Y. Nakada

Interstellar extinction in the open clusters towards galactic longitude around 130

In this paper we present a detailed study of the intra-cluster reddening material in the young open clusters located around l ∼ 130° using colour-excess diagrams and two-colour diagrams. The study supports the universality of the extinction curves for A ≥ λ J , whereas for shorter wavelengths the curve depends upon the value of the R c l u s t e r (total-to-selective absorption in the cluster region). The value of R c l u s t e r in the case of NGC 654, NGC 869 and NGC 884 is found to be normal, whereas the value of R c l u s t e r in the cluster regions NGC 1502 and IC 1805 indicates an anomalous reddening law in these regions. In the case of NGC 1502 the value of R c l u s t e r is found to be lower (2.57 ′ 0.27) whereas in the case of IC 1805 it is higher (3.56 ′ 0.29) than the normal value of 3.1. Although the intra-cluster material indicates a higher value of R c l u s t e r in the NGC 663 region, the error in the estimation of R c l u s t e r is too large to conclude anything. It is also found that the extinction process in the U band in the case of NGC 663 seems to be less efficient, whereas in the case of NGC 869 the process is more efficient.

SiO maser survey of AGB stars in the North Galactic Cap

A SiO maser survey in the J =1 0, v = 1 and 2 transitions has been made for IRAS sources in the North Galactic Cap (b > 30) with the Nobeyama 45 m radio telescope. The sources were selected on the basis of their IRAS 12/25-m and 25/60-m flux ratios as likely oxygen-rich AGB candidates. SiO masers were detected from 24 out of the 97 selected sources, where 17 were new detections. The distances and heights above the Galactic plane are calculated. The Galactic distribution of detected and undetected stars indicates that metallicity is likely to govern the detection rate. The Galactocentric angular velocities of the subsampled stars are derived and their variation with the Galactic height is discussed.

Preparation of fine particles of astrophysical interest by gas evaporation techniques

Abstract Fine particles of various chemical substances—carbon, iron, iron oxide and silica—which are expected to exist in interstellar space are prepared in argon gas. The size, shape, and crystal structure of the powder particles are studied by electron microscopy and electron diffraction, and may have some bearing on models of comets and of the solar nebula. The largest size we have obtained is about 0.1 μm and the smallest about 40A. Generally the size becomes smaller for lower temperature and also for lower pressure. This tendency is discussed in connection with nucleation theories. Except for iron and iron oxide the powder particles have no crystal structure.

New NIR light-curve templates for classical Cepheids

Aims. We present new near-infrared (NIR) light-curve templates for fundamental (FU, J, H, KS) and first overtone (FO, J) classical Cepheids. The new templates together with period-luminosity and period-Wesenheit (PW) relations provide Cepheid distances from single-epoch observations with a precision only limited by the intrinsic accuracy of the method adopted. Methods. The templates rely on a very large set of Galactic and Magellanic Cloud Cepheids (FU, ~600; FO, ~200) with well-sampled NIR (IRSF data set) and optical (V, I; OGLE data set) light-curves. To properly trace the change in the shape of the light-curve as a function of pulsation period, we split the sample of calibrating Cepheids into ten different period bins. The templates for the first time cover FO Cepheids and the short-period range of FU Cepheids (P ≤ 5 days). Moreover, the phase zero-point is anchored to the phase of the mean magnitude along the rising branch. The new approach has several advantages in sampling the light-curve of bump Cepheids when compared with the canonical phase of maximum light. We also provide new empirical estimates of the NIR-to-optical amplitude ratios for FU and FO Cepheids. We perform detailed analytical fits using seventh-order Fourier series and multi-Gaussian periodic functions. The latter are characterized by fewer free parameters (nine vs. fifteen). Results. The mean NIR magnitudes based on the new templates are up to 80% more accurate than single-epoch NIR measurements and up to 50% more accurate than the mean magnitudes based on previous NIR templates, with typical associated uncertainties ranging from 0.015 mag (J band) to 0.019 mag (KS band). Moreover, we find that errors on individual distance estimates for Small Magellanic Cloud Cepheids derived from NIR PW relations are essentially reduced to the intrinsic scatter of the adopted relations. Conclusions. Thus, the new templates are the ultimate tool for estimating precise Cepheid distances from NIR single-epoch observations, which can be safely adopted for future interesting applications, including deriving the 3D structure of the Magellanic Clouds.

Uv (iue) spectra of the central stars of high latitude planetary nebulae hb7 and sp3

We present an analysis of the UV (IUE) spectra of the central stars of Hb7 and Sp3. Comparison with the IUE spectrum of the standard star HD 93205 leads to a spectral classication of O3V for these stars, with an eective temperature of 50 000 K. From the P-Cygni proles of CIV (1550 A), we derive stellar wind velocities and mass loss rates of 1317 km s 1 300 km s 1 and 2:9 10 8 M yr 1 and 1603 km s 1 400 km s 1 and 7 10 9 M yr 1 for Hb7 and Sp3 respectively. From all the available data, we reconstruct the spectral energy distribution of Hb7 and Sp3.

Extended dust shell of the carbon star U Hydrae observed with AKARI

Context. Low- to intermediate-mass stars lose a significant fraction of their mass while they are on the asymptotic giant branch (AGB). This mass loss is considered to determine the final stages of their evolution. The material ejected from the stellar photosphere forms a circumstellar envelope in its surroundings. Layers of circumstellar envelope constitute the footprint of mass-loss history. Aims. Our aim is to probe the mass-loss history in the carbon star U Hya in the last ∼10 4 years by investigating the distribution of dust in the circumstellar envelope with high spatial resolution. Methods. We observed U Hya in the far-infrared (FIR) at 65, 90, 140, and 160 μm simultaneously, using the slow scan observing mode of the far-infrared surveyor (FIS) aboard the infrared astronomical satellite AKARI. It produced a map of ∼10 � × 40 � in size in each band. Results. The FIS maps reveal remarkably circular, ring-like emission structure almost centered on the star, showing the presence of a detached, spherical dust shell. A hollow dust shell model gives the inner radius Rin of 101–107 �� [(2.5–2.6) × 10 17 cm], thickness that covers a half of the total dust mass ΔRhm of 16–23 �� [(3.8–5.6) × 10 16 cm], which gives ΔRhm/Rin ∼ 0.2, and the power-law index of the dust opacity distribution of 1.10–1.15. The dust mass in the shell is well-constrained to be (0.9–1.4) × 10 −4 (κ100/25) −1 M� , where κ100 is the dust absorptivity at 100 μm in units of cm 2 g −1 . The dust mass-loss rate at Rin is found to be (1.8–

Isocam observations of globular clusters in the Magellanic Clouds: The data

Seventeen globular clusters in the Large and Small Magellanic Clouds were observed in the mid-infrared wavelength region with the ISOCAM instrument on board the Infrared Space Observatory (ISO). Observations were made using the broadband filters LW1, LW2, and LW10, corresponding to the effective wavelengths of 4.5, 6.7, and 12 mum, respectively. We present the photometry of point sources in each cluster, as well as their precise positions and finding charts.

IUE and ISO observations of the bipolar proto-planetary nebula Hen 401 (IRAS 10178-5958)

We present ultraviolet (IUE) and infrared (ISO) observations of the bipolar proto-planetary nebula Hen 401 which, combined with previously available optical and near infrared data, are used to reconstruct the overall spectral energy distribution from 1150 A to 100 m. The ISO spectrum is dominated by strong PAH emission superimposed on a very cold continuum which is interpreted as thermal emission originating in the C-rich cool dust (106 K) present in the circumstellar envelope, the remnant of the previous AGB phase. In addition, a second, hotter component detected in the near infrared is attributed to thermal emission from hot dust (640 K), suggesting that mass loss and dust grain formation is still on-going during the current post-AGB phase. The ultraviolet (IUE) spectrum shows a stellar continuum in the wavelength interval 2400 A to 3200 A which corresponds to a moderately reddened B8-type central star. Unexpectedly, the UV flux in the wavelength interval 1150 A to 1900 A is very weak or absent with no evidence of a hotter binary companion which could explain the detection of the nebular emission lines observed in the available ground-based optical spectra of Hen 401. HST WFPC2 high resolution images also show no indication of a hot companion to the B8-type central star observed both in the optical and in the UV. The evolutionary implications of a possible single nature for the central star of Hen 401 are discussed.

An Infrared Camera Based on a Large PtSi Array

A large-format PtSi array (effectively 1k x 0.5k pixels) has been incorporated into an infrared camera intended for survey work using the 0.75-m telescope at Sutherland. The array is very uniform and almost free of cosmetic defects. The camera, its electronics and the operational procedures that we use are described, together with the methods of data reduction. The limiting magnitudes that can be observed in the JHK broad bands are given.

Experiment on the clustering of fine particles

The clustering of fine particles by mutual thermal collisions is investigated experimentally. Fine particles are prepared in an argon gas atmosphere by the gas evaporation technique. Mass distributions of clusters of the particles are obtained from micrographs of specimen grids placed at different heights above the evaporating source. The cluster growth is clearly seen in the change of mass distribution with height. A comparison of the experimental results with a theoretical model indicates that the cluster of fine particles does not grow in the spherical manner usually assumed, but in a planar manner. As an important consequence of the conclusion to the primordial solar nebula, the sedimentation time of the grains sinking towards the equatorial plane of the solar disk becomes longer than the value previously adopted because of the large ratio of surface to volume of a planar cluster. This longer time should alter the scenario of the evolution of the solar system after sedimentation.