AAVSO Alert Notice 791 announces an observing campaign on the eclipsing triple-system b Per. Please see the notice for details and observing instructions.
There are threads for this campaign under the following forums:
Please subscribe to these threads if you are participating in the campaign so you can be updated. Join in the discussion or ask questions there!
Many thanks, and Good observing,
Elizabeth O. Waagen, AAVSO HQ
The Alert Notice asks for "several long time-series observations".
As a novice DSLR observer I would like to understand how long and how many are reasonable for a campaign like this one.
Could someone please provide a little more detail? Thank you!
For b Per I use a normal tripod with Sony alpha 6300 camera and 85 mm lens. In one session I take always 27 pictures of 8 sec at f/4 (RAW, ISO 100, without tracking).
After flat correction these pictures are split in R, G and B channels (for Sony alpha no dark correction is necessary). The 27 (fits) images in G are stacked with median function (Fitswork) to one single file. Simple differential photometry (b Per vs "55" comp, 5,456 mag V) on this file delivers one single observation. Lambda Per (HD: 25642, 4,287mag V) is used as Check star.
How long a single image can be exposed depends on your lens/telescope and the aperture ratio. None of the 3 stars (b Pro, Comp, Check) should saturate. Always take RAW images.
For more information see https://www.aavso.org/dslr-camera-photometry-guide (also in Spanish)
Hans-G. Purucker (PHG)
Thank you Hans! Although now I have more questions :)
I understand the general process you describe because I do photometry with my Canon 600D, but I usually take 20 lights of 12 seconds each, and then stack them in groups of 5 (after bias, dark and flat corrections) to make 4 measurements. With those measurements I use Blackford's Excel sheet to average the numbers and transform them into a V magnitude.
Do you think I should use my standard procedure, or stack all the 20 lights for a single number? How often do you take your 27 lights? Once a night? Once a week?
Thank you in advance for your support!
20 lights at 12 seconds each sounds good to me. It is up to you whether you generate 4 measurements (with larger scatter and close time) or one measurement. But with b Per it is not necessary to transform to V magnitude. You have to do that for Mira stars etc. and there I also do that. For b Per, the most important thing is to use a simple workflow that should not be changed during all observing sessions of an eclipse. It is not necessary to perform a transformation process – simply use the green channel (TG) of your camera; the most important thing is to produce a light curve in which the relative magnitude differences between the individual points are as accurate as possible!
See Alert Notice 791: It is important that observers observe several long time-series observations both before the eclipse and after the eclipse as well as all parts of the eclipse.
When you report all your measurements (always use the same workflow!), your out-of-eclipse points (before and after the eclipse) are used to calculate a value for the magnitude shift (="your" offset) of all your points, so that these points outside the eclipse "sit" on the known sinusoidal light curve of b Per. This is done separately for each observer (they all have individual workflows and different offsets). To see this directly, compare the reported points (without individual offsets - use Enhanced LGC!) with the analysed curve in Alert Notice 791 (e.g. for the last eclipse of b Per).
During the eclipse you can in principle take 20 lights of 12 seconds every half hour - if you can manage that :-). During the last eclipse I tried to generate 8 measurements per night, but I always had to go into the garden and use a tripod because Perseus cannot be observed with my telescope mount from the balcony.
Thank you so much!
The weather forecast tomorrow is pretty good here in Tudela (Spain), so tomorrow night I will try to take my first serie of TG lights before the eclipse.
The eclipse is nearing. Predicted JD:2459852.4 = UT Sept. 29,41
The beginnings of eclipse typically comes 1.5 to 2 days prior to the midpoint. That is ~Sept 26 UT.
There is a possibility that a partial grazing secondary eclipse of b Persei may begin tonight Sept 26-25 (JD 2459859). Remember we expect the center of the 3-4 day transit to be Sept. 29. All observers with clear weather are requested to observe at least one observation per hour (or continuously) throughout the night. If observing intermittently throughout the night, it is important to observe a burst of images especially exposures are short (less than 60 sec). A solution is to expose for many exposures of short duration to prevent saturation of detectors and include enough exposures so that the total integration time (exposure time multiplied by the number of images in a burst of images) be larger than about 60 sec. This reduces the fluctions inherent in scintillations from Earth's atmosphere. I can co-add the multiple photometry results from burst from many rapid observations after downloading the results from the AAVSO database.
Please observe as long as possible each night between now and October 2.
Many Thanks in advance to all observers who are braving the post-midnight observation windows for this fall's event!!
Javier, Your data for those three nights are very good! I hope you have good weather tonight - I expect the first dips to be seen in Europe and maybe the first dip finishes before the viewing gets to N. America. Keep looking!!
Thanks for your work!
Last night's data from my observatory definitely shows a partial eclipse. The third star started passing behind one of the 2 close-orbiting stars. I hope other observers observed the similar dip to confirm. See the data in the light curve generator.
Hope we can get more data tonight (Sept 29-30) and tomorrow night (Sept. 30-31). I expect clouds from Hurricane Ian tonight, but I'll try!
Clear skies to the rest!
I just uploaded my results from last night. Unfortunately clouds obscured my view for a long time. But my last data point is quite low. It was taken just before dawn in Germany, so further measurements were not possible.
Also today the weather conditions are mixed...
Several observers have observed the ingress into eclipse on the night of Sept. 28-29. Last night (Sept 29-30) another observer has reported a second ingress (this is expected from past eclipses), and I expect some more observations from N. America for last night, although I was clouded out from cloud outwash from the hurricane Ian. Tonight I expect a another smaller dip and re-emergence from eclipse detectable from Europe and N. America. Unfortunately I am again clouded out, but I am hoping for European observers and western and mid-western N. American stations to have success! Keep up the good work!
Congrats to all of you for the positive observations !
Indeed after month of clear skies and an historical drought, late september was finally cloudy and rainy here. No observations were possible from SE of France. I only have preliminary observations, dating back from last week, which are useless, of course. So sorry.
See you next time.
Hello, We got some nice time-series data for parts of the secondary eclipse. If you got data between Sept 28 UT and Oct. 2 UT please try to get at least 2 hrs of time-series after the eclipse in the coming week. We need the out-of-eclise data to adapt all data to the common scale - especially since a number of us have not transformed our data.
Special thanks to those observers who were able to transform their data.
Special thanks to all observers who have contributed their observations!
I'll be posting a summary with all the data scaled to the common base line of the out-of-eclipse data, but it will require a few weeks.
Perhaps extinction should be considered for high airmasses. In the evening, b Per is very low in the sky for northern observers!
For example, with an airmass of 3.000 for b Per, the airmass of the comparison star '55' (HD 27084) is 3.043. Using only primary extinction (see AAVSO_DSLR_Observing_Manual_V1.4.pdf, page 102ff) with the primary extinction coefficients for the green channel (TG or V) K'v = 0.219 mag/airmass a correction of 0,219 * (-0,043) = -0.00942 (about -0.01mag) should be considered.
In this case I have corrected the measured instrumental magnitude of '55' by (about) -0,01 mag. The comparison star '55' appears dimmer due to the larger extinction compared to b Per and becomes slightly brighter due to the correction (as it would be without atmosphere).
Conversely, one could also not correct the comparison star, but correct b Per by +0.01mag.
Result without correction: b Per 4.656 mag
Result with extinction correction: b Per 4.666 mag
This time, I took into account extinction correction in all my measurements. But for airmasses of less than 2.0, the correction becomes negligible < +- 0.004 mag.
Hans-Georg, Thank you for your care in reporting b Persei with high air masses and compensating for atmospheric extinction. Your data have added much quality to the eclipse light curves. Thank you for your contributions!
Hello AAVSO observers,
I have just posted the compiled light curve for the b Persei eclipse of September 2022 at its blog:
The compiling consists of adjusting the zero-level magnitude for each observer's set of observations such the out-of-eclipse values coincide with a standardized out-of-eclipse curve.
I apologize for the delay in processing - my family was traveling last month.
Thank you for all the good data that was obtained.