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Home , Capella, Epsilon Aurigae, Zeta Aurigae

, 2009: The begins – observing campaign status Robert E. Stencel University of Denver Observatories Dept. Astronomy & Physics, Univ. Denver, Denver CO 80208 [email protected] & Jeffrey L. Hopkins Hopkins Phoenix Observatory 7812 W. Clayton Dr., Phoenix AZ 85033

Presented at the Society for Astronomical Sciences Symposium, 2009 May

Abstract The eclipse of 3rd magnitude epsilon Aurigae is forecast to begin during August 2009, reaching totality by 's end, based on all fsix prior eclipse events studied - 1982, 1955, 1930, 1902, 1874 and 1847. We have organized a campaign during the past several in order to raise awareness about this rare opportunity, and to promote reporting of observations of all kinds. We have 40 registered participants, 76 people signed up for alert notices, plus numerous informal expressions of interest. Categories of observations being reported in Campaign Newsletters (11 since 2006) which include Photometry, , Polarimetry, and [website: www.hposoft.com/Campaign09.html ]. In this presentation, we provide a brief update on the optical and near-IR photometry obtained to date. The nature of the short term light variations will be discussed in the context of mapping the eclipse behavior. Spectroscopy benefits from small telescope capabilities now widely available, along with traditional large telescope, higher dispersion work. Examples of each will be presented, along with the research objectives. Polarimetry provided key insights during the last eclipse, and we continue to promote the need for new data using this method. Finally, interferometry has come of age since the last eclipse, and a status report on this powerful method to directly detect the passing dark disk will be provided. Along with these traditional measurements, we will briefly discuss efforts to promote Citizen Science opportunities among the public, in coordination with AAVSO and as part of the International Year of Astronomy, IYA 2009.

1. Introduction The reason for the continuing interest in this binary has to do with the difficulty of determining the Epsilon Aurigae (ep-si-lon Awe-rye-gee) is a nature of the companion – a dark, possibly quite very long period eclipsing binary (Algol-like) . The massive disk shaped object, orbiting the seemingly 27 year eclipse interval includes a nearly 2 year normal F that emits all the visible eclipse duration, wherein visual magnitude drops light. from 3.0 to 3.8. As of this year’s SAS symposium, With normal eclipsing systems, one we’re anticipating the start of the first eclipse of the measures the brightness, changes and durations, to millennium during August 2009, with totality reached obtain radii, temperatures of each star in the pair. during December 2009, and lasting ~15 months, With spectroscopy, one can measure Doppler through March 2011. The end of eclipse is expected velocities, and solve for masses. This process during May 2011. This will be only the sixth calibrates all the important parameters that describe a documented eclipse in history (1983, 1956, 1930, star. The Vogt-Russell theorem says the mass, 1902, 1874 and 1847). For additional detail about composition and age of a star uniquely determines epsilon Aurigae, see Hopkins, Schanne and Stencel the stellar structure, when normal laws of physics are (2008), along with the book about the star by applied. This procedure works well, except for Hopkins & Stencel (2009), and a feature article in the epsilon Aurigae: the F supergiant star seems to have May 2009 issue of Sky & Telescope magazine. an equally massive, but invisible companion object. Because this eclipse begins during the International Thus, we have the problem of “hiding” all that mass. Year of Astronomy (IYA), it has been adopted as an Some of the observational questions under element of the Citizen Science component of the US- investigation for this eclipse include: (1) will the pre- IYA activities, with AAVSO leadership. eclipse low-amplitude light variations persist into eclipse; (2) will the beginning and depth of eclipse 1), including 1982-1989 and 2003 to the present. As match prior eclipse trends; (3) will the “mid-eclipse can be seen from the plot, epsilon Aurigae is brightening” seen during the past two , recur. anything but quiet between eclipses. The object of Additional basic questions are receiving attention: these observations is to see if the out-of-eclipse what is the true distance to the binary? HIPPARCOS variations could be better understood. A key feature says 625 pc (with a 72 percent uncertainty!). What is of the pre-eclipse light curves is the appearance of a the physical diameter of the F supergiant star? Can quasi-periodic variation, recently showing a 65 we finally decide between the high mass model for period, deduced with Peranso software (Hopkins et the system (15 F supergiant star primary al. 2008). Interestingly, a long photometry record by and massive dark disk of uncertain origin) or the low Nha et al. (1993) showed similar variations, but with mass model (a rapidly evolving post-AGB “phony” a longer characteristic period, closer to 95 days. supergiant star with a companion shrouded by recent Monitoring will help interpret in-eclipse fluctuations. overflow mass loss)? Once again, If the acceleration trend persists, there may be epsilon Aurigae lies at the crossroads of modern exciting times ahead for the system within a few astrophysics – providing evidence for details of high decades – perhaps destruction of a Jupiter-sized mass , plus an extreme accretion disk object within the accretion disk central region. and possibly planet formation and destruction – all in Beginning with the 2008/2009 season, more one bright star package! observers from around the world became involved Numerous prior observational studies have with the upcoming eclipse. These observers have shown the presence of additional absorptive material submitted UBVRI and JH photometric data to the during eclipse. The prevailing model (Huang 1965 Campaign newsletters. While the Hopkins Phoenix and thereafter) accounts for these data with a thin Observatory uses a PMT based photon counter for disk crossing the body of the F supergiant during UBV photometry, others have used an Optec SSP-3 eclipses (see Carroll et al. 1991). for BVRI data, an Optec SSP-4 for near J In this paper, we will describe the observational and H and data, CCD photometry for BVRI data and efforts already underway, thanks to the interest of DSLR CCD cameras for V data. Excellent numerous observers worldwide, in advance of the photometric data have been reported by: eclipse anticipated to begin after mid 2009. The David Trowbridge (Tinyblue Observatory, ensemble of data streams will help provide a context Greenbank, Washington, USA) within which individual observations can help prove Dr. Tiziano Colombo (S. Giovanni Gatano al or disprove hypotheses about this mysterious system. Observatory, Pisa, Italy) Richard Miles (Golden Hills Observatory, 2. Photometry Stourton Caundle Dorset, England) Paul Beckmann (Jim Beckmann Observatory, Photometry is the measurement of light. During Mendota Heights, Minnesota, USA) recent decades, single channel photometers have Des Loughney (Edinburg, Scotland), become readily available (e.g., the SSP-3 and SSP-4 Brian McCandless (Grand View Observatory, units available from www.optecinc.com ), and Elkton, Maryland, USA), progress with CCD aperture photometry of faint Frank J. Melillo (Holtsville, New York, USA). has been made (see papers at this meeting). Photon counting photometers such as used at the Hopkins These data have been reported in our Campaign Phoenix Observatory have proved to be very accurate Newsletter series, available free in .pdf format at our with even modest telescopes on the brighter stars. Campaign informational website: A serious problem with epsilon Aurigae is that it www.hposoft.com/Campaign09.html . Figure 2 is so bright for modern instruments that saturation shows a composite of V data from multiple and dead-time become problems. Everyone needs to observers. The quasi-periodicuty of out-of-eclipse be reminded that this eclipse is also a fine visual variations remains a mystery. Over the past event – you can easily see epsilon Aurigae dim several years, seasonal period analysis suggested the relative to nearby eta Aurigae (V=3.2) and zeta variation frequency to be increasing (Hopkins et al. Aurigae (V=3.8), which comprise the “Kids” 2008). The 2007/2008 season showed a period of near . A based on visual around 65 days. This past season (2008/2009) reports is assembled at the AAVSO of appears to show a significant period of 148.6 days, the Season page for epsilon Aurigae (Jan. 2008). again deduced using Peranso software - the Hopkins Phoenix Observatory has compiled one Discrete Fourier Transform (Deeming) method, with of the longest and most continuous UBV observing V band data. Other bands yield a similar period. We records leading up to the oncoming eclipse (Figure continue to study these photometric period trends. With the help of Denver U. grad student, Brian portions of prior eclipses (Lambert & Sawyer, 1986), Kloppenborg, we’ve been pursuing J&H band and monitoring of these is encouraged. photometry of epsilon Aurigae during early 2009. Very interesting changes are seen Using an SSP4 photometer on a very unusual 16 inch at higher dispersion. Elizabeth Griffin (DAO) telescope, we have very preliminary evidence of reported changes in the blue region between declines in the J band during a time when the optical December 2008 and February 2009 that indicate light was at a record local minimum near RJD 54900. “reverse P Cygni” profiles appear in difference Whereas we did double check that we measured full spectra. These could be consistent with signal in J, by re-centering the star in the aperture encroachment of the fringes of the disk onto the F repeatedly, these data probably need closer star body as eclipse nears. This work highlights the examination to be verified. Brian McCandless in findings of the long term radial velocity curve, Newsletter 11 reported some J band declines as well discussed by Lambert and Sawyer (1986) and in new during this period, just when V was steeply falling. work by Stefanik et al. (2009). As mentioned above, Spectroscopically, the J band contains Paschen beta by monitoring the strength of H-alpha, sodium, and gamma lines, along with the CN Red 0-0 band, potassium lines, and in the blue region, evidence of but whether these are active in epsilon Aurigae and the disk and its changes may be within reach this causing the J band “dropouts” needs confirmation, cycle. Joel Eaton at Tennessee State University has perhaps because encroaching disk flotsam is the embarked on radial velocity monitoring with an cause. automated spectroscopic telescope, which offers For completeness, we note that infrared spectro- great promise for providing fiducial velocity data photometric measures have been obtained with IRTF against which the light variations can be compared. at Mauna Kea (SpeX – Stencel et al. Figure 3 – Brian McCandless reported a brief appearance of He BASS – M. Sitko et al. U.Cinc. -- and MIRSI – G. I emission in the 6678Å line during 2009 April, and Orton et al., JPL) and the Spitzer Space Telescope observers are encouraged to look for the related He I (MIPS – S. Howell, NOAO). A recent X-ray lines at 4471, 5876 and 7065Å, arising from the UV measurement made by the European XMM satellite source in the system studied with the IUE space has been made (S.Wolk, CfA, private telescope (HST’s precursor) during last eclipse (see communication). Results of these observations will reports in Stencel, 1985). Similarly, Struve and be reported elsewhere. Elvey (1930) reported transient emission in the core of the H-beta line during autumn 1928 (eclipse 3. Spectroscopy ingress). Ake (see Stencel, 1985) cites “extraordinary brightenings” in the ultraviolet near We’re pleased to report that several professional first and third contacts. Spectroscopic monitoring observatories have resumed gathering high dispersion can help narrow the range of phases during which spectra of epsilon Aurigae as it approaches eclipse. this UV window opens toward . In addition, the advent of affordable spectrographs like the LHIRES and SBIG spectrometers make 4. Polarimetry amateur data collecting on bright objects relatively easy. Some of our most active observers include Jeff Another powerful method in astronomy involves Hopkins (Phoenix), Lothar Schanne (Germany), using polarized light. We use polarized lenses in Robin Leadbeater (UK), Joel Eaton (Nashville/TSU) sunglasses to reduce the light reflecting off water or and Elizabeth Griffin (Victoria/DAO). Several other surfaces. The process of reflection can polarize observers are concentrating on the H-alpha line near light, terrestrially or from sources in space. The 6563Å, which shows rapid variations of its emission series of polarized light measurements reported by wings. Attempts to correlate the line attributes with Jack Kemp and collaborators provides the best the visual light curve have been frustrated by the evidence so far for the shape and tilt of the disk. complexity of the variations (see Hopkins & Stencel (Kemp et al. 1986; and see Kemp’s report in Stencel, paper, this volume). Leadbeater and others are also 1985). monitoring the “blue” region of the spectrum, e.g. Kemp invoked a tilted disk and slight non-edge- 4600Å, which Ferluga and Mangiacapra (1991) on to explain asymmetries in the demonstrated is an excellent region for the polarization and previous light curves. Importantly, appearance of “shell lines” during eclipse. Kemp also suggested that the primary star is a non- Similarly, the resonance lines of sodium (D lines near radial pulsator with hotter polar regions tilted towards 5900Å) and potassium (K I 7664/7699Å) have shown earth and/or an equatorial ring, to produce the significant absorption strength increase during asymmetric polarization observed. Modern polarimeters need to observe epsilon and http://www.du.edu/~rstencel/epsaur.htm . Aurigae in order to support this interpretation. To date, eleven Campaign Newsletters have been Several instruments are available, including the produced since Sept. 2006. We encourage all ESPaDOnS instrument at CFHT (Harrington & Kuhn interested parties to provide us with reports of your (2009) which obtained data in 2006 on February 7 observations and analysis. Your photometry and and 8. The observation shows a strong and complex spectroscopy reports are especially welcome. Hα signature. The polarization change is symmetric In addition to formal reports like these, which we at line center and spans the width of the line. The hope to continue, there is ample opportunity for polarization amplitude ~1% at the line center, not “Citizen Science” by members of astronomy clubs unlike other Be stars. Ideally, CFHT will pursue this and the general public. In cooperation with AAVSO opportunity, as indicated in a report by Nadine and the US node of IYA, we hope to inspire Manset in Campaign Newsletter 11. interested persons to learn how to observe and record variable star brightness variations, with epsilon 5. Interferometry Aurigae as the major, unique opportunity starting in 2009. For details about this project, see website: One promising modern technology to apply to http://www.aavso.org/aavso/iya.shtml . epsilon Aurigae’s upcoming eclipse is called An oddity concerning this eclipse is connected to interferometry. This technique has been used for our current economic turmoil. More than once it has decades, but modern computer control and laser been remarked that “certain rates are the most metrology has helped mature the methods to a point extreme since 1983” – bringing to mind events on where a key, direct test of the Huang disk model is earth during the last eclipse. In the recent months, possible. By combining light from two or more when the Dow Jones stock market index dove to a telescopes, one can measure diameters at the milli- record low and then recovered, in early March 2009, arcsecond level over telescope separation baselines of circa RJD 54900, epsilon Aurigae had already a hundred meters. Nordgren et al. (2001) reported dimmed to a pre-eclipse faint record of V=3.14 on the broadband optical diameter of epsilon Aurigae to RJD 54890, and then brightened. Coincidence? be 2.18 milli-arcsec, using the Navy Prototype Probably. Before you invest based on cycles in Optical Interferometer [NPOI]. Stencel et al. (2008) epsilon Aurigae, recognize that past returns are not a reported a Palomar Testbed Interferometer [PTI] guarantee of future performance. infrared diameter of 2.27 milli-arcsecond using a north-south baseline, with indications of a larger 7. Conclusions diameter using a north-west baseline. Very recent 4 telescope observations at the Mt. Wilson-based The eclipse is upon us! By promoting Center for High Angular Resolution Astronomy observation data of all kinds, we can hope to build a [CHARA] array seem to indicate an asymmetry in successful context for competition among the the east-west axis, again as might be expected due to hypotheses that try to explain this mysterious star encroachment onto the F star of the disk’s outer system. Whereas the F star is undoubtedly as or edges. The state of the art has advanced to a point more complex than our , the eclipsing body where “closure phase imaging” is possible, although probably is the source of some of the activity the results are highly dependent on assumptions used detected thus far in epsilon Aurigae eclipse in the deconvolutions. In the best case, imaging monitoring. Secular changes short and long term are interferometry may be able to “see” the bifurcation of being documented, and these will provide a rich the F star orb by the transiting disk during eclipse – ground for theory and debate as the long vigil prior to directly testing the basic Huang model. Continuing the 2036 eclipse begins in a couple of years. For observations are planned. more information and updates, see our campaign websites, plus, new for this year: 6. Citizen Science https://twitter.com/epsilon_Aurigae

We were involved in the 1982-84 eclipse events 8. Acknowledgements and re-started our efforts in 2003, in order to raise awareness of the pending eclipse and to promote We are thrilled to thank the many participants observing and reporting, plus new theory. The and interested parties helping support the eclipse websites for the campaign this cycle are: study. Stencel particularly acknowledges Bobby http://www.hposoft.com/Campaign09.html , Buss, Joel Eaton, Elizabeth Griffin, Brian Kloppenborg, Dale Mais, John Monnier, Ming Zhao and others for observing support, and is grateful to Nordgren, T., Sudol, J. and Mozurkewich, D. William Herschel Womble for a bequest in support of “Comparison of Stellar Angular Diameters from the astronomy at the University of Denver, which is NPOI, the Mark III Optical Interferometer, and the instrumental making this research feasible. Jeff Infrared Flux Method” (2001) Astronomical Journal, Hopkins thanks his correspondents and we thank you, 122 , 2707. dear reader, for your interest! http://adsabs.harvard.edu/abs/2001AJ....122.2707N .

9. References Stefanik, R., Lovegrove, J., Pera, V., Latham, D., Torres, G. and Zajac, J. “Epsilon Aurigae: An Carroll, S.,Guinan, E., McCook, G. and Donahue, R., Improved Spectroscopic Orbital Solution” (2009) “Interpreting epsilon Aurigae” (1991) Astrophys. American Astronomical Society, AAS Meeting #213, Journal 367 , 278. paper #410.10, weblink: http://adsabs.harvard.edu/abs/1991ApJ...367..278C . http://adsabs.harvard.edu/abs/2009AAS...21341010S

Fegluga, S. and Mangiacapra, D., “Epsilon Aurigae. Stencel, R. “The 1982-84 Eclipse of epsilon Aurigae” II – The shell spectrum” (1991) Astron. & Astrophys. (1985) NASA Conf. Publication No. 2384 – weblink: 243 : 230. [ http://www.du.edu/~rstencel/NASAcp2384.pdf ]. http://adsabs.harvard.edu/abs/1991A%26A...243..230F . Stencel, R., Creech-Eakman, M., Hart, A., Harrington, D. and Kuhn, J. “Spectropolarimetric Hopkins, J., Kloppenborg, B., Mais, D., Surveys: HAeBe, Be and Other Emission-Line Stars” “Interferometric Studies of the Extreme Binary (2009) Astrophys. Journal Supplement 180, 138. epsilon Aurigae: Pre-Eclipse Observations” (2008) http://adsabs.harvard.edu/abs/2009ApJ...695..238H . Astrophys. Journal 689 , L137. http://adsabs.harvard.edu/abs/2008ApJ...689L.137S . Hopkins, J., Schanne, L. and Stencel, R. (2008) “Gearing up for Epsilon Aurigae's First Eclipse of the Millennium” in proceedings of the Society for Struve, O. and Elvey, C., (1930) “Preliminary Results Astronomical Sciences 27th Annual Symposium on of Spectroscopic Observations of 7 epsilon Aurigae” Telescope Science, May, 2008, p.67 & arXiv eprint. Astrophys. Journal 71: 136. http://adsabs.harvard.edu/abs/2008SASS...27...67H . http://adsabs.harvard.edu/abs/1930ApJ....71..136S .

Huang, S.S., “An interpretation of epsilon Aurigae” (1965) Astrophys. Journal 141 : 976. http://adsabs.harvard.edu/abs/1965ApJ...141..976H .

Kemp, J., Henson, G., Kraus, D., Beardsley, I., Carroll, L., Ake, T., Simon, T. and Collins, G., “Epsilon Aurigae - Polarization, light curves, and geometry of the 1982-1984 eclipse” (1986) Astrophys. Journal Letters 300 , L11. http://adsabs.harvard.edu/abs/1986ApJ...300L..11K .

Lambert, D. And Sawyer, S. “Epsilon Aurigae in eclipse. II - Optical absorption lines from the secondary” 1986, Publications Astron. Society Pacific 98 : 389. http://adsabs.harvard.edu/abs/1986PASP...98..389L .

Nha, I., Lee, Y., Jeong, J. and Kim, H., “Extreme Long-period Eclipsing Binary epsilon Aurigae” (1993), in Proceedings New frontiers in binary star research, eds. Kam-Ching Leung and Il Seong Nha, ASP Conf. Vol. 38 , p.291. http://adsabs.harvard.edu/abs/1993ASPC...38..291N .

FIGURES ONE AND TWO, TWO COLUMNS WIDE EACH FILLING PAGE THREE

Figure 1. The UBV light curve of epsilon Aurigae between 2003 and 2009, obtained at the Hopkins Phoenix Observatory by Jeffrey Hopkins.

Figure 2. The composite V light curve of epsilon Aurigae for the 2008-2009 season, obtained by campaign observers J. Hopkins (HPO), D. Loughney (DES), B. McCandless (BEM), Frank Melillo (FJM) and Paul Beckmann (JBO). FIGURE THREE, TWO COLUMNS WIDE, FILLING TOP HALF PAGE FIVE

Figure 3. IRTF SpeX pre-eclipse spectrum of epsilon Aurigae (upper trace, 1/9/09, Stencel & Kloppenborg) compared with the much cooler supergiant, (lower trace) – the latter showing strong CO lines. The same CO features are expected to appear in the spectrum of epsilon Aurigae during eclipse.