Abstract
Magnetic star–planet interactions (SPI) provide a detection method and
insight into exoplanet magnetic fields and, in turn, exoplanet interiors and
atmospheric environments. These signatures ...can be sporadic and difficult to
confirm for single-epoch observations of a system due to inhomogeneous stellar
magnetospheres and periodic variability in stellar magnetism. Thus, an ideal SPI
search consists of multiple epochs containing observations on consecutive nights
spanning at least one complete planetary orbit. Such data sets are rare but do
exist for some of the most intensely studied hot Jupiter systems. One such
system is HD 189733 for which six suitable SPI data sets exist, the result of
spectroscopic monitoring to perform some of the first SPI searches and also to
study the star’s magnetic field. Here we perform a uniform analysis of six
archival Ca
ii
K data sets for HD 189733, spanning 2006 June through
2015 July, in order to search for magnetic SPI signatures in the chromospheric
line variations. We find significant evidence for modulations of Ca
ii
K with a 2.29 ± 0.04 day period in the 2013 August data,
which is consistent with the planet’s orbital period. The peak in the
orbital variations occurs at
ϕ
orb
≈ 0.9, which corresponds
to the SPI emission leading the planet with a phase difference of
Δ
ϕ
≈ 40° from the
sub-planetary point. This is consistent with the phase-lead predictions of
nonlinear force-free magnetic field SPI models. The stellar magnetic field
strength at the planet’s orbit was greatest in 2013 August, which, due to
the energy released in magnetic SPI scaling with
B
*
, lends strength to the SPI
interpretation.
The fundamentals of Lyman α exoplanet transits Owen, James E; Murray-Clay, Ruth A; Schreyer, Ethan ...
Monthly notices of the Royal Astronomical Society,
01/2023, Letnik:
518, Številka:
3
Journal Article
Recenzirano
Odprti dostop
ABSTRACT
Lyman α transits have been detected from several nearby exoplanets and are one of our best insights into the atmospheric escape process. However, due to ISM absorption, we typically only ...observe the transit signature in the blue-wing, making them challenging to interpret. This challenge has been recently highlighted by non-detections from planets thought to be undergoing vigorous escape. Pioneering 3D simulations have shown that escaping hydrogen is shaped into a cometary tail receding from the planet. Motivated by this work, we develop a simple model to interpret Lyman α transits. Using this framework, we show that the Lyman α transit depth is primarily controlled by the properties of the stellar tidal field rather than details of the escape process. Instead, the transit duration provides a direct measurement of the velocity of the planetary outflow. This result arises because the underlying physics is the distance a neutral hydrogen atom can travel before it is photoionized in the outflow. Thus, higher irradiation levels, expected to drive more powerful outflows, produce weaker, shorter Lyman α transits because the outflowing gas is ionized more quickly. Our framework suggests that the generation of energetic neutral atoms may dominate the transit signature early, but the acceleration of planetary material produces long tails. Thus, Lyman α transits do not primarily probe the mass-loss rates. Instead, they inform us about the velocity at which the escape mechanism is ejecting material from the planet, providing a clean test of predictions from atmospheric escape models.
Photometric variability attributed to cloud phenomena is common in L/T transition brown dwarfs. Recent studies show that such variability may also trace aurorae, suggesting that localized magnetic ...heating may contribute to observed brown dwarf photometric variability. We assess this potential correlation with a survey of 17 photometrically variable brown dwarfs using the Karl G. Jansky Very Large Array at 4-8 GHz. We detect quiescent and highly circularly polarized flaring emission from one source, 2MASS J17502484-0016151, which we attribute to auroral electron cyclotron maser emission. The detected auroral emission extends throughout the frequency band at ∼5-25 , and we do not detect evidence of a cutoff. Our detection confirms that 2MASS J17502484-0016151 hosts a magnetic field strength of ≥2.9 kG, similar to those of other radio-bright ultracool dwarfs. We show that H emission continues to be an accurate tracer of auroral activity in brown dwarfs. Supplementing our study with data from the literature, we calculate the occurrence rates of quiescent emission in L dwarfs with low- and high-amplitude variability and conclude that high-amplitude optical and infrared variability does not trace radio magnetic activity in L dwarfs.
We introduce a Bayesian method for guiding future directions for detection of life on exoplanets. We describe empirical and theoretical work necessary to place constraints on the relevant ...likelihoods, including those emerging from better understanding stellar environment, planetary climate and geophysics, geochemical cycling, the universalities of physics and chemistry, the contingencies of evolutionary history, the properties of life as an emergent complex system, and the mechanisms driving the emergence of life. We provide examples for how the Bayesian formalism could guide future search strategies, including determining observations to prioritize or deciding between targeted searches or larger lower resolution surveys to generate ensemble statistics and address how a Bayesian methodology could constrain the prior probability of life with or without a positive detection. Key Words: Exoplanets-Biosignatures-Life detection-Bayesian analysis. Astrobiology 18, 779-824.
Abstract
Accurately measuring and modeling the Ly
α
(Ly
α
;
λ
1215.67 Å) emission line from low-mass stars is vital for our ability to build predictive high energy stellar spectra, yet interstellar ...medium (ISM) absorption of this line typically prevents model-measurement comparisons. Ly
α
also controls the photodissociation of important molecules, like water and methane, in exoplanet atmospheres such that any photochemical models assessing potential biosignatures or atmospheric abundances require accurate Ly
α
host star flux estimates. Recent observations of three early M and K stars (K3, M0, M1) with exceptionally high radial velocities (>100 km s
−1
) reveal the intrinsic profiles of these types of stars as most of their Ly
α
flux is shifted away from the geocoronal line core and contamination from the ISM. These observations indicate that previous stellar spectra computed with the
PHOENIX
atmosphere code have underpredicted the core of Ly
α
in these types of stars. With these observations, we have been able to better understand the microphysics in the upper atmosphere and improve the predictive capabilities of the
PHOENIX
atmosphere code. Since these wavelengths drive the photolysis of key molecular species, we also present results analyzing the impact of the resulting changes to the synthetic stellar spectra on observable chemistry in terrestrial planet atmospheres.
Abstract
We have discovered a wide planetary-mass companion to the
β
Pic moving group member 2MASS J02495639−0557352 (M6
vl-g
) using Canada–France–Hawaii Telescope/WIRCam astrometry from the Hawaii ...Infrared Parallax Program. In addition, Keck laser guide star adaptive optics aperture-masking interferometry shows that the host is itself a tight binary. Altogether, 2MASS J0249−0557ABc is a bound triple system with an
object separated by 1950 ± 200 au (40″) from a relatively close (2.17 ± 0.22 au, 0.″04) pair of
and
objects. 2MASS J0249−0557AB is one of the few ultracool binaries to be discovered in a young moving group and the first confirmed in the
β
Pic moving group (22 ± 6 Myr). The mass, absolute magnitudes, and spectral type of 2MASS J0249−0557 c (L2
vl-g
) are remarkably similar to those of the planet
β
Pic b (L2,
). We also find that the free-floating object 2MASS J2208+2921 (L3
vl-g
) is another possible
β
Pic moving group member with colors and absolute magnitudes similar to
β
Pic b and 2MASS J0249−0557 c.
β
Pic b is the first directly imaged planet to have a “twin,” namely an object of comparable properties in the same stellar association. Such directly imaged objects provide a unique opportunity to measure atmospheric composition, variability, and rotation across different pathways of assembling planetary-mass objects from the same natal material.
We present the discovery of an extreme flaring event from Proxima Cen by the Australian Square Kilometre Array Pathfinder(ASKAP), Atacama Large Millimeter/submillimeter Array(ALMA), Hubble Space ...Telescope(HST),Transiting Exoplanet Survey Satellite(TESS), and the du Pont Telescope that occurred on 2019 May 1. In the millimeter and FUV, this flare is the brightest ever detected, brightening by a factor of>1000 and>14,000 as seen by ALMA and HST, respectively. The millimeter and FUV continuum emission trace each other closely during the flare, suggesting that millimeter emission could serve as a proxy for FUV emission from stellar flares and become a powerful new tool to constrain the high-energy radiation environment of exoplanets. Surprisingly, optical emission associated with the event peaks at a much lower level with a time delay. The initial burst has an extremely short duration, lasting for<10 s. Taken together with the growing sample of millimeter M dwarf flares, this event suggests that millimeter emission is actually common during stellar flares and often originates from short burst-like events.
(ProQuest: Formulae and/or non-USASCII text omitted)Transition disks (TDs) are intermediate stage circumstellar disks characterized by an inner gap within the disk structure. To test whether these ...gaps may have been formed by closely orbiting, previously undetected stellar companions, we collected high-resolution optical spectra of 31 TD objects to search for spectroscopic binaries (SBs). Twenty-four of these objects are in Ophiuchus and seven are within the Coronet, Corona Australis, and Chameleon I star-forming regions. We measured radial velocities for multiple epochs, obtaining a median precision of 400 ms super(-1). We identified double-lined SB SSTc2d J163154.7-250324 in Ophiuchus, which we determined to be composed of a K7(+ or -0.5) and a K9(+ or -0.5) star, with orbital limits of a< 0.6 au and P< 150 days. This results in an SB fraction of ... in Ophiuchus, which is consistent with other spectroscopic surveys of non-TD objects in the region. This similarity suggests that TDs are not preferentially sculpted by the presence of close binaries and that planet formation around close binaries may take place over similar timescales to that around single stars.
Searching for Young M Dwarfs with GALEX Shkolnik, Evgenya L; Liu, Michael C; Reid, I. Neill ...
The Astrophysical journal,
01/2011, Letnik:
727, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The census of young moving groups in the solar neighborhood is significantly incomplete in the low-mass regime. We have developed a new selection process to find these missing members based on the ...Galaxy Evolution Explorer (GALEX) All-Sky Imaging Survey (AIS). For stars with spectral types K5 (R -- J 1.5) and younger than 300 Myr, we show that near-UV (NUV) and far-UV (FUV) emission is greatly enhanced above the quiescent photosphere, analogous to the enhanced X-ray emission of young low-mass stars seen by ROSAT but detectable to much larger distances with GALEX. By combining GALEX data with optical (HST Guide Star Catalog) and near-IR (2MASS) photometry, we identified an initial sample of 34 young M dwarf candidates in a 1000 deg2 region around the 10 Myr TW Hydra Association (TWA). Low-resolution spectroscopy of 30 of these found 16 which had H Delta *a in emission, which were then followed up at high resolution to search for spectroscopic evidence of youth and to measure their radial velocities. Four objects have low surface gravities, photometric distances and space motions consistent with TWA, but the non-detection of Li indicates that they may be too old to belong to this moving group. One object (M3.5, 93 ? 19 pc) appears to be the first known accreting low-mass member of the 15 Myr Lower Centaurus Crux OB association. Two objects exhibit all the characteristics of the known TWA members, and thus we designate them as TWA 31 (M4.2, 110 ? 11 pc) and TWA 32 (M6.3, 53 ? 5 pc). TWA 31 shows extremely broad (447 km s--1) H Delta *a emission, making it the sixth member of TWA found to have ongoing accretion. TWA 32 is resolved into a 06 binary in Keck laser guide star adaptive optics imaging. Our search should be sensitive down to spectral types of at least M4-M5 in TWA and thus the small numbers of new member is puzzling. This might indicate TWA has an atypical mass function or that the presence of lithium absorption may be too restrictive a criteria for selecting young low-mass stars.
Abstract
We present high-resolution dayside thermal emission observations of the exoplanet WASP-18 b using IGRINS on Gemini South. We remove stellar and telluric signatures using standard algorithms, ...and we extract the planet signal via cross-correlation with model spectra. We detect the atmosphere of WASP-18 b at a signal-to-noise ratio (S/N) of 5.9 using a full chemistry model, measure H
2
O (S/N = 3.3), CO (S/N = 4.0), and OH (S/N = 4.8) individually, and confirm previous claims of a thermal inversion layer. The three species are confidently detected (>4
σ
) with a Bayesian inference framework, which we also use to retrieve abundance, temperature, and velocity information. For this ultrahot Jupiter (UHJ), thermal dissociation processes likely play an important role. Retrieving abundances constant with altitude and allowing the temperature–pressure profile to adjust freely results in a moderately super-stellar carbon-to-oxygen ratio (C/O =
0.75
−
0.17
+
0.14
) and metallicity (M/H =
1.03
−
1.01
+
0.65
). Accounting for undetectable oxygen produced by thermal dissociation leads to C/O =
0.45
−
0.10
+
0.08
and M/H =
1.17
−
1.01
+
0.66
. A retrieval that assumes radiative–convective–thermochemical equilibrium and naturally accounts for thermal dissociation constrains C/O < 0.34 (2
σ
) and M/H =
0.48
−
0.29
+
0.33
, in line with the chemistry of the parent star. Looking at the velocity information, we see a tantalizing signature of different Doppler shifts at the level of a few kilometers per second for different molecules, which might probe dynamics as a function of altitude and/or location on the planet disk. Our results demonstrate that ground-based, high-resolution spectroscopy at infrared wavelengths can provide meaningful constraints on the compositions and climate of highly irradiated planets. This work also elucidates potential pitfalls with commonly employed retrieval assumptions when applied to the spectra of UHJs.
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