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[vsnet-campaign-xray 106] (fwd) V381 Nor = XTE J1550-564 sequence data
Date: Wed, 16 Jan 2002 13:52:02 -0700 (MST)
From: Brian Skiff <bas@lowell.edu>
Subject: [vsnet-chat 5016] XTE J1550-564 sequence data
Berto Monard wrote me privately today to ask about stars in a sequence
around XTE J1550-564. In my large photometric reference file, I list stars
in the field observed by Jain et al. (2001ApJ...546.1086J). Three of the four
stars are quite red, and the colors seem red compared to what USNO-A2.0 shows.
I have looked into the problem and have found the usual can of worms.
Jain et al. provide separate BVI magnitudes in their source table, which I
have formed into colors. The B-V and V-I colors are consistent with one
another, a check that authors who publish simple magnitudes often (maybe
_usually_) do not make. This is a sign that the data are basically okay, and
there is no 'prima facie' evidence to doubt them short of making new
observations. The red magnitudes at least are also consistent with the "red"
magnitudes in A2.0, GSC-2.2, and UCAC1. So far so good.
Jain et al. mention UBVRi data for field stars was also published by
Sanchez-Fernandez et al. (1999A&A...348L...9S), and that their data is
roughly consistent (though at only the 0.05 to 0.1 mag. level), noting three
stars where the Sanchez-Fernandez table has typos. I have examined this paper,
and find the photometry chart and tables full of errors. First, the chart
says it is north-up/east-left, but in fact it is reverted to the sky (north-up,
but east-right). Coordinates are shown for the comparison stars, all but one
of which is completely erroneous. Unfortunately these stars have been added
to SIMBAD with the wrong positions.
Nothing is specified about the calibrations, notably how the use of a
Gunn i filter affected things or how this was transformed (and to what
system?). Internal evidence suggests it was transformed to Cousins I, but no
details are given about any of it. Two of the stars indeed have non-physical
colors (again the data are published as separate magnitudes rather than as
colors), but the third suspect star seems to be okay within generous errors.
The single star in common with Jain et al. matches, again within generous
errors, though short of making new observations there is no way to tell which,
if either, is preferable.
The lists below show correct positions (from USNO-A2.0) and source data
from the two papers. Stars 4 and 5 from the Sanchez-Fernandez list are simply
wrong and should be ignored. The rest are probably okay, but frankly I
wouldn't trust any of it below the 0.1-mag. level. As an example, S-F star 2
has V-R and V-I colors too blue than required by the B-V value (or B-V is too
red for the given VRI colors) by 0.1-0.2 mag. in either direction. For star 2
if B-V is correct, then V-R needs to be about 0.58, and V-I should be about 1.2
(if Cousins V-I). If V-R and V-I are correct (they are internally consistent),
then B-V needs to be about 0.9 or a little less. So either B-V is wrong or the
VRI pair is wrong. The paper says the numbers are good to 0.01 mag. Baloney!
Finally, I note that the small cluster NGC 5999 is in the field nearby to
the east. There is photometry of it (1999MNRAS.303...65P), but confined to a
tiny postage-stamp CCD field, and probably won't be useful for the x-ray
source. There's also a woider study of variables in the field from the OGLE
group (1998AcA....48..489P, but no constant stars are listed in that paper.
This example should make amateur observers (or anyone for that matter)
all the more appreciative of sequences provided by Arne Henden and others who
do things "right".
\Brian
The source papers are:
2001ApJ...546.1086J: JAIN R.K., BAILYN C.D., OROSZ J.A., McCLINTOCK J.E.,
SOBCZAK G.J. and REMILLARD R.A. <Astrophys. J., 546, 1086-1097 (2001)>
Optical observations of the black hole candidate XTE J1550-564 during
reflare and quiescence.
1999A&A...348L...9S: SANCHEZ-FERNANDEZ C., CASTRO-TIRADO A.J., DUERBECK
H.W., MANTEGAZZA L., BECKMANN V., BURWITZ V., VANZI L., BIANCHINI A.,
DELLA VALLE M., PIEMONTE A., DIRSCH B., HOOK I., YAN L. and GIMENEZ
A. <Astron. Astrophys., 348, L9-L12 (1999)>
Optical observations of the black hole candidate XTE J1550-564 during
the September/October 1998 outburst.
source: 1999A&A...348L...9S
Name RA (2000) Dec V B-V V-R V-i remarks
XTE J1550-564 2 15 50 58.52 -56 28 56.7 14.46 1.08 0.48 0.99
XTE J1550-564 3 15 50 46.43 -56 29 36.3 14.37 1.28 0.70 1.39 crowded
XTE J1550-564 4 15 51 09.99 -56 30 21.6 14.67 -0.89 1.27 1.76 bad
XTE J1550-564 5 15 51 05.65 -56 27 08.5 14.47 3.23 -1.40 -0.76 bad
XTE J1550-564 6 15 51 04.20 -56 28 26.7 14.42 0.80 0.40 0.86 = Jain D
XTE J1550-564 7 15 51 03.94 -56 28 34.9 16.66 1.10 0.53 1.11
XTE J1550-564 8 15 51 01.34 -56 27 53.1 16.28 1.33 0.68 1.38
XTE J1550-564 9 15 51 02.38 -56 27 43.4 16.60 1.20 0.60 1.24 crowded
XTE J1550-564 10 15 51 03.69 -56 27 25.6 16.23 1.12 0.56 1.15
source: 2001ApJ...546.1086J
Name RA (2000) Dec V B-V V-R V-I
XTE J1550-564 A 15 51 03.69 -56 29 21.6 16.13 1.88 2.00
XTE J1550-564 B 15 51 03.44 -56 28 50.8 16.96 1.81 2.09
XTE J1550-564 C 15 51 04.39 -56 28 58.0 16.84 2.27 2.63
XTE J1550-564 D 15 51 04.20 -56 28 26.7 14.48 0.76 0.92
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