Abstract
In the interstellar cold gas, the chemistry of formaldehyde (H
2
CO) can be essential to explain the formation of complex organic molecules. On this matter, the massive and energetic ...protostellar object G331 is still unexplored; hence, we carried out a comprehensive study of the isotopologues of H
2
CO, the formyl cation (HCO
+
), and protonated formaldehyde (H
2
COH
+
) through the APEX observations in a spectral window of ∼159–356 GHz. We employed observational and theoretical methods to derive the physical properties of the molecular gas combining LTE and non-LTE analyses. Formaldehyde was characterized via 35 lines of H
2
CO,
H
2
13
CO, HDCO, and H
2
C
18
O. The formyl cation was detected via eight lines of HCO
+
, H
13
CO
+
, HC
18
O
+
, and HC
17
O
+
. Deuterium was clearly detected via HDCO, whereas DCO
+
remained undetected. The H
2
COH
+
was detected through three clean lines. According to the radiative analysis, formaldehyde appears to be embedded in a bulk gas with a wide range of temperatures (
T
∼ 20–90 K), while HCO
+
and H
2
COH
+
are primarily associated with colder gas (
T
≲ 30 K). The reaction H
2
CO+HCO
+
→ H
2
COH
+
+ CO is crucial for the balance of the three species. We used the Nautilus gas–grain code to predict the evolution of their molecular abundances relative to H
2
; their values at timescales of ∼10
3
yr matched the observations in G331: H
2
CO = (0.2–2) × 10
−8
, HCO
+
= (0.5–4) × 10
−9
, and H
2
COH
+
= (0.2–2) × 10
−10
. Based on the molecular evolution of H
2
CO, HCO
+
, and H
2
COH
+
, we hypothesized about the young lifetime of G331, which is consistent with the active gas–grain chemistry of massive protostellar objects.
Which Molecular Cloud Structures Are Bound? Evans II, Neal J.; Heyer, Mark; Miville-Deschênes, Marc-Antoine ...
The Astrophysical journal,
10/2021, Letnik:
920, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Abstract
We analyze surveys of molecular cloud structures defined by tracers ranging from CO
J
= 1 → 0 through
13
CO
J
= 1 → 0 to dust emission together with NH
3
data. The mean value of the virial ...parameter and the fraction of mass in bound structures depends on the method used to identify structures. Generally, the virial parameter decreases and the fraction of mass in bound structures increases with the effective density of the tracer, the surface density and mass of the structures, and the distance from the center of a galaxy. For the most complete surveys of structures in the Galaxy defined by CO
J
= 1 → 0, the fraction of mass that is in bound structures is 0.19. For catalogs of other galaxies based on CO
J
= 2 → 1, the fraction is 0.35. These results offer substantial alleviation of the fundamental problem of slow star formation. If only clouds found to be bound are counted and they are assumed to collapse in a freefall time at their mean cloud density, the sum over all clouds in a complete survey of the Galaxy yields a predicted star formation rate of 46
M
⊙
yr
−1
, a factor of 6.5 less than if all clouds are bound.
We present observations and analysis of the massive molecular outflow G331.512-0.103, obtained with Atacama Large Millimeter/submillimeter Array band 7, continuing the work from Merello et al. ...Several lines were identified in the observed bandwidth, consisting of two groups: lines with narrow profiles, tracing the emission from the core ambient medium; and lines with broad velocity wings, tracing the outflow and shocked gas emission. The physical and chemical conditions, such as density, temperature, and fractional abundances are calculated. The ambient medium, or core, has a mean density of cm−3 and a temperature of ∼70 K. The SiO and SO2 emission trace the very dense and hot part of the shocked outflow, with values of cm−3 and T ∼ 160-200 K. The interpretation of the molecular emission suggests an expanding cavity geometry powered by stellar winds from a newborn UCHII region, alongside a massive and high-velocity molecular outflow. This scenario, along with the estimated physical conditions, is modeled using the 3D geometry radiative transfer code MOLLIE for the SiO(J = 8 − 7) molecular line. The main features of the outflow and the expanding shell are reproduced by the model.
We present the 1.1 mm Bolocam Galactic Plane Survey (BGPS) observations of the Gemini OB1 molecular cloud complex, and targeted NH{sub 3} observations of the BGPS sources. When paired with molecular ...spectroscopy of a dense gas tracer, millimeter observations yield physical properties such as masses, radii, mean densities, kinetic temperatures, and line widths. We detect 34 distinct BGPS sources above 5{sigma} = 0.37 Jy beam{sup -1} with corresponding 5{sigma} detections in the NH{sub 3}(1,1) transition. Eight of the objects show water maser emission (20%). We find a mean millimeter source FWHM of 1.12 pc and a mean gas kinetic temperature of 20 K for the sample of 34 BGPS sources with detections in the NH{sub 3}(1,1) line. The observed NH{sub 3} line widths are dominated by non-thermal motions, typically found to be a few times the thermal sound speed expected for the derived kinetic temperature. We calculate the mass for each source from the millimeter flux assuming the sources are isothermal and find a mean isothermal mass within a 120'' aperture of 230 {+-} 180 M{sub sun}. We find a total mass of 8400 M{sub sun} for all BGPS sources in the Gemini OB1 molecular cloud, representing 6.5% of the cloud mass. By comparing the millimeter isothermal mass to the virial mass calculated from the NH{sub 3} line widths within a radius equal to the millimeter source size, we find a mean virial parameter (M{sub vir}/M {sub iso}) of 1.0 {+-} 0.9 for the sample. We find mean values for the distributions of column densities of 1.0 x 10{sup 22} cm{sup -2} for H{sub 2}, and 3.0 x 10{sup 14} cm{sup -2} for NH{sub 3}, giving a mean NH{sub 3} abundance of 3.0 x 10{sup -8} relative to H{sub 2}. We find volume-averaged densities on the order of 10{sup 3}-10{sup 4} cm{sup -3}. The sizes and densities suggest that in the Gem OB1 region the BGPS is detecting the clumps from which stellar clusters form, rather than smaller, higher density cores where single stars or small multiple systems form.
Substrate Integrated (SI) technologies, either completely or partially filled with dielectric, as well as completely empty (i.e. without any dielectric material), have been object of intense research ...in the last years. Their performance in terms of losses, cost and size are mid-way between those of classical planar lines and rectangular waveguides. Many communication devices have already been successfully designed, manufactured and measured in all these SI technologies. But these measurements are mostly done at room temperature under atmospheric pressure conditions. However, the good results (in terms of low loss, profile and cost) of these novel technologies, especially the completely empty versions, close to the performance of the rectangular waveguide, make them a very good alternative for being used in small satellite payloads. Up to now, few attention has been given to the thermal analysis of these SI technologies, still missing a complete comparative study of these effects under both, atmospheric pressure and vacuum conditions. In this work the same filter is implemented on four different SI technologies (including completely and partially filled with dielectric, as well as empty -no dielectric- versions). The four filters are designed, manufactured, and measured at different temperatures according to the thermal testing standards for space applications. The thermal study is performed under atmospheric pressure conditions and, for the first time, under high vacuum conditions. Finally, a comparison with all previous available thermal studies (all of them performed at atmospheric pressure levels) is included.
Widespread mortality of Thalassia testudinum was first documented in Florida Bay, USA, during the summer of 1987. This unprecedented event spanned 3 yr, affected 40 km² of seagrass and resulted in ...more than a decade of ecological disturbances. Initial putative causes for seagrass die-off ranged from climatic anomalies and watershed changes to wasting disease and eutrophication. Subsequent experimental research suggested that hypoxic plant tissue, caused by low water column oxygen content or reduced photosynthesis, allowed intrusion of sulfide leading to plant death. Contributing factors included high temperatures, salinities and T. testudinum biomass, together causing lower oxygen water solubility, higher community respiration rates and elevated nighttime oxygen demand. The Fisheries Habitat Assessment Program (FHAP) has tracked the system’s slow recovery since 1995. Recent FHAP data (2012) indicated that T. testudinum had returned to pre-die-off densities in even the most severely affected locations. During the summer of 2015, following several months of drought, National Park Service researchers reported hypersaline conditions and a recurrence of seagrass die-off in north-central Florida Bay. An interagency effort is presently underway to document the duration, extent, impacts and possible factors responsible for the current mortality. Initial field surveys indicate that there is high spatial coincidence between the current and the 1987–1990 events and that hypersalinity, water column stratification and bottom-water anoxia might have once again resulted in mass mortality of T. testudinum in Florida Bay. The goal of this report is to alert the scientific community to the recurrence of this important ecological event.
Although planting seagrass is not technically complex, the ability to plant large areas is limited by the time-consuming nature of manual methods. Additionally, manual methods use small, spatially ...isolated planting units (PUs; shoot bundles or plugs/cores) that are often highly susceptible to disturbance. The likelihood for harvesting intact apical meristems may be higher with large sods compared to smaller units, thus increasing survival and expansion rates. Here, we examined the survival and expansion of large units (1.5 x 1.2 m) of seagrass transplanted using a mechanized planting boat (Giga Unit Transplant System; GUTS). Twenty-seven units of seagrass (18 Halodule wrightii and 9 Thalassia testudinum) were transplanted and monitored for survival, shoot density, and expansion. After 3 years, 74.1% of the units had survived (66.7% H. wrightii and 88.9% T. testudinum) with 12 H. wrightii units having expanded substantially beyond the bounds of the original PU, merging with adjacent units to form spatially continuous patches of seagrass. High survival rates for T. testudinum should be interpreted in light of concomitant declines in density and lack of significant expansion after 3 years. In its tested configuration, the GUTS was a viable method for transplanting H. wrightii where donor and receiver sites were in close proximity (<2 km; a current limitation of the GUTS design used here). However, based on the reduced density and lack of significant expansion of T. testudinum that has persisted 3 years post-transplant, the GUTS cannot yet be fully recommended for transplanting this species.
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