Robustness results in LQG based multivariable control designs

The robustness of control systems with respect to model uncertainty is considered using simple frequency domain criteria. Results are derived under a common framework in which the minimum singular value of the return difference transfer matrix is the key quantity. In particular, the LQ and LQG robustness results are discussed

High Spectral and Spatial Resolution Observations of the PDR Emission in the NGC2023 Reflection Nebula with SOFIA and APEX

We have mapped the NGC 2023 reflection nebula in [CII] and CO(11--10) with the heterodyne receiver GREAT on SOFIA and obtained slightly smaller maps in 13CO(3--2), CO(3--2), CO(4--3), CO(6--5), and CO(7--6) with APEX in Chile. We use these data to probe the morphology, kinematics, and physical conditions of the C II region, which is ionized by FUV radiation from the B2 star HD37903. The [CII] emission traces an ellipsoidal shell-like region at a position angle of ~ -50 deg, and is surrounded by a hot molecular shell. In the southeast, where the C II region expands into a dense, clumpy molecular cloud ridge, we see narrow and strong line emission from high-J CO lines, which comes from a thin, hot molecular shell surrounding the [CII] emission. The [CII] lines are broader and show photo evaporating gas flowing into the C II region. Based on the strength of the [13CII] F=2--1 line, the [CII] line appears to be somewhat optically thick over most of the nebula with an optical depth of a few. We model the physical conditions of the surrounding molecular cloud and the PDR emission using both RADEX and simple PDR models. The temperature of the CO emitting PDR shell is ~ 90 -- 120 K, with densities of 10^5 -- 10^6 cm^-3, as deduced from RADEX modeling. Our PDR modeling indicates that the PDR layer where [CII] emission dominates has somewhat lower densities, 10^4 to a few times 10^5 cm^-3Comment: Accepted by A&

A molecular line study of NGC 1333/IRAS 4

Molecular line surveys and fully sampled spectral line maps at 1.3 and 0.87 mm are used to examine the physical and chemical characteristics of the extreme Class I sources IRAS 4A and 4B in the L1450/NGC 1333 molecular cloud complex. A very well collimated, jetlike molecular outflow emanates from IRAS 4A, with a dynamical age of a few thousand years. Symmetric, clumpy structure along the outflow lobes suggests that there is considerable variability in the mass-loss rate or wind velocity even at this young age. Molecular emission lines toward IRAS 4A and 4B are observed to be weak in the velocity range corresponding to quiescent material surrounding the young stellar objects (YSOs). Depletion factors of 10-20 are observed for αll molecules, including CO, even for very conservative mass estimates from the measured millimeter and submillimeter dust continuum. However, abundances scaled with respect to CO are similar to other dark molecular cloud cores. Such depletions could be mimicked by high dust optical depths or increased grain emissivities at the observing frequencies of 230 and 345 GHz, but the millimeter and submillimeter spectral energy distributions suggest that this is unlikely over the single-dish size scales of 5000-10,000 AU. Dense, outflowing gas is found to be kinematically, but not spatially, distinct from the quiescent material on these size scales. If CO is used as a chemical standard for the high-velocity gas, we find substantial enhancements in the abundances of several molecules in outflowing material, most notably CS, SiO, and CH_30H. The SiO emission is kinematically well displaced from the bulk cloud velocity and likely arises from directly shocked material. As is the case for CO, however, the outflow features from more volatile species are centered near the cloud velocity and are often characterized by quite low rotational temperatures. We suggest that grain-grain collisions induced by velocity shear zones surrounding the outflow axes transiently desorb the grain mantles, resulting in large abundance enhancements of selected species. Similar results have recently been obtained in several other low-mass YSOs, where the outflowing gas is often both kinematically and spatially distinct, and are illustrative of the ability of accretion and outflow processes to simultaneously modify the composition of the gas and dust surrounding young stars

A Submillimeter Study of the Star-Forming Region NGC7129

New molecular (13CO J=3-2) and dust continuum (450 and 850 micron) SCUBA maps of the NGC7129 star forming region are presented, complemented by C18O J=3-2 spectra at several positions within the mapped region. The maps include the Herbig Ae/Be star LkHalpha 234, the far-infrared source NGC 7129 FIRS2 and several other pre-stellar sources embedded within the molecular ridge. The SCUBA maps help us understand the nature of the pre-main sequence stars in this actively star forming region. A deeply embedded submillimeter source, SMM2, not clearly seen in any earlier data set, is shown to be a pre-stellar core or possibly a protostar. The highest continuum peak emission is identified with the deeply embedded source IRS6, a few arcseconds away from LkHalpha 234, and also responsible for both the optical jet and the molecular outflow. The gas and dust masses are found to be consistent, suggesting little or no CO depletion onto grains. The dust emissivity index is lower towards the dense compact sources, beta ~1 - 1.6, and higher, beta ~ 2.0, in the surrounding cloud, implying small size grains in the PDR ridge, whose mantles have been evaporated by the intense UV radiation.Comment: Accepted by Ap

The structure of protostellar envelopes derived from submillimeter continuum images

High dynamic range imaging of submillimeter dust emission from the envelopes of eight young protostars in the Taurus and Perseus star-forming regions has been carried out using the SCUBA submillimeter camera on the James Clerk Maxwell Telescope. Good correspondence between the spectral classifications of the protostars and the spatial distributions of their dust emission is observed, in the sense that those with cooler spectral energy distributions also have a larger fraction of the submillimeter flux originating in an extended envelope compared with a disk. This results from the cool sources having more massive envelopes rather than warm sources having larger disks. Azimuthally-averaged radial profiles of the dust emission are used to derive the power-law index of the envelope density distributions, p (defined by rho proportional to r^-p), and most of the sources are found to have values of p consistent with those predicted by models of cloud collapse. However, the youngest protostars in our sample, L1527 and HH211-mm, deviate significantly from the theoretical predictions, exhibiting values of p somewhat lower than can be accounted for by existing models. For L1527 heating of the envelope by shocks where the outflow impinges on the surrounding medium may explain our result. For HH211-mm another explanation is needed, and one possibility is that a shallow density profile is being maintained in the outer envelope by magnetic fields and/or turbulence. If this is the case star formation must be determined by the rate at which the support is lost from the cloud, rather than the hydrodynamical properties of the envelope, such as the sound speed.Comment: Accepted for publication in the Astrophysical Journa

Extremely large and hot multilayer Keplerian disk around the O-type protostar W51N: The precursors of the HCHII regions?

We present sensitive high angular resolution (0.57$''$-0.78$''$) SO, SO$_2$, CO, C$_2$H$_5$OH, HC$_3$N, and HCOCH$_2$OH line observations at millimeter and submillimeter wavelengths of the young O-type protostar W51 North made with the Submillimeter Array (SMA). We report the presence of a large (of about 8000 AU) and hot molecular circumstellar disk around this object, which connects the inner dusty disk with the molecular ring or toroid reported recently, and confirms the existence of a single bipolar outflow emanating from this object. The molecular emission from the large disk is observed in layers with the transitions characterized by high excitation temperatures in their lower energy states (up to 1512 K) being concentrated closer to the central massive protostar. The molecular emission from those transitions with low or moderate excitation temperatures are found in the outermost parts of the disk and exhibits an inner cavity with an angular size of around 0.7$''$. We modeled all lines with a Local Thermodynamic Equilibrium (LTE) synthetic spectra. A detail study of the kinematics of the molecular gas together with a LTE model of a circumstellar disk shows that the innermost parts of the disk are also Keplerian plus a contracting velocity. The emission of the HCOCH$_2$OH reveals the possible presence of a warm ``companion'' located to the northeast of the disk, however its nature is unclear. The emission of the SO and SO$_2$ is observed in the circumstellar disk as well as in the outflow. We suggest that the massive protostar W51 North appears to be in a phase before the presence of a Hypercompact or an Ultracompact HII (HC/UCHII) region, and propose a possible sequence on the formation of the massive stars.Comment: Accepted to Ap

GREAT [CII] and CO observations of the BD+40{\deg}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

Cold Dust in Kepler's Supernova Remnant

The timescales to replenish dust from the cool, dense winds of Asymptotic Giant Branch stars are believed to be greater than the timescales for dust destruction. In high redshift galaxies, this problem is further compounded as the stars take longer than the age of the Universe to evolve into the dust production stages. To explain these discrepancies, dust formation in supernovae (SNe) is required to be an important process but until very recently dust in supernova remnants has only been detected in very small quantities. We present the first submillimeter observations of cold dust in Kepler's supernova remnant (SNR) using SCUBA. A two component dust temperature model is required to fit the Spectral Energy Distribution (SED) with $T_{warm} \sim 102$K and $T_{cold} \sim 17$K. The total mass of dust implied for Kepler is $\sim 1M_{\odot}$ - 1000 times greater than previous estimates. Thus SNe, or their progenitors may be important dust formation sites.Comment: 12 pages, 2 figures, accepted to ApJL, corrected proof

Towards the automated reduction and calibration of SCUBA data from the James Clerk Maxwell Telescope

The Submillimetre Common User Bolometer Array (SCUBA) instrument has been operating on the James Clerk Maxwell Telescope (JCMT) since 1997. The data archive is now sufficiently large that it can be used to investigate instrumental properties and the variability of astronomical sources. This paper describes the automated calibration and reduction scheme used to process the archive data with particular emphasis on `jiggle-map' observations of compact sources. We demonstrate the validity of our automated approach at both 850- and 450-microns and apply it to several of the JCMT secondary flux calibrators. We determine light curves for the variable sources IRC+10216 and OH231.8. This automation is made possible by using the ORAC-DR data reduction pipeline, a flexible and extensible data reduction pipeline that is used on UKIRT and the JCMT.Comment: 9 pages, 8 figures, accepted for publication in Monthly Notices of the Royal Astronomical Societ

Long-term observations of Uranus and Neptune at 90 GHz with the IRAM 30m telescope - (1985 -- 2005)

The planets Uranus and Neptune with small apparent diameters are primary calibration standards. We investigate their variability at ~90 GHz using archived data taken at the IRAM 30m telescope during the 20 years period 1985 to 2005. We calibrate the planetary observations against non-variable secondary standards (NGC7027, NGC7538, W3OH, K3-50A) observed almost simultaneously. Between 1985 and 2005, the viewing angle of Uranus changed from south-pole to equatorial. We find that the disk brightness temperature declines by almost 10% (~2sigma) over this time span indicating that the south-pole region is significantly brighter than average. Our finding is consistent with recent long-term radio observations at 8.6 GHz by Klein & Hofstadter (2006). Both data sets do moreover show a rapid decrease of the Uranus brightness temperature during the year 1993, indicating a temporal, planetary scale change. We do not find indications for a variation of Neptune's brightness temperature at the 8% level. If Uranus is to be used as calibration source, and if accuracies better than 10% are required, the Uranus sub-earth point latitude needs to be taken into account.Comment: accepted for publication in A&