THE PROPER MOTION OF THE MAGELLANIC CLOUDS. I. FIRST RESULTS AND DESCRIPTION OF THE PROGRAM
- Departamento de AstronomIa, Universidad de Chile, Casilla 36-D, Santiago (Chile)
- Departamento de Fisica, Universidad de Tarapaca, Casilla 7-D, Arica (Chile)
- Instituto de AstrofIsica de Canarias, Tenerife 38200, Islas Canarias (Spain)
- Facultad de Ciencias Astronomicas y GeofIsicas de la UNLP, IALP-CONICET, Paseo El Bosque s/n, La Plata (Argentina)
- European Southern Observatory, Alonso de Cordova 3107, Santiago (Chile)
We present the first results of a ground-based program to determine the proper motion of the Magellanic Clouds (MCs) relative to background quasars (QSO), being carried out using the Irenee du Pont 2.5 m telescope at Las Campanas Observatory, Chile. Eleven QSO fields have been targeted in the Small Magellanic Cloud (SMC) over a time base of six years, and with seven epochs of observation. One quasar field was targeted in the Large Magellanic Cloud (LMC), over a time base of five years, and with six epochs of observation. The shorter time base in the case of the LMC is compensated by the much larger amount of high-quality astrometry frames that could be secured for the LMC quasar field (124 frames), compared to the SMC fields (an average of roughly 45 frames). In this paper, we present final results for field Q0557-6713 in the LMC and field Q0036-7227 in the SMC. From field Q0557-6713, we have obtained a measured proper motion of {mu}{sub {alpha}}cos {delta} = +1.95 {+-} 0.13 mas yr{sup -1}, {mu}{sub {delta}} = +0.43 {+-} 0.18 mas yr{sup -1} for the LMC. From field Q0036-7227, we have obtained a measured proper motion of {mu}{sub {alpha}} cos{delta} = +0.95 {+-} 0.29 mas yr{sup -1}, {mu}{sub {delta}} = -1.14 {+-} 0.18 mas yr{sup -1} for the SMC. Although we went through the full procedure for another SMC field (QJ0036-7225), on account of unsolvable astrometric difficulties caused by blending of the QSO image, it was impossible to derive a reliable proper motion. Current model rotation curves for the plane of the LMC indicate that the rotational velocity (V {sub rot}) at the position of LMC field Q0557-6713 can be as low as 50 km s{sup -1}, or as high as 120 km s{sup -1}. A correction for perspective and rotation effects leads to a center of mass proper motion for the LMC of {mu}{sub {alpha}} cos{delta} = +1.82 {+-} 0.13 mas yr{sup -1}, {mu}{sub {delta}} = +0.39 {+-} 0.15 mas yr{sup -1} (V {sub rot} = 50 km s{sup -1}), and to {mu}{sub {alpha}} cos{delta} = +1.61 {+-} 0.13 mas yr{sup -1}, {mu}{sub {delta}} = +0.60 {+-} 0.15 mas yr{sup -1} (V {sub rot} = 120 km s{sup -1}). Assuming that the SMC has a disk-like central structure, but that it does not rotate, we obtain a center of mass proper motion for the SMC of {mu}{sub {alpha}} cos{delta} = +1.03 {+-} 0.29 mas yr{sup -1}, {mu}{sub {delta}} = -1.09 {+-} 0.18 mas yr{sup -1}. Our results are in reasonable agreement with most previous determinations of the proper motion of the MCs, including recent Hubble Space Telescope measurements. Complemented with published values of the radial velocity of the centers of the LMC and SMC, we have used our proper motions to derive the galactocentric (gc) velocity components of the MCs. For the LMC, we obtain V {sub gc,t} = +315 {+-} 20 km s{sup -1}, V {sub gc,r} = +86 {+-} 17 km s{sup -1} (V {sub rot} = 50 km s{sup -1}), and V {sub gc,t} = +280 {+-} 24 km s{sup -1}, V {sub gc,r} = +94 {+-} 17 km s{sup -1} (V {sub rot} = 120 km s{sup -1}). For the SMC, we obtain V {sub gc,t} = +258 {+-} 50 km s{sup -1}, V {sub gc,r} = +20 {+-} 44 km s{sup -1}. These velocities imply a relative velocity between the LMC and SMC of 84 {+-} 50 km s{sup -1}, for V {sub rot,LMC} = 50 km s{sup -1}, and 62 {+-} 63 km s{sup -1} for V {sub rot,LMC} = 120 km s{sup -1}. Albeit our large errors, these values are not inconsistent with the standard assumption that the MCs are gravitationally bound to each other.
- OSTI ID:
- 21269186
- Journal Information:
- Astronomical Journal (New York, N.Y. Online), Vol. 137, Issue 5; Other Information: DOI: 10.1088/0004-6256/137/5/4339; Country of input: International Atomic Energy Agency (IAEA); ISSN 1538-3881
- Country of Publication:
- United States
- Language:
- English
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