Publication Search Results

ID: 155671
Type: article
Authors: Frustagli, G.; Poretti, E.; Milbourne, Timothy; Malavolta, L.; Mortier, A.; Singh, V.; Bonomo, A. S.; Buchhave, L. A.; Zeng, L.; Vanderburg, Andrew; Udry, S.; Andreuzzi, G.; Collier-Cameron, A.; Cosentino, R.; Damasso, M.; Ghedina, A.; Harutyunyan, A.; Haywood, Raphaëlle D.; Latham, David W.; López-Morales, Mercedes; Lorenzi, V.; Martinez Fiorenzano, A. F.; Mayor, M.; Micela, G.; Molinari, E.; Pepe, F.; Phillips, David; Rice, K.; Sozzetti, A.
Abstract: Ultra-short period (USP) planets are a class of exoplanets with periods shorter than one day. The origin of this sub-population of planets is still unclear, with different formation scenarios highly dependent on the composition of the USP planets. A better understanding of this class of exoplanets will, therefore, require an increase in the sample of such planets that have accurate and precise masses and radii, which also includes estimates of the level of irradiation and information about possible companions. Here we report a detailed characterization of a USP planet around the solar-type star HD 80653 ≡EP 251279430 using the K2 light curve and 108 precise radial velocities obtained with the HARPS-N spectrograph, installed on the Telescopio Nazionale Galileo. From the K2 C16 data, we found one super-Earth planet (R_b = 1.613 ± 0.071 R_⊕) transiting the star on a short-period orbit (P_b = 0.719573 ± 0.000021 d). From our radial velocity measurements, we constrained the mass of HD 80653 b to M_b = 5.60 ± 0.43 M_⊕. We also detected a clear long-term trend in the radial velocity data. We derived the fundamental stellar parameters and determined a radius of R_⋆ = 1.22 ± 0.01 R_☉ and mass of M_⋆ = 1.18 ± 0.04 M_☉, suggesting that HD 80653 has an age of 2.7 ± 1.2 Gyr. The bulk density (ρ_b = 7.4 ± 1.1 g cm^-3) of the planet is consistent with an Earth-like composition of rock and iron with no thick atmosphere. Our analysis of the K2 photometry also suggests hints of a shallow secondary eclipse with a depth of 8.1 ± 3.7 ppm. Flux variations along the orbital phase are consistent with zero. The most important contribution might come from the day-side thermal emission from the surface of the planet at T ~ 3480 K. HARPS-N spectroscopic data are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz- bin/cat/J/A+A/633/A133 Based on observations made with the Italian Telescopio Nazionale Galileo (TNG) operated by the Fundación Galileo Galilei (FGG) of the Istituto Nazionale di Astrofisica (INAF) at the Observatorio del Roque de los Muchachos (La Palma, Canary Islands, Spain).

ID: 155703
Type: article
Authors: Mayo, Andrew W.; Rajpaul, Vinesh M.; Buchhave, Lars A.; Dressing, Courtney D.; Mortier, Annelies; Zeng, Li; Fortenbach, Charles D.; Aigrain, Suzanne; Bonomo, Aldo S.; Collier Cameron, Andrew; Charbonneau, David; Coffinet, Adrien; Cosentino, Rosario; Damasso, Mario; Dumusque, Xavier; Martinez Fiorenzano, A. F.; Haywood, Raphaëlle D.; Latham, David W.; López-Morales, Mercedes; Malavolta, Luca; Micela, Giusi; Molinari, Emilio; Pearce, Logan; Pepe, Francesco; Phillips, David; Piotto, Giampaolo; Poretti, Ennio; Rice, Ken; Sozzetti, Alessandro; Udry, Stephane

ID: 155695
Type: article
Authors: Miklos, M.; Milbourne, Timothy W.; Haywood, Raphaëlle D.; Phillips, David F.; Saar, Steven H.; Meunier, N.; Cegla, H. M.; Dumusque, X.; Langellier, Nicholas; Maldonado, J.; Malavolta, L.; Mortier, A.; Thompson, S.; Watson, C. A.; Cecconi, M.; Cosentino, R.; Ghedina, A.; Li, C. -H; López-Morales, Mercedes; Molinari, E.; Poretti, Ennio; Sasselov, Dimitar; Sozzetti, A.; Walsworth, Ronald L.
Abstract: Efforts to detect low-mass exoplanets using stellar radial velocities (RVs) are currently limited by magnetic photospheric activity. Suppression of convective blueshift is the dominant magnetic contribution to RV variability in low-activity Sun-like stars. Due to convective plasma motion, the magnitude of RV contributions from the suppression of convective blueshift is related to the depth of formation of photospheric spectral lines for a given species used to compute the RV time series. Meunier et al. used this relation to demonstrate a method for spectroscopic extraction of the suppression of convective blueshift in order to isolate RV contributions, including planetary RVs, that contribute equally to the time series for each spectral line. Here, we extract disk-integrated solar RVs from observations over a 2.5 yr time span made with the solar telescope integrated with the HARPS-N spectrograph at the Telescopio Nazionale Galileo (La Palma, Canary Islands, Spain). We apply the methods outlined by Meunier et al. We are not, however, able to isolate physically meaningful contributions due to the suppression of convective blueshift from this solar data set, potentially because our data set is taken during solar minimum when the suppression of convective blueshift may not sufficiently dominate activity contributions to RVs. This result indicates that, for low- activity Sun-like stars, one must include additional RV contributions from activity sources not considered in the Meunier et al. model at different timescales, as well as instrumental variation, in order to reach the submeter per second RV sensitivity necessary to detect low- mass planets in orbit around Sun-like stars.

ID: 158737
Type: article
Authors: Mortier, A.; Zapatero Osorio, M. R.; Malavolta, L.; Alibert, Y.; Rice, K.; Lillo-Box, J.; Vanderburg, A.; Oshagh, M.; Buchhave, L.; Adibekyan, V.; Delgado Mena, E.; Lopez-Morales, Mercedes; Charbonneau, David; Sousa, S. G.; Lovis, C.; Affer, L.; Allende Prieto, C.; Barros, S. C. C.; Benatti, S.; Bonomo, A. S.; Boschin, W.; Bouchy, F.; Cabral, A.; Collier Cameron, A.; Cosentino, R.; Cristiani, S.; Demangeon, O. D. S.; Di Marcantonio, P.; D'Odorico, V.; Dumusque, X.; Ehrenreich, D.; Figueira, P.; Fiorenzano, A.; Ghedina, A.; González Hernández, J. I.; Haldemann, J.; Harutyunyan, A.; Haywood, Raphaëlle D.; Latham, David W.; Lavie, B.; Lo Curto, G.; Maldonado, J.; Manescau, A.; Martins, C. J. A. P.; Mayor, M.; Mégevand, D.; Mehner, A.; Micela, G.; Molaro, P.; Molinari, E.; Nunes, N. J.; Pepe, F. A.; Palle, E.; Phillips, David; Piotto, G.; Pinamonti, M.; Poretti, E.; Riva, M.; Rebolo, R.; Santos, N. C.; Sasselov, Dimitar; Sozzetti, A.; Suárez Mascareño, A.; Udry, S.; West, R. G.; Watson, C. A.; Wilson, T. G.
Abstract: This paper reports on the detailed characterization of the K2-111 planetary system with K2, WASP, and ASAS-SN photometry, as well as high-resolution spectroscopic data from HARPS-N and ESPRESSO. The host, K2-111, is confirmed to be a mildly evolved (log g = 4.17), iron-poor ([Fe/H] = -0.46), but alpha-enhanced ([a/Fe]=0.27), chromospherically quiet, very old thick disc G2 star. A global fit, performed by using PyORBIT, shows that the transiting planet, K2-111 b, orbits with a period P_b = 5.3518 ± 0.0004 d and has a planet radius of $1.82^{+0.11}_{-0.09}$ R_? and a mass of $5.29^{+0.76}_{-0.77}$ M_?, resulting in a bulk density slightly lower than that of the Earth. The stellar chemical composition and the planet properties are consistent with K2-111 b being a terrestrial planet with an iron core mass fraction lower than the Earth. We announce the existence of a second signal in the radial velocity data that we attribute to a non-transiting planet, K2-111 c, with an orbital period of 15.6785 ± 0.0064 d, orbiting in near-3:1 mean motion resonance with the transiting planet, and a minimum planet mass of 11.3 ± 1.1 M_?. Both planet signals are independently detected in the HARPS-N and ESPRESSO data when fitted separately. There are potentially more planets in this resonant system, but more well-sampled data are required to confirm their presence and physical parameters.

ID: 158232
Type: article
Authors: Nava, Chantanelle; López-Morales, Mercedes; Haywood, Raphaëlle D.; Giles, Helen A. C.
Abstract: Accurately modeling effects from stellar activity is a key step in detecting radial velocity (RV) signals of low-mass and long-period exoplanets. RVs from stellar activity are dominated by magnetic active regions that move in and out of sight as the star rotates, producing signals with timescales related to the stellar rotation period. Methods to characterize RV periodograms assume that peaks from magnetic active regions will typically occur at the stellar rotation period or a related harmonic. However, with surface features unevenly spaced and evolving over time, signals from magnetic activity are not perfectly periodic, and the effectiveness of characterizing them with sine curves is unconfirmed. With a series of simulations, we perform the first test of common assumptions about signals from magnetic active regions in RV periodograms. We simulate RVs with quasi-periodic signals that account for evolution and migration of magnetic surface features. As test cases, we apply our analysis to two exoplanet hosts, Kepler-20 and K2-131. Simulating observing schedules and uncertainties of real RV surveys, we find that magnetic active regions commonly produce maximum periodogram peaks at spurious periods unrelated to the stellar rotation period: 81% and 72% of peaks, respectively, for K2-131 and Kepler-20. These unexpected peaks can potentially lead to inaccuracies in derived planet masses. We also find that these spurious peaks can sometimes survive multiple seasons of observation, imitating signals typically attributed to exoplanet companions.

ID: 157129
Type: article
Authors: Thompson, A. P. G.; Watson, C. A.; Haywood, Raphaëlle D.; Costes, J. C.; de Mooij, E.; Collier Cameron, A.; Dumusque, X.; Phillips, David F.; Saar, Steven H.; Mortier, A.; Milbourne, T. W.; Aigrain, S.; Cegla, H. M.; Charbonneau, David; Cosentino, R.; Ghedina, A.; Latham, David W.; López-Morales, M.; Micela, G.; Molinari, E.; Poretti, E.; Sozzetti, A.; Thompson, S.; Walsworth, Ronald L.
Abstract: Stellar activity is the major roadblock on the path to finding true Earth-analogue planets with the Doppler technique. Thus, identifying new indicators that better trace magnetic activity (I.e. faculae and spots) is crucial to aid in disentangling these signals from that of a planet's Doppler wobble. In this work, we investigate activity related features as seen in disc-integrated spectra from the HARPS-N solar telescope. We divide high-activity spectral echelle orders by low-activity master templates (as defined using both $\log {R^{\prime }_{HK}}$ and images from the Solar Dynamics Observatory, SDO), creating 'relative spectra'. With resolved images of the surface of the Sun (via SDO), the faculae and spot filling factors can be calculated, giving a measure of activity independent of, and in addition to, $\log {R^{\prime }_{HK}}$ . We find pseudo-emission (and pseudo-absorption) features in the relative spectra that are similar to those reported in our previous work on α Cen B. In α Cen B, the features are shown to correlate better to changes in faculae filling factor than spot filling factor. In this work, we more confidently identify changes in faculae coverage of the visible hemisphere of the Sun as the source of features produced in the relative spectra. Finally, we produce trailed spectra to observe the radial velocity component of the features, which show that the features move in a redward direction as one would expect when tracking active regions rotating on the surface of a star.

ID: 154146
Type: article
Authors: Collier Cameron, A.; Mortier, A.; Phillips, David; Dumusque, X.; Haywood, Raphaëlle D.; Langellier, Nicholas; Watson, C. A.; Cegla, H. M.; Costes, J.; Charbonneau, David; Coffinet, A.; Latham, David W.; Lopez-Morales, Mercedes; Malavolta, L.; Maldonado, J.; Micela, G.; Milbourne, Timothy; Molinari, Emilio; Saar, S. H.; Thompson, S.; Buchschacher, Nicholas; Cecconi, M.; Cosentino, R.; Ghedina, A.; Glenday, Alexander G.; Gonzalez, M.; Li, C. -H; Lodi, M.; Lovis, C.; Pepe, F.; Poretti, E.; Rice, K.; Sasselov, Dimitar; Sozzetti, A.; Szentgyorgyi, Andrew; Udry, S.; Walsworth, Ronald L.
Abstract: The time-variable velocity fields of solar-type stars limit the precision of radial-velocity determinations of their planets' masses, obstructing detection of Earth twins. Since 2015 July, we have been monitoring disc-integrated sunlight in daytime using a purpose-built solar telescope and fibre feed to the HARPS-N stellar radial-velocity spectrometer. We present and analyse the solar radial-velocity measurements and cross-correlation function (CCF) parameters obtained in the first 3 yr of observation, interpreting them in the context of spatially resolved solar observations. We describe a Bayesian mixture- model approach to automated data-quality monitoring. We provide dynamical and daily differential-extinction corrections to place the radial velocities in the heliocentric reference frame, and the CCF shape parameters in the sidereal frame. We achieve a photon-noise-limited radial-velocity precision better than 0.43 m s^-1 per 5-min observation. The day-to-day precision is limited by zero-point calibration uncertainty with an RMS scatter of about 0.4 m s^-1. We find significant signals from granulation and solar activity. Within a day, granulation noise dominates, with an amplitude of about 0.4 m s^-1 and an autocorrelation half-life of 15 min. On longer time-scales, activity dominates. Sunspot groups broaden the CCF as they cross the solar disc. Facular regions temporarily reduce the intrinsic asymmetry of the CCF. The radial-velocity increase that accompanies an active-region passage has a typical amplitude of 5 m s^-1 and is correlated with the line asymmetry, but leads it by 3d. Spectral line-shape variability thus shows promise as a proxy for recovering the true radial velocity.

ID: 154550
Type: article
Authors: Dubber, Sophie C.; Mortier, Annelies; Rice, Ken; Nava, Chantanelle; Malavolta, Luca; Giles, Helen; Coffinet, Adrien; Charbonneau, David; Vanderburg, Andrew; Bonomo, Aldo S.; Boschin, Walter; Buchhave, Lars A.; Cameron, Andrew Collier; Cosentino, Rosario; Dumusque, Xavier; Ghedina, Adriano; Harutyunyan, Avet; Haywood, Raphaëlle D.; Latham, David; López-Morales, Mercedes; Micela, Giusi; Molinari, Emilio; Pepe, Francesco A.; Phillips, David; Piotto, Giampaolo; Poretti, Ennio; Sasselov, Dimitar; Sozzetti, Alessandro; Udry, Stéphane
Abstract: We present confirmation of the planetary nature of PH-2b, as well as the first mass estimates for the two planets in the Kepler-103 system. PH-2b and Kepler-103c are both long-period and transiting, a sparsely populated category of exoplanets. We use Kepler light-curve data to estimate a radius, and then use HARPS-N radial velocities to determine the semi-amplitude of the stellar reflex motion and, hence, the planet mass. For PH-2b we recover a 3.5σ mass estimate of M_ p = 109^{+30}_{-32} M_⊕ and a radius of R_p = 9.49 ± 0.16 R_⊕. This means that PH-2b has a Saturn-like bulk density and is the only planet of this type with an orbital period P > 200 d that orbits a single star. We find that Kepler-103b has a mass of M_{p,b} = 11.7^{+4.31}_{-4.72} M_⊕ and Kepler-103c has a mass of M_{p,c} = 58.5^{+11.2}_{-11.4} M_⊕. These are 2.5σ and 5σ results, respectively. With radii of R_{p,b} = 3.49^{+0.06}_{-0.05} R_⊕ and R_{p,c} = 5.45^{+0.18}_{-0.17} R_⊕, these results suggest that Kepler-103b has a Neptune-like density, while Kepler-103c is one of the highest density planets with a period P &gt 100 d. By providing high-precision estimates for the masses of the long- period, intermediate-mass planets PH-2b and Kepler-103c, we increase the sample of long-period planets with known masses and radii, which will improve our understanding of the mass-radius relation across the full range of exoplanet masses and radii.

ID: 150911
Type: article
Authors: Kosiarek, Molly R.; Blunt, Sarah; López-Morales, Mercedes; Crossfield, Ian J. M.; Sinukoff, Evan; Petigura, Erik A.; Gonzales, Erica J.; Poretti, Ennio; Malavolta, Luca; Howard, Andrew W.; Isaacson, Howard; Haywood, Raphaëlle D.; Ciardi, David R.; Bristow, Makennah; Collier Cameron, Andrew; Charbonneau, David; Dressing, Courtney D.; Figueira, Pedro; Fulton, Benjamin J.; Hardee, Bronwen J.; Hirsch, Lea A.; Latham, David W.; Mortier, Annelies; Nava, Chantanelle; Schlieder, Joshua E.; Vanderburg, Andrew; Weiss, Lauren; Bonomo, Aldo S.; Bouchy, François; Buchhave, Lars A.; Coffinet, Adrien; Damasso, Mario; Dumusque, Xavier; Lovis, Christophe; Mayor, Michel; Micela, Giusi; Molinari, Emilio; Pepe, Francesco; Phillips, David; Piotto, Giampaolo; Rice, Ken; Sasselov, Dimitar; Ségransan, Damien; Sozzetti, Alessandro; Udry, Stéphane; Watson, Chris
Abstract: K2-291 is a solar-type star with a radius of R _* = 0.899 ± 0.034 R _⊙ and mass of M_* = 0.934 ± 0.038 M _⊙. From the K2 C13 data, we found one super-Earth planet (R _p = {1.589}_-0.072^+0.095 R _⊕) transiting this star on a short period orbit (P = {2.225177}_-6.8{{e}{--}5}^+6.6{{e}{--}5} days). We followed this system up with adaptive-optic imaging and spectroscopy to derive stellar parameters, search for stellar companions, and determine a planet mass. From our 75 radial velocity measurements using High Resolution Echelle Spectrometer on Keck I and High Accuracy Radial velocity Planet Searcher in the northern hemisphere on Telescopio Nazionale Galileo, we constrained the mass of K2-291 b to M _p = 6.49 ± 1.16 M _⊕. We found it necessary to model correlated stellar activity radial velocity signals with a Gaussian process (GP) in order to more accurately model the effect of stellar noise on our data; the addition of the GP also improved the precision of this mass measurement. With a bulk density of ρ = 8.84{}_-2.03^+2.50 g cm^-3, the planet is consistent with an Earth-like rock/iron composition and no substantial gaseous envelope. Such an envelope, if it existed in the past, was likely eroded away by photoevaporation during the first billion years of the star’s lifetime.

ID: 154167
Type: article
Authors: Maldonado, J.; Phillips, David F.; Dumusque, X.; Collier Cameron, A.; Haywood, Raphaëlle D.; Lanza, A. F.; Micela, G.; Mortier, A.; Saar, Steven H.; Sozzetti, A.; Rice, K.; Milbourne, Timothy; Cecconi, M.; Cegla, H. M.; Cosentino, R.; Costes, J.; Ghedina, A.; Gonzalez, M.; Guerra, J.; Hernández, N.; Li, C. -H; Lodi, M.; Malavolta, L.; Molinari, E.; Pepe, F.; Piotto, G.; Poretti, E.; Sasselov, Dimitar; San Juan, J.; Thompson, S.; Udry, S.; Watson, C.
Abstract: Context. Understanding stellar activity in solar-type stars is crucial for the physics of stellar atmospheres as well as for ongoing exoplanet programmes. Aims: We aim to test how well we understand stellar activity using our own star, the Sun, as a test case. Methods: We performed a detailed study of the main optical activity indicators (Ca II H & K, Balmer lines, Na I D₁ D₂, and He I D₃) measured for the Sun using the data provided by the HARPS-N solar-telescope feed at the Telescopio Nazionale Galileo. We made use of periodogram analyses to study solar rotation, and we used the pool variance technique to study the temporal evolution of active regions. The correlations between the different activity indicators as well as the correlations between activity indexes and the derived parameters from the cross-correlation technique are analysed. We also study the temporal evolution of these correlations and their possible relationship with indicators of inhomogeneities in the solar photosphere like sunspot number or radio flux values. Results: The value of the solar rotation period is found in all the activity indicators, with the only exception being Hδ. The derived values vary from 26.29 days (Hγ line) to 31.23 days (He I). From an analysis of sliding periodograms we find that in most of the activity indicators the spectral power is split into several "bands" of periods around 26 and 30 days. They might be explained by the migration of active regions between the equator and a latitude of ̃30°, spot evolution, or a combination of both effects. A typical lifetime of active regions of approximately ten rotation periods is inferred from the pooled variance diagrams, which is in agreement with previous works. We find that Hα, Hβ, Hγ, H∊, and He I show a significant correlation with the S index. Significant correlations between the contrast, bisector span, and the heliocentric radial velocity with the activity indexes are also found. We show that the full width at half maximum, the bisector, and the disc-integrated magnetic field correlate with the radial velocity variations. The correlation ofthe S index and Hα changes with time, increasing with larger sun spot numbers and solar irradiance. A similar tendency with the S index and radial velocity correlation is also present in the data. Conclusions: Our results are consistent with a scenario in which higher activity favours the correlation between the S index and the Hα activity indicators and between the S index and radial velocity variations. Table A.1 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/627/A118

ID: 154640
Type: article
Authors: Mayo, Andrew W.; Rajpaul, Vinesh M.; Buchhave, Lars A.; Dressing, Courtney D.; Mortier, Annelies; Zeng, Li; Fortenbach, Charles D.; Aigrain, Suzanne; Bonomo, Aldo S.; Collier Cameron, Andrew; Charbonneau, David; Coffinet, Adrien; Cosentino, Rosario; Damasso, Mario; Dumusque, Xavier; Martinez Fiorenzano, A. F.; Haywood, Raphaëlle D.; Latham, David W.; López-Morales, Mercedes; Malavolta, Luca; Micela, Giusi; Molinari, Emilio; Pearce, Logan; Pepe, Francesco; Phillips, David; Piotto, Giampaolo; Poretti, Ennio; Rice, Ken; Sozzetti, Alessandro; Udry, Stephane
Abstract: Although several thousands of exoplanets have now been detected and characterized, observational biases have led to a paucity of long- period, low-mass exoplanets with measured masses and a corresponding lag in our understanding of such planets. In this paper we report the mass estimation and characterization of the long-period exoplanet Kepler- 538b. This planet orbits a Sun-like star (V = 11.27) with {M}_* ={0.892}_-0.035^+0.051 M _☉ and {R}_* ={0.8717}_-0.0061^+0.0064 R _☉. Kepler-538b is a {2.215}_-0.034^+0.040 R _⊕ sub-Neptune with a period of P = 81.73778 ± 0.00013 days. It is the only known planet in the system. We collected radial velocity (RV) observations with the High Resolution Echelle Spectrometer (HIRES) on Keck I and High Accuracy Radial velocity Planet Searcher in North hemisphere (HARPS-N) on the Telescopio Nazionale Galileo (TNG). We characterized stellar activity by a Gaussian process with a quasi- periodic kernel applied to our RV and cross-correlation function FWHM observations. By simultaneously modeling Kepler photometry, RV, and FWHM observations, we found a semi-amplitude of K={1.68}_-0.38^+0.39 m s^-1 and a planet mass of {M}_p={10.6}_-2.4^+2.5 M _⊕. Kepler-538b is the smallest planet beyond P = 50 days with an RV mass measurement. The planet likely consists of a significant fraction of ices (dominated by water ice), in addition to rocks/metals, and a small amount of gas. Sophisticated modeling techniques such as those used in this paper, combined with future spectrographs with ultra high-precision and stability will be vital for yielding more mass measurements in this poorly understood exoplanet regime. This in turn will improve our understanding of the relationship between planet composition and insolation flux and how the rocky to gaseous transition depends on planetary equilibrium temperature.

ID: 150413
Type: article
Authors: Ment, Kristo; Dittmann, Jason A.; Astudillo-Defru, Nicola; Charbonneau, David; Irwin, Jonathan; Bonfils, Xavier; Murgas, Felipe; Almenara, Jose-Manuel; Forveille, Thierry; Agol, Eric; Ballard, Sarah; Berta-Thompson, Zachory K.; Bouchy, François; Cloutier, Ryan; Delfosse, Xavier; Doyon, René; Dressing, Courtney D.; Esquerdo, Gilbert A.; Haywood, Raphaëlle D.; Kipping, David M.; Latham, David W.; Lovis, Christophe; Newton, Elisabeth R.; Pepe, Francesco; Rodriguez, Joseph E.; Santos, Nuno C.; Tan, Thiam-Guan; Udry, Stephane; Winters, Jennifer G.; Wünsche, Anaël
Abstract: LHS 1140 is a nearby mid-M dwarf known to host a temperate rocky super-Earth (LHS 1140 b) on a 24.737-day orbit. Based on photometric observations by MEarth and Spitzer as well as Doppler spectroscopy from the High Accuracy Radial velocity Planet Searcher, we report the discovery of an additional transiting rocky companion (LHS 1140 c) with a mass of 1.81 ± 0.39 M _⊕ and a radius of 1.282 ± 0.024 R _⊕ on a tighter, 3.77795-day orbit. We also obtain more precise estimates for the mass and radius of LHS 1140 b, which are 6.98 ± 0.89 M _⊕ and 1.727 ± 0.032 R _⊕. The mean densities of planets b and c are 7.5 ± 1.0 g cm^‑3 and 4.7 ± 1.1 g cm^‑3, respectively, both consistent with the Earth’s ratio of iron to magnesium silicate. The orbital eccentricities of LHS 1140 b and c are consistent with circular orbits and constrained to be below 0.06 and 0.31, respectively, with 90% confidence. Because the orbits of the two planets are coplanar and because we know from previous analyses of Kepler data that compact systems of small planets orbiting M dwarfs are commonplace, a search for more transiting planets in the LHS 1140 system could be fruitful. LHS 1140 c is one of the few known nearby terrestrial planets whose atmosphere could be studied with the upcoming James Webb Space Telescope.

ID: 155443
Type: article
Authors: Milbourne, Timothy W.; Haywood, Raphaëlle D.; Phillips, David F.; Saar, Steve H.; Cegla, H. M.; Cameron, A. C.; Costes, J.; Dumusque, X.; Langellier, Nicholas; Latham, David W.; Maldonado, J.; Malavolta, L.; Mortier, A.; Palumbo, Michael L.,III; Thompson, S.; Watson, C. A.; Bouchy, F.; Buchschacher, N.; Cecconi, M.; Charbonneau, David; Cosentino, R.; Ghedina, A.; Glenday, Alexander G.; Gonzalez, M.; Li, C. -H; Lodi, M.; López-Morales, Mercedes; Lovis, C.; Mayor, M.; Micela, G.; Molinari, E.; Pepe, F.; Piotto, G.; Rice, K.; Sasselov, Dimitar; Ségransan, D.; Sozzetti, A.; Szentgyorgyi, Andrew; Udry, S.; Walsworth, Ronald L.
Abstract: State-of-the-art radial-velocity (RV) exoplanet searches are currently limited by RV signals arising from stellar magnetic activity. We analyze solar observations acquired over a 3 yr period during the decline of Carrington Cycle 24 to test models of RV variation of Sun-like stars. A purpose-built solar telescope at the High Accuracy Radial-velocity Planet Searcher for the Northern hemisphere (HARPS-N) provides disk- integrated solar spectra, from which we extract RVs and {log}{R}_HK}^{\prime }. The Solar Dynamics Observatory (SDO) provides disk-resolved images of magnetic activity. The Solar Radiation and Climate Experiment (SORCE) provides near- continuous solar photometry, analogous to a Kepler light curve. We verify that the SORCE photometry and HARPS-N {log}{R}_HK}^{\prime } correlate strongly with the SDO-derived magnetic filling factor, while the HARPS-N RV variations do not. To explain this discrepancy, we test existing models of RV variations. We estimate the contributions of the suppression of convective blueshift and the rotational imbalance due to brightness inhomogeneities to the observed HARPS-N RVs. We investigate the time variation of these contributions over several rotation periods, and how these contributions depend on the area of active regions. We find that magnetic active regions smaller than 60 Mm² do not significantly suppress convective blueshift. Our area-dependent model reduces the amplitude of activity-induced RV variations by a factor of two. The present study highlights the need to identify a proxy that correlates specifically with large, bright magnetic regions on the surfaces of exoplanet-hosting stars.

ID: 151203
Type: article
Authors: Rice, K.; Malavolta, L.; Mayo, A.; Mortier, A.; Buchhave, L. A.; Affer, L.; Vanderburg, Andrew; Lopez-Morales, Mercedes; Poretti, E.; Zeng, L.; Cameron, A. C.; Damasso, M.; Coffinet, A.; Latham, David W.; Bonomo, A. S.; Bouchy, F.; Charbonneau, David; Dumusque, X.; Figueira, P.; Martinez Fiorenzano, A. F.; Haywood, Raphaëlle D.; Johnson, J. Asher; Lopez, E.; Lovis, C.; Mayor, M.; Micela, G.; Molinari, E.; Nascimbeni, V.; Nava, Chantanelle; Pepe, F.; Phillips, David F.; Piotto, G.; Sasselov, Dimitar; Ségransan, D.; Sozzetti, A.; Udry, S.; Watson, C.
Abstract: Super-Earths belong to a class of planet not found in the Solar system, but which appear common in the Galaxy. Given that some super-Earths are rocky, while others retain substantial atmospheres, their study can provide clues as to the formation of both rocky and gaseous planets, and - in particular - they can help to constrain the role of photoevaporation in sculpting the exoplanet population. GJ 9827 is a system already known to host three super-Earths with orbital periods of 1.2, 3.6, and 6.2 d. Here, we use new HARPS-N radial velocity measurements, together with previously published radial velocities, to better constrain the properties of the GJ 9827 planets. Our analysis cannot place a strong constraint on the mass of GJ 9827 c, but does indicate that GJ 9827 b is rocky with a composition that is probably similar to that of the Earth, while GJ 9827 d almost certainly retains a volatile envelope. Therefore, GJ 9827 hosts planets on either side of the radius gap that appears to divide super-Earths into pre-dominantly rocky ones that have radii below ˜1.5R_⊕, and ones that still retain a substantial atmosphere and/or volatile components, and have radii above ˜2R_⊕. That the less heavily irradiated of the three planets still retains an atmosphere, may indicate that photoevaporation has played a key role in the evolution of the planets in this system.

ID: 147420
Type: article
Authors: Haywood, Raphaëlle D.; Vanderburg, Andrew; Mortier, Annelies; Giles, Helen A. C.; López-Morales, Mercedes; Lopez, Eric D.; Malavolta, Luca; Charbonneau, David; Collier Cameron, Andrew; Coughlin, Jeffrey L.; Dressing, Courtney D.; Nava, Chantanelle; Latham, David W.; Dumusque, Xavier; Lovis, Christophe; Molinari, Emilio; Pepe, Francesco; Sozzetti, Alessandro; Udry, Stéphane; Bouchy, François; Johnson, John A.; Mayor, Michel; Micela, Giusi; Phillips, David; Piotto, Giampaolo; Rice, Ken; Sasselov, Dimitar; Ségransan, Damien; Watson, Chris; Affer, Laura; Bonomo, Aldo S.; Buchhave, Lars A.; Ciardi, David R.; Fiorenzano, Aldo F.; Harutyunyan, Avet
Abstract: We present the confirmation of a small, moderately irradiated (F = 155 ± 7 F _⊕) Neptune with a substantial gas envelope in a P = 11.8728787 ± 0.0000085 day orbit about a quiet, Sun-like G0V star Kepler-1655. Based on our analysis of the Kepler light curve, we determined Kepler-1655b's radius to be 2.213 ± 0.082 R _⊕. We acquired 95 high-resolution spectra with Telescopio Nazionale Galileo/HARPS-N, enabling us to characterize the host star and determine an accurate mass for Kepler-1655b of 5.0{+/- }_2.8^3.1 {M}_\oplus via Gaussian-process regression. Our mass determination excludes an Earth-like composition with 98% confidence. Kepler-1655b falls on the upper edge of the evaporation valley, in the relatively sparsely occupied transition region between rocky and gas-rich planets. It is therefore part of a population of planets that we should actively seek to characterize further.

ID: 146168
Type: article
Authors: Malavolta, Luca; Mayo, Andrew W.; Louden, Tom; Rajpaul, Vinesh M.; Bonomo, Aldo S.; Buchhave, Lars A.; Kreidberg, Laura; Kristiansen, Martti H.; Lopez-Morales, Mercedes; Mortier, Annelies; Vanderburg, Andrew; Coffinet, Adrien; Ehrenreich, David; Lovis, Christophe; Bouchy, Francois; Charbonneau, David; Ciardi, David R.; Collier Cameron, Andrew; Cosentino, Rosario; Crossfield, Ian J. M.; Damasso, Mario; Dressing, Courtney D.; Dumusque, Xavier; Everett, Mark E.; Figueira, Pedro; Fiorenzano, Aldo F. M.; Gonzales, Erica J.; Haywood, Raphaëlle D.; Harutyunyan, Avet; Hirsch, Lea; Howell, Steve B.; Johnson, John Asher; Latham, David W.; Lopez, Eric; Mayor, Michel; Micela, Giusi; Molinari, Emilio; Nascimbeni, Valerio; Pepe, Francesco; Phillips, David F.; Piotto, Giampaolo; Rice, Ken; Sasselov, Dimitar; Ségransan, Damien; Sozzetti, Alessandro; Udry, Stéphane; Watson, Chris
Abstract: Ultra-short period (USP) planets are a class of low-mass planets with periods shorter than one day. Their origin is still unknown, with photo-evaporation of mini-Neptunes and in situ formation being the most credited hypotheses. Formation scenarios differ radically in the predicted composition of USP planets, and it is therefore extremely important to increase the still limited sample of USP planets with precise and accurate mass and density measurements. We report here the characterization of a USP planet with a period of 0.28 days around K2-141 (EPIC 246393474), and the validation of an outer planet with a period of 7.7 days in a grazing transit configuration. We derived the radii of the planets from the K2 light curve and used high-precision radial velocities gathered with the HARPS-N spectrograph for mass measurements. For K2-141b, we thus inferred a radius of 1.51 ± 0.05 R {}_\oplus and a mass of 5.08 ± 0.41 M {}_\oplus , consistent with a rocky composition and lack of a thick atmosphere. K2-141c is likely a Neptune-like planet, although due to the grazing transits and the non-detection in the RV data set, we were not able to put a strong constraint on its density. We also report the detection of secondary eclipses and phase curve variations for K2-141b. The phase variation can be modeled either by a planet with a geometric albedo of 0.30 ± 0.06 in the Kepler bandpass, or by thermal emission from the surface of the planet at ∼3000 K. Only follow-up observations at longer wavelengths will allow us to distinguish between these two scenarios.

ID: 150210
Type: article
Authors: Mortier, A.; Bonomo, A. S.; Rajpaul, V. M.; Buchhave, L. A.; Vanderburg, A.; Zeng, L.; López-Morales, Mercedes; Malavolta, L.; Collier Cameron, A.; Dressing, C. D.; Figueira, P.; Nascimbeni, V.; Rice, K.; Sozzetti, A.; Watson, C.; Affer, L.; Bouchy, F.; Charbonneau, David; Harutyunyan, A.; Haywood, Raphaëlle D.; Johnson, J. A.; Latham, David W.; Lovis, C.; Martinez Fiorenzano, A. F.; Mayor, M.; Micela, G.; Molinari, E.; Motalebi, F.; Pepe, F.; Piotto, G.; Phillips, David F.; Poretti, E.; Sasselov, Dimitar; Ségransan, D.; Udry, S.
Abstract: This paper reports on the validation and mass measurement of K2-263 b, a sub-Neptune orbiting a quiet G9V star. Using K2 data from campaigns C5 and C16, we find this planet to have a period of 50.818947 ± 0.000094 d and a radius of 2.41 ± 0.12 R_⊕. We followed this system with HARPS-N to obtain 67 precise radial velocities (RVs). A combined fit of the transit and radial velocity data reveals that K2-263 b has a mass of 14.8 ± 3.1 M_⊕. Its bulk density (5.7_{-1.4}^{+1.6} g cm^{-3}) implies that this planet has a significant envelope of water or other volatiles around a rocky core. K2-263 b likely formed in a similar way as the cores of the four giant planets in our own Solar System, but for some reason, did not accrete much gas. The planetary mass was confirmed by an independent Gaussian process-based fit to both the RVs and the spectroscopic activity indicators. K2-263 b belongs to only a handful of confirmed K2 exoplanets with periods longer than 40 d. It is among the longest periods for a small planet with a precisely determined mass using RVs.

ID: 143260
Type: article
Authors: Dittmann, Jason A.; Irwin, Jonathan M.; Charbonneau, David; Bonfils, Xavier; Astudillo-Defru, Nicola; Haywood, Raphaëlle D.; Berta-Thompson, Zachory K.; Newton, Elisabeth R.; Rodriguez, Joseph E.; Winters, Jennifer G.; Tan, Thiam-Guan; Almenara, Jose-Manuel; Bouchy, François; Delfosse, Xavier; Forveille, Thierry; Lovis, Christophe; Murgas, Felipe; Pepe, Francesco; Santos, Nuno C.; Udry, Stephane; Wünsche, Anaël; Esquerdo, Gilbert A.; Latham, David W.; Dressing, Courtney D.
Abstract: M dwarf stars, which have masses less than 60 per cent that of the Sun, make up 75 per cent of the population of the stars in the Galaxy. The atmospheres of orbiting Earth-sized planets are observationally accessible via transmission spectroscopy when the planets pass in front of these stars. Statistical results suggest that the nearest transiting Earth-sized planet in the liquid-water, habitable zone of an M dwarf star is probably around 10.5 parsecs away. A temperate planet has been discovered orbiting Proxima Centauri, the closest M dwarf, but it probably does not transit and its true mass is unknown. Seven Earth-sized planets transit the very low-mass star TRAPPIST-1, which is 12 parsecs away, but their masses and, particularly, their densities are poorly constrained. Here we report observations of LHS 1140b, a planet with a radius of 1.4 Earth radii transiting a small, cool star (LHS 1140) 12 parsecs away. We measure the mass of the planet to be 6.6 times that of Earth, consistent with a rocky bulk composition. LHS 1140b receives an insolation of 0.46 times that of Earth, placing it within the liquid-water, habitable zone. With 90 per cent confidence, we place an upper limit on the orbital eccentricity of 0.29. The circular orbit is unlikely to be the result of tides and therefore was probably present at formation. Given its large surface gravity and cool insolation, the planet may have retained its atmosphere despite the greater luminosity (compared to the present-day) of its host star in its youth. Because LHS 1140 is nearby, telescopes currently under construction might be able to search for specific atmospheric gases in the future.

ID: 142825
Type: article
Authors: Dumusque, Xavier; Borsa, F.; Damasso, M.; Díaz, R. F.; Gregory, P. C.; Hara, N. C.; Hatzes, A.; Rajpaul, V.; Tuomi, M.; Aigrain, S.; Anglada-Escudé, G.; Bonomo, A. S.; Boué, G.; Dauvergne, F.; Frustagli, G.; Giacobbe, P.; Haywood, Raphaelle D.; Jones, H. R. A.; Laskar, J.; Pinamonti, M.; Poretti, E.; Rainer, M.; Ségransan, D.; Sozzetti, A.; Udry, S.
Abstract: Context. Radial-velocity (RV) signals arising from stellar photospheric phenomena are the main limitation for precise RV measurements. Those signals induce RV variations an order of magnitude larger than the signal created by the orbit of Earth-twins, thus preventing their detection.
Aims: Different methods have been developed to mitigate the impact of stellar RV signals. The goal of this paper is to compare the efficiency of these different methods to recover extremely low-mass planets despite stellar RV signals. However, because observed

ID: 143334
Type: article
Authors: Malavolta, Luca; Borsato, Luca; Granata, Valentina; Piotto, Giampaolo; Lopez, Eric; Vanderburg, Andrew; Figueira, Pedro; Mortier, Annelies; Nascimbeni, Valerio; Affer, Laura; Bonomo, Aldo S.; Bouchy, Francois; Buchhave, Lars A.; Charbonneau, David; Collier Cameron, Andrew; Cosentino, Rosario; Dressing, Courtney D.; Dumusque, Xavier; Fiorenzano, Aldo F. M.; Harutyunyan, Avet; Haywood, Raphaëlle D.; Johnson, John Asher; Latham, David W.; Lopez-Morales, Mercedes; Lovis, Christophe; Mayor, Michel; Micela, Giusi; Molinari, Emilio; Motalebi, Fatemeh; Pepe, Francesco; Phillips, David F.; Pollacco, Don; Queloz, Didier; Rice, Ken; Sasselov, Dimitar; Ségransan, Damien; Sozzetti, Alessandro; Udry, Stéphane; Watson, Chris
Abstract: We report a detailed characterization of the Kepler-19 system. This star was previously known to host a transiting planet with a period of 9.29 days, a radius of 2.2 R _?, and an upper limit on the mass of 20 M _?. The presence of a second, non-transiting planet was inferred from the transit time variations (TTVs) of Kepler-19b over eight quarters of Kepler photometry, although neither the mass nor period could be determined. By combining new TTVs measurements from all the Kepler quarters and 91 high-precision radial velocities obtained with the HARPS-N spectrograph, using dynamical simulations we obtained a mass of 8.4 ± 1.6 M _? for Kepler-19b. From the same data, assuming system coplanarity, we determined an orbital period of 28.7 days and a mass of 13.1 ± 2.7 M _? for Kepler-19c and discovered a Neptune-like planet with a mass of 20.3 ± 3.4 M _? on a 63-day orbit. By comparing dynamical simulations with non-interacting Keplerian orbits, we concluded that neglecting interactions between planets may lead to systematic errors that can hamper the precision in the orbital parameters when the data set spans several years. With a density of 4.32 ± 0.87 g cm^-3 (0.78 ± 0.16 ? _?) Kepler-19b belongs to the group of planets with a rocky core and a significant fraction of volatiles, in opposition to low-density planets characterized only by transit time variations and an increasing number of rocky planets with Earth-like density. Kepler-19 joins the small number of systems that reconcile transit timing variation and radial velocity measurements.