1,103 research outputs found
High-resolution imaging of planet host candidates. A comprehensive comparison of different techniques
The Kepler mission has discovered thousands of planet candidates. Currently,
some of them have already been discarded; more than 200 have been confirmed by
follow-up observations, and several hundreds have been validated. However, most
of them are still awaiting for confirmation. Thus, priorities (in terms of the
probability of the candidate being a real planet) must be established for
subsequent observations. The motivation of this work is to provide a set of
isolated (good) host candidates to be further tested by other techniques. We
identify close companions of the candidates that could have contaminated the
light curve of the planet host. We used the AstraLux North instrument located
at the 2.2 m telescope in the Calar Alto Observatory to obtain
diffraction-limited images of 174 Kepler objects of interest. The lucky-imaging
technique used in this work is compared to other AO and speckle imaging
observations of Kepler planet host candidates. We define a new parameter, the
blended source confidence level (BSC), to assess the probability of an object
to have blended non-detected eclipsing binaries capable of producing the
detected transit. We find that 67.2% of the observed Kepler hosts are isolated
within our detectability limits, and 32.8% have at least one visual companion
at angular separations below 6 arcsec. We find close companions (below 3
arcsec) for the 17.2% of the sample. The planet properties of this sample of
non-isolated hosts are revised. We report one possible S-type binary
(KOI-3158). We also report three possible false positives (KOIs 1230.01,
3649.01, and 3886.01) due to the presence of close companions. The BSC
parameter is calculated for all the isolated targets and compared to both the
value prior to any high-resolution image and, when possible, to observations
from previous high-spatial resolution surveys in the Kepler sample.Comment: Accepted for publication in A&A on April 29, 2014; 32 pages, 11
figures, 11 table
Spectroscopy of Very Low Mass Stars and Brown Dwarfs in the Lambda Orionis Star Forming Region
Context. Most observational studies so far point towards brown dwarfs sharing
a similar formation mechanism as the one accepted for low mass stars. However,
larger databases and more systematic studies are needed before strong
conclusions can be reached. Aims. In this second paper of a series devoted to
the study of the spectroscopic properties of the members of the Lambda Orionis
Star Forming Region, we study accretion, activity and rotation for a wide set
of spectroscopically confirmed members of the central star cluster Collinder 69
to draw analogies and/or differences between the brown dwarf and stellar
populations of this cluster. Moreover, we present comparisons with other star
forming regions of similar and different ages to address environmental effects
on our conclusions. Methods. We study prominent photospheric lines to derive
rotational velocities and emission lines to distinguish between accretion
processes and chromospheric activity. In addition, we include information about
disk presence and X-ray emission. Results. We report very large differences in
the disk fractions of low mass stars and brown dwarfs (~58%) when compared to
higher mass stars (26+4-3%) with 0.6 Msun being the critical mass we find for
this dichotomy. As a byproduct, we address the implications of the spatial
distribution of disk and diskless members in the formation scenario of the
cluster itself. We have used the Halpha emission to discriminate among
accreting and non-accreting sources finding that 38+8-7% of sources harboring
disks undergo active accretion and that his percentage stays similar in the
substellar regime. For those sources we have estimated accretion rates.
Finally, regarding rotational velocities, we find a high dispersion in vsin(i)
which is even larger among the diskless population.Comment: Accepted for publication in A&A. 18 figs including the Appendix and
an online tabl
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