SA 110 standards

Affiliation
American Association of Variable Star Observers (AAVSO)
Sat, 06/04/2022 - 20:29

     Following on Tom Calderwood's nice presentation today about photometric transformations, I pass along some details about the Landolt Selected Area 110 stars that can be used for determining these, and atmospheric extinction as well.  The field is in Aquila, so is up by late-evening just now, and will be available until October-ish.  This is merely one of many such calibration fields that can be used.  The specific star-field here is led by SA 110-353 = HD 172829, which is the reddest fairly bright Landolt star, with B-V = 2.00.  It has the erroneous variable-star designation of HK Aql, but is simply not variable at any level measureable in the usual way.  Getting it and the other stars properly exposed at shorter/longer wavelengths could require two different sets of exposures in different filters.  The field center is for a 20'x20' field to capture all the stars.

     To use the field simply to measure extinction, you could get away with exposing just to get the red/blue pair SA 110-353 and -340, but you'll get several others stars for free in the process to help beef-up the determination.

     I have trimmed my more detailed working file to show just a name, coordinates, and the photometric magnitudes and color-indices.  I include Sloan z values as available.  For most of the stars the data are taken from Peter Stetson's extensive field calibrations that greatly extend the Landolt sequences around the sky.  For stars in common, his values are typically within a few millimags of what Arlo published, but usually with much higher statistical weight (many more observations with big telescopes).  The nominal errors are < 0.01 for each item.  For one star I show provisional data from APASS and TASS MkIV, which will need to be calibrated more accurately against the other stars in the same field.  That star is probably good to +/- 0.03 mag for V and B-V.  The last entry has curiously inconsistent B-V values from multiple reliable sources, which also needs to be looked at with independent data.  Finally, I note that three stars in the middle range of B-V color have negative U-B color-indices.  These are unreddened very-metal-poor stars, two of which have significant proper motion.  They are useful since they extend the range in U-B color relative to the other mostly reddened stars in the field.

\Brian

(the table will need to be looked at with an equal-space font, or reformatted as csv etc as desired)

---  SA 110-353  field center:  18 41 50  +00 12.0  (J2000)
---  Stetson  2021 Feb 22 data
---  color ranges:  0.31 < B-V < 2.00;  -0.21 < U-B < 2.29

Name                 RA  (J2000)  Dec        V     B-V    U-B    V-R    R-I    V-I      z     spec    source
SA 110-S305       18 41 20.17 +00 13 03.0  12.229  0.663  0.088  0.402  0.400  0.801  11.822          Stetson
SA 110- 339       18 41 26.52 +00 08 25.3  13.605  0.987  0.766  0.591  0.523  1.114                  Stetson
SA 110- 340       18 41 28.45 +00 15 23.0  10.025  0.308  0.124  0.171  0.183  0.354  10.102  A5II    Landolt 2009
GSC 0447-0188     18 41 32.16 +00 16 39.1  12.70   0.81                        0.96   12.022          APASS/TASS MkIV provisional
SA 110-S323       18 41 33.94 +00 04 24.7  13.132  1.022  0.408  0.624  0.673  1.297  12.093  K?      Stetson
SA 110-S329       18 41 35.84 +00 20 40.7  11.308  0.492 -0.212  0.323  0.340  0.663          F8 wl   Stetson, large proper motion
SA 110- 246       18 41 50.76 +00 05 04.5  12.710  0.605 -0.156  0.380  0.415  0.795  12.285  G wl    Stetson, large proper motion
SA 110-S353       18 41 51.84 +00 14 10.8  12.586  0.635 -0.062  0.383  0.375  0.758          G wl    Stetson
SA 110- 248       18 42 00.56 +00 03 18.4  10.800  0.698  0.507  0.391  0.484  0.875  10.242  A0      Stetson
SA 110- 352       18 42 17.16 +00 11 09.6  11.334  0.571  0.073  0.337  0.340  0.677          F2:     Stetson
SA 110- 353       18 42 17.70 +00 09 18.4   8.447  2.002  2.292  1.186  1.120  2.306          K5III   Landolt 1983a
SA 110-S421       18 42 18.42 +00 05 04.7  13.205  1.153  0.745  0.678  0.768  1.446  11.945          Stetson
SA 110- 355       18 42 18.93 +00 08 24.2  11.944  1.023  0.504  0.652  0.727  1.378          A2V     Landolt 1992 = Landolt 2009
                                           11.942  1.056  0.473  0.647  0.748  1.395                  Stetson
                                           11.948  1.051         0.673  0.688  1.361                  Henden n=3
                                           11.957  0.979  0.492  0.663  0.733  1.396                  Clem & Landolt 2013 n=5