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Abstract: We assess the practicality of computing the distance to stellar streams inour Galaxy, using the method of Galactic parallax suggested by Eyre and Binney2009. We find that the uncertainty in Galactic parallax is dependent upon thespecific geometry of the problem in question. In the case of the tidal streamGD-1, the problem geometry indicates that available proper motion data, withindividual accuracy ~4 mas-yr, should allow estimation of its distance withabout 50 percent uncertainty. Proper motions accurate to ~1 mas-yr, which areexpected from the forthcoming Pan-STARRS PS-1 survey, will allow estimation ofits distance to about 10 percent uncertainty. Proper motions from the futureLSST and Gaia projects will be more accurate still, and will allow the parallaxfor a stream 30 kpc distant to be measured with ~14 percent uncertainty.We demonstrate the feasibility of the method and show that our uncertaintyestimates are accurate by computing Galactic parallax using simulated data forthe GD-1 stream. We also apply the method to actual data for the GD-1 stream,published by Koposov et al. 2009. With the exception of one datum, thedistances estimated using Galactic parallax match photometric estimates withless than 1 kpc discrepancy. The scatter in the distances recovered usingGalactic parallax is very low, suggesting that the proper motion uncertaintyreported by Koposov et al. 2009 is in fact over-estimated.We conclude that the GD-1 stream is 8 +- 1 kpc distant, on a retrogradeorbit inclined 37 deg to the plane, and that the visible portion of the streamis likely to be near pericentre.



Autor: Andy Eyre

Fuente: https://arxiv.org/







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