Time filter

Source Type

Assef R.J.,Jet Propulsion Laboratory | Frank S.,Ohio State University | Frank S.,Laboratoire Dastrophysique Of Marseille Lam | Grier C.J.,Ohio State University | And 3 more authors.
Astrophysical Journal Letters | Year: 2012

Estimates of the mass of super-massive black holes (BHs) in distant active galactic nuclei (AGNs) can be obtained efficiently only through single-epoch (SE) spectra, using a combination of their broad emission line widths and continuum luminosities. Yet the reliability and accuracy of the method and the resulting mass estimates, M BH, remain uncertain. A recent study by Croom using a sample of Sloan Digital Sky Survey, 2dF QSO Redshift Survey, and 2dF-SDSS LRG and QSO Survey quasars suggests that line widths contribute little information about the BH mass in these SE estimates and can be replaced by a constant value without significant loss of accuracy. In this Letter, we use a sample of nearby reverberation-mapped AGNs to show that this conclusion is not universally applicable. We use the bulge luminosity (L Bulge) of these local objects to test how well the known M BH-L Bulge correlation is recovered when using randomly assigned line widths instead of the measured ones to estimate M BH. We find that line widths provide significant information about M BH, and that for this sample, the line width information is just as significant as that provided by the continuum luminosities. We discuss the effects of observational biases upon the analysis of Croom and suggest that the results can probably be explained as a bias of flux-limited, shallow quasar samples. © 2012. The American Astronomical Society. All rights reserved.. Source

Milli J.,Joseph Fourier University | Milli J.,European Southern Observatory | Mouillet D.,Joseph Fourier University | Mawet D.,European Southern Observatory | And 5 more authors.
Astronomy and Astrophysics | Year: 2013

Context. Over the past five years, radial-velocity and transit techniques have revealed a new population of Earth-like planets with masses of a few Earth masses. Their very close orbit around their host star requires an exquisite inner working angle to be detected in direct imaging and sets a challenge for direct imagers that work in the visible range, such as SPHERE/ZIMPOL. Aims. Among all known exoplanets with less than 25 Earth masses we first predict the best candidate for direct imaging. Our primary objective is then to provide the best instrument setup and observing strategy for detecting such a peculiar object with ZIMPOL. As a second step, we aim at predicting its detectivity. Methods. Using exoplanet properties constrained by radial velocity measurements, polarimetric models and the diffraction propagation code CAOS, we estimate the detection sensitivity of ZIMPOL for such a planet in different observing modes of the instrument. We show how observing strategies can be optimized to yield the best detection performance on a specific target. Results. In our current knowledge of exoplanetary systems, α Centauri B b is the most promising target with less than 25 Earth masses for ZIMPOL. With a gaseous Rayleigh-scattering atmosphere and favorable inclinations, the planet could be detected in about four hours of observing time, using the four-quadrant phase-mask coronograph in the I band. However, if α Centauri B b should display unfavorable polarimetric and reflective properties similar to that of our Moon, it is around 50 times fainter than the best sensitivity of ZIMPOL. Conclusions. α Centauri B is a primary target for SPHERE. Dedicated deep observations specifically targeting the radial velocity-detected planet can lead to a detection if the polarimetric properties of the planet are favorable. © ESO, 2013. Source

Querejeta M.,Max Planck Institute for Astronomy | Meidt S.E.,Max Planck Institute for Astronomy | Schinnerer E.,Max Planck Institute for Astronomy | Cisternas M.,Institute of Astrophysics of Canarias | And 33 more authors.
Astrophysical Journal, Supplement Series | Year: 2015

The mid-infrared is an optimal window to trace stellar mass in nearby galaxies and the 3.6 mm IRAC band has been exploited to this effect, but such mass estimates can be biased by dust emission. We present our pipeline to reveal the old stellar flux at 3.6 μm and obtain stellar mass maps for more than 1600 galaxies available from the Spitzer Survey of Stellar Structure in Galaxies (S4G). This survey consists of images in two infrared bands (3.6 and 4.5 μm), and we use the Independent Component Analysis (ICA) method presented in Meidt et al. to separate the dominant light from old stars and the dust emission that can significantly contribute to the observed 3.6 mm flux. We exclude from our ICA analysis galaxies with low signal-to-noise ratio (S/N < 10) and those with original [3.6][4.5] colors compatible with an old stellar population, indicative of little dust emission (mostly early Hubble types, which can directly provide good mass maps). For the remaining 1251 galaxies to which ICA was successfully applied, we find that as much as 10%30% of the total light at 3.6 μm typically originates from dust, and locally it can reach even higher values. This contamination fraction shows a correlation with specific star formation rates, confirming that the dust emission that we detect is related to star formation. Additionally, we have used our large sample of mass estimates to calibrate a relationship of effective mass-to-light ratio (M/L) as a function of observed [3.6][4.5] color: log(M/L) = -0.339(±0.057) × ([3.6]-[4.5]) - 0.336(±0.002). Our final pipeline products have been made public through IRSA, providing the astronomical community with an unprecedentedly large set of stellar mass maps ready to use for scientific applications. © 2015. The American Astronomical Society. All rights reserved. Source

Meidt S.E.,Max Planck Institute for Astronomy | Schinnerer E.,Max Planck Institute for Astronomy | Muoz-Mateos J.-C.,U.S. National Radio Astronomy Observatory | Holwerda B.,European Space Agency | And 24 more authors.
Astrophysical Journal Letters | Year: 2012

We examine the effect of circumstellar dust extinction on the near-IR (NIR) contribution of asymptotic giant branch (AGB) stars in intermediate-age clusters throughout the disk of M100. For our sample of 17 AGB-dominated clusters we extract optical-to-mid-IR spectral energy distributions (SEDs) and find that NIR brightness is coupled to the mid-IR dust emission in such a way that a significant reduction of AGB light, of up to 1 mag in the K band, follows from extinction by the dust shell formed during this stage. Since the dust optical depth varies with AGB chemistry (C-rich or O-rich), our results suggest that the contribution of AGB stars to the flux from their host clusters will be closely linked to the metallicity and the progenitor mass of the AGB star, to which dust chemistry and mass-loss rate are sensitive. Our sample of clusters - each the analogue of a 1Gyr old post-starburst galaxy - has implications within the context of mass and age estimation via SED modeling at high-z: we find that the average 0.5 mag extinction estimated here may be sufficient to reduce the AGB contribution in the (rest-frame) K band from 70%, as predicted in the latest generation of synthesis models, to 35%. Our technique for selecting AGB-dominated clusters in nearby galaxies promises to be effective for discriminating the uncertainties associated with AGB stars in intermediate-age populations that plague age and mass estimation in high-z galaxies. © 2012. The American Astronomical Society. All rights reserved.. Source

Feautpier P.,CNRS Grenoble Institute for Particle Astrophysics and Cosmology Laboratory | Gach J.-L.,Laboratoire Dastrophysique Of Marseille Lam | Balard P.,Laboratoire Dastrophysique Of Marseille Lam | Guillaume C.,Observatoire de Haute Provence OHP | And 21 more authors.
Publications of the Astronomical Society of the Pacific | Year: 2011

For the first time, subelectron readout noise has been achieved with a camera dedicated to astronomical wavefront-sensing applications. The OCam system demonstrated this performance at a 1300 Hz frame rate and with 240 × 240 pixel frame size. ESO and JRA2 OPTICON jointly funded e2v Technologies to develop a custom CCD for adaptive optics (AO) wavefront-sensing applications. The device, called CCD220, is a compact Peltier-cooled 240 × 240 pixel frame-transfer eight-output back-illuminated sensor using the EMCCD technology. This article demonstrates, for the first time, subelectron readout noise at frame rates from 25 Hz to 1300 Hz and dark current lower than 0.01 e- pixel-1 frame-1. It reports on the quantitative performance characterization of OCam and the CCD220, including readout noise, dark current, multiplication gain, quantum efficiency, and charge transfer efficiency. OCam includes a low-noise preamplifier stage, a digital board to generate the clocks, and a microcontroller. The data acquisition system includes a user-friendly timer file editor to generate any type of clocking scheme. A second version of OCam, called OCam-, has been designed to offer enhanced performance, a completely sealed camera package, and an additional Peltier stage to facilitate operation on a telescope or environmentally challenging applications. New features of OCam- are presented in this article. This instrumental development will strongly impact the performance of the most advanced AO systems to come. © 2011. The Astronomical Society of the Pacific. All rights reserved. Source

Discover hidden collaborations