Extreme infrared variables from UKIDSS - II. an end-of-survey catalogue of eruptive YSOs and unusual stars

TL;DR

This paper presents a catalogue of 618 high-amplitude infrared variable stars from UKIDSS, predominantly young stellar objects (YSOs), revealing their spatial distribution, spectral properties, and likely variability mechanisms in the Galactic plane.

Contribution

It provides the first large-scale catalogue of high-amplitude infrared variables, especially YSOs, with detailed spatial, spectral, and variability analyses in the Galactic disc.

Findings

60% of variables are YSOs associated with star-forming regions.

Most YSOs are class I or flat spectrum systems.

Variable YSOs likely undergo episodic accretion on yearly timescales.

Abstract

We present a catalogue of 618 high amplitude infrared variable stars (1 < DeltaK < 5 mag) detected by the two widely separated epochs of 2.2 um data in the UKIDSS Galactic plane survey, from searches covering 1470 deg^2. Most were discovered by a search of all fields at 30 < l < 230 deg. Sources include new dusty Mira variables, three new CV candidates, a blazar and a peculiar source that may be an interacting binary system. However, c. 60 per cent are YSOs, based on spatial association with star forming regions at distances ranging from 300 pc to over 10 kpc. This confirms our initial result in Contreras Pena et al.(Paper I) that YSOs dominate the high amplitude infrared variable sky in the Galactic disc. It is also supported by recently published VVV results at 295 < l < 350 deg. The spectral energy distributions of the YSOs indicate class I or flat spectrum systems in most cases, as in the VVV sample. A large number of variable YSOs are associated with the Cygnus X complex and other groups are associated with the North America/Pelican nebula, the Gemini OB1 molecular cloud, the Rosette complex, the Cone nebula, the W51 star forming region and the S86 and S236 HII regions. Most of the YSO variability is likely due to variable/episodic accretion on timescales of years, albeit usually less extreme than classical FUors and EXors. Luminosities at the 2010 WISE epoch range from c. 0.1 Lsun to 10^3 Lsun but only rarely exceed 10^2.5 Lsun.