NEWS * 2012 September
Special issue of the Journal of the Amer. Assoc. Variable Star Observers (JAAVSO Vol.40, #2) will include reports about epsilon Aurigae—including: An Overview of the 2009–2011 Eclipse Campaign Results.
TEN THINGS WE'VE LEARNED AS A RESULT
OF THESE CAMPAIGNS - some of these were recognized last time around, and some
represent working hypotheses that serve as tools to design more clever
measurements and theory to finally resolve the masses and evolutionary status of
epsilon Aurigae components:
FACTS: the eclipsing object is a large, 550K disk [IR];
FACT/INTERPRETATION: neutral potassium monitoring shows disk substructure [LHIRES];
FACT: carbon monoxide re-appeared again after mid-eclipse [SpeX, GNIRS];
NEW FACT: He I 10830A absorption strengthened after mid-eclipse [SpeX];
FACT: the disk facing the F star is heated to 1100K [IR];
FACT: the Far-UV output is somewhat eclipsed [HST/COS];
FACT: no 10 micron silicates [BASS, MIRAC] - INTERPRETATION: large particles ( greater than 1 micron size) dominate the disk;
FACT/INTERPRETATION: light curves feature 0.1 mag variations --> F star oscillations, wind.
SUSPECTED: the disk may contain a B5V star;
SUSPECTED: the mass ratio favors the B star as the more massive object.
Some of these new and old facts lead me to the following considerations. One can compute the equilibrium temperature of an object orbiting a star [see, e.g. http://burro.cwru.edu/Academics/Astr221/SolarSys/equiltemp.html ]. In a blackbody approximation, for a 30,000 solar luminosity primary star, we find that the observed heated face of the disk, 1100K, is reached at a separation of 9 to 11AU, for a range of particle albedos, from 0.3 (somewhat reflecting) to zero (fully absorbing). Given that the F star luminosity estimate increases with larger distances, this separation result is not definitive, but these thermal IR facts provide another constraint on binary separation (hence, total mass). Another interesting constraint on the mass of the central star inside the disk is derived from the velocity shift seen in Robin Leadbeater's neutral potassium line data, approx +/- 35 km/sec rotation speed, plus a current best guess for the radius of the disk itself, 3.8AU. Kepler's third law then tells us the central mass is 3.85 solar masses - a bit below the 6 solar mass B star proposed earlier. Watch this space for developments in coming months.
Thus, although the recent eclipse is fading into memory, the bonanza of data is providing researchers both ample constraints for checking the current model, and inspiration for how to design observations that can confirm ideas without waiting another 27 years for the next eclipse. Key among the goals in these studies is pinpointing the disk’s age and evolutionary state, and whether there might be high levels of activity such as the B star’s accretion of disk matter. The F star itself is an important part of the study: Does it have an active atmosphere or giant convective cells, flares, or even a strong stellar wind? The next eclipse is forecast to start in 2036, but you can enjoy out-of-eclipse variations of Epsilon Aurigae’s light the very next time you see the star, along with Capella and the Kids riding across the evening sky. Post-eclipse observations are still needed — this star retains its capacity to surprise. Thanks again for your interest and participation in this campaign, and keep in touch!
--Dr. Bob Stencel, University of Denver Astronomy, firstname.lastname@example.org
Recent papers: Infrared Studies of Epsilon Aurigae in Eclipse 2011 Nov Astronomical Journal, vol 142, pp.174-183.
plus an interesting olde analysis by Handbury & Williams, 1976:
The Seattle AAS meeting in January 2011 will feature a set of contributed posters plus 6 invited talks, all highlighting developments associated with studies of the current eclipse of epsilon Aurigae. The posters submitted include:
Campaign Photometry During The 2010 Eclipse Of Epsilon Aurigae -
Jeff Hopkins1, R. E. Stencel2
= 1HPO Soft, 2Denver University.
257.02. Analysis of Epsilon Aurigae light curve from the Solar Mass Ejection Imager - John Clover1, B. V. Jackson1, A. Buffington1, P. P. Hick1, B. Kloppenborg2, R. Stencel2 = 1University of California, San Diego, 2University of Denver.
257.03. Interferometric Images Of The Transiting Disk In The Epsilon Aurigae System - Brian K. Kloppenborg1, R. Stencel1, J. D. Monnier2, G. Schaefer3, M. Zhao4, F. Baron2, H. McAlister5, T. ten Brummelaar5, X. Che2, C. Farrington5, E. Pedretti6, P. Sallave-Goldfinger5, J. Sturmann5, L. Sturmann5, N. Thureau7, N. Turner5, S. Carroll8 = 1University of Denver, 2University of Michigan, 3Georgia State, 4Jet Propulsion Laboratory, 5Georgia State University, 6SUPA, University of St. Andrews, United Kingdom, 7University of St. Andrews, United Kingdom, 8California Institute of Technology.
257.04. Spectroscopic Wonders During The 2010 Eclipse Of Epsilon Aurigae - Robin Leadbeater1, C. Buil2, T. Garrell3, S. Gorodenski4, J. Hopkins5, B. Mauclaire6, J. Ribeiro7, L. Schanne8, O. Thizy9, R. Stencel10 = 1Three Hills Observatory, 2Castanet Tolosan Observatory, France, 3Observatoire de Foncaude, France, 4Blue Hills Observatory, 5Hopkins Phoenix Observatory, 6Observatoire du Val de l'Arc, France, 7Observatorio de Instituto Geografico de Exercito, Portugal, 8Voelklingen Observatory, Germany, 9Shelyak Instruments, France, 10University of Denver.
257.05. Optical and NIR Spectroscopy of ε Aurigae at Apache Point Observatory, the First Half of the Eclipse
William F. Ketzeback1, J. Barentine2, R. Leadbeater3, R. McMillan1, J. Dembicky1, G. Saurage1, J. Huehnerhoff1, S. Schmidt4, S. Hawley4, G. Wallerstein4, J. Coughlin5, D. York6 = 1Apache Point Observatory, 2UT Austin, 3Brititsh Astronomical Association, United Kingdom, 4University of Washington, 5New Mexico State University, 6University of Chicago.
257.06. Epsilon Aurigae - Intriguing Changes with Phase - R. E. M. Griffin1 = 1Herzberg Inst. of Astrophysics, Canada.
257.07. Hubble Space Telescope Ultraviolet Observations of Epsilon Aurigae - Steve B. Howell1, R. E. Stencel2, D. W. Hoard3 = 1NOAO, 2University of Denver, 3Spitzer Science Center.
257.08. Ring-like Structures Around Epsilon Aurigae Companion - Sally Seebode1, S. B. Howell2, D. Drumheller3, D. Stanford3, D. W. Hoard4, R. E. Stencel5 = 1San Mateo High School, 2NOAO, 3College of San Mateo, 4Spitzer Science Center, 5University of Denver.
257.09. Infrared Studies of Epsilon Aurigae in Eclipse 2010 - Robert E. Stencel1, B. Kloppenborg1, R. Wall1, S. Howell2, D. Hoard3, J. Rayner4, S. Bus4, A. Tokunaga4, M. Sitko5, R. Russell6, D. Lynch6, S. Brafford7, H. Hammel8, B. Whitney8, G. Orton9, P. Yanamandra-Fisher9, J. Hora10, W. Hoffman11, A. Skemer11 = 1Univ. of Denver, 2NOAO, 3IPAC, 4IRTF, 5Univ. Cincinnati, 6The Aerospace Corp., 7Esq., 8Space Science Institute, 9JPL, 10Harvard Univ., 11Univ. Arizona.
* * * * * * * *
NEWS * 2010 May:
A summary of progress during the first half of eclipse can be found at these websites:
http://xxx.lanl.gov/ftp/arxiv/papers/1005/1005.3738.pdf - "Epsilon Aurigae in Total Eclipse, 2010 - Mid eclipse report" and
http://www.hposoft.com/EAur09/EAUR%20pdfs/SAS2010.PDF - "Epsilon Aurigae Eclipse 2009 - Ingress Photometry"
A trifecta of new reports are beginning to reveal unprecedented details about the nature of the epsilon Aurigae system:
Development #1 - The complete spectral energy distribution: http://arxiv.org/PS_cache/arxiv/pdf/1003/1003.3694v1.pdf
The observed spectral energy distribution can be reproduced using a three component model consisting of a 2.2+0.9/-0.8 Msun F type post-asymptotic giant branch star, and a 5.9+/-0.8 Msun B5+/-1 type main sequence star that is surrounded by a geometrically thick, but partially transparent, disk of gas and dust. At the nominal HIPPARCOS parallax distance of 625 pc, the model normalization yields a radius of 135+/-5 Rsun for the F star, consistent with published interferometric observations. The dusty disk is constrained to be viewed at an inclination of i > 87 deg, and has effective temperature of 550+/-50 K with an outer radius of 3.8 AU and a thickness of 0.95 AU.
Development #2 - Interferometric imaging of the disk during eclipse ingress: To appear in Nature, 8 April issue.
Synopsis: Interferometric images obtained during autumn 2009 show the opaque disk crossing the southern hemisphere of the F star. The measured change over the course of two observations a month apart indicate relative motion, which in combination with well-known orbit of the F star, argue for a mass ratio of 0.6 - which means the F star is lighter than the disk and its contents. Disk opacity can be used to estimate the dust mass of the disk, to be less than one earth mass. Details available on request from this author.
Development #3 - Substructure inside the disk: http://arxiv.org/ftp/arxiv/papers/1003/1003.3617.pdf
Variations in the equivalent width of the neutral potassium line at 7699A are reported, during ingress and into totality of the current eclipse of the enigmatic eclipsing binary epsilon Aurigae. The increase and plateaus of line strength are correlated with new system parameters and interferometric imaging constraints, plus ancillary data being reported contemporaneously. Together, these data reveal structural details of the transiting disc, never before measured.
2010 Jan: A great deal is being learned during this eclipse cycle (2009-2011) and almost too much to keep this humble webpage up-to-date. You can get the latest by going to Jeff Hopkin's campaign website: Campaign newsletter link - which welcomes reports from all serious observers. For breaking news, any google/bing type searches will turn up stories from the Jan 2010 AAS meeting where several papers were presented, watch the Twitter site, Facebook, and importantly CitizenSky where you can report your visual observations. Feel free to contact me directly for the latest as well.
See Sky&Telescope article: http://www.skyandtelescope.com/news/80730537.html
An F supergiant star (or post-AGB star) with an enormous grey disk orbiting each 27 years... eclipses last nearly 2 years! Current one started 2009 mid-August and lasts til late spring 2011! Where to look!
What are the science goals, and what
measurements are crucial? Partial phases of the eclipse have been getting
shorter during the 20th 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 (4000-4500AA and 7699AA). 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 in the Dec. 20, 2008 ApJ Letters.
To join in the campaign effort, send email to phxjeff at hposoft.com
and/or rstencel at du.edu
*For a free copy of the NASA conference publication #2384, "The 1982-84 Eclipse of Epsilon Aurigae", please email email@example.com, and provide your complete airmail address. You can now obtain the same in PDF format HERE. Caution - it is a largish file (5Mb).
Intrerferometry finally can provide a direct test of the Huang model for the eclipse - in that the 2.2 milliarcsec F star disk should be bisected by the dark disk and appear as a "double star" with similar separation.
"H-alpha spectra being regularly acquired by Lothar Schanne (reference IBVS 5747) provide a roadmap of the nebular emission from the binary system that enable another dimension to be added to the revelations of the UBVJH photometry reported by Hopkins. The line center velocity gives a Doppler measurement of the densest material, while the emission bump variation informs us of the movement of lower density clouds associated with one of the components. Once again, having this pre-eclipse record will help place in-eclipse variation into a useful context that largely was absent during the run up to the 1982 eclipse."
Interestingly, the recent V band peak just prior to MJD 54100 does seem to be flanked by shallow minima about 54050 and 54140... of course the brightening overall is dramatic and changes are bigger toward the blue/uv: MJD V band changes B band changes U band H band 3000 min 3.12, max 3.04 mn 3.72, mx 3.60 3.85, 3.60 -- 4000 min 3.05, max 3.00 mn 3.62, mx 3.55 3.75, 3.65 1.50 diffs .07 .04 .10 .05 .10 .05 --
**Hopkins, J. 1990 3rd ed. "Zen and the art of photoelectric photometry" uses epoch 2,435,624 and P=9885 days (HPO, 7812 W. Clayton Dr. Phoenix, AZ 85033)
SOME RECENT PAPERS:2007
Far Ultraviolet Spectra of eps Aur: Epsilon Aurigae;
FUSE Program ID: P135; T. B. Ake
FUSE will be used to study the nature of the unusual eclipsing spectroscopic binary, epsilon Aurigae. The most favored model of this system is that the secondary object is a large, cold disk seen nearly edge-on. IUE and GHRS observations indicate the existence of a far-UV excess compared to other A-F type supergiants, presumably from a hot star in the center of the disk. The main difficulty in interpreting the UV data is that the primary star still contributes significant flux down to 1400-1500 Angstroms. FUSE observations will perform a more direct examination of the secondary, free from contamination by from the photosphere of the primary star. Measurements will be made to determine the physical parameters of the central star, and study variability and gas motions in the disk.
P1350101000 HD31964 05 01 58.13 +43 49 24.0 40 2001-01-07 13:46:00 47715.617 P135 LWRS
Data available at: http://archive.stsci.edu/fuse/index.html
Infrared Photometry of Five Long-Period Binaries, Taranova & Shenavrin
2001 Astron.Let. 27:338
"The 3.5- and 5-micrometer radiation from the eclipsing binary epsilon Aur outside the eclipse exhibits excess (relative to the light from an F supergiant) fluxes which correspond to the emission from a cool source with a temperature of ~1000 K. For the eclipsing binary epsilon Aur, we present the hitherto unpublished results of our optical and IR photometry during 1982-1985, when a primary eclipse was observed in the system."
Intereclipse Spectroscopic Snapshot of epsilon Aurigae with the Hubble Space
Telescope, Sheffer & Lambert, 1999 PASP 111:829.
"The spectrum as recorded between 1175 and 1461 A is rich with emission and absorption lines which include stellar and interstellar components. The emission-line profiles have the appearance of double-peaked emission with a stronger red component at a radial velocity of +108 km s^-1, an overlying unresolved absorption component at -20 km s^-1, and a weaker blue emission bump at ~-92 km s^-1. "
Is the eclipsing variable EE CEP a cousin of epsilon Aur?
Mikolajewski, M.; Graczyk, D.
1999 MNRAS 303: 521
We report the first five-colour Johnson UBVRI observations of the last eclipse of the long-period (5.7 yr) eclipsing binary EE Cep. We propose that the star is a member of the Cep OB1 association at a distance of 2.75 kpc. Using this assumption, we find that the primary is a B5 bright giant of radius ~ 10 R_solar and luminosity M_v ~ -3.1. The observations show that the obscuring body is not a star-like object. We suggest that the invisible companion in EE Cep is a dark, thick disc around a low-luminosity central star or binary, and that the system has a few important similarities to the epsilon Aur system.
At 14:29 -0700 5/3/05, Lucas, Gene wrote: Hi Jeff, I just came upon two historic articles on Epsilon Aurigae which I believe may be of some interest. These were both published in 1904, and give visual magnitudes over a span of years back to 1842!! The first article, by Col. E.E. Marckwick in the Monthly Notices of the Royal Astronomical Society (MNRAS) goes over some of the history, and summarizes his observations back to 1888 (mostly out of eclipse; he missed the actual eclipse in 1902). Marckwick in turn refers to a longer 1904 article by Prof. Lundendorff in the Astronomische Nachrichten (AN) which summarizes known observations back to 1842! Marckwick gives his data (with comparison stars and graphs), and makes the following comment in closing: "There is a moral in all this for variable star observers. Do not tire in watching a variable such as the one now in question, or ?.. One may observe for years without any change, and when one least expects it an important and marked change may occur. Although, according to Lundendorff's result, no further change is due for twenty-five years [written in 1904; the previous eclipse was in 1901-2 -- GAL], yet I would urge observers to keep a watch on (epsilon) Aurigae with a view to confirming the remarkable result already announced." Here are the citations. These are available on the web at the NASA-ADS web pages, and I have printed out both articles and have copies for you. Also, I could send you the files electronically or provide them on a disk. The MNRAS article (PDF file) is about 450 kB, and the Ludendorff article is approx. 2.9 Mb. Marckwick, E.E., "Note on the Variation of (epsilon) Aurigae." MNRAS 1904, Vol. 65, pp. 83-88. Lundendorff, H. Von, "Untersuchungen uber den Lictwechsel von (epsilon) Aurigae." AN 1904, Vol. 164, No. 3918-19-20, pp.81/82 to 113/114. (Note that the pages are double numbered, formatted in two columns; this article is in German language, but with some references given in English.) Here is the NASA-ADS web pages, where you can do searches and download PDF copies of many journal articles.http://cdsads.u-strasbg.fr/bib_abs.html
Keywords: epsilon Aurigae, disks, double stars, infrared, jets, mystery