Anomalous surface brightness fluctuations in NGC 4489^*

¹ Observatoire Midi-Pyrénées, 14 Av. E. Belin, 31400 Toulouse, France
² European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany

Corresponding author: S. Mei, mei@ast.obs-mip.fr

Received: 18 February 2000
Accepted: 30 October 2000

Abstract

Anomalously high K-band surface brightness fluctuations (SBF) have been reported in NGC 4489 by Pahre & Mould ([CITE]), Jensen et al. ([CITE]) and Jensen et al. ([CITE]). However, these conclusions were uncertain because of relatively low signal-to-noise data. New high signal-to-noise data for NGC 4489 have been obtained at the NOAO/KPNO 2.1 m and the ESO/La Silla 3.5 m NTT telescopes. Adopting the I-band SBF distance modulus determined by Tonry et al. ([CITE]) and the versus () calibration of Tonry et al. ([CITE]), a value of mag was derived. Relative to the average empirical derived for giant ellipticals by Jensen et al. ([CITE]) ( mag), the detection of an anomalous K-band SBF in NGC 4489 is confirmed at the two sigma level. Such anomalous fluctuations could be caused by an extended giant branch, consisting of either intermediate-age AGB stars above the tip of the first-ascent giant branch or high-metallicity first-ascent giants, or by lack of a full understanding of the K-band SBF calibration. This result raises questions about the accuracy of K-band SBF distance measurements for elliptical galaxies with unknown stellar composition and underscores the need for measurements over a larger range of color and luminosity.