A blog concerning epsilon Aurigae as it undergoes eclipse 2009-2011.

Constructive comments are welcome - contact rstencel at du dot edu

2009 Jan.10:

Recently I noticed a series of papers about high dispersion spectroscopy of binary stars, by Ulisse Munari and colleagues at the INAF Osservatorio Astronomico di Padova in Italy and wrote to them about the epsilon Aur campaign.  He inquired: “(a) what exactly to investigate of epsilon Aurigae and how and with what instruments, (b) how you plan to organize the collaboration you are mounting on this object.”  To answer these questions, we suggest:  (a) High dispersion spectroscopy can help confirm two important observations made during the course of the previous eclipse, 1982-84.  These include the appearance of shell spectra in the blue region (4000-4500AA) described by Steno Ferluga, http://adsabs.harvard.edu/abs/1991A%26A...243..230F , and the appearance of strong K I 7699AA absorption, starting at mid-eclipse, as reported by Lambert and Sawyer http://adsabs.harvard.edu/abs/1986PASP...98..389L

(b) Jeff Hopkins in Arizona and I have been promoting an observing campaign since 2003 in order to encourage photometry, spectroscopy, polarimetry and interferometric observations of the total eclipse predicted to start August 2009 and running through spring 2011.

 What are the science goals, and what measurements are crucial?  Partial phases of the eclipse have been getting shorter during the 20^th century, and the low amplitude out of eclipse light variations have been getting faster during the past 50 years.  In the context of the prevailing model, where a massive disk eclipses the F supergiant star, these changes can be interpreted as disk evolution, possibly due to planet forming activity.  Thus, testing this idea requires good photometric coverage, ideally UBVRI and JHK.  Also, the most sensitive indicators of the disk have been the optical spectra mentioned above.  If the disk is changing, then the blue region and the K I lines should differ from the past eclipse behavior.  Finally, modern interferometry has the chance to directly resolve the disk transiting the supergiant star, and those observations are underway, with an initial report recently published: Interferometric Studies of the extreme binary, $\epsilon$ Aurigae: Pre-eclipse Observations, by R.Stencel, M. Creech-Eakman, A. Hart, J. Hopkins, B.Kloppenborg & D.Mais [2008 Dec. 20 ApJ Letters] Link: http://arxiv.org/abs/0810.5382

 For reference - Aims of the Asiago program: The aim of Asiago Eclipsing Binaries Program is to derive accurate orbits and physical parameters (in particular masses and radii) for a selection of double-lined eclipsing binaries by means of Echelle high resolution, high S/N spectroscopy, and B, V photometry. Atmospheric parameters (T_eff, log g, [M/H], xi , V_rot) and individual chemical abundances are provided by spectral analysis. Reddening is derived from intensity of NaI (5890.0 & 5895.9 Å) and KI (7699.0 Å) interstellar lines. http://adsabs.harvard.edu/abs/2008MmSAI..79..753T .

Brian Kloppenborg and I had a successful half-night on the NASA Infrared Telescope Facility, a 4 meter atop Mauna Kea.  With remote observing, we collected 80 high quality spectra of epsilon Aur plus spectral ratio and telluric comparison stars, in an effort to monitor the 2.3 micron CO band region.  Pre-eclipse this region is just continuum, but as seen during the last eclipse, we anticipate the appearance of CO bands once eclipse begins.  Whether these persist past end of eclipse, as they did in 1985, is the experimental objective.  See Hinkle and Simon, http://adsabs.harvard.edu/abs/1987ApJ...315..296H .

2009 Jan.3 -- recent papers mentioning epsilon Aur (from simbad):  Astron. Astrophys., 489, 911-921 (2008)
Polarimetric measures of selected variable stars.  ELIAS II N.M., KOCH R.H. and PFEIFFER R.J. -- "The evidence from the B, V and R historical measures (Gehrels & Sylvester 1965; Coyne & Gehrels 1966) and the two tabulated B values is that this atmospherically-eclipsing binary is a polarization variable."

Astron. Astrophys., 490, L7-L10 (2008) An occultation event in the nucleus of the planetary nebula M 2-29.
HAJDUK M., ZIJLSTRA A.A. and GESICKI K.  -- "Eclipses and occultations of post-AGB stars provide a powerful method of exploring the near-stellar environment, including close companions and circumstellar debris disks. Only six eclipsing systems and one dust-occultation system are currently known."  Among objects with similar events, long-lasting minima are observed in wide binary systems, like symbiotic stars; they are ascribed to dusty clouds. In V Hya such a minimum is observed repeatedly with over a 6000 day period (Knapp et al. 1999). NGC 2346 has shown two long-lasting eclipses by clouds (Kato et al. 2001). Either eps Aur or EE Cep are examples of eclipses by a disk placed nearly edge-on to the observer, around an unseen companion (Mikoajewski & Graczyk 1999; Carroll et al. 1991). Such eclipses appear to be flat and almost grey.

Astrophys. J., 689, L137-L140 (2008) Interferometric studies of the extreme binary {epsilon} Aurigae: pre-eclipse observations.  STENCEL R.E., CREECH-EAKMAN M., HART A., HOPKINS J.L., KLOPPENBORG B.K. and MAIS D.E. -- "The measured 2.27±0.11 mas K-band diameter is consistent with a 150 solar diameter F supergiant star at the Hipparcos distance of 625 pc."

2009 Jan.2 -- the year 2008 was a productive one, with the publication of the book on eps Aur, several observing proposals and new data - particularly interferometric measures, leading to an Astrophysical Journal Letter, 12/20/08.

In his 1928 paper 'On the Variability of the Maximum Light of eps Aur', H. Shapley stated: "Although few in number, the observations indicate a period of 355 days (+/- 10 days).  Variability in a period of less than a day is not absolutely excluded, but successive observations on the same night make it improbable."

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