Effects of Rotation on the Spectra of Brown Dwarfs

Abstract

Measured rotational speeds of giant planets and brown dwarfs frequently constitute appreciable fractions of the breakup limit, resulting in centrifugal expansion of these objects at the equator. According to models of internal energy transport, this expansion ought to make the poles of a rotator significantly hotter than the equator, so that inclination of the rotational axis greatly affects both spectral shape and total flux. In this article, we explore the dependence of a substellar object's observables on its rotational speed and axis inclination. To do so, we combine PICASO (a Planetary Intensity Code for Atmospheric Spectroscopy Observations) with software PARS (Paint the Atmospheres of Rotating Stars). The former computer program models radiative transfer within plane-parallel planetary atmospheres, while the latter computes disk-integrated spectra of centrifugally deformed gaseous masses. We find that the specific flux of a typical fast-rotating brown dwarf can increase by as much as a factor of 1.5 with movement from an equator-on to a pole-on view. On the other hand, the distinctive effect of rotation on spectral shape increases toward the equator-on view. The latter effect also increases with lower effective temperature. The bolometric luminosity estimate for a typical fast rotator at extreme inclinations has to be adjusted by as much as about 20% due to the anisotropy of the object's observed flux. We provide a general formula for the calculation of the corresponding adjustment factor in terms of rotational speed and inclination.

11 pages, 4 figures, MNRAS accepted

References in corpus (19)

• The NumPy array: a structure for efficient numerical computation
• The Evolution of L and T Dwarfs in Color-Magnitude Diagrams
• The fast spin-rotation of a young extrasolar planet
• Imaging the Surface of Altair
• A new set of atmosphere and evolution models for cool T-Y brown dwarfs and giant exoplanets
• Discovery of a ~250 K Brown Dwarf at 2 pc from the Sun
• Exoplanet Reflected Light Spectroscopy with PICASO
• Doppler Imaging of Exoplanets and Brown Dwarfs
• Atmospheric circulation of brown dwarfs and directly imaged exoplanets driven by cloud radiative feedback: effects of rotation
• Precise Dynamical Masses and Orbital Fits for $\beta$ Pic b and $\beta$ Pic c
• Weather on Other Worlds. V. The Three Most Rapidly Rotating Ultra-Cool Dwarfs
• On the Radii of Brown Dwarfs Measured with AKARI Near-Infrared Spectroscopy
• Two intermediate-mass transiting brown dwarfs from the TESS mission
• Uniform Forward-Modeling Analysis of Ultracool Dwarfs. I. Methodology and Benchmarking
• Cloud Atlas: Weak color modulations due to rotation in the planetary-mass companion GU Psc b and 11 other brown dwarfs
• Spin-orbit alignment of the $\beta$ Pictoris planetary system
• Microphysics of Water Clouds in the Atmospheres of Y Dwarfs and Temperate Giant Planets
• Synthetic Spectra of Rotating Stars
• The rotation of very low-mass stars and brown dwarfs

Cited by in corpus (2)

• JWST Observations of the Enigmatic Y Dwarf WISE 1828+2650: I. Limits to a Binary Companion
• Exploring the directly imaged HD 1160 system through spectroscopic characterization and high-cadence variability monitoring