Todd R. Hunter

THE 2014 ALMA LONG BASELINE CAMPAIGN: FIRST RESULTS FROM HIGH ANGULAR RESOLUTION OBSERVATIONS TOWARD THE HL TAU REGION

We present Atacama Large Millimeter/submillimeter Array (ALMA) observations from the 2014 Long Baseline Campaign in dust continuum and spectral line emission from the HL Tau region. The continuum images at wavelengths of 2.9, 1.3, and 0.87 mm have unprecedented angular resolutions of 0. ′′ 075 (10 AU) to 0. ′′ 025 (3.5 AU), revealing an astonishing level of detail in the cir cumstellar disk surrounding the young solar analogue HL Tau, with a pattern of bright and dark rings observed at all wavelengths. By fitting ellipses to the most distinct rings, we measure precise values for the disk inclination (46.72 ◦ ± 0.05 ◦ ) and position angle (+138.02 ◦ ± 0.07 ◦ ). We obtain a high-fidelity image of the 1.0 mm spectral index (�), which ranges from � � 2.0 in the optically-thick central peak and two brightest ring s, increasing to 2.3-3.0 in the dark rings. The dark rings are not devoid of emission, and we estimate a grain emissivity index of 0.8 for the innermost dark ring and lower for subsequent dark rings, consistent with some degree of grain growth and evolution. Additional clues that the rings arise from planet formation incl ude an increase in their central offsets with radius and the presence of numerous orbital resonances. At a resolution of 35 AU, we resolve the molecular component of the disk in HCO + (1-0) which exhibits a pattern over LSR velocities from 2-12 km s -1 consistent with Keplerian motion around a �1.3M⊙ star, although complicated by absorption at low blue-shifted velocities. We also serendipitously detect and resolve the nearby protost ars XZ Tau (A/B) and LkH�358 at 2.9 mm. Subject headings: stars: individual (HL Tau, XZ Tau, LkH�358) — protoplanetary disks — stars: formation — submillimeter: planetary systems — techniques: interferometric

Search for CO Outflows toward a Sample of 69 High-Mass Protostellar Candidates. II. Outflow Properties

We present a study of molecular outflows toward a sample of 69 luminous IRAS point sources. The sample is associated with dense molecular gas and has far-infrared luminosities ranging from 102 to 105 L☉, indicating these objects as regions likely forming high-mass stars. Mapping in the CO J = 2-1 line shows that molecular outflows are ubiquitous in these regions. Most of the outflows have masses of tens of M☉. The typical dynamical timescale of the flow, without correcting for inclination of the flow axis, is a few times 104 yr. The typical energy in the outflows is 1046 ergs, comparable to the turbulent energy in the core. Nearly half of the outflows show spatially resolved bipolar lobes. This indicates that low-mass young stars that coexist in the region are not responsible for the bipolar outflows observed. It is the more massive stars that drive the outflow. The large detection rate of outflows in the region favors an accretion process in the formation of massive stars. The maximum mass-loss rate in the wind is about 10-4 M☉ yr-1. If these outflows are driven via accretion, the accretion rate should be as high as a few times 10-4 M☉ yr-1. We compare CO outflows with images at near-infrared wavelengths from the Two Micron All Sky Survey (2MASS) archive and find that some outflows are associated with extended emission in the K band, which may be partly due to vibrationally excited H2 emission at 2.12 μm.

A disk of dust and molecular gas around a high-mass protostar

The processes leading to the birth of low-mass stars such as our Sun have been well studied, but the formation of high-mass (over eight times the Suns mass, M[circdot]) stars remains poorly understood. Recent studies suggest that high-mass stars may form through accretion of material from a circumstellar disk, in essentially the same way as low-mass stars form, rather than through the merging of several low-mass stars. There is as yet, however, no conclusive evidence. Here we report the presence of a flattened disk-like structure around a massive 15M[circdot] protostar in the Cepheus A region, based on observations of continuum emission from the dust and line emission from the molecular gas. The disk has a radius of about 330 astronomical units (au) and a mass of 1 to 8 M[circdot]. It is oriented perpendicular to, and spatially coincident with, the central embedded powerful bipolar radio jet, just as is the case with low-mass stars, from which we conclude that high-mass stars can form through accretion.

Millimeter multiplicity in NGC 6334 I and I(N)

Using the Submillimeter Array (SMA), we have imaged the 1.3 mm continuum emission at the centers of the massive star-forming regions NGC 6334 I and I(N). In both regions, the SMA observations resolvethe emission into multiple millimeter sources, with most of the sources clustered into areas only 10,000 AU in diameter. Toward NGC 6334I, wefindfourcompactsources:thetwo brightest (I-SMA1andI-SMA2)areassociatedwithpreviouslyknown ammonia cores; I-SMA3 coincides with the peak of the compact H ii region (NGC 6334 F), and I-SMA4 is a newly discovered object. While I-SMA3 exhibits a mixture of free-free and dust emission, the rest of the objects are dust cores.TowardNGC6334I(N),sevencompactdustcoresarefound,oneofwhichisassociatedwithafaintcentimeter source. With the exception of I-SMA3, none of the millimeter sources have infrared counterparts in Spitzer Space Telescope3‐8� mimages.Usingasimplephysicalmodelforthedustcontinuumemission,we estimatethatthemass of the interstellar material toward each of these compact objects is in the range of 3‐66 M� . The total mass in the compact objects appears to be similar in I and I(N). The small size of these groups of sources suggest that these objects are proto-Trapezia forming in the centers of clusters of low- to intermediate-mass stars.

Search for CO Outflows toward a Sample of 69 High-Mass Protostellar Candidates: Frequency of Occurrence

A survey for molecular outflows was carried out by mapping the CO J = 2-1 line toward a sample of 69 luminous IRAS point sources. Sixty objects have IRAS luminosities from 103 to 105 L☉ and are associated with dense gas traced by NH3, identifying them as high-mass star-forming regions. Among 69 sources, 65 sources have data that are suitable for outflow identification. Thirty-nine regions show spatially confined high-velocity wing emission in CO, indicative of molecular outflows. Most objects without identifiable outflows lie within 0° < l < 50° where outflow signatures are confused by multiple cloud components along the line of sight. Excluding 26 sources with 0° < l < 50°, we found 35 outflows out of 39 sources, which yields an outflow detection rate of 90%. Many of the outflows contain masses of more than 10 M☉ and have momenta of a few hundred M☉ km s-1, at least 2 orders of magnitude larger than those in typical low-mass outflows. This class of massive and energetic outflows is most likely driven by high-mass young stellar objects. The high detection rate indicates that molecular outflows are common toward high-mass young stars. Given the connection between outflows and accretion disks in low-mass stars, we suggest that high-mass stars may form via an accretion-outflow process, similar to their low-mass counterparts.

Multiple jets from the high-mass (proto)stellar cluster AFGL 5142

We present studies of the massive protocluster AFGL 5142 in the J ¼ 2Y1 transition of the CO isotopologues, SO, CH3OH, and CH3CN lines, as well as in the continuum at 225 GHz and 8.4 GHz. The 225 GHz continuum emission reveals at least five dust continuum peaks. The strongest peaks, MM-1 and MM-2, are associated with hot cores with temperatures of 90 � 20 and 250 � 40 K, respectively. With similar core mass, the higher temperature and CH3CN abundance in the MM-2 core suggest that it might be at a more evolved stage than the MM-1 core. A total of 22 lines fromninemoleculesaredetected.Thelinestrengthvariesremarkablyintheregion.StrongSOemissionisfoundboth in molecular outflows and cloud cores. CH3OH emission, onthe contrary, is much weaker in molecular outflows, and isdetectedtowardhotcoresMM-1andMM-2,butisabsentinthelessmassiveandperhapslessevolvedcoresMM-3, MM-4, and MM-5. The CO and SO emission reveals at least three molecular outflows originating from the center of thedustcore.Theoutflowsarewellcollimated,withterminalvelocitiesupto50kms � 1 fromthecloudvelocity.Since jetlike outflows and disk-mediated accretion process are physically connected, the well-collimated outflows indicate that even in this cluster environment, accretion is responsible for the formation of individual stars in the cluster. Subject headingg s: H ii regions — ISM: clouds — ISM: individual (AFGL 5142) — ISM: kinematics and dynamics — masers — stars: formation

BIPOLAR MOLECULAR OUTFLOWS AND HOT CORES IN GLIMPSE EXTENDED GREEN OBJECTS (EGOs)

We present high angular resolution Submillimeter Array and Combined Array for Research in Millimeter-wave Astronomy observations of two GLIMPSE Extended Green Objects (EGOs)—massive young stellar object (MYSO) outflow candidates identified based on their extended 4.5 μm emission in Spitzer images. The millimeter observations reveal bipolar molecular outflows, traced by high-velocity 12CO(2-1) and HCO+(1-0) emission, coincident with the 4.5 μm lobes in both sources. SiO(2-1) emission confirms that the extended 4.5 μm emission traces active outflows. A single dominant outflow is identified in each EGO, with tentative evidence for multiple flows in one source (G11.92–0.61). The outflow driving sources are compact millimeter continuum cores, which exhibit hot core spectral line emission and are associated with 6.7 GHz Class II CH3OH masers. G11.92–0.61 is associated with at least three compact cores: the outflow driving source, and two cores that are largely devoid of line emission. In contrast, G19.01–0.03 appears as a single MYSO. The difference in multiplicity, the comparative weakness of its hot core emission, and the dominance of its extended envelope of molecular gas all suggest that G19.01–0.03 may be in an earlier evolutionary stage than G11.92–0.61. Modeling of the G19.01–0.03 spectral energy distribution suggests that a central (proto)star (M ~ 10 M ☉) has formed in the compact millimeter core (M gas ~12-16 M ☉), and that accretion is ongoing at a rate of ~10–3 M ☉ year–1. Our observations confirm that these EGOs are young MYSOs driving massive bipolar molecular outflows and demonstrate that considerable chemical and evolutionary diversity are present within the EGO sample.

High-Frequency Measurements of the Spectrum of Sagittarius A*

We report near-simultaneous interferometric measurements of the spectrum of Sagittarius A* over the 5-354 GHz range and single-dish observations that have yielded the first detection of Sgr A* at 850 GHz. We confirm that Sgr A*s spectrum rises more steeply at short millimeter wavelengths than at centimeter wavelengths, leading to a near-millimeter/submillimeter excess that dominates its luminosity. Below 900 GHz, Sgr A*s observed luminosity is 70 ± 30 L. A new upper limit to Sgr A*s 24.3 μm flux, together with a compilation of other extant IR data, imply a far-infrared spectral turnover, which can result from either an intrinsic synchrotron cutoff or excess extinction near Sgr A*. If the former applies, Sgr A*s total synchrotron luminosity is <103 L, while in the latter case it is <3 × 104 L if spherical symmetry also applies.

DIGGING INTO NGC 6334 I(N): MULTIWAVELENGTH IMAGING OF A MASSIVE PROTOSTELLAR CLUSTER

We present a high-resolution, multi-wavelength study of the massive protostellar cluster NGC 6334 I(N) that combines new spectral line data from the Submillimeter Array (SMA) and VLA with a re-analysis of archival VLA continuum data, Two Micron All Sky Survey and Spitzer images. As shown previously, the brightest 1.3 mm source SMA1 contains substructure at subarcsecond resolution, and we report the first detection of SMA1b at 3.6 cm along with a new spatial component at 7 mm (SMA1d). We find SMA1 (aggregate of sources a, b, c, and d) and SMA4 to be comprised of free-free and dust components, while SMA6 shows only dust emission. Our 15 resolution 1.3 mm molecular line images reveal substantial hot-core line emission toward SMA1 and to a lesser degree SMA2. We find CH3OH rotation temperatures of 165 ± 9 K and 145 ± 12 K for SMA1 and SMA2, respectively. We estimate a diameter of 1400 AU for the SMA1 hot-core emission, encompassing both SMA1b and SMA1d, and speculate that these sources comprise a 800 AU separation binary that may explain the previously suggested precession of the outflow emanating from the SMA1 region. Compact line emission from SMA4 is weak, and none is seen toward SMA6. The LSR velocities of SMA1, SMA2, and SMA4 all differ by 1-2 km s–1. Outflow activity from SMA1, SMA2, SMA4, and SMA6 is observed in several molecules including SiO(5-4) and IRAC 4.5 μm emission; 24 μm emission from SMA4 is also detected. Eleven water maser groups are detected, eight of which coincide with SMA1, SMA2, SMA4, and SMA6, while two others are associated with the Sandell source SM2. We also detect a total of 83 Class I CH3OH 44 GHz maser spots which likely result from the combined activity of many outflows. Our observations paint the portrait of multiple young hot cores in a protocluster prior to the stage where its members become visible in the near-infrared.

Dust and gas emission in the prototypical hot core G29.96–0.02 at sub-arcsecond resolution

Context. Hot molecular cores are an early manifestation of massive star formation where the molecular gas is heated to temperatures >100 K undergoing a complex chemistry. Aims. One wants to better understand the physical and chemical processes in this early evolutionary stage. Methods. We selected the prototypical hot molecular core G29.96−0.02 being located at the head of the associated ultracompact Hii region. The 862 µm submm continuum and spectral line data were obtained with the Submillimeter Array (SMA) at sub-arcsecond spatial resolution. Results. The SMA resolved the hot molecular core into six submm continuum sources with the finest spatial resolution of 0.36 �� ×0.25 �� (∼1800 AU) achieved so far. Four of them located within 7800 (AU) 2 comprise a proto-Trapezium system with estimated protostellar densities of 1.4×10 5 protostars/pc 3 . The plethora of ∼80 spectral lines allows us to study the molecular outflow(s), the core kinematics, the temperature structure of the region as well as chemical effects. The derived hot core temperatures are of the order 300 K. We find interesting chemical spatial differentiations, e.g., C 34 S is deficient toward the hot core and is enhanced at the UCHii/ hot core interface, which may be explained by temperature sensitive desorption from grains and following gas phase chemistry. The SiO(8−7) emission outlines likely two molecular outflows emanating from this hot core region. Emission from most other molecules peaks centrally on the hot core and is not dominated by any individual submm peak. Potential reasons for that are discussed. A few spectral lines that are associated with the main submm continuum source, show a velocity gradient perpendicular to the large-scale outflow. Since this velocity structure comprises three of the central protostellar sources, this is not a Keplerian disk. While the data are consistent with a gas core that may rotate and/or collapse, we cannot exclude the outflow(s) and/or nearby expanding UCHii region as possible alternative causes of this velocity pattern.