Determining the Temperature of Exoplanet HAT-P-1b

Exoplanets, or planets orbiting stars other than our Sun, are difficult to detect. It is even more difficult to determine their properties. In this thesis I focus on HAT-P-1b, which is a ¨Dhot Jupiter¡¬ ¨C a gas giant, extremely close to its parent star. It is important for this thesis that HAT-P-1b is also a transiting exoplanet, i.e., it periodically passes directly in front of, or behind, its parent star, which gives scientists unique opportunities to determine its physical properties, to measure its temperature and to study its atmosphere¡¯s chemical properties. The purpose of this thesis is to measure the brightness temperature of the transiting exoplanet HAT-P-1b. The observations used were made with the Spitzer Space Telescope through a filter with center wavelength of 8.0¦Ìm, which covered a secondary eclipse of the planetary system, i.e., when the planet is behind its parent star, ADS 16402B. We created a light curve for the system, detected the eclipse and fitted a model eclipse curve in the data. From the eclipse depth I determined HAT-P-1b¡¯s flux. Knowing the planet¡¯s distance from ADS 16402B and the masses and radii of the star and the planet, I estimated the brightness temperature of the planet. My calculated result is 1300¡À170K. Future research will involve similar measurements in three additional wavebands, which will provide information about the chemical and thermal structure of HAT-P-1b¡¯s atmosphere

Updated Spitzer Emission Spectroscopy of Bright Transiting Hot Jupiter HD189733b

We analyze all existing secondary eclipse time series spectroscopy of hot Jupiter HD189733b acquired with the now defunct Spitzer/IRS instrument. We describe the novel approaches we develop to remove the systematic effects and extract accurate secondary eclipse depths as a function of wavelength in order to construct the emission spectrum of the exoplanet. We compare our results to a previous study by Grillmair et al. that did not examine all data sets available to us. We are able to confirm the detection of a water feature near 6{\mu}m claimed by Grillmair et al. We compare the planetary emission spectrum to three model families -- based on isothermal atmosphere, gray atmosphere, and two realizations of the complex radiative transfer model by Burrows et al., adopted in Grillmair et al.'s study. While we are able to reject the simple isothermal and gray models based on the data at the 97% level just from the IRS data, these rejections hinge on eclipses measured within relatively narrow wavelength range, between 5.5 and 7{\mu}m. This underscores the need for observational studies with broad wavelength coverage and high spectral resolution, in order to obtain robust information on exoplanet atmospheres.Comment: 16 pages, 13 figures and 3 tables. Accepted for publication in Ap

High signal-to-noise spectral characterization of the planetary-mass object HD 106906 b

We spectroscopically characterize the atmosphere of HD 106906b, a young low-mass companion near the deuterium burning limit. The wide separation from its host star of 7.1" makes it an ideal candidate for high S/N and high-resolution spectroscopy. We aim to derive new constraints on the spectral type, effective temperature, and luminosity of HD106906b and also to provide a high S/N template spectrum for future characterization of extrasolar planets. We obtained 1.1-2.5 $\mu$m integral field spectroscopy with the VLT/SINFONI instrument with a spectral resolution of R~2000-4000. New estimates of the parameters of HD 106906b are derived by analyzing spectral features, comparing the extracted spectra to spectral catalogs of other low-mass objects, and fitting with theoretical isochrones. We identify several spectral absorption lines that are consistent with a low mass for HD 106906b. We derive a new spectral type of L1.5$\pm$1.0, one subclass earlier than previous estimates. Through comparison with other young low-mass objects, this translates to a luminosity of log($L/L_\odot$)=$-3.65\pm0.08$ and an effective temperature of Teff=$1820\pm240$ K. Our new mass estimates range between $M=11.9^{+1.7}_{-0.8} M_{\rm Jup}$ (hot start) and $M=14.0^{+0.2}_{-0.5} M_{\rm Jup}$ (cold start). These limits take into account a possibly finite formation time, i.e., HD 106906b is allowed to be 0--3 Myr younger than its host star. We exclude accretion onto HD 106906b at rates $\dot{M}>4.8\times10^{-10} M_{\rm Jup}$yr$^{-1}$ based on the fact that we observe no hydrogen (Paschen-$\beta$, Brackett-$\gamma$) emission. This is indicative of little or no circumplanetary gas. With our new observations, HD 106906b is the planetary-mass object with one of the highest S/N spectra yet. We make the spectrum available for future comparison with data from existing and next-generation (e.g., ELT and JWST) spectrographs.Comment: 11 pages, 5 figures. Accepted for publication in Astronomy & Astrophysics. Fully reduced spectra will be made available for download on CD

Ground-based optical transmission spectrum of the hot Jupiter HAT-P-1b

Time-series spectrophotometric studies of exoplanets during transit using ground-based facilities are a promising approach to characterize their atmospheric compositions. We aim to investigate the transit spectrum of the hot Jupiter HAT-P-1b. We compare our results to those obtained at similar wavelengths by previous space-based observations. We observed two transits of HAT-P-1b with the Gemini Multi-Object Spectrograph (GMOS) instrument on the Gemini North telescope using two instrument modes covering the 320 - 800 nm and 520 - 950 nm wavelength ranges. We used time-series spectrophotometry to construct transit light curves in individual wavelength bins and measure the transit depths in each bin. We accounted for systematic effects. We addressed potential photometric variability due to magnetic spots in the planet's host star with long-term photometric monitoring. We find that the resulting transit spectrum is consistent with previous Hubble Space Telescope (HST) observations. We compare our observations to transit spectroscopy models that marginally favor a clear atmosphere. However, the observations are also consistent with a flat spectrum, indicating high-altitude clouds. We do not detect the Na resonance absorption line (589 nm), and our observations do not have sufficient precision to study the resonance line of K at 770 nm. We show that even a single Gemini/GMOS transit can provide constraining power on the properties of the atmosphere of HAT-P-1b to a level comparable to that of HST transit studies in the optical when the observing conditions and target and reference star combination are suitable. Our 520 - 950 nm observations reach a precision comparable to that of HST transit spectra in a similar wavelength range of the same hot Jupiter, HAT-P-1b. However, our GMOS transit between 320 - 800 nm suffers from strong systematic effects and yields larger uncertainties.Comment: A&A, accepted, 16 pages, 8 figures, 5 table

MIRACLES: atmospheric characterization of directly imaged planets and substellar companions at 4-5 μ\mum. II. Constraints on the mass and radius of the enshrouded planet PDS 70 b

The circumstellar disk of PDS 70 hosts two forming planets, which are actively accreting gas from their environment. In this work, we report the first detection of PDS 70 b in the Br$\alpha$ and $M'$ filters with VLT/NACO, a tentative detection of PDS 70 c in Br$\alpha$, and a reanalysis of archival NACO $L'$ and SPHERE $H23$ and $K12$ imaging data. The near side of the disk is also resolved with the Br$\alpha$ and $M'$ filters, indicating that scattered light is non-negligible at these wavelengths. The spectral energy distribution of PDS 70 b is well described by blackbody emission, for which we constrain the photospheric temperature and photospheric radius to $T_\mathrm{eff}=1193 \pm 20$ K and $R=3.0 \pm 0.2$ $R_\mathrm{J}$. The relatively low bolometric luminosity, $\log(L/L_\odot) = -3.79 \pm 0.02$, in combination with the large radius, is not compatible with standard structure models of fully convective objects. With predictions from such models, and adopting a recent estimate of the accretion rate, we derive a planetary mass and radius in the range of $M_\mathrm{p}\approx 0.5-1.5$ $M_\mathrm{J}$ and $R_\mathrm{p}\approx 1-2.5$ $R_\mathrm{J}$, independently of the age and post-formation entropy of the planet. The blackbody emission, large photospheric radius, and the discrepancy between the photospheric and planetary radius suggests that infrared observations probe an extended, dusty environment around the planet, which obscures the view on its molecular composition. Finally, we derive a rough upper limit on the temperature and radius of potential excess emission from a circumplanetary disk, $T_\mathrm{eff}\lesssim256$ K and $R\lesssim245$ $R_\mathrm{J}$, but we do find weak evidence that the current data favors a model with a single blackbody component.Comment: 19 pages, 7 figures, accepted for publication in A&

Phase curves of WASP-33b and HD 149026b and a New Correlation Between Phase Curve Offset and Irradiation Temperature

We present new 3.6 and 4.5 $\mu m$ Spitzer phase curves for the highly irradiated hot Jupiter WASP-33b and the unusually dense Saturn-mass planet HD 149026b. As part of this analysis, we develop a new variant of pixel level decorrelation that is effective at removing intrapixel sensitivity variations for long observations (>10 hours) where the position of the star can vary by a significant fraction of a pixel. Using this algorithm, we measure eclipse depths, phase amplitudes, and phase offsets for both planets at 3.6 $\mu m$ and 4.5 $\mu m$. We use a simple toy model to show that WASP-33b's phase offset, albedo, and heat recirculation efficiency are largely similar to those of other hot Jupiters despite its very high irradiation. On the other hand, our fits for HD 149026b prefer a very high albedo and an unusually high recirculation efficiency. We also compare our results to predictions from general circulation models, and find that while neither are a good match to the data, the discrepancies for HD 149026b are especially large. We speculate that this may be related to its high bulk metallicity, which could lead to enhanced atmospheric opacities and the formation of reflective cloud layers in localized regions of the atmosphere. We then place these two planets in a broader context by exploring relationships between the temperatures, albedos, heat transport efficiencies, and phase offsets of all planets with published thermal phase curves. We find a striking relationship between phase offset and irradiation temperature--the former drops with increasing temperature until around 3400 K, and rises thereafter. Although some aspects of this trend are mirrored in the circulation models, there are notable differences that provide important clues for future modeling efforts

Water vapour absorption in the clear atmosphere of a Neptune-sized exoplanet

Transmission spectroscopy has so far detected atomic and molecular absorption in Jupiter-sized exoplanets, but intense efforts to measure molecular absorption in the atmospheres of smaller (Neptune-sized) planets during transits have revealed only featureless spectra. From this it was concluded that the majority of small, warm planets evolve to sustain atmospheres with high mean molecular weights (little hydrogen), opaque clouds or scattering hazes, reducing our ability to observe the composition of these atmospheres. Here we report observations of the transmission spectrum of the exoplanet HAT-P-11b (which has a radius about four times that of Earth) from the optical wavelength range to the infrared. We detected water vapour absorption at a wavelength of 1.4 micrometres. The amplitude of the water absorption (approximately 250 parts per million) indicates that the planetary atmosphere is predominantly clear down to an altitude corresponding to about 1 millibar, and sufficiently rich in hydrogen to have a large scale height (over which the atmospheric pressure varies by a factor of e). The spectrum is indicative of a planetary atmosphere in which the abundance of heavy elements is no greater than about 700 times the solar value. This is in good agreement with the core-accretion theory of planet formation, in which a gas giant planet acquires its atmosphere by accreting hydrogen-rich gas directly from the protoplanetary nebula onto a large rocky or icy core

Spitzer Secondary Eclipses of the Dense, Modestly-irradiated, Giant Exoplanet HAT-P-20b Using Pixel-Level Decorrelation

HAT-P-20b is a giant exoplanet that orbits a metal-rich star. The planet itself has a high total density, suggesting that it may also have a high metallicity in its atmosphere. We analyze two eclipses of the planet in each of the 3.6- and 4.5 micron bands of Warm Spitzer. These data exhibit intra-pixel detector sensitivity fluctuations that were resistant to traditional decorrelation methods. We have developed a simple, powerful, and radically different method to correct the intra-pixel effect for Warm Spitzer data, which we call pixel-level decorrelation (PLD). PLD corrects the intra-pixel effect very effectively, but without explicitly using - or even measuring - the fluctuations in the apparent position of the stellar image. We illustrate and validate PLD using synthetic and real data, and comparing the results to previous analyses. PLD can significantly reduce or eliminate red noise in Spitzer secondary eclipse photometry, even for eclipses that have proven to be intractable using other methods. Our successful PLD analysis of four HAT-P-20b eclipses shows a best-fit blackbody temperature of 1134 +/-29K, indicating inefficient longitudinal transfer of heat, but lacking evidence for strong molecular absorption. We find sufficient evidence for variability in the 4.5 micron band that the eclipses should be monitored at that wavelength by Spitzer, and this planet should be a high priority for JWST spectroscopy. All four eclipses occur about 35 minutes after orbital phase 0.5, indicating a slightly eccentric orbit. A joint fit of the eclipse and transit times with extant RV data yields e(cos{omega}) = 0.01352 (+0.00054, -0.00057), and establishes the small eccentricity of the orbit to high statistical confidence. Given the existence of a bound stellar companion, HAT-P-20b is another excellent candidate for orbital evolution via Kozai migration or other three-body mechanism.Comment: version published in ApJ, minor text and figure revision

A transition between the hot and the ultra-hot Jupiter atmospheres

[Abridged] A key hypothesis in the field of exoplanet atmospheres is the trend of atmospheric thermal structure with planetary equilibrium temperature. We explore this trend and report here the first statistical detection of a transition in the near-infrared (NIR) atmospheric emission between hot and ultra-hot Jupiters. We measure this transition using secondary eclipse observations and interpret this phenomenon as changes in atmospheric properties, and more specifically in terms of transition from non-inverted to inverted thermal profiles. We examine a sample of 78 hot Jupiters with secondary eclipse measurements at 3.6 {\mu}m and 4.5 {\mu}m measured with Spitzer Infrared Array Camera (IRAC). We measure the deviation of the data from the blackbody, which we define as the difference between the observed 4.5 {\mu}m eclipse depth and that expected at this wavelength based on the brightness temperature measured at 3.6 {\mu}m. We study how the deviation between 3.6 and 4.5 {\mu}m changes with theoretical predictions with equilibrium temperature and incoming stellar irradiation. We reveal a clear transition in the observed emission spectra of the hot Jupiter population at 1660 +/- 100 K in the zero albedo, full redistribution equilibrium temperature. We find the hotter exoplanets have even hotter daysides at 4.5 {\mu}m compared to 3.6 {\mu}m, which manifests as an exponential increase in the emitted power of the planets with stellar insolation. We propose that the measured transition is a result of seeing carbon monoxide in emission due to the formation of temperature inversions in the atmospheres of the hottest planets. These thermal inversions could be caused by the presence of atomic and molecular species with high opacities in the optical and/or the lack of cooling species. We find that the population of hot Jupiters statistically disfavors high C/O planets (C/O>= 0.85).Comment: Accepted 11th May 202