Interstellar Extinction in Galactic Cirri in SDSS Stripe 82

TL;DR

This study measures interstellar extinction in five Galactic cirri using star counts and multi-band photometry, revealing that the extinction law varies from the standard model and often includes significant gray extinction.

Contribution

It introduces a method combining star counts with multi-band photometry to determine extinction laws in Galactic cirri, highlighting deviations from the standard extinction law.

Findings

Extinction distances range from 140 to 415 pc.

Extinction law often deviates from Cardelli+1989 with R_V=3.1.

Gray extinction contributes significantly in some cirri.

Abstract

We have applied the method of star counts with Wolf diagrams to determine the interstellar extinction in five Galactic cirri in Sloan Digital Sky Survey (SDSS) Stripe 82. For this purpose, we have used the photometry of stars in the GALEX NUV filter and the photometry of red dwarfs in five SDSS bands and four SkyMapper Southern Sky Survey DR2 bands. We have identified the cirri as sky regions with an enhanced infrared emission from the Schlegel+1998 map. The extinction in them has been calculated relative to the nearby comparison regions with a reduced emission. The results for different filters agree well, giving the range of distances and the extinction law for each cirrus. The distances in the range 140--415 pc found are consistent with the 3D reddening maps. In the range between the $B$ and $V$ filters the extinctions found are consistent with the estimates from Schlegel+1998 for the Cardelli+1989 extinction law with $R_\mathrm{V}=3.1$. However, the extinctions found for all of the filters are best described not by the Cardelli+1989 extinction law with some $R_\mathrm{V}=3.1$, but by the inverse proportionality of the extinction and wavelength with its own coefficient for each cirrus. In one of the cirri our results suggest a very slight decrease in extinction with wavelength, i.e., a large contribution of gray extinction. In the remaining cirri a manifestation of gray extinction is not ruled out either. This is consistent with the previous measurements of the extinction law far from the Galactic midplane.