We report the result of our near-infrared observations (JHKs) for type II Cepheids (including possible RV Tau stars) in galactic globular clusters. We detected variations of 46 variables in 26 clusters (10 new discoveries in seven clusters) and present their light curves. Their periods range from 1.2 d to over 80 d. They show a well-defined period-luminosity relation at each wavelength. Two type II Cepheids in NGC6441 also obey the relation if we assume the horizontal branch stars in NGC6441 are as bright as those in metal-poor globular clusters in spite of the high metallicity of the cluster. This result supports the high luminosity which has been suggested for the RR Lyr variables in this cluster. The period-luminosity relation can be reproduced using the pulsation equation (P sqrt(rho)=Q) assuming that all the stars have the same mass. Cluster RR Lyr variables were found to lie on an extrapolation of the period-luminosity relation. These results provide important constraints on the parameters of the variable stars. Using Two Micron All-Sky Survey (2MASS) data, we show that the type II Cepheids in the Large Magellanic Cloud (LMC) fit our period-luminosity relation within the expected scatter at the shorter periods. However, at long periods ($P>40$ d, i.e. in the RV Tau star range) the LMC field variables are brighter by about one magnitude than those of similar periods in galactic globular clusters. The long-period cluster stars also differ from both these LMC stars and galactic field RV Tau stars in a colour-colour diagram. The reasons for these differences are discussed.Comment: 13 pages, 8 figures, Accepted for publication in MNRA

We present a near-infrared ($JHK_{\rm s}$) photometric catalog, including 14811185 point sources for a 40 deg$^2$ area of the Large Magellanic Cloud, 2769682 sources for an 11 deg$^2$ area of the Small Magellanic Cloud, and 434145 sources for a 4 deg$^2$ area of the Magellanic Bridge. The 10$\sigma$ limiting magnitudes are 18.8, 17.8, and 16.6 mag at $J, H$, and $K_{\rm s}$, respectively. The photometric and astrometric accuracies for bright sources are 0.03–0.04 mag and 0$\rlap {.}{^{\prime\prime}}$1, respectively. Based on the catalog, we also present (1) spatial distributions, (2) luminosity functions, (3) color–color diagrams, and (4) color–magnitude diagrams for point sources toward the Magellanic Clouds.

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We have found Herbig Ae/Be star candidates in the western region of the Magellanic Bridge. Using the near infrared camera SIRIUS and the 1.4 m telescope IRSF, we surveyed about 3.0 deg x 1.3 deg (24 deg < RA < 36 deg, -75 deg < Dec. < -73.7 deg) in the J, H, and Ks bands. On the basis of colors and magnitudes, about 200 Herbig Ae/Be star candidates are selected. Considering the contaminations by miscellaneous sources such as foreground stars and early-type dwarfs in the Magellanic Bridge, we estimate that about 80 (about 40%) of the candidates are likely to be Herbig Ae/Be stars. We also found one concentration of the candidates at the young star cluster NGC 796, strongly suggesting the existence of pre-main-sequence (PMS) stars in the Magellanic Bridge. This is the first detection of PMS star candidates in the Magellanic Bridge, and if they are genuine PMS stars, this could be direct evidence of recent star formation. However, the estimate of the number of Herbig Ae/Be stars depends on the fraction of classical Be stars, and thus a more precise determination of the Be star fraction or observations to differentiate between the Herbig Ae/Be stars and classical Be stars are required.Comment: 22 pages, 6 figures. Accepted for publication in Ap

In fracture processes, grain boundaries behave as preferential paths for crack propagation. These grain boundary fractures proceed by the atomic-bond rupture within the grain boundary cores, and thus grain boundary structures have crucial influence on the fracture properties. However, the relationship between grain boundary structures and atomic fracture processes has been a matter of conjecture, especially in the case of dopant-segregated grain boundaries which have complicated local structures and chemistries. Here, we determine the atomic-bond breaking path within a dopant-segregated Al 2 O 3 grain boundary core, via atomic-scale observations of the as-fractured surface and the crack tip introduced by in situ nanoindentation experiments inside a transmission electron microscope. Our observations show that the atomic fracture path is selected to produce less coordination-deficient oxygen polyhedra of dopant cations, which is rationalised using first-principles calculations. The present findings indicate that the atomic coordination geometry at the grain boundary core affects the fracture processes.

We conducted wide-field JHK s imaging polarimetry toward NGC 2024, which is a massive star-forming region in the Orion B cloud. We found a prominent and extended polarized nebula over NGC 2024, and constrained the location of illuminating source of the nebula through the analysis of polarization vectors. A massive star, IRS 2b with a spectral type of O8 − B2, is located in the center of the symmetric vector pattern. Five small polarized nebulae associated with YSOs are discovered on our polarization images. These nebulae are responsible for the structures of circumstellar matter (i.e., disk/envelope systems) that produce strongly polarized light through dust scattering. For the point-like sources, we performed software aperture polarimetry in order to measure integrated polarizations, with which we detected candidate sources associated with circumstellar material by selecting sources with a larger polarization than that estimated from the extinction of foreground material. We investigated the fraction of highly polarized sources against the intrinsic luminosity of stars (∝ mass), and found that the source detection rate remains constant from low (brown dwarfs) to higher luminosity (solar-type) stars. This result indicates the relative disk scale-hight is rather independent of the stellar mass. We confirmed the result using our polarimetry of the stars with known spectral types in NGC 2024. We found five young brown dwarfs with highly polarized integrated emission. These sources serve as direct evidence for the existence of disk/envelope system around brown dwarfs. We investigated the magnetic field structure of NGC 2024 through the measurements of dichroic polarization. The average position angle of projected magnetic fields across the region is found to be 110 • . We found a good consistency in magnetic field structures obtained using near-infrared dichroic polarization and sub-mm/far-infrared dust emission polarization, indicating that the dichroic polarizations at near-infrared wavelengths trace magnetic field structures inside dense (A V < ∼ 50 mag) molecular clouds.

An extensive photometric monitoring of KH 15D, an enigmatic variable in the young star cluster NGC 2264, has been conducted. Simultaneous and accurate near-infrared (JHKs-bands) photometry is presented between 2003 December and 2005 March covering most of the variable phase. The infrared variability is characterized by largeamplitude and long-lasting eclipse, as observed at optical. The period of variability is 48.3 ± 0.2 days, the maximum photometric amplitude of variability is ∼4.2 mag, and the eclipse duration is ∼0.5 in phase units. These are consistent with the most recent period, amplitude, and duration at optical. The blueing of the J-H color (∼0.16 mag) during the eclipse, which has been suggested before, is unambiguously confirmed; a similar blueing at H-Ks is less clear but is probably present at a similar level. The overall shape of the JHKs light curves is very similar to the optical one, including a fair time-symmetry and a less stable flux during the eclipse with a slight hump near the zero phase. Most of these variability features of KH 15D observed at near-infrared wavelengths can be explained with the recent model employing an eclipse by the inclined, precessing disk and an outer scattering region around a pre-main-sequence binary.Subject headings: circumstellar matter -stars: individual (KH 15D) -stars: pre-mainsequence -planetary systems: protoplanetary disks

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