Radio observations of evaporating objects in the Cygnus OB2 region

N. L. ISEQUILLA; M. FERNÁNDEZ-LÓPEZ; P. BENAGLIA; C. H. ISHWARA-CHANDRA; S. DEL PALACIO

ASTRONOMY AND ASTROPHYSICS

EDP SCIENCES S A

Lugar: Paris; Año: 2019 vol. 627

0004-6361

We present observations of the Cygnus OB2 region obtained with the Giant Metrewave Radio Telescope (GMRT) at frequencies of 325and 610 MHz. In this contribution we focus on the study of proplyd-like objects (also known as free-floating evaporating gas globulesor frEGGs) that typically show an extended cometary morphology. We identify eight objects previously studied at other wavelengthsand derive their physical properties by obtaining their optical depth at radio-wavelengths. Using their geometry and the photoionizationrate needed to produce their radio-continuum emission, we find that these sources are possibly ionized by a contribution of the starsCyg OB2 #9 and Cyg OB2 #22. Spectral index maps of the eight frEGGs were constructed, showing a flat spectrum in radio frequenciesin general. We interpret these as produced by optically thin ionized gas, although it is possible that a combination of thermal emission,not necessarily optically thin, produced by a diffuse gas component and the instrument response (which detects more diffuse emissionat low frequencies) can artificially generate negative spectral indices. In particular, for the case of the Tadpole we suggest that theobserved emission is not of non-thermal origin despite the presence of regions with negative spectral indices in our maps.