Alwyn Wootten

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

Water Maser Survey toward Low-Mass Young Stellar Objects in the Northern Sky with the Nobeyama 45 Meter Telescope and the Very Large Array

We give a detailed presentation of all the data from a multiepoch 22 GHz H2O maser survey mainly toward low-mass young stellar objects (YSOs) using the Nobeyama 45 m telescope and the Very Large Array (VLA). Our major results are already published (our Paper I). The Nobeyama survey is the first complete H2O maser survey toward known Class 0 sources in the northern sky (δ > -35°) and is one of the most sensitive surveys ever performed. The survey was conducted from 1996 May through 1999 March over 32 periods. A total of 606 observations were carried out toward 173 YSOs, including 36 unknown luminosity sources, and toward 31 preprotostellar cores (PPSCs) in the Ophiuchus star-forming region. We detected 149 spectra toward 39 YSOs and zero spectra toward the 31 PPSCs. Subsequent to the Nobeyama survey, we performed a follow-up interferometric survey with the VLA in order to associate 19 maser sources detected by the 45 m telescope with individual YSOs. In this paper we compile properties of 142 YSOs together with their H2O maser activity. On the basis of this data set, we use properties of water maser emission as a probe of jet phenomena in low-mass stars.

Cold DCO(+) cores and protostars in the warm Rho Ophiuchi cloud

The decrease of DCO(+) abundance with elevation of a clouds T(K) is used to identify a cluster of a dozen of the coldest, youngest dense cores embedded in the L1688, L1689, and L1709 clouds in the Rho Ophiuchi complex. Most of the cores in L1688 have T(K) = 12-14 K, about half that indicated by CO throughout L1688. Ten cold dust shell, protostellar IR point sources are embedded within these cores. Not every DCO(+) core contains a protostar, but every protostar with a steep spectral index is found in close association with DCO(+) emission. The rotational axes for all of the Rho Oph DCO(+) cores are parallel to the ambient magnetic field, regardless of whether a core is elongated parallel or perpendicular to the direction of the magnetic field. In the Taurus complex the ambient magnetic field is perpendicular to the axes of the major filaments and will inhibit further concentration of material. 53 refs.

Distribution and Motion of the Water Masers near IRAS 05413–0104

We have used the NRAO Very Long Baseline Array to image water masers associated with the low-luminosity, young stellar object (YSO) IRAS 05413-0104 at four epochs over a period of 10 weeks. The maser images show the detail of a symmetric, jetlike structure about 300 mas in extent. The 23° ± 2° position angle of the maser spot distribution is in excellent agreement with measured position angles for the observed larger scale H2 and SiO emission distributions; radial velocities are in agreement with SiO measurements showing redshifted gas to the southwest and blueshifted gas to the northeast. We have detected proper motions of numerous maser spots averaging 30 ± 12 mas yr−1, implying space velocities of 64 ± 27 km s−1 for a source distance of 450 pc. Some masers are located within a projected distance of 40 AU of the origin of expansion, the assumed position of the central source, suggesting that jet formation and acceleration takes place within this radius of the YSO. We compute an inclination of the outflow system to the plane of the sky of 4°, based on the relative magnitude of the proper motions and radial velocities of the masers. VLBI observations of water masers in YSOs are clearly demonstrated to be interesting and competitive probes of the kinematics of the gas in YSO jets.

Synthesis imaging of the DR 21 (OH) cluster. II: Thermal ammonia and water maser emission

High-sensitivity, 4″ resolution images of the thermal ammonia and water maser emission have been made of the DR 21 (OH) molecular cloud. Images of the NH 3 (1,1) and (2,2) transitions show four primary emission regions embedded in a generally clumpy emission distribution. A total 18 ammonia cores are identified in these images. An analysis of the physical properties of these cores has shown that they are massive (M G ⇒15-1000 M ⊙ ) and warm (T k ⇒20 to greater than 80 K) with a range of sizes (θ s ⇒0.06-0.28 pc).

HCOOCH3 as a probe of temperature and structure in Orion-KL

Context. The Orion Kleinmann-Low nebula (Orion-KL) is a complex region of star formation. Whereas its proximity allows studies on a scale of a few hundred AU, spectral confusion makes it difficult to identify molecules with low abundances. Aims: We studied an important oxygenated molecule, HCOOCH3, to characterize the physical conditions, temperature, and density of the different molecular source components. Methyl formate presents strong close rotational transitions covering a wide range of energy, and its emission in Orion-KL is not contaminated by the emission of N-bearing molecules. This study will help in the future 1) to constrain chemical models for the formation of methyl formate in gas phase or on grain mantles and 2) to search for more complex or prebiotic molecules. Methods: We used high-resolution observations from the IRAM Plateau de Bure Interferometer to reduce spectral confusion and to better isolate the molecular emission regions. We used twelve data sets with a spatial resolution down to 1.8″ × 0.8″. Continuum emission was subtracted by selecting apparently line-free channels. Results: We identify 28 methyl formate emission peaks throughout the 50″ field of observations. The two strongest peaks, named MF1 and MF2, are in the Compact Ridge and in the southwest of the Hot Core, respectively. From a comparison with single-dish observations, we estimate that we miss less than 15% of the flux and that spectral confusion is still prevailing as half of the expected transitions are blended over the region. Assuming that the transitions are thermalized, we derive the temperature at the five main emission peaks. At the MF1 position in the Compact Ridge we find a temperature of 80 K in a 1.8″ × 0.8″ beam size and 120 K on a larger scale (3.6″ × 2.2″), suggesting an external source of heating, whereas the temperature is about 130 K at the MF2 position on both scales. Transitions of methyl formate in its first torsionally excited state are detected as well, and the good agreement of the positions on the rotational diagrams between the ground state and the vt = 1 transitions suggests a similar temperature. The LSR velocity of the gas is between 7.5 and 8.0 km s-1 depending on the positions and column density peaks vary from 1.6 × 1016 to 1.6 × 1017 cm-2. A second velocity component is observed around 9-10 km s-1 in a north-south structure stretching from the Compact Ridge up to the BN object, and this component is warmer at the MF1 peak. The two other C2H4O2 isomers are not detected, and the derived upper limit for the column density is ≤3 × 1014 cm-2 for glycolaldehyde and ≤2 × 1015 cm-2 for acetic acid. From the 223 GHz continuum map, we identify several dust clumps with associated gas masses in the range 0.8 to 5.8 Ms. Assuming that the methyl formate is spatially distributed as the dust is, we find relative abundances of methyl formate in the range ≤0.1 × 10-8 to 5.2 × 10-8. We suggest a relation between the methyl formate distribution and shocks as traced by 2.12 μm H2 emission. Based on observations carried out with the IRAM Plateau de Bure Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain).A fits image of the HCOOCH3 integrated intensity map (Fig. 4) is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/532/A32. All spectra can be obtained upon request to the authors.Table 10 and Appendix A are available in electronic form at http://www.aanda.org

Atacama Large Millimeter Array (ALMA)

The Atacama Large Millimeter Array, or ALMA, is an international telescope project which will be built over the coming decade in Northern Chile. With over 7000 m2 of collecting area comprised of 64 12m antennas arrayed over baselines up to 14 km in extent, ALMA will provide images of unprecedented clarity and detail. One revolutionary feature of ALMA will be its ability to combine interferometric and single telescope data, providing complete flux recovery. ALMA will cover a spectral wavelength range from 7mm to 0.3 mm or shorter wavelengths, providing astronomy with its first detailed look at the structures which emit millimeter and submillimeter photons, the most abundant photons in the Universe.

ACCRETION KINEMATICS THROUGH THE WARPED TRANSITION DISK IN HD 142527 FROM RESOLVED CO(6–5) OBSERVATIONS

The finding of residual gas in the large central cavity of the HD 142527 disk motivates questions regarding the origin of its non-Keplerian kinematics and possible connections with planet formation. We aim to understand the physical structure that underlies the intra-cavity gaseous flows, guided by new molecular-line data in CO(6–5) with unprecedented angular resolutions. Given the warped structure inferred from the identification of scattered-light shadows cast on the outer disk, the kinematics are consistent, to first order, with axisymmetric accretion onto the inner disk occurring at all azimuths. A steady-state accretion profile, fixed at the stellar accretion rate, explains the depth of the cavity as traced in CO isotopologues. The abrupt warp and evidence for near free-fall radial flows in HD 142527 resemble theoretical models for disk tearing, which could be driven by the reported low-mass companion, whose orbit may be contained in the plane of the inner disk. The companion’s high inclination with respect to the massive outer disk could drive Kozai oscillations over long timescales; high-eccentricity periods may perhaps account for the large cavity. While shadowing by the tilted disk could imprint an azimuthal modulation in the molecular-line maps, further observations are required to ascertain the significance of azimuthal structure in the density field inside the cavity of HD 142527.

Nitrogen Isotopic Fractionation in Interstellar Ammonia

Using the Green Bank Telescope, we have obtained accurate measurements of the ^(14)N/^(15)N isotopic ratio in ammonia in two nearby cold, dense molecular clouds, Barnard 1 and NGC 1333. The ^(14)N/^(15)N ratio in Barnard 1, 334 ± 50 (3σ), is particularly well constrained and falls in between the local interstellar medium/proto-solar value of ~450 and the terrestrial atmospheric value of 272. The NGC 1333 measurement is consistent with the Barnard 1 result, but has a larger uncertainty. We do not see evidence for the very high ^(15)N enhancements seen in cometary CN. Sensitive observations of a larger, carefully selected sample of prestellar cores with varying temperatures and gas densities can significantly improve our understanding of the nitrogen fractionation in the local interstellar medium and its relation to the isotopic ratios measured in various solar system reservoirs.

The Flattened, Rotating Molecular Gas Core of Protostellar Jet HH 212

The recently discovered protostellar jet known as HH 212 is beautifully symmetric, with a series of paired shock knots and bow shocks on either side of the exciting source region IRAS 05413-0104. We present VLA ammonia maps of the IRAS 05413-0104 molecular gas envelope in which the protostellar jet source is embedded. We find that the envelope, with a mass of 0.2 M☉ detected by the interferometer, is flattened perpendicular to the jet axis with an FWHM diameter of 12,000 AU and an axis ratio of 2 : 1, as seen in NH3 (1, 1) emission. There is a velocity gradient of about 4-5 km s-1 pc-1 across the flattened disklike core, suggestive of rotation around an axis aligned with the jet. Flux-weighted mean velocities increase smoothly with a roughly constant velocity gradient. In young (class 0) systems such as HH 212, a significant amount of material is still distributed in a large surrounding envelope, and thus the observable kinematics of the system may reflect the less centrally condensed, youthful state of the source and obscuration of central dynamics. The angular momentum of this envelope material may be released from infalling gas through rotation in the HH 212 jet, as recent observations suggest. A blueshifted wisp or bowl of emitting gas appears to be swept up along the blue side of the outflow, possibly lining the cavity of a wider angle wind around the more collimated shock jet axis. Our ammonia (2, 2)/(1, 1) ratio map indicates that this very cold core is heated to 14 K in a centrally condensed area surrounding the jet source. This edge-on core and jet system appears to be young and deeply embedded. This environment, however, is apparently not disrupting the pristine symmetry and collimation of the jet.