A web-based tool to access the optical/near-infrared atlas of the Arecibo sample of OH/IR stars
Agudo-Mérida, Laura 1; Jiménez-Esteban, Francisco M.2; Engels, Dieter 2; García-Lario, Pedro 3
1
3 ISO
VILSPA Satellite Tracking Station, Apartado de Correos 50727, E-28080 Madrid, Spain
2 Hamburger Sterwarte, Gojenbergsweg 112, D-21029 Hamburg, Germany
Data Center, Research and Scientific Support Department of ESA, Villafranca del Castillo, Apartado de Correos 50727, E-28080 Madrid, Spain.
We present a web-based tool which provides an easy and direct access to the optical/near-infrared atlas of the Arecibo sample of OH/IR stars (Jiménez-Esteban et al. 2004)
http://www.laeff.esa.es/users/lam/atlas_Arecibo_OH_IR.html
This atlas includes for the time being the optical and near-infrared finding charts of the majority (96%) of the sample (i.e. 385 sources), where the position of the identified
counterparts are indicated, as well as the astrometric and photometric data (J, H, K) derived from our observations. We also plan to include in the near future the IRAS and
the MSX photometry, and other data collected from the literature whenever this is available.
All of these OH/IR stars are included in an ongoing optical and near-infrared monitoring program started in 1999 aimed at deriving the variability properties of these
objects. As soon as we will be able to derive periods, amplitudes and light curves they will also be made available through this web tool.
Identification of the optical and near-infrared counterparts
The Arecibo Sample:
Optical counterparts:
Finding charts:
Containing 385 sources, this is a well-defined sample of farinfrared selected oxygen-rich AGB stars which were detected in
the 1612 MHz OH maser line with the Arecibo radio telescope
(Eder et al 1998; Lewis et al 1990a; Chengalur et al 1993).
Searching at the same position in the Second Digitized
Sky Survey (DSS2) using the red filter (maximum
efficiency around 6700Å) it was usually easy to confirm
the previous near-infrared identification since no optical
counterpart, or a very faint one, was found at the same
location.
For each star of the sample a finding chart has been
created putting together in a mosaic of 4 frames the optical
image form DSS2 in the upper left panel, and the J (1.25
µm), H (1.65 µm), K (2.20 µm) images from our
observations in the upper right, lower left and lower right
panel, respectively.
The size of all images are 4.6’ x 4.6’.
We have marked the optical and near-infrared counterparts
with a circle in each filter and 3 reference stars (used for
astrometric measurements) with a small circle surrounded
by a square.
In those cases where we have been not able to find an
optical or near-infrared counterpart, we have marked with
a circle the position of the invisible source derived from
the best coordinates available (from MSX or VLA).
An example can be seen in Figure 1.
Near-infrared counterparts:
First we considered the best coordinates available from the
literature.
- IRAS Point Source Catalogue: full sample; accuracy ~10” –
15”
- MSX6C Point Source Catalogue: 249 objects; accuracy ~2”
- VLA (Lewis et al. 1990b): 46 objects; accuracy <1”
Then we searched the near-infrared counterparts at these positions
in our images obtained at Calar Alto. Usually one source was
found around these position being the brightest source in the
near-infrared field and/or showing extremely red colours.
However, in crowded fields or with very faint objects only visible
in the K-band, variability between two observing epochs was the
only way to confirm our identification.
Results:
- 61% of the sample have both optical and near-infrared
counterpart.
- 28% have a bright near-infrared counterpart but nothing
was found on the DSS2 image above the detection limit
(~20.8m).
- 9% only have a K-band counterpart.
- And for 2% of the sample (8 objects) neither in the nearinfrared nor in the optical the counterpart were identified
above the detection limits.
Derivation of improved coordinates
To improve the astrometry, we first compared the optical and
near-infrared fields in order to identify at least three reference
stars visible in all the images. Using the relative distance
between the Arecibo source and the reference stars in the nearinfrared images, we could determine the position of the
counterpart on the optical image with an accuracy of less than
one pixel.
If an optical counterpart was found, we derived the new
coordinates directly from the DSS2 image by determining the
centroid of the point-like emission associated to the optical
counterpart. But if we only had a near-infrared counterpart, we
derived the new coordinates from its relative position to the
reference stars in the near-infrared image, which were always
selected to have point-like optical counterparts.
Thanks to the astrometric accuracy (1”/pixel) of the DSS2
images we could improve the accuracy of the astronomical
coordinates of our objects up to an estimated error of only
~1” both in right ascension and in declination.
To analyze the reliability of our new coordinates we compared
them with those previously obtained from the literature. In Table
1 we list the median and the mean separation in right ascension
(α) and in declination (δ) between our Calar Alto coordinates and
the IRAS, MSX and VLA ones, together with the associated
standard deviations.
As we expected, there is a good agreement with MSX and VLA
data. Also we verified that the differences found between Calar
Alto and IRAS coordinates were similar to those found between
MSX/VLA and IRAS coordinates. So, large but consistent
deviations can be attributed to the large errors of IRAS
coordinates.
Coordinates
comparison
N
CA-IRAS
CA-MSX
CA-VLA
363
243
44
∆α
median
3,1"
1,4"
1,0"
∆ α (σ ∆ α )
mean
5.6" (7.1")
1.5" (1.4")
1.0" (0.8")
∆δ
median
2.0"
1.0"
0.6"
∆ δ (σ ∆ δ )
mean
2.3" (2.2")
1.3" (1.4")
1.1" (1.4")
Table 1. Differences between the Calar Alto (CA) coordinates and the IRAS,
MSX and VLA ones.
Figure 1. Finding chart of IRAS 19323+1652.
The web-based tool
This web-based tool was developed following the HTML (HyperText Markup Language) 4.01 specifications of the World Wide Web Consortium W3C®.
Figures 2, 3 and 4 show the description of the information that will be accesible from the different web pages. There are two different levels of information: the first one is devoted to summarize the
main properties of the atlas (Fig. 2:sample description, table information, data accuracy, etc.), and the second one (Figs. 3 and 4) shows the specific information on the selected sources. Finding charts
appear on the top, and tables with coordinates and photometry are provided at the bottom. Permanent access to this information is possible by clicking on the IRAS star name.
As this is an ongoing project, future information (new photometric data, variability analisis, ...) will be included as soon as they will become available.
Figure 2 (left). The portal of the Arecibo atlas web
page contains a general description of the atlas contents
and access to:
- optical and near-infrared finding charts
- astrometric data: CA, MSX, IRAS and VLA.
- photometric data: J, H and K bands.
Figures 3, 4 (rigth): The web pages showing specific
information on individual sources are composed of two
frames:
Left frame: it shows the list of all sources available in
the sample with links to the individual web pages.
Right frame: it displays specific information about the
individual source selected and about the data available
for the star (Fig. 3 is an example of finding chart and
Fig. 4 is an example of the coordinates and photometric
information displayed).
Conclusions
We have presented an atlas of optical/near-infrared finding charts, improved coordinates (accuracy
~1”) and near-infrared photometric data for 371 objects taken from the ‘Arecibo sample of OH/IR
stars’. This new web-based tool provides a rapid access to all these data and constitutes a useful
database for further multiwavelength study of these objects.This atlas is the starting point of a longterm optical/near-infrared monitoring program started in 1999 devoted to study the photometric
properties of these AGB stars in the context of stellar evolution.
References:
Jiménez-Esteban, F. M., Agudo-Mérida, L., Engels, D., García-Lario, P. 2004 A&A (accepted)
Eder, J., Lewis, B.M. &Terzian, Y. 1988, ApJS, 66, 183
Lewis, B.M., Eder, J. & Terzian, Y. 1990a, ApJ 362, 634
Chengalur, J.N., Lewis, B.M., Eder, J. & Terzian, Y. 1993, ApJS, 89, 189
Lewis, B.M., Chengalur, J.N., Schmelz, J., & Terzian, Y. 1990b, MNRAS, 246, 523