No. | B | V | V-R | R-I | K | J-K | H-K | AV | ![]() |
age | mass |
Table 2 | mag | mag | mag | mag | mag | mag | mag | mag |
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8 | 14.3: | 13.22 (3) | 0.98 (1) | 1.08 (1) | 9.02 (5) | 0.86 (6) | 0.20 (6) | 0.7 | -0.45 | 3.2 | 0.6 |
13 | 12.0: | 10.81 (1) | 0.50 (2) | 0.50 (1) | 8.51 (2) | 0.62 (3) | 0.14 (3) | 0.2 | 0.04 | 10 | 1.3 |
19 | 18.8: | 14.99 (3) | 1.24 (3) | 1.34 (2) | 10.14 (4) | 0.91 (16) | 0.25 (7) | 0.0 | -0.68 | 1.6 | 0.3 |
23 | 9.7: | 8.04 (4) | 0.41 (15) | 0.07 (7) | 0.0 | 0.30 | 10 | 1.4 | |||
27 | 12.3: | 12.28 (3) | 0.70 (1) | 0.71 (1) | 8.23 (3) | 1.35 (5) | 0.51 (5) | 1.5 | -0.04 | 10.0 | 1.2 |
30 | 11.3: | 8.38 (3) | 0.71 (5) | 0.18 (5) | 0.1 | 0.07 | 1.0 | 0.9 | |||
31 | 14.3: | 13.1: | 9.38 (3) | 0.85 (6) | 0.22 (5) | 0.1 | -0.64 | 6.3 | 0.6 | ||
36 | 10.0: | 9.2: | 7.18 (3) | 0.44 (5) | 0.10 (5) | 0.3 | 0.73 | 4.0 | 1.5 | ||
39-NE | 11.16 (3) | 0.73 (2) | 0.66 (1) | 7.89 (3) | 0.72 (5) | 0.11 (5) | 0.4 | 0.25 | 0.5 | 0.7 | |
39-SW | 11.43 (2) | 0.24 (1) | 0.66 (1) | 7.89 (3) | 0.72 (5) | 0.11 (5) | 0.5 | 0.20 | 0.5 | 0.6 | |
53 | 12.7: | 12.35 (3) | 0.73 (1) | 0.72 (1) | 9.01 (3) | 0.78 (5) | 0.21 (5) | 1.0 | -0.25 | 10 | 1.1 |
55 | 11.0: | 9.6: | 7.31 (3) | 0.61 (5) | 0.12 (5) | 0.1 | 0.46 | 2.0 | 1.7 | ||
64 | 14.9: | 12.9: | 9.91 (3) | 0.91 (5) | 0.30 (7) | 0.0 | -0.25 | 0.8 | 0.4 | ||
68-E | 15.56 (3) | 1.2 (1) | 1.5 (1) | 10.53 (2) | 0.96 (4) | 0.20 (3) | 0.0 | -0.91 | 2.5 | 0.2 | |
68-W | 16.5 (3) | 1.2 (3) | 1.7 (2) | 11.28 (3) | 0.95 (5) | 0.31 (4) | 0.0 | -1.29 | 2.5 | 0.1 | |
80 | 15.85 (4) | 1.29 (3) | 1.52 (2) | 3.0 | -0.86 | 40 | 0.7 | ||||
82 | 8.7: | 8.2: | 7.07 (3) | 0.23 (5) | 0.05 (5) | 0.0 | 0.30 | 30 | 1.2 | ||
85 | 15.5: | 14.27 (3) | 1.17 (2) | 1.23 (2) | 1.1 | -0.70 | 7.9 | 0.6 | |||
135 | 10.8: | 9.9: | 7.54 (3) | 0.69 (5) | 0.14 (5) | 0.1 | 0.36 | 3.2 | 1.6 | ||
RXJ1855.1-3754 | 13.05 (5) | 0.62 (3) | 0.57 (3) | 0.3 | -0.82 | 40 | 0.7 |
Broad band photometric observations in the VRI filters were carried out in
1997 from June 22 to 30 using the 0.9 m telescope of Cerro Tololo Interamerican
Observatory (CTIO). The detector was a CCD Tektronix 2048 (CTIO # 3) with pixel
size 24 m and a readout noise of 3 to 5 electrons.
The whole CCD was read out. Dome flat-field exposure sequences in each
filter were taken typically before the beginning and upon the end of every
night for flat field correction. Two or three different standard star fields
from Landolt (1992) were also observed every night at different
airmasses for the determination of atmospheric extinction, zero points and
color transformation to the Johnson-Kron-Cousins standard system.
Raw CCD frames were bias subtracted and flat fielded using the IRAF
package CCDRED. Sky flats were used, and the flat field variation
across the final images was spot-checked and found to be negligible.
The photometric solution for each night was determined using the IRAF
tasks APPHOT and PHOTCAL.
First, an aperture for each night was chosen by inspecting the
reduced images from each night. The average FWHM over the run was
about 1.3
.
To insure that all the light from a given
star was in the aperture, a typical aperture for source extraction
was taken as four times the FWHM or about 6
.
Annuli for background subtraction varied but were usually about
2
from inner diameter to outer diameter with an
inner diameter of about 8
.
The background was taken
as the median value within the annuli. An average of 30
calibration standards were observed each night at various airmasses.
Photometric solutions for each night were determined by fitting the
data to a color dependent airmass equation.
The photometric errors dominate the Poisson errors in most cases.
Once the photometric solution for each night was determined, the target
fields were examined. Aperture photometry was performed on all stars
using the same aperture as was used for the standard stars on that
night. The only exception to this was RXJ1857.5-3732.
In this case, the two stars were separated by less
than 4
.
Therefore we
used the IRAF tool SUBSTAR to subtract one star from the image so we
could accurately measure the instrumental magnitude of the other.
The observed magnitude and colors were obtained by applying the
instrumental magnitudes derived from the aperture to the photometric
equation for the given night.
Results are listed in Table 5.
The near-IR data were obtained using the CTIO Infra-Red Imager,
CIRIM,
on the 1.5 m telescope at CTIO. CIRIM is a 256
256
HgCdTe array. We observed at the f/13.5 focus, giving a plate scale of
0.65 arcsec per pixel. The data were obtained on the nights of 1998 July
8 to 14. All nights were photometric. The stellar
point-spread function is well-sampled photometrically.
Dome flats were taken at the start of each night.
Flats were obtained with the dome illumination lamps both on and off,
to determine the thermal contribution to the flat image.
Standard stars, taken from the lists of Elias (1982) and the UKIRT faint
standards (Casali & Hawarden 1992),
were observed hourly, at a full range of airmasses. Exposure times
varied between 0.4 and 3 seconds, based on source magnitude,
with 3 images coadded at each position. We observed the standard stars
using a 2
2 raster, with 30 arcsec spatial offsets between positions.
We observed the targets using exposure times between 0.4 and 20 seconds,
based on expected source
brightness, with 3 images coadded at each position. We observed
using a 2
3 raster, with spatial offsets of 15 arcsec between frames.
We linearized the data using the IRAF routine IRLINCOR. All other processing
was undertaken using our IDL-based CIRIM reduction
package.
The images are divided by the appropriate normalized flat field image.
The images in the raster pattern are median-filtered to determine the
local sky image, which is then subtracted from each flattened image. The
images in the raster pattern are then aligned by cross-correlating on the
brightest sources in the image, and co-added. The image center and plate
scale are determined
by cross-correlating the images with stars in the USNO catalog (Monet
et al. 1998). The photometric solution is determined by fitting the log of
the standard star counts within a 12-pixel (7.8 arcsec) radius region
as a linear function of the air mass.
The solution is edited interactively to remove discrepant stars and/or points.
The rms scatter in the photometric solutions is 1 to
,
and we take
this to be our photometric precision.
Magnitudes are determined by applying the photometric solution to the
net counts observed in a 12-pixel (7.8 arcsec) radius region. In the case of
close binaries, we determined the total flux using a large extraction radius,
and the relative magnitudes using smaller extraction radii. Typical
uncertainties are
mag, but this degrades for the fainter targets.
Results are listed in Table 5.
Copyright The European Southern Observatory (ESO)