A Polarimetric Survey for Dust in 47 Tucanae (NGC 104)

Abstract

We present linear polarization in the V band for 77 stars in the field of the globular cluster 47 Tucanae (NGC 104), and for 14 bright-star-free regions, located along an elliptical isophotal contour of the cluster, as well as UBVRI measurements for the cluster nucleus. The observations show variable foreground polarization that, once removed, leaves marginally significant polarization residuals for the non-variable bright red giants. Although these residuals are small there is, however, a systematic trend in the sense that the larger ones are seen towards the south of the cluster (in a direction opposite to that of the cluster proper motion). In contrast, most of the variable stars do show significant intrinsic polarization. The behavior of the star-free regions is similar to that of the non-variable stars and sets an upper limit to the possible existence of a global pattern of scattered (and polarized) intra-cluster light in the V band. In turn, the multicolor observations of the cluster nucleus cannot be fitted with a Serkowski law and exhibit a polarization excess both in U and B. This polarization could be explained as a combination of the foreground interstellar component and another one arising in dust located in the nucleus and illuminated by a bright blue post-AGB star (at 48" from the cluster center). An inspection of a set of archive HST WFPC2 images reveals the presence of a number of dark patches in the innermost regions of the cluster. A prominent patch (some 5" by 3" in size) located at 12" from the cluster center and with a position angle (N to E) of 120 degrees, has a slightly different polarization, compared to that of the cluster nucleus, and appears as a good candidate to be identified as a dust globule within the cluster.

AASTeX v5.0.2, Submitted to the Astronomical Journal, 20 pages (including title-page and tables.), 11 figures (16 PostScript files), 5 tables

References in corpus (3)

• Detection of ionized gas in the globular cluster 47 Tucanae
• Evolution of the dust mass loss with luminosity along the giant branch of the globular cluster 47 Tuc
• A Polarimetric Survey for Dust in 47 Tucanae (NGC 104)

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• Incidence of the host galaxy on the measured optical linear polarization of blazars
• A Polarimetric Survey for Dust in 47 Tucanae (NGC 104)
• Observations of the Bright Star in the Globular Cluster 47 Tucanae (NGC 104)