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Van Kempen T.A.,Joint ALMA Offices | Van Kempen T.A.,Leiden University | Van Kempen T.A.,Harvard - Smithsonian Center for Astrophysics | Longmore S.N.,Harvard - Smithsonian Center for Astrophysics | And 5 more authors.
Astrophysical Journal | Year: 2012

Intermediate-mass (IM) protostars, the bridge between the very common solar-like protostars and the more massive, but rarer, O and B stars, can only be studied at high physical spatial resolutions in a handful of clouds. In this paper, we present and analyze the continuum results from an observing campaign at the Submillimeter Array (SMA) targeting two well-studied IM protostars in Orion, NGC2071 and L1641 S3 MMS 1. The extended SMA (eSMA) probes structure at angular resolutions up to 02, revealing protostellar disks on scales of 200AU. Continuum flux measurements on these scales indicate that a significant amount of mass, a few tens of M ⊙, is present. Envelope, stellar, and disk masses are derived using compact, extended, and eSMA configurations and compared against spectral energy distribution fitting models. We hypothesize that fragmentation into three components occurred within NGC2071 at an early time, when the envelopes were less than 10% of their current masses, e.g., <0.5 M ⊙. No fragmentation occurred for L1641 S3 MMS 1. For NGC2071, evidence is given that the bulk of the envelope material currently around each source was accreted after the initial fragmentation. In addition, about 30% of the total core mass is not yet associated to one of the three sources. A global accretion model is favored and a potential accretion history of NGC2071 is presented. It is shown that the relatively low level of fragmentation in NGC2071 was stifled compared to the expected fragmentation from a Jeans argument. Similarly, the lack of fragmentation in L1641 S3 MMS 1 is likely due to similar arguments. © 2012. The American Astronomical Society. All rights reserved..

Dunham M.M.,Yale University | Arce H.G.,Yale University | Bourke T.L.,Harvard - Smithsonian Center for Astrophysics | Chen X.,Yale University | And 3 more authors.
Astrophysical Journal | Year: 2012

We present 230GHz Submillimeter Array continuum and molecular line observations of the newly discovered FU Orionis candidate HBC722. We report the detection of seven 1.3mm continuum sources in the vicinity of HBC722, none of which corresponds to HBC722 itself. We compile infrared and submillimeter continuum photometry of each source from previous studies and conclude that three are Class 0 embedded protostars, one is a Class I embedded protostar, one is a Class I/II transition object, and two are either starless cores or very young, very low luminosity protostars or first hydrostatic cores. We detect a northwest-southeast outflow, consistent with the previous detection of such an outflow in low-resolution, single-dish observations, and note that its axis may be precessing. We show that this outflow is centered on and driven by one of the nearby Class 0 sources rather than HBC722, and find no conclusive evidence that HBC722 itself is driving an outflow. The non-detection of HBC722 in the 1.3mm continuum observations suggests an upper limit of 0.02 M for the mass of the circumstellar disk. This limit is consistent with typical T Tauri disks and with a disk that provides sufficient mass to power the burst. © 2012. The American Astronomical Society. All rights reserved.

Fuente A.,Observatorio Astronomico Nacional OAN | Caselli P.,University of Leeds | McCoey C.,University of Waterloo | Cernicharo J.,CSIC - National Institute of Aerospace Technology | And 15 more authors.
Astronomy and Astrophysics | Year: 2012

Context. NGC 7129 FIRS 2 is a young intermediate-mass (IM) protostar, which is associated with two energetic bipolar outflows and displays clear signs of the presence of a hot core. It has been extensively observed with ground based telescopes and within the WISH guaranteed time Herschel key program. Aims. This paper is dedicated to the modeling of the C18O and HDO lines in NGC 7129 FIRS 2. Our goal is to investigate the chemistry in the envelope and hot core of this IM protostar. Methods. We present new observations of the C 18O 3 → 2 and the HDO 312 → 221 lines towards NGC 7129 FIRS 2. Combining these observations with Herschel data and modeling their emissions, we constrain the C18O and HDO abundance profiles across the protostellar envelope. In particular, we derive the abundance of C18O and HDO in the hot core. Results. The intensities of the C18O lines are well reproduced assuming that the C 18O abundance decreases through the protostellar envelope from the outer edge towards the centre until the point where the gas and dust reach the CO evaporation temperature (≈ 20-25 K) where the C18O is released back to the gas phase. Once the C18O is released to the gas phase, the modelled C18O abundance is found to be ≈ 1.6 × 10 -8, which is a factor of 10 lower than the reference abundance. This result is supported by the non-detection of C18O 9 → 8, which proves that even in the hot core (Tk > 100 K) the CO abundance must be 10 times lower than the reference value. Several scenarios are discussed to explain this C18O deficiency. One possible explanation is that during the pre-stellar and protostellar phase, the CO is removed from the grain mantles by reactions to form more complex molecules. Our HDO modeling shows that the emission of HDO 312 → 221 line is maser and comes from the hot core (Tk > 100 K). Assuming the physical structure derived by Crimier et al. (2010), we determine a HDO abundance of ∼0.4-1 × 10-7 in the hot core of this IM protostar. Conclusions.Herschel data combined with ground based observations have allowed us to estimate the C18O and HDO abundance in the protostellar envelope and hot core of an IM protostar. The HDO abundance in the hot core is ∼0.4-1 × 10-7, similar to that found in the hot corinos NGC 1333 IRAS 2A and IRAS 16293-2422. The C18O abundance, at ≈ 1.6 × 10-8, is a factor of 10 lower than the reference value. © 2012 ESO.

Baryshev A.M.,University of Groningen | Baryshev A.M.,SRON Netherlands Institute for Space Research | Hesper R.,University of Groningen | Mena F.P.,SRON Netherlands Institute for Space Research | And 26 more authors.
Astronomy and Astrophysics | Year: 2015

Aims. We describe the design, construction, and characterization of the Band 9 heterodyne receivers (600-720 GHz) for the Atacama Large Millimeter/submillimeter Array (ALMA). First-light Band 9 data, obtained during ALMA commissioning and science verification phases, are presented as well. Methods. The ALMA Band 9 receiver units (so-called "cartridges"), which are installed in the telescope's front end, have been designed to detect and down-convert two orthogonal linear polarization components of the light collected by the ALMA antennas. The light entering the front end is refocused with a compact arrangement of mirrors, which is fully contained within the cartridge. The arrangement contains a grid to separate the polarizations and two beam splitters to combine each resulting beam with a local oscillator signal. The combined beams are fed into independent double-sideband mixers, each with a corrugated feedhorn coupling the radiation by way of a waveguide with backshort cavity into an impedance-tuned superconductor-insulator-superconductor (SIS) junction that performs the heterodyne down-conversion. Finally, the generated intermediate frequency (IF) signals are amplified by cryogenic and room-temperature HEMT amplifiers and exported to the telescope's IF back end for further processing and, finally, correlation. Results. The receivers have been constructed and tested in the laboratory and they show an excellent performance, complying with ALMA requirements. Performance statistics on all 73 Band 9 receivers are reported. Importantly, two different tunnel-barrier technologies (necessitating different tuning circuits) for the SIS junctions have been used, namely conventional AlOx barriers and the more recent high-current-density AlN barriers. On-sky characterization and tests of the performance of the Band 9 cartridges are presented using commissioning data. Continuum and line images of the low-mass protobinary IRAS 16293-2422 are presented which were obtained as part of the ALMA science verification program. An 8 GHz wide Band 9 spectrum extracted over a 0.3′′ × 0.3′′ region near source B, containing more than 100 emission lines, illustrates the quality of the data. © 2015 ESO.

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