We present Magellan adaptive optics Ha imaging of HH 508, which has the highest surface brightness among protostellar jets in the Orion Nebula. We find that HH 508 actually has a shorter component to the west, and a longer and knotty component to the east. The east component has a kink at 0.'' 3 from the jet-driving star theta(1) Ori B-2, so it may have been deflected by the wind/radiation from the nearby theta(1) Ori B1B5. The origin of both components is unclear, but if each of them is a separate jet, then theta(1) Ori B-2 may be a tight binary. Alternatively, HH 508 may be a slow-moving outflow, and each component represents an illuminated cavity wall. The ionization front surrounding theta(1) Ori B2B3 does not directly face theta(1) Ori B1B5, suggesting that the EUV radiation from theta(1) Ori C plays a dominant role in affecting the morphology of proplyds even in the vicinity of theta(1) Ori B1B5. Finally, we report an Ha blob that might be ejected by the binary proplyd LV 1.

Solar-type binaries with short orbital periods (P-close equivalent to 1-10. days; a less than or similar to 0.1. au) cannot form directly via fragmentation of molecular clouds or protostellar disks, yet their component masses are highly correlated, suggesting interaction during the pre-main-sequence (pre-MS) phase. Moreover, the close binary fraction of pre-MS stars is consistent with that of their MS counterparts in the field (F-close = 2.1%). Thus, we can infer that some migration mechanism operates during the early pre-MS phase (tau less than or similar to 5 Myr) that reshapes the primordial separation distribution. We test the feasibility of this hypothesis by carrying out a population synthesis calculation which accounts for two formation channels: Kozai-Lidov (KL) oscillations and dynamical instability in triple systems. Our models incorporate (1) more realistic initial conditions compared to previous studies, (2) octupole-level effects in the secular evolution, (3) tidal energy dissipation via weak-friction equilibrium tides at small eccentricities and via non-radial dynamical oscillations at large eccentricities, and (4) the larger tidal radius of a pre-MS primary. Given a 15% triple-star fraction, we simulate a close binary fraction from KL oscillations alone of F-close approximate to 0.4% after tau = 5. Myr, which increases to F-close 0.8% by tau = 5. Gyr. Dynamical ejections and disruptions of unstable coplanar triples in the disk produce solitary binaries with slightly longer periods P approximate to 10-100. days. The remaining approximate to 60% of close binaries with outer tertiaries, particularly those in compact coplanar configurations with log P-out (days) approximate to 2-5 (a(out) < 50 au), can be explained only with substantial extra energy dissipation due to interactions with primordial gas.

The ubiquity of Lyman alpha (Ly alpha) emission in a sample of four bright [O III]- strong star-forming galaxies with redshifts above seven has led to the suggestion that such luminous sources represent a distinct population compared with their fainter, more numerous counterparts. The presence of Lya emission within the reionization era could indicate that these sources created early ionized bubbles due to their unusually strong radiation, possibly because of the presence of active galactic nuclei. To test this hypothesis, we secured long integration spectra with XSHOOTER on the VLT for three z similar or equal to 7 sources selected to have similar luminosities and prominent excess fluxes in the IRAC 3.6 or 4.5 mu m band, usually attributed to strong [O III] emission. We secured additional spectroscopy for one of these galaxies at z = 7.15 using MOSFIRE at the Keck telescope. For the most well-studied source in our sample with the strongest IRAC excess, we detect significant nebular emission from He II and N V indicative of a non-thermal source. For the other two sources at z = 6.81 and z = 6.85, for which no previous optical/near-infrared spectroscopy was available, Ly alpha is seen in one and C III] emission in the other. Although based on a modest sample, our results further support the hypothesis that the phenomenon of intense [O III] emission is associated preferentially with sources lying in early ionized bubbles. However, even though one of our sources at z = 7.15 suggests the presence of non-thermal radiation, such ionized bubbles may not uniquely arise in this manner. We discuss the unique advantages of extending such challenging diagnostic studies with JWST.

The orbital parameters of binaries at intermediate periods (10(2)-10(3) d) are difficult to measure with conventional methods and are very incomplete. We have undertaken a new survey, applying our pulsation timing method to Kepler light curves of 2224 main-sequence A/F stars and found 341 non-eclipsing binaries. We calculate the orbital parameters for 317 PB1 systems (single-pulsator binaries) and 24 PB2s (double-pulsators), tripling the number of intermediate-mass binaries with full orbital solutions. The method reaches down to small mass ratios q approximate to 0.02 and yields a highly homogeneous sample. We parametrize the mass-ratio distribution using both inversion and Markov-Chain Monte Carlo forward-modelling techniques, and find it to be skewed towards low-mass companions, peaking at q approximate to 0.2. While solar-type primaries exhibit a brown dwarf desert across short and intermediate periods, we find a small but statistically significant (2.6 sigma) population of extreme-mass-ratio companions (q < 0.1) to our intermediate-mass primaries. Across periods of 100-1500 d and at q > 0.1, we measure the binary fraction of current A/F primaries to be 15.4 per cent +/- 1.4 per cent, though we find that a large fraction of the companions (21 per cent +/- 6 per cent) are white dwarfs in post-mass-transfer systems with primaries that are now blue stragglers, some of which are the progenitors of Type Ia supernovae, barium stars, symbiotics, and related phenomena. Excluding these white dwarfs, we determine the binary fraction of original A/F primaries to be 13.9 per cent +/- 2.1 per cent over the same parameter space. Combining our measurements with those in the literature, we find the binary fraction across these periods is a constant 5 per cent for primaries M-1 < 0.8 M-circle dot, but then increases linearly with log M-1, demonstrating that natal discs around more massive protostars M-1 greater than or similar to M-1(circle dot) become increasingly more prone to fragmentation. Finally, we find the eccentricity distribution of the main-sequence pairs to be much less eccentric than the thermal distribution.

Context. One of the key questions of the star formation problem is whether brown dwarfs (BDs) form in the manner of stars directly from the gravitational collapse of a molecular cloud core (star-like) or whether BDs and some very low-mass stars (VLMSs) constitute a separate population that forms alongside stars comparable to the population of planets, for example through circumstellar disk (peripheral) fragmentation. Aims. For young stars in Taurus-Auriga the binary fraction has been shown to be large with little dependence on primary mass above approximate to 0.2 M-circle dot, while for BDs the binary fraction is < 10%. Here we investigate a case in which BDs in Taurus formed dominantly, but not exclusively, through peripheral fragmentation, which naturally results in small binary fractions. The decline of the binary frequency in the transition region between star-like formation and peripheral formation is modelled. Methods. We employed a dynamical population synthesis model in which stellar binary formation is universal with a large binary fraction close to unity. Peripheral objects form separately in circumstellar disks with a distinctive initial mass function (IMF), their own orbital parameter distributions for binaries, and small binary fractions, according to observations and expectations from smoothed particle hydrodynamics (SPH) and grid-based computations. A small amount of dynamical processing of the stellar component was accounted for as appropriate for the low-density Taurus-Auriga embedded clusters. Results. The binary fraction declines strongly in the transition region between star-like and peripheral formation, exhibiting characteristic features. The location of these features and the steepness of this trend depend on the mass limits for star-like and peripheral formation. Such a trend might be unique to low density regions, such as Taurus, which host binary populations that are largely unprocessed dynamically in which the binary fraction is large for stars down to M-dwarfs and small for BDs. Conclusions. The existence of a strong decline in the binary fraction - primary mass diagram will become verifiable in future surveys on BD and VLMS binarity in the Taurus-Auriga star-forming region. The binary fraction -primary mass diagram is a diagnostic of the (non-)continuity of star formation along the mass scale, the separateness of the stellar and BD populations, and the dominant formation channel for BDs and BD binaries in regions of low stellar density hosting dynamically unprocessed populations.

Aims. The aim of this work is to constrain properties of the disk around the archetype FU Orionis object, FU Ori, with as good as similar to 25 au resolution. Methods. We resolved FU Ori at 29-37 GHz using the Karl G. Jansky Very Large Array (JVLA) in the A-array configuration, which provided the highest possible angular resolution to date at this frequency band (similar to 0 ''.07). We also performed complementary JVLA 8-10 GHz observations, Submillimeter Array (SMA) 224 GHz and 272 GHz observations, and compared these with archival Atacama Large Millimeter Array (ALMA) 346 GHz observations to obtain the spectral energy distributions (SEDs). Results. Our 8-10 GHz observations do not find evidence for the presence of thermal radio jets, and constrain the radio jet/wind flux to at least 90 times lower than the expected value from the previously reported bolometric luminosity-radio luminosity correlation. The emission at frequencies higher than 29 GHz may be dominated by the two spatially unresolved sources, which are located immediately around FU Ori and its companion FU Ori S, respectively. Their deconvolved radii at 33 GHz are only a few au, which is two orders of magnitude smaller in linear scale than the gaseous disk revealed by the previous Subaru-HiCIAO 1.6 mu m coronagraphic polarization imaging observations. We are struck by the fact that these two spatially compact sources contribute to over 50% of the observed fluxes at 224 GHz, 272 GHz, and 346 GHz. The 8-346 GHz SEDs of FU Ori and FU Ori S cannot be fit by constant spectral indices (over frequency), although we cannot rule out that it is due to the time variability of their (sub)millimeter fluxes. Conclusions. The more sophisticated models for SEDs considering the details of the observed spectral indices in the millimeter bands suggest that the >29 GHz emission is contributed by a combination of free-free emission from ionized gas and thermal emission from optically thick and optically thin dust components. We hypothesize that dust in the innermost parts of the disks (less than or similar to 0.1 au) has been sublimated, and thus the disks are no longer well shielded against the ionizing photons. The estimated overall gas and dust mass based on SED modeling, can be as high as a fraction of a solar mass, which is adequate for developing disk gravitational instability. Our present explanation for the observational data is that the massive inflow of gas and dust due to disk gravitational instability or interaction with a companion/intruder, was piled up at the few-au scale due to the development of a deadzone with negligible ionization. The piled up material subsequently triggered the thermal instability and the magnetorotational instability when the ionization fraction in the inner sub-au scale region exceeded a threshold value, leading to the high protostellar accretion rate.

We present proper motion measurements of 37 jets and HH objects in the Carina Nebula measured in two epochs of H alpha images obtained similar to 10 yr apart with Hubble Space Telescope/Advanced Camera for Surveys (ACS). Transverse velocities in all but one jet are faster than greater than or similar to 25 km s(-1), confirming that the jet-like H alpha features identified in the first epoch images trace outflowing gas. Proper motions constrain the location of the jet-driving source and provide kinematic confirmation of the intermediate-mass protostars that we identify for 20/37 jets. Jet velocities do not correlate with the estimated protostar mass and embedded driving sources do not have slower jets. Instead, transverse velocities (median similar to 75 km s(-1)) are similar to those in jets from low-mass stars. Assuming a constant velocity since launch, we compute jet dynamical ages (median similar to 10(4) yr). If continuous emission from inner jets traces the duration of the most recent accretion bursts, then these episodes are sustained longer (median similar to 700 yr) than the typical decay time of an FU Orionis outburst. These jets can carry appreciable momentum that may be injected into the surrounding environment. The resulting outflow force, dp/dt, lies between that measured in low- and high-mass sources, despite the very different observational tracers used. Smooth scaling of the outflow force argues for a common physical process underlying outflows from protostars of all masses. This latest kinematic result adds to a growing body of evidence that intermediate-mass star formation proceeds like a scaled-up version of the formation of low-mass stars.

OTS44 is one of only four free-floating planets known to have a disk. We have previously shown that it is the coolest and least massive known free-floating planet (similar to 12 M-Jup) with a substantial disk that is actively accreting. We have obtained Band 6 (233 GHz) ALMA continuum data of this very young disk-bearing object. The data show a clear unresolved detection of the source. We obtained disk-mass estimates via empirical correlations derived for young, higher-mass, central (substellar) objects. The range of values obtained are between 0.07 and 0.63 M-circle plus (dust masses). We compare the properties of this unique disk with those recently reported around higher-mass (brown dwarfs) young objects in order to infer constraints on its mechanism of formation. While extreme assumptions on dust temperature yield disk-mass values that could slightly diverge from the general trends found for more massive brown dwarfs, a range of sensible values provide disk masses compatible with a unique scaling relation between M-dust and M* through the substellar domain down to planetary masses.

Population III (Pop III) stars are the first generation stars forming after the big bang from primordial gas. This dissertation is focused on the various processes that suppress and delay the formation of Pop III stars in the universe and their implications for the observations. We studied the impacts of the Lyman-Werner (LW) radiation that dissociates molecular hydrogen, baryon-dark matter streaming velocity introduced at recombination, ionizing radiation from nearby galaxies, and a model for the composition of dark matter known as the fuzzy dark matter on the formation of Pop III stars. Firstly, we take a closer look at the critical halo mass (Mcrit) that is the typical minimum dark matter halo mass needed to host cold dense gas to form the first stars using cosmological hydrodynamical simulations. LW radiation that dissociates molecular hydrogen and the baryon-dark matter streaming velocity both delay the formation of Pop III stars by increasing the critical halo mass. We describe our simulation suite with varying levels of LW radiation and streaming velocity to provide a fit for Mcrit as a function of LW radiation, streaming velocity, and redshift which can be used in semi-analytic models of early galaxy formation to make predictions for observations. Secondly, we explore a possible mechanism for the formation of large clusters of Pop III stars: a nearby ionizing source that ionizes a late forming halo, delaying its collapse until the halo is sufficiently large enough that the core can self-shield and suffer runaway collapse. We use numerical simulations to examine the fragmentation of the gas near the runaway collapse using the simple estimates and sink particles to show that the number of fragments is generally small, at most a handful, and that the mass accretion rate on the fragments is of order 10⁻³ Msun/yr. This rate is sufficiently high enough that the descent on the main sequence (and hence the suppression of accretion) is delayed until the stellar masses are of order 100-1000 Msun, but not high enough to produce direct collapse black holes of mass ~ 10⁵ Msun. The resulting clusters are larger than those produced in minihalos but are still likely to fall short of being easily detectable in James Webb Space Telescope blind fields. Finally, we investigate the formation of the first stars and galaxies in a fuzzy dark matter cosmology. Fuzzy dark matter, made up of ultra-light axions of mass ~ 10⁻²² eV, is a proposed alternative to the standard cold dark matter to solve its apparent small-scale problems. Its large de Broglie wavelength, of the order of kpc, results in the suppression of small-scale matter power, thus delaying the formation of the first stars and galaxies to lower redshift in much more massive halos. Therefore, first stars can be used to put very strong constraints on the mass of the fuzzy dark matter. We describe our cosmological simulations that accurately evolve the fuzzy dark matter distribution to study the formation of the first stars and galaxies.

In an effort to understand unusual power-law spectral slopes observed in some hypercompact H II regions, we consider the radio continuum energy distribution from an ensemble of spherical clumps. An analytic expression for the free-free emission from a single spherical clump is derived. The radio continuum slope (with Fv ∝ vα) is governed by the population of clump optical depths N(τ) such that (1) at frequencies where all clumps are thick, a continuum slope of +2 is found, (2) at frequencies where all clumps are optically thin, a flattened slope of -0.11 is found, and (3) at intermediate frequencies, a power-law segment of significant bandwidth with slopes between these two limiting values can result. For the ensemble distribution, we adopt a power-law distribution N(T) ∝-γ and find that significant power-law segments in the spectral energy distribution with slopes from +2 to -0.11 result only for a relatively restricted range of 7 values from 1 to 2. Furthermore, a greater range of clump optical depths for this distribution leads to a wider bandwidth over which the intermediate power-law segment exists. The model is applied to the source W49N B2 with an observed slope of α ≈ +0.9, but that may be turning over to become optically thin around 2 mm. An adequate fit is found in which most clumps are optically thin and there is little "shadowing" of rearward clumps by foreground clumps (i.e., the geometrical covering factor C ≪ 1). The primary insight gained from our study is that in the Rayleigh-Jeans limit for the Planck function that applies for the radio band, it is the distribution in optical depth of the clump population that is solely responsible for setting the continuum shape, with variations in the size and temperature of clumps serving to modulate the level of free-free emission.