arXiv subjects

F. Wyrowski

Publications and source records attributed to F. Wyrowski.

At least 271 records · Page 15Linked to original sources

arXiv2007

Protostellar clusters in intermediate-mass (IM) star forming regions

The transition between the low density groups of T Tauri stars and the high density clusters around massive stars occurs in the intermediate-mass (IM) range (M$_*$$\sim$2--8 M$_\odot$). High spatial resolution studies of IM young stellar objects (YSO) can provide important clues to understand the clustering in massive star forming regions. Aims: Our aim is to search for clustering in IM Class 0 protostars. The high spatial resolution and sensitivity provided by the new A configuration of the Plateau de Bure Interferometer (PdBI) allow us to study the clustering in these nearby objects. Methods: We have imaged three IM Class 0 protostars (Serpens-FIRS 1, IC 1396 N, CB 3) in the continuum at 3.3 and 1.3mm using the PdBI. The sources have been selected with different luminosity to investigate the dependence of the clustering process on the luminosity of the source. Results: Only one millimeter (mm) source is detected towards the low luminosity source Serpens--FIRS 1. Towards CB 3 and IC1396 N, we detect two compact sources separated by $\sim$0.05 pc. The 1.3mm image of IC 1396 N, which provides the highest spatial resolution, reveal that one of these cores is splitted in, at least, three individual sources.

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arXiv2007

Interferometric multi-wavelength (sub)millimeter continuum study of the young high-mass protocluster IRAS05358+3543

The young massive star-forming region IRAS05358+3543 was observed at high-spatial resolution in the continuum emission at 3.1 and 1.2mm with the Plateau de Bure Interferometer, and at 875 and 438mum with the Submillimeter Array. We resolve at least four continuum sub-sources that are likely of protostellar nature. Two of them are potentially part of a proto-binary system with a projected separation of 1700AU. Additional (sub)mm continuum peaks are not necessarily harboring protostars but maybe caused by the multiple molecular outflows. The spectral energy distributions (SEDs) of the sub-sources show several features. The main power house mm1, which is associated with CH3OH maser emission, a hypercompact HII region and a mid-infrared source, exhibits a typical SED with a free-free emission component at cm and long mm wavelengths and a cold dust component in the (sub)mm part of the spectrum (spectral index between 1.2mm and 438mum alpha~3.6). The free-free emission corresponds to a Lyman continuum flux of an embedded 13Msun B1 star. The coldest source of the region, mm3, has alpha~3.7 between 1.2mm and 875mum, but has lower than expected fluxes in the shorter wavelength 438mum band. This turnover of the Planck-function sets an upper limit on the dust temperature of mm3 of approximately 20K. The uv-data analysis of the density structure of individual sub-cores reveals distributions with power-law indices between 1.5 and 2. This resembles the density distributions of the larger-scale cluster-forming clump as well as those from typical low-mass cores.

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arXiv2007

Probing the initial conditions of High Mass Star formation -- I. Deuteration and depletion in high mass pre/protocluster clumps

UltraCompact HII regions are signposts of high mass star formation. Since high-mass star formation occurs in clusters, one expects to find even earlier phases of massive star formation in the vicinity of UltraCompact HII regions. Here, we study the amount of deuteration and depletion toward pre/protocluster clumps found in a wide-field (10 X 10 arcmin) census of clouds in 32 massive star-forming regions that are known to harbour UCHII regions. We find that 65% of the observed sources have strong NH2D emission and more than 50% of the sources exhibit a high degree of deuteration, (0.1 < NH2D/NH3 < 0.7), 0.7 being the highest observed deuteration of NH3 reported to date. Our search for NHD2 in two sources did not result in a detection. The enhancement in deuteration coincides with moderate CO depletion onto dust grains. There is no evidence of a correlation between the two processes, though an underlying correlation cannot be ruled out as the depletion factor is very likely to be only a lower limit. In summary, we find CO depletion and high deuteration towards cold cores in massive star forming regions. Therefore, these are good candidates for sources at the early phases of massive star formation. While our sensitive upper limits on NHD2 do not prove the predictions of the gas-phase and grain chemistry models wrong, an enhancement of ~10^4 over the cosmic D/H ratio from NH2D warrants explanation.

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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

First observations with CONDOR, a 1.5 THz heterodyne receiver

The THz atmospheric windows centered at roughly 1.3 and 1.5~THz, contain numerous spectral lines of astronomical importance, including three high-J CO lines, the N+ line at 205 microns, and the ground transition of para-H2D+. The CO lines are tracers of hot (several 100K), dense gas; N+ is a cooling line of diffuse, ionized gas; the H2D+ line is a non-depleting tracer of cold (~20K), dense gas. As the THz lines benefit the study of diverse phenomena (from high-mass star-forming regions to the WIM to cold prestellar cores), we have built the CO N+ Deuterium Observations Receiver (CONDOR) to further explore the THz windows by ground-based observations. CONDOR was designed to be used at the Atacama Pathfinder EXperiment (APEX) and Stratospheric Observatory For Infrared Astronomy (SOFIA). CONDOR was installed at the APEX telescope and test observations were made to characterize the instrument. The combination of CONDOR on APEX successfully detected THz radiation from astronomical sources. CONDOR operated with typical Trec=1600K and spectral Allan variance times of 30s. CONDOR's first light observations of CO 13-12 emission from the hot core Orion FIR4 (= OMC1 South) revealed a narrow line with T(MB) = 210K and delta(V)=5.4km/s. A search for N+ emission from the ionization front of the Orion Bar resulted in a non-detection. The successful deployment of CONDOR at APEX demonstrates the potential for making observations at THz frequencies from ground-based facilities.

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arXiv2006

Revealing the environs of the remarkable southern hot core G327.3-0.6

We present a submm study of the massive hot core G327.3-0.6 that constrains its physical parameters and environment. The APEX telescope was used to image CO and N2H+ emission, to observe lines from other molecules toward a hot and a cold molecular core, and to measure the continuum flux density of the hot core. In the C18O J=3-2 line, two clumps were found, one associated with the HII region G327.3-0.5 and the other associated with the hot core. An additional cold clump is found 30 arcsec (0.4 pc) northeast of the hot core in bright N2H+ emission. From the the continuum data, we calculate a mass of 420 Msol and a size of 0.1 pc for the hot core. A new, more accurate position of the hot core is reported, which allows the association of the core with a bright mid-infrared source. The luminosity of the hot core is estimated to be between 5 and 15 10^4 Lsol. This study revealed several different evolutionary stages of massive star formation in the G327.3-0.6 region.

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arXiv2006

Mid- and high-J CO observations towards UCHIIs

A study of 12 ultracompact HII regions was conducted to probe the physical conditions and kinematics in the inner envelopes of the molecular clumps harboring them. The APEX telescope was used to observe the sources in the CO (4-3) and 13CO (8-7) lines. Line intensities were modeled with the RATRAN radiative transfer code using power laws for the density and temperature to describe the physical structure of the clumps. All sources were detected in both lines. The optically thick CO (4-3) line shows predominantly blue skewed profiles reminiscent of infall. Line intensities can be reproduced well using the physical structure of the clumps taken from the literature. The optically thick line profiles show that CO is a sensitive tracer of ongoing infall in the outer envelopes of clumps harboring ultracompact HII regions and hot molecular cores.

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arXiv2006

Submillimeter spectroscopy of southern hot cores: NGC6334(I) and G327.3-0.6

High-mass star-forming regions are known to have a rich molecular spectrum from many species. Some of the very highly excited lines are emitted from very hot and dense gas close to the central object(s). The physics and chemistry of the inner cores of two high mass star forming regions, NGC6334(I) and G327.3-0.6, shall be characterized. Submillimeter line surveys with the APEX telescope provide spectra which sample many molecular lines at high excitation stages. Partial spectral surveys were obtained, the lines were identified, physical parameters were determined through fitting of the spectra. Both sources show similar spectra that are comparable to that of the only other high mass star forming region ever surveyed in this frequency range}, Orion-KL, but with an even higher line density. Evidence for very compact, very hot sources is found.

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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

APECS - The Atacama Pathfinder Experiment Control System

APECS is the distributed control system of the new Atacama Pathfinder EXperiment (APEX) telescope located on the Llano de Chajnantor at an altitude of 5107 m in the Atacama desert in northern Chile. APECS is based on Atacama Large Millimeter Array (ALMA) software and employs a modern, object-oriented design using the Common Object Request Broker Architecture (CORBA) as the middleware. New generic device interfaces simplify adding instruments to the control system. The Python based observer command scripting language allows using many existing software libraries and facilitates creating more complex observing modes. A new self-descriptive raw data format (Multi-Beam FITS or MBFITS) has been defined to store the multi-beam, multi-frequency data. APECS provides an online pipeline for initial calibration, observer feedback and a quick-look display. APECS is being used for regular science observations in local and remote mode since August 2005.

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arXiv2005

High Mass Starless Cores

We report the identification of a sample of potential High-Mass Starless Cores (HMSCs). The cores were discovered by comparing images of the fields containing candidate High-Mass Protostellar Objects (HMPOs) at 1.2mm and mid-infrared (8.3um; MIR) wavelengths. While the HMPOs are detected at both wavelengths, several cores emitting at 1.2mm in the same fields show absorption or no emission at the MIR wavelength. We argue that the absorption is caused by cold dust. The estimated masses of a few 10^2Msun - 10^3 Msun and the lack of IR emission suggests that they may be massive cold cores in a pre-stellar phase, which could presumably form massive stars eventually. Ammonia (1,1) and (2,2) observations of the cores indicate smaller velocity dispersions and lower rotation temperatures compared to HMPOs and UCHII regions suggesting a quiescent pre-stellar stage. We propose that these newly discovered cores are good candidates for the HMSC stage in high-mass star-formation. This sample of cores will allow us to study the high-mass star and cluster formation processes at the earliest evolutionary stages.

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arXiv2005

Trans-ethyl methyl ether in space - A new look at a complex molecule in selected hot core regions

An extensive search for the complex molecule trans-ethyl methyl ether towards several hot core regions has been performed. Using the IRAM 30m telescope and the SEST 15m we looked at several frequencies where trans-ethyl methyl ether has strong transitions, as well as lines which are particularly sensitive to the physical conditions in which the molecule can be found. We included G34.26, NGC6334(I), Orion KL, and W51e2 which have previously been proven to have a rich chemistry of complex molecules. Our observations cannot confirm the tentative Orion KL detection made by Charnley et al. (2001) within their stated column density limits, but we confirm the existence of the trans-ethyl methyl ether towards W51e2 with a column density of 2x10^14 cm-2. The dimethyl ether/methanol ratio of 0.6 as well as the newly found ethyl methyl ether/ethanol ratio of 0.13 indicate relative high abundances of ethers toward W51e2. Furthermore, the observation of ethyl methyl ether also confirms the importance of ethanol as a grain mantle constituent. We present new upper limits of around 8x10^13 cm-2 for the column densities of the molecule toward Orion KL, G34.26, NGC6334(I) and estimate the column density towards SgrB2(N) to be of the same order. The W51e2 observations are discussed in more detail.

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arXiv2005

Initial Conditions for Massive Star Birth -- Infrared Dark Clouds

We summarize the properties of Infrared Dark Clouds, massive, dense, and cool aggregations of interstellar gas and dust that are found througout the Galaxy in projection against the strong mid-infrared background. We describe their distribution and give an overview of their physical properties and chemistry. These objects appear to be the progenitors of high-mass stars and star clusters, but seem to be largely devoid of star formation, which however is taking place in localized spots.

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arXiv2004

High-spatial-resolution CN and CS observation of two regions of massive star formation

Molecular line CN, CS and mm continuum observations of two intermediate- to high-mass star-forming regions - IRAS20293+3952 and IRAS19410+2336 - obtained with the Plateau de Bure Interferometer at high spatial resolution reveal interesting characteristics of the gas and dust emission. In spite of the expectation that the CN and CS morphology might closely follow the dense gas traced by the dust continuum, both molecules avoid the most central cores. Comparing the relative line strengths of various CN hyperfine components, this appears not to be an opacity effect but to be due to chemical and physical effects. The CN data also indicate enhanced emission toward the different molecular outflows in the region. Regarding CS, avoiding the central cores can be due to high optical depth, but the data also show that the CS emission is nearly always associated with the outflows of the region. Therefore, neither CS nor CN appear well suited for dense gas and disk studies in these two sources, and we recommend the use of different molecules for future massive disk studies. An analysis of the 1 and 3mm continuum fluxes toward IRAS20293+3952 reveals that the dust opacity index beta is lower than the canonical value of 2. Tentatively, we identify a decreasing gradient of beta from the edge of the core to the core center. This could be due to increasing optical depth toward the core center and/or grain growth within the densest cores and potential central disks. We detect 3mm continuum emission toward the collimated outflow emanating from IRAS20293+3952. The spectral index of alpha ~ 0.8 in this region is consistent with standard models for collimated ionized winds.

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arXiv2004

High-velocity gas toward hot molecular cores: evidence for collimated outflows from embedded sources

We present observations made with the Berkeley-Illinois-Maryland Association millimeter array of the H2S 2(2,0)-2(1,1) and C18O 2-1 transitions toward a sample of four hot molecular cores associated with ultracompact HII regions: G9.62+0.19, G10.47+0.03, G29.96-0.02 and G31.41+0.31. The angular resolution varies from 1.5 to 2.4 arcsec, corresponding to scales of ~0.06 pc at the distance of these sources. High-velocity wings characteristic of molecular outflows are detected toward all four sources in the H2S line. In two cases (G29.96 and G31.41) red- and blueshifted lobes are clearly defined and spatially separate, indicating that the flows are collimated. We also confirm the previous detection of the outflow in G9.62F. Although the gas-phase H2S abundance is not well constrained, assuming a value of 10^-7 yields lower limits to total outflow masses of ~8 Msun, values which are consistent with the driving sources being massive protostars. Linear velocity gradients are detected in both C18O and H2S across G9.62, G29.96 and, to a lesser extent, G31.41. These gradients are observed to be at a different position angle to the outflow in G9.62F and G29.96, suggestive of a rotation signature in these two hot cores. Our observations show that these hot cores contain embedded massive protostellar objects which are driving bipolar outflows. Furthermore, the lack of strong centimeter-wave emission toward the outflow centers in G29.96 and G31.41 indicates that the outflow phase begins prior to the formation of a detectable ultracompact HII region.

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arXiv2002

Interactions between a Bright YSO and the MSX Infrared-Dark Cloud G79.3+0.3: An Early Stage of Triggered Star Formation?

Millimeter and mid-infrared observations have been made of the dense clumps of dust and gas and of young stellar objects (YSOs) associated with the bright, compact submillimeter source G79.3+0.3 P1 in the relatively nearby MSX infrared-dark cloud G79.3+0.3. The Gemini mid-infrared observations reported here indicate the presence of three YSOs within the cloud. BIMA 3 mm continuum observations show that the brightest of the YSOs is likely to be a Herbig Ae/Be star. High-angular-resolution molecular-line observations suggest that a wind from this star may be triggering collapse in the adjacent molecular cloud. The submillimeter source G79.3+0.3 P1 itself does not contain infrared sources and may represent an earlier stage of star formation.

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arXiv2002

Subarcsecond Imaging of Hot Cores with BIMA

We present 1.4-mm BIMA observations with subarcsecond resolution of the bright dust and molecular line emission from hot cores associated with a sample of four ultracompact HII regions: G9.62+0.19, G10.47-0.03, G29.96-0.02, G31.41+0.31. Density power laws can reproduce the observed continuum emission but break down on scales smaller than 2000 AU. A total of 38 transitions from 18 species are detected, with G10.47 and G31.41 showing the greatest number of lines. In particular, these sources display emission from two collisionally-excited transitions of methanol lying more than 950 K above the ground state. Outflows traced by H2S emission provide evidence for embedded exciting sources and the observed morphology of molecular lines is consistent with internal heating of the cores.

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