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Mini-Observing Campaign on the Secondary Eclipse of Zeta Aurigae

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Oh boy are we lucky!  Not only is one star in Aurigae undergoing an eclipse this year, but two!  The other star, Zeta Aurigae is a bright (V ~ 3.75 out of eclipse), northern eclipsing variable with a known period of 2.66 years.  The system contains a hot, luminous B7V star and a more luminous K5II star.  During primary eclipse (which occurred in March 2009), the blue B7V star is obscured by the larger orange K5II star.  The secondary eclipse is more difficult to detect, because the B7V star obscures a small portion of the K5II star's light.  The approximate date of the eclipse is November 17, 2009, with an anticipated duration of about 40 days.  The K5II star is known to exhibit variations of 0.05 magnitude, therefore high precision photometry is necessary for this short campaign.

The anticipated eclipse depth is very shallow, perhaps 0.1 mag, and is not well characterized.  Given this information, obtaining visual estimates of the system may prove to be difficult, and obtaining good photometry of the eclipse may be a challenge.  Therefore I request that Experienced observers, both photometric and visual contribute observations of the eclipse during the remainder of the month of November and the first few weeks of December.  Inexperienced observers are encouraged to add Zeta Aurigae to the list of 10-star tutorial target objects and submit their data as detailed in the 10-star tutorial in order to hone their observing skills.

Visual observers may find this particular star difficult to observe due to the anticipated slight change in magnitude.  Please observe the star two or three times per week, using the charts available via. VSP or from the AAVSO website.  

Instrumental observers of all kinds are also requested to take part.  Photoelectric observers belonging to the AAVSO PEP-V program may submit data as usual via. the WebObs feature of the Blue&Gold section of the AAVSO website.

Wide-field CCD and DSLR systems are also encouraged to participate.  Zet Aur is a reasonably bright target object and care must be taken to ensure to not saturate.  We recommend taking a large number (10-100) of very short exposures (< 2 seconds) and stacking the resulting images so that the variable may be observed without saturation, and the faint in-field comparison stars may be easily observed.

A convenient star chart may be obtained by AAVSO's VSP program.  For a wide field of view and comparison stars, this plot may be more convenient.


It is requested that a few observers also submit their raw, uncalibrated data to the Citizen Sky project for use as training data for a photometric reduction workshop at the upcoming Citizen Sky conference in September.  Please contact Brian Kloppenborg (U. of Denver, bkloppenborg on Citizen Sky) or Aaron Price (AAVSO) if you are interested in contributing your data to this project.

It is suggested that observers use lambda Aurigae as the comparison star and eta Aurigae as the check star during these observations.


The following is a summary of the most recent observation of zeta Aurigae submitted to the AAVSO database:
ZET AUR      2455144.2813      NOV 08.7813      3.4      Vis.           SDAV      3.1           SPA           N    
ZETA AUR     2455113.4167     OCT 08.9167     3.1     Vis.     BL     SDAV     3.1         SPA         N   
The J2000 equatorial coordinates of zeta, lambda, and eta Aurigae and their corresponding magnitudes (uncertainties shown in square brackets) are as follows:

zet Aur:
05 02 28.6869 +41 04 33.015
B 4.927 [~], V 3.769 [~] , J 1.154 [0.218] , H 0.358 [0.166]

lam Aur:
05 19 08.4745 +40 05 56.586
B 5.34 [~], V 4.70 [~], R 4.3 [~], I 4.0 [~], J 3.397 [0.260], H 3.154 [0.204]

eta Aur:
05 06 30.8928 +41 14 04.108
U 2.33 [~], B 3.012 [~], V 3.158 [~], J 3.611 [0.262], H 3.761 [0.238]

I will continue to add campaign updates will be posted to this forum as the eclipse progresses.  It'll be short, but well worth observing.

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Hi Brian,I was about to post something similar. Thanks for your posting. I have already alerted most of the epsilon Aurigae Campaign observers, but had not gotten to the CS part yet. As you mentioned this probably will not be seen by visual observers. The most pronounced (deepest) change will be in the longer wavelengths. This will be ideal for the SSP-3 and SSP-4 photometers. CCD can also get the RI bands so they can be very useful too. While the eclipse may be seen in the V band I suspect it will be very shallow.Des Loughney has already started V band measurements of zeta Aurigae using his DSLR camera and his data show no signs of an eclipse yet.I have not been able to find any significant information on the secondary eclipse of zeta Aurigae so anything discovered here could be very important. I too suggest using lambda Aurigae for single channel and CCD photometry. Eta Aurigae should be fine for the V band data.To be consistent with other observations using lambda Aurigae as a comparison star please use the following magnitudes for lambda Aurigae:U= 5.46B= 5.34V= 4.71R= 4.19I = 3.88J = 3.62H= 3.33These are the magnitudes used for the last Epsilon Aurigae Campaign and the current one.Weather here in Phoenix has not been good for photometry, but as soon as I get some clear nights I will be doing UBV photometry of it.Jeff?Counting Photons?Hopkins Phoenix Observatory?Phoenix, Arizona USA?phxjeff@hposoft.com

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Zeta Aurigae is not on the drop down menu for data submission on Citizen Sky, will it be added soon?


There are some magnitude differences for the primary comparison star, and I'd like to resolve them a little. The Johnson B and V magnitudes for lambda Aurigae are essentially identical for Brian and Jeff, as various sources like Mermillod (1991) and Johnson (1966) only differ by 0.01mag. The best values that I have are:B = 5.329V = 4.705with unknown error (dang those catalogs!) but presumably in the 0.01mag range.Likewise, Jeff has the correct J & H magnitudes; if you look at Gezari (1999), a compilation catalog, you getJ = 3.63H = 3.30with unknown error, but presumably a few hundredths. The values that Brian gives are from 2MASS, which saturates at these bright magnitudes.For R and I the situation is far worse. The values Jeff quotes are *Johnson* magnitudes, not the more common Cousins magnitudes. The two systems are quite different. I have all-sky calibration of zet/eta/lam using the Bright Star Monitor, and I'll post those values next week. In the meantime, *do not* use Jeff's values for the R/I filters, or at least be careful and post what magnitudes you did use for your comparison star when submitting observations.For zet Aur, I prefer eta Aur as a comp star since it is spatially close; the big problem, however, is its very blue color (quite different from zet). There are a few fainter comparison stars in the field that could be used. The main point is that during the next month or so, you should not use zet Aur as a comparison star for eps Aur when using a CCD/PEP/DSLR system!Arne

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Our web developer Kate is currently working on adding this object to the pull-down menus!

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zeta Aur is now in the "Submit Data" and "View Data" pull-down menus.


Based on the Bright Star Monitor calibrations, I getStar B V Rc Iclam Aur 5.297 (0.03) 4.683 (0.02) 4.340 (0.02) 3.998 (0.03)eta Aur 3.024 (0.04) 3.185 (0.04) 3.261 (0.04) 3.296 (0.04)zet Aur 5.016 (0.04) 3.710 (0.04) 2.949 (0.04) 2.214 (0.05)where zet Aur is very red, and eta Aur is very blue.These values are based on multiple measures on 4 photometric nights,with the majority of the error due to scintillation.These numbers are consistent with Brian and Jeff for B and V,except for lambda Aur B-band. Note from Jeff's numbers that theseCousins R/I measures are fainter than Johnson R/I.So, what should observers use for magnitudes when submitting CCD/PEP/DSLR data based on one of these three comparison stars (well, ok, two if we are trying to measure the zeta Aur eclipse)?I'd use the following, which is a mix of the previous campaign UBV values, and the new BSM Rc/Ic values:Star U B V Rc Ic J Hlam Aur 5.46 (unkn) 5.329 (unkn) 4.705 (unkn) 4.340 (0.02) 3.998 (0.03) 3.63 (unkn) 3.30 (unkn)eta Aur 2.32 (unkn) 2.994 (unkn) 3.172 (unkn) 3.261 (0.04) 3.296 (0.04) 3.611 (unkn) 3.761 (unkn)HR1644 7.00 (unkn) 6.637 (0.03) 6.179 (0.03) 5.911 (0.04) 5.616 (0.04) 5.167 (0.02) 5.022 (0.04)zet Aur 5.35 (unkn) 5.016 (0.04) 3.710 (0.04) 2.949 (0.04) 2.214 (0.05) 1.154 (unkn) 0.358 (unkn)where HR1644 is the 62 comparison star to the SE of eps Aur, and any error listed as "unkn" isprobably in the 0.03mag range. I've included zeta Aur in this table for completeness.Arne

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Brian,I have done some estimates of zeta since the 31st October which I have entered into the database. Although it is clear that the secondary eclipse has not startedyet the 0.05m variations of the K star seem to happen on a fairly frequent basis. Although it is mostly around 3.72/3.73V there have been several dips to around 3.75 since the 31st. I am looking forward to picking up the start of the eclipse in the next few days.Des Loughney

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Hey there,I've been communicating with Brian and Aaron and hopefully this week I will have time to send out some raw data from the SMEI instrument for these stars. I am still working on the calibrations, but I think I will have to leave that to others, as you will likely get more out of the data if I get it out there.I have run lambda, zet, eta and eps for much of the time from the start of the epsilon eclipse, and will start working my way back to early 2003 when our data started coming in.As you'll see all the stars appear to be dimming in my light curves, but this is an issue with the instrument, I thought it was related to seasonal temperature changes, but that doesn't seem to be consistently the case. The epsilon slope is distinctly different from the others, though, so at least it appears believable.I am juggling about a dozen projects at the moment, but I will try to get these data out asap and hopefully the calibration will follow soon thereafter.Cheers,John

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Hi!Great stuff, looking forward to the final,calibrated data.Is is possiple that eta and zeta are swapped in your diagrams? Eta Aur should be around 3.2 and zeta around 3.8, not the other way round.CSHeinz


Heinz,You made me double-check... the diagrams I listed above are correct. Of the three kids, Zeta Aurigae is the furthest from Capella with a V-mag of 3.89 (from TheSky) or 3.769 (from SIMBAD). Eta Aurigae is the second furthest of the kids from Capella with a V-mag of 3.14 (TheSky) or 3.158 (SIMBAD).If you are referring to the SMEI data, those data are from an unfiltered CCD, therefore their magnitudes will be drastically different from the standard V-mag. If I recall correctly SMEI's CCD peaks out in the R or I-band.

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Hi! Yes, I was referring to the SMEI magnitude diagrams. I kind of believed they were already transformed to V magnitudes because at least on the beginning of the observation interval, that seemed to match more or less. CSHeinz


A Thanksgiving Day Zeta Aurigae Campaign Update:Thank you all for your continued efforts observing zet Aur during the not-well-characterized secondary eclipse. The latest communication from Des Loughney and Jeff Hopkins indicate that the star has been brightening although I haven't seen any numbers or plots of the recently acquired data so whether or not this change in brightness is outside of the 0.05 mag variations seen in the system.Dr. Stencel recently relayed the following information:----Based on KO Wright's orbital elements and dimensions for the system, the relative star sizes are:B6V = 5Rsun at 15000KK4Ib = 130Rsun at 3550KThus B star hides (5/130)2 of the K star, or 0.1% ~ very much like a planetary transit, on scale of Venus/Sun, milli-mag level event in V, larger in R,I,J,H, but worth an attempt.----Any update from other observers would be appreciated.Brian

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I have gotten two data points on zeta Aurigae in H and J-- one set of readings 10 days ago on the 16th and another last night on the 23rd. Cloudy skies prevented anything in between. I have submitted these to the AAVSO-- the "Quick Look" page will show them. I see no evidence of a drop in brightness over the course of the two readings-- in fact, my readings are brighter than those listed by previous posters to this thread. I'm using an 8-inch LX90 with the SSP-4 and am therefore using Capella as my comp star since lambda is out of reach for me. Capella is the comp star recommended by the AAVSO for IR PEP on epsilon Aurigae with instruments smaller than 10-inches so I am going to use it for this eclipse as well. It may be that my equipment is too small for this event and I will detect nothing. I plan on making observations until the end of December.


I've attached a plot of Zet Aur for the last several weeks from Jeff Hopkins and Des Loughney. Jeff's data shows a fairly clear 0.01 mag decrease between 15 Nov. and 22 Nov. This decrease happened around the correct time, but the dip was about half the time of the primary eclipse (~30 day duration). Can any other observers confirm a dip of a similar time period? Brian P.S. I also found a paper with a well-characterized orbit: http://cdsads.u-strasbg.fr/abs/2005Obs...125....1G P (days) 972.164 +- 0.041 T (MJD) 47204.8 +- 0.9 Gamma (km/s) 12.11 +- 0.04 K (km/s) 23.22 +- 0.07 e 0.3930 +- 0.0023 omega (degrees) 327.5 +- 0.4 a_1 sin(i) (Gm) 285.4 +- 0.9 f(m) (M_0) 0.983 +- 0.009 But while skimming the paper I didn't notice any statements about eclipse timing. Edit (Nov, 29 2009): Attached zet Aur plot with error bars. Bars are one standard deviation for the values used to compile that data point.

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Hi Brian,Without error bars, I can't say that a 0.01mag decrease occurred. There is very little earlier data from Jeff on that plot, and from experience, I can say that detecting a 0.01mag shallow dip over a period of many nights is extremely difficult (much easier to do this for a transiting exoplanet in the course of a single night!). You would need about a month earlier and a month later dataset to study in order to begin to believe such a feature. The eye is *so* easy to deceive...You've been reading the literature: is there a light curve of a prior detection of the secondary eclipse? Are there negative reports with upper limits? Any spectroscopy during the secondary eclipse? These would be very interesting items to have posted.We observed zet Aur with the Bright Star Monitor from 20091016UT until 20091121UT and then switched over to our Survey mode (BV obs of 1000 variables). I just recently re-instated the observing plan for zet Aur, and we obtained data on 20091126 and 20091127, but in B filter only, so I'll probably never reduce that data. That problem has been fixed, so we should start getting BVRI data again (perhaps even last night, 20091128, if the Cloud Gods were favorable). It looks miserable in New Mexico for the next couple of nights. Well, miserable to me - Tom Krajci is looking forward to some local skiing!I'm busy helping to get five telescope systems working automatically, but working with our XSi DSLR is high on my priority queue - I am very curious to see how well I can match the good photometry coming from Des!Arne


Arne,Jeff sent me his standard deviations which were 0.01 mag at the largest, 0.001 mag at the smallest with an average of 0.003 mag. Under normal conditions I would have replotted the data, including the error bars, but I didn't have Des' raw data. Jeff was kind enough to send me a copy of his data with standard deviations included. I've plotted that data and attached it. I'll see if I can get the data from Des to redo the plot with his data as well.

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Arne,I see you may be going to do some experiments with a Canon DSLR. In case you have not yet seen it I enclose a copy of a refereed paper on DSLR photometry that I have written for the Journal of the BAA which will be published, I think, in February 2010. You may find it interesting. I have also attached the figures.Des Loughney

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Arne,I see you may be going to do some experiments with a Canon DSLR. In case you have not yet seen it I enclose a copy of a refereed paper on DSLR photometry that I have written for the Journal of the BAA which will be published, I think, in February 2010. You may find it interesting. I have also attached the figures.Des Loughney


Tom,Way to go with the SSP-4 coverage. The upcoming observation of eps Aur on the CHARA interferometer, and seemingly persistent clouds here in Denver, have kept me from using our rooftop 16" scope with the SSP-4 on zet Aur.I took a look at your readings and your numbers are typically 0.3 mags brighter than the readings I took before/during the 2009Mar eclipse. What values are you using for your calibrators? I have Alp Aur J=-1.84 +- 0.02, H=-2.63 +-0.02, and Lam Aur J=3.63 +-0.09, H=3.33+-0.1 mag which were transformed from UKIRT's bright star catalog into the MKO filter set (with full error propagation on the transformation calculations) which is very similar to the SSP-4's filters. Although eta Aur is listed in UKRIT's catalog, it doesn't transform because it is missing a K-mag, so I had to derive this value myself (which I'll have to dig up if you need it). In case you're interested, an Excel version of the catalog, along with my own SSP-4 control software, can be found on my portfolio page (https://portfolio.du.edu/pc/port?page=3&uid=17109).Although I'm still putting the finishing touches on my SSP-4 data analysis suite (it includes full error propagation/uncertainty analysis and near-automatic identification of target/calibrator stars, but lacks IR air mass corrections because it's quite complicated), I think the results are good enough to make public. I've attached preliminary output from the 2009Mar time period, right before the primary eclipse at JD 2454900. You can really see the drop in brightness around JD 2454920. JusT so you know, the error bars are so large because we used a gain of 10 and a 10 second exposure and therefore didn't get enough data to have a high enough SNR to lower the lower-bound of the error to less than 0.1 mag on average. This summer we used the G100x1sec to get 3 sets of 20 exposures on eps Aur and often push 0.01 mag precision, which is trumped by the 0.02 mag uncertainty on the calibrators in the catalog!Also, please note that the error bars are NOT standard deviations, they are full uncertainties in magnitudes... meaning these values have had full uncertainty analysis done on them, including the uncertainty in the calibrator's magnitude. The software creates a single calibration factor for the entire night (typically 2-3 hours of data over a very small air mass range), that is checked for stability and the user is prompted if the individual instrumental calibration factors don't overlap.Cheers,Brian

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Thanks, Brian; adding error bars helps. I'd still be much happier if I sawJeff's observations during October added to the plot, so that I can be sure thatthe 0.01mag decrease is a dip or some other event. Likewise, you mighttry generating a plot with the BSM observations on it - as much scatteras from Des, but perhaps the additional dataset will shed some light(so to speak)...Arne

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Brian:The values that I am using for Alf Aur (Capella) are: J=-1.34, H=-1.73. These are the ones listed by the AAVSO for users of the the SSP-4. I have not transformed them to another system.Tom


Tom,Ah, that explains the DC offset. Arne, could you comment on where AAVSO got those values and the photometric filter for those values?If I recall, Arne's JHK standards paper was for a different photometric system, because the SSP-4 closely matches the MKO filter standard. Is that correct?Brian

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Brian:The AAVSO lists the source for the values given for Capella as "Hendon" (http://www.aavso.org/observing/programs/pep/ssp4.shtml), but they match those on the UKIRT site (http://www.jach.hawaii.edu/UKIRT/astronomy/calib/phot_cal/bright_stds.html). Most of the other AAVSO IR standards also appear to be UKIRT values.Tom


Tom,Yeah, I'll need to talk with the AAVSO about updating their standards list to the new MKO filter. The UKIRT calibration pages are all in the old JHK filter set for IRCAM/TUFTI. The values I list on my website are the transformed UKIRT values from the old JHK filter set to the new MKO filter set.I think it is best for you to continue to use the standard star list from AAVSO so that you can compare with others more easily. I'll discuss a filter change and "conversion" chart from the old to new filter standards.Brian

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Brian: Was anyone successful at detecting the secondary eclipse of zeta Aurigae? I was only able to get seven data points on the star in H and J due to typical southeastern winter weather (not so typical the last couple of weeks, though-- 3ºF this morning-- brrrrr!). Looking at my data it does appear that zeta was fainter during December than it was either back in November or now, in early January. If I had gotten more readings during December, I would be more confident that I had detected it, but this is what I have. Tom

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Tom,As far as I have been able to decern, the eclipse was not detected. Jeff Hopkins did show a decrease in light (as I mentioned above), but a similar effect was not shown in any other observer's data as far as I have seen. I'll check with John Clover to see if SMEI noticed any drops in light (SMEI has three unfiltered CCDs which should be more sensitive to the longer wavelength light).I didn't see the bright star monitor data Arne mentioned in the database, but as I am at AAVSO HQ for a few days I'll try to remember to ask him about the data.Brian


I processed the zet Aur data from BSM, and the first reduction did not satisfy me - the errors should have been less. So I put it on a back burner to look at again. However, it does show that zet Aur is fainter now than during November by about 0.04mag.Arne

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