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We present a multi-wavelength study of the Planck cold clump G181.84+0.31,which is located at the northern end of the extended filamentary structureS242. We have extracted 9 compact dense cores from the SCUBA-2 850 um map, andwe have identified 18 young stellar objects (YSOs, 4 Class I and 14 Class II)based on their Spitzer, Wide-field Infrared Survey Explorer (WISE) andTwo-Micron All-Sky Survey (2MASS) near- and mid-infrared colours. The densecores and YSOs are mainly distributed along the filamentary structures ofG181.84 and are well traced by HCO$^{+}$(1-0) and N$_{2}$H$^{+}$(1-0)spectral-line emission. We find signatures of sequential star formationactivities in G181.84: dense cores and YSOs located in the northern andsouthern sub-structures are younger than those in the central region. We alsodetect global velocity gradients of about 0.8$\pm$0.05 km s$^{-1}$pc$^{-1}$ and1.0$\pm$0.05 km s$^{-1}$pc$^{-1}$ along the northern and southernsub-structures, respectively, and local velocity gradients of 1.2$\pm$0.1 kms$^{-1}$pc$^{-1}$ in the central substructure. These results may be due to thefact that the global collapse of the extended filamentary structure S242 isdriven by an edge effect, for which the filament edges collapse first and thenfurther trigger star formation activities inward. We identify threesubstructures in G181.84 and estimate their critical masses per unit length,which are $\sim$ 101$\pm$15 M$_{\odot}$ pc$^{-1}$, 56$\pm$8 M$_{\odot}$pc$^{-1}$ and 28$\pm$4 M$_{\odot}$ pc$^{-1}$, respectively. These values areall lower than the observed values ($\sim$ 200 M$_{\odot}$ pc$^{-1}$),suggesting that these sub-structures are gravitationally unstable.

Sequential Star Formation in the filamentary structures of Planck Galactic cold clump G181.84+0.31