| 21. |
- Jensen, S. S., et al.
(författare)
-
ALMA observations of water deuteration: a physical diagnostic of the formation of protostars
- 2019
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 631
-
Tidskriftsartikel (refereegranskat)abstract
- Context. How water is delivered to planetary systems is a central question in astrochemistry. The deuterium fractionation of water can serve as a tracer for the chemical and physical evolution of water during star formation and can constrain the origin of water in Solar System bodies. Aims. The aim is to determine the HDO/H20 ratio in the inner warm gas toward three low-mass Class 0 protostars selected to be in isolated cores, i.e., not associated with any cloud complexes. Previous sources for which the HDO/H20 ratio have been established were all part of larger star-forming complexes. Determining the HDO/H20 ratio toward three isolated protostars allows comparison of the water chemistry in isolated and clustered regions to determine the influence of local cloud environment. Methods. We present ALMA Band 6 observations of the HDO 31,2-22,1 and 21,1-21,2 transitions at 225.897 GHz and 241.562 GHz along with the first ALMA Band 5 observations of the H2180 31,3-22,0 transition at 203.407 GHz. The high angular resolution observations (0'.'3-1'.'3) allow the study of the inner warm envelope gas. Model-independent estimates for the HDO/H20 ratios are obtained and compared with previous determinations of the HDO/H20 ratio in the warm gas toward low-mass protostars. Results. We successfully detect the targeted water transitions toward the three sources with signal-to-noise ratio (S/N) > 5. We determine the HDO/H20 ratio toward L483, B335 and BHR71 IRS1 to be (2.2 0.4) x 10-3, (1.7 0.3) x 10-3, and (1.8 0.4) x 10-3, respectively, assuming Tex = 124 K. The degree of water deuteration of these isolated protostars are a factor of 2-4 higher relative to Class 0 protostars that are members of known nearby clustered star-forming regions. Conclusions. The results indicate that the water deuterium fractionation is influenced by the local cloud environment. This effect can be explained by variations in either collapse timescales or temperatures, which depends on local cloud dynamics and could provide a new method to decipher the history of young stars.
|
|
| 22. |
- Jorgensen, J. K., et al.
(författare)
-
The ALMA Protostellar Interferometric Line Survey (PILS) First results from an unbiased submillimeter wavelength line survey of the Class 0 protostellar binary IRAS 16293-2422 with ALMA
- 2016
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 595, s. Art no A117-
-
Tidskriftsartikel (refereegranskat)abstract
- Context. The inner regions of the envelopes surrounding young protostars are characterized by a complex chemistry, with prebiotic molecules present on the scales where protoplanetary disks eventually may form. The Atacama Large Millimeter/submillimeter Array (ALMA) provides an unprecedented view of these regions zooming in on solar system scales of nearby protostars and mapping the emission from rare species. Aims. The goal is to introduce a systematic survey, the Protostellar Interferometric Line Survey (PILS), of the chemical complexity of one of the nearby astrochemical templates, the Class 0 protostellar binary IRAS 16293 2422, using ALMA in order to understand the origin of the complex molecules formed in its vicinity. In addition to presenting the overall survey, the analysis in this paper focuses on new results for the prebiotic molecule glycolaldehyde, its isomers, and rarer isotopologues and other related molecules. Methods. An unbiased spectral survey of IRAS 16293 2422 covering the full frequency range from 329 to 363 GHz (0.8 mm) has been obtained with ALMA, in addition to a few targeted observations at 3.0 and 1.3 mm. The data consist of full maps of the protostellar binary system with an angular resolution of 0.5 '' (60 AU diameter), a spectral resolution of 0.2 km s(-1), and a sensitivity of 4-5 mJy beam(-1) km s(-1), which is approximately two orders of magnitude better than any previous studies. Results. More than 10 000 features are detected toward one component in the protostellar binary, corresponding to an average line density of approximately one line per 3 km s(-1). Glycolaldehyde; its isomers, methyl formate and acetic acid; and its reduced alcohol, ethylene glycol, are clearly detected and their emission well-modeled with an excitation temperature of 300 K. For ethylene glycol both lowest state conformers, aGg' and gGg', are detected, the latter for the first time in the interstellar medium (ISM). The abundance of glycolaldehyde is comparable to or slightly larger than that of ethylene glycol. In comparison to the Galactic Center these two species are over-abundant relative to methanol, possibly an indication of formation of the species at low temperatures in CO-rich ices during the infall of the material toward the central protostar. Both C-13 and the deuterated isotopologues of glycolaldehyde are detected, also for the first time ever in the ISM. For the deuterated species, a D/H ratio of approximate to 5% is found with no differences between the deuteration in the different functional groups of glycolaldehyde, in contrast to previous estimates for methanol and recent suggestions of significant equilibration between water and-OH functional groups at high temperatures. Measurements of the C-13-species lead to a C-12:C-13 ratio of approximate to 30, lower than the typical ISM value. This low ratio may reflect an enhancement of (CO)-C-13 in the ice due to either ion-molecule reactions in the gas before freeze-out or to differences in the temperatures where (CO)-C-12 and (CO)-C-13 ices sublimate. Conclusions. The results reinforce the importance of low-temperature grain surface chemistry for the formation of prebiotic molecules seen here in the gas after sublimation of the entire ice mantle. Systematic surveys of the molecules thought to be chemically related, as well as the accurate measurements of their isotopic composition, hold strong promise for understanding the origin of prebiotic molecules in the earliest stages of young stars.
|
|
| 23. |
- Persson, Magnus V., 1983
(författare)
-
Research night owls
- 2016
-
Ingår i: Science. - 0036-8075 .- 1095-9203. ; 354:6315, s. 965-965
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
|
|
| 24. |
- Tobin, J. J., et al.
(författare)
-
A triple protostar system formed via fragmentation of a gravitationally unstable disk
- 2016
-
Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 538:7626, s. 483-
-
Tidskriftsartikel (refereegranskat)abstract
- Binary and multiple star systems are a frequent outcome of the star formation process(1,2) and as a result almost half of all stars with masses similar to that of the Sun have at least one companion star(3). Theoretical studies indicate that there are two main pathways that can operate concurrently to form binary/multiple star systems: large-scale fragmentation of turbulent gas cores and filaments(4,5) or smaller-scale fragmentation of a massive protostellar disk due to gravitational instability(6,7). Observational evidence for turbulent fragmentation on scales of more than 1,000 astronomical units has recently emerged(8,9). Previous evidence for disk fragmentation was limited to inferences based on the separations of more-evolved pre-main sequence and protostellar multiple systems(10-13). The triple protostar system L1448 IRS3B is an ideal system with which to search for evidence of disk fragmentation as it is in an early phase of the star formation process, it is likely to be less than 150,000 years old(14) and all of the protostars in the system are separated by less than 200 astronomical units. Here we report observations of dust and molecular gas emission that reveal a disk with a spiral structure surrounding the three protostars. Two protostars near the centre of the disk are separated by 61 astronomical units and a tertiary protostar is coincident with a spiral arm in the outer disk at a separation of 183 astronomical units(13). The inferred mass of the central pair of protostellar objects is approximately one solar mass, while the disk surrounding the three protostars has a total mass of around 0.30 solar masses. The tertiary protostar itself has a minimum mass of about 0.085 solar masses. We demonstrate that the disk around L1448 IRS3B appears susceptible to disk fragmentation at radii between 150 and 320 astronomical units, overlapping with the location of the tertiary protostar. This is consistent with models for a protostellar disk that has recently undergone gravitational instability, spawning one or two companion stars.
|
|
| 25. |
- Tobin, J. J., et al.
(författare)
-
Deuterium-enriched water ties planet-forming disks to comets and protostars
- 2023
-
Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 615:7951, s. 227-230
-
Tidskriftsartikel (refereegranskat)abstract
- Water is a fundamental molecule in the star and planet formation process, essential for catalysing the growth of solid material and the formation of planetesimals within disks1,2. However, the water snowline and the HDO:H2O ratio within proto-planetary disks have not been well characterized because water only sublimates at roughly 160 K (ref. 3), meaning that most water is frozen out onto dust grains and that the water snowline radii are less than 10 AU (astronomical units)4,5. The sun-like protostar V883 Ori (M* = 1.3 M⊙)6 is undergoing an accretion burst7, increasing its luminosity to roughly 200 L⊙ (ref. 8), and previous observations suggested that its water snowline is 40-120 AU in radius6,9,10. Here we report the direct detection of gas phase water (HDO and [Formula: see text]) from the disk of V883 Ori. We measure a midplane water snowline radius of approximately 80 AU, comparable to the scale of the Kuiper Belt, and detect water out to a radius of roughly 160 AU. We then measure the HDO:H2O ratio of the disk to be (2.26 ± 0.63) × 10-3. This ratio is comparable to those of protostellar envelopes and comets, and exceeds that of Earth's oceans by 3.1σ. We conclude that disks directly inherit water from the star-forming cloud and this water becomes incorporated into large icy bodies, such as comets, without substantial chemical alteration.
|
|
| 26. |
- Tobin, John J., et al.
(författare)
-
The VLA/ALMA Nascent Disk and Multiplicity (VANDAM) Survey of Orion Protostars. I. Identifying and Characterizing the Protostellar Content of the OMC-2 FIR4 and OMC-2 FIR3 Regions
- 2019
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 886:1
-
Tidskriftsartikel (refereegranskat)abstract
- We present Atacama Large Millimeter/submillimeter Array (0.87 mm) and Very Large Array (9 mm) observations toward OMC-2 FIR4 and OMC-2 FIR3 within the Orion integral-shaped filament, thought to be two of the nearest regions of intermediate-mass star formation. We characterize the continuum sources within these regions on ?40 au (01) scales and associated molecular line emission at a factor of ?30 better resolution than previous observations at similar wavelengths. We identify six compact continuum sources within OMC-2 FIR4, four in OMC-2 FIR3, and one additional source just outside OMC-2 FIR4. This continuum emission is tracing the inner envelope and/or disk emission on less than 100 au scales. HOPS-108 is the only protostar in OMC-2 FIR4 that exhibits emission from high-excitation transitions of complex organic molecules (e.g., methanol and other lines) coincident with the continuum emission. HOPS-370 in OMC-2 FIR3, with L;?;360 L, also exhibits emission from high-excitation methanol and other lines. The methanol emission toward these two protostars is indicative of temperatures high enough to thermally evaporate it from icy dust grains; overall, these protostars have characteristics similar to hot corinos. We do not identify a clear outflow from HOPS-108 in (CO)-C-12, but we find evidence of interaction between the outflow/jet from HOPS-370 and the OMC-2 FIR4 region. A multitude of observational constraints indicate that HOPS-108 is likely a low- to intermediate-mass protostar in its main mass accretion phase and is the most luminous protostar in OMC-2 FIR4. The high-resolution data presented here are essential for disentangling the embedded protostars from their surrounding dusty environments and characterizing them.
|
|
| 27. |
- Tobin, John J., et al.
(författare)
-
The VLA/ALMA Nascent Disk and Multiplicity (VANDAM) Survey of Orion Protostars. II. A Statistical Characterization of Class 0 and Class i Protostellar Disks
- 2020
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 890:2
-
Tidskriftsartikel (refereegranskat)abstract
- We have conducted a survey of 328 protostars in the Orion molecular clouds with the Atacama Large Millimeter/submillimeter Array at 0.87 mm at a resolution of ∼0.″1 (40 au), including observations with the Very Large Array at 9 mm toward 148 protostars at a resolution of ∼0.″08 (32 au). This is the largest multiwavelength survey of protostars at this resolution by an order of magnitude. We use the dust continuum emission at 0.87 and 9 mm to measure the dust disk radii and masses toward the Class 0, Class I, and flat-spectrum protostars, characterizing the evolution of these disk properties in the protostellar phase. The mean dust disk radii for the Class 0, Class I, and flat-spectrum protostars are 44.9-3.4+5.8, 37.0-3.0+4.9, and 28.5-2.3+3.7 au, respectively, and the mean protostellar dust disk masses are 25.9-4.0+7.7, 14.9-2.2+3.8, 11.6-1.9+3.5 M⊙, respectively. The decrease in dust disk masses is expected from disk evolution and accretion, but the decrease in disk radii may point to the initial conditions of star formation not leading to the systematic growth of disk radii or that radial drift is keeping the dust disk sizes small. At least 146 protostellar disks (35% of 379 detected 0.87 mm continuum sources plus 42 nondetections) have disk radii greater than 50 au in our sample. These properties are not found to vary significantly between different regions within Orion. The protostellar dust disk mass distributions are systematically larger than those of Class II disks by a factor of >4, providing evidence that the cores of giant planets may need to at least begin their formation during the protostellar phase.
|
|
| 28. |
- van 't Hoff, Merel L. R., et al.
(författare)
-
Imaging the water snowline in a protostellar envelope with (HCO+)-C-13
- 2018
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 613
-
Tidskriftsartikel (refereegranskat)abstract
- Context. Snowlines are key ingredients for planet formation. Providing observational constraints on the locations of the major snowlines is therefore crucial for fully connecting planet compositions to their formation mechanism. Unfortunately, the most important snowline, that of water, is very difficult to observe directly in protoplanetary disks because of the close proximity of this snowline to the central star. Aims. Based on chemical considerations, HCO+ is predicted to be a good chemical tracer of the water snowline because it is particularly abundant in dense clouds when water is frozen out. This work aims to map the optically thin isotopolog (HCO+)-C-13 toward the envelope of the low-mass protostar NGC1333-IRAS2A, where the snowline is at a greater distance from the star than in disks. Comparison with previous observations of (H2O)-O-18 show whether (HCO+)-C-13 is indeed a good tracer of the water snwline. Methods. NGC1333-IRAS2A was observed using the NOrthern Extended Millimeter Array (NOEMA) at similar to 0:0.9 resolution, targeting the (HCO+)-C-13 J = 3-2 transition at 260.255 GHz. The integrated emission profile was analyzed using 1D radiative transfer modeling of a spherical envelope with a parametrized abundance profile for (HCO+)-C-13. This profile was validated with a full chemical model. Results. The (HCO+)-C-13 emission peaks similar to 2" northeast of the continuum peak, whereas (H2O)-O-18 sh ows compact emission on source. Quantitative modeling shows that a decrease in (HCO+)-C-13 abundance by at least a factor of six is needed in the inner similar to 360 AU to reproduce the observed emission profile. Chemical modeling indeed predicts a steep increase in HCO+ just outside the water snowline; the 50% decrease in gaseous H2O at the snowline is not enough to allow HCO+ to be abundant. This places the water snowline at 225 AU, further away from the star than expected based on the 1D envelope temperature structure for NGC1333-IRAS2A. In contrast, DCO+ observations show that the CO snowline is at the expected location, making an outburst scenario unlikely. Conclusions. The spatial anticorrelation of (HCO+)-C-13 and (H2O)-O-18 emission provide proof of concept that (HCO+)-C-13 can be used as a tracer of the water snowline.
|
|
| 29. |
- Vlemmings, Wouter, 1974, et al.
(författare)
-
Stringent limits on the magnetic field strength in the disc of TW Hya: ALMA observations of CN polarisation
- 2019
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 624
-
Tidskriftsartikel (refereegranskat)abstract
- Despite their importance in the star formation process, measurements of magnetic field strength in proto-planetary discs remain rare. While linear polarisation of dust and molecular lines can give insight into the magnetic field structure, only observations of the circular polarisation produced by Zeeman splitting provide a direct measurement of magnetic field strenghts. One of the most promising probes of magnetic field strengths is the paramagnetic radical CN. Here we present the first Atacama Large Millimeter/submillimeter Array (ALMA) observations of the Zeeman splitting of CN in the disc of TW Hya. The observations indicate an excellent polarisation performance of ALMA, but fail to detect significant polarisation. An analysis of eight individual CN hyperfine components as well as a stacking analysis of the strongest (non-blended) hyperfine components yields the most stringent limits obtained so far on the magnetic field strength in a proto-planetary disc. We find that the vertical component of the magnetic field vertical bar B-z vertical bar < 0.8 mG (1 sigma limit). We also provide a 1 sigma toroidal field strength limit of < 30 mG. These limits rule out some of the earlier accretion disc models, but remain consistent with the most recent detailed models with e ffi cient advection. We detect marginal linear polarisation from the dust continuum, but the almost purely toroidal geometry of the polarisation vectors implies that his is due to radiatively aligned grains.
|
|
| 30. |
- Yamato, Yoshihide, et al.
(författare)
-
The First Interferometric Measurements of NH 2 D/NH 3 Ratio in Hot Corinos
- 2022
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 941:1
-
Tidskriftsartikel (refereegranskat)abstract
- The chemical evolution of nitrogen during star and planet formation is still not fully understood. Ammonia (NH3) is a key specie in the understanding of the molecular evolution in star-forming clouds and nitrogen isotope fractionation. In this paper, we present high-spatial-resolution observations of multiple emission lines of NH3 toward the protobinary system NGC1333 IRAS4A with the Karl G. Jansky Very Large Array. We spatially resolved the binary (hereafter, 4A1 and 4A2) and detected compact emission of NH3 transitions with high excitation energies (≳100 K) from the vicinity of the protostars, indicating the NH3 ice has sublimated at the inner hot region. The NH3 column density is estimated to be ∼1017-1018 cm−2. We also detected two NH2D transitions, allowing us to constrain the deuterium fractionation of ammonia. The NH2D/NH3 ratios are as high as ∼0.3-1 in both 4A1 and 4A2. From comparisons with the astrochemical models in the literature, the high NH2D/NH3 ratios suggest that the formation of NH3 ices mainly started in the prestellar phase after the formation of bulk water ice finished, and that the primary nitrogen reservoir in the star-forming cloud could be atomic nitrogen (or N atoms) rather than nitrogen-bearing species such as N2 and NH3. The implications on the physical properties of IRAS4A’s cores are discussed as well.
|
|
