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Annular structures (rings and gaps) in disks around pre-main-sequence stars have been detected in abundance towards class II protostellar objects that are approximately 1,000,000 years old1. These structures are often interpreted as evidence of planet formation1–3, with planetary-mass bodies carving rings and gaps in the disk4. This implies that planet formation may already be underway in even younger disks in the class I phase, when the protostar is still embedded in a larger-scale dense envelope of gas and dust5. Only within the past decade have detailed properties of disks in the earliest star-forming phases been observed6,7. Here we report 1.3-millimetre dust emission observations with a resolution of five astronomical units that show four annular substructures in the disk of the young (less than 500,000 years old)8protostar IRS 63. IRS 63 is a single class I source located in the nearby Ophiuchus molecular cloud at a distance of 144 parsecs9, and is one of the brightest class I protostars at millimetre wavelengths. IRS 63 also has a relatively large disk compared to other young disks (greater than 50 astronomical units)10. Multiple annular substructures observed towards disks at young ages can act as an early foothold for dust-grain growth, which is a prerequisite of planet formation. Whether or not planets already exist in the disk of IRS 63, it is clear that the planet-formation process begins in the initial protostellar phases, earlier than predicted by current planet-formation theories11.

Double-Fourier interferometry is the most viable path to subarcsecond spatial resolution for future astronomical instruments that will observe the universe at far-infrared wavelengths. The double transform spatio-spectral interferometry couples pupil plane beam combination with detector arrays to enable imaging spectroscopy of wide fields, that will be key to accomplishing top-level science goals. The wide field of view and the necessity for these instruments to fly above the opaque atmosphere create unique characteristics and requirements compared to instruments on ground-based telescopes. In this paper, we discuss some characteristics of single-baseline spatio-spectral interferometers. We investigate the impact of intensity and optical path difference noise on the interferogram and the spectral signal-to-noise ratio. We apply our findings to the special case of the Balloon Experimental Twin Telescope for Infrared Interferometry (BETTII), a balloon payload that will be a first application of this technique at far-infrared wavelengths on a flying platform.

We present observations in eight wavebands from 1.25 to 24 mm of four dense cores: L204C-2, L1152, L1155C-2, and L1228. Our goals are to study the young stellar object (YSO) population of these cores and to measure the mid-infrared extinction law. With our combined near-infrared and Spitzer photometry, we classify each source in the cores as, among other things, background stars, galaxies, or embedded YSOs. L1152 contains three YSOs and L1228 has seven, but neither L204C-2 nor L1155C-2 appear to contain any YSOs. We estimate an upper limit of 7 x 10-5 to 5 x 10-4 L for any undiscovered YSOs in our cores. We also compute the line-of-sight extinction law toward each background star. These measurements are averaged spatially, to create kh2 maps of the changes in the mid-infrared extinction law throughout our cores, and also in different ranges of extinction. From the kh2 maps, we identify two small regions in L1152 and L1228 where the outflows in those cores appear to be destroying the larger dust grains, thus altering the extinction law in those regions. On average, however, our extinction law is relatively flat from 3.6 to 24 mm for all ranges of extinction and in all four cores. From 3.6 to 8 mm, this law is consistent with a dust model that includes larger dust grains than the diffuse interstellar medium, which suggests grain growth has occurred in our cores. At 24 mm, our extinction law is two to four times higher than predicted by dust models. However, it is similar to other empirical measurements.

We present dust opacity spectral indexes (b) of the youngest protostellar systems (so-called Class 0 sources), L1448 IRS 2, L1448 IRS 3, and L1157, obtained between the l = 1.3 mm and 2.7 mm continua, using the Combined Array for Research in Millimeter-wave Astronomy (CARMA). The unprecedented compact configuration and image fidelity of CARMA allow a better detection of the dust continuum emission from Class 0 sources, with a less serious missing flux problem normally associated with interferometry. Through visibility modeling at both l = 1.3 mm and 2.7 mm simultaneously, as well as image and visibility comparison, we show that b of the three Class 0 sources are around or smaller than 1, indicating that dust grains have already significantly grown at the Class 0 stage. In addition, we find a radial dependence of b, which implies faster grain growth in the denser central regions and/or dust segregation. Density distributions of the Class 0 sources are also addressed by visibility modeling.

We compute the mid-IR extinction law from 3.6 to 24 um in three molecular clouds--Ophiuchus, Perseus, and Serpens--by combining data from the "Cores to Disks" Spitzer Legacy Science program with deep JHKs imaging. Using a new technique, we are able to calculate the line-of-sight (LOS) extinction law toward each background star in our fields. With these LOS measurements, we create, for the first time, maps of the kh2 deviation of the data from two extinction law models. Because our kh2 maps have the same spatial resolution as our extinction maps, we can directly observe the changing extinction law as a function of the total column density. In the Spitzer Infrared Array Camera (IRAC) bands, 3.6-8 um, we see evidence for grain growth. Below $A_{K_s} = 0.5$, our extinction law is well fitted by the Weingartner and Draine RV = 3.1 diffuse interstellar-medium dust model. As the extinction increases, our law gradually flattens, and for $A_{K_s} \ge 1$, the data are more consistent with the Weingartner and Draine RV = 5.5 model that uses larger maximum dust grain sizes. At 24 um, our extinction law is 2-4 times higher than the values predicted by theoretical dust models, but is more consistent with the observational results of Flaherty et al. Finally, from our kh2 maps we identify a region in Perseus where the IRAC extinction law is anomalously high considering its column density. A steeper near-IR extinction law than the one we have assumed may partially explain the IRAC extinction law in this region.

Using interferometric data from BIMA observations, combined with detailed modeling in Fourier space of the physical structures predicted by models, we constrain the circumstellar envelope parameters for four Class 0 young stellar objects, as well as their embedded circumstellar disks. The envelopes of these objects are still undergoing collapse, and theoretical collapse models can be compared to the observations. Since it has been suggested in a previous study that both the Larson-Penston and Shu similarity solutions underestimate the age of the system, we adopt Tassis & Mouschovias' model of the collapse process, which includes all relevant magnetic fields effects. The results of the model fitting show a good consistency between theory and data; furthermore, no age problem exists, since the Tassis & Mouschovias' model is age independent for the first 255 kyr. Although the majority of the continuum dust emission arises from the circumstellar envelopes, these objects have well-known outflows, which suggest the presence of circumstellar disks. At the highest resolution, most of the large-scale envelope emission is resolved out by interferometry, but the small-scale residual emission remains, making it difficult to observe only the compact disk component. By modeling the emission of the envelope and subtracting it from the total emission, we constrain the disk masses in our four systems to be comparable to or smaller than the typical disk masses for T Tauri systems.

We present maps of 14.4 deg2 of the Ophiuchus dark clouds observed by the Spitzer Space Telescope Multiband Imaging Photometer for Spitzer (MIPS). These high-quality maps depict both numerous point sources and extended dust emission within the star-forming and non-star-forming portions of these clouds. Using PSF-fitting photometry, we detect 5779 sources at 24 mm and 81 sources at 70 mm at the 10 s level of significance. Three hundred twenty-three candidate young stellar objects (YSOs) were identified according to their positions on the MIPS/2MASS K versus K [?] [ 24] color-magnitude diagrams, as compared to 24 mm detections in the SWIRE extragalactic survey. We find that more than half of the YSO candidates, and almost all those with protostellar Class I spectral energy distributions, are confined to the known cluster and aggregates.

We present maps of 7.78 deg2 of the Lupus molecular cloud complex at 24, 70, and 160 mm. They were made with the Spitzer Space Telescope Multiband Imaging Photometer for Spitzer (MIPS) instrument as part of the Spitzer Legacy Program "From Molecular Cores to Planet-Forming Disks" (c2d). The maps cover three separate regions in Lupus, denoted I, III, and IV. We discuss the c2d pipeline and how our data processing differs from it. We compare source counts in the three regions with two other data sets and predicted star counts from the Wainscoat model. This comparison shows the contribution from background galaxies in Lupus I. We also create two color-magnitude diagrams using the 2MASS and MIPS data. From these results, we can identify background galaxies and distinguish them from probable young stellar objects. The sources in our catalogs are classified based on their spectral energy distribution (SED) from 2MASS and Spitzer wavelengths to create a sample of young stellar object candidates. From 2MASS data, we create extinction maps for each region and note a strong correspondence between the extinction and the 160 mm emission. The masses we derived in each Lupus cloud from our extinction maps are compared to masses estimated from 13CO and C18 O and found to be similar to our extinction masses in some regions, but significantly different in others. Finally, based on our color-magnitude diagrams, we selected 12 of our reddest candidate young stellar objects for individual discussion. Five of the 12 appear to be newly discovered YSOs.

We present maps of 1.5 deg2 of the Serpens dark cloud at 24, 70, and 160 mm observed with the Spitzer Space Telescope MIPS camera. We describe the observations and briefly discuss the data processing carried out by the c2d team on these data. More than 2400 compact sources have been extracted at 24 mm, nearly 100 at 70 mm, and four at 160 mm. We estimate completeness limits for our 24 mm survey from Monte Carlo tests with artificial sources inserted into the Spitzer maps. We compare source counts, colors, and magnitudes in the Serpens cloud to two reference data sets: a 0.50 deg 2 set on a low-extinction region near the dark cloud, and a 5.3 deg2 subset of the SWIRE ELAIS N1 data that was processed through our pipeline. These results show that there is an easily identifiable population of young stellar object candidates in the Serpens cloud that is not present in either of the reference data sets. We also show a comparison of visual extinction and cool dust emission illustrating a close correlation between the two and find that the most embedded YSO candidates are located in the areas of highest visual extinction.

We present deep IRAC images that highlight the scattered light emission around many of the youngest protostars, the so-called Class 0 sources, in L1448. By comparison of the data with the Monte Carlo radiative transfer code of Whitney et al., we demonstrate for the first time that the observed infrared light from these objects is consistent with scattered light from the central protostar. The scattered light escapes out the cavity, carved by molecular outflows, in the circumstellar envelope. In particular, we observe prominent scattered light nebulae associated with the Class 0 sources: L1448-mm, L1448 IRS 2, and 3B, as well as a Class I source: IRS 3A. We use a grid of models with probable protostellar properties to generate model spectral energy distributions (SEDs) and images for bands sensitive to this scattered light: J, H, Ks, and Spitzer IRAC bands. By simultaneously fitting SEDs and images of the outflow cavities, we are able to model geometric parameters, i.e., inclination angle and opening angle, and loosely constrain physical parameters. The opening angle may be an important indicator of the evolutionary state of a source. We compare our results for Class 0 sources to similar studies of Class I sources. There may be a transition phase from Class 0 to Class I when a source has an opening angle between 20deg to 30deg. It is important to note that while the best-fit model image and SED do not fully describe the sources, the fits generally describe the circumstellar structure of Class 0 sources in L1448.

We present IRAC (3.6, 4.5, 5.8, and 8.0 mm) observations of the Chamaeleon II molecular cloud. The observed area covers about 1 deg2 defined by AV > 2. Analysis of the data in the 2005 c2d catalogs reveals a small number of sources (40) with properties similar to those of young stellar or substellar objects (YSOs). The surface density of these YSO candidates is low, and contamination by background galaxies appears to be substantial, especially for sources classified as Class I or flat spectral energy distribution (SED). We discuss this problem in some detail and conclude that very few of the candidate YSOs in early evolutionary stages are actually in the Cha II cloud. Using a refined set of criteria, we define a smaller, but more reliable, set of 24 YSO candidates.

Infrared images of the dark cloud core B59 were obtained with the Spitzer Space Telescope as part of the "Cores to Disks" Legacy Science project. Photometry from 3.6-70 mm indicates at least 20 candidate low-mass young stars near the core, more than doubling the previously known population. Out of this group, 13 are located within ~0.1 pc in projection of the molecular gas peak, where a new embedded source is detected. Spectral energy distributions span the range from small excesses above photospheric levels to rising in the mid-infrared. One other embedded object, probably associated with the millimeter source B59-MMS1, with a bolometric luminosity Lbol ~ 2 L, has extended structure at 3.6 and 4.5 mm, possibly tracing the edges of an outflow cavity. The measured extinction through the central part of the core is AV [?] 45 mag. The B59 core is producing young stars with a high efficiency.

We present N-body simulations illustrating how giant planet migration can significantly affect the conditions for the formation of interior terrestrial planets. A giant planet migrating through a swarm of planetesimals will scatter many of them onto very eccentric and inclined orbits, preventing them from playing any further role in additional planet formation. The magnitude of this excitation is strongly dependent on the mass and migration rate of the giant planet. We found that if planet migration occurs for low-mass planets (one-tenth of the mass of Jupiter) or proceeds very rapidly (10-3 AU yr-1), planetesimal swarms can dynamically cool via gas drag, collisions, and dynamical friction after the giant passes through. Other simulations produce a population of planetesimals on orbits with very high eccentricity and inclination, which may persist and become a signature of a previous migration event. In some cases further growth of terrestrial planets is possible, leading to our prediction of terrestrial planets existing on orbits outside of some hot Jupiters.

We present high-resolution 0.''45 x 0.''32 observations from the BIMA array toward the Herbig Ae system MWC 480 in the l = 1.4 mm dust continuum. We resolve a circumstellar disk of radius ~170 AU and constrain the disk parameters by comparing the observations to flat-disk models. These results show that the typical fit parameters of the disk, such as the mass, MD ~ 0.04-0.18 M, and the surface density power-law index, p = 0.5 or 1, are comparable to those of the lower mass T Tauri stars. The dust in the MWC 480 disk can be modeled as processed dust material (b [?] 0.8), similar to the Herbig Ae star CQ Tau disk; the fitted disk parameters are also consistent with less evolved dust (b [?] 1.2). The possibility of grain growth in the MWC 480 circumstellar disk is supported by the acceptable fits with b [?] 0.8. The surface density power-law profiles of p = 0.5 and p = 1 can be easily fitted to the MWC 480 disk; however, a surface density power-law profile similar to the minimum mass solar nebula model p = 1.5 is ruled out at an 80% confidence level.

We present observations of 3.86 deg2 of the Perseus molecular cloud complex with the Spitzer Space Telescope Infrared Array Camera (IRAC). The maps show strong extended emission arising from shocked H2 in outflows and from polycyclic aromatic hydrocarbon features. More than 120,000 sources are extracted toward the cloud. Based on their IRAC colors and comparison to off-cloud and extragalactic fields, we identify 400 candidate young stellar objects. About two-thirds of these are associated with the young clusters IC 348 and NGC 1333, while the last third is distributed over the remaining cloud. The young stellar objects are classified according to the slope of their spectral energy distributions. Significant differences are found between the numbers of embedded Class I objects and more evolved Class II objects in IC 348, NGC 1333 and the remaining cloud, with the embedded Class I and "flat-spectrum" YSOs constituting 14%, 36% and 47% of the total number of YSOs identified in each of these regions. The high number of Class I objects in the extended cloud (61% of the Class I objects in the entire cloud) suggests that a significant fraction of the current star formation occurs outside the two main clusters. Finally, we discuss a number of outflows and identify their driving sources, including the deeply embedded Class 0 sources outside the two main clusters. The Class 0 objects are detected by Spitzer and have very red [3.6] - [4.5] colors, but they do not show similarly red [5.8] - [8.0] colors. The Class 0 objects are easily identifiable in color-color diagrams but are problematic to extract automatically due to the extended emission from shocked gas or scattered light in cavities related to the associated outflows.

We present maps of 0.89 deg2 of the Serpens dark cloud at 3.6, 4.5, 5.8, and 8.0 mm observed with the Spitzer Space Telescope Infrared Array Camera (IRAC). We discuss in detail the data processing carried out by the c2d team on IRAC data. More than 100,000 compact sources have been extracted, but we confine most of our discussion to the most reliable subset of these sources. This includes those that are detected above 7 s in all four IRAC bands or those detected in the two shorter IRAC bands together with 2MASS. We estimate completeness limits for our survey from Monte Carlo tests with artificial sources inserted into the Spitzer maps. We compare source counts, colors, and magnitudes in the Serpens cloud to two reference data sets, a 0.10 deg2 set of low-extinction regions near the dark cloud and a 1 deg2 subset of the SWIRE Elais N1 data that was processed through our pipeline. We find that it is possible to identify more than 200 young stellar object (YSO) candidates from color-magnitude and color-color diagrams, most of which were previously unknown. In addition to the dense area of new star formation known before in the "core" region (cluster A), we also find a moderately rich area to the south (cluster B). Our mapped area also includes the Herbig Ae star VV Ser, whose Spitzer images have been carefully modeled in a separate study. The extreme sensitivity of Spitzer IRAC allows us to search to very low luminosity limits for young substellar objects. The comparison of the Serpens region with the reference areas suggests that a population of infrared excess sources exists in Serpens at least down to luminosities of L ~ 10-3 L and possibly lower.

We present maps of over 1.5 deg2 in Chamaeleon (Cha) II at 24, 70, and 160 mm observed with the Spitzer Space Telescope Multiband Imaging Photometer for Spitzer (MIPS) and a 1.2 deg2 millimeter map from SIMBA on the Swedish-ESO Submillimetre Telescope (SEST). The c2d Spitzer Legacy Team's data reduction pipeline is described in detail. Over 1500 24 mm sources and 41 70 mm sources were detected by MIPS with fluxes greater than 10 s. More than 40 potential YSOs are identified with a MIPS and 2MASS color-color diagram and by their spectral indices, including two previously unknown sources with 24 mm excesses. Our new SIMBA millimeter map of Cha II shows that only a small fraction of the gas is in compact structures with high column densities. The extended emission seen by MIPS is compared with previous CO observations. Some selected interesting sources, including two detected at 1 mm, associated with Cha II are discussed in detail, and their SEDs are presented. The classification of these sources using MIPS data is found to be consistent with that of previous studies.

Crucial steps in the formation of stars and planets can be studied only at mid- to far-infrared wavelengths, where the Space Infrared Telescope(SIRTF) provides an unprecedented improvement in sensitivity. We will use all three SIRTFinstruments (Infrared Array Camera [IRAC], Multiband Imaging Photometer for SIRTF[MIPS], and Infrared Spectrograph [IRS]) to observe sources that span the evolutionary sequence from molecular cores to protoplanetary disks, encompassing a wide range of cloud masses, stellar masses, and star-forming environments. In addition to targeting about 150 known compact cores, we will survey with IRAC and MIPS (3.6-70 ?m) the entire areas of five of the nearest large molecular clouds for new candidate protostars and substellar objects as faint as 0.001 solar luminosities. We will also observe with IRAC and MIPS about 190 systems likely to be in the early stages of planetary system formation (ages up to about 10 Myr), probing the evolution of the circumstellar dust, the raw material for planetary cores. Candidate planet-forming disks as small as 0.1 lunar masses will be detectable. Spectroscopy with IRS of new objects found in the surveys and of a select group of known objects will add vital information on the changing chemical and physical conditions in the disks and envelopes. The resulting data products will include catalogs of thousands of previously unknown sources, multiwavelength maps of about 20 deg2of molecular clouds, photometry of about 190 known young stars, spectra of at least 170 sources, ancillary data from ground-based telescopes, and new tools for analysis and modeling. These products will constitute the foundations for many follow-up studies with ground-based telescopes, as well as with SIRTFitself and other space missions such as SIM, JWST, Herschel, and TPF/Darwin.

We present modeling results for 6 of the 11 deeply embedded systems from our subarcsecond l = 2.7 mm continuum interferometric survey. The modeling, performed in the u-v plane, assumes dust properties, allows for a power-law density profile, uses a self-consistent, luminosity-conserving temperature profile, and has an embedded point source to represent a circumstellar disk. Even though we have the highest spatial resolution to date at these wavelengths, only the highest signal-to-noise ratio systems can adequately constrain the simple self-similar collapse models. Of the six sources modeled, all were fitted with a density power-law index of 2.0; however, in half of the systems, those with the highest signal-to-noise ratio, a density power-law index of 1.5 can be rejected at the 95% confidence level. Further, we modeled the systems using the pure Larson-Penston (LP) and Shu solutions, with only age and sound speed as parameters. Overall, the LP solution provides a better fit to the data, in both likelihood and providing the observed luminosity, but the ages of the systems required by the fits are surprisingly low (1000-2000 yr). We suggest that either there is some overall time scaling of the self-similar solutions that invalidates the age estimates or, more likely, we are at the limit of the usefulness of these models. With our observations we have begun to reach the stage at which models need to incorporate more of the fundamental physics of the collapse process, probably including magnetic fields and/or turbulence. In addition to constraining collapse solutions, our modeling allows the separation of large-scale emission from compact emission, enabling the probing of the circumstellar disk component embedded within the protostellar envelope. Typically, 85% or more of the total emission is from the extended circumstellar envelope component. Using HL Tauri as a standard candle, the range of circumstellar disk masses allowed in our models is 0.0-0.12 M; our Class 0 systems do not have disks that are significantly more massive than those in Class I/II systems. This implies that the disk in Class 0 systems must quickly and efficiently process ~1 M of material from the envelope onto the protostar.

We have mapped the CO J = 1-0 emission from molecular outflows associated with six young stellar systems using the BIMA array. The systems are all relatively nearby, have low-luminosity, and range from Class 0 to Class II sources. The CO outflows in these systems are complicated, showing multipolar structures, multiple cavities, and asymmetric lobes. The complicated appearance of the CO outflows may result from the interactions between one or more outflows and the nonuniform ambient cloud. The CO emission typically arises from shell structures around the outflow axis. For some outflows, there are also clumpy and bowlike structures in CO along the outflow axis within the shell. Comparing the observed outflow features to that of jet- and wind-driven models, we find that the outflow systems show some features that are characteristic of the jet-driven model and others characteristic of the wind-driven model. Simple models of jets or winds cannot reproduce the full range of kinematic features found in observed outflows. The jet-driven model requires jet wandering to produce the observed outflow width and momentum content for most of these outflows, while the wind-driven model needs to have a collimated core with a strong velocity gradient away from the core to produce the highly collimated outflows and the observed curved internal H2 bow shock structures.

We have modeled the emission from dust in preprotostellar cores, including a self-consistent calculation of the temperature distribution for each input density distribution. Model density distributions include Bonnor-Ebert spheres and power laws. The Bonnor-Ebert spheres fit the data well for all three cores that we have modeled. The dust temperatures decline to very low values (Td ~ 7 K) in the centers of these cores, strongly affecting the dust emission. Compared to earlier models that assume constant dust temperatures, our models indicate higher central densities and smaller regions of relatively constant density. Indeed, for L1544, a power-law density distribution, similar to that of a singular, isothermal sphere, cannot be ruled out. For the three sources modeled herein, there seems to be a sequence of increasing central condensation, from L1512 to L1689B to L1544. The two denser cores, L1689B and L1544, have spectroscopic evidence for contraction, suggesting an evolutionary sequence for preprotostellar cores.

We analyze the dynamics of the shell produced when a bow shock from a collimated jet propagates into the surrounding medium. Under interstellar conditions, the shock is radiative, and a ballistic approximation for the shell flow is appropriate beyond the working surface where the jet impacts its surroundings. The solution is then determined by the ambient and jet densities and velocities and by the momentum impulse applied in the working surface. Using estimates for these impulses (confirmed by separate numerical simulations), we obtain solutions for the shell structure and for the range of velocities in the shell at any point. We provide predictions for the position-velocity and mass-velocity relations expected for plane-of-sky bow shock shells and for the bulk shell properties. In a companion paper, we show that these analytic solutions are in excellent agreement with the results of direct numerical simulations. We argue that classical molecular (CO) outflows cannot be purely jet-driven, because the bow shock shell solutions are much too elongated compared with observations. Finally, we suggest that the "spur" structures seen in position-velocity diagrams of observed molecular outflows are the manifestation of internal bow shocks, which may be fitted with our simple dynamical models.

We present two-dimensional hydrodynamic simulations of both jet- and wind-driven models for protostellar outflows in order to make detailed comparisons to the kinematics of observed molecular outflows. The simulations are performed with the ZEUS-2D hydrodynamic code using a simplified equation of state, simplified cooling and no external heating, and no self-gravity. In simulations of steady jets, swept-up ambient gas forms a thin shell that can be identified as a molecular outflow. We find a simple ballistic bow shock model is able to reproduce the structure and transverse velocity of the shell. Position-velocity (PV) diagrams for the shell cut along the outflow axis show a convex spur structure with the highest velocity at the bow tip and low-velocity red and blue components at any viewing angle. The power-law index of the mass-velocity (MV) relationship ranges from 1.5 to 3.5, depending strongly on the inclination. If the jet is time-variable, the PV diagrams show multiple convex spur structures, and the power-law index becomes smaller than the steady jet simulation. In simulations of isothermal steady wide-angle winds, swept-up ambient gas forms a thin shell that at early stages has a similar shape to the shell in the jet-driven model; it becomes broader at later times. We find the structure and kinematics of the shell is well described by a momentum-conserving model similar to that of Shu et al. (1991). In contrast to the results from jet simulations, the PV diagrams for the shell cut along the outflow axis show a lobe structure tilted with source inclination, with components that are primarily either red or blue unless the inclination is nearly in the plane of sky. The power-law index of the MV relationship ranges from 1.3 to 1.8. If the wind is time-variable, the PV diagrams also show multiple structures, and the power-law index becomes smaller than the steady wind simulation. Comparing the different simulations with observations, we find that some outflows, e.g., HH 212, show features consistent with the jet-driven model, while others, e.g., VLA 0548, are consistent with the wind-driven model.

We have mapped the CO J = 1-0 emission from molecular outflows associated with five young stellar systems of class 0 to class II/III using the BIMA array and the FCRAO 14 m antenna. The systems, VLA 05487, HH 212, HH 240/241, HH 111, and RNO 91, are all relatively nearby and of low luminosity, and the majority have H2 emission or optical jet features. The CO outflow generally forms a shell structure around the outflow axis with the higher velocity emission further out from the source. Two distinctive kinematic features are evident in position-velocity (PV) diagrams: a parabolic structure originating at the driving source (e.g., VLA 05487 and HH 111) and a convex spur structure with the high-velocity tip near known H2 bow shocks (e.g., HH 212, HH 240/241 and HH 111). The parabolic PV structure can be produced by a wide-angle-wind model, while the velocity spur structure can be modeled with a jet-driven bow shock model. VLA 05487, which is not associated with any H2 bow shocks, shows only the parabolic structure and kinematics consistent with the wide-angle wind-driven model. HH 212, which is associated with a series of H2 bow shock structures, shows a striking morphological coincidence between the H2 and CO emission and velocity spurs in the PV diagram. It is our best example of the jet-driven bow shock model, and its kinematics can be qualitatively explained in that context. HH 240/241 is similar to HH 212 and shows a close relationship between the H2 and CO emission. The kinematics of its western lobe can also be explained with the jet-driven model. The kinematics of RNO 91 are similar to VLA 05487 and are broadly consistent with a wide-angle wind-driven model. HH 111 has both parabolic and spur PV structures, a combination that is not easily explained in the simplest version of either model. Thus, these observations provide examples of systems that support either the wide-angle wind-driven or jet-driven model in the simplest interpretation. More detailed calculations are needed to understand whether one model might be able to fit all systems. It is crucial to know if time-dependent or long-lived jet-driven bow shock models can produce the observed outflow widths and parabolic PV structures, or if a wide-angle wind can produce the shock features and velocity spur structures in our observations.

A ? = 1 mm to 3 mm study of the Serpens molecular cloud core on scales of 10' to 10'' is presented, concentrating on the northwest condensation and the embedded sources, S68 FIRS1 and S68 N. We adopt temperatures of 25 K for the extended structure (several arcminute scale) and 35 K for the embedded sources. With these values, we use molecular line ratios and LVG statistical equilibrium calculations to derive physical properties in the region. We obtain densities between 0.4-1.2 × 106cm-3and an overall mass of 250-300 M?. The majority of the mass is found in extended cloud material with two peaks of 30-45 M?each. Values of the molecular column densities are derived on scales of 60''-75'' (condensation) and 25''-30'' (embedded sources). The column densities in the condensation are typically as high as in the embedded sources, despite a factor of 4-5 in beam area, though there is some suggestion of mild depletions on smaller scales based on interferometric observations. Derived abundances for the region show similarities to both warmer cores and colder, dark cloud regions, with some values and ratios falling cleanly between this range of properties. Measurements of several deuterated species indicate enhanced abundances, suggesting the recent evaporation of grain mantles.

We present the results of a l = 2.7 mm continuum interferometric survey of 24 young stellar objects in 11 fields. The target objects range from deeply embedded class 0 sources to optical T Tauri sources. This is the first subarcsecond survey of the l = 2.7 mm dust continuum emission from young, embedded stellar systems. These multiarray observations, utilizing the high dynamic u-v range of the BIMA array, fully sample spatial scales ranging from 0.''4 to 60'', thus allowing the first consistent comparison of dust emission structures in a variety of systems. The images show a diversity of structure and complexity. The optically visible T Tauri stars (DG Tauri, HL Tauri, GG Tauri, and GM Aurigae) have continuum emission dominated by compact ([?]1'') circumstellar disks. In the cases of HL Tauri and DG Tauri, the disks are resolved. The more embedded near-infrared sources (SVS 13 and L1551 IRS 5) have continuum emission that is extended and compact. The embedded sources (L1448 IRS 3, NGC 1333 IRAS 2, NGC 1333 IRAS 4, VLA 1623, and IRAS 16293-2422) have continuum emission dominated by the extended envelope, typically [?]85% of the emission at l = 2.7 mm. In many of the deeply embedded systems, it is difficult to uniquely isolate the disk emission component from the envelope extending inward to AU-sized scales. Simple estimates of the circumstellar mass in the optical/infrared and embedded systems are in the ranges 0.01-0.08 M and 0.04-2.88 M, respectively. All of the target embedded objects are in multiple systems with separations on scales of ~30'' or less. Based on the system separation, we place the objects in three categories: separate envelope (separation [?]6500 AU), common envelope (separation 150-3000 AU), and common disk (separation [?]100 AU). These three groups can be linked with fragmentation events during the star formation process: separate envelopes from prompt initial fragmentation and the separate collapse of a loosely condensed cloud, common envelopes from fragmentation of a moderately centrally condensed spherical system, and common disk from fragmentation of a high angular momentum circumstellar disk.

Nine Herbig Ae/Be stars have been observed at l = 2.7 mm with the IRAM and BIMA interferometers in order to place constraints on the presence of disk material around these objects. Only one Herbig Ae/Be star, Elias 3-1, was detected with certainty; two additional stars, MWC 137 and V645 Cyg, were possibly detected. The remaining six Herbig Ae/Be stars were not detected. Two deeply embedded objects near the target stars, LkHa 198-MM and V1318 Cyg S, were also detected. The emission from Elias 3-1 and V1318 Cyg S is unresolved, while that from LkHa 198 MM is resolved. Two stars (Elias 3-1 and V645 Cyg) were observed with the VLA at l = 7 mm, 1.3 cm, and 3.6 cm. Based on our VLA data and those of Skinner, Brown, & Stewart, it appears that emission from ionized gas may contribute substantially to the millimeter emission from several sources. After correcting for this component where necessary, the remaining emission from most of the sample, attributed to dust, is considerably less than that predicted by assuming that the shorter wavelength emission arises in a disk. Much of the submillimeter and millimeter emission toward most of these stars must therefore arise in an extended envelope. For Elias 3-1, the data are consistent with a disk with mass around 0.1 M. We place limits on the masses of disks around the other stars.

We present results of a search for centimeter-wavelength dust emission from five embedded young stellar objects and three T Tauri stars. Emission was detected from all of the embedded objects; in three of the five objects, this emission is identified as arising from ionized gas, probably associated with stellar winds. In two cases, NGC 1333 IRAS 4A and 4B, dust emission is suspected to be responsible for between 20 and 100% of the λ = 1.3 cm flux. Emission was detected from only one of the T Tauri stars, RY Tau; it is presently unclear if this emission arises from ionized gas or dust. Using standard circumstellar disk models for the dust emission associated with T Tauri stars, the upper limits to the centimeter-wavelength fluxes for DL Tau and GG Tau can be used to constrain the properties of the circumstellar dust. Assuming a power law form for the dust emissivity (ε ∝ vβ), the upper limits require that β, as measured from millimeter to centimeter wavelengths, is greater than 0.8 for DL Tau and greater than 1.6 for GG Tau. These values of β are considerably larger than values measured at submillimeter wavelengths in the same sources (β∼0.0). If the dust emissivity is described as a two-part power law corresponding to two different values of β, as is suggested for dust in the interstellar medium, the GG Tau data indicate that the value of β changes around λ = 2 mm. This change occurs at an order of magnitude greater wavelength than that proposed for interstellar dust and may reflect the growth of grain size in the circumstellar environment.

We have obtained high-resolution far-infrared maps of nine regions with 10 Herbig Ae/Be stars (intermediate-mass pre-main-sequence stars). Similar maps were obtained for 10 embedded IRAS sources with Sn(100 mm) > Sn(60 mm) and L ~ 200 L, which are possible evolutionary precursors of Herbig Ae/Be stars. Single far-infrared sources were found in most maps. The embedded sources have positions in agreement with those of the IRAS PSC, but some of the Herbig Ae/Be stars are offset significantly from the position of peak far-infrared emission. For all objects where it was possible to obtain 100 mm flux densities, they are consistent with those observed by IRAS, but derived 50 mm flux densities are larger than expected. The far-infrared maps reveal that objects in at least 17 of 19 emission regions are significantly extended at the 30''-40'' resolution of the Kuiper Airborne Observatory at 100 mm. Only sources associated with AB Aur and possibly IRAS 05338-0624 have unresolved far-infrared emission. Detailed analyses of the flux densities and positions from our maps suggest the far-infrared emission in regions with Herbig Ae/Be stars may not immediately surround these stars in all cases. Instead, far-infrared emission from these objects may originate from dust heated externally by the Herbig stars, or from dust heated internally by other sources. For other objects arguably surrounded by far-infrared emission, the Herbig stars or embedded IRAS objects have similar mean deconvolved sizes (i.e., 0.10-0.15 pc), but possibly have different mean deconvolved shapes (i.e., aspect ratios). Thus, far-infrared emission here may originate from flattened dust envelopes; the appearance of a far-infrared object as either a Herbig Ae/Be star or an embedded IRAS source may be merely a matter of viewing orientation.

We present new H?, CO, and H Iimages of the high gas surface density flocculent spiral NGC 4414 and compare them to recently published near-infrared observations that reveal kiloparsec-scale structures in the inner disk. The subtraction of an estimated supergiant contribution confirms that the near-infrared enhancements represent primarily variations in the surface density of the old stellar population. As material structures of kiloparsec extent cannot be maintained in a differentially rotating disk for sufficiently long times to be discernible in the old stellar population, the near-infrared observations suggest that global dynamical processes contribute to the formation of structure in NGC 4414. However, variations in the distribution of CO, H I, and H? peaks with respect to near-infrared "arm" structures suggest that stochastic processes are also important.

We present interferometric observations of CO and H I in the prototypical flocculent spiral NGC 5055, which has recently been shown to exhibit weak, two-arm spiral structure in the near-infrared. The morphology and kinematics described by VLA observations of H I emission and FCRAO and Berkeley-Illinois-Maryland Association (BIMA) Array observations of CO emission provide evidence for the presence of low-amplitude density waves in NGC 5055. The distribution of CO and H I emission suggests enhanced gas surface densities along the NIR spiral arms, and structures similar to the giant molecular associations found in the grand design spirals M51 and M100 are detected. An analysis of H I and Ha velocity fields shows the kinematic signature of streaming motions similar in magnitude to those of M100 in both tracers. The lesser degree of organization along the spiral arms of NGC 5055 may be due to the lower overall gas surface density, which in the arms of NGC 5055 is a factor of 2 lower than in M100 and a factor of 6 lower than in M51; an analysis of gravitational instability shows the gas in the arms is only marginally unstable and the interarm gas is marginally stable. The limited extent of the spiral arm pattern is consistent with an isolated density wave with a relatively high pattern speed; other possible formation mechanisms are also discussed.