Constraining dust extinction properties via the VVV survey

¹ Mount Saint Vincent University, Halifax, NS B3M 2J6, Canada
e-mail: dmajaess@ap.smu.ca
² Department of Astronomy & Physics, Saint Mary’s University, Halifax, NS B3H 3C3, Canada
³ Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstr. 12-14, 69120 Heidelberg, Germany
⁴ The Millennium Institute of Astrophysics (MAS), 36- D Santiago, Chile
⁵ Departamento de Ciencias Físicas, Universidad Andrés Bello, Campus La Casona, Fernández Concha 700, Santiago, Chile
⁶ Vatican Observatory, V 00120 Vatican City State, Italy
⁷ Universidad de Concepción, Departamento de Astronomía, Casilla 160-C, Concepción, Chile

Received: 21 April 2016
Accepted: 28 July 2016

Abstract

Near-infrared color-excess and extinction ratios are essential for establishing the cosmic distance scale and probing the Galaxy, particularly when analyzing targets attenuated by significant dust. A robust determination of those ratios followed from leveraging new infrared observations from the VVV survey, wherein numerous bulge RR Lyrae and Type II Cepheids were discovered, in addition to BVJHK_s(3.4 → 22) μm data for classical Cepheids and O stars occupying the broader Galaxy. The apparent optical color-excess ratios vary significantly with Galactic longitude (ℓ), whereas the near-infrared results are comparatively constant with ℓ and Galactocentric distance (). The results derived imply that classical Cepheids and O stars display separate optical trends (R_V,BV) with ℓ, which appear to disfavor theories advocating a strict and marked decrease in dust size with increasing Galactocentric distance. The classical Cepheid, Type II Cepheid, and RR Lyrae variables are characterized by ⟨A_J/E(J−K_s)⟩ = ⟨R_J,JKs⟩ = 1.49 ± 0.05 (⟨A_Ks/A_J⟩ = 0.33 ± 0.02), whereas the O stars are expectedly impacted by emission beyond 3.6 μm. The mean optical ratios characterizing classical Cepheids and O stars are approximately ⟨R_V,BV⟩ ~ 3.1 and ⟨R_V,BV⟩ ~ 3.3, respectively.