ABSTRACT We present 15 new transit observations of the exoplanet WASP-43b in the i′, g′, and R filters with the 1.0 m telescopes of Las Cumbres Observatory Global Telescope Network and the IAC80 ...telescope. We combine our 15 new light curves with 52 others from the literature, to homogeneously analyze all the available transit light curves of this exoplanet. By extending the time span of the monitoring of the transits to more than five years, and by analyzing the individual mid-times of 72 transits, we study the proposed shortening of the orbital period of WASP-43b. We estimate that the times of transit are well-matched by our updated ephemeris equation, using a constant orbital period. We estimate an orbital period change rate no larger than P ˙ = −0.02 6.6 ms yr−1, which is fully consistent with a constant period. Based on the timing analysis, we discard stellar tidal dissipation factors Q* < 105. In addition, we update the system parameters: a/Rs = 4.867(23), i = 82.11(10)°, and Rp/Rs = 0.15942(41), noticing a difference in the relative size of the planet between optical and NIR bands.
Exoplanet hunting efforts have revealed the prevalence of exotic worlds with diverse properties, including Earth-sized bodies, which has fueled our endeavor to search for life beyond the Solar ...System. Accumulating experiences in astrophysical, chemical, and climatological characterization of uninhabitable planets are paving the way to characterization of potentially habitable planets. In this paper, we review our possibilities and limitations in characterizing temperate terrestrial planets with future observational capabilities through the 2030s and beyond, as a basis of a broad range of discussions on how to advance "astrobiology" with exoplanets. We discuss the observability of not only the proposed biosignature candidates themselves but also of more general planetary properties that provide circumstantial evidence, since the evaluation of any biosignature candidate relies on its context. Characterization of temperate Earth-sized planets in the coming years will focus on those around nearby late-type stars. The James Webb Space Telescope (JWST) and later 30-meter-class ground-based telescopes will empower their chemical investigations. Spectroscopic studies of potentially habitable planets around solar-type stars will likely require a designated spacecraft mission for direct imaging, leveraging technologies that are already being developed and tested as part of the Wide Field InfraRed Survey Telescope (WFIRST) mission. Successful initial characterization of a few nearby targets will be an important touchstone toward a more detailed scrutiny and a larger survey that are envisioned beyond 2030. The broad outlook this paper presents may help develop new observational techniques to detect relevant features as well as frameworks to diagnose planets based on the observables. Key Words: Exoplanets-Biosignatures-Characterization-Planetary atmospheres-Planetary surfaces. Astrobiology 18, 739-778.
In a search for common proper motion companions using the VISTA Hemisphere Survey (VHS) and the 2MASS catalogs we have identified a very red (J - K sub(S) = 2.47 mag) late-L dwarf companion of a ...previously unrecognized M dwarf VHS J125601.92-125723.9 (hereafter VHS 1256-1257), located at a projected angular separation of 8''.06 + or - 0''.03. In this work we present a suite of astrometric, photometric, and spectroscopic observations of this new pair in an effort to confirm the companionship and characterize the components. From low-resolution (R ~ 130-600) optical and near-infrared spectroscopy we classified the primary and the companion as M7.5 + or - 0.5 and L7 + or - 1.5, respectively. The primary shows slightly weaker alkali lines than field dwarfs of similar spectral type, but still consistent with either a high-gravity dwarf or a younger object of hundreds of millions of years. The secondary shows spectral features characteristic for low surface gravity objects at ages below several hundred million years, like the peaked triangular shape of the H-band continuum and alkali lines weaker than in field dwarfs of the same spectral type. The absence of lithium in the atmosphere of the primary and the likely kinematic membership to the Local Association allowed us to constrain the age of the system to the range of 150-300 Myr. We report a measurement of the trigonometric parallax pi = 78.8 + or - 6.4 mas, which translates into a distance of 12.7 + or - 1.0 pc; the pair thus has a projected physical separation of 102 + or - 9 AU. We derived the bolometric luminosities of the components and compared them with theoretical evolutionary models to estimate the masses and effective temperatures. For the primary, we determined a luminosity of log(L sub(bol)/L sub(middo t in circle)) = -3.14 + or - 0.10, and inferred a mass of 73 super(+20) sub(-15) M sub(Jup) at the boundary between stars and brown dwarfs and an effective temperature of 2620 + or - 140 K. For the companion we obtained a luminosity of log(L sub(bol)/L sub(middo t in circle)) = -5.05 + or - 0.22 and a mass of 11.2 super(+9.7) sub(-1.8) M sub(Jup), placing it near the deuterium-burning mass limit. The effective temperature derived from evolutionary models is 880 super(+140) sub(-110) K, about 400-700 K cooler than the temperature expected for field late-L dwarfs.
Exoplanets smaller than Neptune are common around red dwarf stars (M dwarfs), with those that transit their host star constituting the bulk of known temperate worlds amenable for atmospheric ...characterization. We analyze the masses and radii of all known small transiting planets around M dwarfs, identifying three populations: rocky, water-rich, and gas-rich. Our results are inconsistent with the previously known bimodal radius distribution arising from atmospheric loss of a hydrogen/helium envelope. Instead, we propose that a density gap separates rocky from water-rich exoplanets. Formation models that include orbital migration can explain the observations: Rocky planets form within the snow line, whereas water-rich worlds form outside it and later migrate inward.
Separating rocky from watery exoplanets
The radii of small transiting exoplanets have a bimodal distribution, usually interpreted as planets with and without a thick atmosphere. Luque and Pallé demonstrate that the planets’ densities (which require measurements of both mass and radius) provide a cleaner separation between the populations than radii alone, at least for exoplanets orbiting red dwarf stars (see the Perspective by Teske). They found that one group is consistent with a purely rocky composition, whereas another group matches a model of 50% rock and 50% water. This split between rocky and water-rich planets could reflect where they formed in their planetary systems, before orbital migration. —KTS
The density of exoplanets orbiting red dwarf stars separates into rocky and water-rich populations.
The Earth’s albedo is the fraction of short-wave solar radiation that is reflected back to space, and is key to understand the observed trends in climate change. Although there have been many ...observational approaches to estimate the Earth’s albedo, different methods have their own drawbacks, for example, artificial satellites have a finite life time, and are operating in a hard environment that could quickly degrade the detectors. The Moon, the only natural satellite of Earth, offers an additional platform for monitoring the Earth’s albedo. In this paper, we calculate the global TOA (top-of-atmosphere) albedo that would be observed by a theoretical observatory on the Moon, and compare it with long-term trends derived from CERES (Clouds and the Earth’s Radiant Energy System, 2000–2020) and earthshine data (1999–2017). We find that the global hourly mean albedo observed in the direction of the Moon is more variable because of the orbital movement of the Moon. However, the regional and long-term global mean albedo anomalies that would be observed by CERES and has a good general agreement by a lunar observer over 20 years the data spans. Similarly, earthshine data show a steady decline during two decades of about 0.7 W/m2 which is in line with the decline of 0.5 W/m2 that would be observed from the Moon. Besides, to compare the regional changes of albedo with CERES, the spatially-resolved decadal anomalies in the albedo are also calculated for analysis. We find that a lunar-based observatory would be capable of detecting similar changes seen from CERES. Thus, it is a a practical option to monitor the long-term trends in albedo from the point of view of capturing the variability in the TOA fluxes of the Earth’s atmosphere.
Hot gas giant exoplanets can lose part of their atmosphere due to strong stellar irradiation, affecting their physical and chemical evolution. Studies of atmospheric escape from exoplanets have ...mostly relied on space-based observations of the hydrogen Lyman-α line in the far ultraviolet which is strongly affected by interstellar absorption. Using ground-based high-resolution spectroscopy we detect excess absorption in the helium triplet at 1083 nm during the transit of the Saturn-mass exoplanet WASP-69b, at a signal-to-noise ratio of 18. We measure line blue shifts of several km s
and post transit absorption, which we interpret as the escape of part of the atmosphere trailing behind the planet in comet-like form.
Abstract
We present the low-resolution transmission spectra of the puffy hot Jupiter HAT-P-65b (0.53 M
Jup
, 1.89 R
Jup
,
T
eq
= 1930 K), based on two transits observed using the OSIRIS spectrograph ...on the 10.4 m Gran Telescopio CANARIAS. The transmission spectra of the two nights are consistent, covering the wavelength range 517–938 nm and consisting of mostly 5 nm spectral bins. We perform equilibrium-chemistry spectral retrieval analyses on the jointly fitted transmission spectrum and obtain an equilibrium temperature of
K and a cloud coverage of
%, revealing a relatively clear planetary atmosphere. Based on free-chemistry retrieval, we report strong evidence for titanium oxide (TiO). Additional individual analyses in each night reveal weak-to-moderate evidence for TiO in both nights, but moderate evidence for Na or VO only in one of the nights. Future high-resolution Doppler spectroscopy as well as emission observations will help confirm the presence of TiO and constrain its role in shaping the vertical thermal structure of HAT-P-65b’s atmosphere.
Abstract
Our simultaneous three-colour (BVR) polarimetric observations of the low-mass black hole X-ray binary V404 Cyg show a small but statistically significant change of polarization degree ...(Δp ∼ 1 per cent) between the outburst in 2015 June and the quiescence. The polarization of V404 Cyg in the quiescent state agrees within the errors with that of the visually close (1.4 arcsec) companion (p
R
= 7.3 ± 0.1 per cent), indicating that it is predominantly of interstellar origin. The polarization pattern of the surrounding field stars supports this conclusion. From the observed variable polarization during the outburst, we show that the polarization degree of the intrinsic component peaks in the V band, p
V
= 1.1 ± 0.1 per cent, at the polarization position angle of θ
V
= −7° ± 2°, which is consistent in all three passbands. We detect significant variations in the position angle of the intrinsic polarization in the R band from −30° to ∼0° during the outburst peak. The observed wavelength dependence of the intrinsic polarization does not support non-thermal synchrotron emission from a jet as a plausible mechanism, but it is in better agreement with the combined effect of electron (Thomson) scattering and absorption in a flattened plasma envelope or outflow surrounding the illuminating source. Alternatively, the polarization signal can be produced by scattering of the disc radiation in a mildly relativistic polar outflow. The position angle of the intrinsic polarization, nearly parallel to the jet direction (i.e. perpendicular to the accretion disc plane), is in agreement with these interpretations.
Abstract
We present a new optical transmission spectrum of the hot Jupiter HAT-P-1b based on two transits observed with the Double Spectrograph (DBSP) on the Palomar 200-inch (P200) telescope. The ...DBSP transmission spectrum, covering a wavelength range from 3250 to 10007 Å, is consistent with that observed with the Hubble Space Telescope (HST), but the former has a finer spectral resolution. The DBSP spectrum alone reveals the presence of a pressure-broadened line wing for Na, the line cores for both Na and K, and tentative evidence for H
2
O. We obtain consistent results from the spectral retrieval analyses performed on the DBSP-only data set and the DBSP, HST, and Spitzer combined data set. Our retrievals suggest a mostly clear atmosphere for HAT-P-1b, with a cloud coverage of
22
−
3
+
5
% that is dominated by enhanced haze. We derive subsolar abundances for Na, K, and C, and subsolar to solar for O. Future observations with James Webb Space Telescope and ground-based high-resolution spectrographs should be able to not only confirm the presence of these species but also stringently constrain the formation and migration pathways for HAT-P-1b.
Abstract Measuring the obliquities of stars hosting giant planets may shed light on the dynamical history of planetary systems. Significant efforts have been made to measure the obliquities of FGK ...stars with hot Jupiters, mainly based on observations of the Rossiter–McLaughlin effect. In contrast, M dwarfs with hot Jupiters have hardly been explored because such systems are rare and often not favorable for such precise observations. Here, we report the first detection of the Rossiter–McLaughlin effect for an M dwarf with a hot Jupiter, TOI-4201, using the Gemini-North/MAROON-X spectrograph. We find TOI-4201 to be well aligned with its giant planet, with a sky-projected obliquity of λ = − 3.0 − 3.2 + 3.7 ° and a true obliquity of ψ = 21.3 − 12.8 + 12.5 ° with an upper limit of 40 ◦ at a 95% confidence level. The result agrees with dynamically quiet formation or tidal obliquity damping that realigned the system. As the first hot Jupiter around an M dwarf with its obliquity measured, TOI-4201b joins the group of aligned giant planets around cool stars ( T eff < 6250 K), as well as the small but growing sample of planets with relatively high planet-to-star mass ratio ( M p / M * ≳ 3 × 10 −3 ) that also appear to be mostly aligned.
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