[vsnet-chat 1367] Re: [AAVSO-DIS] TU Aql

[Taichi Kato <tkato>]

Re: [AAVSO-DIS] TU Aql

   I have examined the field using GSC 1.1 and USNO A1.0 and found the
things are not so simple.  (Observationally the southern component of the
pair is indeed TU Aql).

   There are three different entries (rather than the two given by Kasai)
in GSC 1.1.

GSC469.4113 192736.30 +020320.0 (2000.0) 11.06 0 N
GSC469.5852 192736.36 +020314.1 (2000.0)  8.94 1 N
GSC469.4099 192736.29 +020312.8 (2000.0) 13.72 0 N

   I understand the pair GSC 469.4113 and 469.4099, and another GSC 469.5852
were measured from different plates.  The latter could not resolve the pair
(or the variable near maximum epoch), giving a brighter magnitude.  The GSC
team seems to have assigned different numbers to these different detections
based on the positional difference.

   The brighter two of the GSC entries are given in USNO A1.0, but are only
copies of the GSC measurements, not true detections.  Quite interestingly,
USNO A1.0 gives another star slightly north of these GSC entries.  This is
the single true detection in USNO A1.0.

USNO0900.15270880 192736.398 +020323.08 (2000.0) 10.6 11.5

   It may be possible TU Aql was near minimum at this epoch, and the northern
component was measured (the color is neutral).  The Hipparcos position lies
south of this position; not inconsistent with the component identification.

   Another interesting point in the Hipparcos entry of TU Aql is that no
parallax measurement is given for this star.  It may be possible no 'formal'
solution was possible owing to the presence of the northern companion, and
it may have been possible the astrometry was mistakenly from the HIC
(Hipparcos Input Catalogue).

   Considering these above, the two GSC stars Kasai originally listed may
not correctly refer to the TU Aql and its companion.  Independent astrometry
of the field would solve the inconsistencies.

Regards,
Taichi Kato

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