ADONIS high contrast infrared imaging of Sirius-B

TL;DR

This study uses high contrast infrared imaging with adaptive optics and coronography to explore Sirius's immediate surroundings, providing the deepest infrared images of the system and insights into Sirius-B's properties and potential circumstellar material.

Contribution

First high contrast infrared images of Sirius system in JHKs bands, revealing Sirius-B's photometry and potential circumstellar dust, with implications for detecting exoplanets and understanding white dwarf environments.

Findings

Accurate infrared photometry of Sirius-B consistent with a hot DA white dwarf.

Detection of a small excess in K band suggesting possible circumstellar dust.

No additional companions detected within 25 arcsec, down to 10 Jupiter masses.

Abstract

Sirius is the brightest star in the sky and a strong source of diffuse light for modern telescopes so that the immediate surroundings of the star are still poorly known. We study the close surroundings of the star (2 to 25 arcsec) by means of adaptive optics and coronographic device in the near-infrared, using the ESO/ADONIS system. The resulting high contrast images in the JHKs bands have a resolution of ~ 0.2 arcsec and limiting apparent magnitude ranging from mK = 9.5 at 3 arcsec, from Sirius-A to mK = 13.1 at 10 arcsec. These are the first and deepest images of the Sirius system in this infrared range. From these observations, accurate infrared photometry of the Sirius-B white dwarf companion is obtained. The JH magnitudes of Sirius-B are found to agree with expectations for a DA white dwarf of temperature (T=25000K) and gravity (log(g) = 8.5), consistent with the characteristics determined from optical observations. However, a small, significant excess is measurable for the K band, similar to that detected for "dusty" isolated white dwarfs harbouring suspected planetary debris. The possible existence of such circumstellar material around Sirius-B has still to be confirmed by further observations. These deep images allow us to search for small but yet undetected companions to Sirius. Apart from Sirius-B, no other source is detected within the total 25 arcsec field. The minimum detectable mass is around 10 MJup inside the planetary limit, indicating that an extrasolar planet at a projected distance of ~ 25 AU from Sirius would have been detected (abridged abstract).