arXiv subjects

Rolf Güsten

Publications and source records attributed to Rolf Güsten.

42 records · Page 3Linked to original sources

arXiv2012

GREAT [CII] and CO observations of the BD+40°4124 region

The BD+40\degree4124 region was observed with high angular and spectral resolution with the German heterodyne instrument GREAT in CO J = 13 \rightarrow 12 and [CII] on SOFIA. These observations show that the [CII] emission is very strong in the reflection nebula surrounding the young Herbig Ae/Be star BD+40\degree4124. A strip map over the nebula shows that the [CII] emission approximately coincides with the optical nebulosity. The strongest [CII] emission is centered on the B2 star and a deep spectrum shows that it has faint wings, which suggests that the ionized gas is expanding. We also see faint CO J = 13 \rightarrow 12 at the position of BD+40\degree4124, which suggests that the star may still be surrounded by an accretion disk.We also detected [CII] emission and strong CO J = 13 \rightarrow 12 toward V1318 Cyg. Here the [CII] emission is fainter than in BD+40\degree4124 and appears to come from the outflow, since it shows red and blue wings with very little emission at the systemic velocity, where the CO emission is quite strong. It therefore appears that in the broad ISO beam the [CII] emission was dominated by the reflection nebula surrounding BD+40\degree4124, while the high J CO lines originated from the adjacent younger and more deeply embedded binary system V1318 Cyg.

astro-ph.SR↗

arXiv2012

High-resolution wide-band Fast Fourier Transform spectrometers

We describe the performance of our latest generations of sensitive wide-band high-resolution digital Fast Fourier Transform Spectrometer (FFTS). Their design, optimized for a wide range of radio astronomical applications, is presented. Developed for operation with the GREAT far infrared heterodyne spectrometer on-board SOFIA, the eXtended bandwidth FFTS (XFFTS) offers a high instantaneous bandwidth of 2.5 GHz with 88.5 kHz spectral resolution and has been in routine operation during SOFIA's Basic Science since July 2011. We discuss the advanced field programmable gate array (FPGA) signal processing pipeline, with an optimized multi-tap polyphase filter bank algorithm that provides a nearly loss-less time-to-frequency data conversion with significantly reduced frequency scallop and fast sidelobe fall-off. Our digital spectrometers have been proven to be extremely reliable and robust, even under the harsh environmental conditions of an airborne observatory, with Allan-variance stability times of several 1000 seconds. An enhancement of the present 2.5 GHz XFFTS will duplicate the number of spectral channels (64k), offering spectroscopy with even better resolution during Cycle 1 observations.

astro-ph.IM↗

arXiv2012

Dynamics and PDR properties in IC1396A

We investigate the gas dynamics and the physical properties of photodissociation regions (PDRs) in IC1396A, which is an illuminated bright-rimmed globule with internal structures created by young stellar objects. Our mapping observations of the [CII] emission in IC1396A with GREAT onboard SOFIA revealed the detailed velocity structure of this region. We combined them with observations of the [CI] 3P_1 - 3P_0 and CO(4-3) emissions to study the dynamics of the different tracers and physical properties of the PDRs. The [CII] emission generally matches the IRAC 8 micron, which traces the polycyclic aromatic hydrocarbon (PAH) emissions. The CO(4-3) emission peaks inside the globule, and the [CI] emission is strong in outer regions, following the 8 micron emission to some degree, but its peak is different from that of [CII]. The [CII] emitting gas shows a clear velocity gradient within the globule, which is not significant in the [CI] and CO(4-3) emission. Some clumps that are prominent in [CII] emission appear to be blown away from the rim of the globule. The observed ratios of [CII]/[CI] and [CII]/CO(4-3) are compared to the KOSMA-tau PDR model, which indicates a density of 10^4-10^5 cm-3.

astro-ph.GA↗

arXiv2012

GREAT/SOFIA atmospheric calibration

The GREAT observations need frequency-selective calibration across the passband for the residual atmospheric opacity at flight altitude. At these altitudes the atmospheric opacity has both narrow and broad spectral features. To determine the atmospheric transmission at high spectral resolution, GREAT compares the observed atmospheric emission with atmospheric model predictions, and therefore depends on the validity of the atmospheric models. We discusse the problems identified in this comparison with respect to the observed data and the models, and describe the strategy used to calibrate the science data from GREAT/SOFIA during the first observing periods.

astro-ph.IM↗

arXiv2012

SOFIA observations of CO(12-11) emission along the L1157 bipolar outflow

Carbon monoxide is an excellent tracer of the physical conditions of gas in molecular outflows from young stars. To understand the outflow mechanism we need to investigate the origin of the molecular emission and the structure and interaction of the outflowing molecular gas. Deriving the physical parameters of the gas will help us to trace and understand the various gas components in the flow. We observed CO(12-11) line emission at various positions along the L1157 bipolar outflow with GREAT aboard SOFIA. Comparing these new data with CO(2-1), we find basically constant line ratios along the outflow and even at the position of the source. These line ratios lead us to estimates of 10^5 to 10^6 cm^-3 for the gas density and 60 to 100 K for the gas temperature of the outflowing gas. The constrained density and temperature values indicate that we are mostly tracing a low-velocity gas component everywhere along the outflow, which is intermediate between the already known cold gas component, which gets entrained into the flow, and the hot gas, which gets shocked in the outflow.

astro-ph.SR↗

arXiv2006

The distribution of ND2H in LDN1689N

Finding tracers of the innermost regions of prestellar cores is important for understanding their chemical and dynamical evolution before the onset of gravitational collapse. While classical molecular tracers, such as CO and CS, have been shown to be strongly depleted in cold, dense gas by condensation on grain mantles, it has been a subject of discussion to what extent nitrogen-bearing species, such as ammonia, are affected by this process. As deuterium fractionation is efficient in cold, dense gas, deuterated species are excellent tracers of prestellar cores. A comparison of the spatial distribution of neutral and ionized deuterated species with the dust continuum emission can thus provide important insights into the physical and chemical structure of such regions. We study the spatial distribution of the ground-state 335.5 GHz line of ND2H in LDN1689N, using APEX, and compare it with the distribution of the DCO+(3--2) line, as well as the 350 micron dust continuum emission observed with the SHARC~II bolometer camera at CSO. While the distribution of the ND2H emission in LDN1689N is generally similar to that of the 350 microns dust continuum emission, the peak of the ND2H emission is offset by ~10'' to the East from the dust continuum and DCO+ emission peak. ND2H and ND3 share the same spatial distribution. The observed offset between the ND2H and DCO+ emission is consistent with the hypothesis that the deuterium peak in LDN1689N is an interaction region between the outflow shock from IRAS16293--2422 and the dense ambient gas. We detect the J = 4 - 3 line of H13CO+ at 346.998 GHz in the image side band serendipitously. This line shows the same spatial distribution as DCO+(3--2), and peaks close to the 350 mic emission maximum which provides further support for the shock interaction scenario.

astro-ph↗