Context. Observations have discovered numerous giant molecular filaments (GMFs) in the Milky Way. Their role in the Galactic star formation and Galaxy-scale evolution of dense gas is unknown. Aims. We investigate systematically the star-forming content of all currently known GMFs. This allows us to estimate the star formation rates (SFRs) of the GMFs and to establish relationships between the SFRs and the GMF properties. Methods. We identify and classify the young stellar object (YSO) population of each GMF using multi-wavelength photometry from near-to far-infrared. We estimate the total SFRs assuming a universal and fully sampled initial mass function and luminosity function. Results. We uniformly estimate the physical properties of 57 GMFs. The GMFs show correlations between the 13 CO line width, mass, and size, similar to Larson's relations. We identify 36 394 infrared excess sources in 57 GMFs and obtain SFRs for 46 GMFs. The median SFR surface density (Σ SFR ) and star formation efficiency (SFE) of GMFs are 0.62 M Myr −1 pc −2 and 1%, similar to the nearby star-forming clouds. The star formation rate per free-fall time of GMFs is between 0.002−0.05 with the median value of 0.02. We also find a strong correlation between SFR and dense gas mass that is defined as gas mass above a visual extinction of 7 mag, which suggests that the SFRs of the GMFs scale similarly with dense gas as those of nearby molecular clouds. We also find a strong correlation between the mean SFR per unit length and dense gas mass per unit length. The origin of this scaling remains unknown, calling for further studies that can link the structure of GMFs to their SF activity and explore the differences between GMFs and other molecular clouds.

Abstract. We examine the spatial and temporal relationship between chromospheric H β flares and photospheric current helicities in active regions. All of the data were obtained by the vector magnetograph system at Huairou Solar Observing Station of Beijing Astronomical Observatory. We focus our analysis on NOAA Active Region 6233, which was observed on 30 August 1990. The result shows that rapid and substantial changes of distribution of current helicity in an area or in its vicinity are most likely to trigger flares, but no compelling correlation between peaks of current helicity and flare sites. Furthermore, we study the influence of flares on helicity for several other active regions. We find that the time variations of current helicity in the active regions with highly productive flares are more significant than those of the poorly flare-productive active regions, and that the magnitude of current helicity does not always decrease after flares. Therefore we conclude that the rate of variation of current helicity may be considered as an indicator of flare activity.In this paper we describe the specification of the instrumentation and data used, and we describe the methods for computing helicity. The noises and errors in our data are estimated to be at the 2 − 3σ level.