GeminiFocus May 2014 | Page 11

Figure 2. 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). 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 1). 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, 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 obser- April 2014 vations 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 evide