C.D.S. - SIMBAD4 rel 1.7 - 2021.03.02CET03:32:23

2001A&A...373..657H - Astronomy and Astrophysics, volume 373, 657-664 (2001/7-2)

ADONIS observations of hard X-ray emitting late B-type stars in Lindroos systems.


Abstract (from CDS):

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 140pc (i.e. possible members of the Upper Centaurus Lupus association), (ii) a pair of Main Sequence M-type stars at 60pc and (iii) a pair of K-type giants at 2.6kpc. 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 Copyright:

Journal keyword(s): stars: early-type - stars: binaries - infrared: stars - X-rays: stars

Simbad objects: 5

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Number of rows : 5

N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2021
1 UCAC4 233-072053 * 14 08 48.6904470057 -43 27 47.805062044       13.62   ~ 2 0
2 HD 123445 * 14 08 51.8859074874 -43 28 14.801932182   6.11 6.17     B9V 59 0
3 2MASS J14085231-4328126 * 14 08 52.3198254557 -43 28 12.908981909           ~ 2 0
4 HD 127971 * 14 35 31.4796913146 -41 31 02.798685058   5.79 5.87     B7V 51 0
5 HD 129791 * 14 45 57.6288433606 -44 52 03.028128471 6.96 6.96 6.92     A0V 63 0

    Equat.    Gal    SGal    Ecl

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