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We have conducted observations of the environment around the z 2X15 radio-loud quasar 1550±269 in search of distant galaxies associated either with it or the z 2X09 C iv absorber along its line of sight. Such objects will be distinguished by their red colours, R 2 K . 4X5X We find five such objects in a 1.5 arcmin 2 field around the quasar, with typical K H magnitudes of ,20.4 and no detected R-band emission. We also find a sixth object with K 19X6^0X3Y and undetected at R, just two arcsec from the quasar. The nature of all these objects is currently unclear, and will remain so until we have determined their redshifts. We suggest that it is likely that they are associated with either the quasar or the C iv absorber, in which case their properties might be similar to those of the z 2X38 red Lya emitting galaxies discovered by Francis et al. The small separation between the quasar and the brightest of our objects suggests that it may be the galaxy responsible for the C iv metal line absorption system. The closeness to the quasar and the red colour might have precluded similar objects from being uncovered in previous searches for emission from C iv and damped absorbers.
We have conducted observations of the environment around the z 2X15 radio-loud quasar 1550±269 in search of distant galaxies associated either with it or the z 2X09 C iv absorber along its line of sight. Such objects will be distinguished by their red colours, R 2 K . 4X5X We find five such objects in a 1.5 arcmin 2 field around the quasar, with typical K H magnitudes of ,20.4 and no detected R-band emission. We also find a sixth object with K 19X6^0X3Y and undetected at R, just two arcsec from the quasar. The nature of all these objects is currently unclear, and will remain so until we have determined their redshifts. We suggest that it is likely that they are associated with either the quasar or the C iv absorber, in which case their properties might be similar to those of the z 2X38 red Lya emitting galaxies discovered by Francis et al. The small separation between the quasar and the brightest of our objects suggests that it may be the galaxy responsible for the C iv metal line absorption system. The closeness to the quasar and the red colour might have precluded similar objects from being uncovered in previous searches for emission from C iv and damped absorbers.
Abstract. We present adaptive optics JHKS imaging observations of three main-sequence late B-type stars listed in the Lindroos Catalogue: HD 123445, HD 127971 and HD 129791. Given their spectral types, these stars should not be X-ray emitters. However, they have been detected by ROSAT and their X-ray emission has been attributed to possible unresolved late-type companions. We have carried out near-IR observations with ADONIS at the ESO 3.6 m but have not detected any late-type companions close to HD 127971 and HD 129791. This result leads us to conclude that either (i) they are spectroscopic binaries with unresolved low-mass companions, or (ii) they are intrinsic X-ray emitters. While the former case would be consistent with the reported high multiplicity of early-type (A and B) stars, the latter would yield a revision of stellar activity theories which do not predict X-ray emission from these stars. On the other hand, HD 123445 does indeed show visual companions, namely an apparent subarcsecond faint (Ks ∼ 10) binary system at a projected separation of 5 from the late-B type star. The JHKS magnitudes and colors of the components are consistent with (i) a pair of Pre Main Sequence (PMS) K-type stars at 140 pc (i.e. possible members of the Upper Centaurus Lupus association), (ii) a pair of Main Sequence M-type stars at 60 pc and (iii) a pair of K-type giants at 2.6 kpc. While in the first case the reported X-ray emission can be ascribed to the new objects, in the second and third case it cannot, and we have to assume the late B-type star to be either a spectroscopic binary itself or a single star with intrinsic X-ray emission. Spectroscopy is required to confirm the possible PMS nature of the new binary and Chandra X-ray high spatial resolution (astrometric) imaging observations are required to definitely determine the source of the X-ray emission. If the B9 star results to be the X-ray emitter, near-IR spectroscopy can be used to investigate the presence of a T Tauri like spectroscopic companions.
Abstract.A sample of 115 B-type stars in the Sco OB2 association is examined for existence of visual companions in the J and Ks bands, using the ADONIS near-infrared adaptive optics system and coronograph. Practically all the components in the separation range 0. 3-6. 4 (45-900 AU) and magnitudes down to K = 16 were detected. The K and J −K photometry of the primaries and differential photometry and astrometry of the 96 secondaries are presented. Ten secondaries are new physical components, as inferred from the photometric and statistical criteria, while the rest of the newly detected objects are faint background stars. After a small correction for detection incompleteness and a conversion of the fluxes into masses, an unbiased distribution of the components mass ratio q was derived. The power law f (q) ∝ q −0.5 fits the observations well, whereas a q −1.8 distribution, which corresponds to a random pairing of stars, is rejected. The companion star fraction is 0.20 ± 0.04 per decade of separation which is comparable to the highest measured binary fraction among low-mass PMS stars and ∼1.6 times higher than the binary fraction of low-mass dwarfs in the solar neighborhood and in open clusters in the same separation range.
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