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Astron. Astrophys. 348, 1035-1039 (1999)

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5. Results obtained from the analysis of the observational data

A first examination of the observational data was conducted in November 1997 in order to detect as soon as possible potential TNOs. Using the standard method of blinking, each image was examined carefully and visually on a computer screen. This first examination lead to a successful detection of a TNO appearing clearly in the field 3. This object was apparent on four of the five images in the set, the seeing being too degraded on the last one (about 1.6 arcsec). Unfortunatly, this object could not be re-observed by another observer mainly because of its faintness (magnitude 23.6) and, consequently was not officially registered by the IAU. It is now considered lost, because of the very limited time that occurred between the first and last observation.

The positions of the object detected are given in Table 2. Assuming that the object is a 2:3 Neptune librator at perihelion, B.G. Marsden computed the orbital elements given in Table 4 (TNO 1). These elements are, of course, relatively uncertain. Nevertheless, it is interesting to note the high orbital inclination value (32.9o) would be the highest inclination of any known TNO. With an assumed red geometric albedo of 0.04, its diameter must be about 160 km. Fig. 2 is a composite image obtained with the four frames where the object is apparent.

[FIGURE] Fig. 2. Details of the images showing the TNO 1 detected on October 27th, 1997 (see Table 2). In each frame the circle shows its position.


[TABLE]

Table 2. Positions of the TNO 1 detected during the observations conducted the 27th of October 1997 (field 3). Its magnitude was estimated at 23.6[FORMULA]0.3.


The whole observational data were examined a second time by using the program. The critical parameter of the threshold of detection was fixed to 1.5 times the standard deviation due to the sky background noise. Some false detections appeared, a bit less than 4 for each set of images. The visual examination of the detections permitted to eliminate immediatly nearly all the false detections. Indeed these detections appeared nearly always near a bright star and, sometimes, near a galaxy. Only a very limited number of false detections needed to be examined in more details because they appeared to correspond to very weak objects, may be due to the noise, fortuitously aligned.

Finally two detections appeared to correspond to real faint moving objects. The first one was a new TNO, called TNO 2 (appearing in the field 1), and the second one the TNO already detected by the blinking method and mentioned above. The TNO 2 presents an apparent red magnitude of 23.9[FORMULA]0.3. The apparent positions are given in Table 3 and the orbital elements that can be inferred in Table 4. With an assumed red geometric albedo of 0.04 its diameter must be about 180 km.


[TABLE]

Table 3. Positions of the TNO 2 detected during the observations conducted the 27th of October 1997 (field 1). Its magnitude was estimated at 23.9[FORMULA]0.3.



[TABLE]

Table 4. Orbital elements that can be assumed from the data given in Tables 2 and 3. These elements assume that the TNO 1 (Table 2) is a 2:3 Neptune librator at perihelion. For the TNO 2 a circular orbit (e=0) have been assumed. Seen the very limited set of observations used to compute these elements they should be regarded as relatively uncertain.


It is interesting to compare the number of two TNOs detected in observing three fields of 29´[FORMULA]29´ with a limiting red magnitude [FORMULA]24 with the surveys already published. Indeed the more recent published luminosity function of the Kuiper Belt (Jewitt et al. 1998; their Fig. 4) gives an average surface density of about 3 objects brighter than [FORMULA]24 per square degree. For the surface corresponding to three fields of 29´[FORMULA]29´ it would give 2.1 visible objects. This is in good agreement with our results.

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© European Southern Observatory (ESO) 1999

Online publication: August 13, 199
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