Skip to main content

Proper use of the extinction coefficients

The membership database is currently undergoing upgrading/testing. Web functions that involve an interface with the member database (webobs, etc.) may experience intermittent problems. We hope to have this issue resolved within 24 hours (by 5pm Eastern Time on October 1st or 12:00 UT). Thank you for your patience.
r.furgoni's picture
Joined: 2011-10-26


i need to determine the correct B-V value for the star UCAC4 733-009103 (00 51 40.309 +56 30 33.38). The star is present in APASS with Bmag=13.648 and Vmag=13.337 so B-V is 0.311. The point is that I need to get the value corrected for the extinction at various wavelengths: I then entered the coordinates of the star in the NASA-IPAC extinction calculator but I'm not sure how to use the results.

Here the link to the page.

If for Landolt B the Aλ [mag] is 10.697 and for Landolt V the Aλ [mag] is 8.089, how the two values ​​must be used to obtain the correct B-V?


Riccardo (FRIC)

AAVSO 49 Bay State Rd. Cambridge, MA 02138 617-354-0484