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

Abstract

We present a catalogue of 618 high amplitude infrared variable stars (1 < ∆K < 5 mag) detected by the two widely separated epochs of 2.2 µm 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 • . Sources include new dusty Mira variables, three new CV candidates, a blazar and a peculiar source that may be an interacting binary system. However, ∼60% 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 Peña 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 • . 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 ∼0.1 L to 10 3 L but only rarely exceed 10 2.5 L .

Discovery of a mid-infrared protostellar outburst of exceptional amplitude

“…YSOs dominate the Galactic population of high amplitude near infrared variable stars (Contreras Peña et al 2014, 2017aLucas et al 2017). Given that our search was focussed on IRDCs we would therefore expect most of the 23 variable stars in Table 1 to be YSOs.…”

“…YSOs in the Galactic plane. All the YSO candidates lie in the "YSO region" of the W1 − W2 vs. W3 − W4 diagram that distinguishes YSOs from AGB stars, as defined separately by Koenig & Leisawitz (2014) and Lucas et al (2017), with the exception of source 2 in Table 1, see section 3.1. (We used the WISE All-Sky database to provide contemporaneous colours for this assessment).…”

“…Many of the sources were previously identified as YSO candidates in the infrared colour and SED-based searches of Robitaille et al (2008, Marton et al (2016) or by the time domain searches of (Contreras Peña et al 2017a;Lucas et al 2017) using VVV and the UKIDSS Galactic Plane Survey (Lawrence et al 2007;Lucas et al 2008). Sources 13 and 23 in Table 1 were listed as possible AGB stars by Robitaille et al (2008) but classified as YSOs by Marton et al (2016).…”

The VMC survey – XXXVI. Young stellar variability in the Large Magellanic Cloud

“…The longer exposure time for K s aims at increasing the likelihood of detecting young variables since several Galactic studies have shown that variability in this filter is common amongst young stars (e.g. Contreras Peña et al 2014;Lucas et al 2017). It also allows us to better probe high-extinction regions, where young stars are preferentially located.…”

Near-infrared time-series photometry in the field of Cygnus OB2 association

“…This is especially powerful in the faint limits of optical and infrared surveys, where they are incomplete, and the young stars become blended with reddened background stars. In recent years, various variability surveys have used near-IR to unveil disk-bearing stars both in clusters and associations (e.g., Rice et al 2012;Wolk et al 2013;Meng et al 2019) as well as in the field (e.g., Lucas et al 2017). Recognizing the typical variability of disk-bearing stars requires determining the occurrence and prevalence of different variability mechanisms.…”