Circumstellar dust shells of hot post-AGB stars

Using a radiative transfer code (DUSTY) parameters of the circumstellar dust shells of 15 hot post-AGB stars have been derived. Combining the optical, near and far-infrared (ISO, IRAS) data of the stars, we have reconstructed their spectral energy distributions (SEDs) and estimated the dust temperatures, mass loss rates, angular radii of the inner boundary of the dust envelopes and the distances to these stars. The mass loss rates (10$^{-6}-10^{-5}$M$_{\odot}$yr$^{-1}$) are intermediate between stars at the tip of the AGB and the PN phase. We have also studied the ISO spectra of 7 of these stars. Amorphous and crystalline silicate features were observed in IRAS14331-6435 (Hen3-1013), IRAS18062+2410 (SAO85766) and IRAS22023+5249 (LSIII +5224) indicating oxygen-rich circumstellar dust shells. The presence of unidentified infrared (UIR) band at 7.7$\mu$, SiC emission at 11.5$\mu$ and the "26$\mu$" and "main 30$\mu$" features in the ISO spectrum of IRAS17311-4924 (Hen3-1428) suggest that the central star may be carbon-rich. The ISO spectrum of IRAS17423-1755 (Hen3-1475) shows a broad absorption feature at 3.1$\mu$ due to C$_{2}$H$_{2}$ and/or HCN which is usually detected in the circumstellar shells of carbon-rich stars.Comment: 18 pages, accepted for publication in A&

A review of type Ia supernova spectra

SN 2011fe was the nearest and best-observed type Ia supernova in a generation, and brought previous incomplete datasets into sharp contrast with the detailed new data. In retrospect, documenting spectroscopic behaviors of type Ia supernovae has been more often limited by sparse and incomplete temporal sampling than by consequences of signal-to-noise ratios, telluric features, or small sample sizes. As a result, type Ia supernovae have been primarily studied insofar as parameters discretized by relative epochs and incomplete temporal snapshots near maximum light. Here we discuss a necessary next step toward consistently modeling and directly measuring spectroscopic observables of type Ia supernova spectra. In addition, we analyze current spectroscopic data in the parameter space defined by empirical metrics, which will be relevant even after progenitors are observed and detailed models are refined.Comment: 58 pages, 15 figures, 6 tables, accepted for publication in Ap&SS as an invited revie

Achieving target skills in increments using PBL courses in chemical engineering program at RMIT University

Graduating Chemical Engineering students are expected to have acquired a number of technical and generic skills that include design, project management, communication and team work. In the new Chemical Engineering program at RMIT University, students are offered opportunities to develop these skills in stages through project-based learning (PBL) courses. Each semester has a PBL course which integrates horizontally the scientific and engineering concepts taught in other courses in that semester. The PBL courses in senior years, however, aim to achieve not only the horizontal integration of concepts from that semester but also vertical integration of concepts taught in previous years. In all PBL courses (eight in total), the development of generic skills is given equal opportunity. However the development of design skills are achieved in stages and it occurs mainly in six of the PBL courses. This incremental progression of design skill development prepares the students to face the final year capstone design project with confidence and excitement. The high satisfaction level in the design project as indicated by a high good teaching score (GTS) of 82% in 2008 shows that the progressive development of technical and generic skills using PBL courses is an effective means of preparing work-ready graduates

Light Curve Analysis of Hipparcos Data for the Massive O-type Eclipsing Binary UW CMa

Hipparcos photometric data for the massive O-type binary UW CMa were analysed within the framework of the Roche model. Photometric solutions were obtained for five mass ratios in the $q=M_2/M_1=0.5-1.5$ range. The system is found to be in a contact configuration. Independently of $q$, the best-fitting model solutions correspond to the orbital inclination $i \sim 71^\circ$ and the temperature of the secondary component $T_2 \sim 33500\,K$, at the fixed temperature of the primary $T_1=33750 K$. Considering that the spectrum of the secondary is very weak, photometric solutions corresponding to the contact configuration favor the mass ratio $q$ smaller than unity (in which case the luminosity of the secondary is smaller than that of the primary). The absolute parameters of the system are estimated for different values of the mass ratio.Comment: 18 pages, 6 figure