Erratum: The tidal tails of 47 Tucanae



This article corrects:

  1. The tidal tails of 47 Tucanae Volume 423, Issue 3, 2845–2853, Article first published online: 17 May 2012

E-mail: (RRL); (AHWK); (DCH)

The paper ‘The tidal tails of 47 Tucanae’ was published in Mon. Not. R. Astron. Soc. 423, 2845–2853 (2012). An error was discovered which affected the results reported in that paper. This error is corrected here.

We used, for our proper motion of 47 Tucanae (47 Tuc), the values published by Anderson & King (2004); however, we incorrectly adjusted the published values of μα by cos δ. These values were already published with the cos δ included so this was unnecessary. Our new reference model for this Erratum uses proper motions

display math(1)
display math(2)

All other input parameters were correct and are left unchanged. All references for, and reasons behind, our choices for the input parameters can be found in the original paper. The newly computed models are presented in the following.

The orbit

The last 500 Myr of the (x, y) and (x, z) orbital paths of 47 Tuc derived from the new proper motion and radial velocity of the cluster are shown in Fig. 1. Owing to the significant change in proper motion, various orbital parameters have been altered. The new quantities, defined as per the original paper, are listed in Table 1. We particularly note that (for our choice of Galaxy model) the orbit of 47 Tuc is less eccentric than originally thought (ε = 0.11) and that 47 Tuc is very close to reaching the apocentre of its orbit (porb = +0.97).

Figure 1.

The orbital path of 47 Tuc from 500 Myr ago to the present time in the (x, y) plane (top panel) and in the (x, z) plane (bottom panel), based on parameters from the corrected proper motions (see text). The present-day position of 47 Tuc is marked as a plus (+) symbol and the position of the Sun is marked as a cross (×). Corresponds to fig. 2 of the original paper.

Table 1. Revised orbital parameters of the reference model
Edge radius142 pc
Minimum orbital velocity179 km s−1
Maximum orbital velocity254 km s−1
Current orbital velocity184 km s−1
Apocentre7.65 kpc
Pericentre6.10 kpc
Current Galactocentric distance7.60 kpc
Orbital eccentricity0.11
Orbital phase+0.97

The tidal tails

Figs 2-8 in this Erratum are based on our new models, and correspond to figs 3–9 from the original paper. Table 2 summarizes our corrected results. Qualitatively, the results are effectively equivalent, but the shapes of the tidal tails and, therefore, the positions of their overdensities have changed.

Figure 2.

The final time-step for the reference model. Corresponds to fig. 3 from the original paper.

Figure 3.

As for Fig. 2 except with warm (top) and hot (bottom) escape conditions. Corresponds to fig. 4 of the original paper.

Figure 4.

Contour representation of Fig. 3 with ‘warm’ escape conditions in the top panel and ‘hot’ escape conditions in the bottom panel. Corresponds to fig. 5 of the original paper.

Figure 5.

As for the top panel of Fig. 4, except with μα cos δ = 4.23 mas yr−1 (top panel) and μα cos δ = 7.05 mas yr−1 (bottom panel). Corresponds to fig. 6 of the original paper.

Figure 6.

As for the top panel of Fig. 4, except with μδ = −1.54 mas yr−1 (top panel) and μδ = −2.56 mas yr−1 (bottom panel). Corresponds to fig. 7 of the original paper.

Figure 7.

As for the top panel of Fig. 4, except with M = 0.9 × 106 M (top panel) and M = 1.1 × 106 M (bottom panel). Corresponds to fig. 8 of the original paper.

Figure 8.

As for the top panel of Fig. 4, except with Dhelio = 3.3 kpc (top panel) and Dhelio = 4.7 kpc (bottom panel). Corresponds to fig. 9 of the original paper.

Table 2. The density and Galactic coordinates of the first- and second-order overdensities, the proper motion, final (present-day) cluster mass, heliocentric distance and escape conditions for each of our corrected models. Only the trailing tail is represented here for brevity. Information is for the peak density in each overdensity only. Note that the approximate average density of the stellar background in the regions of the first and second tidal overdensities is 3000 stars per square degree, based on 2MASS point sources
ModelΣ1 stars per deg2Σ2 stars per deg2(l, b)1 deg(l, b)2 degμαcos δ mas yr−1μδ mas yr−1× 106 MD kpcEsc


The authors gratefully thank Radek Poleski for bringing the error to our attention.