The JWST NIRSpec integral field unit (IFU) presents a unique opportunity to observe directly imaged exoplanets from 3-5 um at moderate spectral resolution (R~2,700) and thereby better constrain the ...composition, disequilibrium chemistry, and cloud properties of their atmospheres. In this work, we present the first NIRSpec IFU high-contrast observations of a substellar companion that requires starlight suppression techniques. We develop specific data reduction strategies to study faint companions around bright stars, and assess the performance of NIRSpec at high contrast. First, we demonstrate an approach to forward model the companion signal and the starlight directly in the detector images, which mitigates the effects of NIRSpec's spatial undersampling. We demonstrate a sensitivity to planets that are 3e-6 fainter than their stars at 1'', or 3e-5 at 0.3''. Then, we implement a reference star point spread function (PSF) subtraction and a spectral extraction that does not require spatially and spectrally regularly sampled spectral cubes. This allows us to extract a moderate resolution (R~2,700) spectrum of the faint T-dwarf companion HD 19467 B from 2.9-5.2 um with signal-to-noise ratio (S/N)~10 per resolution element. Across this wavelength range, HD~19467~B has a flux ratio varying between 1e-5-1e-4 and a separation relative to its star of 1.6''. A companion paper by Hoch et al. more deeply analyzes the atmospheric properties of this companion based on the extracted spectrum. Using the methods developed here, NIRSpec's sensitivity may enable direct detection and spectral characterization of relatively old (~1 Gyr), cool (~250 K), and closely separated (~3-5 au) exoplanets that are less massive than Jupiter.
We present the results of a medium resolution optical spectroscopic survey of 92 cool (\(3,000 \lesssim T_{\rm eff} \lesssim 4,500\,\)K) southern TESS candidate planet hosts, and describe our ...spectral fitting methodology used to recover stellar parameters. We quantify model deficiencies at predicting optical fluxes, and while our technique works well for \(T_{\rm eff}\), further improvements are needed for Fe/H. To this end, we developed an updated photometric Fe/H calibration for isolated main sequence stars built upon a calibration sample of 69 cool dwarfs in binary systems, precise to \(\pm0.19\,\)dex, from super-solar to metal poor, over \(1.51 < {\rm Gaia}~(B_P-R_P) < 3.3\). Our fitted \(T_{\rm eff}\) and \(R_\star\) have median precisions of 0.8% and 1.7%, respectively and are consistent with our sample of standard stars. We use these to model the transit light curves and determine exoplanet radii for 100 candidate planets to 3.5% precision and see evidence that the planet-radius gap is also present for cool dwarfs. Our results are consistent with the sample of confirmed TESS planets, with this survey representing one of the largest uniform analyses of cool TESS candidate planet hosts to date.
Biosignature detection in the atmospheres of Earth-like exoplanets is one of the most significant and ambitious goals for astronomy, astrobiology, and humanity. Molecular oxygen is among the ...strongest indicators of life on Earth, but it will be extremely difficult to detect via transmission spectroscopy. We used the Bioverse statistical framework to assess the ability to probe Earth-like O\(_{\mathrm{2}}\) levels on hypothetical nearby habitable zone exoplanets (EECs) using direct imaging and high-resolution spectroscopy on the Giant Magellan Telescope (GMT) and the Extremely Large Telescope (ELT). We found that O\(_{\mathrm{2}}\) could be probed on up to \(\sim\)5 and \(\sim\)15 EECs orbiting bright M dwarfs within 20 pc in a 10-year survey on the GMT and ELT, respectively. Earth-like O\(_{\mathrm{2}}\) levels could be probed on four known super-Earth candidates, including Proxima Centauri b, within about one week on the ELT and a few months on the GMT. We also assessed the ability of the ELT to test the habitable zone oxygen hypothesis \(\unicode{x2013}\) that habitable zone Earth-sized planets are more likely to have O\(_{\mathrm{2}}\) \(\unicode{x2013}\) within a 10-year survey using Bioverse. Testing this hypothesis requires either \(\sim\)1/2 of the EECs to have O\(_{\mathrm{2}}\) or \(\sim\)1/3 if \(\eta_{\oplus}\) is large. A northern hemisphere large-aperture telescope, such as the Thirty Meter Telescope (TMT), would expand the target star pool by about 25%, reduce the time to probe biosignatures on individual targets, and provide an additional independent check on potential biosignature detections.
The Large Interferometer For Exoplanets (LIFE) initiative is developing the science and a technology roadmap for an ambitious space mission featuring a space-based mid-infrared (MIR) nulling ...interferometer in order to detect the thermal emission of hundreds of exoplanets and characterize their atmospheres. In order to quantify the science potential of such a mission, in particular in the context of technical trade-offs, an instrument simulator is required. In addition, signal extraction algorithms are needed to verify that exoplanet properties (e.g., angular separation, spectral flux) contained in simulated exoplanet datasets can be accurately retrieved. We present LIFEsim, a software tool developed for simulating observations of exoplanetary systems with an MIR space-based nulling interferometer. It includes astrophysical noise sources (i.e., stellar leakage and thermal emission from local zodiacal and exo-zodiacal dust) and offers the flexibility to include instrumental noise terms in the future. LIFEsim provides an accessible way for predicting the expected SNR of future observations as a function of various key instrument and target parameters. The SNRs of the extracted spectra are photon-noise dominated, as expected from our current simulations. From single epoch observations in our mock survey of small (\(R < 1.5 R_\mathrm{Earth}\)) planets orbiting within the habitable zones of their stars, we find that typical uncertainties in the estimated effective temperature of the exoplanets are \(\lesssim\)10%, for the exoplanet radius \(\lesssim\)20%, and for the separation from the host star \(\lesssim\)2%. SNR values obtained in the signal extraction process deviate less than 10% from purely photon-counting statistics based SNRs. (abridged)
Kernel-phase is a data analysis method based on a generalization of the notion of closure-phase invented in the context of interferometry, but that applies to well corrected diffraction dominated ...images produced by an arbitrary aperture. The linear model upon which it relies theoretically leads to the formation of observable quantities robust against residual aberrations. In practice, detection limits reported thus far seem to be dominated by systematic errors induced by calibration biases not sufficiently filtered out by the kernel projection operator. This paper focuses on the impact the initial modeling of the aperture has on these errors and introduces a strategy to mitigate them, using a more accurate aperture transmission model. The paper first uses idealized monochromatic simulations of a non trivial aperture to illustrate the impact modeling choices have on calibration errors. It then applies the outlined prescription to two distinct data-sets of images whose analysis has previously been published. The use of a transmission model to describe the aperture results in a significant improvement over the previous type of analysis. The thus reprocessed data-sets generally lead to more accurate results, less affected by systematic errors. As kernel-phase observing programs are becoming more ambitious, accuracy in the aperture description is becoming paramount to avoid situations where contrast detection limits are dominated by systematic errors. Prescriptions outlined in this paper will benefit any attempt at exploiting kernel-phase for high-contrast detection.
Kernel phase imaging (KPI) enables the direct detection of substellar companions and circumstellar dust close to and below the classical (Rayleigh) diffraction limit. We present a kernel phase ...analysis of JWST NIRISS full pupil images taken during the instrument commissioning and compare the performance to closely related NIRISS aperture masking interferometry (AMI) observations. For this purpose, we develop and make publicly available the custom "Kpi3Pipeline" enabling the extraction of kernel phase observables from JWST images. The extracted observables are saved into a new and versatile kernel phase FITS file (KPFITS) data exchange format. Furthermore, we present our new and publicly available "fouriever" toolkit which can be used to search for companions and derive detection limits from KPI, AMI, and long-baseline interferometry observations while accounting for correlated uncertainties in the model fitting process. Among the four KPI targets that were observed during NIRISS instrument commissioning, we discover a low-contrast (~1:5) close-in (~1 \(\lambda/D\)) companion candidate around CPD-66~562 and a new high-contrast (~1:170) detection separated by ~1.5 \(\lambda/D\) from 2MASS~J062802.01-663738.0. The 5-\(\sigma\) companion detection limits around the other two targets reach ~6.5 mag at ~200 mas and ~7 mag at ~400 mas. Comparing these limits to those obtained from the NIRISS AMI commissioning observations, we find that KPI and AMI perform similar in the same amount of observing time. Due to its 5.6 times higher throughput if compared to AMI, KPI is beneficial for observing faint targets and superior to AMI at separations >325 mas. At very small separations (<100 mas) and between ~250-325 mas, AMI slightly outperforms KPI which suffers from increased photon noise from the core and the first Airy ring of the point-spread function.
Directly imaging exoplanets is challenging because quasi-static phase aberrations in the pupil plane (speckles) can mimic the signal of a companion at small angular separations. Kernel phase, which ...is a generalization of closure phase (known from sparse aperture masking), is independent of pupil plane phase noise to second order and allows for a robust calibration of full pupil, extreme adaptive optics observations. We applied kernel phase combined with a principal component based calibration process to a suitable but not optimal, high cadence, pupil stabilized L' band (\(3.8~\mu\text{m}\)) data set from the ESO archive. We detect eight low-mass companions, five of which were previously unknown, and two have angular separations of \(\sim0.8\)-\(1.2~\lambda/D\) (i.e. \(\sim80\)-\(110~\text{mas}\)), demonstrating that kernel phase achieves a resolution below the classical diffraction limit of a telescope. While we reach a \(5\sigma\) contrast limit of \(\sim1/100\) at such angular separations, we demonstrate that an optimized observing strategy with more diversity of PSF references (e.g. star-hopping sequences) would have led to a better calibration and even better performance. As such, kernel phase is a promising technique for achieving the best possible resolution with future space-based telescopes (e.g. JWST), which are limited by the mirror size rather than atmospheric turbulence, and with a dedicated calibration process also for extreme adaptive optics facilities from the ground.
In the Gaia era, the majority of stars in the Solar neighbourhood have
parallaxes and proper motions precisely determined while spectroscopic age
indicators are still missing for a large fraction of ...low-mass young stars. In
this work we select 756 overluminous late K and early M young star candidates
in the southern sky and observe them over 64 nights with the ANU 2.3m Telescope
at Siding Spring Observatory using the Echelle (R=24,000) and Wide Field
spectrographs (WiFeS, R=3000-7000). Our selection is kinematically unbiased to
minimize the preference against low-mass members of stellar associations that
dissipate first, and to include potential members of diffuse components. We
provide measurements of H$\alpha$ and calcium H&K emission, as well as lithium
absorption line, that enable identification of stars as young as $\sim$10-30
Myr which is a typical age of a stellar association. We report on 346 stars
showing a detectable lithium line, 318 of which are not found in the known
catalogs of young stars. We also report 126 additional stars in our sample
which have no detectable lithium but signs of stellar activity indicating
youth. Radial velocities are determined for WiFeS spectra with a precision of
3.2 $\mathrm{km\;s^{-1}}$ and 1.5 $\mathrm{km\;s^{-1}}$ for the Echelle sample.
Clouds are prevalent in many of the exoplanet atmospheres that have been observed to date. For transiting exoplanets, we know if clouds are present because they mute spectral features and cause ...wavelength-dependent scattering. While the exact composition of these clouds is largely unknown, this information is vital to understanding the chemistry and energy budget of planetary atmospheres. In this work, we observe one transit of the hot Jupiter WASP-17b with JWST's MIRI LRS and generate a transmission spectrum from 5-12 \(\rm{\mu}\)m. These wavelengths allow us to probe absorption due to the vibrational modes of various predicted cloud species. Our transmission spectrum shows additional opacity centered at 8.6 \(\rm{\mu}\)m, and detailed atmospheric modeling and retrievals identify this feature as SiO\(_2\)(s) (quartz) clouds. The SiO\(_2\)(s) clouds model is preferred at 3.5-4.2\(\sigma\) versus a cloud-free model and at 2.6\(\sigma\) versus a generic aerosol prescription. We find the SiO\(_2\)(s) clouds are comprised of small \({\sim}0.01\) \(\rm{\mu}\)m particles, which extend to high altitudes in the atmosphere. The atmosphere also shows a depletion of H\(_2\)O, a finding consistent with the formation of high-temperature aerosols from oxygen-rich species. This work is part of a series of studies by our JWST Telescope Scientist Team (JWST-TST), in which we will use Guaranteed Time Observations to perform Deep Reconnaissance of Exoplanet Atmospheres through Multi-instrument Spectroscopy (DREAMS).
To reach its optimal performance, Fizeau interferometry requires that we work to resolve instrumental biases through calibration. One common technique used in high contrast imaging is angular ...differential imaging, which calibrates the point spread function and flux leakage using a rotation in the focal plane. Our aim is to experimentally demonstrate and validate the efficacy of an angular differential kernel-phase approach, a new method for self-calibrating interferometric observables that operates similarly to angular differential imaging, while retaining their statistical properties. We used linear algebra to construct new observables that evolve outside of the subspace spanned by static biases. On-sky observations of a binary star with the SCExAO instrument at the Subaru telescope were used to demonstrate the practicality of this technique. We used a classical approach on the same data to compare the effectiveness of this method. The proposed method shows smaller and more Gaussian residuals compared to classical calibration methods, while retaining compatibility with the statistical tools available. We also provide a measurement of the stability of the SCExAO instrument that is relevant to the application of the technique. Angular differential kernel phases provide a reliable method for calibrating biased observables. Although the sensitivity at small separations is reduced for small field rotations, the calibration is effectively improved and the number of subjective choices is reduced.
