This way to the Egress, augmented 2/26/2011

this updated blog deals mainly with invited talks at the Seattle meeting in Jan. 2011, at the American Astronomical Society and commenting on the remaining weeks of eclipse.  First, we report on a recent cyber-conversation between Edward Guinan (Prof. Astronomy, Villanova University) and Bradley Schaefer (Prof. Astronomy, Louisiana State University).  Both have studied ancient star catalogs for years as part of their research into the lives of stars.  Ed Guinan, in a 1990 conference paper reported the following records for visual estimates of epsilon Aurigae over time:
Era              Visual mag.                   Sources
130BC         4 - 3                               Hipparchus Catalog (Ptolemy)
960CE          4                                    Al Sufi
1437              4                                    Ulugh Beg
1590               4                                   Tycho
The same 4th mag was recorded during 1600, 1700 and early 1800.  Both Guinan and Bradley indicate that uncertainties of +/- 0.5 mag are likely for these records, suggesting a slim but non-zero chance the star was systematically fainter back when.  By the time of Schmidt and Argelander (1880), the value given was 3.3.  It seems odd that the ancient catalogs would systematically record the modern eclipse brightness (3.8).  Could it be possible that the star was engulfed in extra opacity during the past 2 millenia?  If so, what would be the present-day observable consequences?  Observers familiar with delta Sco and R CrB have witnessed this kind of behavior, albeit on more rapid timescales.

The 217th meeting of the American Astronomical Society held in Seattle during early January featured a special session of talks and posters about progress with the recent eclipse of epsilon Aurigae.  Because the light curve is available here at Citizen Sky and the AAVSO webpages, and other blog accounts of the meeting are available here and elsewhere (http://www.hposoft.com/Plots09/VBand.JPG ), let me comment on the following developments deserving further notice.   John Clover provided an update on the SMEI instrument monitoring of epsilon Aurigae (and thousands of other bright stars).  SMEI is designed to watch coronal mass ejections from the Sun and uses wide angle cameras to gain a nearly all sky view every 103 minutes.  Although this instrument like most suffers calibration issues, the composite light curve is impressive despite a few gaps.  Most notable is the argument is has prompted again concerning the fabled mid-eclipse brightening.  The best light curve we have from the 1983 eclipse was generated by Jeff Hopkins, and it shows a pre-mid-eclipse minimum (3.8) near JD 2,445,500, quite consistent with the current pre-mid-eclipse minimum (also 3.8) near JD 2,455,300 or 9800 days later.  For both eclipses, the post-mid-eclipse level has been brighter (circa 3.7), giving the impression of a mid-eclipse brigthening.  Of course, both eclipses have been interrupted by the June solar conjunction, making precise photometry difficult.

The next speaker, John Clover, provided an update on the SMEI instrument monitoring of epsilon Aurigae (and thousands of other bright stars).  SMEI is designed to watch coronal mass ejections from the Sun and uses wide angle cameras to gain a nearly all sky view every 103 minutes.  Although this instrument like most suffers calibration issues, the composite light curve is impressive despite a few gaps.  Most notable is the argument it has prompted again, concerning the fabled mid-eclipse brightening.  The best light curve we have from the 1983 eclipse was generated by Jeff Hopkins, and it shows a pre-mid-eclipse minimum (3.8) near JD 2,445,500, quite consistent with the current pre-mid-eclipse minimum (also 3.8) near JD 2,455,300 or 9800 days later.  For both eclipses, the post-mid-eclipse level has been brighter (circa 3.7), giving the impression of a mid-eclipse brigthening.  Of course, both eclipses have been interrupted by the June solar conjunction, making precise photometry difficult.

The next speaker, Elizabeth Griffin from the Dominion Astrophysical Observatory (DAO), reported on her studies of archival spectroscopic materials, including Mt. Wilson and DAO photographic and newer digital high dispersion work.  She reported that her goals include: (a) to monitor H alpha from different eclipses, to see what repeats - and if anything clearly does NOT repeat then to try to understand what changes can be taking place; and (b) to study the behaviour of those narrow spikes which appear most prominently during ingress and egress, and (again) to see if their behaviour alters from one eclipse to another.  We look forward to learning progress on this.

Next came Bill Ketzeback of Apache Point Observatory and the ARC telescope, where he has been using the optical spectrograph and a near-IR one called TripleSpec to monitor the eclipse.    Their scheduled observing plan was twice per week observation since February, 2009. An optical echelle spectrograph (R = 31,500) and an NIR cross dispersing spectrograph (R=3500) have been primary
instrumentation for this project, mainly aimed at monitoring changes in line strength and profiles for absorption features prior to and during the eclipse.  Some highlights of this observing program to date included changes in the Sodium Doublet (Na D1 & D2), Hydrogen Alpha, Potassium I (K I) at 7699A, and NIR spectra from 0.95 to 1.8 microns.  Much discussion was raised to how unusual the RV curve for sodium appears and what the possible physical explanation could be. The wildly changing absorption of the H alpha line surrounding mid eclipse confirmed a wind feature off the B star and perpendicular to the eclipsing body discussed in Steve Howell's poster discussing UV observations (http://adsabs.harvard.edu/abs/2011AAS...21725707H ). This cooler wind feature showed red and blue shifted components greater than 200 km/s at mid eclipse.  A tail of material seems to follow the cone since the blue shifted component post mid eclipse raises to as high as 275 km/s.  (This is nicely illustrated in a new paper submitted by Chadima et al. - see attached graphic).

Following him was Brian Kloppenborg of the University of Denver, my graduate student, reporting on the latest high resolution images of the transiting disk obtained at the CHARA Array with the MIRC beam combiner.  His own summaries of the dissertation work can be found at www.citizensky.org under the Blog postings, so again no need to be detailed here, except to say these images provide very unique constraints on orbital solutions, and possibly tie-breakers for the distance and component mass problems that have too long been unresolved.  Finally, I spoke about the overall state of the art based on the eclipse to date and thanked all the participants and audience for their continued interest.  Of course, eclipse is not quite over, and some spectroscopic and polarimetric facets are anticipated to persist all year - so observers are still needed!

February 2011 is likely to be the last full month of totality - and it's our shortest month!  Comparison with the last eclipse light curves suggests the prospect for a rapid rise in brightness starting now (RJD ~55,600) - coming up from the 3.75 of late, toward 3.65 and with a more substantial increase in U-B and B-V color.  Duration ~ one month, then a brief quiet period before "3rd contact" (Egress, mid-March) and the beginning of the return to full brightness (mid-May).  If you haven't acquainted your family, friends and neighbors with epsilon Aurigae yet, these are the nights to do so - it's well placed in the evening sky and soon to brighten.  Invite them, as did showman P.T. Barnum, with the words: "This way to the Egress."
...and record your observations here at CitizenSky.org - thanks!
May I recommend participating in Globe At Night while you're at it? 
www.globeatnight.org .