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Hi Folks,
Couple of quick questions if you don’t mind please:
Is a V filter pretty much essential for CCD variable star work or can I just use a UVIR filter?
If V is required, is it possible to get a V filter in 2″ round mounted format to screw onto the 2″ adapter on the camera? Can’t seem to find them on the usual sites.
I have an SBIG ST-1001E camera and C14 scope. I don’t want to have to buy a new filter wheel and large filters unless absolutely necessary.
Thanks,
Michael.
Hello Michael,
the requirement for a filter depends what type of variable star you are observing. I observe Cataclysmic Variables, in particular Dwarf Novae in outburst. I usually do unfiltered photometry to get the best signal-to-noise ratio. I’ll use a V-band comparison star sequence. Observing some eclipsing systems, where timing the eclipse is critical rather than the actual mag, can also been done unfiltered. For much other VS work a filter is highly desirable in order to be able to compare your photometry with other observers – and in the case of coloured variables (like Miras) a filter is essential. Whilst many amateurs use a V-band filter, some use a B, R or I filter. These are specific wavebands, based on the Johnson-Cousins system, which are designed for photometry and are thus different for standard coloured filters for tri-colour imaging (and different from UV or IR cut-off filters).
I am not sure where one can buy 2-inch V filters. The company Astrodon lists them, but they are unmounted. Maybe someone else can advise.
Best regards,
Jeremy
Thanks Jeremy. I rang Custom Scientific – as the name suggests they do custom work. They can make a 2″ round mounted V filter for $400 + shipping. Although it is costs more than the 50mm round unmounted, it would save me the expense of a new filter wheel specifically for the larger unmounted filters. TBH, I have a preference for trying to keep the setup as simple as possible and avoid filters wheels if I can. I’ll think about it a little.
However, your comment re Cataclysmic Variables is interesting. I might look into that a little…..
Ta,
Michael.
Great stuff Michael. Do let me know if I can be of assistance as your plans progress.
If you want to have a dabble with CVs, the VSS is running a campaign on one called NSV 2026, which is in Taurus. Unfiltered CCD obs (or filtered, if you get the V filter) are needed to spot outbursts of this enigmatic dwarf nova – then when an outburst occurs, time series photometry is required for as long as possible. It goes into outburst every couple of weeks, so you won’t have to wait long for something exciting to happen!
More details here: http://www.britastro.org/vss/NSV2026.pdf
Jeremy
Excellent, Michael. The simplest way to start is to image the field of NSV 2026 every clear night to see if it’s in outburst or not (unfiltered is fine). If you spot an outburst, please post the news to the BAA VSS alert group: https://groups.yahoo.com/neo/groups/baavss-alert/info
Jeremy
Hi Michael,
I would actually purchase at least two filters, so you can transform your data onto the standard system. I have BVI, but R is also a good option instead of I.
Welcome to Variable Star World!
John
Michael,
HT Cas has just entered outburst – it may be a superoutburst. Good opportunity to have a go at time series. HT Cas is an eclipsing UGSU star, so your light curve through an orbital period or two will look quite spectacular. There is an eclipse ephemeris on my web page (http://www.garypoyner.pwp.blueyonder.co.uk/HTCAS15.txt). It’s quite old and needs a tweak, but it will give you a good idea as to when to expect minimum.
Good luck,
Gary
Latest news is that it could be a normal outburst, so no lovely superhump profiles on the light curve. However sometimes these normal outbursts can trigger superoutbursts (never been seen in HT Cas though), so worth following after a return to quiescence. Of course you still get eclipses during a normal outburst. Last night (Oct 25.9 UT) it was still bright at 13.2.
Gary
It looks as though Baader do 2″ photometric filters, £171 for the V filter quoted on the FLO website. They are showing out of stock, so you might need to wait for them to order it in, but significantly cheaper than the other options.
https://www.firstlightoptics.com/photometry-filters/baader-ubvri-bessel-photometric-filters.html
I think this has been covered, but unfiltered is definitely preferable to a UVIR blocking filter.
Once you get going, it would be great if you can contribute your observations to the VSS database. I can point you in the direction of different software options to provide the data in one of the upload formats.
Cheers,
Andy (BAAVSS Database Secretary)I think this has been covered, but unfiltered is definitely preferable to a UVIR blocking filter.
For my part I tend to use unfiltered for time-series work (exoplanets previously, asteroids these days) to achieve the greatest SNR and the fastest cadence. As only the minute to minute variation is of interest there is no great need to have the observed magnitudes be comparable with measurements made by other observers.
When making precision measurements I almost always use a V filter but have been known to submit CV measurements — unfiltered with comparison magnitudes given in Johnson V.
No great need for a filter, in other words, except for red stars as noted above. A filter is nice to have, undoubtedly, but no-one should let expense put them off making scientifically valuable measurements.
One day I really must see if I can find a round tuit down the back of the sofa because there are literally thousands of images on disk which were taken with the Seestar’s OSC camera. Trouble is that all of them need de-Bayering and the green channel measurements transformed to standard V. Another example of where external filters are no needed — the Bayer mask consists of filters which are internal to the detector.
I just realised I was replying to a post from 2015! I was not paying attention this morning.
I can see it came back to the top of the forum as someone is attempting to spam this post. The spam was blocked but the date/time and poster were updated. I shall leave it to the WebOps Team to fully remove the spam and spammer.
Andy
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