Erratum: ``A Low-Latitude Halo Stream around the Milky Way'' (ApJ, 588, 824 [2003])

Details Erratum: ``A Low-Latitude Halo Stream around the Milky Way'' (ApJ, 588, 824 [2003]) Erratum: ``A Low-Latitude Halo Stream around the Milky Way'' (ApJ, 588, 824 [2003])

Apr 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004apj...605..575y&link_type=abstract

The Astrophysical Journal, Volume 605, Issue 1, pp. 575-577.

Astronomy and Astrophysics

Astronomy

11

Errata, Addenda

Scientific paper

The zero points of the stellar templates used to measure radial velocity in the main body of this paper have been found to be systematically in error. Correction of the radial velocities significantly increases the derived circular velocity of the stars in the planar stream, to 215+/-25 km s-1. The velocity dispersion of the stream is somewhat lower than earlier results with the modified analysis.
Two types of stars were studied in this paper. The original template for stars of type F, used to study the ``Monoceros arc'' Galactic structure, was incorrectly zero-pointed by 20 km s-1. The original template for stars of type A, used to measure the Sagittarius dwarf tidal stream, produced radial velocities systematically shifted by 49 km s-1. In both cases, the sign of the error is such that for nearly all stars, the correct values of the heliocentric radial velocities are lower than those originally quoted.
A cross-correlation of Sloan Digital Sky Survey (SDSS) spectra with templates from the ELODIE survey (C. Soubiran, D. Katz, & R. Cayrel, ApJ, 588, 824 [2003]) was performed to find new radial velocities for each star (D. Schlegel 2003, private communication). This showed that our radial velocities were systematically shifted by an amount that depends on the type of the star observed and the original template against which it was cross-correlated.
To determine the measurement error with the new templates, we identified 445 F-type stars and 1109 A-type stars that had been observed twice by the SDSS. These stars were chosen with the color and magnitude criteria used to select stars in Figures 6 and 9. The errors in the F stars were a good match to a Gaussian with a σ of 28 km s-1. The errors in the A star comparison were significantly non-Gaussian, with large tails. A χ2 fit to a Gaussian (similar to the technique we use in this paper to measure the width of the streams) yielded a σ of 35 km s-1. Dividing by sqrt(2) to reflect two independent measurements, we derive a random error of 20 km s-1 for F stars and 25 km s-1 for A stars. The template matching errors in these blue (type A) stars using ELODIE spectral templates are somewhat larger than the errors with our previous analysis, but we found it useful to use ELODIE spectral templates to ensure that the zero points were accurate.
We also examined the measured stellar stream dispersions. Electronic versions of Figures 2, 6, and 9 of our paper are presented here with the corrected radial velocity determinations. The data were selected as described in the original paper.
Table 1 has been regenerated in its entirety, replacing columns (8) and (10). The radial velocity in column (8) has been replaced with the radial velocity determined from cross-correlation with ELODIE templates. The status flag in column (10) now indicates stars which were used to generate Figure 2. A ``0'' indicates that the star was either outside the color box or had a high cross-correlation error, and a ``1'' indicates that the star was used to fit stream properties.
Table 2 has been regenerated using the new results as well. Column (10) has been added to indicate the estimated number of spectra in the stream component. These numbers are used to compute the error in radial velocity, as described in the original paper. Column (11) shows the corrected circulation velocities, which are now consistent with those given in J. D. Crane, S. R. Majewski, H. J. Rocha-Pinto, P. M. Frinchaboy, M. F. Skrutskie, & D. R. Law (ApJ, 588, 824 [2003]). Note that the velocity dispersions of the planar stream are even tighter than originally measured, strengthening the case that the motion is coherent. Note that the mean velocity of the Sagittarius stream in the direction (l,b)=(165deg,-55deg) is -160 km s-1, in line with recent simulations by D. Martinez-Delgado, M. A. Gomez-Flechoso, A. Aparicio, & R. Carrera (2004, ApJ, in press [astro-ph/0308009]).
We would like to acknowledge Steve Majewski, who initially pointed out to us that radial velocities for stars he had measured in the halo streams were different from our radial velocities by 20-50 km s-1 (J. D. Crane, S. R. Majewski, H. J. Rocha-Pinto, P. M. Frinchaboy, M. F. Skrutskie, & D. R. Law, ApJ, 588, 824 [2003]). We also acknowledge T. Beers, C. Prieto, and R. Wilhelm for an independent radial velocity analysis, with which we could compare our measured radial velocities.

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