Showing papers by "Netherlands Institute for Space Research published in 2013"

The Hot and Energetic Universe: A White Paper presenting the science theme motivating the Athena+ mission

Abstract: This White Paper, submitted to the recent ESA call for science themes to define its future large missions, advocates the need for a transformational leap in our understanding of two key questions in astrophysics: 1) How does ordinary matter assemble into the large scale structures that we see today? 2) How do black holes grow and shape the Universe? Hot gas in clusters, groups and the intergalactic medium dominates the baryonic content of the local Universe. To understand the astrophysical processes responsible for the formation and assembly of these large structures, it is necessary to measure their physical properties and evolution. This requires spatially resolved X-ray spectroscopy with a factor 10 increase in both telescope throughput and spatial resolving power compared to currently planned facilities. Feedback from supermassive black holes is an essential ingredient in this process and in most galaxy evolution models, but it is not well understood. X-ray observations can uniquely reveal the mechanisms launching winds close to black holes and determine the coupling of the energy and matter flows on larger scales. Due to the effects of feedback, a complete understanding of galaxy evolution requires knowledge of the obscured growth of supermassive black holes through cosmic time, out to the redshifts where the first galaxies form. X-ray emission is the most reliable way to reveal accreting black holes, but deep survey speed must improve by a factor ~100 over current facilities to perform a full census into the early Universe. The Advanced Telescope for High Energy Astrophysics (Athena+) mission provides the necessary performance (e.g. angular resolution, spectral resolution, survey grasp) to address these questions and revolutionize our understanding of the Hot and Energetic Universe. These capabilities will also provide a powerful observatory to be used in all areas of astrophysics.

Detection of water absorption in the day side atmosphere of HD 189733 b using ground-based high-resolution spectroscopy at 3.2 μm

Abstract: We report a 4.8{$σ$} detection of water absorption features in the day side spectrum of the hot Jupiter HD 189733 b. We used high-resolution (R {\tilde} 100 000) spectra taken at 3.2 {$μ$}m with CRIRES on the VLT to trace the radial-velocity shift of the water features in the planet's day side atmosphere during 5 h of its 2.2 d orbit as it approached secondary eclipse. Despite considerable telluric contamination in this wavelength regime, we detect the signal within our uncertainties at the expected combination of systemic velocity (V\_sys=-3\^{}$\{$+5$\}$\_$\{$-6$\}$ km s$^{-1}$) and planet orbital velocity (K\_p=154\^{}$\{$+14$\}$\_$\{$-10$\}$ km s$^{-1}$), and determine a H$_{2}$O line contrast ratio of (1.3 {\plusmn} 0.2) {\times} 10$^{-3}$ with respect to the stellar continuum. We find no evidence of significant absorption or emission from other carbon-bearing molecules, such as methane, although we do note a marginal increase in the significance of our detection to 5.1{$σ$} with the inclusion of carbon dioxide in our template spectrum. This result demonstrates that ground-based, high-resolution spectroscopy is suited to finding not just simple molecules like CO, but also to more complex molecules like H$_{2}$O even in highly telluric contaminated regions of the Earth's transmission spectrum. It is a powerful tool that can be used for conducting an immediate census of the carbon- and oxygen-bearing molecules in the atmospheres of giant planets, and will potentially allow the formation and migration history of these planets to be constrained by the measurement of their atmospheric C/O ratios.

A Keplerian disk around a Class 0 source: ALMA observations of VLA1623A

Abstract: Context. Rotationally supported disks are critical in the star formation process. The questions of when they form and what factors influence or hinder their formation have been studied but are largely unanswered. Observations of early-stage YSOs are needed to probe disk formation. Aims: VLA1623 is a triple non-coeval protostellar system, with a weak magnetic field perpendicular to the outflow, whose Class 0 component, VLA1623A, shows a disk-like structure in continuum with signatures of rotation in line emission. We aim to determine whether this structure is in part or in whole a rotationally supported disk, i.e. a Keplerian disk, and what its characteristics are. Methods: ALMA Cycle 0 Early Science 1.3 mm continuum and C$^{18}$O (2-1) observations in the extended configuration are presented here and used to perform an analysis of the disk-like structure using position-velocity (PV) diagrams and thin disk modeling with the addition of foreground absorption. Results: The PV diagrams of the C$^{18}$O line emission suggest the presence of a rotationally supported component with a radius of at least 50 AU. Kinematical modeling of the line emission shows that the disk out to 180 AU is actually rotationally supported, with the rotation described well by Keplerian rotation out to at least 150 AU, and the central source mass is ~{}0.2 M$_{⊙}$ for an inclination of 55{deg}. Pure infall and conserved angular momentum rotation models are excluded. Conclusions: VLA1623A, a very young Class 0 source, presents a disk with an outer radius R$_{out}$ = 180 AU with a Keplerian velocity structure out to at least 150 AU. The weak magnetic fields and recent fragmentation in this region of {$ρ$} Ophiuchus may have played a leading role in the formation of the disk. Appendices are available in electronic form at http://www.aanda.org

Atmospheric CH4 in the first decade of the 21st century: Inverse modeling analysis using SCIAMACHY satellite retrievals and NOAA surface measurements

Abstract: The causes of renewed growth in the atmospheric CH4 burden since 2007 are still poorly understood and subject of intensive scientific discussion. We present a reanalysis of global CH4 emissions during the 2000s, based on the TM5-4DVAR inverse modeling system. The model is optimized using high-accuracy surface observations from NOAA ESRL's global air sampling network for 2000-2010 combined with retrievals of column-averaged CH4 mole fractions from SCIAMACHY onboard ENVISAT (starting 2003).Using climatological OH fields, derived global total emissions for 2007-2010 are 16-20 Tg CH 4/yr higher compared to 2003-2005. Most of the inferred emission increase was located in the tropics (9-14 Tg CH4/yr) and mid-latitudes of the northern hemisphere (6-8 Tg CH4/yr), while no significant trend was derived for Arctic latitudes. The atmospheric increase can be attributed mainly to increased anthropogenic emissions, but the derived trend is significantly smaller than estimated in the EDGARv4.2 emission inventory. Superimposed on the increasing trend in anthropogenic CH4 emissions are significant inter-annual variations (IAV) of emissions from wetlands (up to ±10 Tg CH4/yr), and biomass burning (up to ±7 Tg CH4/yr). Sensitivity experiments, which investigated the impact of the SCIAMACHY observations (versus inversions using only surface observations), of the OH fields used, and of a priori emission inventories, resulted in differences in the detailed latitudinal attribution of CH4 emissions, but the IAV and trends aggregated over larger latitude bands were reasonably robust. All sensitivity experiments show similar performance against independent shipboard and airborne observations used for validation, except over Amazonia where satellite retrievals improved agreement with observations in the free troposphere. Key Points A reanalysis of global CH4 emissions during the 2000s is presented derived global total emissions 2007-2010 16-20 Tg CH4/yr higher than 2003-2005 increase mainly in the tropics and NH mid-latitudes ©2013. American Geophysical Union. All Rights Reserved.

Detection of carbon monoxide in the high-resolution day-side spectrum of the exoplanet HD 189733b

Abstract: Context. After many attempts over more than a decade, high-resolution spectroscopy has recently delivered its first detections of molecular absorption in exoplanet atmospheres, both in transmission and thermal emission spectra. Targeting the combined signal from individual lines in molecular bands, these measurements use variations in the planet radial velocity to separate the planet signal from telluric and stellar contaminants. Aims: We apply high-resolution spectroscopy to probe molecular absorption in the day-side spectrum of the bright transiting hot Jupiter HD 189733b. Methods: We observed HD 189733b with the CRIRES high-resolution near-infrared spectograph on the Very Large Telescope during three nights, targeting possible absorption from carbon monoxide, water vapour, methane, and carbon dioxide, at 2.0 and 2.3 {$μ$}m. Results: We detect a 5-{$σ$} absorption signal from CO at a contrast level of ~{}4.5 { imes} 10$^{-4}$ with respect to the stellar continuum, revealing the planet orbital radial velocity at 154$^{+4}$$_{-3}$ km s$^{-1}$. This allows us to solve for the planet and stellar mass in a similar way as for stellar eclipsing binaries, resulting in 0.846$^{+0.068}$$_{-0.049}$M{sun} and M$_p$ = 1.162$^{+0.058}$$_{-0.039}$ M$^{Jup}$. No significant absorption is detected from H$_{2}$O, CO$_{2}$, or CH$_{4}$ and we determine upper limits on their line contrasts. Conclusions: The detection of CO in the day-side spectrum of HD 189733b can be made consistent with the haze layer proposed to explain the optical to near-infrared transmission spectrum if the layer is optically thin at the normal incidence angles probed by our observations, or if the CO abundance is high enough for the CO absorption to originate from above the haze. Our non-detection of CO$_{2}$ at 2.0 {$μ$}m is not inconsistent with the deep CO$_{2}$ absorption from low-resolution NICMOS secondary eclipse data in the same wavelength range. If genuine, the absorption would be so strong that it blanks out any planet light completely in this wavelength range, leaving no high-resolution signal to be measured. Based on observations collected at the European Southern Observatory (186.C-0289).

Global CO 2 fluxes estimated from GOSAT retrievals of total column CO 2

Abstract: . We present one of the first estimates of the global distribution of CO 2 surface fluxes using total column CO 2 measurements retrieved by the SRON-KIT RemoTeC algorithm from the Greenhouse gases Observing SATellite (GOSAT). We derive optimized fluxes from June 2009 to December 2010. We estimate fluxes from surface CO 2 measurements to use as baselines for comparing GOSAT data-derived fluxes. Assimilating only GOSAT data, we can reproduce the observed CO 2 time series at surface and TCCON sites in the tropics and the northern extra-tropics. In contrast, in the southern extra-tropics GOSAT X CO 2 leads to enhanced seasonal cycle amplitudes compared to independent measurements, and we identify it as the result of a land–sea bias in our GOSAT X CO 2 retrievals. A bias correction in the form of a global offset between GOSAT land and sea pixels in a joint inversion of satellite and surface measurements of CO 2 yields plausible global flux estimates which are more tightly constrained than in an inversion using surface CO 2 data alone. We show that assimilating the bias-corrected GOSAT data on top of surface CO 2 data (a) reduces the estimated global land sink of CO 2 , and (b) shifts the terrestrial net uptake of carbon from the tropics to the extra-tropics. It is concluded that while GOSAT total column CO 2 provide useful constraints for source–sink inversions, small spatiotemporal biases – beyond what can be detected using current validation techniques – have serious consequences for optimized fluxes, even aggregated over continental scales.

Identifying gaps in flaring Herbig Ae/Be disks using spatially resolved mid-infrared imaging - Are all group I disks transitional?

Abstract: Context. The evolution of young massive protoplanetary disks toward planetary systems is expected to correspond to structural changes in observational appearance, which includes the formation of gaps and the depletion of dust and gas. Aims. A special group of disks around Herbig Ae/Be stars do not show prominent silicate emission features, although they still bear signs of flaring disks, the presence of gas, and small grains. We focus our attention on four key Herbig Ae/Be stars to understand the structural properties responsible for the absence of silicate feature emission. Methods. We investigate Q- and N-band images taken with Subaru/COMICS, Gemini South/T-ReCS and VLT/VISIR. We perform radiative transfer modeling to examine the radial distribution of dust and PAHs. Our solutions require a separation of inner- and outerdisks by a large gap. From this we characterize the radial density structure of dust and PAHs in the disk. Results. The inner edge of the outer disk has a high surface brightness and a typical temperature between 100‐150 K and therefore dominates the emission in the Q-band. All four disks are characterized by large gaps. We derive radii of the inner edge of the outer disk of 34 +4 , 23 +3 , 30 +5 and 63 +4 AU for HD 97048, HD 169142, HD 135344 B and Oph IRS 48 respectively. For HD 97048 this is the first detection of a disk gap. The large gaps deplete the entire population of silicate particles with temperatures suitable for prominent midinfrared feature emission, while small carbonaceous grains and PAHs can still show prominent emission at mid-infrared wavelengths. The continuum emission in the N-band is not due to emission in the wings of PAHs. This continuum emission can be due to VSGs or to thermal emission from the inner disk. We find that PAH emission is not always dominated by PAHs on the surface of the outer disk. Conclusions. The absence of silicate emission features is due to the presence of large gaps in the critical temperature regime. Many, if not all Herbig disks with Spectral Energy Distribution (SED) classification ‘group I’ are disks with large gaps and can be characterized as (pre-) transitional. An evolutionary path from the observed group I to the observed group II sources seems no longer likely. Instead, both might derive from a common ancestor.

Decadal record of satellite carbon monoxide observations

Abstract: . Atmospheric carbon monoxide (CO) distributions are controlled by anthropogenic emissions, biomass burning, transport and oxidation by reaction with the hydroxyl radical (OH). Quantifying trends in CO is therefore important for understanding changes related to all of these contributions. Here we present a comprehensive record of satellite observations from 2000 through 2011 of total column CO using the available measurements from nadir-viewing thermal infrared instruments: MOPITT, AIRS, TES and IASI. We examine trends for CO in the Northern and Southern Hemispheres along with regional trends for Eastern China, Eastern USA, Europe and India. We find that all the satellite observations are consistent with a modest decreasing trend ~ −1 % yr −1 in total column CO over the Northern Hemisphere for this time period and a less significant, but still decreasing trend in the Southern Hemisphere. Although decreasing trends in the United States and Europe have been observed from surface CO measurements, we also find a decrease in CO over E. China that, to our knowledge, has not been reported previously. Some of the interannual variability in the observations can be explained by global fire emissions, but the overall decrease needs further study to understand the implications for changes in anthropogenic emissions.

Water in star-forming regions with Herschel (WISH) - III. Far-infrared cooling lines in low-mass young stellar objects

Abstract: Context. Understanding the physical phenomena involved in the earlierst stages of protostellar evolution requires knowledge of the heating and cooling processes that occur in the surroundings of a young stellar object. Spatially resolved information from its constituent gas and dust provides the necessary constraints to distinguish between different theories of accretion energy dissipation into the envelope. Aims. Our aims are to quantify the far-infrared line emission from low-mass protostars and the contribution of different atomic and molecular species to the gas cooling budget, to determine the spatial extent of the emission, and to investigate the underlying excitation conditions. Analysis of the line cooling will help us characterize the evolution of the relevant physical processes as the protostar ages. Methods. Far-infrared Herschel-PACS spectra of 18 low-mass protostars of various luminosities and evolutionary stages are studied in the context of the WISH key program. For most targets, the spectra include many wavelength intervals selected to cover specific CO, H2O, OH, and atomic lines. For four targets the spectra span the entire 55-200 mu m region. The PACS field-of-view covers similar to 47 '' with the resolution of 9.4 ''. Results. Most of the protostars in our sample show strong atomic and molecular far-infrared emission. Water is detected in 17 out of 18 objects (except TMC1A), including 5 Class I sources. The high-excitation H2O 8(18)-7(07) 63.3 mu m line (E-u/k(B) = 1071 K) is detected in 7 sources. CO transitions from J = 14-13 up to J = 49-48 are found and show two distinct temperature components on Boltzmann diagrams with rotational temperatures of similar to 350 K and similar to 700 K. H2O has typical excitation temperatures of similar to 150 K. Emission from both Class 0 and I sources is usually spatially extended along the outflow direction but with a pattern that depends on the species and the transition. In the extended sources, emission is stronger off source and extended on >= 10 000 AU scales; in the compact sample, more than half of the flux originates within 1000 AU of the protostar. The H2O line fluxes correlate strongly with those of the high-J CO lines, both for the full array and for the central position, as well as with the bolometric luminosity and envelope mass. They correlate less strongly with OH fluxes and not with [O I] fluxes. In contrast, [O I] and OH often peak together at the central position. Conclusions. The PACS data probe at least two physical components. The H2O and CO emission very likely arises in non-dissociative (irradiated) shocks along the outflow walls with a range of pre-shock densities. Some OH is also associated with this component, most likely resulting from H2O photodissociation. UV-heated gas contributes only a minor fraction to the CO emission observed by PACS, based on the strong correlation between the shock-dominated CO 24-23 line and the CO 14-13 line. [O I] and some of the OH emission probe dissociative shocks in the inner envelope. The total far-infrared cooling is dominated by H2O and CO, with the fraction contributed by [O I] increasing for Class I sources. Consistent with previous studies, the ratio of total far-infrared line emission over bolometric luminosity decreases with the evolutionary state.

Initial deep LOFAR observations of epoch of reionization windows. I. The north celestial pole

Abstract: The aim of the LOFAR Epoch of Reionization (EoR) project is to detect the spectral fluctuations of the redshifted HI 21cm signal. This signal is weaker by several orders of magnitude than the astrophysical foreground signals and hence, in order to achieve this, very long integrations, accurate calibration for stations and ionosphere and reliable foreground removal are essential. One of the prospective observing windows for the LOFAR EoR project will be centered at the North Celestial Pole (NCP). We present results from observations of the NCP window using the LOFAR highband antenna (HBA) array in the frequency range 115 MHz to 163 MHz. The data were obtained in April 2011 during the commissioning phase of LOFAR. We used baselines up to about 30 km. With about 3 nights, of 6 hours each, effective integration we have achieved a noise level of about 100 microJy/PSF in the NCP window. Close to the NCP, the noise level increases to about 180 microJy/PSF, mainly due to additional contamination from unsubtracted nearby sources. We estimate that in our best night, we have reached a noise level only a factor of 1.4 above the thermal limit set by the noise from our Galaxy and the receivers. Our continuum images are several times deeper than have been achieved previously using the WSRT and GMRT arrays. We derive an analytical explanation for the excess noise that we believe to be mainly due to sources at large angular separation from the NCP.

Synchronous X-ray and Radio Mode Switches: a Rapid Global Transformation of the Pulsar Magnetosphere

Abstract: Pulsars emit from low-frequency radio waves up to high-energy gamma-rays, generated anywhere from the stellar surface out to the edge of the magnetosphere. Detecting correlated mode changes across the electromagnetic spectrum is therefore key to understanding the physical relationship among the emission sites. Through simultaneous observations, we detected synchronous switching in the radio and x-ray emission properties of PSR B0943+10. When the pulsar is in a sustained radio-"bright" mode, the x-rays show only an unpulsed, nonthermal component. Conversely, when the pulsar is in a radio-"quiet" mode, the x-ray luminosity more than doubles and a 100% pulsed thermal component is observed along with the nonthermal component. This indicates rapid, global changes to the conditions in the magnetosphere, which challenge all proposed pulsar emission theories.

Flux calibration of the Herschel-SPIRE photometer

Abstract: We describe the procedure used to flux calibrate the three-band submillimetre photometer in the Spectral and Photometric Imaging Receiver instrument on the Herschel Space Observatory. This includes the equations describing the calibration scheme, a justification for using Neptune as the primary calibration source, a description of the observations and data processing procedures used to derive flux calibration parameters (for converting from voltage to flux density) for every bolometer in each array, an analysis of the error budget in the flux calibration for the individual bolometers and tests of the flux calibration on observations of primary and secondary calibrators. The procedure for deriving the flux calibration parameters is divided into two parts. In the first part, we use observations of astronomical sources in conjunction with the operation of the photometer internal calibration source to derive the unscaled derivatives of the flux calibration curves. To scale the calibration curves in Jy beam−1 V−1, we then use observations of Neptune in which the beam of each bolometer is mapped using a very fine scan pattern. The total instrumental uncertainties in the flux calibration for most individual bolometers is ∼0.5 per cent, although a few bolometers have uncertainties of ∼1–5 per cent because of issues with the Neptune observations. Based on application of the flux calibration parameters to Neptune observations performed using typical scan map observing modes, we determined that measurements from each array as a whole have instrumental uncertainties of 1.5 per cent. This is considerably less than the absolute calibration uncertainty associated with the model of Neptune, which is estimated at 4 per cent.

The x-ray spectral evolution of galactic black hole x-ray binaries toward quiescence

Abstract: Most transient black hole X-ray binaries (BHXBs) spend the bulk of their time in a quiescent state, where they accrete matter from their companion star at highly sub-Eddington luminosities (we define quiescence here as a normalized Eddington ratio lx = L 0.5-10 keV/L Edd < 10–5). Here, we present Chandra X-ray imaging spectroscopy for three BHXB systems (H 1743–322, MAXI J1659–152, and XTE J1752–223) as they fade into quiescence following an outburst. Multiple X-ray observations were taken within one month of each other, allowing us to track each individual system's X-ray spectral evolution during its decay. We compare these three systems to other BHXB systems. We confirm that quiescent BHXBs have softer X-ray spectra than low-hard-state BHXBs, and that quiescent BHXB spectral properties show no dependence on the binary system's orbital parameters. However, the observed anti-correlation between X-ray photon index (Γ) and lx in the low-hard state does not continue once a BHXB enters quiescence. Instead, Γ plateaus to an average Γ = 2.08 ± 0.07 by the time lx reaches ~10–5. lx ~ 10–5 is thus an observationally motivated upper limit for the beginning of the quiescent spectral state. Our results are discussed in the context of different accretion flow models and across the black hole mass scale.

The outburst decay of the low magnetic field magnetar sgr 0418+5729

Abstract: N.R. is supported by a Ramon y Cajal Research Fellowship, and by grants AYA2009-07391, AYA2012-39303, SGR2009-811, TW2010005, and iLINK 2011-0303. J.A.P. and D.V. acknowledge support from the grants AYA 2010-21097-C03-02 and Prometeo/2009/103. R.T. and S.M. are partially funded through an INAF 2011 PRIN grant. A.P. is supported by a JAE-Doc CSIC fellowship co-funded with the European Social Fund under the program “Junta para la Ampliacion de Estudios,” by the Spanish MICINN grant AYA2011-30228-C03-02 (co-funded with FEDER funds), and by the AGAUR grant 2009SGR1172 (Catalonia).

ALMA imaging of the CO snowline of the HD 163296 disk with DCO

Abstract: Context. The high spatial resolution and line sensitivity of the Atacama Large Millimeter/submillimeter Array (ALMA) opens the possibility of resolving emission from molecules in large samples of circumstellar disks. With an understanding of the conditions under which these molecules can have high abundance, they can be used as direct tracers of distinct physical regions. In particular, DCO+ is expected to have an enhanced abundance within a few Kelvin of the CO freezeout temperature of 19 K, making it a useful probe of the cold disk midplane. Aims. We aim to use line emission from DCO+ to directly resolve the CO "snowline" - the region at which the gas-phase CO abundance drops due to freezeout - and determine the temperature boundaries of the region of DCO+ emission in the HD 163296 disk. This will serve as a test of deuteration models based on enhanced formation of the parent molecule H2D+ and a direct probe of midplane disk structure and ionization. Methods. We compare ALMA line observations of HD 163296 to a grid of models based on the best fit physical model of Qi et al. (2011, ApJ, 740, 84). We vary the upper-and lower-limit temperatures of the region in which DCO+ is present as well as the abundance of DCO+ in order to fit channel maps of the DCO+ J = 5-4 line. To determine the abundance enhancement compared to the general interstellar medium, we carry out similar fitting to HCO+ J = 4-3 and (HCO+)-C-13 J = 4-3 observations. Results. ALMA images show centrally peaked extended emission from HCO+ and (HCO+)-C-13. DCO+ emission lies in a resolved ring from similar to 110 to 160 AU. The outer radius approximately corresponds to the size of the CO snowline as measured by previous lower resolution observations of CO lines in this disk. The ALMA DCO+ data now resolve and image the CO snowline directly. Conclusions. In the best fitting models, HCO+ exists in a region extending from the 19 K isotherm to the photodissociation layer with an abundance of 3 x 10(-10) relative to H-2. DCO+ exists within the 19-21 K region of the disk with an abundance ratio [DCO+]/[HCO+] = 0.3. This represents a factor of 10(4) enhancement of the DCO+ abundance within this narrow region of the HD 163296 disk. Such a high enhancement has only previously been seen in prestellar cores. The inferred abundances provide a lower limit to the ionization fraction in the midplane of the cold outer disk (greater than or similar to 4 x 10(-10)), and suggest the utility of DCO+ as a tracer of its parent molecule H2D+.

Systematic X-Ray Analysis of Radio Relic Clusters with Suzaku

Abstract: We undertook a systematic X-ray analysis of six giant radio relics in four clusters of galaxies using the Suzaku satellite. The sample included CIZA2242.8+5301, Zwcl 2341.1 0000, the South-East part of A 3667 and previously published results of the North-West part of A 3667 and A 3376. Especially, we first observed the narrow (50 kpc) relic of CIZA2242.8+5301 by the Suzaku satellite, which enabled us to reduce the projection effect. We report on X-ray detections of shocks at the positions of the relics in CIZA2242.8+5301 and A 3667 SE. At the positions of the two relics in ZWCL2341.1 0000, we did not detect shocks. From spectroscopic temperature profiles across the relic, we found that the temperature profiles exhibit significant jumps across the relics for CIZA2242.8+5301, A 3376, A 3667NW, and A 3667 SE. We estimated the Mach number from the X-ray temperature or pressure profile using the Rankine-Hugoniot jump condition, and compared it with the Mach number derived from the radio spectral index. The resulting Mach numbers (M = 1.5–3) are almost consistent with each other, while the Mach number of CIZA2242.8+5301, derived from the X-ray data, tends to be lower than that of the radio observation. These results indicate that the giant radio relics in merging clusters are related to the shock structure, as suggested by previous studies of individual clusters.

Alignment between flattened protostellar infall envelopes and ambient magnetic fields

Abstract: We present 350 μm polarization observations of four low-mass cores containing Class 0 protostars: L483, L1157, L1448-IRS2, and Serp-FIR1. This is the second paper in a larger survey aimed at testing magnetically regulated models for core-collapse. One key prediction of these models is that the mean magnetic field in a core should be aligned with the symmetry axis (minor axis) of the flattened young stellar object inner envelope (aka pseudodisk). Furthermore, the field should exhibit a pinched or hourglass-shaped morphology as gravity drags the field inward toward the central protostar. We combine our results for the four cores with results for three similar cores that were published in the first paper from our survey. An analysis of the 350 μm polarization data for the seven cores yields evidence of a positive correlation between mean field direction and pseudodisk symmetry axis. Our rough estimate for the probability of obtaining by pure chance a correlation as strong as the one we found is about 5%. In addition, we combine together data for multiple cores to create a source-averaged magnetic field map having improved signal-to-noise ratio, and this map shows good agreement between mean field direction and pseudodisk axis (they are within 15°). We also see hints of a magnetic pinch in the source-averaged map. We conclude that core-scale magnetic fields appear to be strong enough to guide gas infall, as predicted by the magnetically regulated models. Finally, we find evidence of a positive correlation between core magnetic field direction and bipolar outflow axis.

DETECTION OF MOLECULAR ABSORPTION IN THE DAYSIDE OF EXOPLANET 51 PEGASI b

Abstract: In this paper, we present ground-based high-resolution spectroscopy of 51 Pegasi using CRIRES at the Very Large Telescope. The system was observed for 3 { imes} 5 hr at 2.3 {$μ$}m at a spectral resolution of R = 100,000, targeting potential signatures from carbon monoxide, water vapor, and methane in the planet's dayside spectrum. In the first 2 { imes} 5 hr of data, we find a combined signal from carbon monoxide and water in absorption at a formal 5.9{$σ$} confidence level, indicating a non-inverted atmosphere. We derive a planet mass of M $_P$ = (0.46 {plusmn} 0.02)M $_{Jup}$ and an orbital inclination i between 79.{deg}6 and 82.{deg}2, with the upper limit set by the non-detection of the planet transit in previous photometric monitoring. However, there is no trace of the signal in the final five hours of data. A statistical analysis indicates that the signal from the first two nights is robust, but we find no compelling explanation for its absence in the final night. The latter suffers from stronger noise residuals and greater instrumental instability than the first two nights, but these cannot fully account for the missing signal. It is possible that the integrated dayside emission from 51 Peg b is instead strongly affected by weather. However, more data are required before we can claim any time variability in the planet's atmosphere.

Detecting cosmic rays with the LOFAR radio telescope

Abstract: The low frequency array (LOFAR), is the first radio telescope designed with the capability to measure radio emission from cosmic-ray induced air showers in parallel with interferometric observations. In the first ~2 years of observing, 405 cosmic-ray events in the energy range of 1016−1018 eV have been detected in the band from 30−80 MHz. Each of these air showers is registered with up to ~1000 independent antennas resulting in measurements of the radio emission with unprecedented detail. This article describes the dataset, as well as the analysis pipeline, and serves as a reference for future papers based on these data. All steps necessary to achieve a full reconstruction of the electric field at every antenna position are explained, including removal of radio frequency interference, correcting for the antenna response and identification of the pulsed signal.

Calibrating high-precision Faraday rotation measurements for LOFAR and the next generation of low-frequency radio telescopes

Abstract: Faraday rotation measurements using the current and next generation of low-frequency radio telescopes will provide a powerful probe of astronomical magnetic fields. However, achieving the full potential of these measurements requires accurate removal of the time-variable ionospheric Faraday rotation contribution. We present ionFR, a code that calculates the amount of ionospheric Faraday rotation for a specific epoch, geographic location, and line-of-sight. ionFR uses a number of publicly available, GPS-derived total electron content maps and the most recent release of the International Geomagnetic Reference Field. We describe applications of this code for the calibration of radio polarimetric observations, and demonstrate the high accuracy of its modeled ionospheric Faraday rotations using LOFAR pulsar observations. These show that we can accurately determine some of the highest-precision pulsar rotation measures ever achieved. Precision rotation measures can be used to monitor rotation measure variations - either intrinsic or due to the changing line-of-sight through the interstellar medium. This calibration is particularly important for nearby sources, where the ionosphere can contribute a significant fraction of the observed rotation measure. We also discuss planned improvements to ionFR, as well as the importance of ionospheric Faraday rotation calibration for the emerging generation of low-frequency radio telescopes, such as the SKA and its pathfinders.

Resolved Imaging of the HR?8799 Debris Disk with Herschel

Abstract: We present Herschel far-infrared and submillimeter maps of the debris disk associated with the HR 8799 planetary system. We resolve the outer disk emission at 70, 100, 160 and 250 µm and detect the disk at 350 and 500 µm. A smooth model explains the observed disk emission well. We observe no obvious clumps or asymmetries associated with the trapping of planetesimals that is a potential consequence of planetary migration in the system. We estimate that the disk eccentricity must be < 0.1. As in previous work by Su et al. (2009), we find a disk with three components: a warm inner component and two outer components, a planetesimal belt extending from 100 - 310 AU, with some flexibility (±10 AU) on the inner edge, and the external halo which extends to � 2000 AU. We measure the disk inclination to be 26 ± 3 ◦ from face-on at a position angle of 64 ◦ E of N, establishing that the disk is coplanar with the star and planets. The SED of the disk is well fit by blackbody grains whose semi-major axes lie within the planetesimal belt, suggesting an absence of small grains. The wavelength at which the spectrum steepens from blackbody, 47± 30 µm, however, is short compared to other A star debris disks, suggesting that there are atypically small grains likely populating the halo. The PACS longer wavelength data yield a lower disk color temperature than do MIPS data (24 and 70 µm), implying two distinct halo dust grain populations.

Multiwavelength campaign on Mrk 509 - XII. Broad band spectral analysis

Abstract: The origin of the different spectral components present in the high-energy (UV to X-rays/gamma-rays) spectra of Seyfert galaxies is still being debated a lot. One of the major limitations, in this respect, is the lack of really simultaneous broad-band observations that allow us to disentangle the behavior of each component and to better constrain their interconnections. The simultaneous UV to X-rays/gamma rays data obtained during the multiwavelength campaign on the bright Seyfert 1 Mrk 509 are used in this paper and tested against physically motivated broad band models. Mrk 509 was observed by XMM-Newton and INTEGRAL in October/November 2009, with one observation every four days for a total of ten observations. Each observation has been fitted with a realistic thermal Comptonization model for the continuum emission. Prompted by the correlation between the UV and soft X-ray flux, we used a thermal Comptonization component for the soft X-ray excess. We also included a warm absorber and a reflection component, as required by the precise studies previously done by our consortium. The UV to X-ray/gamma-ray emission of Mrk 509 can be well fitted by these components. The presence of a relatively hard high-energy spectrum points to the existence of a hot (kT ∼ 100 keV), optically-thin (τ ∼ 0.5) corona producing the primary continuum. In contrast, the soft X-ray component requires a warm (kT ∼ 1 keV), optically-thick (τ ∼ 10−20) plasma. Estimates of the amplification ratio for this warm plasma support a configuration relatively close to the “theoretical” configuration of a slab corona above a passive disk. An interesting consequence is the weak luminosity-dependence of its emission, which is a possible explanation of the roughly constant spectral shape of the soft X-ray excess seen in AGNs. The temperature (∼ 3e V) and fl ux of the soft-photon field entering and cooling the warm plasma suggests that it covers the accretion disk down to a transition radius Rin of 10−20 Rg. This plasma could be the warm upper layer of the accretion disk. In contrast, the hot corona has a more photon-starved geometry. The high temperature (∼100 eV) of the soft-photon field entering and cooling it favors a localization of the hot corona in the inner flow. This soft-photon field could be part of the comptonized emission produced by the warm plasma. In this framework, the change in the geometry (i.e. Rin) could explain most of the observed flux and spectral variability.

A candidate circumbinary Keplerian disk in G35.20-0.74 N: A study with ALMA

Abstract: We report on ALMA observations of continuum and molecular line emission with 0 ''4 resolution towards the high-mass star-forming region G3520-074 N Two dense cores are detected in typical hot-core tracers (e g, CH3CN) that reveal velocity gradients In one of these cores, the velocity field can be fitted with an almost edge-on Keplerian disk rotating about a central mass of similar to 18 M-circle dot This finding is consistent with the results of a recent study of the CO first overtone bandhead emission at 23 mu m towards G3520-074 N The disk radius and mass are greater than or similar to 2500 au and similar to 3 M-circle dot To reconcile the observed bolometric luminosity (similar to 3x10(4) L-circle dot) with the estimated stellar mass of 18 M-circle dot, we propose that the latter is the total mass of a binary system

Herschel/HIFI observations of [C II] and [13C II] in photon-dominated regions

Abstract: Context. Chemical fractionation reactions in the interstellar medium can result in molecular isotopologue abundance ratios that differ by many orders of magnitude from the isotopic abundance ratios. Understanding variations in the molecular abundance ratios through astronomical observations provides a new tool to sensitively probe the underlying physical conditions. Aims. Recently, we have introduced detailed isotopic chemistry into the KOSMA-τ model for photon-dominated regions (PDRs), which allows calculating abundances of carbon isotopologues as a function of PDR parameters. Radiative transfer computations then allow to predict the observed [C II]/[^(13)C II] line intensity ratio for specific geometries. Here, we compare these model predictions with new Herschel observations. Methods. We performed Herschel/HIFI observations of the [C II] 158 μm line in a number of PDRs. In all sources, we observed at least two hyperfine components of the [^(13)C II] transition, allowing determination of the [C II]/[^(13)C II] intensity ratio, using revised intrinsic hyperfine ratios. Comparing the observed line ratios with the predictions from the updated KOSMA-τ model, we identify conditions under which the chemical fractionation effects are important, and not masked by the high optical depth of the main isotopic line. Results. An observable enhancement of the [C II]/[^(13)C II] intensity ratio due to chemical fractionation depends mostly on the source geometry and velocity structure, and to a lesser extent on the gas density and radiation field strength. The enhancement is expected to be largest for PDR layers that are somewhat shielded from UV radiation, but not completely hidden behind a surface layer of optically thick [C II]. In our observations the [C II]/[^(13)C II] integrated line intensity ratio is always dominated by the optical depth of the main isotopic line. However, an enhanced intensity ratio is found for particular velocity components in several sources: in the red-shifted material in the ultracompact H II region Mon R2, in the wings of the turbulent line profile in the Orion Bar, and possibly in the blue wing in NGC 7023. Mapping of the [^(13)C II] lines in the Orion Bar gives a C^+ column density map, which confirms the temperature stratification of the C^+ layer, in agreement with the PDR models of this region. Conclusions. Carbon fractionation can be significant even in relatively warm PDRs, but a resulting enhanced [C II]/[^(13)C II] intensity ratio is only observable for special configurations. In most cases, a reduced [C II]/[^(13)C II] intensity ratio can be used instead to derive the [C II] optical depth, leading to reliable column density estimates that can be compared with PDR model predictions. The C^+ column densities show that, for all sources, at the position of the [C II] peak emission, the dominant fraction of the gas-phase carbon is in the form of C^+.

The BETHY/JSBACH Carbon Cycle Data Assimilation System: experiences and challenges

Abstract: We present the concept of the Carbon Cycle Data Assimilation System and describe its evolution over the last two decades from an assimilation system around a simple diagnostic model of the terrestrial biosphere to a system for the calibration and initialization of the land component of a comprehensive Earth system model. We critically review the capability of this modeling framework to integrate multiple data streams, to assess their mutual consistency and with the model, to reduce uncertainties in the simulation of the terrestrial carbon cycle, to provide, in a traceable manner, reanalysis products with documented uncertainty, and to assist the design of the observational network. We highlight some of the challenges we met and experience we gained, give recommendations for operating the system, and suggest directions for future development. (Less)

The chemistry of ions in the Orion Bar I. - CH + , SH + , and CF + . The effect of high electron density and vibrationally excited H 2 in a warm PDR surface

Abstract: Context. The abundances of interstellar CH+ and SH+ are not well understood as their most likely formation channels are highly endothermic. Several mechanisms have been proposed to overcome the high activation barriers, including shocks, turbulence, and H-2 vibrational excitation. Aims. Using data from the Herschel Space Observatory, we studied the formation of ions, in particular CH+ and SH+ in a typical high UV-illumination warm and dense photon-dominated region (PDR), the Orion Bar. Methods. The HIFI instrument on board Herschel provides velocity-resolved line profiles of CH+ 1-0 and 2-1 and three hyperfine transitions of SH+ 1(2)-0(1). The PACS instrument provides information on the excitation and spatial distribution of CH+ by extending the observed CH+ transitions up to J = 6-5. We compared the observed line intensities to the predictions of radiative transfer and PDR codes. Results. All CH+, SH+, and CF+ lines analyzed in this paper are seen in emission. The widths of the CH+ 2-1 and 1-0 transitions are of similar to 5 kms(-1), significantly broader than the typical width of dense gas tracers in the Orion Bar (similar to 2-3 km s(-1)) and are comparable to the width of species that trace the interclump medium such as C+ and HF. The detected SH+ transitions are narrower compared to CH+ and have line widths of similar to 3 kms(-1), indicating that SH+ emission mainly originates in denser condensations. Non-LTE radiative transfer models show that electron collisions affect the excitation of CH+ and SH+ and that reactive collisions need to be taken into account to calculate the excitation of CH+. Comparison to PDR models shows that CH+ and SH+ are tracers of the warm surface region (A(V) < 1.5) of the PDR with temperatures between 500 and 1000 K. We have also detected the 5-4 transition of CF+ at a width of similar to 1.9 kms(-1), consistent with the width of dense gas tracers. The intensity of the CF+ 5-4 transition is consistent with previous observations of lower-J transitions toward the Orion Bar. Conclusions. An analytic approximation and a numerical comparison to PDR models indicate that the internal vibrational energy of H-2 can explain the formation of CH+ for typical physical conditions in the Orion Bar near the ionization front. The formation of SH+ is also likely to be explained by H-2 vibrational excitation. The abundance ratios of CH+ and SH+ trace the destruction paths of these ions, and indirectly, the ratios of H, H-2, and electron abundances as a function of depth into the cloud.

Interstellar medium composition through X-ray spectroscopy of low-mass X-ray binaries

Abstract: Context. The diffuse interstellar medium (ISM) is an integral part of the evolution of the entire Galaxy. Metals are produced by stars and their abundances are the direct testimony of the history of stellar evolution. However, the interstellar dust composition is not well known and the total abundances are yet to be accurately determined.Aims. We probe ISM dust composition, total abundances, and abundance gradients through the study of interstellar absorption features in the high-resolution X-ray spectra of Galactic low-mass X-ray binaries (LMXBs).Methods. We used high-quality grating spectra of nine LMXBs taken with XMM-Newton . We measured the column densities of O, Ne, Mg, and Fe with an empirical model and estimated the Galactic abundance gradients.Results. The column densities of the neutral gas species are in agreement with those found in the literature. Solids are a significant reservoir of metals like oxygen and iron. Respectively, 15–25% and 65–90% of the total amount of O i and Fe i is found in dust. The dust amount and mixture seem to be consistent along all the lines-of-sight (LOS). Our estimates of abundance gradients and predictions of local interstellar abundances are in agreement with those measured at longer wavelengths.Conclusions. Our work shows that X-ray spectroscopy is a very powerful method to probe the ISM. For instance, on a large scale the ISM appears to be chemically homogeneous showing similar gas ionization ratios and dust mixtures. The agreement between the abundances of the ISM and the stellar objects suggests that the local Galaxy is also chemically homogeneous.

Impact of aerosol and thin cirrus on retrieving and validating XCO2 from GOSAT shortwave infrared measurements

Abstract: [1] Inadequate treatment of aerosol scattering can be a significant source of error when retrieving column-averaged dry-air mole fractions of CO2 (XCO2) from space-based measurements of backscattered solar shortwave radiation. We have developed a retrieval algorithm, RemoTeC, that retrieves three aerosol parameters (amount, size, and height) simultaneously with XCO2. Here we evaluate the ability of RemoTeC to account for light path modifications by clouds, subvisual cirrus, and aerosols when retrieving XCO2 from Greenhouse Gases Observing Satellite (GOSAT) Thermal and Near-infrared Sensor for carbon Observation (TANSO)-Fourier Transform Spectrometer (FTS) measurements. We first evaluate a cloud filter based on measurements from the Cloud and Aerosol Imager and a cirrus filter that uses radiances measured by TANSO-FTS in the 2 micron spectral region, with strong water absorption. For the cloud-screened scenes, we then evaluate errors due to aerosols. We find that RemoTeC is well capable of accounting for scattering by aerosols for values of aerosol optical thickness at 750 nm up to 0.25. While no significant correlation of errors is found with albedo, correlations are found with retrieved aerosol parameters. To further improve the XCO2 accuracy, we propose and evaluate a bias correction scheme. Measurements from 12 ground-based stations of the Total Carbon Column Observing Network (TCCON) are used as a reference in this study. We show that spatial colocation criteria may be relaxed using additional constraints based on modeled XCO2 gradients, to increase the size and diversity of validation data and provide a more robust evaluation of GOSAT retrievals. Global-scale validation of satellite data remains challenging and would be improved by increasing TCCON coverage.

MILLIMETER EMISSION STRUCTURE IN THE FIRST ALMA IMAGE OF THE AU Mic DEBRIS DISK

Abstract: We present 1.3 mm ALMA Cycle 0 observations of the edge-on debris disk around the nearby, similar to 10 Myr old, M-type star AU Mic. These observations obtain 0 ''.6 (6 AU) resolution and reveal two distinct emission components: (1) the previously known dust belt that extends to a radius of 40 AU and (2) a newly recognized central peak that remains unresolved. The cold dust belt of mass similar to 1 M-Moon is resolved in the radial direction with a rising emission profile that peaks sharply at the location of the outer edge of the "birth ring" of planetesimals hypothesized to explain the midplane scattered light gradients. No significant asymmetries are discerned in the structure or position of this dust belt. The central peak identified in the ALMA image is similar to 6 times brighter than the stellar photosphere, which indicates an additional emission process in the inner regions of the system. Emission from a stellar corona or activity may contribute, but the observations show no signs of temporal variations characteristic of radio-wave flares. We suggest that this central component may be dominated by dust emission from an inner planetesimal belt of mass similar to 0.01 M-Moon, consistent with a lack of emission shortward of 25 mu m and a location less than or similar to 3 AU from the star. Future millimeter observations can test this assertion, as an inner dust belt should be readily separated from the central star at higher angular resolution.

A recent accretion burst in the low-mass protostar iras 15398-3359: alma imaging of its related chemistry

Abstract: Low-mass protostars have been suggested to show highly variable accretion rates throughout their evolution. Such changes in accretion, and related heating of their ambient envelopes, may trigger significant chemical variations on different spatial scales and from source-to-source. We present images of emission from C17O, H13CO+, CH3OH, C34S and C2H toward the low-mass protostar IRAS 15398-3359 on 0.''5 (75 AU diameter) scales with the Atacama Large Millimeter/submillimeter Array at 340 GHz. The resolved images show that the emission from H13CO+ is only present in a ring-like structure with a radius of about 1-1.''5 (150-200 AU) whereas the CO and other high dipole moment molecules are centrally condensed toward the location of the central protostar. We propose that HCO+ is destroyed by water vapor present on small scales. The origin of this water vapor is likely an accretion burst during the last 100-1000 yr increasing the luminosity of IRAS 15398-3359 by a factor of 100 above its current luminosity. Such a burst in luminosity can also explain the centrally condensed CH3OH and extended warm carbon-chain chemistry observed in this source and furthermore be reflected in the relative faintness of its compact continuum emission compared to other protostars.