GASTON-GP: Source catalogue and millimetre variability of massive protostellar objects

Abstract

The processes governing protostellar mass growth remain debated, although episodic accretion is now understood as a key feature of protostellar evolution across all masses. Luminosity bursts have been observed in both low- and high-mass protostars, but the overall statistics remain limited, especially for high-mass objects. Over the past decade, numerical simulations of high-mass core collapse have provided a theoretical framework for interpreting protostellar variability, yet additional observational constraints are required to determine the characteristics and importance of bursts. In this work, we analyse data from GASTON-GP programme, which mapped a 2.4 square degrees region of the Galactic plane (centred at l = 24 deg) at 1.15 and 2.00 mm using NIKA2 on the IRAM 30 m telescope. The survey obtained 11 epochs over four years, offering the first opportunity to study millimetre variability in a large sample of massive protostellar sources. From the combined dataset, we constructed catalogues of 2925 compact sources at 1.15 mm and 1713 at 2.00 mm. Using a dedicated relative calibration scheme, we generated millimetre light curves for around 200 high-signal-to-noise sources and identified one variable candidate. However, it is not protostellar. Consequently, we report no robust detections of variable protostellar sources in GASTON field. This is the direct consequence of observational limitations (i.e., sensitivity, resolution) combined with the lack of any 100-fold luminosity bursts during the observations, which is consistent with estimates inferred from isolated core collapse simulations. This study highlights the need for future high-resolution, high-cadence surveys to constrain the accretion histories of massive protostars.

Figures (20)

• Figure 1: Scanning strategies used across the various GASTON-GP observing campaigns, overlaid on the 1.15 mm deep SNR map. The campaigns where each scan type was used are listed at the top of the corresponding panels.
• Figure 2: Panel (a): 1.15 mm deep map obtained by combining all 11 GASTON-GP runs at 1.15 mm. The orange and red circle in the left bottom marks the FoV(6.5' diameter) and beam size (11.6$"$) at 1.15mm, respectively. The pink polygon shows the area used for the calculation of the rms noise presented in Tab. \ref{['run-infor']}. Panel (b): 2.00 mm deep map obtained by combining all 11 runs at 2.00 mm. The orange and red circle in the left bottom marks the FoV(6.5$'$ diameter) and beam size (18$"$) at 2.00 mm, respectively. The pink polygon is the same as that in 1.15 mm map, where the rms noise in Tab. \ref{['run-infor']} is estimated.
• Figure 3: Panel (a): 1.15 mm map obtained after applying a 60-arcsec spatial filter with Nebuliser. Panel (b): 2.00 mm map obtained after applying a 60-arcsec spatial filter with Nebuliser. The orange and red circle in the left bottom in both panels refers to the FoV and beam size, respectively.
• Figure 4: Deep map (top-left panel), alongside the maps obtained for each individual run at 1.15 mm.
• Figure 5: Leaves found by Astrodendro at 1.15 mm. The background is the 1.15 mm filtered map. Red contours mark the leaf (compact sources) footprints identified in the filtered SNR map at 1.15 mm.