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  • 1
    Electronic Resource
    Electronic Resource
    Large changes in Pluto's atmosphere as revealed by recent stellar occultations (2003)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 424 (2003), S. 168-170 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Pluto's tenuous nitrogen atmosphere was first detected by the imprint left on the light curve of a star that was occulted by the planet in 1985 (ref. 1), and studied more extensively during a second occultation event in 1988 (refs 2–6). These events are, however, ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/nature01766
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    Paper (German National Licenses)
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  • 2
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    The ATLAS3D project - XXIX. The new look of early-type galaxies and surrounding fields disclosed by extremely deep optical images (2014)
    Oxford University Press
    Details
    Publication Date: 2014-11-12
    Description: Galactic archaeology based on star counts is instrumental to reconstruct the past mass assembly of Local Group galaxies. The development of new observing techniques and data reduction, coupled with the use of sensitive large field of view cameras, now allows us to pursue this technique in more distant galaxies exploiting their diffuse low surface brightness (LSB) light. As part of the ATLAS 3D project, we have obtained with the MegaCam camera at the Canada–France–Hawaii Telescope extremely deep, multiband images of nearby early-type galaxies (ETGs). We present here a catalogue of 92 galaxies from the ATLAS 3D sample, which are located in low- to medium-density environments. The observing strategy and data reduction pipeline, which achieve a gain of several magnitudes in the limiting surface brightness with respect to classical imaging surveys, are presented. The size and depth of the survey are compared to other recent deep imaging projects. The paper highlights the capability of LSB-optimized surveys at detecting new prominent structures that change the apparent morphology of galaxies. The intrinsic limitations of deep imaging observations are also discussed, among those, the contamination of the stellar haloes of galaxies by extended ghost reflections, and the cirrus emission from Galactic dust. The detection and systematic census of fine structures that trace the present and past mass assembly of ETGs are one of the prime goals of the project. We provide specific examples of each type of observed structures – tidal tails, stellar streams and shells – and explain how they were identified and classified. We give an overview of the initial results. The detailed statistical analysis will be presented in future papers.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 3
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    Cygnus OB2 DANCe: A high-precision proper motion study of the Cygnus OB2 association (2016)
    Oxford University Press
    Details
    Publication Date: 2016-06-17
    Description: We present a high-precision proper motion study of 873 X-ray and spectroscopically selected stars in the massive OB association Cygnus OB2 as part of the DANCe project. These were calculated from images spanning a 15 yr baseline and have typical precisions 〈1 mas yr –1 . We calculate the velocity dispersion in the two axes to be $\sigma _\alpha (c) = 13.0^{+0.8}_{-0.7}$ and $\sigma _\delta (c) = 9.1^{+0.5}_{-0.5}$ km s –1 , using a two-component, two-dimensional model that takes into account the uncertainties on the measurements. This gives a three-dimensional velocity dispersion of 3D  = 17.8 ± 0.6 km s –1 implying a virial mass significantly larger than the observed stellar mass, confirming that the association is gravitationally unbound. The association appears to be dynamically unevolved, as evidenced by considerable kinematic substructure, non-isotropic velocity dispersions and a lack of energy equipartition. The proper motions show no evidence for a global expansion pattern, with approximately the same amount of kinetic energy in expansion as there is in contraction, which argues against the association being an expanded star cluster disrupted by process such as residual gas expulsion or tidal heating. The kinematic substructures, which appear to be close to virial equilibrium and have typical masses of 40–400 M , also do not appear to have been affected by the expulsion of the residual gas. We conclude that Cyg OB2 was most likely born highly substructured and globally unbound, with the individual subgroups born in (or close to) virial equilibrium, and that the OB association has not experienced significant dynamical evolution since then.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 4
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    The frequency and properties of young tidal dwarf galaxies in nearby gas-rich groups (2016)
    Oxford University Press
    Details
    Publication Date: 2016-06-17
    Description: We present high-resolution Giant Metrewave Radio Telescope (GMRT) H  i observations and deep Canada–France–Hawaii Telescope (CFHT) optical imaging of two galaxy groups: NGC 4725/47 and NGC 3166/9. These data are part of a multi-wavelength unbiased survey of the gas-rich dwarf galaxy populations in three nearby interacting galaxy groups. The NGC 4725/47 group hosts two tidal knots and one dwarf irregular galaxy (dIrr). Both tidal knots are located within a prominent H  i tidal tail, appear to have sufficient mass ( M gas 10 8 M ) to evolve into long-lived tidal dwarf galaxies (TDGs) and are fairly young in age. The NGC 3166/9 group contains a TDG candidate, AGC 208457, at least three dIrrs and four H  i knots. Deep CFHT imaging confirms that the optical component of AGC 208457 is bluer – with a 0.28 mag g – r colour – and a few Gyr younger than its purported parent galaxies. Combining the results for these groups with those from the NGC 871/6/7 group reported earlier, we find that the H  i properties, estimated stellar ages and baryonic content of the gas-rich dwarfs clearly distinguish tidal features from their classical counterparts. We optimistically identify four potentially long-lived tidal objects associated with three separate pairs of interacting galaxies, implying that TDGs are not readily produced during interaction events as suggested by some recent simulations. The tidal objects examined in this survey also appear to have a wider variety of properties than TDGs of similar mass formed in current simulations of interacting galaxies, which could be the result of pre- or post-formation environmental influences.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 5
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    Identification of old tidal dwarfs near early-type galaxies from deep imaging and H I observations (2014)
    Oxford University Press
    Details
    Publication Date: 2014-04-15
    Description: It has recently been proposed that the dwarf spheroidal galaxies located in the Local Group discs of satellites (DoSs) may be tidal dwarf galaxies (TDGs) born in a major merger at least 5 Gyr ago. Whether TDGs can live that long is still poorly constrained by observations. As part of deep optical and H i surveys with the Canada–France–Hawaii Telescope (CFHT) MegaCam camera and Westerbork Synthesis Radio Telescope made within the ATLAS 3D project, and follow-up spectroscopic observations with the Gemini-North telescope, we have discovered old TDG candidates around several early-type galaxies. At least one of them has an oxygen abundance close to solar, as expected for a tidal origin. This confirmed pre-enriched object is located within the gigantic, but very low surface brightness, tidal tail that emanates from the elliptical galaxy, NGC 5557. An age of 4 Gyr estimated from its SED fitting makes it the oldest securely identified TDG ever found so far. We investigated the structural and gaseous properties of the TDG and of a companion located in the same collisional debris, and thus most likely of tidal origin as well. Despite several Gyr of evolution close to their parent galaxies, they kept a large gas reservoir. Their central surface brightness is low and their effective radius much larger than that of typical dwarf galaxies of the same mass. This possibly provides us with criteria to identify tidal objects which can be more easily checked than the traditional ones requiring deep spectroscopic observations. In view of the above, we discuss the survival time of TDGs and question the tidal origin of the DoSs.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 6
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    An extremely optically dim tidal feature in the gas-rich interacting galaxy group NGC 871/NGC 876/NGC 877 (2014)
    Oxford University Press
    Details
    Publication Date: 2014-08-13
    Description: We present Giant Metrewave Radio Telescope H i observations and deep Canada–France–Hawaii Telescope (CFHT) MegaCam optical images of the gas-rich interacting galaxy group NGC 871/NGC 876/NGC 877 (hereafter NGC 871/6/7). Our high-resolution data sets provide a census of the H i and stellar properties of the detected gas-rich group members. In addition to a handful of spiral, irregular and dwarf galaxies, this group harbours an intriguing H i feature, AGC 749170, that has a gas mass of ~10 9.3 M , a dynamical-to-gas mass ratio of ~1 (assuming that the cloud is rotating and in dynamical equilibrium) and no optical counterpart in previous imaging. Our observations have revealed a faint feature in the CFHT g ' and r ' bands; if it is physically associated with AGC 749170, the latter has $M/L_{\rm g} 〉 1000 \,\mathrm{M}_{{\odot }}/\mathrm{L}_{{\odot }}$ as well as a higher metallicity (estimated using photometric colours) and a significantly younger stellar population than the other low-mass gas-rich group members. These properties, as well as its spectral and spatial location with respect to its suspected parent galaxies, strongly indicate a tidal origin for AGC 749170. Overall, the H i properties of AGC 749170 resemble those of other optically dark/dim clouds that have been found in groups. These clouds could represent a class of relatively long-lived H i -rich tidal remnants that survive in intermediate-density environments.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 7
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    Star formation in the outer regions of the early-type galaxy NGC 4203 (2015)
    Oxford University Press
    Details
    Publication Date: 2015-06-12
    Description: NGC 4203 is a nearby early-type galaxy surrounded by a very large, low-column-density H i disc. In this paper, we study the star formation efficiency in the gas disc of NGC 4203 by using the UV, deep optical imaging and infrared data. We confirm that the H i disc consists of two distinct components: an inner star-forming ring with radius from ~1 to ~3 R eff and an outer disc. The outer H i disc is nine times more massive than the inner H i ring. At the location of the inner H i ring, we detect spiral-like structure both in the deep g ' –  r ' image and in the 8 μm Spitzer -Infrared Array Camera image, extending in radius up to ~ 3 R eff . These two gas components have a different star formation efficiency likely due to the different metallicity and dust content. The inner component has a star formation efficiency very similar to the inner regions of late-type galaxies. Although the outer component has a very low star formation efficiency, it is similar to that of the outer regions of spiral galaxies and dwarfs. We suggest that these differences can be explained with different gas origins for the two components such as stellar mass loss for the inner H i ring and accretion from the inter galactic medium for the outer H i disc. The low-level star formation efficiency in the outer H i disc is not enough to change the morphology of NGC 4203, making the depletion time of the H i gas much too long.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 8
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    Star formation in the outer regions of the early-type galaxy NGC 4203 (2015)
    Oxford University Press
    Details
    Publication Date: 2015-05-24
    Description: NGC 4203 is a nearby early-type galaxy surrounded by a very large, low-column-density H i disc. In this paper, we study the star formation efficiency in the gas disc of NGC 4203 by using the UV, deep optical imaging and infrared data. We confirm that the H i disc consists of two distinct components: an inner star-forming ring with radius from ~1 to ~3 R eff and an outer disc. The outer H i disc is nine times more massive than the inner H i ring. At the location of the inner H i ring, we detect spiral-like structure both in the deep g ' –  r ' image and in the 8 μm Spitzer -Infrared Array Camera image, extending in radius up to ~ 3 R eff . These two gas components have a different star formation efficiency likely due to the different metallicity and dust content. The inner component has a star formation efficiency very similar to the inner regions of late-type galaxies. Although the outer component has a very low star formation efficiency, it is similar to that of the outer regions of spiral galaxies and dwarfs. We suggest that these differences can be explained with different gas origins for the two components such as stellar mass loss for the inner H i ring and accretion from the inter galactic medium for the outer H i disc. The low-level star formation efficiency in the outer H i disc is not enough to change the morphology of NGC 4203, making the depletion time of the H i gas much too long.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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