The Broadband and Spectrally Resolved H-band Eclipse of KELT-1b and the Role of Surface Gravity in Stratospheric Inversions in Hot Jupiters

Abstract

We present a high precision H-band emission spectrum of the transiting brown dwarf KELT-1b, which we spectrophotometrically observed during a single secondary eclipse using the LUCI1 multiobject spectrograph on the Large Binocular Telescope. Using a Gaussian-process regression model, we are able to clearly measure the broadband eclipse depth as ∆H = 1418 ± 94 ppm. We are also able to spectrally-resolve the H-band into five separate wavechannels and measure the eclipse spectrum of KELT-1b at R ≈ 50 with an average precision of ±135 ppm. We find that the day side has an average brightness temperature of 3250 ± 50 K, with significant variation as a function of wavelength. Based on our observations, and previous measurements of KELT-1b's eclipse at other wavelengths, we find that KELT-1b's day side appears identical to an isolated 3200 K brown dwarf, and our modeling of the atmospheric emission shows a monotonically decreasing temperature-pressure profile. This is in contrast to hot Jupiters with similar day side brightness temperatures near 3000 K, all of which appear to be either isothermal or posses a stratospheric temperature inversion. We hypothesize that the lack of an inversion in KELT-1b is due to its high surface gravity, which we argue could be caused by the increased efficiency of cold-trap processes within its atmosphere.

The direct detection of the irradiated brown dwarf in the white dwarf–brown dwarf binary SDSS J141126.20+200911.1

“…Kelt-1b, orbiting a 6500 K F5V star lacks the intense UV irradiation of the white dwarf irradiated systems, and does not show this brightening. Indeed eclipse measurements suggest that this object fits very well with a field dwarf template (Croll et al 2015;Beatty et al 2017).…”

Evidence for Atmospheric Cold-trap Processes in the Noninverted Emission Spectrum of Kepler-13Ab Using HST/WFC3

“…It is possible that Kepler-13-Ab's dayside temperature profile does become inverted at lower pressure levels than probed by the observations, but our inference that Kepler-13Ab's dayside temperature is monotonically decreasing is further supported by the fact that the shape and amplitude of our HST/WFC3 spectrum show that the dayside of Kepler-13Ab appears similar to the spectrum of a field M7 dwarf. We contend that the dual facts that Kepler-13Ab possesses a decreasing temperature-pressure profile and a relatively high surface gravity support the hypothesis of Beatty et al (2016) that both surface gravity and temperature play a role in determining the presence of a stratospheric temperature inversion in hot Jupiters. Specifically, in high-surface-gravity planets such as Kepler-13Ab, the characteristic freefall time within the atmosphere is substantially shorter (Equation (11)).…”

“…Recent observations of KELT-1b's emission spectrum by Beatty et al (2016), which has a dayside temperature of 3150 K and a surface gravity 22 times Jupiter's, showed a noninverted, monotonically decreasing temperature profile, which led those authors to suggest that surface gravity also plays a strong role in setting the vertical temperature of hot Jupiters. The similar dayside temperature, but lower surface gravity, of Kepler-13Ab therefore presented itself as a relevant comparison object.…”

Spitzer Phase Curves of KELT-1b and the Signatures of Nightside Clouds in Thermal Phase Observations

“…The broadband thermal emission from KELT-1b has previously been observed by Spitzer at 3.6 µm and 4.5 µm Beatty et al (2014) K (Croll et al 2015, and z (Siverd et al 2012) eclipses. Beatty et al (2017b) also observed an R ≈ 50 H-band eclipse spectrum.…”