PAH emission from Nova Cen 1986

The discovery of broad emission features between 3.2 and 3.6 microns were reported in the spectrum of Nova Cen 1986 (V842 Cen) some 300 days following outburst and remaining prominent for several months. The general characteristics of these features are similar to those attributed to polycyclic hydrocarbon (PAH) molecules in other dusty sources, although the relative strengths are different, and these observations provide the first clear evidence for molecular constituents other than graphite particles in the ejecta of novae

Star clusters and the structure of the ISM. Tunnels and wakes in giant extragalactic HII regions

Several structures have been discovered embedded in regions of recent or ongoing star formation, which point to the importance of the interaction between fast moving wind-blowing stars and their environment. Using hydrodynamic simulations, we investigate the passage through the interstellar medium of a supersonic stellar wind source, and show how it can naturally lead to the formation of tubes, channels and swamps of globules as interfaces are crossed. The results are in excellent agreement with observation of 30 Doradus.Comment: 12 pages + 5 figures (GIF format) - Accepted for pub. in Astrophys. J. Letter

Star formation in the large Magellanic cloud

What role the Large Magellanic Cloud (LMC), a dwarf irregular galaxy, plays in understanding infrared luminous galaxies is discussed. There are two main reasons the LMC may prove helpful. One, the LMC is only 55 kpc away, very nearby compared to much rarer high luminosity systems. Second, the environment in the LMC is distinctly different than in the Milky Way, at least those parts of the Milky Way interior to the sun, where most of the studies of massive star formation were concentrated. The LMC is an interacting system with a large amount of neutral hydrogen that is pushed around by the galaxy's encounter with the Milky Way. Perhaps a good understanding of star formation process in the LMC will provide guidance in the study of the infrared luminous galaxies. Two questions which will be addressed are: how is star formation in the LMC similar to the Milky Way Galaxy, and how is it different

Far-infrared observations of young clusters embedded in the R Coronae Austrinae and RHO Ophiuchi dark clouds

Multicolor far infrared maps in two nearby dark clouds, R Coronae Austrinae and rho Ophiuchi, were made in order to investigate the individual contribution of low mass stars to the energetics and dynamics of the surrounding gas and dust. Emission from cool dust associated with five low mass stars in Cr A and four in rho Oph was detected; their far infrared luminosities range from 2 far infrared luminosities L. up to 40 far infrared luminosities. When an estimate of the bolometric luminosity was possible, it was found that typically more than 50% of the star's energy was radiated longward of 20 micrometers. meaningful limits to the far infrared luminosities of an additional eleven association members in Cr A and two in rho Oph were also obtained. The dust optical depth surrounding the star R Cr A appears to be asymmetric and may control the dynamics of the surrounding molecular gas. The implications of the results for the cloud energetics and star formation efficiency in these two clouds are discussed

Water Vapour Effects in Mass Measurement

Water vapour inside the mass comparator enclosure is a critical parameter. In fact, fluctuations of this parameter during mass weighing can lead to errors in the determination of an unknown mass. To control that, a proposal method is given and tested. Preliminary results of our observation of water vapour sorption and desorption processes from walls and mass standard are reported

JHK' Imaging Photometry of Seyfert 1 AGNs and Quasars I: Multi-Aperture Photometry

Near-infrared $JHK'$ imaging photometry was obtained of 331 AGNs consisting mainly of Seyfert 1 AGNs and quasars (QSOs). This sample was selected to cover a range of radio emission strength, redshift from $z=0$ to 1, and absolute $B$-magnitude from $M_B=-29$ mag to -18 mag. Among low-$z$ AGNs with $z<0.3$, Seyfert $1-1.5$ AGNs are distributed over a region from a location typical of ``galaxies'' to a location typical of ``QSOs'' in the two-color $J-H$ to $H-K'$ diagram, but Seyfert $1.8-2$ AGNs are distributed around the location of ``galaxies''. Moreover, bright AGNs with respect to absolute $B$-magnitude are distributed near the location of ``QSOs'', while faint AGNs are near the location of ``galaxies''. The distribution of such low-$z$ AGNs in this diagram was found to have little dependence on their 6 cm radio flux. The near-infrared colors of the AGNs observed with an aperture of 7 pixels ($7.49''$) are more QSO-like than those observed with larger apertures up to 15 pixels ($16.1''$). This aperture effect may be explained by contamination from the light of host galaxies within larger apertures. This effect is more prominent for less luminous AGNs

Axial Symmetry and Rotation in the SiO Maser Shell of IK Tauri

We observed v=1, J=1-0 43-GHz SiO maser emission toward the Mira variable IK Tauri (IK Tau) using the Very Long Baseline Array (VLBA). The images resulting from these observations show that SiO masers form a highly elliptical ring of emission approximately 58 x 32 mas with an axial ratio of 1.8:1. The major axis of this elliptical distribution is oriented at position angle of ~59 deg. The line-of-sight velocity structure of the SiO masers has an apparent axis of symmetry consistent with the elongation axis of the maser distribution. Relative to the assumed stellar velocity of 35 km/s, the blue- and red-shifted masers were found to lie to the northwest and southeast of this symmetry axis respectively. This velocity structure suggests a NW-SE rotation of the SiO maser shell with an equatorial velocity, which we determine to be ~3.6 km/s. Such a NW-SE rotation is in agreement with a circumstellar envelope geometry invoked to explain previous water and OH maser observations. In this geometry, water and OH masers are preferentially created in a region of enhanced density along the NE-SW equator orthogonal to the rotation/polar axis suggested by the SiO maser velocities.Comment: 17 Pages, 4 figures (2 color); accepted for publication in Ap

The late infrared development of Nova Serpentis 1970

Broad-band infrared observations of FH Ser (Nova Ser 1970) covering the period 40 to 529 days after discovery are presented. Strong quantitative evidence for grain growth in the period 60–111 days is derived from the agreement between predictions of dust shell models and the observations. Between days 111 and 129 the grains undergo a significant reduction in size. The infrared luminosity is found to fall as t⁻³ for t ≳ 100. However, up until day 200 this is due to a continuing grain size reduction, while the bolometric luminosity remains approximately constant. After day 200 the bolometric luminosity falls off as ∼t⁻¹. At late times, an excess flux in the 1-3 µm region appears above the dominant cool dust emission component. This excess flux is probably due to increasing line emission in the J, H and K bandpasses as the ejected shell expands