Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userLinking ice and gas in the Lambda Orionis Barnard 35A cloud
158
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Dust grains play an important role in the synthesis of molecules in the interstellar medium, from the simplest species to complex organic molecules. How some of these solid-state molecules are converted into gas-phase species is still a matter of debate. Our aim is to directly compare ice and gas abundances of methanol (CH$_3$OH) and CO, and to investigate the relationship between ice and gas in low-mass protostellar envelopes. We present Submillimeter Array and Atacama Pathfinder EXperiment observations of gas-phase CH$_3$OH and CO towards the multiple protostellar system IRAS05417+0907 located in the B35A cloud. We use archival AKARI ice data toward the same target to calculate CH$_3$OH and CO gas-to-ice ratios. The CO isotopologues emissions are extended, whereas the CH$_3$OH emission is compact and traces the giant outflow emanating from IRAS05417+0907. A discrepancy between submillimeter dust emission and H$_2$O ice column density is found for B35A$-$4 and B35A$-$5, similar to what has previously been reported. B35A$-$2 and B35A$-$3 are located where the submillimeter dust emission peaks and show H$_2$O column densities lower than for B35A$-$4. The difference between the submillimeter continuum emission and the infrared H$_2$O ice observations suggests that the distributions of dust and H$_2$O ice differ around the young stellar objects in this dense cloud. The reason for this may be that the sources are located in different environments resolved by the interferometric observations: B35A$-$2, B35A$-$3 and in particular B35A$-$5 are situated in a shocked region plausibly affected by sputtering and heating impacting the submillimeter dust emission pattern, while B35A$-$4 is situated in a more quiescent part of the cloud. Gas and ice maps are essential to connect small-scale variations in the ice composition with large-scale astrophysical phenomena probed by gas observations.
rate research
Read More
Massive stars have a strong impact on their local environments. However, how stellar feedback regulates star formation is still under debate. In this context, we studied the chemical properties of 80 dense cores in the Orion molecular cloud complex composed of the Orion A (39 cores), B (26 cores), and lambda Orionis (15 cores) clouds using multiple molecular line data taken with the Korean Very Long Baseline Interferometry Network (KVN) 21-m telescopes. The lambda Orionis cloud has an H ii bubble surrounding the O-type star lambda Ori, and hence it is exposed to the ultraviolet (UV) radiation field of the massive star. The abundances of C2H and HCN, which are sensitive to UV radiation, appear to be higher in the cores in the lambda Orionis cloud than those in the Orion A and B clouds, while the HDCO to H2CO abundance ratios show an opposite trend, indicating a warmer condition in the lambda Orionis cloud. The detection rates of dense gas tracers such as the N2H+, HCO+, and H13CO+ lines are also lower in the lambda Orionis cloud. These chemical properties imply that the cores in the lambda Orionis cloud are heated by UV photons from lambda Ori. Furthermore, the cores in the lambda Orionis cloud do not show any statistically significant excess in the infall signature of HCO+ (1 - 0), unlike the Orion A and B clouds. Our results support the idea that feedback from massive stars impacts star formation in a negative way by heating and evaporating dense materials, as in the lambda Orionis cloud.
Cold gas-phase water has recently been detected in a cold dark cloud, Barnard 5 located in the Perseus complex, by targeting methanol peaks as signposts for ice mantle evaporation. Observed morphology and abundances of methanol and water are consistent with a transient non-thermal evaporation process only affecting the outermost ice mantle layers, possibly triggering a more complex chemistry. We present the detection of the Complex Organic Molecules (COMs) acetaldehyde and methyl formate as well as formic acid and ketene, and the tentative detection of di-methyl ether towards the methanol hotspot of Barnard 5 located between two dense cores using the single dish OSO 20m, IRAM 30m, and NRO 45m telescopes. The high energy cis- conformer of formic acid is detected, suggesting that formic acid is mostly formed at the surface of interstellar grains and then evaporated. The detection of multiple transitions for each species allows us to constrain their abundances through LTE and non-LTE methods. All the considered COMs show similar abundances between $sim 1$ and $sim 10$ % relative to methanol depending on the assumed excitation temperature. The non-detection of glycolaldehyde, an isomer of methyl formate, with a [glycolaldehyde]/[methyl formate] abundance ratio lower than 6 %, favours gas phase formation pathways triggered by methanol evaporation. According to their excitation temperatures derived in massive hot cores, formic acid, ketene, and acetaldehyde have been designated as lukewarm COMs whereas methyl formate and di-methyl ether were defined as warm species. Comparison with previous observations of other types of sources confirms that lukewarm and warm COMs show similar abundances in low-density cold gas whereas the warm COMs tend to be more abundant than the lukewarm species in warm protostellar cores.
In this work we present ALMA continuum observations at 880 $mu$m of 30 sub-mm cores previously identified with APEX/LABOCA at 870$mu$m in the Barnard 30 cloud. The main goal is to characterize the youngest and lowest mass population in the cloud. As a result, we report the detection of five (out of 30) spatially unresolved sources with ALMA, with estimated masses between 0.9 and 67 M$_{rm Jup}$. From these five sources, only two show gas emission. The analysis of multi-wavelength photometry from these two objects, namely B30-LB14 and B30-LB19, is consistent with one Class II- and one Class I low-mass stellar object, respectively. The gas emission is consistent with a rotating disk in the case of B30-LB14, and with an oblate rotating envelope with infall signatures in the case of LB19. The remaining three ALMA detections do not have infrared counterparts and can be classified as either deeply embedded objects or as starless cores if B30 members. In the former case, two of them (LB08 and LB31) show internal luminosity upper limits consistent with Very Low Luminosity objects, while we do not have enough information for LB10. In the starless core scenario, and taking into account the estimated masses from ALMA and the APEX/LABOCA cores, we estimate final masses for the central objects in the substellar domain, so they could be classified as pre-BD core candidates.
The interaction between dust, ice, and gas during the formation of stars produces complex organic molecules. While observations indicate that several species are formed on ice-covered dust grains and are released into the gas phase, the exact chemical interplay between solid and gas phases and their relative importance remain unclear. Our goal is to study the interplay in regions of low-mass star formation through ice- and gas-mapping and by directly measuring gas-to-ice ratios. This provides constraints on the routes that lead to the chemical complexity that is observed in both phases. We present observations of gas-phase methanol (CH$_3$OH) and carbon monoxide at 1.3 mm towards ten low-mass young protostars in the Serpens SVS4 cluster from the SubMillimeter Array and the Atacama Pathfinder EXperiment telescope. We used archival data from the Very Large Telescope to derive abundances of ice H$_2$O, CO, and CH$_3$OH towards the same region. Finally, we constructed gas-ice maps of SVS4 and directly measured CO and CH$_3$OH gas-to-ice ratios. The CH$_3$OH gas-to-ice ratio agrees with values that were previously reported for embedded Class 0/I low-mass protostars. The CO gas-maps trace an extended gaseous component that is not sensitive to the effect of freeze-out. We find that there is no straightforward correlation between CO and CH$_3$OH gas with their ice counterparts in the cluster. This is likely related to the complex morphology of SVS4: the Class 0 protostar SMM4 and its envelope lie in the vicinity, and the outflow associated with SMM4 intersects the cluster. This study serves as a pathfinder for future observations with ALMA and the James Webb Space Telescope that will provide high-sensitivity gas-ice maps of molecules more complex than methanol. Such comparative maps will be essential to constrain the chemical routes that regulate the chemical complexity in star-forming regions.
Based on the 850 $mu$m dust continuum data from SCUBA-2 at James Clerk Maxwell Telescope (JCMT), we compare overall properties of Planck Galactic Cold Clumps (PGCCs) in the $lambda$ Orionis cloud to those of PGCCs in the Orion A and B clouds. The Orion A and B clouds are well known active star-forming regions, while the $lambda$ Orionis cloud has a different environment as a consequence of the interaction with a prominent OB association and a giant Hii region. PGCCs in the $lambda$ Orionis cloud have higher dust temperatures ($Td=16.13pm0.15$ K) and lower values of dust emissivity spectral index ($ beta=1.65pm0.02$) than PGCCs in the Orion A (Td=13.79$pm 0.21$K, $beta=2.07pm0.03$) and Orion B ($Td=13.82pm0.19$K, $beta=1.96pm0.02$) clouds. We find 119 sub-structures within the 40 detected PGCCs and identify them as cores. Of total 119 cores, 15 cores are discovered in the $lambda$ Orionis cloud, while 74 and 30 cores are found in the Orion A and B clouds, respectively. The cores in the $lambda$ Orionis cloud show much lower mean values of size R=0.08 pc, column density N(H2)=$(9.5pm1.2) times 10^{22}$ cm$^{-2}$, number density n(H2)=$(2.9 pm 0.4)times10^{5}$ cm$^{-3}$, and mass $M_{core}$=$1.0pm0.3$ M$_{odot}$ compared to the cores in the Orion A (R=0.11pc, $N(H2)=(2.3pm0.3) times 10^{23}$ cm$^{-2}$, n(H2)=$(3.8pm0.5) times 10^{5}$cm$^{-3}$, and $M_{core}$=$2.4 pm 0.3$ M$_{odot}$) and Orion B (R=0.16pc, N(H2)=$(3.8 pm 0.4) times 10^{23}$cm$^{-2}$, n(H2)=$(15.6pm1.8)times10^{5}$ cm$^{-3}$, and $M_{core}$= $2.7pm0.3$ M$_{odot}$) clouds. These core properties in the $lambda$ Orionis cloud can be attributed to the photodissociation and external heating by the nearby Hii region, which may prevent the PGCCs from forming gravitationally bound structures and eventually disperse them. These results support the idea of negative stellar feedback on core formation.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
