Abstract
ABSTRACT Studying rotational variability of young stars is enabling us to investigate a multitude of properties of young star-disc systems. We utilize high cadence, multiwavelength optical time series data from the Hunting Outbursting Young Stars citizen science project to identify periodic variables in the Pelican Nebula (IC 5070). A double blind study using nine different period-finding algorithms was conducted and a sample of 59 periodic variables was identified. We find that a combination of four period finding algorithms can achieve a completeness of 85 per cent and a contamination of 30 per cent in identifying periods in inhomogeneous data sets. The best performing methods are periodograms that rely on fitting a sine curve. Utilizing Gaia EDR3 data, we have identified an unbiased sample of 40 periodic young stellar objects (YSOs), without using any colour or magnitude selections. With a 98.9 per cent probability, we can exclude a homogeneous YSO period distribution. Instead, we find a bi-modal distribution with peaks at 3 and 8 d. The sample has a disc fraction of 50 per cent, and its statistical properties are in agreement with other similarly aged YSOs populations. In particular, we confirm that the presence of the disc is linked to predominantly slow rotation and find a probability of 4.8 × 10−3 that the observed relation between period and presence of a disc has occurred by chance. In our sample of periodic variables, we also find pulsating giants, an eclipsing binary, and potential YSOs in the foreground of IC 5070.
Highlights
Variability is one of the key characteristics of young stellar objects (YSOs)
In the right-hand panel of Fig. 2, we show the R – I versus absolute I-Band colour–magnitude diagram of the Hunting Outbursting Young Stars (HOYS) field as the black dots, with the periodic variables over plotted as coloured circles
We have utilized U, B, V, R, I data from the HOYS (Froebrich et al 2018) project to identify a sample of periodic variables in a 1 × 1 deg2 field centred around the Pelican Nebula IC 5070
Summary
Variability is one of the key characteristics of young stellar objects (YSOs). Time-domain observations of star-forming regions provide reliable information about the formation and early evolution of stars. Optical fluxes of YSOs are affected by variable excess emission from accretion shocks, variable emission from the inner disc, and variable extinction along the line of sight (Carpenter, Hillenbrand & Skrutskie 2001). The shape of the light curve indicates the star This group contains eight objects that are mostly near the bottom of the main sequence in our colour–magnitude diagram. 7896 (V1598 Cyg), is situated clearly above the main sequence This source has no infrared excess and Froebrich et al (2020) concluded that it is most likely a close binary and/or a foreground YSO. All but one of the others (6592), have longer periods between about 5 and 8 d These sources most likely represent a foreground population of young main sequence stars, binaries or older weak line T Tauri objects
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