Search

One of the primary goals of exoplanet science has been to precisely measure the abundances of key species in and metallicities of exoplanet atmospheres to gain information on their formation conditions. This information has generally been limited in the past by the low resolution and narrow wavelength coverage of space-based observatories such as the Hubble and Spitzer Space Telescopes. Recently, the method of high-resolution cross-correlation analysis has emerged as an alternative way to precisely measure the abundances of a variety of species in exoplanet atmospheres using ground-based telescopes. Here we present the first results from a large program to measure high-resolution transmission spectra of 11 giant exoplanets using the IGRINS instrument on Gemini-S. We describe the goals of this ongoing program and show results from a high-resolution transit of the ultra-hot Jupiter WASP-76b. We present measurements of the abundances of key molecules, including water, CO, FeH, and OH, in the atmosphere of WASP-76b and use these measurements to precisely constrain its overall metallicity and C/O ratio.

We report measurements of the sky-projected spin-orbit angle for AU\,Mic\,b, a Neptune-size planet orbiting a very young ($\sim20$\,Myr) nearby pre-main sequence M dwarf star which also hosts a bright, edge-on, debris disk. The planet was recently discovered from preliminary analysis of radial velocity observations and confirmed to be transiting its host star from photometric data from the NASA's \textit{TESS} mission. We obtained radial velocity measurements of AU\,Mic over the course of two partially observable transits and one full transit of planet b from high-resolution spectroscopic observations made with the {\textsc{Minerva}}-Australis telescope array. Only a marginal detection of the Rossiter--McLaughlin effect signal was obtained from the radial velocities, in part due to AU Mic being an extremely active star and the lack of full transit coverage plus sufficient out-of-transit baseline. As such, a precise determination of the obliquity for AU\,Mic\,b is not possible in this study and we find a sky-projected spin-orbit angle of $\lambda = 47{^{+26}_{-54}}^{\circ}$. This result is consistent with both the planet's orbit being aligned or highly misaligned with the spin-axis of its host star. Our measurement independently agrees with, but is far less precise than observations carried out on other instruments around the same time that measure a low obliquity orbit for the planet. AU\,Mic is the youngest exoplanetary system for which the projected spin-orbit angle has been measured, making it a key data point in the study of the formation and migration of exoplanets -- particularly given that the system is also host to a bright debris disk., Comment: 15 pages, 6 figures, 3 tables. Published in the Astronomical Journal on 10/09/2021

AU Microscopii (AU Mic) is the second closest pre-main-sequence star, at a distance of 9.79 parsecs and with an age of 22 million years. AU Mic possesses a relatively rare and spatially resolved edge-on debris disk extending from about 35 to 210 astronomical units from the star4, and with clumps exhibiting non-Keplerian motion. Detection of newly formed planets around such a star is challenged by the presence of spots, plage, flares and other manifestations of magnetic ‘activity’ on the star. Here we report observations of a planet transiting AU Mic. The transiting planet, AU Mic b, has an orbital period of 8.46 days, an orbital distance of 0.07 astronomical units, a radius of 0.4 Jupiter radii, and a mass of less than 0.18 Jupiter masses at 3σ confidence. Our observations of a planet co-existing with a debris disk offer the opportunity to test the predictions of current models of planet formation and evolution.

The Habitable Exoplanet Observatory, or HabEx, has been designed to be the Great Observatory of the 2030s. For the first time in human history, technologies have matured sufficiently to enable an affordable space-based telescope mission capable of discovering and characterizing Earthlike planets orbiting nearby bright sunlike stars in order to search for signs of habitability and biosignatures. Such a mission can also be equipped with instrumentation that will enable broad and exciting general astrophysics and planetary science not possible from current or planned facilities. HabEx is a space telescope with unique imaging and multi-object spectroscopic capabilities at wavelengths ranging from ultraviolet (UV) to near-IR. These capabilities allow for a broad suite of compelling science that cuts across the entire NASA astrophysics portfolio. HabEx has three primary science goals: (1) Seek out nearby worlds and explore their habitability; (2) Map out nearby planetary systems and understand the diversity of the worlds they contain; (3) Enable new explorations of astrophysical systems from our own solar system to external galaxies by extending our reach in the UV through near-IR. This Great Observatory science will be selected through a competed GO program, and will account for about 50% of the HabEx primary mission. The preferred HabEx architecture is a 4m, monolithic, off-axis telescope that is diffraction-limited at 0.4 microns and is in an L2 orbit. HabEx employs two starlight suppression systems: a coronagraph and a starshade, each with their own dedicated instrument., Comment: Full report: 498 pages. Executive Summary: 14 pages. More information about HabEx can be found here: https://www.jpl.nasa.gov/habex/

HISPEC (High-resolution Infrared Spectrograph for Exoplanet Characterization) is a proposed diffraction-limited spectrograph for the W.M. Keck Observatory, and a pathfinder for the MODHIS facility project (Multi-Object Diffraction-limited High-resolution Infrared Spectrograph) on the Thirty Meter Telescope. HISPEC/MODHIS builds on diffraction-limited spectrograph designs which rely on adaptively corrected single-mode fiber feeds. Seeing-limited high-resolution spectrographs, by virtue of the conservation of beam etendue, grow in volume following a D^3 power law (D is the telescope diameter), and are subject to daunting challenges associated with their large size. Diffraction-limited spectrographs fed by single mode fibers are decoupled from the telescope input, and are orders of magnitude more compact and have intrinsically stable line spread functions. Their efficiency is directly proportional to the performance of the adaptive optics (AO) system. AO technologies have matured rapidly over the past two decades and are baselined for future extremely large telescopes. HISPEC/MODHIS will take R>100,000 spectra of a few objects in a 10" field-of-view sampled at the diffraction limit (~10-50 mas), simultaneously from 0.95 to 2.4 microns (y-K). The scientific scope ranges from exoplanet infrared precision radial velocities, spectroscopy of transiting, close-in, and directly imaged exoplanets (atmospheric composition and dynamics, RM effect, spin measurements, Doppler imaging), brown dwarf characterization, stellar physics/chemistry, proto-planetary disk kinematics/composition, Solar system, extragalactic science, and cosmology. HISPEC/MODHIS features a compact, cost-effective design optimized to fully exploit the existing Keck-AO and future TMT-NFIRAOS infrastructures and boost the scientific reach of Keck Observatory and TMT soon after first light.

High resolution spectroscopy of the lowest-mass stars and brown dwarfs reveals their origins, multiplicity, compositions and physical properties, with implications for the star formation and chemical evolution history of the Milky Way. We motivate the need for high-resolution, infrared spectroscopic surveys to reach these faint sources., 9 pages, submitted to Astro2020 Science White Paper Call

There is currently a gap in our understanding of wide-orbit planets, which must be filled if we are to understand planet formation and exoplanet habitability. We summarize current and planned exoplanet detection programs using a variety of methods: microlensing (including WFIRST), radial velocities, Gaia astrometry, and direct imaging.

The lowest-mass stars, brown dwarfs and giant exoplanets span a minimum in the mass-radius relationship that probes the fundamental physics of extreme states of matter, magnetism, and fusion. This White Paper outlines scientific opportunities and the necessary resources for modeling and measuring the mass-radius relationship in this regime., Comment: 7 pages, submitted to Astro2020 Science White Paper call

We present a possible NASA key project using the iSHELL near-infrared high-resolution echelle spectrograph on the NASA Infrared Telescope Facility for precise radial velocity follow-up of candidate transiting exoplanets identified by the NASA TESS mission. We briefly review key motivations and challenges with near-infrared radial velocities. We present the current status of our preliminary radial velocity analysis from the first year on sky with iSHELL., Comment: White Paper submitted to the SSB

We investigate the possibility of constraining the sin i degeneracy of α Cen B b—with orbital period P = 3.24 days; a = 0.042 AU; m sin i = 1.1 M_⊕—to estimate the true mass of the newly reported terrestrial exoplanet in the nearest stellar system to our Sun. We present detailed numerical simulations of the dynamical stability of the exoplanet in the α Cen AB binary system for a range of initial inclinations, eccentricities, and semimajor axes. The system represents a benchmark case for the interplay of the Kozai mechanism with general relativistic and tidal forces. From our simulations, there is only a small boundary in initial inclinations and initial semimajor axes which result in the migration via the Kozai mechanism of α Cen B b to its present location. Inside this boundary, the planet orbit is stable for up to 1 Gyr against the Kozai mechanism, and outside this boundary the planet collides with α Cen B or is ejected. In our three simulations where the planet migrates in toward the star via the Kozai mechanism, the final inclination is 46°–53° relative to the AB orbital plane, lower than the initial inclination of 75° in each case. We discuss inclination constraints from the formation of α Cen B b in situ at its present location, migration in a proto-planetary disk, or migration in resonance with additional planets. We conclude that α Cen B b probably has a mass of less than 2.7 M_⊕, implying a likely terrestrial composition warranting future confirmation.

With the loss of two reaction wheels, the period of Kepler's ultra-high precision photometric performance is at an end. Yet Kepler retains unique capabilities impossible to replicate from the ground or with existing or future space missions. This White Paper calls for the use of Kepler to conduct a survey in the ecliptic plane to search for planet transits around stars at high galactic latitudes and to study star forming regions to investigate physics of very young stars not studied by Kepler in its prime mission. Even with reduced photometric precision, Kepler's 1 m aperture will enable it to survey faint M stars to find ice giants and Super Earths in Habitable Zone orbits.

Variability is a defining characteristic of young stellar systems, and optical variability has been heavily studied to select and characterize the photospheric properties of young stars. In recent years, multi-epoch observations sampling a wider range of wavelengths and time-scales have revealed a wealth of time-variable phenomena at work during the star formation process. This splinter session was convened to summarize recent progress in providing improved coverage and understanding of time-variable processes in young stars and circumstellar disks. We begin by summarizing results from several multi-epoch Spitzer campaigns, which have demonstrated that many young stellar objects evidence significant mid-IR variability. While some of these variations can be attributed to processes in the stellar photosphere, others appear to trace short time-scale changes in the circumstellar disk which can be successfully modeled with axisymmetric or non-axisymmetric structures. We also review recent studies probing variability at shorter wavelengths that provide evidence for high frequency pulsations associated with accretion outbursts, correlated optical/X-ray variability in Classical T Tauri stars, and magnetic reversals in young solar analogs., Comment: 4 figures, 13 pages in ASP format; to be published in the proceedings of the Cool Stars 16 Workshop

We describe Spitzer IRAC and MIPS observations of the nearby 25 Myr old open cluster NGC 2232. Combining these data with ROSAT All-Sky Survey observations, proper motions, and optical photometry/spectroscopy, we construct a list of highly probable cluster members. We identify one A-type star, HD 45435, that has definite excess emission at 4.5-24 μm indicative of debris from terrestrial planet formation. We also identify 2-4 late-type stars with possible 8 μm excesses and 8 early-type stars with definite 24 μm excesses. Constraints on the dust luminosity and temperature suggest that the detected excesses are produced by debris disks. From our sample of B and A stars, stellar rotation appears to be correlated with 24 μm excess, a result that would be expected if massive primordial disks evolve into massive debris disks. To explore the evolution of the frequency and magnitude of debris around A-type stars, we combine our results with data for other young clusters. The frequency of debris disks around A-type stars appears to increase from ~25% at 5 Myr to ~50%-60% at 20-25 Myr. Older A-type stars have smaller debris disk frequencies: ~20% at 50-100 Myr. For these ages, the typical level of debris emission increases from 5 to 20 Myr and then declines. Because 24 μm dust emission probes icy planet formation around A-type stars, our results suggest that the frequency of icy planet formation is ηi ≳ 0.5-0.6. Thus, most A-type stars (≈1.5-3 M☉) produce icy planets.

Measuring the mean densities of close-in planets orbiting pre-main-sequence (PMS) stars is crucially needed by planet formation and evolution models. However, PMS stars exhibit intense magnetic activity inducing fluctuations in both photometric and RV curves that overshadow planet signatures. As a result, no close-in planet younger than 25 Myr has a well-constrained bulk density. In this study, we present a spectropolarimetric and velocimetric analysis of 27 near-infrared observations of the nearby active 22 Myr-old red dwarf AU Microscopii collected with SPIRou at the end of the year 2019. We jointly model the planet and stellar activity RV components, resulting in a 3.9σσ-detection of the recently-discovered close-in Neptune-sized planet AU Mic b, with an estimated mass of 17.1+4.7−4.5−4.5+4.7 M⊕⊕, implying a Neptune-like density for the planet. A consistent detection of the planet is independently obtained by simultaneously reconstructing the surface distribution of bright and dark inhomogeneities and estimating the planet parameters using Doppler imaging (DI). Using Zeeman-Doppler Imaging, we invert our time-series of intensity and circularly-polarized line profiles into distributions of brightness and large-scale magnetic field at the surface of the star and explore how these distributions are sheared by latitudinal differential rotation. Finally, we investigate the magnetic activity of AU Mic by computing various indicators and found that the disk-integrated magnetic flux density correlates best with the stellar activity RV signal, in line with recent solar observations., See the associated poster and punlication in MNRAS: https://ui.adsabs.harvard.edu/abs/2021MNRAS.502..188K/abstract