| 1. |
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- 2019
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Tidskriftsartikel (refereegranskat)
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| 2. |
- van Dishoeck, E. F., et al.
(författare)
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Water in Star-forming Regions with the Herschel Space Observatory (WISH). I. Overview of Key Program and First Results
- 2011
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Ingår i: Publications of the Astronomical Society of the Pacific. - : IOP Publishing. - 0004-6280 .- 1538-3873. ; 123:900, s. 138-170
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Tidskriftsartikel (refereegranskat)abstract
- Water In Star-forming regions with Herschel (WISH) is a key program on the Herschel Space Observatory designed to probe the physical and chemical structures of young stellar objects using water and related molecules and to follow the water abundance from collapsing clouds to planet-forming disks. About 80 sources are targeted, covering a wide ranee of luminosities-from low ( 10(5) L-circle dot)-and a wide range of evolutionary stages-from cold prestellar cores to warm protostellar envelopes and outflows to disks around young stars. Both the HIFI and PACS instruments are used to observe a variety of lines of H2O, (H2O)-O-18 and chemically related species at the source position and in small maps around the protostars and selected outflow positions. In addition, high-frequency lines of CO, (CO)-C-13, and (CO)-O-18 are obtained with Herschel and are complemented by ground-based observations of dust continuum, HDO, CO and its isotopologs, and other molecules to ensure a self-consistent data set for analysis. An overview of the scientific motivation and observational strategy of the program is given, together with the modeling approach and analysis tools that have been developed. Initial science results are presented. These include a lack of water in cold gas at abundances that are lower than most predictions, strong water emission from shocks in protostellar environments, the importance of UV radiation in heating the gas along outflow walls across the full range of luminosities, and surprisingly widespread detection of the chemically related hydrides OH+ and H2O+ in outflows and foreground gas. Quantitative estimates of the energy budget indicate that H2O is generally not the dominant coolant in the warm dense gas associated with protostars. Very deep limits on the cold gaseous water reservoir in the outer regions of protoplanetary disks are obtained that have profound implications for our understanding of grain growth and mixing in disks.
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| 3. |
- van Kempen, T. A., et al.
(författare)
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Origin of the hot gas in low-mass protostars Herschel-PACS spectroscopy of HH 46
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 518:Article Number: L121
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Tidskriftsartikel (refereegranskat)abstract
- Aims. "Water In Star-forming regions with Herschel" (WISH) is a Herschel key programme aimed at understanding the physical and chemical structure of young stellar objects (YSOs) with a focus on water and related species. Methods. The low-mass protostar HH 46 was observed with the Photodetector Array Camera and Spectrometer (PACS) on the Herschel Space Observatory to measure emission in H2O, CO, OH, [O I], and [C II] lines located between 63 and 186 mu m. The excitation and spatial distribution of emission can disentangle the different heating mechanisms of YSOs, with better spatial resolution and sensitivity than previously possible. Results. Far-IR line emission is detected at the position of the protostar and along the outflow axis. The OH emission is concentrated at the central position, CO emission is bright at the central position and along the outflow, and H2O emission is concentrated in the outflow. In addition, [O I] emission is seen in low-velocity gas, assumed to be related to the envelope, and is also seen shifted up to 170 km s(-1) in both the red-and blue-shifted jets. Envelope models are constructed based on previous observational constraints. They indicate that passive heating of a spherical envelope by the protostellar luminosity cannot explain the high-excitation molecular gas detected with PACS, including CO lines with upper levels at >2500 K above the ground state. Instead, warm CO and H2O emission is probably produced in the walls of an outflow-carved cavity in the envelope, which are heated by UV photons and non-dissociative C-type shocks. The bright OH and [O I] emission is attributed to J-type shocks in dense gas close to the protostar. In the scenario described here, the combined cooling by far-IR lines within the central spatial pixel is estimated to be 2 x 10(-2) L-circle dot, with 60-80% attributed to J- and C-type shocks produced by interactions between the jet and the envelope.
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| 4. |
- Bower, G. C., et al.
(författare)
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THE ALLEN TELESCOPE ARRAY Pi GHz SKY SURVEY. I. SURVEY DESCRIPTION AND STATIC CATALOG RESULTS FOR THE BOOTES FIELD
- 2010
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 725:2, s. 1792-1804
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Tidskriftsartikel (refereegranskat)abstract
- The Pi GHz Sky Survey (PiGSS) is a key project of the Allen Telescope Array. PiGSS is a 3.1 GHz survey of radio continuum emission in the extragalactic sky with an emphasis on synoptic observations that measure the static and time-variable properties of the sky. During the 2.5 year campaign, PiGSS will twice observe similar to 250,000 radio sources in the 10,000 deg(2) region of the sky with b > 30 degrees to an rms sensitivity of similar to 1 mJy. Additionally, sub-regions of the sky will be observed multiple times to characterize variability on timescales of days to years. We present here observations of a 10 deg(2) region in the Bootes constellation overlapping the NOAO Deep Wide Field Survey field. The PiGSS image was constructed from 75 daily observations distributed over a 4 month period and has an rms flux density between 200 and 250 mu Jy. This represents a deeper image by a factor of 4-8 than we will achieve over the entire 10,000 deg(2). We provide flux densities, source sizes, and spectral indices for the 425 sources detected in the image. We identify similar to 100 new flat-spectrum radio sources; we project that when completed PiGSS will identify 10(4) flat-spectrum sources. We identify one source that is a possible transient radio source. This survey provides new limits on faint radio transients and variables with characteristic durations of months.
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| 5. |
- Fich, M., et al.
(författare)
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Herschel-PACS spectroscopy of the intermediate mass protostar NGC 7129 FIRS 2
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 518:Article Number: L86
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Tidskriftsartikel (refereegranskat)abstract
- Aims. We present preliminary results of the first Herschel spectroscopic observations of NGC 7129 FIRS2, an intermediate mass star-forming region. We attempt to interpret the observations in the framework of an in-falling spherical envelope. Methods. The PACS instrument was used in line spectroscopy mode ( R = 1000-5000) with 15 spectral bands between 63 and 185 mu m. This provided good detections of 26 spectral lines seen in emission, including lines of H2O, CO, OH, O I, and C II. Results. Most of the detected lines, particularly those of H2O and CO, are substantially stronger than predicted by the spherical envelope models, typically by several orders of magnitude. In this paper we focus on what can be learned from the detected CO emission lines. Conclusions. It is unlikely that the much stronger than expected line emission arises in the (spherical) envelope of the YSO. The region hot enough to produce such high excitation lines within such an envelope is too small to produce the amount of emission observed. Virtually all of this high excitation emission must arise in structures such as as along the walls of the outflow cavity with the emission produced by a combination of UV photon heating and/or non-dissociative shocks.
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| 6. |
- Kristensen, L., et al.
(författare)
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Water in star-forming regions with Herschel (WISH) II. Evolution of 557 GHz 1(10)-1(01) emission in low-mass protostars
- 2012
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 542
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Tidskriftsartikel (refereegranskat)abstract
- Context. Water is a key tracer of dynamics and chemistry in low-mass star-forming regions, but spectrally resolved observations have so far been limited in sensitivity and angular resolution, and only data from the brightest low-mass protostars have been published. Aims. The first systematic survey of spectrally resolved water emission in 29 low-mass (L 10 km s(-1)). The water abundance in the outer cold envelope is low, greater than or similar to 10(-10). The different H2O profile components show a clear evolutionary trend: in the younger Class 0 sources the emission is dominated by outflow components originating inside an infalling envelope. When large-scale infall diminishes during the Class I phase, the outflow weakens and H2O emission all but disappears.
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| 7. |
- van der Tak, F. F. S., et al.
(författare)
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Water abundance variations around high-mass protostars: HIFI observations of the DR21 region
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 518:Article Number: L107
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Tidskriftsartikel (refereegranskat)abstract
- Context. Water is a key molecule in the star formation process, but its spatial distribution in star-forming regions is not well known. Aims. We study the distribution of dust continuum and H2O and (CO)-C-13 line emission in DR21, a luminous star-forming region with a powerful outflow and a compact H II region. Methods. Herschel-HIFI spectra near 1100 GHz show narrow (CO)-C-13 10-9 emission and H2O 1(11)-0(00) absorption from the dense core and broad emission from the outflow in both lines. The H2O line also shows absorption by a foreground cloud known from ground-based observations of low-J CO lines. Results. The dust continuum emission is extended over 36 '' FWHM, while the (CO)-C-13 and H2O lines are confined to approximate to 24 '' or less. The foreground absorption appears to peak further North than the other components. Radiative transfer models indicate very low abundances of similar to 2 x 10(-10) for H2O and similar to 8 x 10(-7) for (CO)-C-13 in the dense core, and higher H2O abundances of similar to 4 x 10(-9) in the foreground cloud and similar to 7 x 10(-7) in the outflow. Conclusions. The high H2O abundance in the warm outflow is probably due to the evaporation of water-rich icy grain mantles, while the H2O abundance is kept down by freeze-out in the dense core and by photodissociation in the foreground cloud.
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| 8. |
- Welch, J., et al.
(författare)
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The Allen Telescope Array: The First Widefield, Panchromatic, Snapshot Radio Camera for Radio Astronomy and SETI
- 2009
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Ingår i: Proceedings of the IEEE. - 1558-2256 .- 0018-9219. ; 97:8, s. 1438-1447
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Tidskriftsartikel (refereegranskat)abstract
- The first 42 elements of the Allen Telescope Array (ATA-42) are beginning to deliver data at the Hat Creek Radio Observatory in northern California. Scientists and engineers are actively exploiting all of the flexibility designed into this innovative instrument for simultaneously conducting surveys of the astrophysical sky and conducting searches for distant technological civilizations. This paper summarizes the design elements of the ATA, the cost savings made possible by the use of commercial off-the-shelf components, and the cost/performance tradeoffs that eventually enabled this first snapshot radio camera. The fundamental scientific program of this new telescope is varied and exciting; some of the first astronomical results will be discussed.
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| 9. |
- Bergin, E. A., et al.
(författare)
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Sensitive limits on the abundance of cold water vapor in the DM Tauri protoplanetary disk
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 521, s. L33-
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Tidskriftsartikel (refereegranskat)abstract
- We performed a sensitive search for the ground-state emission lines of ortho-and para-water vapor in the DM Tau protoplanetary disk using the Herschel/HIFI instrument. No strong lines are detected down to 3 sigma levels in 0.5 km s(-1) channels of 4.2 mK for the 1(10)-1(01) line and 12.6 mK for the 1(11)-0(00) line. We report a very tentative detection, however, of the 1(10)-1(01) line in the wide band spectrometer, with a strength of T-mb = 2.7 mK, a width of 5.6 km s(-1) and an integrated intensity of 16.0 mK km s(-1). The latter constitutes a 6 sigma detection. Regardless of the reality of this tentative detection, model calculations indicate that our sensitive limits on the line strengths preclude efficient desorption of water in the UV illuminated regions of the disk. We hypothesize that more than 95-99% of the water ice is locked up in coagulated grains that have settled to the midplane.
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| 10. |
- Chavarria, L., et al.
(författare)
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Water in massive star-forming regions : HIFI observations of W3 IRS5
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 521, s. L37-
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Tidskriftsartikel (refereegranskat)abstract
- We present Herschel observations of the water molecule in the massive star-forming region W3 IRS5. The o-(H2O)-O-17 1(10)-1(01), p-(H2O)-O-18 1(11)-0(00), p-H2O 2(02)-1(11), p-H2O 1(11)-0(00), o-H2O 2(21)-2(12), and o-H2O 2(12)-1(01) lines, covering a frequency range from 552 up to 1669 GHz, have been detected at high spectral resolution with HIFI. The water lines in W3 IRS5 show well-defined high-velocity wings that indicate a clear contribution by outflows. Moreover, the systematically blue-shifted absorption in the H2O lines suggests expansion, presumably driven by the outflow. No infall signatures are detected. The p-H2O 1(11)-0(00) and o-H2O 2(12)-1(01) lines show absorption from the cold material (T similar to 10 K) in which the high-mass protostellar envelope is embedded. One-dimensional radiative transfer models are used to estimate water abundances and to further study the kinematics of the region. We show that the emission in the rare isotopologues comes directly from the inner parts of the envelope (T greater than or similar to 100 K) where water ices in the dust mantles evaporate and the gas-phase abundance increases. The resulting jump in the water abundance (with a constant inner abundance of 10(-4)) is needed to reproduce the o-(H2O)-O-17 1(10)-1(01) and p-(H2O)-O-18 1(11)-0(00) spectra in our models. We estimate water abundances of 10(-8) to 10(-9) in the outer parts of the envelope (T less than or similar to 100 K). The possibility of two protostellar objects contributing to the emission is discussed.
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