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LRG-BEASTS: ground-based detection of sodium and a steep optical slope in the atmosphere of the highly inflated hot-saturn WASP-21bAlderson, L.Kirk, JamesLópez-Morales, MercedesWheatley, P. J.Skillen, I.Henry, G. W.McGruder, ChimaBrogi, M.Louden, T.King, G.DOI: info:10.1093/mnras/staa2315v. 4975182–5202
Alderson, L., Kirk, James, López-Morales, Mercedes, Wheatley, P. J., Skillen, I., Henry, G. W., McGruder, Chima, Brogi, M., Louden, T., and King, G. 2020. "LRG-BEASTS: ground-based detection of sodium and a steep optical slope in the atmosphere of the highly inflated hot-saturn WASP-21b." Monthly Notices of the Royal Astronomical Society 497:5182– 5202.
ID: 157810
Type: article
Authors: Alderson, L.; Kirk, James; López-Morales, Mercedes; Wheatley, P. J.; Skillen, I.; Henry, G. W.; McGruder, Chima; Brogi, M.; Louden, T.; King, G.
Abstract: We present the optical transmission spectrum of the highly inflated Saturn-mass exoplanet WASP-21b, using three transits obtained with the ACAM instrument on the William Herschel Telescope through the LRG-BEASTS survey (Low Resolution Ground-Based Exoplanet Atmosphere Survey using Transmission Spectroscopy). Our transmission spectrum covers a wavelength range of 4635-9000 Å, achieving an average transit depth precision of 197 ppm compared to one atmospheric scale height at 246 ppm. We detect Na I absorption in a bin width of 30 Å at >4σ confidence, which extends over 100 Å. We see no evidence of absorption from K I. Atmospheric retrieval analysis of the scattering slope indicates it is too steep for Rayleigh scattering from H2, but is very similar to that of HD 189733b. The features observed in our transmission spectrum cannot be caused by stellar activity alone, with photometric monitoring of WASP-21 showing it to be an inactive star. We therefore conclude that aerosols in the atmosphere of WASP-21b are giving rise to the steep slope that we observe, and that WASP-21b is an excellent target for infrared observations to constrain its atmospheric metallicity.
Confirmation of WASP-107b's Extended Helium Atmosphere with Keck II/NIRSPECKirk, JamesAlam, Munazza K.López-Morales, MercedesZeng, LiDOI: info:10.3847/1538-3881/ab6e66v. 159115
Kirk, James, Alam, Munazza K., López-Morales, Mercedes, and Zeng, Li. 2020. "Confirmation of WASP-107b's Extended Helium Atmosphere with Keck II/NIRSPEC." The Astronomical Journal 159:115.
ID: 156365
Type: article
Authors: Kirk, James; Alam, Munazza K.; López-Morales, Mercedes; Zeng, Li
Abstract: We present the detection of helium in the extended atmosphere of the sub-Saturn WASP-107b using high-resolution (R ≈ 25,000) near-infrared spectra from Keck II/Near Infrared Echelle Spectrograph (NIRSPEC). We find peak excess absorption of 7.26% ± 0.24% (30σ) centered on the He i triplet at 10833 Å. The amplitude and shape of the helium absorption profile is in excellent agreement with previous observations of escaping helium from this planet made by CARMENES and the Hubble Space Telescope. This suggests there is no significant temporal variation in the signature of escaping helium from the planet over a two year baseline. This result demonstrates Keck II/NIRSPEC's ability to detect atmospheric escape in exoplanets, making it a useful instrument to further our understanding of the evaporation of exoplanetary atmospheres via ground- based observations of He i.
ACCESS: Confirmation of No Potassium in the Atmosphere of WASP-31bMcGruder, Chima D.López-Morales, MercedesEspinoza, NéstorRackham, Benjamin V.Apai, DánielJordán, AndrésOsip, David J.Alam, Munazza K.Bixel, AlexFortney, Jonathan J.Henry, Gregory W.Kirk, JamesLewis, Nikole K.Rodler, FlorianWeaver, Ian C.DOI: info:10.3847/1538-3881/abb806v. 160230
McGruder, Chima D., López-Morales, Mercedes, Espinoza, Néstor, Rackham, Benjamin V., Apai, Dániel, Jordán, Andrés, Osip, David J., Alam, Munazza K., Bixel, Alex, Fortney, Jonathan J., Henry, Gregory W., Kirk, James, Lewis, Nikole K., Rodler, Florian, and Weaver, Ian C. 2020. "ACCESS: Confirmation of No Potassium in the Atmosphere of WASP-31b." The Astronomical Journal 160:230.
ID: 158643
Type: article
Authors: McGruder, Chima D.; López-Morales, Mercedes; Espinoza, Néstor; Rackham, Benjamin V.; Apai, Dániel; Jordán, Andrés; Osip, David J.; Alam, Munazza K.; Bixel, Alex; Fortney, Jonathan J.; Henry, Gregory W.; Kirk, James; Lewis, Nikole K.; Rodler, Florian; Weaver, Ian C.
Abstract: We present a new optical (400-950 nm) transmission spectrum of the hot Jupiter WASP-31b (M = 0.48 MJ; R = 1.54 RJ; 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 ( $\alpha ={5.3}_{-3.1}^{+2.9}$ ), 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 (a = 8.3 ± 1.5) is anchored by STIS wavelengths blueward of 400 nm and only the original STIS observations show significant potassium signal.
ACCESS: A Visual to Near-infrared Spectrum of the Hot Jupiter WASP-43b with Evidence of H2O, but No Evidence of Na or KWeaver, Ian C.López-Morales, MercedesEspinoza, NéstorRackham, Benjamin V.Osip, David J.Apai, DánielJordán, AndrésBixel, AlexLewis, Nikole K.Alam, Munazza K.Kirk, JamesMcGruder, ChimaRodler, FlorianFienco, JenniferDOI: info:10.3847/1538-3881/ab55dav. 15913
Weaver, Ian C., López-Morales, Mercedes, Espinoza, Néstor, Rackham, Benjamin V., Osip, David J., Apai, Dániel, Jordán, Andrés, Bixel, Alex, Lewis, Nikole K., Alam, Munazza K., Kirk, James, McGruder, Chima, Rodler, Florian, and Fienco, Jennifer. 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." The Astronomical Journal 159:13.
ID: 155680
Type: article
Authors: Weaver, Ian C.; López-Morales, Mercedes; Espinoza, Néstor; Rackham, Benjamin V.; Osip, David J.; Apai, Dániel; Jordán, Andrés; Bixel, Alex; Lewis, Nikole K.; Alam, Munazza K.; Kirk, James; McGruder, Chima; Rodler, Florian; Fienco, Jennifer
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 Å and an average photometric precision of 708 ppm in 230 Å 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, Hα, and H2O planetary absorption and stellar spot contamination over a combined spectral range of 5318─16420 Å. We do not detect a statistically significant presence of Na I or K I alkali lines, or Hα 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 {f}het}={0.27}-0.16+0.42 and temperature contrast ∆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.
LRG-BEASTS: Transmission Spectroscopy and Retrieval Analysis of the Highly Inflated Saturn-mass Planet WASP-39bKirk, JamesLópez-Morales, MercedesWheatley, Peter J.Weaver, Ian C.Skillen, IanLouden, TomMcCormac, JamesEspinoza, NéstorDOI: info:10.3847/1538-3881/ab397dv. 158144
Kirk, James, López-Morales, Mercedes, Wheatley, Peter J., Weaver, Ian C., Skillen, Ian, Louden, Tom, McCormac, James, and Espinoza, Néstor. 2019. "LRG-BEASTS: Transmission Spectroscopy and Retrieval Analysis of the Highly Inflated Saturn-mass Planet WASP-39b." The Astronomical Journal 158:144.
ID: 154617
Type: article
Authors: Kirk, James; López-Morales, Mercedes; Wheatley, Peter J.; Weaver, Ian C.; Skillen, Ian; Louden, Tom; McCormac, James; Espinoza, Néstor
Abstract: We present a ground-based transmission spectrum and comprehensive retrieval analysis of the highly inflated Saturn-mass planet WASP-39b. We obtained low-resolution spectra (R ≈ 400) of a transit of WASP-39b using the ACAM instrument on the 4.2 m William Herschel Telescope as part of the LRG-BEASTS survey. Our transmission spectrum is in good agreement with previous ground- and space-based observations of WASP- 39b, and covers a wavelength range of 4000-9000 Å. Previous analyses of this exoplanet have retrieved water abundances that span more than four orders of magnitude, which in turn lead to conclusions of a subsolar or highly supersolar atmospheric metallicity. In order to determine the cause of the large discrepancies in the literature regarding WASP-39b's atmospheric metallicity, we performed retrieval analyses of all literature data sets. Our retrievals, which assume equilibrium chemistry, recovered highly supersolar metallicities for all data sets. When running our retrievals on a combined spectrum, spanning 0.3-5 μm, we recovered an atmospheric metallicity of {282}-58+65× solar. We find that stellar activity has a negligible effect on the derived abundances and instead conclude that different assumptions made during retrieval analyses lead to the reported water abundances that differ by orders of magnitude. This in turn has significant consequences for the conclusions we draw. This is the fourth planet to be observed as part of the LRG-BEASTS survey, which is demonstrating that 4 m class telescopes can obtain low-resolution transmission spectra with precisions of around one atmospheric scale height.
Exoplanet characterisation in the longest known resonant chain: the K2-138 system seen by HARPSLopez, T. A.Barros, S. C. C.Santerne, A.Deleuil, M.Adibekyan, V.Almenara, J. -MArmstrong, D. J.Brugger, B.Barrado, D.Bayliss, D.Boisse, I.Bonomo, A. S.Bouchy, F.Brown, D. J. A.Carli, E.Demangeon, O.Dumusque, X.Díaz, R. F.Faria, J. P.Figueira, P.Foxell, E.Giles, H.Hébrard, G.Hojjatpanah, S.Kirk, JamesLillo-Box, J.Lovis, C.Mousis, O.da Nóbrega, H. J.Nielsen, L. D.Neal, J. J.Osborn, H. P.Pepe, F.Pollacco, D.Santos, N. C.Sousa, S. G.Udry, S.Vigan, A.Wheatley, P. J.DOI: info:10.1051/0004-6361/201936267v. 631A90
Lopez, T. A., Barros, S. C. C., Santerne, A., Deleuil, M., Adibekyan, V., Almenara, J. -M, Armstrong, D. J., Brugger, B., Barrado, D., Bayliss, D., Boisse, I., Bonomo, A. S., Bouchy, F., Brown, D. J. A., Carli, E., Demangeon, O., Dumusque, X., Díaz, R. F., Faria, J. P., Figueira, P., Foxell, E., Giles, H., Hébrard, G., Hojjatpanah, S., Kirk, James et al. 2019. "Exoplanet characterisation in the longest known resonant chain: the K2-138 system seen by HARPS." Astronomy and Astrophysics 631:A90.
ID: 154613
Type: article
Authors: Lopez, T. A.; Barros, S. C. C.; Santerne, A.; Deleuil, M.; Adibekyan, V.; Almenara, J. -M; Armstrong, D. J.; Brugger, B.; Barrado, D.; Bayliss, D.; Boisse, I.; Bonomo, A. S.; Bouchy, F.; Brown, D. J. A.; Carli, E.; Demangeon, O.; Dumusque, X.; Díaz, R. F.; Faria, J. P.; Figueira, P.; Foxell, E.; Giles, H.; Hébrard, G.; Hojjatpanah, S.; Kirk, James; Lillo-Box, J.; Lovis, C.; Mousis, O.; da Nóbrega, H. J.; Nielsen, L. D.; Neal, J. J.; Osborn, H. P.; Pepe, F.; Pollacco, D.; Santos, N. C.; Sousa, S. G.; Udry, S.; Vigan, A.; Wheatley, P. J.
Abstract: The detection of low-mass transiting exoplanets in multiple systems brings new constraints to planetary formation and evolution processes and challenges the current planet formation theories. Nevertheless, only a mere fraction of the small planets detected by Kepler and K2 have precise mass measurements, which are mandatory to constrain their composition. We aim to characterise the planets that orbit the relatively bright star K2-138. This system is dynamically particular as it presents the longest chain known to date of planets close to the 3:2 resonance. We obtained 215 HARPS spectra from which we derived the radial-velocity variations of K2-138. Via a joint Bayesian analysis of both the K2 photometry and HARPS radial-velocities (RVs), we constrained the parameters of the six planets in orbit. The masses of the four inner planets, from b to e, are 3.1, 6.3, 7.9, and 13.0 M with a precision of 34, 20, 18, and 15%, respectively. The bulk densities are 4.9, 2.8, 3.2, and 1.8 g cm-3, ranging from Earth to Neptune- like values. For planets f and g, we report upper limits. Finally, we predict transit timing variations of the order two to six minutes from the masses derived. Given its peculiar dynamics, K2-138 is an ideal target for transit timing variation (TTV) measurements from space with the upcoming CHaracterizing ExOPlanet Satellite (CHEOPS) to study this highly-packed system and compare TTV and RV masses. Full Table A.3 is only available at the CDS via anonymous ftp to ( or via bin/cat/J/A+A/631/A90