[vsnet-chat 2962] (fwd) Re: (fwd) Re: Tycho,Tycho-2,Hipparcos magnitudes

[Taichi Kato <tkato>]

(fwd) Re: [vsnet-chat 2961] (fwd) Re: Tycho,Tycho-2,Hipparcos magnitudes

From: Sebasti疣 Otero <varsao@fullzero.com.ar>
Subject: RE: [vsnet-chat 2961] (fwd) Re: Tycho,Tycho-2,Hipparcos magnitudes
Date: Wed, 24 May 2000 03:27:42 -0300

Dear Brian and friends:
                                            The comments about Tycho and
Tycho 2 catalogues were all on the reduced data and not the BT and VT
magnitudes. The Tycho 2 data (converted to Johnson) has higher B-V's than
Tycho for red stars and lower for  bluer ones. It's interesting to note that
bluer stars are never so blue for  Tycho: all stars with known colour index
bluer than -0.20 appear as -0.15 or so. But I'm always refering to
magnitudes already converted to the standard system.
                                            Concerning Hipparcos, I've been
checking and crossing magnitudes from USNO, BSC and other sources and I
found an almost perfect agreement for the V magnitudes (NOT Hp) between all
of them. In spite of its broadband sensitivity , Hp magnitudes can be
converted (Up to the K spectral type, for M  forget about using Hipparcos)
to V accurately.
                                            But as examples of the
advantages of the use of TYCHO 2, I want to share some numbers with you
which I think are pretty clear:


          STAR                                   TYCHO
TYCHO 2                                                comments
                                              V (Johnson)    B-V
V (Johnson)    B-V

TYC 8627-03103-1       NO DATA (just 8.40 VT)                 7.75
0.84                C comp. of u Car. TYCHO 2 gives B-V and thus a V mag.
TYC 6404-00860-1               10.97          0.60             A=    11.28
0.37               99 AAVSO comp. star for R Aqr. One single entry in Tycho.

B=    11.29      0.08               Both comp. in TYCHO 2 (B= TYC
6404-00860-2) AB= 10.53
TYC 6855-01717-1               10.55          0.65
10.23      0.65               103 AAVSO comp. star for VZ Sgr.
TYC 7427-01589-1               10.00          1.06                        9.
74      1.12                97 AAVSO comp. star for RY Sgr.
TYC 7427-01999-1               10.75          1.06
10.43      1.11               102 AAVSO comp. star for RY Sgr.
TYC 8659-00930-1               10.07          0.71
10.78      0.16               Star in EsB 365 field.
TYC 8659-01286-1                9.72           1.29
10.15      1.56               Star in EsB 365 field.

                                     When you look through the eyepiece it
becomes evident that Tycho 2 values agree with what you see. Since these
stars are used as comparison for popular variables I'm sure some of you must
have noticed the discrepancies.

Best regards,
Sebasti疣 Otero.

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