The NIRSPEC Brown Dwarf Spectroscopic Survey. I. Low‐Resolution Near‐Infrared Spectra

McLean, Ian S.; McGovern, Mark R.; Burgasser, Adam J.; Kirkpatrick, J. Davy; Prato, L.; Kim, Sungsoo S.

doi:10.1086/377636

Cited by 312 publications

(465 citation statements)

References 55 publications

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“…For this reason they favor the high metallicity scenario within in their conclusions. On the other hand, Looper et al (2008) agree with McLean et al (2003) and note the weak KI lines and lacking FeH absorption in the spectrum of J2244, which points to a low gravity. Our models yield the best fitting result for a slight sub-solar metallicity for J2148 and suggest a slight above-solar metal abundance for J2244.…”

Section: Wj1506544+132106 (L3;supporting

confidence: 59%

Dust in brown dwarfs and extra-solar planets

Witte

Helling

Barman

et al. 2011

A&A

107

123

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Context. This work is concerned with dust formation in ultra-cool atmospheres, encompassing the latest type stars, brown dwarfs, and hot giant exoplanets. Dust represents one of the most important and yet least understood sources of opacity in these types of objects. Aims. We compare our model spectra with SpeX data in order to draw conclusions about the dust cloud structure and related quantities in ultra-cool atmospheres. Methods. We use the self-consistent Drift-Phoenix atmosphere code, which features a kinetic dust formation mechanism and accounts for the dust cloud influence on the spectra. Results. We present fits of our latest model spectra to observations that cover a wide range of our model grid. The results are remarkably good, yielding significant improvement over the older Cond-/Dusty-Phoenix models, especially in the L-dwarf regime. The new models are able to properly reproduce observed spectra, including complicated features such as the molecular band strengths. This raises confidence in the reliability of our dust-modeling approach. Conclusions. We demonstrate that our code produces excellent results concerning the fitting with observations. This suggests that our dust cloud and atmosphere structures are reasonably accurate. Like all other current cloud models, ours is not able to produce satisfying results for spectral types later than L6 without manually tuning down the amount of dust. Our results show the formation of convective cells within the cloud, which are able to destroy the lower cloud parts. The dust opacity is reduced significantly without the need to tune the dust cloud thickness. There are indications that the cycle of dust accumulation and cloud destruction by convection is time-dependent on rather long timescales. Considering a statistical distribution of locally variable dust clouds over a dwarf's surface can result in a large number of spectral configurations for the same model atmosphere parameters, hence introducing an additional and more or less random degree of freedom to those atmospheres. Without resorting to the model atmosphere parameters, this alone can account for the unusually red and blue objects that have been discovered.

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Section: Wj1506544+132106 (L3;supporting

confidence: 59%

Dust in brown dwarfs and extra-solar planets

Witte

Helling

Barman

et al. 2011

A&A

107

123

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“…The features seen over 1 to 1.1 μm are mostly real. Several features in the SDSS J1254-0122 spectrum match those of the NIRSPEC spectrum published by McLean et al (2003). Others are barely significant and may be due to systematic errors or noise.…”

Section: Vlt/isaac Spectrasupporting

confidence: 61%

CLOUDS search for variability in brown dwarf atmospheres

Goldman

Cushing

Marley

et al. 2008

A&A

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Context. L-type ultra-cool dwarfs and brown dwarfs have cloudy atmospheres that could host weather-like phenomena. The detection of photometric or spectral variability would provide insight into unresolved atmospheric heterogeneities, such as holes in a global cloud deck. Indeed, a number of ultra-cool dwarfs have been reported to vary. Additional time-resolved spectral observations of brown dwarfs offer the opportunity for further constraining and characterising atmospheric variability. Aims. It has been proposed that growth of heterogeneities in the global cloud deck may account for the L-to T-type transition when brown dwarf photospheres evolve from cloudy to clear conditions. Such a mechanism is compatible with variability. We searched for variability in the spectra of five L6 to T6 brown dwarfs to test this hypothesis. Methods. We obtained spectroscopic time series using the near-infrared spectrographs ISAAC on VLT-ANTU, over 0.99−1.13 μm, and SpeX on the Infrared Telescope Facility for two of our targets in the J, H, and K bands. We searched for statistically variable lines and for a correlation between those. Results. High spectral-frequency variations are seen in some objects, but these detections are marginal and need to be confirmed. We find no evidence of large-amplitude variations in spectral morphology and we place firm upper limits of 2 to 3% on broad-band variability, depending on the targets and wavelengths, on the time scale of a few hours. In contrast to the rest of the sample, the T2 transition brown dwarf SDSS J1254−0122 shows numerous variable features, but a secure variability diagnosis would require further observations. Conclusions. Assuming that any variability arises from the rotation of patterns of large-scale clear and cloudy regions across the surface, we find that the typical physical scale of cloud-cover disruption should be smaller than 5−8% of the disk area for four of our targets, using simplistic heterogeneous atmospheric models. The possible variations seen in SDSS J1254−0122 are not strong enough to allow us to confirm the cloud-breaking hypothesis.

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“…Because of the lack of J-band observations, the magnitude difference between the two components in this wavelength regime had to be estimated. The SED of L dwarfs is comparatively flat between 1.06 μm and 1.15 μm, as well as throughout the J-band (see McLean et al 2003). Thus, the flux ratios between different L spectral types show no significant trend.…”

Section: Resolved Photometry and Spectral Typesmentioning

confidence: 94%

2MASS J03105986 +1648155 AB – a new binary at the L/T transition

Stumpf¹,

Brandner²,

Bouy

et al. 2010

A&A

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Context. The transition from the L to the T spectral type of brown dwarfs is marked by a very rapid transition phase, remarkable brightening in the J-band, and higher binary frequency. Despite being an active area of inquiry, this transition region still remains one of the most poorly understood phases of brown dwarf evolution. Aims. We resolved the L dwarf 2MASS J03105986+1648155 for the first time into two almost equally bright components straddling the L/T transition. Since such a coeval system with common age and composition provides crucial information on this special transition phase, we monitored the system over ∼3 years to derive first orbital parameters and dynamical mass estimates, as well as a spectral type determination. Methods. We obtained resolved high angular resolution, near-IR images with both HST and the adaptive optics instrument NACO at the VLT, including the laser guide star system PARSEC. Results. Based on two epochs of astrometric data, we derive a minimum semi-major axis of 5.2 ± 0.8 AU. The assumption of a face-on circular orbit yields an orbital period of 72 ± 4 years and a total system mass of ∼30-60 M Jup . This places the masses of the individual components of the system at the lower end of the mass regime of brown dwarfs. The achieved photometry allowed a first spectral type determination of L9 ± 1 for each component. In addition, this seems to be only the fifth resolved L/T transition binary with a flux reversal. Conclusions. While ultimate explanations for this effect are still lacking, the 2MASS J03105986+1648155 system adds an important benchmark object for improving our understanding of this remarkable evolutionary phase of brown dwarfs. Additionally, the observational results of 2MASS J03105986+1648155 AB derived with the new PARSEC AO system at the VLT show the importance of this technical capability. The updated AO system allows us to significantly extend the sample of brown dwarfs observable with high resolution from the ground, hence to reveal more of their physical properties.

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The NIRSPEC Brown Dwarf Spectroscopic Survey. I. Low‐Resolution Near‐Infrared Spectra

Cited by 312 publications

References 55 publications

Dust in brown dwarfs and extra-solar planets

Dust in brown dwarfs and extra-solar planets

CLOUDS search for variability in brown dwarf atmospheres

2MASS J03105986 +1648155 AB – a new binary at the L/T transition

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