Affiliation
American Association of Variable Star Observers (AAVSO)
Fri, 09/09/2022 - 19:38
For some reason I acquired a Y band filter and have it in my filter wheel.
It's band is redder than the Ic filter.
What kind of observations should I use this filter for?
Thx,
George
It is useful for red stars, specifically luminous red giants/supergiants, for being in a spectral zone (roughly 1.04 microns) where there is a relatively line-free 'continuum' region in the spectrum. Thus one can obtain something close(r) to real luminosity variations for the red stars versus only the temperature changes that one gets anywhere across the visible. Visible-light photometry of Miras (say), records pretty much only the temperature changes in the stars, _not_ the changes in brightness (luminosity). Tom Calderwood has begun observing with a similar filter on Betelgeuse and other similarly bright (naked-eye) supergiants. This has shown that Betelgeuse is almost dead flat compared to the visual range over the last couple of seasons. See the AAVSO lightcurve. He (or I) can advise about standard stars for this filter. The star list could be extended to fainter objects of interest (the M-supergiants around h & chi Per, VX Sgr, chi Cyg, many others).
Bob Wing and Wes Lockwood did extensive work in the late-1960s and early-1970s on Miras and supergiants using a narrowband 1.04-micron filter along with the bluer TiO and CN filters of the Wing system. I have keyed-in files with essentially their data. At least when working with brighter stars, I would tend to adopt the Wing standards since they involve giants. But see also the re-invention of the 1.04-micron system as 'Y' by Lynne Hillenbrand et al in their 2002 paper:
https://ui.adsabs.harvard.edu/abs/2002PASP..114..708H/abstract
...in which the work of Wing and Lockwood is ignored. The cool standards here are all dwarfs, which was/is the science interest to these folks. As long as your filter cuts on longward of the strong water-vapor band near 9300-9500A, then you shouldn't have much trouble with atmospheric extinction that's a function of humidity. (See Figure 1 of the paper just cited.)
\Brian
Brian, thank you for details on the Y filter.
My earlier experiments with the filter were pretty dark, so I need to pick brighter targets and longer exposures. And make sure there is no IR cut filter in my system!
Recent modifications to the VSD make it easier to add Y data to comp stars. If the standards that you and Tom use are not yet in VSD, I can help with that: just point me to the data!
George
The list by Wing is here:
https://ui.adsabs.harvard.edu/abs/1967lts..conf..205W/abstract
This conference paper also has a more complete description of the usefulness of these sorts of observations and why this wavelength.
You will need to observe a bunch of these stars multiple times together with another filter (probably either V or I should work) in order to get some handle on the color terms on your system. I think Tom C and I had additional correspondence about the standards list, but that may take some effort to recover.
\Brian
There is a longer list of standards that I can supply, but Wing's passband is *much* narrower than Y band
The nominal Y filter certainy does not match the Wing 1.04-micron passband. But given the strong redward fall-off in the CCD sensitivity, it could be that the effective passband is not so much different. The thing to do of course is to _try_it_, specifically observing a bunch of the standards to look at the color terms, particularly among the K/M giant/supergiants.
\Brian
Brian's comments regarding cool stars and the Y filter are good. A couple of other reasons for using Y:
- this is a relatively clear atmospheric window, and you get less extinction and more consistent photometry than with, say, an Ic filter
- for deeply embedded sources, the redder that you can go, the deeper you can probe. Young stars in molecular clouds, stars hidden behind dust, all show up better. An example is the recent nova PGIR22akgylf (ATEL #15587).
The big disadvantage with Y is that it is close to the silicon sensitivity limit, and so the quantum efficiency is at most a couple of percent with amateur sensors. You will also see much more structure in your flats, as the photons penetrate far enough that you start seeing the electronic structure behind each pixel of back-illuminated sensors like the Sony CMOS.
That said, it is a fun band to experiment with.
Arne