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[vsnet-sequence 51] Sequence for SS Cygni
Norwegian Astronomical Society - Variable Star Section
2138+43 SS CYGNI [R.A. = 21h42m42s.8, Decl. = +43o35'10" (2000.0)]
----------------------------------------------------------------------
***** Sequence for the UGSS type dwarf nova SS Cygni *****
Following a request by B. Andresen I have compiled a sequence for this
well-known dwarf nova. It is mainly based on data from the Hipparcos
catalogue (HIP, ESA 1997) and Tycho-2 catalogue (TYC2, Hog et. al 2000).
The list is given in table 1. I have only included stars that are bluer
than B-V = +0.65. For these stars the differences between the Johnson
V and visual magnitudes should not exceed 0.1-0.2 mag. This sequence
should cover the complete light variation of SS Cygni.
Data for some stars that are redder and/or brighter is given in table 2.
Here I have only chosen objects that are labelled on the AAVSO charts
(as magnitudes in units of 0.1 mag.). It should be noted that red stars
are less suitable as comparison stars, mainly due to differences between
the colour responses of the V and visual magnitudes and among different
observers.
The lists in table 1 and 2 contain coordinates, star identifications,
plus V magnitudes and B-V colours with corresponding uncertainties.
The relation between V magnitude, B-V colour and the visual magnitude
(mv) for the "average" observer is derived by R. Stanton (JAAVSO, 2000)
as mv = V + 0.21 (B-V).
V and B-V are not given directly in the Tycho-2 catalogue, but these
values can be obtained from the Tycho VT and BT magnitudes. The
relations are V = VT - 0.09 (BT - BT) and B-V = 0.85 (BT - VT).
My list extends the sequence compiled by B. Sumner from CCD photometry
by A. Henden, USNO (H/S). The Henden/Sumner sequence is available from
ftp://ftp.nofs.navy.mil/pub/outgoing/aah/sequence/sumner/sscyg.seq
For some of the fainter stars I have used data from this sequence
(version September 11, 2000).
Table 1: Sequence stars:
------------------------------------------------------------------------
Id R.A. (2000.0) Decl. Star Name V-mag eV B-V eB-V Ref Notes
h m s o ' "
------------------------------------------------------------------------
A 21 47 41.1 +44 00 40 HIP 107604 7.83 0.01 +0.11 0.01 HIP (1)
B 21 47 02.3 +43 19 19 HIP 107557 8.33 0.01 +0.22 0.01 HIP (2)
C 21 45 24.1 +43 56 08 TYC 3196-1988 8.70 0.03 +0.49 0.04 TYC2 (3*)
D 21 44 21.0 +43 48 19 TYC 3196-2202 9.07 0.02 +0.29 0.02 TYC2 (4)
E 21 44 05.7 +43 42 36 TYC 3196-1227 9.41 0.02 +0.58 0.03 TYC2 (5)
F 21 42 20.2 +43 34 03 HIP 107156 9.80 0.03 +0.40 0.04 HIP (6)
G 21 42 13.8 +43 47 45 TYC 3196-1019 10.32 0.04 +0.39 0.04 TYC2 (7)
H 21 42 27.2 +43 33 45 TYC 3196-0857 10.87 0.07 +0.45 0.07 TYC2 (8)
K 21 42 35.0 +43 39 17 GSC 3196-0829 11.86 0.02 +0.62 0.01 H/S (9)
L 21 42 45.0 +43 40 28 GSC 3196-0831 12.28 0.02 +0.62 0.01 H/S (10)
------------------------------------------------------------------------
Notes:
(1) HIP 107604 = TYC 3196-1605. TYC2 photometry: BT = 7.940 (+/- 0.015)
and VT = 7.823 (+/- 0.011) => V = 7.81 and mv = 7.83. AAVSO mag.
8.4. Dist. 59'.6.
(2) HIP 107557 = TYC 3196-1137. TYC2 photometry: BT = 8.565 (+/- 0.016)
and VT = 8.332 (+/- 0.011) => V = 8.31 and mv = 8.35. Dist. 49'.7.
(3*) TYC 3196-1988. This is a close binary (Ho 168). W. Heintz (Ap.J.
Suppl.Ser., 1998) has sep. = 0".76, PA = 52.9 deg., epoch 1996.870.
TYC2 photometry for TYC 3196-1988-1: BT = 10.035 (+/- 0.024) and
VT = 9.458 (+/- 0.019) => V = 9.41 (+/- 0.02), B-V = +0.49
(+/- 0.03) and mv = 9.51; for TYC 3196-1988-2: BT = 10.129
(+/- 0.025) and VT = 9.552 (+/- 0.021) => V = 9.50 (+/- 0.02),
B-V = +0.49 (+/- 0.03) and mv = 9.60. Combined magnitude and colour
are given in table, while mv = 8.80. AAVSO mag. 8.6. Dist. 35'.9.
(4) TYC 3196-2202. TYC2 photometry: BT = 9.447 (+/- 0.018) and
VT = 9.102 (+/- 0.016) => mv = 9.13. AAVSO mag. 8.9. Dist. 22'.1.
(5) TYC 3196-1227. TYC2 photometry: BT = 10.148 (+/- 0.025) and
VT = 9.471 (+/- 0.019) => mv = 9.53. Dist. 16'.7.
(6) HIP 107156 = TYC 3196-0785. TYC2 photometry: BT = 10.258
(+/- 0.028) and VT = 9.799 (+/- 0.024) => mv = 9.84. Henden/Sumner
photometry: V = 9.849 (+/- 0.188) and B-V = +0.369 (+/- 0.032),
these values are uncertain due to saturation. Sumner star no. 2.
AAVSO V mag. 9.9. Dist. 4'.2.
(7) TYC 3196-1019. TYC2 photometry: BT = 10.817 (+/- 0.038) and
VT = 10.360 (+/- 0.035) => mv = 10.40. AAVSO V mag. 10.3.
Dist. 13'.6.
(8) TYC 3196-0857. TYC2 photometry: BT = 11.449 (+/- 0.062) and
VT = 10.918 (+/- 0.060) => mv = 10.96. Henden/Sumner photometry:
V = 10.895 (+/- 0.035) and B-V = +0.522 (+/- 0.027), these values
are approximate due to saturation. Sumner star no. 3. AAVSO mag.
10.9. Dist. 3'.2.
(9) GSC 3196-0829. Henden/Sumner photometry: V = 11.864 (+/- 0.016)
and B-V = +0.620 (+/- 0.011). Sumner star no. 4. AAVSO mag. 11.8.
Dist. 4'.4.
(10) GSC 3196-0831. Henden/Sumner photometry: V = 12.279 (+/- 0.018)
and B-V = +0.617 (+/- 0.007). Sumner star no. 5. AAVSO mag. 12.3.
Dist. 5'.3.
Table 2: Field stars:
------------------------------------------------------------------------
Id R.A. (2000.0) Decl. Star Name V-mag eV B-V eB-V Ref Notes
h m s o ' "
------------------------------------------------------------------------
21 40 11.1 +43 16 26 75 Cygni 5.09 0.01 +1.60 0.01 HIP (11)
21 46 16.6 +43 03 39 HIP 107488 6.52 0.01 +0.28 0.01 HIP (12)
21 44 44.1 +43 25 45 HIP 107361 7.52 0.01 +1.72 0.02 HIP (13)
21 43 08.7 +43 35 01 TYC 3196-0701 8.49 0.01 +1.33 0.02 TYC2 (14)
21 42 41.3 +43 43 05 TYC 3196-0717 9.54 0.03 +1.01 0.04 TYC2 (15)
21 43 00.3 +43 41 23 TYC 3196-0815 10.84 0.07 +1.25 0.15 TYC2 (16)
21 42 33.6 +43 42 42 TYC 3196-0933 10.86 0.07 +0.76 0.08 TYC2 (17)
21 43 20.1 +43 36 39 TYC 3196-0763 11.68 0.14 +0.19 0.13 TYC2 (18)
------------------------------------------------------------------------
Notes:
(11) 75 Cygni = HIP 106999 = TYC 3196-2204. TYC2 photometry: BT = 7.201
(+/- 0.015) and VT = 5.280 (+/- 0.009) => V = 5.11 and mv = 5.45.
AAVSO mag. 5.4. Dist. 33'.3.
(12) HIP 107488 = TYC 3192-0780. TYC2 photometry: BT = 6.846 (+/-0.014)
and 6.564 (+/- 0.009) => V = 6.54 and mv = 6.59. AAVSO mag. 6.4.
Dist. 50'.1.
(13) HIP 107361 = TYC 3196-1427. TYC2 photometry: BT = 9.852 (+/- 0.022)
and VT = 7.769 (+/- 0.010) => V = 7.58 and mv = 7.95. AAVSO
mag. 8.0. Dist. 23'.9.
(14) TYC 3196-0701. TYC2 photometry: BT = 10.198 (+/- 0.026) and
VT = 8.635 (+/- 0.013) => mv = 8.77. AAVSO V mag. 8.5. Dist. 4'.7.
(15) TYC 3196-0717. TYC2 photometry: BT = 10.827 (+/- 0.039) and
VT = 9.642 (+/- 0.023) => mv = 9.75. AAVSO V mag. 9.6. Dist. 7'.9.
(16) TYC 3196-0815. TYC2 photometry: BT = 12.446 (+/- 0.167) and
VT = 10.970 (+/- 0.060) => mv = 11.10. AAVSO V mag. 11.0.
Dist. 7'.0.
(17) TYC 3196-0933. TYC2 photometry: BT = 11.834 (+/- 0.077) and
VT = 10.941 (+/- 0.060) => mv = 11.02. AAVSO mag. 10.8. Dist. 7'.7.
(18) TYC 3196-0763. TYC2 photometry: BT = 11.923 (+/- 0.092) and
VT = 11.696 (+/- 0.127) => mv = 11.72. AAVSO mag. 11.3. Dist. 6'.9.
Yours sincerely,
Bjorn H. Granslo
[Director, NAS.VSS]
vsnet-adm@kusastro.kyoto-u.ac.jp
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