Observations of a high-mass protostar in NGC 7538S

We present high angular resolution continuum observations of the high-mass protostar NGC 7538S with BIMA and CARMA at 3 and 1.4 mm, VLA observations at 1.3, 2, 3.5 and 6 cm, and archive IRAC observations from the Spitzer Space Observatory, which detect the star at 4.5, 5.8, and 8 $\mu$m. The star looks rather unremarkable in the mid-IR. The excellent positional agreement of the IRAC source with the VLA free-free emission, the OH, CH$_3$OH, H$_2$O masers, and the dust continuum confirms that this is the most luminous object in the NGC 7538S core. The continuum emission at millimeter wavelengths is dominated by dust emission from the dense cold cloud core surrounding the protostar. Including all array configurations, the emission is dominated by an elliptical source with a size of ~ 8" x 3". If we filter out the extended emission we find three compact mm-sources inside the elliptical core. The strongest one, $S_A$, coincides with the VLA/IRAC source and resolves into a double source at 1.4 mm, where we have sub-arcsecond resolution. The measured spectral index, $\alpha$, between 3 and 1.4 mm is ~ 2.3, and steeper at longer wavelengths, suggesting a low dust emissivity or that the dust is optically thick. We argue that the dust in these accretion disks is optically thick and estimate a mass of an accretion disk or infalling envelope surrounding S$_A$ to be ~ 60 solar masses.Comment: ApJ Accepted 2012, 13 pages, 9 figure

NGC7538 IRS1 - an ionized jet powered by accretion

Analysis of high spatial resolution VLA images shows that the free-free emission from NGC7538 IRS1 is dominated by a collimated ionized wind. We have re-analyzed high angular resolution VLA archive data from 6 cm to 7 mm, and measured separately the flux density from the compact bipolar core and the extended (1.5" - 3") lobes. We find that the flux density of the core is proportional to the frequency to the power of alpha, with alpha being about 0.7. The frequency dependence of the total flux density is slightly steeper with alpha = 0.8. A massive optically thick hypercompact core with a steep density gradient can explain this frequency dependence, but it cannot explain the extremely broad recombination line velocities observed in this source. Neither can it explain why the core is bipolar rather than spherical, nor the observed decrease of 4% in the flux density in less than 10 years. An ionized wind modulated by accretion is expected to vary, because the accretion flow from the surrounding cloud will vary over time. BIMA and CARMA continuum observations at 3 mm show that the free-free emission still dominates at 3 mm. HCO+ J = 1 - 0 observations combined with FCRAO single dish data show a clear inverse P Cygni profile towards IRS1. These observations confirm that IRS1 is heavily accreting with an accretion rate of about 2 times 10(-4) solar masses per year.Comment: Accepted for Astrophysical Journal Letter

PDA-BCJR algorithm for factorial hidden Markov models with application to MIMO equalisation

Publication in the conference proceedings of EUSIPCO, Florence, Italy, 200

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&

Aperture Synthesis Imaging of V892 Tau and PV Cep: Disk Evolution

I present a study of two Herbig Ae stars that are in completely different evolutionary stages: V892 Tau and PV Cep. Using sub arc-second interferometric observations obtained with the Combined Array for Research in Millimeter-wave Astronomy (CARMA) at the 1.3 and 2.7 mm wavelengths, I have for the first time resolved their disks. I deduce that the 5 Myr old V892 Tau has a low dust opacity index $\beta$=1.1 and a disk mass of 0.03 \msun. These values correspond to the growth of its dust into large up to centimeters size structures. In contrast, the very young (a few 10$^5$yrs) PV Cep has a quite high opacity index $\beta$ =1.75 and a more massive disk 0.8 \msun. PV Cep has the youngest resolved disk around any Herbig Ae star. Unlike the youngest T Tauri and Class 0 stars, which contain large and processed grains, the young Herbig Ae star, PV Cep, disk contains ISM-like unprocessed dust. This suggests that PV Cep's dust evolution is slower than T Tauri stars'. I also present high spatial resolution interferometric observations of the PV Cep outflow. The outflow inclination is consistent with the orientation of the known Herbig-Haro flow in that region, HH315.Comment: 15 pages, Accepted for publication in Ap