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Allen, N. H., Espinoza, N., Jordan, A., Lopez-Morales, M., Apai, D., Rackham, B. V., et al. (2022). ACCESS: Tentative Detection of H2O in the Ground-based Optical Transmission Spectrum of the Low-density Hot Saturn HATS-5b. Astron. J., 164(4), 153.
Abstract: We present a precise ground-based optical transmission spectrum of the hot Saturn HATS-5b (T (eq) = 1025 K), obtained as part of the ACCESS survey with the IMACS multi-object spectrograph mounted on the Magellan Baade Telescope. Our spectra cover the 0.5-0.9 mu m region and are the product of five individual transits observed between 2014 and 2018. We introduce the usage of additional second-order light in our analyses, which allows us to extract an “extra” transit light curve, improving the overall precision of our combined transit spectrum. We find that the favored atmospheric model for this transmission spectrum is a solar-metallicity atmosphere with subsolar C/O, whose features are dominated by H2O and with a depleted abundance of Na and K. If confirmed, this would point to a “clear” atmosphere at the pressure levels probed by transmission spectroscopy for HATS-5b. Our best-fit atmospheric model predicts a rich near-IR spectrum, which makes this exoplanet an excellent target for future follow-up observations with the James Webb Space Telescope, both to confirm this H2O detection and to superbly constrain the atmosphere's parameters.
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Carleo, I., Gandolfi, D., Barragan, O., Livingston, J. H., Persson, C. M., Lam, K. W. F., et al. (2020). The Multiplanet System TOI-421*. Astron. J., 160(3), 23 pp.
Abstract: We report the discovery of a warm Neptune and a hot sub-Neptune transiting TOI-421 (BD-14 1137, TIC 94986319), a bright (V = 9.9) G9 dwarf star in a visual binary system observed by the Transiting Exoplanet Survey Satellite (TESS) space mission in Sectors 5 and 6. We performed ground-based follow-up observations-comprised of Las Cumbres Observatory Global Telescope transit photometry, NIRC2 adaptive optics imaging, and FIbre-fed Echelle Spectrograph, CORALIE, High Accuracy Radial velocity Planet Searcher, High Resolution echelle Spectrometer, and Planet Finder Spectrograph high-precision Doppler measurements-and confirmed the planetary nature of the 16 day transiting candidate announced by the TESS team. We discovered an additional radial velocity signal with a period of five days induced by the presence of a second planet in the system, which we also found to transit its host star. We found that the inner mini-Neptune, TOI-421 b, has an orbital period of P-b = 5.19672 +/- 0.00049 days, a mass of M-b = 7.17 +/- 0.66 M-circle plus, and a radius of R-b = R-circle plus, whereas the outer warm Neptune, TOI-421 c, has a period of P-c = 16.06819 +/- 0.00035 days, a mass of M-c = 16.42(-1.04)(+1.06)M(circle plus), a radius of R-c = 5.09(-0.15)(+0.16)R(circle plus), and a density of rho(c) = 0.685(-0.072)(+0.080) cm(-3). With its characteristics, the outer planet (rho(c) = 0.685(-0.0072)(+0.080) cm(-3)) is placed in the intriguing class of the super-puffy mini-Neptunes. TOI-421 b and TOI-421 c are found to be well-suited for atmospheric characterization. Our atmospheric simulations predict significant Ly alpha transit absorption, due to strong hydrogen escape in both planets, as well as the presence of detectable CH4 in the atmosphere of TOI-421 c if equilibrium chemistry is assumed.
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Eberhardt, J., Trifonov, T., Kurster, M., Stock, S., Henning, T., Wollbold, A., et al. (2022). Dynamical Architecture of the HD 107148 Planetary System. Astron. J., 163(5), 198.
Abstract: We present an independent Doppler validation and dynamical orbital analysis of the two-planet system HD 107148, which was recently announced in Rosenthal et al. Our detailed analyses are based on literature HIRES data and newly obtained HARPS and CARMENES radial-velocity (RV) measurements as part of our survey in search for additional planets around single-planet systems. We perform a periodogram analysis of the available HIRES and HARPS precise RVs and stellar activity indicators. We do not find any apparent correlation between the RV measurements and the stellar activity indicators, thus linking the two strong periodicities to a moderately compact multiplanet system. We carry out orbital fitting analysis by testing various one- and two-planet orbital configurations and studying the posterior probability distribution of the fitted parameters. Our results solidify the existence of a Saturn-mass planet (HD 107148b, discovered first) with a period of P (b) similar to 77.2 days and a second, eccentric (e (c) similar to 0.4), Neptune-mass exoplanet (HD 107148c) with an orbital period of P (c) similar to 18.3 days. Finally, we investigate the two-planet system's long-term stability and overall orbital dynamics with the posterior distribution of our preferred orbital configuration. Our N-body stability simulations show that the system is long-term stable and exhibits large secular osculations in eccentricity but in no particular mean motion resonance configuration. The HD 107148 system, consisting of a solar-type main-sequence star with two giant planets in a rare configuration, features a common proper-motion white dwarf companion and is therefore a valuable target for understanding the formation and evolution of planetary systems.
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Kirk, J., Rackham, B. V., MacDonald, R. J., Lopez-Morales, M., Espinoza, N., Lendl, M., et al. (2021). ACCESS and LRG-BEASTS: A Precise New Optical Transmission Spectrum of the Ultrahot Jupiter WASP-103b. Astron. J., 162(1), 34.
Abstract: We present a new ground-based optical transmission spectrum of the ultrahot Jupiter WASP-103b (Teq=2484
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McGruder, C. D., Lopez-Morales, M., Espinoza, N., Rackham, B. V., Apai, D., Jordan, A., et al. (2020). ACCESS: Confirmation of No Potassium in the Atmosphere of WASP-31b. Astron. J., 160(5), 22 pp.
Abstract: We present a new optical (400-950 nm) transmission spectrum of the hot Jupiter WASP-31b (M = 0.48 M-J; R = 1.54 R-J; P = 3.41 days), obtained by combining four transit observations. These transits were observed with IMACS on the Magellan Baade Telescope at Las Campanas Observatory as part of the ACCESS project. We investigate the presence of clouds/hazes in the upper atmosphere of this planet, as well as the contribution of stellar activity on the observed features. In addition, we search for absorption features of the alkali elements Na i and K i, with particular focus on K i, for which there have been two previously published disagreeing results. Observations with Hubble Space Telescope (HST)/STIS detected K i, whereas ground-based low- and high-resolution observations did not. We use equilibrium and nonequilibrium chemistry retrievals to explore the planetary and stellar parameter space of the system with our optical data combined with existing near-IR observations. Our best-fit model is that with a scattering slope consistent with a Rayleigh slope (alpha = 5(-3.1)(+2.9)), high-altitude clouds at a log cloud top pressure of -3.6(-2.1)(+2.7) bars, and possible muted H2O features. We find that our observations support other ground-based claims of no K I. Clouds are likely why signals like H2O are extremely muted and Na or K cannot be detected. We then juxtapose our Magellan/IMACS transmission spectrum with existing VLT/FORS2, HST/WFC3, HST/STIS, and Spitzer observations to further constrain the optical-to-infrared atmospheric features of the planet. We find that a steeper scattering slope (alpha = 8.3 +/- 1.5) is anchored by STIS wavelengths blueward of 400 nm and only the original STIS observations show significant potassium signal.
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Nowak, G., Palle, E., Gandolfi, D., Deeg, H. J., Hirano, T., Barragan, O., et al. (2020). K2-280 b – a low density warm sub-Saturn around a mildly evolved star. Mon. Not. Roy. Astron. Soc., 497(4), 4423–4435.
Abstract: We present an independent discovery and detailed characterization of K2-280 b, a transiting low density warm sub-Saturn in a 19.9-d moderately eccentric orbit (e = 0.35(-0.04)(+0.05)) from K2 campaign 7. A joint analysis of high precision HARPS, HARPS-N, and FIES radial velocity measurements and K2 photometric data indicates that K2-280 b has a radius of R-b = 7.50 +/- 0.44 R-circle plus and a mass of M-b = 37.1 +/- 5.6 M-circle plus, yielding a mean density of rho(b) = 0.48(-0.10)(+0.13) g cm(-3). The host star is a mildly evolved G7 star with an effective temperature of T-eff = 5500 +/- 100 K, a surface gravity of log g(star) = 4.21 +/- 0.05 (cgs), and an iron abundance of [Fe/H] = 0.33 +/- 0.08 dex, and with an inferred mass of M-star = 1.03 +/- 0.03 M-circle dot and a radius of R-star = 1.28 +/- 0.07 R-circle dot. We discuss the importance of K2-280 b for testing formation scenarios of sub-Saturn planets and the current sample of this intriguing group of planets that are absent in the Solar system.
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Sedaghati, E., MacDonald, R. J., Casasayas-Barris, N., Hoeijmakers, H. J., Boffin, H. M. J., Rodler, F., et al. (2021). A spectral survey of WASP-19b with ESPRESSO. Mon. Not. Roy. Astron. Soc., 505(1), 435–458.
Abstract: High-resolution precision spectroscopy provides a multitude of robust techniques for probing exoplanetary atmospheres. We present multiple VLT/ESPRESSO transit observations of the hot-Jupiter exoplanet WASP-19b with previously published but disputed atmospheric features from low resolution studies. Through spectral synthesis and modelling of the Rossiter-McLaughlin (RM) effect we calculate stellar, orbital and physical parameters for the system. From narrow-band spectroscopy we do not detect any of Hi, Fei, Mgi, Cai, Nai, and Ki neutral species, placing upper limits on their line contrasts. Through cross-correlation analyses with atmospheric models, we do not detect Fei and place a 3 sigma upper limit of on its mass fraction, from injection and retrieval. We show the inability to detect the presence of H2O for known abundances, owing to lack of strong absorption bands, as well as relatively low S/N ratio. We detect a barely significant peak (3.02 +/- 0.15 sigma) in the cross-correlation map for TiO, consistent with the sub-solar abundance previously reported. This is merely a hint for the presence of TiO and does not constitute a confirmation. However, we do confirm the presence of previously observed enhanced scattering towards blue wavelengths, through chromatic RM measurements, pointing to a hazy atmosphere. We finally present a reanalysis of low-resolution transmission spectra of this exoplanet, concluding that unocculted starspots alone cannot explain previously detected features. Our reanalysis of the FORS2 spectra of WASP-19b finds a similar to 100x sub-solar TiO abundance, precisely constrained to , consistent with the TiO hint from ESPRESSO. We present plausible paths to reconciliation with other seemingly contradicting results.
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Trifonov, T., Wollbold, A., Kurster, M., Eberhardt, J., Stock, S., Henning, T., et al. (2022). A New Third Planet and the Dynamical Architecture of the HD33142 HD 33142 Planetary System. Astron. J., 164(4), 156.
Abstract: Based on recently-taken and archival HARPS, FEROS, and HIRES radial velocities (RVs), we present evidence for a new planet orbiting the first ascent red giant star HD 33142 (with an improved mass estimate of M1.52 +/- 0.03 M-circle dot), already known to host two planets. We confirm the Jovian-mass planets HD 33142b and c, with periods of P-b = 330.0(-0.4)(+0.4) days and P-c = 810. 2(-4.2)(+3.8) days and minimum dynamical masses of m(b) sin i =1.26(-0.05)(+0.05) M-Jup and m(c) sin i = 0.89(-0.05)(+0.06) M-Jup, respectively. Furthermore, our periodogram analysis of the precise RVs shows strong evidence for a short-period Doppler signal in the residuals of a two-planet Keplerian fit, which we interpret as a third, Saturn-mass planet with m(d) sin i = 0.20(-)(0.03)(+0.02) M-Jup in a close-in orbit with an orbital period of P-d = 89.9(-0.1)(+0.1) days. We study the dynamical behavior of the three-planet system configuration with an N-body integration scheme, finding it to be long-term stable with the planets alternating between low and moderate eccentricity episodes. We also perform N-body simulations, including stellar evolution and second-order dynamical effects such as planet-stellar tides and stellar mass loss on the way to the white dwarf phase. We find that planets HD 33142b, c, and d are likely to be engulfed near the tip of the red giant branch phase due to tidal migration. These results make the HD 33142 system an essential benchmark for planet population statistics of the multiple-planet systems found around evolved stars.
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Weaver, I. C., Lopez-Morales, M., Espinoza, N., Rackham, B. V., Osip, D. J., Apai, D., et al. (2020). ACCESS: A Visual to Near-infrared Spectrum of the Hot Jupiter WASP-43b with Evidence of H2O, but No Evidence of Na or K. Astron. J., 159(1), 21 pp.
Abstract: We present a new ground-based visual transmission spectrum of the hot Jupiter WASP-43b, obtained as part of the ACCESS Survey. The spectrum was derived from four transits observed between 2015 and 2018, with combined wavelength coverage between 5300 and 9000 A and an average photometric precision of 708 ppm in 230 A bins. We perform an atmospheric retrieval of our transmission spectrum combined with literature Hubble Space Telescope/WFC3 observations to search for the presence of clouds/hazes as well as Na, K, H alpha, and H2O planetary absorption and stellar spot contamination over a combined spectral range of 5318-16420 A. We do not detect a statistically significant presence of Na i or K i alkali lines, or H alpha in the atmosphere of WASP-43b. We find that the observed transmission spectrum can be best explained by a combination of heterogeneities on the photosphere of the host star and a clear planetary atmosphere with H2O. This model yields a log evidence of 8.26 0.42 higher than a flat (featureless) spectrum. In particular, the observations marginally favor the presence of large, low-contrast spots over the four ACCESS transit epochs with an average covering fraction T = 132 K 132 K. Within the planet's atmosphere, we recover a log H2O volume mixing ratio of -2.78(-1.47)(+1.38), which is consistent with previous H2O abundance determinations for this planet.
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