[Aavso-photometry] Low-pressure sodium lights and photometry (Thuan-Gunn)

[Wolfgang Renz]

Hello Richard

I found your second last email again. I'll answer it this week.

Is Jim Gunn still related with the SDSS ?
(That was the last work from him, I was reading about)

Unfortunatly the LPS is not the only source of light pollution. Against a
bright continuum like with incandescent lamps or sun/moon twilight you
cann't do much (except of making more/longer exposures to reach the
required SNR), but many have their issues more with HP Sodium and
LP & HP Mercury or even with neon lamps. The air glow emission lines
and sometimes the aurora lines will also affect darker skies. And then its
getting tough to find a filter system that isn't affected at all.
But in deed, using the Thuan-Gunn photometric filter set should help
much with LPS light pollution as well as with cutting down the 436, 546
and 558 nm Mercury and Sky Glow emission lines.

The Thuan-Gunn v(iolet) filter with its CWL of 394 nm and PWL of 391
nm is much easier to reach for amateur equipment (in comparison to
the Bessell U band at CWL 360 nm and PWL at 372 nm).
But getting very good results for the Thuan-Gunn u(ltraviolet) band at
CWL 353 nm and PWL at 352 nm filter (good transmission and entirely
shortward of the Balmer jump -> most efficient NUV band filter of the
more common photometric wide-band systems!) is probably as well out
of reach for most amateur equipment (that usually includes glas (FR or
refractor) lenses and/or (SCT) plates, visually optimized multi-coatings
and are situated at lower altitude sites) like the original Johnson U band
at CWL 350 nm and PWL at 355 nm or even the Landolt U band at CWL
340 nm and PWL at 353 nm.

For further info on the Thuan-Gunn uvgr(iz) photometric system see:

GCPD - The Thuan & Gunn uvgr photometric system
http://obswww.unige.ch/gcpd/ph38.html
ADPS - uvgr, Thuan and Gunn, 1976
http://ulisse.pd.astro.it/Astro/ADPS/Systems/Sys_097/index_097.html
http://ulisse.pd.astro.it/Astro/ADPS/Systems/Sys_097/fig_097_b.gif
http://ulisse.pd.astro.it/Astro/ADPS/Systems/Sys_097/sys_097_resp.gif
ADPS 2 - uvgr, Thuan and Gunn, 1976
http://ulisse.pd.astro.it/Astro/ADPS/ADPS2/FileHtml/index_f097.html
http://ulisse.pd.astro.it/Astro/ADPS/ADPS2/Figure/f097_thu76.gif

Jon Holtzman, New Mexico State University
Astronomy 535: OBSERVATIONAL TECHNIQUES
http://astronomy.nmsu.edu/holtz/a535/ay535notes/index.html
Photometric systems
http://astronomy.nmsu.edu/holtz/a535/ay535notes/node56.html
http://astronomy.nmsu.edu/holtz/a535/html/diagrams/a535/ubvri.htm
http://astronomy.nmsu.edu/holtz/a535/html/diagrams/a535/gunn.htm
or all in one file (19 MB, but doesn't include all figures):
http://astronomy.nmsu.edu/holtz/a535/ay535notes.ps
http://astronomy.nmsu.edu/holtz/a535/html/diagrams/a535/preview.htm


1976PASP...88..543T - Thuan, T. X.; Gunn, J. E.
A new four-color intermediate-band photometric system
http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1976PASP...88..543T
http://obswww.unige.ch/gcpd/cgi-bin/getfromADS.cgi?bibcode=1976PASP...88..543T

1985PASP...97..165K - Kent, S. M.
Photometry of stars in the uvgr system
(improved photometry, color conversion formulae)
http://adsabs.harvard.edu/cgi-bin/bib_query?1985PASP...97..165K
http://obswww.unige.ch/gcpd/cgi-bin/getfromADS.cgi?bibcode=1985PASP...97..165K

1994PASP..106..967J - Jorgensen, Inger
Secondary photometric standard stars for the Thuan-Gunn (vgr)
and Johnson-Kron-Cousins (UBV) systems
(new color conversion formulae!)
http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1994PASP..106..967J
http://vizier.cfa.harvard.edu/viz-bin/VizieR?-source=J/PASP/106/967
http://obswww.unige.ch/gcpd/cgi-bin/getfromADS.cgi?bibcode=1994PASP..106..967J


ESO - FORS1 Photometric UBVRI, Gunn & Spectroscopic Standard
Fields & Stars and 'Empty' Fields for Twilight Flats
http://www.eso.org/instruments/fors/tools/FORS_Std/FORS1_Std.html#Gunn


AFAIR, Custom Scientific offered a Thuan-Gunn uvgriz filter set in the
past. But they probably replaced it by the SDSS filter set. I saw their
Thuan-Gunn uvgriz filter set also at the FLI site. And they (in opposite
to CS) still have it on their homepage::
http://www.fli-cam.com/FLIproducts/cs-filters.htm
http://www.fli-cam.com/images/thuangunn.gif
But I don't know if FLI actually still sell them.


Clear skies
  Wolfgang

-- 
Wolfgang Renz, Karlsruhe, Germany
Rz.BAV = WRe.vsnet = RWG.AAVSO


CWL = Central Wave Lenghth
PWL = Peak Wave Lenghth
LP = Low Pressure
HP = High Pressure
LPR = Light Pollution Reduction/Rejection



----- Original Message ----- 
From: "Michael Newberry" <mnewberry at mirametrics.com>
To: "Wolfgang Renz" <w_renz at onlinehome.de>; "Robert Harmon" <roharmon at owu.edu>
Cc: "AAVSO-PHOTOMETRY" <aavso-photometry at mira.aavso.org>
Sent: Sunday, February 26, 2006 8:44 PM
Subject: Re: [Aavso-photometry] Low-pressure sodium lights and photometry


> Hi Bob,
> 
> There is another broadband system that was designed to reduce the effect of 
> the Na-I 5890 doublet on broadband photometry: the Gunn-Thuan "uvgriz" 
> system (as in Jim Gunn, or James E. Gunn, now at Princeton). The uvgri, and 
> z refer to the bandpasses, of which g is blue shifted relative to Johnson V 
> (the Gunn v refers to vio;et, not visual) and the tail of the r filter 
> begins near the edge of the sodium emission---hence the system is almost 
> blind to D-line emission from low pressure sodium lights. Although broadband 
> V photometry is devastated by low pressure sodium emission, the Gunn-Thuan 
> system permits sampling the spectrum across the visible range by defining 
> the g and r bands so as to avoid the D line. The Gunn-Thuan system was 
> developed at Palomar to allow photometry mainly of faint, high redshift 
> galaxies in spite of the growing brightness of sodium vapor lights from the 
> ever-sprawling Los Angeles basin. There is no reason this system cannot
> give good results for stellar photometry. One wrinkle is that there are well 
> defined standards but not large numbers of them, so that means more 
> calibration time spent moving the telescope. Another, wrinkle---the real 
> show-stopper---is that you must find a filter set and I don't believe there 
> are any commercial, off-the-shelf alternatives. However, if there was 
> "enough" interest, I am sure a competent filter vendor would see the 
> business potential in producing one.
> 
> Michael Newberry
> 
> 
> 
> ----- Original Message ----- 
> From: "Robert Harmon" <roharmon at owu.edu>
> To: <aavso-photometry at mira.aavso.org>
> Sent: Saturday, February 25, 2006 10:51 PM
> Subject: [Aavso-photometry] Low-pressure sodium lights and photometry
> 
> > Hello, all,
> >
> > I'm an astronomer at Ohio Wesleyan University, which is about 20 miles
> > north of Columbus. OWU owns and operates Perkins Observatory
> > (www.perkins-observatory.org), which houses a 32-inch reflector. Because
> > it's f/17, it's not very useful for CCD photometry as the field of view
> > is about 3x2 arcmin with our SBIG ST-8E. Thus, the telescope is used
> > mostly for visual observing by students and the many visitors to our
> > twice-weekly public programs. However, I do use 8-inch and 12-inch
> > telescope on site for BVRI photometry.
> >
> > To make a long story short, there is a strong possibility that a
> > Wal-Mart Supercenter and a Toyota dealership will be built within a mile
> > of the observatory to the south. The good news is that both would be on
> > land annexed by the city (pop. ~22,000) in which OWU is located (the
> > observatory is on the outskirts of town) and thus subject to lighting
> > code restrictions which would require them to use low-pressure sodium
> > lamps on 28-foot poles, as opposed to typical broad-spectrum parking lot
> > lights on 40-foot poles. (Wait until the Toyota dealer sees what his
> > cars look like under LPS light!) The bad news, of course, is that the
> > lovely yellow glow will still most likely annihilate the naked-eye views
> > from the observatory grounds and degrade telescopic views of objects
> > like galaxies and clusters.
> >
> > I have two questions for the list. Any insight would be greatly 
> > appreciated!
> >
> > 1. It seems to me that LPS lights should have a minimal effect on BRI
> > photometry, but that V might be a different story. Am I correct in my
> > thinking? Has anybody succeeded in doing good V-filter photometry in the
> > presence of strong LPS skyglow? Any tips?
> >
> > 2. Does anybody know of references for estimating the level of skyglow
> > from a given number of LPS lights at given wattages from a given
> > distance? It would certainly help me make my case more effectively in
> > community meetings if I could give some quantitative estimates of how
> > bright the skyglow will be. Alternatively, does anybody know of any
> > photos showing skyglow from LPS lights at a single large parking lot
> > from a mile or a few miles away? There aren't any comparable facilities
> > in my area.
> >
> > Regards,
> > Bob Harmon
> > _______________________________________________
> >
> > Aavso-photometry mailing list
> > Aavso-photometry at mira.aavso.org
> > http://www.aavso.org/mailman/listinfo/aavso-photometry
> >
> 
>