ABSTRACT
We investigate the potential for the James Webb Space Telescope (JWST) to detect and characterize the atmospheres of the sub-Neptunian exoplanets in the TOI-270 system. Sub-Neptunes are ...considered more likely to be water worlds than gas dwarfs. We model their atmospheres using three atmospheric compositions – two examples of hydrogen-dominated atmospheres and a water-dominated atmosphere. We then simulate the infrared transmission spectra of these atmospheres for JWST instrument modes optimized for transit observation of exoplanet atmospheres: NIRISS, NIRSpec, and MIRI. We then predict the observability of each exoplanet’s atmosphere. TOI-270c and d are excellent targets for detecting atmospheres with JWST transmission spectroscopy, requiring only 1 transit observation with NIRISS, NIRSpec, and MIRI; higher signal-to-noise ratio can be obtained for a clear H-rich atmosphere. Fewer than three transits with NIRISS and NIRSpec may be enough to reveal molecular features. Water-dominated atmospheres require more transits. Water spectral features in water-dominated atmospheres may be detectable with NIRISS in two or three transits. We find that the detection of spectral features in a cloudy, H-rich atmosphere does not require integrations as long as those required for the water-dominated atmosphere, which is consistent with the differences in atmospheric mean molecular weight. TOI-270c and d could be prime targets for JWST transit observations of sub-Neptune atmospheres. These results provide useful predictions for observers who may propose to use JWST to detect and characterize the TOI-270 planet atmospheres.
ABSTRACT
Stellar magnetic activity produces time-varying distortions in the photospheric line profiles of solar-type stars. These lead to systematic errors in high-precision radial-velocity ...measurements, which limit efforts to discover and measure the masses of low-mass exoplanets with orbital periods of more than a few tens of days. We present a new data-driven method for separating Doppler shifts of dynamical origin from apparent velocity variations arising from variability-induced changes in the stellar spectrum. We show that the autocorrelation function (ACF) of the cross-correlation function used to measure radial velocities is effectively invariant to translation. By projecting the radial velocities on to a subspace labelled by the observation identifiers and spanned by the amplitude coefficients of the ACF’s principal components, we can isolate and subtract velocity perturbations caused by stellar magnetic activity. We test the method on a 5-yr time sequence of 853 daily 15-min observations of the solar spectrum from the HARPS-N instrument and solar-telescope feed on the 3.58-m Telescopio Nazionale Galileo. After removal of the activity signals, the heliocentric solar velocity residuals are found to be Gaussian and nearly uncorrelated. We inject synthetic low-mass planet signals with amplitude K = 40 cm s−1 into the solar observations at a wide range of orbital periods. Projection into the orthogonal complement of the ACF subspace isolates these signals effectively from solar activity signals. Their semi-amplitudes are recovered with a precision of ∼ 6.6 cm s−1, opening the door to Doppler detection and characterization of terrestrial-mass planets around well-observed, bright main-sequence stars across a wide range of orbital periods.
ABSTRACT
In this paper, we compare the chemistry and the emission spectra of nitrogen-dominated cool, warm, and hot ultra-short-period (USP) super-Earth atmospheres in and out of chemical equilibrium ...at various surface pressure scenarios ranging from 10−1 to 10 bar. We link the one-dimensional vulcan chemical kinetic code, in which thermochemical kinetic and vertical transport and photochemistry are taken into account, to the one-dimensional radiative transfer model, petitradtrans, to predict the emission spectra of these planets. The radiative–convective temperature–pressure profiles were computed with the helios code. Then, using pandexo noise simulator, we explore the observability of the differences produced by disequilibrium processes with the JWST. Our grids show how different surface pressures can significantly affect the temperature profiles, the atmospheric abundances, and consequently the emission spectra of these planets. We find that the divergences due to disequilibrium processes would be possible to observe in cooler planets by targeting HCN, C2H4, and CO, and in warmer planets by targeting CH4 with HCN, using the NIRSpec and MIRI LRS JWST instruments. These species are also found to be sensitive indicators of the existence of surfaces on nitrogen-dominated USP super-Earths, providing information regarding the thickness of these atmospheres.
We present the first direct distance determination to a detached eclipsing binary in M33, which was found by the DIRECT Project. Located in the OB 66 association at coordinates (a, d) = (01 ...super(h)33 super(m)46."17, + 3044'39."9) for J2000.0, it was one of the most suitable detached eclipsing binaries found by DIRECT for distance determination, given its apparent magnitude and orbital period. We obtained follow-up BV time-series photometry, JHK sub(s) photometry, and optical spectroscopy from which we determined the parameters of the system. It contains two O7 main-sequence stars, with masses of 33.4 c 3.5 and 30.0 c 3.3 M and radii of 12.3 c 0.4 and 8.8 c 0.3 R , respectively. We derive temperatures of 37,000 c 1500 and 35,600 c 1500 K. Using BVR.JHK sub(s) photometry for the flux calibration, we obtain a distance modulus of 24.92 c 0.12 mag (964 c 54 kpc), which is 60.3 mag longer than the Key Project distance to M33. We discuss the implications of our result and the importance of establishing M33 as an independent rung on the cosmological distance ladder.
We report on observations of a gamma-ray burst (GRB 061126) with an extremely bright (R approximately 12 mag at peak) early-time optical afterglow. The optical afterglow is already fading as a power ...law 22 s after the trigger, with no detectable prompt contribution in our first exposure, which was coincident with a large prompt-emission gamma-ray pulse. The optical-infrared photometric SED is an excellent fit to a power law, but it exhibits a moderate red-to-blue evolution in the spectral index at about 500 s after the burst. This color change is contemporaneous with a switch from a relatively fast decay to slower decay. The rapidly decaying early afterglow is broadly consistent with synchrotron emission from a reverse shock, but a bright forward-shock component predicted by the intermediate- to late-time X-ray observations under the assumptions of standard afterglow models is not observed. Indeed, despite its remarkable early-time brightness, this burst would qualify as a dark burst at later times on the basis of its nearly flat optical-to-X-ray spectral index. Our photometric SED provides no evidence of host galaxy extinction, requiring either large quantities of gray dust in the host system (at redshift 1.1588 plus or minus 0.0006, based on our late-time Keck spectroscopy) or separate physical origins for the X-ray and optical afterglows.
We report the discovery and initial characterization of Qatar-1b, a hot Jupiter-orbiting metal-rich K dwarf star, the first planet discovered by the Qatar Exoplanet Survey. We describe the strategy ...used to select candidate transiting planets from photometry generated by the Qatar Exoplanet Survey camera array. We examine the rate of astrophysical and other false positives found during the spectroscopic reconnaissance of the initial batch of candidates. A simultaneous fit to the follow-up radial velocities and photometry of Qatar-1b yields a planetary mass of 1.09 ± 0.08 M
J and a radius of 1.16 ± 0.05 R
J. The orbital period and separation are 1.420 033 ± 0.000 016 d and 0.023 43 ± 0.000 26 au for an orbit assumed to be circular. The stellar density, effective temperature and rotation rate indicate an age greater than 4 Gyr for the system.
We report the discovery of HAT-P-25b, a transiting extrasolar planet orbiting the V = 13.19 G5 dwarf star GSC 1788-01237, with a period P = 3.652836 + or - 0.000019 days, transit epoch Tc = ...2455176.85173 + or - 0.00047 (BJD-barycentric Julian dates throughout the paper are calculated from Coordinated Universal Time, UTC), and transit duration 0.1174 + or - 0.0017 days. The host star has amass of 1.01 + or - 0.03 M radius of (ProQuest: Formulae and/or non-USASCII text omitted) R effective temperature 5500 + or - 80 K, and metallicity Fe/H = +0.31 + or - 0.08. The planetary companion has a mass of 0.567 + or - 0.022 M sub(J) and radius of (ProQuest: Formulae and/or non-USASCII text omitted) R sub(J) yielding a mean density of 0.42 + or - 0.07 g cm super(-3).
We have undertaken a long-term project, Planets in Stellar Clusters Extensive Search (PISCES), to search for transiting planets in open clusters. In this paper we present the results for NGC 6791, a ...very old, populous, metal-rich cluster. We have monitored the cluster for over 300 hr, spread over 84 nights. We have not detected any good transiting planet candidates. Given the photometric precision and temporal coverage of our observations and the current best estimates for the frequency and radii of short-period planets, the expected number of detectable transiting planets in our sample is 1.5. We have discovered 14 new variable stars in the cluster, most of which are eclipsing binaries, and present high-precision light curves spanning 2 years for these new variables and also the previously known variables.
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