| 1. |
- Abramowski, A., et al.
(författare)
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Discovery of variable VHE gamma-ray emission from the binary system 1FGL J1018.6-5856
- 2015
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Ingår i: Astronomy and Astrophysics Supplement Series. - : EDP Sciences. - 0365-0138 .- 1286-4846. ; 577
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Tidskriftsartikel (refereegranskat)abstract
- Re-observations with the HESS telescope array of the very high-energy (VHE) source HESS J1018-589 A that is coincident with the Fermi-LAT γ-ray binary 1FGL J1018.6-5856 have resulted in a source detection significance of more than 9σ and the detection of variability (χ$^2$/ν of 238.3/155) in the emitted γ-ray flux. This variability confirms the association of HESS J1018-589 A with the high-energy γ-ray binary detected by Fermi-LAT and also confirms the point-like source as a new VHE binary system. The spectrum of HESS J1018-589 A is best fit with a power-law function with photon index Γ = 2.20 \plusmn 0.14$_stat$ \plusmn 0.2$_sys$. Emission is detected up to ~20 TeV. The mean differential flux level is (2.9 \plusmn 0.4) \times 10$^-13$ TeV$^-1$ cm$^-2$ s$^-1$ at 1 TeV, equivalent to ~1% of the flux from the Crab Nebula at the same energy. Variability is clearly detected in the night-by-night light curve. When folded on the orbital period of 16.58 days, the rebinned light curve peaks in phase with the observed X-ray and high-energy phaseograms. The fit of the HESS phaseogram to a constant flux provides evidence of periodicity at the level of N$_sigma$\gt 3σ. The shape of the VHE phaseogram and measured spectrum suggest a low-inclination, low-eccentricity system with amodest impact from VHE γ-ray absorption due to pair production (τ \lsim 1 at 300 GeV).
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| 2. |
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| 4. |
- Bååth, Lars, 1948-, et al.
(författare)
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High resolution interferometry of the QSO 1422+202
- 1997
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Ingår i: Astronomy and Astrophysics. Supplement Series. - Berlin : Springer. - 1286-4846 .- 0365-0138. ; 125:1, s. 453-458
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Tidskriftsartikel (refereegranskat)abstract
- We present VLA A-array observations at 8.4 and 15GHz and European VLBI Network (EVN) observations at 1.6GHz of the radio source 1422+202. It is suggested that 1422+202 is a Medium-size Object in the evolutionary sequence from Compact Steep-spectrum Sources to larger sized radio sources. The VLBI data were analysed with the phase referencing technique and we show that the EVN can work as a phase stable instrument for separations between the calibrator source and the target source up to ~ 10 degrees. With the VLA and VLBI observations we investigate some of the issues about the nucleus of 1422+202 and we discuss the possible cause for the low frequency variability detected while monitoring the source.
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| 5. |
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| 6. |
- deLaverny, P, et al.
(författare)
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Long-term UBV(RI)(c) monitoring of 12 southern hemisphere Long Period Variables
- 1997
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Ingår i: ASTRONOMY & ASTROPHYSICS SUPPLEMENT SERIES. - : EDITIONS PHYSIQUE. - 0365-0138. ; 122:3, s. 415-432
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- A program of UBV(RI)(c) photometric observations of twelve southern hemisphere Long Period Variables (LPV or Miras) has been carried out at the European Southern Observatory. Each star was observed on at least 11 occasions up to 29 over a 4-year period. A
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| 7. |
- Feltzing, Sofia, et al.
(författare)
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Abundances in metal-rich stars. Detailed abundance analysis of 47 G and K dwarf stars with [Me/H] > 0.10 dex
- 1998
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Ingår i: Astronomy and Astrophysics Supplement Series. - : EDP Sciences. - 0365-0138 .- 1286-4846. ; 129, s. 237-266
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Tidskriftsartikel (refereegranskat)abstract
- We have derived elemental abundances of O, Na, Mg, Al, Si, Ca, Ti, Cr, Mn, Fe, Co, Ni as well as for a number of s-elements for 47 G and K dwarf, with [Me/H]>0.1 dex. The selection of stars was based on their kinematics as well as on their uvby-beta photometry. One sample of stars on rather eccentric orbits traces the chemical evolution interior to the solar orbit and another, on circular orbits, the evolution around the solar orbit. A few Extreme Population I stars were included in the latter sample. The stars have -0.1 dex < [Fe/H] < 0.42 dex. The spectroscopic [Fe/H] correlate well with the [Me/H] derived from uvby-beta photometry. We find that the elemental abundances of Mg, Al, Si, Ca, Ti, Cr and Ni all follow [Fe/H]. Our data put further constraints on models of galactic chemical evolution, in particular of Cr, Mn and Co which have not previously been studied for dwarf stars with [Me/H] >0.1 dex. The increase in [Na/Fe] and [Al/Fe] as a function of [Fe/H] found previously by cite[Edvardsson et al. (1993a)]{Edv93} has been confirmed for [Na/Fe]. This upturning relation, and the scatter around it, are shown not to be due to a mixture of populations with different mean distances to the galactic centre. We do not confirm the same trend for aluminium, which is somewhat surprising since both these elements are thought to be produced in the same environments in the pre-supernova stars. Nor have we been able to trace any tendency for relative abundances of O, Si, and Ti relative to Fe to vary with the stellar velocities, i.e. the stars present mean distance to the galactic centre. These results imply that there is no significant difference in the chemical evolution of the different stellar populations for stars with [Me/H]>0.1 dex. We find that [O/Fe] continue to decline with increasing [Fe/H] and that oxygen and europium correlate well. However [Si/Fe] and [Ca/Fe] seem to stay constant. A real (``cosmic'') scatter in [Ti/Fe] at given [Fe/H] is suggested as well as a decreasing abundance of the s-elements relative to iron for the most metal-rich dwarf stars. We discuss our results in the context of recent models of galactic chemical evolution. In our sample we have included a few very metal rich stars, sometimes called SMR (super metal rich) stars. We find these stars to be among the most iron-rich in our sample but far from as metal-rich as indicated by their photometric metallicities. SMR stars on highly eccentric orbits, alleged to trace the evolution of the chemical evolution in the galactic Bulge, have previously been found overabundant in O, Mg and Si. We have included three such stars from the study by cite[Barbuy & Grenon (1990)]{Bar90}. We find them to be less metal rich and the other elemental abundances remain puzzling. Detailed spectroscopic abundance analyses of K dwarf stars are rare. Our study includes 5 K dwarf stars and has revealed what appears to be a striking example of overionization. The overionization is especially prominent for Ca, Cr and Fe. The origin of this apparent overionization is not clear and we discuss different explanations in some detail. Based on observations at the McDonald Observatory.
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| 8. |
- Feltzing, Sofia, et al.
(författare)
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Abundances in metal-rich stars - Detailed abundance analysis of 47 G and K dwarf stars with [Me/H]> 0.10 dex
- 1998
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Ingår i: ASTRONOMY & ASTROPHYSICS SUPPLEMENT SERIES. - : E D P SCIENCES. - 0365-0138. ; 129:2, s. 237-266
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Tidskriftsartikel (refereegranskat)abstract
- We have derived elemental abundances of O, Na, Mg, Al, Si, Ca, Ti, Cr, Mn, Fe, Co, Ni as well as for a number of s-elements for 47 G and K dwarf, with [Me/H]> 0.1 dex. The selection of stars was based on their kinematics as well as on their uvby - beta ph
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| 9. |
- GARCIA, JR, et al.
(författare)
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A CATALOG OF VARIABLE-STARS IN THE LOWER INSTABILITY STRIP
- 1995
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Ingår i: ASTRONOMY & ASTROPHYSICS SUPPLEMENT SERIES. - 0365-0138. ; 109:2, s. 201-262
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Identifications, positions, photometry, spectra, some pulsational features, other astrophysical parameters and literature for 302 pulsating variable stars in the lower instability strip, near the ZAMS, are given. About 185 stars have near homogeneous phot
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| 10. |
- Hernius, O, et al.
(författare)
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Astrometry of outer Jovian satellites from the Uppsala-ESO survey of asteroids and comets (UESAC)
- 1996
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Ingår i: ASTRONOMY & ASTROPHYSICS SUPPLEMENT SERIES. - : EDITIONS PHYSIQUE. - 0365-0138. ; 115:2, s. 295-296
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Tidskriftsartikel (refereegranskat)abstract
- In the course of The Uppsala-ESO Survey of Asteroids and Comets astrometric positions of the faint outer Jovian satellites J VI-XIII were obtained from photographic plates and films taken at the European Southern Observatory, La Silla, Chile and at the An
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