| 1. |
- Battersby, C., et al.
(författare)
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The Origins Space Telescope
- 2018
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Ingår i: Nature Astronomy. - : Springer Science and Business Media LLC. - 2397-3366. ; 2:8, s. 596-599
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The Origins Space Telescope, one of four large Mission Concept Studies sponsored by NASA for review in the 2020 US Astrophysics Decadal Survey, will open unprecedented discovery space in the infrared, unveiling our cosmic origins.
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| 2. |
- Benz, A. O., et al.
(författare)
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Water in star-forming regions with Herschel (WISH): VI. Constraints on UV and X-ray irradiation from a survey of hydrides in low- to high-mass young stellar objects
- 2016
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 590, s. Art. no. A105-
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Tidskriftsartikel (refereegranskat)abstract
- Context. Hydrides are simple compounds containing one or a few hydrogen atoms bonded to a heavier atom. They are fundamental precursor molecules in cosmic chemistry and many hydride ions have become observable in high quality for the first time thanks to the Herschel Space Observatory. Ionized hydrides such as CH+ and OH+ (and also HCO+), which affect the chemistry of molecules such as water, provide complementary information on irradiation by far-UV (FUV) or X-rays and gas temperature. Aims. We explore hydrides of the most abundant heavier elements in an observational survey covering young stellar objects (YSOs) with different mass and evolutionary state. The focus is on hydrides associated with the dense protostellar envelope and outflows, contrary to previous work that focused on hydrides in diffuse foreground clouds. Methods. Twelve YSOs were observed with HIFI on Herschel in six spectral settings providing fully velocity-resolved line profiles as part of the Water in star-forming regions with Herschel (WISH) program. The YSOs include objects of low (Class 0 and I), intermediate, and high mass, with luminosities ranging from 4 L? to 2 × 105 L?. Results. The targeted lines of CH+, OH+, H2O+, C+, and CH are detected mostly in blue-shifted absorption. H3O+ and SH+ are detected in emission and only toward some high-mass objects. The observed line parameters and correlations suggest two different origins related to gas entrained by the outflows and to the circumstellar envelope. The derived column densities correlate with bolometric luminosity and envelope mass for all molecules, best for CH, CH+, and HCO+. The column density ratios of CH+/OH+ are estimated from chemical slab models, assuming that the H2 density is given by the specific density model of each object at the beam radius. For the low-mass YSOs the observed ratio can be reproduced for an FUV flux of 2-400 times the interstellar radiation field (ISRF) at the location of the molecules. In two high-mass objects, the UV flux is 20-200 times the ISRF derived from absorption lines, and 300-600 ISRF using emission lines. Upper limits for the X-ray luminosity can be derived from H3O+ observations for some low-mass objects. Conclusions. If the FUV flux required for low-mass objects originates at the central protostar, a substantial FUV luminosity, up to 1.5 L?, is required. There is no molecular evidence for X-ray induced chemistry in the low-mass objects on the observed scales of a few 1000 AU. For high-mass regions, the FUV flux required to produce the observed molecular ratios is smaller than the unattenuated flux expected from the central object(s) at the Herschel beam radius. This is consistent with an FUV flux reduced by circumstellar extinction or by bloating of the protostar.
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| 3. |
- 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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| 4. |
- Berné, O., et al.
(författare)
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A far-ultraviolet-driven photoevaporation flow observed in a protoplanetary disk
- 2024
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Ingår i: Science. - 0036-8075 .- 1095-9203. ; 383:6686, s. 988-992
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Tidskriftsartikel (refereegranskat)abstract
- Most low-mass stars form in stellar clusters that also contain massive stars, which are sources of far-ultraviolet (FUV) radiation. Theoretical models predict that this FUV radiation produces photodissociation regions (PDRs) on the surfaces of protoplanetary disks around low-mass stars, which affects planet formation within the disks. We report James Webb Space Telescope and Atacama Large Millimeter Array observations of a FUV-irradiated protoplanetary disk in the Orion Nebula. Emission lines are detected from the PDR; modeling their kinematics and excitation allowed us to constrain the physical conditions within the gas. We quantified the mass-loss rate induced by the FUV irradiation and found that it is sufficient to remove gas from the disk in less than a million years. This is rapid enough to affect giant planet formation in the disk.
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| 5. |
- Berné, O., et al.
(författare)
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Formation of the methyl cation by photochemistry in a protoplanetary disk
- 2023
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Ingår i: Nature. - 0028-0836 .- 1476-4687. ; 621:7977, s. 56-59
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Tidskriftsartikel (refereegranskat)abstract
- Forty years ago, it was proposed that gas-phase organic chemistry in the interstellar medium can be initiated by the methyl cation CH3+ (refs. 1–3), but so far it has not been observed outside the Solar System 4,5. Alternative routes involving processes on grain surfaces have been invoked 6,7. Here we report James Webb Space Telescope observations of CH3+ in a protoplanetary disk in the Orion star-forming region. We find that gas-phase organic chemistry is activated by ultraviolet irradiation.
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| 6. |
- Bjerkeli, Per, 1977, et al.
(författare)
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Water around IRAS 15398-3359 observed with ALMA
- 2016
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 595, s. Art no A39-
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Tidskriftsartikel (refereegranskat)abstract
- Context. Understanding how protostars accrete their mass is one of the fundamental problems of star formation. High dust column densities and complex kinematical structures make direct observations challenging. Moreover, direct observations only provide a snapshot. Chemical tracers provide an interesting alternative to characterise the infall histories of protostars. Aims. We aim to map the distribution and kinematics of gaseous water towards the low-mass embedded protostar IRAS 15398-3359. Previous observations of H13CO+ showed a depression in the abundance towards IRAS 15398-3359. This is a sign of destruction of HCO+ by an enhanced presence of gaseous water in an extended region, possibly related to a recent burst in the accretion. Direct observations of water vapour can determine the exact extent of the emission and confirm the hypothesis that HCO+ is indeed a good tracer of the water snow-line. Methods. IRAS 15398-3359 was observed using the Atacama Large Millimeter/submillimeter Array (ALMA) at 0.5? resolution in two setups at 390 and 460 GHz. Maps of HDO (101-000) and were taken simultaneously with observations of the CS (8-7) and N2H+ (5-4) lines and continuum at 0.65 and 0.75 mm. The maps were interpreted using dust radiative transfer calculations of the protostellar infalling envelope with an outflow cavity. Results. HDO is clearly detected and extended over the scales of the H13CO+ depression, although it is displaced by ~500 AU in the direction of the outflow. HO is tentatively detected towards the red-shifted outflow lobe, but otherwise it is absent from the mapped region, which suggests that temperatures are low. Although we cannot entirely exclude a shock origin, this indicates that another process is responsible for the water emission. Conclusions. Based on the temperature structure obtained from dust radiative transfer models, we conclude that the water was most likely released from the grains in an extended hour-glass configuration during a recent accretion burst. HDO is only detected in the region closest to the protostar, at distances of up to 500 AU. These signatures can only be explained if the luminosity has recently been increased by orders of magnitudes. Additionally, the densities in the outflow cones must be sufficiently low.
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| 7. |
- Caselli, P., et al.
(författare)
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Water vapor toward starless cores : The Herschel view
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 521, s. L29-
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Tidskriftsartikel (refereegranskat)abstract
- Aims: Previous studies by the satellites SWAS and Odin provided stringent upper limits on the gas phase water abundance of dark clouds (x(H2O) < 7 × 10-9). We investigate the chemistry of water vapor in starless cores beyond the previous upper limits using the highly improved angular resolution and sensitivity of Herschel and measure the abundance of water vapor during evolutionary stages just preceding star formation. Methods: High spectral resolution observations of the fundamental ortho water (o-H2O) transition (557 GHz) were carried out with the Heterodyne Instrument for the Far Infrared onboard Herschel toward two starless cores: Barnard 68 (hereafter B68), a Bok globule, and LDN 1544 (L1544), a prestellar core embedded in the Taurus molecular cloud complex. Detailed radiative transfer and chemical codes were used to analyze the data. Results: The RMS in the brightness temperature measured for the B68 and L1544 spectra is 2.0 and 2.2 mK, respectively, in a velocity bin of 0.59 km s-1. The continuum level is 3.5 ± 0.2 mK in B68 and 11.4 ± 0.4 mK in L1544. No significant feature is detected in B68 and the 3σ upper limit is consistent with a column density of o-H2O N(o-H2O) < 2.5 × 1013 cm-2, or a fractional abundance x(o-H2O) < 1.3 × 10-9, more than an order of magnitude lower than the SWAS upper limit on this source. The L1544 spectrum shows an absorption feature at a 5σ level from which we obtain the first value of the o-H2O column density ever measured in dark clouds: N(o-H2O) = (8 ± 4) × 1012 cm-2. The corresponding fractional abundance is x(o-H2O) ≃ 5 × 10-9 at radii >7000 AU and ≃2 × 10-10 toward the center. The radiative transfer analysis shows that this is consistent with a x(o-H2O) profile peaking at ≃10-8, 0.1 pc away from the core center, where both freeze-out and photodissociation are negligible. Conclusions: Herschel has provided the first measurement of water vapor in dark regions. Column densities of o-H2O are low, but prestellar cores such as L1544 (with their high central densities, strong continuum, and large envelopes) appear to be very promising tools to finally shed light on the solid/vapor balance of water in molecular clouds and oxygen chemistry in the earliest stages of star formation. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
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| 8. |
- Cavalie, T., et al.
(författare)
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Observation of water vapor in the stratosphere of Jupiter with the Odin space telescope
- 2008
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Ingår i: Planetary and Space Science. - : Elsevier BV. - 0032-0633. ; 56:12, s. 1573-1584
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Tidskriftsartikel (refereegranskat)abstract
- The water vapor line at 557 GHz has been observed with the Odin space telescope with a high signal-to-noise ratio and a high spectral resolution on November 8, 2002. The analysis of this observation as well as a re-analysis of previously published observations obtained with the submillimeter wavelength astronomy satellite seem to favor a cometary origin (Shoemaker-Levy 9) for water in the stratosphere of Jupiter, in agreement with the ISO observation results. Our model predicts that the water line should become fainter and broader from 2007. The observation of such a temporal variability would be contradictory with an IDP steady flux, thus supporting the SL9 source hypothesis. © 2008 Elsevier Ltd.
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| 9. |
- Ceccarelli, C., et al.
(författare)
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Herschel spectral surveys of star- forming regions Overview of the 555-636 GHz range
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 521, s. L22-
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Tidskriftsartikel (refereegranskat)abstract
- High resolution line spectra of star-forming regions are mines of information: they provide unique clues to reconstruct the chemical, dynamical, and physical structure of the observed source. We present the first results from the Herschel key project " Chemical HErschel Surveys of Star forming regions", CHESS. We report and discuss observations towards five CHESS targets, one outflow shock spot and four protostars with luminosities bewteen 20 and 2 x 105 L similar to : L1157-B1, IRAS 16293-2422, OMC2-FIR4, AFGL 2591, and NGC 6334I. The observations were obtained with the heterodyne spectrometer HIFI on board Herschel, with a spectral resolution of 1 MHz. They cover the frequency range 555-636 GHz, a range largely unexplored before the launch of the Herschel satellite. A comparison of the five spectra highlights spectacular differences in the five sources, for example in the density of methanol lines, or the presence./absence of lines from S-bearing molecules or deuterated species. We discuss how these differences can be attributed to the different star-forming mass or evolutionary status.
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| 10. |
- Chen, Jo-Hsin, et al.
(författare)
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HERSCHEL HIFI OBSERVATIONS OF O-2 TOWARD ORION: SPECIAL CONDITIONS FOR SHOCK ENHANCED EMISSION
- 2014
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Ingår i: Astrophysical Journal. - 1538-4357 .- 0004-637X. ; 793:2, s. Article nr. 111 -
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Tidskriftsartikel (refereegranskat)abstract
- We report observations of molecular oxygen (O-2) rotational transitions at 487 GHz, 774 GHz, and 1121 GHz toward Orion Peak A. The O-2 lines at 487 GHz and 774 GHz are detected at velocities of 10-12 km s(-1) with line widths similar to 3 km s(-1); however, the transition at 1121 GHz is not detected. The observed line characteristics, combined with the results of earlier observations, suggest that the region responsible for the O-2 emission is similar or equal to 9" (6 x 10(16) cm) in size, and is located close to the H-2 Peak 1 position (where vibrationally excited H-2 emission peaks), and not at Peak A, 23" away. The peak O-2 column density is similar to 1.1 x 10(18) cm(-2). The line velocity is close to that of the 621 GHz water maser emission found in this portion of the Orion Molecular Cloud, and having a shock with velocity vector lying nearly in the plane of the sky is consistent with producing maximum maser gain along the line of sight. The enhanced O-2 abundance compared to that generally found in dense interstellar clouds can be explained by passage of a low-velocity C shock through a clump with preshock density 2 x 10(4) cm(-3), if a reasonable flux of UV radiation is present. The postshock O-2 can explain the emission from the source if its line-of-sight dimension is similar or equal to 10 times larger than its size on the plane of the sky. The special geometry and conditions required may explain why O-2 emission has not been detected in the cores of other massive star-forming molecular clouds.
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