Hello! I’ve been observing RW AUR. There are two other variables in the field - ZTF J050738.71+301649.2 and ZTF J050814.72+301507.8. I get periodic isolated spikes in B,V, and I filters. For example, ZTF J050814.72+301507.8 is a BY Draconis variable listed with a period of 1.2 days and amplitude of about 0.09 mags. I’ve been deleting my observations that show spikes, figuring there was a problem with seeing/technique, etc.
ZTF J050738.71+301649.2 is an EA variable with a period of roughly 3 days and 0.3 mag amplitude. Again, some unusual spikes.
Other observers have uploaded observations similar for these two.
I kept last night’s images in as an example. Should I be deleting these observations that do not seem to fit, or might something going on that these observations are accurate? Thank you.
Actually, RW Aur is a noted binary star system where RW Aur B will flare in the optical and NIR. Perhaps, you have detected the flares from the chromosphere.
If you post a time series with the spikes some of those who are involved in studying flares may be able to confirm what is happening. Exciting!
Rick
Thanks. I have been doing time series. The trouble is, each flare is only one measurement or two in one or two filters, so easily confused with a problematic image. I’ll keep an eye on it and upload as appropriate if the images look good and have reasonable error bares.
A number of AAVSO members have formed a group studying flares of Red Dwarf stars and have posted a lot of data showing flaring of AD Leo and EV Lac, and to a lesser degree, YZ CMi. If you check out the light curves of these stars you will see that the flares can be of such short duration that you might only catch an image or two. This has led our group to want to image these stars with a very short cadence , as short as 15 seconds. Take a look at those light curves and compare to your results.
If you Google Red Dwarf Group, you will find a lot of interesting info.
Clear skies!
Rick
Just looked up RW Aur. This is a complex system. I may add this to my target list (if I ever get another clear night) and give a go. I have a C8 with a QHY 533M camera using Baader B and V filters. I think 30s exposures will work for a high cadence time series in V and maybe 60s for the B. It might be that chromospheric flaring behaviour is mixed in with the variations caused by the orbital motion of materials around the star, making identifying such behaviour tricky. I think a high cadence study of this system could be quite interesting.
I will definitely want to check this out.
Rick
I sequenced the field last night. ZTF J050738.71+301649.2 shows spikes B,V, and I, However, RW AUR and ZTF J050814.72+301507.8 did not. If there was a problem with the images, I would have thought that the error bar would have been large and the same problematic image would have been present in RW AUR and ZTF J050814.72+301507.8. Best regards. Mike
I tried clear/CV last night with cadence of 20 seconds. ZTF J050738.71+301649.2 showed spikes of 1 to 2 mags. ZTF J050814.72+301507.8 and RW AUR showed minor fluctuations. I’ll return to B,V,I for future runs. Best regards. Mike
[quote=“msheald, post:1, topic:3985”]
ZTF J050814.72+301507.8 is a BY Draconis variable
[/quote], Such stars are known to exhibit chromospheric flaring.
The spikes you are seeing may be quite real. Chromospheric flaring of 1 to 2 magnitudes is not common but has been observed a number of times. If you would not mind, could you send me a screenshot of its light curve?(or post to the forum)
This is quite intriguing.
Rick
I posted the data on AAVSO webobs, so they are on the database. A fair amount of scatter around the baseline for ZTF J050814.72+301507.8. Here is the screenshot. Mike
I’m not sure which points you called “unusual spikes” in your plot? I presume the extrema points.
I would not delete your observations unless you have an obvious hardware fail, software fail, or other obvious reason(s) to do so. However, you are always allowed to makes comments in the notes field of your data records commenting on thin clouds, thin fog, etc.
Have you actually looked at your images for things like say thin clouds coming over the field of view like the time period between 04:30 to 05:30 UTC?
SBIG ST402 with BVIC filters and 8"Lx200 working at 1100mm. I went through the images and deleted the ones that had problems, like significant trailing, etc. In the final list, any image with an error bar over 0.15 mags I deleted. I thought that eliminating those with high error bars should have eliminated any with light gradients from thin clouds. Here is one raw image (uploads were all calibrated and transformed) from 10:37 PM local time or 0437 UT. Some thin clouds that, when stretched, give a gradient of a couple hundred ADU from darkest to lightest in the background. For those images that thin clouds created a gradient resulting in an increase in error bar, I did not upload. Best regards. Mike RW AUR_LIGHT_C_20.00_-4.82_2026-02-27_0461.fits (767.8 KB)
A useful diagnostic plot here would be the differences (delta-mags) of two comp stars over the same interval, so one could compare the scatter in them and the variable. The plot you posted looks like instrumental noise to my eye.
I would agree with Brian that the data is noisy. I think we are pushing the limit , maybe, with our 8" scopes when we are getting below 13th mag and trying a fast cadence. The Red Dwarf group has decided that we can be confident of seeing a flare if there is a sharp rise followed by a more gradual dimming, and the flare achieved 3 standard deviations of gain over the quiescent baseline. Based on those criteria, I don’t think we can conclude we are seeing any magnetic flaring. Any real signal would be lost in the noise.
Rick (LRIB)
Here is last night’s run in B,V, and I. ZTF J050738.71+301649.2 shows some unusual activity while RW AUR and ZTF J050814.72+301507.8 are fairly unrevealing. The images did not show any evidence of high clouds. I discarded two readings for error bars of 0.15 mags. All three readings are taken from a single image, that is why I would expect a problematic image to be reflected in all three data sets. Having two that are unrevealing and one that is unusual makes me wonder if something might be going on. Best regards. Mike
If the spikes are like the plot several posts upward from here, there are multiple reasons why these are are non-physical, i.e. can’t or don’t happen in stars. Among them is a light-travel-time argument. Whatever it is producing the spikes can’t be very large since the change is very rapid, so that something like this on a star has to be very small for the process to happen even at the speed of light. Most physical processes don’t go that fast, and in order to make a big change in brightness (as here), then an unrealistic amount energy has to be involved, like a large fraction of the total output of a star.
Another thing are the downward drops, the ‘negative spikes’ in the run of data. A lot of physical process can be eruptive, such as solar flares or similar flares on late-type stars, where the energy can indeed spike up in a few seconds. But then it doesn’t just vanish, but instead there’s some far slower (often more-or-less exponential decay as whatever physical system relaxes: it doesn’t just flip a switch. Now explain more-or-less instantaneous drops, as in your data-run. This is another reason to be skeptical about these being ‘celestial’ (i.e. from the star) rather than very local inside your camera.
But if you’re talking microvolt electronic jitter among camera pixels a few microns across, there’s no problem getting such fast, tiny changes.
More to follow…
Again referring to the plot several messages above, this sort of display to me (my opinion) could conceal all sorts of issues. It’s not ‘wrong’, but I think it is not telling you what you want to know. It is also not what you see in the literature.
Take the simple case in differential photometry of a variable and two comparison stars. For the argument, assume the two comp stars and the variable are similar in brightness, so all have similar signal-to-noise. The reduced data give you three differential magnitudes: comp1 minus comp2, and the variable against each of the comp stars. A very good estimate of the scatter in your data is obtained from the run of the differences ‘comp1 minus comp2’. (And not, by the way, from the S/N of the images.) Where’s that plot, and what’s the rms scatter on that series? If there’s funny stuff going on with the camera, or sky, or whatever, it should show up in that plot of the two comps against each other.
So for the variable, the two plots of comp1-minus-variable and comp2-minus- variable ought to look basically identical – whatever shows up in one had better show up in the other one, or else you have problems (one comp variable also?). So I suggest examining those three plots to see if everything hangs together (comp1-comp2 dead flat, comp1-var and comp2-var look the same).
For the jittery data case, I’m guessing probably that jitter will appear in the variable against each of the two comps and in the two comps against each other, cuz it is just camera noise. Just showing the run of some output without that comparison is not useful in diagnosing what’s going on.
