Large-amplitude periodic outbursts and long-period variables in the VVV VIRAC2-β data base

Abstract

The VISTA Variables in the Via Lactea (VVV) survey obtained near-infrared photometry toward the Galactic bulge and the southern disc plane for a decade (2010 – 2019). We designed a modified Lomb-Scargle method to search for large-amplitude ($\Delta K_{s, 2{{\ \rm per\ cent}}-98{{\ \rm per\ cent}}}$ > 1.5 mag) mid to long-term periodic variables (P>10 d) in the 2nd version of VVV Infrared Astrometric Catalogue (VIRAC2-β). In total, 1520 periodic sources were discovered, including 59 candidate periodic outbursting young stellar objects (YSOs), based on the unique morphology of the phase-folded light curves, proximity to Galactic H ii regions and mid-infrared colours. Five sources are spectroscopically confirmed as accreting YSOs. Both fast-rise/slow-decay and slow-rise/fast-decay periodic outbursts were found, but fast-rise/slow-decay outbursts predominate at the highest amplitudes. The multi-wavelength colour variations are consistent with a variable mass accretion process, as opposed to variable extinction. The cycles are likely to be caused by dynamical perturbations from stellar or planetary companions within the circumstellar disc. An additional search for periodic variability amongst YSO candidates in published Spitzer-based catalogues yielded a further 71 candidate periodic accretors, mostly with lower amplitudes. These resemble cases of pulsed accretion but with unusually long periods and greater regularity. The majority of other long-period variables are pulsating dusty Miras with smooth and symmetric light curves. We find that some Miras have redder W3 − W4 colours than previously thought, most likely due to their surface chemical compositions.

Mira variables in the Milky Way’s nuclear stellar disc: discovery and classification

“…Our cuts on Wesenheit magnitude have sought to eliminate these intrinsically dimmer contaminants. We have checked whether any of our objects are in the young stellar object catalogues of Guo et al (2021) and Guo et al (2022). One source in our catalogue (VIRAC Mira 68) has been identified by Guo et al (2022, VVV_PB_122) as a potential periodic outbursting young stellar object.…”

“…We also employ a number of cuts that remove a further ∼ 40 per cent of the sample. Contaminants include young stellar objects (YSOs, see Guo et al 2022), other fainter giant stars and blended photometry not properly handled in our calibration step. We have found that a small fraction of aliases that appear around 1 year period also 3 Using the Akaike or Bayesian information criteria instead results in minor differences in the final sample.…”

“…No detailed classification was performed such that some level of contamination from young stellar objects (e.g. Guo et al 2022) is likely (although at the magnitude range this survey probed they would be foreground objects so likely dwarfed in number density by 1 As the GLIMPSE-II catalogue puts a requirement on the sources having similar magnitudes at the two GLIMPSE-II epochs, some variable sources are not present in the combined catalogue and instead we use the results from the Epoch 1 catalogue. This affects ∼ 200 stars in our final sample.…”

Accretion Burst Echoes as Probes of Protostellar Environments and Episodic Mass Assembly

“…Variability in the MIR on timescales of days to months has been observed for many YSOs (e.g., Rebull et al 2014;Park et al 2021), though a wide range of phenomena besides accretion variability can be responsible (e.g., rotating disk warps and starspots). Several notable examples show variability attributed to periodic accretion instabilities (L1634 IRS 7; Hodapp & Chini 2015; V347 Aurigae; Dahm & Hillenbrand 2020; see also Guo et al 2022), pulsed accretion from interaction with a binary (L1527 IRS; Cook et al 2019), or rotation of a warped inner disk (LRLL 54361; Muzerolle et al 2013). Investigating such sources with higher-cadence and higher-resolution submillimeter/millimeter observations is thus important for identifying the nature and distribution of rapid accretion variability in protostars.…”

Infrared variability of young solar analogs in the Lagoon Nebula

“…In general, bursts are related with aperiodic behaviour of flux changes due to variable accretion and they can last from days to months, although they can also have durations of hours (Hillenbrand & Findeisen 2015;Cody et al 2014). However, there has been evidence of periodic outbursts due to accretion, when the latter is regulated by the presence of a low-mass companion (Dunhill et al 2015;Teyssandier & Lai 2020;Guo et al 2022). Most importantly, accretion processes will leave a signature in optical and infrared light curves that, depending on the view angle or the location of the spot, could be well correlated.…”