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Some empirical estimates of the H2 formation rate in photon-dominated regions
Boulanger, F.; Walmsley, C. M.; Habart, E. +2 more
We combine recent ISO observations of the vibrational ground state lines of H2 towards Photon-Dominated Regions (PDRs) with observations of vibrationally excited states made with ground-based telescopes in order to constrain the formation rate of H2 on grain surfaces under the physiconditions in the layers responsible for H
A Huge Drop in the X-Ray Luminosity of the Nonactive Galaxy RX J1242.6-1119A, and the First Postflare Spectrum: Testing the Tidal Disruption Scenario
Schartel, Norbert; Komossa, Stefanie; Hasinger, Günther +3 more
In recent years, indirect evidence has emerged suggesting that many nearby nonactive galaxies harbor quiescent supermassive black holes. Knowledge of the frequency of occurrence of black holes, of their masses and spins, is of broad relevance for studying black hole growth and galaxy and active galactic nuclei formation and evolution. It has been …
A multiwavelength study of solar flare waves. I. Observations and basic properties
Magdalenić, J.; Vršnak, B.; Hanslmeier, A. +2 more
Propagating wave-like disturbances associated with solar flares - commonly observed in the chromosphere as Moreton waves - have been known for several decades. Recently, the phenomenon has come back into focus prompted by the observation of coronal waves with the SOHO/EIT instrument (``EIT waves"). It has been suggested that they represent the ant…
Analysing observed star cluster SEDs with evolutionary synthesis models: systematic uncertainties
de Grijs, R.; Anders, P.; Fritze-v. Alvensleben, U. +1 more
We discuss the systematic uncertainties inherent to analyses of observed (broad-band) spectral energy distributions (SEDs) of star clusters with evolutionary synthesis models. We investigate the effects caused by restricting oneself to a limited number of available passbands, choices of various passband combinations, finite observational errors, n…
The Origin of Fe II Emission in Active Galactic Nuclei
Korista, K. T.; Ferland, G. J.; Hamann, F. +2 more
We used a very large set of models of broad emission line region (BELR) clouds in active galactic nuclei to investigate the formation of the observed Fe II emission lines. We show that photoionized BELR clouds cannot produce both the observed shape and observed equivalent width of the 2200-2800 Å Fe II UV bump unless there is considerable velocity…
Stellar Populations and Kinematics of Red Galaxies at z > 2: Implications for the Formation of Massive Galaxies
van Dokkum, Pieter G.; Franx, Marijn; Illingworth, Garth D. +13 more
We recently identified a substantial population of galaxies at z>2 with comparatively red rest-frame optical colors. These distant red galaxies (DRGs) are efficiently selected by the simple observed color criterion Js-Ks>2.3. In this paper we present near-infrared spectroscopy with Keck NIRSPEC of six DRGs with previous…
Selected Problems in Collisionless-Shock Physics
Krasnoselskikh, V.; Kucharek, H.; Scholer, M. +6 more
The physics of collisionless shocks is a very broad topic, which has been well studied for many decades. However, there are a number of important issues which remain unresolved. Moreover, there have been new findings, which cast doubt on well-established ideas. The purpose of this review is to address a subset of unresolved problems in collisionle…
Mapping ices in protostellar environments on 1000 AU scales. Methanol-rich ice in the envelope of Serpens SMM 4
van Dishoeck, E. F.; Pontoppidan, K. M.; Dartois, E.
We present VLT-ISAAC L-band spectroscopy toward 10 stars in SVS 4, a 30 arcsec×45 arcsec dense cluster of pre-main sequence stars deeply embedded in the Serpens star forming cloud. The ISAAC spectra are combined with archival imaging from UKIRT and ISOCAM to derive accurate extinctions toward the SVS 4 stars. The data are then used to construct a …
Evidence for a multizone warm absorber in the XMM-Newton spectrum of Markarian 304
Guainazzi, M.; Schartel, N.; Rodríguez-Pascual, P. M. +3 more
We present a XMM-Newton observation of Markarian 304, a Seyfert 1 galaxy at z= 0.066. The EPIC data show that MKN 304 is affected by heavy (NH~ 1023 cm-2) obscuration arising from ionized gas. A two-phase warm absorber provides an adequate parametrization of this gas. The ionization parameter of the two components …
XMM-Newton observations of the Perseus cluster - II. Evidence for gas motions in the core
Böhringer, H.; Sunyaev, R.; Churazov, E. +2 more
The 5-9 keV spectrum of the inner ~100 kpc of the Perseus cluster measured by XMM-Newton can be well described by an optically thin plasma emission model as predicted by the APEC code, without any need for invoking a strong Ni overabundance or the effects of resonant scattering. For the strongest 6.7-keV line of He-like iron, the optical depth of …