Interstellar extinction law toward the Galactic center. IV. J, H, and Ks bands from VVV red clump stars

Abstract

Abstract We have determined the wavelength dependence of the extinction in the near-infrared bands (J, H, Ks) toward the Galactic center from the VVV (VISTA Variables in the Vía Láctea) aperture photometry of the stars in the region |l| ≲ 2${^{\circ}_{.}}$0 and 0${^{\circ}_{.}}$5 ≲ |b| ≲ 1${^{\circ}_{.}}$0; this region consists of 12 VVV tiles. We have found significant systematic discrepancy up to ∼0.1 mag between the stellar magnitudes of the same stars in overlapping VVV tiles. However, by carefully using the positions of red clump stars in color–magnitude diagrams as a tracer of the extinction and reddening, we are able to determine the average of the ratios of total to selective extinction to be $A(K_{\mathrm{s}}) / E(H-K_{\mathrm{s}}) = 1.44\, \pm \, 0.04$, $A(K_{\mathrm{s}}) / E(J-K_{\mathrm{s}}) = 0.423\, \pm \, 0.024$, $A(H) / E(J-H) = 1.25\, \pm \, 0.04$; from these ratios, a steep power law A(λ) ∝ λ−α whose index α is ∼2.0–2.3 in the J, H, Ks wavelength range is estimated. This wavelength dependence is consistent with those obtained with the Mauna Kea Observatory photometric system employed in the Simultaneous 3-color InfraRed Imager for Unbiased Survey camera attached to the Infrared Survey Facility telescope in previous studies. Such a steep decline of extinction toward the longer wavelengths is also in line with recent results based on deep imaging surveys. The determined extinction law seems to be variable in the VVV from tile to tile, and it is not clear how much of this is due to real sight line variations and how much is due to observational systematic effects. Thus, there might be room for improvement of the extinction law determination from the existing VVV data, but this steep extinction law tends to locate heavily reddened objects in the Galactic plane more distant from us when their distance moduli are calculated from the observed reddening values.