In this paper we study the full sample of known Spitzer 3.6 m and J-band variable brown dwarfs. We calculate the rotational velocities, , of 16 variable brown dwarfs using archival Keck NIRSPEC data ...and compute the inclination angles of 19 variable brown dwarfs. The results obtained show that all objects in the sample with mid-IR variability detections are inclined at an angle , while all objects in the sample displaying J-band variability have an inclination angle . J-band variability appears to be more affected by inclination than Spitzer 3.6 m variability, and is strongly attenuated at lower inclinations. Since J-band observations probe deeper into the atmosphere than mid-IR observations, this effect may be due to the increased atmospheric path length of J-band flux at lower inclinations. We find a statistically significant correlation between the color anomaly and inclination of our sample, where field objects viewed equator-on appear redder than objects viewed at lower inclinations. Considering the full sample of known variable L, T, and Y spectral type objects in the literature, we find that the variability properties of the two bands display notably different trends that are due to both intrinsic differences between bands and the sensitivity of ground-based versus space-based searches. However, in both bands we find that variability amplitude may reach a maximum at ∼7-9 hr periods. Finally, we find a strong correlation between color anomaly and variability amplitude for both the J-band and mid-IR variability detections, where redder objects display higher variability amplitudes.
We report the detection of a faint point-like feature possibly related to ongoing planet-formation in the disk of the transition disk star HD 169142. The point-like feature has a Amag(L) ~ 6.4, at a ...separation of ~0".'11 and position angle ~0degrees. Given its lack of an H or KS counterpart despite its relative brightness, this candidate cannot be explained by purely photospheric emission and must be a disk feature heated by an as yet unknown source. Its extremely red colors make it highly unlikely to be a background object, but future multi-wavelength follow up is necessary for confirmation and characterization of this feature.
We present simultaneous Hubble Space Telescope (HST) WFC3+Spitzer IRAC variability monitoring for the highly variable young (∼20 Myr) planetary-mass object PSO J318.5−22. Our simultaneous HST + ...Spitzer observations covered approximately two rotation periods with Spitzer and most of a rotation period with the HST. We derive a period of 8.6 0.1 hr from the Spitzer light curve. Combining this period with the measured for this object, we find an inclination of 56 2 8 1. We measure peak-to-trough variability amplitudes of 3.4% 0.1% for Spitzer Channel 2 and 4.4%-5.8% (typical 68% confidence errors of ∼0.3%) in the near-IR bands (1.07-1.67 m) covered by the WFC3 G141 prism-the mid-IR variability amplitude for PSO J318.5−22 is one of the highest variability amplitudes measured in the mid-IR for any brown dwarf or planetary-mass object. Additionally, we detect phase offsets ranging from 200° to 210° (typical error of ∼4°) between synthesized near-IR light curves and the Spitzer mid-IR light curve, likely indicating depth-dependent longitudinal atmospheric structure in this atmosphere. The detection of similar variability amplitudes in wide spectral bands relative to absorption features suggests that the driver of the variability may be inhomogeneous clouds (perhaps a patchy haze layer over thick clouds), as opposed to hot spots or compositional inhomogeneities at the top-of-atmosphere level.
A measurement of the wind speed on a brown dwarf Allers, Katelyn N; Vos, Johanna M; Biller, Beth A ...
Science (American Association for the Advancement of Science),
04/2020, Letnik:
368, Številka:
6487
Journal Article
Recenzirano
Odprti dostop
Zonal (latitudinal) winds dominate the bulk flow of planetary atmospheres. For gas giant planets such as Jupiter, the motion of clouds can be compared with radio emissions from the magnetosphere, ...which is connected to the planet's interior, to determine the wind speed. In principle, this technique can be applied to brown dwarfs and/or directly imaged exoplanets if periods can be determined for both the infrared and radio emissions. We apply this method to measure the wind speeds on the brown dwarf 2MASS J10475385+2124234. The difference between the radio period of 1.751 to 1.765 hours and infrared period of 1.741 ± 0.007 hours implies a strong wind (+650 ± 310 meters per second) proceeding eastward. This could be due to atmospheric jet streams and/or low frictional drag at the bottom of the atmosphere.
We present Spitzer Space Telescope variability monitoring observations of three low-gravity L dwarfs with previous detections of variability in the near-IR: 2MASS J0045+16, 2MASS J0501−00, and 2MASS ...J1425−36. We detect significant periodic variability in two of our targets, 2MASS J0045+16 and 2MASS J0501−00. We do not detect variability in 2MASS J1425−36. Combining our new rotation periods with rotational velocities, we calculate inclination angles of 22° 1°, , and for 2MASS J0045+16, 2MASS J0501−00, and 2MASS J1425−36, respectively. Our three new objects are consistent with the tentative relations between inclination, amplitude, and color anomaly previously reported. Objects with the highest variability amplitudes are inclined equator on, while the maximum observed amplitude decreases as the inclination angle decreases. We also find a correlation between the inclination angle and color anomaly for the sample of objects with measured inclinations. Compiling the entire sample of brown dwarfs with Spitzer variability detections, we find no enhancement in amplitude for young, early-L dwarfs compared to the field dwarf population. We find a possible enhancement in amplitude of low-gravity late-L dwarfs at 4.5 m. We do not find a correlation between amplitude ratio and spectral type for field dwarfs or for the young population. Finally, we compile the rotation periods of a large sample of brown dwarfs with ages 1 Myr-1 Gyr and compare the rotation rates predicted by evolutionary models assuming angular momentum conservation. We find that the rotation rates of the current sample of brown dwarfs fall within the expected range set by evolutionary models and breakup limits.
Abstract
Young brown dwarfs are analogs to giant exoplanets, as they share effective temperatures, near-infrared colors, and surface gravities. Thus, the detailed characterization of young brown ...dwarfs might shed light on the study of giant exoplanets that we are currently unable to observe with a sufficient signal-to-noise to allow a precise characterization of their atmospheres. 2MASS J22081363+2921215 is a young L3 brown dwarf, and a member of the
β
-Pictoris young moving group (23 ± 3 Myr), which shares its effective temperature and mass with the
β
Pictoris b giant exoplanet. We performed a ∼2.5 hr spectrophotometric
J
-band monitoring of 2MASS J22081363+2921215 with the MOSFIRE multi-object spectrograph, installed at the Keck I telescope. We measured a minimum variability amplitude of 3.22 ± 0.42% for its
J
-band light curve. The ratio between the maximum and the minimum flux spectra of 2MASS J22081363+2921215 shows a weak wavelength dependence, and a potentially enhanced variability amplitude in its alkali lines. Further analysis suggests that the variability amplitudes of the alkali lines are higher than its overall variability amplitude (4.5%–11%, depending on the lines). The variability amplitudes of these lines are lower if we degrade the resolution of the original MOSFIRE spectra to
R
∼ 100, which explains why this potentially enhanced variability of the alkali lines had not been found previously in Hubble Space Telescope (HST)/WFC3 light curves. Using radiative-transfer models, we obtained the different cloud layers that might be introducing the spectrophotometric variability we observe for 2MASS J22081363+2921215, which further supports the measured enhanced variability amplitudes of the alkali lines. We provide an artistic recreation of the vertical cloud structure of this
β
-Pictoris b analog.
ABSTRACT Time-resolved photometry is an important new probe of the physics of condensate clouds in extrasolar planets and brown dwarfs. Extreme adaptive optics systems can directly image planets, but ...precise brightness measurements are challenging. We present VLT/SPHERE high-contrast, time-resolved broad H-band near-infrared photometry for four exoplanets in the HR 8799 system, sampling changes from night to night over five nights with relatively short integrations. The photospheres of these four planets are often modeled by patchy clouds and may show large-amplitude rotational brightness modulations. Our observations provide high-quality images of the system. We present a detailed performance analysis of different data analysis approaches to accurately measure the relative brightnesses of the four exoplanets. We explore the information in satellite spots and demonstrate their use as a proxy for image quality. While the brightness variations of the satellite spots are strongly correlated, we also identify a second-order anti-correlation pattern between the different spots. Our study finds that KLIP reduction based on principal components analysis with satellite-spot-modulated artificial-planet-injection-based photometry leads to a significant (∼3×) gain in photometric accuracy over standard aperture-based photometry and reaches 0.1 mag per point accuracy for our data set, the signal-to-noise ratio of which is limited by small field rotation. Relative planet-to-planet photometry can be compared between nights, enabling observations spanning multiple nights to probe variability. Recent high-quality relative H-band photometry of the b-c planet pair agrees to about 1%.
We report the results of a J-band survey for photometric variability in a sample of young, low-gravity objects using the New Technology Telescope (NTT) and the United Kingdom Infrared Telescope ...(UKIRT). Surface gravity is a key parameter in the atmospheric properties of brown dwarfs and this is the first large survey that aims to test the gravity dependence of variability properties. We do a full analysis of the spectral signatures of youth and assess the group membership probability of each target using membership tools from the literature. This results in a 30 object sample of young low-gravity brown dwarfs. Since we are lacking in objects with spectral types later than L9, we focus our statistical analysis on the L0–L8.5 objects. We find that the variability occurrence rate of L0–L8.5 low-gravity brown dwarfs in this survey is 30(+16,−8) per cent. We reanalyse the results of Radigan (2014) and find that the field dwarfs with spectral types L0–L8.5 have a variability occurrence rate of 11(+13,−4) per cent. We determine a probability of 98 per cent that the samples are drawn from different distributions. This is the first quantitative indication that the low-gravity objects are more likely to be variable than the field dwarf population. Furthermore, we present follow-up J(S) and K(S) observations of the young, planetary-mass variable object PSO 318.5–22 over three consecutive nights. We find no evidence of phase shifts between the J(S) and K(S) bands and find higher J(S) amplitudes. We use the J(S) light curves to measure a rotational period of 8.45 ± 0.05 h for PSO 318.5–22.
ABSTRACT
Retrieval methods are a powerful analysis technique for modelling exoplanetary atmospheres by estimating the bulk physical and chemical properties that combine in a forward model to best fit ...an observed spectrum, and they are increasingly being applied to observations of directly imaged exoplanets. We have adapted taurex3, the Bayesian retrieval suite, for the analysis of near-infrared spectrophotometry from directly imaged gas giant exoplanets and brown dwarfs. We demonstrate taurex3’s applicability to sub-stellar atmospheres by presenting results for brown dwarf benchmark GJ 570D which are consistent with previous retrieval studies, whilst also exhibiting systematic biases associated with the presence of alkali lines. We also present results for the cool exoplanet 51 Eri b, the first application of a free chemistry retrieval analysis to this object, using spectroscopic observations from GPI and SPHERE. While our retrieval analysis is able to explain spectroscopic and photometric observations without employing cloud extinction, we conclude this may be a result of employing a flexible temperature-pressure profile which is able to mimic the presence of clouds. We present Bayesian evidence for an ammonia detection with a 2.7σ confidence, the first indication of ammonia in a directly imaged exoplanetary atmosphere. This is consistent with this molecule being present in brown dwarfs of a similar spectral type. We demonstrate the chemical similarities between 51 Eri b and GJ 570D in relation to their retrieved molecular abundances. Finally, we show that overall retrieval conclusions for 51 Eri b can vary when employing different spectral data and modelling components, such as temperature–pressure and cloud structures.
Given its relative proximity (∼430 pc), compact size (<20′), young age (∼0.5 Myr), and rich number of young stellar objects, the Serpens-South star-forming region is a promising site for studying ...young substellar objects, yet the low-mass members of this region remain largely undiscovered. In this article we report on a deep photometric survey using a custom 1.45 m filter (W band), as well as standard J and H near-IR filters, in order to identify candidate low-mass young brown dwarfs in the Serpens-South region. We constructed a reddening-insensitive index (Q) by combining J, H and W-band photometry for survey objects, in order to identify candidate low-mass members of Serpens based on the strength of the water-absorption feature at 1.45 m in the atmospheres of mid-M and later objects. We then conducted spectroscopic follow-up to confirm youth and spectral type for our candidates. This is the first survey to identify the very low-mass and coolest members of Serpens-South. We identify four low-mass candidate Serpens members, which all display IR excess emission, indicating the likely presence of circumstellar disks around them. One of the four candidate low-mass members in our list, SERP182918-020245, exhibits Paβ and Brγ emission features, confirming its youth and ongoing magnetospheric accretion. Our new candidate members have spectral types >M4 and are the coolest and lowest mass candidate members yet identified in Serpens-South.
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