Return to Home Page
----- Original Message ----- From: "Brian Skiff" <Brian.Skiff@lowell.edu> To: <varsao@fullzero.com.ar> Cc: <vsnet-chat@ooruri.kusastro.kyoto-u.ac.jp> Sent: Sunday, May 25, 2003 4:26 AM Subject: Re: [vsnet-chat 6413] Re: chart problems > >> 4) Tycho-2 for stars fainter than 8 and brighter than ~9.5. Tycho- > >> magnitudes (transformed to V) suffer for some systematic color -term that > >> makes white and yellow stars to appear with a whiter B-V color (peaking > >> around B-V 0.5 with a difference of 0.06-0.07 mag.) and white and blue stars > >> to appear with a V mag 0.01-0.02 mag. brighter than Johnson's V. > >> In Tycho-1 this effect is less pronounced and thus negligible, but accuracy > >> falls steeper beyond 8th magnitude. > > Do you have some plots demonstrating this with respect to primary > standards (specifically the Landolt and Cousins E-region standards)? > What transformation are you using to get Johnson V from VT? Bessell? > The "official" Tycho-consortium transformation is not adequate at the > level you're talking about, and might introduce just the errors you > are noticing. Brian, I am using Hog (2000) tranformations as stated in the catalogue: V= Vt-0.09*(Bt-Vt) B-V= 0.85*(Bt-Vt) The relation is for ALL stars I used for ALL sequences. (I don't have this specific difference recorded in my files) No zero point differences. V values are from GCPD data and show a ery clear trend. This table is a good example: Star Vmag B-V / Tycho-2 Vmag B-V mu Col 5.17 -0.28 / 5.141 -0.255 eps Lup 3.37 -0.18 / 3.355 -0.165 iot Lup 3.55 -0.18 / 3.517 -0.165 ome1 Sco 3.95 -0.05 / 3.934 -0.049 eps Aqr 3.77 0.00 / 3.757 0.009 lam Boo 4.18 0.08 / 4.173 0.079 alp Vol 4.00 0.15 / 3.995 0.148 n Cen 4.26 0.22 / 4.255 0.197 eta Cru 4.14 0.35 / 4.144 0.305 gam Tuc 3.99 0.40 / 3.994 0.362 gam Pav 4.22v? 0.49 / 4.230 0.431 ups And 4.09 0.54 / 4.099 0.496 bet Hyi 2.79 0.62 / 2.793 0.588 del Vol 3.97 0.78 / 3.973 0.738 d Vel 4.06 0.87 / 4.054 0.843 eps Oph 3.23 0.96 / 3.219 0.960 del Crt 3.56 1.12 / 3.556 1.116 eps Crv 3.00 1.33 / 2.994 1.355 eps1 Ara 4.06 1.45 / 4.063 1.463 0.06 mag. bluer B-V at 0.5. 0.02 mag. brighter V for blue stars. Is there some transformation that corrects this difference? Sebastian.
Return to the Powerful Daisaku Nogami
vsnet-adm@kusastro.kyoto-u.ac.jp
