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Author

Ankan Das

Other affiliations: University of Calcutta
Bio: Ankan Das is an academic researcher from Indian Centre for Space Physics. The author has contributed to research in topics: Germination & Astrochemistry. The author has an hindex of 2, co-authored 8 publications receiving 16 citations. Previous affiliations of Ankan Das include University of Calcutta.

Papers
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Journal ArticleDOI
TL;DR: In this article, a newly discovered hot molecular core in a nearby low-metallicity galaxy, the Large Magellanic Cloud (LMC), with the Atacama Large Millimeter/submillimeter Array was detected towards the high-mass young stellar object, ST16.
Abstract: We present the results of 0.1-pc-scale observations in 250 GHz and 350GHz towards a newly-discovered hot molecular core in a nearby low-metallicity galaxy, the Large Magellanic Cloud (LMC), with the Atacama Large Millimeter/submillimeter Array. A variety of C/N/O/Si/S-bearing molecules are detected towards the high-mass young stellar object, ST16. A rotating protostellar envelope is for the first time detected outside our Galaxy by SO2 and 34SO lines. An outflow cavity is traced by CCH and CN. The isotope abundance of sulfur in the source is estimated to be 32S/34S = 17 and 32S/33S = 53 based on SO, SO2, and CS isotopologues, suggesting that both 34S and 33S are overabundant in the LMC. Rotation diagram analyses show that the source is associated with hot gas (>100K) traced by high-excitation lines of CH3OH and SO2, as well as warm gas (~50K) traced by CH3OH, SO2, 34SO, OCS, CH3CN lines. A comparison of molecular abundances between LMC and Galactic hot cores suggests that organic molecules (e.g., CH3OH, a classical hot core tracer) show a large abundance variation in low metallicity, where the present source is classified into an organic-poor hot core. Our astrochemical simulations suggest that different grain temperature during the initial ice-forming stage would contribute to the chemical differentiation. In contrast, SO2 shows similar abundances within all the known LMC hot cores and the typical abundance roughly scales with the LMC's metallicity. Nitrogen-bearing molecules are generally less abundant in LMC hot cores, except for NO. The present results suggest that chemical compositions of hot cores do not always simply scale with the metallicity.

13 citations

Journal ArticleDOI
TL;DR: In this article, the authors carried out extensive chemical models to follow the fate of P-bearing species in diffuse clouds, photon-dominated or photodissociation regions (PDRs), and hot cores/corinos.
Abstract: Phosphorus related species are not known to be as omnipresent in space as hydrogen, carbon, nitrogen, oxygen, and sulfur-bearing species. Astronomers spotted very few P-bearing molecules in the interstellar medium and circumstellar envelopes. Limited discovery of the P-bearing species imposes severe constraints in modeling the P-chemistry. In this paper, we carry out extensive chemical models to follow the fate of P-bearing species in diffuse clouds, photon-dominated or photodissociation regions (PDRs), and hot cores/corinos. We notice a curious correlation between the abundances of PO and PN and atomic nitrogen. Since N atoms are comparatively abundant in diffuse clouds and PDRs than in the hot core/corino region, PO/PN reflects 1 in the late warm-up evolutionary phase of the hot core/corino regions. During the end of the post-warm-up phase, we obtain PO/PN > 1 for hot core and < 1 for its low mass analog. We employ a radiative transfer model to investigate the transitions of some of the P-bearing species in diffuse cloud and hot core regions and estimate the line profiles. Our study estimates the required integration time to observe these transitions with ground-based and space-based telescopes. We also carry out quantum chemical computation of the infrared features of PH3 along with various impurities. We notice that SO2 overlaps with the PH3 bending-scissoring modes around ~ (1000 - 1100) cm-1. We also find that the presence of CO2 can strongly influence the intensity of the stretching modes around ~ 2400 cm-1 of PH3 .

8 citations

Book ChapterDOI
01 Jan 2018
TL;DR: The post-harvest management of spices appears to be more crucial here as discussed by the authors, as most of the freshly harvested spices are very high in their moisture content, highly perishable and susceptible to microbial contamination.
Abstract: Spices not only help imparting taste, flavour, aroma and colour but also act as a preservative by preventing the spoilage of various food and beverage products. They are huge reservoir of essential oils and aromatic constituents which are of great demand in pharmaceutical and cosmetic industries, both in national and international trade. They also possess nutritional, antimicrobial, antioxidant and pharmaceutical properties and, hence, regarded as one of the most functionally important food ingredients. Efforts are, therefore, directed towards enhancing area, increasing productivity and improving quality of spices. However, in today’s scenario, real challenges confronting us not only on how to sustain the productivity of spices but also on how to minimize their losses. Post harvest management of spices appears to be more crucial here. Most of the freshly harvested spices are very high in their moisture content, highly perishable and susceptible to microbial contamination. Steps like harvesting at optimum stage, proper transportation to processing units, cleaning, blanching, treating with recommended chemicals, dehydration, packaging and storage or processing leading those to value added products etc. are very much crucial so far as reduction of post harvest losses are concerned. The irony is that due to lack of proper knowledge, awareness and improper technology dissemination, the post-harvest management, especially in the developing countries is still not up to the mark. Therefore it is necessary to process the spices by exploiting both classical and innovative post-harvest technology to ensure their long term preservation and optimum utilization.

5 citations

Journal ArticleDOI
TL;DR: In this paper, a newly discovered hot molecular core in a nearby low-metallicity galaxy, the Large Magellanic Cloud (LMC), with the Atacama Large Millimeter/submillimeter Array was detected towards the high-mass young stellar object, ST16.
Abstract: We present the results of 0.1-pc-scale observations in 250 GHz and 350GHz towards a newly-discovered hot molecular core in a nearby low-metallicity galaxy, the Large Magellanic Cloud (LMC), with the Atacama Large Millimeter/submillimeter Array. A variety of C/N/O/Si/S-bearing molecules are detected towards the high-mass young stellar object, ST16. A rotating protostellar envelope is for the first time detected outside our Galaxy by SO2 and 34SO lines. An outflow cavity is traced by CCH and CN. The isotope abundance of sulfur in the source is estimated to be 32S/34S = 17 and 32S/33S = 53 based on SO, SO2, and CS isotopologues, suggesting that both 34S and 33S are overabundant in the LMC. Rotation diagram analyses show that the source is associated with hot gas (>100K) traced by high-excitation lines of CH3OH and SO2, as well as warm gas (~50K) traced by CH3OH, SO2, 34SO, OCS, CH3CN lines. A comparison of molecular abundances between LMC and Galactic hot cores suggests that organic molecules (e.g., CH3OH, a classical hot core tracer) show a large abundance variation in low metallicity, where the present source is classified into an organic-poor hot core. Our astrochemical simulations suggest that different grain temperature during the initial ice-forming stage would contribute to the chemical differentiation. In contrast, SO2 shows similar abundances within all the known LMC hot cores and the typical abundance roughly scales with the LMC's metallicity. Nitrogen-bearing molecules are generally less abundant in LMC hot cores, except for NO. The present results suggest that chemical compositions of hot cores do not always simply scale with the metallicity.

5 citations

Journal ArticleDOI
TL;DR: In this article, an observational study and astrochemical modeling are coupled together to illustrate the connection between aldehydes and their corresponding alcohols in the ALMA Cycle 4 data of a hot molecular core, G10.47+0.03.
Abstract: It is speculated that there might be some linkage between interstellar aldehydes and their corresponding alcohols. Here, an observational study and astrochemical modeling are coupled together to illustrate the connection between them. The ALMA Cycle 4 data of a hot molecular core, G10.47+0.03 is utilized for this study. Various aldehydes (acetaldehyde, propanal, and glycolaldehyde), alcohols (methanol and ethylene glycol), and a ketone (acetone) are identified in this source. The excitation temperatures and the column densities of these species were derived via the rotation diagram method assuming LTE conditions. An extensive investigation is carried out to understand the formation of these species. Six pairs of aldehyde-alcohol: i) methanal and methanol; ii) ethanal and ethanol; iii) propanal and 1-propanol; iv) propenal and allyl alcohol; v) propynal and propargyl alcohol; vi) glycolaldehyde and ethylene glycol; vii) along with one pair of ketone-alcohol (acetone and isopropanol) and viii) ketene-alcohol (ethenone and vinyl alcohol) are considered for this study. Two successive hydrogenation reactions in the ice phase are examined to form these alcohols from aldehydes, ketone, and ketene, respectively. Quantum chemical methods are extensively executed to review the ice phase formation route and the kinetics of these species. Based on the obtained kinetic data, astrochemical modeling is employed to derive the abundances of these aldehydes, alcohols, ketone, and ketene in this source. It is seen that our model could successfully explain the observed abundances of various species in this hot molecular core.

4 citations


Cited by
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Journal ArticleDOI
TL;DR: The UMIST Database for Astrochemistry (UDfaa) as discussed by the authors contains 6173 gas-phase reactions involving 467 species, 47 of which are new to this release.
Abstract: We present the fifth release of the UMIST Database for Astrochemistry (UDfA). The new reaction network contains 6173 gas-phase reactions, involving 467 species, 47 of which are new to this release. We have updated rate coefficients across all reaction types. We have included 1171 new anion reactions and updated and reviewed all photorates. In addition to the usual reaction network, we also now include, for download, state-specific deuterated rate coefficients, deuterium exchange reactions and a list of surface binding energies for many neutral species. Where possible, we have referenced the original source of all new and existing data. We have tested the main reaction network using a dark cloud model and a carbon-rich circumstellar envelope model. We present and briefly discuss the results of these models.

608 citations

Journal ArticleDOI
TL;DR: In this article, the authors calculated the gas-grain chemical reaction network considering a layered ice-mantle structure in star-forming cores, to investigate how the hot corino chemistry and warm carbon chain chemistry depend on the physical condition of the static phase before the onset of gravitational collapse.
Abstract: Hot corino chemistry and warm carbon chain chemistry (WCCC) are driven by gas-grain interactions in star-forming cores: radical-radical recombination reactions to form complex organic molecules (COMs) in the ice mantle, sublimation of CH$_4$ and COMs, and their subsequent gas-phase reactions These chemical features are expected to depend on the composition of ice mantle which is set in the prestellar phase We calculated the gas-grain chemical reaction network considering a layered ice-mantle structure in star-forming cores, to investigate how the hot corino chemistry and WCCC depend on the physical condition of the static phase before the onset of gravitational collapse We found that WCCC becomes more active, if the temperature is lower, or the visual extinction is lower in the static phase, or the static phase is longer Dependence of hot corino chemistry on the static-phase condition is more complex While CH$_3$OH is less abundant in the models with warmer static phase, some COMs are formed efficiently in those warm models, since there are various formation paths of COMs If the visual extinction is lower, photolysis makes COMs less abundant in the static phase Once the collapse starts and visual extinction increases, however, COMs can be formed efficiently Duration of the static phase does not largely affect COM abundances Chemical diversity between prototypical hot corinos and hybrid sources, in which both COMs and carbon chains are reasonably abundant, can be explained by the variation of prestellar conditions Deficiency of gaseous COMs in prototypical WCCC sources is, however, hard to reproduce within our models

30 citations

01 Jan 2018
TL;DR: In this paper, the first extragalactic detection of the complex organic molecules (COMs) dimethyl ether (CH3OCH3) and methyl formate (CH 3OCHO) with the Atacama Large Millimeter/submillimeter Array (ALMA) was reported.
Abstract: We report the first extragalactic detection of the complex organic molecules (COMs) dimethyl ether (CH3OCH3) and methyl formate (CH3OCHO) with the Atacama Large Millimeter/submillimeter Array (ALMA). These COMs, together with their parent species methanol (CH3OH), were detected toward two 1.3 mm continuum sources in the N 113 star-forming region in the low-metallicity Large Magellanic Cloud (LMC). Rotational temperatures (Trot approx. 130 K) and total column densities (Nrot 10 approx. 16 cm−2) have been calculated for each source based on multiple transitions of CH3OH. We present the ALMA molecular emission maps for COMs and measured abundances for all detected species. The physical and chemical properties of two sources with COMs detection, and the association with H2O and OH maser emission, indicate that they are hot cores. The fractional abundances of COMs scaled by a factor of 2.5 to account for the lower metallicity in the LMC are comparable to those found at the lower end of the range in Galactic hot cores. Our results have important implications for studies of organic chemistry at higher redshift.

18 citations

Journal ArticleDOI
TL;DR: In this article, the authors investigated how the hot corino chemistry and warm carbon chain chemistry depend on the physical condition of the static phase before the onset of gravitational collapse, and found that WCCC becomes more active, if the temperature is lower, or the visual extinction is lower in a static phase, or longer in a longer static phase.
Abstract: Hot corino chemistry and warm carbon chain chemistry (WCCC) are driven by gas-grain interactions in star-forming cores: radical-radical recombination reactions to form complex organic molecules (COMs) in the ice mantle, sublimation of CH$_4$ and COMs, and their subsequent gas-phase reactions. These chemical features are expected to depend on the composition of ice mantle which is set in the prestellar phase. We calculated the gas-grain chemical reaction network considering a layered ice-mantle structure in star-forming cores, to investigate how the hot corino chemistry and WCCC depend on the physical condition of the static phase before the onset of gravitational collapse. We found that WCCC becomes more active, if the temperature is lower, or the visual extinction is lower in the static phase, or the static phase is longer. Dependence of hot corino chemistry on the static-phase condition is more complex. While CH$_3$OH is less abundant in the models with warmer static phase, some COMs are formed efficiently in those warm models, since there are various formation paths of COMs. If the visual extinction is lower, photolysis makes COMs less abundant in the static phase. Once the collapse starts and visual extinction increases, however, COMs can be formed efficiently. Duration of the static phase does not largely affect COM abundances. Chemical diversity between prototypical hot corinos and hybrid sources, in which both COMs and carbon chains are reasonably abundant, can be explained by the variation of prestellar conditions. Deficiency of gaseous COMs in prototypical WCCC sources is, however, hard to reproduce within our models.

12 citations

Journal ArticleDOI
TL;DR: In this article, the first detection of a hot molecular core in the extreme outer Galaxy was reported, which is an excellent laboratory to study star formation and interstellar medium in a Galactic low-metallicity environment.
Abstract: Interstellar chemistry in low metallicity environments is crucial to understand chemical processes in the past metal-poor universe. Recent studies of interstellar molecules in nearby low-metallicity galaxies have suggested that the metallicity has a significant effect on chemistry of star-forming cores. Here we report the first detection of a hot molecular core in the extreme outer Galaxy, which is an excellent laboratory to study star formation and interstellar medium in a Galactic low-metallicity environment. The target star-forming region, WB89-789, is located at the galactocentric distance of 19 kpc. Our ALMA observations in 241-246, 256-261, 337-341, and 349-353 GHz have detected a variety of carbon-, oxygen-, nitrogen-, sulfur-, and silicon-bearing species, including complex organic molecules (COMs) containing up to nine atoms, towards a warm (>100 K) and compact (<0.03 pc) region associated with a protostar (~8x10^3 L_sun). Deuterated species such as HDO, HDCO, D2CO, and CH2DOH are also detected. A comparison of fractional abundances of COMs relative to CH3OH between the outer Galactic hot core and an inner Galactic counterpart shows a remarkable similarity. On the other hand, the molecular abundances in the present source do not resemble those of low-metallicity hot cores in the Large Magellanic Cloud. The results suggest that a great molecular complexity exists even in a primordial environment of the extreme outer Galaxy. The detection of another embedded protostar associated with high-velocity SiO outflows is also reported.

11 citations