The Wavelength Dependence of Interstellar Extinction from 1.25 to 8.0 μm Using GLIMPSE Data

Abstract

We determine and tabulate A [λ] /A K , the wavelength dependence of interstellar extinction, in the Galactic plane for 1.25µm ≤ λ ≤ 8.0µm along two lines of sight: l = 42 • and l = 284 • . The first is a relatively quiescent and unremarkable region; the second contains the giant H II region RCW 49 as well as a "field" region unrelated to the cluster and nebulosity. Areas near these Galactic longitudes were imaged at J, H, and K bands by 2MASS and at 3-8µm by Spitzer for the GLIMPSE Legacy program. We measure the mean values of the color excess ratios (A [λ] − A K )/(A J − A K ) directly from the color distributions of observed stars. The extinction ratio between two of the filters, e.g. A J /A K , is required to calculate A [λ] /A K from those measured ratios. We use the apparent JHK magnitudes of giant stars along our two sightlines, and fit the reddening as a function of magnitude (distance) to determine A J /kpc, A K /kpc, and A J /A K . Our values of A [λ] /A K show a flattening across the 3-8µm wavelength range, roughly consistent with the Lutz et al. (1996) extinction measurements derived for the sightline toward the Galactic center.

SS 433: a phenomenon imitating a Wolf-Rayet star

“…As an example, Moneti et al (2001) used the Lutz law to deredden their 2.5-8 µm ISO data on the Quintuplet Cluster, although this young cluster is in the vicinity of the Galactic Centre. Indebetouw et al (2005) presented very recent extinction measurements in the 1.25-8.0 µm range along the l = 42 • and l = 284 • line of sight in the galactic plane, which are similar and consistent with measurements of Lutz et al (1996) toward the Galactic Centre. This shows that the Lutz law could almost be universal or, at least, more common than previously thought.…”

Infrared spectroscopy of asymptotic giant branch stars in the Galactic bulge

“…Indeed, it is well known that the IR extinction towards the GC has a somewhat different shape than the extinction in the local ISM (Lutz et al 1996); moreover, there is more silicate per unit of visual extinction towards the GC compared to the local ISM, resulting in a stronger 10-µm feature in the GC extinction curve. These extinction laws are consistent with earlier work by Lutz et al (1996) and Indebetouw et al (2005). On the other hand, Román-Zúñiga et al (2007) found small differences with Chiar & Tielens (2006), indicating that the extinction law in the near-and mid-IR may vary slightly as a function of environment.…”

Spatial distribution of Galactic Wolf–Rayet stars and implications for the global population

“…Indebetouw et al (2005). For the purpose of calculating the absolute magnitude of each calibration star, we take an average,ĀK S , from Equations 1 and 2.…”

“…For the purpose of calculating the absolute magnitude of each calibration star, we take an average,ĀK S , from Equations 1 and 2. Since extinction in the IRAC bands is lower, we opt for a more straightforward approach and use the relations given by Indebetouw et al (2005), independent of sight line.…”