Eruptive YSOs in Cygnus-X: a mid-infrared variability study with NEOWISE and SPICY

TL;DR

This study analyzes decade-long mid-infrared variability of young stellar objects in Cygnus-X, revealing a higher prevalence of eruptive behavior among younger Class I stars and identifying new candidate eruptive variables.

Contribution

It provides the first comprehensive mid-infrared variability analysis of YSOs in Cygnus-X, highlighting the increased eruptive activity in early evolutionary stages and characterizing their photometric behaviors.

Findings

Higher incidence of eruptive YSOs among Class I objects.

Many eruptive YSOs show redder-when-brighter MIR behavior.

Identification of four long-term rising YSO behaviors.

Abstract

The mass accretion process controls pre-main-sequence evolution, although its intrinsic instability has yet to be fully understood, especially towards the protostellar stage. In this work, we have undertaken a thorough examination of the mid-infrared variability of Spitzer-selected YSOs in the Cygnus-X star-forming region over the last decade, using the NEOWISE time series. This work compares two groups of young stars: embedded Class I objects, and the more evolved flat-spectrum/Class II sources. We report on 48 candidate eruptive variables within these groups, including 14 with characteristics that resemble the photometric behaviour of FUors. We also include an additional 20 YSOs, which are of a less certain categorisation. We find the candidate FUors to be an order of magnitude more common among the younger Class I systems than more evolved objects. A large number of the identified short-duration eruptive YSOs display mid-infrared colour behaviour that is redder-when-brighter, which contrasts with optically bright outbursts seen in YSOs. Finally, we note the unusual long-term rising behaviours of four Class I YSOs, with rise timescales longer than five years, which is far slower than 6-12 month timescale for the majority of optically discovered FUors. Additionally, our broader investigation of MIR variability for embedded class I YSOs shows that there is a higher incidence of high amplitude variability for these stars, than is seen in class II sources. This holds true for all variable class I YSOs, not just the eruptive sources.