期刊
ASTRONOMICAL JOURNAL
卷 163, 期 1, 页码 -出版社
IOP Publishing Ltd
DOI: 10.3847/1538-3881/ac3095
关键词
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资金
- Harlan J. Smith McDonald Observatory Fellowship
- Heising-Simons Foundation 51 Pegasi b Fellowship
- NASA through a grant from the Space Telescope Science Institute [HST-GO-15947, HST-AR-16142]
- Association of Universities for Research in Astronomy, Incorporated, under NASA [NAS5-26555]
- international Gemini Observatory
- program of NSFs NOIRLab
Studying the properties of atmospheres around brown dwarfs in close-in orbits around white dwarfs, phase-resolved observations and spectral analysis reveal rotational modulations, hot spots, and day/night heat transfer limitations in the irradiated objects.
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 mu m 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 similar to 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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