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  • 1001.
    Zackrisson, Erik
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics.
    Persson, Carina
    Bergvall, Nils
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics.
    On planetary-mass compact objects as dark matter2004In: Dark matter in galaxies, 2004Conference paper (Other (popular scientific, debate etc.))
  • 1002.
    Zackrisson, Erik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics.
    Riehm, T.
    High-redshift microlensing and the spatial distribution of dark matter in the form of MACHOs2007In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 475, no 2, p. 453-465Article in journal (Refereed)
    Abstract [en]

    A substantial part of the dark matter of the Universe could be in the form of compact objects (MACHOs), detectable through gravitational microlensing effects as they pass through the line of sight to background light sources. So far, most attempts to model the effects of high-redshift microlensing by a cosmologically distributed population of MACHOs have assumed the compact objects to be randomly and uniformly distributed along the line of sight. Here, we present a more realistic model, in which the MACHOs are assumed to follow the spatial clustering of cold dark matter. Because of sightline-to-sightline variations in surface mass density, this scenario leads to substantial scatter in MACHO optical depths, which we quantify as a function of source redshift. We find that while optical depth estimates based on a uniform line-of-sight distribution are reasonable for the highest-redshift light sources, such estimates can be incorrect by a factor of approximate to 2 for the nearby (z approximate to 0.25) Universe. Hence, attempts to derive the cosmological density of MACHOs from microlensing observations of only a few independent sightlines can be subject to substantial uncertainties. We also apply this model to the prediction of microlensing-induced variability in quasars not subject to macrolensing, and demonstrate that relaxing the assumption of randomly and uniformly distributed MACHOs only has a modest impact on the predicted light curve amplitudes. This implies that the previously reported problems with microlensing as the dominant mechanism for the observed long-term optical variability of quasars cannot be solved by taking the large-scale clustering of dark matter into account.

  • 1003. Zima, W.
    et al.
    Wright, D.
    Bentley, J.
    Cottrell, P. L.
    Heiter, Ulrike
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics.
    et al.,
    A new method for the spectroscopic identification of stellar non-radial pulsation modes: II. Mode identification of the delta Scuti star FG Virginis2006In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 455, no 1, p. 235-246Article in journal (Refereed)
    Abstract [en]

    Aims. We present a mode identification based on new high-resolution time-series spectra of the non-radially pulsating delta Scuti star FG Vir (HD 106384, V = 6.57, A5V). From 2002 February to June a global Delta Scuti Network (DSN) campaign, utilizing high-resolution spectroscopy and simultaneous photometry has been conducted for FG Vir in order to provide a theoretical pulsation model. In this campaign we have acquired 969 Echelle spectra covering 147 h at six observatories.

    Methods. The mode identification was carried out by analyzing line profile variations by means of the Fourier parameter fit method, where the observational Fourier parameters across the line are fitted with theoretical values. This method is especially well suited for determining the azimuthal order m of non-radial pulsation modes and thus complementary with the method of Daszynska-Daszkiewicz (2002) which does best at identifying the degree l.

    Results. 15 frequencies between 9.2 and 33.5 d(-1) were detected spectroscopically. We determined the azimuthal order m of 12 modes and constrained their harmonic degree l. Only modes of low degree (l <= 4) were detected, most of them having axisymmetric character mainly due to the relatively low projected rotational velocity of FG Vir. The detected non-axisymmetric modes have azimuthal orders between -2 and 1. We derived an inclination of 19 degrees, which implies an equatorial rotational rate of 66 km s(-1).

  • 1004. Zucca, C.
    et al.
    Andrushchenko, Zh. N.
    Pavlenko, V. P.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics.
    Predator-prey phenomena in interchange mode turbulence2004In: 31st EPS Conference on Plasma Physics, 28th June - 2nd July 2004, London, UK, 2004Conference paper (Refereed)
  • 1005.
    Örndahl,  E.
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics.
    Rönnback,  J.
    Broadband optical colours of intermediate redshift QSO host galaxies2001In: QSO hosts and their environments, Proceedings of an international workshop, held January 10-12, 2001, in Granada, Spain, 2001Conference paper (Other scientific)
  • 1006.
    Örndahl,  E.
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics.
    Rönnback,  J.
    van Groningen,  E.
    An optical imaging study of 0.4 <= z <= 0.8 quasar host galaxies. I. Observations and reduction2003In: Astronomy and Astrophysics, ISSN 0004-6361, Vol. 404, p. 883-899Article in journal (Refereed)
    Abstract [en]

    We have conducted an optical imaging study aimed at resolving the host galaxies of 79 radio-loud and radio-quiet quasars at z=0.4-0.8, extending the number of investigated objects in this redshift range by ~ 45%. Observations were performed mainly in

  • 1007.
    Örndahl, Eva
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics, The Uppsala Astronomical Observatory.
    Quasar host galaxies at intermediate and high redshifts2003Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Quasars form one of the most energetic phenomena in the universe, and can be traced out to very large redshifts. By studying the galaxies which host the active nuclei, important insights can be gained into the processes that trigger and maintain the quasar powerhouse. The evolution rate of the quasar population is furthermore similar to that of ordinary galaxies, which implies a connection between black hole accretion and star formation in the host galaxies. While the properties of quasar host galaxies at low redshift have become better constrained in recent years, less is known about hosts at earlier cosmic epochs. In addition, though radio-quiet quasars are by far more common than their radio-loud counterparts their host galaxies have not been studied to the same extent, in particular not at higher redshifts.

    An imaging campaign of a large sample of quasars at intermediate redshift (0.4 < z < 0.8) was carried out at optical wavelengths using the Nordic Optical Telescope, and is studied in this thesis together with two smaller samples. The joint material forms more than half of the total number of observed sources in this redshift interval and increases the number of resolved radio-quiet hosts at z>0.4 considerably. The morphology and mean magnitudes are found to be similar for radio-loud and radio-quiet host galaxies. Both types of host are shown to have optical colours as blue as those of present-day late-type spirals and starburst galaxies, which is likely the result of ongoing star formation.

    With increasing redshift, observations of host galaxies become more difficult. High spatial resolution can be achieved with adaptive optics, but the variation of the point spread function in the near-infrared wavelength band which is most suited for detection is large and rapid. A statistical approach to the problem of characterizing the point spread function has been developed, making use of simulated objects which are matched to the different atmospheric conditions. Bright, compact host galaxies showing signs of merging and interaction were detected in this way for three quasars at z~2.2, which were observed with the ESO 3.6 m telescope. The method is not restricted to host galaxy analysis but can be utilized in other applications as well, provided that the underlying extended source can be described by an analytical model.

    List of papers
    1. An optical imaging study of 0.4 < z < 0.8 quasar host galaxies: I. Observations and reduction
    Open this publication in new window or tab >>An optical imaging study of 0.4 < z < 0.8 quasar host galaxies: I. Observations and reduction
    2003 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, Vol. 404, p. 883-899Article in journal (Refereed) Published
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:uu:diva-90498 (URN)
    Available from: 2003-05-07 Created: 2003-05-07 Last updated: 2013-03-17
    2. An optical imaging study of 0.4 < z < 0.8 quasar host galaxies: II. Analysis and interpretation
    Open this publication in new window or tab >>An optical imaging study of 0.4 < z < 0.8 quasar host galaxies: II. Analysis and interpretation
    2005 In: Astronomy and Astrophysics, ISSN 0004-6361, Vol. 443, p. 61-78Article in journal (Refereed) Published
    Identifiers
    urn:nbn:se:uu:diva-90499 (URN)
    Available from: 2003-05-07 Created: 2003-05-07Bibliographically approved
    3. High-redshift quasar host galaxy analysis with adaptive optics: A statistical approach
    Open this publication in new window or tab >>High-redshift quasar host galaxy analysis with adaptive optics: A statistical approach
    2005 In: Astronomy and Astrophysics, ISSN 0004-6361, Vol. 439, p. 497-512Article in journal (Refereed) Published
    Identifiers
    urn:nbn:se:uu:diva-90500 (URN)
    Available from: 2003-05-07 Created: 2003-05-07Bibliographically approved
    Download full text (pdf)
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  • 1008.
    Örndahl, Eva
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics, The Uppsala Astronomical Observatory.
    Rönnback, Jari
    An optical imaging study of 0.4 < z < 0.8 quasar host galaxies: II. Analysis and interpretation2005In: Astronomy and Astrophysics, ISSN 0004-6361, Vol. 443, p. 61-78Article in journal (Refereed)
  • 1009.
    Örndahl, Eva
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics, The Uppsala Astronomical Observatory.
    Rönnback, Jari
    van Groningen, Ernst
    An optical imaging study of 0.4 < z < 0.8 quasar host galaxies: I. Observations and reduction2003In: Astronomy and Astrophysics, ISSN 0004-6361, Vol. 404, p. 883-899Article in journal (Refereed)
  • 1010.
    Östlin, Göran A.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics, The Uppsala Astronomical Observatory.
    On the origin and evolution of blue compact galaxies1998Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis is focused on the origin and evolution of blue compact galaxies (BCGs). BCGs are low mass galaxies characterised by blue colours, low chemical abundances and high star formation rates. The gas consumtion time scale is considerable shorter than the age of the universe and thus the high star formation rate must be transient. Such a non sustainable star formation rate is commonly referred to as a "starburst". It has been proposed that BCGs are genuinely young galaxies or alternatively that theyoccasionally undergo starbursts, separated by long quiesent periods. It is of importance for the understanding of the evolution of galaxies, and in particular dwarf galaxies, to understand under what conditions a galaxy can become a starbursting BCG.

    The properties of in particular intrinsically luminous BCGs have been examined photometrically and kinematically. The results show that the studied galaxies have a population of old stars underlying the luminous starbursts. Thus they are not young galaxies. It is shown that infrared photometry is a powerful method to detect underlying old populations in BCGs. Kinematical studies of the velocity field suggests that the galaxies have been perturbed by mergers, and it is proposed that mergers betweengas rich dwarf galaxies is the triggering mechanism for starbursts in luminous BCGs. Low surface brightness galaxies are promising ingredients in such mergers.

    Observations with the Hubble Space Telescope of the BCG ESO 338- IG04 reveal the presence of a very rich population of globular clusters (GCs) of various ages. Apparently GC formation is still going on in this starbursting galaxy. The age dating of GCs offers an efficient way of studying the starburst history of BCGs and galaxies in general. The relation between BCGs and other types of low mass galaxies is discussed.

  • 1011. Östlin, Göran
    et al.
    Amram, Philippe
    Boulesteix, Jaques
    Bergvall, Nils
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics and Astronomy. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics and Astronomy, Observational Astronomy.
    Masegosa, Josefa
    Márquez, Isabel
    Kinematics of luminous blue compact galaxies2001In: Astrophysics and Space Science, p. 433-Article in journal (Refereed)
    Abstract [en]

    We present results from a Fabry-Perot study of the Hα velocity fields and morphologies of a sample of luminous blue compact galaxies. We estimate masses from photometry and kinematics and show that many of these BCGs are not rotationally supported. Mergers or strong interactions appear to be the triggering mechanism of the extreme starbursts seen in these galaxies.

  • 1012.
    Östlin, Göran
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics.
    Bergvall, Nils
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics.
    Rönnback, Jari
    HST photometry of ESO 338-IG04 globular clusters (Östlin+, 1998)2001Other (Other scientific)
  • 1013. Östlin, Göran
    et al.
    Cumming, Robert
    Bergvall, Nils
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Astronomy and Space Physics.
    Dynamical masses of two young globular clusters in the blue compact galaxy ESO 338-IG042007In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 461, no 2, p. 471-483Article in journal (Refereed)
    Abstract [en]

    We present high-resolution échelle spectroscopy, obtained with the UVES spectrograph on ESO/VLT, of two luminous star clusters in the metal-poor blue compact galaxy ESO 338-IG04 at a distance of 37.5 Mpc. Cross-correlating with template stars, we obtain line-of-sight velocity dispersions of 33 and 17 km s-1. By combining with size estimates from Hubble Space Telescope images we infer dynamical masses of 1.3×107 M_ȯ and 4.0×106 M_ȯ for the two clusters, making them among the most massive known. The less massive cluster is the faintest cluster for which a dynamical mass has yet been obtained. In both clusters we detect Balmer absorption lines which we use to estimate their ages. From the younger (~6 Myr) and more massive cluster, we detect H ii λ4686 emission of intermediate width, indicating the presence of very massive O-stars. Moreover, analysis of the [O iii] λ5007 and Hα emission lines from the region near the younger cluster indicates that it is associated with a bubble expanding at ~40 km s-1. We also see from the Na i D absorption lines indications of neutral gas flows towards the younger cluster. We compare the dynamical masses with those derived from photometry and discuss implications for the stellar initial mass function (IMF) in each cluster. Both clusters are compatible with rather normal IMFs which will favour their long-term survival and evolution into massive bona fide globular clusters.

  • 1014.
    Östlin, Göran
    et al.
    Stockholm Observatory.
    Cummings, R.J.
    Stockholm Observatory.
    Amram, P.
    Bergvall, Nils
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics.
    Kunth, D.
    Marquez, I.
    Masegosa, J.
    Zackrisson, Erik
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics.
    Stellar dynamics of blue compact galaxies: I. Decoupled star-gas kinematics in ESO 400-G432004In: Astronomy & Astrophysics, no 419, p. L43-Article in journal (Refereed)
  • 1015.
    Östlin, Göran
    et al.
    Stockholm Observatory.
    Zackrisson, Erik
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics.
    Bergvall, Nils
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics.
    Rönnback, Jari
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics.
    The temporal and spatial evolution of the starburst in ESO 338-IG04 as probed by its star clusters2003In: Astronomy & Astrophysics, no 408, p. 887-Article in journal (Refereed)
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