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Dr.Bob's blog posts
Half-way through ingress by most estimates, but epsilon Aurigae continues to confound. Middle of October, the star changed its rate of decline in brightness, from rapid to less rapid - see the visual light curve data link. This change of slope seems to be more pronounced at shorter wavelengths, less pronounced at longer wavelengths. Clues like these will help us define the nature of the eclipsing body more precisely. If purely due to effective area, it says that the disk is slightly thinner-looking in bluer light, relative to red wavelengths. Ultraviolet light curves during last eclipse seem consistent with this trend.Read more
Mid-November, ingress nominally 2/3 over, and the snows are arriving in the mountains. We made one last attempt to reach Mt.Evans observatory on 14 Nov but huge drifts defeated the stout Unimog vehicles we used. However, intrepid observers elsewhere are still getting peeks at the star, sometimes between clouds. Some interesting trends are emerging since mid-October: the B filter photometry shows a decreased rate of decline, as does V filter (less so), but R and I filters appear to continue the decline in a linear fashion. This means the star is relatively brighter in bluer wavelengths compared to redder ones - suggesting a hotter source - perhaps the F star pulsations continuing (like those seen pre-eclipse) and/or some of the supposed hot B star light is leaking out of the dark disk. Richard Miles reports an ~0.1 mag jump in V-Ic after mid-Oct.Read more
Greetings again from historic Mount Wilson Observatory, perched in the Angeles National Forest mountains, above Los Angeles. As previously mentioned, we're here using the Center for High Angular Resolution Astronomy (CHARA) telescope array of 6 one-meter telescopes, operated by Georgia State University. The light from 4 of these telescopes at a time can be merged in the Michigan IR Combiner, or MIRC. Each pair of telescopes is capable of producing interference fringes. Measuring the fringe contrast and knowing the wavelength and telescope separation for each pair over the course of an evening, provides pieces of information that can be used to construct an image.Read more
Greetings from Mount Wilson, home of the 100 inch telescope used by Hubble, and home of the CHARA interferometric array. Brian K and I have been assigned CHARA time with the team to pursue high resolution imaging of epsilon Aur as it undergoes eclipse. With the light 50% diminished (see previous blog), the Huang model predicts that the dark disk should be significantly intruding across the face of the F star.Read more
Observers are reporting visual magnitude approaching 3.4, which is half-way between the out of eclipse average, close to 3.0, and the anticipated magnitude during totality, 3.8. Hopkins and Santangelo have begun to converge on JD 2,455,065 (+/- a few days) as the likely time of first contact (start of eclipse). Today being JD 2,455,127 (23 Oct), that was 62 days ago. At this rate, we'll bottom out in totality by JD 2,455,189 or slightly sooner - close to winter solstice. Jeff Hopkins predicts 2,455,183 for visual, and earlier in photometrically bluer wavelengths.Read more
As the light of the primary star continues to wane, discussions of the time of "first contact" have arisen - that's when the dark disk began to encroach on the F star photosphere. Pre-eclipse predictions indicated the date could be JD 2,455,055 = 2009 Aug.11 (Hopkins & Stencel, 2008 Epsilon Aurigae - book - p.97). Different observers point to slightly different times to represent the start of ingress.
Jeff Hopkins (Hopkins Phoenix Observatory) has analyzed light curve data and concluded the eclipse began (V band) on JD 2,455,072 = Aug 28.
See his webpage at http://www.hposoft.com/Plots09/FirstContact.JPG .
Italian observer, M.M.M.Santangelo (Osservatorio Astronomico di Capannori) has published statistical results of his independent photometry in issue 2224 of the Astronomer's Telegram and states that the eclipse "did not still take place until at least August 17th" = JD 2,455,060. Read more
Like the autumn leaves, light from epsilon Aurigae is dropping fast. I've been using a simple digital camera and recorded a fade to V ~ 3.35 this weekend (10/3/09). If you have been watching the show week to week, epsilon is clearly fainter than eta now, and on its way to being no brighter than zeta in a matter of week, if all keeps to schedule.
As Aurigae is rising by 10pm local time, you no longer need to catch it during pre-dawn hours to see the eclipse happening before your eyes. Catch those clear, cool nights of autumn and enjoy the spectacle!Read more
Eclipse is underway (V = 3.23 on 9/25/09)and the debate over when First Contact really occurred has begun. Initially, Jeff Hopkins figures it to be RJD 55072 (late Aug) while Richard Miles likes a date several days prior to that (mid-August). Whether the final answer is JD 2,455,072 or a week earlier, in either event it appears to be at least one week after predicted start (55055, early August). This arguably means further changes in eclipse shape and duration can be expected. Read more
Jeff Hopkins, photon-counting, reports that epsilon Aurigae has faded to match eta Aur at V = 3.17 on the morning of 15 Sept 2009. If you have been hesitating to get out and see the eclipse, NOW IS THE TIME to get in gear and watch it happen. If you have any sort of digital camera capable of recording the scene, start recording and archiving your data. Over the coming weeks, we anticipate posting more instructional material on the Data Analysis formum about how to process your images and deduce magnitudes - from visual comparisons as found in the 10 Star Tutorial, to aperture photometry tools available online (such as IRIS - http://astrosurf.com/buil/us/iris/astro/astro.htm - or with licensed software like CCDsoft, MaximDL, MIRA, etc...). Happy observRead more
Seems like epsilon Aurigae has decided to take the plunge this week, dropping to an estimated 3.14 mag visual as of Friday morning 9/11/09 Denver time - down by nearly 0.1 mag in just under a week. Fast phase may have arrived early - keep watching!
Robin LEadbeater has posted an excellent summary of his spectroscopic monitoring in the form of a poster presented at a recent BAA meeting:
Check it out!Read more