English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

We present results of a radial velocity ( RV ) survey for planets and brown dwarf (BD) companions to very young BDs and (very) low-mass stars in the Cha I star-forming cloud. Time-resolved high-resolution echelle spectra of Cha H α  1–8 and Cha H α  12 (M6–M8), B34 (M5), CHXR 74 (M4.5), and Sz 23 (M2.5) were taken with UVES at the VLT between 2000 and 2004. The precision achieved for the relative RV s range between 40 and 670 m s -1 and is sufficient to detect Jupiter mass planets around the targets. This is the first RV  survey of very young BDs. It probes multiplicity, which is a key parameter for formation in an as yet unexplored domain, in terms of age, mass, and orbital separation. We find that the subsample of ten BDs and very low-mass stars (VLMSs, $M\la 0.12\,M_{\odot}$, spectral types M5-M8) has constant RV s on time scales of 40 days and less. For this group, estimates of upper limits for masses of hypothetical companions range between 0.1  M Jup and 1.5  M Jup for assumed orbital separations of 0.1 AU. This hints at a rather small multiplicity fraction for very young BDs/VLMSs, for orbital separations of $\la$0.1 AU and orbital periods of $\la$40 days. Furthermore, the non-variable objects demonstrate the lack of any significant RV  noise due to stellar activity down to the precision necessary to detect giant planets. Thus, very young BDs/VLMSs are suitable targets for RV  surveys for planets. Three objects of the sample exhibit significant RV  variations with peak-to-peak RV  differences of 2-3 km s -1 . For the highest mass object observed with UVES (Sz 23, ~0.3 $M_{\odot}$), the variations are on time scales of days, which might be explained by rotational modulation. On the other hand, the BD candidate Cha H α  8 (M6.5) and the low-mass star CHXR 74 (M4.5) both display significant RV  variations on times scales of $\ga$150 days, while they are both RV  constant or show only much smaller amplitude variations on time scales of days to weeks, i.e. of the rotation periods. A suggested explanation for the detected RV  variations of CHXR 74 and Cha H α  8 is that they are caused by giant planets or very low-mass BDs of at least a few Jupiter masses orbiting with periods of several months or longer. Thus, the presented RV  data indicate that orbital periods of companions to very young BDs and (very) low-mass stars are possibly several months or longer, and that orbital separations are $\ga$0.2 AU. This parameter range has not been covered for all targets yet, but will be probed by follow-up observations. Furthermore, we show that the scaled down equivalent to the BD desert found around solar-like stars would be a giant planet desert around BD and VLMS primaries, if formed by the same mechanism. The present data test its existence for the targets in the limited separation range of the survey. So far, no hints of companions in a “giant planet desert” have been found.

Radial velocity survey for planets and brown dwarf companions to very young brown dwarfs and very low-mass stars in Chamaeleon I with UVES at the VLT