Bibcode
Costa, Edgardo; Méndez, René A.; Pedreros, Mario H.; Moyano, Maximiliano; Gallart, C.; Noël, Noelia
Bibliographical reference
The Astronomical Journal, Volume 141, Issue 4, article id. 136 (2011).
Advertised on:
4
2011
Citations
21
Refereed citations
20
Description
We present new results from a ground-based program to determine the
proper motion of the Magellanic Clouds (MCs) relative to background
quasars (QSOs), being carried out with the Iréneé du Pont
2.5 m telescope at Las Campanas Observatory, Chile. The data were
secured over a time base of seven years and with eight epochs of
observation "As measured" (field) proper motions were obtained for five
QSO fields in the Small Magellanic Cloud (SMC): QJ0033-7028,
QJ0035-7201, QJ0047-7530, QJ0102-7546, and QJ0111-7249. Assuming that
the SMC has a disklike central structure, but that it does not rotate,
we determined a center-of-mass (CM) proper motion for the SMC from two
of these fields, QJ0033-7028 and QJ0035-7201, located to the northwest
and west of the main body of the SMC, respectively. Combining these
latter proper motions with the CM proper motion presented by Costa et
al. (hereafter CMP09) for the SMC (from the field QJ0036-7227, located
to the west of the main body of the SMC), we obtain a weighted mean of
μα cos δ = +0.93 ± 0.14 mas
yr-1 and μδ = -1.25 ± 0.11 mas
yr-1. This CM proper motion is in good agreement with recent
results by Piatek et al. and Vieira et al., and we are confident that it
is a good representation of the "bulk" transverse motion of the SMC. On
the contrary, the results we obtain from the fields QJ0047-7530 and
QJ0102-7546, located to the south of the main body of the SMC, and the
field QJ0111-7249, located to the east of its main body, seem to be
affected by streaming motions. For this reason, we have not used the
latter to determine the SMC CM proper motion. These streaming motions
could be evidence that the SMC was tidally disrupted in a close
encounter with the Large Magellanic Cloud (LMC). Complementing the SMC
CM proper motions given here and in CMP09, with the currently accepted
radial velocity of its center, we have derived its galactocentric (gc)
velocity components, obtaining a weighted mean of V gc,t =
+289 ± 25 km s-1 and V gc,r = +14 ±
24 km s-1. These velocities, together with the galactocentric
velocity components given for the LMC in CMP09, imply a relative
velocity between the LMC and SMC of 67 ± 42 km s-1 for
V rot,LMC = 50 km s-1 and of 98 ± 48 km
s-1 for V rot,LMC = 120 km s-1. Despite
our large errors, these values are consistent with the standard
assumption that the MCs are gravitationally bound to each other.