significant eclipse depth of (0.228 ± 0.023)%. Together with other planet atmosphere measurements, including the Hubble Space Telescope near-infrared emission spectrum, current data support more involved atmosphere models with species producing emission and absorption features, rather than simple smooth blackbody emission. Analysis of the time difference between the primary and secondary eclipses and the durations of these events yields an eccentricity of e = 0.0207 ± 0.0153, which is consistent with the earlier estimates of low or zero eccentricity, but with a smaller error. Comparing the observed occultation depth in the K band with the one derived under the assumption of zero Bond albedo and full heat redistribution, we find that WASP-121b has a deeper observed occultation depth than predicted. Together with the sample of 31 systems with K-band occultation data, this observation lends further support to the idea of inefficient heat transport between the day and night sides for most of the hot Jupiters.

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Hunting for brown dwarfs in the globular cluster M4: second epoch HST NIR observations

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz996 ◽

2019 ◽

Vol 486 (2) ◽

pp. 2254-2264 ◽

Cited By ~ 3

Author(s):

A Dieball ◽

L R Bedin ◽

C Knigge ◽

M Geffert ◽

R M Rich ◽

...

Keyword(s):

Globular Cluster ◽

White Dwarf ◽

Near Infrared ◽

Magnitude Estimate ◽

Cluster Member ◽

Imaging Data ◽

Brown Dwarf ◽

Data Set ◽

Bona Fide ◽

Low Mass

ABSTRACT We present an analysis of the second epoch Hubble Space TelescopeWide Field Camera 3 F110W near-infrared (NIR) imaging data of the globular cluster M 4. The new data set suggests that one of the previously suggested four brown dwarf candidates in this cluster is indeed a high-probability cluster member. The position of this object in the NIR colour–magnitude diagrams (CMDs) is in the white dwarf/brown dwarf area. The source is too faint to be a low-mass main-sequence (MS) star, but, according to theoretical considerations, also most likely somewhat too bright to be a bona-fide brown dwarf. Since we know that the source is a cluster member, we determined a new optical magnitude estimate at the position the source should have in the optical image. This new estimate places the source closer to the white dwarf sequence in the optical–NIR CMD and suggests that it might be a very cool (Teff ≤ 4500 K) white dwarf at the bottom of the white dwarf cooling sequence in M 4, or a white dwarf/brown dwarf binary. We cannot entirely exclude the possibility that the source is a very massive, bright brown dwarf, or a very low-mass MS star, however, we conclude that we still have not convincingly detected a brown dwarf in a globular cluster, but we expect to be very close to the start of the brown dwarf cooling sequence in this cluster. We also note that the MS ends at F110W ≈ 22.5 mag in the proper-motion cleaned CMDs, where completeness is still high.

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Environmental effects on the ionisation of brown dwarf atmospheres

Astronomy and Astrophysics ◽

10.1051/0004-6361/201832685 ◽

2018 ◽

Vol 618 ◽

pp. A107 ◽

Cited By ~ 7

Author(s):

M. I. Rodríguez-Barrera ◽

Ch. Helling ◽

K. Wood

Keyword(s):

White Dwarf ◽

Binary Systems ◽

Brown Dwarfs ◽

High Energy ◽

Radiation Environment ◽

Brown Dwarf ◽

Star Forming ◽

Star Forming Regions ◽

Lyman Continuum ◽

Low Mass

Context. Brown dwarfs emit bursts of Hα, white-light flares, and show radio flares and quiescent radio emission. They are suggested to form aurorae, similar to planets in the solar system, but much more energetic. All these processes require a source gas with an appropriate degree of ionisation, which, so far, is mostly postulated to be sufficient. Aims. We aim to demonstrate that the Galactic environment influences atmospheric ionisation, and that it hence amplifies or enables the magnetic coupling of the atmospheres of ultra-cool objects, like brown dwarfs and free-floating planets. Methods. We build on our previous work on thermal ionisation of ultra-cool atmospheres and explore the effect of environmental high-energy radiation on the degree of ionisation in the atmosphere. We consider the effect of photoionisation by Lyman-continuum radiation in three different environments: in the interstellar radiation field (ISRF), O and B stars in star-forming regions, and in white dwarf companions in binary systems. We apply our Monte Carlo radiation transfer code to investigate the effect of Lyman-continuum photoionisation for prescribed atmosphere structures for very low-mass objects. Results. The external radiation environment plays an important role for the atmospheric ionisation of very low-mass, ultra-cool objects. Lyman-continuum irradiation greatly increases the level of ionisation in the uppermost atmospheric regions. Our results suggest that a shell of an almost fully ionised atmospheric gas emerges for brown dwarfs in star-forming regions and brown dwarfs in white dwarf binary systems. As a consequence, brown dwarf atmospheres can be magnetically coupled, which is the presumption for chromospheric heating to occur and for aurorae to emerge. First tests for assumed chromosphere-like temperature values suggest that the resulting free-free X-ray luminosities are comparable with those observed from non-accreting brown dwarfs in star-forming regions.

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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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The First Young Brown Dwarf in the Serpens Cloud

Symposium - International Astronomical Union ◽

10.1017/s0074180900210334 ◽

2003 ◽

Vol 211 ◽

pp. 83-86

Author(s):

Jean-Louis Monin ◽

Emmanuel Caux ◽

Alain Klotz ◽

Nicolas Lodieu

Keyword(s):

Star Formation ◽

Spectral Type ◽

Near Infrared ◽

Nir Spectroscopy ◽

Brown Dwarfs ◽

Brown Dwarf ◽

Star Formation Region ◽

Formation Region

We report the discovery of the first young brown dwarf in the Serpens cloud (BD-Ser 1). It is obscured by more than ten magnitudes of visual absorption as indicated by near infrared (NIR) photometric survey at the NTT and confirmed by NIR spectroscopy at the VLT. We estimate the mass of this brown dwarf to be M ~ 0.05 M⊙ and its age to be ~ 3.5 Myr. Available NIR indices in the literature (designed for field brown dwarfs) fail to provide its current spectral type but using a model they correctly determine its future spectral type to be T. This is the first young brown dwarf ever found deeply embedded in the Serpens star formation region

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Characterizing the Atmospheres of Hot Jupiters: From Spectra to Multi-Color Maps

Proceedings of the International Astronomical Union ◽

10.1017/s1743921308026471 ◽

2008 ◽

Vol 4 (S253) ◽

pp. 255-261

Author(s):

Heather A. Knutson

Keyword(s):

Emission Spectrum ◽

Inversion Layer ◽

Emission Spectra ◽

Phase Curve ◽

Hot Jupiters ◽

Thermal Phase ◽

Additional Support ◽

Temperature Inversions ◽

The Relationship ◽

Hot Jupiter

AbstractWe present new observations of the emission spectrum of the hot Jupiter TrES-4 designed to test the theory that the presence of temperature inversions in the atmospheres of these planets are correlated with the amount of radiation received by the planet. Our observations reveal that TrES-4 has an emission spectrum similar to that of HD 209458b, which requires the presence of an inversion layer high in the atmosphere and water emission bands in order to explain the observed features, providing additional support for that theory. We also present new observations of the thermal phase curve of HD 189733b at 24 μm, which we combine with our previous observations at 8 μm to examine how circulation in this planet's atmosphere varies as a function of depth. We discuss the relationship between the strength of the day-night circulation on both planets and their other observable properties, in particular their emission spectra.

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The GAPS Programme at TNG

Astronomy and Astrophysics ◽

10.1051/0004-6361/201937369 ◽

2020 ◽

Vol 638 ◽

pp. A5 ◽

Cited By ~ 6

Author(s):

I. Carleo ◽

L. Malavolta ◽

A. F. Lanza ◽

M. Damasso ◽

S. Desidera ◽

...

Keyword(s):

Radial Velocity ◽

Near Infrared ◽

Semimajor Axis ◽

Young Stars ◽

Homogeneous Sample ◽

Stellar Activity ◽

Orbital Parameters ◽

Hot Jupiters ◽

Multi Band ◽

Hot Jupiter

Context. The existence of hot Jupiters is still not well understood. Two main channels are thought to be responsible for their current location: a smooth planet migration through the protoplanetary disk or the circularization of an initial highly eccentric orbit by tidal dissipation leading to a strong decrease in the semimajor axis. Different formation scenarios result in different observable effects, such as orbital parameters (obliquity and eccentricity) or frequency of planets at different stellar ages. Aims. In the context of the GAPS Young Objects project, we are carrying out a radial velocity survey with the aim of searching and characterizing young hot-Jupiter planets. Our purpose is to put constraints on evolutionary models and establish statistical properties, such as the frequency of these planets from a homogeneous sample. Methods. Since young stars are in general magnetically very active, we performed multi-band (visible and near-infrared) spectroscopy with simultaneous GIANO-B + HARPS-N (GIARPS) observing mode at TNG. This helps in dealing with stellar activity and distinguishing the nature of radial velocity variations: stellar activity will introduce a wavelength-dependent radial velocity amplitude, whereas a Keplerian signal is achromatic. As a pilot study, we present here the cases of two known hot Jupiters orbiting young stars: HD 285507 b and AD Leo b. Results. Our analysis of simultaneous high-precision GIARPS spectroscopic data confirms the Keplerian nature of the variation in the HD 285507 radial velocities and refines the orbital parameters of the hot Jupiter, obtaining an eccentricity consistent with a circular orbit. Instead, our analysis does not confirm the signal previously attributed to a planet orbiting AD Leo. This demonstrates the power of the multi-band spectroscopic technique when observing active stars.

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