541 research outputs found
Hier ist wahrhaftig ein Loch im Himmel: The NGC1999 dark globule is not a globule
The NGC1999 reflection nebula features a dark patch with a size of ~10 000 AU, which has been interpreted as a small, dense foreground globule and possible site of imminent star formation. We present Herschel PACS far-infrared 70 and 160 ÎŒmmaps, which reveal a flux deficit at the location of the globule. We estimate the globule mass needed to produce such an absorption feature to be a few tenths to a few M_â. Inspired by this Herschel observation, we obtained APEX LABOCA and SABOCA submillimeter continuum maps, and Magellan PANIC near-infrared images of the region. We do not detect a submillimer source at the location of the Herschel flux decrement; furthermore our observations place an upper limit on the mass of the globule of ~2.4Ă10^(â2) M_â. Indeed, the submillimeter maps appear to show a flux depression as well. Furthermore, the nearâinfrared images detect faint background stars that are less affected by extinction inside the dark patch than in its surroundings. We suggest that the dark patch is in fact a hole or
cavity in the material producing the NGC1999 reflection nebula, excavated by protostellar jets from the V380 Ori multiple system
Herschel-PACS imaging of protostars in the HH 1â2 outflow complex
We present 70 and 160 ÎŒm Herschel science demonstration images of a field in the Orion A molecular cloud that contains the prototypical Herbig-Haro objects HH 1 and 2, obtained with the Photodetector Array Camera and Spectrometer (PACS). These observations demonstrate Herschelâs unprecedented ability to study the rich population of protostars in the Orion molecular clouds
at the wavelengths where they emit most of their luminosity. The four protostars previously identified by Spitzer 3.6â40 ÎŒm imaging and spectroscopy are detected in the 70 ÎŒm band, and three are clearly detected at 160 ÎŒm. We measure photometry of the protostars in the PACS bands and assemble their spectral energy distributions (SEDs) from 1 to 870 ÎŒm with these data, Spitzer spectra and
photometry, 2MASS data, and APEX sub-mm data. The SEDs are fit to models generated with radiative transfer codes. From these fits we can constrain the fundamental properties of the protostars. We find luminosities in the range 12â84 L_â and envelope densities spanning over two orders of magnitude. This implies that the four protostars have a wide range of envelope infall rates and evolutionary
states: two have dense, infalling envelopes, while the other two have only residual envelopes. We also show the highly irregular and filamentary structure of the cold dust and gas surrounding the protostars as traced at 160 ÎŒm
Spatial mapping of ices in the Oph-F core: A direct measurement of CO depletion and the formation of CO2
Aims: Ices in dense star-forming cores contain the bulk of volatile molecules apart from H2 and thus represent a large fraction of dark cloud chemistry budget.To directly constrain the freeze-out profile of CO, the formation route of CO2 and the carrier of the 6.8 micron band, the spatial distribution of the CO/CO2 ice system and the 6.8 micron band carrier are measured in a nearby dense core. Methods: VLT-ISAAC, ISOCAM-CVF and Spitzer-IRS archival mid-infrared (3-20 micron) spectroscopy of young stellar objects is used to construct a map of the abundances of CO and CO2 ices in the Oph-F star-forming core, probing core radii from 2 10^3 to 14 10^3 AU or densities from 5 10^4 to 5 10^5 cm^-3 with a resolution of ~ 3000 AU. Results: The line-of-sight averaged abundances relative to water ice of both CO and CO2 ices increase monotonously with decreasing distance to the core center. The map traces the shape of the CO abundance profile between freeze-out ratios of 5-60% and shows that the CO2 ice abundance increases by a factor of 2 as the CO freezes out. It is suggested that this indicates a formation route of CO2 on a CO ice surface to produce a CO2 component dilute in CO ice, in addition to a fraction of the CO2 formed at lower densities along with the water ice mantle. It is predicted that the CO2 bending mode band profile should reflect a high CO:CO2 number ratio in the densest parts of dark clouds. In contrast to CO and CO2, the abundance of the carrier of the 6.8 micron band remains relatively constant throughout the core. A simple freeze-out model of the CO abundance profile is used to estimate the binding energy of CO on a CO ice surface to 814+/-30 K
Dust, Ice, and Gas In Time (DIGIT) Herschel program first results: A full PACS-SED scan of the gas line emission in protostar DK Chamaeleontis
Aims. We aim to study the composition and energetics of the circumstellar material of DK Cha, an intermediate-mass star in transition from an
embedded configuration to a star plus disk stage, during this pivotal stage of its evolution.
Methods. Using the range scan mode of PACS on the Herschel Space Observatory, we obtained a spectrum of DK Cha from 55 to 210 ÎŒm as part
of the DIGIT key program.
Results. Almost 50 molecular and atomic lines were detected, many more than the 7 lines detected in ISO-LWS. Nearly the entire ladder of CO
from J = 14â13 to 38â37 (E_u/k = 4080 K), water from levels as excited as J_(Kâ1 K+1) = 7_(07) (E_u/k = 843 K), and OH lines up to E_u/k = 290 K were
detected.
Conclusions. The continuum emission in our PACS SED scan matches the flux expected by a model consisting of a star, a surrounding disk of
0.03 M_â, and an envelope of a similar mass, supporting the suggestion that the object is emerging from its main accretion stage. Molecular, atomic,
and ionic emission lines in the far-infrared reveal the outflowâs influence on the envelope. The inferred hot gas may be photon-heated, but some
emission may be caused by C-shocks in the walls of the outflow cavity
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