42 research outputs found
Detectability of planetesimal impacts on giant exoplanets
The detectability of planetesimal impacts on imaged exoplanets can be measured using Jupiter during the 1994 comet Shoemaker-Levy 9 events as a proxy. By integrating the whole planet flux with and without impact spots, the effect of the impacts at wavelengths from 2 to 4 μμm is revealed. Jupiter’s reflected light spectrum in the near-infrared is dominated by its methane opacity including a deep band at 2.3 μμm. After the impact, sunlight that would have normally been absorbed by the large amount of methane in Jupiter’s atmosphere was instead reflected by the cometary material from the impacts. As a result, at 2.3 μμm, where the planet would normally have low reflectivity, it brightened substantially and stayed brighter for at least a month
The Mysterious Affair of the H in AU Mic
Molecular hydrogen is the most abundant molecule in the Galaxy and plays
important roles for planets, their circumstellar environments, and many of
their host stars. We have confirmed the presence of molecular hydrogen in the
AU Mic system using high-resolution FUV spectra from HST-STIS during both
quiescence and a flare. AU Mic is a 23 Myr M dwarf which hosts a debris
disk and at least two planets. We estimate the temperature of the gas at 1000
to 2000 K, consistent with previous detections. Based on the radial velocities
and widths of the H line profiles and the response of the H lines to a
stellar flare, the H line emission is likely produced in the star, rather
than in the disk or the planet. However, the temperature of this gas is
significantly below the temperature of the photosphere (3650 K) and the
predicted temperature of its star spots (2650 K). We discuss the
possibility of colder star spots or a cold layer in the photosphere of a
pre-main sequence M dwarf.Comment: accepted to ApJ, 20 pages, many figure
High-Resolution Transmission Spectroscopy of the Terrestrial Exoplanet GJ 486b
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 exoplanet GJ 486b
( 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/He-dominated atmosphere, nor a clear 100%
water-vapor atmosphere. Other secondary atmospheres with high mean molecular
weights or H/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.Comment: Accepted for publication in A
Characterizing the Near-infrared Spectra of Flares from TRAPPIST-1 During JWST Transit Spectroscopy Observations
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 m with NIRISS and 0.6--3.5 m with NIRSpec
during transits of TRAPPIST-1b, f, and g. We discover P and Br
line emission and characterize flare continuum at wavelengths from 1--3.5
m for the first time. Observed lines include H,
P-P, Br, He I 0.7062m, two Ca II
infrared triplet (IRT) lines, and the He I IRT. We observe a reversed Paschen
decrement from P-P 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 temperatures
typically observed at optical wavelengths. The 0.6--1 m spectra were
convolved with the TESS response, enabling us to measure the flare rate of
TRAPPIST-1 in the TESS bandpass. We find flares of 10 erg large enough
to impact transit spectra occur at a rate of 3.6 flare
d, 10 higher than previous predictions from K2. We measure
the amount of flare contamination at 2 m for the TRAPPIST-1b and f
transits to be 500450 and 2100400 ppm, respectively. We find up to
80% of flare contamination can be removed, with mitigation most effective from
1.0--2.4 m. These results suggest transits affected by flares may still be
useful for atmospheric characterization efforts.Comment: 29 pages, 17 figures, 3 tables, accepted to The Astrophysical Journa
Atmospheric Reconnaissance of TRAPPIST-1 b with JWST/NIRISS: Evidence for Strong Stellar Contamination in the Transmission Spectra
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.Comment: 26 pages, 11 figures, accepted for publication in The Astrophysical
Journal Letter
Detection of carbon monoxide's 4.6 micron fundamental band structure in WASP-39b's atmosphere with JWST NIRSpec G395H
Carbon monoxide (CO) is predicted to be the dominant carbon-bearing molecule in giant planet atmospheres and, along with water, is important for discerning the oxygen and therefore carbon-to-oxygen ratio of these planets. The fundamental absorption mode of CO has a broad, double-branched structure composed of many individual absorption lines from 4.3 to 5.1 μm, which can now be spectroscopically measured with JWST. Here we present a technique for detecting the rotational sub-band structure of CO at medium resolution with the NIRSpec G395H instrument. We use a single transit observation of the hot Jupiter WASP-39b from the JWST Transiting Exoplanet Community Early Release Science (JTEC ERS) program at the native resolution of the instrument (R ~ 2700) to resolve the CO absorption structure. We robustly detect absorption by CO, with an increase in transit depth of 264 ± 68 ppm, in agreement with the predicted CO contribution from the best-fit model at low resolution. This detection confirms our theoretical expectations that CO is the dominant carbon-bearing molecule in WASP-39b's atmosphere and further supports the conclusions of low C/O and supersolar metallicities presented in the JTEC ERS papers for WASP-39b
Planets Around Low-Mass Stars (PALMS). V. Age-Dating Low-Mass Companions to Members and Interlopers of Young Moving Groups
Copyright © 2015. The American Astronomical Society. All rights reserved.We present optical and near-infrared adaptive optics (AO) imaging and spectroscopy of 13 ultracool (>M6) companions to late-type stars (K7-M4.5), most of which have recently been identified as candidate members of nearby young moving groups (YMGs; 8-120 Myr) in the literature. The inferred masses of the companions (~10-100 Mjup) are highly sensitive to the ages of the primary stars so we critically examine the kinematic and spectroscopic properties of each system to distinguish bona fide YMG members from old field interlopers. 2MASS J02155892-0929121 C is a new M7 substellar companion (40-60 Mjup) with clear spectroscopic signs of low gravity and hence youth. The primary, possibly a member of the ~40 Myr Tuc-Hor moving group, is visually resolved into three components, making it a young low-mass quadruple system in a compact (1 Gyr) tidally-locked spectroscopic binaries without convincing kinematic associations with any known moving group. The high rate of false positives in the form of old active stars with YMG-like kinematics underscores the importance of radial velocity and parallax measurements to validate candidate young stars identified via proper motion and activity selection alone. Finally, we spectroscopically confirm the cool temperature and substellar nature of HD 23514 B, a recently discovered M8 benchmark brown dwarf orbiting the dustiest-known member of the Pleiades.NASANSFMt. Cuba Astronomical FoundationSamuel OschinAlfred P. Sloan Foundatio
A roadmap to the efficient and robust characterization of temperate terrestrial planet atmospheres with JWST
Ultra-cool dwarf stars are abundant, long-lived, and uniquely suited to
enable the atmospheric study of transiting terrestrial companions with JWST.
Amongst them, the most prominent is the M8.5V star TRAPPIST-1 and its seven
planets, which have been the favored targets of eight JWST Cycle 1 programs.
While Cycle 1 observations have started to yield preliminary insights into the
planets, they have also revealed that their atmospheric exploration requires a
better understanding of their host star. Here, we propose a roadmap to
characterize the TRAPPIST-1 system -- and others like it -- in an efficient and
robust manner. We notably recommend that -- although more challenging to
schedule -- multi-transit windows be prioritized to constrain stellar
heterogeneities and gather up to 2 more transits per JWST hour spent.
We conclude that in such systems planets cannot be studied in isolation by
small programs, thus large-scale community-supported programs should be
supported to enable the efficient and robust exploration of terrestrial
exoplanets in the JWST era