Dirk Froebrich

WFCAM, Spitzer/IRAC and SCUBA observations of the massive star-forming region DR21/W75 – I. The collimated molecular jets

We present wide-field near-infrared (IR) images of the DR21/W75 high-mass star-forming region, obtained with the Wide Field Camera (WFCAM) on the United Kingdom Infrared Telescope. Broad-band JHK and narrow-band H 2 1-0S(1) images are compared to archival mid-IR images from the Spitzer Space Telescope, and 850-μm dust-continuum maps obtained with the Submillimeter Common User Bolometer Array (SCUBA). Together these data give a complete picture of dynamic star formation across this extensive region, which includes at least four separate star-forming sites in various stages of evolution. The H 2 data reveal knots and bow shocks associated with more than 50 individual flows. Most are well collimated, and at least five qualify as parsec-scale flows. Most appear to be driven by embedded, low-mass protostars. The orientations of the outflows, particularly from the few higher mass sources in the region (DR21, DR21(OH), W75N and ERO 1), show some degree of order, being preferentially orientated roughly orthogonal to the chain of dusty cores that runs north-south through DR21. Clustering may inhibit disc accretion and therefore the production of outflows; we certainly do not see enhanced outflow activity from clusters of protostars. Finally, although the low-mass protostellar outflows are abundant and widely distributed, the current generation does not provide sufficient momentum and kinetic energy to account for the observed turbulent motions in the DR21/W75 giant molecular clouds. Rather, multiple epochs of outflow activity are required over the million-year time-scale for turbulent decay.

Which Are the Youngest Protostars? Determining Properties of Confirmed and Candidate Class 0 Sources by Broadband Photometry

The most up to date and comprehensive catalogue of Class 0 protostars and their observational properties. Its data is made publicly available to the entire astronomical community via a widely used web page. It allowed us to discover some protostars have a significantly different time evolution of their mass accretion rate, caused by the environment they are forming in.

New Galactic star clusters discovered in the VVV survey

Context. VISTA Variables in the V´oa Lactea (VVV) is one of the six ESO Public Surveys operating on the new 4-meter Visible and Infrared Survey Telescope for Astronomy (VISTA). VVV is scanning the Milky Way bulge and an adjacent section of the disk, where star formation activity is high. One of the principal goals of the VVV Survey is to find new star clusters of different ages. Aims. In order to trace the early epochs of star cluster formation we concentrated our search in the directions to those of known star formation regions, masers, radio, and infrared sources. Methods. The disk area covered by VVV was visually inspected using the pipeline processed and calibrated KS-band tile images for stellar overdensities. Subsequently, we examined the composite JHKS and ZJKS color images of each candidate. PSF photometry of 15 × 15 arcmin fields centered on the candidates was then performed on the Cambridge Astronomy Survey Unit reduced images. After statistical field-star decontamination, color-magnitude and color-color diagrams were constructed and analyzed. Results. We report the discovery of 96 new infrared open clusters and stellar groups. Most of the new cluster candidates are faint and compact (with small angular sizes), highly reddened, and younger than 5Myr. For relatively well populated cluster candidates we derived their fundamental parameters such as reddening, distance, and age by fitting the solar- metallicity Padova isochrones to the color-magnitude diagrams.

The structure of molecular clouds – I. All-sky near-infrared extinction maps

We are studying the column density distribution of all nearby giant molecular clouds. As part of this project, we generated several all-sky extinction maps. They are calculated using the median near-infrared colour excess technique applied to data from the Two-Micron All-Sky Survey. Our large-scale approach allows us to fit spline functions to extinction-free regions in order to accurately determine the colour excess values. Two types of maps are presented: (i) maps with a constant noise and variable spatial resolution and (ii) maps with a constant spatial resolution and variable noise. Our standard A V map uses the nearest 49 stars to the centre of each pixel for the determination of the extinction. The 1σ variance is constant at 0.28 mag A V in the entire map. The distance to the 49th nearest star varies from below 1 arcmin near the Galactic plane to about 10 arcmin at the poles, but is below 5 arcmin for all giant molecular clouds (|b| < 30°). A comparison with existing large-scale maps shows that our extinction values are systematically larger by 20 per cent compared to Dobashi et al. and 40 per cent smaller compared to Schlegel et al. This is most likely caused by the applied star counting technique in Dobashi et al. and systematic uncertainties in the dust temperature and emissivity in Schlegel et al. Our superior resolution allows us to detect more small-scale high-extinction cores as compared to the other two maps.

UWISH2 -- The UKIRT Widefield Infrared Survey for H2

The definitive version can be found at : http://onlinelibrary.wiley.com/ Copyright Wiley-Blackwell

Molecular Outflows in the Young Open Cluster IC 348

We present a wide-field survey of the young open cluster IC 348 for molecular H2 outflows. Outflow activity is only found at its southwestern limit, where a new subcluster of embedded sources is in an early phase of its formation. If the IC 348 cluster had been built up by such subclusters forming at different times, this could explain the large age-spread that Herbig (1998) found for the IC 348 member stars. In addition to several compact groups of H2 knots, our survey reveals a large north-south oriented outflow, and we identify the newly discovered far-infrared and millimeter object IC 348 MMS as its source. New deep images in the 1-0 S(1) line of molecular hydrogen trace the HH 211 jet and counterjet as highly collimated chains of knots, resembling the interferometric CO and SiO jets. This jet system appears rotated counterclockwise by about 3° with respect to the prominent H2 bow shocks. Furthermore, we resolve HH 211-mm as a double pointlike source in the millimeter continuum.

WFCAM, Spitzer/IRAC and SCUBA observations of the massive star‐forming region DR21/W75 – II. Stellar content and star formation

Wide field near-infrared observations and Spitzer Space Telescope IRAC observations of the DR21/W75 star formation regions are presented. The photometric data are used to analyse the extinction, stellar content and clustering in the entire region by using standard methods. A young stellar population is identified all over the observed field, which is found to be distributed in embedded clusters that are surrounded by a distributed halo population extending over a larger projected area. The Spitzer/IRAC data are used to compute a spectral index value, �, for each YSO in the field. We use these data to separate pure photospheres from disk excess sources. We find a small �

Far‐infrared photometry of deeply embedded outflow sources

We present far-infrared maps and spectroscopy for a number of deeply embedded protostellar objects (Cep E, HH 211-MM, IC 1396 W, L 1157, L 1211, and RNO 15 FIR) from data that we acquired with the Infrared Space Observatory (ISO) photopolarimeter (PHOT) and Long Wavelength Spectrometer (LWS). Several previously undetected deeply embedded sources are found in the vicinity of our targets. We determine temperatures and luminosities of seven objects and locate them on an L b o l -T b o l diagram - the equivalent of a Hertzsprung-Russell diagram for protostars. Their masses and ages, according to their location on tracks taken from our evolutionary model, are derived. L 1211 and Cep E appear to be intermediate-mass objects which will reach final masses of about 3 M O ., whereas the other sources are in or below the solar mass range. The derived ages of 15 000 to 30000 yr are consistent with their current Class 0 state. A comparison of the luminosity of the associated outflows in the 1 - 0 S(1) line of molecular hydrogen with the source properties (bolometric luminosity, bolometric temperature and envelope mass) of 16 Class 0 sources shows no statistically significant correlations. Nevertheless, the data are consistent with a scheme in which the outflow strength and protostar evolve simultaneously. We show that the relationship is partially disguised, however, by the local properties of the surrounding material, the extinction and by short-term flux variability.

Molecular jets driven by high-mass protostars: a detailed study of the IRAS20126+4104 jet

Context. Protostellar jets from intermediate- and high-mass protostars provide an excellent opportunity to understand the mechanisms responsible for intermediate- and high-mass star-formation. A crucial question is if they are scaled-up versions of their low-mass counterparts. Such high-mass jets are relatively rare and, usually, they are distant and highly embedded in their parental clouds. The IRAS 20126+4104 molecular jet, driven by a 10 4 Lprotostar, represents a suitable target to investigate. Aims. We present here an extensive analysis of this protostellar jet, deriving the kinematical, dynamical, and physical conditions of the H2 gas along the flow. Methods. The jet was investigated by means of near-IR H2 and (Fe ii) narrow-band imaging, high-resolution spectroscopy of the 1-0 S(1) line (2.12 μm), NIR (0.9-2.5 μm) low-resolution spectroscopy, along with ISO-SWS and LWS spectra (from 2.4 to 200 μm). Results. The flow shows a complex morphology. In addition to the large-scale jet precession presented in previous studies, we detect a small-scale wiggling close to the source, which may indicate the presence of a multiple system. The peak radial velocities of the H2 knots range from -42 to -14 km s −1 in the blue lobe, and from -8 to 47 km s −1 in the red lobe. The low-resolution spectra are rich in H2 emission, and relatively faint (Fe ii )( NIR), (Oi )a nd (Cii) (FIR) emission is observed in the region close to the source. A warm H2 gas component has an average excitation temperature that ranges between 2000 K and 2500 K. Additionally, the ISO-SWS spectrum reveals a cold component (520 K) that strongly contributes to the radiative cooling of the flow and plays a major role in the dynamics of the flow. The estimated LH2 of the jet is 8.2 ± 0.7 L� , suggesting that IRAS 20126+4104 has a significantly increased accretion rate compared to low-mass YSOs. This is also supported by the derived mass flux rate from the H2 lines ( u Mout(H2) ∼ 7.5 × 10 −4 Myr −1 ). The comparison between the H2 and the outflow parameters strongly indicates that the jet is driving the outflow, at least partially. As already found for low-mass protostellar jets, the measured H2 outflow luminosity is tightly related to the source bolometric luminosity. Conclusions. As for a few other intermediate- and high-mass protostellar jets in the literature, we conclude that IRAS 20126+4104 jet is a scaled-up version of low-mass protostellar counterparts.

Properties of star clusters – II. Scaleheight evolution of clusters

Until now, it has been impossible to observationally measure how star cluster scaleheight evolves beyond 1 Gyr as only small samples have been available. Here, we establish a novel method to determine the scaleheight of a cluster sample using modelled distributions and Kolmogorov-Smirnov tests. This allows us to determine the scaleheight with a 25 per cent accuracy for samples of 38 clusters or more. We apply our method to investigate the temporal evolution of cluster scaleheight, using homogeneously selected sub-samples of Kharchenko et al. (MWSC), Dias et al. (DAML02), WEBDA, and Froebrich et al. (FSR). We identify a linear relationship between scaleheight and log(age/yr) of clusters, considerably different from field stars. The scaleheight increases from about 40 pc at 1Myr to 75 pc at 1 Gyr,most likely due to internal evolution and external scattering events. After 1 Gyr, there is amarked change of the behaviour, with the scaleheight linearly increasing with log(age/yr) to about 550 pc at 3.5 Gyr. The most likely interpretation is that the surviving clusters are only observable because they have been scattered away from the mid-plane in their past. A detailed understanding of this observational evidence can only be achieved with numerical simulations of the evolution of cluster samples in the Galactic disc. Furthermore, we find a weak trend of an age-independent increase in scaleheight with Galactocentric distance. There are no significant temporal or spatial variations of the cluster distribution zero-point. We determine the Suns vertical displacement from the Galactic plane as Z± = 18.5 ± 1.2 pc. ©2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.