Figure 12.
NIRI/Altair
observations of LkCa
15 in the Ks band at
four epochs (labeled
K1 through K4),
reduced using angular
differential imaging
techniques (top row,
a–d). Corresponding
model observations
of the disk emission
appear in the bottom
row (e–h).
One challenge in identifying B[e] supergiants
is to distinguish them from luminous blue
variable (LBV) stars — another short-lived
phase in the post-main sequence evolution
of massive stars. This study’s original targets
were selected from stars previously identified
as “LBV candidates.” These newly discovered
examples lie in a typical region of the near-infrared color-color diagram, one distinct from
the location of luminous blue variables.
More important, B[e] supergiants have two
identifying characteristics in the infrared: hydrogen Pfund series emission lines and carbon monoxide (CO) bands (Figure 11). Both
12
CO and 13CO are detected, and their relative
strength indicates the isotope ratio of 12C/13C
at the stellar surface (7 ± 2). The relative enrichment of 13C here is greater than that observed
in lower-metallicity environments of the Milky
Way and Magellanic Clouds.
This paper can be found in The Astrophysical
Journal Letters, 780:10, 2014
Detailed Observations and
Modeling of a Young Star’s Disk
Planets form in the dusty disks left over
from star formation. Planet development
can shape these disks, especially by carving
holes in the dense medium. LkCa 15, a nearby young star somewhat similar to the Sun,
32
GeminiFocus
has one of these residual disks. It is an excellent target for detailed studies, because previous evidence shows a Solar-System-sized
gap (~50 astronomical units) around the
star. Now, in a new work, Christian Thalmann
(ETH Zurich and University of Amsterdam)
and collaborators use four epochs of observations to provide a detailed model of this
star’s disk.
One important new result is that they distinguish the disk’s geometry, identifying bright
emission as the near side (where light is
forward scattered toward the viewer) as opposed to direct illumination of the far side.
The team finds evidence for disk asymmetry,
namely, an offset between the star and disk
center, which could be due to an unseen
planet. In addition, the disk’s inner wall has
a rounded or irregular shape, rather than being flat. This characteristic, too, could be related to the presence of a companion.
The disk is directly evident in observations
obtained with the Near-Infrared Imager
(NIRI) and the Altair adaptive optics facility
on Gemini North; the researchers used data
reduction techniques to enhance the contrast of the faint disk near the bright central
star. While such angular differential imaging
increases contrast, the resulting images cannot be used for quantitative analysis. Therefore, the researchers model a variety of disk
2014 Year in Review
January 2015