Affiliation
American Association of Variable Star Observers (AAVSO)
Thu, 05/05/2022 - 14:43
In the presentations about SNEWS they talk about how amateurs can contribute with DSLR observations.
The advantages are:
- It would be quick to setup
- It's 3 color photometry automatically
But there are problems:
- the target might be very bright
- what if comp stars are not available?
I'd like to start a discussion about how to be prepared to do DSLR observations of a SN.
If the event is so bright that it can be done in daylight, how does one calibrate and establish comps?
George
Thanks for starting this discussion!
To clarify, as we are talking about SNEWS (Super Nova early warning system) here, this is about the next SN in our own galaxy!
I'd like to throw in some additional "pros & cons" :
The advantages are:
- wide field of view : the initial sky localization from a neutrino burst alert issued by SNEWS for the next galactic SN can be quite poor (at the moment, the initial alert will not give a sky localization at all, but that will change with "SNEWS 2.0" soon-ish)
- relative small aperture of DSLR+telephoto lens means we might have a smaller problem with particular bright sources compared to the big guns
- big target audience: lots of people have DSLRs and comparable cameras with "telephoto" lenses (say f>=50mm)
But there are problems:
- angular resolution: The next galactic SN is statistically much more likely to happen at low galactic latitudes as seen from Earth, close to or even within the band of the Milkyway ==> problems with blending of sources
- actually, if the next galactic SN happens within the band of the Milky way, it is likely to be very red (after passing through a lot of dust etc) and not very bright, both is not good for DSLRs with IR cut filters and small apertures. So while the next galactic SN could be very bright for us, it could also be quite dim!
In the case of super bright SN, could we cal our DSLRs for differential exposure time photometry?? IE: cal shutter so we KNOW what 1/4 sec exposure really is vs say 10 sec exposure. Use that cal factor comparing 2 images of SN region: 1 where SN is not saturating and the other where SN is blown out but cal stars are not saturated?? Doesn't seem ideal, but doable in a pinch IFF we know the shutter cal factors before the event.
Peter
I think this is a good idea, and doing the same for aperture is also possible. So the advice would be: take images with the target not saturated (short exposure, stopped down aperture, also defocused) and figure out the photon count with the recorded metadata afterwards. You can spend weeks and months if needs be to get the analysis right, but you cannot repeat the early light curve. Either observe it or wait very likely many decades for the next opportinity, ... if you are young enough for that....
But really, the super bright SNs are not the primary concern and I would strongly discourage people to focus on that for their prepartions for such an event. For a scientific estimation of observability of the most interesting, initial part of the light curve, you can consult this study:
Scott M. Adams, C. S. Kochanek, John F. Beacom, Mark R. Vagins, and K. Z. Stanek.
Observing the Next Galactic Supernova. Astrophysical Journal, 778(2):164, December
2013.
Preprint here : https://arxiv.org/pdf/1306.0559.pdf
It is a very interesting and accessible read, and the information about expected apparent brightness in different fiter bands is given nicely condensed in Figure 4. You will see that the probabiilty that a galactic core collapse SN "shock breakout" event (the most interesting part) will be bright enough to reach (say) mag 5 in V is only around 15 % .... which would translate to a rate of once every couple of hundred years (matching historical record, or the relative lack of it).
And mag 5 just means visble by naked eye in the night sky, it's not like "super bright" for a DSLR.
But if we take mag 12 (V) as a limit what can be done with a DSLR and telephoto lens, we get a probability (again from Fig. 4 of said paper) of around 50 % (!!!) , and if we consider DSLRs red pixels as well, we are more likely than not to be able to see it with a DSLR and telephoto lens!! We DSLR owners are in the game!!!
But please let's spead the message among astronomy fans and potential observers that the next galactic core collapse supernova (as seen from Earth), contrary to widespread belief, will almost certainly NOT be super bright, and not even a naked eye object. It's important for the preparation.
Cheers
HB
The importance of being prepared for the super-bright ones is that those are the objects that professionals may not be able to observe at all in photometry, and something so near and unextincted would give dramatically more information than something that is further and reddened. You're totally right about the probabilities, but in terms of the opportunities for amateur astronomers to make a totally unique contribution, the rarer events are a niche that is completely un-served by professional facilities. If something like that happens, you'll see professionals rushing to the observatories they have on the roofs of their buildings that are just used for undergrad lab classes.
Cameras other than DSLRS can be used for bright targets. My current setup is a ZWO ASI1600MM (12 bit mono CMOS) camera, ZWO filter wheel, adapter for Canon lenses, and a Canon 200mm EF f/2.8 L lens. A tripod collar on the lens allows balancing in DEC on a Star Advenrurer Pro sky tracker with a counterweight. The setup is used for time series photometry of southern eclipsing binaries to 9th mag. Advantages are quick setup (I don't have an observatory), and the fact that, with care, a meridian flip is not necessary.
Roy
Indeed! Perhaps a better thread title would be "wide field observations" (you can also put a DSLR at the focus of a 14 " telescope but that's not what we wanted to discuss here I guess).
CS
HB
I wonder tho whether all-sky cameras have us covered already for the super bright events. Very likely , super-bright will also be not within the band of the Milky Way , so the very low angular resolution of all sky cameras would not hurt that much. The most important thing wth all-sky cameras would be, tho to actually make them RECORD the date, and if possible even in raw formats, after an alert happens (at many places all-sky cameras will just be used as cloud monitors in streaming mode to check the sky at any given time, without keeping a record of frames).
CS
HB
All-sky cameras that record would be fine for localizing events and getting a white light time series, but ideally we would get as much color information as possible.
There are definitely some all-sky cameras that look for meteors, and hence do record the data.
True for most installed all-sky-cameras, but there is no reason that all-sky camera must mean b&w only. E.g. many of the low end ZWO ASI cameras , e.g. ZWO ASI 178mc camera , are actually sold with (inexpensive) fish-eye lenses so are immediately usable as (near) all-sky cameras. I guess many of us have these lenses lying around still somewhere after buyiong one of those ZWO ASI cameras.
Others have used the Raspberry Pi HQ camera for inexpensive all-sky projects , e.g.
https://hackaday.com/2020/10/14/cheap-all-sky-camera-is-easy-as-pi/
These cameras would give simultaneous 3 color photometry data just as DSLRs would.
Cheers
HB
This is a great idea. I am preparing suggestions to amateurs for the St Louis Astronomical Society. My recommendation would be that any All-Sky system be put into record mode as soon as you get the SNEWS alert.
Which reminds me, there is an organization that maintains a meteor watch with All Sky cameras, CAMS ( http://cams.seti.org/ ). I'll see about getting them invited into the SNEWS party.
George