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b Per campaign for November 2018 eclipse

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weo
weo's picture
b Per campaign for November 2018 eclipse

AAVSO Alert Notice 655 announces an observing campaign on the bright multiple, eclipsing system b Per. Please see the notice for details and photometry and spectroscopy observing instructions.

Many thanks, and Good observing,

Elizabeth O. Waagen, AAVSO HQ

weo
weo's picture
Eclipse info added to Alert Notice

I accidentally omitted from Alert Notice 655 the date and time on which the predicted eclipse window is centered. I have added this information to the webpage version of the notice and sent a revised version by email to subscribers.

Good observing,

Elizabeth

weo
weo's picture
Check star position

In Alert Notice 655, the position given for the check star (HIP 20370) was incorrect. The correct position is R.A. 04 21 45.47  Dec. +50 02 06.64. The Alert Notice text has been corrected. Thanks to Shawn Dvorak for reporting this mis-position, and our apologies for any inconvenience.

Good observing,

Elizabeth

James Chase Geary
Hello. I'm a sporadic

Hello. I'm a sporadic binocular observer. I noticed that there have been almost no visual observations of b Persei. Would visual observations be helpful at all? It's so rare that a precipitous campaign pops up for something in my available range.

Thanks,

James Chase Geary, GJCA

Bikeman
Bikeman's picture
Challenging at best

I understand that this eclipse should resemble the one of December 2016, see figure 4 in https://www.aavso.org/aavso-alert-notice-655 . You can judge for yourself whether you would be able to confidently detect the eclipse (and I guess there won't be many other visual observers for averaging observations across observers). So I'm a bit sceptical whether this is a good target for visual observing. But it could be a great project to start DSLR observing, if you wnt to consider something new.

CS

HBE

cdk
Visual observations of b Persei

James, All observations are certainly welcome!  Certainly, if the visual observations compliment CCD and DSLR observations when only one other observer reports.  We expect 0.2 to 0.3 magnitude dips for this event. 

I believe that most contributers to the previous campaigns observe with DSLR's and modest focal lengths in order to get a large FOV.  You also do not need a clock drive, but would have to be at the camera a good fraction of the night beginning about 8:30 pm local standard time when the star is high enough.

Good observing!

Don

SFS
DSLR photometry using neutral density filters

I read with interest the article  that was touted in the Alert Notice, but am a bit skeptical about the advice to use ISO 100 with a 15 second exposure.  Measurements with my camera indicate that ISO 100 is barely within the linear dynamic range regime, and because of that, I generally use ISO 200 or 400.  I realize the situation might be different for other cameras.

Certainly, a 15 second exposure at ISO 200 will put my system deep into saturation, and so I am going to try using a neutral density filter in front of my (71 mm aperture) telescope.  I do not know whether anyone has done this before, or has any ideas.  If so, I would certainly like to hear them.  My plan is to do a test tonight if it clears up, or if not, next clear evening.

Thoughts, anyone?

CS,

Stephen

cdk
Stop down the aperture

Stephen, If the ND filter over the objective to the telescope doesn't solve your problem, you can alternatively try stopping down the aperture.  I've been using an 80 mm aperture on a CCD with a V filter, stopping down the aperture from 80 mm to 30 mm using black paper fitted over the lens bezel with reasonable results.  I still reach close to saturation at 15 sec, so I need to average about 9 frames (after extracting the photometry) for each reported observation.  If the co-adding is inconvenient, I can apply the co-adding on your downloaded data from AAVSO.   I had tried a 10% ND "lunar filter" on my CCD camera last year (in addition to the V filter for the CCD).  The results were encouraging, but one night they were very sporatic.  I suspect the quality of the filter - meant for eyepiece viewing of the Moon.  I imagine a full aperture ND filter over the aperture of the telescope will be superior to a poor quality filter near the detector.  Defects at the objective will be completely de-focused across the whole image.  De-focusing is also helpful, if de-focusing is not extreme.  Please share the results of your full-aperture ND filter with us!

I assume you are trying de-focusing your images.

Good observing!

Don

SFS
The filter I plan on using is

The filter I plan on using is one designed for photography; in untold decades of taking pictures I've yet to see an artifact resulting from use of a quality photo filter.  (But there is always that first time!)

And yes, of course I defocus, to achieve a peak SNR with an inner aperture in the 8-10 pixel range (AIP4WIN).  And it is my standard practice to capture 10 frames so as to get a decent estimate of the standard deviation.  Just like Mark taught me in the DSLR Photometry course :-}

CS,

Stephen

Bikeman
Bikeman's picture
DSLR challenges

I agree that 15 seconds exposures will make it hard to avoid saturation.

Two thoughts:

a) Actually you will want 15+ seconds integration time , or total exposure time, per datapoint, to avoid your reported datapoints from being contaminated by athmospheric effects. Whether you collect those 15+ seconds worth of photons by using one long exposure, by stacking a number of shorter exposures or simply by averaging over several measurements is not really important.

b) Instead of using a DSLR on a small telescope, consider using a telephoto lens. If you want to do ensemble photometry, you'll need a wide field of view anyway to get more comparison stars in your field. E.g. this time I'm planning to use a small (vintage) 85mm F2.0 lens on my Canon EOS 1100D, which gives the field shown below (shown with the AAVSO FOV=7.5° finder chart overlay). Seems just about right in terms of field of view, and even with this tiny aperture I don't dare to use more than 2.5 seconds exposure per image (ISO 200). I plan to combine perhaps some 10 ... 25 images per datapoint, will do some more testing, weather permitting) . This should get the statistical error below 0.01mag, as requested.

 

SFS
The filter experiment was a failure

As planned, I attempted to do photometry on b Per by placing an ND4 filter over the objective of my scope, and collecting a series of 15 second exposures at ISO 400.  (It would have been better to use an ND2 filter at ISO 200, but I don't have one.)  Images collected for the preceding target showed maximum SNR with aperture set to 8/15/25 in the green, but for this star I needed to increase the outer aperture to an absurd degree - doubling it!  With an aperture setting of 10/30/50 I was able to get a reasonably well behaved SNR plot; the profile showed a peak of around 5500 ADU and a slow exponential decay.

I am at a loss as to how to explain this; the filter should have no defocusing effect, but somehow it did.  In answer to the obvious question, yes, I checked the focus setting on the telescope, and no, it did not change.  So much for that short cut!

Bikeman
Bikeman's picture
filters

> by placing an ND4 filter over the objective of my scope

I cannot quite figure this...this is a filter that covers the aperture of the telescope, not a screw-in filter at the eyepiece/camera end?

Could dew be a problem here?

Just guessing, sorry,

CS
HB

SFS
Heinz-Bernd,

Heinz-Bernd,

After posting, I arrived at the very same idea.  The dew was truly awful last night, and I am thinking the objective had a fat layer of dew on it. When I put the filter in place; the water filled the space and thus effectively changed the shape of the lens. 

CS,

Stephen

cdk
Dew Shield

Here is a dew shield I had made a number of years ago for small lenses.  The tube is some aluminum flashing wrapped in  a cylinder and clamped to the 135 mm FL lens shown.  The Al cylinder is wrapped with insulating sticky tape to wrap heating and air-cond ducts.  The tape came in a 2 inch roll from a Home Depot, I believe.  The lens from a used photography shop and wcrewed (T-thread) into the ST7 CCD camera.  It also helps to occasionally use a hair dryer.  I don't use this anymore, but the quality of the data were about the same as the stopped down 80 mm telescope with a 400 mm focal length.  See attached photo.  Good Observing!

Bikeman
Bikeman's picture
No chance to use the 135mm on

No chance to use the 135mm on your DSLR?

HB

SFS
Still a failure

Last night I tried again.  No dew whatsoever.  Fifteen minutes before doing the series on b Per, I did one on RU Peg.  Processing today indicated (AIP4WIN) apertures for maximizing SNR for RU Peg were 9/15/25 in both channels.  With b Per, the B channel maximized SNR for an aperture of 13/18/25 (!) and the G channel maximized SNR with an aperture of 10/15/25.  So, there is some sort of defocusing effect in the blue.  But moreover, I found that lambda Per saturated in the green, which it should not do. 

I cannot explain the defocusing effect but it is clear to me that ND4 may provide "about" two f/ stops of absorption for photographic purposes, but not for photometric purposes.  At least, for the above average quality commercial photographic filter I was using.

As far as I am concerned, my b Per experiment is at an end.  If anyone wants to see any of the images, let me know relatively soon.

CS,

Stephen

cdk
135 mm on DSLR

For using the DSLR for bright stars such as b Per I had used a Canon stock lens zoomed to 135 mm or 100 mm focal length.

I don't use a DSLR anymore as opposed to CCD for b Per because the loading of the images into a photometry program (Maxim DL 6.11) take incredibly long. .  However, I encourage observers to continue using their DSLR's for b Per to continue to get the excellent results.  I would like to know how observers get around the download problem. 

Thanks,

CDK

Don

cdk
Reducing aperture at objective a problem

I have concluded that reducing the aperture to 30 mm on a 400 mm FL telescope is a problem.  The problems occur because this reduces the aperture from f/5 to about f/8.  The dust specks on the objective are much more noticeable than at the f/5 (full 80 mm aperture) or f/7 (43mm aperture) and harder to flat-field out.  I plan to use the configuration for the last 4 eclipses (43 mm aperture) that gave good results.  I plan to try a 3-stop and 4-stop objective filter film - but not until after this eclipse which begins this Saturday or Sunday!  Defects in the filter and objective will be way out of focus at full 80 mm aperture. 

Good observing, everyone!

CDK - Don

Bikeman
Bikeman's picture
Estimated start of eclipse

> but not until after this eclipse which begins this Saturday or Sunday!

I wonder, is this based on the older period estimate of ca 702 days (Hill 1976)? The latest estimate, also based on our AAVSO observations, is more like 704.9 days (see the alert notice). From the lightcurve of the Dec 2016 event, I would think that the eclipse back then must have started near JD 2457738 +/- 0.25 d . If you add 704.9 days, I get  Tuesday,  2018 Nov 20  09:36:00 UT . The Jan 2015 campaign actually spotted the beginning of the eclipse pretty well near  2457033.5 , if you add two periods you get to 2458443.3 or Tuesday, 2018 Nov 20 19:12:00 UT.

I'm not saying that people shouldn't start observing already on the weekend, but I guess one should not bet on the eclipse starting then. Or am I missing something?

CS

HBE

 

 

cdk
My prediction of the eclipse

My prediction of the eclipse is based on the AAVSO observed long period for the C star of 704.9 d (+- .5 d) for the center of the eclipse.  This is based on all the previous observered eclipses dating from the low time-resolved eclipse of 2013.  We are still not sure of the length of the eclipses since our Pacific/Asian window have given us no data.  Thus I predict the center of this eclipse will occur on Nov. 21, 2018 10:00 am UT. (+- 0.5 d)

The beginning of the eclipse will be highly dependent on the angle of the A-B stars in the sky as the C-star crosses behind the orbiting pair.  The start of eclipse could be between 1 - 2 days before the predicted mid-eclipse.  I have worked on simulating the eclipses, but am hesitant to share those because I want to verify that I have a reasonable solution, so our uncertainty in the eclipse start is still rather high.  After we observe  this fifth high time resolved eclipse I plan to return to work on the simulations and plan to share progress on this forum and plan to present our results to the spring 2019 AAVSO meeting in Toronto.

So - please begin observing in ernest as soon as possible to get the good "base-line".  This week has been terrible weather in Eastern USA.

Good Observing!

 

 

Bikeman
Bikeman's picture
Ah I see.. silly me didn't

Ah I see.. silly me didn't realise that the period estimation is actually comming from you when I replied :-) .

Weather isn't so good here in Germany as well, but the forecast is a bit optimistic for the weekend. I'm trying to take test frames this night.

CS

HB

cdk
Simulated b Per lightcurve prediction

Hello b Per observers,

I have worked this past summer on simulating the light curves for the b Persei events - including a prediction for the upcoming light curve as the third star is predicted to pass behind the close-orbiting A-B stars.  The prediction is far from certain. It requires many geometric parameters: stellar sizes; separations; line of nodes axis (the intersection of the AB orbital plane with the Earths celestial sky at b Persei);  date of mid eclipse (when the third star passes the center of mass of the AB pair); the "impact" parameter (the closest distance of the C star celestial path to the AB center of mass); and more.  Maximum ellipsoidal light appears when the A-B stars' orbit crosses the line of nodes (when the stars present their widest cross-section to the Earth direction).  The three stars' luminosities in the simulation are simple luminous disks with the stellar relative luminosity spread uniformly over the area of each respective disk.  There is no limb-darkening nor ellipsoidal stellar distortion taken into account.  Some of these parameters are displayed on the attached picture of the light curve.  The parameters are based on a relatively good fit to the four AAVSO light curves (only as far as timing and general shapes of the dips) based on what we know about the astrophysical nature of the three stars (spectral class, luminosity), which are relatively unknown for the B and C stars. I've worked mostly with the timings, the angles, and the impact parameter.  I have not tried to fine-tune the relative luminosities and stellar radii.  The mid-point of the predicted eclipse ~JD 2458444.0 is around noon UT (Nov. 21.5 UT)  The N. American observers have the best opportunity to observe the expected first dip at ~1442.75 (before dawn on Tuesday, Nov. 20) - if my time calculations are correct.  Let me emphasize that photometry for extended times are requested for all weather-permitting nights from now for the next two weeks in order to get a good "base-line" for the out-of-eclipse light curve as well as possibilities that the prediction of first contact is off by a day.

The largest uncertainty in the simulations is the determination of which star (A or B) is interacting with the C star for each dip in brightness.  After this eclipse I plan to "play" with the parameters and look for plausable alternate solutions which would give the "best" fit to the 5 observed light curves.

Let me know if observers would like to see my simulations for the 4 previous high time-resolved b Per events.

Good observing!

Don

perdiguero
perdiguero's picture
Hello,

Hello,

the instrumentation (ED scope, V-filter and CCD) is fine ready but the forecast for Spain is desperately bad for the next 7-10 days. But I will keep in alert if there is a change in forecast.

Greetings,

Fran

Bikeman
Bikeman's picture
Weather

> but the forecast for Spain is desperately bad

Same here (source calsky.com , self-explaining I guess..)

File upload: 
Roger Pieri
Weather

Here in Dijon/France I got three good sessions of observation of the oscillation in past nights, but the forecast for the critical days of the eclipse is very bad too, llike Heinz-Bernd said. Only the 22nd  night could provide some "holes in between the clouds", maybe... 

I use a 280 mm focal photolens at F/4, the EOS M3, Iso 100, 15 sec exposure at low elevation, down to 13 sec when approaching the zenith. Defocus is 11 Bayer cells wide taking the advantage of the good shape of the "Bokeh" of such photolens. SNR above 1000 per image, series of 20 images, each image processed and series averaged. The comp is 55 and the check 74, I use another ensemble of stars to check the sky condition and the large air-mass variation of this particular observation. 

Clear Skies !  

Roger

 

Bikeman
Bikeman's picture
Good luck !

In theory we have a nice string of observers (Poland, Germany, France), let's see what  the weather allows.

Out of desperation, I made a last minute effort to get at least some images with iTelescope from New Mexico as I cannot stand the thought of having no data at all for this event :-(, but I don't have experience with the smaller telescopes there (e.g. T20, T14) with respect to how much they can be defocused with the "defocus for photometry" option and what the headroom for saturation is ...

Clear Skies

HB

 

cdk
First contact expected tonight - Monday, Nov. 19 eastern USA

Hi all,

I expect first contact tonight based on simulations that may be correct.  Nov 20.0 UT is this evening in eastern N. America.  Later in Europe.   See my expected light curve in my last post.  I had 3 good nights of all-nighters the last 3 nights,\; intermittent clouds last night I'm working on now.  Weather is "iffy" for tonight for eastern USA.  Arizona looks good on Satellite.  We all are hoping to shoot between clouds...

Good luck!

Don

cdk
first contact!

It is almost 6:00 am tues AM  EST (11:00 UT Nov 20).  Having gone to bed last night amidst heavy clouds, b Persei comes in at magnitude 4.8 V.  Last night I got some images briefly before the rain closed me down.  b Per at 4.7 V.  Looks like we had first contact.   Looking for any confirmations!

Don

Bikeman
Bikeman's picture
I had to give up, there weren

I had to give up, there weren't  even cloud gaps where I live.

 

However I managed to get a few frames that seem usable perhaps from iTelescope in New Mexico , around midnight local time, at most I'll get a single datpoint from it. I'll do the reduction at home this evening.

CS

HB

 

rybi
rybi's picture
Yesterday I discovered on

Yesterday I discovered on sat24 a 100km hole in clouds moving west. I managed to get only 6 valuable RAWs (each exposured 30 sec) because it didn't pass centrally through my location. I got only 1 point on LC (19,19 UT 19th of Nov).

Tonight I will hunt for more pieces of clear sky. I should be ready for observations starting from about 18UT.

 

Sorry I couldn't resist ...
I made some rough "graphical" comparison between current AAVSO LC of b Per and Don's ephemeris.

 

CS,

Richard  (BRIA)

cdk
I Have Problems!

I have some serious problems:(.  The check star magnitude for last night's data and this morning's data has suddenly changed from the previous series of observations.  Thus the "First Contact" shout that I gave this morning is pre-mature.  I can't find what is doing this, but I am working on it.  I'm investigating other check stars in my rather small fov to see if they are any more consistent.  Everyone please keep up the good work in finding stars on these cloudy nights!!. 

Don

cdk
First Contact Confirmed

Congratulations to Gerald Persha for getting a nice light curve of the first contact as b Per  C enters eclipse behind the A-B pair!  As mentioned earlier, I have some problems with my results from last night (a few points ahead of Gerald's), which I am frantically working on to figure out.

Keep observing everyone!

Don

James Chase Geary
Visual observations

Had clear skies here in Little Rock. As of 1200a CST, I still had b Per at 4.6 mag, using the 43, 45, and 50 check stars on chart X23456ATG. Should be clear tonight as well, I'll try and get more observations (my almost-3-year-old had a bad dream last night I had to help take care of -- not just clouds can interfere with astronomy!). 

Clear skies,

James Chase Geary, GJCA

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