Discarded candidate companions to low-mass members of Chamaeleon I

• Published in: Astronomy and astrophysics (Berlin) Vol. 537; p. A97
• Main Author: COMERON, F
• Format: Journal Article
• Language: English
• Published: Les Ulis EDP Sciences 01.01.2012
• Subjects: Astronomy; binaries: general; brown dwarfs; Earth, ocean, space; Exact sciences and technology; stars: formation; stars: low-mass; stars: pre-main sequence; Stellar cores; Stellar spectra; Spectroscopy; Stellar formation region; Color; Member star; Luminosity; Spectral type; Proto planetary nebula; Fragmentation; stars: formation; stars: pre-main sequence; Nearby stars; brown dwarfs; Star formation; Low-mass stars; Brown dwarf stars; Adaptive optics; binaries: general; stars: low-mass; Photometry
• ISSN: 0004-6361; 1432-0746
• DOI: 10.1051/0004-6361/201117590

Context. Direct detections of brown dwarfs and planetary-mass companions to members of nearby star-forming regions provide important clues about the process of star formation, core fragmentation, and protoplanetary disk evolution. Aims. We study two faint objects at a very small angular distance from the low-mass star ESO-Hα-558 and the possible massive brown dwarf ESO-Hα-566, both of which are members of the Chamaeleon I star-forming region, to establish whether they are physical companions to those sources. If they are, their low luminosities should imply L or T spectral types, which have clearly detectable spectral features. Methods. Adaptive optics-assisted imaging and spectroscopy of both faint candidate companions has been obtained with the NACO instrument at the Very Large Telescope (VLT). Results. Photometry shows that the colors of both objects are compatible with them being moderately reddened, normal stars in the background of the Chamaeleon I clouds. This interpretation is confirmed spectroscopically, as the spectrum between 1.4 and 2.4 μm of both objects has a featureless, monotonic slope lacking the strong H2O absorption features that dominate cool stellar and substellar spectra in that domain. Conclusions. We demonstrate that the two faint sources seen very close to ESO-Hα-558 and ESO-Hα-566 are unrelated background stars, instead of giant planetary-mass companions as might be expected based on their faintness and angular proximity.