ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    facet.materialart.
    Unknown
    HD 181068: a red giant in a triply eclipsing compact hierarchical triple system (2011)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2011-04-09
    Description: Hierarchical triple systems comprise a close binary and a more distant component. They are important for testing theories of star formation and of stellar evolution in the presence of nearby companions. We obtained 218 days of Kepler photometry of HD 181068 (magnitude of 7.1), supplemented by ground-based spectroscopy and interferometry, which show it to be a hierarchical triple with two types of mutual eclipses. The primary is a red giant that is in a 45-day orbit with a pair of red dwarfs in a close 0.9-day orbit. The red giant shows evidence for tidally induced oscillations that are driven by the orbital motion of the close pair. HD 181068 is an ideal target for studies of dynamical evolution and testing tidal friction theories in hierarchical triple systems.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Derekas, A -- Kiss, L L -- Borkovits, T -- Huber, D -- Lehmann, H -- Southworth, J -- Bedding, T R -- Balam, D -- Hartmann, M -- Hrudkova, M -- Ireland, M J -- Kovacs, J -- Mezo, Gy -- Moor, A -- Niemczura, E -- Sarty, G E -- Szabo, Gy M -- Szabo, R -- Telting, J H -- Tkachenko, A -- Uytterhoeven, K -- Benko, J M -- Bryson, S T -- Maestro, V -- Simon, A E -- Stello, D -- Schaefer, G -- Aerts, C -- ten Brummelaar, T A -- De Cat, P -- McAlister, H A -- Maceroni, C -- Merand, A -- Still, M -- Sturmann, J -- Sturmann, L -- Turner, N -- Tuthill, P G -- Christensen-Dalsgaard, J -- Gilliland, R L -- Kjeldsen, H -- Quintana, E V -- Tenenbaum, P -- Twicken, J D -- New York, N.Y. -- Science. 2011 Apr 8;332(6026):216-8. doi: 10.1126/science.1201762.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Astronomy, Eotvos University, Budapest, Hungary. derekas@konkoly.hu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21474755" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 2
    facet.materialart.
    Unknown
    The excitation of solar-like oscillations in a deltaSct star by efficient envelope convection (2011)
    Nature Publishing Group (NPG)
    Details
    Publication Date: 2011-09-16
    Description: Delta Scuti (deltaSct) stars are opacity-driven pulsators with masses of 1.5-2.5 Mmiddle dot in circle, their pulsations resulting from the varying ionization of helium. In less massive stars such as the Sun, convection transports mass and energy through the outer 30 per cent of the star and excites a rich spectrum of resonant acoustic modes. Based on the solar example, with no firm theoretical basis, models predict that the convective envelope in deltaSct stars extends only about 1 per cent of the radius, but with sufficient energy to excite solar-like oscillations. This was not observed before the Kepler mission, so the presence of a convective envelope in the models has been questioned. Here we report the detection of solar-like oscillations in the deltaSct star HD187547, implying that surface convection operates efficiently in stars about twice as massive as the Sun, as the ad hoc models predicted.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Antoci, V -- Handler, G -- Campante, T L -- Thygesen, A O -- Moya, A -- Kallinger, T -- Stello, D -- Grigahcene, A -- Kjeldsen, H -- Bedding, T R -- Luftinger, T -- Christensen-Dalsgaard, J -- Catanzaro, G -- Frasca, A -- De Cat, P -- Uytterhoeven, K -- Bruntt, H -- Houdek, G -- Kurtz, D W -- Lenz, P -- Kaiser, A -- Van Cleve, J -- Allen, C -- Clarke, B D -- England -- Nature. 2011 Sep 29;477(7366):570-3. doi: 10.1038/nature10389.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Institute of Astronomy, University of Vienna, Turkenschanzstrasse 18, A-1180 Vienna, Austria. victoria.antoci@univie.ac.at〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21918514" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 3
    facet.materialart.
    Unknown
    A comprehensive study of the open cluster NGC 6866 (2015)
    Oxford University Press
    Details
    Publication Date: 2015-08-25
    Description: We present CCD UBVRI photometry of the field of the open cluster NGC 6866. Structural parameters of the cluster are determined utilizing the stellar density profile of the stars in the field. We calculate the probabilities of the stars being physical members of the cluster, using their astrometric data, and perform further analyses using only the most probable members. The reddening and metallicity of the cluster were determined by independent methods. The LAMOST spectra and the ultraviolet excess of the F- and G-type main-sequence stars in the cluster indicate that the metallicity of the cluster is about the solar value. We estimated the reddening E ( B – V ) = 0.074 ± 0.050 mag using the U – B versus B – V two-colour diagram. The distance modula, the distance and the age of NGC 6866 were derived as μ = 10.60 ± 0.10 mag, d  = 1189 ± 75 pc and t  = 813 ± 50 Myr, respectively, by fitting colour–magnitude diagrams of the cluster with the PARSEC isochrones. The Galactic orbit of NGC 6866 indicates that the cluster is orbiting in a slightly eccentric orbit with e  = 0.12. The mass function slope x  = 1.35 ± 0.08 was derived by using the most probable members of the cluster.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 4
    facet.materialart.
    Unknown
    Analysis of Kepler B stars: rotational modulation and Maia variables (2015)
    Oxford University Press
    Details
    Publication Date: 2015-06-07
    Description: We examine 4 yr almost continuous Kepler photometry of 115 B stars. We find that the light curves of 39 per cent of these stars can be described by a low-frequency sinusoid and its harmonic, usually with variable amplitude, which we interpret as rotational modulation. A large fraction (32 stars or 28 per cent) might be classified as ellipsoidal variables, but a statistical argument suggests that these are probably rotational variables as well. Ten stars (8 per cent of the total) have a peculiar periodogram feature which is common among A stars. The physical cause of this feature is unknown but very likely related to rotation. The large number of rotating variables suggests that star-spots are common in B stars and indicates that magnetic fields can be generated in radiative stellar envelopes. We find five stars (4 per cent) to be β Cep (BECP) variables, all of which have low frequencies with relatively large amplitudes. The presence of low frequencies in BECP stars is an unsolved problem. There are 21 stars (18 per cent) with multiple low frequencies which could be described as slowly pulsating B (SPB) variables. Other pulsating stars do not fit into the general definition of BECP or SPB variables in that they are cool but pulsate with high frequencies. We assume that these are further examples of the anomalous pulsating stars which in the past have been called ‘Maia’ variables. There are 11 stars (10 per cent) of this type. We also examined 300 B stars observed in the K2 Campaign 0 field. We find 12 BECP/Maia candidates and 15 SPB variables.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 5
    facet.materialart.
    Unknown
    Spectroscopic survey of Kepler stars. I. HERMES/Mercator observations of A- and F-type stars (2015)
    Oxford University Press
    Details
    Publication Date: 2015-05-10
    Description: The Kepler space mission provided near-continuous and high-precision photometry of about 207 000 stars, which can be used for asteroseismology. However, for successful seismic modeling it is equally important to have accurate stellar physical parameters. Therefore, supplementary ground-based data are needed. We report the results of the analysis of high-resolution spectroscopic data of A- and F-type stars from the Kepler field, which were obtained with the HERMES spectrograph on the Mercator telescope. We determined spectral types, atmospheric parameters and chemical abundances for a sample of 117 stars. Hydrogen Balmer, Fe i , and Fe ii lines were used to derive effective temperatures, surface gravities, and microturbulent velocities. We determined chemical abundances and projected rotational velocities using a spectrum synthesis technique. The atmospheric parameters obtained were compared with those from the Kepler Input Catalogue (KIC), confirming that the KIC effective temperatures are underestimated for A stars. Effective temperatures calculated by spectral energy distribution fitting are in good agreement with those determined from the spectral line analysis. The analysed sample comprises stars with approximately solar chemical abundances, as well as chemically peculiar stars of the Am, Ap, and  Boo types. The distribution of the projected rotational velocity, v sin i , is typical for A and F stars and ranges from 8 to about 280 km s –1 , with a mean of 134 km s –1 .
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 6
    facet.materialart.
    Unknown
    Spectroscopic survey of {gamma} Doradus stars - I. Comprehensive atmospheric parameters and abundance analysis of {gamma} Doradus stars (2016)
    Oxford University Press
    Details
    Publication Date: 2016-03-24
    Description: We present a spectroscopic survey of known and candidate  Doradus stars. The high-resolution, high signal-to-noise spectra of 52 objects were collected by five different spectrographs. The spectral classification, atmospheric parameters ( T eff , log g , ), v sin i and chemical composition of the stars were derived. The stellar spectral and luminosity classes were found between G0–A7 and IV–V, respectively. The initial values for T eff and log g were determined from the photometric indices and spectral energy distribution. Those parameters were improved by the analysis of hydrogen lines. The final values of T eff , log g and were derived from the iron lines analysis. The T eff values were found between 6000 K and 7900 K, while log g  values range from 3.8 to 4.5 dex. Chemical abundances and v sin i values were derived by the spectrum synthesis method. The v sin i values were found between 5 and 240 km s –1 . The chemical abundance pattern of  Doradus stars were compared with the pattern of non-pulsating stars. It turned out that there is no significant difference in abundance patterns between these two groups. Additionally, the relations between the atmospheric parameters and the pulsation quantities were checked. A strong correlation between the v sin i and the pulsation periods of  Doradus variables was obtained. The accurate positions of the analysed stars in the Hertzsprung–Russell diagram have been shown. Most of our objects are located inside or close to the blue edge of the theoretical instability strip of  Doradus.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 7
    facet.materialart.
    Unknown
    KIC 4768731: a bright long-period roAp star in the Kepler field (2015)
    Oxford University Press
    Details
    Publication Date: 2015-08-06
    Description: We report the identification of 61.45 d –1 (711.2 μHz) oscillations, with amplitudes of 62.6 μmag, in KIC 4768731 (HD 225914) using Kepler photometry. This relatively bright ( V  = 9.17) chemically peculiar star with spectral type A5 Vp SrCr(Eu) has previously been found to exhibit rotational modulation with a period of 5.21 d. Fourier analysis reveals a simple dipole pulsator with an amplitude that has remained stable over a 4-yr time span, but with a frequency that is variable. Analysis of high-resolution spectra yields stellar parameters of T eff  = 8100 ± 200 K, log g  = 4.0 ± 0.2, [Fe/H] = +0.31 ± 0.24 and v sin i  = 14.8 ± 1.6 km s –1 . Line profile variations caused by rotation are also evident. Lines of Sr, Cr, Eu, Mg and Si are strongest when the star is brightest, while Y and Ba vary in antiphase with the other elements. The abundances of rare earth elements are only modestly enhanced compared to other roAp stars of similar T eff and log g . Radial velocities in the literature suggest a significant change over the past 30 yr, but the radial velocities presented here show no significant change over a period of 4 yr.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 8
    facet.materialart.
    Unknown
    Analysis of Kepler B stars: rotational modulation and Maia variables (2015)
    Oxford University Press
    Details
    Publication Date: 2015-06-12
    Description: We examine 4 yr almost continuous Kepler photometry of 115 B stars. We find that the light curves of 39 per cent of these stars can be described by a low-frequency sinusoid and its harmonic, usually with variable amplitude, which we interpret as rotational modulation. A large fraction (32 stars or 28 per cent) might be classified as ellipsoidal variables, but a statistical argument suggests that these are probably rotational variables as well. Ten stars (8 per cent of the total) have a peculiar periodogram feature which is common among A stars. The physical cause of this feature is unknown but very likely related to rotation. The large number of rotating variables suggests that star-spots are common in B stars and indicates that magnetic fields can be generated in radiative stellar envelopes. We find five stars (4 per cent) to be β Cep (BECP) variables, all of which have low frequencies with relatively large amplitudes. The presence of low frequencies in BECP stars is an unsolved problem. There are 21 stars (18 per cent) with multiple low frequencies which could be described as slowly pulsating B (SPB) variables. Other pulsating stars do not fit into the general definition of BECP or SPB variables in that they are cool but pulsate with high frequencies. We assume that these are further examples of the anomalous pulsating stars which in the past have been called ‘Maia’ variables. There are 11 stars (10 per cent) of this type. We also examined 300 B stars observed in the K2 Campaign 0 field. We find 12 BECP/Maia candidates and 15 SPB variables.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 9
    facet.materialart.
    Unknown
    The classification of frequencies in the {gamma} Doradus/{delta} Scuti hybrid star HD 49434 (2015)
    Oxford University Press
    Details
    Publication Date: 2015-01-16
    Description: Hybrid stars of the  Doradus and  Scuti pulsation types have great potential for asteroseismic analysis to explore their interior structure. To achieve this, mode identifications of pulsational frequencies observed in the stars must be made, a task which is far from simple. In this work we begin the analysis by scrutinizing the frequencies found in the CoRoT photometric satellite measurements and ground-based high-resolution spectroscopy of the hybrid star HD 49434. The results show almost no consistency between the frequencies found using the two techniques and no characteristic period spacings or couplings were identified in either data set. The spectroscopic data additionally show no evidence for any long-term (5 yr) variation in the dominant frequency. The 31 spectroscopic frequencies identified have standard deviation profiles suggesting multiple modes sharing ( l , m ) in the  Scuti frequency region and several skewed modes sharing the same ( l , m ) in the  Doradus frequency region. In addition, there is a clear frequency in the  Doradus frequency region that appears to be unrelated to the others. We conclude HD 49434 remains a  Scuti/ Doradus candidate hybrid star but more sophisticated models dealing with rotation are sought to obtain a clear picture of the pulsational behaviour of this star.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 10
    facet.materialart.
    Unknown
    Extensive study of HD 25558, a long-period double-lined binary with two SPB components (2014)
    Oxford University Press
    Details
    Publication Date: 2014-02-20
    Description: We carried out an extensive observational study of the Slowly Pulsating B (SPB) star, HD 25558. The 2000 spectra obtained at different observatories, the ground-based and MOST satellite light curves revealed that this object is a double-lined spectroscopic binary with an orbital period of about nine years. The observations do not allow the inference of an orbital solution. We determined the physical parameters of the components, and found that both lie within the SPB instability strip. Accordingly, both show line-profile variations due to stellar pulsations. 11 independent frequencies were identified in the data. All the frequencies were attributed to one of the two components based on pixel-by-pixel variability analysis of the line profiles. Spectroscopic and photometric mode identification was also performed for the frequencies of both stars. These results suggest that the inclination and rotation of the two components are rather different. The primary is a slow rotator with 6 d period, seen at 60° inclination, while the secondary rotates fast with 1.2 d period, and is seen at 20° inclination. Spectropolarimetric measurements revealed that the secondary component has a magnetic field with at least a few hundred Gauss strength, while no magnetic field can be detected in the primary.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...