Young, low-mass stars in the solar neighborhood are vital for completing the mass function for nearby, young coeval groups, establishing a more complete census for evolutionary studies, and providing ...targets for direct-imaging exoplanet and/or disk studies. We present properties derived from high-resolution optical spectra for 336 candidate young nearby, low-mass stars. These include measurements of radial velocities and age diagnostics such as H and Li λ6707 equivalent widths. Combining our radial velocities with astrometry from Gaia DR2, we provide full 3D kinematics for the entire sample. We combine the measured spectroscopic youth information with additional age diagnostics (e.g., X-ray and UV fluxes, color-magnitude diagram positions) and kinematics to evaluate potential membership in nearby, young moving groups and associations. We identify 77 objects in our sample as bona fide members of 10 different moving groups, 14 of which are completely new members or have had their group membership reassigned. We also reject 44 previously proposed candidate moving group members. Furthermore, we have newly identified or confirmed the youth of numerous additional stars that do not belong to any currently known group and find 69 comoving systems using Gaia DR2 astrometry. We also find evidence that the Carina association is younger than previously thought, with an age similar to the β Pictoris moving group (∼22 Myr).
We acquired high-resolution infrared spectra of CI Tau, the host star of one of the few young planet candidates amenable to direct spectroscopic detection. We confirm the planet's existence with a ...direct detection of CO in the planet's atmosphere. We also calculate a mass of 11.6 MJ based on the amplitude of its radial velocity variations. We estimate its flux contrast with its host star to get an absolute magnitude estimate for the planet of 8.17 in the K-band. This magnitude implies the planet formed via a "hot start" formation mechanism. This makes CI Tau b the youngest confirmed exoplanet as well as the first exoplanet around a T Tauri star with a directly determined, model-independent dynamical mass.
Abstract
TRAPPIST-1 is a nearby system of seven Earth-sized, temperate, rocky exoplanets transiting a Jupiter-sized M8.5V star, ideally suited for in-depth atmospheric studies. Each TRAPPIST-1 planet ...has been observed in transmission both from space and from the ground, confidently rejecting cloud-free, hydrogen-rich atmospheres. Secondary eclipse observations of TRAPPIST-1 b with JWST/MIRI are consistent with little to no atmosphere given the lack of heat redistribution. Here we present the first transmission spectra of TRAPPIST-1 b obtained with JWST/NIRISS over two visits. The two transmission spectra show moderate to strong evidence of contamination from unocculted stellar heterogeneities, which dominates the signal in both visits. The transmission spectrum of the first visit is consistent with unocculted starspots and the second visit exhibits signatures of unocculted faculae. Fitting the stellar contamination and planetary atmosphere either sequentially or simultaneously, we confirm the absence of cloud-free, hydrogen-rich atmospheres, but cannot assess the presence of secondary atmospheres. We find that the uncertainties associated with the lack of stellar model fidelity are one order of magnitude above the observation precision of 89 ppm (combining the two visits). Without affecting the conclusion regarding the atmosphere of TRAPPIST-1 b, this highlights an important caveat for future explorations, which calls for additional observations to characterize stellar heterogeneities empirically and/or theoretical works to improve model fidelity for such cool stars. This need is all the more justified as stellar contamination can affect the search for atmospheres around the outer, cooler TRAPPIST-1 planets for which transmission spectroscopy is currently the most efficient technique.
Abstract
Terrestrial exoplanets orbiting M-dwarf stars are promising targets for transmission spectroscopy with existing or near-future instrumentation. The atmospheric composition of such rocky ...planets remains an open question, especially given the high X-ray and ultraviolet flux from their host M dwarfs that can drive atmospheric escape. The 1.3
R
⊕
exoplanet GJ 486b (
T
eq
∼ 700 K), orbiting an M3.5 star, is expected to have one of the strongest transmission spectroscopy signals among known terrestrial exoplanets. We observed three transits of GJ 486b using three different high-resolution spectrographs: IRD on Subaru, IGRINS on Gemini-South, and SPIRou on the Canada–France–Hawai’i Telescope. We searched for atmospheric absorption from a wide variety of molecular species via the cross-correlation method, but did not detect any robust atmospheric signals. Nevertheless, our observations are sufficiently sensitive to rule out several clear atmospheric scenarios via injection and recovery tests, and extend comparative exoplanetology into the terrestrial regime. Our results suggest that GJ 486b does not possess a clear H
2
/He-dominated atmosphere, nor a clear 100% water-vapor atmosphere. Other secondary atmospheres with high mean molecular weights or H
2
/He-dominated atmospheres with clouds remain possible. Our findings provide further evidence suggesting that terrestrial planets orbiting M-dwarf stars may experience significant atmospheric loss.
Abstract
We present the first analysis of JWST near-infrared spectroscopy of stellar flares from TRAPPIST-1 during transits of rocky exoplanets. Four flares were observed from 0.6–2.8
μ
m with the ...Near Infrared Imager and Slitless Spectrograph and 0.6–3.5
μ
m with the Near Infrared Spectrograph during transits of TRAPPIST-1b, f, and g. We discover P
α
and Br
β
line emission and characterize flare continuum at wavelengths from 1–3.5
μ
m for the first time. Observed lines include H
α
, P
α
–P
ϵ
, Br
β
, He
i
λ
0.7062
μ
m, two Ca
ii
infrared triplet (IRT) lines, and the He
i
IRT. We observe a reversed Paschen decrement from P
α
–P
γ
alongside changes in the light-curve shapes of these lines. The continuum of all four flares is well described by blackbody emission with an effective temperature below 5300 K, lower than the temperatures typically observed at optical wavelengths. The 0.6–1
μ
m spectra were convolved with the Transiting Exoplanet Survey Satellite (TESS) response, enabling us to measure the flare rate of TRAPPIST-1 in the TESS bandpass. We find flares of 10
30
erg, large enough to impact transit spectra occur at a rate of
3.6
−
1.3
+
2.1
flare day
−1
, ∼10× higher than previous predictions from K2. We measure the amount of flare contamination at 2
μ
m for the TRAPPIST-1b and f transits to be 500 ± 450 and 2100 ± 400 ppm, respectively. We find up to 80% of flare contamination can be removed, with mitigation most effective from 1.0–2.4
μ
m. These results suggest transits affected by flares may still be useful for atmospheric characterization efforts.
Abstract
Recent observations of the ultra-hot Jupiter WASP-76b have revealed a diversity of atmospheric species. Here we present new high-resolution transit spectroscopy of WASP-76b with GRACES at ...the Gemini North Observatory, serving as a baseline for the Large and Long Program “Exploring the Diversity of Exoplanet Atmospheres at High Spectral Resolution” (Exoplanets with Gemini Spectroscopy, or ExoGemS for short). With a broad spectral range of 400–1050 nm, these observations allow us to search for a suite of atomic species. We recover absorption features due to neutral sodium (Na
i
), and report a new detection of the ionized calcium (Ca
ii
) triplet at ∼850 nm in the atmosphere of WASP-76b, complementing a previous detection of the Ca
ii
H and K lines. The triplet has line depths of 0.295% ± 0.034% at ∼849.2 nm, 0.574% ± 0.041% at ∼854.2 nm, and 0.454% ± 0.024% at ∼866.2 nm, corresponding to effective radii close to (but within) the planet’s Roche radius. These measured line depths are significantly larger than those predicted by model LTE and NLTE spectra obtained on the basis of a pressure–temperature profile computed assuming radiative equilibrium. The discrepancy suggests that the layers probed by our observations are either significantly hotter than predicted by radiative equilibrium and/or in a hydrodynamic state. Our results shed light on the exotic atmosphere of this ultra-hot world, and will inform future analyses from the ExoGemS survey.
Abstract
Exoplanet atmosphere studies are often enriched by synergies with brown dwarf analogs. However, many key molecules commonly seen in brown dwarfs have yet to be confirmed in exoplanet ...atmospheres. An important example is chromium hydride (CrH), which is often used to probe atmospheric temperatures and classify brown dwarfs into spectral types. Recently, tentative evidence for CrH was reported in the low-resolution transmission spectrum of the hot Jupiter WASP-31b. Here, we present high spectral resolution observations of WASP-31b’s transmission spectrum from GRACES/Gemini North and UVES/Very Large Telescope. We detect CrH at 5.6
σ
confidence, representing the first metal hydride detection in an exoplanet atmosphere at high spectral resolution. Our findings constitute a critical step in understanding the role of metal hydrides in exoplanet atmospheres.
Abstract
We present high-resolution transmission spectroscopy of WASP-76b with Gemini Remote Access to CFHT ESPaDOnS Spectrograph (GRACES)/Gemini North obtained as part of the ExoGemS survey. With a ...broad spectral range of 400–1050 nm and a relatively high resolution of ∼66,000, these observations are particularly well suited to searching for atomic and molecular atmospheric species via the Doppler cross-correlation technique. We recover absorption features due to neutral iron (Fe
i
), sodium (Na
i
), and ionized calcium (Ca
ii
) at high significance (>5
σ
), and investigate possible atmospheric temperatures and wind speeds. We also report tentative (>3
σ
) detections of Li
i
, K
i
, Cr
i
, and V
i
in the atmosphere of WASP-76b. Finally, we report nondetections of a number of other species, some of which have previously been detected with other instruments. Through model injection/recovery tests, we demonstrate that many of these species are not expected to be detected in our observations. These results allow us to place GRACES and the ExoGemS survey in context with other high-resolution optical spectrographs.
Abstract The signal from a transiting planet can be diluted by astrophysical contamination. In the case of circumstellar debris disks, this contamination could start in the mid-infrared and vary as a ...function of wavelength, which would then change the observed transmission spectrum for any planet in the system. The MIRI/Low Resolution Spectrometer WASP-39b transmission spectrum shows an unexplained dip starting at ∼10 μ m that could be caused by astrophysical contamination. The spectral energy distribution displays excess flux at similar levels to that which are needed to create the dip in the transmission spectrum. In this Letter, we show that this dip is consistent with the presence of a bright circumstellar debris disk, at a distance of >2 au. We discuss how a circumstellar debris disk like that could affect the atmosphere of WASP-39b. We also show that even faint debris disks can be a source of contamination in MIRI exoplanet spectra.
Abstract The hot Neptune desert is one of the most sparsely populated regions of the exoplanet parameter space, and atmosphere observations of its few residents can provide insights into how such ...planets have managed to survive in such an inhospitable environment. Here, we present transmission observations of LTT 9779 b, the only known hot Neptune to have retained a significant H/He-dominated atmosphere, taken with JWST NIRISS/SOSS. The 0.6–2.85 μ m transmission spectrum shows evidence for muted spectral features, rejecting a perfectly flat line at >5 σ . We explore water- and methane-dominated atmosphere scenarios for LTT 9779 b’s terminator, and retrieval analyses reveal a continuum of potential combinations of metallicity and cloudiness. Through comparisons to previous population synthesis works and our own interior structure modeling, we are able to constrain LTT 9779 b’s atmosphere metallicity to 20–850× solar. Within this range of metallicity, our retrieval analyses prefer solutions with clouds at millibar pressures, regardless of whether the atmosphere is water or methane dominated—though cloud-free atmospheres with metallicities >500× solar cannot be entirely ruled out. By comparing self-consistent atmosphere temperature profiles with cloud condensation curves, we find that silicate clouds can readily condense in the terminator region of LTT 9779 b. Advection of these clouds onto the dayside could explain the high dayside albedo previously inferred for this planet and be part of a feedback loop aiding the survival of LTT 9779 b’s atmosphere in the hot Neptune desert.
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