Universitats Sternwarte

München, Germany

Universitats Sternwarte

München, Germany
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Markova N.,Institute of Astronomy with NAO | Puls J.,Universitats Sternwarte | Simon-Diaz S.,Institute of Astrophysics of Canarias | Simon-Diaz S.,University of La Laguna | And 4 more authors.
Astronomy and Astrophysics | Year: 2014

Context. Rotation is of key importance for the evolution of massive star, including their fate as supernovae or gamma-ray bursts. However, the rotational velocities of OB stars are difficult to determine. Aims. Based on our own data for 31 Galactic O stars and incorporating similar data for 86 OB supergiants from the literature, we aim at investigating the properties of rotational and extra line-broadening as a function of stellar parameters and at testing model predictions about the evolution of stellar rotation. Methods. Fundamental stellar parameters were determined by means of the code FASTWIND. Projected rotational and extra broadening velocities, v sin i and θRT, originate from a combined Fourier transform and the goodness-of-fit method. Model calculations published previously were used to estimate the initial evolutionary masses, Minit evol. Results. The sample O stars with Minit evol50 M rotate with less that 26% of their break-up velocity, and they also lack slow rotators (v sin i 50 km s -1). For the more massive stars (Minit evol ≥ 35 M) on the hotter side of the bi-stability jump, the observed and predicted rotational rates agree quite well; for those on the cooler side of the jump, the measured velocties are systematically higher than the predicted ones. In general, the derived θRT values decrease toward cooler T eff, whilst for later evolutionary phases they appear, at the same v sin i, higher for high-mass stars than for low-mass ones. None of the sample stars shows θRT ≥ 110 km s-1. For the majority of the more massive stars, extra broadening either dominates or is in strong competition with rotation. Conclusions. For OB stars of solar metallicity, extra broadening is important and has to be accounted for in the analysis. When appearing at or close to the zero-age main sequence, most of the single and more massive stars rotate slower than previously thought. Model predictions for the evolution of rotation in hot massive stars may need to be updated. © ESO 2014.

Umetsu K.,Academia Sinica, Taiwan | Zitrin A.,California Institute of Technology | Gruen D.,Universitats Sternwarte | Gruen D.,Max Planck Institute for Extraterrestrial Physics | And 5 more authors.
Astrophysical Journal | Year: 2016

We present a comprehensive analysis of strong-lensing, weak-lensing shear and magnification data for a sample of 16 X-ray-regular and 4 high-magnification galaxy clusters at 0.19 ≲ z ≲ 0.69 selected from Cluster Lensing And Supernova survey with Hubble (CLASH). Our analysis combines constraints from 16-band Hubble Space Telescope observations and wide-field multi-color imaging taken primarily with Suprime-Cam on the Subaru Telescope, spanning a wide range of cluster radii (10″-16′). We reconstruct surface mass density profiles of individual clusters from a joint analysis of the full lensing constraints, and determine masses and concentrations for all of the clusters. We find the internal consistency of the ensemble mass calibration to be ≤5% ± 6% in the one-halo regime (200-2000 kpc h-1) compared to the CLASH weak-lensing-only measurements of Umetsu et al. For the X-ray-selected subsample of 16 clusters, we examine the concentration-mass (c-M) relation and its intrinsic scatter using a Bayesian regression approach. Our model yields a mean concentration of c|z=0.34 = 3.95 ± 0.35 at M200c ≃14 × 1014M⊙ and an intrinsic scatter of σ (ln c200c) = 0.13 ± 0.06, which is in excellent agreement with Λ cold dark matter predictions when the CLASH selection function based on X-ray morphological regularity and the projection effects are taken into account. We also derive an ensemble-averaged surface mass density profile for the X-ray-selected subsample by stacking their individual profiles. The stacked lensing signal is detected at 33σ significance over the entire radial range ≤4000 kpc h-1, accounting for the effects of intrinsic profile variations and uncorrelated large-scale structure along the line of sight. The stacked mass profile is well described by a family of density profiles predicted for cuspy dark-matter-dominated halos in gravitational equilibrium, namely, the Navarro-Frenk-White (NFW), Einasto, and DARKexp models, whereas the single power-law, cored isothermal and Burkert density profiles are disfavored by the data. We show that cuspy halo models that include the large-scale two-halo term provide improved agreement with the data. For the NFW halo model, we measure a mean concentration of c200c= 3.79+0.30 -0.28 at M200c= 14.1+1.0 -1.0 × 1014 M⊙, demonstrating consistency between thecomplementary analysis methods. © 2016. The American Astronomical Society. All rights reserved.

Zeidler S.,Japan National Astronomical Observatory | Mutschke H.,Universitats Sternwarte | Posch Th.,Institute For Astrophysik
Astrophysical Journal | Year: 2015

Since the Infrared Space Observatory (ISO) mission, it has become clear that dust in circumstellar disks and outflows consists partly of crystalline silicates of pyroxene and olivine type. An exact mineralogical analysis of the dust infrared emission spectra relies on laboratory spectra, which, however, have been mostly measured at room temperature so far. Given that infrared spectral features depend on the thermal excitation of the crystal's vibrational modes, laboratory spectra measured at various (low and high) temperatures, corresponding to the thermal conditions at different distances from the star, can improve the accuracy of such analyses considerably. We have measured the complex refractive index in a temperature range of 10-973 K for one mineral of each of those types of silicate, i.e., for an olivine and an enstatite of typical (terrestrial) composition. Thus, our data extend the temperature range of previous data to higher values and the compositional range to higher iron contents. We analyze the temperature dependence of oscillator frequencies and damping parameters governing the spectral characteristics of the bands and calculate absorption cross-sectional spectra that can be compared with astronomical emission spectra. We demonstrate the usefulness of our new data by comparing spectra calculated for a 100 K dust temperature with the ISO SWS spectrum of IRAS 09425-6040. © 2015. The American Astronomical Society. All rights reserved.

MacIejewski G.,Universitats Sternwarte | MacIejewski G.,Nicolaus Copernicus University | Errmann R.,Universitats Sternwarte | Raetz S.,Universitats Sternwarte | And 3 more authors.
Astronomy and Astrophysics | Year: 2011

Aims. The transiting extrasolar planet WASP-12 b was found to be one of the most intensely irradiated exoplanets. It is unexpectedly bloated and is losing mass that may accrete into the host star. Our aim was to refine the parameters of this intriguing system and search for signs of transit timing variations. Methods. We gathered high-precision light curves for two transits of WASP-12 b. Assuming various limb-darkening laws, we generated best-fitting models and redetermined the parameters of the system. Error estimates were derived by the prayer-bead method and Monte Carlo simulations. Results. System parameters obtained by us are found to agree with previous studies within one sigma. Use of the non-linear limb-darkening laws results in the best-fitting models. With two new mid-transit times, the ephemeris was refined to BJDTDB = (2 454 508.97682 ± 0.00020) + (1.09142245 ± 0.00000033)E. Interestingly, indications of transit timing variation are detected at the level of 3.4 sigma. This signal can be induced by an additional planet in the system. Simplified numerical simulations show that a perturber could be a terrestrial-type planet if both planets are in a low-order orbital resonance. However, we emphasise that further observations are needed to confirm variation and to constrain properties of the perturber. © 2011 ESO.

Broderick A.E.,Perimeter Institute for Theoretical Physics | Broderick A.E.,University of Waterloo | Narayan R.,Harvard - Smithsonian Center for Astrophysics | Kormendy J.,University of Texas at Austin | And 6 more authors.
Astrophysical Journal | Year: 2015

The 6 × 109 MO supermassive black hole at the center of the giant elliptical galaxy M87 powers a relativistic jet. Observations at millimeter wavelengths with the Event Horizon Telescope have localized the emission from the base of this jet to angular scales comparable to the putative black hole horizon. The jet might be powered directly by an accretion disk or by electromagnetic extraction of the rotational energy of the black hole. However, even the latter mechanism requires a confining thick accretion disk to maintain the required magnetic flux near the black hole. Therefore, regardless of the jet mechanism, the observed jet power in M87 implies a certain minimum mass accretion rate. If the central compact object in M87 were not a black hole but had a surface, this accretion would result in considerable thermal near-infrared and optical emission from the surface. Current flux limits on the nucleus of M87 strongly constrain any such surface emission. This rules out the presence of a surface and thereby provides indirect evidence for an event horizon. © 2015. The American Astronomical Society. All rights reserved.

Strazzullo V.,U.S. National Radio Astronomy Observatory | Pannella M.,U.S. National Radio Astronomy Observatory | Owen F.N.,U.S. National Radio Astronomy Observatory | Bender R.,Universitats Sternwarte | And 5 more authors.
Astrophysical Journal | Year: 2010

We present a study of a 20cm selected sample in the Deep Spitzer Wide-area InfraRed Extragalactic Legacy Survey Very Large Array Field, reaching a 5σ limiting flux density at the image center of S 1.4 GHz 13.5 μJy. In a 0.6 × 0.6deg2 field, we are able to assign an optical/IR counterpart to 97% of the radio sources. Up to 11 passbands from the NUV to 4.5 μm are then used to sample the spectral energy distribution (SED) of these counterparts in order to investigate the nature of the host galaxies. By means of an SED template library and stellar population synthesis models, we estimate photometric redshifts, stellar masses, and stellar population properties, dividing the sample into three sub-classes of quiescent, intermediate, and star-forming galaxies. We focus on the radio sample in the redshift range 0.3 < z < 1.3 where we estimate to have a redshift completeness higher than 90% and study the properties and redshift evolution of these sub-populations. We find that, as expected, the relative contributions of active galactic nuclei (AGNs) and star-forming galaxies to the μJy population depend on the flux density limit of the sample. At all flux levels, a significant population of "green-valley" galaxies is observed. While the actual nature of these sources is not definitely understood, the results of this work may suggest that a significant fraction of faint radio sources might be composite (and possibly transition) objects, thus a simple "AGN versus star-forming" classification might not be appropriate to fully understand what faint radio populations really are. © 2010 The American Astronomical Society. All rights reserved.

Kormendy J.,University of Texas at Austin | Kormendy J.,Universitats Sternwarte | Kormendy J.,Max Planck Institute for Extraterrestrial Physics | Drory N.,Max Planck Institute for Extraterrestrial Physics | And 3 more authors.
Astrophysical Journal | Year: 2010

To better understand the prevalence of bulgeless galaxies in the nearby field, we dissect giant Sc-Scd galaxies with Hubble Space Telescope (HST) photometry and Hobby-Eberly Telescope (HET) spectroscopy. We use the HET High Resolution Spectrograph (resolution R = λ/FWHM ≡ 15,000) to measure stellar velocity dispersions in the nuclear star clusters and (pseudo)bulges of the pure-disk galaxies M33, M101, NGC 3338, NGC 3810, NGC 6503, and NGC 6946. The dispersions range from 20 ±1 km s-1 in the nucleus of M33 to 78 ±2 km s-1 in the pseudobulge of NGC 3338. We use HST archive images to measure the brightness profiles of the nuclei and (pseudo)bulges in M101, NGC 6503, and NGC 6946 and hence to estimate their masses. The results imply small mass-to-light ratios consistent with young stellar populations. These observations lead to two conclusions. (1) Upper limits on the masses of any supermassive black holes are Mmiddot; ≲ (2.6 ±0.5) × 106M⊙ in M101 and M · ≲ (2.0 ±0.6) × 106M⊙ in NGC 6503. (2) We show that the above galaxies contain only tiny pseudobulges that make up ≲3% of the stellar mass. This provides the strongest constraints to date on the lack of classical bulges in the biggest pure-disk galaxies. We inventory the galaxies in a sphere of radius 8 Mpc centered on our Galaxy to see whether giant, pure-disk galaxies are common or rare. We find that at least 11 of 19 galaxies with Vcirc > 150 km s-1, including M101, NGC 6946, IC 342, and our Galaxy, show no evidence for a classical bulge. Four may contain small classical bulges that contribute 5%-12% of the light of the galaxy. Only four of the 19 giant galaxies are ellipticals or have classical bulges that contribute ∼1/3 of the galaxy light. We conclude that pure-disk galaxies are far from rare. It is hard to understand how bulgeless galaxies could form as the quiescent tail of a distribution of merger histories. Recognition of pseudobulges makes the biggest problem with cold dark matter galaxy formation more acute: How can hierarchical clustering make so many giant, pure-disk galaxies with no evidence for merger-built bulges? Finally, we emphasize that this problem is a strong function of environment: the Virgo cluster is not a puzzle, because more than 2/3 of its stellar mass is in merger remnants.

Ruiz-Rodriguez D.,Lowell Observatory | Prato L.,Lowell Observatory | Torres G.,Harvard - Smithsonian Center for Astrophysics | Wasserman L.H.,Lowell Observatory | Neuhauser R.,Universitats Sternwarte
Astronomical Journal | Year: 2013

RX J0513.1+0851 and RX J0539.9+0956 were previously identified as young, low-mass, single-lined spectroscopic binary systems and classified as weak-lined T Tauri stars at visible wavelengths. Here we present radial velocities, spectral types, vsin i values, and flux ratios for the components in these systems resulting from two-dimensional cross-correlation analysis. These results are based on high-resolution, near-infrared spectroscopy taken with the Keck II telescope to provide a first characterization of these systems as double-lined rather than single-lined. It applies the power of infrared spectroscopy to the detection of cool secondaries; the flux scales as a less steep function of mass in the infrared than in the visible, thus enabling an identification of low-mass secondaries. We found that the RX J0513.1+0851 and RX J0539.9+0956 primary stars are fast rotators, 60 km s-1 and 80 km s-1, respectively; this introduces extra difficulty in the detection of the secondary component as a result of the quite broad absorption lines. To date, these are the highest rotational velocities measured for a pre-main sequence spectroscopic binary. The orbital parameters and mass ratios were determined by combining new visible light spectroscopy with our infrared data for both systems. For RX J0513.1+0851, we derived a period of ∼4 days and a mass ratio of q = 0.46 ± 0.01 and for RX J0539.9+0956, a period of ∼1117 days and a mass ratio of q = 0.66 ± 0.01. Based on our derived properties for the stellar components, we estimate the luminosities and hence distances to these binaries at 220 pc and 90 pc. They appear to be significantly closer than previously estimated. © 2013. The American Astronomical Society. All rights reserved.

Kormendy J.,University of Texas at Austin | Kormendy J.,Universitats Sternwarte | Kormendy J.,Max Planck Institute for Extraterrestrial Physics | Bender R.,Universitats Sternwarte | Bender R.,Max Planck Institute for Extraterrestrial Physics
Astrophysical Journal Letters | Year: 2013

We construct the Faber-Jackson correlation between velocity dispersion σ and total galaxy luminosity LV separately for elliptical galaxies with and without cores. The coreless ellipticals show the well-known, steep relationship dlog σ/dlog LV = 0.268 or LV ασ3.74. This corresponds to dlog σ/dlog M = 0.203, where M is the stellar mass and we use M/LαL 0.32. In contrast, the velocity dispersions of core ellipticals increase much more slowly with LV and M: dlog σ/dlog LV = 0.120, LV ασ8.33, and dlog σ/dlog M = 0.091. Dissipationless major galaxy mergers are expected to preserve σ according to the simplest virial-theorem arguments. However, numerical simulations show that σ increases slowly in dry major mergers, with dlog σ/dlog M ≃ +0.15. In contrast, minor mergers cause σ to decrease, with dlog σ/dlog M ≃ -0.05. Thus, the observed relation argues for dry major mergers as the dominant growth mode of the most massive ellipticals. This is consistent with what we know about the formation of cores. We know no viable way to explain galaxy cores except through dissipationless mergers of approximately equal-mass galaxies followed by core scouring by binary supermassive black holes. The observed, shallow relation for core ellipticals provides further evidence that they formed in dissipationless and predominantly major mergers. Also, it explains the observation that the correlation of supermassive black hole mass with velocity dispersion, M •ασ4, "saturates" at high M • such that M • becomes almost independent of σ. © 2013. The American Astronomical Society. All rights reserved..

Butler K.,Universitats Sternwarte
EAS Publications Series | Year: 2012

A brief summary of some aspects of atomic physics theory useful for stellar atmospheres is given. © EAS, EDP Sciences 2010.

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