| 1. |
- van Genderen, A. M., et al.
(author)
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A discussion on new VBLUW observations of the X-ray binary Sk. 160=SMC X-1
- 1981
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In: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 101:1, s. 101-104104
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Journal article (peer-reviewed)abstract
- VBLUW photometry (Walraven system) of Sk. 160=SMC X-1 made in 1973, 1975, and 1977 are discussed. They are compared with those of van Paradijs (1977) made in 1976. Using all available photometric and X-ray mid-eclipse data, a period is determined by a weighted least-squares solution: P=3.89235 dplusmn0.00002 d m.e
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| 2. |
- van Genderen, A. M., et al.
(author)
-
VBLUW photometry of the association Sco OB1 (containing the open cluster NGC 6231). A discussion on the evolutionary status of the hypergiant zeta 1 Sco (B1 Ia +)
- 1984
-
In: Astronomy and Astrophysics Supplement Series. - 0365-0138 .- 1286-4846. ; 58:3, s. 537-548548
-
Journal article (peer-reviewed)abstract
- VBLUW photometry of nearly 190 stars in the very young association Sco OB1, including the cluster NGC 6231, is presented and discussed. Temperature and surface gravity are determined with the aid of theoretical colours. Individual reddenings are also obtained. The distance modulus ( m- M) 0=11.00plusmn0.25 is similar to the value found by Shobbrook (1983). It appears that the reddening is not uniformly distributed across the association (~2degtimes1deg), but that areas of low and high reddening, varying from E( B- V) J=0.35 up to 0.67, can be distinguished. Practically all reddening is caused by dust in the local spiral arm up to a distance of at most 700 pc from the Sun. The Sagittarius-Carina arm where Sco OB1 is situated is practically transparent over a distance of ~0.5 kpc. The kinematical age of ~10 6 yr is in reasonable agreement with the average evolutionary age of ~(3.6plusmn0.6)times10 6 yr of the 12 brightest stars. The evolutionary status of the hypergiant zeta 1 Sco (B1 Ia +) is discussed
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| 3. |
- van Groningen, E.
(author)
-
Accretion disks in Seyfert nuclei : broad line profiles and asymmetries
- 1983
-
In: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 126:2, s. 363-371371
-
Journal article (peer-reviewed)abstract
- Keplerian rotation around a massive object in the centre of a Seyfert galaxy is considered as the main broadening mechanism for the broad emission lines. The resultant line profiles are shown to be of power-law form in the wings and are compared with recently published high quality observations. Several possible solutions are given for the [O III]-problem raised by Shields (1978). Asymmetries in the line profiles are explained by anisotropically radiating filaments in two oppositely directed jets emanating from the centre of the disk and by radial motions in or above the disk
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| 4. |
- Van Groningen, E., et al.
(author)
-
One-sided jets in extragalactic radiosources
- 1980
-
In: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 90:1-2, s. L7-L9L9
-
Journal article (peer-reviewed)abstract
- Some explanations for the existence of one-sided jets in symmetrical extended radio sources are discussed. It is shown that in the case of the quasar 4C32.69, a relativistic Doppler interpretation is improbable. Observational constraints on a model involving anisotropic radiation are also examined. This model cannot be ruled out, although non-relativistic interpretations of one-sided jets are most likely
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