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Showing papers in "Astronomy and Astrophysics in 2011"


Journal ArticleDOI
TL;DR: In this paper, the authors examined the infrared (IR) 3-500μm spectral energy distributions (SEDs) of galaxies at 0 < z < 2.5, supplemented by a local reference sample from IRAS, ISO, Spitzer, and AKARI data.
Abstract: We present the deepest 100 to 500 μm far-infrared observations obtained with the Herschel Space Observatory as part of the GOODS-Herschel key program, and examine the infrared (IR) 3–500 μm spectral energy distributions (SEDs) of galaxies at 0 < z < 2.5, supplemented by a local reference sample from IRAS, ISO, Spitzer, and AKARI data. We determine the projected star formation densities of local galaxies from their radio and mid-IR continuum sizes. We find that the ratio of total IR luminosity to rest-frame 8 μm luminosity, IR8 (≡ L_(IR)^(tot)/L_8), follows a Gaussian distribution centered on IR8 = 4 (σ = 1.6) and defines an IR main sequence for star-forming galaxies independent of redshift and luminosity. Outliers from this main sequence produce a tail skewed toward higher values of IR8. This minority population ( 3 × 10^(10) L_⊙ kpc^(-2)) and a high specific star formation rate (i.e., starbursts). The rest-frame, UV-2700 A size of these distant starbursts is typically half that of main sequence galaxies, supporting the correlation between star formation density and starburst activity that is measured for the local sample. Locally, luminous and ultraluminous IR galaxies, (U)LIRGs (L_(IR)^(tot)≥ 10^(11) L_☉), are systematically in the starburst mode, whereas most distant (U)LIRGs form stars in the “normal” main sequence mode. This confusion between two modes of star formation is the cause of the so-called “mid-IR excess” population of galaxies found at z > 1.5 by previous studies. Main sequence galaxies have strong polycyclic aromatic hydrocarbon (PAH) emission line features, a broad far-IR bump resulting from a combination of dust temperatures (T_(dust) ~ 15–50 K), and an effective T_(dust) ~ 31 K, as derived from the peak wavelength of their infrared SED. Galaxies in the starburst regime instead exhibit weak PAH equivalent widths and a sharper far-IR bump with an effective T_(dust)~ 40 K. Finally, we present evidence that the mid-to-far IR emission of X-ray active galactic nuclei (AGN) is predominantly produced by star formation and that candidate dusty AGNs with a power-law emission in the mid-IR systematically occur in compact, dusty starbursts. After correcting for the effect of starbursts on IR8, we identify new candidates for extremely obscured AGNs.

1,235 citations


Journal ArticleDOI
TL;DR: In this article, a more general differential equation was used, which now takes into account local gravity variations and the effects of convection, which turn out to be very significant for cool stars.
Abstract: Aims The complex physics of close binary stars is made even more challenging by the proximity effects that affect it Understanding the influence of these proximity effects is one of the most important tasks in theoretical stellar astrophysics It is crucial to know how the specific intensity is distributed over the stellar disk for a correct modelling of the light curves of eclipsing binaries and planetary transits To provide theoretical input for light curve modelling codes, we present new calculations of gravity- and limb-darkening coefficients for a wide range of effective temperatures, gravities, metallicities, and microturbulent velocities Methods We computed limb-darkening coefficients for several atmosphere models, which cover the transmission curves of the Kepler , CoRoT, and Spitzer space missions as well as more widely used passbands (Stromgren, Johnson-Cousins, Sloan) In addition to these computations, which were made adopting the least-square method, we also performed calculations for the bi-parametric approximations by adopting the flux conservation method to provide users with an additional tool to estimate the theoretical error bars To facilitate the modelling of the effects of tidal and rotational distortions, we computed the gravity-darkening coefficients y (λ ) using the same models of stellar atmospheres as for the limb-darkening Compared to previous work, a more general differential equation was used, which now takes into account local gravity variations and the effects of convection Results The limb-darkening coefficients were computed with a higher numerical resolution (100 μ points instead of 15 or 17, as is often used in the ATLAS models), and five equations were used to describe the specific intensities (linear, quadratic, root-square, logarithmic, and a 4-coefficient law) Concerning the gravity-darkening coefficients, the influence of the local gravity on y (λ ) is shown as well as the effects of convection, which turn out to be very significant for cool stars The results are tabulated for log g ′s ranging from 00 to 50, –50 ≤ log [M/H] ≤ +1, 2000 K ≤ T eff ≤ 50 000 K and for five values of the microturbulent velocity ATLAS and PHOENIX plane-parallel atmosphere models were used for all computations

1,199 citations


Journal ArticleDOI
TL;DR: X-shooter as mentioned in this paper is the first 2nd generation instrument of the ESO Very Large Telescope (VLT), which was installed at the Cassegrain focus of UT2 in 2009.
Abstract: X-shooter is the first 2nd generation instrument of the ESO Very Large Telescope(VLT). It is a very efficient, single-target, intermediate-resolution spectrograph that was installed at the Cassegrain focus of UT2 in 2009. The instrument covers, in a single exposure, the spectral range from 300 to 2500 nm. It is designed to maximize the sensitivity in this spectral range through dichroic splitting in three arms with optimized optics, coatings, dispersive elements and detectors. It operates at intermediate spectral resolution (R~4,000 - 17,000, depending on wavelength and slit width) with fixed echelle spectral format (prism cross-dispersers) in the three arms. It includes a 1.8"x4" Integral Field Unit as an alternative to the 11" long slits. A dedicated data reduction package delivers fully calibrated two-dimensional and extracted spectra over the full wavelength range. We describe the main characteristics of the instrument and present its performance as measured during commissioning, science verification and the first months of science operations.

1,031 citations


Journal ArticleDOI
TL;DR: In this article, the Geneva-Copenhagen survey was used for a re-analysis of the spectral properties of the stars in the solar neighborhood and the results showed that the stars are on average 100 K hotter and 0.1 dex more metal rich, which shifted the peak of the metallicity distribution function around the solar value.
Abstract: We present a re-analysis of the Geneva-Copenhagen survey, which benefits from the infrared flux method to improve the accuracy of the derived stellar effective temperatures and uses the latter to build a consistent and improved metallicity scale. Metallicities are calibrated on high-resolution spectroscopy and checked against four open clusters and a moving group, showing excellent consistency. The new temperature and metallicity scales provide a better match to theoretical isochrones, which are used for a Bayesian analysis of stellar ages. With respect to previous analyses, our stars are on average 100 K hotter and 0.1 dex more metal rich, which shift the peak of the metallicity distribution function around the solar value. From Stromgren photometry we are able to derive for the first time a proxy for [alpha/Fe] abundances, which enables us to perform a tentative dissection of the chemical thin and thick disc. We find evidence for the latter being composed of an old, mildly but systematically alpha-enhanced population that extends to super solar metallicities, in agreement with spectroscopic studies. Our revision offers the largest existing kinematically unbiased sample of the solar neighbourhood that contains full information on kinematics, metallicities, and ages and thus provides better constraints on the physical processes relevant in the build-up of the Milky Way disc, enabling a better understanding of the Sun in a Galactic context. (Less)

827 citations


Journal ArticleDOI
TL;DR: In this paper, a dense grid of evolutionary tracks and isochrones of rotating massive main-sequence stars is presented to compare with early OB stars in the Small and Large Magellanic Clouds and in the Galaxy.
Abstract: We present a dense grid of evolutionary tracks and isochrones of rotating massive main-sequence stars. We provide three grids with different initial compositions tailored to compare with early OB stars in the Small and Large Magellanic Clouds and in the Galaxy. Each grid covers masses ranging from 5 to 60 M ⊙ and initial rotation rates between 0 and about 600 km s-1 . To calibrate our models we used the results of the VLT-FLAMES Survey of Massive Stars. We determine the amount of convective overshooting by using the observed drop in rotation rates for stars with surface gravities log g < 3.2 to determine the width of the main sequence. We calibrate the efficiency of rotationally induced mixing using the nitrogen abundance determinations for B stars in the Large Magellanic cloud. We describe and provide evolutionary tracks and the evolution of the central and surface abundances. In particular, we discuss the occurrence of quasi-chemically homogeneous evolution, i.e. the severe effects of efficient mixing of the stellar interior found for the most massive fast rotators. We provide a detailed set of isochrones for rotating stars. Rotation as an initial parameter leads to a degeneracy between the age and the mass of massive main sequence stars if determined from its observed location in the Hertzsprung-Russell diagram. We show that the consideration of surface abundances can resolve this degeneracy.

827 citations


Journal ArticleDOI
TL;DR: In this paper, the results of the Herschel Gould Belt survey toward the IC 5146 molecular cloud were analyzed and a preliminary analysis of the filamentary structure in this region was presented.
Abstract: We provide a first look at the results of the Herschel Gould Belt survey toward the IC 5146 molecular cloud and present a preliminary analysis of the filamentary structure in this region. The column density map, derived from our 70–500 μm Herschel data, reveals a complex network of filaments and confirms that these filaments are the main birth sites of prestellar cores. We analyze the column density profiles of 27 filaments and show that the underlying radial density profiles fall off as r-1.5 to r-2.5 at large radii. Our main result is that the filaments seem to be characterized by a narrow distribution of widths with a median value of 0.10 ± 0.03 pc, which is in stark contrast to a much broader distribution of central Jeans lengths. This characteristic width of ~0.1 pc corresponds to within a factor of ~2 to the sonic scale below which interstellar turbulence becomes subsonic in diffuse gas, which supports the argument that the filaments may form as a result of the dissipation of large-scale turbulence.

753 citations


Journal ArticleDOI
TL;DR: An online database for extrasolar planetary-mass candidates, which is updated regularly as new data are available, has been described in this article, where criteria for inclusion of objects in the catalog: "definition" of a planet and several aspects of the confidence level of planet candidates.
Abstract: We describe an online database for extrasolar planetary-mass candidates, which is updated regularly as new data are available. We first discuss criteria for inclusion of objects in the catalog: “definition” of a planet and several aspects of the confidence level of planet candidates. We are led to point out the contradiction between the sharpness of criteria for belonging to a catalog and the fuzziness of the confidence level for an object to be a planet. We then describe the different tables of extrasolar planetary systems, including unconfirmed candidates (which will ultimately be confirmed, or not, by direct imaging). It also provides online tools: histograms of planet and host star data, cross-correlations between these parameters, and some Virtual Observatory services. Future evolutions of the database are presented.

687 citations


Journal ArticleDOI
TL;DR: In this article, a new solution for the astronomical computation of the orbital motion of the Earth spanning from 0 to −250 Myr is presented, which is valid over more than 50 Myr in the past or into the future with proper phases of the eccentricity variations.
Abstract: We present here a new solution for the astronomical computation of the orbital motion of the Earth spanning from 0 to −250 Myr. The main improvement with respect to our previous numerical solution La2004 is an improved adjustment of the parameters and initial conditions through a fit over 1 Myr to a special version of the highly accurate numerical ephemeris INPOP08 (Integration Numerique Planetaire de l'Observatoire de Paris). The precession equations have also been entirely revised and are no longer averaged over the orbital motion of the Earth and Moon. This new orbital solution is now valid over more than 50 Myr in the past or into the future with proper phases of the eccentricity variations. Owing to the chaotic behavior, the precision of the solution decreases rapidly beyond this time span, and we discuss the behavior of various solutions beyond 50 Myr. For paleoclimate calibrations, we provide several different solutions that are all compatible with the most precise planetary ephemeris. We have thus reached the time where geological data are now required to discriminate between planetary orbital solutions beyond 50 Myr.

662 citations


Journal ArticleDOI
TL;DR: In this article, the authors used cross-correlation techniques to correct the radial velocities of the offset stars and the penalised pixel-fitting method, together with different sets of stellar templates, to re-assess the spectral resolution of the MILES stellar library and models.
Abstract: Aims: We present a number of improvements to the MILES library and stellar population models. We correct some small errors in the radial velocities of the stars, measure the spectral resolution of the library and models more accurately, and give a better absolute flux calibration of the models. Methods: We use cross-correlation techniques to correct the radial velocities of the offset stars and the penalised pixel-fitting method, together with different sets of stellar templates, to re-assess the spectral resolution of the MILES stellar library and models. We have also re-calibrated the zero-point flux level of the models using a new calibration scheme. Results: The end result is an even more homogeneously calibrated stellar library than the originally released one, with a measured spectral resolution of ~2.5 A, almost constant with wavelength, for both the MILES stellar library and models. Furthermore, the new absolute flux calibration for the spectra excellently agrees with predictions based on independent photometric libraries. Conclusions: This improved version of the MILES library and models (version 9.1) is available at the project's website (http://miles.iac.es).

599 citations


Journal ArticleDOI
TL;DR: The MCXC the authors is a meta-catalog of X-ray detected clusters of galaxies, which is based on publicly available ROSAT All Sky Survey-based (NORAS, the authorsLEX, BCS, SGP, NEP, MACS, and CIZA) and serendipitous (160SD, 400SD, SHARC, WARPS, and EMSS) cluster catalogues.
Abstract: We present the compilation and properties of a meta-catalogue of X-ray detected clusters of galaxies, the MCXC. This very large catalogue is based on publicly available ROSAT All Sky Survey-based (NORAS, REFLEX, BCS, SGP, NEP, MACS, and CIZA) and serendipitous (160SD, 400SD, SHARC, WARPS, and EMSS) cluster catalogues. Data have been systematically homogenised to an overdensity of 500, and duplicate entries from overlaps between the survey areas of the individual input catalogues are carefully handled. The MCXC comprises 1743 clusters with virtually no duplicate entries. For each cluster the MCXC provides three identifiers, a redshift, coordinates, membership in the original catalogue, and standardised 0.1−2.4 keV band luminosity L500 ,t otal massM500, and radius R500. The meta-catalogue additionally furnishes information on overlaps between the input catalogues and the luminosity ratios when measurements from different surveys are available, and gives notes on individual objects. The MCXC is available in electronic format for maximum usefulness in X-ray, SZ, and other multiwavelength studies.

562 citations


Journal ArticleDOI
Peter A. R. Ade1, Nabila Aghanim, Monique Arnaud, M. Ashdown2  +291 moreInstitutions (57)
TL;DR: The European Space Agency's Planck satellite was launched on 14 May 2009, and has been surveying the sky stably and continuously since 13 August 2009 as mentioned in this paper, and it will continue to gather scientific data until the end of its cryogenic lifetime.
Abstract: The European Space Agency's Planck satellite was launched on 14 May 2009, and has been surveying the sky stably and continuously since 13 August 2009. Its performance is well in line with expectations, and it will continue to gather scientific data until the end of its cryogenic lifetime. We give an overview of the history of Planck in its first year of operations, and describe some of the key performance aspects of the satellite. This paper is part of a package submitted in conjunction with Planck's Early Release Compact Source Catalogue, the first data product based on Planck to be released publicly. The package describes the scientific performance of the Planck payload, and presents results on a variety of astrophysical topics related to the sources included in the Catalogue, as well as selected topics on diffuse emission.

Journal ArticleDOI
TL;DR: The PACS Evolutionary Probe (PEP) guaranteed time key program as discussed by the authors has been used in the entire set of Herschel surveys, and the field selection that includes popular multi-wavelength fields such as GOODS, COSMOS, Lockman Hole, ECDFS, and EGS.
Abstract: Deep far-infrared photometric surveys studying galaxy evolution and the nature of the cosmic infrared background are a key strength of the Herschel mission. We describe the scientific motivation for the PACS Evolutionary Probe (PEP) guaranteed time key program and its role within the entire set of Herschel surveys, and the field selection that includes popular multiwavelength fields such as GOODS, COSMOS, Lockman Hole, ECDFS, and EGS. We provide an account of the observing strategies and data reduction methods used. An overview of first science results illustrates the potential of PEP in providing calorimetric star formation rates for high-redshift galaxy populations, thus testing and superseding previous extrapolations from other wavelengths, and enabling a wide range of galaxy evolution studies.

Journal ArticleDOI
TL;DR: In this article, a multi-scale multi-frequency deconvolution algorithm for wide-band synthesis-imaging is presented, where the wideband sky-brightness distribution is modeled as a linear combination of spatial and spectral basis functions.
Abstract: Aims. We describe MS-MFS, a multi-scale multi-frequency deconvolution algorithm for wide-band synthesis-imaging, and present imaging results that illustrate the capabilities of the alg orithm and the conditions under which it is feasible and gives accurate results. Methods. The MS-MFS algorithm models the wide-band sky-brightness distribution as a linear combination of spatial and spectral basis functions, and performs image-reconstruction by combining a linear-least-squares approach with iterativeχ 2 minimization. This method extends and combines the ideas used in the MS-CLEAN and MF-CLEAN algorithms for multi-scale and multi-frequency deconvolution respectively, and can be used in conjunction with existing wide-field imaging algorithms. We also discus s a simpler hybrid of spectral-line and continuum imaging methods and point out situations where it may suffi ce. Results. We show via simulations and application to multi-frequency VLA data and wideband EVLA data, that it is possible to reconstruct both spatial and spectral structure of compact and extended emission at the continuum sensitivity level and at the angular resolution allowed by the highest sampled frequency.

Journal ArticleDOI
TL;DR: The HERMES high-resolution spectrograph project as discussed by the authors is based on the white-pupil beam folding for high resolution spectroscopy with a spectral resolution of 85'000 (63'000) for the low-resolution fiber.
Abstract: The HERMES high-resolution spectrograph project aims at exploiting the specific potential of small but flexible telescopes in observational astrophysics. The optimised optical design of the spectrograph is based on the well-proven concept of white-pupil beam folding for high-resolution spectroscopy. In this contribution we present the complete project, including the spectrograph design and procurement details, the telescope adaptor and calibration unit, the detector system, as well as the optimised data-reduction pipeline. We present a detailed performance analysis to show that the spectrograph performs as specified both in optical quality and in total efficiency. With a spectral resolution of 85 000 (63 000 for the low-resolution fibre), a spectral coverage from 377 to 900 nm in a single exposure and a peak efficiency of 28%, HERMES proves to be an ideal instrument for building up time series of high-quality data of variable (stellar) phenomena.

Journal ArticleDOI
TL;DR: Bifrost as mentioned in this paper is a massively parallel numerical code for simulating stellar convection and photospheres from the convection zone to the corona, which can be used to simulate the whole atmosphere.
Abstract: Context. Numerical simulations of stellar convection and photospheres have been developed to the point where detailed shapes of observed spectral lines can be explained. Stellar atmospheres are very complex, and very di erent physical regimes are present in the convection zone, photosphere, chromosphere, transition region and corona. To understand the details of the atmosphere it is necessary to simulate the whole atmosphere since the di erent layers interact strongly. These physical regimes are very diverse and it takes a highly e cient massively parallel numerical code to solve the associated equations. Aims. The design, implementation and validation of the massively parallel numerical code Bifrost for simulating stellar atmospheres from the convection zone to the corona. Methods. The code is subjected to a number of validation tests, among them the Sod shock tube test, the Orzag-Tang colliding shock test, boundary condition tests and tests of how the code treats magnetic field advection, chromospheric radiation, radiative transfer in an isothermal scattering atmosphere, hydrogen ionization and thermal conduction. Results. Bifrost completes the tests with good results and shows near linear e ciency scaling to thousands of computing cores.

Journal ArticleDOI
Peter A. R. Ade1, Nabila Aghanim2, Monique Arnaud3, M. Ashdown4  +245 moreInstitutions (60)
TL;DR: In this paper, an all sky map of the apparent temperature and optical depth of thermal dust emission is constructed using the Planck-HFI (350μm to 2 mm) and IRAS(100μm) data.
Abstract: An all sky map of the apparent temperature and optical depth of thermal dust emission is constructed using the Planck-HFI (350μm to 2 mm) andIRAS(100μm) data. The optical depth maps are correlated with tracers of the atomic (Hi) and molecular gas traced by CO. The correlation with the column density of observed gas is linear in the lowest column density regions at high Galactic latitudes. At high N(H), the correlation is consistent with that of the lowest NH, for a given choice of the CO-to-H(2) conversion factor. In the intermediate NH range, a departure from linearity is observed, with the dust optical depth in excess of the correlation. This excess emission is attributed to thermal emission by dust associated with a dark gas phase, undetected in the available Hi and CO surveys. The 2D spatial distribution of the dark gas in the solar neighbourhood (|b(II)| > 10°) is shown to extend around known molecular regions traced by CO. The average dust emissivity in the Hi phase in the solar neighbourhood is found to be τ(D)/N(H)(tot) = 5.2×10(-26) cm(2) at 857 GHz. It follows roughly a power law distribution with a spectral index β = 1.8 all the way down to 3 mm, although the SED flattens slightly in the millimetre. Taking into account the spectral shape of the dust optical depth, the emissivity is consistent with previous values derived fromFIRAS measurements at high latitudes within 10%. The threshold for the existence of the dark gas is found at N(H)(tot) = (8.0±0.58)×10(20) H cm(−2) (A(V )= 0.4mag). Assuming the same high frequency emissivity for the dust in the atomic and the molecular phases leads to an average X(CO) = (2.54 ± 0.13) × 10(20) H(2) cm(-2)/(K km s(-1)). The mass of dark gas is found to be 28% of the atomic gas and 118% of the CO emitting gas in the solar neighbourhood. The Galactic latitude distribution shows that its mass fraction is relatively constant down to a few degrees from the Galactic plane. A possible explanation for the dark gas lies in a dark molecular phase, where H2 survives photodissociation but CO does not. The observed transition for the onsetof this phase in the solar neighbourhood (AV = 0.4mag) appears consistent with recent theoretical predictions. It is also possible that up to half of the dark gas could be in atomic form, due to optical depth effects in the Hi measurements.

Journal ArticleDOI
Peter A. R. Ade1, Nabila Aghanim2, Monique Arnaud3, M. Ashdown4  +284 moreInstitutions (66)
TL;DR: The first all-sky sample of galaxy clusters detected blindly by the Planck satellite through the Sunyaev-Zeldovich (SZ) effect from its six highest frequencies was presented in this paper.
Abstract: We present the first all-sky sample of galaxy clusters detected blindly by the Planck satellite through the Sunyaev-Zeldovich (SZ) effect from its six highest frequencies. This early SZ (ESZ) sample is comprised of 189 candidates, which have a high signal-to-noise ratio ranging from 6 to 29. Its high reliability (purity above 95%) is further ensured by an extensive validation process based on Planck internal quality assessments and by external cross-identification and follow-up observations. Planck provides the first measured SZ signal for about 80% of the 169 previouslyknown ESZ clusters. Planck furthermore releases 30 new cluster candidates, amongst which 20 meet the ESZ signal-to-noise selection criterion. At the submission date, twelve of the 20 ESZ candidates were confirmed as new clusters, with eleven confirmed using XMM-Newton snapshot observations, most of them with disturbed morphologies and low luminosities. The ESZ clusters are mostly at moderate redshifts (86% with z below 0.3) and span more than a decade in mass, up to the rarest and most massive clusters with masses above 1 × 10 15 M� .

Journal ArticleDOI
TL;DR: In this article, the authors used the spectral energy distribution (SED) of the galactic interstellar medium dust emission, from the mid-IR to the mm range, with an unprecedented sensitivity and down to spatial scales ∼30 ��.
Abstract: The Planck and Herschel missions are currently measuring the far-infrared to millimeter emission of dust, which combined with existing IR data, will for the first time provide the full spectral energy distribution (SED) of the galactic interstellar medium dust emission, from the mid-IR to the mm range, with an unprecedented sensitivity and down to spatial scales ∼30 �� . Such a global SED will allow a systematic study of the dust evolution processes (e.g. grain growth or fragmentation) that directly affect the SED because they redistribute the dust mass among the observed grain sizes. The dust SED is also affected by variations of the radiation field intensity. Here we present a versatile numerical tool, DustEM, that predicts the emission and extinction of dust grains given their size distribution and their optical and thermal properties. In order to model dust evolution, DustEM has been designed to deal with a variety of grain types, structures and size distributions and to be able to easily include new dust physics. We use DustEM to model the dust SED and extinction in the diffuse interstellar medium at high-galactic latitude (DHGL), a natural reference SED that will allow us to study dust evolution. We present a coherent set of observations for the DHGL SED, which has been obtained by correlating the IR and HI-21 cm data. The dust components in our DHGL model are (i) polycyclic aromatic hydrocarbons; (ii) amorphous carbon and (iii) amorphous silicates. We use amorphous carbon dust, rather than graphite, because it better explains the observed high abundances of gas-phase carbon in shocked regions of the interstellar medium. Using the DustEM model, we illustrate how, in the optically thin limit, the IRAS/Planck HFI (and likewise Spitzer/Herschel for smaller spatial scales) photometric band ratios of the dust SED can disentangle the influence of the exciting radiation field intensity and constrain the abundance of small grains (a < 10 nm) relative to the larger grains. We also discuss the contributions of the different grain populations to the IRAS, Planck (and similarly to Herschel) channels. Such information is required to enable a study of the evolution of dust as well as to systematically extract the dust thermal emission from CMB data and to analyze the emission in the Planck polarized channels. The DustEM code described in this paper is publically available. Dust plays a key role in the physics (e.g. heating of the gas, coupling to the magnetic field) and chemistry (formation of H2, shielding of molecules from dissociative radiation) of the interstellar medium (ISM). Heated by stellar photons, dust grains radiate away the absorbed energy by emission in the near-IR to mm range. Dust emission can thus be used as a tracer of the radiation field intensity and, hence, of star formation activity. Assuming a constant dust abundance, the far-IR to mm dust emission is also used to derive the total column density along a line of sight and to provide mass estimates. The impact of dust on the ISM and the use of its emission as a tracer of the local conditions depends on the dust properties and abundances. It is therefore of major importance to understand dust properties and their evolution throughout the ISM. The instruments onboard the Herschel and Planck satel

Journal ArticleDOI
TL;DR: In this paper, the authors presented an extensive grid of non-LTE calculations for several Na I lines in cool stellar atmospheres, including metal-ric h and metal-poor dwarfs and giants.
Abstract: Neutral sodium is a minority species in the atmospheres of late-type stars, and line formation in local thermodynamic equilibrium (LTE) is often a poor assumption, in particular for strong li nes. We present an extensive grid of non-LTE calculations for several Na I lines in cool stellar atmospheres, including metal-ric h and metal-poor dwarfs and giants. For the first time, we cons tructed a Na model atom that incorporates accurate quantum mechanical calculations for collisional excitation and ionisation b y electrons as well as collisional excitation and charge exchange reactions with neutral hydrogen. Similar to Li I, the new rates for hydrogen impact excitation do not affect the statistical equilibrium calculations, while charg e exchange reactions have a small but non-negligible influence. The presented LTE and non-LTE curves-of-growth c an be interpolated to obtain non-LTE abundances and abundance corrections for arbitrary stellar parameter combinations and line strengths. The typical corrections for weak lines a re−0: 1::: − 0: 2 dex, whereas saturated lines may overestimate the abundance in LTE by more than 0.5 dex. The non-LTE Na abundances appear very robust with respect to uncertainties in the input collision al data.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the nature of the observed short-term variability of the progenitor of V1309-Sco and found that the binary was a contact binary with an orbital period of 1.4 days.
Abstract: Context. Stellar mergers are expected to take place in numerous circumstences in the evolution of stellar systems. In particular, they are considered as a plausible origin of stellar eruptions of the V838 Mon type. V1309 Sco is the most recent eruption of this type in our Galaxy. The object was discovered in September 2008.Aims. Our aim is to investigate the nature of V1309 Sco.Methods. V1309 Sco has been photometrically observed in course of the OGLE project since August 2001. We analyse these observations in different ways. In particular, periodogram analyses were done to investigate the nature of the observed short-term variability of the progenitor.Results. We find that the progenitor of V1309 Sco was a contact binary with an orbital period of ~1.4 day. This period was decreasing with time. The light curve of the binary was also evolving, indicating that the system evolved towards its merger. The violent phase of the merger, marked by the systematic brightenning of the object, began in March 2008, i.e. half a year before the outburst discovery. We also investigate the observations of V1309 Sco during the outburst and the decline and show that they can be fully accounted for within the merger hypothesis. Conclusions. For the first time in the literature we show from direct observations that contact binaries indeed end up by merging into a single object, as was suggested in numerous theoretical studies of these systems. Our study also shows that stellar mergers indeed result in eruptions of the V838 Mon type.

Journal ArticleDOI
TL;DR: PIONIER as mentioned in this paper is an integrated optics combiner that combines four 1.8m Auxilliary Telescopes or four 8m Unit Telescopes of the Very Large Telescope Interferometer (ESO, Chile).
Abstract: PIONIER stands for Precision Integrated-Optics Near-infrared Imaging ExpeRiment. It combines four 1.8m Auxilliary Telescopes or four 8m Unit Telescopes of the Very Large Telescope Interferometer (ESO, Chile) using an integrated optics combiner. The instrument has been integrated at IPAG starting in December 2009 and commissioned at the Paranal Observatory in October 2010. It provides scientific observations since November 2010. In this paper, we detail the instrumental concept, we describe the standard operational modes and the data reduction strategy. We present the typical performance and discuss how to improve them. This paper is based on laboratory data obtained during the integrations at IPAG, as well as on-sky data gathered during the commissioning at VLTI. We illustrate the imaging capability of PIONIER on the binaries deltaSco and HIP11231. PIONIER provides 6 visibilities and 3 independent closure phases in the H band, either in a broadband mode or with a low spectral dispersion (R=40), using natural light (i.e. unpolarized). The limiting magnitude is Hmag=7 in dispersed mode under median atmospheric conditions (seeing 3ms) with the 1.8m Auxiliary Telescopes. We demonstrate a precision of 0.5deg on the closure phases. The precision on the calibrated visibilities ranges from 3 to 15% depending on the atmospheric conditions. PIONIER has been installed and successfully tested as a visitor instrument for the VLTI. It permits high angular resolution imaging studies at an unprecedented level of sensitivity. The successful combination of the four 8m Unit Telescopes in March 2011 demonstrates that VLTI is ready for 4-telescope operation.

Journal ArticleDOI
TL;DR: In this article, the radial distribution of dust in disks around a sample of young stars from an observational point of view, and, when possible, in a model-independent way, by using parametric laws.
Abstract: Context. Proto-planetary disks are thought to provide the initial environment for planetary system formation. The dust and gas distribution and its evolution with time is one of the key elements in the process.Aims. We attempt to characterize the radial distribution of dust in disks around a sample of young stars from an observational point of view, and, when possible, in a model-independent way, by using parametric laws.Methods. We used the IRAM PdBI interferometer to provide very high angular resolution (down to 0.4′′ in some sources) observations of the continuum at 1.3 mm and 3 mm around a sample of T Tauri stars in the Taurus-Auriga region. The sample includes single and multiple systems, with a total of 23 individual disks. We used track-sharing observing mode to minimize the biases. We fitted these data with two kinds of models: a “truncated power law” model and a model presenting an exponential decay at the disk edge (“viscous” model).Results. Direct evidence for tidal truncation is found in the multiple systems. The temperature of the mm-emitting dust is constrained in a few systems. Unambiguous evidence for large grains is obtained by resolving out disks with very low values of the dust emissivity index β . In most disks that are sufficiently resolved at two different wavelengths, we find a radial dependence of β , which appears to increase from low values (as low as 0) at the center to about 1.7−2 at the disk edge. The same behavior could apply to all studied disks. It introduces further ambiguities in interpreting the brightness profile, because the regions with apparent β ≈ 0 can also be interpreted as being optically thick when their brightness temperature is high enough. Despite the added uncertainty on the dust absorption coefficient, the characteristic size of the disk appears to increase with a higher estimated star age. Conclusions. These results provide the first direct evidence of the radial dependence of the grain size in proto-planetary disks. Constraints of the surface density distributions and their evolution remain ambiguous because of a degeneracy with the β (r ) law.

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TL;DR: In this paper, the authors derived the infrared luminosity function (LF) over the last 4/5ths of cosmic time using deep 24 and 70 μm imaging of the GOODS North and South fields.
Abstract: Aims. We derive the evolution of the infrared luminosity function (LF) over the last 4/5ths of cosmic time using deep 24 and 70 μm imaging of the GOODS North and South fields. Methods. We use an extraction technique based on prior source positions at shorter wavelengths to build the 24 and 70 μm source catalogs. The majority (93%) of the sources have a spectroscopic (39%) or a photometric redshift (54%) and, in our redshift range of interest (i.e., 1.3 < z < 2.3) ~20% of the sources have a spectroscopic redshift. To extend our study to lower 70 μm luminosities we perform a stacking analysis and we characterize the observed L_(24/(1 + z)) vs. L_(70/(1 + z)) correlation. Using spectral energy distribution (SED) templates which best fit this correlation, we derive the infrared luminosity of individual sources from their 24 and 70 μm luminosities. We then compute the infrared LF at z ~ 1.55 ± 0.25 and z ~ 2.05 ± 0.25. Results. We observe the break in the infrared LF up to z ~ 2.3. The redshift evolution of the infrared LF from z = 1.3 to z = 2.3 is consistent with a luminosity evolution proportional to (1 + z)^(1.0 ± 0.9) combined with a density evolution proportional to (1 + z)^9−1.1 ± 1.5). At z ~ 2, luminous infrared galaxies (LIRGs: 10^(11)L_⊙ < L_(IR) < 10^(12) L_⊙) are still the main contributors to the total comoving infrared luminosity density of the Universe. At z ~ 2, LIRGs and ultra-luminous infrared galaxies (ULIRGs: 10^(12)L_⊙ < L_(IR)) account for ~49% and ~17% respectively of the total comoving infrared luminosity density of the Universe. Combined with previous results using the same strategy for galaxies at z < 1.3 and assuming a constant conversion between the infrared luminosity and star-formation rate (SFR) of a galaxy, we study the evolution of the SFR density of the Universe from z = 0 to z = 2.3. We find that the SFR density of the Universe strongly increased with redshift from z = 0 to z = 1.3, but is nearly constant at higher redshift out to z = 2.3. As part of the online material accompanying this article, we present source catalogs at 24 μm and 70 μm for both the GOODS-North and -South fields.

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TL;DR: In this article, the authors used the coronal models of stars to calculate the EUV contribution to the stellar spectra, assuming that thermal losses dominate the mass loss of their atmospheres.
Abstract: Context. The current distribution of planet mass vs. incident stellar X-ray flux supports the idea that photoevaporation of the atmosphere may take place in close-in planets. Integrated effects have to be accounted for. A proper calculation of the mass loss rate through photoevaporation requires the estimation of the total irradiation from the whole XUV (X-rays and extreme ultraviolet, EUV) range. Aims. The purpose of this paper is to extend the analysis of the photoevaporation in planetary atmospheres from the accessible X-rays to the mostly unobserved EUV range by using the coronal models of stars to calculate the EUV contribution to the stellar spectra. The mass evolution of planets can be traced assuming that thermal losses dominate the mass loss of their atmospheres. Methods. We determine coronal models for 82 stars with exoplanets that have X-ray observations available. Then a synthetic spectrum is produced for the whole XUV range (∼1−912 A). The determination of the EUV stellar flux, calibrated with real EUV data, allows us to calculate the accumulated effects of the XUV irradiation on the planet atmosphere with time, as well as the mass evolution for planets with known density. Results. We calibrate for the first time a relation of the EUV luminosity with stellar age valid for late-type stars. In a sample of 109 exoplanets, few planets with masses larger than ∼1.5 MJ receive high XUV flux, suggesting that intense photoevaporation takes place in a short period of time, as previously found in X-rays. The scenario is also consistent with the observed distribution of planet masses with density. The accumulated effects of photoevaporation over time indicate that HD 209458b may have lost 0.2 MJ since an age of 20 Myr. Conclusions. Coronal radiation produces rapid photoevaporation of the atmospheres of planets close to young late-type stars. More complex models are needed to explain the observations fully. Spectral energy distributions in the XUV range are made available for stars in the sample through the Virtual Observatory for the use in future planet atmospheric models.

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TL;DR: In this paper, the EGMF bound on the hidden assumptions it rests upon was derived from the simultaneous GeV-TeV data on the blazars RGB J0710+591, 1ES 0229+200 and 1ES 1218+304.
Abstract: Context. Attenuation of the TeV γ-ray flux from distant blazars through pair production with extragalactic background light leads to the development of electromagnetic cascades and subsequent, lower energy, GeV secondary γ-ray emission. Due to the deflection of VHE cascade electrons by extragalactic magnetic fields (EGMF), the spectral shape of this arriving cascade γ-ray emission is dependent on the strength of the EGMF. Thus, the spectral shape of the GeV–TeV emission from blazars has the potential to probe the EGMF strength along the line of sight to the object. Constraints on the EGMF previously derived from the gamma-ray data suffer from an uncertainty related to the non-simultaneity of GeV and TeV band observations. Aims. We investigate constraints on the EGMF derived from observations of blazars for which TeV observations simultaneous with those by Fermi telescope were reported. We study the dependence of the EGMF bound on the hidden assumptions it rests upon. Methods. We select blazar objects for which simultaneous Fermi/LAT GeV and Veritas, MAGIC or HESS TeV emission have been published. We model the development of electromagnetic cascades along the gamma-ray beams from these sources using Monte Carlo simulations, including the calculation of the temporal delay incurred by cascade photons, relative to the light propagation time of direct γ-rays from the source. Results. Constraints on the EGMF could be derived from the simultaneous GeV–TeV data on the blazars RGB J0710+591, 1ES 0229+200, and 1ES 1218+304. The measured source flux level in the GeV band is lower than the flux of the expected cascade component calculated under the assumption of zero EGMF. Assuming that the reason for the suppression of the cascade component is the extended nature of the cascade emission, we find that B 10 −15 G (assuming an EGMF correlation length of ≥1 Mpc) is consistent with the data. Alternatively, the assumption that the suppression of the cascade emission is caused by the time delay of the cascade photons the data are consistent with B 10 −17 G for the same correlation length.

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TL;DR: In this article, the authors present a first general characterization of the pulsational behavior of A-F type stars as observed in the Kepler light curves of a sample of 750 candidate A-f type stars, and observationally investigate the relation between γ Doradus (γ Dor), δ Scuti (δ Sct), and hybrid stars.
Abstract: Context. The Kepler spacecraft is providing time series of photometric data with micromagnitude precision for hundreds of A-F type stars. Aims. We present a first general characterization of the pulsational behaviour of A-F type stars as observed in the Kepler light curves of a sample of 750 candidate A-F type stars, and observationally investigate the relation between γ Doradus (γ Dor), δ Scuti (δ Sct), and hybrid stars. Methods. We compile a database of physical parameters for the sample stars from the literature and new ground-based observations. We analyse the Kepler light curve of each star and extract the pulsational frequencies using different frequency analysis methods. We construct two new observables, “energy ”a nd “efficiency”, related to the driving energy of the pulsation mode and the convective efficiency of the outer convective zone, respectively. Results. We propose three main groups to describe the observed variety in pulsating A-F type stars: γ Dor, δ Sct, and hybrid stars. We assign 63% of our sample to one of the three groups, and identify the remaining part as rotationally modulated/active stars, binaries, stars of different spectral type, or stars that show no clear periodic variability. 23% of the stars (171 stars) are hybrid stars, which is a much higher fraction than what has been observed before. We characterize for the first time a large number of A-F type stars (475 stars) in terms of number of detected frequencies, frequency range, and typical pulsation amplitudes. The majority of hybrid stars show frequencies with all kinds of periodicities within the γ Dor and δ Sct range, also between 5 and 10 d −1 , which is a challenge for the current models. We find indications for the existence of δ Sct and γ Dor stars beyond the edges of the current observational instability strips. The hybrid stars occupy the entire region within the δ Sct and γ Dor instability strips and beyond. Non-variable stars seem to exist within the instability strips. The location of γ Dor and δ Sct classes in the (Teff ,l ogg)-diagram has been extended. We investigate two newly constructed variables, “efficiency ”a nd “energy”, as a means to explore the relation between γ Dor and δ Sct stars. Conclusions. Our results suggest a revision of the current observational instability strips of δ Sct and γ Dor stars and imply an investigation of pulsation mechanisms to supplement the κ mechanism and convective blocking effect to drive hybrid pulsations. Accurate physical parameters for all stars are needed to confirm these findings.

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TL;DR: In this paper, the HARPS-Upgrade GTO program was used to collect very precise radial velocity data with high cadence and continuity to detect tiny signatures of very low-mass stars that are potentially present in the habitable zone of their parent stars.
Abstract: Context. In 2009 we started an intense radial-velocity monitoring of a few nearby, slowly-rotating and quiet solar-type stars within the dedicated HARPS-Upgrade GTO program.Aims. The goal of this campaign is to gather very-precise radial-velocity data with high cadence and continuity to detect tiny signatures of very-low-mass stars that are potentially present in the habitable zone of their parent stars.Methods. Ten stars were selected among the most stable stars of the original HARPS high-precision program that are uniformly spread in hour angle, such that three to four of them are observable at any time of the year. For each star we recorded 50 data points spread over the observing season. The data points consist of three nightly observations with a total integration time of 10 min each and are separated by two hours. This is an observational strategy adopted to minimize stellar pulsation and granulation noise.Results. We present the first results of this ambitious program. The radial-velocity data and the orbital parameters of five new and one confirmed low-mass planets around the stars HD 20794, HD 85512, and HD 192310 are reported and discussed, among which is a system of three super-Earths and one that harbors a 3.6 M ⊕ -planet at the inner edge of the habitable zone. Conclusions. This result already confirms previous indications that low-mass planets seem to be very frequent around solar-type stars and that this may occur with a frequency higher than 30%.

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TL;DR: In this article, an evolutionary pre-main sequence (pre-MS) model and isochrones for a fine grid of mass, age, metallicity, and helium values are presented.
Abstract: Context. In recent years new observations of pre-main sequence stars (pre-MS) with Z ≤ Z ⊙ have been made available. To take full advantage of the continuously growing amount of data of pre-MS stars in different environments, we need to develop updated pre-MS models for a wide range of metallicity to assign reliable ages and masses to the observed stars.Aims. We present updated evolutionary pre-MS models and isochrones for a fine grid of mass, age, metallicity, and helium values.Methods. We use a standard and well-tested stellar evolutionary code (i.e. FRANEC), that adopts outer boundary conditions from detailed and realistic atmosphere models. In this code, we incorporate additional improvements to the physical inputs related to the equation of state and the low temperature radiative opacities essential to computing low-mass stellar models.Results. We make available via internet a large database of pre-MS tracks and isochrones for a wide range of chemical compositions (Z = 0.0002−0.03), masses (M = 0.2−7.0 M ⊙ ), and ages (1−100 Myr) for a solar-calibrated mixing length parameter α (i.e. 1.68). For each chemical composition, additional models were computed with two different mixing length values, namely α = 1.2 and 1.9. Moreover, for Z ≥ 0.008, we also provided models with two different initial deuterium abundances. The characteristics of the models have been discussed in detail and compared with other work in the literature. The main uncertainties affecting theoretical predictions have been critically discussed. Comparisons with selected data indicate that there is close agreement between theory and observation.

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TL;DR: In this paper, the authors presented a physically consistent reconstruction of the total solar irradiance for the Holocene, based on the SATIRE (Spectral And Total Irradiance REconstruction) models.
Abstract: Context. Long-term records of solar radiative output are vital for understanding solar variability and past climate change. Measurements of solar irradiance are available for only the last three decades, which calls for reconstructions of this quantity over longer time scales using suitable models. Aims. We present a physically consistent reconstruction of the total solar irradiance for the Holocene. Methods. We extend the SATIRE (Spectral And Total Irradiance REconstruction) models to estimate the evolution of the total (and partly spectral) solar irradiance over the Holocene. The basic assumption is that the variations of the solar irradiance are due to the evolution of the dark and bright magnetic features on the solar surface. The evolution of the decadally averaged magnetic flux is computed from decadal values of cosmogenic isotope concentrations recorded in natural archives employing a series of physics-based models connecting the processes from the modulation of the cosmic ray flux in the heliosphere to their record in natural archives. We then compute the total solar irradiance (TSI) as a linear combination of the jth and jth + 1 decadal values of the open magnetic flux. In order to evaluate the uncertainties due to the evolution of the Earth’s magnetic dipole moment, we employ four reconstructions of the open flux which are based on conceptually different paleomagnetic models. Results. Reconstructions of the TSI over the Holocene, each valid for a different paleomagnetic time series, are presented. Our analysis suggests that major sources of uncertainty in the TSI in this model are the heritage of the uncertainty of the TSI since 1610 reconstructed from sunspot data and the uncertainty of the evolution of the Earth’s magnetic dipole moment. The analysis of the distribution functions of the reconstructed irradiance for the last 3000 years, which is the period that the reconstructions overlap, indicates that the estimates based on the virtual axial dipole moment are significantly lower at earlier times than the reconstructions based on the virtual dipole moment. We also present a combined reconstruction, which represents our best estimate of total solar irradiance for any given time during the Holocene. Conclusions. We present the first physics-based reconstruction of the total solar irradiance over the Holocene, which will be of interest for studies of climate change over the last 11 500 years. The reconstruction indicates that the decadally averaged total solar irradiance ranges over approximately 1.5 W/m 2 from grand maxima to grand minima.

Journal ArticleDOI
TL;DR: In this article, the authors presented a reconstruction of the total and spectral solar irradiance covering 130nm-10μ m from 1610 to the present with an annual resolution and for the Holocene with a 22-year resolution.
Abstract: Context. The variable Sun is the most likely candidate for the natural forcing of past climate changes on time scales of 50 to 1000 years. Evidence for this understanding is that the terrestrial climate correlates positively with the solar activity. During the past 10 000 years, the Sun has experienced the substantial variations in activity and there have been numerous attempts to reconstruct solar irradiance. While there is general agreement on how solar forcing varied during the last several hundred years – all reconstructions are proportional to the solar activity – there is scientific controversy on the magnitude of solar forcing.Aims. We present a reconstruction of the total and spectral solar irradiance covering 130 nm–10 μ m from 1610 to the present with an annual resolution and for the Holocene with a 22-year resolution. Methods. We assume that the minimum state of the quiet Sun in time corresponds to the observed quietest area on the present Sun. Then we use available long-term proxies of the solar activity, which are 10 Be isotope concentrations in ice cores and 22-year smoothed neutron monitor data, to interpolate between the present quiet Sun and the minimum state of the quiet Sun. This determines the long-term trend in the solar variability, which is then superposed with the 11-year activity cycle calculated from the sunspot number. The time-dependent solar spectral irradiance from about 7000 BC to the present is then derived using a state-of-the-art radiation code.Results. We derive a total and spectral solar irradiance that was substantially lower during the Maunder minimum than the one observed today. The difference is remarkably larger than other estimations published in the recent literature. The magnitude of the solar UV variability, which indirectly affects the climate, is also found to exceed previous estimates.We discuss in detail the assumptions that lead us to this conclusion.