Model Atmospheres and Spectra: The Role of Dust

Allard, F.; Guillot, T.; Ludwig, Hans-Günter; Hauschildt, P. H.; Schweitzer, A.; Alexander, D. R.; Ferguson, Jason W.

doi:10.1017/s0074180900210875

Cited by 94 publications

(115 citation statements)

References 10 publications

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“…Note that the final solution does not depend on the initial profile T 0 or on the choice of α. For T 0 , we used one of the three temperature profiles calculated by Allard et al (2003) for T eff = 900, 1300, and 1700 K. We choose that having T eff closest to the input value to ensure rapid convergence.…”

Section: Discussionmentioning

confidence: 99%

“…The purpose is to link the photometric errors to the uncertainties in the physical parameters of planetary atmospheres. A related analysis to derive log(g) and T eff was performed by Vigan et al (2010) with the narrowband differential filters of SPHERE combined with AMES-Cond/Dusty (Allard et al 2001(Allard et al , 2003, BT-Settl (Allard et al 2007) and Burrows models (Burrows et al 2006) .…”

Section: Sphere Expected Observationsmentioning

confidence: 99%

“…BT-Settl (Allard et al 2003) is a more complex model, which compares condensation, sedimentation, and mixing timescales of dust to define cloud parameters.…”

Section: Introductionmentioning

confidence: 99%

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Interpreting the photometry and spectroscopy of directly imaged planets: a new atmospheric model applied toβPictoris b and SPHERE observations

Baudino

Bézard

Boccaletti

et al. 2015

A&A

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Context. Since the end of 2013 a new generation of instruments optimized to image young giant planets around nearby stars directly is becoming available on 8-m class telescopes, both at Very Large Telescope and Gemini in the southern hemisphere. Beyond the achievement of high contrast and the discovery capability, these instruments are designed to obtain photometric and spectral information to characterize the atmospheres of these planets. Aims. We aim to interpret future photometric and spectral measurements from these instruments, in terms of physical parameters of the planets, with an atmospheric model using a minimal number of assumptions and parameters. Methods. We developed the Exoplanet Radiative-convective Equilibrium Model (Exo-REM) to analyze the photometric and spectroscopic data of directly imaged planets. The input parameters are a planet's surface gravity (g), effective temperature (T eff ), and elemental composition. The model predicts the equilibrium temperature profile and mixing ratio profiles of the most important gases. Opacity sources include the H 2 -He collision-induced absorption and molecular lines from eight compounds (including CH 4 updated with the Exomol line list). Absorption by iron and silicate cloud particles is added above the expected condensation levels with a fixed scale height and a given optical depth at some reference wavelength. Scattering was not included at this stage.Results. We applied Exo-REM to photometric and spectral observations of the planet β Pictoris b obtained in a series of near-infrared filters. We derived T eff = 1550 ± 150 K, log(g) = 3.5 ± 1, and radius R = 1.76 ± 0.24 R Jup (2σ error bars from photometric measurements). These values are comparable to those found in the literature, although with more conservative error bars, consistent with the model accuracy. We were able to reproduce, within error bars, the J-and H-band spectra of β Pictoris b. We finally investigated the precision to which the above parameters can be constrained from SPHERE measurements using different sets of near-infrared filters as well as low-resolution spectroscopy.

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Section: Discussionmentioning

confidence: 99%

Section: Sphere Expected Observationsmentioning

confidence: 99%

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Interpreting the photometry and spectroscopy of directly imaged planets: a new atmospheric model applied toβPictoris b and SPHERE observations

Baudino

Bézard

Boccaletti

et al. 2015

A&A

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“…2. The SEDs show the PHOENIX-based (Hauschildt et al 1999), "BT-settl" models (Allard et al 2003(Allard et al , 2011 for targets with T eff > 2700 K and the "AMES-Dusty" models (Allard et al 2001) for targets with T eff < 2700 K. The redding law from Mathis (1990) with the optical total-to-selective extinction ratio of R v = 3.1 was applied to the stellar atmospheric models.…”

Section: Construction Of Spectral Energy Distributionsmentioning

confidence: 99%

The Taurus Boundary of Stellar/Substellar (TBOSS) Survey

Bulger

Patience

Ward-Duong

et al. 2014

A&A

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With the PACS instrument on Herschel, 134 low mass members of the Taurus star-forming region spanning the M4-L0 spectral type range and covering the transition from low mass stars to brown dwarfs were observed. Combining the new Herschel results with other Herschel programs, a total of 150 of the 154 M4-L0 Taurus members have observations, and we have added an additional 3 targets from Spitzer to form the 153-object TBOSS (Taurus Boundary of Stellar/Substellar) sample, a 99% complete study. Among the 150 targets, 70 µm flux densities were measured for 7 of the 7 Class I objects, 48 of the 67 Class II objects, and 3 of the 76 Class III objects. For the detected Class II objects, the median 70 µm flux density level declines with spectral type; however, the distribution of excess relative to central object flux density does not change across the stellar/substellar boundary in the M4-L0 range. Connecting the 70 µm TBOSS values with the results from K0-M3 Class II members results in the first comprehensive census of far-IR emission across the full mass spectrum of the stellar and substellar population of a star-forming region, and the median flux density declines with spectral type in a trend analogous to the flux density decline expected for the central objects. Spectral energy distributions (SEDs) were constructed for all TBOSS targets covering the optical to far-IR range and extending to the submm/mm for a subset of sources with longer wavelength data. Based on an initial exploration of the impact of different physical parameters on the Herschel flux densities, geometrical factors such as inclination and structural parameters such as scale height and flaring have the largest influence on the flux densities in the PACS bands. From the 24 µm to 70 µm spectral index of the SEDs, 5 new candidate transition disks were identified. Considering the previously known and new candidate transition disks, the spectral indices over longer wavelengths (≥70 µm) are not distinct from those of the full Class II population, suggesting that the outer regions of the transition disks are similar to Class II disks. The steep 24 µm to 70 µm slope for a subset of 8 TBOSS targets may be an indication of truncated disks in these systems, however additional measurements are required to establish the outer radii of these disks conclusively. From existing high angular resolution companion search observations, two examples of mixed pair systems that include secondaries with disks were measured in the Herschel data. Finally, comparing the TBOSS results with a Herschel study of Ophiuchus brown dwarfs reveals a lower fraction of disks around the Taurus substellar population with flux densities comparable to the Ophiuchus disks.

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“…To compare the best-fit solution found for the observed SED of G 196-3 B with theoretical model atmospheres, we retrieved the BT-Settl synthetic spectrum computed for T * = 1800 K, surface gravity of log g = 4.5 [cm s −2 ], and solar metallicity (Allard et al 2003(Allard et al , 2012, which are close to the accepted physical parameters of the brown dwarf. The BT-Settl models include all of the significant sources of atmospheric gas opacity, the condensation of certain refractory elements in layers where physical conditions favour such condensation, and the opacity due to the new condensate species.…”

Section: Comparison With Dusty Model Atmospheresmentioning

confidence: 99%

Spectral energy distribution simulations of a possible ring structure around the young, red brown dwarf G 196-3 B

Zakhozhay

Osorio

Béjar

et al. 2016

Mon. Not. R. Astron. Soc.

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The origin of the very red optical and infrared colours of intermediate-age (∼10-500 Myr) L-type dwarfs remains unknown. It has been suggested that low-gravity atmospheres containing large amounts of dust may account for the observed reddish nature. We explored an alternative scenario by simulating protoplanetary and debris discs around G 196-3 B, which is an L3 young brown dwarf with a mass of ∼ 15 M Jup and an age in the interval 20-300 Myr. The best-fit solution to G 196-3 B's photometric spectral energy distribution from optical wavelengths through 24 µm corresponds to the combination of an unreddened L3 atmosphere (T eff ≈ 1870 K) and a warm (≈ 1280 K), narrow (≈ 0.07-0.11 R ⊙ ) debris disc located at very close distances (≈ 0.12-0.20 R ⊙ ) from the central brown dwarf. This putative, optically thick, dusty belt, whose presence is compatible with the relatively young system age, would have a mass ≥ 7 × 10 −10 M ⊕ comprised of sub-micron/micron characteristic dusty particles with temperatures close to the sublimation threshold of silicates. Considering the derived global properties of the belt and the disc-to-brown dwarf mass ratio, the dusty ring around G 196-3 B may resemble the rings of Neptune and Jupiter, except for its high temperature and thick vertical height (≈ 6 × 10 3 km). Our inferred debris disc model is able to reproduce G 196-3 B's spectral energy distribution to a satisfactory level of achievement.

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Model Atmospheres and Spectra: The Role of Dust

Cited by 94 publications

References 10 publications

Interpreting the photometry and spectroscopy of directly imaged planets: a new atmospheric model applied toβPictoris b and SPHERE observations

Interpreting the photometry and spectroscopy of directly imaged planets: a new atmospheric model applied toβPictoris b and SPHERE observations

The Taurus Boundary of Stellar/Substellar (TBOSS) Survey

Spectral energy distribution simulations of a possible ring structure around the young, red brown dwarf G 196-3 B

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