This web page is meant for use with typical stars and asteroids
in converting between magnitude systems: BVRcIc and g'r'i'z'.
There are four types of conversions: 1) within BVRcIc, 2) within
g'r'i'z', 3) from BVRcIc to g'r'i'z' and 4) g'r'i'z' to BVRcIc. A
few miscellaneous "mixed" conversions are of interest (e.g., BVr'
to V) which are included.
This web page is possible because of two crucial
publications, culminating in the heroic work by Arno Landolt
and staff of the Flagstaff Station of the U. S. Naval
Observatory: Landolt (2009) and Smith et al (2002). The
Landolt publication lists 598 stars with carefully measured
BVRcIc mags. The Smith et al publication lists 158 stars with
SDSS magnitudes (u'g'r'i'z'). I have identified "same stars"
to produce a list of 94 stars with both BVRcIc and g'r'i'z'
mags. The following graphs and conversion equations are based
on these 94 stars. A few "outlier" stars can be seen in the
graphs, and they have been omitted in creating the conversion
equations. A related web page describes how to create a SED
(Spectral Energy Distribution) from BVRcIC and g'r'i'z' and
JHK mags: SED.
Links on this web pageBVRcIc to BVRcIc
BVRcIc to g'r'i'z'
g'r'i'z' to BVRcIc
1) Suppose we've measured an asteroid's spectrum to resemble the
solar spectrum, i.e., it has a gray color. How would we convert an
r'-mag to V? In the "BVRcIc to g'r'i'z'" section above, there a
graph plotting V - r' vs. B-V (repeated blow). The sun's B-V =
0.64, so from this graph we note that V - r' = 0.165 ± 0.023. In
other words, for a solar-like star or asteroid (with very small
B-V color uncertainty): V = r' + 0.165 ± 0.023. Consider a
realistic B-V measurement, with an associated SE, such as B-V =
+0.77 ± 0.10. For this color the graph states that V = r' + 0.23 ±
0.08 (where SE uncertainties for both B-V and the graphical
relationship have been included). This illustrates how a measured
B-V, with an associated SE, can be used to convert an r'-mag
measurement to V-mag.
Landolt, Arlo U. and Alan K. Uomoto, AJ, 133,
768-790, 2007 March
Landolt, Arlo U., AJ, 137, #5, 2009 May
Smith, J. Allyn and 21 others, AJ, 123,
2121-2144, 2002 April
Related Web Pages
Data Release 6 Transformations
SDSS III Transformation Between SDSS & Other Systems
Creating a SED
B. Gary's master list of web pages & resume
WebMaster: B. Gary. Nothing on this web page is copyrighted. This site opened: Nov 03, 2015