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Nova photometry

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HQA
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Nova photometry

Munari, Maitan, Moretti and Tomaselli just published a very interesting peper on V339 Del:

http://arxiv.org/abs/1504.05483

As you know, one of the difficult aspects of nova photometry is that they enter a "nebular phase", where the flux is dominated by nebular lines like Halpha and [OIII].  Since wide-band filters include these lines, you end up measuring the emission line strength rather than the underlying white dwarf continuum.  Since filters from different manufacturers have different response curves, you end up with parallel light curves with offsets between observers.  This is very obvious in the AAVSO light curve for V339 Del.  Because these are emission lines, and don't obey any kind of black-body curve, the resultant measures cannot be properly transformed.  You just have to get enough overlapping data from each observer to hand-transform the data onto a common system.

An alternative is to choose different filters, perhaps customized for nova photometry, or perhaps already existing for other projects but can be re-used for nova photometry.  That is what Ulisse Munari and his team have done.  They've chosen three common filters: Stromgren y for measuring the continuum (this filter is often used for reproducing Johnson V from the Stromgren set), and Halpha and [OIII] to measure the emission line strengths.  You can buy the emission line filters from several vendors including Baader and Astrodon; the Stromgren y is available from Astrodon.

I have a set of these 3 filters that are being shipped to Munari for obtaining transmission curves, and then will be placed on BSM_NM for monitoring novae.  Don Goldman of Astrodon has loaned me the Stromgren y filter for this purpose (he is a really nice guy), and I had leftover emission-line Astrodon filters from other projects.  I'm hoping to put another set down on BSM_Berry in Perth, so that we have a northern and a southern set.  If you have space in your filter wheel, you might consider going this route - it seems to do an excellent job of producing science with 2-D imaging.

Arne

AAVSO 49 Bay State Rd. Cambridge, MA 02138 aavso@aavso.org 617-354-0484