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Amaro-Seoane P.,Max Planck Institute For Gravitationsphysik | Glaschke P.,Astronomisches Rechen Institute | Spurzem R.,Astronomisches Rechen Institute | Spurzem R.,CAS National Astronomical Observatories | Spurzem R.,Peking University
Monthly Notices of the Royal Astronomical Society | Year: 2014

The formation and evolution of protoplanetary discs remains a challenge from both a theoretical and numerical standpoint. In this work, we first perform a series of tests of our new hybrid algorithm presented in Glaschke, Amaro-Seoane and Spurzem (henceforth Paper I) that combines the advantages of high accuracy of direct-summation N-body methods with a statistical description for the planetesimal disc based on Fokker-Planck techniques. We then address the formation of planets, with a focus on the formation of protoplanets out of planetesimals. We find that the evolution of the system is driven by encounters as well as direct collisions and requires a careful modelling of the evolution of the velocity dispersion and the size distribution over a large range of sizes. The simulations show no termination of the protoplanetary accretion due to gap formation, since the distribution of the planetesimals is only subjected to small fluctuations. We also show that these features are weakly correlated with the positions of the protoplanets. The exploration of different impact strengths indicates that fragmentation mainly controls the overall mass-loss, which is less pronounced during the early runaway growth. We prove that the fragmentation in combination with the effective removal of collisional fragments by gas drag sets an universal upper limit of the protoplanetary mass as a function of the distance to the host star, which we refer to as the mill condition. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Anglada-Escude G.,Queen Mary, University of London | Amado P.J.,Institute Astrofisica Of Andalucia Consejo Superior Of Investigaciones Cientificas | Barnes J.,Open University Milton Keynes | Berdinas Z.M.,Institute Astrofisica Of Andalucia Consejo Superior Of Investigaciones Cientificas | And 27 more authors.
Nature | Year: 2016

At a distance of 1.295 parsecs, the red dwarf Proxima Centauri (α Centauri C, GL 551, HIP 70890 or simply Proxima) is the Sun's closest stellar neighbour and one of the best-studied low-mass stars. It has an effective temperature of only around 3,050 kelvin, a luminosity of 0.15 per cent of that of the Sun, a measured radius of 14 per cent of the radius of the Sun and a mass of about 12 per cent of the mass of the Sun. Although Proxima is considered a moderately active star, its rotation period is about 83 days (ref. 3) and its quiescent activity levels and X-ray luminosity are comparable to those of the Sun. Here we report observations that reveal the presence of a small planet with a minimum mass of about 1.3 Earth masses orbiting Proxima with a period of approximately 11.2 days at a semi-major-axis distance of around 0.05 astronomical units. Its equilibrium temperature is within the range where water could be liquid on its surface. © 2016 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.


PubMed | Astroimagen, University of Texas at Austin, Montpellier University, Astronomisches Rechen Institute and 10 more.
Type: Journal Article | Journal: Nature | Year: 2016

At a distance of 1.295 parsecs, the red dwarf Proxima Centauri ( Centauri C, GL 551, HIP 70890 or simply Proxima) is the Suns closest stellar neighbour and one of the best-studied low-mass stars. It has an effective temperature of only around 3,050 kelvin, a luminosity of 0.15 per cent of that of the Sun, a measured radius of 14 per cent of the radius of the Sun and a mass of about 12 per cent of the mass of the Sun. Although Proxima is considered a moderately active star, its rotation period is about 83 days (ref. 3) and its quiescent activity levels and X-ray luminosity are comparable to those of the Sun. Here we report observations that reveal the presence of a small planet with a minimum mass of about 1.3 Earth masses orbiting Proxima with a period of approximately 11.2 days at a semi-major-axis distance of around 0.05 astronomical units. Its equilibrium temperature is within the range where water could be liquid on its surface.


Bik A.,Max Planck Institute for Astronomy | Henning Th.,Max Planck Institute for Astronomy | Stolte A.,Argelander Institute For Astronomie | Brandner W.,Max Planck Institute for Astronomy | And 9 more authors.
Astrophysical Journal | Year: 2012

We present near-infrared multi-object spectroscopy and JHK s imaging of the massive stellar content of the Galactic star-forming region W3 Main, obtained with LUCI at the Large Binocular Telescope. We confirm 15 OB stars in W3 Main and derive spectral types between O5V and B4V from their absorption line spectra. Three massive young stellar objects are identified by their emission line spectra and near-infrared excess. The color-color diagram of the detected sources allows a detailed investigation of the slope of the near-infrared extinction law toward W3 Main. Analysis of the Hertzsprung-Russell diagram suggests that the Nishiyama extinction law fits the stellar population of W3 Main best (E(J - H)/E(H - K s) = 1.76 and = 1.44). From our spectrophotometric analysis of the massive stars and the nature of their surrounding H II regions, we derive the evolutionary sequence of W3 Main and we find evidence of an age spread of at least 2-3Myr. While the most massive star (IRS2) is already evolved, indications for high-mass pre-main-sequence evolution are found for another star (IRS N1), deeply embedded in an ultracompact H II (UCH II) region, in line with the different evolutionary phases observed in the corresponding H II regions. We derive a stellar mass of W3 Main of (4 ± 1) × 103 M ⊙ by extrapolating from the number of OB stars using a Kroupa initial mass function and correcting for our spectroscopic incompleteness. We have detected the photospheres of OB stars from the more evolved diffuse H II region to the much younger UCH II regions, suggesting that these stars have finished their formation and cleared away their circumstellar disks very fast. Only in the hyper-compact H II region (IRS5) do the early-type stars seem to be still surrounded by circumstellar material. © 2012. The American Astronomical Society. All rights reserved.


Demleitner M.,Astronomisches Rechen Institute | Greene G.,US Space Telescope Science Institute | Le Sidaner P.,Paris Observatory | Plante R.L.,Urbana University
Astronomy and Computing | Year: 2014

In the Virtual Observatory (VO), the Registry provides the mechanism with which users and applications discover and select resources-typically, data and services-that are relevant for a particular scientific problem. Even though the VO adopted technologies in particular from the bibliographic community where available, building the Registry system involved a major standardisation effort, involving about a dozen interdependent standard texts. This paper discusses the server-side aspects of the standards and their application, as regards the functional components (registries), the resource records in both format and content, the exchange of resource records between registries (harvesting), as well as the creation and management of the identifiers used in the system based on the notion of authorities. Registry record authors, registry operators or even advanced users thus receive a big picture serving as a guideline through the body of relevant standard texts. To complete this picture, we also mention common usage patterns and open issues as appropriate. © 2014 Elsevier B.V.


Muller A.,European Southern Observatory | Roccatagliata V.,Ludwig Maximilians University of Munich | Henning T.,Max Planck Institute for Astronomy | Fedele D.,Max Planck Institute for Extraterrestrial Physics | And 8 more authors.
Astronomy and Astrophysics | Year: 2013

Aims. We reanalyze FEROS observations of the star HIP 11952 to reassess the existence of the proposed planetary system. Methods. The radial velocity of the spectra were measured by cross-correlating the observed spectrum with a synthetic template. We also analyzed a large dataset of FEROS and HARPS archival data of the calibrator HD 10700 spanning over more than five years. We compared the barycentric velocities computed by the FEROS and HARPS pipelines. Results. The barycentric correction of the FEROS-DRS pipeline was found to be inaccurate and to introduce an artificial one-year period with a semi-amplitude of 62 m s-1. Thus the reanalysis of the FEROS data does not support the existence of planets around HIP 11952. © ESO, 2013.


Melchior P.,Institute For Theoretische Astrophysik | Viola M.,Institute For Theoretische Astrophysik | Schafer B.M.,Astronomisches Rechen Institute | Bartelmann M.,Institute For Theoretische Astrophysik
Monthly Notices of the Royal Astronomical Society | Year: 2011

We introduce a novel method for weak-lensing measurements, which is based on a mathematically exact deconvolution of the moments of the apparent brightness distribution of galaxies from the telescope's point spread function (PSF). No assumptions on the shape of the galaxy or the PSF are made. The (de)convolution equations are exact for unweighted moments only, while in practice a compact weight function needs to be applied to the noisy images to ensure that the moment measurement yields significant results. We employ a Gaussian weight function, whose centroid and ellipticity are iteratively adjusted to match the corresponding quantities of the source. The change of the moments caused by the application of the weight function can then be corrected by considering higher order weighted moments of the same source. Because of the form of the deconvolution equations, even an incomplete weighting correction leads to an excellent shear estimation if galaxies and PSF are measured with a weight function of identical size. We demonstrate the accuracy and capabilities of this new method in the context of weak gravitational lensing measurements with a set of specialized tests and show its competitive performance on the GREAT08 Challenge data. A complete c++ implementation of the method can be requested from the authors. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.


Setiawan J.,Max Planck Institute for Astronomy | Roccatagliata V.,Max Planck Institute for Astronomy | Roccatagliata V.,US Space Telescope Science Institute | Fedele D.,Johns Hopkins University | And 9 more authors.
Astronomy and Astrophysics | Year: 2012

Aims. We carried out a radial-velocity survey to search for planets around metal-poor stars. In this paper we report the discovery of two planets around HIP 11952, a metal-poor star with [Fe/H] = -1.9 that belongs to our target sample. Methods. Radial velocity variations of HIP 11952 were monitored systematically with FEROS at the 2.2 m telescope located at the ESO La Silla observatory from August 2009 until January 2011. We used a cross-correlation technique to measure the stellar radial velocities (RV). Results. We detected a long-period RV variation of 290 d and a short-period one of 6.95 d. The spectroscopic analysis of the stellar activity reveals a stellar rotation period of 4.8 d. The Hipparcos photometry data shows intra-day variabilities, which give evidence for stellar pulsations. Based on our analysis, the observed RV variations are most likely caused by the presence of unseen planetary companions. Assuming a primary mass of 0.83 M o, we computed minimum planetary masses of 0.78 M Jup for the inner and 2.93 M Jup for the outer planet. The semi-major axes are a 1 = 0.07 AU and a 2 = 0.81 AU, respectively. Conclusions. HIP 11952 is one of very few stars with [Fe/H] < -1.0 which have planetary companions. This discovery is important to understand planet formation around metal-poor stars. © ESO, 2012.


Pfalzner S.,Max Planck Institute for Radio Astronomy | Parmentier G.,Astronomisches Rechen Institute | Steinhausen M.,Max Planck Institute for Radio Astronomy | Vincke K.,Max Planck Institute for Radio Astronomy | Menten K.,Max Planck Institute for Radio Astronomy
Astrophysical Journal | Year: 2014

Stars mostly form in groups consisting of a few dozen to several ten thousand members. For 30 years, theoretical models have provided a basic concept of how such star clusters form and develop: they originate from the gas and dust of collapsing molecular clouds. The conversion from gas to stars being incomplete, the leftover gas is expelled, leading to cluster expansion and stars becoming unbound. Observationally, a direct confirmation of this process has proved elusive, which is attributed to the diversity of the properties of forming clusters. Here we take into account that the true cluster masses and sizes are masked, initially by the surface density of the background and later by the still present unbound stars. Based on the recent observational finding that in a given star-forming region the star formation efficiency depends on the local density of the gas, we use an analytical approach combined with N-body simulations to reveal evolutionary tracks for young massive clusters covering the first 10 Myr. Just like the Hertzsprung-Russell diagram is a measure for the evolution of stars, these tracks provide equivalent information for clusters. Like stars, massive clusters form and develop faster than their lower-mass counterparts, explaining why so few massive cluster progenitors are found. © 2014. The American Astronomical Society. All rights reserved..


De Rosa G.,Max Planck Institute for Astronomy | Decarli R.,Max Planck Institute for Astronomy | Walter F.,Max Planck Institute for Astronomy | Fan X.,University of Arizona | And 4 more authors.
Astrophysical Journal | Year: 2011

Quasars (QSOs) at the highest known redshift (z 6) are unique probes of the early growth of supermassive black holes (BHs). Until now, only the most luminous QSOs have been studied, often one object at a time. Here we present the most extensive consistent analysis to date of 4 < z < 6.5 QSOs with observed near-infrared spectra, combining three new z 6 objects from our ongoing Very Large Telescope-Infrared Spectrometer And Array Camera program with nineteen sources from the literature. The new sources extend the existing Sloan Digital Sky Survey (SDSS) sample toward the faint end of the QSO luminosity function. Using a maximum likelihood fitting routine optimized for our spectral decomposition, we estimate the BH mass (M BH), the Eddington ratio (defined as L bol/L Edd), and the Fe II/Mg II line ratio, a proxy for the chemical abundance, to characterize both the central object and the broad-line region gas. The QSOs in our sample host BHs with masses of 109 M⊙ that are accreting close to the Eddington luminosity, consistent with earlier results. We find that the distribution of observed Eddington ratios is significantly different than that of a luminosity-matched comparison sample of SDSS QSOs at lower redshift (0.35 < z < 2.25): the average 〈log (L bol/L Edd)〉 = -0.37 (L bol/L Edd 0.43) with a scatter of 0.20dex for the z > 4 sample and the 〈log (L bol/L Edd)〉 = -0.80 (L bol/L Edd 0.16) with a scatter of 0.24dex for the 0.35 < z < 2.25 sample. This implies that, at a given luminosity, the M BH at high-z is typically lower than the average M BH of the lower-redshift population, i.e., the z > 4 sources are accreting significantly faster than the lower-redshift ones. We show that the derived Fe II/Mg II ratios depend sensitively on the analysis performed: our self-consistent, homogeneous analysis significantly reduces the Fe II/Mg II scatter found in previous studies. The measured Fe II/Mg II line ratios show no sign of evolution with cosmic time in the redshift range 4 < z < 6.5. If the Fe II/Mg II line ratio is used as a secondary proxy of the Fe/Mg abundance ratio, this implies that the QSOs in our sample have undergone a major episode of Fe enrichment in the few 100 Myr preceding the cosmic age at which they are observed. © 2011. The American Astronomical Society. All rights reserved..

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