Thirty years ago, the only planets we knew were the ones orbiting our own sun; we now know of thousands of other worlds orbiting distant stars. In this book, astronomer Niall Deacon journeys to ...twenty of these globes: from giant, blisteringly hot planets orbiting close to their parent stars to planets that float through the cold wilderness of space alone, and from dead stars shredding asteroids to worlds made of diamond—and even planets that may be similar to the Earth. Deacon also takes in the latest exoplanet discoveries and explains how astronomers have come to learn so much about these strange and distant worlds. Twenty Worlds tells a sweeping story, of real planets around other stars, and it will fascinate a universe of fans of popular science and astronomy.
We have discovered using Pan-STARRS1 an extremely red late-L dwarf, which has (J - K) sub(MKO) = 2.78 and (J - K) sub(2MASS) = 2.84, making it the reddest known field dwarf and second only to 2MASS ...J1207-39b among substellar companions. Near-IR spectroscopy shows a spectral type of L7 + or - 1 and reveals a triangular H-band continuum and weak alkali (K I and Na I) lines, hallmarks of low surface gravity. Near-IR astrometry from the Hawaii Infrared Parallax Program gives a distance of 24.6 + or - 1.4 pc and indicates a much fainter J-band absolute magnitude than field L dwarfs. The position and kinematics of PSO J318.5-22 point to membership in the beta Pic moving group. Evolutionary models give a temperature of (ProQuest: Formulae and/or non-USASCII text omitted) K and a mass of (ProQuest: Formulae and/or non-USASCII text omitted) M sub(Jup), making PSO J318.5-22 one of the lowest mass free-floating objects in the solar neighborhood. This object adds to the growing list of low-gravity field L dwarfs and is the first to be strongly deficient in methane relative to its estimated temperature. Comparing their spectra suggests that young L dwarfs with similar ages and temperatures can have different spectral signatures of youth. For the two objects with well constrained ages (PSO J318.5-22 and 2MASS J0355+11), we find their temperatures are approximate400 K cooler than field objects of similar spectral type but their luminosities are similar, i.e., these young L dwarfs are very red and unusually cool but not "underluminous." Altogether, PSO J318.5-22 is the first free-floating object with the colors, magnitudes, spectrum, luminosity, and mass that overlap the young dusty planets around HR 8799 and 2MASS J1207-39.
Abstract
We derive the bolometric luminosities (
L
bol
) of 865 field-age and 189 young ultracool dwarfs (spectral types M6–T9, including 40 new discoveries presented here) by directly integrating ...flux-calibrated optical to mid-infrared (MIR) spectral energy distributions (SEDs). The SEDs consist of low-resolution (
R
∼ 150) near-infrared (NIR; 0.8–2.5
μ
m) spectra (including new spectra for 97 objects), optical photometry from the Pan-STARRS1 survey, and MIR photometry from the CatWISE2020 survey and Spitzer/IRAC. Our
L
bol
calculations benefit from recent advances in parallaxes from Gaia, Spitzer, and UKIRT, as well as new parallaxes for 19 objects from CFHT and Pan-STARRS1 presented here. Coupling our
L
bol
measurements with a new uniform age analysis for all objects, we estimate substellar masses, radii, surface gravities, and effective temperatures (
T
eff
) using evolutionary models. We construct empirical relationships for
L
bol
and
T
eff
as functions of spectral type and absolute magnitude, determine bolometric corrections in optical and infrared bandpasses, and study the correlation between evolutionary model-derived surface gravities and NIR gravity classes. Our sample enables a detailed characterization of
BT-Settl
and
ATMO
2020 atmospheric model systematics as a function of spectral type and position in the NIR color–magnitude diagram. We find the greatest discrepancies between atmospheric and evolutionary model-derived
T
eff
(up to 800 K) and radii (up to 2.0
R
Jup
) at the M/L spectral type transition boundary. With 1054 objects, this work constitutes the largest sample to date of ultracool dwarfs with determinations of their fundamental parameters.
ABSTRACT We present 197 planet candidates discovered using data from the first year of the NASA K2 mission (Campaigns 0-4), along with the results of an intensive program of photometric analyses, ...stellar spectroscopy, high-resolution imaging, and statistical validation. We distill these candidates into sets of 104 validated planets (57 in multi-planet systems), false positives, and 63 remaining candidates. Our validated systems span a range of properties, with median values of RP = , P = days, = K, and Kp = mag. Stellar spectroscopy provides precise stellar and planetary parameters for most of these systems. We show that K2 has increased by 30% the number of small planets known to orbit moderately bright stars (1-4 R⊕, Kp = 9-13 mag). Of particular interest are planets smaller than 2 R⊕, orbiting stars brighter than Kp = 11.5 mag, 5 receiving Earth-like irradiation levels, and several multi-planet systems-including 4 planets orbiting the M dwarf K2-72 near mean-motion resonances. By quantifying the likelihood that each candidate is a planet we demonstrate that our candidate sample has an overall false positive rate of 15%-30%, with rates substantially lower for small candidates ( ) and larger for candidates with radii and/or with . Extrapolation of the current planetary yield suggests that K2 will discover between 500 and 1000 planets in its planned four-year mission, assuming sufficient follow-up resources are available. Efficient observing and analysis, together with an organized and coherent follow-up strategy, are essential for maximizing the efficacy of planet-validation efforts for K2, TESS, and future large-scale surveys.
Abstract
We present a uniform forward-modeling analysis of 90 late-M and L dwarfs in nearby young (∼10–200 Myr) moving groups, the Pleiades, and the Hyades using low-resolution (
R
≈ 150) ...near-infrared (0.9–2.4
μ
m) spectra and the BT-Settl model atmospheres. We derive the objects’ effective temperatures, surface gravities, radii, and masses by comparing our spectra to the models using a Bayesian framework with nested sampling and calculate the same parameters using evolutionary models. Assuming the evolutionary-based parameters are more robust, our spectroscopically inferred parameters from BT-Settl exhibit two types of systematic behavior for objects near the M-L spectral type boundary. Several objects are clustered around
T
eff
≈ 1800 K and
log
g
≈
5.5
dex, implying impossibly large masses (150–1400
M
Jup
), while others are clustered around
T
eff
≳ 3000 K and
log
g
≲
3.0
dex, implying unphysically low masses and unreasonably young ages. We find the fitted BT-Settl model spectra tend to overpredict the peak
J
- and
H
-band flux for objects located near the M-L boundary, suggesting the dust content included in the model atmospheres is insufficient to match the observations. By adding an interstellar medium–like reddening law to the BT-Settl model spectra, we find the fits between models and observed spectra are greatly improved, with the largest reddening coefficients occurring at the M-L transition. This work delivers a systematic examination of the BT-Settl model atmospheres and constitutes the largest spectral analysis of benchmark late-M- and L-type brown dwarfs to date.
Metallicity is a fundamental parameter that contributes to the physical characteristics of a star. The low temperatures and complex molecules present in M dwarf atmospheres make it difficult to ...measure their metallicities using techniques that have been commonly used for Sun-like stars. Although there has been significant progress in developing empirical methods to measure M dwarf metallicities over the last few years, these techniques have been developed primarily for early- to mid-M dwarfs. We present a method to measure the metallicity of mid- to late-M dwarfs from moderate resolution (R ~ 2000) K-band (Asymptotically = to2.2 mu m) spectra. We calibrate our formula using 44 wide binaries containing an F, G, K, or early-M primary of known metallicity and a mid- to late-M dwarf companion. We show that similar features and techniques used for early-M dwarfs are still effective for late-M dwarfs. Our revised calibration is accurate to ~0.07 dex for M4.5-M9.5 dwarfs with -0.58 < Fe/H < +0.56 and shows no systematic trends with spectral type, metallicity, or the method used to determine the primary star metallicity. We show that our method gives consistent metallicities for the components of M+M wide binaries. We verify that our new formula works for unresolved binaries by combining spectra of single stars. Lastly, we show that our calibration gives consistent metallicities with the Mann et al. study for overlapping (M4-M5) stars, establishing that the two calibrations can be used in combination to determine metallicities across the entire M dwarf sequence.
We report the discovery of an unusually red brown dwarf found in a search for high proper motion objects using WISE and 2MASS data. WISEP J004701.06+680352.1 is moving at 0".44 yr super(-1) and lies ...relatively close to the Galactic plane (b = 5degrees.2). Near-infrared photometry and spectroscopy reveals that this is one of the reddest (2MASS J - K sub(s) = 2.55 + or - 0.08 mag) field L dwarfs yet detected, making this object an important member of the class of unusually red L dwarfs. We discuss evidence for thick condensate clouds and speculate on the age of the object. Although models by different research groups agree that thick clouds can explain the red spectrum, they predict dramatically different effective temperatures, ranging from 1100 K to 1600 K. This brown dwarf is well suited for additional studies of extremely dusty substellar atmospheres because it is relatively bright (K sub(s) = 13.05 + or - 0.03 mag), which should also contribute to an improved understanding of young gas-giant planets and the transition between L and T brown dwarfs.
We present two epochs of MPG/ESO 2.2 m GROND simultaneous six-band (r'i'z' JHK) photometric monitoring of the closest known L/T transition brown dwarf binary WISE J104915.57-531906.1AB. We report ...here the first resolved variability monitoring of both the T0.5 and L7.5 components. We obtained 4 hr of focused observations on the night of 2013 April 22 (UT), as well as 4 hr of defocused (unresolved) observations on the night of 2013 April 16 (UT). We note a number of robust trends in our light curves. The r' and i' light curves appear to be anti-correlated with z' and H for the T0.5 component and in the unresolved light curve. In the defocused dataset, J appears correlated with z' and H and anti-correlated with r' and i', while in the focused dataset we measure no variability for J at the level of our photometric precision, likely due to evolving weather phenomena. In our focused T0.5 component light curve, the K band light curve displays a significant phase offset relative to both H and z'. We argue that the measured phase offsets are correlated with atmospheric pressure probed at each band, as estimated from one-dimensional atmospheric models. We also report low-amplitude variability in i' and z' intrinsic to the L7.5 component.
We report the discovery of a thin stellar stream found in Pan-STARRS1 photometry near the Galactic bulge in the constellation of Ophiuchus. It appears as a coherent structure in the colour-selected ...stellar density maps produced to search for tidal debris around nearby globular clusters. The stream is exceptionally short and narrow; it is about 2
$_{.}^{\circ}$
5 long and 6 arcmin wide in projection. The colour–magnitude diagram of this object, which harbours a blue horizontal-branch, is consistent with an old and relatively metal-poor population (Fe/H ∼−1.3) located 9.5 ± 0.9 kpc away at (l, b) ∼ (5°, +32°), and 5.0 ± 1.0 kpc from the Galactic centre. These properties argue for a globular cluster as progenitor. The finding of such a prominent, nearby stream suggests that many streams could await discovery in the more densely populated regions of our Galaxy.
ABSTRACT We present the results of a Hubble Space Telescope Wide Field Camera 3 (WFC3) imaging survey of 11 of the lowest mass brown dwarfs in the Pleiades known (25-40 MJup). These objects represent ...the predecessors to T dwarfs in the field. Using a semi-empirical binary point-spread function (PSF)-fitting technique, we are able to probe to 0 03 (0.75 pixel), better than 2x the WFC3/UVIS diffraction limit. We did not find any companions to our targets. From extensive testing of our PSF-fitting method on simulated binaries, we compute detection limits which rule out companions to our targets with mass ratios of 0.7 and separations 4 AU. Thus, our survey is the first to attain the high angular resolution needed to resolve brown dwarf binaries in the Pleiades at separations that are most common in the field population. We constrain the binary frequency over this range of separation and mass ratio of 25-40 MJup Pleiades brown dwarfs to be <11% for 1 (<26% at 2 ). This binary frequency is consistent with both younger and older brown dwarfs in this mass range.
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