The APM Survey for Cool Carbon Stars in the Galactic Halo - II The Search for Dwarf Carbon Stars

We present proper motion measurements for carbon stars found during the APM Survey for Cool Carbon Stars in the Galactic Halo (Totten & Irwin, 1998). Measurements are obtained using a combination of POSSI, POSSII and UKST survey plates supplemented where necessary by CCD frames taken at the Isaac Newton Telescope. We find no significant proper motion for any of the new APM colour-selected carbon stars and so conclude that there are no dwarf carbon stars present within this sample. We also present proper motion measurements for three previously known dwarf carbon stars and demonstrate that these measurements agree favourably with those previously quoted in the literature, verifying our method of determining proper motions. Results from a complimentary program of JHK photometry obtained at the South African Astronomical Observatory are also presented. Dwarf carbon stars are believed to have anomalous near-infrared colours, and this feature is used for further investigation of the nature of the APM carbon stars. Our results support the use of JHK photomtery as a dwarf/giant discriminator and also reinforce the conclusion that none of the new APM-selected carbon stars are dwarfs. Finally, proper motion measurements combined with extant JHK photometry are presented for a sample of previously known Halo carbon stars, suggesting that one of these stars, CLS29, is likely to be a previously unrecognised dwarf carbon star.Comment: 13 pages, 5 figures, accepted for publication in MNRAS, Also available at http://www.astro.keele.ac.uk/~ejt/publications.htm

Rotation and activity in the solar-type stars of NGC 2547

We present high resolution spectroscopy of a sample of 24 solar-type stars in the young (15-40 Myr), open cluster, NGC 2547. We use our spectra to confirm cluster membership in 23 of these stars, determine projected equatorial velocities and chromospheric activity, and to search for the presence of accretion discs. We have found examples of both fast (vsini>50kms) and slow (vsini<10kms) rotators, but find no evidence for active accretion in any of the sample. The distribution of projected rotation velocities is indistinguishable from the slightly older IC 2391 and IC 2602 clusters, implying similar initial angular momentum distributions and circumstellar disc lifetimes. The presence of very slow rotators indicates that either long (10-40 Myr) disc lifetimes or internal differential rotation are needed, or that NGC 2547 (and IC 2391/2602) were born with more slowly rotating stars than are presently seen in even younger clusters and associations. The solar-type stars in NGC 2547 follow a similar rotation-activity relationship to that seen in older clusters. X-ray activity increases until a saturation level is reached for vsini>15-20kms. We are unable to explain why this saturation level, of log (L_x/L_bol)~-3.3, is a factor of two lower than in other clusters, but rule out anomalously slow rotation rates or uncertainties in X-ray flux calculations.Comment: Accepted by MNRA

Rethinking evaluation of teaching in higher education.

Evaluation of teaching in higher education is an important, yet difficult, process for deans, other administrators and teachers. The purpose of this dissertation is to advance helpful ideas to those who are charged with the responsibility to judge teaching, and to those who are being judged. A rethinking of four central questions ((1) What is education? (2) What is teaching? (3) Can we teach? (4) Are we doing a good job teaching?) is accomplished with help from the work of Hannah Arendt, Joseph Epstein, Louis Hartz, Richard Hofstadter, Robert Pirsig, Plato, Jean-Paul Sartre and others. A significant issue raised by these four questions is the whole notion of quality and excellence. In addition, judgment itself is explored through Kant\u27s ideas of purposiveness and exemplary validity. The particular stories of three teachers in higher education are given wherein they relate their attitudes toward the four central questions, reflections on their best teachers from higher education and their ideas about quality and excellence in teaching. In conclusion, a review of several approaches or reactions taken toward evaluations is presented. Through this rethinking process it is learned that deans, administrators and teachers need to, and can, take evaluation of teaching seriously. A framework of ideas, including excellence in teaching, philosophical agreement, shared judgment and hope for the future, and an experiment in thought which outlines a possible approach to the essentials in an evaluation process is provided to help us start anew in evaluating teaching. From this framework of ideas and the thought experiment, further research could implement the experiment and monitor the experiences. In all evaluations, the underlying notion of the pursuit and recognition of excellence in teaching must remain intact

The discovery of a low mass, pre-main-sequence stellar association around gamma Velorum

We report the serendipitous discovery of a population of low mass, pre-main sequence stars (PMS) in the direction of the Wolf-Rayet/O-star binary system gamma^{2} Vel and the Vela OB2 association. We argue that gamma^{2} Vel and the low mass stars are truly associated, are approximately coeval and that both are at distances between 360-490 pc, disagreeing at the 2 sigma level with the recent Hipparcos parallax of gamma^{2} Vel, but consistent with older distance estimates. Our results clearly have implications for the physical parameters of the gamma^{2} Vel system, but also offer an exciting opportunity to investigate the influence of high mass stars on the mass function and circumstellar disc lifetimes of their lower mass PMS siblings.Comment: Monthly Notices of the Royal Astronomical Society, Letters - in pres

Brother Bill

https://digitalcommons.library.umaine.edu/mmb-vp/1129/thumbnail.jp

Enzyme profiles during synchronous development

Enzyme profiles during synchronous developmen

Fiber glass loops for rapid manipulation of Neurospora ascospores

Fiber glass loops for rapid manipulation of Neurospora ascospore

Rotation and activity in the solar-type stars of NGC 2547

We present high-resolution spectroscopy of a sample of 24 solar-type stars in the young (15-40 Myr), open cluster NGC 2547. We use our spectra to confirm cluster membership in 23 of these stars, to determine projected equatorial velocities and chromospheric activity, and to search for the presence of accretion discs. We find examples of both fast (ve sin i>50 km s−1) and slow (ve sin i15-20 km s−1. We are unable to explain why this saturation level, of log(LxLbol)≃−3.3, is a factor of 2 lower than in other clusters, but rule out anomalously slow rotation rates or uncertainties in X-ray flux calculation

The lithium depletion boundary and the age of NGC 2547

We present the results of a photometric and spectroscopic survey of cool M dwarf candidates in the young open cluster NGC 2547. Using the 2dF fiber spectrograph, we have searched for the luminosity at which lithium remains unburned in an attempt to constrain the cluster age. The lack of a population of individual lithium-rich objects towards the faint end of our sample places a very strong lower limit to the cluster age of 35 Myr. However, the detection of lithium in the averaged spectra of our faintest targets suggests that the lithium depletion boundary lies at 9.5 < M(I) < 10.0 and that the cluster age is < 54 Myr. The age of NGC 2547 judged from fitting isochrones to low-mass pre-main-sequence stars in colour-magnitude diagrams is 20-35 Myr using the same evolutionary models. The sense and size of the discrepancy in age determined by these two techniques is similar to that found in another young cluster, IC 2391, and in the low-mass pre main-sequence binary system, GJ 871.1AB. We suggest that the inclusion of rotation or dynamo-generated magnetic fields in the evolutionary models could reconcile the two age determinations, but only at the expense of increasing the cluster ages beyond that currently indicated by the lithium depletion. Alternatively, some mechanism is required that increases the rate of lithium depletion in young, very low-mass fully convective stars.Comment: 14 pages, 7 figures, 3 tables, accepted by MNRA