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We have recently published observations of significant flux density variations at 1.3 cm in HII regions in the star forming regions Sgr B2 Main and North (De Pree et al. 2014). To further study these variations, we have made new 7 mm continuum and recombination line observations of Sgr B2 at the highest possible angular resolution of the Karl G. Jansky Very Large Array (VLA). We have observed Sgr B2 Main and North at 42.9 GHz and at 45.4 GHz in the BnA configuration (Main) and the A configuration (North). We compare these new data to archival VLA 7 mm continuum data of Sgr B2 Main observed in 2003 and Sgr B2 North observed in 2001. We find that one of the 41 known ultracompact and hypercompact HII regions in Sgr B2 (K2-North) has decreased $sim$27% in flux density from 142$pm$14 mJy to 103$pm$10 mJy (2.3$sigma$) between 2001 and 2012. A second source, F3c-Main has increased $sim$30% in flux density from 82$pm$8 mJy to 107 $pm$11 mJy (1.8$sigma$) between 2003 and 2012. F3c-Main was previously observed to increase in flux density at 1.3 cm over a longer time period between 1989 and 2012 (De Pree et al. 2014). An observation of decreasing flux density, such as that observed in K2-North, is particularly significant since such a change is not predicted by the classical hypothesis of steady expansion of HII regions during massive star accretion. Our new observations at 7 mm, along with others in the literature, suggest that the formation of massive stars occurs through time-variable and violent accretion.
The ionized core in the Sgr B2 Main star-forming region was imaged using the Submillimeter Array archival data observed for the H26$alpha$ line and continuum emission at 0.86 millimeter with an angular resolution 0.3arcsec. Eight hyper-compact H26$al
We report the discovery of the first 14NH3 (2,2) maser, seen in the Sgr B2 Main star forming region near the center of the Milky Way, using data from the Very Large Array radio telescope. The maser is seen in both lower resolution (3 or ~0.1 pc) data
We have measured multi-band optical flux and colour variations for a sample of 12 low energy peaked blazars on short, day-to-month, timescales. Our sample contains six BL Lacertae objects and six flat spectrum radio quasars. These photometric observa
Elongated magnetic polarities are observed during the emergence phase of bipolar active regions (ARs). These extended features, called magnetic tongues, are interpreted as a consequence of the azimuthal component of the magnetic flux in the toroidal
We present initial result of a large spectroscopic survey aimed at measuring the timescale of mass accretion in young, pre-main-sequence stars in the spectral type range K0 - M5. Using multi-object spectroscopy with VIMOS at the VLT we identified the