Kapteyn Institute

Groningen, Netherlands

Kapteyn Institute

Groningen, Netherlands
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Podio L.,Institute Of Planetologie Et Dastrophysique Of Grenoble | Podio L.,Kapteyn Institute | Kamp I.,Kapteyn Institute | Flower D.,Durham University | And 9 more authors.
Astronomy and Astrophysics | Year: 2012

Context. Observations of the atomic and molecular line emission associated with jets and outflows emitted by young stellar objects provide sensitive diagnostics of the excitation conditions, and can be used to trace the various evolutionary stages they pass through as they evolve to become main sequence stars. Aims. To understand the relevance of atomic and molecular cooling in shocks, and how accretion and ejection efficiency evolves with the evolutionary state of the sources, we will study the far-infrared counterparts of bright optical jets associated with Class I and II sources in Taurus (T Tau, DG Tau A, DG Tau B, FS Tau A+B, and RW Aur). Methods. We have analysed Herschel/PACS observations of a number of atomic ([O i]63 μm, 145 μm, [C ii]158 μm) and molecular (high-J CO, H 2O, OH) lines, collected within the open time key project GASPS (PI: W. R. F. Dent). To constrain the origin of the detected lines we have compared the obtained FIR emission maps with the emission from optical-jets and millimetre-outflows, and the measured line fluxes and ratios with predictions from shock and disk models. Results. All of the targets are associated with extended emission in the atomic lines; in particular, the strong [O≠i] 63 μm≠emission is correlated with the direction of the optical jet/mm-outflow. The line ratios suggest that the atomic lines can be excited in fast dissociative J-shocks occurring along the jet. The molecular emission, on the contrary, originates from a compact region, that is spatially and spectrally unresolved, and lines from highly excited levels are detected (e.g., the o-H 2O 8 18-7 07 line, and the CO J = 36-35 line). Disk models are unable to explain the brightness of the observed lines (CO and H 2O line fluxes up to 10 -15-6 × 10 -16 W m -2). Slow C-or J-shocks with high pre-shock densities reproduce the observed H 2O and high-J CO lines; however, the disk and/or UV-heated outflow cavities may contribute to the observed emission. Conclusions. Similarly to Class 0 sources, the FIR emission associated with Class I and II jet-sources is likely to be shock-excited. While the cooling is dominated by CO and H 2O lines in Class 0 sources, [O i] becomes an important coolant as the source evolves and the environment is cleared. The cooling and mass loss rates estimated for Class II and I sources are one to four orders of magnitude lower than for Class 0 sources. This provides strong evidence to indicate that the outflow activity decreases as the source evolves. © 2012 ESO.

Krecke K.,MPIA | Armus L.,California Institute of Technology | Groves B.,MPIA | Lyubenova M.,Kapteyn Institute | And 2 more authors.
Proceedings of the International Astronomical Union | Year: 2014

Galaxy outflows are a vital mechanism in the regulation of galaxy evolution through feedback and enrichment. NGC 2146, a nearby infrared luminous galaxy (LIRG), presents evidence for outflows along the disk minor axis in all gas phases (ionized, neutral atomic and molecular). We present new far-IR Herschel imaging and spectroscopy of this galaxy from the Key Insights on Nearby Galaxies: a Far-Infrared Survey with Herschel (KINGFISH) project, as well as new optical integral field unit spectroscopy, to map the kinematics and gas excitation in the central 5 kpc and trace the dust distribution (Kreckel et al. 2014). We observe an increased velocity dispersion in the [OI] 62 um, [OIII] 88 um, [NII] 122 um and [CII] 158 um fine-structure lines that is spatially coincident with shocked gas above and below the disk. Unhampered by extinction, the far-IR lines trace the outflow to the base of the superwind at the disk center, and we discuss the potential for using [CII] as a tracer of outflows such as this in high redshift systems with ALMA. The stellar kinematics are decoupled from the disk rotation seen in all gas phases, which we attribute to a merger that has not produced a fully elliptical morphology. © International Astronomical Union 2015.

Fillion J.H.,University Pierre and Marie Curie | Fillion J.H.,French National Center for Scientific Research | Dulieu F.,Cergy-Pontoise University | Romanzin C.,University Pierre and Marie Curie | And 2 more authors.
EPJ Web of Conferences | Year: 2012

Detailed laboratory studies and progress in surface science technique, have allowed in recent years the first experimental confirmation of surface reaction schemes, as introduced by Tielens, Hagen and Charnley [1,2]. In this paper, we review few heterogeneous processes which give routes to form elementary molecules considered as precursors for explaining the variety and richness of molecular species in the interstellar medium. Adsorption, diffusion and reaction processes are discussed. With emphasis on the experimental approaches, but also supported by theoretical developments, progresses in the understanding of the "catalytic role" of a dust grain surface in various physical conditions are described. Recent advances made on few important species (H2, H2O, CH3OH) are used to illustrate basic properties and raise open questions. © 2011 Owned by the authors, published by EDP Sciences.

Swaters R.A.,University of Maryland University College | Swaters R.A.,Johns Hopkins University | Swaters R.A.,US Space Telescope Science Institute | Sanders R.H.,Kapteyn Institute | McGaugh S.S.,University of Maryland University College
Astrophysical Journal | Year: 2010

Dwarf and low surface brightness (LSB) galaxies are ideal objects to test modified Newtonian dynamics (MOND), because in most of these galaxies the accelerations fall below the threshold where MOND supposedly applies. We have selected from the literature a sample of 27 dwarf and LSB galaxies. MOND is successful in explaining the general shape of the observed rotation curves for roughly three quarters of the galaxies in the sample presented here. However, for the remaining quarter, MOND does not adequately explain the observed rotation curves. Considering the uncertainties in distances and inclinations for the galaxies in our sample, a small fraction of poor MOND predictions is expected and is not necessarily a problem for MOND. We have also made fits taking the MOND acceleration constant, a0, as a free parameter in order to identify any systematic trends. We find that there appears to be a correlation between central surface brightness and the best-fit value of a0, in the sense that lower surface brightness galaxies tend to have lower a0. However, this correlation depends strongly on a small number of galaxies whose rotation curves might be uncertain due to either bars or warps. Without these galaxies, there is less evidence of a trend, but the average value we find for a0 ≈ 0.7 × 10-8 cm s-2 is somewhat lower than derived from previous studies. Such lower fitted values of a0 could occur if external gravitational fields are important. © 2010. The American Astronomical Society. All rights reserved.

Brocksopp C.,University College London | Kaiser C.R.,University of Southampton | Schoenmakers A.P.,Stichting ASTRON | De Bruyn A.G.,Stichting ASTRON | De Bruyn A.G.,Kapteyn Institute
Monthly Notices of the Royal Astronomical Society | Year: 2011

Double-double radio galaxies (DDRGs) offer a unique opportunity for us to study multiple episodes of jet activity in large-scale radio sources. We use radio data from the Very Large Array and the literature to model two DDRGs, B1450+333 and B1834+620, in terms of their dynamical evolution. We find that the standard Fanaroff-Riley II model is able to explain the properties of the two outer lobes of each source, whereby the lobes are formed by ram-pressure balance of a shock at the end of the jet with the surrounding medium. The inner pairs of lobes, however, are not well described by the standard model. Instead we interpret the inner lobes as arising from the emission of relativistic electrons within the outer lobes, which are compressed and re-accelerated by the bow shock in front of the restarted jets and within the outer lobes. The predicted rapid progression of the inner lobes through the outer lobes requires the eventual development of a hotspot at the edge of the outer lobe, causing the DDRG ultimately to resemble a standard Fanaroff-Riley II radio galaxy. This may suggest that DDRGs are a brief, yet normal, phase of the evolution of large-scale radio galaxies. © 2010 The Authors. Journal compilation © 2010 RAS.

Ellerbroek L.E.,University of Amsterdam | Podio L.,Institute Of Planetologie Et Dastrophysique Of Grenoble | Podio L.,Kapteyn Institute | Kaper L.,University of Amsterdam | And 6 more authors.
Astronomy and Astrophysics | Year: 2013

Jets around low-and intermediate-mass young stellar objects (YSOs) contain a fossil record of the recent accretion and outflow activity of their parent star-forming systems. We aim to understand whether the accretion/ejection process is similar across the entire stellar mass range of the parent YSOs. To this end we have obtained optical to near-infrared spectra of HH 1042 and HH 1043, two newly discovered jets in the massive star-forming region RCW 36, using X-shooter on the ESO Very Large Telescope. HH 1042 is associated with the intermediate-mass YSO 08576nr292. Over 90 emission lines are detected in the spectra of both targets. High-velocity (up to 220 km s-1) blue-and redshifted emission from a bipolar flow is observed in typical shock tracers. Low-velocity emission from the background cloud is detected in nebular tracers, including lines from high ionization species. We applied combined optical and infrared spectral diagnostic tools in order to derive the physical conditions (density, temperature, and ionization) in the jets. The measured mass outflow rates are Mjet 10-7M· yr-1. It is not possible to determine a reliable estimate for the accretion rate of the driving source of HH 1043 using optical tracers. We measure a high accretion rate for the driving source of HH 1042 (Macc 10-6M · yr-1). For this system the ratio ájetMacc 0.1, which is comparable to low-mass sources and consistent with models for magneto-centrifugal jet launching. The knotted structure and velocity spread in both jets are interpreted as fossil signatures of a variable outflow rate. While the mean velocities in both lobes of the jets are comparable, the variations in mass outflow rate and velocity in the two lobes are not symmetric. This asymmetry suggests that the launching mechanism on either side of the accretion disk is not synchronized. For the HH 1042 jet, we have constructed an interpretative physical model with a stochastic or periodic outflow rate and a description of a ballistic flow as its constituents. We have simulated the flow and the resulting emission in position-velocity space, which is then compared to the observed kinematic structure. The knotted structure and velocity spread can be reproduced qualitatively with the model. The results of the simulation indicate that the outflow velocity varies on timescales on the order of 100 yr. © ESO, 2013.

Pizzo R.F.,Kapteyn Institute | De Bruyn A.G.,Kapteyn Institute | Bernardi G.,Kapteyn Institute | Bernardi G.,Harvard - Smithsonian Center for Astrophysics | Brentjens M.A.,ASTRON
Astronomy and Astrophysics | Year: 2010

Aims. By studying the polarimetric properties of the radio galaxies and the radio filaments belonging to the galaxy cluster Abell 2255, we aim to unveil their 3-dimensional location within the cluster. Methods. We performed WSRT observations of A2255 at 18, 21, 25, 85, and 200 cm. The polarization images of the cluster were processed through rotation measure (RM) synthesis, producing three final RM cubes. Results. The radio galaxies and the filaments at the edges of the halo are detected in the high-frequency RM cube, obtained by combining the data at 18, 21, and 25 cm. Their Faraday spectra show different levels of complexity. The radio galaxies lying near by the cluster center have Faraday spectra with multiple peaks, while those at large distances show only one peak, as do the filaments. Similar RM distributions are observed for the external radio galaxies and for the filaments, with much lower average RM values and RM variance than those found in previous works for the central radio galaxies. The 85 cm RM cube is dominated by the Galactic foreground emission, but it also shows features associated with the cluster. At 2 m, no polarized emission from A2255 nor our Galaxy is detected. Conclusions. The radial trend observed in the RM distributions of the radio galaxies and in the complexity of their Faraday spectra favors the interpretation that the external Faraday screen for all the sources in A2255 is the ICM. Its differential contribution depends on the amount of medium that the radio signal crosses along the line of sight. The filaments should therefore be located at the periphery of the cluster, and their apparent central location comes from projection effects. Their high fractional polarization and morphology suggest that they are relics rather than part of a genuine radio halo. Their inferred large distance from the cluster center and their geometry could argue for an association with large-scale structure (LSS) shocks. © 2010 ESO.

Kamp I.,European Space Agency | Kamp I.,Kapteyn Institute
EAS Publications Series | Year: 2012

A-type stars with their shallow convection zones serve as ideal physics laboratories for stellar atmosphere research. In the absence of large scale mixing, processes such as diffusion, mass loss and accretion leave their characteristic imprint on the chemical composition of the photosphere. This characteristic surface pattern can be studied by means of stellar abundance analysis. However, such patterns can be hidden in the large uncertainties of LTE abundances. Thus, detailed NLTE studies that can push stellar abundance analysis beyond the 0.1 dex uncertainty limit are a pre-requisite for using A star atmospheres as physics laboratories. © EAS, EDP Sciences 2010.

Kamp I.,European Space Agency | Kamp I.,Kapteyn Institute
EAS Publications Series | Year: 2012

In NLTE computations of trace elements in stellar atmospheres, background opacities are generally treated in LTE. It is thus important to assess the impact of different methods of including this background opacity on the statistical equilibrium of the trace element and its resulting NLTE abundance. This article illustrates these effects using two examples, nitrogen in Vega and carbon in the Sun. © EAS, EDP Sciences 2010.

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