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Subaru Near-Infrared Imaging of Herbig Ae Stars
We report results of H-band (? = 1.65?m) imaging observationsof young intermediate-mass stars using the Subaru 8.2-m Telescope withthe adaptive optics AO36 and the infrared coronagraph CIAO. The targetsconsist of 16 Herbig Ae/Be stars (15 Herbig Ae stars and one Herbig Bestar) and four additional main-sequence stars with infrared excesses.Five protoplanetary disks have been spatially resolved around the HerbigAe stars with ages of 2-8 Myr. The resolved disks have outer radii ofseveral 100 AU, and their surface brightnesses range from 10 magarcsec-2 to 18 mag arcsec-2. The images revealvarious morphologies in optically thick disks: spiral arms around ABAur, a banana-split structure with an outer arm for HD 142527, a compactcircumprimary disk of HD 150193, a faint discontinuous ring around HD163296, and an unstructured face-on disk of HD 169142. The detection ofan optically thick disk in scattered light implies that it is verticallyflared, and intercepts stellar light at least in the outer region wherethose images were obtained. However, the surface brightnessdistribution, the resolved structure, and other observationalcharacteristics suggest that the disks are unlikely to be continuouslyflared young disks with small grains well mixed with gas. The detectionrate and the disk brightness do not correlate with the stellar age andthe disk mass, but there is a tendency that the brightest disks arestill surrounded by long-lived envelopes (AB Aur, HD 100546, HD 142527).The significant diversity of the disk structure can be attributed to themultiplicity and the initial condition of the local star-formingenvironments. The detections of companion candidates around our targetedstars are also reported.
| A spectroscopic survey for lambda Bootis stars. II. The observational data
lambda Bootis stars comprise only a small number of all A-type stars andare characterized as nonmagnetic, Population i, late B to early F-typedwarfs which show significant underabundances of metals whereas thelight elements (C, N, O and S) are almost normal abundant compared tothe Sun. In the second paper on a spectroscopic survey for lambda Bootisstars, we present the spectral classifications of all program starsobserved. These stars were selected on the basis of their Strömgrenuvbybeta colors as lambda Bootis candidates. In total, 708 objects insix open clusters, the Orion OB1 association and the Galactic field wereclassified. In addition, 9 serendipity non-candidates in the vicinity ofour program stars as well as 15 Guide Star Catalogue stars were observedresulting in a total of 732 classified stars. The 15 objects from theGuide Star Catalogue are part of a program for the classification ofapparent variable stars from the Fine Guidance Sensors of the HubbleSpace Telescope. A grid of 105 MK standard as well as ``pathological''stars guarantees a precise classification. A comparison of our spectralclassification with the extensive work of Abt & Morrell(\cite{Abt95}) shows no significant differences. The derived types are0.23 +/- 0.09 (rms error per measurement) subclasses later and 0.30 +/-0.08 luminosity classes more luminous than those of Abt & Morrell(\cite{Abt95}) based on a sample of 160 objects in common. The estimatederrors of the means are +/- 0.1 subclasses. The characteristics of oursample are discussed in respect to the distribution on the sky, apparentvisual magnitudes and Strömgren uvbybeta colors. Based onobservations from the Observatoire de Haute-Provence, OsservatorioAstronomico di Padova-Asiago, Observatório do Pico dosDias-LNA/CNPq/MCT, Chews Ridge Observatory (MIRA) and University ofToronto Southern Observatory (Las Campanas).
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