We present the results of a single-pointing survey of 207 dense cores embedded in Planck Galactic Cold Clumps distributed in five different environments (λ Orionis, Orion A, Orion B, the Galactic ...plane, and high latitudes) to identify dense cores on the verge of star formation for the study of the initial conditions of star formation. We observed these cores in eight molecular lines at 76-94 GHz using the Nobeyama 45 m telescope. We find that early-type molecules (e.g., CCS) have low detection rates and that late-type molecules (e.g., N2H+ and c-C3H2) and deuterated molecules (e.g., N2D+ and DNC) have high detection rates, suggesting that most of the cores are chemically evolved. The deuterium fraction (D/H) is found to decrease with increasing distance, indicating that it suffers from differential beam dilution between the D/H pair of lines for distant cores (>1 kpc). For λ Orionis, Orion A, and Orion B located at similar distances, D/H is not significantly different, suggesting that there is no systematic difference in the observed chemical properties among these three regions. We identify at least eight high-D/H cores in the Orion region and two at high latitudes, which are most likely to be close to the onset of star formation. There is no clear evidence of the evolutionary change in turbulence during the starless phase, suggesting that the dissipation of turbulence is not a major mechanism for the beginning of star formation as judged from observations with a beam size of 0.04 pc.
As climate change brings reduced sea ice cover and longer ice-free summers to the Arctic, northern Canada is experiencing an increase in shipping and industrial activity in this sensitive region. ...Disappearing sea ice, therefore, makes the Arctic region susceptible to accidental releases of different types of oil and fuel pollution resulting in a pressing need for the development of appropriate scientific knowledge necessary to inform regulatory policy formulation.
In this study, we examine the microstructure of the surficial layers of sea ice exposed to oil using X-ray microtomography. Through analysis, 3D imaging of the spatial distribution of the ice's components (brine, air, and oil) were made. Additional quantitative information regarding the size, proximity, orientation, and geometry of oil inclusions were computed to ascertain discernable relationships between oil and the other components of the ice. Our results indicate implications for airborne remote sensing and bioremediation of the upper sea ice layers.
•Polypropylene tube enhanced the capacity for imaging oil-in-ice.•Oil was incorporated in the sea ice matrix and appeared dispersed.•Oil remained separate from the brine.•Oil inclusions resemble the geometry of a disk or oblate spheroid.•Inclusions were randomly oriented and had feature sizes less than 1 mm.
Deuteration in infrared dark clouds Lackington, Matias; Fuller, Gary A; Pineda, Jaime E ...
Monthly notices of the Royal Astronomical Society,
01/2016, Volume:
455, Issue:
1
Journal Article
Peer reviewed
Open access
Much of the dense gas in molecular clouds has a filamentary structure but the detailed structure and evolution of this gas is poorly known. We have observed 54 cores in infrared dark clouds (IRDCs) ...using ... (1-0) and (3-2) to determine the kinematics of the densest material, where stars will form. We also observed ... (3-2) towards 29 of the brightest peaks to analyse the level of deuteration which is an excellent probe of the quiescent of the early stages of star formation. There were 13 detections of ... (3-2). This is one of the largest samples of IRDCs yet observed in these species. The deuteration ratio in these sources ranges between 0.003 and 0.14. For most of the sources the material traced by ... and ... (3-2) still has significant turbulent motions, however three objects show subthermal ... velocity dispersion. Surprisingly the presence or absence of an embedded 70...m source shows no correlation with the detection of ... (3-2), nor does it correlate with any change in velocity dispersion or excitation temperature. Comparison with recent models of deuteration suggest evolutionary time-scales of these regions of several free-fall times or less. (ProQuest: ... denotes formulae/symbols omitted.)
Abstract
In this study, 36 cores (30 starless and six protostellar) identified in Orion were surveyed to search for inward motions. We used the Nobeyama 45 m radio telescope, and mapped the cores in ...the
J
= 1 → 0 transitions of HCO
+
, H
13
CO
+
, N
2
H
+
, HNC, and HN
13
C. The asymmetry parameter
δV
, which was the ratio of the difference between the HCO
+
and H
13
CO
+
peak velocities to the H
13
CO
+
line width, was biased toward negative values, suggesting that inward motions were more dominant than outward motions. Three starless cores (10% of all starless cores surveyed) were identified as cores with blue-skewed line profiles (asymmetric profiles with more intense blueshifted emission), and another two starless cores (7%) were identified as candidate blue-skewed line profiles. The peak velocity difference between HCO
+
and H
13
CO
+
of them was up to 0.9 km s
−1
, suggesting that some inward motions exceeded the speed of sound for the quiescent gas (∼10–17 K). The mean of
δV
of the five aforementioned starless cores was derived to be −0.5 ± 0.3. One core, G211.16−19.33North3, observed using the Atacama Compact Array of the Atacama Large Millimeter/submillimeter Array in DCO
+
J
= 3 → 2 exhibited blue-skewed features. Velocity offset in the blue-skewed line profile with a dip in the DCO
+
J
= 3 → 2 line was larger (∼0.5 km s
−1
) than that in HCO
+
J
= 1 → 0 (∼0.2 km s
−1
), which may represent gravitational acceleration of inward motions. It seems that this core is at the last stage in the starless phase, judging from the chemical evolution factor version 2.0 (CEF2.0).
We describe a pilot survey conducted with the Mopra 22 m radio telescope in preparation for the Millimeter Astronomy Legacy Team Survey at 90 GHz (MALT90). We identified 182 candidate dense molecular ...clumps using six different selection criteria and mapped each source simultaneously in 16 different lines near 90 GHz. We present a summary of the data and describe how the results of the pilot survey shaped the design of the larger MALT90 survey. We motivate our selection of target sources for the main survey based on the pilot detection rates and demonstrate the value of mapping in multiple lines simultaneously at high spectral resolution.
A 39-cm sediment core from Castle Lake, California (USA) spans the last ~ 450 years and was analyzed for diatoms and organic geochemistry (δ
15
N, δ
13
C, and C:N), with the goal of determining ...sensitivity to natural climate variation and twentieth century anthropogenic effects. Castle Lake is a subalpine, nitrogen-limited lake with ~ 5 months of annual ice cover. Human impacts include light recreational use, past fish stocking, and experimental use by the Castle Lake Research Station. The base of the core (below 32 cm; pre mid-1700s) represents the period of maximum ice cover. In contrast, the end of the Little Ice Age (mid 1700s–early 1800s) is dominated by cyclotelloids (mostly
Discostella stelligera
), indicating significant open-water periods, a condition that persisted into the early 1900s. Cyclotelloids began to decline in the 1960s and were replaced by the
Fragilaria tenera
grp. (peak in 1970s), succeeded by
Asterionella formosa
(peak ~ 2010), and accompanied by a reduction in δ
15
N values and a decrease in C:N that may represent increased atmospheric nitrogen deposition. Another anthropogenic signal was discerned in the core and was interpreted to be the result of an ammonium nitrate fertilization experiment of the epilimnion that was conducted in 1980 and 1981. This signal was manifested in the core largely by a negative excursion in δ
15
N, possibly caused by fractionation during denitrification in surface sediment. A phytoplankton monitoring dataset collected by the Castle Lake Research Station from 1967 to 1984 corroborates the timing of increased araphid euplanktonic species in the 1970s, and increases in two benthic diatoms (
Staurosirella pinnata
and
Tabellaria fenestrata)
, entrained in the phytoplankton tows during the experimentation years. Both ice cover and nitrogen addition appear to be strong drivers that affected the lake diatoms, although additional drivers, such as fish stocking and associated cascade effects need further exploration. These data will be helpful for interpreting longer core records from Castle Lake, should the opportunity arise, as well as cores from similar systems in the region.
Abstract
We present the results of on-the-fly mapping observations of 44 fields containing 107 SCUBA-2 cores in the emission lines of molecules N
2
H
+
, HC
3
N, and CCS at 82–94 GHz using the ...Nobeyama 45 m telescope. This study aimed at investigating the physical properties of cores that show high deuterium fractions and might be close to the onset of star formation. We found that the distributions of the N
2
H
+
and HC
3
N line emissions are approximately similar to the distribution of the 850
μ
m dust continuum emission, whereas the CCS line emission is often undetected or is distributed in a clumpy structure surrounding the peak position of the 850
μ
m dust continuum emission. Occasionally (12%), we observe CCS emission, which is an early-type gas tracer toward the young stellar object, probably due to local high excitation. Evolution toward star formation does not immediately affect the nonthermal velocity dispersion.
In the multi-scale view of the star formation process the material flows from large molecular clouds down to clumps and cores. In this paradigm it is still unclear if it is gravity or turbulence that ...drives the observed supersonic non-thermal motions during the collapse, in particular in high-mass regions, and at which scales gravity becomes eventually dominant over the turbulence of the interstellar medium. To investigate this problem we have combined the dynamics of a sample of 70 μm-quiet clumps, selected to cover a wide range of masses and surface densities, with the dynamics of the parent filaments in which they are embedded. We observe a continuous interplay between turbulence and gravity, where the former creates structures at all scales and the latter takes the lead when a critical value of the surface density is reached, Σ
th
= 0.1 g cm
−2
. In the densest filaments this transition can occur at the parsec, or even larger scales, leading to a global collapse of the whole region and most likely to the formation of the massive objects.
In the early stages of star formation, a protostar is deeply embedded in an optically thick envelope such that it is not directly observable. Variations in the protostellar accretion rate, however, ...will cause luminosity changes that are reprocessed by the surrounding envelope and are observable at submillimeter wavelengths. We searched for submillimeter flux variability toward 12 Planck Galactic Cold Clumps detected by the James Clerk Maxwell Telescope (JCMT)-SCUBA-2 Continuum Observations of Pre-protostellar Evolution (SCOPE) survey. These observations were conducted at 850 using the JCMT/SCUBA-2. Each field was observed three times over about 14 months between 2016 April and 2017 June. We applied a relative flux calibration and achieved a calibration uncertainty of ∼3.6% on average. We identified 136 clumps across 12 fields and detected four sources with flux variations of ∼30%. For three of these sources, the variations appear to be primarily due to large-scale contamination, leaving one plausible candidate. The flux change of the candidate may be associated with low- or intermediate-mass star formation assuming a distance of 1.5 kpc, although we cannot completely rule out the possibility that it is a random deviation. Further studies with dedicated monitoring would provide a better understanding of the detailed relationship between submillimeter flux and accretion rate variabilities while enhancing the search for variability in star-forming clumps farther away than the Gould Belt.
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