I have spent most of the day making figures presenting time series photometry of brown dwarfs that are not variable. This was photometry from the Spitzer Space Telescope in the course of the Weather on Other Worlds program. The figures are important for the paper we are about to publish presenting the main results of this survey. However, constructing them was boring, repetitive work and doesn't give me much to write about here. One interesting thing that did come out of the figures was a graphic illustration of just how much better Spitzer/IRAC photometry of late T dwarfs was in the 4.5 micron channel vs. the 3.6 micron channel. For most objects, 4.5 microns was comparable but not quite as precise as 3.6 microns. For the late T dwarfs 4.5 microns was far better. This, of course, is because the late T dwarfs are much brighter at 4.5 microns relative to 3.6 microns, and so there is far less noise in the data at the longer wavelength.
Since there is little to write about my own scientific activities for the day, I will mention a few interesting papers I have read recently.
Many of us, of course, are thinking about new science that will be enabled by results from the GAIA mission. One somewhat neglected area is occultation science. GAIA will produce an exquisite astrometric catalog that should make catalog-related systematics in measured positions of asteroids and Kuiper Belt Objects (KBOs) a thing of the past. Thus, provided ground-based observers keep observing these objects, we should soon be able to calculate considerably improved orbits for them. At the same time, GAIA will tell us where the stars are with greater accuracy -- thus improving our ability to predict occultations in two very significant ways. I found a paper that presents an interesting study of some of these issues: Tanga and Delbo (2007).
Two further points on this topic: by removing systematic catalog biases, GAIA will increase the potential benefit of highly intensive observations of known objects. The accumulation of hundreds to thousands of well-timed observations, even with relatively small telescopes, could enable us to enter a new era in terms of the accuracy with which the orbits of asteroids and Kuiper Belt Objects are known. Lastly, occultations by small known Kuiper Belt Objects are extremely interesting because the albedo of such objects is highly uncertain, and occultation timing could allow us to measure it. This feeds directly into our estimates of the total mass of the Kuiper Belt.
On a completely different topic: I did some reading recently about dynamical measurements of the most massive stars known. I was curious because for some time I have felt an inconsistency between statements of the theoretical (and even observational) upper limits to the stellar mass function on the one hand, and measured masses of O stars on the other. The former set the limits in the range of 100-200 solar masses. The latter (actual measurements of O stars) I understood to be usually coming out at less than 50 solar masses. I read two papers that measured the masses of some of the most massive stellar binaries known: Schnurr et al.(2008) and Niemela et al.(2008). The former, in particular, resolved my confusion. The most massive main-sequence stars are not O stars, they are actually emission-line stars with Wolf-Rayet classifications. Even though most Wolf-Rayet stars are evolved objects, a small minority are instead the most massive hydrogen-fusing stars known. Their emission lines and resulting Wolf-Rayet classification are due to their intense stellar winds. This was a very interesting and satisfying recognition for me, and is I think a major discovery in astronomy that I was unaware of at the time.
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