[Iaude] CBET 4703: OCCULTATION BY (87)

quai at eps.harvard.edu quai at eps.harvard.edu
Tue Dec 10 18:19:04 EST 2019

                                                  Electronic Telegram No. 4703
Central Bureau for Astronomical Telegrams
Mailing address:  Hoffman Lab 209; Harvard University;
 20 Oxford St.; Cambridge, MA  02138; U.S.A.
e-mail:  cbatiau at eps.harvard.edu (alternate cbat at iau.org)
URL http://www.cbat.eps.harvard.edu/index.html
Prepared using the Tamkin Foundation Computer Network

     F. Vachier and J. Berthier Observatoire de Paris; B. Carry, Observatoire
de la Cote d'Azur; J. Desmars, D. Souami, J. Lecacheux, F. Braga Ribas, and
B. Sicardy, Observatoire de Paris; and dozens of other observers (including
E. Frappa, J. Manek, O. Kloes, A. Pratt, O. Canales, D. Lafuente, P. Andre,
P. M. Berge, J. C. Lachurie, F. Pailler, C. Schnabel, C. Perello, A. Selva,
J. M. Lechopier, F. Van Den Abbeel, O. Schreurs, E. Fernandez, A. Wuensche, M.
Bretton, P. Sogorb, M. Conjat, F. Huebner, J. Ohlert, M. Letz, T. Schaefer,
M. Koch, B. Gaehrken, T. Berthold, R. Koehrbrueck, J. Polak, L. Smid, C.
Weber, S. Molau, K. Halir, D. Ewald, P. Enskonatus, J. Kubanek, J. Lev, M.
Rottenborn, J. Zahajsky, J. Jindra, S. Holy, L. Cervinka, M. Gembec, M. Antos,
T. Kluwak, K. Kaminski, A. Marciniak, A. Wrembel, W. Broczkowski, M. Urbanik,
M. Zawilski, D. Miller, D. Tamonis, N. Morales, J. L. Ortiz, P. Santos-Sanz,
A. Malvache, E. Vanhoutte, F. Marchis, A. Martin, E. Arbouch, and C. Harder),
on behalf of the International Occultation Timing Association (IOTA), report
the successful observation of the occultation of the 10th-magnitude Tycho
Catalogue star TYC 1932-00469-1 by the triple-minor-planet system (87) Sylvia
on 2019 Oct. 29.9885 UTC.  This is the first time that occultations by all the
components of a triple system were simultaneously recorded.  Among 44 reports
(cf. website URL http://www.euraster.net/results/2019/index.html#1029-87),
28 positive chords of the occultation by the primary, lasting between 6.5 and
21.76 s, have been reported.  They confirm the validity of the non-convex
model of (87) that was determined by Hanus et al. (2017, A.Ap. 601, 114),
with its equivalent diameter of 277 +/- 5 km.  Two positive chords of the
occultation observed by (87) Sylvia II = Remus, lasting 0.92 and 0.24 s, and
two positive chords of the occultation by (87) Sylvia I = Romulus, lasting
0.6 and 1.18 s, have also been reported.  The derived relative apparent
positions of the moonlets are, respectively, x = +266 +/- 1 mas, y = -4 +/- 1
mas, and x = +498 +/- 1 mas, y = 131 +/- 1 mas at epoch Oct. 29.985352 UT,
with x = Delta(R.A.) and y = Delta(Decl.).  According to the predicted paths
for the event (cf. URL http://fredvachier.free.fr/results/2019-10-29_87_),
the difference between the observed (O) and computed (C) positions of the
components are O-C(x,y) = (5, 1) mas for Remus, and O-C(x,y) = (5, 0) mas for
Romulus.  A preliminary analysis suggests that Remus is slightly elongated
(7.2 +/- 0.2 by 5.0 +/- 0.1 km), and tends to confirm the elongated shape of
Romulus with a mean axis ratio a/b = 2.7 +/- 0.3 km reported by Berthier et
al. (2014, Icarus 239, 118).

NOTE: These 'Central Bureau Electronic Telegrams' are sometimes
      superseded by text appearing later in the printed IAU Circulars.

                         (C) Copyright 2019 CBAT
2019 December 10                 (CBET 4703)              Daniel W. E. Green

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