Affiliation
American Association of Variable Star Observers (AAVSO)
Thu, 04/18/2024 - 18:08
Alert Notice 859 announces a photometry and spectroscopy observing campaign beginning immediately on several bright (V mag 2 - 6) binary stars in support of observations with CHARA. Please see the notice for details and observing instructions.
This campaign is followed under the following AAVSO forum:
- Campaigns and Observation Reports: https://www.aavso.org/chara-bright-binaries-photometry-spectroscopy-2024
Please subscribe to this thread if you are participating in the campaign so you can be updated regarding observing instructions and campaign progress, ask questions, and join in the discussion!
Many thanks, and Good observing,
Elizabeth O. Waagen, AAVSO HQ
Am I correct in reading the request that you want observations during the eclipse period? Or would any observation provide some useful information?
Hi John,
Thanks for asking - observations at all phases of the light curve are welcome, as the astronomers want to study the entire orbit.
Good observing,
Elizabeth
I was going to do some tests tonight of bright objects using a DSLR and a 56mm lens in practice for T CrB when it bright, in outburst. Starting with Melotte 111 to get some transform coeficients. Since few of us do PEP and my CCD-based system has only about 1 degree field of view it would be useful to get some ideas on observing. The DSLR with a medium fl lens is the only way I can get variable, comps & checks in one FOV. It is perhaps implied in the announcement that a CCD/CMOS-based system can be used in a photon counting mode like in PEP? Any practical ideas on how to observe these bright objects with of order 0.1 amplitude?
Jim (DEY)
To achieve the desired FOVs it looks like we need to use a lens between about 50mm and 105mm depending on sensor size
Full Field APS-C
50 mm 27° x 40° 18° x 28°
105 mm 13° x 19° 9° x 13°
Peter
BPEC
A simple test was performed using a DSLR (3.89 micron pixels) and a medium fl (56mm @ f/4) lens on the Beta Aur and RR Lyn fields with all stacked images having total integration time of at least 10s. The Comp and Chk are Omicron Aur and 45 Aur for Beta Aur and reversed for RR Lyn. Classic aperture photometry of the DSLR images shows that the photometry errors are very large as the star images are tiny and the Bayer matrix is extremely undersampled. Any attempt at defocusing to sample the Bayer matrix will not repeatable from night to night. There is little hope sinple wide-field imaging with all stars in one field-of-view will produce anything useful.
Next experiment will be to use my Atik490EX + Esprit 100 + Astrodon B&V filters and observe in the classic PEP sequence roundabout to see what can be done.
Jim (DEY)
Jim,
You wrote: "Any attempt at defocusing to sample the Bayer matrix will not be repeatable from night to night."
I'm curious. Do you have evidence that is a problem? After all, it is a standard guideline to defocus for DSLR photometry, so replicating (or not) the degree of defocus will always potentially exist.
Roy
Roy,
I was using a DSLR (Bayer matrix sensor) with a short focal length lens. The DSLR I used has pixels 3.89 microns in size. The focal length of the lens used was 56 mm. Using an online CCD calculator astronomy.tools and entering the two values it gives the size of a single pixel to be about 14.3 arc seconds. The seeing at my observing location is typically between 3 to 5 arc seconds, sometimes lower.on a maybe 10% of my clear nights. So a good focus would put all the light of a star into one pixel ignoring lens aberrations. Now to defocus the star light to get some light to fall on the other color filter pixels I would have to defocus by a very large amount, exposures would increase as the star light is spread to adjacent pixels.. Using this camera and lens and some test images I found that the photometry errors were too large for a star with order 0.1 magnitude amplitude.
The results described above do not negate the general DSLR/CMOS manual suggestion to defocus and is what should be done for "normal" telescope focal lengths with image scales that are closer to your typical seeing fwhm.
Try one or more of the bright photometry targets using a similar focal length/sensor pixel size and let us know how it goes!
Jim (DEY)
Jim,
It turns out that I already have data of this sort from 2021, using a Canon EOS 500D camera with a pixel pitch of 4.68 microns, imaging through a 50mm f/1.8 lens. My targets were 3rd to 5th mag stars. I don't have results repeatable from night to night (the original issue of this discussion) but I have data from one night, which was posted on the Forum in April 2021. The link is here
Bright standard star system for CMOS RGB photometry | aavso
which will reveal the context and includes my results in two posts, dated respectively Sunday 5/16/2021 and Wednesday 5/26/2021. There were errors in the first of these, so concentrate on the second.
Roy
There is no information on how much you defocused. I'm guessing you defocused a great deal but how much? What were the fwhm of the stars after defocus? How many of each R,G,B pixels were illuminated? What exposures did you use?
The central limit theorem is playing a part surely when ensemble photometry is used and averaging of images. I have never used ensemble photometry so I didn't use that method. It would be useful to see how the accuracy values behave over time in a similar or same setup.
I still have to process the Melotte 111 data to get transform coefficients for the DSLR I used on my test. I suspect the coefficient standard errors will be larger than my normal CCD/DSLR at much better sampling of the point-spread-function of the stars.
Are you going to use a DSLR and report data for any of the program stars?
Unfortunately, here on the east coast USA, the weather is not looking good for the next week or more...
Jim (DEY)
I've gone back to my original images. It turns out I took data on more than one night, but it would take time to re-analyse. The FWHM varied between nights, something like 12 - 20 pixels. If we take the FWHM of 12 pixels, the number of illuminated pixels was about 20 across the image of the star. Assuming the seeing disk was circular (it was not quite so, because the camera was in a fixed position on a tripod) a diameter of 10 pixels would give about 315 illuminated pixels, so half of those would be green and one quarter blue and red. Exposure was 15 seconds.
I cannot take part in this programme. My DSLR camera is malfunctitoning, my northern view is compromised by buildings and vegetation and I live in Brisbane near the central east coast of Australia, south latitude 27.5 degrees.
Roy
Roy,
The information you provide on defocus level and exposure time provides a point of departure for next time I get some clear weather. I'll try something similar and see how it goes.
Best regards,
Jim (DEY)
Jim,
Best wishes for good results.
Roy
A few nights ago, on a decent photometric night for the east coast of the U.S., I was able to get photon counting style images for testing using my Atik490EX CCD + Esprit 100 + Astrodon B & V filters of RR Lyn. Exposures were 0.15s V and 0.30s B for all. Due to the fact my CCD takes about 15s to read out there is a large amount of dead-time to deal with. I took 10 images per filter and then moved to the next object--this is under-sampling the 10s recommended for smoothing scintillation. The basic observing sequence was comparison, variable, check, comparison. The ADUs were in the aporoximate range of 40,000 to 20000 which is in the linear portion of the CCD.
The preliminary B&V photometry has been uploaded to the AAVSO db.
This CCD is new and I don't have transformation coefficients yet, so the current magnitudes are not transformed and thus preliminary. The data will be updated when the coefficients arrive. There is one PEP V magnitude about 0.5 days before mine for comparison.
Using a CCD for photon counting (PEP style) for bright objects seems to hold promise.
Jim (DEY)
The notice states that it is planned to measure the RV of both components. Are both components visible in the spectra of all these binaries ?
What is the required RV precision (to confirm if it matches the capability of my setup)? and should measurements of an RV standard also be made (To allow observations from different observers to be combined)?
Cheers
Robin
At the risk of being "preachy": This is one of the 1st opportunities we have to show the CHARA users our value in supporting their observations. If you have the capability, please step up and support these requests, even just one or two if you can't do all four!
Peter
BPEC
Following a meeting on this campaign with the astronomer, relevant AAVSO Section leaders, and AAVSO staff, some revisions/clarifications/additions will be made to Alert Notice 859 and a new version will be issued. There is nothing incorrect in the Alert Notice issued on April 18, but the revisions will enable observers to maximize the efficiency and scientific value of their observing.
Good observing,
Elizabeth
I would like to ask everyone planning on obtaining spectra for this campaign to contact me to coordinate on targets and cadence. I can be reached on the contact link under the Leadership section in the Spectroscopy Observing Section page. https://www.aavso.org/spectroscopy-observing-section
For spectroscopy, there are eleven targets with a requested 20 observations per target, so 220 total observations over the next 12 weeks or so. V magnitudes of the targets range from 1.89 to 5.62 and spectra for these objects should be attainable for typical amateur instruments and with reasonable integration times. That being said, I recommend that larger telescopes go after the fainter stars and smaller telescopes concentrate on the brighter ones. I also recommend that higher resolution (R>>10,000) spectrometers go after targets with smaller radial velocity ranges and lower resolution spectrometers (R>10,000) go after targets with higher radial velocity ranges. I am expecting the Principal Investigator(PI) to provide me with radial velocity ranges for this purpose. For now, use your best judgment to select your targets. When you contact me please provide the aperture of your telescope and your instrument’s R value at H alpha or H beta so I can attempt to match targets to capabilities.
The goal for us in supporting this investigation is to obtain high resolution spectra centered on a prominent spectral feature, such as H alpha or H beta lines, to observe the splitting of the line due to the relative orbital motion of the two components. We will submit these spectra into AVSpec where the PI will later extract them for analysis. We will not be making any radial velocity determinations ourselves and the PI has not requested spectra of radial velocity standard stars. Processing of the 2D spectrum to produce the 1D profile should be that which is typical for high resolution spectra which you all have much experience in doing - and consistent with the requirements for submission into AVSpec.
I will be tracking our progress on this to ensure that, as a group, we achieve the objective of the 220 spectroscopic observations for these objects.
Let me know if you have any questions or suggestions.
Scott
All,
I was wondering why, in some cases, are the choosen comps and chks stars so far away from the target.
I've not reviewed all the 4 photometric targets, but, in the case of RR Lyn, we have :
11 Lyn = V5.890, B-V = 0, variation 0.001 (TESS), 1°38' (this star is the chk star)
HD44061 = V6.47 (Tycho2), not seen in VSX, 49'
HD46318 = V6.555 (Tycho2), not seen inVSX, 1°20'
Thanx in advance,
Christophe
Eclipses for RR Lynx will be largely unaccessible for observers in North America.
See https://www.aavso.org/vsx/index.php?view=detail.ephemeris&nolayout=1&oid=17906
(Jerry Persha pointed this out to me)
Tom
https://www.aavso.org/vsx/index.php?view=detail.ephemeris&nolayout=1&oid=4298
I checked the…
Yeah.
I checked the observing possibilities for europeans observers ... not a lot for those four stars. V1022 cas being very low, by the way.
So, maybe determining the secondary minimum should be easier ? Not sure they are even observable, nor when they would be seen. Don't no how to compute this, with eccentricity not null.
Christophe
I have the same question as Christophe. How to calculate the times of the secondary minimum, when the eccentricity ≠ 0?
In the case of bet Aur there is no problem: ecc = 0, so the secondary minimum is halfway between two primary minima.
I did some internet search, and I found the following site: https://www.as.up.krakow.pl
Secondary minima of RR Lyn: HJD = 2452511.453 + E x 9.9450753
Secondary minima of V1143 Cyg: HJD = 2452510.506 + E x 7.640729
Elements of V1022 Cas are not available on that site.
Thanks for those elements.
Interresting ; I will have a close look at it thereafter.
***
I found a paper (2022) with in depth study of V1022 Cas, from which I could derive the instants of the secondary eclipse, at phase 0.666 (or so).
https://doi.org/10.3847/1538-3881/ac84de
By the way, the Epoch and period are subtancially different than those found on the VSX and in the alert notice 859.
So, I re-computed a few primary eclipse dates. See table below.
(It should be alright if someone made some verifications of my computations, juste in case.)
It appears that the VSX instants are off by more than 4 hours from the real instants ...
Also, my two cents. As this star (V1022 Cas) was observed by TESS two years ago, I can't figure out why professionnals are requesting photometric observations by amateurs, with a star so low above the horizon, at a so defavorable season, with small optic like telelens, and comps located on the other side of the sky, or so.
Are we supposed to do better than TESS in photometry precision, and instant calculations ?
Observations out of eclipses seems surrealistic too.
Maybe some detailed explainations should help. Im pretty sure that we are in capacity of understanding some simple astrophysical concepts behind those call for observations ;-)
Well well well.
Christophe
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Hi Christophe,
I updated V1022 Cas's VSX ephemeris using TESS and Hipparcos data. Predictions are now much more closer to the times you derived from the 2022 paper. Hipparcos allowed to expand the time baseline a little longer.
The most interesting thing is that the system is another heartbeat system (with amplitude of only 0.002 mag.), the second in this campaign after tet Aql, both found by revising the VSX information with TESS. TESS is really a goldmine!
Cheers,
Sebastian
Alert Notice 859 has been revised and re-issued. Its URL is unchanged: https://www.aavso.org/aavso-alert-notice-859.
Additional information/instructions for photometry and spectroscopy observers has been added, as well as more information on the comp and check stars required for photometry.
Be sure to watch the campaign forum thread (the one this post is coming from) for discussion regarding this challenging campaign:
- Campaigns and Observation Reports: https://www.aavso.org/chara-bright-binaries-photometry-spectroscopy-2024
Good observing,
Elizabeth