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External UV environment of stellar nurseries plays a major role on evolution of protoplanetary disks around young stellar objects. Photoevaporating protoplanetary disks (proplyds) have been found mainly around O stars in strong radiation environments, most of which are found in the Orion Nebula Cluster. However our recent studies also found proplyds in immediate vicinity of B stars, which implies that intermediate UV radiation environment can also affect disk evolution of young stellar objects, and potentially planet formation in such disks. We present our recent studies of proplyds around low mass young stellar- and sub-stellar objects, some of which may be potentially forming free-floating planetary mass objects. We will present our findings of the proplyds in NGC 1977 and NGC 2024, and show some selected proplyds around low mass sub-stellar objects. We will discuss the implication and the role of external UV environment in star and planet formation.&nbsp

The L/T transition is an important evolutionary phase in brown dwarf atmospheres, providing us with a unique opportunity to explore the effects of clouds, convection, winds, gravity and metallicity across a very narrow temperature range. Understanding these physical processes is critical for understanding ultracool atmospheres. In the next decade, we will answer three key questions regarding L/T transition atmospheres: 1. What is the physical mechanism behind the L/T transition? 2. What is the spatial extent of atmospheric structures at the L/T transition? 3. How do gravity and metallicity affect the L/T transition? The theory and methods developed for brown dwarfs will be used in the 2030s and beyond for solar-system age giant exoplanets and eventually habitable zone earth analogues. Developing these techniques now are crucial.

High resolution spectroscopy of the lowest-mass stars and brown dwarfs reveals their origins, multiplicity, compositions and physical properties, with implications for the star formation and chemical evolution history of the Milky Way. We motivate the need for high-resolution, infrared spectroscopic surveys to reach these faint sources., 9 pages, submitted to Astro2020 Science White Paper Call

Although the final observations of the Spitzer Warm Mission are currently scheduled for March 2019, it can continue operations through the end of the decade with no loss of photometric precision. As we will show, there is a strong science case for extending the current Warm Mission to December 2020. Spitzer has already made major impacts in the fields of exoplanets (including microlensing events), characterizing near Earth objects, enhancing our knowledge of nearby stars and brown dwarfs, understanding the properties and structure of our Milky Way galaxy, and deep wide-field extragalactic surveys to study galaxy birth and evolution. By extending Spitzer through 2020, it can continue to make ground-breaking discoveries in those fields, and provide crucial support to the NASA flagship missions JWST and WFIRST, as well as the upcoming TESS mission, and it will complement ground-based observations by LSST and the new large telescopes of the next decade. This scientific program addresses NASA's Science Mission Directive's objectives in astrophysics, which include discovering how the universe works, exploring how it began and evolved, and searching for life on planets around other stars., 75 pages. See page 3 for Table of Contents and page 4 for Executive Summary

Deducing the cloud cover and its temporal evolution from the observed planetary spectra and phase curves can give us major insight into the atmospheric dynamics. In this paper, we present Aeolus, a Markov-Chain Monte Carlo code that maps the structure of brown dwarf and other ultracool atmospheres. We validated Aeolus on a set of unique Jupiter Hubble Space Telescope (HST) light curves. Aeolus accurately retrieves the properties of the major features of the jovian atmosphere such as the Great Red Spot and a major 5um hot spot. Aeolus is the first mapping code validated on actual observations of a giant planet over a full rotational period. For this study, we applied Aeolus to J and H-bands HST light curves of 2MASSJ21392676+0220226 and 2MASSJ0136565+093347. Aeolus retrieves three spots at the top-of-the-atmosphere (per observational wavelength) of these two brown dwarfs, with a surface coverage of 21+-3% and 20.3+-1.5% respectively. The Jupiter HST light curves will be publicly available via ADS/VIZIR., Comment: Accepted by ApJ; A high-quality version of this paper can be found at http://mapotofu.as.arizona.edu/poster/Karalidi_et_al_2015.pdf

Recent discoveries of variable brown dwarfs have provided us with a new window into their three-dimensional cloud structure. The highest variables are found at the L/T transition, where the cloud cover is thought to break up, but variability has been found to occur also for both cloudy L dwarfs and (mostly) cloud-free mid T dwarfs. We summarize results from recent HST programs measuring the spectral variability of brown dwarfs in the near-infrared and compare to results from ground-based programs. We discuss the patchy cloud structure of L/T transition objects, for which it is becoming increasingly certain that the variability does not arise from cloud holes into the deep hot regions but from varying cloud thickness. We present a new patchy cloud model to explain the spectral variability of 2MASSJ21392676+0220226. We also discuss the curious multi-wavelength variability behavior of the recently discovered very nearby early T dwarf WISE J104915.57-531906.1B (Luhman 16B) and the mid T dwarf 2MASS J22282889-431026., Comment: 4 pages, 1 figure, submitted to the proceedings of "Gaia and the unseen - the brown dwarf question", Torino, 24-26 March 2014, to be published in Memorie della Societa' Astronomica Italiana (SAIt), eds Ricky Smart, David Barrado, Jackie Faherty

As the only directly imaged multiple planet system, HR 8799 provides a unique opportunity to study the physical properties of several planets in parallel. In this paper, we image all four of the HR 8799 planets at H-band and 3.3 microns with the new LBT adaptive optics system, PISCES, and LBTI/LMIRCam. Our images offer an unprecedented view of the system, allowing us to obtain H and 3.3$ micron photometry of the innermost planet (for the first time) and put strong upper-limits on the presence of a hypothetical fifth companion. We find that all four planets are unexpectedly bright at 3.3 microns compared to the equilibrium chemistry models used for field brown dwarfs, which predict that planets should be faint at 3.3 microns due to CH4 opacity. We attempt to model the planets with thick-cloudy, non-equilibrium chemistry atmospheres, but find that removing CH4 to fit the 3.3 micron photometry increases the predicted L' (3.8 microns) flux enough that it is inconsistent with observations. In an effort to fit the SED of the HR 8799 planets, we construct mixtures of cloudy atmospheres, which are intended to represent planets covered by clouds of varying opacity. In this scenario, regions with low opacity look hot and bright, while regions with high opacity look faint, similar to the patchy cloud structures on Jupiter and L/T transition brown-dwarfs. Our mixed cloud models reproduce all of the available data, but self-consistent models are still necessary to demonstrate their viability., Accepted to ApJ

We review the current picture of disks around cool stars and brown dwarfs, including disk fractions, mass estimates, disk structure and dispersal, accretion, dust composition, and the debris disk phase. We discuss these in the framework of recent planet formation models., Summary of the Cool Stars 14 Splinter Session "Disks around Brown Dwarfs and Cool Stars". 8 pages, 1 figure

This thesis aims to further our understanding in four important, strongly related topics of star formation: Disk evolution, stellar multiplicity, FU Ori phenomenon and the formation of massive stars. The main results are the following: 1. By applying the novel method of polarimetric differential imaging and the NACO/VLT instrument we probe one of the closest circumstellar disks in the planet-forming age at scales of our inner Solar System. 2. Our adaptive optics survey discovers six companion candidates to young stars. The most interesting one is close to the well-known outburst star FU Ori and is a good candidate for being the outburst trigger. 3. We identify the second-closest cluster of young stars around the intermediate-mass star HD 104237, with at least three of them showing signs of disks. 4. The first global picture on the prototypical massive star-forming region IRAS 09002-4732 is provided and its stellar content, reflection nebula, compact H II region and globular dust filaments are analysed. 5. The first multi-epoch radial velocity survey of very young, embedded massive stars is presented. Two massive close binary stars are identified. The radial velocity measurements show large differences explainable only if substantial fraction of the young massive stars are close binaries. This high intrinsic binarity rate is naturally explained by the coalescence-type formation of massive stars.

Recent discoveries of variable brown dwarfs have provided us with a new window into their three dimensional cloud structure. The highest variables are found at the L/T transition where the cloud cover is thought to break up but variability has been found to occur also for both cloudy L dwarfs and (mostly) cloud free mid T dwarfs. We summarize results from recent HST programs measuring the spectral variability of brown dwarfs in the near infrared and compare to results from ground based programs. We discuss the patchy cloud structure of L/T transition objects for which it is becoming increasingly certain that the variability does not arise from cloud holes into the deep hot regions but from varying cloud thickness. We present a new patchy cloud model to explain the spectral variability of 2MASSJ21392676+0220226. We also discuss the curious multi wavelength variability behavior of the recently discovered very nearby early T dwarf WISE J104915.57 531906.1B (Luhman 16B) and the mid T dwarf 2MASS J22282889 431026.

We explore the extent to which Spitzer Infrared Spectrograph (IRS) spectra taken at low spectral resolution can be used in quantitative studies of organic molecular emission from disks surrounding low-mass young stars. We use Spitzer IRS spectra taken in both the high- and low-resolution modules for the same sources to investigate whether it is possible to define line indices that can measure trends in the strength of the molecular features in low-resolution data. We find that trends in the HCN emission strength seen in the high-resolution data can be recovered in low-resolution data. In examining the factors that influence the HCN emission strength, we find that the low-resolution HCN flux is modestly correlated with stellar accretion rate and X-ray luminosity. Correlations of this kind are perhaps expected based on recent observational and theoretical studies of inner disk atmospheres. Our results demonstrate the potential of using the large number of low-resolution disk spectra that reside in the Spitzer archive to study the factors that influence the strength of molecular emission from disks. Such studies would complement results for the much smaller number of circumstellar disks that have been observed at high resolution with IRS.