A1 Refereed original research article in a scientific journal
Star formation, structure, and formation mechanism of cometary globules: near-infrared observations of CG 1 and CG 2
Authors: M M Mäkelä, L K Haikala
Publisher: EDP SCIENCES S A
Publishing place: LES ULIS CEDEX A; 17, AVE DU HOGGAR, PA COURTABOEUF, BP 112, F-91944 LES ULIS CEDEX A, FRANCE
Publication year: 2013
Journal: Astronomy and Astrophysics
Journal name in source: Astronomy & Astrophysics
Journal acronym: Astron.Astrophys.
Volume: 550
First page : A83
Last page: A83
Number of pages: 22
ISSN: 0004-6361
DOI: https://doi.org/10.1051/0004-6361/201220027
Abstract
Context. Cometary globule (CG) 1 and CG 2 are "classic" cometary globules in the Gum Nebula. They have compact heads and long dusty tails that point away from the centre of the Gum Nebula. Aims. We study the structure of CG 1 and CG 2 and the star formation in them to find clues to the CG formation mechanism. The two possible CG formation mechanisms, radiation-driven implosion (RDI) and a supernova blast wave, produce a characteristic mass distribution where the major part of the mass is situated in either the head (RDI) or the tail (supernova blast). Methods. CG 1 and CG 2 were imaged in the near infrared (NIR) JsHKs bands. NIR photometry was used to locate NIR excess objects and to create visual extinction maps of the CGs. The A(V) maps allow us to analyse the large-scale structure of CG 1 and CG 2. Archival images from the WISE and Spitzer satellites and HIRES-processed IRAS images were used to study the globule's small-scale structure. Fits were made to the spectral energy distribution plots of the NIR-excess stars to estimate their age and mass. Results. In addition to the previously known CG 1 IRS 1 we discovered three new NIR-excess objects in IR imaging, two in CG 1 and one in CG 2. CG 2 IRS 1 is the first detection of star formation in CG 2. The objects are young low-mass stars. CG 1 IRS 1 is probably a class I protostar in the head of CG 1. CG 1 IRS 1 drives a bipolar outflow, which is very weak in CO, but the cavity walls are seen in reflected light in our NIR and in the Spitzer 3.6 and 4.5 mu m images. Strong emission from excited polycyclic aromatic hydrocarbon particles and very small grains were detected in the CG 1 tail. The total mass of CG 1 in the observed area is 41.9 M-circle dot of which 16.8 M-circle dot lies in the head. For CG 2 these values are 31.0 M-circle dot total and 19.1 M-circle dot in the head. The observed mass distribution does not offer a firm conclusion for the formation mechanism of the two CGs: CG 1 is in too evolved a state, and in CG 2 part of the globule tail was outside the observed area. Conclusions. Even though the masses of the two CGs are similar, star formation has been more efficient in CG 1. By now, altogether six young low-mass stars have been detected in CG 1 and only one in CG 2. A possible new outflow was discovered to be emanating from CG 1 IRS 1.
Context. Cometary globule (CG) 1 and CG 2 are "classic" cometary globules in the Gum Nebula. They have compact heads and long dusty tails that point away from the centre of the Gum Nebula. Aims. We study the structure of CG 1 and CG 2 and the star formation in them to find clues to the CG formation mechanism. The two possible CG formation mechanisms, radiation-driven implosion (RDI) and a supernova blast wave, produce a characteristic mass distribution where the major part of the mass is situated in either the head (RDI) or the tail (supernova blast). Methods. CG 1 and CG 2 were imaged in the near infrared (NIR) JsHKs bands. NIR photometry was used to locate NIR excess objects and to create visual extinction maps of the CGs. The A(V) maps allow us to analyse the large-scale structure of CG 1 and CG 2. Archival images from the WISE and Spitzer satellites and HIRES-processed IRAS images were used to study the globule's small-scale structure. Fits were made to the spectral energy distribution plots of the NIR-excess stars to estimate their age and mass. Results. In addition to the previously known CG 1 IRS 1 we discovered three new NIR-excess objects in IR imaging, two in CG 1 and one in CG 2. CG 2 IRS 1 is the first detection of star formation in CG 2. The objects are young low-mass stars. CG 1 IRS 1 is probably a class I protostar in the head of CG 1. CG 1 IRS 1 drives a bipolar outflow, which is very weak in CO, but the cavity walls are seen in reflected light in our NIR and in the Spitzer 3.6 and 4.5 mu m images. Strong emission from excited polycyclic aromatic hydrocarbon particles and very small grains were detected in the CG 1 tail. The total mass of CG 1 in the observed area is 41.9 M-circle dot of which 16.8 M-circle dot lies in the head. For CG 2 these values are 31.0 M-circle dot total and 19.1 M-circle dot in the head. The observed mass distribution does not offer a firm conclusion for the formation mechanism of the two CGs: CG 1 is in too evolved a state, and in CG 2 part of the globule tail was outside the observed area. Conclusions. Even though the masses of the two CGs are similar, star formation has been more efficient in CG 1. By now, altogether six young low-mass stars have been detected in CG 1 and only one in CG 2. A possible new outflow was discovered to be emanating from CG 1 IRS 1.
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