Max Planck Institute For Extraterretrische Physik

Garching bei München, Germany

Max Planck Institute For Extraterretrische Physik

Garching bei München, Germany
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Ebrero J.,Newton Science Operations Center | Kaastra J.S.,SRON Netherlands Institute for Space Research | Kaastra J.S.,Leiden University | Kriss G.A.,US Space Telescope Science Institute | And 15 more authors.
Astronomy and Astrophysics | Year: 2016

Context. We observed the archetypal Seyfert 1 galaxy NGC 5548 in 2013-2014 in the context of an extensive multiwavelength campaign involving several satellites, which revealed the source to be in an extraordinary state of persistent heavy obscuration. Aims. We re-analyzed the archival grating spectra obtained by XMM-Newton and Chandra between 1999 and 2007 in order to characterize the classic warm absorber (WA) using consistent models and up-to-date photoionization codes and atomic physics databases and to construct a baseline model that can be used as a template for the physical state of the WA in the 2013 observations. Methods. We used the latest version of the photoionization code CLOUDY and the SPEX fitting package to model the X-ray grating spectra of the different archival observations of NGC 5548. Results. We find that the WA in NGC 5548 is composed of six distinct ionization phases outflowing in four kinematic regimes. The components seem to be in the form of a stratified wind with several layers intersected by our line of sight. Assuming that the changes in the WA are solely due to ionization or recombination processes in response to variations in the ionizing flux among the different observations, we are able to estimate lower limits on the density of the absorbing gas, finding that the farthest components are less dense and have a lower ionization. These limits are used to put stringent upper limits on the distance of the WA components from the central ionizing source, with the lowest ionization phases at several pc distances (<50, <20, and <5 pc, respectively), while the intermediately ionized components lie at pc-scale distances from the center (<3.6 and <2.2 pc, respectively). The highest ionization component is located at ∼0.6 pc or closer to the AGN central engine. The mass outflow rate summed over all WA components is ∼0.3 M° yr-1, about six times the nominal accretion rate of the source. The total kinetic luminosity injected into the surrounding medium is a small fraction (∼0.03%) of the bolometric luminosity of the source. After adding the contribution of the UV absorbers, this value augments to ∼0.2% of the bolometric luminosity, well below the minimum amount of energy required by current feedback models to regulate galaxy evolution. © ESO, 2016.


Bozzo E.,Data Center for Astrophysics | Pjanka P.,Centrum Astronomiczne Im. M. Kopernika | Pjanka P.,Princeton University | Romano P.,Istituto di Astrofisica Spaziale e Fisica Cosmica | And 11 more authors.
Astronomy and Astrophysics | Year: 2016

In this paper we report on the available X-ray data collected by INTEGRAL, Swift, and XMM-Newton during the first outburst of the INTEGRAL transient IGR J17451-3022, discovered in 2014 August. The monitoring observations provided by the JEM-X instruments on board INTEGRAL and the Swift /XRT showed that the event lasted for about 9 months and that the emission of the source remained soft for the entire period. The source emission is dominated by a thermal component (kT ∼ 1.2 keV), most likely produced by an accretion disk. The XMM-Newton observation carried out during the outburst revealed the presence of multiple absorption features in the soft X-ray emission that could be associated with the presence of an ionized absorber lying above the accretion disk, as observed in many high inclination, low mass X-ray binaries. The XMM-Newton data also revealed the presence of partial and rectangular X-ray eclipses (lasting about 820 s) together with dips. The rectangular eclipses can be associated with increases in the overall absorption column density in the direction of the source. The detection of two consecutive X-ray eclipses in the XMM-Newton data allowed us to estimate the source orbital period at Porb = 22620.5+2.0 -1.8 s (1σ confidence level). © ESO, 2016.


Harsono D.,Leiden University | Harsono D.,SRON Netherlands Institute for Space Research | Harsono D.,University of Heidelberg | Bruderer S.,Max Planck Institute For Extraterretrische Physik | And 2 more authors.
Astronomy and Astrophysics | Year: 2015

Context. Models of the young solar nebula assume a hot initial disk in which most volatiles are in the gas phase. Water emission arising from within 50 AU radius has been detected around low-mass embedded young stellar objects. The question remains whether an actively accreting disk is warm enough to have gas-phase water up to 50 AU radius. No detailed studies have yet been performed on the extent of snowlines in an accreting disk embedded in a dense envelope (stage 0). Aims.We aim to quantify the location of gas-phase volatiles in the inner envelope and disk system for an actively accreting embedded disk. Methods. Two-dimensional physical and radiative transfer models were used to calculate the temperature structure of embedded protostellar systems. Heating due to viscous accretion was added through the di usion approximation. Gas and ice abundances of H2O, CO2, and CO were calculated using the density-dependent thermal desorption formulation. Results. The midplane water snowline increases from 3 to 55 AU for accretion rates through the disk onto the star between 10.9-10.4 M yr.1. CO2 can remain in the solid phase within the disk for .M10.-5 M yr.-1 down to 20 AU. Most of the CO is in the gas phase within an actively accreting disk independent of disk properties and accretion rate. The predicted optically thin water isotopolog emission is consistent with the detected H18 2 O emission toward the stage 0 embedded young stellar objects, originating from both the disk and the warm inner envelope (hot core). An accreting embedded disk can only account for water emission arising from R.


Harsono D.,Leiden University | Harsono D.,SRON Netherlands Institute for Space Research | Van Dishoeck E.F.,Leiden University | Van Dishoeck E.F.,Max Planck Institute For Extraterretrische Physik | And 3 more authors.
Astronomy and Astrophysics | Year: 2015

Context. Recent simulations have explored different ways to form accretion disks around low-mass stars. However, it has been difficult to differentiate between the proposed mechanisms because of a lack of observable predictions from these numerical studies. Aims. We aim to present observables that can differentiate a rotationally supported disk from an infalling rotating envelope toward deeply embedded young stellar objects (Menv>Mdisk) and infer their masses and sizes. Methods. Two 3D magnetohydrodynamics (MHD) formation simulations are studied with a rotationally supported disk (RSD) forming in one but not the other (where a pseudo-disk is formed instead), together with the 2D semi-analytical model. We determine the dust temperature structure through continuum radiative transfer RADMC3D modeling. A simple temperature-dependent CO abundance structure is adopted and synthetic spectrally resolved submm rotational molecular lines up to Ju = 10 are compared with existing data to provide predictions for future ALMA observations. Results. The 3D MHD simulations and 2D semi-analytical model predict similar compact components in continuum if observed at the spatial resolutions of 0.5-1″ (70-140 AU) typical of the observations to date. A spatial resolution of ~14 AU and high dynamic range (>1000) are required in order to differentiate between RSD and pseudo-disk formation scenarios in the continuum. The first moment maps of the molecular lines show a blue- to red-shifted velocity gradient along the major axis of the flattened structure in the case of RSD formation, as expected, whereas it is along the minor axis in the case of a pseudo-disk. The peak position-velocity diagrams indicate that the pseudo-disk shows a flatter velocity profile with radius than does an RSD. On larger scales, the CO isotopolog line profiles within large (>9″) beams are similar and are narrower than the observed line widths of low-J (2-1 and 3-2) lines, indicating significant turbulence in the large-scale envelopes. However a forming RSD can provide the observed line widths of high-J (6-5, 9-8, and 10-9) lines. Thus, either RSDs are common or a higher level of turbulence (b ~ 0.8 km? s-1) is required in the inner envelope compared with the outer part (0.4 km? s-1). Conclusions. Multiple spatially and spectrally resolved molecular line observations can differentiate between the pseudo-disk and the RSD much better than continuum data. The continuum data give a better estimate of disk masses, whereas the disk sizes can be estimated from the spatially resolved molecular lines observations. The general observable trends are similar between the 2D semi-analytical models and 3D MHD RSD simulations. © ESO, 2015.


Harsono D.,Leiden University | Harsono D.,SRON Netherlands Institute for Space Research | Jorgensen J.K.,Copenhagen University | Van Dishoeck E.F.,Leiden University | And 6 more authors.
Astronomy and Astrophysics | Year: 2014

Context. Disks are observed around pre-main sequence stars, but how and when they form is still heavily debated. While disks around young stellar objects have been identified through thermal dust emission, spatially and spectrally resolved molecular line observations are needed to determine their nature. Only a handful of embedded rotationally supported disks have been identified to date. Aims. We identify and characterize rotationally supported disks near the end of the main accretion phase of low-mass protostars by comparing their gas and dust structures. Methods. Subarcsecond observations of dust and gas toward four Class I low-mass young stellar objects in Taurus are presented at significantly higher sensitivity than previous studies. The 13 CO and C18O J = 2-1 transitions at 220 GHz were observed with the Plateau de Bure Interferometer at a spatial resolution of ≤0.8" (56 AU radius at 140 pc) and analyzed using uv-space position velocity diagrams to determine the nature of their observed velocity gradient. Results. Rotationally supported disks (RSDs) are detected around 3 of the 4 Class I sources studied. The derived masses identify them as Stage I objects; i.e., their stellar mass is higher than their envelope and disk masses. The outer radii of the Keplerian disks toward our sample of Class I sources are ≤100 AU. The lack of on-source C18O emission for TMR1 puts an upper limit of 50 AU on its size. Flattened structures at radii >100 AU around these sources are dominated by infalling motion μ∝r-1). A large-scale envelope model is required to estimate the basic parameters of the flattened structure from spatially resolved continuum data. Similarities and differences between the gas and dust disk are discussed. Combined with literature data, the sizes of the RSDs around Class I objects are best described with evolutionary models with an initial rotation of Ω= 10-14 Hz and slow sound speeds. Based on the comparison of gas and dust disk masses, little CO is frozen out within 100 AU in these disks. Conclusions. Rotationally supported disks with radii up to 100 AU are present around Class I embedded objects. Larger surveys of both Class 0 and I objects are needed to determine whether most disks form late or early in the embedded phase. © 2014 ESO.


Walsh C.,Leiden University | Nomura H.,Tokyo Institute of Technology | Van Dishoeck E.,Leiden University | Van Dishoeck E.,Max Planck Institute For Extraterretrische Physik
Astronomy and Astrophysics | Year: 2015

Context. Near- to mid-infrared observations of molecular emission from protoplanetary disks show that the inner regions are rich in small organic volatiles (e.g., C2H2 and HCN). Trends in the data suggest that disks around cooler stars (Teff 3000 K) are potentially (i) more carbon-rich; and (ii) more molecule-rich than their hotter counterparts (Teff ≤ 4000 K). Aims. We explore the chemical composition of the planet-forming region (<10 AU) of protoplanetary disks around stars over a range of spectral types (from M dwarf to Herbig Ae) and compare with the observed trends. Methods. Self-consistent models of the physical structure of a protoplanetary disk around stars of different spectral types are coupled with a comprehensive gas-grain chemical network to map the molecular abundances in the planet-forming zone. The effects of (i) N2 self shielding; (ii) X-ray-induced chemistry; and (iii) initial abundances, are investigated. The chemical composition in the "observable" atmosphere is compared with that in the disk midplane where the bulk of the planet-building reservoir resides. Results. M dwarf disk atmospheres are relatively more molecule rich than those for T Tauri or Herbig Ae disks. The weak far-UV flux helps retain this complexity which is enhanced by X-ray-induced ion-molecule chemistry. N2 self shielding has only a small effect in the disk molecular layer and does not explain the higher C2H2/HCN ratios observed towards cooler stars. The models underproduce the OH/H2O column density ratios constrained in Herbig Ae disks, despite reproducing (within an order of magnitude) the absolute value for OH: the inclusion of self shielding for H2O photodissociation only increases this discrepancy. One possible explanation is the adopted disk structure. Alternatively, the "hot" H2O (T 300 K) chemistry may be more complex than assumed. The results for the atmosphere are independent of the assumed initial abundances; however, the composition of the disk midplane is sensitive to the initial main elemental reservoirs. The models show that the gas in the inner disk is generally more carbon rich than the midplane ices. This effect is most significant for disks around cooler stars. Furthermore, the atmospheric C/O ratio appears larger than it actually is when calculated using observable tracers only. This is because gas-phase O2 is predicted to be a significant reservoir of atmospheric oxygen. Conclusions. The models suggest that the gas in the inner regions of disks around cooler stars is more carbon rich; however, calculations of the molecular emission are necessary to definitively confirm whether the chemical trends reproduce the observed trends. © ESO, 2015.

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