arXiv subjects

M. Nielbock

Publications and source records attributed to M. Nielbock.

25 records · Page 2Linked to original sources

arXiv2010

The structured environments of embedded star-forming cores. PACS and SPIRE mapping of the enigmatic outflow source UYSO 1

The intermediate-mass star-forming core UYSO 1 has previously been found to exhibit intriguing features. While deeply embedded and previously only identified by means of its (sub-)millimeter emission, it drives two powerful, dynamically young, molecular outflows. Although the process of star formation has obviously started, the chemical composition is still pristine. We present Herschel PACS and SPIRE continuum data of this presumably very young region. The now complete coverage of the spectral energy peak allows us to precisely constrain the elevated temperature of 26 - 28 K for the main bulge of gas associated with UYSO1, which is located at the interface between the hot HII region Sh 2-297 and the cold dark nebula LDN 1657A. Furthermore, the data identify cooler compact far-infrared sources of just a few solar masses, hidden in this neighbouring dark cloud.

astro-ph.SR↗

arXiv2008

Probing the centre of the large circumstellar disc in M17

We investigated the nature of the hitherto unresolved elliptical infrared emission in the centre of the ~20000 AU disc silhouette in M 17. We combined high-resolution JHKsL'M' band imaging carried out with NAOS/CONICA at the VLT with [Fe II] narrow band imaging using SOFI at the NTT. The analysis is supported by Spitzer/GLIMPSE archival data and by already published SINFONI/VLT Integral Field Spectroscopy data. For the first time, we resolve the elongated central infrared emission into a point-source and a jet-like feature that extends to the northeast in the opposite direction of the recently discovered collimated H2 jet. They are both orientated almost perpendicular to the disc plane. In addition, our images reveal a curved southwestern emission nebula whose morphology resembles that of the previously detected northeastern one. Both nebulae are located at a distance of 1500 AU from the disc centre. We describe the infrared point-source in terms of a protostar that is embedded in circumstellar material producing a visual extinction of 60 <= Av <= 82. The observed Ks band magnitude is equivalent to a stellar mass range of 2.8 Msun <= Mstar <= 8 Msun adopting conversions for a main-sequence star. Altogether, we suggest that the large M 17 accretion disc is forming an intermediate to high-mass protostar. Part of the accreted material is expelled through a symmetric bipolar jet/outflow.

astro-ph↗

arXiv2007

The Morphology of M17-UC1 - A Disk Candidate Surrounding a Hypercompact HII Region

We investigate the morphology and the evolutionary stage of the hypercompact HII region M17-UC1 using observations at infrared wavelengths and NIR radiative transfer modeling. For the first time, this region is resolved into two emission areas separated by a dark lane reminiscent of an obscuring silhouette of a circumstellar disk. So far, the observational data as well as model calculations suggest that M17-UC1 is surrounded by a disk of cool dust. This direct direct detection of a circumstellar disk candidate around a hypercompact HII region is in agreement with the expectations of the disk accretion model for high-mass star formation.

astro-ph↗

arXiv2006

2.3 micron CO emission and absorption from young high-mass stars in M17

We are studying the extremely young cluster of M17 to investigate the birth of high-mass stars and the initial mass function. Deep JHKL imaging and K-band spectroscopy from the VLT of 201 stars toward the cluster is presented. The majority of 104 stars show the CO band-head in absorption. Half of them emit X-rays and/or have infrared excess, indicative of very young objects. Their intrinsic IR luminosity is compatible with intermediate and high-mass pre-main sequence stars. Nine additional stars have the CO feature in emission, while sixty sources are lacking any stellar spectral feature due to veiling by circumstellar dust. We suggest that CO absorption is - as in the case of low-mass stars - also a common feature during the early evolution of stars with higher masses. According to model calculations the observed CO absorption is most likely a sign of heavily accreting protostars with mass accretion rates above 10^-5 solar masses/yr.

astro-ph↗

arXiv2004

The Giant Molecular Cloud associated with RCW 106 -- A 1.2 mm continuum mapping study

We have mapped the dust continuum emission from the molecular cloud covering a region of 28pcx94pc associated with the well-known HII region RCW 106 at 1.2 mm using SIMBA on SEST. The observations, having an HPBW of 24" (0.4 pc), reveal 95 clumps. Owing to the higher sensitivity to colder dust and higher angular resolution the present observations identify new emission features and also show that most of the IRAS sources in this region consist of multiple dust emission peaks. The detected millimeter sources (MMS) include on one end the exotic MMS5 (associated with IRAS 16183-4958, one of the brightest infrared sources in our Galaxy) and the bright (and presumably cold) source MMS54, with no IRAS or MSX associations on the other end. Around 10% of the sources are associated with signposts of high mass star formation activity. Assuming a uniform dust temperature of 20 K we estimate the total mass of the GMC associated with RCW 106 to be ~10^5\msun. The constituent millimeter clumps cover a range of masses and radii between 40 to 10^4 \msun and 0.3 to 1.9 pc. Densities of the clumps range between (0.5-6) 10^4 cm^{-3}. We have decomposed the continuum emission into gaussian and arbitrary shaped clumps using the two independent structure analysis tools gaussclumps and clumpfind respectively. The clump mass spectrum was found to have an index of 1.6+-0.3, independent of the decomposition algorithm used. The index of the mass spectrum for the mass and length scales covered here are consistent with results derived from large scale CO observations.

astro-ph↗

arXiv2004

SIMBA's view of the epsilon Eri disk

We present the first observational confirmation for an extended circumstellar dust disk around epsilon Eri. The observations were obtained with the bolometer array SIMBA at the 15 m radio telescope SEST in Chile and measure the dust continuum at 1.2 mm. The emission, with a total flux of 21.4 mJy and a rms of 2.2 mJy/beam, is resolved to a deconvolved size of 27.4 arcsec which corresponds to 88 AU. No clear indication for a ring-like disk structure is seen, possibly also due to the telescope's large beam width of 24 arcsec. Models of the object's spectral energy distribution from IR to mm-wavelengths show that the emission can also be explained by a simple disk model. We further demonstrate the strong influence of noise and propose to be cautious with interpretations of the ring substructure.

astro-ph↗

arXiv2003

Dust and Molecules in V4743 Sgr

We present 1.2 mm continuum images and spectral line observations of CO(1--0) and SiO(3--2) rotational transitions of the recent nova V4743 Sgr. The nova is detected at 1.2 mm showing a variable millimetre emission. Only upper limits of T_A* = 0.06 K for CO and T_A* = 0.03 K for SiO could be derived. We discuss the results in terms the nature of the millimetre emission favouring dust from a phase before the recent outburst as the likely radiating source. We also comment on the possibility of free-free emission from the ionised shell as the source of the measured millimetre radiation.

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