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SA 110 extended sequences

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SA 110 extended sequences

In hopes of getting comp-star calibration for some strongly reddened Cepheids, I have had a look at the strongly reddened Landolt standards in SA 110.  This region is superposed on the Aquila dark rift, and so contains both unreddened foreground stars as well as stars behind the rift that are reddened to varying degrees.  After poking around a bit I have chosen two 15'x15' fields in SA 110 that contain stars of a range of colors that make a good start on getting some quite red objects that ought to be stable.  The two short tables are attached.  The data are drawn mainly from the 1992 Landolt standards paper, but importantly, also from Peter Stetson's extensive calibration work somewhat hidden at the CADC site, and from Arne Henden's observation files (when I could access then ~20 years ago).  The latter two observers got data on dozens or scores of nights, and so the data should be very close to the standard system defined by the Landolt stars in the same frames.  Star-by-star comparison shows this is the case at the ~0.005 mag level, which most of us are unlikely to match.  The APASS data in this region, despite having something like a thousand CCD frames involved, are rather noisy.

     The topic of red leak in filters came up during Stan Walker's recent presentation about Miras, so the stars here should help with assessing that.  Similarly, for simply observing Miras or other very red/reddened stars, in determining one's color terms out at the red end, it is helpful to have multiple reference stars to standardize results.

     The SA 110-353 region contains (on its east side) the star SA 110-353 = HD 172829.  This is the brightest 'very red' Landolt standard, which many observers (including myself) confirm is constant, despite the GCVS designation HK Aql.  The area also contains two unreddened metal-weak G dwarf stars that have relatively blue U-B colors.

     The SA 110-502 region is anchored by the asterism including the red star SA 110-502, commonly mentioned in the literature when folks calibrate CCD data.  I have taken the center to be somewhat to the southeast of this asterism in order to include brighter stars with diverse colors.  This is especially to include the red/blue pair SA 110-516 + 521, which Arne has measured on 'many' nights.  A further 'very red' star, SA 110-446, lies to the south near the brighter blue star SA 110-441.  Finally, on the east side of the 15' field is SA 110-520.  Arlo Landolt measured this star only in his early 1973 paper, but he did so with 14 measurements on 7 nights.  That's enough to call it a standard, though perhaps only to ~0.015 mag external accuracy --- plenty good enough for most of us.  It fills a nice spot in the B-V color sequence, so is useful to bring along in the calibration process.

     I hope folks find this useful.


arx's picture
Thank you Brian,

Thank you Brian,

Greatly appreciated.


SA 110 extended sequences

I found a couple of typos in the SA 110-502 list; a revised version is attached.  The V magnitudes for 110-499 and 110-516 are corrected.

     I wrote originally that the main working list was the 1992 Landolt paper; what I intended to say was the 2009 Landolt list, though for most of the stars the data are identical.  I am also seeking Sloan z magnitudes for these stars, but there are few Sloan data as yet for bright/intermediate stars.


File upload: 
SA110 extended sequences


I observed SA110 three times during August 2019.  I didn't use exposures that allowed use of all three of the red stars, SA110-353 (R84), SA110-516 (R112) & SA110-446 (R140) but I was able to add R112 and R140 to my linear least-squares fits for my DSLR transform coefficients.  Btw, all three stars appear on but are currently unmarked on the VSP standard chart 3061 SA110.

Not too surprising but on all three nights and for each B,V, R color the correlation coeffficients, over-all fit standard error and the slope coefficient standard errors improved. 

There is definite worth in using the extended red stars in your linear L-S fits for transform coefficients!

Jim DeYoung (DEY)

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