arXiv subjects

B. Parise

Publications and source records attributed to B. Parise.

49 records · Page 3Linked to original sources

arXiv2010

H2CO and CH3OH maps of the Orion Bar photodissociation region

A previous analysis of methanol and formaldehyde towards the Orion Bar concluded that the two molecular species may trace different physical components, methanol the clumpy material, and formaldehyde the interclump medium. To verify this hypothesis, we performed multi-line mapping observations of the two molecules to study their spatial distributions. The observations were performed with the IRAM-30m telescope at 218 and 241 GHz, with an angular resolution of ~11''. Additional data for H2CO from the Plateau de Bure array are also discussed. The data were analysed using an LVG approach. Both molecules are detected in our single-dish data. Our data show that CH3OH peaks towards the clumps of the Bar, but its intensity decreases below the detection threshold in the interclump material. When averaging over a large region of the interclump medium, the strongest CH3OH line is detected with a peak intensity of ~0.06K. Formaldehyde also peaks on the clumps, but it is also detected in the interclump gas. We verified that the weak intensity of CH3OH in the interclump medium is not caused by the different excitation conditions of the interclump material, but reflects a decrease in the column density of methanol. The abundance of CH3OH relative to H2CO decreases by at least one order of magnitude from the dense clumps to the interclump medium.

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arXiv2009

Deuterium chemistry in the Orion Bar PDR - "warm" chemistry starring CH2D+

High levels of deuterium fractionation in gas-phase molecules are usually associated with cold regions, such as prestellar cores. Significant fractionation ratios are also observed in hot environments such as hot cores or hot corinos, where they are believed to be produced by the evaporation of the icy mantles surrounding dust grains, and thus are remnants of a previous cold (either gas-phase or grain surface) chemistry. The recent detection of DCN towards the Orion Bar, in a clump at a characteristic temperature of 70K, has shown that high deuterium fractionation can also be detected in PDRs. The Orion Bar clumps thus appear as a good environment for the observational study of deuterium fractionation in luke-warm gas, allowing to validate chemistry models in a different temperature range, where dominating fractionation processes are predicted to be different than in cold gas (< 20K). We aimed at studying observationally in detail the chemistry at work in the Orion Bar PDR, to understand if DCN is produced by ice mantle evaporation, or is the result of warm gas-phase chemistry, involving the CH2D+ precursor ion (which survives higher temperatures than the usual H2D+ precursor). Using the APEX and the IRAM 30m telescopes, we targetted selected deuterated species towards two clumps in the Orion Bar. We confirmed the detection of DCN and detected two new deuterated molecules (DCO+ and HDCO) towards one clump in the Orion Bar PDR. Significant deuterium fractionations are found for HCN and H2CO, but a low fractionation in HCO+. We also give upper limits for other molecules relevant for the deuterium chemistry. (...) We show evidence that warm deuterium chemistry driven by CH2D+ is at work in the clumps.

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arXiv2006

The high velocity outflow in NGC6334I

We observed the high velocity outflow originating from NGC6334I in several CO transitions with the APEX telescope, with the goal of deriving the physical parameters of the gas. Using an LVG analysis, we studied line ratios between the CO(3-2), CO(4-3), and CO(7-6) data as a function of the density and of the kinetic temperature of the gas. An upper limit on the CO column density is derived by comparison with 13CO data. We constrained the temperature to be higher than 50 K and the H_2 density to values higher than n~10^4 cm^{-3} towards the peak position in the red lobe, while T>15 K and n>10^3 cm^{-3} are derived towards the peak position in the blue lobe. The physical parameters of the outflow, its mass and its energetics, have been computed using the temperatures derived from this analysis. We conclude that high kinetic temperatures are present in the outflow and traced by high excitation CO lines. Observations of high-J CO lines are thus needed to infer reliable values of the kinetic temperatures and of the other physical parameters in outflows.

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arXiv2006

APEX 1 mm line survey of the Orion Bar

Unbiased molecular line surveys are a powerful tool for analyzing the physical and chemical parameters of astronomical objects and are the only means for obtaining a complete view of the molecular inventory for a given source. The present work stands for the first such investigation of a photon-dominated region. The first results of an ongoing millimeter-wave survey obtained towards the Orion Bar are reported. The APEX telescope in combination with the APEX-2A facility receiver was employed in this investigation. We derived the physical parameters of the gas through LVG analyses of the methanol and formaldehyde data. Information on the sulfur and deuterium chemistry of photon-dominated regions is obtained from detections of several sulfur-bearing molecules and DCN.

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arXiv2006

The evolutionary state of the southern dense core Cha-MMS1

Aims: Our goal is to set constraints on the evolutionary state of the dense core Cha-MMS1 in the Chamaeleon I molecular cloud. Methods: We analyze molecular line observations carried out with the new submillimeter telescope APEX. We look for outflow signatures around the dense core and probe its chemical structure, which we compare to predictions of models of gas-phase chemistry. We also use the public database of the Spitzer Space Telescope (SST) to compare Cha-MMS1 with the two Class 0 protostars IRAM 04191 and L1521F, which are at the same distance. Results: We measure a large deuterium fractionation for N2H+ (11 +/- 3 %), intermediate between the prestellar core L1544 and the very young Class 0 protostar L1521F. It is larger than for HCO+ (2.5 +/- 0.9 %), which is probably the result of depletion removing HCO+ from the high-density inner region. Our CO(3-2) map reveals the presence of a bipolar outflow driven by the Class I protostar Ced 110 IRS 4 but we do not find evidence for an outflow powered by Cha-MMS1. We also report the detection of Cha-MMS1 at 24, 70 and 160 microns by the instrument MIPS of the SST, at a level nearly an order of magnitude lower than IRAM 04191 and L1521F. Conclusions: Cha-MMS1 appears to have already formed a compact object, either the first hydrostatic core at the very end of the prestellar phase, or an extremely young protostar that has not yet powered any outflow, at the very beginning of the Class 0 accretion phase.

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arXiv2006

CO and CH3OH observations of the BHR71 outflows with APEX

Context : Highly-collimated outflows are believed to be the earliest stage in outflow evolution, so their study is essential for understanding the processes driving outflows. The BHR71 Bok globule is known to harbour such a highly-collimated outflow, which is powered by a protostar belonging to a protobinary system. Aims : We aimed at investigating the interaction of collimated outflows with the ambient molecular cloud by using molecular tracers. Methods : We mapped the BHR71 highly-collimated outflow in CO(3-2) with the APEX telescope, and observed several bright points of the outflow in the molecular transitions CO(4-3), 13CO(3-2), C18O(3-2), and CH3OH(7-6). We use an LVG code to characterise the temperature enhancements in these regions. Results : In our CO(3-2) map, the second outflow driven by IRS2, which is the second source of the binary system, is completely revealed and shown to be bipolar. We also measure temperature enhancements in the lobes. The CO and methanol LVG modelling points to temperatures between 30 and 50K in the IRS1 outflow, while the IRS2 outflow seems to be warmer (up to 300K).

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arXiv2006

Testing grain surface chemistry : a survey of deuterated formaldehyde and methanol in low-mass Class 0 protostars

Context : Despite the low cosmic abundance of deuterium (D/H ~ 1e-5), large degrees of deuterium fractionation in molecules are observed in star forming regions with enhancements that can reach 13 orders of magnitude, which current models have difficulties to account for. Aims : Multi-isotopologue observations are a very powerful constraint for chemical models. The aim of our observations is to understand the processes forming the observed large abundances of methanol and formaldehyde in low-mass protostellar envelopes (gas-phase processes ? chemistry on the grain surfaces ?) and better constrain the chemical models. Methods : Using the IRAM 30m single-dish telescope, we observed deuterated formaldehyde (HDCO and D2CO) and methanol (CH2DOH, CH3OD, and CHD2OH) towards a sample of seven low-mass class 0 protostars. Using population diagrams, we then derive the fractionation ratios of these species (abundance ratio between the deuterated molecule and its main isotopologue) and compare them to the predictions of grain chemistry models. Results : These protostars show a similar level of deuteration as in IRAS16293-2422, where doubly-deuterated methanol -- and even triply-deuterated methanol -- were first detected. Our observations point to the formation of methanol on the grain surfaces, while formaldehyde formation cannot be fully pined down. While none of the scenarii can be excluded (gas-phase or grain chemistry formation), they both seem to require abstraction reactions to reproduce the observed fractionations.

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arXiv2005

Theoretical HDO emission from low-mass protostellar envelopes

We present theoretical predictions of the rotational line emission of deuterated water in low-mass protostar collapsing envelopes. The model accounts for the density and temperature structure of the envelope, according the inside-out collapse framework. The deuterated water abundance profile is approximated by a step function, with a low value in the cold outer envelope and a higher value in the inner envelope where the grain mantles evaporate. The two abundances are the two main parameters of the modeling, along with the temperature at which the mantles evaporate. We report line flux predictions for a 30 and 5 L$_\odot$ source luminosity respectively. We show that ground based observations are capable to constrain the three parameters of the model in the case of bright low-mass protostars (L$>$10 L$_{\odot}$), and that no space based observations, like for example HSO observations, are required in this case. On the contrary, we show that the study of low-luminosity sources (L$<$10 L$_{\odot}$), assuming the same HDO abundance profile, requires too much integration time to be carried out either with available ground-based telescopes or with the HIFI instrument on board HSO. For these sources, only the large interferometer ALMA will allow to constrain the HDO abundance.

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arXiv2004

HDO abundance in the envelope of the solar-type protostar IRAS16293-2422

We present IRAM 30m and JCMT observations of HDO lines towards the solar-type protostar IRAS 16293-2422. Five HDO transitions have been detected on-source, and two were unfruitfully searched for towards a bright spot of the outflow of IRAS 16293-2422. We interpret the data by means of the Ceccarelli, Hollenbach and Tielens (1996) model, and derive the HDO abundance in the warm inner and cold outer parts of the envelope. The emission is well explained by a jump model, with an inner abundance of 1e-7 and an outer abundance lower than 1e-9 (3 sigma). This result is in favor of HDO enhancement due to ice evaporation from the grains in theinner envelope. The deuteration ratio HDO/H2O is found to be f_in=3% and f_out < 0.2% (3 sigma) in the inner and outer envelope respectively and therefore, the fractionation also undergoes a jump in the inner part of the envelope. These results are consistent with the formation of water in the gas phase during the cold prestellar core phase and storage of the molecules on the grains, but do not explain why observations of H2O ices consistently derive a H2O ice abundance of several 1e-5 to 1e-4, some two orders of magnitude larger than the gas phase abundance of water in the hot core around IRAS 16293-2422.

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arXiv2003

First detection of triply-deuterated methanol

We report the first detection of triply-deuterated methanol, with 12 observed transitions, towards the low-mass protostar IRAS 16293-2422, as well as multifrequency observations of 13CH3OH, used to derive the column density of the main isotopomer CH3OH. The derived fractionation ratio [CD3OH]/[CH3OH] averaged on a 10'' beam is 1.4%. Together with previous CH2DOH and CHD2OH observations, the present CD3OH observations are consistent with a formation of methanol on grain surfaces, if the atomic D/H ratio is 0.1 to 0.3 in the accreting gas. Such a high atomic ratio can be reached in the frame of gas-phase chemical models including all deuterated isotopomers of H3+.

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arXiv2003

Search for solid HDO in low-mass protostars

We present ground-based 2.1 to 4.2 microns observations of four low-mass protostars. We searched for the 4.1 microns OD stretch band, characteristic of solid HDO in grain mantles. We did not detect solid HDO in any of the four sources, but we derive 3-sigma upper limits from 0.5% to 2% for the HDO/H2O ratio depending on the source. These ratios provide strong constraints to solid-state deuteration models when compared to deuterium fractionation values observed in the gas phase. We discuss various scenarios that could lead to such a low water deuteration compared to the high formaldehyde and methanol deuteration observed in the gas phase.

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arXiv2002

Detection of doubly-deuterated methanol in the solar-type protostar IRAS16293-2422

We report the first detection of doubly-deuterated methanol (CHD2OH), as well as firm detections of the two singly-deuterated isotopomers of methanol (CH2DOH and CH3OD), towards the solar-type protostar IRAS16293-2422. From the present multifrequency observations, we derive the following abundance ratios: [CHD2OH]/[CH3OH] = 0.2 +/- 0.1, [CH2DOH]/[CH3OH] = 0.9 +/- 0.3, [CH3OD]/[CH3OH] = 0.04 +/- 0.02. The total abundance of the deuterated forms of methanol is greater than that of its normal hydrogenated counterpart in the circumstellar material of IRAS16293-2422, a circumstance not previously encountered. Formaldehyde, which is thought to be the chemical precursor of methanol, possesses a much lower fraction of deuterated isotopomers (~ 20%) with respect to the main isotopic form in IRAS16293-2422. The observed fractionation of methanol and formaldehyde provides a severe challenge to both gas-phase and grain-surface models of deuteration. Two examples of the latter model are roughly in agreement with our observations of CHD2OH and CH2DOH if the accreting gas has a large (0.2-0.3) atomic D/H ratio. However, no gas-phase model predicts such a high atomic D/H ratio, and hence some key ingredient seems to be missing.

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arXiv2001

Imaging Polarimetric Observations of a New Circumstellar Disk System

Few circumstellar disks have been directly observed. Here we use sensitive differential polarimetric techniques to overcome atmospheric speckle noise in order to image the circumstellar material around HD 169142. The detected envelope or disk is considerably smaller than expectations based on the measured strength of the far-IR excess from this system.

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